WO2018012385A1

WO2018012385A1 - Positive electrode active material for nonaqueous electrolyte secondary batteries, transition metal hydroxide precursor, method for producing transition metal hydroxide precursor, method for producing positive electrode active material for nonaqueous electrolyte secondary batteries, electrode for nonaqueous electrolyte secondary batteries, nonaqueous electrolyte secondary battery and electricity storage device

Info

Publication number: WO2018012385A1
Application number: PCT/JP2017/024741
Authority: WO
Inventors: 弘将村松; 遠藤　大輔
Original assignee: 株式会社Ｇｓユアサ
Priority date: 2016-07-14
Filing date: 2017-07-05
Publication date: 2018-01-18
Also published as: JP2019149222A

Abstract

[Problem] To provide: a positive electrode active material which has high discharge capacity per unit volume; a high-density hydroxide precursor for producing this positive electrode active material; an electrode for nonaqueous electrolyte secondary batteries, which uses this positive electrode active material; and a nonaqueous electrolyte secondary battery. [Solution] A positive electrode active material for nonaqueous electrolyte secondary batteries, which contains a lithium transition metal composite oxide, and wherein: the lithium transition metal composite oxide has an α-NaFeO₂ type crystal structure; the molar ratio of Li to the transition metal (Me), namely, the molar ratio Li/Me is more than 1; the transition metal (Me) comprises Mn and Ni, or Mn, Ni and Co, and the molar ratio Mn/Me is more than 0.5; the lithium transition metal composite oxide has an X-ray diffraction pattern belonging to R3-m; the ratio of the half width of a diffraction peak of the (003) plane to the half width (FWHM(104)) of a diffraction peak of the (104) plane by the Miller indices hkl as obtained by X-ray diffraction measurement using a CuKα ray, namely, (FWHM(003)/FWHM(104)) is 0.6 or less; and the total pore volume as determined by a BJH method from the adsorption isotherm using a nitrogen gas adsorption method is 0.05 cm³/g or less.

Description

Cathode active material for nonaqueous electrolyte secondary battery, transition metal hydroxide precursor, method for producing transition metal hydroxide precursor, method for producing cathode active material for nonaqueous electrolyte secondary battery, nonaqueous electrolyte secondary battery Electrode, non-aqueous electrolyte secondary battery and power storage device

The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a transition metal hydroxide precursor used for manufacturing a lithium transition metal composite contained in the positive electrode active material, and a method for manufacturing the transition metal hydroxide precursor The present invention also relates to a method for producing a positive electrode active material using the transition metal precursor, a nonaqueous electrolyte secondary battery electrode containing the positive electrode active material, a nonaqueous electrolyte secondary battery, and a power storage device.

Conventionally, as a positive electrode active material for a non-aqueous electrolyte secondary battery represented by a lithium secondary battery, a “LiMeO ₂ type” active material (Me is a transition metal) having an α-NaFeO ₂ type crystal structure has been studied, and LiCoO Non-aqueous electrolyte secondary batteries using ₂ have been widely put into practical use. However, the discharge capacity of LiCoO ₂ was about 120 to 130 mAh / g. As Me, it has been desired to use abundant Mn as a global resource. However, the “LiMeO ₂ type” active material containing Mn as Me, when the molar ratio Mn / Mn in Me exceeds 0.5, the structural change occurs to the spinel type when charged, Since the crystal structure cannot be maintained, the charge / discharge cycle performance is remarkably inferior.

Accordingly, various “LiMeO ₂ type” active materials having a Mn molar ratio Mn / Me in Me of 0.5 or less and excellent in charge / discharge cycle performance have been proposed and partially put into practical use. For example, a positive electrode active material containing LiNi _1/2 Mn _1/2 O ₂ or LiNi _1/3 Co _1/3 Mn _1/3 O ₂ which is a lithium transition metal composite oxide has a discharge capacity of 150 to 180 mAh / g. Have

On the other hand, for the so-called “LiMeO ₂ type” active material as described above, the composition ratio Li / Me of lithium (Li) with respect to the ratio of transition metal (Me) is larger than 1, for example, Li / Me is 1.2 to 1 A so-called “lithium-excess type” active material is also known, which includes a lithium transition metal composite oxide having a composition formula of Li _{1 + α} Me _1-α O ₂ (α> 0). It is also known to produce the above lithium transition metal composite oxide from a hydroxide precursor (see, for example, Patent Documents 1 to 4).

Patent Document 1 discloses lithium having an α-NaFeO ₂ type crystal structure and represented by a composition formula Li _{1 + α} Me _1-α O ₂ (Me is a transition metal containing Co, Ni, and Mn, α> 0). A positive electrode active material for a lithium secondary battery containing a transition metal composite oxide, wherein the positive electrode active material for a lithium secondary battery is (1), ((1 + α)). The positive electrode active material for a lithium secondary battery according to claim 1, wherein the molar ratio Li / Me of Li to Me represented by / (1-α) is 1.25 to 1.5. (Claim 2), "The method for producing a positive electrode active material for a lithium secondary battery according to claim 1 or 2, wherein precursors for the synthesis of the lithium transition metal composite oxide are Co, Ni and Mn Lithium secondary, characterized by being a transition metal hydroxide containing The manufacturing method of the positive electrode active material for batteries "(Claim 3) is described.
Further, “the pH in the step of producing a precursor by coprecipitation of a compound containing Co, Ni and Mn in a solution is not limited, but the coprecipitation precursor is used as a coprecipitation hydroxide precursor. In the case of production, it can be set to 10.5 to 14. In order to increase the tap density, it is preferable to control the pH, and by setting the pH to 11.5 or less, the tap density can be reduced. 1.00 g / cm ³ or more can improve the high rate discharge performance, and further, by adjusting the pH to 11.0 or less, the particle growth rate can be accelerated, so It is possible to shorten the stirring time of “(paragraph [0032])”.

Patent Document 2 discloses that “a method for producing an active material for a lithium secondary battery according to claim 1 or 2, wherein a compound of a transition metal element Me containing Co, Ni, and Mn is coprecipitated in a solution. A step of obtaining a coprecipitation precursor of a transition metal hydroxide, a step of drying the coprecipitation precursor, and the coprecipitation precursor and a lithium compound with respect to the transition metal element Me of the lithium transition metal composite oxide An active material for a lithium secondary battery comprising a step of mixing so that a molar ratio of Li is 1 <(1 + α) / (1-α) ≦ 1.5 and firing at 700 to 800 ° C. Manufacturing method "(Claim 3) is described.
Further, “the pH in the step of producing a precursor by coprecipitation of a compound containing Co, Ni and Mn in a solution is not limited, but the coprecipitation precursor is used as a coprecipitation hydroxide precursor. If it is to be produced, it can be 10-14, and if it is intended to produce the coprecipitated precursor as a coprecipitated carbonate precursor, it can be 7.5-11. In order to increase the density, it is preferable to control the pH, and for the coprecipitated carbonate precursor, the tap density can be increased to 1.25 g / cc or higher by setting the pH to 9.4 or lower. The high-rate discharge performance can be improved "(paragraph [0035]).

Patent Document 3 discloses that “Li _x Ni _a Co _b Mn _c M _d O _y (where x is 1.1 to 1.7, a is 0.15 to 0.5, and b is 0 to 0.33, c is 0.33 to 0.85, M is a metal element other than Li, Ni, Co, and Mn, and d is 0 to 0.05 , A + b + c + d = 1, and y is the number of moles of oxygen (O) required to satisfy the valences of Li, Ni, Co, Mn, and M.)
In the X-ray diffraction pattern, the peak of the (020) plane attributed to the crystal structure of the space group C2 / m with respect to the integrated intensity (I ₀₀₃ ) of the peak of the (003) plane attributed to the crystal structure of the space group R-3m A lithium-containing composite oxide having an integral intensity (I ₀₂₀ ) ratio (I ₀₂₀ / I ₀₀₃ ) of 0.02 to 0.3 and a tap density of 1.8 to 2.5 g / cm ³ is produced. When
A hydroxide containing Ni and Mn as essential components, Co and M optionally including a specific surface area of 20 to 50 m ² / g, and a lithium compound were mixed, and the resulting mixture was fired. A method for producing a lithium-containing composite oxide, wherein the fired product is crushed. (Claim 1).

Patent Document 3 discloses that “(Example 1)... As a complexing agent, ammonium sulfate was dissolved in distilled water so as to have a concentration of 1.5 mol / kg” to obtain an aqueous ammonium sulfate solution (paragraph). [0088]), “Distilled water was put into a 2 L baffled glass reaction vessel and heated with a mantle heater to 50 ° C. While stirring the solution in the reaction vessel with a paddle type stirring blade, Hydroxides containing Ni and Mn by adding 0.0 g / min, ammonium sulfate aqueous solution at a rate of 0.5 g / min for 28 hours, and adding a pH adjusting solution so as to keep the pH of the mixed solution at 10.5 Nitrogen gas was allowed to flow into the reaction vessel at a flow rate of 1.0 L / min while the raw material solution was added, and the amount of liquid in the reaction vessel was not allowed to exceed 2 L. Use a non-woven cloth to continuously remove hydroxide. In order to remove impurity ions from the obtained hydroxide, washing was repeated by repeated pressure filtration and dispersion in distilled water, when the electrical conductivity of the filtrate reached 20 mS / m. The hydroxide was dried at 120 ° C. for 15 hours. ”(Paragraph [0089]),“ (Example 3)... Example 1 except that an aqueous ammonia solution was used instead of the aqueous ammonium sulfate solution. In the same manner, a hydroxide was obtained ”(paragraph [0093]).
In Table 2, as Example 3, Ni: 30.0 mol%, Mn: 70.0 mol%, complexing agent: ammonia, D ₅₀ : 6.7 μm, tap density: 1.41 g / cm ³ , specific surface area : 18.0 m ² / g hydroxide is shown (see paragraph [0103]), “Example 3 is a lithium with a high tap density without crushing by increasing the tap density of the hydroxide. However, since the specific surface area of the lithium-containing composite oxide is small, the discharge capacity of the lithium secondary battery per unit mass of the positive electrode active material is low, and as a result, the positive electrode active material The discharge capacity of the lithium secondary battery per unit volume is also low ”(paragraph [0106]).

