JP6965850B2 - Manufacturing method of positive electrode active material - Google Patents

Description

The present disclosure relates to a method for producing a positive electrode active material.

Unlike batteries that use an electrolytic solution, all-solid-state batteries have a small contact area between materials. Therefore, in order to improve the output characteristics, it is necessary to ensure the ionic conductivity between the materials. For example, a technique for forming a _{LiNbO 3} coating layer on the surface of a positive electrode active material is known for the purpose of ensuring ionic conductivity at the interface between the solid electrolyte and the positive electrode active material.

In Patent Document 1, _{when LiNbO 3} is coated on the surface of the positive electrode active material, a sol-gel solution containing the raw material of the coating layer is first applied to the positive electrode active material by the sol-gel method, and a precursor layer is formed on the surface of the positive electrode active material. There is a description that the coating step of forming and the heat treatment step of heat-treating the precursor layer are carried out.

JP-A-2015-72818

However, in the method for producing a coated positive electrode active material as disclosed in Patent Document 1, there is a problem that the lithium ion conductivity of the coated layer after heat treatment is low.
In view of the above circumstances, it is an object of the present disclosure to provide a method for producing a positive electrode active material containing a coating layer having excellent lithium ion conductivity.

The method for producing a positive electrode active material of the present disclosure, the positive electrode active material material, and a coating material comprising a coating layer comprising a coating vital LiNbO ₃ the surface of the positive electrode active material feedstock, and the absolute humidity of the exposure time and the atmosphere It is characterized by having a step of exposing to the atmosphere so that the exposure amount defined by the product of 29.3 to 880.2 (min · g / kg).

According to the present disclosure, by keeping the exposure amount within a specific range, an appropriate amount of lithium carbonate can be generated on the surface of the obtained positive electrode active material, and as a result, the output characteristics of the battery using the positive electrode active material are improved as compared with the conventional case. Can be improved.

Relationship between the exposure amount of the positive electrode active material of Examples 1 to 3 and Comparative Example 1 during production, the concentration of carbonate ions contained in the positive electrode active material, and the output of each all-solid-state battery corresponding to the positive electrode active material. It is a graph which shows.

The method for producing a positive electrode active material of the present disclosure, the positive electrode active material material, and a coating material comprising a coating layer comprising a coating vital LiNbO ₃ the surface of the positive electrode active material feedstock, and the absolute humidity of the exposure time and the atmosphere It is characterized by having a step of exposing to the atmosphere so that the exposure amount defined by the product of 29.3 to 880.2 (min · g / kg).

The present inventors have found that by properly controlling the amount exposure coated positive electrode active material material (coating material) with a covering layer containing LiNbO _3, found that the ionic conductivity of the resulting coated layer is improved bottom. It can be said that this is a new discovery that overturns the common general knowledge that the performance of the coating deteriorates due to air exposure.
The method for producing the positive electrode active material of the present disclosure is based on the above findings, and the amount of lithium carbonate produced in the coating layer is controlled by intentionally exposing the coating material to the atmosphere and then controlling the exposure amount. It is a method of obtaining a positive electrode active material that can be appropriately maintained and, as a result, can improve the output characteristics of the battery when used in the battery.

An example of a method for producing a positive electrode active material will be described below. The method for producing the positive electrode active material is not limited to the following examples.
First, a peroxo complex solution to be used for coating is prepared as follows. This peroxo complex solution becomes a raw material for the coating layer. Specifically, for example, to a mixed aqueous solution of niobium trihydrate _{(Nb 2 O 5 · 3H 2} O) and the hydrogen peroxide solution, by stirring by adding ammonia water to prepare a clear solution .. A peroxo complex solution is obtained by adding lithium hydroxide monohydrate (LiOH · H _{2 O) to this aqueous solution.}
The water content (content ratio of hydrated water) of the material niobate hydrate is not particularly limited. The amount of ammonia water added may be any amount as long as niobate is dissolved and a transparent aqueous solution is obtained. As the lithium salt, lithium nitrate, lithium sulfate and the like can be used in addition to lithium hydroxide monohydrate.

