JP7031296B2 - Manufacturing method of nickel composite oxide and positive electrode active material - Google Patents

Description

The present invention relates to a nickel composite oxide and a positive electrode active material.

In recent years, with the spread of portable electronic devices such as mobile phones and notebook personal computers, there is a demand for the development of small and lightweight secondary batteries having a high energy density. There is also a demand for the development of high-output secondary batteries as batteries for electric vehicles such as hybrid vehicles. As a non-aqueous electrolyte secondary battery satisfying such a requirement, there is a lithium ion secondary battery.

The 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 the active material of the negative electrode and the positive electrode.

A lithium ion secondary battery using a lithium composite oxide, particularly a lithium cobalt composite oxide that is relatively easy to synthesize, as a positive electrode material is expected as a battery having a high energy density because a high voltage of 4V class can be obtained. Practical use is progressing. Batteries using lithium cobalt composite oxides have been developed in many ways to obtain excellent initial capacity characteristics and cycle characteristics, and various results have already been obtained.

However, since the lithium cobalt composite oxide uses an expensive cobalt compound as a raw material, the unit price per capacity of the battery using this lithium cobalt composite oxide is significantly higher than that of the nickel hydrogen battery, and the applicable applications are considerable. Limited.

For this reason, it is possible to reduce the cost of positive electrode materials and manufacture cheaper lithium-ion secondary batteries for small secondary batteries for portable devices and large secondary batteries for power storage and electric vehicles. There are great expectations for this, and it can be said that its realization has great industrial significance.

As a new material for the active material for a lithium ion secondary battery, a lithium nickel composite oxide using nickel, which is cheaper than cobalt, can be mentioned. Since this lithium nickel composite oxide exhibits a lower electrochemical potential than the lithium cobalt composite oxide, decomposition due to oxidation of the electrolytic solution is less likely to be a problem, higher capacity can be expected, and a high battery voltage similar to that of cobalt-based batteries is expected. Therefore, development is being actively carried out.

However, when a lithium-ion secondary battery is manufactured using a lithium-nickel composite oxide synthesized purely from nickel as a positive electrode material, the cycle characteristics are inferior to those of a cobalt-based battery, and it is used and stored in a high temperature environment. Therefore, it has a drawback that the battery performance is relatively easily impaired. Therefore, a lithium nickel composite oxide in which a part of nickel is replaced with cobalt or aluminum is generally known.

Among them, the lithium nickel composite oxide in which a part of nickel is replaced with at least aluminum is the battery characteristics and safety of the lithium secondary battery when the lithium nickel composite oxide is used as a positive electrode material of the lithium secondary battery. It is attracting attention because it can enhance the sex.

Various proposals have been made for the method for producing a lithium nickel composite oxide, and a method for producing a lithium nickel composite oxide by baking a mixture of a nickel composite oxide and a lithium compound and then washing with water has been proposed. ing.

For example, in Patent Document 1, an alkaline solution is added to a mixed aqueous solution of Ni salt and M salt to co-precipitate the hydroxide of Ni and M, and the obtained precipitate is filtered, washed with water and dried to form a nickel composite. Hydroxide: A crystallization step to obtain Ni _x M1 _-x (OH) ₂ and
The obtained nickel composite hydroxide: Ni _x M1 _-x (OH) ₂ and the lithium compound have a molar ratio of Li to the total of Ni and M: Li / (Ni + M) of 1.00 to 1.15. The lithium nickel composite oxide is obtained by firing the mixture at a temperature of 700 ° C. or higher and 1000 ° C. or lower.
Disclosed is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which comprises a water washing step of washing the obtained lithium nickel composite oxide with water.

Further, in Patent Document 1, after the crystallization step and before the firing step, the nickel composite hydroxide obtained in the crystallization step: Ni _x M1 _-x (OH) ₂ is provided in an air atmosphere. It is also disclosed to have an oxidative roasting step of obtaining a composite oxide by roasting at a temperature of less than 800 ° C. for 1 hour or more.

Japanese Unexamined Patent Publication No. 2012-119093

However, the lithium nickel composite oxidation obtained when a lithium nickel composite oxide in which a part of nickel is replaced with aluminum is manufactured by the method for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery disclosed in Patent Document 1. The content of aluminum in the product was low, and in some cases it was significantly lower than the charged composition.

As described above, aluminum in which a part of nickel in the lithium nickel composite oxide is replaced can be used as a battery of the lithium secondary battery when the lithium nickel composite oxide is used as a positive electrode material of the lithium secondary battery. It has the function of enhancing the characteristics and safety. Therefore, when the positive electrode active material for a non-aqueous electrolyte secondary battery is used, the nickel composite oxide, which is a precursor of the positive electrode active material for a non-aqueous electrolyte secondary battery, which can suppress the decrease in the aluminum content, is used. I was asked.

