WO2023175731A1

WO2023175731A1 - Electrode, battery, and battery pack

Info

Publication number: WO2023175731A1
Application number: PCT/JP2022/011680
Authority: WO
Inventors: 諒原; 一浩安田; 隆敏粕壁; 祐輝渡邉
Original assignee: 株式会社東芝
Priority date: 2022-03-15
Filing date: 2022-03-15
Publication date: 2023-09-21
Also published as: JPWO2023175731A1

Abstract

According to an embodiment of the present invention, provided is an electrode including an active material that contains a titanium-containing oxide and that has an average primary particle diameter in the range 200–600 nm. The ratio D₉₀/D₁₀ in the particle diameter distribution of the electrode is in the range 17–27. At least part of a surface of the electrode contains aluminum. As regards the electrode, the value of the ratio I_B/I_A is in the range 3.5–9, said ratio being of the peak intensities of a peak A appearing in the range 1.1–1.5 Å and a peak B appearing in the range 2.8–3.2 Å in a radial distribution function based on a Fourier transform of a broad-spectrum X-ray absorbing microstructure spectrum at the aluminum K-edge with respect to the surface.

Description

Electrodes, batteries, and battery packs

Embodiments of the present invention relate to electrodes, batteries, and battery packs.

Lithium-ion secondary batteries, which are charged and discharged by the movement of lithium ions between the positive and negative electrodes, take advantage of their high energy density and high output, and are used for everything from small applications such as portable electronic devices to electric vehicles and power sources. It is being widely applied to large-scale applications such as supply and demand adjustment.

Non-aqueous electrolyte batteries have also been put into practical use that use spinel-type lithium titanate, which has a high lithium intercalation and desorption potential of approximately 1.55 V (vs. Li/Li ⁺ ) based on lithium electrodes, instead of carbon materials as the negative electrode active material. ing. Spinel-type lithium titanate has excellent cycle performance because it undergoes little volume change during charging and discharging. Furthermore, since a negative electrode containing spinel-type lithium titanate does not precipitate lithium metal during intercalation and desorption of lithium, a secondary battery equipped with this negative electrode can be charged at high currents and at low temperatures. In order to further improve high-current performance and low-temperature performance, attempts have been made to reduce the diameter of spinel-type lithium titanate particles.

Japanese Patent Application Publication No. 2014-143004 Japanese Patent Application Publication No. 2019-169276

The purpose of the present invention is to provide an electrode that can realize a battery with excellent large current performance and storage performance at low temperatures and high energy density, a battery equipped with this electrode, and a battery pack equipped with this battery.

According to the embodiment, an electrode is provided that includes an active material that includes a titanium-containing oxide and has an average primary particle size of 200 nm or more and 600 nm or less. The ratio D ₉₀ /D 10 of the particle diameter D ₉₀ at which the cumulative frequency from the small particle diameter side is 90% to the particle diameter D ₁₀ at _which the cumulative frequency from the small particle diameter side is 10% in the particle size distribution of the electrode is 17. 27 or less. The electrode contains Al on at least a portion of its surface. The electrode has a peak A that appears in the range of 1.1 Å to 1.5 Å and a peak A of 2.8 Å to 3.2 Å in the radial distribution function obtained by Fourier transformation of the wide-range X-ray absorption fine structure spectrum of the K absorption edge of Al with respect to the surface. Includes peak B that appears in the range. The ratio I B /I _A of the peak intensity I _B of peak _B to the peak intensity I _A of peak A is 3.5 or more and 9 or less.

According to another embodiment, a battery is provided that includes a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes the above electrode.

According to yet another embodiment, a battery pack is provided. The battery pack includes the battery described above.

FIG. 1 is a plan view schematically showing an example of an electrode according to an embodiment. FIG. 2 is a graph showing the particle size distribution of an example electrode according to the embodiment. FIG. 3 is a graph showing a radial distribution function obtained by Fourier transformation of a wide-range X-ray absorption fine structure spectrum of the K absorption edge of Al for the surface of an example electrode according to the embodiment. FIG. 4 is a cross section of an example battery according to the embodiment cut in the thickness direction. FIG. 5 is an enlarged sectional view of section E in FIG. 4. FIG. 6 is a partially cutaway perspective view of another example battery according to the embodiment. FIG. 7 is an exploded perspective view of an example battery pack according to the embodiment. FIG. 8 is a block diagram showing an electric circuit of the battery pack shown in FIG. 7.

Embodiment

Input performance can be improved by making the active material smaller particles. On the other hand, when the particle size of the active material becomes smaller, problems may arise such as a decrease in electrode density and an increase in resistance due to surface side reactions.

Embodiments will be described below with reference to the drawings. Note that common components throughout the embodiments are denoted by the same reference numerals, and redundant explanations will be omitted.

In addition, each figure is a schematic diagram to facilitate explanation and understanding of the embodiment, and the shape, dimensions, ratio, etc. may differ from the actual device, but these are based on the following explanation and known techniques. The design may be changed as appropriate, taking into account the following.

(First embodiment)
According to a first embodiment, an electrode is provided. The electrode includes an active material. The active material contains a titanium-containing oxide and has an average primary particle diameter of 200 nm or more and 600 nm or less. The ratio D ₉₀ /D 10 of the particle diameter D ₉₀ at which the cumulative frequency from the small particle diameter side is 90% to the particle diameter D ₁₀ at _which the cumulative frequency from the small particle diameter side is 10% in the particle size distribution of the electrode is 17. 27 or less. The electrode contains Al on at least a portion of its surface. The electrode has a peak A that appears in the range of 1.1 Å to 1.5 Å and a peak A of 2.8 Å to 3.2 Å in the radial distribution function obtained by Fourier transformation of the wide-range X-ray absorption fine structure spectrum of the K absorption edge of Al with respect to the surface. Includes peak B that appears in the range. The ratio I B /I _A of the peak intensity I _B of peak _B to the peak intensity I _A of peak A is 3.5 or more and 9 or less.

The electrode according to the embodiment may be a battery electrode. Examples of batteries that can include the electrodes according to the embodiments include secondary batteries such as lithium ion secondary batteries. The secondary battery includes a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte. The electrode can be, for example, a negative electrode for a battery.

A secondary battery equipped with a negative electrode containing a titanium-containing oxide has excellent cycle life performance and storage performance, and is also capable of charging and discharging at large currents and charging under low-temperature conditions. In order to further improve such large current performance and low temperature performance, attempts have been made to reduce the diameter of active material particles. On the one hand, reducing the size of active material particles improves input/output performance, but on the other hand, it poses problems such as a decrease in electrode density and an increase in resistance due to surface side reactions.

The present inventors conducted extensive research to solve this problem regarding non-aqueous electrolyte batteries equipped with negative electrodes containing titanium-containing oxides, and as a result, they discovered an electrode according to the first embodiment. Specifically, the presence of a specific alkoxide compound on the surface of the titanium-containing oxide suppresses the increase in resistance due to surface side reactions and makes it easier to adjust the titanium-containing oxide to the desired particle size distribution. It has been found that by doing so, it is possible to suppress a decrease in electrode density.

The electrode according to the first embodiment is an electrode containing a titanium-containing oxide having an average primary particle size of 200 nm or more and 600 nm or less as an electrode active material, and the cumulative frequency from the small particle size side in the particle size distribution of the electrode is The ratio D 90 /D ₁₀ of the particle diameter D ₉₀ at which the cumulative frequency from the small particle diameter side is 90% with respect to the particle diameter D ₁₀ which is 10 _% is 17 or more and 27 or less. In addition, at least a portion of the electrode surface contains aluminum (Al). The radial distribution function obtained by Fourier transformation of the extended X-ray absorption fine structure (EXAFS) spectrum of the K absorption edge of Al for the electrode surface is a peak A appearing in the range of 1.1 Å to 1.5 Å and a peak A of 2.8 Å to 3.2 Å. Contains peak B appearing in the following range. The ratio I B /I _A of the peak intensity I _B of peak _B to the peak intensity I _A of peak A is 3.5 or more and 9 or less. By having such a configuration, the electrode can provide a battery that has high electrode density, suppresses resistance increase during low-temperature storage, and has excellent low-temperature input performance.

Although the mechanism by which such an electrode improves low-temperature storage performance is not completely understood, it is thought to be as follows, for example.

By reducing the primary particle diameter of the active material particles, the specific surface area increases, so the ability of the active material itself to accept lithium ions at low temperatures improves. However, as the primary particle size decreases, the proportion of active sites on the surface of the active material increases. Therefore, side reactions between the active material and the electrolyte, etc. increase, resulting in an increase in electrical resistance during low-temperature storage.

When the aluminum alkoxide compound exists in a specific state on the surface of the active material, side reactions with the electrolyte and the like can be suppressed. Specifically, the radial distribution function obtained by Fourier transform (FT-EXAFS) of the EXAFS spectrum of Al has a peak A in the range of 1.1 Å to 1.5 Å and a peak B in the range of 2.8 Å to 3.2 Å. In an electrode in which the peak intensity ratio I _B /I _A of these peaks is in a state of 3.5 or more and 9 or less, the aluminum alkoxide compound is applied to the surface of the active material in a state that is effective in suppressing the above side reactions. It is determined that it exists. It is thought that at least a portion of the aluminum alkoxide compound is condensed with a functional group present on the surface of the active material that can become an active site, thereby suppressing side reactions. In addition, by incorporating some of it as a coating on the surface of the active material, it is possible to smooth the insertion and insertion of lithium ions, reduce uneven charging and discharging, and reduce side reactions caused by local overcharging. Conceivable. Furthermore, it is considered that the aluminum alkoxide compound enhances the interaction between active material particles, making it easier to obtain a desired particle size distribution, thereby making it possible to achieve a high electrode density. Furthermore, it is possible to provide a non-aqueous electrolyte secondary battery with excellent low-temperature performance.

In such an electrode, since the average primary particle diameter of the active material particles is 200 nm or more and 600 nm or less, it can exhibit good input performance even under low temperature conditions. Specifically, since the average primary particle diameter is 200 nm or more, the crystallinity of the active material can be increased, so that the charge/discharge cycle performance and energy density of a battery using the electrode can be improved. When the average primary particle diameter is 600 nm or less, a battery with excellent low temperature input performance can be obtained.

