JP2011146158A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery excellent in cycle characteristics through reduction of reaction resistance (especially, that at low temperature) and restraint of decomposition reaction of electrolyte. <P>SOLUTION: The lithium secondary battery is provided with a cathode 66, an anode, and electrolyte. The cathode is provided with a cathode active material layer 64 containing a cathode collector 62 and a particulate cathode active material formed on the collector. The anode is provided with an anode active material layer containing an anode collector and a particulate anode active material formed on the collector. In the active material layer of at least either of the electrodes out of the cathode and the anode, an active material with a decomposition inhibitor 72 carrying a decomposition inhibitor for inhibiting decomposition of the electrolyte on the surface of the active material, a non-carrying active material 68 not having a decomposition inhibitor on the surface of the active material, and a non-carrying decomposition inhibitor 70 not carried on the surface of the active material are intermingled. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery including an electrode with a decomposition inhibitor that suppresses decomposition of an electrolyte.

  Lithium secondary batteries that charge and discharge when lithium ions move between the positive and negative electrodes (for example, lithium ion batteries) are lightweight and have high energy density, so they are used as power sources for personal computers and mobile terminals, especially in vehicles. The importance is increasing as what is preferably used for a power supply for a vehicle.

  In general, a lithium secondary battery undergoes a decomposition reaction of an electrolyte (typically, an electrolytic solution) on the surface of an active material under a high voltage, and the battery performance (for example, cycle) of the lithium secondary battery is performed by repeatedly charging and discharging. Tend to decrease. Patent document 1 is mentioned as a technical document regarding a lithium secondary battery. In Patent Document 1, a decomposition inhibitor is provided in the positive electrode layer, and the concentration of the decomposition inhibitor in the positive electrode layer is a region far from the positive electrode current collector (that is, a region relatively close to the counter electrode (negative electrode)). Describes a technique capable of reducing the decomposition of the organic electrolyte by adjusting the region relatively closer to the positive electrode current collector (hereinafter simply referred to as the positive electrode current collector side) to be higher. In addition, Patent Document 2 is cited as a conventional technique.

JP 2009-064715 A Japanese Patent Laying-Open No. 2005-320184

  By the way, the thickness of the electrodes (positive electrode and negative electrode) of a lithium secondary battery (typically, a lithium ion battery) is greatly involved in the movement of lithium ions and electrons during charging and discharging. That is, the movement of lithium ions tends to be hindered at a portion far from the counter electrode (here, the negative electrode) (here, the portion near the positive electrode current collector), while the electron is a current collector (here, the positive electrode current collector). ) In the part far from (here, the part close to the negative electrode). This tendency appears particularly in a low temperature range (for example, about −30 ° C.). In the technique described in Patent Document 1, the decomposition reaction of the electrolyte can be reduced by including a decomposition inhibitor in the electrode layer (positive electrode layer). However, the inclusion of the decomposition inhibitor in the thickness direction of the electrode layer. There is a risk that the reaction resistance increases because the movement of lithium ions or electrons is hindered.

  Therefore, the present invention has been created to solve the above-described conventional problems, and its purpose is to reduce reaction resistance (particularly, reaction resistance at low temperatures) and to reduce the amount of electrolyte (typically, electrolyte). An object of the present invention is to provide a lithium secondary battery excellent in cycle characteristics by suppressing the decomposition reaction.

  In order to achieve the above object, the present invention provides a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte. In the lithium secondary battery disclosed herein, the positive electrode has a positive electrode current collector and a positive electrode active material layer including a granular positive electrode active material formed on the current collector, and the negative electrode is a negative electrode It has a current collector and a negative electrode active material layer including a granular negative electrode active material formed on the current collector. In the active material layer of at least one of the positive electrode and the negative electrode, an active material with a decomposition inhibitor in which a decomposition inhibitor that suppresses decomposition of the electrolyte is supported on the surface of the active material, and the active material The unsupported active material not having the decomposition inhibitor on the surface of the substance and the unsupported decomposition inhibitor that is the decomposition inhibitor and not supported on the surface of the active material are mixed.

In the present specification, the “lithium secondary battery” refers to a secondary battery that is charged and discharged by the movement of lithium ions between the positive and negative electrodes. A secondary battery generally referred to as a lithium ion battery is a typical example included in the lithium secondary battery in this specification.
In this specification, the “positive electrode active material” means a positive electrode side capable of reversibly occluding and releasing (typically inserting and removing) chemical species (here, lithium ions) which are charge carriers in a secondary battery. The active material.
Furthermore, in this specification, the “negative electrode active material” refers to a negative electrode capable of reversibly occluding and releasing (typically inserting and removing) chemical species (here, lithium ions) that serve as charge carriers in a secondary battery. The active material on the side.

The lithium secondary battery provided by the present invention includes an active material with a decomposition inhibitor, an unsupported active material, and an unsupported decomposition inhibitor in at least one of the positive electrode active material layer and the negative electrode active material layer. (That is, a decomposition inhibitor present free from the active material) and these are present in a mixture.
As described above, since the decomposition inhibitor (including the unsupported decomposition inhibitor) is contained in the active material layer, the electrolyte on the surface of the active material can be prevented from being repeatedly charged and discharged under a high voltage. Decomposition reaction can be suppressed. Further, the lithium secondary battery disclosed herein further includes an unsupported active material in addition to the active material with a decomposition inhibitor. By this, compared with the active material layer which consists only of an active material with a decomposition inhibitor, the mobility of the lithium ion in the said active material layer can be improved. Moreover, since the active material with a decomposition inhibitor, the unsupported active material, and the unsupported decomposition inhibitor are mixed, a sufficient effect of suppressing decomposition is ensured.
Therefore, according to the present invention, it is possible to provide a lithium secondary battery having excellent cycle characteristics by reducing reaction resistance (particularly, reaction resistance at low temperatures) and suppressing decomposition reaction of an electrolyte (typically, electrolyte). Can do.

  In a preferred aspect of the lithium secondary battery disclosed herein, the active material layer containing the decomposition inhibitor is formed in a laminated structure including at least two layers having different configurations. In the active material layer of the laminated structure, the content ratio of the unsupported decomposition inhibitor is such that the layer farther from the current collector than the layer close to the current collector (that is, the layer on the counter electrode side). Is smaller. Thus, by making the content ratio of the unsupported decomposition inhibitor smaller in the layer on the counter electrode side than in the layer close to the current collector, in the region far from the current collector (here, the counter electrode side) Electron mobility can be improved. For this reason, reaction resistance can be reduced more.

  In a preferred aspect of the lithium secondary battery disclosed herein, the active material layer containing the decomposition inhibitor is formed in a laminated structure including at least two layers having different configurations. And in the active material layer of the laminated structure, the content ratio of the active material with the decomposition inhibitor in the layer adjacent to the current collector is in the layer (that is, the layer on the counter electrode side) away from the current collector. It is smaller than the content rate of the active material with a decomposition inhibitor. Furthermore, the content ratio of the unsupported active material in the layer adjacent to the current collector is larger than the content ratio of the unsupported active material in the layer away from the current collector. As described above, since the content ratio of the unsupported active material is large in the layer adjacent to the current collector, the mobility of lithium ions in a region near the current collector can be further improved. For this reason, reaction resistance can be reduced more.

  In a preferred embodiment of the lithium secondary battery disclosed herein, the active material layer (typically, the positive electrode active material layer) containing the decomposition inhibitor further contains a conductive material. And the content rate of the said electrically conductive material contained in the part close | similar to the said electrical power collector is smaller than the content rate of the said electrically conductive material contained in the part (part on the counter electrode side) away from the said electrical power collector. According to such an embodiment, it is possible to improve the electron mobility in a portion away from the current collector, which is a region where the electron mobility is generally relatively low, by the conductive material.

