JP5110565B2 - Lithium secondary battery, method for producing positive electrode active material coating particles, and method for producing lithium secondary battery - Google Patents

Description

  The present invention relates to a lithium secondary battery having a positive electrode layer containing a positive electrode active material, a solid electrolyte and an electrolyte decomposition inhibitor, and an organic electrolyte.

Conventionally, in a lithium secondary battery using an organic electrolyte, LiCoO ₂ or the like is mainly used as a positive electrode active material. In such a positive electrode active material, the capacity and stability of the positive electrode active material are determined by a reversible insertion / extraction reaction of lithium ions.
Increasing the amount of Li desorption from the positive electrode active material increases the capacity. Extracting a large amount of Li also leads to an increase in the charging voltage. However, when the amount of Li desorption from the positive electrode active material is increased, the crystal structure of the positive electrode active material may be destroyed or the organic electrolyte may be oxidatively decomposed due to an increase in charging voltage. As a result, there is a concern about deterioration of cycle characteristics.

In recent years, in order to improve cycle characteristics, a method of coating a positive electrode active material with an oxide such as Al ₂ O ₃ , ZrO ₂ , TiO ₂ , SiO ₂ , AlPO ₄ has been proposed (see, for example, Patent Document 1). . However, since these oxides are insulators, there is a problem that the lithium ion conduction path and the electron transfer path are hindered particularly during rapid charge and discharge, leading to an increase in electrode reaction resistance and a decrease in battery capacity.

On the other hand, in an all-solid lithium secondary battery, since a solid electrolyte is used, the solid electrolyte is not oxidatively decomposed at the time of charging even at a high voltage, and there is no problem like the lithium secondary battery using the above organic electrolyte. . However, in the all solid lithium secondary battery, since the electrode active material and the solid electrolyte are both solid, the electrode active material and the solid electrolyte are easily disconnected from each other, and the lithium ion conduction path is hindered. Therefore, it is difficult to achieve excellent rapid charge / discharge characteristics in an all-solid lithium secondary battery.
Therefore, recently, in an all solid lithium secondary battery, a method of coating a positive electrode active material with a conductive agent and a lithium ion conductive solid electrolyte has been proposed in order to secure a lithium ion conduction path (see, for example, Patent Document 2). .

JP 2003-7299 A JP 2003-59492 A

  In a lithium secondary battery using an organic electrolyte, it is considered that the positive electrode active material may be coated with a solid electrolyte and an oxide in order to ensure a lithium ion conduction path while improving cycle characteristics. Furthermore, it is considered that the mixed state of the positive electrode active material, the solid electrolyte, and the oxide is important for effectively maintaining the high discharge rate capacity and suppressing the decrease in the cycle capacity.

  The present invention has been made in view of the above circumstances, and is a lithium secondary battery having a positive electrode layer containing a positive electrode active material, a lithium ion conductive solid electrolyte, and an electrolyte decomposition inhibitor, and has a high discharge rate capacity. And a method for manufacturing a positive electrode active material coating particle and a method for manufacturing a lithium secondary battery are provided. .

  In order to achieve the above object, the present invention provides a positive electrode active material having a solid powder containing primary particles containing a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor on the surface. Provided is a lithium secondary battery comprising a positive electrode layer, a negative electrode layer, and an organic electrolyte disposed so as to be in contact with a positive electrode active material having the solid powder on the surface thereof.

  According to the present invention, primary particles containing a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor adhere to the surface of the positive electrode active material, and crystalline or amorphous lithium Since the ion-conducting solid electrolyte and the crystalline electrolyte decomposition inhibitor are present in a microphase-separated state, it is possible to simultaneously improve cycle capacity reduction during high-voltage charging and capacity reduction during rapid charge / discharge. It is.

In the above invention, the crystalline or amorphous lithium ion conductive solid electrolyte is represented by the general formula Li _{1 + x} Al _x M _2-x (PO ₄ ) ₃ (M is a group consisting of Ti, Ge and Zr). It is preferably at least one selected and a NASICON type phosphoric acid compound represented by 0 ≦ x ≦ 1). For example, when a raw material mixture of a NASICON type phosphoric acid compound is mechanically mixed and ground to be amorphous to form an amorphous body, and then the amorphous body is heat-treated to be crystallized. Is a microphase-separated state of crystalline or amorphous NASICON-type phosphate compound (crystalline or amorphous lithium ion conductive solid electrolyte) and crystalline metal oxide (crystalline electrolyte decomposition inhibitor) Primary particles can be obtained. Moreover, a NASICON type | mold phosphate compound has the advantage that stability in air is favorable.

In the present invention, the crystalline electrolyte decomposition inhibitor is at least one crystalline metal oxide selected from the group consisting of AlPO ₄ , TiP ₂ O ₇ , Li ₃ PO ₄ , Al ₂ O ₃ and TiO _2. in is preferably ones, and more preferably AlPO _4. When the lithium ion conductive solid electrolyte is the above-mentioned NASICON type phosphoric acid compound and the electrolyte decomposition inhibitor is AlPO ₄ , it suppresses the oxidative decomposition of the organic electrolyte particularly during high voltage charging, and rapidly This is because the electrode reaction resistance during charge / discharge can be reduced.

  Furthermore, the present invention is a method for producing particles for coating a positive electrode active material containing a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor, wherein the lithium ion conductive solid electrolyte The raw material mixture containing the constituent elements is mechanically mixed and ground to make it amorphous, and the amorphous body forming the amorphous body, and the amorphous body is heated to crystallize, And a crystallization step of forming a crystalline electrolyte decomposition inhibitor. A method for producing particles for coating a positive electrode active material is provided.

  According to the present invention, a lithium ion conductive solid electrolyte having a high lithium ion conductivity can be obtained as compared with the case of producing a lithium ion conductive solid electrolyte by a solid phase reaction method or a sol-gel method. Further, according to the present invention, it is possible to easily produce particles for coating a positive electrode active material.

In the above invention, the lithium ion conductive solid electrolyte is a general formula Li _{1 + x} Al _x M _2-x (PO ₄ ) ₃ (M is at least one selected from the group consisting of Ti, Ge and Zr). Yes, it is preferably a NASICON type phosphoric acid compound represented by 0 ≦ x ≦ 1). In this case, as described above, a crystalline or amorphous NASICON type phosphoric acid compound (crystalline or amorphous lithium ion conductive solid electrolyte) and a crystalline metal oxide (crystalline electrolyte decomposition) It is possible to obtain particles that are in a microphase-separated state.

In the present invention, the crystalline electrolyte decomposition inhibitor is at least one crystalline metal oxide selected from the group consisting of AlPO ₄ , TiP ₂ O ₇ , Li ₃ PO ₄ , Al ₂ O ₃ and TiO _2. It is preferable that it is a thing. When the lithium ion conductive solid electrolyte is the above-mentioned NASICON type phosphoric acid compound and the electrolyte decomposition inhibitor is the above-mentioned crystalline metal oxide, it is possible to effectively oxidize the organic electrolyte during high voltage charging. This is because decomposition can be suppressed and electrode reaction resistance during rapid charge / discharge can be reduced.

Furthermore, in the present invention, the raw material mixture is a mixture of Li ₂ O, Al ₂ O ₃ , at least one selected from the group consisting of TiO ₂ , GeO ₂ and ZrO ₂ and P ₂ O _5. Preferably there is. This is because when such a raw material mixture is used, AlPO ₄ can be formed as an electrolyte decomposition inhibitor. When the electrolyte decomposition inhibitor is AlPO _4, it is possible to suppress oxidative decomposition of the organic electrolyte particularly during high voltage charging and to reduce electrode reaction resistance during rapid charge / discharge.

  In the present invention, the mechanical mixing / grinding method is preferably a mechanical milling method. In the mechanical milling method, a plurality of crystal phases can be generated by appropriately selecting a raw material mixture, and a plurality of types of electrolyte decomposition inhibitors can be formed. Moreover, the oxidative decomposition of the organic electrolyte can be effectively suppressed by appropriately selecting a raw material mixture and leaving a part of the raw material having an electrolyte decomposition inhibiting action unreacted. Furthermore, since the crystallization temperature of the amorphous material obtained by the mechanical milling method is lower than the crystallization temperature of the amorphous material obtained by the melt quenching method or the sol-gel method, the heating temperature in the crystallization process Can be lowered.

  The present invention also relates to a method for manufacturing a lithium secondary battery having a positive electrode layer, a negative electrode layer, and an organic electrolyte, the positive electrode active material coating particles obtained by the above-described manufacturing method of the positive electrode active material coating particles And a positive electrode active material preparation step of preparing the positive electrode active material having the positive electrode active material coating particles on the surface thereof by mixing with the positive electrode active material. To do.

  According to the present invention, since the positive electrode active material coating particles obtained by the above-described method for manufacturing the positive electrode active material coating particles are used, it is possible to maintain a high discharge rate capacity and to suppress reduction in cycle capacity. It is possible to obtain a secondary battery.

  Furthermore, the present invention is a method for producing a lithium secondary battery having a positive electrode layer, a negative electrode layer, and an organic electrolyte, which is obtained in the amorphization step of the above-described method for producing positive electrode active material coating particles. After the amorphous body and the positive electrode active material are mechanically mixed, the amorphous body and the positive electrode active material mixture are heated to crystallize the amorphous body, thereby suppressing crystalline electrolyte decomposition. There is provided a method for producing a lithium secondary battery, comprising a positive electrode active material preparation step of forming an agent and preparing the positive electrode active material having the positive electrode active material coating particles on the surface thereof.

