JP6937152B2 - Method for producing lithium composite metal oxide - Google Patents

Description

The present invention relates to a method for producing a lithium composite metal oxide.

Lithium composite metal oxides are used as positive electrode active materials for lithium secondary batteries. Lithium secondary batteries have already been put into practical use not only in small power sources for mobile phones and notebook computers, but also in medium- and large-sized power sources for automobiles and power storage.

The method for producing a lithium composite metal oxide generally includes a raw material mixing step, a firing step, and a cleaning step. Water is used as the cleaning liquid used in the cleaning process. For example, Patent Document 1 describes a step of calcining a lithium composite metal oxide having a specific composition and then stirring and washing the lithium composite metal oxide at a ratio of 50 to 200 parts by weight of water with respect to 100 parts by weight of the lithium composite metal oxide. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery is described.

JP-A-2007-242288

As the application fields of lithium secondary batteries continue to expand, the positive electrode active material of lithium secondary batteries is required to further improve battery characteristics such as high initial charge / discharge efficiency.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a lithium composite metal oxide having high initial charge / discharge efficiency.

As a result of diligent studies by the present inventors, it has been found that when the cleaning step is carried out with water, lithium in the lithium composite metal oxide is eluted and the battery characteristics are deteriorated. As a result of diligent studies by the present inventors, the above-mentioned problems have been solved by performing the cleaning step of the lithium composite metal oxide step by step and further using a specific cleaning liquid.
That is, the present invention includes the following inventions [1] to [5].
[1] A method for producing a lithium composite metal oxide containing at least nickel, wherein a first cleaning step of cleaning the lithium composite metal oxide with a first cleaning liquid and a cleaning product obtained in the first cleaning step are used. The first cleaning liquid is an alkaline cleaning liquid containing a compound containing an alkali metal, and the second cleaning liquid is an alkaline cleaning liquid. A method for producing a lithium composite metal oxide, wherein the concentration of the alkali metal in the first cleaning liquid is higher than the concentration of the alkali metal in the second cleaning liquid.
[2] The method for producing a lithium composite metal oxide according to [1], wherein the lithium composite metal oxide is represented by the following composition formula (I).
_{Li [Li x (Ni (1} -y-z-w) Co y Mn z M w) 1-x] O 2 ··· (I)
(However, M is one or more metal elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga and V, and 0 ≦ x ≦ 0.2, 0 <y ≦ 0.4, 0 ≦ z ≦ 0.4, 0 ≦ w ≦ 0.1 is satisfied.)
[3] The method for producing a lithium composite metal oxide according to [2], wherein y + z + w ≦ 0.3 in the composition formula (I).
[4] The method for producing a lithium composite metal oxide according to any one of [1] to [3], wherein the second cleaning liquid is an aqueous solution of lithium hydroxide.
[5] The method for producing a lithium composite metal oxide according to any one of [1] to [4], wherein the lithium hydroxide concentration of the second cleaning liquid is 1% by mass or more and 30% by mass or less.
[6] The method for producing a lithium composite metal oxide according to any one of [1] to [5], wherein the second cleaning liquid is aqueous ammonia.

According to the present invention, it is possible to provide a method for producing a lithium composite metal oxide having high initial charge / discharge efficiency.

It is a schematic block diagram which shows an example of a lithium ion secondary battery.

<Manufacturing method of lithium composite metal oxide>
In the method for producing a lithium composite metal oxide of the present invention, the manufacturing step of the metal composite compound and the manufacturing step of the lithium composite metal oxide are arbitrary steps, and the subsequent first cleaning step and the second cleaning step are indispensable. Prepare as a process.
Hereinafter, each step will be described.

In the method for producing a lithium composite metal oxide of the present invention, first, a metal other than lithium, that is, an essential metal composed of Ni, Co and Mn, and Fe, Cu, Ti, Mg, Al, W, B, It is preferable to prepare a metal composite compound containing any one or more arbitrary metals of Mo, Nb, Zn, Sn, Zr, Ga and V, and to calcin the metal composite compound with an appropriate lithium salt. As the metal composite compound, a metal composite hydroxide or a metal composite oxide is preferable. Hereinafter, an example of a method for producing a positive electrode active material will be described separately for a process for producing a metal composite compound and a process for producing a lithium composite metal oxide.

(Manufacturing process of metal composite compound)
The metal composite compound can be produced by a commonly known batch coprecipitation method or continuous coprecipitation method. Hereinafter, the production method thereof will be described in detail by taking a metal composite hydroxide containing nickel, cobalt and manganese as an example.

First co-precipitation method, in particular by a continuous method described in 2002-201028 JP-nickel salt solution, cobalt salt solution, is reacted manganese salt solution and a complexing _{agent, Ni a Co b Mn c (} OH) ₂ (In the formula, a + b + c = 1) is produced as a composite metal hydroxide.

The nickel salt which is the solute of the nickel salt solution is not particularly limited, and for example, any one of nickel sulfate, nickel nitrate, nickel chloride and nickel acetate can be used. As the cobalt salt which is the solute of the cobalt salt solution, for example, any one of cobalt sulfate, cobalt nitrate, and cobalt chloride can be used. As the manganese salt which is the solute of the manganese salt solution, for example, any one of manganese sulfate, manganese nitrate, and manganese chloride can be used. The above metal salts are used in a ratio corresponding to the composition ratio of _{the above Ni a} Co _b Mn _c (OH) _2. Also, water is used as the solvent.

The complexing agent can form a complex with ions of nickel, cobalt, and manganese in an aqueous solution, and includes, for example, an ammonium ion feeder (ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc.), hydrazine, and the like. Examples include ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracildiacetic acid, and glycine.

At the time of precipitation, alkali metal hydroxides (for example, sodium hydroxide and potassium hydroxide) are added if necessary in order to adjust the pH value of the aqueous solution.