  In a preferred aspect of the lithium secondary battery disclosed herein, the decomposition inhibitor is a metal oxide. By including such a compound as a decomposition inhibitor, decomposition of the electrolyte can be effectively suppressed. A particularly preferred decomposition inhibitor is tungsten oxide.

  Moreover, according to this invention, a vehicle provided with one of the lithium secondary batteries disclosed here is provided. The lithium secondary battery provided by the present invention may exhibit a quality suitable for a lithium secondary battery mounted on a vehicle (for example, excellent cycle characteristics). Therefore, the lithium secondary battery can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile equipped with an electric motor such as a hybrid vehicle, an electric vehicle, and a fuel cell vehicle.

It is a perspective view which shows typically the external shape of the lithium secondary battery which concerns on one Embodiment. It is a longitudinal cross-sectional view which follows the II-II line | wire in FIG. It is a schematic diagram which shows the positive electrode active material layer formed in the positive electrode electrical power collector which concerns on one Embodiment. It is a schematic diagram which shows the positive electrode active material layer formed in the positive electrode electrical power collector which concerns on other one Embodiment. It is a schematic diagram which shows the positive electrode active material layer formed in the positive electrode electrical power collector which concerns on other one Embodiment. It is a schematic diagram which shows the positive electrode active material layer formed in the positive electrode electrical power collector which concerns on other one Embodiment. It is a schematic diagram which shows the positive electrode active material layer formed in the positive electrode electrical power collector which concerns on other one Embodiment. It is a side view which shows typically the vehicle (automobile) provided with the lithium secondary battery which concerns on this invention.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than matters specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  Hereinafter, although the case where the active material layer containing the above-described decomposition inhibitor is formed on the positive electrode will be described, the active material layer containing the above-described decomposition inhibitor may be formed on the negative electrode instead of the positive electrode, Or the active material layer containing the decomposition inhibitor mentioned above may be formed in both the positive electrode and the negative electrode.

  The positive electrode provided in the lithium secondary battery disclosed herein can have the same configuration as the conventional one except that the positive electrode active material layer characterizing the present invention is provided. As a positive electrode current collector constituting such a positive electrode, a conductive material made of a metal having good conductivity is used as in the current collector used in the positive electrode of a conventional lithium secondary battery (typically, a lithium ion battery). A member is preferably used. For example, aluminum or an alloy containing aluminum as a main component can be used. The shape of the positive electrode current collector can vary depending on the shape of the lithium secondary battery, and is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. Typically, a sheet-like positive electrode current collector made of aluminum is used.

  Next, a material constituting the positive electrode active material layer formed on the surface of the positive electrode current collector will be described. On the surface of the positive electrode current collector, at least a positive electrode active material (unsupported positive electrode active material), a decomposition inhibitor (unsupported decomposition inhibitor) that suppresses decomposition of an electrolyte (typically, an electrolyte), And a positive electrode active material layer including a positive electrode active material (positive electrode active material with a decomposition inhibitor) carrying a decomposition inhibitor on the surface. Furthermore, the positive electrode active material layer may contain a conductive material, a binder (binder), and the like as necessary.

The positive electrode active material included in the positive electrode active material layer formed on the positive electrode of the lithium secondary battery disclosed herein as either an unsupported positive electrode active material or a positive electrode active material with a decomposition inhibitor is an object of the present invention. As long as it is a positive electrode active material having a property capable of realizing the above, there is no particular limitation on its composition and shape. A typical positive electrode active material includes a composite oxide containing lithium and at least one transition metal element. For example, cobalt lithium composite oxide (LiCoO ₂ ), nickel lithium composite oxide (LiNiO ₂ ), manganese lithium composite oxide (LiMn ₂ O ₄ ), or nickel-cobalt-based LiNi _x Co _1-x O ₂ ( 0 <x <1), cobalt / manganese-based LiCo _x Mn _1-x O ₂ (0 <x <1), nickel / manganese-based LiNi _x Mn _1-x O ₂ (0 <x <1) and LiNi as represented by _{x Mn 2-x O 4 (} 0 <x <2), a so-called binary lithium-containing composite oxide containing two kinds of transition metal elements, or nickel cobalt containing three transition metal elements A ternary lithium-containing composite oxide such as manganese may be used.
The positive electrode active material has a general formula of LiMAO ₄ (where M is at least one metal element selected from the group consisting of Fe, Co, Ni and Mn, and A is P, Si, S and A polyanionic compound represented by the following formula is also preferably used: an element selected from the group consisting of V. In the above general formula, A is P and / or Si (for example, LiFePO ₄ , LiFeSiO ₄ , LiCoPO ₄ , LiCoSiO ₄ , LiFe _0.5 Co _0.5 PO ₄ , LiFe _0.5 Co _0.5 SiO ₄ given as _{LiMnPO 4, LiMnSiO 4, LiNiPO 4} , LiNiSiO 4) is particularly preferred polyanionic compound.

  The compound which comprises such a positive electrode active material can be prepared and provided by a conventionally well-known method, for example. For example, the oxide can be prepared by mixing several raw material compounds appropriately selected according to the atomic composition at a predetermined molar ratio and firing the mixture at a predetermined temperature by an appropriate means. Further, the fired product is pulverized, granulated and classified by an appropriate means to obtain a granular positive electrode active material powder substantially composed of secondary particles having a desired average particle size and / or particle size distribution. be able to. In addition, the preparation method itself of a positive electrode active material (lithium containing complex oxide powder etc.) does not characterize this invention at all.

In addition, as a decomposition inhibitor contained in the positive electrode active material layer formed on the positive electrode as either the above unsupported decomposition inhibitor or the decomposition inhibitor supported on the positive electrode active material, an electrolyte used in a lithium secondary battery can be used. As long as decomposition can be suppressed, it is not limited to a specific decomposition inhibitor. For example, a metal oxide, a metal composite oxide, a metal phosphate, a boride, a carbide, a nitride, a silicide, or a fluoride can be used. Metal oxides are preferred, and examples include tungsten oxide, zirconium dioxide, aluminum oxide, titanium oxide, germanium dioxide, zinc oxide, tin oxide, magnesium oxide, and aluminum phosphate. Examples of other compounds include boron oxide, silicon dioxide, aluminum fluoride, and boron trifluoride. A particularly preferred decomposition inhibitor is tungsten oxide. Such a decomposition inhibitor may be used individually by 1 type, and may combine 2 or more types.
Although the amount of the decomposition inhibitor contained in the positive electrode active material layer is appropriately determined, a degree that does not hinder the conductivity of the positive electrode active material layer and suppresses decomposition of the electrolyte is preferable. For example, the unsupported decomposition inhibitor is preferably used in an amount of about 1 to 20 parts by mass with respect to 100 parts by mass of the positive electrode active material. More preferably, it is about 1-10 mass parts. When there is too much quantity of a decomposition inhibitor, there exists a possibility that electroconductivity may fall and battery performance may fall. Moreover, when there is too little quantity of a decomposition inhibitor, there exists a possibility that decomposition | disassembly of electrolyte cannot be suppressed effectively.

