JP2010251217A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery suppressing reduction of an additive for improving safety, due to side effects for improving safety. <P>SOLUTION: The lithium secondary battery is formed via a lithium absorbing and emitting positive electrode, a lithium absorbing and emitting negative electrode and a lithium salt containing nonaqueous electrolyte. The positive electrode includes a positive electrode mixture and a collector; the positive electrode mixture includes a lithium and transition metal containing composite oxide, a conductive assistant and a binder resin; and the positive electrode mixture contains a halogen element containing polymer compound. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery.

  Advances in electronic technology have improved the performance of electronic devices, leading to miniaturization and portability, and secondary batteries with high energy density are desired as power sources. In response to these requirements, in recent years, non-aqueous electrolyte secondary batteries that can significantly improve energy density, that is, organic electrolyte lithium ion secondary batteries (hereinafter simply referred to as “lithium secondary batteries”) have been developed. Developed and rapidly spreading. In recent years, lithium secondary batteries are expected to be used for electric vehicles and hybrid vehicles as a high-capacity, high-voltage power source.

  However, in these applications, in addition to the long life and high output of the lithium secondary battery, it is also important to ensure the safety of the battery during abuse.

  Because current lithium secondary batteries use flammable organic electrolytes as electrolytes, it is becoming more difficult to ensure safety during abuse due to overcharge, internal short-circuiting, etc., as the energy density of batteries increases. .

  In the lithium secondary battery, when the heat generation of the battery proceeds during an internal short circuit, the positive electrode and the negative electrode may react with the electrolyte. At this time, when the heat generation cannot be suppressed, the electrolyte solution is vaporized, and the vaporized reaction product is released from the battery can and may ignite.

  Thus, in order to improve safety against heat generation and ignition of the lithium secondary battery due to volatilization of the electrolytic solution, it has been studied to add an additive to the electrolytic solution.

  Conventionally, as additives used as flame retardants, phosphate esters, phosphazenes that are compounds of phosphorus elements and nitrogen elements, and additives of halogen compounds have been studied. These have the effect of trapping oxygen radicals generated during combustion and suppressing the combustion reaction. Improvement of the safety of lithium secondary batteries has been studied by adding such additives.

  Patent Document 1 discloses mixing the phosphate ester and the like.

JP-A-4-184870

  In order for the additive to be effective for improving safety, the additive needs to be present in the lithium secondary battery. It is known that the phosphate ester used as an additive is reduced by decomposition due to a side reaction on the negative electrode when it is dissolved in the electrolytic solution. Therefore, in a situation where the effect of the additive is actually required, there is a drawback that the additive is not sufficiently present in the battery.

  An object of the present invention is to provide a lithium secondary battery in which safety is improved by suppressing a decrease in additives for improving safety due to side reactions.

  The lithium secondary battery of the present invention is a lithium secondary battery formed through a positive electrode that occludes and releases lithium, a negative electrode that occludes and releases lithium, and a non-aqueous electrolyte containing a lithium salt. It has a high molecular compound containing an element.

  According to the present invention, a lithium secondary battery excellent in safety can be obtained.

1 is a half sectional view of a cylindrical lithium secondary battery according to an embodiment. The expanded sectional view of the positive electrode of the lithium secondary battery concerning a present Example.

  The lithium secondary battery of the present invention is a lithium secondary battery formed through a non-aqueous electrolyte containing a positive electrode that occludes and releases lithium, an anode that occludes and releases lithium, and a lithium salt, and the positive electrode is a positive electrode It has a mixture and a current collector, the positive electrode mixture has a composite oxide containing lithium and a transition metal, a conductive additive and a binder resin, and the positive electrode mixture has a polymer compound containing a halogen element It is characterized by that. Further, the halogen element is preferably a phosphorus element, a bromine element or a chlorine element. Among them, the halogen element is polyphosphoric acid, ammonium polyphosphate, sodium polyphosphate or a compound represented by the chemical formula (1). Is more preferable.

