JP2014170656A - Method for producing positive electrode active material for nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a uniform coat with a thin film thickness sufficiently preventing a contact with a nonaqueous electrolyte or a solid electrolyte and achieving favorable charge/discharge characteristics, on a surface of a lithium transition metal composite oxide particle.SOLUTION: A coat is formed on a surface of a lithium transition metal composite oxide particle by means of an atomic layer deposition method. In the formation, at least one of a precursor and a co-reactant which are introduced in each cycle of the atomic layer deposition method is made to be smaller than an amount required for forming a coat covering the entire surface of the lithium transition metal composite oxide particle.

Description

  The present invention relates to a method for producing a positive electrode active material for a non-aqueous secondary battery such as a lithium ion secondary battery. In particular, the present invention relates to a method for producing a positive electrode active material having excellent output characteristics and cycle characteristics.

  In recent years, portable devices such as VTRs, cellular phones, and notebook personal computers have been widely used and miniaturized, and non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been used for power sources. Furthermore, as environmental awareness increases, non-aqueous electrolyte secondary batteries are attracting attention as power sources for electric vehicles and the like.

As a positive electrode active material for a lithium ion secondary battery, lithium cobaltate (LiCoO ₂ ) having a layered structure is mainly put into practical use. In such a secondary battery, a 4V class battery voltage and a discharge capacity of about 160 mAh / g are realized.

  Cobalt, which is a raw material for lithium cobaltate, is a scarce resource and is unevenly distributed geographically, and therefore costs high. Moreover, anxiety arises about supply of raw materials.

In view of these circumstances, a lithium transition metal composite oxide having a layer structure such as lithium nickel cobalt manganate (Li (Ni, Co, Mn) O ₂ ) in which cobalt of lithium cobalt oxide is substituted with an element such as nickel or manganese, spinel Lithium manganate (LiMn ₂ O ₄ ) having a structure, lithium iron phosphate having an olivine structure (LiFePO ₄ ), and the like have also been developed. Each of these has advantages and disadvantages, and is selected according to the purpose.

  In various positive electrode active materials for non-aqueous electrolyte secondary batteries, techniques for coating the surfaces of positive electrode active material particles with specific compounds according to the purpose have been proposed.

  In Patent Document 1, in order to improve the uniformity of the coating layer formed on the particle surface of the lithium cobalt double oxide powder and to further improve the cycle characteristics, an aqueous solution of alumina sol is added to the lithium cobalt double oxide powder having a fluidized bed. A technique for forming an amorphous alumina coating layer by spraying and drying is proposed.

  In Patent Document 2, in order to improve the rate characteristics of the secondary battery, a technique of coating the particle surface of the lithium transition metal composite oxide with aluminum oxide or the like is proposed. A specifically disclosed coating method is to mix base positive electrode active material particles and coating material particles and mechanically combine them.

  On the other hand, there is a thin film formation technique called an atomic layer deposition (ALD) method or an atomic layer epitaxy method, and there is also a proposal for applying this technique to powder.

  Non-Patent Document 1 describes that cycle characteristics are improved by coating lithium cobalt oxide with aluminum oxide by the ALD method. However, it is also described that if the film thickness is too thick (about 1 nm or more), the electron conductivity and the discharge capacity are lowered.

  Non-Patent Document 2 describes that the cycle characteristics are improved by coating lithium-excess lithium nickel cobalt manganate with aluminum oxide as in Non-Patent Document 1. It is also described that the discharge capacity decreases when the film thickness is too thick (about 1 nm or more).

  In the ALD method conditions described in Non-Patent Documents 1 and 2, TMA (trimethylaluminum) and water vapor are added in an amount more than necessary to form a monomolecular layer in each cycle. In addition, a thin film having a thickness of about 0.1 nm per cycle is formed on the surface of the lithium transition metal composite oxide particles.

