JP2023009668A - Coated positive electrode active material for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery including the same - Google Patents

Abstract

To increase the battery capacity and cycle-keeping rate of a nonaqueous electrolyte secondary battery.SOLUTION: A coated positive electrode active material comprises: a positive electrode active material particle; and a coating layer that coats the surface of each positive electrode active material particle. The coating layer contains LiAlF4, LiF and Li3AlF6.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a coated positive electrode active material for non-aqueous electrolyte secondary batteries and a non-aqueous electrolyte secondary battery containing the coated positive electrode active material.

As a property of non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, it is sometimes required that they can be used at a high operating voltage such as about 4.5V.
When a lithium ion secondary battery is used at such a high operating voltage, side reactions may occur between the positive electrode active material and the non-aqueous electrolyte.

This side reaction causes deterioration of battery performance, such as a decrease in battery capacity and a decrease in cycle maintenance rate, due to the formation of a resistance component at the interface between the positive electrode active material and the non-aqueous electrolyte.
Therefore, in order to reduce such side reactions, it has been considered to cover the positive electrode active material with a coating layer (Patent Document 1).

Japanese translation of PCT publication No. 2015-533257

The present invention
In order to further improve the performance of the non-aqueous electrolyte secondary battery by the coating layer, the present inventors have made extensive studies, and as a result,
The present invention was completed only after realizing that the battery capacity and the cycle retention rate can be further improved by coating the positive electrode active material with a coating layer containing a predetermined component.

That is, the coated positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention includes positive electrode active material particles and a coating layer that coats the surface of the positive electrode active material particles, and the coating layer comprises LiAlF ₄ , LiF and It is characterized by containing Li ₃ AlF ₆ .

According to such a coated positive electrode active material, the battery capacity and cycle maintenance rate of the non-aqueous electrolyte secondary battery can be further improved as compared with the case where the positive electrode active material is covered with a conventional coating layer.

It is preferable that the coating layer has a thickness of 0.6 nm or more and 9 nm or less. Moreover, it is preferable that the central position of the F1s spectrum of the coating layer observed by an X-ray photoelectron spectrometer is 685.05 eV or more and 685.60 eV or less.

The content of LiAlF ₄ in the coating layer is 30% by mass or more and 80% by mass or less, the content of LiF is 1% by mass or more and 30% by mass or less, and the content of Li ₃ AlF ₆ is 1% by mass or more. It is preferably 70% by mass or less.

If the specific surface area of the coated positive electrode active material can be increased, the charge/discharge capacity of the non-aqueous electrolyte secondary battery can be increased as much as possible. Therefore, in order to increase the specific surface area of the coated positive electrode active material, the average secondary particle size of the coated positive electrode active material is preferably 10 μm or less.

It is more preferable that the positive electrode active material has a spinel structure because it has a high resistance to use at a high voltage. It is particularly preferable that the positive electrode active material is a lithium salt of a ternary transition metal oxide represented by LiNi _x Co _y Al _z O ₂ or LiN _x Co _y Mn _z O ₂ .

The present invention also includes a non-aqueous electrolyte secondary battery containing a coated positive electrode active material having the characteristics described above.

According to the coated positive electrode active material, the battery capacity and cycle maintenance rate of the non-aqueous electrolyte secondary battery can be further improved compared to the case where the positive electrode active material is coated with a conventional coating layer.

FIG. 2 is a schematic diagram showing the coated positive electrode active material according to the present embodiment; 1 is an SEM image of a coated cathode active material according to an example of the present invention; 4 is a graph showing results of X-ray photoelectron spectroscopic analysis of a coating layer according to an example of the present invention; 4 is an image showing the distribution state of Al element and F element on the LNMO surface obtained by X-ray photoelectron spectroscopic analysis of the coating layer according to one example of the present invention.

