JP2006202529A - Nonaqueous electrolyte secondary battery and its charging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which is superior in charge and discharge cycle property, and charged at a high voltage of 4.4 to 4.6 V based on lithium, and provide its charging method. <P>SOLUTION: In the nonaqueous electrolyte secondary battery 10 that is provided with a positive electrode 11 having a positive electrode active material, a negative electrode 12 having a negative electrode active material, and the nonaqueous electrolyte having a nonaqueous solvent and electrolyte salt, the positive electrode active material is obtained by mixing a lithium-cobalt compound oxide to which at least both zirconium and magnesium are added, and a lithium-manganese-nickel compound oxide containing at least both manganese and nickel having a laminar structure, and the potential of the positive electrode active material is 4.4 to 4.6 V based on lithium, and H-CMC in which ammonia is desorbed from carboxymethyl cellulose-ammonium (NH<SB>4</SB>-CMC) is contained as a binder in the negative electrode. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte secondary battery that is charged at a high voltage using a positive electrode active material having an electrode potential of 4.4 V to 4.6 V on a lithium basis, and particularly to a method for charging the same, and at least zirconium as the positive electrode active material. It consists of a mixture of a lithium cobalt composite oxide to which both of magnesium is added and a lithium manganese nickel composite oxide containing at least both manganese and nickel having a layered structure, and the potential is 4.4 V to 4.4 on the basis of lithium. A non-aqueous electrolyte excellent in cycle characteristics in which a positive electrode using a 6 V positive electrode active material and a negative electrode using a carbon material such as graphite as a negative electrode active material are charged at a high voltage of 4.3 V to 4.5 V The present invention relates to a secondary battery and a charging method thereof.

  With the rapid spread of portable electronic devices, the required specifications for the batteries used for them are becoming stricter year by year, and in particular, small and thin, high capacity, excellent cycle characteristics, and stable performance are required. Yes. In the field of secondary batteries, lithium non-aqueous electrolyte secondary batteries, which have a higher energy density than other batteries, are attracting attention, and the proportion of lithium non-aqueous electrolyte secondary batteries shows a significant increase in the secondary battery market. ing.

  By the way, in a device in which this type of non-aqueous electrolyte secondary battery is used, the space for accommodating the battery is often a square (flat box shape), so the power generation element is accommodated in a rectangular outer can. The formed rectangular non-aqueous electrolyte secondary battery is often used. Such a rectangular nonaqueous electrolyte secondary battery is generally manufactured as follows.

  That is, a negative electrode plate in which a negative electrode mixture containing a negative electrode active material is applied on both sides of a negative electrode core (current collector) made of a long sheet-like copper foil, and a positive electrode core made of a long, thin sheet-like aluminum foil A separator made of a microporous polyethylene film or the like is disposed between a positive electrode plate coated with a positive electrode mixture containing a positive electrode active material on both sides, and a cylindrical shape with the negative electrode plate and the positive electrode plate insulated from each other by the separator. A cylindrical spiral electrode body is manufactured by winding it in a spiral shape. The cylindrical electrode body is crushed with a press machine and formed into a shape that can be inserted into a rectangular battery outer can. Then, the cylindrical electrode body is accommodated in the rectangular outer can, and an electrolyte is injected to inject the rectangular nonaqueous electrolyte. Next battery.

  The configuration of such a conventional rectangular nonaqueous electrolyte secondary battery will be described with reference to the drawings. FIG. 1 is a perspective view showing a rectangular nonaqueous electrolyte secondary battery disclosed in Patent Document 1 below, cut in the vertical direction. This nonaqueous electrolyte secondary battery 10 accommodates a flat spiral electrode body 14 in which a positive electrode plate 11 and a negative electrode plate 12 are wound via a separator 13 inside a rectangular battery outer can 15, The battery outer can 15 is sealed with a sealing plate 16.

  The spiral electrode body 14 is wound so that the positive electrode plate 11 is exposed at the outermost periphery, and the exposed outermost positive electrode plate 11 is in direct contact with the inner surface of the battery outer can 15 that also serves as a positive electrode terminal. And are electrically connected. Further, the negative electrode plate 12 is electrically connected via a current collector 19 to a negative electrode terminal 18 that is formed at the center of the sealing plate 16 and attached via an insulator 17 that also serves as a negative electrode terminal. .

  Since the battery outer can 15 is electrically connected to the positive electrode plate 11, in order to prevent a short circuit between the negative electrode plate 12 and the battery outer can 15, the upper end of the spiral electrode body 14 and the sealing plate 16 The insulating spacer 20 is inserted between the negative electrode plate 12 and the battery outer can 15 so as to be electrically insulated.

  In this rectangular nonaqueous electrolyte secondary battery, after the spiral electrode body 14 is inserted into the battery outer can 15, the sealing plate 16 is laser welded to the opening of the battery outer can 15, and then the electrolyte injection hole 21. The nonaqueous electrolytic solution is injected from the above, and the electrolytic solution injection hole 21 is sealed. Such a rectangular non-aqueous electrolyte secondary battery has an excellent effect that there is little wasted space during use, and the battery performance and battery reliability are high.

  As a negative electrode active material used in such non-aqueous electrolyte secondary batteries, dendrites grow while carbonaceous materials such as graphite and amorphous carbon have discharge potentials comparable to lithium metals and lithium alloys. Therefore, it is widely used because it has excellent properties such as high safety, excellent initial efficiency, good potential flatness, and high density.