  According to the present invention, a lithium ion conductive solid electrolyte having a high lithium ion conductivity can be obtained as compared with the case of producing a lithium ion conductive solid electrolyte by a solid phase reaction method or a sol-gel method. Further, it is possible to easily produce a positive electrode active material having particles for coating the positive electrode active material on the surface. Further, a positive electrode active material having positive electrode active material coating particles on its surface is produced using the amorphous body and positive electrode active material obtained in the amorphization step of the method for producing positive electrode active material coating particles described above. Therefore, it is possible to obtain a lithium secondary battery that can maintain a high discharge rate capacity and can suppress a decrease in cycle capacity.

  In the above invention, the mechanical mixing method is preferably a mechanical milling method. In the mechanical milling method, a plurality of crystal phases can be generated by appropriately selecting a raw material mixture, and a plurality of types of electrolyte decomposition inhibitors can be formed. Moreover, the oxidative decomposition of the organic electrolyte can be effectively suppressed by appropriately selecting a raw material mixture and leaving a part of the raw material having an electrolyte decomposition inhibiting action unreacted. Furthermore, since the crystallization temperature of the amorphous material obtained by the mechanical milling method is lower than the crystallization temperature of the amorphous material obtained by the melt quenching method or the sol-gel method, the heating temperature in the crystallization process Can be lowered.

  In the present invention, particles containing a crystalline or amorphous lithium ion conductive solid electrolyte formed from an amorphous material and a crystalline electrolyte decomposition inhibitor are attached to the surface of the positive electrode active material, and the crystalline Alternatively, the amorphous lithium ion conductive solid electrolyte and the crystalline electrolyte decomposition inhibitor are present in the microphase separation state, reducing the cycle capacity during high-voltage charging and the capacity during rapid charge / discharge. There is an effect that it can be improved at the same time.

  Hereinafter, the lithium secondary battery, the method for producing the positive electrode active material coating particles, and the method for producing the lithium secondary battery of the present invention will be described in detail.

A. Lithium secondary battery The lithium secondary battery of the present invention is a positive electrode active material having a solid powder containing primary particles containing a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor on the surface. A positive electrode layer, a negative electrode layer, and an organic electrolyte disposed so as to be in contact with a positive electrode active material having the solid powder on the surface thereof.

  FIG. 1 is a schematic cross-sectional view showing an example of the lithium secondary battery of the present invention. A lithium secondary battery illustrated in FIG. 1 includes a positive electrode current collector 1 and a solid powder containing primary particles 2 containing a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor ( Between the positive electrode layer 4 containing the positive electrode active material 3 having a surface thereof, a negative electrode current collector 5, a negative electrode layer 7 containing the negative electrode active material 6, and the positive electrode layer 4 and the negative electrode layer 7. And an organic electrolyte (not shown) disposed so as to contact the positive electrode active material 3 and the negative electrode active material 6 having a solid powder on the surface.

  According to the present invention, since the positive electrode active material has a solid powder containing primary particles containing a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor on its surface, The oxidative decomposition of the organic electrolyte can be suppressed by the conductive electrolyte decomposition inhibitor, and the lithium ion conductive path can be formed by the crystalline or amorphous lithium ion conductive solid electrolyte. Therefore, it is possible to simultaneously improve the decrease in cycle capacity during high voltage charging and the decrease in capacity during rapid charge / discharge.

Crystalline or amorphous lithium ion conductive solid electrolytes exhibit relatively high lithium ion conductivity (eg 10 ^-4 S / cm to 10 ^-3 S / cm) at room temperature, and single ion conductivity (lithium The property of conducting only ions). According to the present invention, since the positive electrode active material has a solid powder containing primary particles containing a crystalline or amorphous lithium ion conductive solid electrolyte on its surface, the crystalline or amorphous lithium ion conductive A lithium ion conduction path can be formed by the solid electrolyte. Since the crystalline or amorphous lithium ion conductive solid electrolyte can selectively conduct only lithium ions as described above, when LiCoO ₂ is used as the positive electrode active material, for example, in LiCoO ₂ It is possible to form a conduction path of only lithium ions while preventing elution of Co.
In addition, since the organic electrolyte is disposed so as to contact the positive electrode active material having the solid powder on the surface, a lithium ion transport route can be easily secured through the organic electrolyte.

  Furthermore, crystalline or amorphous lithium ion conductive solid electrolytes exhibit Arrhenius-type temperature dependence. Since the temperature dependence of the conductivity of crystalline or amorphous lithium ion conducting solid electrolytes follows the Arrhenius equation, the conductivity of crystalline or amorphous lithium ion conducting solid electrolytes at relatively high temperatures It is comparable to or exceeds the conductivity of organic electrolytes.

  In addition, the lithium ion conductive solid electrolyte has an advantage that when a crystalline lithium ion conductive solid electrolyte is produced from an amorphous body, high ion conductive crystals are precipitated. For example, a raw material mixture of lithium ion conductive solid electrolyte is mechanically mixed and powdered to make it amorphous to form an amorphous body, and then the amorphous body is heat treated to crystallize and crystallize. When a crystalline lithium ion conductive solid electrolyte is produced, the crystalline lithium ion conductivity is higher than when a crystalline lithium ion conductive solid electrolyte is produced by a solid phase reaction method or a sol-gel method. There is a tendency to obtain a lithium ion conductive solid electrolyte.

Further, the lithium ion conductive solid electrolyte has an advantage that a metastable crystal is deposited when the crystalline lithium ion conductive solid electrolyte is deposited. For example, when a raw material mixture of lithium ion conductive solid electrolyte is mechanically mixed and powdered to make it amorphous to form an amorphous body, and then this amorphous body is heat treated to crystallize It is easy to obtain a mixed phase. Specifically, when Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 1) (hereinafter sometimes abbreviated as LATP) by the above method, the first phase LATP and second-phase AlPO ₄ may be formed at the same time. Further, when Al ₂ O ₃ having a predetermined particle size is used as a raw material for LATP, TiP ₂ O ₇ may be generated. Further, when a predetermined compound is used as a raw material for LATP, Li ₃ PO ₄ may be generated. These AlPO ₄ , TiP ₂ O ₇ , Li ₃ PO _{4 and the} like have high oxidation resistance and function as an electrolyte decomposition inhibitor.

  Therefore, after mixing the raw material mixture of the lithium ion conductive solid electrolyte mechanically and making it amorphous to form an amorphous body, the amorphous body is heat-treated and crystallized. Primary particles containing a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor can be obtained.

In primary particles containing such crystalline or amorphous lithium ion conductive solid electrolyte and crystalline electrolyte decomposition inhibitor, crystalline or amorphous lithium ion conductive solid electrolyte and crystalline electrolyte decomposition inhibition The agent is in a microphase separation state. In the above example, LATP and AlPO ₄ are in a microphase separation state, LATP, AlPO ₄ and TiP ₂ O ₇ are in a microphase separation state, LATP, AlPO ₄ and Li ₃ PO ₄ and Is in a microphase separation state.

According to the present invention, the positive electrode active material has, on the surface thereof, a solid powder containing primary particles containing the crystalline or amorphous lithium ion conductive solid electrolyte and the crystalline electrolyte decomposition inhibitor. On the surface of the positive electrode active material, particles made of a crystalline or amorphous lithium ion conductive solid electrolyte and particles made of a crystalline electrolyte decomposition inhibitor are not separately present, but crystalline or There are primary particles comprising an amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte degradation inhibitor. That is, as described above, a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor are present in a microphase-separated state on the surface of the positive electrode active material. As a result, in the present invention, the action of suppressing the oxidative decomposition of the organic electrolyte by the crystalline electrolyte decomposition inhibitor and the formation of the lithium ion conduction path by the crystalline or amorphous lithium ion conductive solid electrolyte are simultaneously achieved. Therefore, it is considered that a reduction in cycle capacity during high-voltage charging and a reduction in capacity during rapid charge / discharge can be simultaneously improved. In particular, since the electrolyte decomposition inhibitor is crystalline, it is considered that the characteristics of the electrolyte decomposition inhibitor itself, that is, the property of suppressing the oxidative decomposition of the organic electrolyte is sufficiently exhibited.
Hereinafter, the lithium secondary battery of this invention is demonstrated for every structure.

1. Positive electrode layer The positive electrode layer in the present invention contains a positive electrode active material having on its surface solid powder containing primary particles containing a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor It is. Hereinafter, each structure of the positive electrode layer will be described.

(1) Solid powder The solid powder used in the present invention comprises primary particles that adhere to the surface of the positive electrode active material and contain a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor. It contains.

  The average particle size of the solid powder may be smaller than the average particle size of the positive electrode active material, but it is particularly preferable that the solid powder has a size that can enter the gap filled with the positive electrode active material. Specifically, the average particle size of the solid powder is preferably about 1/100 to 1/2 times the average particle size of the positive electrode active material. More specifically, the average particle size of the solid powder is preferably about 0.1 μm to 10 μm, more preferably in the range of 0.1 μm to 5 μm, and still more preferably in the range of 0.1 μm to 0.5 μm. It is. This is because if the average particle size of the solid powder is within the above range, the solid powder easily adheres to the surface of the positive electrode active material. Further, if the average particle size of the solid powder is too small, the handleability may be deteriorated, and if the average particle size of the solid powder is too large, it may be difficult to adhere to the surface of the positive electrode active material. Because.

  The average particle size of the solid powder is smaller than the average particle size of the positive electrode active material by, for example, observing the particle size of the positive electrode active material and the solid powder in the positive electrode layer with a scanning electron microscope (SEM). Can be confirmed. Moreover, the average particle diameter of solid powder can be calculated | required by measuring and averaging the particle diameter of the solid powder observed, for example with a scanning electron microscope (SEM).

