JP2018190719A - Positive electrode active material for nonaqueous electrolyte secondary battery, and method for manufacturing positive electrode active material for nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for a nonaqueous electrolyte secondary battery, which is to be used for a nonaqueous electrolyte secondary battery, and which can suppress the gas generation even in the case of performing charging and discharging actions repeatedly.SOLUTION: Provided is a positive electrode active material for a nonaqueous electrolyte secondary battery, which comprises: particles of a lithium nickel composite oxide represented by LiNiCoAlO(where "x" satisfies 0.01≤x≤0.20, "y" satisfies 0.01≤y≤0.15, "z" satisfies 0.90≤z≤1.20, and "α" satisfies -0.2≤α≤0.2); and a coating disposed on at least a part of the surface of each particle of the lithium nickel composite oxide, and including a hydrolysate of a silicon compound. In the positive electrode active material, a silicon content is 0.01 mass% or more and 0.5 mass% or less; a carbon content is 0.01 mass% or more and 0.5 mass% or less; and the hydrolytic rate of the silicon compound included in the coating is 85% or more and 100% or less.SELECTED DRAWING: Figure 1

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 widespread use 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, development of a high-power secondary battery is strongly desired as a power source for electric vehicles including hybrid vehicles.

  As a secondary battery satisfying such requirements, there is a lithium ion secondary battery which is a kind of non-aqueous electrolyte secondary battery. A lithium ion secondary battery includes 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 are actively conducted. Among them, a lithium ion secondary battery using a layered or spinel type lithium metal composite oxide as a positive electrode material can be used as a battery having a high energy density because a voltage of 4 V class can be obtained.

The main positive electrode active materials that have been proposed so far include lithium-cobalt composite oxides typified by lithium cobaltate (LiCoO ₂ ) as a layered material, and lithium nickel typified by lithium nickelate (LiNiO ₂ ). As the composite oxide, a lithium manganese composite oxide represented by lithium manganate (LiMn ₂ O ₄ ) as a spinel material can be given.

  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 a positive electrode of a lithium ion secondary battery. Since the cycle characteristics can be obtained, it is widely spread 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 or manganese, which are cheaper than cobalt, have attracted attention.

Although lithium nickelate can provide larger charge / discharge capacity than lithium cobaltate as a lithium ion secondary battery, it has a drawback that thermal stability and cycle characteristics are inferior to those of other positive electrode active materials. In view of this, lithium nickel composite oxides have been developed in which a part of nickel constituting lithium nickelate is replaced with another element to improve thermal stability and cycle characteristics. Examples of the lithium nickel composite oxide include lithium nickel cobalt aluminum oxide (LiNi _X Co _y Al _Z O 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. And lithium nickel cobalt manganese oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and the like.

  By the way, for lithium-nickel composite oxides, charge and discharge due to surface oxidation due to atmospheric exposure, and when used in the positive electrode of a lithium ion secondary battery, due to reaction with the electrolyte and surface deterioration due to elution of metal components in the electrolyte, etc. There is a problem that the capacity decreases.

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

  For example, Patent Document 1 includes a lithium-containing composite oxide and a coating layer that covers at least a part of the surface of the lithium-containing composite oxide, the lithium-containing composite oxide containing Ni, and the coating The layer includes a metal element M and a halogen element, and the metal element M includes 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.

  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, A lithium composite compound particle powder in which a surface treatment component containing at least one element selected from Y) is present is disclosed. And as the manufacturing method, while using the alkoxide of A element as A raw material in the water suspension containing the complex oxide which consists of lithium-transition metal element (TM) which is a core particle, it contains fluorine as a neutralizing agent After depositing a surface treatment component containing at least element A and fluorine on the surface of the composite oxide particle comprising lithium-transition metal element (TM) using a solution of A method for producing a lithium composite compound particle powder that is 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 production process, which is problematic in terms of safety. was there.

  In addition, the lithium composite compound particle powder disclosed in Patent Document 2 needs 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 be reduced.

JP 2008-251480 A JP 2013-232438 A

  Therefore, the inventor of the present invention does not need to immerse the lithium nickel composite oxide in water at the time of formation, and contains a hydrolyzate of a silicon compound as a positive electrode active material provided with a coating that does not use a halogen-based gas. The positive electrode active material provided with a coating film was found and studied.

  However, in the case of a positive electrode active material provided with 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, an object of one aspect of the present invention is 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.

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

  According to one embodiment 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.