On the other hand, as a positive electrode active material, a high energy density 4V class non-aqueous electrolyte secondary battery is obtained by combining a lithium composite oxide such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ and LiFeO _{2 with} a negative electrode made of a carbon material. Is known to be obtained. Among them, LiCoO ₂ is often used because various battery characteristics are superior to others. However, since cobalt is expensive and abundant as a resource, this LiCoO ₂ is not used. In order to continue to be used as a positive electrode material for water electrolyte secondary batteries, further improvement in performance and life of non-aqueous electrolyte secondary batteries is desired, and by using other transition elements instead of cobalt. Many developments have been made so far to achieve various battery characteristics equivalent to or better than those obtained when cobalt is used.

For example, as disclosed in Patent Documents 2 and 3 below, as a method for improving the characteristics of a non-aqueous electrolyte secondary battery using LiCoO ₂ as a positive electrode active material, different elements such as Zr and Mg are added to LiCoO ₂ . The method is known. The following Patent Document 2, the addition of zirconium to LiCoO ₂ as a cathode active material, and generates a high voltage, and the non-aqueous electrolyte secondary battery exhibiting excellent charge and discharge characteristics and storage characteristics are disclosed . The effect of the nonaqueous electrolyte secondary battery using LiCoO ₂ to which zirconium is added is stabilized by covering the surface of LiCoO ₂ particles with zirconium oxide ZrO ₂ or a composite oxide Li ₂ ZrO ₃ of lithium and zirconium. As a result, a positive electrode active material having excellent cycle characteristics and storage characteristics can be obtained without causing a decomposition reaction or crystal destruction of the electrolyte even at a high potential. It cannot be obtained simply by mixing zirconium or a zirconium compound with LiCoO ₂ later, but can be obtained by adding zirconium to a mixture of a lithium salt and a cobalt compound and baking.

In Patent Document 3 below, at least one element selected from not only zirconium (Zr) but also titanium (Ti) and fluorine (F) is added as a heterogeneous element to be added to the positive electrode active material LiCoO _2. It has been shown that the load characteristics and cycle characteristics of the lithium non-aqueous electrolyte secondary battery can be improved by the addition.

Furthermore, in Patent Document 4 below, a Li transition metal composite oxide having a layer structure in which the composition ratio of Ni and Mn is substantially equal has a voltage in the vicinity of 4 V equivalent to LiCoO ₂ and is excellent in high capacity. Further, it is disclosed that the following Patent Document 5 contains at least Ni and Mn as transition metals and further contains fluorine in a lithium transition metal composite oxide having a layered structure. When a positive electrode active material is used, a non-aqueous electrolyte secondary battery that can be charged at a charge voltage of 4.4 V or more and combined with a negative electrode containing a carbon material as a negative electrode active material and has excellent thermal stability In addition, the following non-patent document 1 discloses that, among lithium transition metal composite oxides containing Ni, Co, and Mn, the chemical formula LiMn has the same composition ratio of Mn and Ni. material expressed with _{x Ni x Co (1-2x) O} 2 has been shown to exhibit specific high thermal stability even charged state (high oxidation state).

At present, in a non-aqueous electrolyte secondary battery using a lithium-containing transition metal oxide such as lithium cobaltate LiCoO ₂ as a positive electrode active material and a carbon material as a negative electrode active material, When combined, the charging voltage is generally 4.1 to 4.2 V (the potential of the positive electrode active material is 4.2 to 4.3 V based on lithium). Under such charging conditions, the positive electrode is used only 50 to 60% of the theoretical capacity. Therefore, if the charging voltage can be further increased, the capacity of the positive electrode can be utilized at 70% or more of the theoretical capacity, and the capacity and energy density of the battery can be increased.

  Based on the development status of the positive electrode active material for a non-aqueous electrolyte secondary battery as described above, the present applicant has conducted various studies to obtain a positive electrode active material that can achieve a more stable and high charge voltage. A novel non-aqueous electrolyte secondary battery using a mixture of lithium cobaltate to which different elements are added as active materials and layered lithium manganese nickelate has been developed. Japanese Patent Application Nos. 2004-094475 and 2004-320394 have already been developed. (Hereinafter collectively referred to as “prior application”).

  The positive electrode active material of the non-aqueous electrolyte secondary battery according to the invention of the prior application improves the structural stability at high voltage (up to 4.5V) by adding at least Zr and Mg different elements to lithium cobaltate, Furthermore, safety is ensured by mixing layered lithium manganese nickelate with high voltage and high thermal stability. When combined with a positive electrode using this positive electrode active material and a negative electrode having a negative electrode active material made of a carbon material, a non-aqueous electrolyte secondary battery that can be charged at a high voltage of 4.3 V to 4.5 V is obtained. .

  If a fluorine-based resin such as polyvinylidene fluoride, which has been widely used, is used as a binder, the film-forming property of this fluorine-based resin is not good. Adhesion and adhesion between the carbon material and the metal foil current collector are not good, and furthermore, fluorine-based resin decomposes at high temperatures. Since the lithium reacts violently and causes a problem in terms of safety (see Patent Document 6 below), a styrene-butadiene rubber (as a binder) is used as a binder in the production of the negative electrode of the non-aqueous electrolyte secondary battery of the above-mentioned prior application. A binder made of SBR) latex and a thickener made of carboxymethyl cellulose (CMC) are used in combination.