Therefore, in view of the problems of the above-mentioned prior art, in one aspect of the present invention, aluminum is used as a precursor of a positive electrode active material for a non-aqueous electrolyte secondary battery and is used as a positive electrode active material for a non-aqueous electrolyte secondary battery. It is an object of the present invention to provide a nickel composite oxide capable of suppressing a decrease in the content of the nickel composite oxide.

According to one aspect of the present invention in order to solve the above problems.
A nickel composite oxide containing Ni, Co, and Al, which are precursors of positive electrode active materials for non-aqueous electrolyte secondary batteries.
Provided is a nickel composite oxide in which the ratio of Al in the metal element on the surface of the nickel composite oxide is 11.5 at% or less.

According to one aspect of the present invention, the aluminum content is reduced when the positive electrode active material for a non-aqueous electrolyte secondary battery is used as the precursor of the positive electrode active material for a non-aqueous electrolyte secondary battery. It is possible to provide a nickel composite oxide that can be suppressed.

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.
[Nickel composite oxide]
First, a configuration example of the nickel composite oxide of the present embodiment will be described.

The nickel composite oxide of the present embodiment is a precursor of a positive electrode active material for a non-aqueous electrolyte secondary battery, and may contain Ni, Co, and Al. Then, the ratio of Al in the metal element on the surface of the nickel composite oxide can be set to 11.5 at% or less.

The inventors of the present invention have diligently investigated the cause of a decrease in the Al (aluminum) content when producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which may be significantly lower than the charged composition.

As a result, in the manufacturing process of the positive electrode active material for the non-aqueous electrolyte secondary battery, when a mixture of the nickel composite oxide and the lithium compound is fired and then washed with water, lithium aluminate elutes, which is obtained. It was found that the aluminum content in the lithium-nickel composite oxide was reduced.

Then, by using a nickel composite oxide having an Al content of a certain amount or less in the metal element present on the surface as a raw material, the elution of Al during washing with water is suppressed, and Al in the obtained lithium nickel composite oxide is suppressed. The present invention has been completed by finding that it is possible to suppress a decrease in the content of aluminum.

Therefore, the nickel composite oxide of the present embodiment is a precursor of the positive electrode active material for a non-aqueous electrolyte secondary battery as described above, and contains Ni (nickel), Co (cobalt), and Al (aluminum). Can include. Then, the ratio of Al in the metal element on the surface of the nickel composite oxide can be set to 11.5 at% or less.

When producing a positive electrode active material for a non-aqueous electrolyte secondary battery, a mixture of a nickel composite oxide and a lithium compound is fired to obtain lithium derived from the lithium compound while maintaining the form of the nickel composite oxide. It is diffused into a nickel composite oxide to form a lithium nickel composite oxide. Therefore, by setting the ratio of Al in the metal element present on the surface of the nickel composite oxide particles to a certain amount or less, the aluminum present on the particle surface of the lithium nickel composite oxide particles obtained after firing. Since the proportion of the compound can also be suppressed, it is considered that the elution of Al during washing with water can be suppressed.

Then, by setting the ratio of Al in the metal element on the surface of the nickel composite oxide as a raw material to 11.5 at% or less, the lithium nickel composite oxide obtained by using the nickel composite oxide is compared with that before washing with water. It is preferable because the retention rate of aluminum after washing with water can be 90% or more.

According to the studies by the inventors of the present invention, in the process of producing the lithium nickel composite oxide, almost no elution or the like occurs in Al and other metals except when the lithium nickel composite oxide is washed with water. , The charged composition is maintained. Therefore, the retention rate of aluminum for the lithium nickel composite oxide after washing with water as compared with that before washing with water is the same as the retention rate of aluminum with respect to the charged composition for the lithium nickel composite oxide. Then, by suppressing the elution of Al during washing with water as described above, it is possible to suppress the change in the aluminum content of the lithium nickel composite oxide from the charged composition.

Further, when the obtained lithium-nickel composite oxide is washed with water, almost no Ni elutes. Therefore, the retention rate of aluminum after washing with water as compared with that before washing with water, that is, the maintenance rate of aluminum with respect to the charged composition, depends on, for example, the rate of change in the mass ratio of Al and Ni contained in the lithium nickel composite oxide before and after washing with water. Can be evaluated. Further, the metal element on the surface of the nickel composite oxide means all the metal elements including Al present on the surface of the nickel composite oxide.

It is more preferable that the ratio of Al in the metal element on the surface of the nickel composite oxide is 10.0 at% or less from the viewpoint of particularly suppressing the elution of Al during washing with water.