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

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and the following embodiments are not departed from the scope of the present invention. Various modifications and substitutions can be made.
[Positive electrode active material for non-aqueous electrolyte secondary battery]
One structural example of the positive electrode active material for a 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 according to the present embodiment (hereinafter also simply referred to as “positive electrode active material”) includes at least one of lithium nickel composite oxide particles and lithium nickel composite oxide particle surfaces. And a coating film containing a hydrolyzate of a silicon compound disposed in the portion.

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

In addition, the said hydrolysis rate can be calculated | required from the following formula | equation (A), for example.
(Hydrolysis rate) = [(Number of alkoxy groups contained in silicon compound) − (Number of alkoxy groups remaining in the film)] / (Number of alkoxy groups contained in silicon compound) × 100 (A )
The coating can be formed using a silicon compound having an alkoxy group. And since a hydrolysis rate is a ratio of the group which hydrolyzed and became a hydroxyl group when forming a film among the alkoxy groups which a silicon compound used when forming a film formed, the above-mentioned formula (A ).
The silicon compound is preferably an alkoxysilane compound.
The hydrolysis rate can also be obtained from the following formulas (1) and (2) when, for example, the alkoxy groups contained in the silicon compound used as a raw material when forming a film have the same structure.
(Hydrolysis rate) = [(C / Si molar ratio of silicon compound) − (C / Si molar ratio of coating)] / [(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 lithium nickel composite oxide particles provided with coating) − (number of carbon moles of particles of lithium nickel composite oxide)] / (lithium provided with coating) Number of moles of silicon in nickel composite oxide particles) (2)
The lithium nickel composite oxide has a general formula: Li _z Ni _1-xy Co _x Al _y O _{2 + α} (wherein x is 0.01 ≦ x ≦ 0.20 and y is 0.01 ≦ y ≦ 0.15, z is 0.90 ≦ z ≦ 1.20, and α is −0.2 ≦ α ≦ 0.2).

First, the lithium nickel composite oxide particles and the coating film contained in the positive electrode active material of this embodiment will be described.
(Lithium nickel composite oxide particles)
The particles of the lithium nickel composite oxide have a general formula: Li _z Ni _1-xy Co _x Al _y O _{2 + α} (where x is 0.01 ≦ x ≦ 0.20, y is 0.01 ≦ y ≦ 0.15, z is 0.90 ≦ z ≦ 1.20, and α is −0.2 ≦ α ≦ 0.2). In particular, the lithium nickel composite oxide particles are preferably composed of such 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 to be within the range.

  By setting x to 0.01 or more, sufficient cycle characteristics of a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as “secondary battery”) using a positive electrode active material containing the lithium nickel composite oxide are sufficiently obtained. Can be increased. Moreover, the charging / discharging capacity | capacitance of the secondary battery using the positive electrode active material containing the lithium nickel complex oxide can be made high enough because x shall be 0.20 or less.

  In the above general formula, y indicating the aluminum (Al) content is preferably in the range of 0.01 ≦ y ≦ 0.15, and in the range of 0.01 ≦ y ≦ 0.10. More preferably.

  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. Moreover, it can prevent more reliably that aluminum precipitates without forming a solid solution in lithium nickel complex oxide by making y into 0.15 or less. That is, by setting y to 0.15 or less, it is possible to prevent the occurrence of a heterogeneous phase and sufficiently increase the charge / discharge capacity of the secondary battery using the positive electrode active material containing the lithium nickel composite oxide.

  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. More preferably. 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. Moreover, the thermal stability of the secondary battery using the positive electrode active material containing the lithium nickel composite oxide can be sufficiently increased by setting z to 1.20 or less.

  In the above general formula, 1-xy indicating the content of nickel (Ni) is preferably in the range of 0.65 to 0.98, and in the range of 0.80 to 0.95. More preferably, it is within. 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. Moreover, the thermal stability of the secondary battery using the positive electrode active material containing the lithium nickel composite oxide can be sufficiently increased by setting 1-xy to 0.98 or less.

  In the above general formula, as for oxygen, the amount of oxygen may be deficient from 2 or excessive so as not to affect the present invention. For this reason, the amount of oxygen can be represented by 2 + α as in the above general formula, and α can be set to −0.2 ≦ α ≦ 0.2, for example.

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

  Furthermore, in the particles of the lithium nickel composite oxide, the average particle diameter of secondary particles formed by aggregation of 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 diameter 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, This is preferable because the charge / discharge capacity of the secondary battery can be increased.

  When the average particle diameter of the secondary particles of the lithium nickel composite oxide is 20 μm or less, in the secondary battery using the positive electrode active material containing the lithium nickel composite oxide particles, the positive electrode active material and the electrolytic solution This 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 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. More preferably. 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 secured, and battery characteristics can be particularly improved. Moreover, it is because heat stability can fully be improved by setting it as 1.5 m < ² > / g or less, and it is preferable.
(Coating)
The coating is disposed on at least a part of the surface of the lithium nickel composite oxide particles, and can contain a hydrolyzate of a silicon compound. More preferably, the coating is disposed on the entire surface of the lithium nickel composite oxide particles.