When a complexing agent is continuously supplied to the reaction vessel in addition to the nickel salt solution, cobalt salt solution, and manganese salt solution, nickel, cobalt, and manganese react with each other, and Ni _a Co _b Mn _c (OH) ₂ Is manufactured. During the reaction, the temperature of the reaction vessel is controlled within the range of, for example, 20 ° C. or higher and 80 ° C. or lower, preferably 30 ° C. or higher and 70 ° C. or lower, and the pH value in the reaction vessel is, for example, pH 9 or higher and pH 13 or lower, preferably pH 11 or higher and pH 13 or lower. The substance in the reaction vessel is appropriately stirred under the control within the following range. The reaction vessel is of a type in which the formed reaction precipitate overflows for separation.

By appropriately controlling the concentration of the metal salt supplied to the reaction vessel, the stirring speed, the reaction temperature, the reaction pH, the firing conditions described later, etc., the finally obtained lithium composite metal oxide is controlled to have desired physical properties. Can be done.

After the above reaction, the obtained reaction precipitate is washed with water and then dried to isolate nickel cobalt manganese hydroxide as a nickel cobalt manganese composite compound. Further, if necessary, it may be washed with a weak acid water or an alkaline solution containing sodium hydroxide or potassium hydroxide. In the above example, the nickel-cobalt-manganese composite hydroxide is produced, but the nickel-cobalt-manganese composite oxide may be prepared.

(Lithium composite metal oxide manufacturing process)
The metal composite oxide or hydroxide is dried and then mixed with a lithium salt. The drying conditions are not particularly limited, but for example, conditions under which the metal composite oxide or hydroxide is not oxidized or reduced (the oxide is maintained as an oxide, the hydroxide is maintained as a hydroxide). , The condition that the metal composite hydroxide is oxidized (the hydroxide is oxidized to the oxide) and the condition that the metal composite oxide is reduced (the oxide is reduced to the hydroxide) good. An inert gas such as a rare gas such as nitrogen, helium or argon may be used under the condition that the oxidation / reduction is not carried out, and oxygen or air may be used as an atmosphere under the condition that the hydroxide is oxidized. good. Further, as a condition for reducing the metal composite oxide, a reducing agent such as hydrazine or sodium sulfite may be used in an inert gas atmosphere. As the lithium salt, any one or a mixture of lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium hydroxide hydrate, and lithium oxide can be used.
After drying the metal composite oxide or hydroxide, classification may be performed as appropriate. The above lithium salt and metal composite metal hydroxide are used in consideration of the composition ratio of the final target product. For example, when using a nickel-cobalt-manganese composite hydroxide, lithium salt and the composite metal hydroxide _is used in a proportion corresponding to _{LiNi a Co b Mn c O 2} ( where, a + b + c = 1 ) composition ratio of .. A lithium-nickel-cobalt-manganese composite oxide is obtained by calcining a mixture of a nickel-cobalt-manganese composite metal hydroxide and a lithium salt. For firing, dry air, an oxygen atmosphere, an inert atmosphere, or the like is used according to a desired composition, and a plurality of heating steps are carried out if necessary.

The firing temperature of the metal composite oxide or hydroxide and a lithium compound such as lithium hydroxide or lithium carbonate is not particularly limited, but is preferably 600 ° C. or higher and 1100 ° C. or lower, and is 750 ° C. or higher and 1050 ° C. or higher. The temperature is more preferably 800 ° C. or higher, and further preferably 800 ° C. or higher and 1025 ° C. or lower.

The firing time is preferably 3 hours or more and 50 hours or less. If the firing time exceeds 50 hours, the battery performance tends to be substantially inferior due to the volatilization of lithium. If the firing time is less than 3 hours, crystal development tends to be poor and battery performance tends to be poor. It is also effective to perform temporary firing before the above firing. The temperature of such temporary firing is preferably 1 hour or more and 10 hours or less in the range of 300 ° C. or higher and 850 ° C. or lower.

(Washing process)
The present embodiment includes a first cleaning step and a second cleaning step of cleaning the cleaning product obtained in the first cleaning step. The first cleaning step is a step of cleaning and removing residual lithium carbonate derived from the raw material. The second cleaning step is a step of cleaning and removing residual components of the cleaning liquid used in the first cleaning step.

-First cleaning step After firing, the first cleaning step of cleaning with the first cleaning liquid is performed. The first cleaning solution is an alkaline cleaning solution containing a compound containing an alkali metal.
Examples of the alkali metal-containing compound contained in the alkaline cleaning solution include LiOH (lithium hydroxide), NaOH (sodium hydroxide), KOH (potassium hydroxide), Li ₂ CO ₃ (lithium carbonate), and Na ₂ CO _3. Examples thereof include one or more anhydrides selected from the group consisting of (sodium carbonate) and K ₂ CO _{3 (potassium carbonate), and hydrates thereof.} Lithium hydroxide or lithium carbonate is preferable, and lithium hydroxide is more preferable, from the viewpoint of being able to further suppress the elution of lithium from the lithium composite metal oxide.

The first cleaning liquid can be prepared by dissolving the above-mentioned compound containing an alkali metal in water. The concentration of the aqueous solution of the compound containing an alkali metal is preferably 1% by mass or more, more preferably 5% by mass or more, and particularly preferably 10% by mass or more. Further, 30% by mass or less is preferable, 25% by mass or less is more preferable, and 20% by mass or less is particularly preferable.
When the concentration of the first cleaning liquid is at least the above lower limit value, the elution of lithium from the lithium composite metal oxide can be further suppressed.
When the concentration of the first cleaning liquid is not more than the above upper limit value, it is possible to prevent the compound containing an alkali metal from remaining in the produced lithium composite metal oxide.

The present embodiment is characterized in that the concentration of the alkali metal in the first cleaning liquid is higher than the concentration of the alkali metal in the second cleaning liquid described later.
It is presumed that by performing the cleaning step using the first cleaning liquid, it is possible to suppress the elution of the lithium component in the lithium composite metal oxide into the cleaning liquid. Therefore, it is considered that the concentration gradient of the lithium component on the particle surface of the produced lithium composite metal oxide is small and the lithium concentration on the particle surface can be increased. As a result, a lithium composite metal oxide having high initial charge / discharge efficiency can be produced.