JP 2005-276454 A JP 2008-103204 A

Journal of The Electrochemical Society, 157 (1) A75-A81 (2010) Journal of The Electrochemical Society, 158 (12) A1298-A1302 (2011)

  According to the coating methods of Patent Documents 1 and 2, in order to form a film that is difficult to form or can be said to be uniform, the film thickness of the film must be increased (about 100 nm or more). Moreover, the ratio (film formation efficiency) which contributes to the film formation of an input raw material is not good. For this reason, to form a sufficiently uniform film means to reduce the lithium ion conductivity or electronic conductivity of the whole positive electrode active material. In addition, since such a coating is electrochemically inactive, a large proportion of the coating causes a reduction in charge / discharge capacity of the entire positive electrode active material.

  On the other hand, when the ALD method is used as in Non-Patent Documents 1 and 2, a thin film (about 0.2 to 0.8 nm) and a uniform film can be formed. However, when a complete monomolecular layer is formed on the particle surface in each cycle, the charge / discharge characteristics tend to deteriorate.

  The present invention has been made in view of these circumstances. An object of the present invention is to provide a method for forming a coating that can uniformly and thinly coat the surface of lithium transition metal composite oxide particles and that does not deteriorate charge / discharge characteristics.

  In order to achieve the above object, the present inventors have conducted intensive studies and have completed the present invention. The present inventors have found that the tendency of deterioration of charge / discharge characteristics is suppressed by preventing a complete monomolecular layer from being formed in each cycle of the ALD method. The production method of the present invention is a method for producing a positive electrode active material for a non-aqueous secondary battery in which a film is formed on the surface of lithium transition metal composite oxide particles by an atomic layer deposition method, which is introduced in each cycle of the atomic deposition method. It is characterized in that at least one of the precursor or the co-reactant to be produced is less than the amount necessary to form a coating covering the entire surface of the lithium transition metal composite oxide particles.

  The positive electrode active material of the present invention is obtained by the production method of the present invention.

  The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the positive electrode includes the positive electrode active material of the present invention.

  The solid electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, and a fixed electrolyte, and the positive electrode includes the positive electrode active material of the present invention.

  Since the production method of the present invention has the above characteristics, the lithium transition metal composite oxide particles have a thin film thickness, can sufficiently prevent contact with a non-aqueous electrolyte or a solid electrolyte, and have charge / discharge characteristics. Can form a good film. Therefore, the proportion of the coating film in the obtained positive electrode active material is extremely small, and the lithium ion conductivity, electronic conductivity, and charge / discharge capacity of the positive electrode active material are not impaired. In addition, the deterioration due to the non-aqueous electrolyte during charging / discharging can be prevented, or the interface resistance with the solid electrolyte can be reduced. Therefore, the nonaqueous electrolyte secondary battery using the positive electrode active material obtained by the production method of the present invention for the positive electrode has excellent cycle characteristics and output characteristics. Moreover, the solid electrolyte secondary battery using the positive electrode active material obtained by the manufacturing method of the present invention can increase the discharge current.

FIG. 1 is an example of the pressure change of each gas in the reaction vessel when the production method of the present invention is carried out. FIG. 2 is an equivalent circuit assumed in the secondary battery for evaluation in this specification. FIG. 3 is a comparison of Nyquist plots (Cole-Cole plots) before charging and discharging for non-aqueous electrolyte secondary batteries using positive electrode active materials obtained according to examples and comparative examples of the present invention. FIG. 4 is a comparison of Nyquist plots after 200 cycles for a non-aqueous electrolyte secondary battery using a positive electrode active material obtained by Examples and Comparative Examples of the present invention.

  Hereinafter, the manufacturing method of the positive electrode active material of this invention is demonstrated in detail. The production method of the present invention is called a so-called atomic layer deposition (ALD) method or an atomic layer epitaxy method. Hereinafter, the present invention may be described using terms such as the ALD method.

[Cycle of ALD method]
The ALD method cycle consists of the following four steps.
1) A precursor (or a co-reactant) is introduced into a reaction vessel and adsorbed on a sample in the reaction vessel.
2) The precursor (or co-reactant) not adsorbed on the sample is discharged from the reaction vessel.
3) A co-reactant (or precursor) is introduced into the reaction vessel to form a film on the sample surface.
4) The co-reactant (or precursor) that has not participated in the film formation is discharged from the reaction vessel.