  In addition, it is preferable that the particles of the lithium nickel composite oxide contain secondary particles in which primary particles are aggregated as described above. And it is preferable that the film is arrange | positioned at least one part of the surface of the primary particle and secondary particle which concern.

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

  Thus, by disposing the coating containing the hydrolyzate of the silicon compound on at least a part of the surface of the lithium nickel composite oxide particles, surface oxidation due to exposure to the atmosphere, reaction with the electrolytic solution, to the electrolytic solution Occurrence of surface degradation due to elution of metal components can be suppressed. For this reason, in the secondary battery using the positive electrode active material of this embodiment, even when charging / discharging is performed repeatedly, the maintenance rate of charge / discharge capacity can be increased. That is, a secondary battery having excellent cycle characteristics can be obtained.

  However, according to the study of the inventors of the present invention, as described above, when the positive electrode active material is provided with a film containing a hydrolyzate of a silicon compound, a secondary battery using the positive electrode active material is used. In some cases, gas is generated when charging and discharging are repeated. And according to examination of the inventor of the present invention, such gas generation is attributed to a certain ratio or more of carbon contained in the coating.

  Therefore, the lithium nickel composite oxide film contained in the positive electrode active material of the present embodiment contains a hydrolyzate of a silicon compound as described above, and is a ratio in which the silicon compound is 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, hydrolysis of the silicon compound used as a raw material proceeds, and the mass ratio of carbon to silicon contained in the coating can be greatly reduced. For this reason, in the secondary battery using the positive electrode active material, even when charging and discharging are repeatedly performed, generation of gas due to carbon can be suppressed, which is preferable.

  Moreover, the denseness of the film containing the hydrolyzate of a silicon compound can be improved by raising the hydrolysis rate to 85% or more. For this reason, about the positive electrode active material of this embodiment, generation | occurrence | production of the surface oxidation by exposure to air | atmosphere, reaction with electrolyte solution, surface degradation by the metal component elution to electrolyte solution, etc. can be suppressed especially. Furthermore, in the secondary battery using the positive electrode active material of the present embodiment, the charge / discharge capacity retention rate can be increased even when repeated charge / discharge is performed. That is, a secondary battery having excellent cycle characteristics can be obtained.

  Since the hydrolysis rate does not exceed the theoretical value, the upper limit value 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).
(Hydrolysis rate) = [(Number of alkoxy groups contained in silicon compound) − (Number of alkoxy groups remaining in coating)] / (Number of alkoxy groups contained in silicon compound) × 100 (A )
The number of alkoxy groups contained in the silicon compound before hydrolysis and the number of alkoxy groups in the formed coating used to form the coating in formula (A) should be determined using various analytical devices such as NMR. Can be obtained.
Moreover, when the alkoxy group which the silicon compound used for the raw material contains when forming a film has the same structure, the hydrolysis rate of the silicon compound is expressed by the following formula (1) and formula (2). It can be calculated.

(Hydrolysis rate) = [(C / Si molar ratio of silicon compound) − (C / Si molar ratio of coating)] / [(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 lithium nickel composite oxide particles provided with coating) − (number of carbon moles of particles of lithium nickel composite oxide)] / (lithium provided with coating) Number of moles of silicon in nickel composite oxide particles) (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, Si (OH) ₂ (CH ₃ ) ₂ is obtained. Therefore, the C / Si molar ratio is 2 when the silicon compound is completely hydrolyzed.

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

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

  The positive electrode active material of the present embodiment preferably has a silicon content of 0.01% by mass to 0.5% by mass and a carbon content of 0.01% by mass to 0.5% by mass. . As described above, since the coating film of the positive electrode active material of this embodiment contains a hydrolyzate of a silicon compound, the coating film of the positive electrode active material of this embodiment can contain silicon and carbon. For this reason, by setting the silicon content to 0.01% by mass or more and the carbon content to 0.01% by mass or more, the lithium nickel composite oxide particles can be obtained with a sufficient thickness and uniform coating. This is because it can be formed on the surface.

  However, if the coating becomes too thick, the coating may inhibit the lithium intercalation / deintercalation reaction to 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 this embodiment, the surface of the lithium nickel composite oxide has a coating. For this reason, generation | occurrence | production of the surface deterioration by the surface oxidation by exposure to air | atmosphere, reaction with electrolyte solution, metal component elution to electrolyte solution, etc. can be suppressed. For this reason, in the secondary battery using the positive electrode active material of this embodiment, even when charging / discharging is performed repeatedly, the maintenance rate of charging / discharging capacity | capacitance can be made high. That is, a secondary battery having excellent cycle characteristics can be obtained.