A specific configuration of the secondary battery according to one embodiment of the present invention will be described below.
<1. Basic Configuration of Nonaqueous Electrolyte Secondary Battery>
A lithium-ion secondary battery according to this embodiment includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte.
The charge ultimate voltage (oxidation-reduction potential) of this lithium ion secondary battery is preferably, for example, 4.0 V (vs. Li/Li+) or more and 5.0 V or less, and particularly preferably 4.2 V or more and 5.0 V or less. The shape of the lithium-ion secondary battery is not particularly limited, and may be, for example, cylindrical, prismatic, laminate, button, or the like.

(1-1. Positive electrode)
The positive electrode includes a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector.
The positive electrode current collector may be any conductive material, for example, plate-like or foil-like, aluminum, stainless steel, and nickel-coated steel. etc. is preferable.
The positive electrode mixture layer contains at least the positive electrode active material 1, and may further contain a conductive agent and a positive electrode binder that binds the positive electrode active material 1 and the conductive agent onto the positive electrode current collector.

The positive electrode active material 1 used in the positive electrode mixture layer according to the present embodiment is a coated positive electrode active material 100 whose surface is covered with a coating layer 2, as shown in FIG.

The positive electrode active material 1 is, for example, a transition metal oxide or solid solution oxide containing lithium, and is not particularly limited as long as it can electrochemically occlude and release lithium ions. Examples of transition metal oxides containing lithium include Li _1.0 Ni _0.88 Co _0.1 Al _{0.01 Mg 0.01} O ₂ and the like. , _LiNiCoMn compound oxides such as _{LiNixCoyMnzO2} , _LiNiCo compound _oxides such as _LiNiO2 , or _{LiMn2O4 such} as Li.Mn-based composite oxides and the like can be exemplified. Solid solution oxides include _{LiaMnxCoyNizO2 ( 1.150≤a≤1.430} , _{0.45≤x≤0.6} , _{0.10≤y≤0.15} , 0.20 ≦z≦0.28), LiMn _1.5 Ni _0.5 O ₄ and the like. Among the materials described above, the positive electrode active material 1 is preferably a lithium salt of a ternary transition metal oxide represented by LiNi _x Co _y Al _z O ₂ or LiNi _x Co _y Mn _z O ₂ . Moreover, it is more preferable to have a spinel-type crystal structure. In addition, these compounds may be used alone, or a mixture of two or more of them may be used. Although the shape of the positive electrode active material 1 is not particularly limited, it is preferably in the form of particles.

The coating layer 2 is a feature of the non-aqueous electrolyte secondary battery according to this embodiment, and will be described later.

The conductive agent is not particularly limited as long as it enhances the conductivity of the positive electrode. Specific examples of the conductive agent include those containing one or more selected from carbon black, natural graphite, artificial graphite, and fibrous carbon.
Examples of the carbon black include furnace black, channel black, thermal black, ketjen black, and acetylene black.
Examples of the fibrous carbon include carbon nanotubes, graphene, and carbon nanofibers.
The content of the conductive agent is not particularly limited as long as it is applicable to the positive electrode mixture layer of the non-aqueous electrolyte secondary battery.

Examples of the positive electrode binder include fluorine-containing resins such as polyvinylidene fluoride, ethylene-containing resins such as styrene-butadiene rubber, and ethylene-propylene-diene terpolymers. diene terpolymer), acrylonitrile-butadiene rubber, fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, methyl cellulose, polyvinyl alcohol carboxymethyl cellulose), carboxymethyl cellulose derivatives (such as salts of carboxymethyl cellulose), nitrocellulose, and the like. The positive electrode binder is not particularly limited as long as it can bind the positive electrode active material 1 and the conductive agent onto the positive electrode current collector.

(1-2. Negative electrode)
The negative electrode includes a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector.
The negative electrode current collector may be any conductor as long as it is a conductor, for example, it is plate-shaped or foil-shaped, and may be made of copper, stainless steel, nickel-plated steel, or the like. preferable.

The negative electrode mixture layer contains at least a negative electrode active material, and may further contain a conductive agent and a negative electrode binder that binds the positive electrode active material and the conductive agent to the positive electrode current collector.