  The content of the solid powder contained in the positive electrode layer includes the types of crystalline or amorphous lithium ion conductive solid electrolyte and crystalline electrolyte decomposition inhibitor constituting the primary particles contained in the solid powder, solid powder Although it varies depending on the type of other compounds contained in the catalyst, specifically, it is preferably about 0.1 to 30 parts by weight, more preferably 0.5 parts by weight with respect to 100 parts by weight of the positive electrode active material. Part to 20 parts by weight, more preferably 1 part to 7 parts by weight. If the content of the solid powder is too large, the content of the positive electrode active material is relatively reduced, so that the battery capacity may be reduced. If the content of the solid powder is too small, the lithium ion conductivity is reduced. This is because there is a possibility that the effect of improving and suppressing the oxidative decomposition of the organic electrolyte cannot be sufficiently obtained.

  The solid powder may be attached to the surface of the positive electrode active material, but among them, it is preferable that the solid powder is uniformly attached to the surface of the positive electrode active material. Further, the solid powder may be densely attached to the surface of the positive electrode active material or may be loosely attached.

  The method for producing the solid powder is described in detail in “B. Method for producing particles for coating positive electrode active material”, which will be described later.

  The solid powder contains primary particles including at least a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor. Hereinafter, each configuration of the solid powder will be described.

(I) Primary particles The primary particles in the present invention contain a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor.

  The shape of the primary particle is not particularly limited, and examples thereof include a spherical shape and an elliptical sphere.

  The average particle size of the primary particles may be smaller than the average particle size of the positive electrode active material, but it is preferable that the primary particle has a size that can enter the gap filled with the positive electrode active material. Specifically, the average particle size of the primary particles is preferably about 1/500 to 1/4 times the average particle size of the positive electrode active material. More specifically, the average particle diameter of the primary particles is preferably about 0.05 μm to 5 μm, more preferably in the range of 0.05 μm to 1 μm, and still more preferably in the range of 0.05 μm to 0.1 μm. It is. This is because when the average particle diameter of the primary particles is within the above range, the primary particles easily adhere to the surface of the positive electrode active material. In addition, when the average particle size of the primary particles is too small, the handleability may be deteriorated, and when the average particle size of the primary particles is too large, it may be difficult to adhere to the surface of the positive electrode active material. Because there is.

  Note that the average particle size of the primary particles is smaller than the average particle size of the positive electrode active material by, for example, observing the particle size of the positive electrode active material and the primary particles in the positive electrode layer with a scanning electron microscope (SEM). Can be confirmed. Moreover, the average particle diameter of primary particles can be calculated | required by measuring the particle diameter of the primary particle observed, for example with a scanning electron microscope (SEM), and averaging.

  The primary particles contain a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor. Hereinafter, constituent components of the primary particles will be described.

(Crystalline or amorphous lithium ion conductive solid electrolyte)
The crystalline or amorphous lithium ion conductive solid electrolyte used in the present invention is not particularly limited as long as it is a solid electrolyte having lithium ion conductivity. It is preferable that it can be produced by the method described in “Production method for particles”.

As such a lithium ion conductive solid electrolyte, the general formula Li _{1 + x} Al _x M _2-x (PO ₄ ) ₃ (M is at least one selected from the group consisting of Ti, Ge and Zr, A NASICON type phosphoric acid compound represented by 0 ≦ x ≦ 1) is preferably used. In addition to the above-described advantages of the lithium ion conductive solid electrolyte, the NASICON type phosphoric acid compound has an advantage that it is stable in air and easy to handle. As described above, for example, a raw material mixture of Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 1) (LATP), which is one of NASICON type phosphoric acid compounds, is mechanically used. When the amorphous body is formed by mixing and grinding to form an amorphous body, and then the amorphous body is heat-treated to crystallize, a mixed phase can be obtained. For example, LATP and AlPO ₄ may be produced simultaneously, LATP, AlPO ₄ and TiP ₂ O ₇ may be produced simultaneously, or LATP, AlPO ₄ and Li ₃ PO ₄ may be produced simultaneously. As a result, microphase separation of crystalline or amorphous NASICON type phosphoric acid compound (crystalline or amorphous lithium ion conductive solid electrolyte) and crystalline metal oxide (crystalline electrolyte decomposition inhibitor) Primary particles in a state can be obtained.

  The lithium ion conductive solid electrolyte may be either crystalline or amorphous, but is preferably crystalline. This is because if the lithium ion conductive solid electrolyte is a crystal, the characteristics of the lithium ion conductive solid electrolyte itself, that is, lithium ion conductivity is sufficiently exhibited. A crystalline lithium ion conductive solid electrolyte and an amorphous lithium ion conductive solid electrolyte may be mixed.

  When the lithium ion conductive solid electrolyte is a crystal, it can be identified by X-ray diffraction measurement (XRD) and electron diffraction (ED). On the other hand, when the lithium ion conductive solid electrolyte is amorphous, it can be identified by X-ray diffraction measurement (XRD), electron diffraction (ED), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). it can.

(Crystalline electrolyte decomposition inhibitor)
The crystalline electrolyte decomposition inhibitor used in the present invention is not particularly limited as long as it has crystallinity and has an electrolyte decomposition inhibitory action that suppresses oxidative decomposition of the organic electrolyte. It is formed when the raw material mixture of conductive solid electrolyte is mechanically mixed and ground to make it amorphous to form an amorphous body, and then the amorphous body is heated to crystallize. A crystalline phase other than the lithium ion conductive solid electrolyte is preferable. That is, the electrolyte decomposition inhibitor is preferably a compound containing a part or all of the constituent elements of the lithium ion conductive solid electrolyte.

  Examples of such a crystalline electrolyte decomposition inhibitor include a crystalline metal oxide containing a part or all of constituent elements of a lithium ion conductive solid electrolyte.

The crystalline metal oxide varies depending on the type of the lithium ion conductive solid electrolyte. For example, when the lithium ion conductive solid electrolyte is the NASICON phosphoric acid compound, AlPO ₄ , TiP ₂ O ₇ , Examples include Li ₃ PO ₄ , Al ₂ O ₃ , TiO ₂ , GeO ₂ , and ZrO ₂ . Among these, at least one selected from the group consisting of AlPO ₄ , TiP ₂ O ₇ , Li ₃ PO ₄ , Al ₂ O ₃ and TiO ₂ is preferable, and AlPO ₄ is particularly preferable. When the lithium ion conductive solid electrolyte is the above-mentioned NASICON phosphoric acid compound and the electrolyte decomposition inhibitor is AlPO ₄ , it suppresses the oxidative decomposition of the organic electrolyte particularly during high voltage charging, and at the time of rapid charge / discharge This is because the electrode reaction resistance can be reduced.

  The crystalline electrolyte decomposition inhibitor can be identified by X-ray diffraction measurement (XRD) and electron diffraction (ED).

(Ii) Other components Although the solid powder should just contain the said primary particle, it may contain the raw material of lithium ion conductive solid electrolyte further. That is, the solid powder may further contain a compound containing part or all of the constituent elements of the lithium ion conductive solid electrolyte. This is because a part of the raw material for the lithium ion conductive solid electrolyte may remain when the lithium ion conductive solid electrolyte is produced.

The compound containing part or all of the constituent elements of the lithium ion conductive solid electrolyte varies depending on the type of the lithium ion conductive solid electrolyte. For example, the lithium ion conductive solid electrolyte is the NASICON phosphoric acid. In the case of a compound, Al ₂ O ₃ , TiO ₂ , GeO ₂ , ZrO _{2 and the} like can be exemplified.

Especially, it is preferable that the compound containing a part or all of the constituent elements of the lithium ion conductive solid electrolyte is an oxide. This is because the oxide has high oxidation resistance and has an electrolyte decomposition inhibiting action. In this case, oxidative decomposition of the organic electrolyte can be effectively suppressed.
Examples of such an oxide include Al ₂ O ₃ , TiO ₂ , GeO ₂ , and ZrO ₂ . That is, the solid powder may contain at least one oxide selected from the group consisting of Al ₂ O ₃ , TiO ₂ , GeO ₂ and ZrO ₂ .

(2) Cathode Active Material The cathode active material used in the present invention is not particularly limited as long as it can occlude / release lithium ions. For example, LiCoO ₂ , LiCoPO ₄ , LiMn ₂ O ₄ , LiNiO ₂ , LiFePO ₄ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiMnPO ₄ , LiNi _0.5 Mn _1.5 O _{4 and the} like. Of these, LiCoO ₂ is preferable.

  The shape of the positive electrode active material is not particularly limited, and examples thereof include a granular shape, a plate shape, and a needle shape. Especially, it is preferable that the shape of a positive electrode active material is granular. Examples of the shape of the spherical positive electrode active material include a spherical shape and an elliptical sphere.

  The average particle size of the positive electrode active material only needs to be larger than the average particle size of the solid powder. Specifically, it is preferably about 1 μm to 50 μm, more preferably in the range of 10 μm to 20 μm, and still more preferably It is in the range of 3 μm to 5 μm. If the average particle size of the positive electrode active material is too small, the handleability may be deteriorated, and if the average particle size of the positive electrode active material is too large, it may be difficult to obtain a flat positive electrode layer. is there.

  Note that the average particle size of the positive electrode active material is larger than the average particle size of the solid powder, as described above, for example, by the scanning electron microscope (SEM), the particle size of the positive electrode active material and the solid powder in the positive electrode layer. This can be confirmed by observing. Moreover, the average particle diameter of a positive electrode active material can be calculated | required by measuring and averaging the particle diameter of the positive electrode active material observed, for example with a scanning electron microscope (SEM).

  The content of the positive electrode active material contained in the positive electrode layer varies depending on the type of the positive electrode active material, but is specifically preferably about 60 wt% to 97 wt%, more preferably 75 wt% to 97 wt%. It is in the range of wt%, more preferably in the range of 90 wt% to 97 wt%.

(3) Others The positive electrode layer used in the present invention may further contain a conductive agent and a binder (binder).
Examples of the binder include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).
Examples of the conductive agent include carbon black such as acetylene black and ketjen black.

