JP6799551B2 - Manufacturing method of positive electrode active material for lithium secondary battery - Google Patents

Description

The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode for a lithium secondary battery, and a lithium secondary battery.

Lithium composite 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.

Attempts have been made to focus on the particle strength of the positive electrode active material for a lithium secondary battery in order to improve the performance of the lithium secondary battery such as the initial discharge capacity (for example, Patent Documents 1 to 6).

Japanese Unexamined Patent Publication No. 2001-80920 Japanese Unexamined Patent Publication No. 2004-335152 International Publication No. 2005/124898 JP-A-2007-257985 Japanese Unexamined Patent Publication No. 2011-119092 Japanese Unexamined Patent Publication No. 2013-232318

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 the initial charge / discharge efficiency.
However, there is room for improvement in the positive electrode active material for a lithium secondary battery as described in Patent Documents 1 to 6 from the viewpoint of improving the initial charge / discharge efficiency.
The present invention has been made in view of the above circumstances, and is a positive electrode active material for a lithium secondary battery having excellent initial charge / discharge efficiency, a positive electrode for a lithium secondary battery using the positive electrode active material for a lithium secondary battery, and the positive electrode for a lithium secondary battery. An object of the present invention is to provide a lithium secondary battery having a positive electrode for a lithium secondary battery.

That is, the present invention includes the following inventions [1] to [9].
[1] A positive electrode active material for a lithium secondary battery made of a lithium metal composite oxide powder represented by the general formula (1), wherein the lithium metal composite oxide powder aggregates with primary particles and the primary particles aggregate. The lithium metal composite oxide powder has a BET specific surface area of 1 m ² / g or more and 3 m ² / g or less, and the average crushing strength of the secondary particles is 10 MPa or more and 100 MPa or more. A positive electrode active material for a lithium secondary battery, which is characterized by the following.
_{Li [Li x (Ni (1} -y-z-w) Co y Mn z M w) 1-x] O 2 (1) ( however, M is Fe, Cu, Ti, Mg, Al, W, B, It is one or more metal elements selected from the group consisting of Mo, Nb, Zn, Sn, Zr, Ga and V, and is −0.1 ≦ x ≦ 0.2, 0 <y ≦ 0.4, 0 <. z ≦ 0.4, 0 ≦ w ≦ 0.1, 0.25 <y + z + w is satisfied.)
[2] The positive electrode active material for a lithium secondary battery according to [1], wherein y <z in the general formula (1).
[3] The positive electrode active material for a lithium secondary battery according to [1] or [2], wherein the average particle size of the lithium metal composite oxide powder is 2 μm or more and 10 μm or less.
[4] In powder X-ray diffraction measurement using CuKα ray, the half width of the diffraction peak in the range of 2θ = 18.7 ± 1 ° is set to A, and the diffraction peak in the range of 2θ = 44.4 ± 1 °. The positive electrode active material for a lithium secondary battery according to any one of [1] to [3], wherein the product of A and B is 0.014 or more and 0.030 or less, where B is the full width at half maximum.
[5] The positive electrode active material for a lithium secondary battery according to [4], wherein the range of the half width A is 0.115 or more and 0.165 or less.
[6] The positive electrode active material for a lithium secondary battery according to [4] or [5], wherein the range of the half width B is 0.120 or more and 0.180 or less.
[7] The positive electrode active material for a lithium secondary battery according to any one of [1] to [6], wherein the lithium carbonate component contained in the lithium metal composite oxide powder is 0.4% by mass or less.
[8] The positive electrode active material for a lithium secondary battery according to any one of [1] to [7], wherein the lithium hydroxide component contained in the lithium metal composite oxide powder is 0.35% by mass or less.
[9] A positive electrode for a lithium secondary battery having the positive electrode active material for the lithium secondary battery according to any one of [1] to [8].
[10] A lithium secondary battery having the positive electrode for the lithium secondary battery according to [9].

According to the present invention, a positive electrode active material for a lithium secondary battery having excellent initial charge / discharge efficiency, a positive electrode for a lithium secondary battery using the positive electrode active material for the lithium secondary battery, and a lithium having a positive electrode for the lithium secondary battery. A secondary battery can be provided.

It is a schematic block diagram which shows an example of a lithium ion secondary battery. It is a schematic diagram explaining the effect of this invention. It is an SEM image of the secondary particle cross section of Example 2. It is an SEM image of the secondary particle cross section of Comparative Example 4.

<Positive electrode active material for lithium secondary batteries>
The present invention is a positive electrode active material for a lithium secondary battery made of a lithium metal composite oxide powder represented by the general formula (1), wherein the lithium metal composite oxide powder is the primary particles and the primary particles are aggregated. The BET specific surface area of the lithium metal composite oxide powder is 1 m ² / g or more and 3 m ² / g or less, and the average crushing strength of the secondary particles is 10 MPa or more. It is a positive electrode active material for a lithium secondary battery, which is characterized by having a pressure of 100 MPa or less.
_{Li [Li x (Ni (1} -y-z-w) Co y Mn z M w) 1-x] O 2 (1) ( however, M is Fe, Cu, Ti, Mg, Al, W, B, It is one or more metal elements selected from the group consisting of Mo, Nb, Zn, Sn, Zr, Ga and V, and is −0.1 ≦ x ≦ 0.2, 0 <y ≦ 0.4, 0 <. z ≦ 0.4, 0 ≦ w ≦ 0.1, 0.25 <y + z + w is satisfied.)

The positive electrode active material for a lithium secondary battery of the present embodiment (hereinafter, may be referred to as “positive electrode active material”) has a BET specific surface area of the lithium metal composite oxide powder in a specific range, and further, is secondary. It is characterized in that the average crushing strength of the particles is in a specific range. The lithium metal composite oxide powder used in the present embodiment has low particle strength because the average crushing strength of the secondary particles is within the above-mentioned specific range. It is presumed that this is a secondary particle structure in which the contact area between the primary particles is small and there are many voids. That is, since the positive electrode active material of the present embodiment uses secondary particles having many voids, the contact area with the electrolytic solution is large. Therefore, desorption (charging) and insertion (discharging) of lithium ions are likely to proceed inside the secondary particles. Therefore, the positive electrode active material of the present embodiment is excellent in initial charge / discharge efficiency.

In the present embodiment, the lithium metal composite oxide powder is represented by the following general formula (1).
_{Li [Li x (Ni (1} -y-z-w) Co y Mn z M w) 1-x] O 2 (1) ( however, M is Fe, Cu, Ti, Mg, Al, W, B, It is one or more metal elements selected from the group consisting of Mo, Nb, Zn, Sn, Zr, Ga and V, and is −0.1 ≦ x ≦ 0.2, 0 <y ≦ 0.4, 0 <. z ≦ 0.4, 0 ≦ w ≦ 0.1, 0.25 <y + z + w is satisfied.)

In order to obtain a lithium secondary battery having high cycle characteristics, x in the composition formula (1) is preferably more than 0, more preferably 0.01 or more, and further preferably 0.02 or more. .. Further, in order to obtain a lithium secondary battery having a higher initial coulombic efficiency, x in the composition formula (1) is preferably 0.1 or less, more preferably 0.08 or less, and 0.06. The following is more preferable.
The upper limit value and the lower limit value of x can be arbitrarily combined.
In the present specification, "high cycle characteristics" means that the discharge capacity retention rate is high.

Further, y in the composition formula (1) is preferably 0.005 or more, preferably 0.01 or more, in order to obtain a lithium secondary battery having a low battery resistance at low temperature (-15 ° C to 0 ° C). More preferably, it is more preferably 0.05 or more. Further, in order to obtain a lithium secondary battery having high thermal stability, y in the composition formula (1) is preferably 0.4 or less, more preferably 0.35 or less, and 0.33. The following is more preferable.
The upper limit value and the lower limit value of y can be arbitrarily combined.

Further, in order to obtain a lithium secondary battery having high cycle characteristics, z in the composition formula (1) is preferably 0.01 or more, more preferably 0.03 or more, and 0.1 or more. It is more preferable to have. Further, in order to obtain 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 (1) is preferably 0.4 or less, preferably 0.38 or less. More preferably, it is more preferably 0.35 or less.
The upper limit value and the lower limit value of z can be arbitrarily combined.

Further, w in the composition formula (1) preferably exceeds 0, and is 0.0005 or more, in the sense of obtaining a lithium secondary battery having a low battery resistance at a low temperature (-15 ° C to 0 ° C). More preferably, it is more preferably 0.001 or more. Further, in order to obtain a lithium secondary battery having a high discharge capacity at a high current rate, w in the composition formula (1) is preferably 0.09 or less, more preferably 0.08 or less, and 0. It is more preferably .07 or less.
The upper limit value and the lower limit value of w can be arbitrarily combined.