The negative electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. natural graphite coated with artificial graphite, etc.), Si-based active materials or Sn-based active materials (for example, silicon (Si) or tin (Sn) or a mixture of fine particles of their oxides and graphite active materials, silicon or tin fine particles, silicon or tin-based alloys), metallic lithium and titanium oxide compounds such as Li ₄ Ti ₅ O ₁₂ , lithium nitrides, and the like. As the negative electrode active material, one of the materials listed above may be used, or two or more of them may be used in combination. Silicon oxide is represented by SiOx (0≦x≦2).
Depending on the composition of the negative electrode active material and the negative electrode mixture layer, the negative electrode current collector described above is not necessarily an essential component.

The conductive agent is not particularly limited as long as it enhances the conductivity of the negative electrode, and for example, the same one as described in the section on the positive electrode can be used.

The negative electrode binder is not particularly limited as long as it can bind the negative electrode active material and the conductive agent onto the negative electrode current collector. For example, one similar to that described in the section on the positive electrode can be used.

(1-3. Separator)
The separator is not particularly limited, and may be of any type as long as it is used as a separator for lithium ion secondary batteries. As the separator, it is preferable to use, alone or in combination, a porous membrane, a non-woven fabric, or the like, which exhibits excellent high-rate discharge performance. Examples of the resin constituting the separator include polyolefin resins such as polyethylene and polypropylene, polyethylene terephthalate, and polybutylene terephthalate.ポリエステル（ｐｏｌｙｅｓｔｅｒ）系樹脂、ポリフッ化ビニリデン（ｐｏｌｙｖｉｎｙｌｉｄｅｎｅ ｄｉｆｌｕｏｒｉｄｅ）、フッ化ビニリデン－ヘキサフルオロプロピレン共重合体（ｖｉｎｙｌｉｄｅｎｅ ｄｉｆｌｕｏｒｉｄｅ－ｈｅｘａｆｌｕｏｒｏｐｒｏｐｙｌｅｎｅ ｃｏｐｏｌｙｍｅｒ）、フッ化ビニリデン－パーフルオロビニルエーテル共重合体（ｖｉｎｙｌｉｄｅｎｅ ｄｉｆｌｕｏｒｉｄｅ－ｐｅｒｆｌｕｏｒｏｎｉｎｙｌｅｔｈｅｒ ｃｏｐｏｌｙｍｅｒ） , vinylidene difluoride-tetrafluoroethylene copolymer, vinylidene difluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene-difluoride fluoroethylene copolymer), vinylidene fluoride-hexafluoroacetone copolymer, vinylidene difluoride-hexafluoroacetone copolymer, vinylidene difluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer propylene copolymer), vinylidene difluoride-trifluoropropylene copolymer, vinylidene difluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride copolymer -ethylene-tetrafluoroethylene copolymer (vinylidene difluoride-ethylene-tetrafluoroethylene copolymer) and the like. The porosity of the separator is not particularly limited, and any porosity of a conventional lithium ion secondary battery separator can be applied.

The surface of the separator may have a heat-resistant layer containing inorganic particles for improving heat resistance, or a layer containing an adhesive for fixing the battery element by adhering to the electrode. Examples of the aforementioned inorganic particles include Al ₂ O ₃ , AlOOH, Mg(OH) ₂ and SiO ₂ . Examples of adhesives include vinylidene fluoride-hexafluoropropylene copolymers, acid-modified vinylidene fluoride polymers, and styrene-(meth)acrylate copolymers.