[Introduction amount of precursor or co-reactant]
At least one of the precursor and the co-reactant is introduced in an amount smaller than the amount necessary to form a film covering the entire surface of the lithium transition metal composite oxide particles as a sample. Either one or both may be adjusted for the amount of introduction. Film formation is made on the basis of a smaller amount of introduction. In this specification, a metal-containing raw material involved in film formation is a precursor, and a metal-free raw material is a coreactant. For example, when a film of aluminum oxide is formed by a reaction between TMA (trimethylaluminum) and water vapor, TMA is used as a precursor and water vapor is used as a co-reactant.

In the ALD method, a precursor and a co-reactant (collectively referred to as a precursor or the like) are introduced using a pressure difference between a vapor pressure of the precursor or the like and a pressure in a reaction vessel. The mass m ₀ of a precursor or the like necessary for forming the entire sample surface in one cycle is represented by the following formula (1).
_{m 0 = (aρmS p r)} (M 1 / M) (1)
a: Necessary for forming 1 mole of the substance constituting the coating
Amount of precursor or co-reactant material
ρ: Density of the material constituting the coating
M: molar mass of the substance constituting the coating
M ₁ : molar mass of precursor, etc.
m: mass of lithium transition metal composite oxide particles in the reaction vessel
S _p : Specific surface area of lithium transition metal composite oxide particles
r: Lithium transition metal composite oxide particles coated on the entire surface
Film thickness when covered with a monolayer of constituent substances

On the other hand, the mass m ₁ of the precursor or the like introduced into the reaction vessel can be approximated by the following formula (2).
m ₁ = {(PV) / (RT)} M ₁ (1-exp [−kt]) (2)
P: saturated vapor pressure of precursor, etc. R: gas constant V: volume in the reaction vessel T: temperature in the reaction vessel t: introduction time k: proportionality constant The proportionality constant k has a value specific to the substance.

Since m ₁ <m ₀ suffices, the following equation (3) may be satisfied from equations (1) and (2).
P (1-exp [-kt] ) <(aρmS p r / M) (RT / V) (3)

The vapor pressure and the introduction time of the precursor or the like may be determined so as to satisfy the above formula (3), but when m ₁ / m ₀ is determined to be 0.2 or more and 0.8 or less, the state is not completely covered. Therefore, it is preferable.

  On the other hand, when at least one of the precursor and the co-reactant is set to an introduction time after the saturated vapor pressure is 10 to 100 times the stable pressure (described later) in the reaction vessel, the precursor or the co-reactant is introduced. The amount is preferred because it is easy to control.

Alternatively, when the right side of Equation (3) is P ₀ , the introduction time may be determined after setting the ratio P / P ₀ to the saturated vapor pressure P to be 2.5 or more and 50 or less.

[Stable pressure]
In each cycle of the ALD method, there is a step of exhausting the gas from the reaction vessel. However, the inert gas may be introduced simultaneously with the exhaust so that the pressure in the reaction vessel reached by the exhaust becomes substantially constant. The pressure reached by exhaust is hereinafter referred to as stable pressure. If the stable pressure is set high, such as when the saturated vapor pressure of the precursor is extremely high, it is easy to set an appropriate introduction time. The stable pressure can be adjusted by the molar flow rate of the inert gas if the conductance of the reaction vessel and the capacity of the exhaust system (such as a vacuum pump) are roughly known. The inert gas may be appropriately selected according to the purpose as long as it is a substance that does not react with a reaction vessel such as nitrogen, a sample, or a precursor.

  Hereinafter, more specific examples will be described in Examples.

Lithium transition metal composite oxide particles represented by the general formula Li _1.12 Ni _0.33 Co _0.33 Mn _0.33 W _0.005 O ₂ and having a specific surface area (S _p ) of 1.47 m ² / g (M =) 100 g is put into a reaction vessel having a volume (V) of about 13 L and sealed. After sealing, the inside of the reaction vessel is depressurized to 10 Pa or less using a vacuum pump. After decompression, nitrogen is introduced at 6.82 × 10 ⁻⁵ mol / sec, and the pressure in the reaction vessel is stabilized at about 70 Pa (stable pressure 70 Pa).

