JP7099033B2 - Method for manufacturing positive electrode active material for non-aqueous electrolyte secondary battery, positive electrode active material for non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.

In recent years, with the spread of portable electronic devices such as mobile phones and notebook computers, there is an increasing demand for small and lightweight secondary batteries having high energy density. In addition, the development of a high-output secondary battery is strongly desired as a power source for electric vehicles such as hybrid vehicles.

As a secondary battery satisfying such a requirement, there is a lithium ion secondary battery which is a kind of non-aqueous electrolyte secondary battery. A lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolytic solution, and the like, and a material capable of desorbing and inserting lithium is used as an active material used as a material for the negative electrode and the positive electrode.

Currently, research and development of such lithium-ion secondary batteries is being actively carried out. Among them, a lithium ion secondary battery using a layered or spinel type lithium metal composite oxide as a positive electrode material is being put into practical use as a battery having a high energy density because a voltage of 4V class can be obtained.

The main positive electrode active materials proposed so far are lithium cobalt composite oxide represented by lithium cobalt oxide (LiCoO ₂ ) as a layered material, and lithium nickel represented by lithium nickel oxide (LiNiO ₂ ). Examples thereof include a composite oxide and a lithium-manganese composite oxide represented by lithium manganate (LiMn ₂ O ₄ ) as a spinel-based material.

Among the main positive electrode active materials proposed so far, the lithium cobalt composite oxide is relatively easy to synthesize and has relatively excellent charge / discharge characteristics when used as the positive electrode of a lithium ion secondary battery. Since it has cycle characteristics, it is widely used mainly in portable electronic devices. However, the problem is that cobalt is expensive and the price fluctuates greatly, and lithium nickelate and lithium manganate using nickel and manganese, which are cheaper than cobalt, are attracting attention.

Lithium nickel oxide has a larger charge / discharge capacity than lithium cobalt oxide as a lithium ion secondary battery, but has a drawback that it is inferior in thermal stability and cycle characteristics to other positive electrode active materials. Therefore, a lithium-nickel composite oxide has been developed in which a part of nickel constituting lithium nickelate is replaced with another kind of element to improve thermal stability and cycle characteristics. Examples of the lithium nickel composite oxide include lithium nickel cobalt aluminum oxide (LiNi _X Coy Al ZO ₂ , x + _y + _z = 1) in which a part of nickel is replaced with cobalt and aluminum, and a part of nickel is cobalt and manganese. Examples thereof include lithium nickel cobalt manganese oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) substituted with.

By the way, the lithium nickel composite oxide is charged and discharged due to surface oxidation due to atmospheric exposure, reaction with the electrolytic solution when used for the positive electrode of a lithium ion secondary battery, and surface deterioration due to elution of metal components into the electrolytic solution. There is a problem that the capacity is reduced.

In order to solve the above problem, a positive electrode active material having a coating film placed on the surface of the lithium nickel composite oxide particles is used to suppress surface oxidation due to atmospheric exposure, reaction with the electrolytic solution, and elution of metal components into the electrolytic solution. The method is being tried.

For example, Patent Document 1 has a lithium-containing composite oxide and a coating layer that covers at least a part of the surface of the lithium-containing composite oxide, and the lithium-containing composite oxide contains Ni and the coating. A non-aqueous electrolyte II in which the layer contains a metal element M and a halogen element, wherein the metal element M contains at least one selected from the group consisting of Al, Ta, W, Zr, Nb, Sn and B. A positive electrode active material for a secondary battery is disclosed.

Further, in Patent Document 2, a composite oxide composed of a lithium-transition metal element (TM) is used as a core particle, and at least fluorine and a metal element A (A is Li, Mg, Al, Zn, are used on the particle surface of the core particle. A lithium composite compound particle powder containing a surface treatment component containing at least one element selected from Y) is disclosed. Then, as a manufacturing method thereof, an alkoxide of element A is used as a raw material of A in an aqueous suspension containing a composite oxide composed of lithium-transition metal element (TM) which is a core particle, and fluorine is contained as a neutralizing agent. After precipitating a surface treatment component containing at least element A and fluorine on the particle surface of a composite oxide composed of lithium-transition metal element (TM) using the solution of the above, the temperature is 300 to 700 ° C. under an oxygen atmosphere. A method for producing a lithium composite compound particle powder to be heat-treated in a temperature range is disclosed.

However, according to the positive electrode active material for a non-aqueous electrolyte secondary battery disclosed in Patent Document 1, it is necessary to use a corrosive gaseous metal halide in the manufacturing process, which is problematic in terms of safety. was there.

Further, in the lithium composite compound particle powder disclosed in Patent Document 2, it is necessary to mix the positive electrode active material and water in the manufacturing process, and lithium on the surface of the positive electrode active material may be eluted into water. When a non-aqueous electrolyte secondary battery is made using a substance, the charge / discharge capacity may decrease.

Japanese Unexamined Patent Publication No. 2008-251480 Japanese Unexamined Patent Publication No. 2013-232438

Therefore, the inventor of the present invention contains a hydrolyzate of a silicon compound as a positive electrode active material having a coating film that does not require a lithium nickel composite oxide to be immersed in water at the time of formation and does not use a halogen-based gas. We found a positive electrode active material with a coating film and examined it.

However, with respect to the positive electrode active material having a film containing a hydrolyzate of a silicon compound, gas generation may occur when a non-aqueous electrolyte secondary battery using the positive electrode active material is used.

Therefore, one aspect of the present invention is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery, which is used in a non-aqueous electrolyte secondary battery and can suppress the generation of gas even when repeatedly charged and discharged.

According to one aspect of the present invention in order to solve the above problems.
General formula: Li _z Ni _1-xy Co _x Al _y O _{2 + α} (in the formula, x is 0.01 ≦ x ≦ 0.20, y is 0.01 ≦ y ≦ 0.15, z is 0.90. ≦ z ≦ 1.20, α is −0.2 ≦ α ≦ 0.2), and the particles of the lithium nickel composite oxide.
It has a film containing a hydrolyzate of a silicon compound, which is arranged on at least a part of the surface of the particles of the lithium nickel composite oxide.
The silicon content is 0.01% by mass or more and 0.5% by mass or less, and the carbon content is 0.01% by mass or more and 0.5% by mass or less.
Provided is a positive electrode active material for a non-aqueous electrolyte secondary battery in which the hydrolysis rate of the silicon compound contained in the coating film is 85% or more and 100% or less.

According to one aspect of the present invention, it is possible to provide a positive electrode active material for a non-aqueous electrolyte secondary battery that can be used in a non-aqueous electrolyte secondary battery and can suppress the generation of gas even when repeatedly charged and discharged.

It is a schematic diagram of the apparatus used when forming a film on the surface of the particle of a lithium nickel composite oxide in an Example and a comparative example. It is a figure which shows the secondary particle shape of the lithium nickel composite oxide used in an Example and a comparative example. It is explanatory drawing of the cross-sectional structure of the coin-type battery produced in an Example and a comparative example.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments and does not deviate from the scope of the present invention. Can be modified and substituted in various ways.
[Positive electrode active material for non-aqueous electrolyte secondary batteries]
An example of the configuration of the positive electrode active material for the non-aqueous electrolyte secondary battery of the present embodiment will be described below.

