JP6016029B2 - Positive electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery.

In recent years, along with the development of portable electronic devices such as mobile phones and notebook computers, and the practical application of electric vehicles, secondary batteries with small and light weight and high capacity are required. Currently, lithium ion secondary batteries using lithium cobalt oxide (LiCoO ₂ ) as a positive electrode material and a carbon-based material as a negative electrode material are commercialized as high capacity secondary batteries.

  Lithium ion secondary batteries are required to be usable even in high temperature and high voltage environments. In this specification, use at a voltage of 4.3 V or higher is defined as high voltage use. However, when driven at a high temperature and a high voltage, the lithium ion secondary battery has a problem that the cycle characteristics are extremely deteriorated.

  It is thought that this is because the electrolyte solution is oxidatively decomposed in the vicinity of the positive electrode during charging, and metal components such as the positive electrode active material are eluted by acid generated by oxidative decomposition. In addition, the decomposition product of the electrolytic solution and the elution product of the metal component move from the positive electrode side to the negative electrode side, are reduced and decomposed on the negative electrode surface, and the decomposition product is deposited on the negative electrode active material surface. When deposits are thus generated on the surface of the negative electrode active material, insertion of lithium into the negative electrode active material is hindered.

  Various studies have been conducted to improve cycle characteristics in a high-voltage usage environment. For example, in the nonaqueous electrolyte battery described in Patent Document 1, an inorganic particle layer is disposed on the surface of at least one of a positive electrode and a negative electrode. The inorganic particle layer traps the eluate from the positive electrode active material and the decomposition product of the electrolytic solution. Patent Document 1 describes that an inorganic particle layer is preferably disposed on the surface of the negative electrode instead of the surface of the positive electrode. The reason is that if an inorganic particle layer is formed on the surface of the negative electrode, it is possible to prevent deposits from directly depositing on the surface of the negative electrode. Further, it is described that inorganic particles made of rutile type titania or alumina are preferable. It is described that the thickness of the inorganic particle layer is preferably 1 μm or more and 4 μm or less.

  It is necessary to adjust the thickness and porosity of the inorganic particle layer within a predetermined range. It is difficult to control the thickness of the inorganic particle layer and the porosity of the inorganic particle layer. Therefore, there is a demand for a method of trapping a decomposition product of an electrolytic solution or an elution product of a metal component without forming an inorganic particle layer.

JP 2009-70797 A

  The present inventors examined whether or not an eluate of a metal component or a decomposition product of an electrolytic solution could be trapped without forming an inorganic particle layer on the electrode surface.

  The present invention has been made in view of such circumstances, and a positive electrode for a lithium ion secondary battery capable of trapping an eluate of a metal component and a decomposition product of an electrolytic solution without forming an inorganic particle layer. And it aims at providing a lithium ion secondary battery.

As a result of intensive studies by the present inventors, it has been newly found that the SiO _x particles (0 <x <2) have an effect of trapping the eluate of the metal component and the decomposition product of the electrolytic solution. Then, the inventors have newly conceived of dispersing SiO _x particles (0 <x <2) in the positive electrode active material layer.

That is, the positive electrode for a lithium ion secondary battery of the present invention has a current collector and a positive electrode active material layer that is on the surface of the current collector and includes a positive electrode active material and a binder. The material layer further includes SiO _x particles (0 <x <2) dispersed therein.

The content of SiO _x particles in the positive electrode active material layer is preferably 0.1% by mass or more and less than 1% by mass when the entire positive electrode active material layer is 100% by mass.

It is preferable that the average particle diameter _{D 50} of the SiO _x particles are 2μm or more 20μm or less.

  Moreover, the lithium ion secondary battery of this invention has the said positive electrode for lithium ion secondary batteries, It is characterized by the above-mentioned.

The positive electrode active material layer in the positive electrode for a lithium ion secondary battery of the present invention contains dispersed SiO _x particles (0 <x <2) that have the effect of trapping the eluate of the metal component and the decomposition product of the electrolytic solution. . According to the positive electrode for a lithium ion secondary battery of the present invention, the eluate of the metal component and the decomposition product of the electrolytic solution can be trapped in the positive electrode active material layer.