（式中、Ｒ¹，Ｒ²はリン元素に結合する官能基、ｎは重合度を示す）

(Wherein R ¹ and R ² are functional groups bonded to the phosphorus element, and n represents the degree of polymerization)

  Furthermore, the particle size of the polymer compound containing a halogen element is 20% or less of the particle size of the composite oxide.

  The lithium secondary battery of the present invention is a lithium secondary battery formed through a non-aqueous electrolyte containing a positive electrode that occludes and releases lithium, an anode that occludes and releases lithium, and a lithium salt. And the non-aqueous electrolyte includes polyphosphoric acid, ammonium polyphosphate, sodium polyphosphate, or a compound represented by the chemical formula (2).

（式中、Ｒ¹，Ｒ²はリン元素に結合する官能基、ｎは重合度を示す）

(Wherein, R ^1, R ² is a functional group bonded to the phosphorus element, n represents shows the degree of polymerization)

Here, R ¹ and R ² are preferably an alkyl group, a cycloalkyl group, an alkenyl group, an alkoxy-substituted alkyl group, or an aryl group.

  By adopting the above configuration, it has become possible to prevent side reactions on the negative electrode and to maintain the effect of improving the safety of the additive in the lithium secondary battery.

  Specifically, by reducing the reaction between the electrolytic solution and the positive electrode active material and suppressing the exothermic reaction in the battery without reducing the additive by decomposition due to side reaction of the additive on the negative electrode, The vaporization of the liquid can be suppressed and safety is improved. Moreover, a flame retardance improves by disperse | distributing an additive in electrolyte solution. Here, it is thought that oxygen radicals generated from the positive electrode active material oxidize the electrolyte solution. However, the phenomenon in which the oxygen radicals react with the electrolyte solution is an oxidation reaction and generates heat. As a result, the side reaction is more likely to occur. Therefore, in the present invention, the presence of a radical scavenger that captures these radicals and makes them safe so as to capture the radicals during abuse and suppress the reaction with the electrolyte, thereby improving the safety of the lithium secondary battery. I can expect that. Therefore, in consideration of the action of trapping oxygen radicals generated at the positive electrode, it is effective to fix the additive in the positive electrode, and a greater effect is exhibited.

  Specifically, the additive is a compound for suppressing heat generation between the non-aqueous electrolyte and the positive electrode active material, and is a solid and insoluble or difficult to dissolve in the electrolyte at room temperature to 100 ° C. or less. It is preferable that it is soluble. Also, when the lithium secondary battery is used under normal conditions, it does not work even if it is present in the electrolyte, but when the lithium secondary battery is heated to a high temperature of 100 ° C. or higher Alternatively, it may be dissolved in the electrolytic solution to exert its effect.

  Hereinafter, although embodiment of this invention is described, this invention is not limited only to the following embodiment.

  First, this embodiment will be described with reference to FIG. 2 showing an enlarged cross section of a positive electrode of a lithium secondary battery.

  A positive electrode of a lithium secondary battery is formed by mixing an aluminum (Al) current collector 5 with a positive electrode active material 21, a conductive agent 23, and a binder resin 24, and a solid additive 22 is contained therebetween. Yes.

  The particle size of the positive electrode active material 21 is about 10 μm, and the particle size of the additive 22 is about 1 to 2 μm. Although the particle size of the additive also changes according to the change in the particle size of the positive electrode active material, the particle size of the additive is preferably about 20% of the particle size of the positive electrode active material. In addition, the thickness of the positive electrode material apply | coated on the electrical power collector is 20-100 micrometers.

  The additive is a polymer compound containing phosphorus element, bromine element, and chlorine element, and is preferably hardly soluble or insoluble in the electrolytic solution.

  About these polymers, polyphosphoric acid, ammonium polyphosphate, and sodium polyphosphate are mentioned as a polymer containing a phosphorus element.