Further, a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide that defines the half-value width of diffraction peaks on the (003) plane and the (104) plane by X-ray diffraction measurement is known (for example, And Patent Documents 4 to 6).

Patent Document 4 discloses that “a current collector and an active material layer including active material particles held by the current collector are provided, and the active material particles are a collection of a plurality of primary particles of a lithium transition metal oxide. The secondary particle has a hollow structure having a hollow part formed inside the secondary particle and a shell part surrounding the hollow part, and the secondary particle includes the hollow part from the outside. In the powder X-ray diffraction pattern of the active material particles, the half-value width A of the diffraction peak obtained by the (003) plane and the diffraction peak obtained by the (104) plane (A / B) satisfying the following formula: (A / B) ≦ 0.7 ”(Claim 1),“ The lithium transition metal oxide is: General formula of:
Li _{1 + x} Ni _y Co _z Mn _(1-yz) W _α M _β O ₂
(X, y, z, α and β in the formula (1) are 0 ≦ x ≦ 0.2, 0.1 <y <0.9, 0.1 <z <0.4, 0.0005 ≦ It is a real number that satisfies all α ≦ 0.01 and 0 ≦ β ≦ 0.01, and M is absent or Zr, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, Al, B and One or more elements selected from the group consisting of F.)
The lithium secondary battery according to claim 1, which is a compound having a layered crystal structure represented by: (Claim 6).
In paragraphs [0073] to [0082], the W addition amount is 0.5 mol% with respect to 100 mol% of the raw material having a Ni: Co: Mn molar ratio of 0.33: 0.33: 0.33. The composite hydroxide particles obtained by adjusting so as to become lithium carbonate and lithium carbonate are mixed and fired so that Li / Me is about 1.15, thereby comprising a lithium transition metal composite oxide. It describes that an active material particle having a hollow structure or a solid structure was produced.

In Patent Document 5, “Having a layered structure and having a composition represented by the following formula (1), the half-value width FWHM ₀₀₃ of the (003) plane and the half-value width of the (104) plane in the powder X-ray diffraction diagram. An active material characterized in that the ratio to FWHM ₁₀₄ is represented by the following formula (2), and the average primary particle diameter is 0.2 μm to 0.5 μm.
_{_{_{_{Li y Ni a Co b Mn c}}}} M d O x ··· (1)
[In the above formula (1), the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba and V, and 1.9 ≦ (a + b + c + d + y) ≦ 2.1, 1.0 <y ≦ 1.3, 0 <a ≦ 0.3, 0 <b ≦ 0.25, 0.3 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.1, 9 ≦ x ≦ 2.1. ]
FWHM ₀₀₃ / FWHM ₁₀₄ ≦ 0.57 (2) ”(Claim 1).
In the examples, citric acid was added to an aqueous solution of a raw material mixture such as lithium acetate dihydrate, cobalt acetate tetrahydrate, manganese acetate tetrahydrate, nickel acetate tetrahydrate, etc., and reacted. After obtaining the precursor, it is shown that this precursor is fired to obtain a lithium compound (active material) such as Li _1.2 Ni _0.17 Co _0.07 Mn _0.56 O ₂ ( Paragraphs [0050], [0051], [0062]).

Patent Document 6 discloses an active material for a lithium secondary battery including a solid solution of a sodium-containing lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, wherein the chemical composition formula of the solid solution is Li _{1 + x− y} Na _y Co _a Ni _b Mn _c O _{2 + d} (0 <y ≦ 0.1, 0.4 ≦ c ≦ 0.7, x + a + b + c = 1, 0.1 ≦ x ≦ 0.25, −0.2 ≦ d ≦ 0.2) and an X-ray diffraction pattern that can be assigned to a hexagonal crystal (space group P3 ₁ 12), and the half width of the diffraction peak on the (003) plane at the Miller index hkl is 0.30 °. The active material for a lithium secondary battery is characterized in that the half-width of the diffraction peak of the (114) plane is 0.50 ° or less ”(Claim 1).
In addition, paragraph [0052] has “half-value width of the X-ray diffraction peak described above as indicating the degree of crystallization. In the present invention, in order to improve the low temperature characteristics, the space group P3 ₁ 12 In the X-ray diffraction pattern attributed to (3), it is necessary that the half width of the (003) plane diffraction peak is 0.30 ° or less and the half width of the (114) plane diffraction peak is 0.50 ° or less. The half-value width of the (003) plane diffraction peak is preferably 0.17 ° to 0.30 °, and the half-value width of the (114) plane diffraction peak is preferably 0.35 ° to 0.50 °. It is described.
In Examples 1 to 31, an active material obtained by mixing a coprecipitated hydroxide precursor of a transition metal, lithium hydroxide monohydrate, and sodium carbonate so as to have various compositions and firing at 1000 ° C. As a result of the crystal structure analysis, the half-value width of the (003) plane diffraction peak was “0.19 to 0.21 °” and the half-value width of the (114) plane diffraction peak was “0.39 to 0.41”. (See paragraphs [0074] to [0078], [0102] Table 1).

Also, a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide having a defined pore volume is known (see, for example, Patent Documents 7 to 9).

Patent Document 7 states that “porous particles made of a lithium composite oxide mainly composed of one or more elements selected from the group consisting of Co, Ni, and Mn and lithium, and having pores formed by mercury porosimetry. Non-aqueous system comprising particles having an average pore diameter in the range of 0.1 to 1 μm in distribution measurement and a total volume of pores having a diameter of 0.01 to 1 μm of 0.01 cm ³ / g or more The positive electrode active material for secondary batteries "(Claim 1) is described.

Patent Document 7 states that “[Example 1] obtained by mixing and pulverizing lithium hydroxide, nickel hydroxide, and cobalt hydroxide in a ball mill at a molar ratio of each metal of 105: 90: 10. The mixed powder was pressure-molded under a pressure of 1 ton / cm ² , and this molded body was used as a raw material for firing, which was fired (calcined) in an air stream at 770 ° C. for 10 hours. The granulated powder was fired at 800 ° C. for 2 hours in an oxygen stream (main firing), pulverized with a mortar-type pulverizer, and then sized with a screen classifier. The product was porous spherical secondary particles having a pore average diameter of 0.363 μm and a total volume of pores having a diameter of 0.01 to 1 μm and a total volume of 8.4 × 10 ⁻² cm ³ / g ”(paragraph [0026]. ] ”,“ The calcination temperature was changed to 650 ° C. with respect to Example 1. Compared to Example 1, the calcination temperature was lowered to lower the crystallinity of the primary particles. Sintering between primary particles was promoted and the pore volume was controlled.The lithium composite oxide thus obtained had a pore average diameter of 0.137 μm and a total volume of pores having a diameter of 0.01 to 1 μm. Was a porous spherical secondary particle having a density of 1.8 × 10 ⁻² cm ³ / g ”.

Patent Document 8 states that “(Example 1)... Nickel sulfate aqueous solution, cobalt sulfate aqueous solution and manganese sulfate aqueous solution has an atomic ratio of nickel atom, cobalt atom and manganese atom of 0.33: 0.33: The mixed raw material solution was adjusted by mixing to 0.33 .... Next, the mixed raw material solution and the aqueous ammonium sulfate solution were continuously added as a complexing agent to the reaction vessel with stirring. A sodium hydroxide aqueous solution was added dropwise as needed so that the pH of the solution in the reaction vessel was 11.7 to obtain nickel cobalt manganese composite hydroxide particles, which were filtered, washed with water, and dried at 100 ° C. In this way, a dry powder of nickel cobalt manganese composite hydroxide was obtained .... The dry powder of nickel cobalt manganese composite hydroxide obtained as described above and lithium carbonate powder were mixed with Li. It was weighed and mixed so that (Ni + Co + Mn) = 1.07, and then fired at 950 ° C. for 10 hours in an air atmosphere to obtain the target positive electrode active material 1, that is, lithium-nickel cobalt manganese composite oxide. (Paragraphs [0141] to [0144]). Further, “A composition analysis of the obtained positive electrode active material 1 was performed, and the molar ratio of Li: Ni: Co: Mn was 1.02: 0.34: 0.33: 0.33.” (Paragraph [0145]), “From the pore distribution measurement result of the positive electrode active material 1 (FIG. 2), the peak volume is 65 nm, and the pore volume in the range of 10 nm to 200 nm is 0.012 cm ³ / g. (Paragraph [0148]).

Furthermore, Patent Document 8 discloses that the positive electrode active material 2 has a Li: Ni: Co: Mn molar ratio of 1.10: 0.34: 0.33: 0.33 (paragraph [0151]). It was described that the pore volume was 0.030 cm ³ / g (paragraph [0154]), and the positive electrode active material 3 had a molar ratio of Li: Ni: Co: Mn of 1.05: 0.34: 0. 33: 0.33 (paragraph [0156]) and the pore volume was 0.034 cm ³ / g (paragraph [0159]), and the positive electrode active material 4 was Li: Ni: Co: The molar ratio of Mn was 1.08: 0.33: 0.33: 0.34 (paragraph [0163]), and the pore volume was 0.025 cm ³ / g (paragraph [0166]). The positive electrode active material 5 has a molar ratio of Li: Ni: Co: Mn of 1.09: 0.33: 0.3. : 0.33 (paragraph [0170]), it pore volume was 0.030 cm ³ / g (paragraph [0173]) have been described.

Patent Document 9 states that “as the positive electrode active material 1 and the positive electrode active material 2, lithium-containing transition metal oxides having the following chemical formulas were synthesized using a composite carbonate method. The starting materials include nickel, cobalt, and manganese. Using a sulfate, a 2 mol / L nickel sulfate aqueous solution, a cobalt sulfate aqueous solution and a manganese sulfate aqueous solution were prepared, a 2 mol / L sodium carbonate aqueous solution was used as a precipitating agent, and a pH adjusting agent was adjusted to a concentration of 0.8. A 2 mol / L aqueous ammonia solution was used "(paragraph [0231]). Further, “<Composition and physical properties of positive electrode active material 1> Chemical formula: Li _1.5 [Ni _0.2 Co _0.2 Mn _0.8 [Li] _0.3 ] O ₃ (a + b + c + d = 1.5, d = 0.3, a + b + c = 1.2) Pore volume: 0.008 cm ³ / g... (Paragraph [0234]), “<Composition and physical properties of positive electrode active material 2> Chemical formula: Li _1.5 [Ni _0.2 Co _0.2 Mn _0.8 [Li] _0.3 ] O ₃ (a + b + c + d = 1.5, d = 0.3, a + b + c = 1.2) Pore volume: 0.024 cm ³ / g ” (Paragraph [0235]).