-Second cleaning step After the first cleaning step, there is a second step of cleaning with a second cleaning liquid. The second cleaning solution is an alkaline cleaning solution.
Examples of the alkaline component contained in the second cleaning liquid include LiOH (lithium hydroxide), NaOH (sodium hydroxide), KOH (potassium hydroxide), Li ₂ CO ₃ (lithium carbonate), and Na ₂ CO ₃ (carbonate). Examples thereof include one or more anhydrides selected from the group consisting of (sodium), K ₂ CO ₃ (potassium carbonate) and (NH ₄ ) ₂ CO _{3 (ammonium carbonate), and hydrates thereof.} The second cleaning liquid is preferably an aqueous solution of lithium hydroxide. Ammonia water can also be used as the second cleaning liquid.

The alkaline cleaning liquid as the second cleaning liquid may be a cleaning liquid containing an alkali metal as an alkaline component, ammonia water may be used as a cleaning liquid without containing an alkali metal as an alkaline component, and an alkali metal may be used as an alkaline component. A cleaning solution containing, and further containing aqueous ammonia, may be used. In the present embodiment, when the second alkaline cleaning solution contains an alkali metal as an alkaline component, the concentration of the alkali metal in the first cleaning solution is higher than the concentration of the alkali metal in the second cleaning solution. It is a feature.
When ammonia water is used as the second alkaline cleaning solution without containing an alkali metal as an alkaline component, the concentration of ammonia and ammonium ions in the second alkaline cleaning solution is higher than the concentration of the alkali metal in the first cleaning solution. It may be expensive.
The concentration of the alkali metal in the first cleaning liquid is preferably twice or more the concentration of the alkali metal in the second cleaning liquid.

The second cleaning solution can be prepared by dissolving the above alkaline component in water. The concentration of the aqueous solution of the alkaline component is preferably 0.1% by mass or more, more preferably 1.0% by mass or more, and particularly preferably 2.0% by mass or more. Further, the upper limit value may be lower than the concentration of the alkaline component in the first cleaning liquid, for example, 30% by mass or less is preferable, 20% by mass or less is more preferable, and 10% by mass or less is particularly preferable.
When the concentration of the second cleaning liquid is equal to or higher than the above lower limit value, the residual components of the first cleaning liquid can be cleaned by cleaning while suppressing the elution of the lithium component contained in the produced lithium composite metal oxide. Can be removed.
When the concentration of the second cleaning liquid is not more than the above upper limit value, the residual component of the first cleaning liquid is removed by cleaning while suppressing the residual alkali metal-containing compound contained in the second cleaning liquid. can.

In the first cleaning step and the second cleaning step, as a method of bringing the cleaning liquid into contact with the lithium composite metal oxide, a method of adding the lithium composite metal oxide into the aqueous solution of each cleaning liquid and stirring the mixture, or a method of stirring each cleaning liquid. A method of applying the aqueous solution to the lithium composite metal oxide as shower water, or washing with the first cleaning liquid, and then adding the lithium composite metal oxide wet cake separated from the first cleaning liquid to the second cleaning liquid. Examples thereof include a stirring method (reslurry, repulp).
In a preferred embodiment, the lithium composite metal oxide is added to the first cleaning liquid and stirred, and then the lithium composite metal oxide is separated from the aqueous solution of each cleaning liquid, and then the second cleaning liquid is used as shower water. Examples thereof include a method of applying to a lithium composite metal oxide after separation.

(Drying process)
After the above cleaning step, the lithium composite metal oxide is separated from the cleaning liquid by filtration or the like. After that, it is dried, pulverized, and appropriately classified to obtain a positive electrode active material applicable to a lithium secondary battery.

In the present embodiment, the lithium composite metal oxide produced is preferably represented by the following composition formula (I).
_{Li [Li x (Ni (1} -y-z-w) Co y Mn z M w) 1-x] O 2 ··· (I)
(However, M is one or more metal elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga and V, and 0 ≦ x ≦ 0.2, 0 <y ≦ 0.4, 0 ≦ z ≦ 0.4, 0 ≦ w ≦ 0.1 is satisfied.)

From the viewpoint of obtaining a lithium secondary battery having high cycle characteristics, x in the composition formula (I) is preferably more than 0, more preferably 0.01 or more, and particularly preferably 0.02 or more. .. Further, from the viewpoint of obtaining a lithium secondary battery having a higher initial coulombic efficiency, x in the composition formula (I) is preferably 0.1 or less, more preferably 0.08 or less, and 0.06. The following is particularly preferable.
The upper limit value and the lower limit value of x can be arbitrarily combined.

Further, from the viewpoint of obtaining a lithium secondary battery having a low battery resistance, y in the composition formula (I) is preferably 0.005 or more, more preferably 0.01 or more, and 0.05 or more. It is particularly preferable to have. Further, from the viewpoint of obtaining a lithium secondary battery having high thermal stability, y in the composition formula (I) is more preferably 0.35 or less, and particularly preferably 0.33 or less.
The upper limit value and the lower limit value of y can be arbitrarily combined.

Further, from the viewpoint of obtaining a lithium secondary battery having high cycle characteristics, z in the composition formula (I) is preferably 0.01 or more, more preferably 0.03 or more, and 0.1 or more. It is particularly preferable to have. Further, from the viewpoint of obtaining a lithium secondary battery having high storage characteristics at a high temperature (for example, in an environment of 60 ° C.), z in the composition formula (I) is preferably 0.4 or less, preferably 0.38 or less. It is more preferable, and it is particularly preferable that it is 0.35 or less.
The upper limit value and the lower limit value of z can be arbitrarily combined.

Further, from the viewpoint of obtaining a lithium secondary battery having a low battery resistance, w in the composition formula (I) is preferably more than 0, more preferably 0.0005 or more, and more preferably 0.001 or more. Especially preferable. Further, from the viewpoint of obtaining a lithium secondary battery having a high discharge capacity at a high current rate, w in the composition formula (I) is preferably 0.09 or less, more preferably 0.08 or less, and 0. It is particularly preferable that it is .07 or less.
The upper limit value and the lower limit value of w can be arbitrarily combined.