  In addition, as the polymer containing a phosphorus element, a phosphazene polymer represented by the formula (1) in which a phosphazene having a cyclic structure is opened and polymerized may be used.

（式中、Ｒ¹，Ｒ²はリン元素に結合する官能基、ｎは重合度を表す。）

(In the formula, R ¹ and R ² are functional groups bonded to the phosphorus element, and n represents the degree of polymerization.)

In the formula (1), R ¹ and R ² are an alkyl group, a cycloalkyl group, an alkenyl group, an alkoxy-substituted alkyl group or an aryl group. Examples of the alkyl group in R ¹ and R ² in the formula (1) include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, and a hexyl group, and the cycloalkyl group includes a cyclopropyl group and a cyclohexyl group. Alkenyl groups include allyl groups and methallyl groups, alkoxy-substituted alkyl groups include methoxyethyl groups and methoxyethoxyethyl groups, and aryl groups include phenyl groups and methyl groups. A phenyl group, a methoxyphenyl group, etc. are mentioned. The hydrogen element in the substituent may be substituted with a halogen element. Among these, a methyl group, an ethyl group, a propyl group, a trifluoroethyl group, a phenyl group, and a 3-fluorophenyl group are preferable because of excellent flame retardancy.

  The degree of polymerization n is related to the molecular weight of the polymer, but is related to the temperature at which a phenomenon called depolymerization that decomposes from polymer to monomer by heat occurs. For this reason, a degree of polymerization that allows polymerization at an appropriate temperature to act as an additive is desirable.

  Regarding the amount of additive added, the greater the additive content, the greater the contribution to safety improvement, but the current collector for conducting electricity between the current collector and the positive electrode active material by the conductive assistant in the positive electrode. It becomes difficult to form a structure.

  As the halogen-containing polymer used as an additive, a chlorinated or brominated polymer can be used. Specific examples of the polymer include polymers obtained by chlorinating and bromating polyoxyethylene, polymethyl methacrylate, polyethylene, polystyrene, and cellulose.

  In particular, those in which the halogen bond is easily broken and those in which the proportion of halogen in the molecule is high are effective.

Further, as a positive electrode active material that reversibly occludes and releases lithium, a layered compound such as lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), or one substituted with one or more transition metals, or manganic acid lithium _{(Li 1 + x Mn 2-} x O 4 ( provided that _{x = 0~0.33), Li 1 +} x Mn 2-xy M y O 4 ( provided that, M is Ni, Co, Cr, Cu, Fe, Including at least one metal selected from Al and Mg, x = 0 to 0.33, y = 0 to 1.0, ₂ -xy> 0), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , LiMn _2−x M _x O ₂ (where M includes at least one metal selected from Co, Ni, Fe, Cr, Zn, and Ta, x = 0.01 to 0.1), Li ₂ Mn ₃ MO ₈ (where M is selected from Fe, Co, Ni, Cu, Zn) Or a layered lithium manganese oxide Li (1 + a) NixCoyMnzO ₂ (where -0.1 <a <0.2, 0 <x <0.9, 0 <y). <0.9, 0 <z <0.9, 0.9 <(x + y + z) <1.1), copper-lithium oxide (Li ₂ CuO ₂ ), or LiV ₃ O ₈ , LiFe ₃ O ₄ , V 1 type or 2 types or more, such as a mixture containing vanadium oxides such as ₂ O ₅ , V ₆ O ₁₂ , VSe, Cu ₂ V ₂ O ₇ , chemical disulfide compounds, Fe ₂ (MoO ₄ ) _3, etc. It is done.

  In addition, as a negative electrode active material that reversibly occludes and releases lithium, an easily graphitized material obtained from natural graphite, petroleum coke, coal pitch coke, or the like is heat-treated at a high temperature of 2500 ° C. or higher, mesophase carbon, or amorphous Carbon, carbon fiber, lithium metal, metal alloying with lithium, or a material having a metal supported on the surface of carbon particles is used. For example, a metal or alloy selected from lithium, aluminum, tin, silicon, indium, gallium, and magnesium. Further, the metal or the oxide of the metal can be used as a negative electrode active material.