  Moreover, the positive electrode active material with a decomposition inhibitor contained in the positive electrode active material layer formed in the positive electrode disclosed here will be described. The positive electrode active material with a decomposition inhibitor is a positive electrode active material carried by the decomposition inhibitor on the surface of the positive electrode active material. Examples of the method for supporting the decomposition inhibitor on the surface of the positive electrode active material include a sol-gel method, a mechanical milling method, an electrochemical deposition method, and a vapor deposition method. Of these, the sol-gel method can be preferably used. For example, a method in which a positive electrode active material and a precursor of a decomposition inhibitor (here, metal oxide) are mixed in an appropriate solvent, and then the solvent is evaporated and baked, and the like. The amount of the decomposition inhibitor supported on the surface of the positive electrode active material is appropriately determined and is preferably about 0.1 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material. More preferably, it is about 0.1-5 mass parts.

  In addition, when a conductive material is included in the positive electrode active material layer formed in the positive electrode disclosed herein, the conductive material may be any material that has been conventionally used in this type of secondary battery. It is not limited to the conductive material. For example, carbon materials such as carbon powder and carbon fiber can be used. As the carbon powder, various carbon blacks (for example, acetylene black, furnace black, ketjen black), graphite powder, and the like can be used. Among these, you may use together 1 type, or 2 or more types. The amount of the conductive material is preferably about 3 to 20 parts by mass with respect to the positive electrode active material. More preferably, it is about 5-10 mass parts.

  Furthermore, as a binder (binder) contained in the positive electrode active material layer formed in the positive electrode disclosed herein, for example, an aqueous liquid composition (typically, a composition for forming the positive electrode active material layer) Is a composition prepared in the form of a paste or slurry, hereinafter referred to as a positive electrode active material layer forming paste), a polymer material that is dissolved or dispersed in water can be preferably employed. Cellulose polymers such as carboxymethylcellulose (CMC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropylmethylcellulose (HPMC), etc .; polyvinyl alcohol (PVA) And the like are exemplified. Examples of polymer materials that can be dispersed in water (water-dispersible) include fluorine resins such as polytetrafluoroethylene (PTFE) and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA); vinyl acetate copolymer Combined; rubbers such as styrene butadiene rubber (SBR) are exemplified. Alternatively, when a solvent-based liquid composition (positive electrode active material layer forming paste) is used as a composition for forming the positive electrode active material layer, an organic material such as polyvinylidene fluoride (PVDF) or polyvinylidene chloride (PVDC) is used. A polymer material that is soluble in a solvent (non-aqueous solvent) can be used. In addition, the polymer material illustrated above may be used as a thickener and other additives in the above composition in addition to being used as a binder.

  Here, the “aqueous liquid composition” is a concept indicating a composition using water or a mixed solvent mainly composed of water (aqueous solvent) as a dispersion medium of the active material. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. The “solvent-based liquid composition” is a concept indicating a composition in which a dispersion medium of an active material is mainly an organic solvent (non-aqueous solvent). As the organic solvent, for example, N-methylpyrrolidone (NMP) can be used.

Hereinafter, the positive electrode that can be manufactured by using various materials as described above will be described in detail.
FIG. 3 is a view schematically showing a positive electrode 66 including a positive electrode active material layer 64 that characterizes the present embodiment (first embodiment). As shown in this figure, the positive electrode active material layer 64 according to this embodiment is formed by a laminated structure having two different structures. That is, it is a laminated structure of a decomposition inhibitor dispersion layer 74 that is a layer close to the positive electrode current collector 62 and a decomposition inhibitor carrying layer 76 that is a layer separated from the positive electrode current collector 62. Hereinafter, a method for forming such a two-layer structure will be described in detail.

  A positive electrode (for example, a sheet-like positive electrode, hereinafter referred to as “positive electrode sheet 66”) 66 according to the present embodiment is formed on a long positive electrode current collector (for example, a long aluminum foil) 62. 64 is formed. In forming the positive electrode active material layer 64, first, a granular (powdered) positive electrode active material (for example, lithium cobaltate particles) 68 and a decomposition inhibitor (for example, tungsten oxide) 70 are mixed to decompose. The active material for the dispersion layer is preferably prepared by pulverization and mixing. At this time, the amount of the decomposition inhibitor is preferably about 1 to 20 parts by mass with respect to 100 parts by mass of the positive electrode active material. More preferably, it is about 1-10 mass parts. Then, the prepared active material for the decomposition inhibitor dispersion layer (the positive electrode active material 68 and the decomposition inhibitor 70), the conductive material (for example, graphite), and the binder (for example, PVDF) are used in a predetermined solvent. A paste for a decomposition inhibitor dispersion layer (that is, a positive electrode active material layer forming paste) dispersed in (for example, NMP) is prepared.

  On the other hand, a decomposition inhibitor (for example, tungsten oxide) 70 is supported on the surface of the positive electrode active material (for example, lithium cobaltate particles) 68 by using, for example, the sol-gel method described above. The amount of the decomposition inhibitor at this time is the same as in the case of preparing the active material for the decomposition inhibitor dispersion layer. And the positive electrode active material 68 (henceforth "the positive electrode active material 72 with a decomposition inhibitor") provided with the decomposition inhibitor 70 obtained by the said method on the surface, a electrically conductive material (for example, graphite), and a binder ( For example, a decomposition inhibitor-supporting layer paste (that is, a positive electrode active material layer forming paste) prepared by dispersing PVDF) in a predetermined solvent (for example, NMP) is prepared. At this time, it is preferable that the content ratio of the positive electrode active material contained in the paste for the decomposition inhibitor dispersion layer and the content ratio of the positive electrode active material contained in the paste for the decomposition inhibitor support layer are approximately the same.

  Then, the prepared paste for the decomposition inhibitor dispersion layer is applied to the positive electrode current collector 62. Furthermore, the decomposition inhibitor carrying layer paste is applied on the applied paste for the decomposition inhibitor dispersion layer. In addition, as a method of apply | coating the said paste, the technique similar to a conventionally well-known method can be employ | adopted suitably. For example, the paste can be suitably applied to the positive electrode current collector 62 and the dispersion inhibitor dispersion layer paste by using an appropriate application device such as a slit coater, a die coater, a gravure coater, or a comma coater. it can. At this time, the ratio of the coating amount of the dispersion inhibitor dispersion layer paste and the dispersion inhibitor support layer paste is about 60:40 to 40:60 (preferably about 55:45 to 45:55, more preferably 50). : 50).

  The coating applied to the positive electrode current collector 62 (that is, the dispersion inhibitor dispersion layer paste and the dispersion inhibitor support layer paste) is dried and then pressed (compressed), whereby the decomposition inhibitor dispersion layer 74 (hereinafter referred to as the dispersion inhibitor dispersion layer 74). , “Dispersion layer 74”) and a decomposition inhibitor carrying layer 76 (hereinafter, “carrying layer 76”) are formed. At this time, the dispersion layer 74 and the support layer 76 are pressed so that the thickness ratio is about 60:40 to 40:60 (preferably about 55:45 to 45:55, more preferably 50:50). Is appropriate. In addition, as said press (compression) method, compression methods, such as a conventionally well-known roll press method and a flat plate press method, are employable. In adjusting the thickness, the thickness may be measured with a film thickness measuring instrument, and the press pressure may be adjusted to compress a plurality of times until a desired thickness is obtained. Alternatively, after the dispersion layer paste is dried and pressed, the support layer paste may be applied onto the dried product, and the paste (application product) may be dried for pressing.