(1-4. Non-aqueous electrolyte)
As the non-aqueous electrolyte, the same non-aqueous electrolyte as conventionally used in lithium ion secondary batteries can be used without particular limitation. The non-aqueous electrolyte has a composition in which an electrolyte salt is contained in a non-aqueous solvent, which is a solvent for the electrolyte. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, fluoroethylene carbonate, and vinylene carbonate. cyclic esters such as γ-butyrolactone, γ-valerolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate chain carbonates such as (ethylmethyl carbonate), chain esters such as methylformate, methylacetate, methylbutyrate, ethyl propionate, and propyl propionate , tetrahydrofuran or its derivatives, 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1 ,4-dibutoxyethane, or ethers such as methyldiglyme, ethylene glycol monopropyl ether, propylene glycol monopropyl ether , acetonitrile, nitriles such as benzonitrile, dioxolane or derivatives thereof, ethylene sulfide, sulfolane, sultone or derivatives thereof, etc. alone or Mixing and using two or more of them can be done. When two or more of the non-aqueous solvents are mixed and used, the mixing ratio of each non-aqueous solvent can be the mixing ratio used in conventional lithium ion secondary batteries.

Examples of electrolyte salts include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LIPF ₆ −x(C _n F _2n+1 )x [where 1<x<6, n=1or2], LiSCN, LiBr, LiI, inorganic ion salts containing one of lithium (Li), sodium (Na) or potassium ₍ K) such as _Li2SO4 , _Li2B10Cl10 , _NaClO4 , NaI, NaSCN, _NaBr , _KClO4 , KSCN _{; LiCF3SO3 ,} LiN _{( CF3SO2} ) ₂ , LiN _{( C2F5SO2} ) ₂ , LiN _{( CF3SO2} ) _{( C4F9SO2} ), _{LiC ( CF3SO2} ) _{3 , LiC ( C2F5SO2} ) ₃ , _{( CH3} ) _4NBF4 , _{( CH3} ) _4NBr , _{( C2H5} ) _4NClO4 , ( _{C2H5 ) 4NI} , _{( C3H7} ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (n-C ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, ( C ₂ H ₅ ) ₄ N-phtalate, lithium stearyl sulfonic acid lithium, octyl sulfonic acid lithium, lithium dodecyl benzene sulfonic acid lithium, etc. These ionic compounds can be used alone or in combination of two or more. The concentration of the electrolyte salt may be the same as that of the non-aqueous electrolyte used in conventional lithium ion secondary batteries, and is not particularly limited. In this embodiment, it is preferable to use a non-aqueous electrolytic solution containing the above-described lithium compound (electrolyte salt) at a concentration of about 0.8 mol/l or more and 1.5 mol/l or less.

Various additives may be added to the non-aqueous electrolyte. Examples of such additives include negative-acting additives, positive-acting additives, ester-based additives, carbonate-based additives, sulfate-based additives, phosphate-based additives, and borate-based additives. additives, acid anhydride-based additives, electrolyte-based additives, and the like. Any one of these may be added to the non-aqueous electrolyte, or a plurality of additives may be added to the non-aqueous electrolyte.

<2. Characteristic configuration of the non-aqueous electrolyte secondary battery according to the present embodiment>
Characteristic configurations of the non-aqueous electrolyte secondary battery according to the present embodiment will be described below.
The positive electrode active material 1 used in the non-aqueous electrolyte secondary battery according to this embodiment is the coated positive electrode active material 100 whose surface is covered with the coating layer 2 as described above.

This coating layer 2 contains LiAlF ₄ , LiF and Li ₃ AlF ₆ . In this embodiment, the coating layer 2 consists of a mixture of these LiAlF ₄ , LiF and Li ₃ AlF ₆ .

When the mass of the entire coating layer 2 is 100% by mass, the content of LiAlF ₄ in the coating layer is preferably 30% by mass or more and 80% by mass or less, and is 40% by mass or more and 65% by mass or less. is more preferred.
When the mass of the entire coating layer 2 is 100% by mass, the content of LiF in the coating layer is preferably 1% by mass or more and 30% by mass or less, and is preferably 5% by mass or more and 10% by mass or less. more preferred.
When the mass of the entire coating layer 2 is 100% by mass, the content of Li ₃ AlF ₆ in the coating layer is preferably 1% by mass or more and 70% by mass or less, and is preferably 25% by mass or more and 55% by mass or less. It is more preferable to have