The lower limit of the ratio of Al in the metal element on the surface of the nickel composite oxide is not particularly limited, but Al is not present on the surface of the nickel composite oxide from the viewpoint of preventing the elution of Al during washing with water. Is preferable, so it can be set to 0 or more, for example.

The nickel composite oxide of the present embodiment can be a nickel composite oxide powder composed of a plurality of nickel composite oxide particles, for example, a metal element on the surface of an arbitrarily selected nickel composite oxide particles. It is preferable that the ratio of Al in the mixture satisfies the above-mentioned range. In particular, it is more preferable that the ratio of Al in the metal element satisfies the above-mentioned range on the surface of each nickel composite oxide particle.

The ratio of Al in the metal element on the surface of the nickel composite oxide is calculated from the abundance of each metal on the surface of the nickel composite oxide measured by, for example, XPS (X-ray Photoelectron Spectroscopy) or the like. can.

The composition of the nickel composite oxide of the present embodiment is not particularly limited, and for example, the substance amount ratio (molar ratio) of Ni, Co, and Al (Ni: Co: Al) is Ni: Co: Al = 1-x−. A nickel composite oxide having y: x: y (where 0.05 ≦ x ≦ 0.35, 0 <y ≦ 0.05) can be preferably used.

When the content ratio of aluminum in the nickel composite oxide is small, when the lithium nickel composite oxide is produced using the nickel composite oxide, when the content ratio of aluminum is significantly lower than the charged composition, the lithium nickel composite It may have a particularly large effect on the properties of the oxide. Then, in the nickel composite oxide of the present embodiment, when a lithium nickel composite oxide is produced using the nickel composite oxide, it is possible to suppress a decrease in the content ratio of aluminum from the charged composition. Therefore, the positive electrode active material of the present embodiment exerts a particularly high effect when the content ratio of aluminum is small. Therefore, the content ratio of aluminum in the metal component contained in the nickel composite oxide of the present embodiment is preferably 5% or less, and more preferably less than 4%.

When the metal components contained in the nickel composite oxide of the present embodiment are only Ni, Co, and Al, the above-mentioned formula shown as the substance amount ratio of Ni, Co, and Al (Ni: Co: Al) is shown. The y indicating the substance amount ratio of Al in the substance is preferably 0.05 or less, and more preferably less than 0.04.

According to the nickel composite oxide of the present embodiment described above, when a positive electrode active material for a non-aqueous electrolyte secondary battery, that is, a lithium nickel composite oxide is used, the Al content is reduced from the charged composition. Can be suppressed.
[Manufacturing method of nickel composite oxide]
Next, a configuration example of the method for producing the nickel composite oxide of the present embodiment will be described.

The method for producing the nickel composite oxide of the present embodiment is not particularly limited, but can have a roasting step of roasting the nickel composite hydroxide in an oxygen-containing gas atmosphere.

The conditions for roasting the nickel composite hydroxide are not particularly limited. However, for example, the ratio of Al in the metal element on the surface of the obtained nickel composite oxide changes depending on the composition of the nickel composite hydroxide, the atmosphere at the time of roasting, etc., so a preliminary test should be conducted in advance. Is preferable. Then, it is preferable to confirm the relationship between the roasting conditions and the ratio of Al in the metal element on the surface of the obtained nickel composite oxide by a preliminary test, and set the conditions for producing the nickel composite oxide.

According to the studies by the inventors of the present invention, for example, the roasting step is performed at the first roasting temperature, the first roasting step, and the second roasting temperature, which is lower than the first roasting temperature. The target product can be obtained by roasting in two steps, that is, the second roasting step.

This is done by removing water in a short time by roasting at the first roasting temperature, which is a high roasting temperature, and roasting at the second roasting temperature, which is a temperature lower than the first roasting temperature. It is considered that the position of each component in the nickel composite oxide can be optimized.

When the first roasting step and the second roasting step are carried out as described above, the first roasting temperature and the second roasting temperature depend on the composition of the nickel composite oxide used in the roasting step and the like. The temperature is not particularly limited, but is preferably less than 750 ° C, more preferably 700 ° C or lower. The lower limit of the first roasting temperature and the second roasting temperature is not particularly limited, but may be 400 ° C. or higher in consideration of productivity and the like.

The temperature difference between the first roasting temperature and the second roasting temperature is not particularly limited, but can be, for example, 30 ° C. or higher and 100 ° C. or lower.

The atmosphere when roasting the nickel composite hydroxide is not particularly limited and may be an oxygen-containing gas atmosphere, but it is particularly preferable to perform the roasting in an oxygen-containing gas stream. The oxygen-containing gas is not particularly limited, and oxygen, a mixed gas of oxygen and an inert gas, air, or the like can be used, but it is preferable to use air that can be easily performed.