A SiO _x particles (0 <x <2) surface observation after the cycle test to confirm the effect of trapping the decomposition of the metal components and the electrolyte by. A SiO _x particles (0 <x <2) surface observation after the storage test to confirm the effect of trapping the decomposition of the metal components and the electrolyte by.

<Positive electrode for lithium ion secondary battery>
The positive electrode for a lithium ion secondary battery of the present invention has a current collector and a positive electrode active material layer.

  The current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. Examples of materials that can be used for the current collector include metal materials such as stainless steel, titanium, nickel, aluminum, and copper, or conductive resins. The current collector can take the form of a foil, a sheet, a film, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector.

  The thickness of the current collector is preferably 10 μm to 100 μm.

The positive electrode active material layer is formed on the surface of the current collector. This positive electrode active material layer contains a positive electrode active material and a binder, and further contains SiO _x particles (0 <x <2) dispersed therein.

  The positive electrode active material is preferably suitable for use in an electrode of a lithium ion secondary battery driven at a high voltage. As a positive electrode active material, what consists of a lithium containing compound or another metal compound can be used, for example.

Examples of the lithium-containing compound include a lithium nickel composite oxide having a layered structure, a lithium manganese composite oxide having a spinel structure, a general formula: LiCo _p Ni _q Mn _r D _S O ₂ (D is a doping component, Al , Mg, Ti, Sn, Zn, W, Zr, Mo, Fe and Na, p + q + r + s = 1, 0 <p ≦ 1, 0 ≦ q <1, 0 ≦ r <1, 0 Lithium cobalt-containing composite metal oxide having a layered structure represented by ≦ s <1), an olivine-type lithium phosphate composite oxide represented by the general formula: LiMPO ₄ (M is one of Mn, Fe, Co, and Ni) at least one), the general _formula: at least one of Li 2 MPO ₄ fluoride olivine-type lithium phosphate compound oxide represented by F (M is Mn, Fe, Co and Ni , General _formula: Li 2 MSiO silicate lithium composite oxide represented by ₄ (M is _{one or more of} at least one of Mn, Fe, Co and Ni) can be used.

  Examples of other metal compounds include oxides such as titanium oxide, vanadium oxide, and manganese dioxide, and disulfides such as titanium sulfide and molybdenum sulfide.

Particularly positive electrode active material, the general _{formula: LiCo p Ni q Mn r D} s O 2 (D is the doping component, at least selected Al, Mg, Ti, Sn, Zn, W, Zr, Mo, Fe and Na And a lithium cobalt-containing composite metal oxide having a layered structure represented by p + q + r + s = 1, 0 <p ≦ 1, 0 ≦ q <1, 0 ≦ r <1, 0 ≦ s <1) It is preferable. Here, in particular, the above-mentioned p, q, and r are preferably in the ranges of 0 <p <1, 0 <q <1, and 0 <r <1, respectively.

  The lithium cobalt-containing composite metal oxide is excellent in thermal stability and low in cost. By using the lithium cobalt-containing composite metal oxide as a positive electrode active material, a lithium ion secondary battery with high thermal stability and low cost can be obtained.

Examples of the lithium cobalt-containing composite metal oxide include LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , and LiNi _0.5 Co _0.2. Mn _0.3 O ₂ , LiCoO ₂ , LiNi _0.8 Co _0.2 O ₂ , LiCoMnO ₂ can be used. Among these, LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ and LiNi _0.5 Co _0.2 Mn _0.3 O ₂ are preferable in terms of thermal stability.

The positive electrode active material preferably has an average particle diameter _{D 50} is a powder shape is 1 m to 20 m. The average particle diameter D ₅₀ of the positive electrode active material is 1μm smaller, only the specific surface area of the positive electrode active material becomes large, too increase the reaction area of the electrolyte decomposition occurring near the surface of the positive electrode active material. The average particle diameter D ₅₀ of the positive electrode active material is larger than 20 [mu] m, the resistance of the positive electrode increases, decreases the output characteristics of the lithium ion secondary battery. Note that the average particle diameter D ₅₀ refers to the particle size cumulative value of the volume distribution in the particle size distribution measurement by laser diffraction method is equivalent to 50%. That is, the D _50, means the median size measured by volume.