The composition of the coating layer 2 can be analyzed by, for example, an X-ray photoelectron spectrometer.
Specifically, for example, the central position of the F1s spectral peak (spectral peak It is possible to calculate what kind of component is contained and how much is contained from the peak), peak area, waveform, and the like. In addition, as in the present embodiment, when LiAlF ₄ , LiF and Li ₃ AlF ₆ are each contained in the above-mentioned preferable ratio, the center position of the F1s spectrum peak is 685.05 eV or more and 685.60 eV or less. It is

The coating layer 2 may cover at least part of the surface of the positive electrode active material 1, and the coating amount of the coating layer 2 when the mass of the positive electrode active material 1 is 100% by mass is LiAlF ₄ , LiF and The Li ₃ AlF ₆ mixture as a whole is preferably 1% by mass or more and 10% by mass or less.
The thickness of the coating layer 2 is preferably 0.6 nm or more and 9 nm or less, more preferably 1 nm or more and 5 nm or less. The thickness of the coating layer 2 can be estimated, for example, by observing the cross section of the formed coating layer 2 with a transmission electron microscope (TEM).
The coating layer 2 is preferably made of a mixture of LiAlF ₄ , LiF and Li ₃ AlF ₆ as described above, but may contain a component derived from the positive electrode active material 1, for example.
The smaller the average secondary particle diameter of the coated positive electrode active material 100 is, the larger the specific surface area of the coated positive electrode active material 100 is. The larger the specific surface area of the coated positive electrode active material 100, the larger the charge/discharge capacity of the non-aqueous electrolyte secondary battery containing this coated positive electrode active material. Therefore, the average secondary particle size of the coated positive electrode active material 100 is preferably 10 μm or less. The "average particle secondary diameter" represents the number average diameter (D50) in the particle size distribution of particles obtained by a scattering method or the like, and can be measured by a particle size distribution analyzer or the like.

<3. Method for manufacturing non-aqueous electrolyte secondary battery>
Next, a method for manufacturing a lithium ion secondary battery using the coated positive electrode active material 100 described above will be described.
First, the coated positive electrode active material 100 can be manufactured by the following steps.
Reagents such as LiNO ₃ , Al(NO ₃ ) ₃ , and NH ₄ F, which are the materials of the coating layer 2, are each weighed so as to have a target composition and dissolved in water to form an aqueous solution. Particles of the positive electrode active material 1 are added to this aqueous solution, and mixed with stirring for 4 hours or more and 8 hours or less while the temperature is kept at 70° C. or more and 90° C. or less. Next, the coated positive electrode active material 100 in which the surface of the positive electrode active material 1 is covered with the coating layer 2 can be obtained by removing water from the aqueous solution by evaporation or the like and drying the dried product. It has been confirmed that almost all of the added material of the coating layer 2 added to the aqueous solution is used in the reaction to form the coating layer 2 .

A positive electrode is produced as follows. First, a positive electrode slurry is formed by dispersing a mixture of the coated positive electrode active material 100 produced as described above, a conductive agent, and a positive electrode binder in a desired ratio in a positive electrode slurry solvent. Next, this positive electrode slurry is applied onto a positive electrode current collector and dried to form a positive electrode mixture layer. In addition, the method of application is not particularly limited. Examples of coating methods include a knife coater method, a gravure coater method, a reverse roll coater, a slit die coater, and the like. The following coating steps are also performed by the same method. Then, the positive electrode material mixture layer is pressed to a desired density using a press machine. Thereby, a positive electrode is produced.

The negative electrode is also made in the same manner as the positive electrode. First, a negative electrode slurry is prepared by dispersing a mixture of materials constituting a negative electrode mixture layer in a negative electrode slurry solvent. Next, the negative electrode mixture layer is formed by applying the negative electrode slurry onto the negative electrode current collector and drying it. Next, a pressing machine is used to press the negative electrode mixture layer to a desired density. Thus, a negative electrode is produced.

Next, an electrode structure is produced by sandwiching the separator between the positive electrode and the negative electrode. Next, the electrode structure is processed into a desired shape (for example, cylindrical, rectangular, laminated, button-shaped, etc.) and inserted into a container of that shape. Next, by injecting a non-aqueous electrolyte into the container, the pores in the separator and the gaps between the positive electrode and the negative electrode are impregnated with the electrolyte. Thereby, a lithium ion secondary battery is produced.