In the particle size distribution obtained by the laser diffraction/scattering method for the electrode, the average particle size D ₁₀ makes the cumulative frequency from the small particle size side 10%, and the particle size D 90 makes the cumulative frequency from the small particle size side ₉₀ %. The ratio D ₉₀ /D ₁₀ is 17 or more and 27 or less. An electrode having such a particle size distribution has an appropriate electrode density. Therefore, it is excellent in terms of input/output performance and energy density.

The above particle size distribution may include maximum values within the range of 0.5 μm or more and 1 μm or less and within the range of 3 μm or more and 10 μm or less. That is, the particle size distribution of the electrode can have a bimodal shape. When a peak with a maximum value within the range of 0.5 μm or more and 1 μm or less is defined as the first peak, and a peak with a maximum value within the range of 3 μm or more and 10 μm or less is defined as the second peak, the first peak with respect to the frequency of the second peak is defined as the second peak. It is preferable that the ratio of peak frequencies is 0.18 or more and 0.35 or less. An electrode with a ratio of 0.18 or more has better low-temperature storage performance. An electrode with a ratio of 0.35 or less has better energy density.

It is preferable that the specific pore surface area of the electrode measured by nitrogen adsorption is in the range of 2 m ² /g or more and 10 m ² /g or less. When the pore specific surface area of the electrode is 2 m ² /g or more, good low-temperature input performance can be exhibited. When the pore specific surface area is 10 m ² /g or less, side reactions between the electrode and the electrolyte can be kept small.

Regarding the titanium-containing oxide contained in the active material, in the XRD spectrum measured by powder X-ray diffraction (XRD) described below, the half width of the peak attributed to the (111) plane is 0.15 or less. It is desirable that there be. (111) When the half width of the peak is 0.15 or less, the crystallinity of the titanium-containing oxide particles is high and the diffusivity of lithium ions within the particles is good, so the low temperature input performance is high and the electrode Side reactions on the surface are reduced. Alternatively, even when the crystallite diameter is large, the half width may be 0.15 or less. Particles with a large crystallite diameter have fewer grain boundaries within the particles and improve the diffusivity of lithium ions within the particles, resulting in higher low-temperature input performance. Note that the (111) plane here refers to a crystal lattice plane expressed by Miller index.

Next, the electrode according to the first embodiment will be described in more detail.

The electrode can include a current collector and an active material-containing layer (electrode mixture layer). The active material-containing layer may be formed, for example, on one side or both the front and back sides of the band-shaped current collector. The active material-containing layer can include an active material and optionally a conductive agent and a binder.

The active material includes a titanium-containing oxide having an average primary particle diameter of 200 nm or more and 600 nm or less. The titanium-containing oxide preferably includes a lithium-titanium composite oxide. Electrodes containing titanium-containing oxides, such as lithium-titanium composite oxides, can exhibit a Li storage potential of 0.4 V (vs. Li/Li ⁺ ) or more relative to the oxidation-reduction potential of lithium, and therefore have a large It is possible to prevent metal lithium from being deposited on the electrode surface when inputting and outputting with electric current is repeated. It is particularly preferable that the titanium-containing oxide includes a lithium-titanium composite oxide having a spinel-type crystal structure. A specific example of such a spinel-type lithium titanium composite oxide is represented by Li _4+a Ti ₅ O ₁₂ , and has a spinel structure in which the value of the subscript a changes with charging and discharging within the range of 0≦a≦3. Mention may be made of lithium titanate.

The active material may include primary particles and secondary particles of the titanium-containing oxide. The primary particles of the titanium-containing oxide have the above average primary particle diameter. The secondary particles of the titanium-containing oxide include a plurality of primary particles having the above average primary particle diameter.

The average particle diameter (average secondary particle diameter) of the secondary particles is preferably 1 μm or more and 100 μm or less. When the average particle diameter of the secondary particles is within this range, it is easy to handle in industrial production, and the mass and thickness of the coating film for producing the electrode can be made uniform. Furthermore, deterioration of the surface smoothness of the electrode can be prevented. The average particle diameter of the secondary particles is more preferably 2 μm or more and 30 μm or less.

It is preferable that the specific surface area of the secondary particles measured by the BET method is 3 m ² /g or more and 50 m ² /g or less. When the specific surface area is 3 m ² /g or more, it becomes possible to sufficiently secure lithium ion intercalation and desorption sites. When the specific surface area is 50 m ² /g or less, it becomes easier to handle in terms of industrial production. More preferably, the secondary particles have a specific surface area of 5 m ² /g or more and 50 m ² /g or less as measured by the BET method. A method for measuring the specific surface area using the BET method will be described later.

The active material may contain further active materials other than the titanium-containing oxide. Here, for convenience, the active material containing the titanium-containing oxide described above may be referred to as a "first active material", and the other active material may be referred to as a "second active material". When a second active material is further included in addition to the first active material, it is desirable to use an active material that can exhibit a Li storage potential of 0.4 V (vs. Li/Li ⁺ ) or more as the second active material. . When the second active material is included, the mass ratio of the second active material to the first active material is preferably 5% by mass or more and 40% by mass or less, more preferably 10% by mass or more and 30% by mass or less. preferable.

The conductive agent can have the effect of improving current collection performance and suppressing the contact resistance between the active material and the current collector. Examples of conductive agents include carbonaceous materials such as acetylene black, carbon black, graphite, carbon nanofibers, and carbon nanotubes. These carbonaceous substances may be used alone, or a plurality of carbonaceous substances may be used.

The binder can have the effect of binding the active material, the conductive agent, and the current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine rubber, styrene-butadiene rubber, acrylic resin and its copolymers, polyacrylic acid, and Examples include polyacrylonitrile.

The compounding ratio of the active material, conductive agent, and binder is 70% by mass or more and 97.5% by mass or less for the active material, 2% by mass or more and 20% by mass or less for the conductive agent, and 0 for the binder. It is preferably within the range of .5% by mass or more and 10% by mass or less. By setting the amount of the conductive agent to 2% by mass or more, the current collection performance of the active material-containing layer can be improved, and excellent large current performance and low-temperature performance can be expected. Further, by setting the amount of the binder to 0.5% by mass or more, the binding property between the active material-containing layer and the current collector becomes sufficient, and excellent life performance can be expected.

On the other hand, from the viewpoint of increasing capacity, the content of the conductive agent and the binder is preferably 20% by mass or less, and more preferably 10% by mass or less each.

The current collector is preferably formed from aluminum foil or an aluminum alloy foil containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 20 μm or less, more preferably 15 μm or less.

Next, a specific example of the electrode according to the first embodiment will be described with reference to the drawings.

FIG. 1 is a partially cutaway plan view schematically showing an example of an electrode according to an embodiment. Here, an example of a negative electrode is illustrated as an example of the electrode.

The negative electrode 4 shown in FIG. 1 includes a negative electrode current collector 4a and a negative electrode active material-containing layer 4b provided on the surface of the negative electrode current collector 4a. The negative electrode active material containing layer 4b is supported on the main surface of the negative electrode current collector 4a.

Further, the negative electrode current collector 4a includes a portion on its surface where the negative electrode active material-containing layer 4b is not provided. This portion serves, for example, as the negative electrode current collecting tab 4c. In the illustrated example, the negative electrode current collector tab 4c is a narrow portion narrower in width than the negative electrode active material-containing layer 4b. The width of the negative electrode current collecting tab 4c may be narrower than the width of the negative electrode active material containing layer 4b as described above, or may be the same as the width of the negative electrode active material containing layer 4b. Instead of the negative electrode current collecting tab 4c that is a part of the negative electrode current collector 4a, a separate conductive member may be electrically connected to the negative electrode 4 and used as the electrode current collecting tab (negative electrode current collecting tab). good.

[Manufacture of electrodes]
Such an electrode can be manufactured as follows.

First, an active material containing a titanium-containing oxide is prepared. The titanium-containing oxide can be synthesized, for example, by a solid phase method. The titanium-containing oxide can also be synthesized by a wet synthesis method such as a sol-gel method or a hydrothermal method.

First, for example, a Ti source and a Li source are prepared according to the target composition. These raw materials can be, for example, compounds such as oxides or salts. As the Li source, lithium hydroxide, lithium oxide, lithium carbonate, etc. can be used.

The prepared raw materials are then mixed in the appropriate stoichiometric ratio to obtain a mixture. For example, when synthesizing a spinel-type lithium titanium composite oxide represented by the composition formula Li ₄ Ti ₅ O ₁₂ , titanium oxide TiO ₂ and lithium carbonate Li ₂ CO ₃ are mixed at a molar ratio of Li:Ti in the mixture. They can be mixed in a ratio of 4:5.

When mixing the raw materials, it is preferable to thoroughly crush the raw materials before mixing. By mixing sufficiently pulverized raw materials, the raw materials can easily react with each other, and the generation of impurities can be suppressed when synthesizing a titanium-containing oxide. Further, Li may be mixed in an amount greater than a predetermined amount. In particular, since there is a concern that Li may be lost during heat treatment, more than a predetermined amount may be added.

When using a wet method, the raw materials are dissolved in pure water, and the resulting solution is dried while stirring to obtain a fired precursor. Drying methods include spray drying, granulation drying, freeze drying, or a combination thereof.

Next, the mixture or fired precursor obtained by the above mixing is heat-treated at a temperature of 750° C. or more and 1000° C. or less for a period of 30 minutes or more and 24 hours or less. At temperatures below 750°C, it is difficult to obtain sufficient crystallization. On the other hand, if the temperature is 1000° C. or higher, grain growth progresses too much, resulting in coarse particles, which is not preferable. Similarly, if the heat treatment time is less than 30 minutes, sufficient crystallization will be difficult to obtain. Moreover, if the heat treatment time is made longer than 24 hours, grain growth will proceed too much, resulting in coarse particles, which is not preferable. Firing may be performed in the atmosphere. Further, the firing may be performed in an oxygen atmosphere, nitrogen atmosphere, or argon atmosphere.