JP-A-2001-273931 (Claims, paragraphs [0003] to [0004], FIG. 1) JP-A-4-319260 (Claims, paragraphs [0006], [0008] to [0011]) JP 2004-299975 A (claims, paragraphs [0006] to [0008]) JP 2002-042813 A (claims, paragraphs [0011] to [0016]) JP 2004-296098 A (Claims) JP 2002-313323 A (claims, paragraphs [0003] to [0006]) Electrochemical and Solid-State Letters, 4 (12) A200-A203 (2001)

  However, the nonaqueous electrolyte secondary battery that can achieve a high charging voltage according to the invention of the prior application as described above can achieve high capacity and high energy density, but on the other hand, the conventional 4.2V charging can be achieved. There was a problem that the cycle characteristics were insufficient as compared with the specification non-aqueous electrolyte secondary battery.

  The inventors of the present application have examined the cause of deterioration of cycle characteristics of the nonaqueous electrolyte secondary battery according to the invention of the prior application, and as a result, estimated that the following is the cause. That is, the nonaqueous electrolyte secondary battery according to the invention of the prior application increases the capacity of the positive electrode by raising the end-of-charge voltage, but it is necessary to increase the coating amount of the negative electrode active material correspondingly. However, as a result, it was considered that the resistance to insertion / extraction of lithium in the negative electrode increased, and the deterioration of the negative electrode occurred, which contributed to the deterioration of cycle characteristics.

  Therefore, the inventors of the present application, as a result of repeating various experiments to prevent the above-described deterioration of the negative electrode, by using a material that can impart porosity to the negative electrode surface as a binder to be mixed with the negative electrode active material, It has been found that the resistance to insertion / extraction of lithium in the negative electrode can be reduced, and as a result, the deterioration of the negative electrode during the charge / discharge cycle can be suppressed, and in addition, the deterioration of the negative electrode during this charge / discharge cycle is It has been found that the use of a graphite material that is a negative electrode active material having a predetermined particle size characteristic can further suppress the problem, and the present invention has been completed.

  That is, the present invention is a lithium-cobalt composite oxide excellent in charge / discharge cycle characteristics, to which at least both zirconium and magnesium are added as a positive electrode active material, and lithium manganese containing at least both manganese and nickel having a layered structure. An object of the present invention is to provide a non-aqueous electrolyte secondary battery using a mixture of nickel composite oxide and having a positive electrode active material having a potential of 4.4 V to 4.6 V based on lithium, and a method for charging the same. .

The above object of the present invention can be achieved by the following configurations. That is, the nonaqueous electrolyte secondary battery according to claim 1 is a nonaqueous electrolyte comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a nonaqueous electrolyte having a nonaqueous solvent and an electrolyte salt. In secondary batteries,
The positive electrode active material is a mixture of a lithium cobalt composite oxide to which at least both zirconium and magnesium are added, and a lithium manganese nickel composite oxide containing at least manganese and nickel having a layered structure,
The potential of the positive electrode active material is 4.4V to 4.6V on the basis of lithium; and
The negative electrode contains H-CMC in which ammonia is eliminated from carboxymethylcellulose-ammonium (NH ₄ -CMC) as a binder.

In the present invention, Li _a Co _(1-xyz) Zr _x Mg _y M _z O ₂ (where 0 ≦ a ≦ 1.1, x> 0, y> 0 _{) is} used as the lithium cobalt composite oxide. Z ≧ 0, 0 <x + y + z ≦ 0.03, M = Al, Ti, Sn.). Addition of Zr and Mg as dissimilar metals is essential. If the amount of addition of these dissimilar metals together with Al, Ti and Sn is small, the effect of improving the cycle characteristics is small. Since dissimilar metals are not directly involved in the electrode reaction, the initial capacity is reduced. As the layered lithium-manganese-nickel composite oxide, Ni and Mn are substantially equal in a molar ratio of _{Li b Mn s Ni t Co u} O 2 ( however, 0 ≦ b ≦ 1.2,0 <s ≦ 0. 5, 0 <t ≦ 0.5, u ≧ 0, s + t + u = 1, 0.95 ≦ s / t ≦ 1.05), and an active material having high thermal stability can be obtained with the above composition.

  The mixing ratio of the lithium cobalt composite oxide (active material A) to which both at least zirconium and magnesium are added and the layered lithium manganese nickel composite oxide (active material B) is a mass ratio, and the active material A: The active material B is preferably in the range of 51:49 to 90:10, more preferably 70:30 to 80:20. When the active material A is less than 51%, the initial capacity becomes small, and the cycle characteristics and the storage characteristics deteriorate. Moreover, safety | security falls that the active material B is less than 10%.

  In the present invention, carbonates, lactones, ethers, esters and the like can be used as the nonaqueous solvent (organic solvent) constituting the nonaqueous solvent electrolyte, and two or more of these solvents can be used. Can also be used in combination. Among these, carbonates, lactones, ethers, ketones, esters and the like are preferable, and carbonates are more preferably used.

  Specific examples include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl. -1,3-oxazolidine-2-one, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, γ -Butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, 1,4-dio Xanthan can be mentioned. In the present invention, a mixed solvent containing EC is preferably used from the viewpoint of increasing the charge / discharge efficiency. However, since cyclic carbonate is generally easily oxidized and decomposed at a high potential, the EC content in the non-aqueous electrolyte is 5% by volume or more and 25% by volume. % Or less is preferable.