When the pressure in the reaction vessel is stabilized, the inside of the reaction vessel is adjusted to 200 ° C. On the other hand, water vapor is prepared as a co-reactant and TMA is prepared as a precursor, and the containers storing these are adjusted to 30 ° C., respectively. In formula (3), the k value of water vapor is 1.5 × 10 ⁻² sec ⁻¹ , and the k value of TMA is 1.2 × 10 ⁻² sec ⁻¹ . Further, the saturated vapor pressure of water vapor at 30 ° C. is 4.2 kPa (from Chemical Handbook Fundamentals II (edited by the Chemical Society of Japan)), and the saturated vapor pressure of TMA is about 2 kPa (from the attached materials of the reagent manufacturer).

The reaction between TMA and water vapor is 2Al (CH ₃ ) ₃ + 3H ₂ O → Al ₂ O ₃ + 3CH ₄
Therefore, a _p = 2 and a _c = 3. In addition, ρ = 4 g / cm ³ and r = 0.1 nm. By substituting these into equation (3), the value of P ₀ is about 350 Pa for TMA and about 520 Pa for water vapor. Therefore, if the TMA introduction time is shorter than about 16 seconds or the water vapor introduction time is shorter than about 9 seconds, a complete monomolecular layer is not formed on the particle surface in each cycle.

  After confirming that the temperature of each vessel containing the reaction vessel and the precursor and the co-reactant was stabilized, 1) water vapor was introduced into the reaction vessel for about 2 seconds, and 2) the gas in the reaction vessel was discharged for 60 seconds. 3) TMA is introduced into the reaction vessel for about 2 seconds, and 4) the gas in the reaction vessel is discharged for 60 seconds. Steps 1), 3) and before and after that for about 1 to 3 seconds interrupt the exhaust. In addition, the molar flow rate of nitrogen is kept constant throughout the entire cycle. FIG. 1 shows a part of changes in pressure in the reaction vessel and introduction of water vapor, TMA, and on / off of exhaust.

  After 100 cycles, the reaction vessel is allowed to cool to room temperature, nitrogen introduction and exhaust are stopped, and a sample is taken out from the reaction vessel. In this way, a positive electrode active material having an aluminum oxide film formed on the surface of the lithium transition metal composite oxide particles is obtained.

[Comparative Example 1]
The lithium transition metal composite oxide in Example 1 is used as a comparative positive electrode active material.

[Comparative Example 2]
(Sol addition method)
100 g of the lithium transition metal composite oxide in Example 1 is installed in the sample installation part in the reaction vessel. With the reaction vessel open to the outside, the flow apparatus is operated, and alumina sol with a central particle size of 30 nm and 7.2% by weight is dropped at 18 mL / min for 3 minutes, and aluminum oxide is deposited on the surface of the lithium transition metal composite oxide particles. A positive electrode active material on which a coating film is formed is obtained. The obtained positive electrode active material is heat-treated at 500 ° C. to obtain a target positive electrode active material.

A lithium transition metal composite oxide 100 g represented by the general formula Li _1.12 Ni _0.33 Co _0.33 Mn _0.33 O ₂ and having a specific surface area (S _p ) of 0.44 m ² / g is used as a sample. Otherwise, the target positive electrode active material is obtained in the same manner as in Example 1.

When the _{S p} in Example 2 into equation (3), the value of _{P 0} is about 160Pa cases of about 110 Pa, water vapor TMA. Therefore, if the TMA introduction time is shorter than about 5 seconds or the water vapor introduction time is shorter than about 3 seconds, a complete monomolecular layer is not formed on the particle surface in each cycle.

[Comparative Example 3]
The lithium transition metal composite oxide in Example 2 is used as a comparative positive electrode active material.

[Comparative Example 4]
(Sol addition method)
Lithium transition metal composite oxide particles in the same manner as in Comparative Example 2 except that 100 g of the lithium transition metal composite oxide represented by the general formula Li _1.12 Ni _0.33 Co _0.33 Mn _0.33 O ₂ was used as a sample. A positive electrode active material having an aluminum oxide film formed on the surface is obtained. The obtained positive electrode active material is heat-treated at 400 ° C. to obtain a target positive electrode active material.

[Evaluation of positive electrode active material]
The positive electrode active material is evaluated as follows.
(Elemental analysis)
Elemental analysis of the positive electrode active material is performed by ICP-AES, and elements contained in the positive electrode active material are obtained.