The mixture is preferably heat-treated at a temperature of 800° C. or higher and 950° C. or lower for a period of 1 hour or more and 5 hours or less. A titanium-containing oxide can be obtained by such heat treatment. Further, preliminary firing may be performed before main firing. Temporary firing is performed at a temperature of 450° C. or more and 700° C. or less for 5 hours or more and 24 hours or less.

When using a method that uses water, such as a wet method, pay attention to the amount of moisture remaining after firing. The remaining moisture may react with the aluminum alkoxide compound added later to form a resistance component. Therefore, adjusting the firing temperature and firing time also leads to control of the radial distribution function of Al by FT-EXAFS.

The sample obtained by main firing can be subjected to a pulverization treatment to obtain primary particles in which aggregates (secondary particles) are crushed. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a bead mill, a jet mill, a counter jet mill, a swirling air jet mill, etc. can be used as the pulverizing method. In the case of pulverization, wet pulverization in which a liquid pulverization aid such as water, ethanol, ethylene glycol, benzene or hexane coexists can also be used. Grinding aids are effective in improving grinding efficiency and increasing the amount of fine powder produced. A more preferable method is a ball mill using zirconia balls as the media, and wet grinding with a liquid grinding aid added is preferable. Furthermore, an organic substance such as a polyol that improves the grinding efficiency may be added as a grinding aid. The type of polyol is not particularly limited, but pentaerythritol, triethylolethane, trimethylolpropane, etc. can be used alone or in combination.

Furthermore, re-firing may be performed after the pulverization treatment. By adjusting the firing conditions, the average crystallite diameter of the titanium-containing oxide particles can be controlled. Re-firing may be performed in the air, or may be performed in an inert atmosphere using an oxygen atmosphere, nitrogen, argon, or the like. Re-firing may be performed at a temperature of 250° C. or more and 900° C. or less for about 1 minute or more and 10 hours or less. If the temperature is 900° C. or higher, the calcination of the pulverized powder will proceed, and even if the heat treatment is performed for a short time, the pores in the electrode will be collapsed due to sintering between the powder particles, which may reduce the input/output performance. If the temperature is less than 250°C, impurities (organic substances) attached during wet pulverization cannot be removed, resulting in a decrease in battery performance. Preferably, the re-firing is performed at a temperature of 400° C. or more and 700° C. or less for 10 minutes or more and 3 hours or less. Further, it is preferable to wash with an aqueous solvent before re-firing.

Additionally, methods such as a spray dryer can be used to obtain secondary particles. Classification can be performed as necessary to obtain primary particles or secondary particles having a specific particle size.

Next, an electrode slurry is prepared using the active material containing the titanium-containing oxide prepared as described above. When a second active material other than a titanium-containing oxide is further used, an electrode slurry is prepared using the second active material together with an active material containing a titanium-containing oxide (first active material). Specifically, an active material, a conductive agent, a binder, and an aluminum alkoxide compound are suspended in a solvent to prepare a slurry. As the solvent (dispersion medium), for example, N-methylpyrrolidone (NMP) can be used.

As the aluminum alkoxide compound added to the electrode slurry, it is preferable to use an alkoxide compound having a substituent having 4 or more carbon atoms. For example, di-2-butoxyaluminum ethyl acetoacetate (Al(C ₄ H ₉ O) ₂ (C ₆ H ₉ O ₃ )), aluminum tri-2-butoxide (Al(OC ₄ H ₉ ) ₃ ), di- 2-butoxyaluminum acetylacetate (Al(C ₄ H ₉ O) ₂ (C ₅ H ₇ O ₂ )), aluminum trisec-butoxide (Al(O-sec-C ₄ H ₉ ) ₃ ), etc. can be used. . In the electrode to which the aluminum alkoxide compound is added, the above-mentioned state in which the value of the peak intensity ratio I _B /I _A is 3.5 or more and 9 or less is easily obtained in the radial distribution function of Al by FT-EXAFS. That is, the addition of these aluminum alkoxide compounds is effective in suppressing side reactions on the electrode. Other aluminum alkoxide compounds in which the substituent has less than 4 carbon atoms include, for example, aluminum isopropoxide (Al(Oi-Pr) ₃ ). One type of aluminum alkoxide compound may be added, or two or more types may be added.

Adjust the content ratio and particle size of each component (active material, conductive agent, binder) included in the electrode, the content ratio of primary particles and secondary particles of the active material, and the type and amount of the aluminum alkoxide compound added. By doing so, the particle size distribution in the electrode can be controlled. Moreover, the pore specific surface area of the electrode can also be controlled by these adjustments. Note that the particle size distribution reflects not only the primary particles and secondary particles of the active material, but also the content ratio of the conductive agent and the presence or absence of aggregation between the active material and the conductive agent. That is, the particle size distribution and pore specific surface area of the obtained electrode are influenced by the content ratio of each member in the electrode slurry, and the state and content ratio of the primary particles and secondary particles of the active material.

The particle size distribution in the electrode can also be controlled by the amount of aluminum alkoxide compound added. When the amount of aluminum alkoxide added is large, agglomeration within the electrode tends to increase. If the amount added is small, agglomeration tends to decrease. Therefore, the ratio D ₉₀ /D ₁₀ in the particle size distribution is proportional to the amount of aluminum alkoxide added. The amount of the aluminum alkoxide compound added may be, for example, 0.1% by mass or more and 1% by mass or less based on the active material.

When preparing a slurry, when suspending the active material, conductive agent, binder, and aluminum alkoxide in a solvent, a rotation-revolution mixer, planetary mixer, etc. It is preferable to use a Lee mixer, a jet paster, a homogenizer, or the like. The solid content concentration of the slurry is preferably 40 wt% or more and 70 wt% or less. For addition of the conductive agent, a paste in which the conductive agent is previously dispersed in a solvent to which a dispersant is added may be used. By using such a paste, kneading time can be shortened and crushing of secondary particles can be suppressed.

The particle size distribution and pore specific surface area of the resulting electrode can also be controlled by the stirring conditions during slurry preparation. For example, the higher the stirring speed and the longer the stirring time, the higher the pore specific surface area, and the ratio of the frequency of the first peak to the frequency of the second peak in the above-mentioned particle size distribution tends to be lower. The lower the stirring speed and the slower the stirring time, the lower the pore specific surface area and the higher the ratio of the frequency of the first peak to the frequency of the second peak.

The slurry prepared as described above is applied to one or both sides of the current collector, and then the coating film is dried. In this way, an electrode mixture layer (active material-containing layer) can be formed. After that, the electrode mixture layer is pressed. In this way, the electrode according to the first embodiment can be obtained.

<Measurement of electrodes>
Various measurement methods for electrodes will be explained. Specifically, a method for confirming that an electrode contains a titanium-containing oxide, a method for measuring the average primary particle diameter of particles of a titanium-containing oxide, a method for measuring the pore specific surface area by a nitrogen adsorption method, and a method for measuring the particle specific surface area of titanium-containing oxides. We will explain the measurement method of the diameter distribution and the method of obtaining the radial distribution function by Fourier transforming the EXAFS spectrum obtained by measuring the extended X-ray absorption fine structure (EXAFS) of the K absorption edge of Al. .

If the electrode to be measured is built into a battery, remove the electrode as a measurement sample from the battery as follows. Discharge the battery and remove the electrodes by disassembling it in a glove box with an inert atmosphere, such as an argon atmosphere. After washing the electrode with diethyl carbonate, it is vacuum dried. In this way, a measurement sample is obtained.

[Confirmation of titanium-containing oxide]
The active material contained in the electrode can be identified as described below, and the presence or absence of titanium-containing oxide can be confirmed.

After washing and drying the electrode taken out from the battery as described above, the obtained electrode is attached to a glass sample plate. At this time, be careful to use double-sided tape or the like to prevent the electrodes from peeling off or floating. If necessary, the electrodes may be cut to an appropriate size for attachment to the glass sample plate. Furthermore, a Si standard sample may be added on the electrode to correct the peak position.

Next, the glass plate with the electrode attached is placed in a powder X-ray diffraction (XRD) device, and a diffraction pattern is obtained using Cu-Kα rays. An X-ray diffraction pattern can be obtained by performing measurements using Cu-Kα radiation as a radiation source and changing 2θ in a measurement range of 5° to 90°.

As a device for powder X-ray diffraction measurement, for example, SmartLab manufactured by Rigaku is used. The measurement conditions are as follows:
X-ray source: Cu target Output: 45kV, 200mA
Solar slit: 5° for both incident and receiving light
Step width: 0.02deg
Scan speed: 20deg/min Semiconductor detector: D/teX Ultra 250
Sample plate holder: flat glass sample plate holder (thickness 0.5mm)
Measurement range: 5°≦2θ≦90°.

When using other equipment, in order to obtain measurement results equivalent to those above, perform measurements using standard Si powder for powder X-ray diffraction to obtain peak intensities and peaks equivalent to those obtained with the above equipment. Find a condition where the top position matches the above device, and measure the sample under that condition.

When the active material to be measured contains a spinel-type lithium titanium composite oxide, it can be confirmed by X-ray diffraction measurement that an X-ray diffraction pattern belonging to the space group Fd-3m is obtained. The peaks in this X-ray diffraction pattern that exist within a 2θ range of 17° to 20° can be assigned to the (111) plane.

Next, the sample containing the active material is observed using a scanning electron microscope (SEM). Even during SEM observation, it is desirable to prevent the sample from coming into contact with the atmosphere and to perform the observation in an inert atmosphere such as argon or nitrogen.

In the 3000x SEM observation image, select some particles that have the form of primary particles or secondary particles that are confirmed within the field of view. At this time, the particles are selected so that the particle size distribution of the selected particles is as wide as possible. For the observed active material particles, the types and composition of the constituent elements of the active material are identified using energy dispersive X-ray spectroscopy (EDX). Thereby, the type and amount of elements other than Li among the elements contained in each selected particle can be specified. The same operation is performed for each of the plurality of active material particles to determine the mixed state of the active material particles.