  As the electrolytic solution, a lithium salt as an electrolyte, which is dissolved in an organic solvent can be used.

As the lithium salt, one or more of LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF _6, etc. Can be selected and used.

  As the organic solvent, carbonates, esters, ethers and the like can be used. For example, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, diethyl carbonate, γ-butyrolactron, methyl acetate, 1,3-dioxolane, 1,3-dimethoxyethane, 1,2-diethoxy Ethane, tetrahydrofuran and the like can be used, and organic solvents such as sulfur compounds such as sulfolane, nitrogen-containing compounds, silicon-containing compounds, fluorine-containing compounds and phosphorus-containing compounds can also be used.

  However, it is not desirable to chemically react with the additive added to the positive electrode because the effect of the additive will be significantly impaired.

  Moreover, the lithium secondary battery according to the present example can be mounted on an electrical device as described below. For example, electric cars, electric bicycles, personal computers, mobile phones, digital cameras, video recorders, mini-disc portable players, personal digital assistants, watches, radios, electronic notebooks, electric tools, vacuum cleaners, toys, elevators, disaster robots, The lithium secondary battery of the present embodiment can be used as a power source for medical care walking assist devices, medical care wheelchairs, medical care mobile beds, emergency power supplies, load conditioners, power storage systems, and the like. It can be used as a home-use rechargeable battery due to improved safety, and can be increased in size, making it suitable for home / regional distributed power supplies. In addition to these consumer applications, it can also be used for military use and space.

  The shape of the lithium secondary battery shown in this embodiment is not particularly limited, and may be various shapes such as a cylindrical shape, a square shape, a coin shape, and a button shape as necessary. Also, the battery exterior material is not limited to the stainless steel can but may be a laminated one.

  EMBODIMENT OF THE INVENTION Below, one Embodiment concerning this invention is described concretely by showing an Example and a comparative example.

Example 1
It shows below about Example 1 which added solid polyphosphoric acid in the positive electrode.

[Production of positive electrode]
The positive electrode was produced by the following procedure.

Polyvinylidene fluoride (PVDF), which is a binder resin, was dissolved in NMP to prepare a solution having a concentration of 10%. To 34 parts by weight of this solution, 60 parts by weight of the positive electrode active material LiNi _0.33 Co _0.33 Mn _0.33 O ₂ powder and 6 parts by weight of polyphosphoric acid are mixed, and further NMP is added and kneaded to prepare a positive electrode mixture slurry. The slurry was applied on a positive electrode current collector of 0.02 mm thick aluminum foil and dried by blowing warm air of 120 ° C. Similarly, the positive electrode mixture slurry was applied to the back surface of the positive electrode current collector and dried to form a positive electrode mixture layer.

  Thereafter, the positive electrode was obtained by press molding to a predetermined thickness and then drying under reduced pressure. This becomes a positive electrode plate.

[Production of negative electrode]
About the negative electrode, it produced in the following procedures.

  PVDF, which is a binder resin, was dissolved in NMP to prepare a 10% concentration solution. To 50 parts by weight of this solution, 30 parts by weight of an amorphous carbon powder having an average particle size of 10 μm, which is a carbon material, and 50 parts by weight of an active material powder are mixed, and NMP is added to adjust the viscosity. A negative electrode mixture slurry was prepared by kneading, and this slurry was coated on a copper foil having a thickness of 0.01 mm as a current collector, and dried by blowing hot air at 120 ° C.

  Similarly, the negative electrode mixture slurry was applied to the back surface of the current collector and dried to form a negative electrode mixture layer. Thereafter, the negative electrode (plate) was obtained by press molding to a predetermined thickness and drying under reduced pressure.

[Production of cylindrical lithium secondary battery]
The obtained negative electrode and positive electrode are wound through a separator to form a roll-shaped electrode. This was stored in a battery can and dried under reduced pressure.