Further, Patent Document 9 states that “the positive electrode active material 3 is composed of lithium carbonate, nickel sulfate aqueous solution, cobalt sulfate aqueous solution, and manganese sulfate so that lithium, nickel, cobalt, and manganese have the following chemical formula ratios. It was prepared in the same manner as the positive electrode active material 1 except that the aqueous solution was mixed. "(Paragraph [0248]),"<Composition and physical properties of the positive electrode active material 3> Chemical formula: Li _1.5 [Ni _0.25 Co _{0. 25} Mn _0.73 [Li] _0.27 ] O ₃ (a + b + c + d = 1.5, d = 0.27, a + b + c = 1.23) Pore volume: 0.007 cm ³ / g ”(paragraph [0249]) “The positive electrode active material 4 is also mixed with lithium carbonate, nickel sulfate aqueous solution, and manganese sulfate aqueous solution so that lithium, nickel, and manganese have the following chemical formula ratios. Except for the above, it was prepared in the same manner as the positive electrode active material 1 ”(paragraph [0250]),“ <Composition and physical properties of the positive electrode active material 4> Chemical formula: Li _1.5 [Ni _0.46 Mn _0.86 [ Li] _0.18 ] O ₃ (a + b + c + d = 1.5, d = 0.18, a + b + c = 1.32) pore volume: 0.015 cm ³ / g ”(paragraph [0251]).

JP 2014-29828 A JP 2014-63707 A Japanese Unexamined Patent Publication No. 2016-17017 JP 2013-51172 A JP 2013-206552 A WO2012 / 039413 JP 2000-323142 A JP2015-118945A JP 2013-179044 A

The discharge capacity of the so-called “lithium-rich” active material is generally larger than that of the so-called “LiMeO ₂ type” active material, as described in Patent Documents 1-9.
Further, as described above, hydroxide precursors and carbonate precursors are known as precursors of “lithium-rich” positive electrode active materials.
By using a carbonate precursor and firing at a specific transition metal composition, a specific Li / Me ratio and a specific firing temperature, the primary particles of the active material become finer, and a positive electrode active material having a high discharge capacity per mass is obtained. Obtainable. However, since there are many pores in the secondary particles, there is a problem that the discharge capacity per volume is small.
Therefore, the present invention seeks to solve the above problems by using a hydroxide precursor as a precursor of a “lithium-rich” positive electrode active material.
However, it is very difficult to increase the density of the hydroxide precursor due to the high Mn / Me ratio. This is related to the feature that the primary particles of Ni (OH) ₂ and Co (OH) ₂ are granular, whereas the primary particles of Mn (OH) ₂ are flaky.

As described in Patent Documents 1 to 3, the hydroxide precursor has been usually produced by a method of adjusting the pH to 10 to 14 when coprecipitating from an aqueous solution of a transition metal compound.
As described in Patent Document 2, with respect to the carbonate precursor, the tap density is 1.25 g / cm ³ or more by a method in which the pH when coprecipitating from the aqueous solution of the transition metal compound is 9.4 or less. As for the hydroxide precursor, if the synthesis pH is lowered, the high rate discharge performance of the positive electrode active material tends to be lowered. It was not done to increase the density. Therefore, it is difficult to increase the discharge capacity per volume of the positive electrode active material.

Patent Documents 4 to 6 describe a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide that defines a half-value width of diffraction peaks on the (003) plane and the (104) plane. However, it has not been shown to increase the discharge capacity per volume of the positive electrode active material.
Patent Documents 7 to 9 describe a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide having a defined pore volume. The discharge capacity per volume of the positive electrode active material is described as follows. It is not shown to be high.

The present invention relates to a positive electrode active material having a large discharge capacity per volume, a high-density hydroxide precursor for producing the positive electrode active material, a nonaqueous electrolyte secondary battery electrode using the positive electrode active material, and It is an object to provide a non-aqueous electrolyte secondary battery.

In order to solve the above problems, one aspect of the present invention is “a positive electrode active material for a non-aqueous electrolyte battery including a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide is α-NaFeO ₂ type. The molar ratio (Li / Me) of Li and transition metal (Me) constituting the lithium transition metal composite oxide having a crystal structure is greater than 1, and the transition metal (Me) is Mn and Ni, or Mn, X-rays using CuKα rays, which contain Ni and Co, have a Mn molar ratio Mn / Me in the transition metal (Me) greater than 0.5, have an X-ray diffraction pattern that can be assigned to R3-m The ratio (FWHM (003) / FWHM (104)) of the half value width of the diffraction peak of the (003) plane to the half width of the diffraction peak of the (104) plane (FWHM (104)) at the Miller index hkl by diffraction measurement is 0. 6 Is lower, the lithium transition metal composite oxide pore volume determined by the BJH method from an adsorption isotherm using a nitrogen gas adsorption method of the particles is less than 0.05 cm 3 / ^g, a non-aqueous electrolyte secondary battery The positive electrode active material is used.

Another aspect of the present invention is “a transition metal hydroxide precursor used for producing a lithium transition metal composite oxide contained in the positive electrode active material for a nonaqueous electrolyte secondary battery, wherein the transition metal (Me ) Contains Mn and Ni, or Mn, Ni and Co, the molar ratio of Mn in the transition metal (Me) is Mn / Me larger than 0.5, and the tap density is 1.3 g / cm ³ or more. Transition metal hydroxide precursor. "

Another aspect of the present invention is “a method for producing the transition metal hydroxide precursor, wherein a reaction vessel contains a transition metal (Me) -containing solution, an alkali metal hydroxide, a complexing agent, And a method for producing a transition metal hydroxide precursor, wherein an alkaline solution containing a reducing agent is added to adjust the pH of the solution in the reaction vessel to less than 9 to 9.8 to coprecipitate the transition metal hydroxide. It is.

Another aspect of the present invention is “having an α-NaFeO ₂ type crystal structure in which the transition metal hydroxide precursor and a lithium compound are mixed and fired at 750 to 900 ° C. The manufacturing method of the positive electrode active material for nonaqueous electrolyte batteries containing the lithium transition metal complex oxide whose metal (Me) molar ratio (Li / Me) is larger than 1. "

Another aspect of the present invention is a nonaqueous electrolyte secondary battery electrode containing the positive electrode active material, and is a nonaqueous electrolyte secondary battery including the electrode.

According to the present invention, a positive electrode active material having a large discharge capacity (energy density) per volume, a high-density hydroxide precursor for producing the positive electrode active material, and a nonaqueous electrolyte containing the positive electrode active material. A secondary battery electrode and a non-aqueous electrolyte secondary battery including the electrode can be provided.

The figure which shows the total pore volume of the positive electrode active material of an Example and a comparative example Figure showing the relationship between the total pore volume of the positive electrode active material and the discharge capacity per volume 1 is an external perspective view showing a nonaqueous electrolyte secondary battery according to one embodiment of the present invention. Schematic showing a power storage device in which a plurality of nonaqueous electrolyte secondary batteries according to one embodiment of the present invention are assembled.

[Positive electrode active material and lithium transition metal composite oxide]
The positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention (hereinafter referred to as “this embodiment”) is a positive electrode active material containing a lithium transition metal composite oxide.
The composition of the lithium transition metal composite oxide contains Mn and Ni, or a transition metal element Me containing Mn, Ni and Co, and Li, and Li _{1 + α} Me _1-α from the viewpoint of obtaining a high discharge capacity. This is a so-called “lithium-excess type” which can be expressed as O ₂ (α> 0).

In this embodiment, in the lithium transition metal composite oxide represented by the composition formula Li _{1 + α} Me _1-α O ₂ (α> 0), the transition metal element Me represented by (1 + α) / (1-α) The molar ratio Li / Me to Li is preferably 1.1 or more and less than 1.4, more preferably 1.1 or more and 1.3 or less, and 1.1 or more and 1.2 or less. Is particularly preferred. Within this range, the discharge capacity per volume of the positive electrode active material is improved.
The molar ratio Mn / Me of the transition metal element Me is greater than 0.5. It is preferably 0.51 or more and less than 0.7, and more preferably 0.51 to 0.60. Within this range, the tap density of the hydroxide precursor can be improved and the discharge capacity per volume is improved.
Co contained in the lithium transition metal composite oxide has an effect of improving the initial efficiency. However, when there is too much Co, the tap density of the precursor is lowered and the peak differential pore volume is increased. Moreover, since it is a scarce resource, it is expensive. Therefore, the molar ratio Co / Me of Co to the transition metal element Me is preferably 0.20 or less, and may be 0.
The molar ratio Ni / Me of Ni to the transition metal element Me is preferably 0.2 to 0.5, more preferably 0.25 to 0.4. Within this range, the tap density of the hydroxide precursor can be improved and the discharge capacity per volume is improved.
By using the lithium transition metal composite oxide having the above composition, a nonaqueous electrolyte secondary battery having a large discharge capacity per volume can be obtained.

The lithium transition metal composite oxide according to this embodiment has an α-NaFeO ₂ structure. The lithium transition metal composite oxide after synthesis (before charge and discharge) is attributed to the space group P3 ₁ 12 or R3-m. Among these, those belonging to the space group P3 ₁ 12 are superlattice peaks (Li [Li _1/3 Mn _2/3 ] O ₂ near 2θ = 21 ° on the X-ray diffraction diagram using the CuKα tube. The peak observed in the monoclinic type) is confirmed. However, once the charge is performed and Li in the crystal is desorbed, the symmetry of the crystal changes, whereby the superlattice peak disappears and the lithium transition metal composite oxide belongs to the space group R3-m. Will come to be. Here, P3 ₁ 12 is a crystal structure model in which the atomic positions of the 3a, 3b, and 6c sites in R3-m are subdivided, and when ordering is recognized in the atomic arrangement in R3-m, the P3 ₁ 12 model Is adopted. Note that “R3-m” is originally represented by adding a bar “-” on “3” of “R3m”.