  According to the lithium secondary battery constructed using the positive electrode sheet 66 according to the present embodiment, the dispersion layer 74 that is a layer adjacent to the positive electrode current collector 62 of the positive electrode sheet 66 includes the positive electrode active material 68 (unsupported positive electrode active material). ) And a decomposition inhibitor 70, and the surface 68 of the positive electrode active material does not carry the decomposition inhibitor 70 (that is, the decomposition inhibitor 70 is a non-supported decomposition inhibitor). In addition, it is possible to suppress the decomposition of the electrolyte during charging and discharging, and to further improve the lithium ion mobility. Further, the support layer 76, which is a layer separated from the positive electrode current collector 62, includes a positive electrode active material 68 and a decomposition inhibitor 70, and the decomposition inhibitor 70 is supported on the surface of the positive electrode active material 68. Since it is the positive electrode active material 72 with a decomposition inhibitor, the decomposition of the electrolyte can be suppressed and the electron mobility can be improved during charging and discharging of the lithium secondary battery. As described above, the lithium secondary battery constructed using the positive electrode sheet 66 is a lithium secondary battery excellent in cycle characteristics by reducing the reaction resistance and suppressing the decomposition reaction of the electrolyte.

  Next, an embodiment in the case where a lithium secondary battery is constructed using the positive electrode will be described. First, a negative electrode, a separator and the like suitable for use in combination with the positive electrode (positive electrode sheet 66) described above will be described. The negative electrode can have the same configuration as before. As a negative electrode current collector constituting such a negative electrode, for example, a copper material, a nickel material, or an alloy material mainly composed of them is preferably used. The shape of the negative electrode current collector can be the same as the shape of the positive electrode. Typically, a sheet-like copper negative electrode current collector is used.

The negative electrode active material contained in the negative electrode active material layer formed in the negative electrode disclosed herein may be any material that can occlude and release lithium. For example, carbon materials such as graphite, lithium / titanium Metal materials made of oxide materials such as oxides (Li ₄ Ti ₅ O ₁₂ ), metals such as tin, aluminum (Al), zinc (Zn), silicon (Si), or metal alloys mainly composed of these metal elements , Etc. A typical example is the amount of powdery carbon material made of graphite or the like. For example, graphite particles can be preferably used.

  The negative electrode active material layer formed in the negative electrode disclosed herein may contain one or more materials that can be blended in the positive electrode active material layer, if necessary, in addition to the negative electrode active material. it can. As such a material, various materials that can function as a binder as listed as a constituent material of the positive electrode active material layer can be similarly used.

  The negative electrode disclosed here can be manufactured by the same method as that for the positive electrode. A paste-like (or slurry-like) composition (hereinafter referred to as a negative electrode active material layer forming paste) is prepared by dispersing a negative electrode active material and a binder in an appropriate solvent. The prepared negative electrode active material layer forming paste is applied to the negative electrode current collector, dried, and then compressed (pressed) to form the negative electrode current collector and the negative electrode active material formed on the negative electrode current collector A negative electrode provided with a layer can be produced.

  Moreover, as a separator used with a positive electrode and a negative electrode, the separator similar to the past can be used. For example, a porous sheet made of resin (a microporous resin sheet) can be preferably used. As a constituent material of such a porous sheet, polyolefin resins such as polyethylene (PE), polypropylene (PP), and polystyrene are preferable. In particular, a porous structure such as a PE sheet, a PP sheet, a two-layer structure sheet in which a PE layer and a PP layer are laminated, and a three-layer structure sheet in which one PE layer is sandwiched between two PP layers. A polyolefin sheet can be suitably used. When a solid electrolyte or a gel electrolyte is used as the electrolyte, a separator may not be necessary (that is, in this case, the electrolyte itself can function as a separator).

As the electrolyte, the same electrolyte as a non-aqueous electrolyte (typically, an electrolytic solution) conventionally used for a lithium secondary battery can be used without particular limitation. Such a non-aqueous electrolyte typically has a composition in which a suitable non-aqueous solvent (organic solvent) contains a lithium salt that can function as an electrolyte. As the electrolyte, a lithium salt conventionally used in lithium secondary batteries can be appropriately selected and used. Examples of the lithium salt include LiPF ₆ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiBF ₄ , LiCF ₃ SO _{3 and the} like. Such electrolytes can be used alone or in combination of two or more. A particularly preferred example is LiPF ₆ . Examples of the non-aqueous solvent include carbonates such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and propylene carbonate (PC). Such non-aqueous solvents can be used alone or in combination of two or more.

Hereinafter, although one form of a lithium secondary battery provided with the positive electrode provided with the said positive electrode active material layer is demonstrated with reference to drawings, it is not intending to limit this invention to this embodiment. That is, as long as the positive electrode active material layer containing the decomposition inhibitor disclosed here is employed, the shape (outer shape and size) of the lithium secondary battery to be constructed is not particularly limited. The battery outer case may have a rectangular shape, a cylindrical shape, or a small button shape. Moreover, the thin sheet | seat type comprised by a laminated film etc. may be sufficient as an exterior. In the following embodiment, a rectangular battery will be described.
In addition, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted. Moreover, the dimensional relationship (length, width, thickness, etc.) in each drawing does not necessarily reflect the actual dimensional relationship.

FIG. 1 is a perspective view schematically showing a lithium secondary battery according to an embodiment. FIG. 2 is a longitudinal sectional view taken along line II-II in FIG.
As shown in FIGS. 1 and 2, the lithium secondary battery 10 according to the present embodiment includes the above-described lithium secondary battery constituent materials (active material for each positive and negative electrode, current collector for each positive and negative electrode, separator, etc.). An electrode body 50 is provided, and a battery case 15 having a rectangular shape (typically a flat rectangular parallelepiped shape) that accommodates the electrode body 50 and a suitable nonaqueous electrolyte (typically, an electrolyte).

  The case 15 includes a box-shaped case main body 30 in which one of the narrow surfaces in the flat rectangular parallelepiped shape is an opening 20, and the opening 20 is attached (for example, welded) to the opening 20. And a lid 25 for closing. As a material constituting the case 15, the same material as that used in a general lithium secondary battery can be used as appropriate, and there is no particular limitation. For example, a metal (for example, aluminum, steel, etc.) container, a synthetic resin (for example, a polyolefin resin, a high melting point resin such as a polyamide resin, etc.), or the like can be preferably used. The case 15 according to the present embodiment is made of, for example, aluminum.

  The lid body 25 is formed in a rectangular shape that matches the shape of the opening 20 of the case body 30. Further, the lid body 25 is provided with a positive terminal 60 and a negative terminal 80 for external connection, respectively, and a part of these terminals 60 and 8070 protrudes from the lid body 25 toward the outside of the case 15. It is formed to do. Similarly to the case of the conventional lithium secondary battery, the lid 25 is provided with a safety valve 40 for discharging the gas generated inside the case 15 to the outside of the case 15 when the battery is abnormal. The safety valve 40 can be used without particular limitation as long as the safety valve 40 has a mechanism that opens and discharges gas to the outside of the case 15 when the pressure inside the case 15 rises above a predetermined level.

  As shown in FIG. 2, the lithium secondary battery 10 includes a wound electrode body 50 in the same manner as a normal lithium secondary battery. The electrode body 50 is accommodated in the case main body 30 in a posture in which the winding axis is laid down (that is, in the direction in which the opening 20 is positioned in the lateral direction with respect to the winding axis). The electrode body 50 includes a positive electrode sheet (positive electrode) 66 having a positive electrode active material layer 64 formed on the surface of a long sheet-like positive electrode current collector 62 and a negative electrode active material on the surface of a long sheet-like negative electrode current collector 82. The negative electrode sheet (negative electrode) 86 on which the material layer 84 is formed is overlapped with the two long separator sheets 100 and wound, and the obtained electrode body 50 is flattened by crushing and ablating from the side surface direction. It is formed into a shape.