  As a method for forming the positive electrode layer, a general method can be used. For example, a positive electrode layer forming paste containing the positive electrode active material having the above-mentioned solid powder on the surface, a binder, and a conductive agent is applied on a positive electrode current collector and dried, and then pressed. Thus, a positive electrode layer can be formed.

  The positive electrode layer may be formed on the positive electrode current collector. The material for the positive electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include aluminum, SUS, nickel, iron, and titanium. Of these, aluminum and SUS are preferably used.

2. Organic Electrolyte The organic electrolyte used in the present invention is disposed so as to be in contact with the positive electrode active material having the above-mentioned solid powder on the surface.

  The organic electrolyte is not particularly limited as long as it can be disposed so as to be in contact with the positive electrode active material having a solid powder on its surface and can be oxidatively decomposed. For example, an organic electrolyte, a polymer electrolyte, A gel electrolyte etc. can be mentioned.

As the organic electrolyte, a non-aqueous electrolyte containing a lithium salt and a non-aqueous solvent is usually used.
The lithium salt is not particularly limited as long as it is a lithium salt used in a general lithium secondary battery. For example, LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , Examples thereof include LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ and LiClO ₄ .
The non-aqueous solvent is not particularly limited as long as it can dissolve the lithium salt. For example, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane. 1,2-diethoxyethane, acetonitrile, propionitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ-butyrolactone, etc. It is done. These non-aqueous solvents may be used alone or in combination of two or more. Moreover, room temperature molten salt can also be used as a non-aqueous electrolyte.

The polymer electrolyte contains a lithium salt and a polymer.
As a lithium salt, the thing similar to the lithium salt used for the said organic electrolyte solution can be used.
The polymer is not particularly limited as long as it forms a complex with a lithium salt, and examples thereof include polyethylene oxide.

The gel electrolyte contains a lithium salt, a polymer, and a nonaqueous solvent.
As the lithium salt and the non-aqueous solvent, the same lithium salt and non-aqueous solvent as those used in the organic electrolyte can be used.
The polymer is not particularly limited as long as it can be gelled. For example, polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyvinylidene fluoride (PVDF), polyurethane, polyacrylate, cellulose Etc.

3. Negative electrode layer The negative electrode layer used in the present invention contains at least a negative electrode active material, and may contain a conductive agent and a binder as necessary.

The negative electrode active material is not particularly limited as long as it can occlude and release lithium ions. For example, metal lithium, lithium alloy, metal oxide, metal sulfide, metal nitride, and graphite And the like. The negative electrode active material may be in the form of a powder or a thin film.
In addition, about the binder and electrically conductive agent used for a negative electrode layer, the thing similar to the binder and electrically conductive agent used for the said positive electrode layer can be used.
Moreover, since the formation method of a negative electrode layer is the same as the formation method of the said positive electrode layer, description here is abbreviate | omitted.

  The negative electrode layer may be formed on the negative electrode current collector. The material of the negative electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include copper, stainless steel, and nickel.

4). Other Member The lithium secondary battery of the present invention may have a separator disposed between the positive electrode layer and the negative electrode layer. The separator used in the present invention is not particularly limited as long as it has a function of retaining an organic electrolyte. For example, a porous film such as polyethylene and polypropylene, a nonwoven fabric such as a resin nonwoven fabric, and a glass fiber nonwoven fabric can be used. Can be mentioned.

  The shape of the battery case used in the present invention is not particularly limited as long as it can accommodate the positive electrode layer, the negative electrode layer, the organic electrolyte, the separator, the positive electrode current collector, the negative electrode current collector, and the like. Specific examples include a cylindrical shape, a square shape, a coin shape, and a laminate shape. Moreover, the lithium secondary battery of this invention has an electrode body comprised from a positive electrode layer, a separator, and a negative electrode layer. The shape of the electrode body is not particularly limited, and specific examples include a flat plate type and a wound type.

B. Method for Producing Cathode Active Material Coating Particles The method for producing a positive electrode active material coating particle of the present invention comprises a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor. A method for producing a coating particle, wherein an amorphous material is formed by mechanically mixing and grinding a raw material mixture containing constituent elements of the lithium ion conductive solid electrolyte to form an amorphous body. And a crystallization step of heating and crystallizing the amorphous body to form the crystalline electrolyte decomposition inhibitor.

  According to the present invention, since an amorphous body is crystallized to form a crystalline electrolyte decomposition inhibitor, a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor are provided. The positive electrode active material coating particles in a microphase separation state can be obtained. When such positive electrode active material coating particles are mixed with the positive electrode active material, a positive electrode active material having positive electrode active material coating particles on the surface can be obtained. Therefore, when the positive electrode active material coating particles obtained by the present invention are used in a lithium secondary battery having an organic electrolyte, lithium ion conductivity can be improved while suppressing oxidative decomposition of the organic electrolyte. .

  Moreover, compared with the case where a lithium ion conductive solid electrolyte is produced by a solid phase reaction method or a sol-gel method, a lithium ion conductive solid electrolyte having a high lithium ion conductivity can be obtained in the present invention.

Furthermore, an amorphous material can be obtained simply by mechanically mixing and grinding a raw material mixture of a lithium ion conductive solid electrolyte. The amorphous material can be obtained by heating the amorphous material only at a predetermined temperature. Thus, the positive electrode active material coating particles can be easily produced. Moreover, since a mixture of general-purpose oxides or the like can be used as the raw material mixture of the lithium ion conductive solid electrolyte, the positive electrode active material coating particles can be manufactured at low cost.
Hereafter, each process in the manufacturing method of the particle | grains for positive electrode active material coating | coated of this invention is demonstrated.

1. Amorphization process The amorphization process according to the present invention mechanically mixes and grinds the raw material mixture containing the constituent elements of the lithium ion conductive solid electrolyte to form an amorphous body. It is a process to do. Hereinafter, the raw material mixture and the method of mechanically mixing and grinding will be described.

(1) Raw material mixture The raw material mixture used in the present invention is not particularly limited as long as it contains a constituent element of a lithium ion conductive solid electrolyte. In the present invention, since the constituent elements of the crystalline electrolyte decomposition inhibitor usually overlap with the constituent elements of the lithium ion conductive solid electrolyte, a raw material mixture containing the constituent elements of the lithium ion conductive solid electrolyte is used.

The raw material compound varies depending on the type of the lithium ion conductive solid electrolyte. For example, the lithium ion conductive solid electrolyte is represented by the general formula Li _{1 + x} Al _x M _2-x (PO ₄ ) ₃ (M is Ti, A lithium-containing compound, an aluminum-containing compound, a titanium-containing compound, and germanium in the case of a Nasicon type phosphoric acid compound that is at least one selected from the group consisting of Ge and Zr and is represented by 0 ≦ x ≦ 1) A mixture of at least one compound selected from the group consisting of a containing compound and a zirconium-containing compound and a phosphorus-containing compound is used.

Examples of the lithium-containing compound, is not particularly limited as long as it contains lithium atoms, and examples thereof include Li ₂ O, LiOH, a Li ₂ CO ₃ or the like. Only one type of lithium-containing compound may be used, or two or more types may be used in combination.

The aluminum-containing compound is not particularly limited as long as it contains an aluminum atom, and examples thereof include Al ₂ O ₃ and Al (OH) ₃ . Of these, Al ₂ O ₃ is preferably used. Since Al ₂ O ₃ has an electrolyte decomposition inhibiting action, by leaving a part of the unreacted Al ₂ O ₃ , when the cathode active material coating particles are used in a lithium secondary battery, the oxidative decomposition of the organic electrolyte It is because it can suppress effectively. Only one type of aluminum-containing compound may be used, or two or more types may be used in combination.
When Al ₂ O ₃ is used, TiP ₂ O ₇ can be formed as a crystalline electrolyte decomposition inhibitor in the crystallization step by appropriately adjusting the particle size of Al ₂ O ₃ . Specifically, when a mixture of Li ₂ O, Al ₂ O ₃ , TiO ₂ and P ₂ O ₅ is used as a raw material mixture, TiP ₂ O ₇ is adjusted by appropriately adjusting the particle size of Al ₂ O _3. Can be generated. In this case, the average particle size of Al ₂ O ₃ is preferably about 0.05 μm to 1 μm, more preferably in the range of 0.1 μm to 0.8 μm, and still more preferably 0.3 μm to 0.5 μm. Is within the range. If the average particle diameter of Al ₂ O ₃ is in the above range, TiP ₂ O ₇ can be generated.

The titanium-containing compound is not particularly limited as long as it contains a titanium atom, but TiO ₂ is preferably used. Similar to Al ₂ O ₃ , TiO ₂ has an electrolyte decomposition inhibiting action, so that a part of the unreacted TiO ₂ remains, so that when the positive electrode active material coating particles are used in a lithium secondary battery, This is because the oxidative decomposition of the electrolyte can be effectively suppressed. Only one type of titanium-containing compound may be used, or two or more types may be used in combination.

The germanium-containing compound is not particularly limited as long as it contains a germanium atom, but GeO ₂ is preferably used. Similar to Al ₂ O ₃ , GeO ₂ has an action of suppressing electrolyte decomposition. Therefore, by leaving a part of unreacted GeO ₂ , when the positive electrode active material coating particles are used in a lithium secondary battery, This is because the oxidative decomposition of the electrolyte can be effectively suppressed. Only one type of germanium-containing compound may be used, or two or more types may be used in combination.

The zirconium-containing compound is not particularly limited as long as it contains a zirconium atom, but ZrO ₂ is preferably used. Similar to Al ₂ O ₃ , ZrO ₂ has an electrolyte decomposition inhibiting action. Therefore, by leaving a part of unreacted ZrO ₂ , when the positive electrode active material coating particles are used in a lithium secondary battery, This is because the oxidative decomposition of the electrolyte can be effectively suppressed. One type of zirconium-containing compound may be used, or two or more types may be used in combination.