Next, using the peroxo complex solution, a coating layer containing _{LiNbO 3} is formed on the surface of the positive electrode active material raw material (coating).
The positive electrode active material raw material is not particularly limited as long as it can be used as the electrode active material of the battery. Examples of the raw material for the positive electrode active material include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), Li _{1 + x} Ni _1/3 Mn _1/3 Co _1/3 O ₂ , and lithium manganate (LiMn ₂ O _4). ), Li _{1 + x} Mn _{2- xy My} O ₄ (M is one or more metal elements selected from Al, Mg, Co, Fe, Ni, Zn). Spinel compound, lithium titanate (Li _x TiO _y ), lithium metal phosphate (LiMPO ₄ , M = Fe, Mn, Co, Ni), transition metal oxide vanadium oxide (V ₂ O ₅ ), molybdenum oxide (V 2 O 5) MoO _3), titanium sulfide _(TiS 2), carbon materials such as graphite and hard carbon (C), lithium cobalt nitride (LiCoN), lithium silicon oxide _{(Li x Si y O z)} , lithium metal (Li), or Lithium alloys (LiM, M = Sn, Si, Al, Ge, Sb, P, etc.), lithium-storable intermetallic compounds (Mg _x M, M = Sn, Ge, Sb, or _Ny Sb, N = In, Cu , Mn) and their derivatives.

A coated body is obtained by applying (coating) the above-mentioned peroxo complex solution on the surface of the positive electrode active material raw material.
The method for coating the positive electrode active material raw material with the peroxo complex solution is not particularly limited. For example, a coating method may be used in which the solvent is distilled off after immersing the positive electrode active material raw material in the peroxo complex solution, or a coating method in which the peroxo complex solution is sprayed onto the positive electrode active material raw material by a spray dryer or the like.
As an example of the coating method, a film coating method using a coating device is used, in which the procedure of spraying a liquid on the positive electrode active material raw material particles and drying the obtained coating material is repeated only once or twice or more. Can be mentioned. As a specific coating device, for example, a rolling flow coating device, a fluidized bed granulation coating device (above, manufactured by Paulec Co., Ltd.), a flow coater (; product name, manufactured by Freund Sangyo Co., Ltd.) and the like can be used.
After the coating is completed, the mixture is taken out from the coating apparatus and subjected to the next heat treatment step.

Subsequently, the covering body is subjected to heat treatment. The heat treatment conditions are not particularly limited as long as the water content in the coating can be removed.
An example of the heat treatment conditions is as follows.
・ Heat treatment equipment: Hot plate (manufactured by AS ONE)
・ Heat treatment atmosphere: Argon ・ Final temperature: 250 ℃
・ Dew point: -49 ° C
・ Heat treatment time: 45 minutes

In the present disclosure, the step of _{exposing the positive electrode active material raw material (coating body) whose surface is coated with LiNbO 3} to the atmosphere so that the exposure amount is 29.3 to 880.2 (min · g / kg). Having is one of the main features. Here, the exposure amount (min · g / kg) is a value defined by the product of the exposure time (min) and the absolute humidity (g / kg) in the atmosphere.
_{LiNbO 3 on the} surface of the coating reacts with carbon dioxide and moisture in the atmosphere upon exposure to the atmosphere, resulting in the formation of lithium carbonate. It was generally thought that the produced lithium carbonate would form a resistance layer covering the surface of the coating, and as a result, the performance of the obtained positive electrode active material might deteriorate.

However, studies made by the present inventors ventured exposed to the atmosphere the covering member, by generating an appropriate amount of lithium carbonate in the coating material, the lithium ion conductivity of the coating layer containing LiNbO ₃ is rather improved I found that. The reason is presumed to be as follows.
In the coating body exposed to the air, the positive electrode active material raw material is more likely to generate lithium carbonate than _{LiNbO 3 contained in the coating layer.} Therefore, on the surface of the positive electrode active material raw material exposed to the atmosphere at the portion of the coating layer in which LiNbO ₃ is deficient (that is, the defective portion of the coating layer), lithium carbonate is preferentially produced over the surface of the coating layer. As a result, since the defective portion of the coating layer is filled with lithium carbonate, the coating state in the coating body becomes better than the initial state. Then, in the obtained battery, deterioration of the solid electrolyte in contact with the positive electrode active material is suppressed, and it is considered that the output of the battery is improved.