<4. Effect of the present embodiment>
According to the coated positive electrode active material 100 described above, the battery capacity and cycle retention rate of the non-aqueous electrolyte secondary battery can be improved.
As a mechanism by which such an effect can be obtained, the following can be considered. The coating layer 2 included in the coated positive electrode active material 100 according to this embodiment is formed of a mixture containing LiAlF ₄ , LiF and Li ₃ AlF ₆ as described above. LiAlF ₄ has high ionic conductivity, Li ₃ AlF ₆ has a wide potential window, and LiF has stability and ionic conductivity. It is thought that they complement each other and produce the above-mentioned effects.

<5. Other Embodiments>
The invention is not limited to the embodiments described above.
For example, the coating layer may cover a part of the surface of the positive electrode active material particles, or may cover the entire surface.
The coated positive electrode active material according to the present invention can also be used for solid secondary batteries using solid electrolytes and all-solid secondary batteries.
In addition, the present invention is not limited to these embodiments, and it goes without saying that various modifications are possible without departing from the spirit of the present invention.

Hereinafter, the present invention will be described in more detail based on specific examples. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.
(Example 1)
<Preparation of coated positive electrode active material>
First, reagents LiNO ₃ , Al(NO ₃ ) ₃ and NH ₄ F, which are coating layer materials, were weighed so as to have the target composition shown in Table 1, and each of them was made into an aqueous solution and then mixed. LiNi _x Co _{y Mnz} O ₂ (LNMO), which is a positive electrode active material, was added to this mixed solution, and mixed with stirring at 80° C. for about 6 hours. At this time, the aqueous solution of the coating layer material was adjusted so that the ratio of the coating layer was 1% by mass when the positive electrode active material was 100% by mass. Water was evaporated from the aqueous solution to obtain a precursor, and the precursor was dried in vacuum and then calcined at 400° C. for 1 hour to obtain a coated positive electrode active material.

<Properties of coated positive electrode active material>
For the purpose of confirming the state of coating of the surface of the positive electrode active material with the coating layer, SEM and EDS observations of the coated positive electrode active material after baking were performed. As a result of observation, it was confirmed that LiAlF ₄ was present in the form of nanoparticles on the surface of the positive electrode active material LNMO. Similar XPS measurements confirmed the presence of Al and F elements on the surface of the LNMO (Fig. 4). From the above, it was confirmed that the surface of the positive electrode active material was covered with the coating layer having the desired composition. Further, from the F 1s and Al 2p spectrum analysis in the XPS measurement, the spectrum of the mixed component of _{LiAlF 4} , LiF and Li ₃ AlF ₆ was obtained from the coating layer. and Li ₃ AlF ₆ in the proportions shown in Table 1.

<Production of non-aqueous electrolyte secondary battery>
The non-aqueous electrolyte secondary battery using the coated positive electrode active material obtained as described above was evaluated by manufacturing a 2032 type coin cell using a lithium negative electrode. At that time, the positive electrode was made by mixing the above-mentioned coated positive electrode active material, Acetylene Black (AB; Denka Black, FX-35, Denka Co., Ltd.) and PolyVinylidene Fluoride (weight ratio 8:1:1), and aluminum It was made by coating on foil. The electrolyte used was 1 mol/L LiPF ₆ EC:DMC (1:1 v/v%), and a porous polypropylene membrane (Celgard 2400) was used as the separator. The coin cell was assembled in a glove box under an argon gas atmosphere.

<Evaluation of Nonaqueous Electrolyte Secondary Battery>
Using a charge/discharge measuring device (8CH Charge/Discharge Unit 10V 1A HJ 1001SM8A, HOKUTO DENKO), the charge/discharge of the non-aqueous electrolyte secondary battery prepared as described above was measured under a constant current condition of 146.5mA/g at 3.0 The non-aqueous electrolyte secondary battery was evaluated in the voltage range of V-5.0V. Table 1 shows the evaluation results. The cycle retention rate was obtained from the ratio of the discharge capacity after 100 cycles to the initial discharge capacity.