M in the composition formula (I) represents one or more metals selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga and V. ..

Further, from the viewpoint of obtaining a lithium secondary battery having high cycle characteristics, M in the composition formula (I) is one or more metals selected from the group consisting of Ti, Mg, Al, W, B and Zr. Is preferable, and from the viewpoint of obtaining a lithium secondary battery having high thermal stability, it is more preferable that the metal is one or more selected from the group consisting of Al, W, B, and Zr.

(Layered structure)
The crystal structure of the lithium nickel composite oxide is a layered structure, and more preferably a hexagonal crystal structure or a monooblique crystal structure.

Hexagonal crystal structures are P3, P3 ₁ , P3 ₂ , R3, P-3, R-3, P312, P321, P3 ₁ 12, P3 ₁ 21, P3 ₂ 12, P3 ₂ 21, R32, P3 m1, P31m, P3c1, P31c, R3m, R3c, P-31m, P-31c, P-3m1, P-3c1, R-3m, R-3c, P6, P6 ₁ , P6 ₅ , P6 ₂ , P6 ₄ , P6 _{3 , P6, P6 / m, P6} 3 / m, P622, P6 1 22, P6 5 22, P6 2 22, P6 4 22, P6 3 22, P6mm, P6cc, P6 3 cm, P6 3 mc, P- It belongs to any one space group selected from the group consisting of 6m2, P-6c2, P-62m, P-62c, P6 / mmm, P6 / mcc, P6 ₃ / mcm, and P6 _{3 / mmc.}

The monoclinic crystal structure is P2, P2 ₁ , C2, Pm, Pc, Cm, Cc, P2 / m, P2 ₁ / m, C2 / m, P2 / c, P2 ₁ / c, C2 /. It belongs to any one space group selected from the group consisting of c.

Of these, from the viewpoint of obtaining a lithium secondary battery having a high discharge capacity, the crystal structure is a hexagonal crystal structure belonging to the space group R-3m or a monoclinic crystal structure belonging to C2 / m. It is particularly preferable to have a crystal structure.

The lithium compound used in the present invention is used by using any one or a mixture of lithium carbonate, lithium nitrate, lithium sulfate, lithium acetate, lithium hydroxide, lithium oxide, lithium chloride and lithium fluoride. can do. Among these, either one or both of lithium hydroxide and lithium carbonate is preferable.
From the viewpoint of improving the handleability of the positive electrode active material for a lithium secondary battery, the lithium carbonate component contained in the lithium composite metal oxide powder is preferably 0.4% by mass or less, and preferably 0.39% by mass or less. Is more preferable, and 0.38% by mass or less is particularly preferable.
Further, from the viewpoint of improving the handleability of the positive electrode active material for the lithium secondary battery, the lithium hydroxide component contained in the lithium composite metal oxide powder is preferably 0.35% by mass or less, preferably 0.25% by mass or less. Is more preferable, and 0.2% by mass or less is particularly preferable.

<Lithium secondary battery>
Next, while explaining the configuration of the lithium secondary battery, the positive electrode using the positive electrode active material for the lithium secondary battery of the present invention as the positive electrode active material of the lithium secondary battery, and the lithium secondary battery having this positive electrode will be described. do.

An example of the lithium secondary battery of the present embodiment has a positive electrode and a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolytic solution arranged between the positive electrode and the negative electrode.

FIG. 1 is a schematic view showing an example of the lithium secondary battery of the present embodiment. The cylindrical lithium secondary battery 10 of the present embodiment is manufactured as follows.

First, as shown in FIG. 1A, a pair of strip-shaped separators 1, a strip-shaped positive electrode 2 having a positive electrode lead 21 at one end, and a strip-shaped negative electrode 3 having a negative electrode lead 31 at one end are combined with the separator 1 and the positive electrode. 2. The separator 1 and the negative electrode 3 are laminated in this order and wound to form an electrode group 4.

Next, as shown in FIG. 1 (b), after accommodating the electrode group 4 and an insulator (not shown) in the battery can 5, the bottom of the can is sealed, the electrode group 4 is impregnated with the electrolytic solution 6, and the positive electrode 2 and the positive electrode 2 are formed. An electrolyte is placed between the negative electrode 3 and the negative electrode 3. Further, the lithium secondary battery 10 can be manufactured by sealing the upper part of the battery can 5 with the top insulator 7 and the sealing body 8.

The shape of the electrode group 4 is, for example, a columnar shape such that the cross-sectional shape when the electrode group 4 is cut in the direction perpendicular to the winding axis is a circle, an ellipse, a rectangle, or a rectangle with rounded corners. Can be mentioned.

Further, as the shape of the lithium secondary battery having such an electrode group 4, the shape defined by IEC60086 or JIS C8500, which is a standard for batteries defined by the International Electrotechnical Commission (IEC), can be adopted. .. For example, a cylindrical shape, a square shape, or the like can be mentioned.

Further, the lithium secondary battery is not limited to the above-mentioned winding type configuration, and may have a laminated configuration in which a laminated structure of a positive electrode, a separator, a negative electrode, and a separator is repeatedly laminated. Examples of the laminated lithium secondary battery include so-called coin-type batteries, button-type batteries, and paper-type (or sheet-type) batteries.

Hereinafter, each configuration will be described in order.
(Positive electrode)
The positive electrode of the present embodiment can be manufactured by first preparing a positive electrode mixture containing a positive electrode active material, a conductive material, and a binder, and then supporting the positive electrode mixture on a positive electrode current collector.

(Conductive material)
A carbon material can be used as the conductive material contained in the positive electrode of the present embodiment. Examples of the carbon material include graphite powder, carbon black (for example, acetylene black), and fibrous carbon material. Since carbon black is fine and has a large surface area, it is possible to improve the conductivity inside the positive electrode by adding a small amount to the positive electrode mixture, and improve the charge / discharge efficiency and output characteristics. Both the binding force between the positive electrode mixture and the positive electrode current collector and the binding force inside the positive electrode mixture decrease, which causes an increase in internal resistance.