The positive electrode active material for a non-aqueous electrolyte secondary battery of the present embodiment (hereinafter, also simply referred to as “positive electrode active material”) is a lithium nickel composite oxide particle and at least one of the surfaces of the lithium nickel composite oxide particle. It can have a film containing a hydrolyzate of a silicon compound, which is arranged in a portion.

The positive electrode active material has a silicon content of 0.01% by mass or more and 0.5% by mass or less and a carbon content of 0.01% by mass or more and 0.5% by mass or less, and the silicon contained in the coating film. The hydrolysis rate of the compound can be 85% or more and 100% or less.

The hydrolysis rate can be obtained, for example, from the following formula (A).
(Hydration rate) = [(Number of alkoxy groups contained in the silicon compound)-(Number of alkoxy groups remaining in the film)] / (Number of alkoxy groups contained in the silicon compound) × 100 ... (A) )
The film can be formed by using a silicon compound having an alkoxy group. Since the hydrolysis rate is the ratio of the alkoxy groups of the silicon compound used when forming the film to the groups that were hydrolyzed to become hydroxyl groups when forming the film, the above formula (A). ) Can be calculated.
The silicon compound is preferably an alkoxysilane compound.
The hydrolysis rate can also be obtained from the following formulas (1) and (2), for example, when the alkoxy group contained in the silicon compound used as a raw material when forming a film has the same structure.
(Hydration rate) = [(C / Si molar ratio of silicon compound)-(C / Si molar ratio of film)] / [(C / Si molar ratio of silicon compound)-(Silicon compound is completely hydrolyzed. C / Si molar ratio)] × 100 ・ ・ ・ (1)
(C / Si molar ratio of coating) = [(number of carbon moles of particles of lithium nickel composite oxide having a coating)-(number of carbon moles of particles of lithium nickel composite oxide)] / (lithium having a coating) Number of moles of silicon in particles of nickel composite oxide) ... (2)
The lithium nickel composite oxide has a general formula: Liz Ni _{1-xy Co x Aly} O _{2 + α} (in the formula, x is 0.01 ≦ x ≦ 0.20 and y is 0.01 ≦ y ≦. 0.15 and z are represented by 0.90 ≦ z ≦ 1.20, and α is represented by −0.2 ≦ α ≦ 0.2).

Here, first, the particles of the lithium nickel composite oxide contained in the positive electrode active material of the present embodiment and the coating film will be described.
(Lithium-nickel composite oxide particles)
The particles of the lithium nickel composite oxide have a general formula: Liz Ni _{1-xy Co x Aly} O _{2 + α} (in the formula, x is 0.01 ≦ x ≦ 0.20, y is 0.01 ≦ y ≦. 0.15, z contains a lithium nickel composite oxide represented by 0.90 ≦ z ≦ 1.20, α means −0.2 ≦ α ≦ 0.2). In particular, the particles of the lithium nickel composite oxide are preferably composed of the lithium nickel composite oxide.

In the above general formula of the lithium nickel composite oxide, x indicating the content of cobalt (Co) is preferably in the range of 0.01 ≦ x ≦ 0.20, and 0.03 ≦ x ≦ 0.15. It is more preferable that it is within the range of.

By setting x to 0.01 or more, the cycle characteristics of the non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as “secondary battery”) using the positive electrode active material containing the lithium nickel composite oxide are sufficiently sufficient. Can be enhanced. Further, by setting x to 0.20 or less, the charge / discharge capacity of the secondary battery using the positive electrode active material containing the lithium nickel composite oxide can be sufficiently increased.

Further, in the above general formula, y indicating the content of aluminum (Al) is preferably in the range of 0.01 ≦ y ≦ 0.15, and is in the range of 0.01 ≦ y ≦ 0.10. It is more preferable to have.

By setting y to 0.01 or more, the thermal stability of the secondary battery using the positive electrode active material containing the lithium nickel composite oxide can be sufficiently enhanced. Further, by setting y to 0.15 or less, it is possible to more reliably prevent aluminum from precipitating in the lithium nickel composite oxide without solid solution. That is, by setting y to 0.15 or less, it is possible to prevent the occurrence of different phases and sufficiently increase the charge / discharge capacity of the secondary battery using the positive electrode active material containing the lithium nickel composite oxide.

Further, in the above general formula, z indicating the content of lithium (Li) is preferably in the range of 0.90 ≦ z ≦ 1.20, and in the range of 0.95 ≦ z ≦ 1.15. It is more preferable to have. By setting z to 0.90 or more, the charge / discharge capacity of the secondary battery using the positive electrode active material containing the lithium nickel composite oxide can be sufficiently increased. Further, by setting z to 1.20 or less, the thermal stability of the secondary battery using the positive electrode active material containing the lithium nickel composite oxide can be sufficiently improved.

In the above general formula, 1-xy indicating the nickel (Ni) content is preferably in the range of 0.65 or more and 0.98 or less, and preferably in the range of 0.80 or more and 0.95 or less. It is more preferable to be inside. By setting 1-xy to 0.65 or more, the charge / discharge capacity of the secondary battery using the positive electrode active material containing the lithium nickel composite oxide can be sufficiently increased. Further, by setting 1-xy to 0.98 or less, the thermal stability of the secondary battery using the positive electrode active material containing the lithium nickel composite oxide can be sufficiently improved.

In the above general formula, with respect to oxygen, the amount of oxygen may be deficient or excessive to the extent that it does not affect the present invention. Therefore, the amount of oxygen can be expressed by 2 + α as in the above general formula, and α can be, for example, −0.2 ≦ α ≦ 0.2.

The particles of the lithium nickel composite oxide preferably include secondary particles formed by aggregating primary particles, and more preferably composed of such secondary particles.

Further, in the particles of the lithium nickel composite oxide, the average particle diameter of the secondary particles formed by aggregating the primary particles is preferably 3 μm or more and 20 μm or less, and more preferably 4 μm or more and 15 μm or less. ..

The average particle size means the particle size at an integrated value of 50% in the particle size distribution obtained by the laser diffraction / scattering method.

When the average particle size of the secondary particles of the lithium nickel composite oxide particles is 3 μm or more, the packing density of the positive electrode active material containing the lithium nickel composite oxide particles can be sufficiently increased when forming the positive electrode. It is preferable because the charge / discharge capacity of the secondary battery can be increased.

When the average particle size of the secondary particles of the lithium nickel composite oxide particles is 20 μm or less, the positive electrode active material and the electrolytic solution are used in the secondary battery using the positive electrode active material containing the lithium nickel composite oxide particles. It is preferable because a sufficient contact area can be secured and the charge / discharge capacity of the secondary battery can be increased.