  These titanium-containing compound, germanium-containing compound and zirconium-containing compound are appropriately selected according to the composition of the NASICON type phosphoric acid compound.

The phosphorus-containing compound is not particularly limited as long as it has a phosphorus atom, and examples thereof include P ₂ O ₅ , (NH ₄ ) ₂ HPO ₄ , and NH ₄ H ₂ PO ₄ . Among these, P ₂ O ₅ is preferably used. Only one type of phosphorus-containing compound may be used, or two or more types may be used in combination.

The combination of each compound used for a raw material mixture is suitably selected according to the kind of target lithium ion conductive solid electrolyte and electrolyte decomposition inhibitor. For example, in order to form TiP ₂ O ₇ as a crystalline electrolyte decomposition inhibitor in the crystallization step, it is necessary to use a mixture of Li ₂ O, Al ₂ O ₃ , TiO ₂ and P ₂ O ₅ as a raw material mixture. preferable. For example, in order to form Li ₃ PO ₄ as a crystalline electrolyte decomposition inhibitor in the crystallization step, it is preferable to use a mixture containing LiO ₂ and P ₂ O ₅ as a raw material mixture. In order to form AlPO ₄ as a crystalline electrolyte decomposition inhibitor in the crystallization step, the raw material mixture is selected from the group consisting of, for example, Li ₂ O, Al ₂ O ₃ , TiO ₂ , GeO ₂ and ZrO ₂ A mixture of at least one of the above and P ₂ O ₅ can be used.

As a ratio of a lithium-containing compound, an aluminum-containing compound, at least one compound selected from the group consisting of a titanium-containing compound, a germanium-containing compound, and a zirconium-containing compound, and a phosphorus-containing compound contained in the raw material mixture, It depends on the type of the intended lithium ion conductive solid electrolyte and electrolyte decomposition inhibitor. For example, when producing Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 1), the lithium-containing compound: aluminum-containing compound: titanium-containing compound: phosphorus-containing compound on a molar basis. 1.3-1.5: 0.3-0.5: 0.5-1.5: 2.95-3.05.

(2) Method of mechanically mixing and grinding In the present invention, the raw material mixture is mechanically mixed and ground. The method of mechanically mixing and grinding is not particularly limited as long as it is a method capable of obtaining an amorphous body, but among them, the mechanical milling method is preferable.

  The mechanical milling (hereinafter sometimes abbreviated as MM) method applies mechanical energy such as crushing, impact, friction, etc. to a solid material to activate the material surface and react the material or change the structure. (This is also called a mechanochemical reaction). The MM method has advantages such as that the temperature condition may be room temperature (no heat treatment is required), fine particles can be produced, and the surface of the particles can be modified.

  When such an MM method is used, an amorphous body can be obtained in one step by mixing and grinding the raw material mixture by the MM method, and only by heat-treating this amorphous body, The positive electrode active material coating particles containing a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor can be easily obtained.

In the MM method, by appropriately selecting raw materials, not only the second phase (second component) but also the third phase (third component) and the fourth phase (fourth component) are generated, that is, three or more. It becomes possible to produce | generate the phase (component) of this. Therefore, it is possible to form multiple types of electrolyte decomposition inhibitors.
Further, in the MM method, for example, when Al ₂ O ₃ , TiO ₂ , GeO ₂ , ZrO ₂ is used as a raw material, Al ₂ O ₃ , TiO ₂ , GeO ₂ , ZrO ₂ is not reacted during the formation of the amorphous body. Some may remain. These Al ₂ O ₃ , TiO ₂ , GeO ₂ , and ZrO ₂ have an action of inhibiting electrolyte decomposition. Therefore, when the positive electrode active material coating particles are used in a lithium secondary battery, Al ₂ O ₃ , TiO ₂ , GeO ₂ , and ZrO ₂ are left by using the MM method to oxidize and decompose the organic electrolyte. It can be effectively suppressed.

For example, when a mixture of P ₂ O ₅ and at least one selected from the group consisting of Li ₂ O, Al ₂ O ₃ , TiO ₂ , GeO ₂ and ZrO _{2 is} used as the raw material mixture, MM In the amorphous body obtained by the method, the crystallization temperature is around 600 ° C., the crystallization temperature of the amorphous body obtained by the melt quenching method (690 ° C.) and the amorphous body obtained by the sol-gel method Lower than the crystallization temperature (660 ° C.). Therefore, by using the MM method, the heating temperature in the crystallization process described later can be lowered.

Further, for example, when a mixture of Li ₂ O, Al ₂ O ₃ , TiO ₂ and P ₂ O ₅ is used as a raw material mixture, by appropriately adjusting the particle size of Al ₂ O ₃ , TiP ₂ O ₇ can be produced as a crystalline electrolyte decomposition inhibitor. Therefore, by using the MM method and appropriately adjusting the particle size of Al ₂ O _3, a desired crystalline electrolyte decomposition inhibitor can be formed in the crystallization step.

Examples of the mechanical milling method include a method using a ball mill apparatus. The method using a ball mill apparatus is a general-purpose method, and can uniformly mix and grind the raw material mixture.
As the ball mill device, for example, a planetary ball mill or the like can be used.

  When using a ball mill apparatus, the diameter and material of the crushing ball used, the material of the reaction vessel, and the like are the same as those of a general ball mill apparatus, and are not particularly limited. The diameter of the crushing ball is, for example, preferably in the range of 3 mm to 20 mm, and more preferably in the range of 5 mm to 15 mm. Specific examples of the material of the crushed ball include zirconium oxide. Specific examples of the material for the reaction vessel include stainless steel.

The number of rotations when mixing and grinding using a ball mill device is not particularly limited as long as an amorphous material can be obtained, but can be set at about 300 rpm to 600 rpm, for example, 350 rpm to It is preferable to be within a range of 550 rpm, particularly within a range of 400 rpm to 450 rpm.
In addition, the time for mixing and grinding using a ball mill device is not particularly limited, but can be set, for example, in the range of about 5 hours to 50 hours, and particularly within the range of 7 hours to 30 hours. It is preferably within a range of 10 hours to 20 hours.

When the raw material mixture is mechanically mixed and ground, it is preferably mixed and ground in an inert gas atmosphere. Examples of the inert gas include Ar, N ₂ , and He.

  The raw material mixture may be mixed and ground by adding each raw material simultaneously, or may be mixed and ground by sequentially adding each raw material.

  In this step, formation of an amorphous body can be confirmed by X-ray diffraction measurement (XRD).

2. Crystallization Step The crystallization step in the present invention is a step in which the amorphous body is heated and crystallized to form the crystalline electrolyte decomposition inhibitor.

The heating temperature only needs to be equal to or higher than the crystallization temperature of the crystalline electrolyte decomposition inhibitor, and is appropriately selected according to the type of the crystalline electrolyte decomposition inhibitor. For example, when forming AlPO ₄ as a crystalline electrolyte decomposition inhibitor, the heating temperature is preferably equal to or higher than the crystallization temperature of AlPO ₄ .
In order to form an amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor, the heating temperature is equal to or higher than the crystallization temperature of the crystalline electrolyte decomposition inhibitor. It is set below the crystallization temperature. On the other hand, in order to form a crystalline lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor, the heating temperature is equal to or higher than the crystallization temperature of the crystalline electrolyte decomposition inhibitor, and the lithium ion conductive solid electrolyte. Or higher than the crystallization temperature.
Specifically, the heating temperature can be set at about 550 ° C to 1000 ° C, preferably in the range of 570 ° C to 900 ° C, more preferably in the range of 600 ° C to 850 ° C. This is because if the heating temperature is too low, the crystalline electrolyte decomposition inhibitor is difficult to crystallize, and if the heating temperature is too high, lithium may evaporate, resulting in a composition lacking lithium. Moreover, the crystallinity of the lithium ion conductive solid electrolyte and the electrolyte decomposition inhibitor can be improved by setting the heating temperature higher.

  The holding time at the above heating temperature varies depending on the conditions such as the heating temperature, but can be set in the range of about 1 hour to 10 hours, and particularly in the range of 2 hours to 5 hours, especially 2 hours to It is preferably within a range of 3 hours. This is because if the heating and holding time is too short, crystal growth may be insufficient, and if the heating and holding time is too long, lithium may evaporate, resulting in a composition lacking lithium.

  The heating device is not particularly limited, and a general heating device can be used.

  The atmosphere for heating the amorphous body may be, for example, an air atmosphere or an inert gas atmosphere.

In this step, at least a crystalline electrolyte decomposition inhibitor may be formed, but a crystalline lithium ion conductive solid electrolyte may be formed.
In this step, the formation of the crystalline electrolyte decomposition inhibitor and the crystalline lithium ion conductive solid electrolyte can be confirmed by the method described in “A. Lithium secondary battery” above.
In addition, the positive electrode active material coating particles also contain a crystalline or amorphous lithium ion conductive solid charge and a crystalline electrolyte decomposition inhibitor, as described in "A. Lithium secondary battery" above. The method can be confirmed.

  The details of the crystalline or amorphous lithium ion conductive solid electrolyte and the crystalline electrolyte decomposition inhibitor are described in “A. Lithium secondary battery” above, and thus the description thereof is omitted here.

C. 2. Manufacturing method of lithium secondary battery The manufacturing method of the lithium secondary battery of this invention has two embodiments. In the following, each embodiment will be described separately.

1. 1st embodiment 1st embodiment of the manufacturing method of the lithium secondary battery of this invention is a manufacturing method of the lithium secondary battery which has a positive electrode layer, a negative electrode layer, and an organic electrolyte, Comprising: Said positive electrode active material A cathode active material preparation step of preparing the cathode active material having the cathode active material coating particles on the surface by mixing the cathode active material coating particles obtained by the coating particle manufacturing method and the cathode active material. It is characterized by having.