Next, the active material-containing layer is separated from the current collector using, for example, a spatula to obtain a powdered electrode mixture sample containing the active material. The collected powder sample is washed with acetone and dried. The resulting powder is dissolved in hydrochloric acid, the conductive agent is removed by filtration, and then diluted with ion-exchanged water to prepare a measurement sample. The metal content ratio in the measurement sample is calculated by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

If there are multiple types of active materials, the mass ratio is estimated from the content ratio of elements specific to each active material. The ratio between the specific element and the mass of the active material is determined from the composition of the constituent elements determined by energy dispersive X-ray spectroscopy.

In this way, the active material contained in the electrode can be identified.

[Measurement of average primary particle diameter of active material]
After washing and drying the electrode taken out from the battery as described above, the active material-containing layer is separated from the current collector using, for example, a spatula to obtain a powdered electrode composite sample containing the active material. .

Next, the powdered sample is analyzed using the above-described X-ray diffraction measurement and SEM-EDX to confirm the presence of the active material particles to be measured.

The magnification for SEM observation is preferably about 5000x. If the particle morphology is difficult to distinguish due to additives such as conductive agents, use a SEM (FIB-SEM) equipped with a focused ion beam (FIB) to examine the cross section of the electrode (for example, the cross section of the active material-containing layer). ) and observe it. The magnification is adjusted to obtain an image containing 50 or more particles.

Next, the particle diameters of all particles included in the obtained image are measured. For particles having the form of secondary particles, the particle diameter of each primary particle contained in the secondary particles is measured. When the particles are spherical, the diameter is defined as the particle size. If the particles have a shape other than spherical, first measure the length of the smallest diameter of the particle and the length of the largest diameter of the same particle. Let these average values be the average primary particle diameter.

[Measurement of pore specific surface area by nitrogen adsorption method]
The pore specific surface area of the electrode determined by the nitrogen adsorption method corresponds to the BET specific surface area of the electrode. The BET specific surface area is a specific surface area determined by the BET method, and is calculated by the nitrogen adsorption method. The analysis is performed, for example, by the following method.

The electrode obtained by washing and drying after being removed from the battery as described above is cut to match the size of the measurement cell and used as a measurement sample. For example, a 1/2 inch glass cell is used as the measurement cell. As a pretreatment method, this measurement cell is degassed by drying under reduced pressure at a temperature of about 100° C. or more for 15 hours. As the measuring device, for example, Quantasorb QS-20 manufactured by Quantachrome is used.

A cut electrode as a measurement sample is placed in a measurement cell, and a mixed gas of 30% nitrogen-helium balance is flowed. The glass cell is immersed in liquid nitrogen while the gas is flowing, and the nitrogen in the mixed gas is adsorbed onto the sample surface. After the adsorption is completed, the glass cell is returned to room temperature and the adsorbed nitrogen is desorbed. Then, since the nitrogen concentration of the mixed gas increases, the amount of increase is quantified. The surface area (m ² ) of the sample is calculated from this amount of nitrogen and the cross-sectional area of the nitrogen molecules. This is divided by the sample amount (g) to calculate the pore specific surface area (numerical unit: m ² /g).

[Measurement of particle size distribution]
The particle size distribution of the electrode can be measured by the laser diffraction/scattering method described below.

After cleaning and drying the electrode taken out from the battery, the active material-containing layer is separated from the current collector using, for example, a spatula to obtain a powdered electrode mixture sample containing the active material. Next, a powdered sample is placed into a measurement cell filled with N-methylpyrrolidone (NMP) until a measurable concentration is reached. Note that the capacity of the measurement cell and the measurable concentration vary depending on the particle size distribution measuring device.

The measurement cell containing NMP and the electrode mixture sample dissolved therein is irradiated with ultrasonic waves for 5 minutes. The output of the ultrasonic wave is, for example, within the range of 35W to 45W. For example, when about 50 ml of NMP is used as a solvent, the solvent mixed with the measurement sample is irradiated with ultrasonic waves with an output of about 40 W for 300 seconds. Such ultrasonic irradiation allows the conductive agent particles and active material particles to be deagglomerated.

Insert the measurement cell into a particle size distribution measuring device using laser diffraction/scattering method to measure particle size distribution. Examples of particle size distribution measuring devices include Microtrac3100 and Microtrac3000II.

In this way, the particle size distribution of the electrode can be obtained.

An example of the particle size distribution measured by the laser diffraction/scattering method for such an electrode is shown in FIG. 2 as a graph. The graph corresponds to a histogram representing the particle size distribution of particles included in the electrode.

The particle size distribution of one example is shown by a solid line 41, and the particle size distribution of another example is shown by a broken line 42. A solid line 41 represents the particle size distribution for a more preferred embodiment of the electrode. The particle size distribution indicated by the broken line 42 includes a peak showing a maximum value within a range of 0.5 μm or more and 1 μm or less, and does not include any other portion showing a maximum value. The particle size distribution shown by the solid line 41 is bimodal, including a first peak showing a maximum value within the range of 0.5 μm or more and 1 μm or less, and a second peak showing the maximum value within the range of 3 μm or more and 10 μm or less. It has a shape.

[Measurement of wide-area X-ray absorption fine structure and Fourier transformation]
Broad-area X-ray absorption fine structure measurements and Fourier transformations can be performed as follows.

After cleaning and drying the electrode taken out from the battery under an inert atmosphere, introduce the sample into the vacuum chamber of the measuring machine. The X-ray absorption fine structure (XAFS) spectrum is measured by irradiating the sample with X-rays and measuring the amount of X-ray absorption (electron yield method). In the XAFS spectrum, the structure near the absorption edge is XANES (X-ray Absorption Near Edge Structure), and the wide-range X-ray absorption fine structure that appears on the higher energy side of about 100 eV or more from the absorption edge is EXAFS (Extended X-ray Absorpt). ion Fine Structure) . Information on the valence and structure of the atom of interest can be obtained from XANES, and in EXAFS analysis, the local structure of the sample (atomic species around the atom of interest, Information on valence, distance) can be obtained. The obtained spectrum data is normalized before and after the absorption edge to derive a XANES spectrum.

EXAFS oscillation (χ(k)) obtained by EXAFS analysis is expressed by the following equation based on plane wave single scattering theory.

Here, the subscript i is the coordination sphere number, S ₀ ² is the attenuation factor, N _i is the number of atoms in the i-th coordination sphere, F _i (k _i ) is the backscattering intensity, k _i is the wave number, r _i is the bond distance, σ _i is the Debye-Waller (DW) factor, and φi (k _i ) is the phase shift.

Generally, as the number of atoms in each coordination sphere (N _i ) decreases, the amplitude of the EXAFS vibration (χ(k)) decreases. Furthermore, from the above equation, the shorter the bond distance (r _i ) with the measurement atom, the more information about the atom is reflected in the EXAFS vibration (χ(k)).

The EXAFS function (k ³ χ(k)) is obtained by multiplying the EXAFS vibration (χ(k)) by a weight of k ³ to enhance the vibration on the high wave number side. By comparing the amplitudes of the EXAFS functions (k ³ χ(k)), it is possible to estimate the number of coordination atoms of the measured atoms.

In this embodiment, a radial distribution function derived by Fourier transforming the EXAFS spectrum in the region of 2.5≦k≦7 (corresponding to the EXAFS region) of the EXAFS function (k ³ χ (k)) is obtained. . Athena (Non-Patent Document 1) can be used as the analysis software.

An example of the radial distribution function obtained by FT-EXAFS for such an electrode is shown as a graph in FIG. 3.

A solid line 49 indicates the spectrum obtained for the electrode, and a broken line 90 indicates the spectrum obtained for the aluminum alkoxide additive alone used to prepare the electrode. As shown in FIG. 3, the shapes of both spectra are similar. Therefore, it can be seen that the added aluminum alkoxide exists on the active material on the electrode surface in a form that generally maintains its chemical structure, and has not changed into other components such as alumina.

The peak A within the range of 1.1 Å or more and 1.5 Å or less can be attributed to the Al--O bond. Peak B within the range of 2.8 Å or more and 3.2 Å or less can be attributed to the Al--O--C bond. In an electrode in which the Al--O--C bond of a single aluminum alkoxide remains intact even on the surface of the active material, side reactions on the surface of the active material are suppressed.

The electrode according to the first embodiment includes an active material having an average primary particle diameter of 200 nm or more and 600 nm or less. The active material includes a titanium-containing oxide. The electrode has a particle size distribution _{in which the ratio D 90} _/ D ₁₀ of the particle size D 90 is 17 or more and 27 or less. The electrode surface contains Al, and in the radial distribution function obtained by FT-EXAFS of the K absorption edge of Al, peak A appears in the range of 1.1 Å to 1.5 Å and peak A of 2.8 Å to 3.2 Å. The respective peak intensities I _A and I _B of the peak B appearing in the range satisfy the relationship 3.5≦I _B /I _A ≦9. The electrode has excellent large current performance and storage performance at low temperatures, and can realize a battery with high energy density.

(Second embodiment)
According to a second embodiment, a battery is provided. The battery includes a positive electrode, a negative electrode, and an electrolyte. At least one of the positive electrode and the negative electrode includes the electrode according to the first embodiment.

Such a battery may further include a separator placed between the positive electrode and the negative electrode. The positive electrode, negative electrode, and separator can constitute an electrode group. An electrolyte may be retained in the electrode group.

Moreover, such a battery can further include an exterior member that houses the electrode group and the electrolyte.

Furthermore, such a battery can further include a positive electrode terminal electrically connected to the positive electrode and a negative electrode terminal electrically connected to the negative electrode. At least a portion of the positive electrode terminal and at least a portion of the negative electrode terminal may extend outside the exterior member.

Such a battery may be, for example, a lithium ion secondary battery. Further, the battery includes, for example, a non-aqueous electrolyte battery containing a non-aqueous electrolyte as an electrolyte.

Hereinafter, the negative electrode, positive electrode, electrolyte, separator, exterior member, positive electrode terminal, and negative electrode terminal will be explained in detail.