The specific surface area of the lithium nickel composite oxide particles by the BET method is preferably 0.2 m ² / g or more and 1.5 m ² / g or less, and 0.3 m ² / g or more and 1.2 m ² / g or less. It is more preferable to have. This is because by setting the specific surface area to 0.2 m ² / g or more, a sufficient contact area between the positive electrode active material and the electrolytic solution can be sufficiently secured, and the battery characteristics can be particularly improved. Further, it is preferable that the temperature is 1.5 m ² / g or less because the thermal stability can be sufficiently improved.
(Coating)
The coating is located on at least a portion of the surface of the lithium nickel composite oxide particles and can contain a hydrolyzate of a silicon compound. It is more preferable that the coating film is arranged on the entire surface of the particles of the lithium nickel composite oxide.

The lithium nickel composite oxide particles preferably contain secondary particles in which primary particles are aggregated as described above. The coating is preferably arranged on at least a part of the surface of the primary particles and the secondary particles.

As described later, the film can be formed by using an organic compound containing silicon such as an alkoxysilane compound as a raw material, for example, as a silicon compound. Therefore, the coating film can contain carbon derived from the organic compound in addition to silicon. Furthermore, since the film contains a hydrolyzate of a silicon compound, it can also contain oxygen and hydrogen. Thus, the coating can contain, for example, silicon, carbon, oxygen, and hydrogen.

By arranging the film containing the hydrolyzate of the silicon compound on at least a part of the surface of the particles of the lithium nickel composite oxide in this way, surface oxidation due to atmospheric exposure, reaction with the electrolytic solution, and the electrolytic solution can be obtained. It is possible to suppress the occurrence of surface deterioration due to the elution of metal components. Therefore, in the secondary battery using the positive electrode active material of the present embodiment, the maintenance rate of the charge / discharge capacity can be increased even when the charge / discharge is repeatedly performed. That is, it is possible to obtain a secondary battery having excellent cycle characteristics.

However, according to the study of the inventor of the present invention, as described above, when a positive electrode active material having a film containing a hydrolyzate of a silicon compound is used, a secondary battery using the positive electrode active material is used. However, gas may be generated when charging and discharging are repeated. According to the study by the inventor of the present invention, the gas generation is caused by a certain percentage or more of carbon contained in the coating film.

Therefore, as described above, the film of the lithium nickel composite oxide contained in the positive electrode active material of the present embodiment contains a hydrolyzate of the silicon compound, which is the ratio of the silicon compound hydrolyzed. The hydrolysis rate of the silicon compound is preferably 85% or more and 100% or less.

By setting the hydrolysis rate of the silicon compound to 85% or more, the hydrolysis of the silicon compound used as a raw material proceeds, and the mass ratio of carbon to silicon contained in the coating film can be significantly reduced. Therefore, in a secondary battery using the positive electrode active material, it is possible to suppress the generation of gas due to carbon even when the battery is repeatedly charged and discharged, which is preferable.

Further, by increasing the hydrolysis rate to 85% or more, the denseness of the film containing the hydrolyzate of the silicon compound can be enhanced. Therefore, with respect to the positive electrode active material of the present embodiment, it is possible to particularly suppress the occurrence of surface oxidation due to atmospheric exposure, reaction with the electrolytic solution, surface deterioration due to elution of the metal component into the electrolytic solution, and the like. Further, in the secondary battery using the positive electrode active material of the present embodiment, the maintenance rate of the charge / discharge capacity can be increased even when the charge / discharge is repeatedly performed. That is, it is possible to obtain a secondary battery having excellent cycle characteristics.

Since the hydrolysis rate does not exceed the theoretical value, the upper limit can be 100%. That is, the hydrolysis rate is preferably 100% or less.

The hydrolysis rate of the silicon compound can be calculated using, for example, the following formula (A).
(Hydration rate) = [(Number of alkoxy groups contained in the silicon compound)-(Number of alkoxy groups remaining in the film)] / (Number of alkoxy groups contained in the silicon compound) × 100 ... (A) )
The number of alkoxy groups contained in the silicon compound before hydrolysis used to form the film in the formula (A) and the number of alkoxy groups in the formed film shall be determined by using various analyzers such as NMR. Can be found at.
When the alkoxy group contained in the silicon compound used as the raw material for forming the film has the same structure, the hydrolysis rate of the silicon compound is determined by using the following formulas (1) and (2). Can be calculated.

(Hydration rate) = [(C / Si molar ratio of silicon compound)-(C / Si molar ratio of film)] / [(C / Si molar ratio of silicon compound)-(Silicon compound is completely hydrolyzed. C / Si molar ratio)] × 100 ・ ・ ・ (1)
(C / Si molar ratio of coating) = [(number of carbon moles of particles of lithium nickel composite oxide having a coating)-(number of carbon moles of particles of lithium nickel composite oxide)] / (lithium having a coating) Number of moles of silicon in particles of nickel composite oxide) ... (2)
The C / Si molar ratio of the silicon compound in the formula (1) means the ratio of carbon to silicon contained in the silicon compound used as a raw material when forming a film. For example, in the case of dimethoxydimethylsilane represented by Si (OCH ₃ ) ₂ (CH ₃ ) ₂ , the C / Si molar ratio of the silicon compound is 4. When dimethoxydimethylsilane is completely hydrolyzed, that is, 100% hydrolyzed, it becomes Si (OH) ₂ (CH ₃ ) ₂ , so that the C / Si molar ratio is 2 when the silicon compound is completely hydrolyzed.

The C / Si molar ratio of the coating film in the formula (1) means the C / Si molar ratio in the coating film of the positive electrode active material actually produced, and can be calculated by the formula (2). The number of carbon moles in the film is calculated by measuring and calculating the number of carbon moles contained in the particles of the lithium nickel composite oxide before and after the film formation treatment, and the particles of the lithium nickel composite oxide having the film after the film formation treatment. It can be calculated by subtracting the number of carbon moles of the particles of the lithium nickel composite oxide before forming the film from the number of carbon moles of.

The form of the film is not particularly limited, but the lithium component (lithium hydroxide, lithium carbonate, etc.) present on the surface of the particles of the lithium nickel composite oxide and the hydroxyl group generated by the hydrolysis of the silicon compound. Is considered to have reacted to form a form having a Li—O—Si bond.

Further, the positive electrode active material of the present embodiment preferably has a silicon content of 0.01% by mass or more and 0.5% by mass or less and a carbon content of 0.01% by mass or more and 0.5% by mass or less. .. As described above, since the film of the positive electrode active material of the present embodiment contains the hydrolyzate of the silicon compound, the film of the positive electrode active material of the present embodiment can contain silicon and carbon. Therefore, by setting the silicon content to 0.01% by mass or more and the carbon content to 0.01% by mass or more, the particles of the lithium nickel composite oxide can be formed into a uniform film having a sufficient thickness. This is because it is formed on the surface of the above, which is preferable.

However, if the coating is excessively thick, the coating may inhibit the reaction of lithium intercalation / deintercalation with the lithium-nickel composite oxide, so the silicon content is 0.5% by mass or less. The carbon content is preferably 0.5% by mass or less.

According to the positive electrode active material of the present embodiment, the surface of the lithium nickel composite oxide has a film. Therefore, it is possible to suppress the occurrence of surface oxidation due to atmospheric exposure, reaction with the electrolytic solution, surface deterioration due to elution of metal components into the electrolytic solution, and the like. Therefore, in the secondary battery using the positive electrode active material of the present embodiment, the maintenance rate of the charge / discharge capacity can be increased even when the charge / discharge is repeatedly performed. That is, it is possible to obtain a secondary battery having excellent cycle characteristics.