  The binder has a function of connecting the positive electrode active material and the conductive additive to the current collector. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and fluororubber, thermoplastic resins such as polypropylene, polyethylene, ethylene vinyl alcohol and polyvinyl acetate resin, poly Acrylic resins such as acrylate and sodium polyacrylate, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, polyurethane, carboxymethyl cellulose (CMC), and rubbers such as styrene butadiene copolymer (SBR) can be used.

  The conductive auxiliary agent is added to the positive electrode active material layer in order to increase the conductivity of the electrode as necessary. As the conductive auxiliary agent, for example, carbon black, graphite, acetylene black (AB), ketjen black (registered trademark) (KB), vapor grown carbon fiber (VGCF), etc., which are carbonaceous fine particles, are used alone or in combination. Can be used in combination. The amount of the conductive auxiliary agent used is not particularly limited, but can be, for example, about 1 part by mass to 30 parts by mass with respect to 100 parts by mass of the active material contained in the positive electrode.

SiO _x (0 <x <2) is a general formula representing a generic name of amorphous silicon oxides obtained using silicon dioxide (SiO ₂ ) and metal silicon (Si) as raw materials. It is known that SiO _x decomposes into Si and SiO ₂ when heat-treated. This is called a disproportionation reaction, and if it is a homogeneous solid silicon monoxide SiO having a ratio of Si to O of approximately 1: 1, it is separated into two phases of Si phase and SiO ₂ phase by solid internal reaction. . The Si phase obtained by separation is very fine and is dispersed in the SiO ₂ phase. Further, the SiO ₂ phase covering the Si phase has a function of suppressing decomposition of the electrolytic solution.

In general, when oxygen is turned off, it is said that almost all SiO _x disproportionates and separates into two phases at 800 ° C. or higher. Specifically, the raw material silicon oxide powder containing amorphous SiO _x particles is subjected to heat treatment at 800 ° C. to 1200 ° C. for 1 hour to 5 hours in an inert atmosphere such as in a vacuum or an inert gas. By carrying out, a powder composed of SiO _x particles containing two phases of an amorphous SiO ₂ phase and a crystalline Si phase is obtained.

The SiO _x particles generally have a higher electron density than other materials contained in the positive electrode active material layer. The eluate from the positive electrode active material is a transition metal ion. Examples of the transition metal include Mn, Ni, and Co. Transition metal ions are likely to be adsorbed to those with a high electron density. Therefore, transition metal ions are likely to be adsorbed on the SiO _x particles in the positive electrode active material layer. In addition, decomposition products of the electrolytic solution are easily adsorbed to the SiO _x particles. Examples of decomposition products of the electrolyte include inorganic compounds such as LiF, Li ₂ CO ₃ , Li ₂ O, and LiO ₂ , lithium alkyl carbonate (ROCO ₂ Li), lithium alkoxide, and ethylene oxide (—CH ₂ —CH ₂ —O). Organic compounds such as-).

SiO _x particles (0 <x <2) are dispersed and included in the positive electrode active material layer. The SiO _x particles are preferably uniformly dispersed throughout the positive electrode active material layer. The metal component eluted from the positive electrode active material is first trapped by SiO _x particles present in the vicinity of the positive electrode active material. The metal component is also trapped by SiO _x particles dispersed and present in the positive electrode active material layer when moving in the positive electrode active material layer toward the positive electrode surface. Similarly, a decomposition product of the electrolytic solution moving in the positive electrode active material layer is trapped by SiO _x particles dispersed in the positive electrode active material layer. When the SiO _x particles are uniformly dispersed throughout the positive electrode active material layer, the eluate from the positive electrode active material and the decomposition product of the electrolytic solution are effectively trapped in the SiO _x particles.