(1) Negative electrode The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer (negative electrode composite material layer) supported on one side or both surfaces of the negative electrode current collector and containing a negative electrode active material, a conductive agent, and a binder. including.

The negative electrode may be the electrode according to the first embodiment. In the embodiment as a negative electrode, the negative electrode current collector, negative electrode active material, and negative electrode active material-containing layer of the negative electrode correspond to the current collector, active material, and active material-containing layer of the electrode according to the first embodiment, respectively. . Since the electrode according to the first embodiment has been described in detail above, the description of the negative electrode will be omitted here.

(2) Positive electrode The positive electrode includes a positive electrode current collector, a positive electrode active material-containing layer (positive electrode composite layer) supported on one side or both front and back surfaces of the positive electrode current collector, and containing a positive electrode active material, a conductive agent, and a binder. including.

The battery according to the second embodiment may include the electrode according to the first embodiment as a positive electrode. Alternatively, the battery may include a positive electrode having a different configuration from the electrode according to the first embodiment. Hereinafter, a positive electrode different from the electrode according to the first embodiment will be described.

As the positive electrode active material, lithium-containing nickel cobalt manganese oxide (for example, a compound represented by Li _w _Nix Co _y Mn _z O ₂ where 0<w≦1, x+y+z=1; or Li _{1 -s} Ni _1-t-u-v Co _t Mn _u M1 _v O ₂ , where M1 is 1 selected from the group consisting of Mg, Al, Si, Ti, Zn, Zr, Ca and Sn. -0.2<s<0.5, 0<t<0.5, 0<u<0.5, 0≦v<0.1, t+u+v<1) can. In addition, various oxides such as lithium-containing cobalt oxide (e.g., LiCoO ₂ ), manganese dioxide, lithium-manganese composite oxide (e.g., LiMn ₂ O ₄ , LiMnO ₂ ), lithium-containing nickel oxide (e.g., LiNiO ₂ ), lithium-containing nickel cobalt oxide (e.g., LiNi _0.8 Co _0.2 O ₂ ), lithium-containing iron oxide, lithium-containing vanadium oxide, and chalcogen compounds such as titanium disulfide and molybdenum disulfide. It may also include. The number of types of positive electrode active materials used can be one or more.

Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, styrene-butadiene rubber (SBR), and carboxymethyl cellulose. ;CMC), polyimide, polyamide, etc. The number of types of binders can be one or more.

Examples of the conductive agent include carbon black such as acetylene black and Ketjen black, graphite, carbon fiber, carbon nanotubes, and fullerene. The number of types of conductive agents can be one or more.

The mixing ratio of the positive electrode active material, conductive agent, and binder in the positive electrode active material-containing layer is 80% by mass or more and 95% by mass or less of the positive electrode active material, 3% by mass or more and 18% by mass or less of the conductive agent, and 2% by mass of the binder. The content is preferably 17% by mass or less.

As the current collector, aluminum foil or aluminum alloy foil is preferable, and the average crystal grain size thereof is desirably 50 μm or less, more preferably 30 μm or less, and still more preferably 5 μm or less. A current collector made of aluminum foil or aluminum alloy foil with such an average crystal grain size can dramatically increase the strength, and it becomes possible to increase the density of the positive electrode with high pressing pressure, making it possible to improve the battery. Capacity can be increased.

Aluminum foil or aluminum alloy foil with an average grain size of 50 μm or less is complexly influenced by many factors such as material composition, impurities, processing conditions, heat treatment history, and annealing heating conditions, and the above (diameter) depends on the manufacturing process. It is adjusted by combining the above factors.

The thickness of the current collector is preferably 20 μm or less, more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% or more. As the aluminum alloy, an alloy containing elements such as magnesium, zinc, and silicon is preferable. On the other hand, the content of transition metals such as iron, copper, nickel, and chromium is preferably 1% or less.

For the positive electrode, for example, a positive electrode active material-containing layer is prepared by suspending a positive electrode active material, a conductive agent, and a binder in an appropriate solvent, applying the resulting slurry to a current collector and drying it, and then pressing. It is produced by applying. Alternatively, the positive electrode active material, the conductive agent, and the binder may be formed into pellets and used as the positive electrode active material-containing layer.

The positive electrode active material-containing layer preferably has a porosity of 20% or more and 50% or less. A positive electrode including a positive electrode active material-containing layer having such a porosity has high density and excellent affinity with an electrolyte. A more preferable porosity is 25% or more and 40% or less.

The density of the positive electrode active material-containing layer is preferably 2.5 g/cm ³ or more.

(3) Electrolyte Examples of the electrolyte include a liquid non-aqueous electrolyte prepared by dissolving an electrolyte salt (solute) in a non-aqueous solvent, a gel-like non-aqueous electrolyte made by combining a liquid non-aqueous electrolyte and a polymer material, and the like.

Examples of the electrolyte salt include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), and difluorophosphate. Examples include lithium salts such as lithium (LiPO ₂ F ₂ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), and lithium bistrifluoromethylsulfonylimide [LiN(CF ₃ SO ₂ ) ₂ ]. These electrolyte salts may be used alone or in combination of two or more.

The electrolyte salt is preferably dissolved in the nonaqueous solvent in a range of 0.5 mol/L or more and 2.5 mol/L or less.

Examples of nonaqueous solvents include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC); dimethyl carbonate (DMC), and ethyl methyl. Chain carbonates such as carbonate (EMC) and diethyl carbonate (DEC); cyclic ethers such as tetrahydrofuran (THF) and 2-methyl tetrahydrofuran (2MeTHF); dimethoxyethane ( Chain ethers such as dimethoxy ethane (DME); cyclic esters such as γ-butyrolactone (BL); chain esters such as methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate; acetonitrile (AN ); organic solvents such as sulfolane (SL); These organic solvents can be used alone or in the form of a mixture of two or more.

Examples of polymeric materials used in the gel-like nonaqueous electrolyte include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), and the like.

(4) Separator Examples of the separator include porous films containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), nonwoven fabrics made of synthetic resin, etc. I can do it.

(5) Exterior member The exterior member may be formed from a laminate film or may be constructed from a metal container. If a metal container is used, the lid may be integral with the container or a separate member. The wall thickness of the metal container is preferably 0.5 mm or less, more preferably 0.2 mm or less. Examples of the shape of the exterior member include a flat type, square type, cylindrical type, coin type, button type, sheet type, and laminated type. The exterior member may be an exterior member for a small battery mounted on a portable electronic device or the like, as well as a large battery mounted on a two-wheel or four-wheel vehicle.

The thickness of the laminate film exterior member is preferably 0.2 mm or less. Examples of laminate films include multilayer films that include a resin film and a metal layer disposed between the resin films. The metal layer is preferably aluminum foil or aluminum alloy foil for weight reduction. For the resin film, a polymer material such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate (PET) can be used. The laminate film can be sealed by heat fusion and formed into the shape of the exterior member.

The metal container is made from aluminum or aluminum alloy. As the aluminum alloy, an alloy containing elements such as magnesium, zinc, and silicon is preferable. In aluminum or an aluminum alloy, the content of transition metals such as iron, copper, nickel, and chromium is preferably 100 ppm or less in order to dramatically improve long-term reliability and heat dissipation in a high-temperature environment.

It is desirable that the metal container made of aluminum or aluminum alloy has an average crystal grain size of 50 μm or less, more preferably 30 μm or less, and still more preferably 5 μm or less. By setting the average crystal grain size to 50 μm or less, the strength of a metal container made of aluminum or an aluminum alloy can be dramatically increased, and the container can be made even thinner. As a result, it is possible to create a battery that is lightweight, has high output, and has excellent long-term reliability, making it suitable for use in vehicles.

An example of such a battery will be described with reference to FIGS. 4 and 5. The flat battery shown in FIG. 4 includes a flat wound electrode group 1, an exterior member 2, a positive terminal 7, a negative terminal 6, and an electrolyte (not shown). The exterior member 2 is a bag-shaped exterior member made of a laminate film. The wound electrode group 1 is housed in an exterior member 2. The wound electrode group 1 includes a positive electrode 3, a negative electrode 4, and a separator 5, as shown in FIG. It is formed by winding and press molding.

The positive electrode 3 includes a positive electrode current collector 3a and a positive electrode active material-containing layer 3b. The positive electrode active material containing layer 3b contains a positive electrode active material. The positive electrode active material containing layer 3b is formed on both sides of the positive electrode current collector 3a. The negative electrode 4 includes a negative electrode current collector 4a and a negative electrode active material-containing layer 4b. The negative electrode active material containing layer 4b contains a negative electrode active material. In the outermost portion of the negative electrode 4, a negative electrode active material-containing layer 4b is formed only on one inner surface of the negative electrode current collector 4a. In other parts of the negative electrode 4, negative electrode active material-containing layers 4b are formed on both sides of the negative electrode current collector 4a.

As shown in FIG. 4, the positive electrode terminal 7 is connected to the positive electrode 3 near the outer peripheral end of the wound electrode group 1. Further, a negative electrode terminal 6 is connected to the negative electrode 4 in the outermost layer portion. The positive electrode terminal 7 and the negative electrode terminal 6 extend outside through the opening of the exterior member 2.

Such a battery is not limited to the configuration shown in FIGS. 4 and 5 described above, but may have the configuration shown in FIG. 6, for example.

In the square battery shown in FIG. 6, the wound electrode group 11 is housed in a metal bottomed rectangular cylindrical container 12 that serves as an exterior member. A rectangular lid 13 is welded to the opening of the container 12. The flat wound electrode group 11 may have the same configuration as the wound electrode group 1 described with reference to FIGS. 3 and 4, for example.

One end of the negative electrode tab 14 is electrically connected to the negative electrode current collector, and the other end is electrically connected to the negative electrode terminal 15. The negative electrode terminal 15 is fixed to the rectangular lid 13 by a hermetic seal with a glass material 16 interposed therebetween. One end of the positive electrode tab 17 is electrically connected to a positive electrode current collector, and the other end is electrically connected to a positive electrode terminal 18 fixed to the rectangular lid 13.