M in the composition formula (1) 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, in order to obtain a lithium secondary battery having high cycle characteristics, M in the composition formula (1) is preferably Ti, Mg, Al, W, B, Zr, and the lithium secondary has high thermal stability. In terms of obtaining a battery, it is preferably Al, W, B, Zr.

(BET specific surface area)
In the present embodiment, the BET specific surface area (m ² / g) of the lithium metal composite oxide powder is preferably 1 m ² / g or more in order to obtain a lithium secondary battery having high initial charge / discharge efficiency. more preferably 05m ² / g or more, further preferably 1.1 m ² / g or more. Further, in order to improve the handleability of the positive electrode active material for a lithium secondary battery, it is preferably 3 m ² / g or less, more preferably 2.95 m ² / g or less, and 2.9 m ² / g or less. Is more preferable.
The upper and lower limits of the BET specific surface area can be arbitrarily combined.

(Average crush strength)
In the present embodiment, the lithium metal composite oxide powder is composed of primary particles and secondary particles formed by aggregating the primary particles.
In the present embodiment, in order to obtain a lithium secondary battery having high initial charge / discharge efficiency, the average crushing strength of the secondary particles is preferably 10 MPa or more, more preferably 11 MPa or more, and 12 MPa or more. Is even more preferable. Further, in the sense of obtaining a lithium secondary battery having a high discharge capacity at a high current rate, it is preferably 100 MPa or less, more preferably 99 MPa or less, and further preferably 98 MPa or less.
The upper and lower limits of the average crush strength can be arbitrarily combined.

The secondary particles having a dense particle structure that have been conventionally used have an average crushing strength of more than 100 MPa. In comparison, the secondary particles having the average crushing strength in the above-mentioned specific range are particles having a lower particle strength and more voids than the conventional secondary particles having a dense particle structure.
FIG. 2A shows a schematic view of a cross section of the secondary particles of the present embodiment. As shown in FIG. 2A, the positive electrode active material of the present embodiment has many voids, so that the contact area with the electrolytic solution is large. Therefore, the desorption (charging) of the lithium ions shown by the reference numeral A in FIG. 2A and the insertion (discharge) of the lithium ions shown by the reference numeral B are likely to proceed inside and on the surface of the secondary particles. Therefore, the initial discharge efficiency can be improved.
FIG. 2B shows a schematic view of a cross section of a secondary particle having a dense particle structure that has been conventionally used. As described in FIG. 2B, in the case of a dense particle structure, the desorption (charging) of lithium ions shown by reference numeral A and the insertion (discharge) of lithium ions shown by reference numeral B are performed only near the surface of the particles. proceed. On the other hand, as described above, in the present embodiment, since the particles proceed not only inside the secondary particles but also on the surface, the initial discharge efficiency can be improved.
In the present embodiment, the average crushing strength of the secondary particles is a value measured by the following measuring method.

[Measurement method of average crush strength]
In the present invention, the "average crush strength" of the secondary particles present in the lithium metal composite oxide powder refers to a value measured by the following method.

First, for lithium metal composite oxide powder, a test pressure (load) was applied to one arbitrarily selected secondary particle using the "micro-compression tester MCT-510" manufactured by Shimadzu Corporation, and the secondary particle was used. Measure the amount of displacement of. When the test pressure is gradually increased, the pressure value at which the displacement amount is maximized while the test pressure remains almost constant is defined as the test force (P), and the formula of Hiramatsu et al. (Journal of the Japan Mining Association, Vol.81, (1965)) was used to calculate the crushing strength (St). This operation was performed a total of 5 times, and the average crush strength was calculated from the average value of the crush strength 5 times.
St = 2.8 × P / (π × d × d) (d: secondary particle diameter)… (A)

(Composition of transition metal)
In the present embodiment, y <z is preferable in the general formula (1) in the sense of obtaining a lithium secondary battery having high cycle characteristics. When y ≧ z, the cycle characteristics of the lithium secondary battery may deteriorate.

(Average particle size)
In the present embodiment, the average particle size of the lithium metal composite oxide powder is preferably 2 μm or more, more preferably 2.1 μm or more, in order to improve the handleability of the positive electrode active material for the lithium secondary battery. It is preferably 2.2 μm or more, and more preferably 2.2 μm or more.
Further, in order to obtain a lithium secondary battery having a high discharge capacity at a high current rate, it is preferably 10 μm or less, more preferably 9.9 μm or less, and further preferably 9.8 μm or less.
The upper and lower limits of the average particle size can be arbitrarily combined.
In the present invention, the "average particle size" of the lithium metal composite oxide powder refers to a value measured by the following method (laser diffraction / scattering method).

Using a laser diffraction particle size distribution meter (manufactured by HORIBA, Ltd., model number: LA-950), 0.1 g of lithium metal composite oxide powder was added to 50 ml of a 0.2 mass% sodium hexametaphosphate aqueous solution, and the powder was dispersed. The dispersion liquid was obtained. The particle size distribution of the obtained dispersion is measured, and a volume-based cumulative particle size distribution curve is obtained. In the obtained cumulative particle size distribution curve, the value of the particle size (D ₅₀ ) seen from the fine particle side at the time of 50% accumulation was taken as the average particle size of the lithium metal composite oxide powder.

In the present embodiment, the BET specific surface area of the lithium metal composite oxide is in the above-mentioned specific range, and the average crushing strength of the secondary particles is in the above-mentioned specific range, thereby improving the initial charge / discharge efficiency. be able to. Further, when the BET specific surface area and the average crushing strength are within the above-mentioned specific ranges, the contact area between the lithium metal composite oxide and the electrolytic solution increases, and the viscosity of the electrolytic solution increases under low temperature conditions (-15 ° C to 0). Battery resistance can be lowered at (° C.). Further, by adding the element M in the general formula (1), the conductivity of lithium ions in the lithium metal composite oxide is increased, and the battery resistance can be lowered under low temperature conditions.

(Half width)
In the present embodiment, in the powder X-ray diffraction measurement using CuKα ray, the half width of the diffraction peak within the range of 2θ = 18.7 ± 1 ° is set to A, and the diffraction within the range of 2θ = 44.4 ± 1 °. When the half width of the peak is B, the product of A and B is preferably 0.014 or more, preferably 0.015 or more, in order to obtain a lithium secondary battery having a high discharge capacity at a high current rate. Is more preferable, and 0.016 or more is further preferable. Further, in the sense of obtaining a lithium secondary battery having high cycle characteristics, it is preferably 0.030 or less, more preferably 0.029 or less, and further preferably 0.028 or less.
The upper and lower limits of the product of A and B can be arbitrarily combined.
First, regarding the positive electrode active material, in the powder X-ray diffraction measurement using CuKα ray, the diffraction peak within the range of 2θ = 18.7 ± 1 ° (hereinafter, may be referred to as peak A'), 2θ = 44. The diffraction peak within the range of 4 ± 1 ° (hereinafter, may be referred to as peak B') is determined.
Further, the determined half-value width A of the peak A'and the half-value width B of the peak B'are calculated, and the Scherrer equation D = Kλ / Bcosθ (D: crystallite size, K: Scherrer constant, B: peak line width). The crystallite size can be calculated by using. Calculating the crystallite size by this formula is a conventionally used method (for example, "X-ray structure analysis-determining the arrangement of atoms-", April 30, 2002, 3rd edition, Yoshio Waseda, By Eiichiro Matsubara, see).

In the present embodiment, in the sense of obtaining a lithium secondary battery having a high discharge capacity at a high current rate, the range of the half width A of the positive electrode active material is preferably 0.115 or more, preferably 0.116 or more. Is more preferable, and 0.117 or more is further preferable. Further, in the sense of obtaining a lithium secondary battery having high cycle characteristics, it is preferably 0.165 or less, more preferably 0.164 or less, and further preferably 0.163 or less.
The upper limit value and the lower limit value of the half width A can be arbitrarily combined.

In the present embodiment, the range of the half-value width B of the positive electrode active material is preferably 0.120 or more, preferably 0.125 or more, in order to obtain a lithium secondary battery having a high discharge capacity at a high current rate. Is more preferable, and 0.126 or more is further preferable. Further, in the sense of obtaining a lithium secondary battery having high cycle characteristics, it is preferably 0.180 or less, more preferably 0.179 or less, and further preferably 0.178 or less.
The upper limit value and the lower limit value of the half price B can be arbitrarily combined.