The equipment used for roasting is not particularly limited as long as it can heat the nickel composite hydroxide in an oxygen-containing gas atmosphere, and an electric furnace or the like that does not generate gas is preferably used.

The method for producing the nickel composite hydroxide used in the roasting step is not particularly limited, and the nickel composite hydroxide can be produced by coprecipitating the contained metals such as Ni, Co, Al, and any other additive element. ..

The composition of the nickel composite hydroxide used in the roasting step is not particularly limited, and the composition can be a composition corresponding to the nickel composite oxide to be produced. For example, the substance amount ratio of Ni, Co, and Al (Ni: Co: Al) is Ni: Co: Al = 1-xy: x: y (where 0.05 ≦ x ≦ 0.35, 0 <. It can be a nickel composite hydroxide having y ≦ 0.05).

The content ratio of aluminum in the metal component contained in the nickel composite hydroxide used in the roasting step is preferably 5% or less, and more preferably less than 4%.

When the metal components contained in the nickel composite hydroxide used in the roasting step are only Ni, Co, and Al, the above-mentioned description is shown as the substance amount ratio of Ni, Co, and Al (Ni: Co: Al). The y indicating the substance amount ratio of Al in the above formula is preferably 0.05 or less, and more preferably less than 0.04.
[Non-aqueous electrolyte positive electrode active material]
Next, a configuration example of the non-aqueous electrolyte positive electrode active material of the present embodiment will be described.

The non-aqueous electrolyte positive electrode active material of the present embodiment (hereinafter, also simply referred to as “positive electrode active material”) contains Ni, Co, and Al, and the retention rate of aluminum with respect to the charged composition can be 90% or more. ..

Here, the retention rate of aluminum with respect to the charged composition means the retention rate of aluminum in the obtained positive electrode active material with respect to the charged composition in the raw material prepared for producing the positive electrode active material, that is, the lithium nickel composite oxide. ..

As described above, conventionally, when the positive electrode active material is manufactured, the Al component elutes when the positive electrode active material is washed with water after the firing step, and the Al content in the obtained lithium nickel composite oxide is low. In some cases, the composition was significantly lower than that of the charged composition. On the other hand, with respect to the positive electrode active material of the present embodiment, since the elution of Al can be suppressed even after washing with water, the retention rate of aluminum of the positive electrode active material with respect to the charged composition can be 90% or more. Since there is almost no elution of Al and other metals except during washing with water, the retention rate of aluminum with respect to the charged composition of the positive electrode active material is the post-washing compared with that before washing with the positive electrode active material. It can be said that it is the maintenance rate of aluminum.

Here, washing the positive electrode active material after the firing step with water means that the positive electrode active material after the firing step is put into pure water to form a slurry, stirred for a predetermined time, and then separated from water. For washing the positive electrode active material with water after the firing step, for example, the positive electrode active material is weighed so that the mass ratio is 0.5 or more and 2 or less with respect to 1 water, and the positive electrode active material is added to pure water to form a slurry. It can be carried out by stirring for 1 minute or more and 60 minutes or less, then filtering and drying.

Further, as described above, when the positive electrode active material is washed with water, almost no Ni elutes. Therefore, the retention rate of aluminum for the charged composition of the positive electrode active material, that is, the retention rate of aluminum of the positive electrode active material after washing with water for the positive electrode active material before washing with water is, for example, the positive electrode active material after washing with water before washing with water. It can be evaluated by the maintenance rate of the mass ratio of Al and Ni contained.

Specifically, the mass of aluminum in the positive electrode active material before washing with water is W _Al1 , the mass of nickel in the positive electrode active material before washing with water is W _Ni1 , and the mass of aluminum in the positive electrode active material after washing with water is W _Al2 . When the mass of nickel in the positive electrode active material after washing with water is W _Ni2 , the retention rate of aluminum with respect to the charged composition can be calculated by the following formula.
(Aluminum retention rate:%) = 100 × (W _Al2 / W _Ni2 ) / (W _Al1 / W _Ni1 )
The positive electrode active material of the present embodiment can be produced by using the nickel composite oxide described above, and the composition thereof is not particularly limited.

In the positive electrode active material of the present embodiment, for example, the substance amount ratio (Ni: Co: Al) of Ni, Co, and Al is Ni: Co: Al = 1-xy: x: y (however, 0.05). ≦ x ≦ 0.35, 0 <y ≦ 0.05).

The content ratio of aluminum in the amount of substance of the metal components other than Li contained in the positive electrode active material of the present embodiment is preferably 5% or less, and more preferably less than 4%.