Furthermore, the mass ratio of carbon to silicon contained in the coating is greatly increased by increasing the hydrolysis rate of the silicon compound calculated from the above-described formula (A) or the above-described formula (1) and formula (2). Has been reduced. For this reason, in the secondary battery using the positive electrode active material of the present embodiment, even when charging / discharging is repeated, generation of gas due to carbon contained in the coating can be suppressed.
[Method for producing positive electrode active material for non-aqueous electrolyte secondary battery]
Next, a configuration example of the method for producing the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present embodiment will be described.

  In addition, the above-mentioned positive electrode active material can be manufactured with the manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries of this embodiment. For this reason, some of the matters already described are 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”) comprises lithium nickel composite oxide particles and a carrier compound containing a silicon compound. It is possible to have a film forming step of contacting the added atmospheric gas. The film forming step can be performed 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: Li _z Ni _1-xy Co _x Al _y O _{2 + α} (wherein x is 0.01 ≦ x ≦ 0.20 and y is 0.01 ≦ y ≦ 0.15, z can be expressed by 0.90 ≦ z ≦ 1.20, and α can be expressed by −0.2 ≦ α ≦ 0.2).

  In the film forming step, an atmosphere gas obtained by adding a silicon compound to a carrier gas, that is, a gas, can be brought into contact with the surfaces of the lithium nickel composite oxide particles.

Since the silicon compound is hydrolyzed when the film is formed, the silicon compound can have an alkoxy group that is a group that generates a hydroxyl group by hydrolysis. The silicon compound is preferably an alkoxysilane compound.
And as a silicon compound, it is preferable that it is 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. A plurality of silicon compounds having different structures can be used at the same time.

  As a silicon compound to be used, the lower limit of the boiling point is preferably 50 ° C. from the viewpoints 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. ], Vinyltrimethoxysilane [Si (C ₂ H ₃ ) (OCH ₃ ) ₃ ] having a boiling point of 123 ° C., triethoxymethylsilane [Si (CH ₃ ) (OC ₂ H ₅ ) ₃ having a boiling point of 143 ° C. ], a boiling point of 165 ° C. tetraethyl orthosilicate _{(tetraethoxysilane) [Si (OC 2 H 5} ) 4], under reduced pressure, specifically to 2kPa Kicking boiling point can be preferably used one or more selected from the 92 ° C. is 3-aminopropyl trimethoxysilane _{[Si (C 3 H 6 NH} 2) (OCH 3) 3] and the like.

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

  As shown in FIG. 1, the film forming step is performed after the first storage container 11 storing the lithium nickel composite oxide particles 111 and the second storage container 12 storing the silicon compound 121 are installed in the reaction container 10. The carrier gas can be filled in the reaction vessel 10 and the fan 13 can be rotated as necessary.

  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 outside. 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, metals such as stainless steel (SUS304, SUS316, and the like), titanium, and the like. However, the material is not limited to the above materials as long as it does not react with the silicon compound or its vapor.

  The first storage container 11 and the second storage container 12 preferably do not react with the lithium nickel composite oxide particles 111 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 oxide. The particle 111 and the silicon compound 121 can be selected as appropriate.

The carrier gas filled in the reaction vessel 10 preferably does not react with the lithium nickel composite oxide particles 111 and 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 moisture (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 with an increased hydrolysis rate of the silicon compound, in the carrier gas filled in the reaction vessel 10 when performing the coating process, It is preferable that a certain amount of moisture is present.

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

  This is because the carbon dioxide gas concentration in the carrier gas is 500 ppm or less and the dew point temperature is 0 ° C. or less, so that the lithium nickel composite oxide particles and silicon compound can be prevented from excessively reacting with carbon dioxide and moisture. This is because generation of by-products can be suppressed. Moreover, by making the dew point temperature in the carrier gas higher than −50 ° C., hydrolysis of the silicon compound is promoted, and a film with an increased hydrolysis rate of the silicon compound can be formed.

  The dew point of the carrier gas is more preferably higher than −30 ° C. and lower than 0 ° C. Further, the lower limit value of the carbon dioxide gas concentration is not particularly limited because it depends on the type of carrier gas to be used, but can be set to, for example, 0 ppm.