In addition, as a solute of the nonaqueous electrolyte in the present invention, a lithium salt generally used as a solute in a nonaqueous electrolyte secondary battery can be used. Such lithium salts include LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl ₁₂ , and mixtures thereof Illustrated. Among these, LiPF ₆ (lithium hexafluorophosphate) is preferably used. When charged with a high charging voltage, although aluminum is a current collector of the positive electrode is easily dissolved in the presence of LiPF _6, by LiPF ₆ decomposes, coating is formed on the aluminum surface, the aluminum by the coating Can be dissolved. Therefore, it is preferable to use LiPF ₆ as the lithium salt. The amount of solute dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / L.

  The invention according to claim 2 is the nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material of the negative electrode is a graphite material having a particle diameter D10 of 5 μm to 10 μm when the volume fraction is 10%. It is characterized by that.

  The particle size D10 when the volume fraction is 10% represents the particle size of 10% from the small particle size side as D10 when the graphite materials are arranged in the order of different particle sizes. Therefore, in the invention according to claim 2, the graphite material as the negative electrode active material has many particles having a particle size larger than 5 μm to 10 μm, and the graphite fine particles enter the gaps between the large graphite particles. It will be equipped with.

  The invention according to claim 3 is the nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the nonaqueous electrolyte further contains 0.5% by mass to 5% by mass of vinylene carbonate. And

  The invention according to claim 4 is the non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the lithium manganese nickel composite oxide of the positive electrode active material further contains cobalt.

  The invention according to claim 5 is the non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the positive electrode active material has a charge capacity ratio between the positive electrode and the negative electrode of 1.0 to 1.2. And the said negative electrode active material is contained, It is characterized by the above-mentioned.

Furthermore, another object of the present invention can be achieved by the following configuration. That is, the invention of the method for charging a nonaqueous electrolyte secondary battery according to claim 6 includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, a nonaqueous electrolyte having a nonaqueous solvent and an electrolyte salt, With
The positive electrode active material comprises a mixture of a lithium cobalt composite oxide to which at least both zirconium and magnesium are added, and a lithium manganese nickel composite oxide having a layered structure,
And in the method for charging a non-aqueous electrolyte secondary battery in which H-CMC in which ammonia is eliminated from carboxymethylcellulose-ammonium (NH ₄ -CMC) as a binder is contained in the negative electrode,
The positive electrode active material is charged at a potential of 4.4 V to 4.6 V based on lithium.

By providing the above configuration, the present invention has the following excellent effects. That is, according to the first aspect of the present invention, the negative electrode is coated with a slurry of carboxymethylcellulose-ammonium (NH ₄ -CMC) and the negative electrode active material on the surface of the negative electrode current collector according to a known method, and then the solvent ( For example, water) can be produced by drying at 100 ° C. or higher, but during this drying, ammonia (NH ₃ ) in NH ₄ -CMC is desorbed to form H-CMC, and this NH ₃ Since fine voids are formed on the negative electrode surface in the process of desorption, the negative electrode surface is in a porous state. Therefore, since the graphite surface that is not partially covered with H-CMC is exposed in the process of desorption of NH ₃ , the contact resistance between the graphite particles is reduced. An increase in resistance to insertion / extraction of lithium in the negative electrode is reduced, and a non-aqueous electrolyte secondary battery in which the positive electrode active material having improved cycle characteristics is as large as 4.4 V to 4.6 V on the basis of lithium can be obtained.

  According to the invention of claim 2, since the graphite material having a low potential (about 0.1 V on the basis of lithium) is used as the negative electrode active material, the battery voltage is as high as 4.3 V to 4.5 V, and the positive electrode active material is A battery with a high utilization rate of the substance can be obtained. In addition, the use of graphite particles having a particle size of D10 of 5 μm to 10 μm as the negative electrode active material allows the contained fine graphite particles to enter the gaps between the large graphite particles, so the contact resistance between the graphite particles Therefore, the resistance to insertion / extraction of lithium in the negative electrode is further reduced, and a nonaqueous electrolyte secondary battery with greatly improved cycle characteristics can be obtained. In this case, it is not preferable that D10 is less than 5 μm because the graphite fine powder particles are too small, so that the decrease in electric resistance of the negative electrode is small and the effect of improving the cycle characteristics is small. On the other hand, if D10 exceeds 10 μm, there are too many fine graphite particles and the contact between large graphite particles is reduced, so that the electrical resistance increases. In this case as well, the effect of improving the cycle characteristics is reduced, which is not preferable. .

  According to the invention of claim 3, VC is conventionally used conventionally as an additive for suppressing reductive decomposition of an organic solvent. By adding this VC, the negative electrode by the first charge is used. Before insertion of lithium into the negative electrode active material layer, a negative electrode surface coating (SEI: Solid Electrolyte Interface) is formed on the negative electrode active material layer, and this SEI prevents the insertion of solvent molecules around the lithium ions. Since it functions as a barrier, the negative electrode active material does not directly react with the organic solvent, so that an effect of improving cycle characteristics is seen and a long-life nonaqueous electrolyte secondary battery is obtained. The addition amount of VC is 0.5-5 mass% with respect to the whole electrolyte solution, Preferably it is 1-3 mass%. If the amount of VC added is less than 0.5% by mass, the effect of improving the cycle characteristics is small, and if it exceeds 3% by mass, the initial capacity decreases and the battery swells at high temperatures, which is not preferable.