  According to this embodiment, since the positive electrode active material coating particles obtained by the above-described method for manufacturing the positive electrode active material coating particles are used, the crystalline or amorphous lithium ion conductive solid electrolyte and the crystalline electrolyte decomposition are used. It is possible to obtain a positive electrode active material having positive electrode active material coating particles on the surface of which an inhibitor is present in a microphase separation state. By forming a positive electrode layer using such a positive electrode active material, a lithium secondary capable of suppressing a decrease in cycle capacity during high-voltage charging and suppressing a decrease in capacity during rapid charge / discharge A battery can be obtained.

Moreover, since the positive electrode active material coating particles obtained by the above-described method for manufacturing the positive electrode active material coating particles are used, a lithium ion conductive solid electrolyte having a relatively high lithium ion conductivity can be obtained, and high lithium ion conductivity can be obtained. Can be realized.
Hereinafter, each process in the manufacturing method of the lithium secondary battery of this embodiment is demonstrated.

(1) Positive electrode active material preparation process The positive electrode active material preparation process in this embodiment mixes the positive electrode active material coating particles obtained by the above-described method for producing positive electrode active material coating particles and the positive electrode active material, This is a step of preparing a positive electrode active material having the positive electrode active material coating particles on its surface.

  The method for mixing the positive electrode active material coating particles and the positive electrode active material is not particularly limited as long as the positive electrode active material having the positive electrode active material coating particles on the surface thereof can be obtained. Further, a mechanical milling method may be used as a mixing method.

  The atmosphere for mixing the positive electrode active material coating particles and the positive electrode active material may be, for example, an air atmosphere or an inert gas atmosphere.

  The positive electrode active material is described in “A. Lithium secondary battery”, and the positive electrode active material coating particles are described in “B. Method for producing positive electrode active material coating particles”. Description is omitted.

(2) Other steps The method for producing a lithium secondary battery of this embodiment is not particularly limited as long as it has at least the positive electrode active material preparation step. For example, in the positive electrode active material preparation step, A positive electrode layer forming step for forming a positive electrode layer containing a positive electrode active material having particles for coating a positive electrode active material on its surface, a negative electrode layer forming step for forming a negative electrode layer, and a battery assembly step for assembling a lithium secondary battery Etc. may be included. Since these steps are the same as those in a general lithium secondary battery, description thereof is omitted here.
Further, the obtained lithium ion battery is the same as that described in the above-mentioned “A. Lithium secondary battery”, and therefore the description thereof is omitted here.

2. Second Embodiment A second embodiment of the method for producing a lithium secondary battery according to the present invention is a method for producing a lithium secondary battery having a positive electrode layer, a negative electrode layer, and an organic electrolyte, wherein the positive electrode active material described above is used. After mechanically mixing the amorphous body obtained in the amorphization step of the coating particle manufacturing method and the positive electrode active material, the mixture of the amorphous body and the positive electrode active material is heated. Characterized by having a positive electrode active material preparation step of crystallizing the amorphous body to form a crystalline electrolyte decomposition inhibitor and preparing the positive electrode active material having the positive electrode active material coating particles on its surface. To do.

  According to this embodiment, since the amorphous body is crystallized to form a crystalline electrolyte decomposition inhibitor, a crystalline or amorphous lithium ion conductive solid electrolyte, a crystalline electrolyte decomposition inhibitor, It is possible to obtain particles for coating the positive electrode active material in which the microphase separation state is present. And a positive electrode active material having particles on the surface for coating a positive electrode active material containing a crystalline or amorphous lithium ion conductive solid electrolyte present in a microphase-separated state and a crystalline electrolyte decomposition inhibitor Obtainable. By forming a positive electrode layer using such a positive electrode active material, a lithium secondary capable of suppressing a decrease in cycle capacity during high-voltage charging and suppressing a decrease in capacity during rapid charge / discharge A battery can be obtained.

  Moreover, since the amorphous body obtained in the amorphization step of the method for producing particles for coating positive electrode active material is crystallized, a lithium ion conductive solid electrolyte having a relatively high lithium ion conductivity can be obtained. And high lithium ion conductivity can be realized.

  Furthermore, the crystallinity existing in the microphase-separated state can be obtained simply by mechanically mixing the positive electrode active material and the amorphous material and heating the mixture of the positive electrode active material and the amorphous material at a predetermined temperature. Alternatively, a positive electrode active material having particles for coating a positive electrode active material containing an amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor can be obtained. A positive electrode active material having particles on the surface can be manufactured.

In the present embodiment, the positive electrode active material and the amorphous material obtained in the amorphization step of the above-described method for producing the positive electrode active material coating particles are mechanically mixed, and then the positive electrode active material and the amorphous material are mixed. When the body is heated, the amorphous body is first softened in the vicinity of the glass transition temperature, and then a crystalline electrolyte decomposition inhibitor is generated at a crystallization temperature higher than the glass transition temperature. As a result, a positive electrode active material having positive electrode active material coating particles containing a crystalline or amorphous lithium ion conductive solid electrolyte and a crystalline electrolyte decomposition inhibitor on the surface can be obtained.
Hereinafter, each process in the manufacturing method of the lithium secondary battery of this embodiment is demonstrated.

(1) Positive electrode active material preparation step The positive electrode active material preparation step in the present embodiment includes an amorphous body obtained in the amorphization step of the above-described method for producing positive electrode active material coating particles, a positive electrode active material, And then mixing the amorphous body and the positive electrode active material to crystallize the amorphous body to form a crystalline electrolyte decomposition inhibitor, and coating the positive electrode active material. It is the process of preparing the said positive electrode active material which has particle | grains for the surface.

  The method of mechanically mixing the amorphous body and the positive electrode active material is not particularly limited as long as it is a method capable of obtaining a positive electrode active material having an amorphous body on the surface. The milling method is preferred.

Examples of the mechanical milling method include a method using a ball mill apparatus. A method using a ball mill apparatus is a general-purpose method, and an amorphous body and a positive electrode active material can be uniformly and mechanically mixed.
As the ball mill device, for example, a planetary ball mill or the like can be used.

  When using a ball mill apparatus, the diameter and material of the crushing ball used, the material of the reaction vessel, and the like are the same as those of a general ball mill apparatus, and are not particularly limited. The diameter of the crushing ball is, for example, preferably in the range of 3 mm to 20 mm, and more preferably in the range of 5 mm to 15 mm. Specific examples of the material of the crushed ball include zirconium oxide. Specific examples of the material for the reaction vessel include stainless steel.

The number of rotations when mixing using a ball mill device is not particularly limited as long as a positive electrode active material having an amorphous body on the surface can be obtained, but can be set at, for example, about 100 rpm to 350 rpm. In particular, it is preferably within the range of 150 rpm to 300 rpm, particularly within the range of 200 rpm to 250 rpm.
Further, the mixing time using the ball mill device is not particularly limited, but can be set, for example, in the range of 1 hour to 10 hours, and in particular, in the range of 1 hour to 5 hours, particularly 1 hour to It is preferably within a range of 2 hours.

  The atmosphere for mechanically mixing the amorphous body and the positive electrode active material may be, for example, an air atmosphere or an inert gas atmosphere.

In addition, about the heating temperature of the mixture of an amorphous body and a positive electrode active material, a heating holding time, a heating atmosphere, and other points, the above-mentioned "B. Method for producing particles for coating positive electrode active material 2. Crystallization step" Since it is the same as that described in the above, description thereof is omitted here.
The details of the positive electrode active material, the crystalline or amorphous lithium ion conductive solid electrolyte, and the crystalline electrolyte decomposition inhibitor are described in “A. Lithium secondary battery” above. Description is omitted.

(2) Other steps The method for producing a lithium secondary battery of this embodiment is not particularly limited as long as it has at least the positive electrode active material preparation step. For example, in the positive electrode active material preparation step, A positive electrode layer forming step for forming a positive electrode layer containing a positive electrode active material having particles for coating a positive electrode active material on its surface, a negative electrode layer forming step for forming a negative electrode layer, and a battery assembly step for assembling a lithium secondary battery Etc. may be included. Since these steps are the same as those in a general lithium secondary battery, description thereof is omitted here.
Further, the obtained lithium ion battery is the same as that described in the above-mentioned “A. Lithium secondary battery”, and therefore the description thereof is omitted here.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

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

[Example 1]
(Preparation of positive electrode active material coating particles)
Li ₂ CO ₃ , Al ₂ O ₃ , TiO ₂ and (NH ₄ ) ₂ HPO ₄ are used as raw materials, and these have a molar ratio of Li ₂ O: Al ₂ O ₃ : TiO ₂ : P ₂ O ₅ of 14: 9. : After mixing so that it might become 38:39, it calcined at 700 degreeC in the air for 2 hours. Next, in a planetary ball mill using a zirconium oxide pulverized ball having a diameter of 10 mm, mechanical milling (MM) treatment was performed at room temperature in an argon gas atmosphere at a rotational speed of 350 rpm for 40 hours to make it amorphous. Next, the obtained powder (amorphous) was crystallized by heating in air at 850 ° C. for 4 hours.