The average particle diameter D ₅₀ of the SiO _x particles is preferably 2 μm or more. The average particle diameter _{D 50} of the SiO _x particles is preferably 20μm or less. The average particle diameter _{D 50} of the SiO _x particulate preferably small increases the specific surface area of the SiO _x particles. The larger the specific surface area of the SiO _x particles, the easier it is to trap metal components and decomposition products. Further, since the SiO _x particles have low conductivity, if the average particle diameter D ₅₀ is larger than 20 μm, the conductivity of the entire electrode becomes non-uniform, and the charge / discharge characteristics deteriorate.

As the SiO _x particles (0 <x <2), commercially available SiO _x particles having a desired average particle diameter D ₅₀ can be used.

The content of SiO _x particles in the positive electrode active material layer is preferably 0.1% by mass or more and less than 1% by mass when the entire positive electrode active material layer is 100% by mass. If the content of SiO _x particles in the positive electrode active material layer is 0.1% by mass or more, the eluate from the positive electrode active material and the decomposition product of the electrolytic solution in the positive electrode active material layer can be sufficiently trapped. It is not preferable that the content of SiO _x particles in the positive electrode active material layer is 1% by mass or more.

For the positive electrode, a composition for forming a positive electrode active material layer containing a positive electrode active material, a conductive additive, a binder, and SiO _x particles (0 <x <2) is prepared, and an appropriate solvent is added to the composition. It can be formed in a paste form, applied to the surface of the current collector, then dried, and compressed as necessary to increase the electrode density.

  As a method for applying the composition for forming a positive electrode active material layer, a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method may be used.

  As the solvent for adjusting the viscosity, N-methyl-2-pyrrolidone (NMP), methanol, methyl isobutyl ketone (MIBK) and the like can be used.

<Lithium ion secondary battery>
The lithium ion secondary battery of the present invention includes the positive electrode of the present invention. In the lithium ion secondary battery of the present invention, known materials can be used for the negative electrode, the separator and the electrolytic solution.

  The negative electrode has a current collector and a negative electrode active material layer bound to the surface of the current collector. A negative electrode active material layer contains a negative electrode active material and a binder, and contains a conductive support agent as needed. The current collector, binder and conductive additive are the same as those described for the positive electrode.

  As the negative electrode active material, a carbon-based material that can occlude and release lithium, an element that can be alloyed with lithium, an elemental compound that has an element that can be alloyed with lithium, or a polymer material can be used.

  Examples of the carbon-based material include non-graphitizable carbon, artificial graphite, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon, and carbon blacks. Here, the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature.

  Elements that can be alloyed with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi can be exemplified. In particular, silicon (Si) or tin (Sn) is preferable.

Examples of elemental compounds having elements that can be alloyed with lithium include ZnLiAl, AlSb, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , _{CaSi 2, CrSi 2, Cu 5} Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO or LiSnO can be used. As the elemental compound having an element capable of alloying with lithium, a silicon compound or a tin compound is preferable. As the silicon compound, SiO _v (0.5 ≦ v ≦ 1.5) is preferable. As the tin compound, for example, a tin alloy (Cu-Sn alloy, Co-Sn alloy, or the like) can be used.

  As the polymer material, polyacetylene, polypyrrole, or the like can be used.

It is preferable to use SiO _v (0.5 ≦ v ≦ 1.5) having a high capacity as the negative electrode active material.

  The separator separates the positive electrode and the negative electrode and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. As the separator, for example, a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a porous film made of ceramics can be used.

  The electrolytic solution includes a solvent and an electrolyte dissolved in the solvent.

  As the solvent, for example, cyclic esters, chain esters, and ethers can be used. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of the chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. As ethers, for example, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane can be used.

As the electrolyte, for example, lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ can be used.

Examples of the electrolytic solution include 0.5 mol / l to 1.7 mol / l of a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , and LiCF ₃ SO _{3 in} a solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and dimethyl carbonate. A solution dissolved at a concentration of about 1 can be used.

  The lithium ion secondary battery can be mounted on a vehicle.

  The vehicle may be a vehicle that uses electric energy from a battery as a whole or a part of a power source. Bicycles and electric motorcycles are examples.