[Production of secondary battery]
A secondary battery for evaluation is produced in the following manner.

<Nonaqueous electrolyte secondary battery>
A non-aqueous electrolyte secondary battery is produced by the following procedure.

(Preparation of positive electrode)
A positive electrode slurry is prepared by dispersing and dissolving 85 parts by weight of a positive electrode active material powder, 5 parts by weight of acetylene black, and 5 parts by weight of PVDF (polyvinylidene fluoride) in NMP (normal methyl-2-pyrrolidone). The obtained positive electrode slurry is applied to a current collector made of aluminum foil, dried, compression-molded with a roll press, and cut into a predetermined size to obtain a positive electrode.

(Preparation of negative electrode)
A negative electrode slurry is prepared by dispersing and dissolving 97.5 parts by weight of artificial graphite, 1.5 parts by weight of CMC (carboxymethylcellulose) and 1.0 part by weight of SBR (styrene butadiene rubber) in pure water. The obtained negative electrode slurry is applied to a current collector made of copper foil, dried, compression-molded with a roll press, and cut into a predetermined size to obtain a negative electrode.

(Preparation of non-aqueous electrolyte)
EC (ethylene carbonate) and DEC (diethyl carbonate) are mixed at a volume ratio of 3: 7 to obtain a solvent. Lithium hexafluorophosphate (LiPF ₆ ) is dissolved in the obtained mixed solvent so as to have a concentration of 1 mol / L to obtain a nonaqueous electrolytic solution.

(Battery assembly)
A lead electrode is attached to each of the positive and negative electrode current collectors, and vacuum drying is performed at 120 ° C. After drying, a separator made of porous polyethylene is arranged between the positive electrode and the negative electrode, and they are stored in a bag-like laminate pack. After storage, it is vacuum-dried at 60 ° C. to remove moisture adsorbed on each member. After drying, a non-aqueous electrolyte is injected into the laminate pack, and the laminate pack is sealed to obtain a laminate-type non-aqueous electrolyte secondary battery.

<Solid electrolyte secondary battery>
A solid electrolyte secondary battery is produced by the following procedure.

(Production of solid electrolyte)
Lithium sulfide (Li ₂ S) and phosphorus pentasulfide (P ₂ S ₅ ) are weighed in a molar ratio of Li ₂ S: P ₂ S ₅ = 70: 30 under an argon atmosphere. After weighing, these are mixed in an agate mortar, and further pulverized and mixed to obtain sulfide glass. Let the obtained sulfide glass be a solid electrolyte. A part of the solid electrolyte is mixed with a positive electrode active material to form a positive electrode mixture described later.

(Preparation of positive electrode mixture)
60 parts by weight of the positive electrode active material, 36 parts by weight of the solid electrolyte, and 4 parts by weight of VGCF (vapor phase grown carbon fiber) are mixed to obtain a positive electrode mixture.

(Preparation of negative electrode)
An indium foil having a thickness of 0.05 mm is cut into a circle having a diameter of 11.00 mm to form a negative electrode.

(Battery assembly)
A cylindrical lower mold having an outer diameter of 11.00 mm is inserted into a cylindrical outer mold having an inner diameter of 11.00 mm from the lower part of the outer mold. The lower mold is fixed so that the upper end of the lower mold is positioned in the middle of the outer mold. In this state, 80 mg of solid electrolyte is charged from the upper part of the outer mold to the upper end of the lower mold. After charging, a cylindrical upper mold having an outer diameter of 11.00 mm is inserted from the upper part of the outer mold. After insertion, a pressure of 90 MPa is applied to the solid electrolyte from above the upper mold to form a solid electrolyte layer. After molding, the upper mold is pulled out from the upper part of the outer mold, and 20 mg of the positive electrode mixture is put into the upper part of the solid electrolyte layer from the upper part of the outer mold. After the addition, the upper mold is inserted again, and this time, a pressure of 360 MPa is applied to the positive electrode mixture to form a positive electrode layer. After the molding, the upper die is fixed, the lower die is released and pulled out from the lower part of the outer mold, and the negative electrode is put into the lower part of the solid electrolyte layer from the lower part of the lower mold. After the charging, the lower mold is inserted again, and the negative electrode is formed by applying a pressure of 150 MPa from below the lower mold to form a negative electrode layer. After molding, the lower die is fixed, the positive electrode terminal is attached to the upper die, and the negative electrode terminal is attached to the lower die to obtain a solid electrolyte secondary battery.