  The carrier gas for performing the film forming step is preferably at least one selected from dry air, nitrogen, oxygen, argon and the like subjected to carbon dioxide removal 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 carbon dioxide removal treatment and a certain amount of dehydration treatment. This is because the positive electrode active material manufactured using such dry air as the carrier gas has a higher electrical conductivity because the densification of the coating is promoted compared to the case where an inert gas such as nitrogen or argon is used. Because it is. For this reason, when the obtained positive electrode active material is used as a positive electrode of a secondary battery, an excellent charge / discharge characteristic is obtained, which is more preferable.

  Depending on the type of silicon compound, there may be a risk of explosion due to the mixing ratio of silicon compound vapor and dry air, or it may be oxidized and deteriorated by oxygen. It is preferable to use an inert gas such as nitrogen or argon. Thus, the carrier gas can be appropriately selected according to the type of silicon compound used.

  In the reaction container 10, the vapor of the silicon compound 121 diffuses into the carrier gas in the reaction container 10 from the second storage container 12 that stores the silicon compound 121. That is, an atmosphere 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 into 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. For this reason, the silicon compound 121 is mass-transferred to the lithium-nickel composite oxide particles 111 stored in the first storage container 11 as the reaction time elapses.

  Here, the amount of the coating (or the thickness of the coating) formed on the surface of the lithium nickel composite oxide particles can be controlled as follows. First, a predetermined amount of lithium nickel composite oxide particles are placed in the first storage container 11, and the amount of silicon compound 121 to be formed on the lithium nickel composite oxide particles 111 is added to the second storage container 12. Put in. Thereafter, a desired carrier gas is filled into the reaction vessel 10 and left as it is while rotating the fan 13 as necessary, and the reaction is terminated when the silicon compound 121 in the second storage vessel 12 has completely disappeared. Just do it.

  As another method for controlling the amount of coating (or coating thickness) different from the above, first, an excessive amount of silicon compound 121 in the second storage container 12 is formed in excess of the amount of coating to be formed on the particles of the lithium nickel composite oxide. Put in. Next, the reaction vessel 10 is filled with a carrier gas, and the fan 13 is rotated as necessary, and is left as it is. After a predetermined time has passed, the silicon compound is accommodated while the silicon compound remains partially. 2 The storage container 12 may be taken out from the reaction container 10 to terminate the reaction.

  The manufacturing method of the positive electrode active material of this embodiment can also have arbitrary processes.

  For example, a heat treatment step for performing a heat treatment after the film forming step can be included.

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

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

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

  In addition, in the heat treatment step, it is preferable to use an atmospheric gas in which carbon dioxide gas and moisture are reduced and removed in order to prevent deterioration of the particles of the lithium nickel composite oxide. For example, the atmosphere gas includes dry air and oxygen. Note that when an inert gas such as nitrogen or argon is used as the atmosphere gas, the lithium nickel composite oxide particles may be reduced and the battery characteristics may be deteriorated. Therefore, an oxidizing atmosphere, for example, oxygen as described above is contained. It is preferable to use an atmosphere.

  By performing the heat treatment step, the crystallinity of the film formed on the surface of the lithium nickel composite oxide particles may be increased, or impurities such as excessive 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, since a simple method of forming a film by bringing an atmosphere gas in which a silicon compound is added to a carrier gas into contact with the surfaces of lithium nickel composite oxide particles is used, Can be manufactured at cost. In addition, since it is not necessary to immerse the lithium nickel composite oxide in water, it is possible to prevent performance deterioration such as charge / discharge capacity reduction due to elution of lithium ions.
[Nonaqueous 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 this embodiment can 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. Note that the embodiments described below are merely examples, and the nonaqueous electrolyte secondary battery of the present invention can be variously modified based on the knowledge of those skilled in the art based on the embodiments described herein. It can be implemented in an improved form. Moreover, the use of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited.
[Positive electrode]
The positive electrode is a sheet-like member, and can be formed, for example, by applying a positive electrode mixture paste containing the above-described positive electrode active material to the surface of an aluminum foil current collector and drying it. The positive electrode can also be formed by molding a positive electrode mixture. In addition, a positive electrode is suitably processed according to the battery to be used. For example, a cutting process for forming an appropriate size according to a target battery, a pressure compression process using a roll press or the like for increasing the electrode density, and the like can be performed.

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

  The conductive material is added to give an 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 plays a role of holding the positive electrode active material. The binder used for such a positive electrode mixture is not particularly limited. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, polyacrylic. One or more selected from acids and the like can be used.

  In addition, activated carbon etc. can also be added to a positive electrode compound material. 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. Although the solvent is not particularly limited, for example, an organic solvent such as N-methyl-2-pyrrolidone can be used.