The exposure is usually 29.3 to 880.2 (min · g / kg), preferably 35 to 850 (min · g / kg), more preferably 40 to 800 (min · g / kg). kg). As shown in FIG. 1 described later ^{, whether the exposure amount is less than the order of 10 1} (min · g / kg) ^{or more than the order of 10 3} (min · g / kg) is sufficient. No output is obtained. Exposure is ^{10 1 (min · g / kg} ) order or ^more, 10 3 is less than the order of (min · g / kg), in particular 29.3~880.2 (min · g / kg) The output of the obtained all-solid-state battery can be improved in the case of the exposure amount of.

As long as the above exposure amount is feasible, the mode of the exposure step is not particularly limited. As an exposure step for achieving the above exposure amount, for example, exposure of the coating material to the atmosphere at a dew point of -3 ° C. for 10 to 60 minutes can be mentioned.

The concentration of lithium carbonate in the positive electrode active material is preferably 0.10 to 0.40% by mass, more preferably 0.13 to 0.35% by mass, and further preferably 0.15 to 0. .30% by mass. As described above, by including lithium carbonate in the positive electrode active material at an appropriate content ratio, the output of the all-solid-state battery using the positive electrode active material can be improved as compared with the conventional case.
The lithium carbonate concentration in the positive electrode active material can be determined from the carbonate ion concentration measured by an ion chromatograph method using, for example, an ion chromatographic analyzer (product name: DX-500, manufactured by Nippon Dionex Corporation).

By using the positive electrode active material obtained by the above manufacturing method, for example, an all-solid-state battery can be manufactured. Examples of the configuration of the all-solid-state battery include a configuration including a positive electrode containing the positive electrode active material, a negative electrode, and a separator existing between the positive electrode and the negative electrode.

The positive electrode contains at least the above-mentioned positive electrode active material, and may further contain a solid electrolyte, a conductive material, a binder, and the like, if necessary.
The solid electrolyte used for the positive electrode is not particularly limited, and examples thereof include sulfide-based solid electrolytes such as _{Li 3} PS _4.
The binder used for the positive electrode is not particularly limited, and examples thereof include butylene rubber.
The conductive material used for the positive electrode is not particularly limited, and for example, layered carbon, vapor-grown carbon fiber (VGCF), acetylene black (AB), Ketjen black (KB), carbon nanotube (CNT), carbon nano Fiber (CNF) and the like can be mentioned. The shape of the conductive material is not particularly limited, and examples thereof include layered, granular, and fibrous.

The negative electrode contains at least the negative electrode active material, and may contain a solid electrolyte, a binder, and the like, if necessary.
As the negative electrode active material, the same material as the above-mentioned positive electrode active material raw material can be used. Regarding the type of material, there is no clear distinction between the above-mentioned positive electrode active material raw material and the negative electrode active material. By comparing the charge / discharge potentials of the two types of electrode active materials, the one showing a more noble potential is used as the raw material for the positive electrode active material, and the one showing a lower potential is used as the negative electrode active material. All-solid-state batteries can be manufactured.
The solid electrolyte and binder used for the negative electrode are the same as those materials used for the positive electrode.

The separator exists between the positive electrode and the negative electrode. Ion conduction between the positive electrode active material and the negative electrode active material occurs through the separator.
Examples of the separator include a layer containing a sulfide-based solid electrolyte such as _{Li 3} PS _4.

The all-solid-state battery can be manufactured by forming a positive electrode on one surface of the separator and forming a negative electrode on the other surface of the separator.

Hereinafter, the present disclosure will be described in more detail with reference to Examples, but the present disclosure is not limited to these Examples.