The ratio of the conductive material in the positive electrode mixture is preferably 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. When a fibrous carbon material such as graphitized carbon fiber or carbon nanotube is used as the conductive material, this ratio can be reduced.

(binder)
A thermoplastic resin can be used as the binder contained in the positive electrode of the present embodiment. The thermoplastic resin includes polyvinylidene fluoride (hereinafter, may be referred to as PVdF), polytetrafluoroethylene (hereinafter, may be referred to as PTFE), ethylene tetrafluoride, propylene hexafluoride, and vinylidene fluoride. Fluororesin such as copolymer, propylene hexafluoride / vinylidene fluoride-based copolymer, ethylene tetrafluoride / perfluorovinyl ether-based copolymer; polyolefin resin such as polyethylene and polypropylene; can be mentioned.

Two or more kinds of these thermoplastic resins may be mixed and used. Fluororesin and polyolefin resin are used as binders, and the ratio of fluororesin to the entire positive electrode mixture is 1% by mass or more and 10% by mass or less, and the ratio of polyolefin resin is 0.1% by mass or more and 2% by mass or less. It is possible to obtain a positive electrode mixture having high adhesion to the current collector and high bonding force inside the positive electrode mixture.

(Positive current collector)
As the positive electrode current collector included in the positive electrode of the present embodiment, a band-shaped member made of a metal material such as Al, Ni, or stainless steel can be used. Of these, Al is used as a forming material and processed into a thin film because it is easy to process and inexpensive.

Examples of the method of supporting the positive electrode mixture on the positive electrode current collector include a method of pressure molding the positive electrode mixture on the positive electrode current collector. Further, the positive electrode mixture is made into a paste using an organic solvent, and the obtained positive electrode mixture paste is applied to at least one surface side of the positive electrode current collector, dried, pressed and fixed to the positive electrode current collector. The mixture may be carried.

When the positive electrode mixture is made into a paste, the organic solvents that can be used include amine solvents such as N, N-dimethylaminopropylamine and diethylenetriamine; ether solvents such as tetrahydrofuran; ketone solvents such as methyl ethyl ketone; methyl acetate. Etc.; amide-based solvents such as dimethylacetamide and N-methyl-2-pyrrolidone (hereinafter, may be referred to as NMP);

Examples of the method of applying the paste of the positive electrode mixture to the positive electrode current collector include a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method and an electrostatic spray method.

The positive electrode can be manufactured by the method described above.
(Negative electrode)
The negative electrode of the lithium secondary battery of the present embodiment may be capable of doping and dedoping lithium ions at a lower potential than that of the positive electrode, and a negative electrode mixture containing a negative electrode active material is supported on the negative electrode current collector. Examples of the electrode and an electrode composed of the negative electrode active material alone.

(Negative electrode active material)
Examples of the negative electrode active material of the negative electrode include carbon materials, chalcogen compounds (oxides, sulfides, etc.), nitrides, metals, or alloys that can be doped and dedoped with lithium ions at a lower potential than that of the positive electrode. Be done.

Examples of the carbon material that can be used as the negative electrode active material include graphite such as natural graphite and artificial graphite, coke, carbon black, pyrolytic carbon, carbon fiber, and a calcined organic polymer compound.

Oxides that can be used as the negative electrode active material include silicon oxides represented by the formula SiO _x (where x is a positive real number) _{such as SiO 2} , SiO; the formula TiO _{x such as TiO 2} and TiO (here). , X is a positive real number) titanium oxide; V ₂ O ₅ , VO _2, etc. Formula VO _x (where x is a positive real number) vanadium oxide; Fe ₃ O ₄ , Fe ₂ O ₃ , FeO, etc. _{Iron oxide represented by the formula FeO x} (where x is a positive real number); SnO ₂ , SnO, etc. Formula SnO _x (where x is a positive real number) Oxides of tin; oxides of tungsten represented by the general formula WO _x (where x is a positive real number) _{such as WO 3} and WO ₂ ; lithium and titanium such as _{Li 4} Ti ₅ O ₁₂ and LiVO _2. Alternatively, a composite metal oxide containing vanadium; can be mentioned.

Sulfides that can be used as the negative electrode active material include Ti ₂ S ₃ , TiS ₂ , TiS, and _{other sulfides of titanium represented by the formula TiS x} (where x is a positive real number); V ₃ S ₄ , VS. _2. VS, etc. _{The sulfide of vanadium represented by the formula VS x} (where x is a positive real number); Fe ₃ S ₄ , FeS ₂ , FeS, etc. formula FeS _x (where x is a positive real number) sulfides of iron _represented; Mo ₂ S 3, MoS _2, etc. formula MoS _x (wherein, x represents a positive real number) sulfides of molybdenum represented _{by; SnS} 2, SnS formula SnS _x (wherein such, Tin sulfide represented by x is a positive real number); WS _{2 and the} like formula WS _x (where x is a positive real number) and represented by tungsten sulfide; Sb ₂ S _{3 and the} like formula SbS _x (here) in, x is antimony represented by a positive real _{number); Se 5 S 3, SeS} 2, SeS formula SeS _x (wherein such, sulfide selenium x is represented by a positive real number); the Can be mentioned.

The nitrides that can be used as the negative electrode active material include Li ₃ N and Li _3-x A _x N (where A is either or both of Ni and Co, and 0 <x <3). Such as lithium-containing nitrides can be mentioned.

These carbon materials, oxides, sulfides, and nitrides may be used alone or in combination of two or more. Further, these carbon materials, oxides, sulfides and nitrides may be either crystalline or amorphous.

Examples of the metal that can be used as the negative electrode active material include lithium metal, silicon metal, and tin metal.

Alloys that can be used as the negative electrode active material include lithium alloys such as Li-Al, Li-Ni, Li-Si, Li-Sn, and Li-Sn-Ni; silicon alloys such as Si-Zn; Sn-Mn, Sn. Tin alloys such as −Co, Sn—Ni, Sn—Cu, Sn—La; alloys such as Cu ₂ Sb, La ₃ Ni ₂ Sn ₇ ; can also be mentioned.