The negative electrode tab 14 is made of, for example, a material such as aluminum or an aluminum alloy containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, and Si. The negative electrode tab 14 is preferably made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

The positive electrode tab 17 is made of, for example, a material such as aluminum or an aluminum alloy containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, and Si. The positive electrode tab 17 is preferably made of the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

Note that the illustrated battery uses a wound-type electrode group in which a separator is wound together with a positive electrode and a negative electrode, but a laminated-type electrode group in which the separator is folded ninety-nine times and positive and negative electrodes are alternately arranged at the folded parts is also used. Groups may also be used.

The battery according to the second embodiment includes the electrode according to the first embodiment. Therefore, the battery can be used at a large current even under low temperature conditions, and can exhibit excellent storage performance even under low temperature conditions. Batteries also have high energy density.

(Third embodiment)
According to a third embodiment, a battery pack is provided. This battery pack includes the battery according to the second embodiment.

The battery pack according to the third embodiment can include one or more batteries (single cells) according to the second embodiment described above. A plurality of batteries that can be included in such a battery pack can also be electrically connected to each other in series or parallel to form a battery pack. Such a battery pack may include a plurality of assembled batteries.

Next, an example battery pack according to the third embodiment will be described with reference to the drawings.

FIG. 7 is an exploded perspective view of an example battery pack according to the second embodiment. FIG. 8 is a block diagram showing an electric circuit of the battery pack of FIG. 7.

The battery pack 20 shown in FIGS. 7 and 8 includes a plurality of single cells 21. The unit cell 21 may be an example of a flat battery according to the second embodiment described with reference to FIG. 6 .

The plurality of unit cells 21 are stacked so that the negative terminals 51 and positive terminals 61 extending to the outside are aligned in the same direction, and are fastened with adhesive tape 22 to form the assembled battery 23. These unit cells 21 are electrically connected to each other in series as shown in FIG.

The printed wiring board 24 is arranged to face the side surface from which the negative terminal 51 and the positive terminal 61 of the unit cell 21 extend. As shown in FIG. 8, the printed wiring board 24 is equipped with a thermistor 25, a protection circuit 26, and a terminal 27 for supplying electricity to an external device. Note that an insulating plate (not shown) is attached to the printed wiring board 24 on the surface facing the assembled battery 23 in order to avoid unnecessary connection with the wiring of the assembled battery 23.

The positive lead 28 is connected to the positive terminal 61 located at the bottom of the battery pack 23, and its tip is inserted into the positive connector 29 of the printed wiring board 24 to be electrically connected. The negative electrode lead 30 is connected to a negative electrode terminal 51 located at the top layer of the assembled battery 23, and its tip is inserted into the negative electrode connector 31 of the printed wiring board 24 and electrically connected thereto. These

connectors

29 and 31 are connected to the protection circuit 26 through

wiring

32 and 33 formed on the printed wiring board 24.

The thermistor 25 detects the temperature of the cell 21, and its detection signal is transmitted to the protection circuit 26. The protection circuit 26 can cut off the positive wiring 34a and the negative wiring 34b between the protection circuit 26 and the terminal 27 for supplying electricity to an external device under predetermined conditions. An example of the predetermined condition is, for example, when the temperature detected by the thermistor 25 becomes a predetermined temperature or higher. Another example of the predetermined condition is, for example, when overcharging, overdischarging, overcurrent, etc. of the single battery 21 is detected. This detection of overcharging and the like is performed for each individual cell 21 or the entire assembled battery 23. When detecting each cell 21, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 21. In the case of the battery pack 20 shown in FIGS. 7 and 8, a wiring 35 for detecting voltage is connected to each cell 21. A detection signal is transmitted to the protection circuit 26 through these wirings 35.

Protective sheets 36 made of rubber or resin are arranged on three sides of the assembled battery 23, excluding the sides from which the positive electrode terminal 61 and the negative electrode terminal 51 protrude.

The assembled battery 23 is stored in a storage container 37 together with each protective sheet 36 and printed wiring board 24. That is, the protective sheet 36 is arranged on both inner surfaces in the long side direction and the inner surface in the short side direction of the storage container 37, and the printed wiring board 24 is arranged on the inner surface on the opposite side in the short side direction. The assembled battery 23 is located in a space surrounded by the protective sheet 36 and the printed wiring board 24. The lid 38 is attached to the upper surface of the storage container 37.

Note that heat shrink tape may be used to fix the battery pack 23 instead of the adhesive tape 22. In this case, protective sheets are placed on both sides of the battery pack, a heat-shrink tape is wound around the battery pack, and the battery pack is bundled by heat-shrinking the heat-shrink tape.

Although FIGS. 7 and 8 show a form in which the single cells 21 are connected in series, they may be connected in parallel to increase the battery capacity. Furthermore, assembled battery packs can be connected in series and/or in parallel.

Further, the aspect of the battery pack may be changed as appropriate depending on the use. The preferred use of the battery pack is one in which good cycle performance is desired when drawing a large current. Specific applications include power sources for digital cameras, and in-vehicle applications such as two- to four-wheel hybrid electric vehicles, two- to four-wheel electric vehicles, and assisted bicycles. Such a battery pack is particularly suitable for use in a vehicle.

The battery pack according to the third embodiment includes the battery according to the second embodiment. Therefore, such a battery pack can be used with a large current even under low temperature conditions, and can exhibit excellent storage performance even under low temperature conditions. Additionally, the battery pack has a high energy density.

[Example]
Examples will be described below, but the present invention is not limited to the examples listed below unless it goes beyond the gist of the present invention.

(Example 1)
In Example 1, the non-aqueous electrolyte battery of Example 1 was produced by the following procedure.

[Preparation of negative electrode]
A lithium titanium composite oxide powder having a composition of Li ₄ Ti ₅ O ₁₂ and a spinel structure was prepared in the following procedure.

First, anatase titanium oxide was added to a solution of lithium hydroxide dissolved in pure water, stirred, and dried. These raw materials were mixed so that the molar ratio of Li:Ti in the mixture was 4:5. Prior to mixing, the raw materials were thoroughly ground.

The mixed raw materials were fired at 870°C for 2 hours in an air atmosphere. Next, the fired product was pulverized with a ball mill using zirconia balls as the media, and then washed with water. After being subjected to heat treatment at 600° C. for 30 minutes in an air atmosphere, it was classified. Thus, a product powder was obtained.

The average primary particle diameter of the obtained product powder was analyzed using SEM. As a result, it was found that the obtained product powder was in the form of primary particles with an average primary particle size of 400 nm.

A part of the above primary particles were granulated using a spray dryer. In this way, a powder in the form of secondary particles in which primary particles were aggregated was obtained.

The composition and crystal structure of the obtained product were also analyzed using ICP and X-ray diffraction measurements. As a result, it was found that the obtained product was a lithium titanium composite oxide having a spinel crystal structure and a composition of Li ₄ Ti ₅ O ₁₂ . In the X-ray diffraction spectrum, the half width of the peak attributed to the (111) plane was 0.15 or less, indicating that a product with high crystallinity was obtained. A powder of this product was used as a negative electrode active material.

Next, acetylene black as a conductive agent was added to the spinel-type lithium titanium composite oxide powder as a negative electrode active material, and mixed with a Henschel mixer to obtain a mixture. Polyvinylidene fluoride (PVdF) as a binder, N-methylpyrrolidone (NMP) as a dispersion medium, and aluminum alkoxide were added to this mixture, and the mixture was kneaded with a jet paster. Di-2-butoxyaluminum ethyl acetoacetate was added as the aluminum alkoxide. In this way, a slurry (slurry for producing a negative electrode) was obtained.

In the above mixing, the amounts of acetylene black and PVdF added were adjusted so that the ratio of negative electrode active material: acetylene black: PVdF in the resulting slurry was 88 parts by mass: 10 parts by mass: 2 parts by mass. Further, the amount of aluminum alkoxide added was adjusted to 0.5% by mass based on the negative electrode active material.

This slurry was applied to both sides of a current collector made of aluminum foil having a thickness of 15 μm, and the coating film was dried at 125°C. Next, the dried coating film was subjected to roll press treatment. Furthermore, vacuum drying was performed in a 90°C environment for 12 hours. In this way, a negative electrode was produced that included a current collector and negative electrode active material-containing layers formed on both surfaces of the current collector and having an electrode density (not including the current collector) of 2.1 g/cm ³ . The thickness of the negative electrode active material-containing layer formed on each surface of the current collector was 30 μm.

[Preparation of positive electrode]
First, a powder of lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) was prepared as a positive electrode active material. 5 parts by mass of acetylene black as a conductive agent was added to 90 parts by mass of the positive electrode active material, and mixed with a Henschel mixer to obtain a mixed positive electrode active material. Next, 5 parts by mass of PVdF and N-methylpyrrolidone (NMP) were added to this mixed positive electrode active material at a constant ratio, and the mixture was kneaded with a planetary mixer to form a slurry. This slurry was applied to both sides of a current collector made of aluminum foil with a thickness of 15 μm, and the coating film was dried. Furthermore, the dried coating film was subjected to roll press treatment. In this way, a positive electrode was produced that included a current collector and positive electrode active material-containing layers formed on both surfaces of the current collector and having an electrode density (excluding the current collector) of 3.0 g/cm ³ .

[Preparation of electrode group]
Two separators made of porous polyethylene films with a thickness of 20 μm were prepared.

Next, the previously produced positive electrode, one separator, the previously produced negative electrode, and another separator were laminated in this order to obtain a laminate. This laminate was spirally wound. By hot pressing this at 90° C., a flat electrode group having a width of 30 mm and a thickness of 3.0 mm was produced.

The obtained electrode group was housed in a pack made of a laminate film and vacuum-dried at 85° C. for 24 hours. The laminate film was constructed by forming polypropylene layers on both sides of a 40 μm thick aluminum foil, and had a total thickness of 0.1 mm.

[Preparation of liquid nonaqueous electrolyte]
A mixed solvent was prepared by mixing propylene carbonate (PC) and dimethyl carbonate (MEC) at a volume ratio of 1:1. A liquid non-aqueous electrolyte was prepared by dissolving 1M of LiPF ₆ as an electrolyte in this mixed solvent.