[Example 1]
1. 1. Preparation concentration of 30 wt% aqueous hydrogen peroxide solution 870.4g of production (1) peroxo complex solution of the positive electrode active material, ion-exchanged water 987.4G, and niobate trihydrate _{(Nb 2 O 5 · 3H 2} O (Nb ₂ O ₅ content 72%)) 44.2 g was added. To the obtained aqueous solution, 87.9 g of aqueous ammonia having a concentration of 28% by mass was added, and the mixture was sufficiently stirred to obtain a transparent aqueous solution.
10.1 g of lithium hydroxide monohydrate (LiOH · H ₂ O) was added to this aqueous solution to obtain a peroxo complex solution containing lithium and a niobium complex. The molar concentration of Li in this peroxo complex solution was 0.12 mol / kg, and the molar concentration of Nb was 0.12 mol / kg.

(2) Complex coating on the positive electrode active material raw material 2840 g of the above peroxo complex solution was _{sprayed on 1 kg of the positive electrode active material raw material (LiNiMnCoO 2} ) using a coating device to perform complex coating on the positive electrode active material raw material. .. The details of the operating conditions of the coating device are as follows.
-Coating device: Rolling flow coating device (Product name: MP-01, manufactured by Paulec)
・ Intake gas: Nitrogen ・ Intake temperature: 120 ° C
・ Intake air volume: 0.4m ³ / min
・ Rotor rotation speed: 400 rpm
・ Spray speed: 4.8 g / min
・ Spray time: 9.9 hours

(3) Heat treatment of the covering body After the above spraying time had elapsed, the covering body was taken out from the coating apparatus. Then, the covering body was heat-treated using a hot plate. The details of the heat treatment conditions are as follows.
・ Heat treatment equipment: Hot plate (manufactured by AS ONE)
・ Heat treatment atmosphere: Argon ・ Final temperature: 250 ℃
・ Dew point: -49 ° C
・ Heat treatment time: 45 minutes

(4) Air Exposure 10 g of the heat-treated coating material was exposed to the atmosphere for 10 minutes in an environment with a dew point of -3 ° C., and the obtained powder was used as the positive electrode active material of Example 1. The exposure amount determined by the following formula (A) was 29.3 (min · g / kg).
Equation (A)
Exposure (min · g / kg) = Exposure time (min) x Absolute atmospheric humidity (g / kg)

2. Manufacture of all-solid-state battery (1) Preparation of positive electrode The following materials were mixed to prepare a positive electrode slurry.
-Positive electrode active material of Example 1-Sulfide-based solid electrolyte: Li ₃ PS ₄
-Conductive material: VGCF (manufactured by Showa Denko) 3% by mass
-Binder: Butylene rubber (manufactured by JSR) 0.7% by mass
-Dispersion medium: heptane However, the mixing ratio of the positive electrode active material and the sulfide-based solid electrolyte was set to (positive electrode active material) :( sulfide-based solid electrolyte) = 6: 4 in terms of volume ratio.
The obtained positive electrode slurry was dispersed by an ultrasonic homogenizer and then coated on an aluminum foil. The obtained coated product was dried at 100 ° C. for 30 minutes, and then punched into a disk shape so that ^{the cross-sectional area was 1 cm 2, and this was used as a positive electrode.}

(2) Preparation of negative electrode The following materials were mixed to prepare a negative electrode slurry.
・ Negative electrode active material: Layered carbon ・ Sulfide-based solid electrolyte: Li ₃ PS ₄
-Binder: Butylene rubber 1.2% by mass
-Dispersion medium: heptane However, the mixing ratio of the negative electrode active material and the sulfide-based solid electrolyte was set to (negative electrode active material) :( sulfide-based solid electrolyte) = 6: 4 in terms of volume ratio.
The obtained negative electrode slurry was dispersed by an ultrasonic homogenizer and then coated on a copper foil. The obtained coated product was dried at 100 ° C. for 30 minutes, and then punched into a disk shape so that ^{the cross-sectional area was 1 cm 2, and this was used as a negative electrode.}

(3) Manufacture of solid-state battery Separator by adding 64.8 mg of sulfide-based solid electrolyte (Li ₃ PS ₄ ) to cylindrical ceramics (inner diameter cross-sectional area: 1 cm ² ), smoothing the surface, and pressing with 1 ton. Was formed. The above-mentioned positive electrode and negative electrode were added to both surfaces thereof, and the mixture was pressed at 4.3 ton for 1 minute. The all-solid-state battery of Example 1 was obtained by restraining both electrode surface sides of the obtained laminate by applying a pressure of 1 ton with a stainless rod.