These metals and alloys are mainly used alone as electrodes after being processed into a foil, for example.

Among the above negative electrode active materials, the potential of the negative electrode hardly changes from the uncharged state to the fully charged state during charging (potential flatness is good), the average discharge potential is low, and the capacity retention rate when repeatedly charged and discharged is high. A carbon material containing graphite as a main component, such as natural graphite or artificial graphite, is preferably used because of its high value (good cycle characteristics). The shape of the carbon material may be, for example, a flaky shape such as natural graphite, a spherical shape such as mesocarbon microbeads, a fibrous shape such as graphitized carbon fiber, or an agglomerate of fine powder.

The negative electrode mixture may contain a binder, if necessary. Examples of the binder include thermoplastic resins, and specific examples thereof include PVdF, thermoplastic polyimide, carboxymethyl cellulose, polyethylene and polypropylene.

(Negative electrode current collector)
Examples of the negative electrode current collector included in the negative electrode include a band-shaped member made of a metal material such as Cu, Ni, or stainless steel as a forming material. Among them, Cu is used as a forming material and processed into a thin film because it is difficult to form an alloy with lithium and it is easy to process.

As a method of supporting the negative electrode mixture on such a negative electrode current collector, as in the case of the positive electrode, a method by pressure molding, a paste using a solvent or the like, coating on the negative electrode current collector, drying and pressing are performed. A method of crimping can be mentioned.

(Separator)
Examples of the separator included in the lithium secondary battery of the present embodiment include a porous film, a non-woven fabric, and a woven fabric made of a material such as a polyolefin resin such as polyethylene and polypropylene, a fluororesin, and a nitrogen-containing aromatic polymer. A material having the above can be used. Further, two or more kinds of these materials may be used to form a separator, or these materials may be laminated to form a separator.

In the present embodiment, the separator has an air permeation resistance of 50 seconds / 100 cc or more and 300 seconds / 100 cc according to the Garley method defined by JIS P 8117 in order to allow the electrolyte to permeate well when the battery is used (during charging / discharging). It is preferably 50 seconds / 100 cc or more, and more preferably 200 seconds / 100 cc or less.

The porosity of the separator is preferably 30% by volume or more and 80% by volume or less, and more preferably 40% by volume or more and 70% by volume or less. The separator may be a laminate of separators having different porosities.

(Electrolytic solution)
The electrolytic solution contained in the lithium secondary battery of the present embodiment contains an electrolyte and an organic solvent.

The electrolytes contained in the electrolytic solution include LiClO ₄ , LiPF ₆ , _{LiAsF 6} , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN. (SO ₂ CF ₃ ) (COCF ₃ ), Li (C ₄ F ₉ SO ₃ ), LiC (SO ₂ CF ₃ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , LiBOB (where BOB is bis (oxalato) boronate) ), LiFSI (here, FSI stands for bis (fluorosulfonyl) image), lower aliphatic carboxylic acid lithium salt, lithium salt _{such as LiAlCl 4,} and a mixture of two or more of these. May be used. Among them, the electrolyte is at least selected from the group consisting of _{LiPF 6} , _{LiAsF 6} , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ and LiC (SO ₂ CF ₃ ) _{3 containing fluorine.} It is preferable to use one containing one type.

Examples of the organic solvent contained in the electrolytic solution include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, 1,2-di. Carbonates such as (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropylmethyl ether, 2,2,3,3-tetrafluoropropyldifluoromethyl ether, tetrahydrofuran, 2- Ethers such as methyl tetrahydrofuran; esters such as methyl formate, methyl acetate, γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; amides such as N, N-dimethylformamide, N, N-dimethylacetamide; 3-methyl Carbamates such as -2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethylsulfoxide, and 1,3-propanesartone, or those in which a fluoro group is further introduced into these organic solvents (1 of the hydrogen atoms of the organic solvent). The above is replaced with a fluorine atom).

As the organic solvent, it is preferable to use a mixture of two or more of these. Of these, a mixed solvent containing carbonates is preferable, and a mixed solvent of cyclic carbonate and acyclic carbonate and a mixed solvent of cyclic carbonate and ethers are more preferable. As the mixed solvent of the cyclic carbonate and the acyclic carbonate, a mixed solvent containing ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is preferable. An electrolytic solution using such a mixed solvent has a wide operating temperature range, is not easily deteriorated even when charged and discharged at a high current rate, is not easily deteriorated even when used for a long time, and is made of natural graphite as an active material of a negative electrode. It has many features that it is resistant to decomposition even when a graphite material such as artificial graphite is used.

Further, as the electrolytic solution, since the safety of the obtained lithium secondary battery is enhanced, it is preferable to use an electrolytic solution containing a lithium salt containing fluorine such as _{LiPF 6 and an organic solvent having a fluorine substituent.} A mixed solvent containing ethers having a fluorine substituent such as pentafluoropropylmethyl ether and 2,2,3,3-tetrafluoropropyldifluoromethyl ether and dimethyl carbonate has a capacity even when charged and discharged at a high current rate. It is more preferable because of its high maintenance rate.

A solid electrolyte may be used instead of the above electrolytic solution. As the solid electrolyte, for example, an organic polymer electrolyte such as a polyethylene oxide-based polymer compound, a polymer compound containing at least one of a polyorganosiloxane chain or a polyoxyalkylene chain can be used. Further, a so-called gel type compound in which a non-aqueous electrolytic solution is retained in a polymer compound can also be used. The _{Li 2 S-SiS 2, Li} 2 S-GeS 2, Li 2 S-P 2 S 5, Li 2 S-B 2 S 3, Li 2 S-SiS 2 -Li 3 PO 4, Li 2 S-SiS _{2 -Li 2 SO 4, Li 2} S-GeS 2 -P 2 S 5 inorganic solid electrolytes containing a sulfide, and the like, may be used a mixture of two or more thereof. By using these solid electrolytes, the safety of the lithium secondary battery may be further enhanced.

Further, in the lithium secondary battery of the present embodiment, when a solid electrolyte is used, the solid electrolyte may serve as a separator, and in that case, the separator may not be required.