  As mentioned above, although embodiment of the positive electrode for lithium ion secondary batteries and lithium ion secondary battery of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be described in more detail with reference to examples.

<Trapping confirmation test of metal component of SiO _x particle (0 <x <2) and decomposition product of electrolyte>
First, a laminate type lithium ion secondary battery of Test Example 1 is manufactured, and a cycle test at 55 ° C. and a storage test at 60 ° C. are performed, and at that time, the SiO _x particles trap the decomposition product of the metal component and the electrolytic solution. Confirmed whether to do.

<Production of laminated lithium-ion secondary battery>
(Test Example 1)
An aluminum foil having a thickness of 20 μm was prepared as a positive electrode current collector. A positive electrode active material layer was formed on the surface of the aluminum foil as follows. First, LiNi _0.5 Co _0.2 Mn _0.3 O ₂ having an average particle diameter D ₅₀ of 10 μm as a positive electrode active material, acetylene black as a conductive additive, and polyvinylidene fluoride (PVDF as a binder) ) Were mixed as 88 parts by mass, 6 parts by mass, and 6 parts by mass, respectively, and this mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a slurry.

The slurry was placed on the aluminum foil and applied with a doctor blade so that the slurry became a film. The aluminum foil coated with the slurry was dried at 80 ° C. for 20 minutes, and NMP was removed by volatilization to form a positive electrode active material layer on the surface of the aluminum foil. Thereafter, the aluminum foil and the positive electrode active material layer on the aluminum foil were firmly bonded to each other by a roll press. The basis weight of the positive electrode active material layer of the electrode was 12.0 mg / cm ² . The joined product was heated with a vacuum dryer at 120 ° C. for 6 hours, cut into a predetermined shape (rectangular shape of 25 mm × 30 mm), and formed into a positive electrode having a thickness of about 40 μm.

The negative electrode was produced as follows. The average particle diameter _{D 50} 10μm of SiO _x particles (0.5 <x <1.5) (manufactured by Sigma-Aldrich Japan LLC) 32 parts by weight and an average particle diameter _{D 50} of 50 parts by mass of graphite powder 10μm And 8 parts by mass of acetylene black as a conductive additive and 10 parts by mass of polyvinylidene fluoride (PVDF) as a binder, and this mixture is mixed with an appropriate amount of N-methyl-2-pyrrolidone (NMP). To prepare a slurry. This slurry was applied to a copper foil having a thickness of 20 μm, which is a negative electrode current collector, in a film shape using a doctor blade, and the current collector coated with the slurry was pressed after drying. The basis weight of the negative electrode active material layer of the electrode was set to 7.0 mg / cm ² . The joined product was heated with a vacuum dryer at 120 ° C. for 6 hours, cut into a predetermined shape (rectangular shape of 25 mm × 30 mm), and made into a negative electrode having a thickness of about 40 μm.

A laminate type lithium ion secondary battery was manufactured using the positive electrode and the negative electrode. Specifically, a rectangular sheet (27 × 32 mm, thickness 25 μm) made of polypropylene resin as a separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then an electrolyte solution was injected into the bag-like laminated film. As an electrolytic solution, 1 mol / liter of LiPF ₆ was added to a solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) at EC: EMC: DMC = 3: 3: 4 (volume ratio). A solution dissolved so as to be L was used. Thereafter, the remaining one side was sealed to obtain a laminate type lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. Note that the positive electrode and the negative electrode each have a tab that can be electrically connected to the outside, and a part of the tab extends to the outside of the laminated lithium ion secondary battery. Through the above steps, a laminate type lithium ion secondary battery of Test Example 1 was produced.

<Cycle test>
A cycle test was conducted using the laminate type lithium ion secondary battery of Test Example 1. In the cycle test, charge and discharge were repeated under the following conditions. At the time of charging, CCCV charging (constant current constant voltage charging) was performed at 55 ° C. at a 1C rate and a voltage of 4.5V. The voltage was held for 1 hour. When discharging, CC discharge (constant current discharge) was performed at 3.0 V and 1 C rate. This charging / discharging was made into 1 cycle, and the cycle test was done to 200 cycles.