[Evaluation of battery characteristics]
The battery characteristics are evaluated in the following manner using the evaluation secondary battery.

<Nonaqueous electrolyte secondary battery>
For Example 1 and Comparative Examples 1 and 2, the DC-IR, cycle characteristics, and resistance change rate are measured below.

(DC-IR)
A weak current is passed through the evaluation secondary battery to perform aging, and the electrolyte is sufficiently blended with the positive electrode and the negative electrode. After aging, constant current discharge at several C and constant current / constant voltage charge at weak current are repeated. The charge capacity in the 10th charge is defined as the total charge capacity of the battery. After the 10th discharge, charge up to 40% of the total charge capacity. After charging, the battery is placed in a temperature-controlled thermostat and left for 6 hours. After standing, the battery is discharged at a current of 0.02 A, 0.04 A, and 0.06 A for 10 seconds each, and the voltage at that time is measured. The discharge current and the measured voltage are plotted, and the direct current resistance (DC-IR) in the battery is obtained from the absolute value of the slope of the approximate line. A low DC-IR means that the output characteristics are good. Note that DC-IR at a temperature t is R (t).

(Cycle characteristics)
A weak current is passed through the evaluation secondary battery to perform aging, and the electrolyte is sufficiently blended with the positive electrode and the negative electrode. After aging, the battery is placed in a thermostat set at 60 ° C. and left for 6 hours. After standing, constant voltage and constant voltage charging at a charging voltage of 4.2 V and a charging load of 1.0 C (current density at which discharging ends in 1 C≡1 hour), a discharging voltage of 2.75 V and a discharging load of 1.0 C Charge / discharge is repeated with one cycle of constant current discharge. 200 th cycle discharge capacity _Q d (200) ratio first cycle discharge capacity _Q d (1) of the _{(Q d (200) / Q} d (1)) and the capacity retention rate _{P sq.} High P _sq means that the cycle characteristics are good.

(Resistance change rate)
The battery before and after the cycle characteristic evaluation is connected to an AC power source, and resistance measurement is performed by the AC impedance method. The frequency of the AC power supply is changed logarithmically from 10 kHz to 0.1 Hz. The equivalent circuit is assumed as shown in FIG. 2, and the sum of the diameter of the leftmost semicircle and the diameter of the second semicircle from the left in the Nyquist plot (Cole-Cole plot) is the resistance between the electrodes (at the positive electrode / electrolyte interface). The sum of the resistance component in the impedance 22 and the resistance component in the impedance 23 at the negative electrode / electrolyte interface). If one or both ends of the semicircle is not in contact with the real axis of impedance, extrapolate to the real axis. Also, if the two semicircles cannot be clearly separated, the overlapping part of the diameter (assumed to be) is not calculated twice. The ratio (Imp (200) / Imp (1)) of the resistance Imp (200) after the cycle characteristic evaluation to the resistance Imp (1) before the evaluation is defined as a resistance change rate _Psr . Low P _sr also means good cycle characteristics.

<Solid electrolyte secondary battery>
The following characteristics are measured for Example 2 and Comparative Examples 3 and 4.

(Initial charge / discharge characteristics)
Constant current and constant voltage charging is performed at a current density of 0.185 μA / cm ² and a charging voltage of 4.0 V. After charging, constant current discharge is performed at a current density of 0.185 μA / cm ² and a discharge voltage of 1.9 V, and the discharge capacity Q _d is measured.

  With respect to Example 1 and Comparative Examples 1 and 2, the production conditions and characteristics of the positive electrode active material are shown in Table 1, and the battery characteristics of the nonaqueous electrolyte secondary battery are shown in Table 2, FIG. 3 and FIG. In Example 1 and Comparative Examples 1 and 2 and Example 1 in FIG. 4, semicircles derived from impedances 22 and 23 overlap).

  From Tables 1 and 2 and FIGS.