  In addition, the mixing ratio of each substance in the positive electrode mixture paste is not particularly limited, and can be the same as that of the positive electrode of a general nonaqueous electrolyte secondary battery, for example. 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 binder content can be 1 part by mass or more and 20 parts by mass or less.

However, the method for manufacturing the positive electrode is not limited to the above-described examples, and other methods may be used. For example, it can also be produced by press-molding a positive electrode mixture and then drying 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 foil current collector such as copper and drying it. Further, the negative electrode can be a sheet-like member made of a material containing lithium, such as metallic lithium.

  When the negative electrode is produced using the negative electrode mixture paste, the components constituting the negative electrode mixture paste and the composition thereof, the material of the current collector, etc. are different, but are formed by substantially the same method as the above positive electrode, Similar to the positive electrode, various treatments are performed as necessary.

  The negative electrode mixture paste can be prepared by adding a suitable solvent to the negative electrode mixture in which the negative electrode active material and the binder are mixed to form a paste.

  As the negative electrode active material, for example, a material containing lithium, such as metallic lithium or a lithium alloy, or an occlusion material that can occlude and desorb lithium ions can be employed.

  The occlusion material is not particularly limited, and for example, one or more kinds selected from natural graphite, artificial graphite, a fired organic compound such as phenol resin, and a powdery carbon material such as coke can be used.

When such an occlusion material is employed as the negative electrode active material, a fluorine-containing resin such as PVDF can be used as the binder, as with the positive electrode, and as a solvent for dispersing the negative electrode active material in the binder, An organic solvent such as N-methyl-2-pyrrolidone can be used.
[Separator]
The separator is disposed 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 the electrolyte.

As a material for the separator, for example, a thin film such as polyethylene or polypropylene and a film having a large number of fine holes can be used. However, the separator is not particularly limited as long as it has the above 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; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; Ether compounds such as methyltetrahydrofuran and dimethoxyethane; sulfur compounds such as ethyl methyl sulfone and butane sultone; phosphorus compounds such as triethyl phosphate and trioctyl phosphate 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 complex salts thereof can be used.

  The non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, etc. for improving battery characteristics.

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

The secondary battery of the present embodiment constituted by the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte that have been described above can have various shapes such as a cylindrical shape and a laminated shape. In any case, 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, connect between the positive electrode current collector and the positive electrode terminal that communicates with the outside, and between the negative electrode current collector and the negative electrode terminal that communicates with the outside using a current collecting lead or the like, and seal the battery case. It can be set as a secondary battery.
In addition, although an example using a liquid non-aqueous electrolyte has been described here, the secondary battery of the present embodiment is not limited to such a form, for example, a secondary battery using a solid non-aqueous electrolyte. That is, it can also be set as an all-solid-state battery. When it is set as an all-solid-state battery, structures other than a positive electrode active material can be changed as needed.

  The secondary battery of the present embodiment using the above-described positive electrode active material uses the lithium nickel composite oxide having a coating on the surface as the positive electrode active material. For this reason, it can be set as the secondary battery excellent in cycling characteristics, and since it can suppress especially generation | occurrence | production of the gas in the case of charging / discharging, it can be set as the secondary battery which improved safety | security.

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 lithium nickel composite oxide particles is shown in FIG.

As shown in FIG. 2, the lithium nickel composite oxide particles used are composed of secondary particles formed by agglomeration of primary particles, and the average particle diameter of the secondary particles obtained by the laser diffraction scattering method is 12 μm. Yes, 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 lithium nickel composite oxide is placed in the first storage container 11 and placed in the reaction container 10, and then dimethoxydimethylsilane [Si (OCH ₃ ) ₂ ( The second storage container 12 containing 12.6 g of CH ₃ ) ₂ ] was placed in the reaction container 10.

  Next, after filling instrument air (carbon dioxide concentration 440 ppm, dew point temperature −23 ° C.) as dry air as a carrier gas in the reaction vessel 10, the fan 13 is stirred at room temperature while stirring the atmosphere in the reaction vessel 10. 25 ° C.). Thereby, the film formation process which makes the gas containing the silicon compound dimethoxydimethylsilane contact the surface of the particle | grains of lithium nickel complex oxide was implemented, and the positive electrode active material which concerns on Example 1 which has a film was obtained.

  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.

Moreover, when the positive electrode active material for non-aqueous electrolyte secondary batteries was quantitatively analyzed by high-frequency combustion infrared spectroscopy, it was confirmed that 0.16% by mass of carbon (C) was contained.
[Battery characteristics evaluation]
A coin-type battery using the obtained positive electrode active material for the positive electrode was produced, and 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 battery 30 includes a case 31 and an electrode 32 accommodated in the case 31.