Furthermore, by increasing the hydrolysis rate of the silicon compound calculated from the above-mentioned formula (A) or the above-mentioned formulas (1) and (2), the mass ratio of carbon to silicon contained in the coating film can be significantly increased. It has been reduced to. Therefore, in the secondary battery using the positive electrode active material of the present embodiment, it is possible to suppress the generation of gas due to carbon contained in the coating film even when the secondary battery is repeatedly charged and discharged.
[Manufacturing method of positive electrode active material for non-aqueous electrolyte secondary battery]
Next, a configuration example of a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to this embodiment will be described.

The above-mentioned positive electrode active material can be produced by the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present embodiment. Therefore, some of the items already explained will be omitted.

The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present embodiment (hereinafter, also simply referred to as “method for producing a positive electrode active material”) uses lithium nickel composite oxide particles and a silicon compound as a carrier gas. It is possible to have a film forming step of bringing the added atmospheric gas into contact with the gas. The film forming step can be carried out using a carrier gas having a carbon dioxide gas concentration of 500 ppm or less and a dew point temperature higher than −50 ° C. and 0 ° C. or lower.

The lithium nickel composite oxide has a general formula: Liz Ni _{1-xy Co x Aly} O _{2 + α} (in the formula, x is 0.01 ≦ x ≦ 0.20 and y is 0.01 ≦ y ≦. 0.15, z can be represented by 0.90 ≦ z ≦ 1.20, and α can be represented by −0.2 ≦ α ≦ 0.2).

In the film forming step, an atmospheric gas in which a silicon compound is added to a carrier gas, that is, a gas can be brought into contact with the surface of the particles of the lithium nickel composite oxide.

Since the silicon compound is hydrolyzed when forming a film, it can have an alkoxy group which is a group that produces a hydroxyl group by hydrolysis. The silicon compound is preferably an alkoxysilane compound.
The silicon compound is preferably a volatile silicon compound. The silicon compound is more preferably an alkoxysilane compound having a boiling point of 300 ° C. or lower, and further preferably an alkoxysilane compound having a boiling point of 250 ° C. or lower. It should be noted that a plurality of silicon compounds having different structures can be used at the same time.

As the silicon compound to be used, the lower limit of the boiling point is preferably 50 ° C. from the viewpoint of handleability and safety. That is, the boiling point of the silicon compound is preferably 50 ° C. or higher.

Specific examples of the silicon compound include dimethoxydimethylsilane [Si (CH ₃ ) ₂ (OCH ₃ ) ₂ ] having a boiling point of 81 ° C. and trimethoxysilane [Si (H) (OCH)) having a boiling point of 83 ° C. ₃ ) ₃ ], trimethoxymethylsilane [Si (CH ₃ ) (OCH ₃ ) ₃ ] having a boiling point of 103 ° C, tetramethyl orthosilicate (tetramethoxysilane) [Si (OCH ₃ ) ₄ ] having a boiling point of 122 ° C. ], Vinyl trimethoxysilane [Si (C ₂ H ₃ ) (OCH ₃ ) ₃ ] having a boiling point of 123 ° C., Triethoxymethyl silane [Si (CH ₃ ) (OC ₂ H ₅ ) ₃ ] having a boiling point of 143 ° C. ], Tetraethyl orthosilicate (tetraethoxysilane) [Si (OC _{2H 5 ) 4} ] having a boiling point of 165 ° C., 3-aminopropyltrimethoxysilane having a boiling point of 92 ° C. under reduced pressure, specifically at 2 kPa [ One or more selected from Si (C ₃ H ₆ NH ₂ ) (OCH ₃ ) ₃ ] and the like can be preferably used.

As the silicon compound, a material having a relatively low boiling point, that is, a material having a relatively high volatility and low toxicity can be preferably used. Specifically, one or more selected from dimethoxydimethylsilane, trimethoxysilane, trimethoxymethylsilane, vinyltrimethoxysilane, triethoxymethylsilane, tetraethyl orthosilicate (tetraethoxysilane) and the like may be more preferably used. can.

In the film forming step, as shown in FIG. 1, after installing the first storage container 11 containing the lithium nickel composite oxide particles 111 and the second storage container 12 containing the silicon compound 121 in the reaction container 10. , The carrier gas can be filled in the reaction vessel 10 and the fan 13 can be rotated as needed.

The reaction vessel 10 is preferably a highly airtight container so that the carrier gas in the reaction vessel 10 and the vapor of the silicon compound 121 do not leak to the outside. Further, the reaction vessel 10 is preferably a material that does not react with the silicon compound 121 or its vapor.

Examples of the material of the reaction vessel 10 include plastics such as polyethylene, polypropylene and Teflon (registered trademark), ceramics such as alumina, quartz and glass, stainless steel (SUS304, SUS316 and the like), metals such as titanium and the like. However, it does not have to react with the silicon compound or its vapor, and is not limited to the above materials.

It is preferable that the first storage container 11 and the second storage container 12 do not react with the particles 111 of the lithium nickel composite oxide and the silicon compound 121, respectively, and have durability. Examples of the material of the first storage container 11 and the second storage container 12 include plastics such as polyethylene, polypropylene and teflon, ceramics such as alumina, quartz and glass, metals such as stainless steel and titanium, and lithium nickel composite oxides. Can be appropriately selected depending on the type of the particles 111 and the silicon compound 121.

It is preferable that the carrier gas filled in the reaction vessel 10 does not react with the particles 111 of the lithium nickel composite oxide or the silicon compound 121. Further, since the lithium nickel composite oxide particles 111 and the silicon compound 121 generally easily react with carbon dioxide (CO ₂ ) and water (H ₂ O), it is preferable to sufficiently remove them from the carrier gas. .. However, in the positive electrode active material of the present embodiment, since it is preferable to form a film having an increased hydrolysis rate of the silicon compound, the carrier gas filled in the reaction vessel 10 when the coating step is carried out is contained in the carrier gas. , It is preferable that a certain amount of water is present.

The degree of decarbonization and dehydration treatment of the carrier gas is not particularly limited, but for example, it is preferable that the carbon dioxide gas concentration (carbon dioxide concentration) is 500 ppm or less and the dew point temperature is higher than −50 ° C. and 0 ° C. or lower.

By setting the carbon dioxide gas concentration in the carrier gas to 500 ppm or less and the dew point temperature to 0 ° C. or less, it is possible to suppress excessive reaction of lithium nickel composite oxide particles and silicon compounds with carbon dioxide and water. This is because it is possible to suppress the generation of by-products. Further, by making the dew point temperature in the carrier gas higher than −50 ° C., the hydrolysis of the silicon compound is promoted, and a film having an increased hydrolysis rate of the silicon compound can be formed.

It is more preferable that the dew point of the carrier gas is higher than −30 ° C. and 0 ° C. or lower. Further, the lower limit of the carbon dioxide gas concentration is not particularly limited because it depends on the type of carrier gas used and the like, but can be, for example, 0 ppm.