Next, after injecting an electrolyte solution in which LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate (2: 4: 4 (volume ratio)) at a rate of 1 mol / liter into the battery can. The cylindrical lithium secondary battery (diameter 15 mm, length 65 mm) shown in FIG. 1 was produced by caulking the lid. In addition, using a charger / discharger, charging / discharging was performed 20 cycles at 25 ° C. with a current of 300 mA and a charging termination voltage of 4.2 to 3.0 V.

[Differential scanning calorimetry]
Differential scanning calorimetry was performed to investigate the exothermic behavior. After the charge and discharge, the lithium secondary battery charged to 4.2 V was disassembled, and the positive electrode plate holding the electrolyte was punched out to 3.5 mmφ to obtain a sample piece. This sample piece is sealed in a stainless steel pressure-resistant airtight container, and heated by a differential scanning calorimeter (DSC) from room temperature to 400 ° C. under a temperature rising condition of 5 ° C./min. Was used as an index of heat resistance of the positive electrode. From the DSC measurement results, the exothermic peak height was 2.1 mW and the exothermic peak temperature was 330 ° C.

(Example 2)
Example 2 in which a solid phosphazene derivative was added to the positive electrode is shown below.

  As phosphazene derivatives,

（式中、Ｒ¹，Ｒ²はリン元素に結合する官能基、ｎは重合度を表す。）を用い、Ｒ¹はプロピル基、Ｒ²はトルフルオロエチル基、重合度ｎは１００のものを使用した。

(Wherein R ¹ and R ² are functional groups bonded to the phosphorus element, n represents the degree of polymerization), R ¹ is a propyl group, R ² is a trifluoroethyl group, and the degree of polymerization n is 100. It was used.

[Production of positive electrode]
The positive electrode was produced by the following procedure.

Polyvinylidene fluoride (PVDF), which is a binder resin, was dissolved in NMP to prepare a solution having a concentration of 10%. To this solution 34 parts by weight, the positive electrode active material LiNi _0.33 Co _0.33 Mn _0.33 powder 60 parts by weight of O ₂ and the phosphazene derivative (formula (1), R ¹ is propyl, R ² is trifluoroethyl ethyl group, polymerization Mixing 6 parts by weight of NMP and kneading with NMP, a positive electrode mixture slurry is prepared, and this slurry is applied to a positive electrode current collector aluminum foil having a thickness of 0.02 mm. And dried by blowing warm air of 120 ° C. Similarly, the positive electrode mixture slurry was applied to the back surface of the positive electrode current collector and dried to form a positive electrode mixture layer.

  Thereafter, the positive electrode was obtained by press molding to a predetermined thickness and then drying under reduced pressure. This was used as a positive electrode plate.

[Production of negative electrode]
The negative electrode was prepared in the same procedure as in Example 1.

[Production of cylindrical lithium secondary battery]
The obtained negative electrode and positive electrode were wound through a separator to form a roll-shaped electrode. This was stored in a battery can and dried under reduced pressure.

Next, after injecting an electrolyte solution in which LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate (2: 4: 4 (volume ratio)) at a rate of 1 mol / liter into the battery can. Then, a lithium secondary battery (diameter: 15 mm, length: 65 mm) was produced by caulking the lid. In addition, using a charger / discharger, charging / discharging was performed 20 cycles at 25 ° C. with a current of 300 mA and a charging termination voltage of 4.2 to 3.0 V.

[Differential scanning calorimetry]
Differential scanning calorimetry was performed to investigate the exothermic behavior. After the charge and discharge, the lithium secondary battery charged to 4.2 V was disassembled, and the positive electrode plate holding the electrolyte was punched out to 3.5 mmφ to obtain a sample piece. This sample piece is sealed in a stainless steel pressure-resistant airtight container, and heated by a differential scanning calorimeter (DSC) from room temperature to 400 ° C. under a temperature rising condition of 5 ° C./min. Was used as an index of heat resistance of the positive electrode. From the DSC measurement results, the exothermic peak height was 2.0 mW and the exothermic peak temperature was 325 ° C.