When the space group R3-m is used as a crystal structure model based on the X-ray diffraction pattern, the lithium transition metal composite oxide according to the present embodiment is (003) relative to the half-value width of the diffraction peak attributed to the (104) plane. ) The ratio of the half width of the diffraction peak attributed to the plane, that is, the value of FWHM (003) / FWHM (104) is 0.6 or less. Such a crystal structure makes it possible to increase the discharge capacity per volume.
The diffraction peak at 2θ = 18.6 ° ± 1 ° is indexed to the (003) plane at the Miller index hkl in the space groups P3 ₁ 12 and R3-m, and the diffraction at 2θ = 44.1 ° ± 1 °. peaks, the space group _P3 1 12 (114) plane, is indexed to the space group R3-m (104) plane. Therefore, for the part belonging to the space group P3 ₁ 12, the part described as (104) in this specification is read as (114).

The FWHM (104) is an index of crystallinity from all directions. If it is too small, crystallization proceeds too much, the crystallite becomes large, and Li ions are not sufficiently diffused. If it is too large, the crystallinity is low, and the transport efficiency of Li ions is reduced. Therefore, the FWHM (104) is preferably in the range of 0.21 ° to 0.55 °.

The FWMH ratio is an index of crystallinity along the c-axis direction with respect to crystallinity from all directions in the crystal structure. If FWHM (003) / FWHM (104) is too large, the degree of crystal growth in the c-axis direction will be small, and Li ions will not be smoothly inserted and removed from the interlayer. Therefore, FWHM (003) / FWHM (104) is set to 0.6 or less. In addition, when FWHM (003) / FWHM (104) is not too small, elution of Mn due to an increase in the contact area between the crystal grain boundary and the electrolytic solution can be suppressed. Therefore, FWHM (003) / FWHM (104) is preferably set to 0.4 or more.

(Measurement of half width)
The half width of the lithium transition metal composite oxide is measured using an X-ray diffractometer (manufactured by Rigaku, model name: MiniFlex II). Specifically, it is performed according to the following conditions and procedures.
The radiation source is CuKα, and the acceleration voltage and current are 30 kV and 15 mA, respectively. The sampling width is 0.01 deg, the scanning time is 14 minutes (scanning speed is 5.0), the divergence slit width is 0.625 deg, the light receiving slit width is open, and the scattering slit is 8.0 mm. The obtained X-ray diffraction data is indexed to the (003) plane in the space group R3-m using “PDXL” which is the software attached to the X-ray diffractometer without removing the peak derived from K _α2. The half-value width FWHM (003) for the diffraction peak existing at 2θ = 18.6 ± 1 ° on the X-ray diffractogram, and indexed to the (104) plane, 2θ = 44 ± 1 ° on the X-ray diffractogram The half-width FWHM (104) for the existing diffraction peak is determined.

In the lithium transition metal composite oxide particles according to the present embodiment, the total pore volume determined by the BJH method from the adsorption isotherm using the nitrogen gas adsorption method is 0.05 cm ³ / g or less. The total pore volume is preferably 0.04 cm ³ / g or less. The peak differential pore volume is preferably 0.2mm ³ / (g · nm) or less, more preferably 0.18mm ³ / (g · nm) or ^{less, 0.12mm 3 / (g · nm} ) or less is particularly preferable. Such a high-density active material can be obtained by firing a high-density transition metal hydroxide precursor and a lithium compound.
In FIG. 1, the total pore volume of the lithium transition metal complex oxide particle of an Example and a comparative example is shown. Specifically, based on the measurement results of the pore distribution for lithium transition metal composite oxide particles according to Example 1, Comparative Example 1, and Comparative Example 3 described later, the horizontal axis represents the pore diameter, and the vertical axis represents the fine particle. It is the figure which plotted the total pore volume corresponding to the pore below a pore diameter. The lithium transition metal composite oxide particles of Example 1 obtained from the high density hydroxide precursor were the same as the lithium transition metal composite oxide particles of Comparative Example 1 obtained from the low density hydroxide precursor, carbonic acid. Compared with the lithium transition metal composite oxide particles of Comparative Example 3 obtained from the salt precursor, the total pore volume is remarkably reduced.
FIG. 2 shows the relationship between the total pore volume [cm ³ / g] and the 0.1 C discharge capacity [mAh / cm ³ ] of the lithium transition metal composite oxide particles according to the examples and comparative examples shown in Table 1. Is plotted. By setting the total pore volume of the lithium transition metal composite oxide particles to 0.05 cm ³ / g or less, the discharge capacity per volume can be increased. In addition, when the total pore volume is very small, the discharge capacity per volume is low because the FWHM (003) / FWHM (104) is too large.

(Measurement of total pore volume and peak differential pore volume)
In the present specification, the total pore volume and the peak differential pore volume of the lithium transition metal composite oxide particles are measured by the following method. By putting 1.00 g of the powder of the sample to be measured into a sample tube for measurement and vacuum drying at 120 ° C. for 12 hours, moisture in the measurement sample is sufficiently removed. Next, isotherms on the adsorption side and desorption side are measured within a range of relative pressure P / P0 (P0 = about 770 mmHg) from 0 to 1 by a nitrogen gas adsorption method using liquid nitrogen. Then, the pore distribution is evaluated by calculating by the BJH method using the desorption side isotherm, and the peak differential pore volume and the total pore volume are obtained.

The lithium transition metal composite oxide particles according to this embodiment preferably have a tap density of 1.6 g / cm ³ or more, and more preferably 1.7 g / cm ³ or more. By increasing the tap density of the lithium transition metal composite oxide particles, a nonaqueous electrolyte secondary battery having a large discharge capacity per volume can be obtained.

(Measurement of tap density of lithium transition metal composite oxide)
In this specification, the tap density of the lithium transition metal composite oxide is measured by the following method. ² g ± 0.2 g of the powder of the sample to be measured is put into a 10 ⁻² dm ³ graduated cylinder, and REI ELECTRIC CO. LTD. A value obtained by dividing the volume of the sample to be measured after counting 300 times by the input mass using a tapping device manufactured by the company is adopted.

If the sample used for the above various measurements is an active material powder before electrode preparation, it is used for measurement as it is. When a sample is collected from an electrode taken out by disassembling the battery, the battery is put into a discharged state by the following procedure before disassembling the battery. First, constant current charging is performed up to a battery voltage at which the positive electrode potential becomes 4.3 V (vs. Li ^/ Li ⁺ ) with a current of 0.1 C, and the current value decreases to 0.01 C at the same battery voltage. Charge the battery at a constant voltage until the end of charge. After a 30-minute pause, constant current discharge is performed at a current of 0.1 C until the battery voltage reaches a positive electrode potential of 2.0 V (vs. Li ^/ Li ⁺ ), and a discharge end state is obtained. If the battery uses a metal lithium electrode as the negative electrode, the battery may be disassembled after the battery is brought into the end-of-discharge state or the end-of-charge state, and the electrode may be taken out. In order to accurately control the positive electrode potential, after disassembling the battery and taking out the electrode, after assembling the battery using the metal lithium electrode as a counter electrode, the battery is adjusted to the end of discharge state according to the above procedure.

The work from disassembly of the battery to measurement is performed in an argon atmosphere with a dew point of -60 ° C or lower. The taken-out positive electrode plate uses dimethyl carbonate to sufficiently wash the electrolytic solution adhering to the electrode, and after drying at room temperature for a whole day and night, the mixture on the aluminum foil current collector is collected. This mixture is fired at 600 ° C. for 4 hours using a small electric furnace to remove the carbon as the conductive agent and the PVdF binder as the binder, and take out the lithium transition metal composite oxide particles.

[Hydroxide precursor and production method thereof]
The transition metal hydroxide precursor used for producing the lithium transition metal composite oxide includes a transition metal (Me) containing Mn and Ni, or Mn, Ni and Co, and a mole of Mn in the transition metal (Me). The ratio Mn / Me is larger than 0.5, the crystal form is a high-density granule, and the tap density is 1.3 g / cm ³ or more. The tap density is preferably 1.4 g / cm ³ or more. Although there is no particular upper limit, a hydroxide precursor having a tap density of up to 1.7 g / cm ³ can be obtained.
In this specification, the tap density of the hydroxide precursor and the carbonate precursor is measured by the same method as the tap density of the lithium transition metal composite oxide.

Since the lithium transition metal composite oxide produced using the transition metal hydroxide precursor according to this embodiment is a “lithium-excess” active material, Mn of the transition metal element Me in the hydroxide precursor The molar ratio Mn / Me is greater than 0.5. Within this range, it is possible to improve the tap density of the hydroxide precursor.
Further, the molar ratio Co / Me of Co to the transition metal element Me in the hydroxide precursor is preferably 0.2 or less, may be 0, but is preferably 0.1 or more. The molar ratio Ni / Me is preferably 0.2 to 0.5. Within this range, it is possible to improve the tap density of the hydroxide precursor.

When producing the transition metal hydroxide precursor, alkali metal hydroxide (sodium hydroxide, lithium hydroxide, etc.), complexation, together with a solution containing transition metal (Me), in a reaction tank that maintains alkalinity It is preferable to coprecipitate the transition metal hydroxide by adding an alkali solution containing an agent and a reducing agent.
As the complexing agent, ammonia, ammonium sulfate, ammonium nitrate or the like can be used, and ammonia is preferable. A precursor having a higher tap density can be produced by a crystallization reaction using a complexing agent. It is preferable to use a reducing agent together with the complexing agent. As the reducing agent, hydrazine, sodium borohydride and the like can be used, and hydrazine is preferable. Here, sodium hydroxide or lithium hydroxide can be used for the alkali metal hydroxide (neutralizing agent).