According to the invention of claim 4, a lithium transition metal composite oxide containing Ni, Co, and Mn, particularly represented by the chemical formula LiMn _x Ni _x Co _(1-2x) O _{2 in} which the composition ratio of Mn and Ni is equal. Since the material to be used exhibits a specific high thermal stability even in a charged state (high oxidation state), a safe non-aqueous electrolyte secondary battery can be obtained even when charged at a high charging voltage.

  According to the invention of claim 5, since the positive electrode active material and the negative electrode active material are included so that the charge capacity ratio of the positive electrode to the negative electrode is 1.0 to 1.2, A non-aqueous electrolyte secondary battery that is safe even when charged at a high charging voltage and has a high capacity can be obtained. That is, when the charge capacity ratio between the positive electrode and the negative electrode is less than 1.0, the positive electrode capacity is larger than the negative electrode capacity, so that lithium that cannot be occluded in the negative electrode is deposited on the negative electrode and the safety is lowered. On the other hand, when the charge capacity ratio between the positive electrode and the negative electrode exceeds 1.2, the proportion of the positive electrode active material in the battery decreases, which is disadvantageous in terms of capacity.

  Furthermore, according to the invention of claim 6, since the potential of the positive electrode active material whose charging voltage is higher than that of the conventional one can be 4.4 to 4.6 V on the basis of lithium, high capacity and high energy density can be obtained. In addition, the non-aqueous electrolyte secondary battery is excellent in cycle characteristics.

  Hereinafter, the best mode for carrying out the present invention will be described in detail using examples and comparative examples. However, the examples described below are merely examples of non-aqueous electrolyte secondary batteries and their charging methods for embodying the technical idea of the present invention, and the present invention is specified in this example. The present invention can be equally applied to various modifications without departing from the technical idea shown in the claims.

<Preparation of positive electrode>
The heterogeneous element-added lithium cobalt oxide was produced as follows. As a starting material, lithium carbonate is used as lithium source (Li ₂ CO ₃ ), and cobalt source is zirconium (Zr) as a heterogeneous element at the time of cobalt carbonate synthesis, 0.2 mol% with respect to cobalt and magnesium (Mg). Coprecipitation was performed from an aqueous solution added with 0.5 mol%, and then zirconium and magnesium-added tricobalt tetroxide (Co ₃ O ₄ ) obtained by a thermal decomposition reaction were used. A predetermined amount of these were weighed and mixed, and then calcined at 850 ° C. for 24 hours in an air atmosphere to obtain zirconium and magnesium-added lithium cobalt oxide. This was pulverized with a mortar to an average particle size of 14 μm to obtain a positive electrode active material A.

The layered lithium manganese nickelate was prepared as follows. As starting materials, lithium carbonate (Li ₂ CO ₃ ) is used for the lithium source, and co-precipitated hydroxide represented by Ni _0.33 Mn _0.33 Co _0.34 (OH) ₂ is used for the transition metal source. It was. A predetermined amount of these were weighed and mixed, and then fired at 1000 ° C. for 20 hours in an air atmosphere to obtain a layered lithium manganese nickelate represented by LiMn _0.33 Ni _0.33 Co _0.34 O ₂ . This was pulverized to an average particle size of 5 μm with a mortar to obtain a positive electrode active material B.

  The positive electrode active material A and the positive electrode active material B obtained as described above were mixed so that the mass ratio was 7: 3. Next, the mixed positive electrode active material was 94 parts by mass, and carbon powder as a conductive agent. Was mixed with 3 parts by mass of polyvinylidene fluoride powder as a binder, and this was mixed with an N-methylpyrrolidone (NMP) solution to prepare a slurry. This slurry was applied to both sides of an aluminum current collector having a thickness of 15 μm by a doctor blade method and dried to form active material layers on both sides of the positive electrode current collector. Then, it compressed using the compression roller and produced the positive electrode whose length of a short side is 36.5 mm.

<Production of negative electrode>
95 parts by mass of natural graphite powder having a particle size D10 of 5 μm at a volume fraction of 10%, 3 parts by mass of carboxymethylcellulose-ammonium salt (NH ₄ -CMC) as a thickener, and SBR latex as a binder A binder consisting of 2 parts by mass (in terms of solid content) was dispersed in water to prepare a slurry. After applying this slurry on both sides of a copper current collector having a thickness of 8 μm by the doctor blade method, the slurry is dried at 100 ° C. or higher to evaporate water and to desorb NH ₃ from NH ₄ -CMC, thereby producing a negative electrode current collector. An active material layer was formed on both sides. Then, it compressed using the compression roller and produced the negative electrode whose length of a short side is 37.5 mm. As for the coating amount of the positive electrode and the negative electrode, the charging capacity ratio (negative electrode charging capacity / positive electrode charging capacity) at the portion where the positive electrode and the negative electrode face each other is 1.1 at the charging voltage (4.4 V) as a design standard. Adjusted as follows. The charge capacity of the positive electrode active material varies depending on the charge voltage. As an example, the relationship between the charge positive electrode potential and the positive electrode capacity in the case of zirconium and magnesium-added lithium cobaltate / layered lithium manganese nickelate (mixing ratio 7: 3) is shown. Table 1 shows.