(Comparative Example 1)
Comparative Example 1 using an electrolytic solution obtained by adding 20% of a liquid trimethyl phosphate to the electrolytic solution is shown below.

[Production of positive electrode]
The positive electrode was produced by the following procedure.

Polyvinylidene fluoride (PVDF), which is a binder resin, was dissolved in NMP to prepare a solution having a concentration of 10%. To this solution 40 parts by weight, were mixed 60 parts by weight powder of the positive active material _{LiNi 0.33 Co 0.33 Mn 0.33 O 2} , a positive electrode mixture slurry was prepared by kneading in addition to NMP, positive electrode and the slurry The film was applied on an aluminum foil having a thickness of 0.02 mm and dried by blowing warm air at 120 ° C. Similarly, the positive electrode mixture slurry was applied to the back surface of the positive electrode current collector and dried to form a positive electrode mixture layer. Thereafter, the positive electrode was obtained by press molding to a predetermined thickness and then drying under reduced pressure. This was used as a positive electrode plate.

[Production of negative electrode]
The negative electrode was prepared in the same procedure as in Example 1.

[Production of cylindrical lithium secondary battery]
The obtained negative electrode and positive electrode were wound through a separator to form a roll-shaped electrode. This was stored in a battery can and dried under reduced pressure.

Then, a mixed solvent of ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate in a battery can (2: 4: 4 (volume ratio)) to 80 parts by weight by adding 20 parts by weight of trimethyl phosphate ester, 1 mol of LiPF ₆ After injecting the electrolytic solution dissolved at a ratio of 1 / liter, the lid was caulked to produce a lithium secondary battery (diameter 15 mm, length 65 mm). In addition, using a charger / discharger, charging / discharging was performed 20 cycles at 25 ° C. with a current of 300 mA and a charging termination voltage of 4.2 to 3.0 V.

[Differential scanning calorimetry]
Differential scanning calorimetry was performed to investigate the exothermic behavior. After the charge and discharge, the lithium secondary battery charged to 4.2 V was disassembled, and the positive electrode plate holding the electrolyte was punched out to 3.5 mmφ to obtain a sample piece. This sample piece is sealed in a stainless steel pressure-resistant airtight container, and heated by a differential scanning calorimeter (DSC) from room temperature to 400 ° C. under a temperature rising condition of 5 ° C./min. Was used as an index of heat resistance of the positive electrode. From the DSC measurement results, the exothermic peak height was 2.4 mW and the exothermic peak temperature was 307 ° C.

(Comparative Example 2)
The comparative example 2 which does not add the additive concerning this invention to electrolyte solution and a positive electrode is shown below.

[Production of positive electrode]
The positive electrode was produced by the following procedure.

Polyvinylidene fluoride (PVDF), which is a binder resin, was dissolved in NMP to prepare a solution having a concentration of 10%. To 40 parts by weight of this solution, 60 parts by weight of the powder of the positive electrode active material LiNi _0.33 Co _0.33 Mn _0.33 O ₂ is mixed, and further NMP is added and kneaded to prepare a positive electrode mixture slurry. It was applied onto an aluminum foil having a thickness of 0.02 mm and dried by blowing hot air at 120 ° C. Similarly, the positive electrode mixture slurry was applied to the back surface of the current collector and dried to form a positive electrode mixture layer. Thereafter, the positive electrode was obtained by press molding to a predetermined thickness and then drying under reduced pressure. This was used as a positive electrode plate.

[Production of negative electrode]
The negative electrode was prepared in the same procedure as in Example 1.

[Production of cylindrical lithium secondary battery]
The obtained negative electrode and positive electrode were wound through a separator to form a roll-shaped electrode. This was stored in a battery can and dried under reduced pressure.