When the metal components other than Li contained in the positive electrode active material of the present embodiment are only Ni, Co, and Al, the above-mentioned formula shown as the substance amount ratio (Ni: Co: Al) of Ni, Co, and Al is shown. The y indicating the substance amount ratio of Al in the substance is preferably 0.05 or less, and more preferably less than 0.04.

The positive electrode active material of the present embodiment can be a lithium nickel composite oxide, which is a substance amount ratio of, for example, Li and another metal element Me, that is, the total of, for example, Ni, Co, and Al. Li / Me can be 0.90 or more and 1.10 or less.

Since the positive electrode active material of the present embodiment can be produced from the above-mentioned nickel composite oxide, the positive electrode active material can suppress the elution of aluminum when washed with water in the production process. Therefore, when the non-aqueous electrolyte secondary battery using the positive electrode active material of the present embodiment as the positive electrode material is used, the non-aqueous electrolyte secondary battery having excellent battery characteristics can be obtained.
[Manufacturing method of positive electrode active material]
The method for producing the positive electrode active material of the present embodiment is not particularly limited. The method for producing a positive electrode active material of the present embodiment can include, for example, the following steps.

A mixing step of preparing a mixture of the above-mentioned nickel composite oxide and a lithium compound.
A firing step for firing the above mixture.
A water washing process in which the fired product obtained in the firing process is washed with water.

Hereinafter, each step will be described.
(Mixing process)
In the mixing step, the nickel composite oxide and the lithium compound can be mixed to obtain a mixture (mixture powder).

The ratio when the nickel composite oxide and the lithium compound are mixed is not particularly limited, and can be selected according to the composition of the positive electrode active material to be produced.

Since Li / Me hardly changes before and after the firing step described later, the Li / Me in the mixture to be subjected to the firing step is almost the same as the Li / Me in the obtained positive electrode active material. Therefore, it is preferable to mix Li / Me in the mixture prepared in the mixing step so as to be the same as Li / Me in the positive electrode active material to be obtained.

For example, in the mixing step, the mixture is mixed so that the ratio (Li / Me) of the number of atoms of a metal other than lithium in the mixture to the number of atoms of lithium (Li) is 0.90 or more and 1.10 or less. Is preferable. In particular, it is more preferable to mix so that the ratio (Li / Me) of the number of atoms of lithium in the mixture to the number of atoms of a metal other than lithium is 1.00 or more and 1.08 or less.

The lithium compound to be used in the mixing step is not particularly limited, but for example, one or more selected from lithium hydroxide, lithium carbonate and the like can be preferably used.

In the mixing step, a general mixer can be used as a mixing means for mixing the nickel composite oxide and the lithium compound, and for example, a shaker mixer, a ladygemixer, a juriamixer, a V blender, or the like can be used. good.
(Baking process)
The firing step is a step of firing the mixture obtained in the above mixing step to obtain a positive electrode active material. When the mixture is fired in the firing step, lithium in the lithium compound is diffused in the nickel composite oxide to form a lithium nickel composite oxide which is a positive electrode active material.

In the firing step, the firing temperature for firing the mixture is not particularly limited, but is preferably 600 ° C. or higher and 950 ° C. or lower, and more preferably 700 ° C. or higher and 900 ° C. or lower.

By setting the firing temperature to 600 ° C. or higher, the diffusion of lithium into the nickel composite oxide can be sufficiently promoted, and the crystal structure of the obtained positive electrode active material, lithium nickel composite oxide, can be made uniform. Can be done. Therefore, when the product is used as the positive electrode active material, the battery characteristics can be particularly improved, which is preferable. Further, since the reaction can be sufficiently proceeded, it is possible to suppress the residual of excess lithium and the residual of unreacted particles.

By setting the firing temperature to 950 ° C. or lower, it is possible to suppress the progress of sintering between the particles of the positive electrode active material to be produced. In addition, it is possible to suppress the occurrence of abnormal grain growth and suppress the coarsening of the particles of the obtained positive electrode active material.

Further, in the process of raising the temperature to the heat treatment temperature, it is preferable to keep the temperature near the melting point of the lithium compound for about 1 hour or more and 5 hours or less so that the reaction can be carried out more uniformly.

Of the firing times in the firing step, the holding time at a predetermined temperature, that is, the above-mentioned firing temperature is not particularly limited, but is preferably 2 hours or longer, more preferably 4 hours or longer. This is because by setting the holding time at the firing temperature to 2 hours or more, it is possible to sufficiently promote the production of the positive electrode active material and more reliably prevent the unreacted substance from remaining.

The upper limit of the holding time at the firing temperature is not particularly limited, but is preferably 24 hours or less in consideration of productivity and the like.