As the carrier gas for performing the film forming step, it is preferable that the carrier gas is one or more selected from dry air, nitrogen, oxygen, argon and the like that have been subjected to decarbonization treatment and dehydration treatment to a certain extent.

In particular, as the carrier gas, it is preferable to use dry air that has been subjected to decarbonization treatment and dehydration treatment to a certain extent. This is because the positive electrode active material produced by using the dry air as a carrier gas has higher electric conductivity due to the promotion of densification of the coating film as compared with the case of using an inert gas such as nitrogen or argon. Because it is possible. Therefore, when the obtained positive electrode active material is used as the positive electrode of the secondary battery, excellent charge / discharge characteristics can be obtained, which is more preferable.

Depending on the type of silicon compound, there is a risk of explosion depending on the mixing ratio of the vapor of the silicon compound and dry air, or oxidative deterioration may occur due to oxygen. In such a case, dry air may be used. Instead, it is preferable to use an inert gas such as nitrogen or argon. As described above, the carrier gas can be appropriately selected according to the type of silicon compound to be used and the like.

In the reaction vessel 10, the vapor of the silicon compound 121 diffuses into the carrier gas in the reaction vessel 10 from the second storage vessel 12 containing the silicon compound 121. That is, an atmospheric gas can be generated by adding a silicon compound to the carrier gas.

On the other hand, the vapor of the silicon compound 121 diffused in the carrier gas comes into contact with the surface of the lithium nickel composite oxide particles 111 in the first storage container 11 and is consumed for film formation. Therefore, as the reaction time elapses, the silicon compound 121 mass transfers to the lithium nickel composite oxide particles 111 stored in the first storage container 11.

Here, the amount of the film (or the thickness of the film) formed on the surface of the particles of the lithium nickel composite oxide can be controlled as follows. First, a predetermined amount of lithium nickel composite oxide particles is placed in the first storage container 11, and the silicon compound 121 in the amount of the film to be formed on the lithium nickel composite oxide particles 111 is placed in the second storage container 12. put in. After that, the desired carrier gas is filled in the reaction vessel 10, the fan 13 is rotated as needed, and the reaction is left as it is, and the reaction is terminated when the silicon compound 121 in the second storage vessel 12 completely disappears. Just do it.

As a method of controlling the amount (or coating thickness) of the coating film different from the above, first, the silicon compound 121 in excess of the amount of the coating film desired to be formed for the particles of the lithium nickel composite oxide is placed in the second storage container 12. put in. Next, the carrier gas was filled in the reaction vessel 10 and left as it was while rotating the fan 13 as needed, and after a lapse of a predetermined time, the silicon compound was stored with a part of the silicon compound remaining. 2 The storage container 12 may be taken out from the reaction container 10 to terminate the reaction.

The method for producing a positive electrode active material of the present embodiment may further have an arbitrary step.

For example, it is also possible to have a heat treatment step of performing a heat treatment after the film forming step.

A configuration example of the heat treatment process will be described below.

In the heat treatment step, if necessary, the positive electrode active material obtained in the film forming step can be heat-treated to enhance the crystallinity of the film formed on the surface of the particles of the lithium nickel composite oxide.

The heat treatment temperature in the heat treatment step is not particularly limited, and is preferably 100 ° C. or higher and 500 ° C. or lower, and more preferably 150 ° C. or higher and 300 ° C. or lower.

Further, in the heat treatment step, in order to prevent deterioration of the particles of the lithium nickel composite oxide, it is preferable to use an atmospheric gas in which carbon dioxide gas and water content have been reduced or removed. For example, the atmosphere gas includes dry air and oxygen. If an inert gas such as nitrogen or argon is used as the atmosphere gas, the particles of the lithium nickel composite oxide may be reduced and the battery characteristics may deteriorate. Therefore, an oxidizing atmosphere, for example, oxygen as described above is contained. It is preferable to use an atmosphere that produces oxygen.

By performing the heat treatment step, the crystallinity of the film formed on the surface of the particles of the lithium nickel composite oxide may be enhanced, or impurities such as excess organic components and trace moisture may be removed from the film.

According to the method for producing a positive electrode active material of the present embodiment, a simple method of contacting an atmospheric gas in which a silicon compound is added to a carrier gas with the surface of particles of a lithium nickel composite oxide to form a film is used, so that the value is low. It can be manufactured at a cost. Further, since it is not necessary to immerse the lithium nickel composite oxide in water, it is possible to prevent performance deterioration such as a decrease in charge / discharge capacity due to elution of lithium ions.
[Non-aqueous electrolyte secondary battery]
Next, a configuration example of the non-aqueous electrolyte secondary battery of the present embodiment will be described.

The secondary battery of the present embodiment may have a configuration including a positive electrode using the positive electrode active material described above, a negative electrode, a separator, and a non-aqueous electrolyte.

Each member of the secondary battery of this embodiment will be described. The embodiments described below are merely examples, and the non-aqueous electrolyte secondary battery of the present invention may be modified in various ways based on the embodiments described in the present specification based on the knowledge of those skilled in the art. , Can be carried out in an improved form. Further, the use of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited.
[Positive electrode]
The positive electrode is a sheet-shaped member, and for example, a positive electrode mixture paste containing the above-mentioned positive electrode active material can be applied to the surface of a current collector made of aluminum foil and dried. Further, the positive electrode can also be formed by molding a positive electrode mixture. The positive electrode is appropriately processed according to the battery used. For example, it is possible to perform a cutting process for forming the battery into an appropriate size according to the target battery, a pressure compression process using a roll press or the like in order to increase the electrode density, and the like.

The above-mentioned positive electrode mixture paste can be formed by adding a solvent to the positive electrode mixture, if necessary, and kneading the paste. Then, the positive electrode mixture can be formed by mixing the above-mentioned positive electrode active material in powder form, the conductive material, and the binder.

The conductive material is added to give appropriate conductivity to the electrode. The material of the conductive material is not particularly limited, and for example, graphite such as natural graphite, artificial graphite and expanded graphite, and carbon black materials such as acetylene black and Ketjen black (registered trademark) can be used.

The binder serves to hold the positive electrode active material together. The binder used for the positive electrode mixture is not particularly limited, and for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylenepropylenediene rubber, styrene-butadiene, cellulose resin, and polyacrylic. One or more types selected from acids and the like can be used.

Activated carbon or the like can also be added to the positive electrode mixture. By adding activated carbon or the like to the positive electrode mixture, the electric double layer capacity of the positive electrode can be increased.

The solvent has a function of dissolving the binder and dispersing the positive electrode active material, the conductive material, activated carbon and the like in the binder. The solvent is not particularly limited, but an organic solvent such as N-methyl-2-pyrrolidone can be used.

Further, the mixing ratio of each substance in the positive electrode mixture paste is not particularly limited, and can be, for example, the same as in the case of the positive electrode of a general non-aqueous electrolyte secondary battery. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 parts by mass or more and 95 parts by mass or less, and the content of the conductive material is 1 part by mass or more and 20 parts by mass or less. The content of the binder can be 1 part by mass or more and 20 parts by mass or less.