Since the positive electrode active material having the above configuration uses the lithium-containing composite metal oxide of the present embodiment described above, it is possible to improve the initial charge / discharge efficiency of the lithium secondary battery using the positive electrode active material. ..

Further, since the positive electrode having the above configuration has the positive electrode active material for the lithium secondary battery of the present embodiment described above, the initial charge / discharge efficiency of the lithium secondary battery can be improved.

Further, since the lithium secondary battery having the above configuration has the above-mentioned positive electrode, it is a secondary battery having a higher initial charge / discharge efficiency than the conventional one.

Next, the present invention will be described in more detail with reference to Examples.

In this example, the evaluation of the lithium composite metal oxide and the production evaluation of the positive electrode for the lithium secondary battery and the lithium secondary battery were carried out as follows.

<Composition analysis>
The composition analysis of the lithium composite metal oxide powder produced by the method described below is carried out by dissolving the obtained lithium composite metal oxide powder in hydrochloric acid and then inductively coupled plasma emission spectrometry (SI Nanotechnology Co., Ltd.). Manufactured by SPS3000).

<Manufacturing positive electrodes for lithium secondary batteries>
The lithium composite metal oxide obtained by the production method described later is used as the positive electrode active material, and the positive electrode active material, the conductive material (acetylene black) and the binder (PVdF) are used as the positive electrode active material for the lithium secondary battery: conductive material: binder. A paste-like positive electrode mixture was prepared by adding and kneading so as to have a composition of = 92: 5: 3 (mass ratio). N-methyl-2-pyrrolidone was used as an organic solvent when preparing the positive electrode mixture.

The obtained positive electrode mixture was applied to an Al foil having a thickness of 40 μm as a current collector and vacuum dried at 150 ° C. for 8 hours to obtain a positive electrode for a lithium secondary battery. The electrode area of the positive electrode for the lithium secondary battery was 1.65 cm ² .

<Manufacturing of negative electrode for lithium secondary battery>
Next, artificial graphite (MAGD manufactured by Hitachi Kasei Co., Ltd.) as the negative electrode active material, CMC (manufactured by Daiichi Kogyo Yakuhin Co., Ltd.) and SBR (manufactured by Nippon A & L Co., Ltd.) as binders, and negative electrode active material: CMC: A paste-like negative electrode mixture was prepared by adding and kneading so as to have a composition of SRR = 98: 1: 1 (mass ratio). Ion-exchanged water was used as the solvent when preparing the negative electrode mixture.

The obtained negative electrode mixture was applied to a Cu foil having a thickness of 12 μm as a current collector and vacuum dried at 60 ° C. for 8 hours to obtain a negative electrode for a lithium secondary battery. The electrode area of the negative electrode for the lithium secondary battery was 1.77 cm ² .

<Manufacturing of lithium secondary battery (coin type half cell)>
The following operations were performed in a glove box with an argon atmosphere.
Place the positive electrode for the lithium secondary battery manufactured in <Manufacturing the positive electrode for the lithium secondary battery> on the lower lid of the part for the coin-type battery R2032 (manufactured by Hosen Co., Ltd.) with the aluminum foil side facing down. A laminated film separator (a heat-resistant porous layer laminated (thickness 16 μm) on a porous polyethylene film) was placed on the laminated film separator. 300 μl of the electrolytic solution was injected therein. The electrolytic solution is ethylene carbonate (hereinafter, may be referred to as EC), dimethyl carbonate (hereinafter, may be referred to as DMC), and ethyl methyl carbonate (hereinafter, may be referred to as EMC) at 30:35. A mixture of 35 (volume ratio) in which LiPF ₆ was dissolved so as to be 1.0 mol / l (hereinafter, _{may be referred to as LiPF 6} / EC + DMC + EMC) was used.
Next, using metallic lithium as the negative electrode, the negative electrode is placed on the upper side of the laminated film separator, the upper lid is closed through a gasket, and the lithium secondary battery (coin type half cell R2032; hereinafter, “half cell”) is crimped with a caulking machine. It may be referred to as).

<Discharge test>
Using the half cell prepared in <Preparation of lithium secondary battery (coin type half cell)>, the initial charge / discharge test was carried out under the following conditions.

<Charging / discharging test conditions>
Test temperature: 25 ° C
Maximum charging voltage 4.3V, charging time 6 hours, charging current 0.2CA, constant current constant voltage charging Minimum discharge voltage 2.5V, discharge time 5 hours, discharge current 0.2CA, constant current discharge

(Example 1)
1. 1. Production of Lithium Composite Metal Oxide 1 After putting water in a reaction vessel equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added to maintain the liquid temperature at 50 ° C.

The atomic ratio of nickel atom, cobalt atom, manganese atom and aluminum atom of nickel sulfate aqueous solution, cobalt sulfate aqueous solution, manganese sulfate aqueous solution and aluminum sulfate aqueous solution is 87.5: 9.5: 2.0: 1.0. The mixture was mixed so as to prepare a mixed raw material solution.

Next, the mixed raw material solution and the ammonium sulfate aqueous solution were continuously added as a complexing agent into the reaction vessel under stirring, and nitrogen gas was continuously aerated. An aqueous sodium hydroxide solution was added dropwise at appropriate times so that the pH of the solution in the reaction vessel became 11.0 to obtain nickel-cobalt manganese-aluminum composite hydroxide particles, washed with the aqueous sodium hydroxide solution, and then dehydrated with a centrifuge. , Isolated and dried at 105 ° C. to obtain a nickel cobalt manganese aluminum composite hydroxide.
An aqueous solution of lithium hydroxide in which tungsten oxide was dissolved at 61 g / L was prepared. The produced aqueous solution of tungsten-dissolved lithium hydroxide was adhered to the nickel cobalt manganese aluminum composite hydroxide so that W / (Ni + Co + Mn + W) = 0.004 to obtain nickel cobalt manganese aluminum tungsten composite hydroxide 1. rice field.