[Manufacture of non-aqueous electrolyte secondary battery]
A liquid nonaqueous electrolyte was injected into the laminate film pack containing the electrode group as described above. Thereafter, the pack was completely sealed by heat sealing. In this way, a nonaqueous electrolyte secondary battery having the structure shown in FIGS. 4 and 5 described above, having a width of 35 mm, a thickness of 3.2 mm, a height of 65 mm, and a rated capacity of 1 Ah was manufactured.

Next, the produced non-aqueous electrolyte secondary battery was charged at a charging rate of 1 A (1 C) in a 25° C. environment to adjust the SOC to 40%, and was subjected to heat treatment at 70° C. for 24 hours. Next, the battery was allowed to cool to room temperature, and then discharged to 1.5 V at 1 A in a 25° C. environment, and then charged at 1 A to adjust the SOC to 50%.

[measurement]
Regarding the nonaqueous electrolyte battery manufactured as described above, the pore specific surface area (BET specific surface area) of the negative electrode was measured by the nitrogen adsorption method described above. The results obtained are shown in Table 1 below.

The particle size distribution of the negative electrode contained in the battery was measured using the laser diffraction/scattering method described above. The ratio D ₉₀ /D ₁₀ of D ₉₀ to D ₁₀ in the obtained particle size distribution was calculated. In addition, we confirmed the first peak with a maximum value in the range of 0.5 μm or more and 1 μm or less, and the second peak with a maximum value in the range of 3 μm or more and 10 μm or less, and determined the particle size distribution of the second peak. The ratio of the frequency of the first peak to the frequency was calculated. The calculation results are shown in Table 1 below.

In addition, component analysis of the negative electrode was performed using FT-EXAFS as described above. Check the peak A within the range of 1.1 Å to 1.5 Å and the peak B within the range of 2.8 Å to 3.2 Å in the obtained radial distribution function, and calculate the intensity ratio I _B between these peaks. /I _A was found. The results obtained are shown in Table 1 below.

(Example 2 and 3)
In Examples 2 and 3, the same procedure as in Example 1 was used except that the conditions for kneading with a jet paster when preparing the negative electrode slurry were changed so that negative electrodes with the design shown in Table 1 below were obtained. An electrolyte battery was manufactured. Specifically, in Example 2, the conditions were changed to decrease the rotational speed and the kneading time, and in Example 3, the conditions were changed to increase the rotational speed and the kneading time.

(Example 4)
In Example 4, a nonaqueous electrolyte battery was manufactured in the same manner as in Example 1, except that the ball mill conditions when preparing the negative electrode active material were changed so that the average primary particle size of the negative electrode active material was 200 nm. did. Specifically, the conditions were changed to increase the rotation speed of the ball mill and the grinding time.

(Example 5)
In Example 5, a non-aqueous electrolyte battery was produced in the same manner as in Example 1, except that the firing conditions for the raw materials when preparing the negative electrode active material were changed so that the average primary particle size of the negative electrode active material was 600 nm. Manufactured. Specifically, the conditions were changed to a higher firing temperature and longer firing time.

(Example 6)
In Example 6, a non-aqueous electrolyte battery was manufactured in the same manner as in Example 1, except that the aluminum alkoxide added to the slurry for producing the negative electrode was changed from di-2-butoxyaluminum ethyl acetoacetate to aluminum trisec-butoxide. did.

(Example 7)
In Example 7, a non-aqueous electrolyte battery was manufactured in the same manner as in Example 1, except that the heat treatment conditions after washing with water were changed to adjust the residual moisture content when preparing the negative electrode active material. Specifically, the conditions were changed to lower the heat treatment temperature and shorten the heat treatment time.

(Examples 8 and 9)
In Examples 8 and 9, the non-aqueous electrolyte was prepared in the same manner as in Example 1, except that the degree of aggregation of the negative electrode active material particles was controlled by the amount of aluminum alkoxide added so as to obtain the negative electrode designed as shown in Table 1 below. Manufactured a battery. Specifically, in Example 8, the amount added was reduced to reduce aggregation, and in Example 9, the amount added was increased to increase aggregation.

(Examples 10 and 11)
In Examples 10 and 11, the same procedure as in Example 1 was followed except that the firing conditions for the negative electrode active material raw material and the kneading conditions with a jet paster were changed so that negative electrodes with the design shown in Table 1 below were obtained. A non-aqueous electrolyte battery was manufactured. Specifically, in Example 10, the firing temperature was increased, the firing time was increased, and the rotational speed and kneading time during kneading were decreased. In Example 11, the firing temperature was lowered and the firing time was shortened, and the rotational speed and kneading time during kneading were increased.

(Example 12)
In Example 12, a non-aqueous electrolyte battery was prepared in the same manner as in Example 1, except that the conditions for kneading with a jet paster when preparing the negative electrode slurry were changed so that a negative electrode with the design shown in Table 1 below was obtained. was manufactured. Specifically, the conditions were changed to increase the rotation speed and kneading time.

(Example 13)
In Example 13, the conditions of the ball mill when preparing the negative electrode active material were changed so that the average primary particle size of the negative electrode active material was 300 nm, and the negative electrode slurry was prepared so that the negative electrode designed as shown in Table 1 below was obtained. A non-aqueous electrolyte battery was manufactured in the same manner as in Example 1, except that the conditions for kneading with a jet paster were changed. Specifically, the conditions were changed to increase the rotation speed and grinding time of the ball mill, and the conditions were changed to decrease the rotation speed and kneading time of the jet paster.

(Example 14)
Example 14 was the same as Example 1 except that Li ₂ Na ₂ Ti ₆ O ₁₄ having a rectangular crystal structure was used as the negative electrode active material instead of Li ₄ Ti ₅ O ₁₂ having a spinel structure. A non-aqueous electrolyte battery was manufactured according to the procedure.

(Comparative example 1)
In Comparative Example 1, a non-aqueous electrolyte battery was produced in the same manner as in Example 1, except that the ball mill conditions when preparing the negative electrode active material were changed so that the average primary particle size of the negative electrode active material was 100 nm. did. Specifically, the conditions were changed to increase the rotation speed of the ball mill and the grinding time.

(Comparative example 2)
In Comparative Example 2, a non-aqueous electrolyte battery was produced in the same manner as in Example 1, except that the firing conditions for the raw materials when preparing the negative electrode active material were changed so that the average primary particle size of the negative electrode active material was 700 nm. Manufactured. Specifically, the conditions were changed to a higher firing temperature and longer firing time.

(Comparative example 3)
Comparative Example 3 was the same as Example 1 except that the aluminum alkoxide added to the negative electrode manufacturing slurry was changed from di-2-butoxyaluminum ethyl acetoacetate to aluminum isopropoxide (Al(Oi-Pr) ₃ ). A non-aqueous electrolyte secondary battery was manufactured according to the procedure.

(Comparative example 4)
In Comparative Example 4, a nonaqueous electrolyte battery was manufactured in the same manner as in Example 1, except that the heat treatment conditions after washing with water were changed to adjust the residual moisture content when preparing the negative electrode active material. Specifically, the conditions were changed to lower heat treatment temperature and shorter heat treatment time than in Example 7.

(Comparative example 5-6)
In Comparative Examples 5 and 6, the non-aqueous electrolyte was prepared in the same manner as in Example 1, except that the degree of aggregation of the negative electrode active material particles was controlled by the amount of aluminum alkoxide added so as to obtain the negative electrode designed as shown in Table 1 below. Manufactured a battery. Specifically, in Comparative Example 5, the amount added was decreased to reduce aggregation, and in Comparative Example 6, the amount added was increased to increase aggregation.

(Comparative Example 7)
In Comparative Example 7, a non-aqueous electrolyte battery was manufactured in the same manner as in Example 1, except that the addition of aluminum alkoxide to the slurry for preparing the negative electrode was omitted.

The same measurements as performed for the battery manufactured in Example 1 were also performed on each of the nonaqueous electrolyte batteries manufactured in Example 2-14 and Comparative Example 1-7. The results obtained are summarized in Table 1 below. Specifically, the composition and average primary particle diameter of the negative electrode active material, the specific pore surface area of the negative electrode determined by the nitrogen adsorption method, the ratio D ₉₀ /D ₁₀ determined from the particle size distribution of the negative electrode, and the frequency of the second peak. The ratio of the frequency of the first peak to the frequency of the first peak (frequency of the first peak/frequency of the second peak) and the peak intensity ratio I _B /I _A determined by FT-EXAFS are shown.

<Evaluation>
The performance of each of the non-aqueous electrolyte batteries manufactured in Example 1-14 and Comparative Example 1-7 was evaluated as follows. Specifically, the input performance and storage performance of each battery in a low-temperature environment were evaluated, and the energy density was measured.

(Low temperature input performance)
The input performance of the battery under low temperature conditions was evaluated by measuring the low temperature input resistance below.

First, the battery was charged at a constant current of 1A (1C) in a thermostatic chamber at 25°C until the battery voltage reached 2.7V, then constant voltage was charged until the current value reached 50mA, and then There was a pause of 1 minute. Next, after discharging to 1.5 V at a constant current of 200 mA, a rest period of 10 minutes was provided. This charge/discharge cycle was repeated three times, and the discharge capacity at the third discharge was measured and used as the reference charge capacity.

Next, constant current charging was performed at a charging rate of 1 A (1 C) until the battery voltage reached 2.7 V, followed by constant voltage charging until the current value reached 50 mA, and then 50% of the reference capacity was discharged.

Thereafter, the temperature of the thermostatic oven was set to -20°C, and the battery was left in the thermostatic oven for 3 hours. The voltage change was measured when the battery was charged at a constant current of 1 A for 10 seconds in a constant temperature bath at a low temperature (-20° C.). The value calculated by dividing the voltage change during charging for 10 seconds under low temperature conditions by the current value was defined as the low temperature input resistance.

However, for Example 1-13 and Comparative Example 1-7, the upper limit voltage during charging was set to 2.7V, but only for Example 14, which used a different negative electrode active material, the upper limit voltage during charging was set to 2.7V. It was set to 2.9V.