The result of the powder X-ray diffraction measurement is shown in FIG. 2A to 2C are X-ray diffraction patterns after calcining at 700 ° C. for 2 hours, MM treatment, and heating at 850 ° C. for 4 hours, respectively. 2 are JCPDS X-ray diffraction patterns of Al ₂ O ₃ , TiO ₂ , AlPO ₄ , and LiTi ₂ (PO ₄ ) ₃ , respectively.
After the MM treatment, weak peaks of unreacted Al ₂ O ₃ and TiO ₂ were confirmed, but a halo pattern was shown and it became amorphous at room temperature (FIG. 2 (b)). When heat treatment was performed in air at 850 ° C. for 4 hours, peaks mainly attributed to LiTi ₂ (PO ₄ ) ₃ and AlPO ₄ were confirmed (FIG. 2 (c)). As a result, Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ and AlPO _{4 in} which Ti ⁴⁺ is partially substituted and dissolved in Al ³⁺ are generated (composition formula is approximately 2 [Li _1.3 It was found that Al _0.3 Ti _1.7 (PO ₄ ) ₃ ] -AlPO ₄ ), unreacted Al ₂ O ₃ and TiO ₂ remained.

(Preparation of positive electrode layer)
A positive electrode material was prepared by mixing LiCoO ₂ and the above crystallized powder in a weight ratio of 95: 5. Subsequently, acetylene black (AB) was mixed with this positive electrode material, and a polyvinylidene fluoride (PVDF) binder dissolved in n-methylpyrrolidone (NMP) was added to prepare a slurry. The mixing ratio of the positive electrode material, AB, and PVDF was 85: 5: 10 (weight ratio). This slurry was applied to an Al current collector, pressed and vacuum dried to produce a positive electrode layer.

(Production of lithium secondary battery)
Lithium hexafluorophosphate (LiPF ₆ ) as a supporting salt is used as a supporting salt in a mixed solvent in which the positive electrode layer is used, metallic Li is used for the negative electrode layer, EC and EMC are mixed in an electrolyte solution, and volume ratio is 3: 7. Using the one dissolved in ³ , a bipolar coin cell was produced.

[Example 2]
(Preparation of positive electrode active material coating particles)
A glove box using Li ₂ O, Al ₂ O ₃ , TiO ₂ , and P ₂ O ₅ as raw materials and filled with high purity argon gas (purity 99.99%) at 14: 9: 38: 39 (molar ratio). After mixing in, it was put together with a 10 mm diameter pulverized ball of zirconium oxide into a completely sealable container of stainless steel. The sealed container was taken out from the glove box, mounted on a planetary ball mill device, and made amorphous by MM treatment at a platform rotation speed of 450 rpm for 20 hours at room temperature.

The result of the powder X-ray diffraction measurement is shown in FIG. 3A to 3D are X-ray diffraction patterns after MM treatment, after heating at 700 ° C. for 2 hours, after heating at 800 ° C. for 2 hours, and after heating at 850 ° C. for 2 hours, respectively. Further, I to V in FIG. 3 are JCPDS X-ray diffraction patterns of Al ₂ O ₃ , TiO ₂ , AlPO ₄ , and LiTi ₂ (PO ₄ ) ₃ , respectively.
In the MM treatment at a rotation speed of 450 rpm for 20 hours, weak peaks of unreacted Al ₂ O ₃ and TiO ₂ were confirmed, but it showed a halo pattern and became amorphous at room temperature (FIG. 3 (a )).
Moreover, the result of the TG-DTA measurement in the air atmosphere of the powder (amorphous body) obtained after MM processing is shown in FIG. From FIG. 4, an exothermic peak considered to be crystallized was observed at around 600 ° C.

Therefore, the powder (amorphous) after MM treatment was heat-treated in air at 700 ° C., 800 ° C., and 850 ° C. for 2 hours. As a result, peaks attributed mainly to LiTi ₂ (PO ₄ ) ₃ and AlPO ₄ were confirmed (FIGS. 3B to 3D). As a result, Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ and AlPO _{4 in} which Ti ⁴⁺ is partially substituted and dissolved in Al ³⁺ are generated (composition formula is approximately 2 [Li _1.3 It was found that Al _0.3 Ti _1.7 (PO ₄ ) ₃ ] -AlPO ₄ ), unreacted Al ₂ O ₃ and TiO ₂ remained. Moreover, these peak intensities became stronger as the heat treatment temperature increased, and it was confirmed that the crystallinity was improved.

(Preparation of positive electrode layer)
A positive electrode material was prepared by mixing LiCoO ₂ and each of the powders after crystallization at 95: 5 (weight ratio). Thereafter, acetylene black (AB) as a conductive additive was mixed with the positive electrode material, and a polyvinylidene fluoride (PVDF) binder dissolved in NMP was added to prepare a slurry. The mixing ratio of the positive electrode material, AB, and PVDF was 85: 5: 10 (weight ratio). This slurry was applied to an Al current collector, pressed and vacuum dried to produce a positive electrode layer.

(Production of lithium secondary battery)
Lithium hexafluorophosphate (LiPF ₆ ) as a supporting salt is used as a supporting salt in a mixed solvent in which the positive electrode layer is used, metallic Li is used for the negative electrode layer, EC and EMC are mixed in an electrolyte solution, and volume ratio is 3: 7. Using the one dissolved in ³ , a bipolar coin cell was produced.

[Example 3]
(Preparation of cathode active material having cathode active material coating particles on its surface)
A glove box using Li ₂ O, Al ₂ O ₃ , TiO ₂ , and P ₂ O ₅ as raw materials and filled with high purity argon gas (purity 99.99%) at 14: 9: 38: 39 (molar ratio). After mixing in, it was put together with a 10 mm diameter pulverized ball of zirconium oxide into a completely sealable container of stainless steel. The sealed container was taken out from the glove box, mounted on a planetary ball mill device, and made amorphous by MM treatment at a platform rotation speed of 450 rpm for 20 hours at room temperature. Next, the obtained powder (amorphous body) and LiCoO ₂ were mixed at 95: 5 (weight ratio), and heat-treated at 850 ° C., which is higher than the crystallization temperature of the amorphous body, for 2 hours.

(Preparation of positive electrode layer)
Acetylene black (AB) as a conductive assistant was mixed with the above-mentioned amorphous and LiCoO ₂ heat-treated powder, and a polyvinylidene fluoride (PVDF) binder dissolved in NMP was added to prepare a slurry. The mixing ratio of the positive electrode material, AB, and PVDF was 85: 5: 10 (weight ratio). This slurry was applied to an Al current collector, pressed and vacuum dried to produce a positive electrode layer.

(Production of lithium secondary battery)
Lithium hexafluorophosphate (LiPF ₆ ) as a supporting salt is used as a supporting salt in a mixed solvent in which the positive electrode layer is used, metallic Li is used for the negative electrode layer, EC and EMC are mixed in an electrolyte solution, and volume ratio is 3: 7. Using the one dissolved in ³ , a bipolar coin cell was produced.

[Comparative Example 1]
A positive electrode layer was prepared using the same LiCoO ₂ used in Examples 1 to 3. First, LiCoO ₂ and acetylene black (AB), which is a conductive additive, were mixed, and a polyvinylidene fluoride (PVDF) binder dissolved in NMP was added to prepare a slurry. The mixing ratio of LiCoO ₂ , AB and PVDF was 85: 5: 10 (weight ratio). This slurry was applied to an Al current collector, pressed and vacuum dried to produce a positive electrode layer.
Using this positive electrode layer, lithium hexafluorophosphate (LiPF ₆ ) was used as a supporting salt in a mixed solvent prepared by mixing metallic Li in the negative electrode layer, electrolyte, EC and EMC at a volume ratio of 3: 7, and a concentration of 1 mol / dm ³ A bipolar coin cell was prepared using the material dissolved in (1).

[Example 4]
(Preparation of positive electrode active material coating particles)
Li ₂ O, Al ₂ O ₃ , TiO ₂ , and P ₂ O ₅ were mixed at a molar ratio of 14: 9: 38: 39, respectively, in a planetary ball mill at room temperature in an argon atmosphere at 450 rpm for 40 hours. Milling (MM) treatment was performed. Subsequently, it baked at 800 degreeC in the air for 2 hours.
When the obtained powder was subjected to powder X-ray diffraction measurement, peaks attributable to LiTi ₂ (PO ₄ ) ₃ and AlPO ₄ were confirmed. Thus, it was found that Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ and AlPO _{4 in} which Ti ⁴⁺ was partially substituted and dissolved in Al ³⁺ were produced.

(Preparation of positive electrode layer)
In 125 mL of n-methylpyrrolidone solution in which 5 g of polyvinylidene fluoride (PVDF) as a binder is dissolved, 80.75 g of LiCoO ₂ powder as a positive electrode active material, 4.25 g of the above powder, and carbon black as a conductive agent 10 g was introduced and kneaded until uniformly mixed to prepare a paste.
This paste was applied on one side onto a 15 μm thick Al current collector and then dried to produce an electrode. The electrode basis weight was 6 mg / cm ² . This electrode was pressed to a paste thickness of 45 μm and a paste density of 2.4 g / cm ³ . Then, this electrode was cut out to have a diameter of 16 mm.

(Preparation of negative electrode layer)
92.5 g of graphite powder as the negative electrode active material is introduced into 125 mL of n-methylpyrrolidone solution in which 7.5 g of polyvinylidene fluoride (PVDF) as a binder is dissolved, and the paste is kneaded until uniformly mixed. Produced.
This paste was applied on one side onto a 15 μm thick Cu current collector and then dried to prepare an electrode. The electrode basis weight was 4 mg / cm ² . This electrode was pressed to a paste thickness of 20 μm and a paste density of 1.2 g / cm ³ . Then, this electrode was cut out to have a diameter of 19 mm.

(Production of lithium secondary battery)
A CR2032 type coin cell was obtained using the obtained positive electrode and negative electrode. A PP separator was used as the separator. For the electrolyte, lithium hexafluorophosphate (LiPF ₆ ) was dissolved as a supporting salt in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) mixed at a volume ratio of 3: 7 at a concentration of 1 mol / L. Things were used.

[Example 5]
A lithium secondary battery was produced in the same manner as in Example 4 except that the positive electrode active material coating particles were produced as follows.