In producing a hydroxide precursor, Mn is easily oxidized among Ni, Co, and Mn, and Ni, Mn, or a coprecipitation precursor in which Ni, Co, and Mn are uniformly distributed in a divalent state is produced. Therefore, uniform mixing at the atomic level of Ni, Mn, or Ni, Co, and Mn tends to be insufficient. In particular, in the composition range of the present embodiment, since the Mn ratio is higher than the Ni and Co ratios, it is particularly important to remove dissolved oxygen in the aqueous solution. Examples of the method for removing dissolved oxygen include a method of bubbling a gas not containing oxygen. The gas not containing oxygen is not limited, but nitrogen gas, argon gas, carbon dioxide (CO ₂ ), or the like can be used.

In order to increase the tap density, the pH in the step of producing a hydroxide precursor by coprecipitation of a compound containing Ni, Mn or Ni, Co, Mn in the solution is 8 Is preferably less than 9.8, and more preferably less than 9-9.8 (9.7 or less). By co-precipitation at a low pH, the tap density can be 1.3 g / cm ³ or more. Moreover, since the particle growth rate can be accelerated, the stirring continuation time after the raw material aqueous solution dropping is completed can be shortened.

The raw material of the hydroxide precursor is manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese acetate, etc. as the Mn compound, and nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, acetic acid as the Ni compound. Examples of the Co compound such as nickel and the like include cobalt sulfate, cobalt nitrate, and cobalt acetate.

While the raw material aqueous solution of the hydroxide precursor (aqueous solution containing a transition metal) is supplied dropwise, an alkali metal hydroxide such as sodium hydroxide (neutralizing agent), a complexing agent such as ammonia, hydrazine, etc. A method in which a mixed alkaline solution containing the reducing agent is appropriately dropped is preferable. The concentration of the alkali metal hydroxide to be dropped is preferably 1.0 to 8.0M. The concentration of the complexing agent is preferably 0.4M or more, and more preferably 0.6M or more. Moreover, it is preferable that it is 2.0M or less, It is more preferable that it is 1.6M or less, It is further more preferable to set it as 1.5M or less. The concentration of the reducing agent is preferably 0.05 to 1.0M, and more preferably 0.1 to 0.5M. The tap density of the hydroxide precursor can be increased by lowering the pH of the reaction vessel and setting the concentration of ammonia (complexing agent) to 0.6 M or more.
The manufacturing method or the manufacturing conditions described characteristically above may be combined with a configuration in which the precursor Co / Me is 0, but by combining with a configuration in which Co / Me is 0.02 or more, high density The effect | action which a hydroxide precursor is obtained can be exhibited more effectively. The Co / Me ratio is more preferably 0.05 or more, and further preferably 0.1 or more.

The dropping speed of the raw material aqueous solution greatly affects the uniformity of element distribution within one particle of the hydroxide precursor to be produced. In particular, Mn is difficult to form a uniform element distribution with Ni or Co, so care must be taken. The preferred dropping rate is influenced by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but is preferably 30 mL / min or less. In order to improve the discharge capacity, the dropping rate is more preferably 10 mL / min or less, and most preferably 5 mL / min or less.

Further, when a complexing agent such as ammonia is present in the reaction tank and a certain convection condition is applied, the particles are rotated and revolved in the stirring tank by continuing the stirring after the dropwise addition of the raw material aqueous solution. In this process, particles collide with each other, and the particles grow concentrically in stages. That is, the hydroxide precursor undergoes two stages of reaction: a metal complex formation reaction when the raw material aqueous solution is dropped into the reaction tank, and a precipitation formation reaction that occurs while the metal complex is retained in the reaction tank. Formed through. Therefore, a hydroxide precursor having a target particle diameter can be obtained by appropriately selecting a time for continuing stirring after the dropping of the raw material aqueous solution.

The preferable stirring duration after completion of dropping of the raw material aqueous solution is influenced by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but 0.5 h or more is required to grow the particles as uniform spherical particles. Preferably, 1 h or more is more preferable. Further, in order to reduce the possibility that the output performance in the low SOC region of the battery is not sufficient due to the particle size becoming too large, it is preferably 15 h or less, more preferably 10 h or less, and most preferably 5 h or less.

In addition, the preferable stirring duration time for controlling D50, which is a particle diameter at which the cumulative volume in the particle size distribution of the secondary particles of the hydroxide precursor and the lithium transition metal composite oxide is 50%, to 13 μm or less is the pH to be controlled. It depends on. For example, when the pH is controlled to 8 to 9.7, the stirring duration is preferably 0.5 to 3 h, and when the pH is controlled to 9 to 9.7, the stirring duration is 1 to 5 h. preferable.

When the hydroxide precursor particles are prepared using a sodium compound such as sodium hydroxide as a neutralizing agent, sodium ions adhering to the particles are removed by washing in the subsequent washing step. For example, when the produced hydroxide precursor is removed by suction filtration, a condition that the number of washings with 100 mL of ion-exchanged water is 5 times or more can be employed.

[Method for producing positive electrode active material (lithium transition metal composite oxide)]
The lithium transition metal composite oxide of the present embodiment can be suitably produced by a method of firing after mixing the hydroxide precursor and a lithium compound (Li compound).
The lithium transition metal composite oxide produced by this method has an α-NaFeO ₂ type crystal structure, and the molar ratio of Li to transition metal (Me) constituting the lithium transition metal composite oxide (Li / Me) Is greater than 1, the transition metal (Me) contains Mn and Ni, or Mn, Ni and Co, and the molar ratio of Mn in the transition metal (Me) Mn / Me is greater than 0.5.
As the Li compound, lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, or the like can be used. However, regarding the amount of the Li compound, it is preferable to add an excess of about 1 to 5% in view of the disappearance of a part of the Li compound during firing.

The firing temperature affects the reversible capacity of the active material.
When the firing temperature is too high, the obtained active material collapses with an oxygen releasing reaction, and in addition to the hexagonal crystal of the main phase, the monoclinic Li [Li _1/3 Mn _2/3 ] O ₂ type is obtained. The defined phase tends to be observed as a phase separation rather than as a solid solution phase. If too many such phase separations are contained, it is not preferable because it leads to a reduction in the reversible capacity of the active material. In such materials, impurity peaks are observed around 35 ° and 45 ° on the X-ray diffraction pattern. Therefore, the firing temperature is preferably less than the temperature at which the oxygen release reaction of the active material affects. The oxygen release temperature of the active material is approximately 1000 ° C. or higher in the composition range according to the present embodiment, but there is a slight difference in the oxygen release temperature depending on the composition of the active material. It is preferable to confirm. In particular, it is confirmed that the oxygen release temperature of the hydroxide precursor shifts to a lower temperature side as the amount of Co contained in the sample increases. As a method for confirming the oxygen release temperature of the active material, a mixture of a hydroxide precursor and a lithium compound may be subjected to thermogravimetric analysis (DTA-TG measurement) in order to simulate the firing reaction process. However, in this method, the platinum used in the sample chamber of the measuring instrument may be corroded by the Li component volatilized, and the instrument may be damaged, so a crystallization temperature is advanced to some extent by adopting a firing temperature of about 500 ° C. in advance. The composition may be subjected to thermogravimetric analysis.

On the other hand, if the firing temperature is too low, crystallization does not proceed sufficiently and the electrode characteristics tend to deteriorate. In the present embodiment, the firing temperature is preferably higher than 700 ° C. By sufficiently crystallizing, the resistance of the crystal grain boundary can be reduced and smooth lithium ion transport can be promoted.
In addition, as a result of detailed analysis of the half-value width of the diffraction peak of the active material according to the present embodiment, the inventors have found that strain remains in the lattice in the sample synthesized at a temperature lower than 750 ° C. It was found that almost all strains can be removed by synthesis at the above temperature. It was also found that the crystallite size increased in proportion to the increase in the synthesis temperature. Therefore, it was found that in the composition of the active material according to the present embodiment, particles having almost no lattice distortion in the system and having a sufficiently grown crystallite size can be obtained, and a favorable discharge capacity can be obtained. Specifically, it is preferable to employ a synthesis temperature (firing temperature) and a Li / Me ratio composition in which the amount of strain affecting the lattice constant is 2% or less and the crystallite size grows to 50 nm or more. When charging / discharging the electrode using this active material, it was found that the crystallite size was maintained at 30 nm or more in the charging / discharging process, although it changed due to expansion / contraction. That is, an active material having a remarkably large reversible capacity can be obtained only by selecting the firing temperature as close as possible to the oxygen release temperature of the active material.

As described above, since the preferable firing temperature varies depending on the oxygen release temperature of the active material, it is generally difficult to set a preferable range of the firing temperature, but the molar ratio Li / Me is 1.1 to 1.3. In this case, the firing temperature is preferably 750 to 940 ° C., more preferably 750 to 900 ° C., in order to ensure a sufficient discharge capacity per volume.
As described above, the lithium transition metal composite oxide used as the positive electrode active material of the present embodiment is manufactured.

[Negative electrode active material]
The negative electrode active material is not limited. Any form that can deposit or occlude lithium ions may be selected. For example, titanium-based materials such as lithium titanate having a spinel crystal structure represented by Li [Li _1/3 Ti _5/3 ] O ₄ , alloy-based materials such as Si, Sb, and Sn-based lithium metal, lithium alloys (Lithium metal-containing alloys such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys), lithium composite oxide (lithium-titanium), silicon oxide In addition, an alloy capable of inserting and extracting lithium, a carbon material (for example, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.) can be used.

The positive electrode active material powder and the negative electrode active material powder preferably have an average particle size of 100 μm or less. In particular, the positive electrode active material powder is preferably 15 μm or less for the purpose of improving the high output characteristics of the nonaqueous electrolyte battery. In order to obtain the powder in a predetermined shape, there are a method for producing a precursor having a predetermined size, a method using a pulverizer, a classifier, and the like. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, or the like is used. At the time of pulverization, wet pulverization in the presence of water or an organic solvent such as hexane may be used. There is no particular limitation on the classification method, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

[Other electrode components]
As described above, the positive electrode active material and the negative electrode active material which are main components of the positive electrode and the negative electrode have been described in detail. In addition to the main component, the positive electrode and the negative electrode include a conductive agent, a binder, a thickener, A filler etc. may be contained as another structural component.