The atmosphere at the time of firing is not particularly limited, but an oxidizing atmosphere is preferable. As the oxidizing atmosphere, an oxygen-containing gas atmosphere can be preferably used, and for example, an atmosphere having an oxygen concentration of 18% by volume or more and 100% by volume or less is more preferable.

This is because the crystallinity of the positive electrode active material can be particularly enhanced by setting the oxygen concentration in the atmosphere at the time of firing to 18% by volume or more.

In the case of an oxygen-containing gas atmosphere, for example, the atmosphere, oxygen, a mixed gas of oxygen and an inert gas, or the like can be used as the gas constituting the atmosphere.

When a mixed gas of oxygen and an inert gas is used as the gas constituting the oxygen-containing gas atmosphere, for example, the oxygen concentration in the mixed gas preferably satisfies the above range.

In particular, the firing step is preferably carried out in an oxygen-containing gas stream, and more preferably in the atmosphere or an oxygen stream. In particular, considering the battery characteristics, it is more preferable to perform the operation in an oxygen stream.

The furnace used for firing is not particularly limited as long as it can fire the mixture in an oxidizing atmosphere, but from the viewpoint of keeping the atmosphere in the furnace uniform, an electric furnace that does not generate gas. Is preferable, and either a batch type or a continuous type furnace can be used.

The positive electrode active material obtained by the firing step may be aggregated or slightly sintered. In this case, it may be crushed.

Here, crushing is to apply mechanical energy to an agglomerate composed of a plurality of secondary particles generated by sintering necking between secondary particles during firing to almost destroy the secondary particles themselves. It is an operation to separate secondary particles and loosen aggregates.

Further, it is preferable to carry out temporary firing before the firing step.

When the calcination is carried out, the calcination temperature is not particularly limited, but may be lower than the calcination temperature in the calcination step. The calcination temperature is preferably, for example, 250 ° C. or higher and 600 ° C. or lower, and more preferably 350 ° C. or higher and 550 ° C. or lower.

The tentative firing time, that is, the holding time at the tentative firing temperature is preferably, for example, about 1 hour or more and 10 hours or less, and more preferably 3 hours or more and 6 hours or less.

After the temporary firing, it can be cooled once and then subjected to the firing step, but it is also possible to continuously carry out the firing step by raising the temperature from the temporary firing temperature to the firing temperature.

The atmosphere when performing the temporary firing is not particularly limited, but can be, for example, the same atmosphere as in the firing step.

By carrying out the calcination, lithium is sufficiently diffused into the nickel composite oxide, and a particularly uniform positive electrode active material can be obtained.
(Washing process)
A water washing step of washing the fired product obtained by the firing step with water can be carried out. In the water washing step, for example, the obtained calcined product can be put into pure water to form a slurry, stirred for a predetermined time, and then separated from water. For example, the positive electrode active material is 0.5 or more with respect to 1 water by mass ratio. It is weighed to 2 or less, and the positive electrode active material is added to pure water to form a slurry, which can be stirred for 5 minutes or more and 60 minutes or less, and then filtered and dried.
[Non-aqueous electrolyte secondary battery]
Next, a configuration example of the non-aqueous electrolyte secondary battery of the present embodiment will be described.

The non-aqueous electrolyte secondary battery of the present embodiment can have a positive electrode using the above-mentioned positive electrode active material as a positive electrode material.

First, a configuration example of the structure of the non-aqueous electrolyte secondary battery of the present embodiment will be described.

The non-aqueous electrolyte secondary battery of the present embodiment can have substantially the same structure as a general non-aqueous electrolyte secondary battery except that the above-mentioned positive electrode active material is used as the positive electrode material.

Specifically, the non-aqueous electrolyte secondary battery of the present embodiment can have a structure including a case and a positive electrode, a negative electrode, a non-aqueous electrolyte solution, and a separator housed in the case.

More specifically, a positive electrode and a 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 electrolytic solution. Then, the positive electrode current collector of the positive electrode and the positive electrode terminal communicating with the outside are connected, and the negative electrode current collector of the negative electrode and the negative electrode terminal communicating with the outside are connected by using a current collector lead or the like, and connected to the case. It can have a closed structure.

Needless to say, the structure of the non-aqueous electrolyte secondary battery of the present embodiment is not limited to the above example, and various shapes such as a tubular shape and a laminated shape can be adopted as the outer shape thereof.

A configuration example of each member will be described below.
(Positive electrode)
First, the positive electrode will be described.

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 and dried on the surface of a current collector made of aluminum foil. 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 and kneading it. 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 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, ethylene propylene diene rubber, styrene butadiene, cellulose resin, and polyacrylic acid. One or more 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.
(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.

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. Will be done.