<Production of electrolyte>
A mixed solvent in which 20% by volume of ethylene carbonate, 50% by volume of ethyl methyl carbonate, and 30% by volume of diethyl carbonate were prepared, and LiPF ₆ was dissolved in 1 mol / L to obtain an electrolyte.

<Production of battery>
A square nonaqueous electrolyte secondary battery (5 mm × 34 mm × 43 mm) according to Example 1 was fabricated using the above positive electrode, negative electrode, and electrolyte, and using a polyethylene microporous membrane as a separator.

95 parts by mass of natural graphite powder having a particle size D10 of 10 μm at a volume fraction of 10%, 3 parts by mass of carboxymethylcellulose-ammonium salt (NH ₄ -CMC) as a thickener, and SBR latex as a binder A binder consisting of 2 parts by mass (in terms of solid content) was dispersed in water to prepare a slurry. After applying this slurry on both sides of a copper current collector having a thickness of 8 μm by the doctor blade method, the slurry is dried at 100 ° C. or higher to evaporate water and to desorb NH ₃ from NH ₄ -CMC, thereby producing a negative electrode current collector. An active material layer was formed on both sides. Then, it compressed using the compression roller and produced the negative electrode whose short side length is 37.5 mm. As for the coating amount of the positive electrode and the negative electrode, the charging capacity ratio (negative electrode charging capacity / positive electrode charging capacity) at the portion where the positive electrode and the negative electrode face each other is 1.1 at the charging voltage (4.4 V) as a design standard. Adjusted as follows. Next, a square nonaqueous electrolyte secondary battery (5 mm × 34 mm × 43 mm) according to Example 2 was fabricated using the above-described negative electrode and the same positive electrode, electrolyte, and separator as those of Example 1.

[Comparative Example 1]
95 parts by mass of natural graphite powder having a particle size D10 of 5 μm at a volume fraction of 10%, 3 parts by mass of carboxymethylcellulose-sodium salt (Na-CMC) as a thickener, and 2 parts of SBR latex as a binder A slurry was prepared by dispersing the binder consisting of parts (in terms of solid content) in water. This slurry was applied to both sides of a copper current collector having a thickness of 8 μm by a doctor blade method, and then dried at 100 ° C. or more to evaporate water, thereby forming an active material layer on both sides of the negative electrode current collector. Then, it compressed using the compression roller and produced the negative electrode whose short side length is 37.5 mm. As for the coating amount of the positive electrode and the negative electrode, the charging capacity ratio (negative electrode charging capacity / positive electrode charging capacity) at the portion where the positive electrode and the negative electrode face each other is 1.1 at the charging voltage (4.4 V) as a design standard. Adjusted as follows. Next, a square nonaqueous electrolyte secondary battery (5 mm × 34 mm × 43 mm) according to Comparative Example 1 was prepared using the above negative electrode and the same positive electrode, electrolyte, and separator as in Example 1.

[Comparative Example 2]
95 parts by mass of natural graphite powder having a particle size D10 of 10 μm at a volume fraction of 10%, 3 parts by mass of carboxymethylcellulose-sodium salt (Na-CMC) as a thickener and 2 parts of SBR latex as a binder A slurry was prepared by dispersing the binder consisting of parts (in terms of solid content) in water. This slurry was applied to both sides of a copper current collector having a thickness of 8 μm by a doctor blade method, and then dried at 100 ° C. or more to evaporate water, thereby forming an active material layer on both sides of the negative electrode current collector. Then, it compressed using the compression roller and produced the negative electrode whose short side length is 37.5 mm. As for the coating amount of the positive electrode and the negative electrode, the charging capacity ratio (negative electrode charging capacity / positive electrode charging capacity) at the portion where the positive electrode and the negative electrode face each other is 1.1 at the charging voltage (4.4 V) as a design standard. Adjusted as follows. Next, a square nonaqueous electrolyte secondary battery (5 mm × 34 mm × 43 mm) according to Comparative Example 1 was prepared using the above negative electrode and the same positive electrode, electrolyte, and separator as in Example 1.

[Comparative Example 3]
95 parts by mass of natural graphite powder having a particle size D10 of 15 μm at a volume fraction of 10%, 3 parts by mass of carboxymethylcellulose-ammonium salt (NH ₄ -CMC) as a thickener, and SBR latex 2 as a binder The slurry which prepared the binder which consists of a mass part (solid content conversion) in water was prepared. After applying this slurry on both sides of a copper current collector having a thickness of 8 μm by the doctor blade method, the slurry is dried at 100 ° C. or higher to evaporate water and to desorb NH ₃ from NH ₄ -CMC, thereby producing a negative electrode current collector. An active material layer was formed on both sides. Then, it compressed using the compression roller and produced the negative electrode whose short side length is 37.5 mm. As for the coating amount of the positive electrode and the negative electrode, the charging capacity ratio (negative electrode charging capacity / positive electrode charging capacity) at the portion where the positive electrode and the negative electrode face each other is 1.1 at the charging voltage (4.4 V) as a design standard. Adjusted as follows. Next, a square nonaqueous electrolyte secondary battery (5 mm × 34 mm × 43 mm) according to Comparative Example 3 was fabricated using the above negative electrode and the same positive electrode, electrolyte, and separator as those of Example 1.