The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect the battery performance. Usually, natural graphite (such as scaly graphite, scaly graphite, earthy graphite), artificial graphite, carbon black, acetylene black, Conductive materials such as ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, and conductive ceramic material can be included as one kind or a mixture thereof. .

Among these, as the conductive agent, acetylene black is preferable from the viewpoints of electronic conductivity and coatability. The addition amount of the conductive agent is preferably 0.1% by weight to 50% by weight, and particularly preferably 0.5% by weight to 30% by weight with respect to the total weight of the positive electrode or the negative electrode. In particular, acetylene black is preferably used after being pulverized into ultrafine particles of 0.1 to 0.5 μm because the necessary carbon amount can be reduced. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, it is possible to mix by a dry type or a wet type using a powder mixer such as a V-type mixer, an S-type mixer, a grinding machine, a ball mill, or a planetary ball mill.

The binder is usually a thermoplastic resin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene. Polymers having rubber elasticity such as rubber (SBR) and fluororubber can be used as one kind or a mixture of two or more kinds. The amount of the binder added is preferably 1 to 50% by weight, particularly 2 to 30% by weight, based on the total weight of the positive electrode or the negative electrode.

As the filler, any material that does not adversely affect battery performance may be used. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The addition amount of the filler is preferably 30% by weight or less with respect to the total weight of the positive electrode or the negative electrode.

[Production of positive electrode and negative electrode]
For the positive electrode and the negative electrode, the main components (positive electrode active material for the positive electrode, negative electrode material for the negative electrode) and other materials are kneaded and mixed into an organic solvent such as N-methylpyrrolidone or toluene or water. After that, the obtained liquid mixture is applied on a current collector described in detail below, or is pressed and heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. . About the application method, for example, it is preferable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. It is not limited.

As the current collector, a current collector foil such as an Al foil or a Cu foil can be used. The positive electrode current collector foil is preferably an Al foil, and the negative electrode current collector foil is preferably a Cu foil. The thickness of the current collector foil is preferably 10 to 30 μm. The thickness of the mixture layer is preferably 40 to 150 μm (excluding the thickness of the current collector foil) after pressing.

[Nonaqueous electrolyte]
The nonaqueous electrolyte used for the nonaqueous electrolyte secondary battery according to the present embodiment is not limited, and those generally proposed for use in lithium batteries and the like can be used. Nonaqueous solvents used for the nonaqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or derivatives thereof Examples thereof include a conductor alone or a mixture of two or more thereof, but are not limited thereto.

Examples of the electrolyte salt used for the non-aqueous electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, and NaBr. , KClO ₄ , KSCN, and other inorganic ion salts containing one of lithium (Li), sodium (Na), or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ (SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , ( CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (nC ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthalate, Examples thereof include organic ionic salts such as lithium stearyl sulfonate, lithium octyl sulfonate, and lithium dodecylbenzene sulfonate. These ionic compounds can be used alone or in admixture of two or more.

Further, by using a mixture of LiPF ₆ or LiBF ₄ and a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ , the viscosity of the electrolyte can be further reduced, Low temperature characteristics can be further improved, and self-discharge can be suppressed, which is more preferable.
Moreover, you may use normal temperature molten salt and an ionic liquid as a nonaqueous electrolyte.

The concentration of the electrolyte salt in the nonaqueous electrolyte is preferably from 0.1 mol / L to 5 mol / L, more preferably from 0.5 mol / L to 2 in order to reliably obtain a nonaqueous electrolyte battery having high battery characteristics. 0.5 mol / L.

[Separator]
As the separator, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the material constituting the separator for a nonaqueous electrolyte battery include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, fluorine Vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride - tetrafluoroethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.

The separator may be a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride, and an electrolyte. Use of the non-aqueous electrolyte in the gel state as described above is preferable in that it has an effect of preventing leakage.

Furthermore, it is preferable that the separator is used in combination with the above-described porous film, nonwoven fabric, or the like and a polymer gel because the liquid retention of the electrolyte is improved. That is, by forming a film in which the surface of the polyethylene microporous membrane and the microporous wall are coated with a solvophilic polymer having a thickness of several μm or less, and holding the electrolyte in the micropores of the film, Gels.

Examples of the solvophilic polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a polymer having a monomer having an isocyanate group, and the like crosslinked. The monomer can be subjected to a crosslinking reaction by irradiation with an electron beam (EB) or heating or ultraviolet (UV) irradiation with a radical initiator added.

[Configuration of non-aqueous electrolyte secondary battery]
The configuration of the nonaqueous electrolyte secondary battery according to the present embodiment is not particularly limited, and a cylindrical battery, a square battery (rectangular battery), and a flat battery having a positive electrode, a negative electrode, and a roll separator. Etc. are mentioned as an example.
FIG. 3 is an external perspective view of a rectangular lithium secondary battery 1 which is a nonaqueous electrolyte secondary battery according to one embodiment of the present invention. In the figure, the inside of the container is seen through. In the nonaqueous electrolyte secondary battery 1 shown in FIG. 3, an electrode group 2 is housed in a battery container 3. The electrode group 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material via a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4 ′, and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5 ′.

[Configuration of power storage device]
This embodiment can also be realized as a power storage device in which a plurality of the nonaqueous electrolyte secondary batteries are assembled. A power storage device according to one embodiment of the present invention is illustrated in FIG. In FIG. 4, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of nonaqueous electrolyte secondary batteries 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV).

Example 1
<Production process of hydroxide precursor>
Example In preparing an active material, a hydroxide precursor was prepared using a reaction crystallization method. First, 315.4 g of nickel sulfate hexahydrate, 168.6 g of cobalt sulfate heptahydrate, and 530.4 g of manganese sulfate pentahydrate were weighed, and all of these were dissolved in 4 L of ion-exchanged water, and Ni: Co A 1.0 M aqueous sulfate solution having a molar ratio of: Mn of 30:15:55 was prepared. Next, ₂ L of ion exchange water was poured into a 5 L reaction tank, and N ₂ gas was bubbled for 30 minutes to remove oxygen contained in the ion exchange water. The temperature of the reaction vessel is set to 50 ° C. (± 2 ° C.) and the reaction vessel is stirred at a rotational speed of 1500 rpm using a paddle blade equipped with a stirring motor, so that sufficient convection occurs in the reaction vessel. did. The sulfate aqueous solution was dropped into the reaction vessel at a rate of 1.3 mL / min for 50 hr. Here, the pH of the aqueous solution in the reaction vessel was appropriately dropped by adding a mixed alkaline solution consisting of 4.0 M sodium hydroxide, 1.25 M ammonia, and 0.1 M hydrazine from the start to the end of the dropping. Was controlled to always maintain 9.5 (± 0.1), and a part of the reaction solution was discharged by overflow, so that the total amount of the reaction solution was always controlled not to exceed 2 L. After completion of the dropwise addition, stirring in the reaction vessel was continued for 1 hour. After stopping stirring, the mixture was allowed to stand at room temperature for 12 hours or longer.
Next, using a suction filtration device, the hydroxide precursor particles generated in the reaction tank are separated, and further, sodium ions adhering to the particles are washed and removed using ion exchange water, and an electric furnace is used. Then, it was dried in an air atmosphere at 80 ° C. under normal pressure for 20 hours. Then, in order to arrange | equalize a particle size, it grind | pulverized for several minutes with the smoked automatic mortar. In this way, a hydroxide precursor was produced.

<Baking process>
1.294 g of lithium hydroxide monohydrate is added to 2.262 g of the hydroxide precursor and mixed well using a smoked automatic mortar. The molar ratio of Li: (Ni, Co, Mn) is 120: A mixed powder of 100 was prepared. Using a pellet molding machine, molding was performed at a pressure of 6 MPa to obtain pellets having a diameter of 25 mm. The amount of the mixed powder subjected to pellet molding was determined by conversion so that the mass of the assumed final product was 2.5 g. One pellet was placed on an alumina boat having a total length of about 100 mm, placed in a box-type electric furnace (model number: AMF20), heated in air atmosphere at normal pressure from room temperature to 800 ° C. over 10 hours, Baked at 800 ° C. for 4 h. The box-type electric furnace has internal dimensions of 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was turned off and allowed to cool naturally with the alumina boat placed in the furnace. As a result, the temperature of the furnace decreases to about 200 ° C. after 5 hours, but the subsequent temperature decrease rate is somewhat moderate. After the passage of day and night, it was confirmed that the furnace temperature was 100 ° C. or lower, and then the pellets were taken out and pulverized for several minutes in a smoked automatic mortar in order to make the particle diameter uniform. In this way, lithium transition metal composite oxide Li _1.09 Ni _0.27 Co _0.14 Mn _0.50 O _{2 according} to Example 1 was produced.

(Example 2)
In the firing step, 1.214 g of lithium hydroxide monohydrate is added to 2.315 g of the hydroxide precursor, and a mixed powder having a molar ratio of Li: (Ni, Co, Mn) of 110: 100 is obtained. A lithium transition metal composite oxide according to Example 2 was produced in the same manner as Example 1 except that it was prepared.

(Examples 3 and 4)
Lithium transition metal composite oxides according to Examples 3 and 4 were produced in the same manner as in Example 1, except that in the firing step, the firing temperature was changed from 800 ° C. to 750 ° C. and 900 ° C., respectively.

(Example 5)
In the step of preparing the hydroxide precursor, 315.4 g of nickel sulfate hexahydrate, 112.4 g of cobalt sulfate heptahydrate, and 578.6 g of manganese sulfate pentahydrate were weighed, and all of these were ion-exchanged water. A 1.0M sulfate aqueous solution having a Ni: Co: Mn molar ratio of 30:10:60 was prepared by dissolving in 4 L, and 4.0 M In the firing step, the pH of the aqueous solution in the reaction vessel was controlled to be constantly maintained at 9.3 by appropriately dropping a mixed alkaline solution composed of sodium hydroxide, 0.6M ammonia, and 0.3M hydrazine. And 1.373 g of lithium hydroxide monohydrate were added to 2.211 g of the hydroxide precursor to prepare a mixed powder having a molar ratio of Li: (Ni, Co, Mn) of 130: 100 Outside, in the same manner as in Example 1 to prepare a lithium transition metal composite oxide according to Example 5.