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

The hexagonal crystal structure is 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, in the sense 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 not particularly limited as long as it satisfies the above formula (1), and includes lithium carbonate, lithium nitrate, lithium sulfate, lithium acetate, lithium hydroxide, lithium oxide, lithium chloride, and lithium fluoride. Any one of them, or a mixture of two or more of them can be used. Among these, either one or both of lithium hydroxide and lithium carbonate is preferable.
In order to improve the handleability of the positive electrode active material for the lithium secondary battery, the lithium carbonate component contained in the lithium metal composite 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, in order to improve the handleability of the positive electrode active material for the lithium secondary battery, the lithium hydroxide component contained in the lithium metal composite 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.

[Manufacturing method of lithium metal composite oxide]
In producing the lithium metal composite 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 the method for producing the positive electrode active material will be described separately for the process for producing the metal composite compound and the process for producing the lithium metal composite oxide.

(Manufacturing process of metal composite compound)
The metal composite compound can be produced by a commonly known batch co-precipitation method or continuous co-precipitation method. Hereinafter, the production method thereof will be described in detail using 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 x Co y Mn z (} OH) ₂ A metal composite hydroxide represented by (x + y + z = 1 in the formula) is produced.

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, cobalt chloride, and cobalt acetate 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, manganese chloride, and manganese acetate can be used. More metal salts are used in proportions corresponding to the composition ratio of the _{Ni x Co y Mn z (OH} ) 2.
In addition, water is used as a solvent.

The complexing agent can form a complex with ions of nickel, cobalt, and manganese in an aqueous solution, and is, for example, an ammonium ion feeder (ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc.). ), Hydrazin, 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.

The nickel salt solution, cobalt salt solution, and other manganese salt solution and is supplied continuously complexing agent to the reaction vessel, nickel, cobalt, and manganese to _{react, Ni x Co y Mn z (} OH) 2 Is manufactured. In the reaction, the temperature of the reaction vessel is controlled in the range of, for example, 20 ° C. or higher and 80 ° C. or lower, preferably 30 to 70 ° C., and the pH value in the reaction vessel is, for example, pH 9 or higher and pH 13 or lower, preferably pH 11 to 13. Controlled within, the material in the reaction vessel is stirred as appropriate. 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 primary particle size of the lithium metal composite oxide finally obtained in the following steps, Various physical properties such as secondary particle size, size of each crystallite, BET specific surface area, and average crushing strength can be controlled. In particular, in order to realize the desired average crushing strength, pore distribution, and voids of the secondary particles, in addition to controlling the above conditions, various gases such as nitrogen, argon, carbon dioxide, and other inert gases are used. , Air, oxidizing gas such as oxygen, or bubbling with a mixed gas thereof may be used in combination. In addition to gas, peroxides such as hydrogen peroxide, peroxide salts such as permanganate, perchlorate, hypochlorite, nitric acid, halogen, ozone, etc. are used to promote the oxidation state. be able to. In addition to the gas, organic acids such as oxalic acid and formic acid, sulfites, hydrazine and the like can be used to promote the reducing state.

For example, when the reaction pH in the reaction vessel is increased, the primary particle size of the metal composite compound becomes smaller, and a metal composite compound having a high BET specific surface area can be easily obtained. On the other hand, when the reaction pH is lowered, the primary particle size of the metal composite compound becomes large, and a metal composite compound having a low BET specific surface area can be easily obtained. Further, when the oxidation state in the reaction vessel is raised, a metal composite oxide having many voids can be easily obtained. On the other hand, when the oxidation state is lowered, a dense metal composite compound can be easily obtained. Finally, the reaction pH and the conditions of the oxidation state may be appropriately controlled so that the metal composite compound has desired physical properties.
The BET specific surface area of the lithium metal composite oxide powder and the average crushing strength of the secondary particles in the present invention are within a specific range of the present invention by controlling the firing conditions and the like described later using the metal composite compound. Can be inside.

Since the reaction conditions depend on the size of the reaction vessel used and the like, the reaction conditions may be optimized while monitoring various physical properties of the finally obtained lithium composite oxide.

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.

(Manufacturing process of lithium metal composite oxide)
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 / reduced (oxide → oxide, hydroxide → hydroxide), and the metal composite hydroxide are oxidized. Any of the conditions (hydroxide → oxide) and the condition for reducing the metal composite oxide (oxide → hydroxide) may be used. An inert gas such as nitrogen, helium, or argon may be used under the condition of not being oxidized or reduced, and oxygen or air may be used under the condition of oxidizing the hydroxide.
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 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 metal complex hydroxide _is used in a proportion corresponding to LiNi _x Co y _Mn z _{O 2} composition ratio of (wherein, x + y + z = 1 ) .. A lithium-nickel cobalt manganese composite oxide is obtained by calcining a mixture of a nickel cobalt manganese metal composite 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 the BET specific surface area of the lithium metal composite oxide and the average crushing of secondary particles are crushed. In order to keep the strength within the specific range of the present invention, it is preferably 600 ° C. or higher and 1100 ° C. or lower, more preferably 750 ° C. or higher and 1050 ° C. or lower, and further preferably 800 ° C. or higher and 1025 ° C. or lower. When the firing temperature is lower than 600 ° C., it is difficult to obtain a lithium metal composite oxide having a regular crystal structure, the BET specific surface area of the lithium metal composite oxide exceeds the upper limit of the present invention, or the average crushing of secondary particles is performed. The strength may be lower than the lower limit of the present invention, and problems such as energy density (discharge capacity) and charge / discharge efficiency (discharge capacity ÷ charge capacity) are likely to decrease.

On the other hand, when the firing temperature exceeds 1100 ° C., in addition to problems in production such as difficulty in obtaining a lithium metal composite oxide having a target composition due to volatilization of Li, the BET specific surface area may fall below the lower limit of the present invention. The average crushing strength of the secondary particles of the lithium metal composite oxide may exceed the upper limit of the present invention due to the influence of the densification of the particles, which tends to cause a problem that the battery performance is deteriorated. It is considered that this is because the primary particle growth rate increases and the crystal particles of the lithium metal composite oxide become too large when the temperature exceeds 1100 ° C. By setting the firing temperature in the range of 600 ° C. or higher and 1100 ° C. or lower, it is possible to manufacture a battery that exhibits a particularly high energy density and is excellent in charge / discharge efficiency and output characteristics.

The firing time is preferably 3 hours to 50 hours. If the firing time exceeds 50 hours, there is no problem in battery performance, but the battery performance tends to be substantially inferior due to the volatilization of Li. 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 in the range of 300 to 850 ° C. for 1 to 10 hours.

The lithium metal composite oxide obtained by calcination is appropriately classified after pulverization to obtain a positive electrode active material applicable to a lithium secondary battery.

<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. To 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 is used. 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, which is a standard for batteries defined by the International Electrotechnical Commission (IEC), or JIS C 8500 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 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 to improve charge / discharge efficiency and output characteristics, but if too much is added, it depends on the binder. 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.
This thermoplastic resin may be referred to as polyvinylidene fluoride (hereinafter referred to as PVdF).
), Polytetrafluoroethylene (hereinafter sometimes referred to as PTFE), ethylene tetrafluoride / propylene hexafluoride / vinylidene fluoride copolymer, propylene hexafluoride / vinylidene fluoride copolymer, tetrafluoropolymer. Fluororesin such as ethylene / 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. Ester-based solvents such as dimethylacetamide and amide-based solvents such as 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 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, cokes, carbon black, pyrolyzed carbons, carbon fibers, and calcined organic polymer compounds.

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 metal composite 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 titanium sulfides 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) Iron sulfide represented by; Mo ₂ S ₃ , MoS _2, etc. Formula MoS _x (where x is a positive real number) Molybdenum sulfide represented by the formula MoS _x (where x is a positive real number); SnS _2, SnS, etc. formula SnS _x (here, here) 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. Also mentioned are tin alloys such as −Co, Sn—Ni, Sn—Cu, Sn—La; alloys such as Cu ₂ Sb, La ₃ Ni ₂ Sn ₇ ;

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. 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 stack of separators having different porosity.

(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 (where FSI stands for bis (fluorosulfonyl) image), lower aliphatic carboxylic acid lithium salts, lithium salts such as LiAlCl _4, and mixtures 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, ethyl methyl 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, 1,3-propanesartone, or those in which a fluoro group is further introduced into an organic solvent (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, 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 because the safety of the obtained lithium secondary battery is enhanced. 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 electrolyte. 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. In addition, 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 metal composite oxide of the present embodiment described above, the life of the lithium secondary battery using the positive electrode active material can be extended.

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 life of the lithium secondary battery can be extended.