(Examples 2 and 3)
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that the coating layer material used in producing the coated positive electrode active material was weighed so as to have the target composition shown in Table 1. and evaluated. Table 1 shows the evaluation results.

(Comparative example 1)
A non-aqueous electrolyte secondary battery was produced and evaluated using the same method as in Example 1, except that the positive electrode active material was not coated at all. Table 1 shows the evaluation results.

(Comparative Examples 2-4)
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that the coating layer material used in producing the coated positive electrode active material was weighed so as to have the target composition shown in Table 1. and evaluated. Table 1 shows the evaluation results.

As shown in Table 1, when the coating layer in the coated positive electrode active material is formed from a mixed phase containing LiAlF ₄ , LiF and Li ₃ AlF ₆ , the initial discharge capacity, initial efficiency and cycle characteristics are all excellent. It was found that a water electrolyte secondary battery can be produced.
In addition, when LiAlF ₄ , LiF and Li ₃ AlF ₆ are contained, it can be confirmed that similar effects can be obtained even when the content ratio and coating amount (coating concentration) of these are varied. rice field.

(Example 4)
The same method as in Example 1, except that LiCoO ₂ (LCO) was used as the positive electrode active material, and charge/discharge evaluation was performed under a constant current condition of 137 mA/g in a voltage range of 3.0 V to 5.0 V. was used to fabricate and evaluate a non-aqueous electrolyte secondary battery. Table 2 shows the evaluation results.

(Examples 5 and 6)
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 4, except that the coating layer material used in producing the coated positive electrode active material was weighed so as to have the target composition shown in Table 2. and evaluated. Table 2 shows the evaluation results.

(Comparative Example 5)
A non-aqueous electrolyte secondary battery was produced and evaluated using the same method as in Example 4, except that the positive electrode active material was not coated at all. Table 2 shows the evaluation results.

(Comparative Examples 6 and 7)
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 4, except that the coating layer material used in producing the coated positive electrode active material was weighed so as to have the target composition shown in Table 2. and evaluated. Table 2 shows the evaluation results.

As shown in Table 2, even when the type of positive electrode active material is changed, when the coating layer in the coated positive electrode active material is formed from a mixed phase containing LiAlF ₄ , LiF and Li ₃ AlF ₆ , the first time It was found that a non-aqueous electrolyte secondary battery having excellent discharge capacity, initial efficiency and cycle characteristics could be produced.

(Example 7)
A non-aqueous electrolyte secondary battery was produced and evaluated in the same manner as in Example 4, except that the charging and discharging evaluation was performed under a constant current condition of 137 mA / g and in a voltage range of 3.0 V to 4.7 V. went. Table 3 shows the evaluation results.

(Examples 8 and 9)
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 7, except that the coating layer material used in producing the coated positive electrode active material was weighed so as to have the target composition shown in Table 3. and evaluated. Table 3 shows the evaluation results.

(Comparative Examples 8 and 9)
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 7, except that the coating layer material used in producing the coated positive electrode active material was weighed so as to have the target composition shown in Table 3. and evaluated. Table 3 shows the evaluation results.

As shown in Table 3, even when the conditions in the charge-discharge test are changed, the coating layer in the coated positive electrode active material is a non-aqueous electrolyte formed from a mixed phase containing LiAlF ₄ , LiF and Li ₃ AlF ₆ It was found that the secondary battery exhibited excellent results in all of initial discharge capacity, initial efficiency and cycle characteristics.