However, the method for producing the positive electrode is not limited to the above-mentioned example, and other methods may be used. For example, it can be manufactured by press-molding a positive electrode mixture and then drying it in a vacuum atmosphere.
[Negative electrode]
The negative electrode is a sheet-like member formed by applying a negative electrode mixture paste to the surface of a metal leaf current collector such as copper and drying it. Further, the negative electrode may be a sheet-like member made of a lithium-containing substance such as metallic lithium.

When the negative electrode is manufactured using the negative electrode mixture paste, the negative electrode is formed by substantially the same method as the above-mentioned positive electrode, although the components constituting the negative electrode mixture paste, their composition, the material of the current collector, etc. are different. Similar to the positive electrode, various treatments are performed as needed.

The negative electrode mixture paste can be prepared by adding an appropriate solvent to the negative electrode mixture, which is a mixture of the negative electrode active material and the binder, to form a paste.

As the negative electrode active material, for example, a substance containing lithium such as metallic lithium or a lithium alloy, or a storage substance capable of storing and desorbing lithium ions can be adopted.

The storage substance is not particularly limited, but one or more selected from, for example, a calcined body of an organic compound such as natural graphite, artificial graphite, and phenol resin, and a powdery body of a carbon substance such as coke can be used.

When such an occlusion substance is adopted as the negative electrode active material, a fluororesin such as PVDF can be used as the binder as in the case of the positive electrode, and the solvent for dispersing the negative electrode active material in the binder can be used. An organic solvent such as N-methyl-2-pyrrolidone can be used.
[Separator]
The separator is arranged so as to be sandwiched between the positive electrode and the negative electrode, and has a function of separating the positive electrode and the negative electrode and holding an electrolyte.

As the material of the separator, a thin film such as polyethylene or polypropylene, which has a large number of fine pores, can be used, but is not particularly limited as long as it has the above-mentioned function.
[Non-aqueous electrolyte]
The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.

Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate; and chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate; further, tetrahydrofuran and 2-. Ether compounds such as methyl tetrahydrofuran and dimethoxyethane; sulfur compounds such as ethylmethyl sulfone and butane sulton; phosphorus compounds such as triethyl phosphate and trioctyl phosphate are used alone or in combination of two or more. be able to.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and a composite salt thereof can be used.

The non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, or the like in order to improve the battery characteristics.

Next, an example of arrangement and configuration of the members of the secondary battery of the present embodiment will be described.

The secondary battery of the present embodiment composed of the positive electrode, the negative electrode, the separator and the non-aqueous electrolyte described above can have various shapes such as a cylindrical shape and a laminated shape. Regardless of the shape, the positive electrode and the negative electrode can be laminated via a separator to form an electrode body, and the obtained electrode body can be impregnated with a non-aqueous electrolyte. Then, the positive electrode current collector and the positive electrode terminal leading to the outside and the negative electrode current collector and the negative electrode terminal leading to the outside are connected by using a current collector lead or the like, and sealed in a battery case. It can be a secondary battery.
Further, although the description has been made here using an example using a liquid non-aqueous electrolyte, the secondary battery of the present embodiment is not limited to such an embodiment, and for example, a secondary battery using a solid non-aqueous electrolyte is used. That is, it can also be an all-solid-state battery. In the case of an all-solid-state battery, the configurations other than the positive electrode active material can be changed as needed.

The secondary battery of the present embodiment using the above-mentioned positive electrode active material uses the above-mentioned lithium nickel composite oxide having a coating film on the surface as the positive electrode active material. Therefore, it is possible to obtain a secondary battery having excellent cycle characteristics, and it is possible to obtain a secondary battery having improved safety because the generation of gas during charging / discharging can be particularly suppressed.

Hereinafter, the present invention will be specifically described with reference to Examples. However, the present invention is not limited to the following examples.
[Example 1]
A lithium nickel composite oxide represented by Li _1.03 Ni _0.88 Co _0.09 Al _0.03 O ₂ was used. A scanning electron microscope (SEM) photograph of the particles of the lithium nickel composite oxide is shown in FIG.

As shown in FIG. 2, the particles of the lithium nickel composite oxide used are composed of secondary particles composed of aggregated primary particles, and the average particle size of the secondary particles determined by the laser diffraction scattering method is 12 μm. The specific surface area measured by the BET method was 0.33 m ² / g.
[Film formation process]
As shown in FIG. 1, 504.6 g of the above-mentioned lithium nickel composite oxide is placed in the first storage container 11 and placed in the reaction vessel 10, and then dimethoxydimethylsilane [Si (OCH ₃ ) ₂ ( CH ₃ ) ₂ ] A second storage container 12 containing 12.6 g was placed in the reaction container 10.

Next, after filling the reaction vessel 10 with measuring air (carbon dioxide gas concentration 440 ppm, dew point temperature -23 ° C.) which is dry air as the carrier gas, the air temperature in the reaction vessel 10 is stirred by the fan 13 at room temperature (at room temperature). It was left at 25 ° C.). As a result, a film forming step was carried out in which a gas containing a silicon compound dimethoxydimethylsilane was brought into contact with the surface of the particles of the lithium nickel composite oxide to obtain a positive electrode active material having a film according to Example 1.

When the obtained positive electrode active material was quantitatively analyzed by ICP emission spectrometry, it was confirmed that 0.08% by mass of silicon (Si) derived from the dimethoxydimethylsilane component was contained.

Further, when the positive electrode active material for the non-aqueous electrolyte secondary battery was quantitatively analyzed by high frequency combustion infrared spectroscopy, it was confirmed that carbon (C) was contained in an amount of 0.16% by mass.
[Battery characteristic evaluation]
A coin-type battery using the obtained positive electrode active material as the positive electrode was produced, and the charge / discharge characteristics were evaluated.

Specifically, a 2032 type coin-type battery 30 (hereinafter referred to as “coin-type battery”) shown in FIG. 3 was produced and evaluated.

The coin-type battery 30 is composed of a case 31 and an electrode 32 housed in the case 31.

The case 31 has a positive electrode can 311 that is hollow and has one end opened, and a negative electrode can 312 that is arranged in the opening of the positive electrode can 311. , A space for accommodating the electrode 32 is formed between the negative electrode can 312 and the positive electrode can 311.

Further, the electrode 32 is composed of a positive electrode 321 and a separator 322 and a negative electrode 323, and is laminated so as to be arranged in this order. The positive electrode 32 contacts the inner surface of the positive electrode can 311 and the negative electrode 323 is on the inner surface of the negative electrode can 312. It is housed in the case 31 so as to come into contact with it. The case 31 is provided with a gasket 313, and the gasket 313 fixes the relative movement between the positive electrode can 311 and the negative electrode can 312 so as to maintain a non-contact state.

Further, the gasket 313 also has a function of sealing the gap between the positive electrode can 311 and the negative electrode can 312 to airtightly block the space between the inside and the outside of the case 31.

Such a coin-type battery 30 was manufactured as follows.

First, 52.5 mg of the obtained positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene (PTFE) resin are mixed, press-molded, and thin-filmed to a weight of about 10 mg with a diameter of 10 mm. A positive electrode 321 was prepared and dried in a vacuum dryer at 120 ° C. for 12 hours.