  The case 31 has a positive electrode can 311 that is hollow and open at one end, and a negative electrode can 312 that is disposed in the opening of the positive electrode can 311, and the negative electrode can 312 is disposed 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.

  The electrode 32 includes a positive electrode 321, a separator 322, and a negative electrode 323, which are stacked in this order. The positive electrode 321 contacts the inner surface of the positive electrode can 311, and the negative electrode 323 contacts the inner surface of the negative electrode can 312. It is accommodated in the case 31 so as to come into contact. The case 31 includes a gasket 313, and relative movement is fixed by the gasket 313 so that the positive electrode can 311 and the negative electrode can 312 are maintained in 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 and blocking the inside and outside of the case 31 in an airtight and liquid tight manner.

  Such a coin-type battery 30 was produced 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 were mixed, then press-molded, and a thin film was obtained until the weight became about 10 mg with a diameter of 10 mm. To produce a positive electrode 321, which was dried in a vacuum dryer at 120 ° C. for 12 hours.

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

The separator 322 is a porous polyethylene film having a thickness of 25 μm, and the electrolyte is a 3: 7 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiPF ₆ as a supporting electrolyte (Toyama Chemical) Kogyo Co., Ltd.) was used.

  For the coin-type battery, the C rate, which is the ratio of the charge / discharge current value to the battery capacity, is set to 0.05 C, the battery is charged to a cutoff voltage of 4.3 V, and then discharged to a cutoff voltage of 3.0 V. As a result, the charge capacity was 220 mAh / g and the discharge capacity was 198 mAh / g. Moreover, the positive electrode resistance measured by the alternating current impedance method was 2.2Ω.

In addition, even if charging / discharging was repeated, no swelling was observed in the coin-type battery, and gas generation was not observed.
[Example 2]
Example 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 the silicon compound were used in the film forming step. In the same manner as in Example 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 0.34% by mass of silicon (Si) derived from the trimethoxymethylsilane component was contained.

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

  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. Moreover, the positive electrode resistance measured by the alternating current impedance method was 3.6Ω.

In addition, even if charging / discharging was repeated, no swelling was observed in the coin-type battery, and gas generation was not observed.
[Example 3]
In the film forming step, the same as Example 1 except that 509.6 g of the same lithium nickel composite oxide as in Example 1 and tetraethyl orthosilicate [Si (OC ₂ H ₅ ) ₄ ] 12.5 g as a silicon compound were used. Thus, a 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 0.31% by mass of silicon (Si) derived from the tetraethyl orthosilicate component was contained.

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

  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. Moreover, the positive electrode resistance measured by the alternating current impedance method was 3.3Ω.

In addition, even if charging / discharging was repeated, no swelling was observed in the coin-type battery, and gas generation was not observed.
[Comparative Example 1]
In the film formation 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, and nitrogen gas as the carrier gas A positive electrode active material according to Comparative Example 1 was obtained in the same manner as in Example 1 except that the carbon dioxide 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 0.05 mass% of silicon (Si) derived from the dimethoxydimethylsilane component was contained.

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

  Furthermore, 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. Moreover, the positive electrode resistance measured by the alternating current impedance method was 2.2Ω.
[Comparative Example 2]
In the film formation 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 the silicon compound, and nitrogen gas as the carrier gas A positive electrode active material according to Comparative Example 2 was obtained in the same manner as in Example 1 except that the carbon dioxide 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 0.26% by mass of silicon (Si) derived from the trimethoxymethylsilane component was contained.

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

  Furthermore, 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. Moreover, the positive electrode resistance measured by the alternating current impedance method was 3.1Ω.
[Comparative Example 3]
In the film forming step, 499.6 g of the same lithium nickel composite oxide as in Example 1 and 12.6 g of tetraethyl orthosilicate [Si (OC ₂ H ₅ ) ₄ ] as the silicon compound were used, and nitrogen gas (carbon dioxide gas) was used as the carrier gas. A 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.

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

  Furthermore, 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. Moreover, the positive electrode resistance measured by the alternating current impedance method was 2.9Ω.
[Comparative Example 4]
A 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 performed.

  Therefore, the obtained positive electrode active material is not subjected to a film formation treatment on the surface of the lithium nickel composite oxide particles, and no film is formed on the surface.

  When the above 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 mass% (lower detection limit).

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

  Furthermore, 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. Moreover, the positive electrode resistance measured by the alternating current impedance method was 2.4Ω.
[Hydrolysis rate of silicon compound]
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 formation treatment is described from the analysis values of silicon (Si) and carbon (C). (1) and (2).