Next, an electrolytic solution in which LiPF ₆ was dissolved at a rate of 1 mol / liter was mixed into the battery can in a mixed solvent of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate (2: 4: 4 (volume ratio)). Later, the lid was caulked to produce a lithium secondary battery (diameter 15 mm, length 65 mm). In addition, using a charger / discharger, charging / discharging was performed 20 cycles at 25 ° C. with a current of 300 mA and a charging termination voltage of 4.2 to 3.0 V.

[Differential scanning calorimetry]
Differential scanning calorimetry was performed to investigate the exothermic behavior. After the charge and discharge, the lithium secondary battery charged to 4.2 V was disassembled, and the positive electrode plate holding the electrolyte was punched out to 3.5 mmφ to obtain a sample piece. This sample piece is sealed in a stainless steel pressure-resistant airtight container, and heated by a differential scanning calorimeter (DSC) from room temperature to 400 ° C. under a temperature rising condition of 5 ° C./min. Was used as an index of heat resistance of the positive electrode. From the DSC measurement results, the exothermic peak temperature was 320 ° C.

  Table 1 shows the results of differential scanning calorimetry for Examples 1 and 2 and Comparative Examples 1 and 2. Like Example 1 and 2, the exothermic peak can be suppressed and the exothermic peak temperature can be shifted to a high temperature side by mixing the additive concerning a present Example in a positive electrode.

  From the above results, by adding the additive according to the present invention to the positive electrode, the effect can be maintained after the charge / discharge cycle, the exothermic peak can be reduced, and the exothermic peak temperature can be shifted to a high temperature. it can.

DESCRIPTION OF SYMBOLS 1 Positive electrode collector 2 Positive electrode mixture layer 3 Negative electrode collector 4 Negative electrode mixture layer 7 Separator 8 Current cutoff valve 9 Negative electrode lead 10 Positive electrode lead 11 Positive electrode insulator 12 Negative electrode insulator 13 Battery can 14 Gasket 15 Battery lid 21 Positive electrode active material 22 Additive 23 Conductive agent 24 Binder resin 25 Aluminum (Al) current collector

Claims (7)

In a lithium secondary battery formed through a non-aqueous electrolyte containing a positive electrode that occludes and releases lithium, a negative electrode that occludes and releases lithium, and a lithium salt,
The positive electrode has a positive electrode mixture and a current collector,
The positive electrode mixture has a composite oxide having lithium and a transition metal, a conductive additive and a binder resin,
The lithium secondary battery, wherein the positive electrode mixture has a polymer compound containing a halogen element.   The lithium secondary battery according to claim 1, wherein the halogen element is a phosphorus element, a bromine element, or a chlorine element. The lithium secondary battery according to claim 1, wherein the halogen element is polyphosphoric acid, ammonium polyphosphate, sodium polyphosphate, or a compound represented by the chemical formula (1).

(Wherein R ¹ and R ² are functional groups bonded to the phosphorus element, and n represents the degree of polymerization)   2. The lithium secondary battery according to claim 1, wherein a particle size of the polymer compound containing the pre-halogen element is 20% or less of a particle size of the composite oxide. In a lithium secondary battery formed through a non-aqueous electrolyte containing a positive electrode that occludes and releases lithium, a negative electrode that occludes and releases lithium, and a lithium salt,
A lithium secondary battery, wherein the positive electrode and the non-aqueous electrolyte have polyphosphoric acid, ammonium polyphosphate, sodium polyphosphate, or a compound represented by the chemical formula (2).

(Wherein R ¹ and R ² are functional groups bonded to the phosphorus element, and n represents the degree of polymerization) 6. The lithium secondary battery according to claim 5, wherein, in the chemical formula (2), R ¹ and R ² are an alkyl group, a cycloalkyl group, an alkenyl group, an alkoxy-substituted alkyl group, or an aryl group. 6. The lithium secondary battery according to claim 5, wherein in the chemical formula (2), R ¹ is a propyl group, R ² is a trifluoroethyl group, and a polymerization degree n is 100. 6.

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