Further, since the lithium secondary battery having the above configuration has the above-mentioned positive electrode, it is a lithium secondary battery having a longer life 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 positive electrode active material for the lithium secondary battery and the production evaluation of the positive electrode for the lithium secondary battery and the lithium secondary battery were carried out as follows.
(1) Evaluation of positive electrode active material for lithium secondary batteries 1. Average crushing strength of secondary particles The average crushing strength of secondary particles was measured using a microcompression tester (MCT-510, manufactured by Shimadzu Corporation), and was arbitrarily selected from among lithium metal composite oxide powders. The test pressure was applied to one particle for measurement. The pressure value at which the test pressure was substantially constant and the displacement amount of the secondary particles was maximized was defined as the test force (P), and the crushing strength (St) was calculated by the above-mentioned formula of Hiramatsu et al. Finally, the average crush strength was obtained from the average value obtained by performing the crush strength test a total of 5 times.

2. 2. BET Specific Surface Area Measurement 1 g of lithium metal composite oxide powder was dried at 105 ° C. for 30 minutes in a nitrogen atmosphere, and then measured using Macsorb (registered trademark) manufactured by Mountec.

3. 3. Measurement of average particle size For the measurement of the average particle size, 0.1 g of lithium metal composite oxide powder was used to measure 0.2 mass% sodium hexametaphosphate using a laser diffraction particle size distribution counter (LA-950, manufactured by Horiba Seisakusho Co., Ltd.). It was put into 50 ml of an aqueous solution to obtain a dispersion liquid in which the powder was dispersed. The particle size distribution of the obtained dispersion is measured, and a volume-based cumulative particle size distribution curve is obtained. In the obtained cumulative particle size distribution curve, the value of the particle size (D ₅₀ ) seen from the fine particle side at the time of 50% accumulation was taken as the average particle size of the lithium metal composite oxide powder.

4. Powder X-ray diffraction measurement The powder X-ray diffraction measurement was performed using an X-ray diffractometer (X'Pert PRO manufactured by PANalytical). A powder X-ray diffraction pattern was obtained by filling a dedicated substrate with a lithium metal composite oxide powder and measuring in a diffraction angle range of 2θ = 10 ° to 90 ° using a Cu-Kα radiation source. .. Using the powder X-ray diffraction pattern comprehensive analysis software JADE5, the half width A of the diffraction peak of 2θ = 18.7 ± 1 ° and the half width of the diffraction peak of 2θ = 44.4 ± 1 ° from the powder X-ray diffraction pattern. I asked for B.
Diffraction peak of full width at half maximum: 2θ = 18.7 ± 1 °
Diffraction peak of full width at half maximum: 2θ = 44.4 ± 1 °

5. Composition analysis The composition analysis of the lithium metal composite oxide powder produced by the method described below is performed by dissolving the obtained lithium metal composite oxide powder in hydrochloric acid and then inductively coupled plasma emission spectrometry (SI Nanotechnology). This was performed using SPS3000) manufactured by SPS Co., Ltd.

6. Quantification of residual lithium contained in lithium metal composite oxide powder (neutralization titration)
20 g of lithium metal composite oxide powder and 100 g of pure water were placed in a 100 ml beaker and stirred for 5 minutes. After stirring, the lithium metal composite oxide was filtered, 0.1 mol / L hydrochloric acid was added dropwise to 60 g of the remaining filtrate, and the pH of the filtrate was measured with a pH meter. The titration amount of hydrochloric acid at pH = 8.3 ± 0.1 is Aml, and the titration amount of hydrochloric acid at pH = 4.5 ± 0.1 is Bml. From the following formula, the lithium metal composite oxide is contained. The remaining lithium carbonate and lithium hydroxide concentrations were calculated. In the formula below, the molecular weights of lithium carbonate and lithium hydroxide were calculated with each atomic weight as H; 1.000, Li; 6.941, C; 12, O; 16.
Lithium carbonate concentration (%) =
0.1 x (BA) / 1000 x 73.882 / (20 x 60/100) x 100 Lithium hydroxide concentration (%) =
0.1 x (2A-B) / 1000 x 23.941 / (20 x 60/100) x 100

(2) Preparation of Positive Electrode for Lithium Secondary Battery The positive electrode active material for lithium secondary battery, conductive material (acetylene black) and binder (PVdF) obtained by the manufacturing method described later are used as the positive electrode active material for lithium secondary battery: A paste-like positive electrode mixture was prepared by adding and kneading the conductive material so as to have a composition of binder = 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 .

(3) Preparation 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 (Nippon A & L Inc.) as the binder. The negative electrode active material: CMC: SRR = 98: 1: 1 (mass ratio) was added and kneaded to prepare a paste-like negative electrode mixture. 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 100 ° 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 .

(4) Preparation of lithium secondary battery (coin type half cell) The following operation was performed in a glove box with an argon atmosphere.
Place the positive electrode for the lithium secondary battery manufactured in "(2) Fabrication of 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 surface 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 at 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).

(5) Preparation of Lithium Secondary Battery (Coin-type Full Cell) The following operation was performed in a glove box with an argon atmosphere.
Place the positive electrode for the lithium secondary battery manufactured in "(2) Fabrication of 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 surface 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 16:10 of 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). : 74 (volume ratio) A mixture of vinylene carbonate (hereinafter, may be referred to as VC) in an amount of 1% by volume, and LiPF ₆ dissolved therein so as to be 1.3 mol / l (hereinafter, LiPF _6). / EC + DMC + EMC may be expressed.) Was used.
Next, the negative electrode for the lithium secondary battery prepared in "(3) Preparation of the negative electrode for the lithium secondary battery" is placed on the upper side of the laminated film separator, the upper lid is closed through the gasket, and the lithium secondary is crimped with a caulking machine. A battery (coin-type full cell R2032; hereinafter, may be referred to as "full cell") was produced.

(6) Initial charge / discharge test Using the half cell prepared in "(4) Preparation of lithium secondary battery (coin type half cell)", the initial charge / discharge test was carried out under the following conditions.
<First charge / discharge test>
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 Also, initial charge / discharge efficiency Was calculated as follows.
Initial charge / discharge efficiency (% = 0.2CA initial discharge capacity / 0.2CA initial charge capacity x 100

(7) Low-temperature discharge test Using the full cell prepared in "(5) Preparation of lithium secondary battery (coin type full cell)", the initial charge / discharge test was carried out under the following conditions.
<Charging / discharging test conditions>
Test temperature: 25 ° C
Maximum charging voltage 4.2V, charging time 6 hours, charging current 0.2CA, constant current constant voltage charging Minimum discharge voltage 2.7V, discharge time 5 hours, discharge current 0.2CA, constant current discharge <Battery resistance measurement>
The battery resistance of 15% SOC and 50% SOC was measured at −15 ° C. with the discharge capacity measured above as 100% of the charging depth (hereinafter, may be referred to as SOC). The adjustment to each SOC was performed in an environment of 25 ° C. For battery resistance measurement, a full cell with SOC adjusted is allowed to stand in a constant temperature bath at -15 ° C for 2 hours, discharged at 20 μA for 15 seconds, left to stand for 5 minutes, charged at 20 μA for 15 seconds, left to stand for 5 minutes, and left at 40 μA for 15 minutes. Discharge for 2 seconds, stand for 5 minutes, charge for 30 seconds at 20 μA, stand for 5 minutes, discharge for 15 seconds at 80 μA, stand for 5 minutes, charge for 60 seconds at 20 μA, stand for 5 minutes, discharge for 15 seconds at 160 μA, discharge for 5 minutes It was placed, charged at 20 μA for 120 seconds, and allowed to stand for 5 minutes in that order. The battery resistance was calculated by using the least squares approximation method from the plot of the battery voltage after 10 seconds measured at 20, 40, 80, and 120 μA discharge and each current value, and this slope was used as the battery resistance. ..

(Example 1)
1. 1. Manufacture of positive electrode active material 1 for lithium secondary battery
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.

A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution are mixed so that the atomic ratio of nickel atom, cobalt atom, and manganese atom is 0.315: 0.330: 0.355 to prepare a mixed raw material solution. It was adjusted.

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 air was mixed with nitrogen gas so that the oxygen concentration became 4.0%. The oxygen-containing gas was continuously ventilated. An aqueous sodium hydroxide solution was added dropwise at appropriate times so that the pH of the solution in the reaction vessel became 11.7 to obtain nickel-cobalt-manganese composite hydroxide particles, which were washed and then dehydrated with a centrifuge, washed, dehydrated. The nickel-cobalt-manganese composite hydroxide 1 was obtained by isolating and drying at 105 ° C.