(Example 6)
In the step of preparing the hydroxide precursor, 262.8 g of nickel sulfate hexahydrate, 224.8 g of cobalt sulfate heptahydrate, and 530.4 g of manganese sulfate pentahydrate were weighed, and all of these were ion-exchanged water. A 1.0M sulfate aqueous solution having a Ni: Co: Mn molar ratio of 25:20:55 is prepared by dissolving in 4 L, and 4.0 M By appropriately dropping a mixed alkaline solution consisting of sodium hydroxide, 1.5M ammonia, and 0.2M hydrazine, the pH of the aqueous solution in the reaction vessel is always controlled to be 9.5 (± 0.1). A lithium transition metal composite oxide according to Example 6 was produced in the same manner as Example 1 except for the above.

(Example 7)
In the step of preparing the hydroxide precursor, a mixed alkaline solution composed of 4.0 M sodium hydroxide, 0.8 M ammonia, and 0.3 M hydrazine is added from the start to the end of the dropwise addition of the sulfate aqueous solution. The lithium transition metal composite according to Example 7 was the same as Example 1 except that the pH of the aqueous solution in the reaction vessel was controlled to be always kept at 9.5 (± 0.1) by dropping appropriately. An oxide was produced.

(Example 8)
In the step of preparing the hydroxide precursor, a mixed alkaline solution composed of 4.0 M sodium hydroxide, 2 M ammonia, and 0.3 M hydrazine is appropriately dropped from the start to the end of the dropping of the sulfate aqueous solution. Thus, the pH of the aqueous solution in the reaction vessel was controlled so as to always maintain 9.5 (± 0.1). In the firing step, 2.212 g of the hydroxide precursor was added to lithium hydroxide monohydrate. Lithium transition according to Example 8 in the same manner as in Example 1 except that 1.371 g of the product was added and a mixed powder having a molar ratio of Li: (Ni, Co, Mn) of 130: 100 was prepared. A metal composite oxide was produced.

(Comparative Example 1)
In the step of preparing the hydroxide precursor, a mixed alkaline solution composed of 4.0 M sodium hydroxide, 0.5 M ammonia, and 0.3 M hydrazine was added from the start to the end of the dropwise addition of the sulfate aqueous solution. The lithium transition metal composite according to Comparative Example 1 was used in the same manner as in Example 1 except that the pH of the aqueous solution in the reaction vessel was controlled so as to always maintain 10.55 (± 0.1) by dropping appropriately. An oxide was produced.

(Comparative Example 2)
In the step of preparing the hydroxide precursor, a mixed alkaline solution composed of 4.0 M sodium hydroxide, 0.5 M ammonia, and 0.3 M hydrazine was added from the start to the end of the dropwise addition of the sulfate aqueous solution. The lithium transition metal composite according to Comparative Example 2 was prepared in the same manner as in Example 1 except that the pH of the aqueous solution in the reaction vessel was controlled so as to always maintain 9.8 (± 0.1) by dropping appropriately. An oxide was produced.

(Comparative Example 3)
210.3 g of nickel sulfate hexahydrate, 140.6 g of cobalt sulfate heptahydrate, and 651.2 g of manganese sulfate pentahydrate were weighed, and all of these were dissolved in 4 L of ion-exchanged water, and Ni: Co: A 1M aqueous sulfate solution with a Mn molar ratio of 20: 12.5: 67.5 was prepared. Next, ₂ L of ion exchange water was poured into a 5 L reaction vessel, and CO ₂ gas was bubbled for 30 minutes to dissolve CO _{2 in the} ion exchange water. The temperature of the reaction vessel was set to 50 ° C. (± 2 ° C.), and the aqueous sulfate solution was adjusted to 1.3 mL / min while stirring the reaction vessel at a rotational speed of 1500 rpm using a paddle blade equipped with a stirring motor. It was dripped at a speed. Here, from the start to the end of the dropping, an aqueous solution containing 1 M sodium carbonate and 0.5 M ammonia is appropriately dropped, so that the pH of the aqueous solution in the reaction tank is always 7.9 (± 0.1 ) Was controlled. After completion of the dropping, stirring in the reaction vessel was continued for 3 hours. After stopping the stirring, the mixture was allowed to stand for 12 hours or more.
Next, using a suction filtration device, the coprecipitated carbonate particles produced in the reaction vessel are separated, and sodium ions adhering to the particles are washed away using ion-exchanged water, and an electric furnace is used. Then, it was dried in an air atmosphere at 80 ° C. under normal pressure for 20 hours. Then, in order to arrange | equalize a particle size, it grind | pulverized for several minutes with the smoked automatic mortar. In this way, a carbonate precursor was produced.

Instead of the hydroxide precursor prepared in Example 1, the carbonate precursor prepared as described above was used, and in the firing step, 1.047 g of lithium carbonate was added to 2.204 g of the carbonate precursor. , Li: (Ni, Co, Mn) The lithium transition metal composite oxide according to Comparative Example 3 was the same as Example 1 except that a mixed powder having a molar ratio of 145: 100 was prepared and fired. Was made.

(Comparative Example 4)
A lithium transition metal composite oxide according to Comparative Example 4 was produced in the same manner as in Example 2 except that the firing temperature was 1000 ° C.

(Examples 9 to 15)
In the step of preparing the hydroxide precursor, the concentration of ammonia in the mixed alkali solution added from the start to the end of the dropwise addition of the sulfate aqueous solution is changed from 1.25 M to 0.4 M and 0.6 M, respectively. , 0.8M, 1M, 1.4M, 1.6M, and 2M, hydroxide precursors according to Examples 9 to 15 were produced in the same manner as in Example 1.

(Example 16)
In the step of preparing the hydroxide precursor, 473.4 g of nickel sulfate hexahydrate and 530.6 g of manganese sulfate pentahydrate were weighed, and all of these were dissolved in 4 L of ion-exchanged water, and Ni: Co: Mn A hydroxide precursor according to Example 16 was produced in the same manner as in Example 1 except that a 1.0 M sulfate aqueous solution having a molar ratio of 45: 0: 55 was produced.

(Measurement of tap density of precursor and lithium transition metal composite oxide)
Tap densities of hydroxide precursors according to Examples 1 to 16 and Comparative Examples 1, 2, and 4, Tap densities of carbonate precursors according to Comparative Example 3, Examples 1 to 8 and Comparative Examples 1 to 4 The tap density of the lithium transition metal composite oxide is determined by REI ELECTRIC CO. LTD. Using a tapping device (manufactured in 1968) manufactured by the company, the measurement was performed according to the conditions and procedures described above.

(Confirmation of α-NaFeO type ₂ crystal structure)
It was confirmed that the lithium transition metal composite oxides according to Examples 1 to 8 and Comparative Examples 1 to 4 had an α-NaFeO ₂ type crystal structure because the structural model and the diffraction pattern in the X-ray diffraction measurement coincided with each other. .

(Measurement of half width)
The full width at half maximum of the lithium transition metal composite oxide according to Examples 1 to 8 and Comparative Examples 1 to 4 was measured using an X-ray diffractometer (manufactured by Rigaku, model name: MiniFlex II) according to the conditions and procedures described above. Went. A diffraction peak existing at 2θ = 18.6 ° ± 1 ° on the X-ray diffractogram, indexed to the (003) plane in the space group R3-m, using “PDXL” which is software attached to the X-ray diffractometer. FWHM (003) and FWHM (104) for the diffraction peak at 2θ = 44 ± 1 ° on the X-ray diffractogram indexed to the (104) plane. From the measurement result, FWHM (003) / FWHM (104) was obtained.

[Preparation of electrode for non-aqueous electrolyte secondary battery]
Using the lithium transition metal composite oxides according to Examples 1 to 8 and Comparative Examples 1 to 4 as positive electrode active materials, respectively, the non-aqueous electrolyte secondary according to Examples 1 to 8 and Comparative Examples 1 to 4 were performed in the following procedure. A battery electrode was prepared.

Using N-methylpyrrolidone as a dispersion medium, a coating paste in which the active material, acetylene black (AB) and polyvinylidene fluoride (PVdF) were kneaded and dispersed at a mass ratio of 90: 5: 5 was prepared. The coating paste was applied to one side of an aluminum foil current collector having a thickness of 20 μm to produce a positive electrode plate. In addition, the application thickness of the active material applied per fixed area was unified so that the test conditions for obtaining the discharge capacity per volume between the lithium secondary batteries according to all Examples and Comparative Examples were the same. The nonaqueous electrolyte secondary battery electrode thus produced was partially cut out, a test battery that was a nonaqueous electrolyte secondary battery (lithium secondary battery) was produced by the following procedure, and the battery characteristics were evaluated. .

[Production and evaluation of nonaqueous electrolyte secondary battery]
For the purpose of accurately observing the single behavior of the positive electrode, metallic lithium was used in close contact with the nickel foil current collector for the counter electrode, that is, the negative electrode. Here, a sufficient amount of metallic lithium was disposed on the negative electrode so that the capacity of the lithium secondary battery was not limited by the negative electrode.

As an electrolytic solution, LiPF ₆ was dissolved in a mixed solvent in which ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) had a volume ratio of 6: 7: 7 so that the concentration would be 1 mol / L. The solution was used. As the separator, a polypropylene microporous film whose surface was modified with polyacrylate was used. A metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) was used for the outer package. The electrode is housed so that the open ends of the positive electrode terminal and the negative electrode terminal are exposed to the outside, and the fusion margin where the inner surfaces of the metal resin composite film face each other is hermetically sealed except for the portion serving as a liquid injection hole, After injecting the electrolytic solution, the injection hole was sealed.

The lithium secondary battery produced by the above procedure was subjected to an initial charge / discharge process at 25 ° C. Charging was performed at a constant current and a constant voltage with a current of 0.1 C and a voltage of 4.6 V, and the charge termination condition was when the current value was attenuated to 1/6. The discharge was a constant current discharge with a current of 0.1 C and a final voltage of 2.0 V. This charge / discharge was performed for two cycles. Here, a pause process of 30 minutes was provided after charging and after discharging, respectively.