[Comparative Example 4]
95 parts by mass of natural graphite powder having a particle size D10 of 3 μm at a volume fraction of 10%, 3 parts by mass of carboxymethylcellulose-ammonium salt (NH ₄ -CMC) as a thickener, and SBR latex 2 as a binder The slurry which prepared the binder which consists of a mass part (solid content conversion) in water was prepared. After applying this slurry to both sides of a copper current collector having a thickness of 8 μm by a doctor blade method, the slurry is dried at 100 ° C. or higher to evaporate water and to desorb NH ₃ from NH ₄ -CMC, thereby producing a negative electrode current collector. An active material layer was formed on both sides. Then, it compressed using the compression roller and produced the negative electrode whose short side length is 37.5 mm. As for the coating amount of the positive electrode and the negative electrode, the charging capacity ratio (negative electrode charging capacity / positive electrode charging capacity) at the portion where the positive electrode and the negative electrode face each other is 1.1 at the charging voltage (4.4 V) as a design standard. Adjusted as follows. Next, a square nonaqueous electrolyte secondary battery (5 mm × 34 mm × 43 mm) according to Comparative Example 4 was produced using the above negative electrode and the same positive electrode, electrolyte, and separator as in Example 1.

<Measurement of cycle characteristics>
The batteries of Examples 1 and 2 and Comparative Examples 1 to 4 manufactured as described above were charged at a constant current of 1 It (1 C) at 25 ° C., and the battery voltage was 4.4 V (the positive electrode potential was lithium). After that, the battery was initially charged at a constant voltage of 4.4 V until the charging current value became 1/50 It (1/50 C). The initially charged battery was discharged at 25 ° C. with a constant current of 1 It until the battery voltage reached 3 V, and the discharge capacity at this time was determined as the initial discharge capacity. The cycle characteristics were measured for each battery whose initial discharge capacity was measured at 25 ° C. until the battery voltage reached 4.4 V at a constant current of 1 It, and then the current value was 1/50 It at a constant voltage of 4.4 V. Then, discharging was performed at a constant current of 1 It until the battery voltage reached 3 V as one cycle, and the discharge capacity after 500 cycles was obtained repeatedly until reaching 500 cycles. And about each battery, the capacity | capacitance maintenance factor (%) after 500 cycles in 25 degreeC was calculated | required based on the following formulas. The results are summarized in Table 2.
Capacity retention rate (%) = (discharge capacity after 500 cycles / initial discharge capacity) × 100

From the results shown in Table 2, the following can be understood. That is, as in Examples 1 and 2, when NH ₄ -CMC was used as the negative electrode binder and graphite having a particle size D10 of 5 μm to 10 μm at a volume fraction of 10% was used as the negative electrode active material, 500 cycles The subsequent capacity retention ratio was 86% to 88%, indicating good cycle characteristics. On the other hand, when Na-CMC is used as the negative electrode binder as in Comparative Examples 1 and 2, graphite having a particle size D10 of 5 μm to 10 μm at a volume fraction of 10% may be used as the negative electrode active material. The capacity retention rate after 500 cycles is 61% to 65%, and the cycle characteristics are degraded.

Further, as in Comparative Examples 3 and 4, even when NH ₄ -CMC is used as the negative electrode binder, the particle size D10 when the volume fraction of the negative electrode active material is 10% exceeds 10 μm and is less than 5 μm. The capacity retention rate after 500 cycles is 72% to 75%, which indicates that the effect of improving the cycle characteristics is insufficient.

From the above results, a battery voltage of 4.3 V to 4.5 V was obtained by using, as a positive electrode, a mixture of lithium cobalt composite oxide obtained by adding at least both zirconium and magnesium to LiCoO ₂ and lithium manganese nickelate having a layered structure. In a battery charged at a high voltage (positive electrode potential 4.4 V to 4.6 V based on lithium), CMC used as a negative electrode binder is an ammonium salt, and particularly when the volume fraction is 10% as a negative electrode active material. When graphite having a particle size D10 of 5 to 10 μm is used, it has been found that the cycle characteristics can be significantly improved.

  In Examples 1 and 2 and Comparative Examples 1 to 4, examples in which a mixed solvent composed of ethylene carbonate (EC), methyl ethyl carbonate (MEC) and diethyl carbonate (DEC) was used as the electrolyte solvent were shown. It will be apparent that various solvents known from US Pat. However, it is better to add the cyclic carbonate from the viewpoint of increasing the charge / discharge efficiency, but since it is easily oxidatively decomposed at a high potential, the content in the nonaqueous electrolyte solvent is 5% by volume particularly when EC is used. It is desirable to set it as 25 volume% or less.

  Further, in the electrolyte solvent, vinylene carbonate (VC), which is conventionally used as an additive for suppressing reductive decomposition of the organic solvent as necessary, is 0.5 to 5 with respect to the entire electrolyte solution. A mass%, preferably 1 to 3 mass% can also be added. This addition of VC forms a negative electrode surface film (SEI: Solid Electrolyte Interface), also called a passivation layer, on the negative electrode active material layer before lithium is inserted into the negative electrode by the first charge. Since the negative electrode active material does not react directly with the organic solvent because it functions as a barrier that prevents the insertion of solvent molecules around the battery, the cycle characteristics are further improved, and a long-life nonaqueous electrolyte secondary battery Is obtained. If the amount of VC added is less than 0.5% by mass, the effect of improving the cycle characteristics is small, and if it exceeds 3% by mass, the initial capacity decreases and the battery swells at high temperatures, which is not preferable.