Nickel cobalt manganese composite hydroxide 1 and lithium carbonate powder are weighed and mixed so that Li / (Ni + Co + Mn) = 1.13, then calcined at 690 ° C. for 5 hours in an air atmosphere, and further, the atmosphere. The target positive electrode active material 1 for a lithium secondary battery was obtained by firing at 925 ° C. for 6 hours in an atmosphere.

2. 2. Evaluation of positive electrode active material 1 for lithium secondary battery
When the composition of the positive electrode active material 1 for the lithium secondary battery was analyzed and corresponded to the general formula (1), it was x = 0.06, y = 0.328, z = 0.356, w = 0. ..

The average crushing strength of the positive electrode active material 1 for a lithium secondary battery is 52.2 MPa, the BET specific surface area is 2.4 m ² / g, the average particle size D ₅₀ is 3.4 μm, and the half width of 2θ = 18.7 ± 1 °. A × B, which is the product of A and the half width B of 2θ = 44.4 ± 1 °, was 0.020, the half width A was 0.134, and the half width B was 0.147.

The residual lithium of the positive electrode active material 1 for the lithium secondary battery was quantified, and lithium carbonate was 0.10% by mass and lithium hydroxide was 0.11% by mass.

3. 3. Evaluation of lithium secondary battery
A coin-type half cell was prepared using the positive electrode active material 1 for a lithium secondary battery, and the initial charge / discharge test was carried out. The initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency were 170.4 mAh / g, 161.1 mAh / g, and 94.5%, respectively.

A coin-type full cell was prepared using the positive electrode active material 1 for a lithium secondary battery, and a low-temperature discharge test at −15 ° C. was conducted. The DC resistance at SOC 15% and SOC 50% was 423Ω and 384Ω, respectively.

(Example 2)
1. 1. Manufacture of positive electrode active material 2 for lithium secondary batteries
Nickel cobalt manganese composite hydroxide 1 was obtained in the same manner as in Example 1.

A LiOH aqueous solution in which WO ₃ was dissolved at 61 g / L was prepared. The prepared W-dissolved LiOH aqueous solution was adhered to nickel-cobalt-manganese composite hydroxide 1 so as to have W / (Ni + Co + Mn + W) = 0.005 with a Ladyge mixer. The nickel-cobalt-manganese composite hydroxide coated with W and the lithium carbonate powder were weighed and mixed so that Li / (Ni + Co + Mn + W) = 1.13, and then calcined at 690 ° C. for 5 hours in an air atmosphere. Further, it was calcined at 925 ° C. for 6 hours in an air atmosphere to obtain the target positive electrode active material 2 for a lithium secondary battery.

2. 2. Evaluation of positive electrode active material 2 for lithium secondary batteries
When the composition of the positive electrode active material 2 for the lithium secondary battery was analyzed and made to correspond to the general formula (1), M was W, x = 0.06, y = 0.327, z = 0.354, w =. It was 0.005.

The average crushing strength of the positive electrode active material 2 for lithium secondary batteries is 54.0 MPa, the BET specific surface area is 2.0 m ² / g, the average particle size D ₅₀ is 3.6 μm, and the half width of 2θ = 18.7 ± 1 °. A × B, which is the product of A and the half width B of 2θ = 44.4 ± 1 °, was 0.023, the half width A was 0.141, and the half width B was 0.161.

The residual lithium of the positive electrode active material 2 for the lithium secondary battery was quantified, and lithium carbonate was 0.17% by mass and lithium hydroxide was 0.11% by mass.

3. 3. Evaluation of lithium secondary battery
A coin-type half cell was prepared using the positive electrode active material 2 for a lithium secondary battery, and the initial charge / discharge test was carried out. The initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency were 170.6 mAh / g, 161.2 mAh / g, and 94.5%, respectively.

A coin-shaped full cell was prepared using the positive electrode active material 2 for a lithium secondary battery, and a low temperature discharge test at −15 ° C. was conducted. The DC resistance at SOC 15% and SOC 50% was 296Ω and 269Ω, respectively.

(Example 3)
1. 1. Manufacture of positive electrode active material 3 for lithium secondary batteries
Nickel cobalt manganese composite hydroxide 1 was obtained in the same manner as in Example 1.

Nickel-cobalt-manganese composite hydroxide 1 and ZrO ₂ were added so that Zr / (Ni + Co + Mn + Zr) = 0.003 and mixed to obtain a ZrO _2- containing mixed powder. This mixed powder and lithium carbonate powder are weighed and mixed so that Li / (Ni + Co + Mn + Zr) = 1.13, then fired in an air atmosphere at 690 ° C. for 5 hours, and further in an air atmosphere at 925 ° C. for 6 hours. It was fired to obtain the desired positive electrode active material 3 for a lithium secondary battery.

2. 2. Evaluation of positive electrode active material 3 for lithium secondary batteries
When the composition of the positive electrode active material 3 for the lithium secondary battery was analyzed and made to correspond to the general formula (1), M was Zr, x = 0.06, y = 0.328, z = 0.354, w =. It was 0.003.

The average crushing strength of the positive electrode active material 3 for a lithium secondary battery is 57.6 MPa, the BET specific surface area is 2.4 m ² / g, the average particle size D ₅₀ is 3.5 μm, and the half width of 2θ = 18.7 ± 1 °. A × B, which is the product of A and the half width B of 2θ = 44.4 ± 1 °, was 0.021, the half width A was 0.133, and the half width B was 0.161.

The residual lithium of the positive electrode active material 3 for the lithium secondary battery was quantified, and lithium carbonate was 0.15% by mass and lithium hydroxide was 0.12% by mass.

3. 3. Evaluation of lithium secondary battery
A coin-shaped half cell was prepared using the positive electrode active material 3 for a lithium secondary battery, and the initial charge / discharge test was carried out. The initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency were 170.5 mAh / g, 160.2 mAh / g, and 94.0%, respectively.

A coin-shaped full cell was prepared using the positive electrode active material 3 for a lithium secondary battery, and a low-temperature discharge test at −15 ° C. was conducted. The DC resistance at SOC 15% and SOC 50% was 298Ω and 271Ω, respectively.

(Example 4)
1. 1. Manufacture of positive electrode active material 4 for lithium secondary battery
The same procedure as in Example 1 was carried out except that the operation was performed so that the oxygen concentration was 2.1% and the pH of the solution in the reaction vessel was 11.2, to obtain a nickel cobalt-manganese composite hydroxide 2.

Nickel-cobalt-manganese composite hydroxide 2 and MgO were added so that Mg / (Ni + Co + Mn + Mg) = 0.003 and mixed to obtain an MgO-containing mixed powder. This mixed powder and lithium carbonate powder are weighed and mixed so that Li / (Ni + Co + Mn + Mg) = 1.08, then fired at 690 ° C. for 5 hours in an air atmosphere, and further at 950 ° C. for 6 hours in an air atmosphere. It was fired to obtain the desired positive electrode active material 4 for a lithium secondary battery.

2. 2. Evaluation of positive electrode active material 4 for lithium secondary battery
When the composition of the positive electrode active material 4 for the lithium secondary battery was analyzed and made to correspond to the general formula (1), M was Mg, x = 0.04, y = 0.328, z = 0.355, w =. It was 0.003.

The average crushing strength of the positive electrode active material 4 for a lithium secondary battery is 92.6 MPa, the BET specific surface area is 1.1 m ² / g, the average particle size D ₅₀ is 9.8 μm, and the half width of 2θ = 18.7 ± 1 °. A × B, which is the product of A and the half width B of 2θ = 44.4 ± 1 °, was 0.019, the half width A was 0.133, and the half width B was 0.142.

The residual lithium of the positive electrode active material 4 for the lithium secondary battery was quantified, and lithium carbonate was 0.04% by mass and lithium hydroxide was 0.10% by mass.

3. 3. Evaluation of lithium secondary battery
A coin-type half cell was prepared using the positive electrode active material 4 for a lithium secondary battery, and the initial charge / discharge test was carried out. The initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency were 173.4 mAh / g, 157.1 mAh / g, and 90.6%, respectively.

A coin-type full cell was prepared using the positive electrode active material 4 for a lithium secondary battery, and a low-temperature discharge test at −15 ° C. was conducted. The DC resistance at SOC 15% and SOC 50% was 480Ω and 332Ω, respectively.

(Example 5)
1. 1. Manufacture of positive electrode active material 5 for lithium secondary battery
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 nickel sulfate aqueous solution, the cobalt sulfate aqueous solution, and the manganese sulfate aqueous solution are mixed so that the atomic ratio of the nickel atom, the cobalt atom, and the manganese atom is 0.510: 0.225: 0.265 to prepare a mixed raw material solution. It was adjusted.