  (2) When calculating (C / Si molar ratio of coating film) in the formula [(number of carbon moles of particles of lithium nickel composite oxide provided with coating film)-(carbon moles of particles of lithium nickel composite oxide] Number)] is the amount of carbon before carrying out the film formation treatment from the carbon amount of the positive electrode active material obtained after the film formation treatment in each example and comparative example (C analysis value of each example and comparative example) ( 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 amount after performing the film forming process is 0.16% by mass, and the carbon amount before performing the film forming process of Comparative Example 4 is 0.09% by mass. The amount of carbon contained in the coating is 0.07% by mass. Then, the value obtained by dividing the calculated amount of carbon 0.07% by mass contained in the coating by the atomic weight of carbon in the formula (2) in Example 1 [(particles of lithium nickel composite oxide provided with coating The number of carbon moles of the lithium nickel composite oxide particles)].

  Further, (the number of moles of silicon in the particles of the lithium nickel composite oxide provided with a coating) in the formula (2) was obtained by dividing the Si analysis value of each example and comparative example by the atomic weight of silicon.

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

In Examples 1 to 3, the film forming step was performed 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 performed 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 positive electrode active material coatings obtained in Examples 1 to 3 was higher than the hydrolysis rate of the silicon compound contained in the positive electrode active material coatings of Comparative Examples 1 to 3. It was confirmed that it was higher.

  For this reason, when Example 1 and Comparative Example 1 using the same silicon compound when forming a film are compared, Example 1 and Comparative Example 1 have a mass ratio of C / Si (carbon / silicon) of 2.00. 3.00 and it was confirmed that Example 1 was lower. That is, in Example 1, the mass ratio of carbon in the coating 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. It was able to be suppressed.

  In addition, even when Example 2 and Comparative Example 2, and Example 3 and Comparative Example 3 using the same silicon compound when forming a film were compared, the same tendency was seen.

  Further, as described above, when a secondary battery using a positive electrode active material is repeatedly charged and discharged, gas may be generated due to a certain ratio or more of carbon in the coating. For this reason, generation | occurrence | production of the gas concerned is suppressed by reducing the mass ratio of the carbon in a film, and the safety | security as a secondary battery improves. In addition to contributing to the suppression of surface oxidation due to atmospheric exposure, the coating can suppress surface degradation due to reaction with the electrolyte when used in the positive electrode of a lithium ion secondary battery, further reducing the amount of gas generated, and cycle characteristics Contributes to the improvement of

  Further, when Examples 1 to 3 and Comparative Example 4 are compared, the positive electrode active materials of Examples 1 to 3 in which a film is formed on the surface of the lithium nickel composite oxide particles are comparative examples 4 in which no film is formed. It can be confirmed that the same charge / discharge capacity and positive electrode resistance as those of the positive electrode active material were obtained. Therefore, it was also confirmed that a 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} (wherein x is 0.01 ≦ x ≦ 0.20, y is 0.01 ≦ y ≦ 0.15, z is 0.90) ≦ z ≦ 1.20, α is a particle of lithium nickel composite oxide represented by −0.2 ≦ α ≦ 0.2),
A film containing a hydrolyzate of a silicon compound, disposed on at least a part of the surface of the particles of the lithium nickel composite oxide,
The silicon content is 0.01 mass% or more and 0.5 mass% or less, and the carbon content is 0.01 mass% or more and 0.5 mass% or less,
The positive electrode active material for nonaqueous electrolyte secondary batteries whose hydrolysis rate of the said silicon compound contained in the said 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 obtained from the formula (A).
(Hydrolysis rate) = [(Number of alkoxy groups contained in silicon compound) − (Number of alkoxy groups remaining in coating)] / (Number of alkoxy groups contained in 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).
(Hydrolysis rate) = [(C / Si molar ratio of the silicon compound) − (C / Si molar ratio of the coating)] / [(C / Si molar ratio of the silicon compound) − (the silicon compound is completely C / Si molar ratio when hydrolyzed to 1)] × 100 (1)
(C / Si molar ratio of the coating) = [(number of carbon moles of particles of the lithium nickel composite oxide provided with the coating) − (number of carbon moles of particles of the lithium nickel composite oxide)] / (above Number of silicon moles of the lithium nickel composite oxide particles provided with a coating) (2) General formula: Li _z Ni _1-xy Co _x Al _y O _{2 + α} (wherein 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 a film is formed by contacting particles of lithium-nickel composite oxide and an atmosphere gas obtained by adding a silicon compound to a carrier gas. Having a process,
The said film formation process is a manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries implemented using the carrier gas whose carbon dioxide gas concentration is 500 ppm or less and whose dew point temperature is higher than -50 degreeC and 0 degreeC or less.   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 less.