(Example 10)
Using the coated positive electrode active material prepared in the same manner as in Example 1 except that the coating amount of the coating layer was 2% by mass, an all-solid secondary battery was produced and evaluated by the following procedure.
<Preparation of solid electrolyte>
A solid electrolyte was synthesized by the following method. When making _Li3YCl6 as the solid electrolyte, the molar ratio of LiCl/YCl3= ₃ / ₁ was loaded into the zirconia pot using 5 mm diameter zirconia balls. This work was done in an argon-filled glove box. The mixed material was ground in a planetary ball mill at 500 rpm for 50 hours. When Li ₃ InCl ₆ was produced as a solid electrolyte, synthesis was performed in the same manner at a molar ratio of LiCl/InCl ₃ =3/1.

<Production of all-solid secondary battery>
Next, an all-solid secondary battery was produced using the coated positive electrode active material and the solid electrolyte produced as described above. As the negative electrode, a Li--In alloy formed of metallic lithium foil (200 μm thick) and indium foil (400 μm thick) was used. Li ₃ YCl ₆ was used as the solid electrolyte layer. As the positive electrode, a material obtained by mixing the coated LNMO, solid electrolyte (Li ₃ InCl ₆ ), and conductive agent (Acetylene Black (AB)) at a weight ratio of 66.5:28.5:5 was used. A test cell was obtained by stacking these positive electrode, solid electrolyte, and negative electrode and pressing with a pressure of 3 ton/cm ² .

<Evaluation of all-solid secondary battery>
The solid-state battery fabricated by the above method was measured using a charge/discharge measuring device (8CH Charge/Discharge Unit 10V 1A HJ 1001SM8A, HOKUTO DENKO) under a constant current condition of 5μA in the voltage range of 2.0V-6.0V. A charge/discharge test was performed. Table 4 shows the evaluation results. The cycle retention rate was obtained from the ratio of the discharge capacity after 10 cycles to the initial discharge capacity.

(Comparative Example 10)
A non-aqueous electrolyte secondary battery was produced and evaluated using the same method as in Example 10, except that the positive electrode active material was not coated at all. Table 4 shows the evaluation results.

As shown in Table 4, even in the case of an all-solid secondary battery, when the coating layer in the coated positive electrode active material is formed from a mixed phase containing LiAlF ₄ , LiF and Li ₃ AlF ₆ , the first time It was found that the discharge capacity, initial efficiency and cycle characteristics all gave excellent results. Further, although not described here, from the results of Examples 1 to 9 and Comparative Examples 1 to 9, Example 10, in which the coating layer contains all of LiAlF ₄ , LiF and Li ₃ AlF ₆ , has a coating layer compared to an all-solid secondary battery containing only one or two of LiAlF ₄ , LiF and Li ₃ AlF ₆ , the initial discharge capacity, initial efficiency and cycle characteristics are all excellent. I can guess.

100... Coated positive electrode active material 1... Positive electrode active material particles 2... Coating layer

Claims (8)

positive electrode active material particles;
A coating layer that coats the surface of the positive electrode active material particles,
A coated positive electrode active material, wherein the coating layer contains LiAlF ₄ , LiF and Li ₃ AlF ₆ . The coated positive electrode active material according to claim 1, wherein the coating layer has a thickness of 0.6 nm or more and 9 nm or less. 3. The coated positive electrode active material according to claim 1, having an average secondary particle size of 10 μm or less. 2. The coated positive electrode active material according to claim 1, wherein the central position of the F1s spectrum of said coating layer observed by an X-ray photoelectron spectrometer is 685.05 eV or more and 685.60 eV or less. The content of LiAlF ₄ in the coating layer is 30% by mass or more and 80% by mass or less, the content of LiF is 1% by mass or more and 30% by mass or less, and the content of Li ₃ AlF ₆ is 1% by mass or more. The coated positive electrode active material according to any one of claims 1 to 4, which is 70% by mass or less. The coated positive electrode active material according to any one of claims 1 to 5, wherein the positive electrode active material has a spinel structure. 7. The positive electrode active material is a lithium salt of a ternary transition metal oxide represented by LiNi _x Co _y Al _z O ₂ or LiNi _x Co _y Mn _z O ₂ . The coated positive electrode active material according to Item 1. A nonaqueous electrolyte secondary battery containing the coated positive electrode active material according to any one of claims 1 to 7.

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