Next, in the reaction vessel, the mixed raw material solution and the ammonium sulfate aqueous solution were continuously added as a complexing agent under stirring, and air was mixed with nitrogen gas so that the oxygen concentration became 8.3%. The oxygen-containing gas was continuously ventilated. An aqueous sodium hydroxide solution was added dropwise at appropriate times so that the pH of the solution in the reaction vessel became 12.2 to obtain nickel-cobalt-manganese composite hydroxide particles, which were washed and then dehydrated with a centrifuge, washed, dehydrated. The nickel cobalt-manganese composite hydroxide 3 was obtained by isolating and drying at 105 ° C.

Nickel-cobalt-manganese composite hydroxide 3 and lithium carbonate powder are weighed and mixed so that Li / (Ni + Co + Mn) = 1.06, and then calcined at 720 ° C. for 3 hours in an air atmosphere. The target positive electrode active material 5 for a lithium secondary battery was obtained by firing at 875 ° C. for 10 hours.

2. 2. Evaluation of Positive Electrode Active Material 5 for Lithium Secondary Battery
When the composition of the positive electrode active material 5 for the lithium secondary battery was analyzed and corresponded to the general formula (1), it was x = 0.03, y = 0.222, z = 0.267, w = 0. ..

The average crushing strength of the positive electrode active material 5 for a lithium secondary battery is 71.8 MPa, the BET specific surface area is 1.3 m ² / g, the average particle size D ₅₀ is 7.8 μm, and the half width of 2θ = 18.7 ± 1 °. A × B, which is the product of A and the half width B of 2θ = 44.4 ± 1 °, was 0.015, the half width A was 0.120, and the half width B was 0.125.

The residual lithium of the positive electrode active material 5 for the lithium secondary battery was quantified, and lithium carbonate was 0.15% by mass and lithium hydroxide was 0.19% by mass.

3. 3. Evaluation of lithium secondary battery
A coin-shaped half cell was prepared using the positive electrode active material 5 for a lithium secondary battery, and the initial charge / discharge test was carried out. The initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency were 189.6 mAh / g and 174.1 mAh / g, respectively, and 91.8%.

A coin-shaped full cell was prepared using the positive electrode active material 5 for a lithium secondary battery, and a low-temperature discharge test at −15 ° C. was conducted. The DC resistance at SOC 15% and SOC 50% was 340Ω and 301Ω, respectively.

(Example 6)
1. 1. Production of positive electrode active material 6 for lithium secondary batteries
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 nickel sulfate aqueous solution, the cobalt sulfate aqueous solution, and the manganese sulfate aqueous solution are mixed so that the atomic ratio of the nickel atom, the cobalt atom, and the manganese atom is 0.550: 0.210: 0.240 to prepare a mixed raw material solution. It was adjusted.

Next, in the reaction vessel, the mixed raw material solution and the ammonium sulfate aqueous solution were continuously added as a complexing agent under stirring, and air was mixed with nitrogen gas so that the oxygen concentration became 9.5%. The oxygen-containing gas was continuously ventilated. An aqueous sodium hydroxide solution was added dropwise at appropriate times so that the pH of the solution in the reaction vessel became 12.5 to obtain nickel-cobalt-manganese composite hydroxide particles, which were washed, then dehydrated with a centrifuge, washed, and dehydrated. The nickel cobalt-manganese composite hydroxide 4 was obtained by isolating and drying at 105 ° C.

Nickel cobalt manganese composite hydroxide 4 and lithium carbonate powder are weighed and mixed so that Li / (Ni + Co + Mn) = 1.06, then fired at 790 ° C. for 3 hours in an air atmosphere, and further in an oxygen atmosphere. The target positive electrode active material 6 for a lithium secondary battery was obtained by firing at 830 ° C. for 10 hours.

2. 2. Evaluation of Positive Electrode Active Material 6 for Lithium Secondary Battery
When the composition of the positive electrode active material 6 for the lithium secondary battery was analyzed and corresponded to the general formula (1), it was x = 0.03, y = 0.208, z = 0.242, w = 0. ..

The average crushing strength of the positive electrode active material 6 for a lithium secondary battery is 13.6 MPa, the BET specific surface area is 2.8 m ² / g, the average particle size D ₅₀ is 2.5 μm, and the half width of 2θ = 18.7 ± 1 °. A × B, which is the product of A and the half width B of 2θ = 44.4 ± 1 °, was 0.028, the half width A was 0.160, and the half width B was 0.175.

Residual lithium of the positive electrode active material 6 for a lithium secondary battery was quantified, and lithium carbonate was 0.16% by mass and lithium hydroxide was 0.11% by mass.

3. 3. Evaluation of lithium secondary battery
A coin-shaped half cell was prepared using the positive electrode active material 6 for a lithium secondary battery, and the initial charge / discharge test was carried out. The initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency were 192.3 mAh / g and 175.8 mAh / g, respectively, and 91.4%.

A coin-type full cell was prepared using the positive electrode active material 6 for a lithium secondary battery, and a low temperature discharge test at −15 ° C. was conducted. The DC resistance at SOC 15% and SOC 50% was 463Ω and 413Ω, respectively.

(Example 7)
1. 1. Manufacture of positive electrode active material 7 for lithium secondary batteries
Nickel cobalt manganese composite hydroxide 4 was obtained in the same manner as in Example 6.

A LiOH aqueous solution in which WO ₃ was dissolved at 61 g / L was prepared. The prepared W-dissolved LiOH aqueous solution was adhered to nickel-cobalt-manganese composite hydroxide 4 so that W / (Ni + Co + Mn + W) = 0.003 with a Ladyge mixer. The nickel-cobalt-manganese composite hydroxide on which W was adhered and the lithium carbonate powder were weighed and mixed so that Li / (Ni + Co + Mn + W) = 1.08, and then fired at 790 ° C. for 3 hours in an air atmosphere. Further, it was fired at 860 ° C. for 10 hours in an oxygen atmosphere to obtain the target positive electrode active material 7 for a lithium secondary battery.

2. 2. Evaluation of positive electrode active material 7 for lithium secondary battery
When the composition of the positive electrode active material 7 for the lithium secondary battery was analyzed and made to correspond to the general formula (1), M was W, x = 0.04, y = 0.208, z = 0.241, w =. It was 0.003.

The average crushing strength of the positive electrode active material 7 for a lithium secondary battery is 23.9 MPa, the BET specific surface area is 2.0 m ² / g, the average particle size D ₅₀ is 3.4 μm, and the half width of 2θ = 18.7 ± 1 °. A × B, which is the product of A and the half width B of 2θ = 44.4 ± 1 °, was 0.023, the half width A was 0.142, and the half width B was 0.163.

The residual lithium of the positive electrode active material 7 for the lithium secondary battery was quantified, and lithium carbonate was 0.29% by mass and lithium hydroxide was 0.30% by mass.

3. 3. Evaluation of lithium secondary battery
A coin-shaped half cell was prepared using the positive electrode active material 7 for a lithium secondary battery, and the initial charge / discharge test was carried out. The initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency were 191.6 mAh / g, 184.1 mAh / g, and 96.1%, respectively.

A coin-type full cell was prepared using the positive electrode active material 7 for a lithium secondary battery, and a low-temperature discharge test at −15 ° C. was conducted. The DC resistance at SOC 15% and SOC 50% was 328Ω and 269Ω, respectively.

(Example 8)
1. 1. Manufacture of positive electrode active material 8 for lithium secondary battery
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 60 ° C.

An aqueous solution of nickel sulfate, an aqueous solution of cobalt sulfate, and an aqueous solution of manganese sulfate are mixed so that the atomic ratio of nickel atom, cobalt atom, and manganese atom is 0.750: 0.150: 0.100 to prepare a mixed raw material solution. It was adjusted.

Next, in the reaction vessel, the mixed raw material solution and the ammonium sulfate aqueous solution were continuously added as a complexing agent under stirring, and air was mixed with nitrogen gas so that the oxygen concentration became 7.5%. The oxygen-containing gas was continuously ventilated. 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 composite hydroxide particles, which were washed and then dehydrated with a centrifuge, washed, dehydrated. The nickel-cobalt-manganese composite hydroxide 5 was obtained by isolating and drying at 105 ° C.