The negative electrode mixture paste can be made into a paste by adding an appropriate solvent to the negative electrode mixture in which the negative electrode active material and the binder are mixed.

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

The occluded 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 a phenol resin, and a powdered body of a carbon substance such as coke can be used.

When the occlusal substance is used 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 electrolytic solution.

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

The non-aqueous electrolyte secondary battery of the present embodiment includes a positive electrode using the above-mentioned positive electrode active material as the positive electrode material. Therefore, it is possible to obtain a non-aqueous electrolyte secondary battery having excellent battery characteristics and safety.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following examples.
[Example 1]
(Manufacturing of nickel composite oxide)
A nickel composite oxide was produced by the following procedure.

Ni _0.869 Co _0.094 Al _0.037 (OH) ₂ was prepared as the nickel composite hydroxide, and the nickel composite hydroxide was placed in an air (oxygen: 21% by volume) air stream at 645 ° C. After roasting at the first roasting temperature for 0.5 hours (first roasting step), the temperature was lowered to the second roasting temperature of 600 ° C. and roasting was performed for 1 hour (second roasting). Step) (roasting process).

By roasting the nickel composite hydroxide in this way, the water contained in the nickel composite hydroxide is removed, and the nickel composite represented by Ni _0.869 Co _0.094 Al _0.037 O is obtained. It was converted to oxide and recovered.

In addition, about the obtained nickel composite oxide, according to XPS (model: Versa Provide II manufactured by ULVAC-Phi), each component on the particle surface under measurement conditions (Exciting substance: Monochromated Al-Kα, Tilto Angle: 45 °). When the content (amount of substance) was evaluated and the ratio of Al in the metal element (Ni, Co, Al) (Al / (Ni + Co + Al)) was calculated, it was confirmed that it was 7.3 at%.

Further, from the measurement result by XPS, it was confirmed that the oxygen content ratio on the particle surface of the nickel composite oxide was calculated to be 47 at%.

Table 1 shows the evaluation results of the surface of the nickel composite oxide particles obtained in "Evaluation Results of Nickel Composite Oxide", that is, the ratio of Al in the metal element and the oxygen content allocation.
(Manufacturing of positive electrode active material)
A mixture of the lithium compound and the above-mentioned nickel composite oxide was prepared by the following procedure (mixing step).

As the lithium compound, lithium hydroxide monohydrate (LiOH · _H2O ) was subjected to anhydrous treatment by vacuum drying, and the obtained anhydrous lithium hydroxide was used.

In the mixing step, the lithium compound and the nickel composite oxide were weighed and mixed so that the ratio of the number of atoms in the mixture was 1.025, and the mixture was prepared. Note that Me here means the total number of atoms of metals other than Li, and is the total of Ni, Co, and Al.

The mixture obtained in the mixing step is placed in a firing container having an internal size of 280 mm (L) × 280 mm (W) × 90 mm (H), and this is charged with oxygen using a roller hearth kiln which is a continuous firing furnace. Baking was performed at a maximum temperature of 765 ° C. in an atmosphere having a concentration of 80% by volume and the balance being nitrogen (firing step). A part of the positive electrode active material obtained in the firing step was sampled, and the content ratio (wt%) of nickel and aluminum in the positive electrode active material was evaluated by ICP-AES described later.

Further, the obtained calcined product was added to pure water so that the mass ratio was 0.75 with respect to 1 water to form a slurry, and after stirring for 30 minutes, the mixture was filtered and dried to obtain a positive electrode active material (). Washing process).

The content ratio (wt%) of nickel and aluminum in the positive electrode active material obtained after washing with water was evaluated using ICP-AES (model: ICPE-9000 manufactured by Shimadzu Corporation).

The retention rate of aluminum with respect to the charged composition was calculated from the change in the content ratio (Al / Ni) of nickel and aluminum in the positive electrode active material before and after washing with water. The maintenance rate of aluminum with respect to the charged composition is shown as "aluminum maintenance rate" in Table 1.

The results are shown in Table 1.

［実施例２］
ニッケル複合酸化物を製造する際の焙焼工程において、ニッケル複合水酸化物を、空気（酸素：２１容量％）気流中にて、７４５℃の第１焙焼温度で０．５時間の焙焼を行った（第１焙焼ステップ）後、７００℃の第２焙焼温度まで降温して１時間の焙焼を行った（第２焙焼ステップ）点以外は、実施例１と同様にしてニッケル複合酸化物を製造、評価した。

[Example 2]
In the roasting process for producing a nickel composite oxide, the nickel composite hydroxide is roasted in an air (oxygen: 21% by volume) air stream at a first roasting temperature of 745 ° C. for 0.5 hours. After the above (first roasting step), the temperature was lowered to the second roasting temperature of 700 ° C. and roasting was performed for 1 hour (second roasting step), except that the same procedure as in Example 1 was performed. A nickel composite oxide was produced and evaluated.