  Further, in the wound positive electrode sheet 66, the positive electrode current collector 62 is exposed without forming the positive electrode active material layer 64 at one end portion along the longitudinal direction, while the negative electrode is wound. Also in the sheet 86, the negative electrode current collector 82 is exposed at one end portion along the longitudinal direction without forming the negative electrode active material layer 84. A positive electrode terminal 60 is joined to the exposed end of the positive electrode current collector 62, and is electrically connected to the positive electrode sheet 66 of the wound electrode body 50 formed in the flat shape. Similarly, a negative electrode terminal 80 is joined to the exposed end portion of the negative electrode current collector 82 and is electrically connected to the negative electrode sheet 86. The positive and negative electrode terminals 60 and 80 and the positive and negative electrode current collectors 62 and 82 can be joined by, for example, ultrasonic welding, resistance welding, or the like.

  The material and the member itself constituting the wound electrode body 50 having the above-described configuration are other than employing a positive electrode (here, the positive electrode sheet 66) in which the positive electrode active material layer disclosed herein is formed on the positive electrode current collector as the positive electrode. The electrode body of the conventional lithium secondary battery may be the same as that of the conventional lithium secondary battery, and is not particularly limited.

  The positive electrode sheet 66 is produced as described above. On the other hand, the negative electrode sheet 86 is produced by forming a negative electrode active material layer 84 on a long negative electrode current collector (for example, a long copper foil) 82. That is, a negative electrode active material layer forming paste is prepared by dispersing a negative electrode active material (for example, graphite) and a binder (for example, PVDF) in an organic solvent (for example, NMP). The prepared paste is applied to the negative electrode current collector 82, dried, and then compressed (pressed) to form the negative electrode active material layer 84. Since the method of forming the negative electrode active material layer 84 is the same as that of the positive electrode side, detailed description thereof is omitted.

The produced positive electrode sheet 66 and negative electrode sheet 86 are stacked together with two separators (for example, porous polyolefin resin) 100 and wound, and the wound electrode body 50 obtained is placed in the case body 30 with its winding shaft lying sideways. Non-aqueous electrolysis such as a mixed solvent of EC and DMC (for example, a mass ratio of 1: 1) containing an appropriate amount of a supporting salt (for example, a lithium salt such as LiPF ₆ ) (for example, a concentration of 1M). After injecting the liquid, the lithium secondary battery 10 of the present embodiment can be constructed by mounting the lid 25 on the opening 20 and sealing (for example, laser welding).

  In the positive electrode active material layer 64 of the positive electrode sheet 66 according to the first embodiment described above, a layer (dispersion layer 74) including a positive electrode active material 68 (unsupported positive electrode active material) and a decomposition inhibitor 70 (unsupported decomposition inhibitor). ) And a layer containing the positive electrode active material 72 with a decomposition inhibitor (supporting layer 76), but is not limited to this form. Hereinafter, a suitable example of the positive electrode 166 including the positive electrode active material layer 164 according to the second embodiment will be described with reference to the drawings. FIG. 4 is a diagram schematically showing a positive electrode 166 including a positive electrode active material layer 164 that characterizes the present embodiment. As shown in this figure, the positive electrode active material layer 164 according to this embodiment includes a decomposition inhibitor mixed layer 173 in which a positive electrode active material 168, a decomposition inhibitor 170, and a positive electrode active material 172 with a decomposition inhibitor are mixed. It is composed of Hereinafter, a method for forming the decomposition inhibitor mixed layer 173 will be described in detail.

  The positive electrode sheet 166 according to this embodiment is manufactured by forming a positive electrode active material layer 164 on a long positive electrode current collector 162. In forming the positive electrode active material layer 164, first, a mixture of a granular (powdered) positive electrode active material (for example, lithium cobaltate particles) 168 and a decomposition inhibitor 170 (for example, tungsten oxide) is preferably ground and Prepare by mixing process. The amount of the decomposition inhibitor at this time is the same as that when the active material for the decomposition inhibitor dispersion layer of the first embodiment is prepared. Next, a positive electrode active material 172 with a decomposition inhibitor having a decomposition inhibitor 170 supported on the surface of the positive electrode active material 168 is prepared in the same manner as the positive electrode active material 72 with a decomposition inhibitor of the first embodiment. And the mixture obtained by mixing and the positive electrode active material with a decomposition inhibitor are mixed (The content rate of a mixture and the positive electrode active material with a decomposition inhibitor is about 40: 60-60: 40, for example, Preferably it is 45. : 55-55: 45, more preferably 50:50) A positive electrode active material for a decomposition inhibitor mixed layer (hereinafter referred to as “positive electrode active material for mixed layer”) was prepared. Furthermore, a paste for a decomposition inhibitor mixed layer (that is, a paste obtained by dispersing a positive electrode active material for the mixed layer, a conductive material (for example, graphite), and a binder (for example, PVDF) in a predetermined solvent (for example, NMP)). A positive electrode active material layer forming paste) is prepared.

Then, the prepared paste for the decomposition inhibitor mixed layer is applied to the positive electrode current collector 162. Furthermore, after drying the applied material (that is, the paste for the decomposition inhibitor mixed layer) applied to the positive electrode current collector 162, the mixture is pressed (compressed), whereby the decomposition inhibitor mixed layer 173 (hereinafter “mixed layer 173”). A positive electrode active material layer 164 is formed.
According to the lithium secondary battery constructed using the positive electrode sheet 166 according to the present embodiment, the mixed layer 173 (that is, the positive electrode active material layer 164) of the positive electrode sheet 166 includes the positive electrode active material 168 (unsupported positive electrode active material), It contains a decomposition inhibitor 170 (unsupported decomposition inhibitor) and a positive electrode active material 172 with a decomposition inhibitor, which are uniformly mixed, so that the electrolyte is decomposed during charging and discharging of the lithium secondary battery. In addition to being suppressed, the mobility of lithium ions in a region near the positive electrode current collector 162 can be partially improved, and the mobility of electrons in a region far from the positive electrode current collector 162 can be partially improved. .

In the positive electrode active material layer 164 (decomposition inhibitor mixed layer 173) of the positive electrode sheet 166 according to the second embodiment described above, the positive electrode active material 168, the decomposition inhibitor 170, and the positive electrode active material 172 with a decomposition inhibitor are mixed. However, the present invention is not limited to such a form. Hereinafter, a suitable example of the positive electrode active material layer 264 according to the third embodiment will be described with reference to the drawings.
FIG. 5 is a diagram schematically showing a positive electrode 266 including a positive electrode active material layer 264 characterizing the present embodiment. As shown in this figure, the positive electrode active material layer 264 according to this embodiment is formed by a laminated structure having two different structures. That is, it is a laminated structure of a first decomposition inhibitor mixed layer 280 that is a layer close to the positive electrode current collector 262 and a second decomposition inhibitor mixed layer that is a layer away from the positive electrode current collector 62. Hereinafter, a method for forming such a two-layer structure will be described in detail.