<60 ° C storage test>
A 60 ° C. storage test was conducted using the laminate type lithium ion secondary battery of Test Example 1. In this test, the laminate type lithium ion secondary battery of Test Example 1 was subjected to a charge / discharge test once under the following conditions, and the recharged battery was left at 60 ° C. for 18 days. Charging was performed at 60 ° C. at a SOC of 90% (state of charge), and CCCV charging (constant current constant voltage charging) was performed at a rate of 1C. The voltage was held for 1 hour. When discharging, CC discharge (constant current discharge) was performed at 3.0 V and 1 C rate.

<Surface observation>
The negative electrode after the cycle test and the surface of the negative electrode after the storage test were observed with a scanning electron microscope (SEM) and an energy dispersive X-ray analyzer (EDX). FIG. 1 shows the surface observation results of the negative electrode after the cycle test, and FIG. 2 shows the surface observation results of the negative electrode after the storage test.

  FIG. 1 shows one SEM image and three EDX images side by side. The three EDX images are detected images of Si, Mn, and P, respectively. These four images are observation results of the same place.

From FIG. 1, the location where Si was detected, the location where Mn was detected, and the location where P was detected were almost the same. From this, it was found that the SiO _x particles adsorbed Mn and P by a cycle test. P is presumed to be a decomposition product of the electrolytic solution.

  FIG. 2 also shows one SEM image and three EDX images side by side as in FIG. The three EDX images are detected images of Si, Mn, and P, respectively. These four images are observation results of the same place.

From the image in which Mn was detected in FIG. 2, it was found that Mn was adsorbed on the entire surface of the negative electrode. Moreover, it was found from the image in which P in FIG. 2 was detected that P was adsorbed to the entire negative electrode. From this, it was found that the SiO _x particles adsorbed Mn and P in the storage test.

Here, in the cycle test, lithium ions move with the charge / discharge of the battery, but in the storage test, the charge / discharge of the battery is not repeated, so the lithium ion does not move with the charge / discharge of the battery. . Therefore, from the results of FIGS. 1 and 2, it was confirmed that Mn and P were adsorbed on the SiO _x particles regardless of the movement of lithium ions.

<Production of Laminated Lithium Ion Secondary Battery of Example 1>
The average particle diameter _{D 50} of the positive electrode active material and _LiNi 0.5 _Co 0.2 _Mn 0.3 _{O 2} of 10 [mu] m, an average particle diameter _{D 50} of 10 [mu] m of SiO _x particles (0.5 <x <1.5 ) (Manufactured by Sigma Aldrich Japan LLC), acetylene black as a conductive additive, and PVDF as a binder are mixed as 93 parts by mass, 1 part by mass, 3 parts by mass, and 3 parts by mass, respectively. A laminated lithium ion secondary battery of Example 1 was produced in the same manner as in Test Example 1 except that the mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to produce a slurry. In the positive electrode active material layer in the laminated lithium ion secondary battery of Example 1, the content of the SiO _x particles was less than 1% by mass when the entire positive electrode active material layer was 100% by mass.

From the results of Test Example 1, when the cycle test and the storage test are performed in the laminated lithium ion secondary battery of Example 1, the SiO _x particles dispersed and contained in the positive electrode active material layer trap Mn and P. It is expected that.

Claims (3)

A current collector,
A positive electrode active material layer present on the surface of the current collector and including a positive electrode active material and a binder;
The positive electrode active material includes a transition metal,
The positive electrode active material layer further includes SiO _x particles ( 0.5 <x < 1.5 ) , and includes a trap material dispersed to trap the transition metal ,
The content of the SiO _x particles in the positive electrode active material layer is 0.1% by mass or more and less than 1% by mass when the entire positive electrode active material layer is 100% by mass. Battery positive electrode. 2. The positive electrode for a lithium ion secondary battery according to claim 1, wherein an average particle diameter D ₅₀ of the SiO _x particles is 2 μm or more and 20 μm or less. Lithium ion secondary battery having a positive electrode for a lithium ion secondary battery according to any one of claims 1-2.