In this embodiment, the nickel composite hydroxide is roasted to remove the water contained in the nickel composite hydroxide, which is represented by Ni _0.869 Co _0.094 Al _0.037 O. It was converted to a nickel composite oxide and recovered.

Then, using the obtained nickel composite oxide, the positive electrode active material was produced and evaluated in the same manner as in the case of Example 1.

The results are shown in Table 1.
[Example 3]
A nickel composite oxide was produced and evaluated in the same manner as in Example 1 except that Ni _0.82 Co _0.15 Al _0.03 (OH) ₂ was used as the nickel composite hydroxide.

In this embodiment, the nickel composite hydroxide is roasted to remove the water contained in the nickel composite hydroxide, which is represented by Ni _0.82 Co _0.15 Al _0.03 O. It was converted to a nickel composite oxide and recovered.

Then, using the obtained nickel composite oxide, the positive electrode active material was produced and evaluated in the same manner as in the case of Example 1.

The results are shown in Table 1.
[Example 4]
A nickel composite oxide was produced and evaluated in the same manner as in Example 1 except that Ni _0.91 Co _0.06 Al _0.03 (OH) ₂ was used as the nickel composite hydroxide.

In this embodiment, the nickel composite hydroxide is roasted to remove the water contained in the nickel composite hydroxide, which is represented by Ni _0.91 Co _0.06 Al _0.03 O. It was converted to a nickel composite oxide and recovered.

Then, using the obtained nickel composite oxide, the positive electrode active material was produced and evaluated in the same manner as in the case of Example 1.

The results are shown in Table 1.
[Comparative Example 1]
In the roasting process for producing a nickel composite oxide, the nickel composite hydroxide is roasted in an air (oxygen: 21% by volume) air stream at a first roasting temperature of 795 ° C. for 0.5 hours. After performing (first roasting step), the temperature was lowered to the second roasting temperature of 750 ° C. and roasting was performed for 1 hour (second roasting step), except that the same procedure as in Example 1 was performed. A nickel composite oxide was produced and evaluated.

In this comparative example, the water contained in the nickel composite hydroxide is removed by roasting the nickel composite hydroxide, which is represented by Ni _0.869 Co _0.094 Al _0.037 O. It was converted to a nickel composite oxide and recovered.

Then, using the obtained nickel composite oxide, the positive electrode active material was produced and evaluated in the same manner as in the case of Example 1.

The results are shown in Table 1.

As shown in Table 1, in Examples 1 to 4, it can be confirmed that the nickel composite oxide having the ratio of Al to the metal element on the surface of the nickel composite oxide of 11.5 at% or less is obtained. rice field.

When the positive electrode active material was produced using the nickel composite oxide, it was confirmed that the elution of aluminum was suppressed before and after washing with water, and the retention rate of aluminum was 90% or more. That is, it was confirmed that the content of aluminum in the positive electrode active material was almost the same as the charged composition.

On the other hand, in Comparative Example 1, it was confirmed that the ratio of Al to the metal element on the surface of the nickel composite oxide was 11.9 at%, which was higher than that of Examples 1 to 4.

When the positive electrode active material was produced using the nickel composite oxide, it was confirmed that the amount of aluminum eluted before and after washing with water was large, and the aluminum retention rate was less than 90%. That is, it was confirmed that the content of aluminum in the positive electrode active material was low, which was significantly lower than the charged composition.

Claims (4)

A nickel composite oxide containing Ni, Co, and Al, which are precursors of positive electrode active materials for non-aqueous electrolyte secondary batteries.
A nickel composite oxide having an Al content of 11.5 at% or less in the metal element on the surface of the nickel composite oxide. The substance amount ratio of Ni, Co, and Al (Ni: Co: Al) is Ni: Co: Al = 1-xy: x: y (where 0.05 ≦ x ≦ 0.35, 0 <y). ≦ 0.05) The nickel composite oxide according to claim 1. A method for producing a positive electrode active material containing Ni, Co, and Al.
A mixing step of preparing a mixture of the nickel composite oxide according to claim 1 or 2 and a lithium compound,
The firing step of firing the mixture and
Including a water washing step of washing the fired product obtained in the firing step with water,
A method for producing a positive electrode active material in which the retention rate of aluminum after washing with water is 90% or more as compared with that before washing with water . The substance amount ratio of Ni, Co, and Al (Ni: Co: Al) is Ni: Co: Al = 1-xy: x: y (where 0.05 ≦ x ≦ 0.35, 0 <y). ≤0.05) The method for producing a positive electrode active material according to claim 3.