Next, using the positive electrode 321, a coin-type battery 30 was manufactured in a glove box having an Ar atmosphere in which the dew point was controlled to −80 ° C. At this time, as the negative electrode 323, a lithium foil punched into a disk shape having a diameter of 14 mm was used.

The separator 322 is a polyethylene porous membrane having a thickness of 25 μm, and the electrolytic solution is a 3: 7 mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiPF ₆ as a supporting electrolyte (Tomiyama Pure Chemical Industries, Ltd.). (Manufactured by Kogyo Co., Ltd.) was used.

Then, the coin-type battery is evaluated by charging it to a cutoff voltage of 4.3 V and then discharging it to a cutoff voltage of 3.0 V, with the C rate, which is the ratio of the charge / discharge current value to the battery capacity, to 0.05 C. As a result, the charge capacity was 220 mAh / g and the discharge capacity was 198 mAh / g. The positive electrode resistance measured by the AC impedance method was 2.2Ω.

No swelling was observed in the coin-type battery even after repeated charging and discharging, and no gas generation was observed.
[Example 2]
Examples except that 485.1 g of the same lithium nickel composite oxide as in Example 1 and 12.5 g of trimethoxymethylsilane [Si (OCH ₃ ) ₃ (CH ₃ )] as a silicon compound were used in the film forming step. In the same manner as in No. 1, a positive electrode active material according to Example 2 was obtained.

When the obtained positive electrode active material was quantitatively analyzed by ICP emission spectrometry, it was confirmed that silicon (Si) derived from the trimethoxymethylsilane component was contained in an amount of 0.34% by mass.

Further, when the obtained positive electrode active material was quantitatively analyzed by high frequency combustion infrared spectroscopy, it was confirmed that carbon (C) was contained in an amount of 0.26% by mass.

Further, a coin-type battery was produced and evaluated in the same manner as in Example 1 except that the positive electrode active material produced in this example was used.

As a result, the charge capacity was 223 mAh / g and the discharge capacity was 194 mAh / g. The positive electrode resistance measured by the AC impedance method was 3.6 Ω.

No swelling was observed in the coin-type battery even after repeated charging and discharging, and no gas generation was observed.
[Example 3]
Same as Example 1 except that 509.6 g of the same lithium nickel composite oxide as in Example 1 and 12.5 g of tetraethyl orthosilicate [Si (OC ₂ H ₅ ) ₄ ] as a silicon compound were used in the film forming step. The positive electrode active material according to Example 3 was obtained.

When the obtained positive electrode active material was quantitatively analyzed by ICP emission spectrometry, it was confirmed that silicon (Si) derived from the tetraethyl orthosilicate component was contained in an amount of 0.31% by mass.

Further, when the obtained positive electrode active material was quantitatively analyzed by high frequency combustion infrared spectroscopy, it was confirmed that carbon (C) was contained in an amount of 0.22% by mass.

Further, a coin-type battery was produced and evaluated in the same manner as in Example 1 except that the positive electrode active material produced in this example was used.

As a result, the charge capacity was 222 mAh / g and the discharge capacity was 200 mAh / g. The positive electrode resistance measured by the AC impedance method was 3.3 Ω.

No swelling was observed in the coin-type battery even after repeated charging and discharging, and no gas generation was observed.
[Comparative Example 1]
In the film forming step, 496.8 g of the same lithium nickel composite oxide as in Example 1, 12.8 g of dimethoxydimethylsilane [Si (OCH ₃ ) ₂ (CH ₃ ) ₂ ] as the silicon compound was used, and nitrogen gas was used as the carrier gas. The positive electrode active material according to Comparative Example 1 was obtained in the same manner as in Example 1 except that (carbon dioxide gas concentration 0 ppm, dew point temperature −50 ° C. or lower) was used.

When the obtained positive electrode active material was quantitatively analyzed by ICP emission spectrometry, it was confirmed that 0.05% by mass of silicon (Si) derived from the dimethoxydimethylsilane component was contained.

Further, when the obtained positive electrode active material was quantitatively analyzed by high frequency combustion infrared spectroscopy, it was confirmed that carbon (C) was contained in an amount of 0.15% by mass.

Further, a coin-type battery was produced and evaluated in the same manner as in Example 1 except that the positive electrode active material produced in this comparative example was used.

As a result, the charge capacity was 222 mAh / g and the discharge capacity was 199 mAh / g. The positive electrode resistance measured by the AC impedance method was 2.2Ω.
[Comparative Example 2]
In the film forming step, 447.5 g of the same lithium nickel composite oxide as in Example 1, 12.6 g of trimethoxymethylsilane [Si (OCH ₃ ) ₃ (CH ₃ )] as a silicon compound was used, and nitrogen gas was used as a carrier gas. The positive electrode active material according to Comparative Example 2 was obtained in the same manner as in Example 1 except that (carbon dioxide gas concentration 0 ppm, dew point temperature −50 ° C. or lower) was used.

When the obtained positive electrode active material was quantitatively analyzed by ICP emission spectrometry, it was confirmed that 0.26% by mass of silicon (Si) derived from the trimethoxymethylsilane component was contained.

Further, when the obtained positive electrode active material was quantitatively analyzed by high frequency combustion infrared spectroscopy, it was confirmed that carbon (C) was contained in an amount of 0.26% by mass.

Further, a coin-type battery was produced and evaluated in the same manner as in Example 1 except that the positive electrode active material produced in this comparative example was used.

As a result, the charge capacity was 222 mAh / g and the discharge capacity was 194 mAh / g. The positive electrode resistance measured by the AC impedance method was 3.1 Ω.
[Comparative Example 3]
In the film forming step, 499.6 g of the same lithium nickel composite oxide as in Example 1, 12.6 g of tetraethyl orthosilicate [Si (OC ₂ H ₅ ) ₄ ] as a silicon compound was used, and nitrogen gas (carbon dioxide gas) was used as a carrier gas. The positive electrode active material according to Comparative Example 3 was obtained in the same manner as in Example 1 except that the concentration was 0 ppm and the dew point temperature was −50 ° C. or lower).

When the obtained positive electrode active material was quantitatively analyzed by ICP emission spectrometry, it was confirmed that 0.13% by mass of silicon (Si) derived from the tetraethyl orthosilicate component was contained.

Further, when the obtained positive electrode active material was quantitatively analyzed by high frequency combustion infrared spectroscopy, it was confirmed that carbon (C) was contained in an amount of 0.18% by mass.

Further, a coin-type battery was produced and evaluated in the same manner as in Example 1 except that the positive electrode active material produced in this comparative example was used.

As a result, the charge capacity was 225 mAh / g and the discharge capacity was 201 mAh / g. The positive electrode resistance measured by the AC impedance method was 2.9Ω.
[Comparative Example 4]
The positive electrode active material according to Comparative Example 4 was produced in the same manner as in Example 1 except that the film forming step was not carried out.

Therefore, in the obtained positive electrode active material, the surface of the particles of the lithium nickel composite oxide has not been subjected to the film forming treatment, and no film has been formed on the surface.

When the positive electrode active material was quantitatively analyzed by ICP emission spectrometry, it was confirmed that the content of silicon (Si) was less than 0.02% by mass (the lower limit of detection).