[Example 2, Example 3 and Comparative Example 1]
The table below describes the exposure time (min) and exposure amount (min · g / kg) of the coating active material to the atmosphere in “(4) Air exposure” in “1. Production of positive electrode active material” of Example 1. The positive electrode active materials of Example 2, Example 3 and Comparative Example 1 and the all-solid-state battery were produced in the same manner as in Example 1 except that the changes were made as described in 1.

3. 3. Measurement of Carbonate Ion Concentration of Positive Electrode Active Material Ion chromatographic analyzer (product name: DX-500, manufactured by Nippon Dionex Co., Ltd.) measures the carbonate ion concentration (mass%) in the positive electrode active material of Examples 1 to 3 and Comparative Example 1. ) Was measured by an ion chromatograph method.

4. Output measurement of all-solid-state batteries The all-solid-state batteries of Examples 1 to 3 and Comparative Example 1 were charged to a voltage of 4.55 V and then discharged to 2.5 V. Then, the output of the all-solid-state battery at 3.6 V was measured by the AC impedance method.

Table 1 below shows the relationship between the atmospheric exposure conditions of the positive electrode active material of Examples 1-3 and Comparative Example 1, the carbonate ion concentration of the obtained positive electrode active material, and the output of the all-solid-state battery corresponding to the positive electrode active material. It is a table that summarizes.

5. Discussion Fig. 1 shows the exposure amount of the positive electrode active materials of Examples 1 to 3 and Comparative Example 1 during production, the concentration of carbonate ions contained in the positive electrode active material, and each all-solid-state battery corresponding to the positive electrode active material. It is a graph which shows the relationship with the output of. In FIG. 1, diamonds represent data on carbonate ion concentration (mass%) (vertical axis on the left side), and squares represent data on output (mW) (vertical axis on the right side). The curve in FIG. 1 is an approximate curve of the output data.

As is clear from FIG. 1, there is a range of exposure amounts at which the output characteristics of the battery are maximized. In order to obtain an output characteristic of 122.0 mW or more, which is higher than that of a conventional all-solid-state battery, the coating active material after heat treatment should be 29.3 (min · g / kg) or more, 880.2 (min · g / kg) or more. ) It is necessary to expose to the air so that the exposure amount is as follows.

The relationship between the exposure amount, the carbonate ion concentration, and the output of the all-solid-state battery shown in FIG. 1 can be interpreted as follows.
By the heat treatment step in the method for producing the positive electrode active material, the water contained and adhered to the covering body can be removed. As a result, in the all-solid-state battery, deterioration of the solid electrolyte in contact with the positive electrode active material is suppressed, so that the output characteristics of the all-solid-state battery are improved. Then, by _{exposing the formed LiNbO 3} layer to the atmosphere, _{the moisture in the air is adsorbed on the LiNbO 3} layer, and as a result, the moisture adsorbed portion reacts with carbon dioxide to generate lithium carbonate. In FIG. 1, the increase in the carbonate ion concentration in proportion to the exposure amount indicates an increase in the water-adsorbed portion and an increase in the reaction portion with carbon dioxide.
However, if the exposure amount is too large, the proportion of lithium carbonate in the positive electrode active material becomes too large, and the output characteristics of the resulting all-solid-state battery deteriorate. That is, if the exposure amount is too small or too large, the output characteristics of the all-solid-state battery will be lowered, so that there is a range of exposure amounts at which the output characteristics are maximized. The present disclosure reveals for the first time that exposures in the range of 29.3 (min · g / kg) or more and 880.2 (min · g / kg) or less are appropriate (FIG. 1).

Claims (1)

It is a method for producing a positive electrode active material.
The positive electrode active material material, and a coating material comprising a coating layer comprising a coating vital LiNbO ₃ the surface of the positive electrode active material material, the amount of exposure as defined by the product of the absolute humidity of the exposure time and the atmosphere 29. A method for producing a positive electrode active material, which comprises a step of exposing to the atmosphere so as to be 3 to 880.2 (min · g / kg).

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