The nickel cobalt manganese aluminum tungsten composite hydroxide 1 obtained as described above and the lithium hydroxide powder are weighed and mixed so as to have Li / (Ni + Co + Mn + Al + W) = 1.10, and then mixed at 760 ° C. under an oxygen atmosphere. The product was fired for 5 hours to obtain a fired product 1.

[First cleaning step]
200 g of the fired product 1 was added to 467 g of a 15 mass% lithium hydroxide aqueous solution to prepare a slurry-like liquid, and the slurry-like liquid was stirred for 10 minutes to perform the first washing step.

[Second cleaning step]
The slurry-like liquid obtained in the first cleaning step is suction-filtered, and 2000 g of a 1.0 mass% lithium hydroxide aqueous solution is further added to the obtained wet cake and suction-filtered to perform a second cleaning. The process was performed. Then, it was dried in the air atmosphere at 150 ° C. for 12 hours.
Alumina nanopowder was adhered to the obtained dry powder and calcined at 760 ° C. for 10 hours in an oxygen atmosphere to obtain the desired lithium composite metal oxide 1.

2. Evaluation of Lithium Composite Metal Oxide 1 The composition of the obtained lithium composite metal oxide 1 was analyzed and made to correspond to the composition formula (I). As a result, x = 0.02, y = 0.092, z = 0. It was 020, w = 0.024, M = W, Al.

(Example 2)
1. 1. Production of Lithium Composite Metal Oxide 2 Lithium composite metal oxide 2 is produced by the same method as in Example 1 except that the first cleaning step and the second cleaning step are performed using the cleaning liquid shown in Table 1 below. Manufactured.

2. Evaluation of Lithium Composite Metal Oxide 2 The composition of the obtained lithium composite metal oxide 2 was analyzed and made to correspond to the composition formula (I). As a result, x = 0.02, y = 0.092, z = 0. It was 020, w = 0.023, M = W, Al.

(Comparative Example 1)
1. 1. Production of Lithium Composite Metal Oxide 3 Lithium composite metal oxide 3 is produced by the same method as in Example 1 except that the first cleaning step and the second cleaning step are performed using the cleaning liquid shown in Table 1 below. Manufactured.

2. Evaluation of Lithium Composite Metal Oxide 3 The composition of the obtained lithium composite metal oxide 3 was analyzed and made to correspond to the composition formula (I). As a result, x = -0.02, y = 0.093, z = 0. It was .021, w = 0.024, M = W, Al.

(Comparative Example 2)
1. 1. Production of Lithium Composite Metal Oxide 4 Lithium composite metal oxide 4 is produced by the same method as in Example 1 except that the first cleaning step and the second cleaning step are performed using the cleaning liquid shown in Table 1 below. Manufactured.

2. Evaluation of Lithium Composite Metal Oxide 4 When the composition of the obtained lithium composite metal oxide 4 was analyzed and made to correspond to the composition formula (I), x = -0.01, y = 0.092, z = 0. It was .018, w = 0.023, M = W, Al.

(Comparative Example 3)
1. 1. Production of Lithium Composite Metal Oxide 5 Lithium composite metal oxide 5 is produced by the same method as in Example 1 except that the first cleaning step and the second cleaning step are performed using the cleaning liquid shown in Table 1 below. Manufactured.

2. Evaluation of Lithium Composite Metal Oxide 5 The composition of the obtained lithium composite metal oxide 5 was analyzed and made to correspond to the composition formula (I). As a result, x = -0.02, y = 0.092, z = 0. It was .018, w = 0.023, M = W, Al.

As shown in the above results, Examples 1 and 2 in which the cleaning step to which the present invention was applied had higher initial charge / discharge efficiency than Comparative Examples 1 to 2 to which the present invention was not applied. This is because when the present invention is applied, the elution of lithium from the lithium composite metal oxide is smaller and the lithium concentration gradient on the surface of the lithium composite metal oxide is smaller than when washed with pure water. Can be considered.

1 ... Separator, 2 ... Positive electrode, 3 ... Negative electrode, 4 ... Electrode group, 5 ... Battery can, 6 ... Electrolyte, 7 ... Top insulator, 8 ... Seal, 10 ... Lithium secondary battery, 21 ... Positive lead, 31 … Negative lead

Claims (6)

A method for producing a lithium composite metal oxide containing at least nickel.
The first cleaning step of cleaning the lithium composite metal oxide with the first cleaning liquid, and
It has a second cleaning step of cleaning the washed product obtained in the first cleaning step with a second cleaning liquid.
The first cleaning liquid is an aqueous solution containing a compound containing an alkali metal, and is an aqueous solution.
The second cleaning solution is an aqueous solution containing an alkaline component, and is an aqueous solution .
The concentration of the alkali metal of the first in the cleaning liquid, rather higher than the concentration of the alkali metal of said second in the cleaning solution,
The concentration of the aqueous solution of the compound containing the alkali metal in the first cleaning liquid is 1% by mass or more and 30% by mass or less.
A method for producing a lithium composite metal oxide, wherein the concentration of the aqueous solution of the alkaline component in the second cleaning liquid is 0.1% by mass or more and 30% by mass or less. The method for producing a lithium composite metal oxide according to claim 1, wherein the lithium composite metal oxide is represented by the following composition formula (I).
_{Li [Li x (Ni (1} -y-z-w) Co y Mn z M w) 1-x] O 2 ··· (I)
(However, M is one or more metal elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga and V, and 0 ≦ x ≦ 0.2, 0 <y ≦ 0.4, 0 ≦ z ≦ 0.4, 0 ≦ w ≦ 0.1 is satisfied.) The method for producing a lithium composite metal oxide according to claim 2, wherein in the composition formula (I), y + z + w ≦ 0.3. The method for producing a lithium composite metal oxide according to any one of claims 1 to 3, wherein the second cleaning liquid is an aqueous solution of lithium hydroxide. The method for producing a lithium composite metal oxide according to any one of claims 1 to 4, wherein the lithium hydroxide concentration of the second cleaning liquid is 1% by mass or more and 30% by mass or less. The method for producing a lithium composite metal oxide according to any one of claims 1 to 5, wherein the second cleaning liquid is aqueous ammonia.

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