The positive electrode sheet 266 according to this embodiment is manufactured by forming a positive electrode active material layer 264 on a long positive electrode current collector 262. In forming the positive electrode active material layer 264, a positive electrode active material for the first decomposition inhibitor mixed layer, which is a layer adjacent to the positive electrode current collector 262, is prepared in the same manner as in the second embodiment ( The content ratio of the mixture (the positive electrode active material 268 and the decomposition inhibitor 270) and the positive electrode active material 272 with a decomposition inhibitor is less than 50% by mass when both are taken as 100, and the positive electrode active material with a decomposition inhibitor is included. For example, approximately 55:45 to 90:10). Similarly, a positive electrode active material for the second decomposition inhibitor mixed layer that is a layer away from the positive electrode current collector 262 is prepared (when the content ratio of the mixture and the positive electrode active material with the decomposition inhibitor is 100) The mixture is contained in a proportion of less than 50% by weight (for example, approximately 45:55 to 10:90).
That is, the content ratio of the active material 272 with the decomposition inhibitor in the layer adjacent to the positive electrode current collector 262 (here, the first decomposition inhibitor mixed layer 280, hereinafter referred to as “first mixed layer 280”) is It is smaller than the content ratio of the positive electrode active material 272 with a decomposition inhibitor in a layer away from the positive electrode current collector 262 (herein, a second decomposition inhibitor mixed layer 282, hereinafter referred to as “second mixed layer 282”). Thus, the positive electrode active material for each mixed layer is prepared, and the content ratio of the positive electrode active material 268 in the first mixed layer 280 is the positive electrode active material 268 in the second mixed layer 282.
The positive electrode active material for each mixed layer is prepared so as to be larger than the content ratio of.
As shown in FIG. 5, in the present embodiment, the content ratio of the mixture in the first decomposition inhibitor mixed layer 280 and the positive electrode active material with the decomposition inhibitor is 2: 1. On the other hand, the content ratio of the mixture in the second decomposition inhibitor mixed layer 282 and the positive electrode active material with a decomposition inhibitor is 1: 2.

  For a first decomposition inhibitor mixed layer obtained by dispersing a positive electrode active material for a first mixed layer, a conductive material (for example, graphite), and a binder (for example, PVDF) in a predetermined solvent (for example, NMP). A paste (that is, a positive electrode active material layer forming paste, hereinafter referred to as “first mixed layer paste”) is prepared. On the other hand, in the same manner as in the case where the first mixed layer paste is prepared using the positive electrode active material for the second mixed layer instead of the positive electrode active material for the first mixed layer, the second decomposition is performed. An inhibitor mixed layer paste (that is, a positive electrode active material layer forming paste, hereinafter referred to as “second mixed layer paste”) is prepared.

  Then, the prepared first mixed layer paste is applied to the positive electrode current collector 262, and the prepared second mixed layer paste is applied onto the coated material (first mixed layer paste). The coated material (the first mixed layer paste and the second mixed layer paste are laminated) is dried and then pressed (compressed), whereby the first mixed layer 280 and the second mixed layer are mixed. A positive electrode active material layer 264 including the layer 282 is formed.

According to the lithium secondary battery constructed using the positive electrode sheet 266 according to the present embodiment, the content ratio of the positive electrode active material (unsupported positive electrode active material) 268 is large in the first mixed layer 280 of the positive electrode sheet 266. , The mobility of lithium ions can be improved. Further, in the second mixed layer 282, since the content ratio of the positive electrode active material 272 with the decomposition inhibitor is large (that is, the content ratio of the unsupported decomposition inhibitor is small), the electron mobility is relatively low. Even in a layer away from the current collector, the electron mobility can be improved.
In addition, when the positive electrode active material layer is formed of a plurality of layers (three or more layers, for example, three to five layers), an unsupported positive electrode is provided for each layer toward a layer away from a layer close to the positive electrode current collector. While the content ratio of the active material decreases, the content ratio of the positive electrode active material with the decomposition inhibitor increases for each layer toward the layer away from the layer close to the positive electrode current collector.

In the various embodiments described above, when the conductive material is included in each positive electrode active material layer, the content ratio of the conductive material included in each positive electrode active material layer is the content ratio included in the portion adjacent to the positive electrode current collector. Is preferably smaller than the content of the portion away from the positive electrode current collector. Hereinafter, a suitable example of the positive electrode active material layer 364 according to the fourth embodiment will be described with reference to the drawings.
FIG. 6 is a diagram schematically illustrating a positive electrode 366 including a positive electrode active material layer 364 that characterizes the present embodiment. As shown in this figure, the positive electrode active material layer 364 according to this embodiment is formed by a laminated structure having two different structures. That is, it is a laminated structure of a decomposition inhibitor dispersion layer 374 that is a layer adjacent to the positive electrode current collector 362 and a decomposition inhibitor carrying layer that is a layer separated from the positive electrode current collector 62. Hereinafter, a method for forming such a two-layer structure will be described in detail.

  The positive electrode sheet 366 according to this embodiment is manufactured by forming a positive electrode active material layer 364 on a long positive electrode current collector 362. In the same manner as in the first embodiment, a paste for a decomposition inhibitor dispersion layer and a paste for a decomposition inhibitor support layer are prepared. At this time, the content ratio of the conductive material contained in the decomposition inhibitor dispersion layer paste and the decomposition inhibitor support layer paste is about 3: 100 to 20: 100 (preferably about 5: 100 to 10: 100). is there. Then, the prepared paste for the decomposition inhibitor dispersion layer is applied to the positive electrode current collector 362. Furthermore, the decomposition inhibitor carrying layer paste is applied on the applied paste for the decomposition inhibitor dispersion layer. The coated material is dried and then pressed to form the positive electrode active material layer 364.

According to the lithium secondary battery constructed using the positive electrode sheet 366 according to the present embodiment, the decomposition inhibitor dispersion layer 374 that is a layer adjacent to the positive electrode current collector 362 of the positive electrode sheet 366 includes the positive electrode active material 368 (unsupported). A decomposition inhibitor-supporting layer 376, which is a layer separated from the positive electrode current collector 362, includes a positive electrode active material), a decomposition inhibitor 370 (unsupported decomposition inhibitor), and a conductive material 377. Since the active material 372 and the conductive material 377 are included, the conductivity of the positive electrode active material 364 as a whole is improved. Further, since the decomposition inhibitor-carrying layer 376 has a higher content of the conductive material, conductivity is improved in a layer away from the positive electrode current collector 362, and electron mobility can be improved.
When the positive electrode active material layer is formed of three or more layers, a paste in which the content ratio of the conductive material included in each layer is increased toward the layer away from the layer adjacent to the positive electrode current collector can be used. Good.

  Further, when the positive electrode active material layer is a single layer (that is, when it is not a laminated structure), for example, it is included in the portion adjacent to the positive electrode current collector by a method using the difference in specific gravity between the positive electrode active material and the conductive material. The content ratio can be made smaller than the content ratio of the portion away from the positive electrode current collector. Specifically, a positive electrode active material layer forming paste containing the above materials and having a predetermined fluidity is prepared and applied on the positive electrode current collector. At this time, when the specific gravity of the positive electrode active material is larger than the specific gravity of the conductive material, if the positive electrode active material layer is left in a state where fluidity is maintained, the positive electrode active material having a higher specific gravity will settle more and the specific gravity will be lighter. Since the conductive material floats more, the content ratio contained in the portion close to the positive electrode current collector can be made smaller than the content ratio in the portion away from the positive electrode current collector. When the specific gravity of the positive electrode active material is larger than the specific gravity of the conductive material, a positive electrode active material layer similar to the above can be obtained by turning the positive electrode current collector upside down.

  In the various embodiments described above, the positive electrode active material layer includes a positive electrode active material (unsupported positive electrode active material), a decomposition inhibitor (unsupported decomposition inhibitor), and a positive electrode active material with a decomposition inhibitor. It is not limited to such a form. Hereinafter, a suitable example of the positive electrode active material layer 464 according to the fifth embodiment will be described with reference to the drawings. FIG. 7 is a diagram schematically showing a positive electrode 466 including a positive electrode active material layer 464 that characterizes this embodiment. As shown in this figure, the positive electrode active material layer 464 according to this embodiment is formed by a laminated structure having two different structures. That is, it is a laminated structure of a decomposition inhibitor mixed layer 480 that is a layer close to the positive electrode current collector 462 and a decomposition inhibitor carrying layer that is a layer away from the positive electrode current collector 462. Hereinafter, a method for forming such a two-layer structure will be described in detail.