Nickel-cobalt-manganese composite hydroxide 5 and Al ₂ O ₃ were added so that Al / (Ni + Co + Mn + Al) = 0.05 and mixed to obtain an Al ₂ O _3- containing mixed powder. This mixed powder and lithium carbonate powder are weighed and mixed so that Li / (Ni + Co + Mn + Al) = 1.02, then fired at 750 ° C. for 5 hours in an oxygen atmosphere, and further at 800 ° C. for 5 hours in an oxygen atmosphere. It was fired to obtain the desired positive electrode active material 8 for a lithium secondary battery.

2. 2. Evaluation of Positive Electrode Active Material 8 for Lithium Secondary Battery
When the composition of the positive electrode active material 8 for the lithium secondary battery was analyzed and made to correspond to the general formula (1), M was Al, x = 0.01, y = 0.142, z = 0.095, w =. It was 0.05.

The average crushing strength of the positive electrode active material 8 for a lithium secondary battery is 30.1 MPa, the BET specific surface area is 1.5 m ² / g, the average particle size D ₅₀ is 6.2 μm, and the half width of 2θ = 18.7 ± 1 °. A × B, which is the product of A and the half width B of 2θ = 44.4 ± 1 °, was 0.018, the half width A was 0.134, and the half width B was 0.138.

The residual lithium of the positive electrode active material 8 for the lithium secondary battery was quantified, and lithium carbonate was 0.36% by mass and lithium hydroxide was 0.34% by mass.

3. 3. Evaluation of lithium secondary battery
A coin-shaped half cell was prepared using the positive electrode active material 8 for a lithium secondary battery, and the initial charge / discharge test was carried out. The initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency were 205.4 mAh / g, 197.6 mAh / g, and 96.2%, respectively.

A coin-type full cell was prepared using the positive electrode active material 8 for a lithium secondary battery, and a low-temperature discharge test at −15 ° C. was conducted. The DC resistance at SOC 15% and SOC 50% was 301Ω and 262Ω, respectively.

(Comparative Example 1)
1. 1. Manufacture of positive electrode active material 9 for lithium secondary battery
Nickel cobalt manganese composite hydroxide 1 was obtained in the same manner as in Example 1.

Nickel cobalt manganese composite hydroxide 1 and lithium carbonate powder are weighed and mixed so that Li / (Ni + Co + Mn) = 1.00, calcined at 690 ° C. for 5 hours in an air atmosphere, and further air atmosphere. The target positive electrode active material 9 for a lithium secondary battery was obtained by firing at 850 ° C. for 6 hours.

2. 2. Evaluation of positive electrode active material 9 for lithium secondary battery
When the composition of the positive electrode active material 9 for the lithium secondary battery was analyzed and corresponded to the general formula (1), it was x = 0.00, y = 0.328, z = 0.356, w = 0. ..

The average crushing strength of the positive electrode active material 9 for a lithium secondary battery is 7.5 MPa, the BET specific surface area is 3.6 m ² / g, the average particle size D ₅₀ is 3.0 μm, and the half width of 2θ = 18.7 ± 1 °. A × B, which is the product of A and the half width B of 2θ = 44.4 ± 1 °, was 0.031, the half width A was 0.165, and the half width B was 0.185.

Residual lithium of the positive electrode active material 9 for a lithium secondary battery was quantified, and lithium carbonate was 0.41% by mass and lithium hydroxide was 0.45% by mass.

3. 3. Evaluation of lithium secondary battery
A coin-type half cell was prepared using the positive electrode active material 9 for a lithium secondary battery, and the initial charge / discharge test was carried out. The initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency were 172.4 mAh / g, 153.3 mAh / g, and 88.9%, respectively.

A coin-shaped full cell was prepared using the positive electrode active material 9 for a lithium secondary battery, and a low temperature discharge test at −15 ° C. was conducted. The DC resistance at SOC 15% and SOC 50% was 710Ω and 651Ω, respectively.

(Comparative Example 2)
1. 1. Manufacture of positive electrode active material 10 for lithium secondary battery
Nickel cobalt manganese composite hydroxide 1 was obtained in the same manner as in Example 1.

Nickel cobalt manganese composite hydroxide 1 and lithium carbonate powder are weighed and mixed so that Li / (Ni + Co + Mn) = 1.00, calcined at 690 ° C. for 5 hours in an air atmosphere, and further air atmosphere. The target positive electrode active material 10 for a lithium secondary battery was obtained by firing at 980 ° C. for 6 hours.

2. 2. Evaluation of Positive Electrode Active Material 10 for Lithium Secondary Battery
When the composition of the positive electrode active material 10 for the lithium secondary battery was analyzed and made to correspond to the general formula (1), it was found that x = 0, y = 0.329, z = 0.356, and w = 0.

Positive electrode active material for lithium secondary battery 10 Average crush strength is 62.1 MPa, BET specific surface area is 0.8 m ² / g, average particle size D ₅₀ is 3.2 μm, 2θ = 18.7 ± 1 ° half width A A × B, which is the product of the half width B of 2θ = 44.4 ± 1 °, was 0.017, the half width A was 0.128, and the half width B was 0.132.

Residual lithium of the positive electrode active material 10 for a lithium secondary battery was quantified, and lithium carbonate was 0.18% by mass and lithium hydroxide was 0.11% by mass.

3. 3. Evaluation of lithium secondary battery
A coin-shaped half cell was prepared using the positive electrode active material 10 for a lithium secondary battery, and the initial charge / discharge test was carried out. The initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency were 172.9 mAh / g, 154.4 mAh / g, and 89.3%, respectively.

A coin-shaped full cell was prepared using the positive electrode active material 10 for a lithium secondary battery, and a low-temperature discharge test at −15 ° C. was conducted. The DC resistance at SOC 15% and SOC 50% was 621Ω and 532Ω, respectively.

(Comparative Example 3)
1. 1. Manufacture of positive electrode active material 11 for lithium secondary battery
Nickel cobalt manganese composite hydroxide 6 was obtained in the same manner as in Example 5 except that the oxygen concentration in the reaction vessel was 6.2% and the pH of the solution in the reaction vessel was 12.4.

Nickel cobalt manganese composite hydroxide 6 and lithium carbonate powder are weighed and mixed so that Li / (Ni + Co + Mn) = 1.00, calcined at 720 ° C. for 3 hours in an air atmosphere, and further air atmosphere. The target positive electrode active material 11 for a lithium secondary battery was obtained by firing at 875 ° C. for 10 hours.

2. 2. Evaluation of Positive Electrode Active Material 11 for Lithium Secondary Battery
When the composition of the positive electrode active material 11 for the lithium secondary battery was analyzed and corresponded to the general formula (1), it was x = 0, y = 0.222, z = 0.266, w = 0.

The average crushing strength of the positive electrode active material 11 for a lithium secondary battery is 105.3 MPa, the BET specific surface area is 1.4 m ² / g, the average particle size D ₅₀ is 5.2 μm, and the half width of 2θ = 18.7 ± 1 °. A × B, which is the product of A and the half width B of 2θ = 44.4 ± 1 °, was 0.019, the half width A was 0.133, and the half width B was 0.144.

The residual lithium of the positive electrode active material 11 for the lithium secondary battery was quantified, and lithium carbonate was 0.21% by mass and lithium hydroxide was 0.18% by mass.

3. 3. Evaluation of lithium secondary battery
A coin-type half cell was prepared using the positive electrode active material 11 for a lithium secondary battery, and the initial charge / discharge test was carried out. The initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency were 192.7 mAh / g, 171.6 mAh / g, and 89.1%, respectively.

A coin-shaped full cell was prepared using the positive electrode active material 11 for a lithium secondary battery, and a low temperature discharge test at −15 ° C. was conducted. The DC resistance at SOC 15% and SOC 50% was 532Ω and 503Ω, respectively.

(Comparative Example 4)
1. 1. Manufacture of positive electrode active material 12 for lithium secondary battery
Nickel-cobalt-manganese composite hydroxide 7 was obtained in the same manner as in Example 5 except that the liquid temperature in the reaction vessel was 60 ° C., the oxygen concentration was 0%, and the pH of the solution in the reaction vessel was 11.5. It was.

Nickel-cobalt-manganese composite hydroxide 7 and lithium carbonate powder are weighed and mixed so that Li / (Ni + Co + Mn) = 1.04, and then calcined at 720 ° C. for 3 hours in an air atmosphere. The target positive electrode active material 12 for a lithium secondary battery was obtained by firing at 900 ° C. for 10 hours.

2. 2. Evaluation of Positive Electrode Active Material 12 for Lithium Secondary Battery
When the composition of the positive electrode active material 12 for a lithium secondary battery was analyzed and made to correspond to the general formula (1), it was x = 0.02, y = 0.221, z = 0.265, w = 0. ..