(Preparation of positive electrode active material coating particles)
Li ₂ O, Al ₂ O ₃ , TiO ₂ , P ₂ O ₅ were used as raw materials, and these were increased in the ratio of Al ₂ O ₃ and TiO ₂ with respect to the molar ratio of Example 2 12:10:40: After mixing in a glove box filled with high-purity argon gas (purity 99.99%) at 38 (molar ratio), it was put together with a 10 mm diameter zirconium oxide ball into a completely sealable container made of stainless steel. . The sealed container was taken out from the glove box, mounted on a planetary ball mill device, and made amorphous by MM treatment at a platform rotation speed of 450 rpm for 20 hours at room temperature.
From the result of the powder X-ray diffraction measurement, the peaks of unreacted Al ₂ O ₃ and TiO ₂ were strongly confirmed as compared with the result of Example 2. Moreover, it turned out that it shows a halo pattern and becomes amorphous at room temperature.

Next, the obtained powder was heat-treated in air at 700 ° C. for 2 hours.
From the result of the powder X-ray diffraction measurement, in addition to the peaks attributed to Al ₂ O ₃ and TiO ₂ , peaks attributed to LiTi ₂ (PO ₄ ) ₃ and AlPO ₄ were confirmed. As a result, Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ and AlPO _{4 in} which Ti ⁴⁺ is partially substituted and dissolved in Al ³⁺ are produced, and unreacted Al ₂ O ₃ , It was found that TiO ₂ remained actively.

[Example 6]
A lithium secondary battery was produced in the same manner as in Example 4 except that the positive electrode active material coating particles were produced as follows.

(Preparation of positive electrode active material coating particles)
Li ₂ O, Al ₂ O ₃ , TiO ₂ and P ₂ O ₅ were used as raw materials. At this time, Al ₂ O ₃ having a particle diameter of about 0.1 μm smaller than that of Al ₂ O ₃ used in Example 2 was used. After mixing Li ₂ O, Al ₂ O ₃ , TiO ₂ , and P ₂ O ₅ in a glove box filled with high purity argon gas (purity 99.99%) at 14: 9: 38: 39 (molar ratio) Then, it was put together with a pulverized ball of zirconium oxide having a diameter of 10 mm into a completely sealable container made of stainless steel. The sealed container was taken out from the glove box, mounted on a planetary ball mill device, and made amorphous by MM treatment at a platform rotation speed of 450 rpm for 20 hours at room temperature.
From the results of powder X-ray diffraction measurement, weak peaks of unreacted Al ₂ O ₃ and TiO ₂ were confirmed, but they showed a halo pattern and became amorphous at room temperature.

Next, the obtained powder was heat-treated in air at 700 ° C. for 2 hours.
From the result of the powder X-ray diffraction measurement, in addition to the peaks attributed to LiTi ₂ (PO ₄ ) ₃ and AlPO ₄ , the peak attributed to TiP ₂ O ₇ was confirmed. As a result, Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ and AlPO _{4 in} which Ti ⁴⁺ is partially substituted and dissolved in Al ³⁺ are produced, and TiP ₂ O ₇ is produced. It was found that unreacted Al ₂ O ₃ and TiO ₂ remained. This is thought to be due to the increased reactivity of TiO ₂ and P ₂ O ₅ by using Al ₂ O ₃ having a small particle size (for example, submicron order).

[Comparative Example 2]
In the production of the positive electrode layer of Example 4, a lithium secondary battery was produced in the same manner as in Example 4 except that AlPO ₄ was used instead of the powder obtained in the production of the positive electrode active material coating particles. .

[Evaluation]
The discharge capacity ratios and cycle characteristics of the coin cells obtained in Examples 1 to 6 and Comparative Examples 1 and 2 were evaluated. In Example 2, a coin cell manufactured using a powder heat-treated at 850 ° C. for 2 hours was evaluated.

(Discharge capacity ratio)
First, conditioning of 3.0 to 4.1 V was performed at a current value of 0.1 mA / cm ² . Thereafter, the battery was charged to 4.1 V at a current value of 1 mA / cm ² for 2.5 hours, discharged to 3.0 V at a current value of 1 mA / cm ² , and the capacity was measured. Furthermore, after charging to 4.1 V at a current value of 1 mA / cm ² for 2.5 hours, the battery was discharged to 3.0 V at a current value of 20 mA / cm ² and the capacity was measured. Then, (discharge capacity at 20 mA / cm ² ) / (discharge capacity at 1 mA / cm ² ) was obtained.
(Cycle characteristics)
After measuring the discharge rate capacity, the discharge capacity retention rate was measured at 500 cycles of 3.0 to 4.1 V, 2 C, 60 ° C.
The results are shown in Table 1.

  In Example 2, the same result as in Example 1 was obtained. The same results as in Example 1 were also obtained for coin cells prepared using powders heat treated at 700 ° C. and 800 ° C. for 2 hours. In Example 3, the same effect as in Examples 1 and 2 was obtained. On the other hand, in Comparative Example 1, the cycle capacity was significantly reduced as compared with Examples 1 to 3. It was also suggested that the overvoltage at the time of discharge was large, causing a decrease in capacity during rapid charge / discharge.

It is a schematic sectional drawing which shows an example of the lithium secondary battery of this invention. 2 is a graph showing an X-ray diffraction pattern of the powder of Example 1. 4 is a graph showing an X-ray diffraction pattern of the powder of Example 2. It is a graph which shows the TG-DTA curve of the powder of Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Positive electrode collector 2 ... Primary particle | grains containing crystalline or amorphous lithium ion conductive solid electrolyte and crystalline electrolyte decomposition inhibitor 3 ... Positive electrode active material 4 ... Positive electrode layer 5 ... Negative electrode collector 6 ... Negative electrode active material 7 ... Negative electrode layer 8 ... Separator

Claims (12)

Crystalline or amorphous lithium ion conductive solid electrolyte, and viewed including the crystalline electrolyte decomposition inhibitor is a crystal phase other than the lithium ion conductive solid electrolyte, the lithium ion conductive solid electrolyte and the electrolyte decomposition A positive electrode layer containing a positive electrode active material having solid powder on the surface containing primary particles in which the inhibitor is in a microphase-separated state ;
A negative electrode layer;
A lithium secondary battery comprising: an organic electrolyte disposed so as to be in contact with a positive electrode active material having the solid powder on a surface thereof. The crystalline or amorphous lithium ion conductive solid electrolyte has a general formula of Li _{1 + x} Al _x M _2−x (PO ₄ ) ₃ (M is at least one selected from the group consisting of Ti, Ge and Zr) 2. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is a NASICON phosphoric acid compound that is a seed and is represented by 0 ≦ x ≦ 1). The crystalline electrolyte decomposition inhibitor is at least one crystalline metal oxide selected from the group consisting of AlPO ₄ , TiP ₂ O ₇ , Li ₃ PO ₄ , Al ₂ O ₃ and TiO _2. The lithium secondary battery according to claim 2. The lithium secondary battery according to claim 3, wherein the crystalline electrolyte decomposition inhibitor is AlPO ₄ . Crystalline or amorphous lithium ion conductive solid electrolyte, and a method for producing a positive electrode active material coating particles containing a crystalline electrolyte decomposition inhibitor is a crystal phase other than the lithium ion conductive solid electrolyte ,
An amorphization step of mechanically mixing and grinding the raw material mixture containing the constituent elements of the lithium ion conductive solid electrolyte to form an amorphous body;
A method for producing particles for coating a positive electrode active material, comprising: a crystallization step of crystallizing the amorphous body by heating to form the crystalline electrolyte decomposition inhibitor. The crystalline or amorphous lithium ion conductive solid electrolyte has a general formula of Li _{1 + x} Al _x M _2−x (PO ₄ ) ₃ (M is at least one selected from the group consisting of Ti, Ge and Zr) 6. The method for producing particles for coating a positive electrode active material according to claim 5, wherein the phosphoric acid compound is a seed and is a Nasicon type phosphoric acid compound represented by 0 ≦ x ≦ 1). The crystalline electrolyte decomposition inhibitor is at least one crystalline metal oxide selected from the group consisting of AlPO ₄ , TiP ₂ O ₇ , Li ₃ PO ₄ , Al ₂ O ₃ and TiO _2. A method for producing particles for coating a positive electrode active material according to claim 6. The raw material mixture, to a Li ₂ O, and Al ₂ O _3, at least one member selected from the group consisting of TiO _2, GeO ₂ and ZrO _2, characterized in that it is a mixture of P ₂ O ₅ The manufacturing method of the particle | grains for positive electrode active material coating | coated of Claim 6 or Claim 7.   The method for producing particles for coating a positive electrode active material according to any one of claims 5 to 8, wherein the mechanical mixing and grinding method is a mechanical milling method. A method for producing a lithium secondary battery having a positive electrode layer, a negative electrode layer, and an organic electrolyte,
The positive electrode active material coating particles obtained by mixing the positive electrode active material coating particles obtained by the method for producing positive electrode active material coating particles according to any one of claims 5 to 9 and the positive electrode active material, A method for producing a lithium secondary battery, comprising a positive electrode active material preparation step of preparing the positive electrode active material having a surface thereof. A method for producing a lithium secondary battery having a positive electrode layer, a negative electrode layer, and an organic electrolyte,
After mechanically mixing the amorphous body obtained in the amorphization step of the method for producing positive electrode active material coating particles according to any one of claims 5 to 9, and the positive electrode active material The amorphous body and the positive electrode active material are heated to crystallize the amorphous body to form a crystalline electrolyte decomposition inhibitor, and the positive electrode active material coating particles are on the surface. A method for producing a lithium secondary battery, comprising a positive electrode active material preparation step of preparing a positive electrode active material.   The method of manufacturing a lithium secondary battery according to claim 11, wherein the mechanical mixing method is a mechanical milling method.

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