The positive electrode sheet 466 according to the present embodiment is manufactured by forming a positive electrode active material layer 464 on a long positive electrode current collector 462. In the formation of the positive electrode active material layer 464, a positive electrode active material 472 with a decomposition inhibitor is prepared in the same manner as in the first embodiment to prepare a paste for a decomposition inhibitor carrying layer.
On the other hand, the decomposition inhibitor 470 is supported on the surface of the positive electrode active material 468 in the same manner as in the first embodiment. However, the amount of the decomposition inhibitor 470 supported on the surface of the positive electrode active material 468 at this time is about half of the amount of the decomposition inhibitor 470 included in the paste for the decomposition inhibitor supporting layer. Then, the obtained positive electrode active material 478 with a decomposition inhibitor and the decomposition inhibitor 470 are mixed (the amount of the decomposition inhibitor 470 to be mixed is the decomposition suppression carried on the positive electrode active material 478 with the decomposition inhibitor). And the total amount of the decomposition inhibitor 470 contained in the paste is the same as that of the paste for the decomposition inhibitor supporting layer), the mixed active material, and a conductive material (eg, graphite). Then, a paste for a decomposition inhibitor mixed layer (that is, a paste for forming a positive electrode active material layer) is prepared by dispersing a binder (for example, PVDF) in a predetermined solvent (for example, NMP).
Then, the prepared mixed layer paste is applied to the positive electrode current collector 462. Furthermore, the paste for decomposition inhibitor carrying layer is applied on the applied paste for mixed decomposition inhibitor layer. The coated material is dried and then pressed to form the positive electrode active material layer 464.

  According to the lithium secondary battery constructed using the positive electrode sheet 466 according to the present embodiment, the decomposition inhibitor mixed layer 480 that is a layer adjacent to the positive electrode current collector 462 of the positive electrode sheet 466 is the positive electrode active material with a decomposition inhibitor. 478 and a decomposition inhibitor 470 (unsupported decomposition inhibitor), but the loading ratio of the decomposition inhibitor 470 supported on the positive electrode active material 478 with the decomposition inhibitor is the decomposition ratio of the decomposition inhibitor supporting layer 476. Since it is smaller than the positive electrode active material 472 with an inhibitor, the movement of lithium ions can be improved. Thereby, reaction resistance may be reduced.

In each of the above-described embodiments, the positive electrode contains the decomposition inhibitor. However, the negative electrode active material layer of the negative electrode may contain a decomposition inhibitor. As a decomposition inhibitor, the thing similar to what was used for the positive electrode active material layer of the said positive electrode can be used. The amount of the decomposition inhibitor contained in the negative electrode active material layer is appropriately determined. For example, the unsupported decomposition inhibitor is preferably used in an amount of about 1 to 20 parts by mass with respect to 100 parts by mass of the negative electrode active material. More preferably, it is about 1-10 mass parts.
In the case of a negative electrode active material with a decomposition inhibitor (an active material in which a decomposition inhibitor is supported on the surface of the negative electrode active material by a method similar to that of the positive electrode (for example, sol-gel method)), the surface of the negative electrode active material It is preferable to use about 0.1 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material. More preferably, it is about 0.1-5 mass parts.
In addition, since the structure of the negative electrode active material layer can take the same structure as the positive electrode active material layer according to the above-described various embodiments, a duplicate description is omitted.
According to this structure, the same effect as the case where the said positive electrode contains the decomposition inhibitor can be acquired.

  In order to confirm that a lithium secondary battery excellent in reduction of reaction resistance and cycle characteristics (capacity retention ratio) can be constructed by constructing the lithium secondary battery, the following experiment was conducted as an example. It should be noted that the present invention is not intended to be limited to those shown in the specific examples.

[Example 1]
(1) Preparation of Active Material for Decomposition Inhibitor Dispersion Layer Weighed so that the mass ratio of lithium cobaltate as the positive electrode active material and tungsten oxide as the decomposition inhibitor was 100: 1, and then mortar for 30 minutes Mixed.
(2) Preparation of active material for decomposition inhibitor-carrying layer (positive electrode active material with decomposition inhibitor) Lithium cobaltate as a positive electrode active material was added to an ethanol solution of tungsten ethoxide and stirred at room temperature for 10 hours while mixing. did. Thereafter, ethanol was evaporated while stirring the mixture at 70 ° C. Next, the obtained residue was baked at 600 ° C. for 24 hours to obtain lithium cobaltate (positive electrode active material with a decomposition inhibitor) supported by tungsten oxide. At this time, the mass ratio of lithium cobaltate and tungsten oxide was adjusted to be 100: 1.

(3) Production of positive electrode (a) Into 125 mL of NMP in which 5 g of polyvinylidene fluoride (PVDF) as a binder was dissolved, 85 g of the active material prepared in the above (1) and 10 g of carbon black as a conductive material were introduced. The paste for the dispersion inhibitor dispersion layer was prepared by kneading until uniformly mixed.
(B) A paste for a decomposition inhibitor carrying layer was prepared in the same manner as (a) except that the active material prepared in (2) was used.

Then, the paste for the decomposition inhibitor dispersion layer was applied on one side with a coating amount of 3 mg / cm ² onto an aluminum current collector having a thickness of 15 μm, and then dried at 80 ° C. for 30 minutes. Subsequently, a paste for a decomposition inhibitor-carrying layer was applied onto the coated material at a coating amount of 3 mg / cm ² and then dried at 80 ° C. for 30 minutes. At this time, the coating amount of the paste for the decomposition inhibitor dispersion layer and the paste for the decomposition inhibitor support layer was 6 mg / cm ^{2 in} total. After drying, the coated material was pressed to a positive electrode active material layer (laminated structure of a decomposition inhibitor dispersion layer and a decomposition inhibitor support layer) having a thickness of 40 μm and a positive electrode active material layer density of 2.5 g / cm ³ . An electrode was obtained. Finally, this electrode was cut out to have a diameter of 16 mm to produce a positive electrode.

(4) Production of Battery A CR2032-type coin cell (lithium secondary battery) was produced using the produced positive electrode and a negative electrode made of metallic lithium having a diameter of 19 mm and a thickness of 35 μm. In addition, the porous separator made from a polypropylene was used as a separator. As the electrolyte, a nonaqueous electrolytic solution having a composition in which 1 mol / L LiPF ₆ was dissolved as a supporting salt in a 3: 7 (volume ratio) mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) was used.

[Example 2]
(1) Preparation of Active Material for Decomposition Inhibitor Mixing Layer Weigh the active material prepared in Example 1 (1) and the active material prepared in Example 1 (2) so as to be equal to each other. And mixed in a mortar for 30 minutes.
(2) Production of positive electrode In 125 mL of NMP in which 5 g of polyvinylidene fluoride (PVDF) as a binder is dissolved, 85 g of an active material for the decomposition inhibitor mixed layer prepared in (1) above, and carbon black as a conductive material 10 g was introduced and kneaded until uniformly mixed to obtain a paste for a decomposition inhibitor mixed layer.
Then, the paste for the decomposition inhibitor mixed layer was applied to a 15 μm thick aluminum current collector at a coating amount of 6 mg / cm ² and then dried at 80 ° C. for 30 minutes. After drying, the coated material was pressed to obtain an electrode having a positive electrode active material layer (decomposition inhibitor mixed layer) thickness of 40 μm and a positive electrode active material layer density of 2.5 g / cm ³ . Finally, this electrode was cut out to have a diameter of 16 mm to produce a positive electrode.
A coin cell according to Example 2 was manufactured in the same manner as in Example 1 except that the obtained positive electrode was used.