Positive electrode active material for lithium secondary battery 12 Average crush strength is 146.2 MPa, BET specific surface area is 0.2 m ² / g, average particle size D ₅₀ is 11.2 μm, 2θ = 18.7 ± 1 ° half width A A × B, which is the product of the half-value width B of 2θ = 44.4 ± 1 °, was 0.014, the half-value width A was 0.116, and the half-value width B was 0.121.

Residual lithium of the positive electrode active material 12 for a lithium secondary battery was quantified, and lithium carbonate was 0.18% by mass and lithium hydroxide was 0.26% by mass.

3. 3. Evaluation of lithium secondary battery
A coin-shaped half cell was prepared using the positive electrode active material 12 for a lithium secondary battery, and the initial charge / discharge test was carried out. The initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency were 194.7 mAh / g, 169.2 mAh / g, and 86.9%, respectively.

A coin-shaped full cell was prepared using the positive electrode active material 12 for a lithium secondary battery, and a low temperature discharge test at −15 ° C. was conducted. The DC resistance at SOC 15% and SOC 50% was 854Ω and 621Ω, respectively.

(Comparative Example 5)
1. 1. Manufacture of positive electrode active material 13 for lithium secondary battery
Nickel-cobalt-manganese composite hydroxide 8 was obtained in the same manner as in Example 6 except that the liquid temperature in the reaction vessel was 60 ° C., the oxygen concentration was 0%, and the pH of the solution in the reaction vessel was 11.5. It was.

Nickel cobalt manganese composite hydroxide 8 and lithium carbonate powder are weighed and mixed so that Li / (Ni + Co + Mn) = 1.04, then fired at 790 ° C. for 3 hours in an air atmosphere, and further in an oxygen atmosphere. The target positive electrode active material 13 for a lithium secondary battery was obtained by firing at 850 ° C. for 10 hours.

2. 2. Evaluation of Positive Electrode Active Material 13 for Lithium Secondary Battery
When the composition of the positive electrode active material 13 for the lithium secondary battery was analyzed and corresponded to the general formula (1), it was x = 0.02, y = 0.209, z = 0.241, w = 0. ..

The average crushing strength of the positive electrode active material 13 for a lithium secondary battery is 115.6 MPa, the BET specific surface area is 3.2 m ² / g, the average particle size D ₅₀ is 10.8 μm, and the half width of 2θ = 18.7 ± 1 °. A × B, which is the product of A and the half width B of 2θ = 44.4 ± 1 °, was 0.015, the half width A was 0.119, and the half width B was 0.123.

The residual lithium of the positive electrode active material 13 for the lithium secondary battery was quantified, and lithium carbonate was 0.23% by mass and lithium hydroxide was 0.27% by mass.

3. 3. Evaluation of lithium secondary battery
A coin-shaped half cell was prepared using the positive electrode active material 13 for a lithium secondary battery, and the initial charge / discharge test was carried out. The initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency were 195.5 mAh / g, 172.4 mAh / g, and 88.2%, respectively.

A coin-shaped full cell was prepared using the positive electrode active material 13 for a lithium secondary battery, and a low temperature discharge test at −15 ° C. was conducted. The DC resistance at SOC 15% and SOC 50% was 583Ω and 552Ω, respectively.

Table 1 below shows the composition of the positive electrode active materials of Examples 1 to 8 and Comparative Examples 1 to 5, average crushing strength, BET specific surface area, half width of powder X-ray diffraction peak, residual lithium amount, initial charge / discharge capacity, and initial charge / discharge capacity. The discharge capacity, initial discharge efficiency, and -15 ° C DC resistance values are listed together.

The SEM image of the secondary particle cross section of Example 2 is shown in FIG.

The SEM image of the secondary particle cross section of Comparative Example 4 is shown in FIG.

As shown in the above results, in Examples 1 to 8 to which the present invention was applied, the initial charge / discharge efficiency was as high as 90% or more. In addition to this, in Examples 1 to 8 to which the present invention was applied, the DC resistance was low even at a low temperature in the results of the low temperature discharge test.
As shown in the results shown in FIG. 3, it was clear from the cross-sectional view that the secondary particles of Example 2 to which the present invention was applied were particles having many voids.
On the other hand, in Comparative Examples 1 to 5 to which the present invention was not applied, the initial charge / discharge efficiency was as low as 90% or less. Moreover, in the low temperature discharge test, the DC resistance became high at low temperature.
As shown in the results shown in FIG. 4, it was clear from the cross-sectional view that the secondary particles of Comparative Example 4 to which the present invention was not applied were dense particles with almost no voids.

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 (9)

A method for producing a positive electrode active material for a lithium secondary battery, which is made of a lithium metal composite oxide powder represented by the general formula (1).
The lithium metal composite oxide powder is composed of primary particles and secondary particles formed by aggregating the primary particles.
The BET specific surface area of the lithium metal composite oxide powder is 1 m ² / g or more and 3 m ² / g or less.
The average crushing strength of the secondary particles is 10 MPa or more and 100 MPa or less.
A step of preparing a mixed raw material solution containing a nickel salt solution, a cobalt salt solution and a manganese salt solution, and
While continuously supplying the mixed raw material liquid and the complexing agent to the reaction tank, the oxygen-containing gas obtained by mixing air with nitrogen gas so that the oxygen concentration becomes 2.1% or more in the reaction tank is continuously supplied. And the process of obtaining a metal composite compound by aeration
The ratio of lithium to the total amount (Ni + Co + Mn + M) of nickel, cobalt, manganese and element M contained in the obtained metal composite compound (Li / (Ni + Co + Mn + M)) is 1.02 or more. A method for producing a positive electrode active material for a lithium secondary battery, which comprises a step of mixing a compound and a step of firing the mixed mixed powder.
_{Li [Li x (Ni (1} -y-z-w) Co y Mn z M w) 1-x] O 2 (1)
(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. .1 ≤ x ≤ 0.2, 0 <y ≤ 0.4, 0 <z ≤ 0.4, 0 ≤ w ≤ 0.1, 0.25 <y + z + w.) A method for producing a positive electrode active material for a lithium secondary battery, which is made of a lithium metal composite oxide powder represented by the general formula (1).
The lithium metal composite oxide powder is composed of primary particles and secondary particles formed by aggregating the primary particles.
The BET specific surface area of the lithium metal composite oxide powder is 1 m. ² / G or more 3m ² It is less than / g
The average crushing strength of the secondary particles is 10 MPa or more and 100 MPa or less.
A step of preparing a mixed raw material solution containing a nickel salt solution, a cobalt salt solution and a manganese salt solution, and
While continuously supplying the mixed raw material liquid and the complexing agent to the reaction vessel, an oxygen-containing gas having an oxygen concentration of 2.1% or more and 9.5% or less is continuously aerated in the reaction vessel to form a metal composite. The process of obtaining the compound and
The ratio of lithium (Li / (Ni + Co + Mn + M)) to the total amount (Ni + Co + Mn + M) of nickel, cobalt, manganese and element M contained in the obtained metal composite compound is 1.02 or more. A method for producing a positive electrode active material for a lithium secondary battery, which comprises a step of mixing a compound and a step of firing the mixed mixed powder.
Li [Li _x (Ni _(1-yz-w) Co _y Mn _z M _w ) _1-x ] O ₂ (1)
(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. .1 ≤ x ≤ 0.2, 0 <y ≤ 0.4, 0 <z ≤ 0.4, 0 ≤ w ≤ 0.1, 0.25 <y + z + w.) The method for producing a positive electrode active material for a lithium secondary battery according to claim 1 or 2 , wherein y <z in the general formula (1). The method for producing a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 3, wherein the lithium metal composite oxide powder has an average particle size of 2 μm or more and 10 μm or less. In powder X-ray diffraction measurement using CuKα ray, the half-value width of the diffraction peak within the range of 2θ = 18.7 ± 1 ° is A, and the half-value width of the diffraction peak within the range of 2θ = 44.4 ± 1 °. The method for producing a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 4 , wherein the product of A and B is 0.014 or more and 0.030 or less when B is used. The method for producing a positive electrode active material for a lithium secondary battery according to claim 5 , wherein the range of the half width A is 0.115 or more and 0.165 or less. The method for producing a positive electrode active material for a lithium secondary battery according to claim 5 or 6 , wherein the range of the half width B is 0.120 or more and 0.180 or less. The method for producing a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 7 , wherein the lithium carbonate component contained in the lithium metal composite oxide powder is 0.4% by mass or less. The method for producing a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 8 , wherein the lithium hydroxide component contained in the lithium metal composite oxide powder is 0.35% by mass or less.