  Comparing Comparative Example 1 with Example 1 and Comparative Example 2, the cycle characteristics are improved in terms of capacity retention rate and resistance change rate by forming the aluminum oxide film. However, when Example 1 and Comparative Example 2 are compared, the film formation by ALD is markedly improved in terms of the resistance change rate. When DC-IR is compared, the initial output characteristics tend to be slightly lowered due to the formation of the film, but considering the rate of change in resistance, Example 1 coated with ALD is not coated or is a comparative example coated with a sol addition method. It can be said that the output characteristics are improved with respect to 1 and 2.

  Regarding Example 2 and Comparative Examples 3 and 4, the production conditions and characteristics of the positive electrode active material are shown in Table 3, and the battery characteristics of the solid electrolyte secondary battery are shown in Table 4, respectively.

  Table 3 and Table 4 show the following. The discharge capacity is increased by forming the film. This is presumably because the interface resistance between the positive electrode active material and the solid electrolyte is lowered, and the voltage drop inside the battery is suppressed. On the other hand, when Example 2 and Comparative Examples 3 and 4 are compared, it can be seen that if the coating amount is the same, the discharge capacity increases when the film is formed by ALD than when the film is formed by the sol addition method. This is presumably because the film formed by the sol addition method is non-uniform, and part of it simply decreased the electrochemical activity of the positive electrode active material and finally offset the increase in discharge capacity.

  By the production method of the present invention, a uniform film having good charge / discharge characteristics can be efficiently formed on the surface of the lithium transition metal composite oxide particles. The non-aqueous electrolyte secondary battery using the positive electrode active material thus obtained for the positive electrode has good output characteristics, cycle characteristics, and charge / discharge capacity, so it can be suitably used as a power source for electric tools, electric vehicles, etc. It is. Moreover, since the solid electrolyte secondary battery using the positive electrode active material obtained by the production method of the present invention for the positive electrode has both output characteristics and discharge capacity and does not use a non-aqueous electrolyte, It can be suitably used as a power source for electrical equipment that requires high output in a severely and thermally severe environment.

2 Equivalent circuit 21 Resistance of circuit itself 22 Impedance of positive electrode / electrolyte interface 23 Impedance of negative electrode / electrolyte interface 24 Impedance of electrolyte

Claims (7)

A method for producing a positive electrode active material for a non-aqueous secondary battery, wherein a film is formed on the surface of a lithium transition metal composite oxide particle by an atomic layer deposition method,
A production method in which at least one of a precursor or a co-reactant introduced in each cycle of the atomic deposition method is less than an amount necessary to form a film covering the entire surface of the lithium transition metal composite oxide particles.   At least one of the precursor or the co-reactant supplied in each cycle is 20% or more and 80% or less of the amount necessary to form a coating covering the entire surface of the lithium transition metal composite oxide particles. Item 2. The manufacturing method according to Item 1.   The production method according to claim 1 or 2, wherein the saturated vapor pressure of at least one of the precursor or the co-reactant is 10 times or more and 100 times or less the stable pressure in the reaction vessel. The manufacturing method as described in any one of Claims 1 thru | or 3 satisfy | filling following formula (1) when the saturated vapor pressure of the said precursor or a co-reactant is set to P.
2.5 ≦ P / P ₀ ≦ 50 (1)
_{P 0 = (aρmS p r /} M) (RT / V)
R: Gas constant
a: Necessary for forming 1 mole of the substance constituting the coating
Amount of precursor or co-reactant material
ρ: Density of the material constituting the coating
M: molar mass of the substance constituting the coating
m: mass of lithium transition metal composite oxide particles in the reaction vessel
S _p : Specific surface area of lithium transition metal composite oxide particles
r: Lithium transition metal composite oxide particles coated on the entire surface
Film thickness when covered with a monolayer of constituent substances
T: temperature in the reaction vessel
V: Volume in the reaction vessel   The positive electrode active material for non-aqueous secondary batteries obtained by the manufacturing method as described in any one of Claims 1 thru | or 4.   A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode includes the positive electrode active material according to claim 5.   A solid electrolyte secondary battery including a positive electrode, a negative electrode, and a solid electrolyte, wherein the positive electrode includes the positive electrode active material according to claim 6.

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