[Comparative Example 1]
Comparative Example 1 was carried out in the same manner as in Example 1 except that only one of the above prepared paste for the decomposition inhibitor dispersion layer was used to produce a positive electrode, and was coated on one surface at a coating amount of 6 mg / cm ² on an aluminum current collector. The coin cell which concerns on was produced.

[Comparative Example 2]
During the positive electrode produced by using only decomposition inhibitor carrying layer paste prepared above, except that one-side coated on an aluminum current collector at a coverage of 6 mg / cm ² in the same manner as in Example 1, Comparative Example 2 The coin cell which concerns on was produced.

[Comparative Example 3]
In 125 mL of NMP in which 5 g of polyvinylidene fluoride (PVDF) as a binder is dissolved, 85 g of lithium cobaltate as a positive electrode active material and 10 g of carbon black as a conductive material are introduced and kneaded until uniformly mixed. A paste for forming a positive electrode active material layer was obtained.
A coin cell according to Comparative Example 3 was prepared in the same manner as in Example 1 except that only the positive electrode active material layer forming paste was used to produce a positive electrode, and one side of the paste was applied onto the aluminum current collector at a coating amount of 6 mg / cm ^2. Was made.

[Measurement of positive electrode reaction resistance]
Each coin cell of Examples 1 and 2 and Comparative Examples 1 to 3 manufactured as described above was subjected to an appropriate conditioning treatment under a temperature condition of 25 ° C. (constant current constant up to 4.1 V at a charge rate of 0.1 C). After performing an operation of charging with a voltage and an operation of repeating a constant current and a constant voltage discharge to 3.0 V at a discharge rate of 0.1 C three times), the state of charge was adjusted to 60% SOC. And reaction resistance was measured with the alternating current impedance method at the frequency of 10 mHz-1MHz on the temperature conditions of -30 degreeC with respect to each coin cell of Examples 1, 2 and Comparative Examples 1-3. The obtained resistance values are shown in Table 1.

[Charge / discharge cycle test]
After measuring the positive electrode reaction resistance, charging and discharging were repeated 100 cycles for each of the coin cells of Examples 1 and 2 and Comparative Examples 1 to 3, and the discharge capacity retention rate (%) after 100 cycles was determined. The charge / discharge conditions for one cycle are as follows: at a measurement temperature of 25 ° C., CCCV charge (constant current / constant voltage charge) is performed at 1C to an upper limit voltage of 4.4V for 2.5 hours, and then CC discharge (constant current to a lower limit voltage of 3.0V at 1C. Current discharge). The discharge capacity retention ratio (%) was calculated from the discharge capacity at the 500th cycle relative to the discharge capacity at the first cycle. The results are shown in Table 1.

  As shown in Table 1, it was confirmed that the reaction resistance of the coin cell according to Example 1 and Example 2 was low. Furthermore, it has confirmed that the discharge capacity maintenance rate of the coin cell which concerns on Example 1 and Example 2 was a high maintenance rate compared with the comparative example 3 which does not contain a decomposition inhibitor. In particular, the coin cell according to Example 1 had a low reaction resistance and a high capacity retention rate. From the above, it was confirmed that the coin cell according to Example 1 and Example 2 (particularly the coin cell according to Example 1) has low reaction resistance at low temperature and excellent cycle characteristics.

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible.

  The lithium secondary battery (for example, lithium ion battery) according to the present invention is suitable as a power source for a motor (electric motor) mounted on a vehicle such as an automobile because it can output a large current and has excellent cycle characteristics as described above. Can be used for Therefore, as schematically shown in FIG. 8, the present invention provides a vehicle (typically, a battery (typically, an assembled battery formed by connecting a plurality of such batteries 10 in series) as a power source. An automobile including an electric motor such as a hybrid car, an electric car, and a fuel car is provided.

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Lithium secondary battery 15 Battery case 20 Opening part 25 Cover body 30 Case main body 40 Safety valve 50 Winding electrode body 60 Positive electrode terminal 62 Positive electrode current collector 64 Positive electrode active material layer 66 Positive electrode sheet (positive electrode)
68 Cathode active material 70 Decomposition inhibitor 72 Cathode active material with decomposition inhibitor 74 Decomposition inhibitor dispersion layer (dispersion layer)
76 Decomposition inhibitor carrying layer (carrying layer)
80 Negative electrode terminal 82 Negative electrode current collector 84 Negative electrode active material layer 86 Negative electrode sheet 100 Separator sheet 162 Positive electrode current collector 164 Positive electrode active material layer 166 Positive electrode sheet 168 Positive electrode active material 170 Decomposition inhibitor 172 Decomposition agent positive electrode active material 173 Decomposition Inhibitor mixed layer (mixed layer)
262 Cathode current collector 264 Cathode active material layer 266 Cathode sheet 268 Cathode active material 270 Decomposition inhibitor 272 Cathode active material 280 with decomposition inhibitor First decomposition inhibitor mixed layer (first mixture layer)
282 Second decomposition inhibitor mixed layer (second mixed layer)
362 Cathode current collector 364 Cathode active material layer 366 Cathode sheet 368 Cathode active material 370 Decomposition inhibitor 372 Cathode active material 374 with decomposition inhibitor Decomposition inhibitor dispersion layer 376 Decomposition inhibitor carrying layer 377 Conductive material 462 Cathode current collector 464 Positive electrode active material layer 466 Positive electrode sheet 468 Positive electrode active material 470 Decomposition inhibitor 472 Positive electrode active material with decomposition inhibitor 476 Decomposition inhibitor carrying layer 478 Positive electrode active material with decomposition inhibitor 480 Decomposition agent mixture layer

Claims (7)

A lithium secondary battery comprising a positive electrode, a negative electrode and an electrolyte,
The positive electrode has a positive electrode current collector and a positive electrode active material layer containing a granular positive electrode active material formed on the current collector,
The negative electrode has a negative electrode current collector and a negative electrode active material layer containing a granular negative electrode active material formed on the current collector,
In the active material layer of at least one of the positive electrode and the negative electrode,
An active material with a decomposition inhibitor in which a decomposition inhibitor that suppresses decomposition of the electrolyte is supported on the surface of the active material;
An unsupported active material not having the decomposition inhibitor on the surface of the active material;
A lithium secondary battery comprising the decomposition inhibitor and a non-supported decomposition inhibitor not supported on the surface of the active material. The active material layer containing the decomposition inhibitor is formed of a laminated structure composed of at least two layers having different configurations,
The content ratio of the unsupported decomposition inhibitor in the active material layer having the laminated structure is smaller in a layer away from the current collector than in a layer adjacent to the current collector. The lithium secondary battery as described in. The active material layer containing the decomposition inhibitor is formed of a laminated structure composed of at least two layers having different configurations,
In the active material layer of the laminated structure, the content ratio of the active material with a decomposition inhibitor in a layer adjacent to the current collector is the content ratio of the active material with a decomposition inhibitor in a layer away from the current collector. Smaller than
The content ratio of the unsupported active material in a layer adjacent to the current collector is larger than the content ratio of the unsupported active material in a layer away from the current collector. The lithium secondary battery as described. The active material layer containing the decomposition inhibitor further contains a conductive material,
The content ratio of the conductive material included in a portion adjacent to the current collector is smaller than the content ratio of the conductive material included in a portion away from the current collector. The lithium secondary battery in any one.   The lithium secondary battery according to claim 1, wherein the decomposition inhibitor is a metal oxide.   The lithium secondary battery according to claim 5, wherein the metal oxide is tungsten oxide.   A vehicle comprising the lithium secondary battery according to claim 1.

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