(Low temperature storage performance)
The low temperature storage performance of the battery was evaluated as follows.

First, the battery was charged at a constant current of 1A (1C) in a thermostatic chamber at 25°C until the battery voltage reached 2.7V, then constant voltage was charged until the current value reached 50mA, and then There was a pause of 1 minute. Then, it was discharged to 1.5V at a constant current of 200mA. The discharge capacity obtained at this time was measured. Subsequently, the battery was charged at 200 mA to a capacity equivalent to 50% of the measured discharge capacity. After a 10-minute rest period, charging was performed at 10 A for 10 seconds. The charging resistance of 10 A charging for 10 seconds was measured.

Next, the battery was charged so that the SOC (state of charge) was 100% and the battery voltage was 2.7V, and then stored in a thermostatic oven set at -20°C for 5 weeks. Thereafter, the resistance increase rate was measured by the following method.

The battery was taken out of the -20°C constant temperature bath and left in a room temperature environment until the battery temperature reached room temperature. Subsequently, the battery was placed in a constant temperature bath at 25° C., and after being discharged to 1.5 V at 1 A, a rest period of 10 minutes was provided. Next, the battery was charged to 2.7V at 1A in a constant temperature bath at 25°C, and the battery was charged at constant voltage at 2.7V until the current value reached 50mA. Thereafter, a rest period of 10 minutes was provided. Then, it was discharged to 1.5V at a constant current of 200mA. The discharge capacity obtained at this time was measured and defined as the recovery capacity. Thereafter, the battery was charged at 200 mA to a capacity corresponding to 50% of the recovery capacity. After a 10-minute rest period, charging was performed at 10 A for 10 seconds. The charging resistance of 10 A charging for 10 seconds was measured.

The ratio of the charging resistance measured after storage to the charging resistance measured before storage was calculated and used as the resistance increase rate.

However, only in Example 14, the upper limit voltage during charging was set to 2.9V.

(Energy density)
The energy density of the battery was measured as follows.

First, the battery was charged at a constant current of 1A (1C) in a thermostatic chamber at 25°C until the battery voltage reached 2.7V, then constant voltage was charged until the current value reached 50mA, and then There was a pause of 1 minute. Next, after discharging to 1.5 V at a constant current of 200 mA, a rest period of 10 minutes was provided. This charging/discharging cycle was repeated three times, and the discharge capacity obtained during the third cycle of discharge was measured and used as the reference discharge capacity.

Battery energy was determined by multiplying the standard discharge capacity by the average operating voltage during discharge. Next, the (volume) energy density of the battery was calculated by dividing the battery energy by the volume of the battery.

Table 2 below summarizes the performance evaluation results for each non-aqueous electrolyte battery manufactured in Examples 1-14 and Comparative Examples 1-7. As a result of the performance evaluation, the evaluation results of the above-mentioned low temperature input resistance, resistance increase rate during low temperature storage, and energy density were calculated relative to this reference value, with the performance value and measured value for Example 1 set as a reference value of 100. Indicates a numerical value.

As shown in Table 2, the negative electrode active material contains a titanium-containing oxide having an average primary particle diameter of 200 nm or more and 600 nm or less, and the ratio D ₉₀ /D ₁₀ in the particle size distribution of the negative electrode is 17 or more and 27 or less and FT. -For the battery of Example 1-14 in which the peak intensity ratio I _B /I _A in the radial distribution function obtained by EXAFS was 3.5 or more and 9 or less, the low-temperature input resistance and the resistance increase during low-temperature storage were The energy density was also kept low, and a good energy density was obtained.

On the other hand, in Comparative Example 1, the rate of increase in resistance when the battery was stored at low temperature was high, and the energy density of the battery was low. In Comparative Example 1, the average primary particle diameter of the negative electrode active material was small. It is presumed that because the negative electrode active material particles were small, there were many side reactions between the active material and the electrolyte, resulting in low storage performance and low energy density of the battery.

In Comparative Example 2, the low temperature input performance was low. In Comparative Example 2, the average primary particle diameter of the negative electrode active material was large. It is presumed that the input performance was low due to the large size of the negative electrode active material particles.

In Comparative Example 3, the rate of increase in resistance during low temperature storage was high. In Comparative Example 3, the value of the ratio I _B /I _A obtained from FT-EXAFS of Al for the negative electrode was low. It is assumed that the aluminum isopropoxide added to the negative electrode of Comparative Example 3 had a small amount of Al-O-C bonds present on the surface of the active material, and had little effect in reducing side reactions between the active material and the electrolyte. be done.

In Comparative Example 4, both the low-temperature input resistance and the rate of increase in resistance during low-temperature storage were high. In Comparative Example 4, the value of the ratio I _B /I _A obtained from FT-EXAFS of Al for the negative electrode was high. When preparing the negative electrode active material (spinel structure lithium titanate) used in Comparative Example 4, the heat treatment conditions after washing with water were moderated, resulting in a large amount of residual moisture. It is presumed that components derived from alkoxide were formed in excess.

In both Comparative Examples 5 and 6, the rate of increase in resistance during low temperature storage was high. In Comparative Examples 5 and 6, the degree of aggregation within the negative electrode was increased or decreased by increasing or decreasing the amount of aluminum alkoxide added. It is presumed that side reactions within the negative electrode increased due to the extreme degree of aggregation of the negative electrode material.

In Comparative Example 7, the rate of increase in resistance during low temperature storage was high. In Comparative Example 7, since aluminum alkoxide was not added to the negative electrode, the effect of reducing side reactions between the active material and the electrolyte could not be obtained by adding aluminum alkoxide.

Further, from a comparison between Example 1 and Example 14, which have similar battery designs other than the composition of the negative electrode active material, it is seen that the use of lithium titanate having a spinel structure tends to have better low-temperature performance. The operating potential of Li ₂ Na ₂ Ti ₆ O ₁₄ used in Example 14, which has a rectangular crystal structure, is lower than that of Li ₄ Ti ₅ O ₁₂ used in Example 1, so its reactivity with the electrolyte is high. be. This shows that the reaction between the negative electrode active material and the electrolyte occurs even under low temperature conditions.

According to one or more embodiments and examples described above, an electrode is provided that includes an active material that includes a titanium-containing oxide. The active material includes an active material having an average primary particle diameter of 200 nm or more and 600 nm or less. Regarding the electrode, the ratio D ₉₀ /D ₁₀ of the particle diameter D ₉₀ to the particle diameter D ₁₀ in the particle diameter distribution is 17 or more and 27 or less. In addition, at least a portion of the electrode surface contains Al, and the radial distribution function of Al on the electrode surface by FT-EXAFS has a peak A in the range of 1.1 Å to 1.5 Å and a peak 3 of 2.8 Å to 3. .2 Å or less, and the ratio I B / _{I A} of the peak intensity I _B of peak B to the peak intensity I _A of peak _A is 3.5 or more and 9 or less. The electrode has excellent large current performance and storage performance at low temperatures, and can realize batteries and battery packs with high energy density.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention as well as within the scope of the invention described in the claims and its equivalents.

DESCRIPTION OF SYMBOLS 1... Electrode group, 2... Exterior member, 3... Positive electrode, 3a... Positive electrode current collector, 3b... Positive electrode active material containing layer, 4... Negative electrode, 4a... Negative electrode current collector, 4b... Negative electrode active material containing layer, 4c... Negative electrode current collector tab, 5... Separator, 6... Negative electrode terminal, 7... Positive electrode terminal, 11... Electrode group, 12... Container, 13... Rectangular lid, 14... Negative electrode tab, 16... Glass material, 17... Positive electrode tab, 18 ...Positive electrode terminal, 20...Battery pack, 21...Single cell, 22...Adhesive tape, 23...Battery assembly, 24...Printed wiring board, 25...Thermistor, 26...Protection circuit, 27...Terminal for energizing external equipment, 28 ...Positive side lead, 29...Positive side connector, 30...Negative side lead, 31...Negative side connector, 32...Wiring, 33...Wiring, 34a...Positive side wiring, 34b...Minus side wiring, 35...Wiring, 36...Protection Sheet, 37... Storage container, 38... Lid, 51... Negative electrode terminal, 61... Positive electrode terminal.

Claims

An active material containing a titanium-containing oxide and having an average primary particle diameter of 200 nm or more and 600 nm or less,
The ratio D 90 /D 10 of the particle diameter D 90 at which the cumulative frequency from the small particle diameter side is 90% to the particle diameter D 10 at which the cumulative frequency from the small particle diameter side in the particle size distribution is 10 % is 17 or more. 27 or less,
At least a portion of its surface contains Al, and appears in a range of 1.1 Å or more and 1.5 Å or less in a radial distribution function obtained by Fourier transformation of a wide-range X-ray absorption fine structure spectrum of the K absorption edge of Al for the surface. It includes peak A and peak B appearing in the range of 2.8 Å to 3.2 Å, and the ratio I B /I A of the peak intensity I B of the peak B to the peak intensity I A of the peak A is 3.5. An electrode having a value of at least 9 and not more than 9.
The electrode according to claim 1, wherein the pore specific surface area measured by a nitrogen adsorption method is in a range of 2 m 2 /g or more and 10 m 2 /g or less.
The particle size distribution includes a first peak having a maximum value within a range of 0.5 μm or more and 1 μm or less, and a second peak having a maximum value within a range of 3 μm or more and 10 μm or less, and the frequency of the second peak The electrode according to claim 1 or 2, wherein the ratio of the frequency of the first peak to the frequency of the first peak is 0.18 or more and 0.35 or less.
The electrode according to any one of claims 1 to 3, wherein the half width of the (111) peak in the X-ray diffraction spectrum of the titanium-containing oxide is 0.15 or less.
The electrode according to any one of claims 1 to 4, wherein the titanium-containing oxide includes lithium titanate having a spinel structure.
a positive electrode;
a negative electrode;
Equipped with an electrolyte,
A battery, wherein the negative electrode includes the electrode according to any one of claims 1 to 5.
A battery pack comprising the battery according to claim 6.