Further, when the positive electrode active material was quantitatively analyzed by high frequency combustion infrared spectroscopy, it was confirmed that carbon (C) was contained in an amount of 0.09% by mass.

Further, a coin-type battery was produced and evaluated in the same manner as in Example 1 except that the positive electrode active material produced in this comparative example was used.

As a result, the charge capacity was 230 mAh / g and the discharge capacity was 206 mAh / g. The positive electrode resistance measured by the AC impedance method was 2.4Ω.
[Hydrolysis rate of silicon compounds]
Regarding the positive electrode active materials obtained in Examples 1 to 3 and Comparative Examples 1 to 3, the hydrolysis rate (%) of the silicon compound by the film forming treatment is described above from the analytical values of silicon (Si) and carbon (C). It was calculated by the equations (1) and (2).

[(Number of carbon moles of lithium nickel composite oxide particles having a coating)-(Carbon moles of lithium nickel composite oxide particles) when calculating (C / Si molar ratio of coating) in equation (2) Number)] is the carbon amount (C analysis value of each Example and Comparative Example) of the positive electrode active material obtained after the film forming treatment in each Example and Comparative Example, and the carbon amount before the film forming treatment (C analysis value). The value obtained by dividing the value obtained by subtracting the C analysis value of Comparative Example 4) by the atomic weight of carbon was used.

For example, in the case of Example 1, the carbon content after the film forming treatment is 0.16% by mass, and the carbon content before the film forming treatment of Comparative Example 4 is 0.09% by mass. , The amount of carbon contained in the coating film is 0.07% by mass. Then, the calculated amount of 0.07% by mass of carbon contained in the film was divided by the atomic weight of carbon, and the particles in the formula (2) in Example 1 were [(particles of lithium nickel composite oxide having a film). (Number of carbon moles of lithium nickel composite oxide particles)-(number of carbon moles of particles of lithium nickel composite oxide)].

Further, as (the number of silicon moles of the particles of the lithium nickel composite oxide having a coating) in the formula (2), the Si analysis values of each Example and Comparative Example were divided by the atomic weight of silicon.

The results of the calculated hydrolysis rate are also shown in Table 1.

実施例１～３は炭酸ガス濃度が５００ｐｐｍ以下であり、かつ露点温度が－５０℃より高く０℃以下のキャリアガスを用い、被膜形成工程を実施した。

In Examples 1 to 3, a film forming step was carried out using a carrier gas having a carbon dioxide gas concentration of 500 ppm or less and a dew point temperature higher than −50 ° C. and 0 ° C. or lower.

On the other hand, in Comparative Examples 1 to 3, the film forming step was carried out using a carrier gas having a carbon dioxide gas concentration of 0 ppm and a dew point temperature of −50 ° C. or lower.

As a result, the hydrolysis rate of the silicon compound contained in the coating film of the positive electrode active material obtained in Examples 1 to 3 is higher than the hydrolysis rate of the silicon compound contained in the coating film of the positive electrode active material of Comparative Examples 1 to 3. It was confirmed that it was getting higher.

Therefore, when Example 1 and Comparative Example 1 in which the same silicon compound is used when forming the film are compared, Example 1 and Comparative Example 1 have a mass ratio of C / Si (carbon / silicon) of 2.00, respectively. , 3.00, and it was confirmed that the value in Example 1 was lower. That is, in Example 1, the mass ratio of carbon in the coating film is suppressed, and in the secondary battery using the positive electrode active material of Example 1, gas is generated even when charging and discharging are repeated. I was able to suppress it.

The same tendency was observed when Example 2 and Comparative Example 2 and Example 3 and Comparative Example 3 were compared using the same silicon compound when forming the film.

Further, when a secondary battery using a positive electrode active material is repeatedly charged and discharged as described above, gas may be generated due to a certain percentage or more of carbon in the coating film. Therefore, by reducing the mass ratio of carbon in the coating film, the generation of such gas is suppressed, and the safety as a secondary battery is improved. The coating contributes to the suppression of surface oxidation due to atmospheric exposure, and when used for the positive electrode of a lithium ion secondary battery, it can suppress surface deterioration due to the reaction with the electrolytic solution, further suppresses the amount of gas generated, and has cycle characteristics. Contributes to the improvement of

Further, comparing Examples 1 to 3 with Comparative Example 4, the positive electrode active materials of Examples 1 to 3 in which a film was formed on the surface of the particles of the lithium nickel composite oxide had no film formed in Comparative Example 4. It can be confirmed that the charge / discharge capacity and the positive electrode resistance are about the same as those of the positive electrode active material of. Therefore, it was also confirmed that the film was formed without significantly impairing the battery characteristics.

Claims (5)

General formula: Li _z Ni _1-xy Co _x Al _y O _{2 + α} (in the formula, x is 0.01 ≦ x ≦ 0.20, y is 0.01 ≦ y ≦ 0.15, z is 0.90. ≦ z ≦ 1.20, α is −0.2 ≦ α ≦ 0.2), and the particles of the lithium nickel composite oxide.
It has a film containing a hydrolyzate of a silicon compound, which is arranged on at least a part of the surface of the particles of the lithium nickel composite oxide.
The silicon content is 0.01% by mass or more and 0.5% by mass or less, and the carbon content is 0.01% by mass or more and 0.5% by mass or less.
A positive electrode active material for a non-aqueous electrolyte secondary battery in which the hydrolysis rate of the silicon compound contained in the coating film is 85% or more and 100% or less. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the hydrolysis rate is determined from the formula (A).
(Hydration rate) = [(Number of alkoxy groups contained in the silicon compound)-(Number of alkoxy groups remaining in the film)] / (Number of alkoxy groups contained in the silicon compound) × 100 ... (A) ) The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the hydrolysis rate is obtained from the formulas (1) and (2).
(Hydration rate) = [(C / Si molar ratio of the silicon compound)-(C / Si molar ratio of the coating film)] / [(C / Si molar ratio of the silicon compound)-(The silicon compound is complete) C / Si molar ratio when hydrolyzed to)] × 100 ・ ・ ・ (1)
(C / Si molar ratio of the coating) = [(the number of carbon moles of the lithium nickel composite oxide particles having the coating)-(the number of carbon moles of the lithium nickel composite oxide particles)] / (the above Number of moles of silicon in the particles of the lithium nickel composite oxide having a film) ... (2) General formula: Li _z Ni _1-xy Co _x Al _y O _{2 + α} (in the formula, x is 0.01 ≦ x ≦ 0.20, y is 0.01 ≦ y ≦ 0.15, z is 0.90. Forming a film in which the particles of the lithium nickel composite oxide represented by ≦ z ≦ 1.20 and α is −0.2 ≦ α ≦ 0.2) and the atmospheric gas obtained by adding a silicon compound to the carrier gas are brought into contact with each other. Have a process,
The film forming step is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which is carried out using a carrier gas having a carbon dioxide gas concentration of 500 ppm or less and a dew point temperature higher than −50 ° C. and 0 ° C. or lower. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4, wherein the silicon compound is an alkoxysilane compound having a boiling point of 300 ° C. or lower.

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