In Examples 1 and 2 and Comparative Examples 1 to 4, examples in which a lithium cobalt composite oxide to which zirconium and magnesium were added were used as the positive electrode active material A. A lithium transition metal composite oxide represented by the following chemical formula (1) containing another element M (M: Al, Ti, Sn) in addition to magnesium can also be used.
Li _a Co _(1-xyz) Zr _x Mg _y M _z O ₂ (1)
(However, 0 ≦ a ≦ 1.1, x> 0, y> 0, z ≧ 0, 0 <x + y + z ≦ 0.03.)
In this case, the addition of Zr and Mg is indispensable. If the addition amount of these dissimilar metals is small in combination with Al, Ti, and Sn, the effect of improving the cycle characteristics is small. Since dissimilar metals are not directly involved in the electrode reaction, the initial capacity is reduced. Preferably, x ≧ 0.0001, y ≧ 0.0001, and 0.0002 ≦ x + y + z ≦ 0.03.

Further, in Examples 1 and 2 and Comparative Examples 1 to 4, examples in which LiMn _0.33 Ni _0.33 Co _0.34 O ₂ having a layered structure was used as the positive electrode active material B were shown. A lithium manganese nickel composite oxide represented by the following chemical formula (2) having substantially the same composition ratio can also be used.
_{Li b Mn s Ni t Co u} O 2 (2)
(However, 0 ≦ b ≦ 1.2, 0 <s ≦ 0.5, 0 <t ≦ 0.5, u ≧ 0, s + t + u = 1, 0.95 ≦ s / t ≦ 1.05.)
In the lithium manganese nickel composite oxide having a layered structure represented by the chemical formula (2), the presence of Mn and Ni is essential, and the thermal stability is high if the composition ratio of Mn and Ni is substantially equal. Become active material. Preferably, 0.1 ≦ s ≦ 0.5 and 0.1 ≦ t ≦ 0.5.

The lithium manganese nickel composite oxide having this layered structure is represented by the following chemical formula (3) containing a trace amount of at least one other metal selected from Mg, Zr, Al, Ti, and Sn. Lithium manganese nickel composite oxide can also be used.
_{Li b Mn s Ni t Co u} M 'v O 2 (3)
(However, 0 ≦ b ≦ 1.2, 0.1 ≦ s ≦ 0.5, 0.1 ≦ t ≦ 0.5, u ≧ 0, 0.0001 ≦ v ≦ 0.03, s + t + u + v = 1, M '= Mg, Zr, Al, Ti, Sn, 0.95 ≦ s / t ≦ 1.05.)

  The mixing ratio of the active material A and the active material B can be used in a mass ratio of active material A: active material B = 51: 49 to 90:10, preferably 70:30 to 80: 20. When the active material A is less than 51%, the initial capacity becomes small, and the cycle characteristics and the storage characteristics deteriorate. Moreover, safety | security falls that the active material B is less than 10%.

It is a perspective view which cut | disconnects and shows the conventional square nonaqueous electrolyte secondary battery to the vertical direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Nonaqueous electrolyte secondary battery 11 Positive electrode plate 12 Negative electrode plate 13 Separator 14 Flat spiral electrode body 15 Rectangular battery outer can 16 Sealing plate 17 Insulator 18 Negative electrode terminal 19 Current collector 20 Insulating spacer 21 Electrolyte injection Liquid hole

Claims (6)

In a non-aqueous electrolyte secondary battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte having a non-aqueous solvent and an electrolyte salt,
The positive electrode active material is a mixture of a lithium cobalt composite oxide to which at least both zirconium and magnesium are added, and a lithium manganese nickel composite oxide containing at least manganese and nickel having a layered structure,
The potential of the positive electrode active material is 4.4V to 4.6V on the basis of lithium; and
The non-aqueous electrolyte secondary battery, wherein the negative electrode contains H-CMC in which ammonia is eliminated from carboxymethyl cellulose-ammonium (NH ₄ -CMC) as a binder.   2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material of the negative electrode is a graphite material having a particle diameter D10 of 5 μm to 10 μm at a volume fraction of 10%.   The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the nonaqueous electrolyte further contains 0.5% by mass to 5% by mass of vinylene carbonate. The nonaqueous electrolyte secondary battery according to claim 1, wherein the lithium manganese nickel composite oxide of the positive electrode active material further contains cobalt.   When the potential of the positive electrode active material in the positive electrode is 4.4V to 4.6V with respect to lithium, the positive electrode active material and the positive electrode active material The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material is contained. A positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte having a non-aqueous solvent and an electrolyte salt,
The positive electrode active material comprises a mixture of a lithium cobalt composite oxide to which at least both zirconium and magnesium are added, and a lithium manganese nickel composite oxide having a layered structure,
And in the method for charging a non-aqueous electrolyte secondary battery in which H-CMC in which ammonia is eliminated from carboxymethylcellulose-ammonium (NH ₄ -CMC) as a binder is contained in the negative electrode,
A method for charging a non-aqueous electrolyte secondary battery, wherein the positive electrode active material is charged at a potential of 4.4 V to 4.6 V based on lithium.

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