Next, a one-cycle charge / discharge test was performed. Charging was performed at a constant current and a constant voltage with a current of 0.1 C and a voltage of 4.45 V, and the charge termination condition was when the current value was attenuated to 1/6. The discharge was a constant current discharge with a current of 0.1 C and a final voltage of 2.0 V. Here, a pause process of 10 minutes was provided after charging and discharging, respectively. The discharge capacity (mAh / g) of the positive electrode active material in this cycle was recorded.

(Measurement of limit mixture density)
A plurality of non-aqueous electrolyte secondary battery electrodes according to Examples 1 to 8 and Comparative Examples 1 to 4 prepared above were cut into a size of 2 cm × 2 cm, respectively, and a flat plate press (manufactured by RIKEN SEIKI Co. LTD. CDM-20M TYPE P-1B), various post-pressing electrodes having different electrode plate thicknesses were produced by applying various pressing pressures from 1 MPa to 15 MPa. The mixture density (g / cm ³ ) was calculated from the thickness and weight of each post-press electrode.
Each pressed electrode was dried under reduced pressure for 12 h under a temperature environment of 120 ° C., and after sufficiently removing the contained water, a line connecting each midpoint of two opposing sides of a 2 cm × 2 cm square was folded. As described above, nothing was sandwiched between the valleys, and it was folded by hand to make the other two opposite sides coincide. Furthermore, the crest portion of the fold that was curved and formed into a U-shape was pressed to bring the surfaces of the electrodes into contact with each other over the entire surface. Next, the sheet is spread again to the original flat shape, the electrode is directed toward the visible light source, the bent portion is visually observed, and the portion of the mixture layer is determined depending on whether visible light is observed through the bent portion. The presence or absence of damage was confirmed. And the electrode which has the smallest thickness among the electrodes by which damage was not recognized was determined, and the said mixture density (g / cm < ³ >) which concerns on the said electrode is the nonaqueous electrolyte secondary which concerns on the said Example or a comparative example It was defined as “limit mixture density (g / cm ³ )” of the battery electrode.

For each of the examples and comparative examples, the discharge capacity per unit volume “0.1 C” is obtained by multiplying the value of the discharge capacity (mAh / g) by the value of the limit mixture density (g / cm ³ ). The capacity (mAh / cm ³ ) ”was calculated.

(Measurement of total pore volume and peak differential pore volume)
For the measurement of the total pore volume and the peak differential pore volume of the lithium transition metal composite oxide particles according to Examples 1 to 8 and Comparative Examples 1 to 4, the above test batteries in a discharged state were disassembled according to the procedure described above. Then, the positive electrode plate was taken out, and the particles of the lithium transition metal composite oxide, which is an active material in the collected positive electrode plate, were measured using “autosorb iQ” manufactured by Quantachrome and control / analysis software “ASiQwin”.

Li / Me ratio of lithium transition metal composite oxides according to Examples 1 to 8 and Comparative Examples 1 to 4, firing temperature, FWHM (003) / FWHM (104), total pore volume, peak differential pore volume, Table 1 shows the 0.1 C capacity of a lithium secondary battery using a lithium transition metal composite oxide as a positive electrode active material and the tap density of the lithium transition metal composite oxide (active material).
Ni / Me ratio, Co / Me ratio, Mn / Me ratio of precursors according to Examples 1 to 16 and Comparative Examples 1 to 4, types of precursors, pH of the reaction tank, alkaline solution dropped into the reaction tank Table 2 shows the concentrations of ammonia and hydrazine and the tap density of the precursor.

From Table 1, the lithium transition according to Examples 1 to 8 having a crystal structure in which FWHM (003) / FWHM (104)) is 0.6 or less and the total pore volume is 0.05 cm ³ / g or less. It can be seen that a lithium secondary battery using a metal composite oxide has a large 0.1 C capacity, which is a discharge capacity per volume. It can also be seen that the peak differential pore volume of the lithium transition metal composite oxide is preferably 0.2 mm ³ / (g · nm) or less.
From Table 1 and Table 2, such crystal structure and microstructure have a composition in which Li / Me is larger than 1 and Mn / Me is larger than 0.5, and the coprecipitation precursor is a hydroxide, It can be seen that the pH of the aqueous solution in the reaction vessel in the production process of the hydroxide precursor is less than 9.8, and the lithium transition metal composite oxide is obtained when calcined at a temperature of 750 to 900 ° C. When the pH of the aqueous solution in the reaction vessel is 9 to less than 9.8, the tap density of the hydroxide precursor is 1.3 g / cm ³ or more.
In view of Examples 1 and 9 to 15, in order to improve the tap density of the hydroxide precursor, the concentration of ammonia (complexing agent) to be dropped is preferably 0.6 M or more. The tap density of the hydroxide precursor can be 1.4 g / cm ³ or more at 0.6 to 1.6M. The concentration of hydrazine (reducing agent) is preferably 0.1M or higher.
When Examples 1 to 5 and 16 are compared, the tap density of the hydroxide precursor is higher when the Co / Me ratio is 0.10 or more than when the Co / Me ratio is 0. It can be seen that the 1C capacity is also higher.

As in Comparative Examples 1 and 2, when the pH of the aqueous solution in the reaction vessel in the hydroxide precursor preparation step is 9.8 or more, the tap density of the hydroxide precursor is 1.3 g / cm ³ or more. do not become. In addition, the lithium transition metal composite oxide obtained by firing these hydroxide precursors has a FWHM (003) / FWHM (104) of 0.6 or less, but the total pore volume is 0.05 cm ^3. / C and 0.1 C capacity per volume becomes small. Further, such a lithium transition metal composite oxide has a peak differential pore volume larger than 0.2 mm ³ / (g · nm).

As in Comparative Example 3, when carbonate is used as a coprecipitation precursor and the pH of the aqueous solution in the reaction vessel is lowered to about 8, the tap density of the carbonate precursor is 1.6 g / cm ³ or more. In the lithium transition metal composite oxide obtained by firing this carbonate precursor, FWHM (003) / FWHM (104) is larger than 0.6, and the 0.1 C capacity per volume is small.

Even when the tap density of the hydroxide precursor was 1.3 g / cm ³ or more as in Comparative Example 4, when this hydroxide precursor was baked at 1000 ° C., the obtained lithium transition metal composite oxidation As for a thing, FWHM (003) / FWHM (104) becomes larger than 0.6, and the 0.1C capacity per volume becomes small.

As described above, Li / Me is larger than 1, Mn / Me is larger than 0.5, FWHM (003) / FWHM (104)) is 0.6 or less, and the total pore volume is 0.00. It can be said that the discharge capacity per volume is increased by using a lithium transition metal composite oxide that satisfies the requirement of not more than 05 cm ³ / g as the positive electrode active material of the nonaqueous electrolyte secondary battery.
In such a lithium transition metal composite oxide, the pH of the aqueous solution in the reaction vessel in the hydroxide precursor preparation step is less than 9.8, and the lithium transition metal composite oxide is heated at a temperature of 750 to 900 ° C. Obtained when fired.

By using the positive electrode active material including the lithium transition metal composite oxide according to one aspect of the present invention, a nonaqueous electrolyte secondary battery having a large discharge capacity per volume can be provided. The battery is useful as a nonaqueous electrolyte secondary battery for hybrid vehicles and electric vehicles.

1 Nonaqueous electrolyte secondary battery (lithium secondary battery)
2 Electrode group 3 Battery container 4 Positive electrode terminal 4 ′ Positive electrode lead 5 Negative electrode terminal 5 ′ Negative electrode lead 20 Power storage unit 30 Power storage device

Claims

A positive electrode active material for a non-aqueous electrolyte battery comprising a lithium transition metal composite oxide,
The lithium transition metal composite oxide has an α-NaFeO 2 type crystal structure,
The molar ratio (Li / Me) of Li and transition metal (Me) constituting the lithium transition metal composite oxide is greater than 1,
The transition metal (Me) contains Mn and Ni, or Mn, Ni and Co, and the molar ratio Mn / Me of Mn in the transition metal (Me) is greater than 0.5,
(003) plane with half-width (FWHM (104)) of diffraction peak of (104) plane at Miller index hkl by X-ray diffraction measurement using CuKα ray having an X-ray diffraction pattern that can be assigned to R3-m The half-width ratio (FWHM (003) / FWHM (104)) of the diffraction peak of B is the BJH method from the adsorption isotherm using the nitrogen gas adsorption method of the lithium transition metal composite oxide particles. The positive electrode active material for nonaqueous electrolyte secondary batteries whose total pore volume calculated | required by 0.05 is 0.05 cm < 3 > / g or less.
The peak differential pore volume determined by the BJH method from the adsorption isotherm using the nitrogen gas adsorption method of the particles of the lithium transition metal composite oxide is 0.2 mm 3 / (g · nm) or less. The positive electrode active material for nonaqueous electrolyte secondary batteries as described.
The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the molar ratio Li / Me is 1.1 or more and 1.3 or less.
4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein a molar ratio Co / Me of Co in the transition metal (Me) is 0.2 or less.
The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein a molar ratio Co / Me of Co in the transition metal (Me) is 0.1 or more.
A transition metal hydroxide precursor used for producing a lithium transition metal composite oxide contained in the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the transition metal (Me ) Contains Mn and Ni, or Mn, Ni and Co, the molar ratio of Mn in the transition metal (Me) is Mn / Me larger than 0.5, and the tap density is 1.3 g / cm 3 or more. Transition metal hydroxide precursor.
The transition metal hydroxide precursor according to claim 5, wherein a molar ratio Co / Me of Co in the transition metal (Me) is 0.2 or less.
The transition metal hydroxide precursor according to claim 6 or 7, wherein a molar ratio Co / Me of Co in the transition metal (Me) is 0.1 or more.
A method for producing a transition metal hydroxide precursor according to any one of claims 6 to 8, wherein the reaction tank contains a solution containing a transition metal (Me), an alkali metal hydroxide, a complexing agent, And a method for producing a transition metal hydroxide precursor, wherein an alkaline solution containing a reducing agent is added to adjust the pH of the solution in the reaction vessel to less than 9 to 9.8 to coprecipitate the transition metal hydroxide.
The method for producing a transition metal hydroxide precursor according to claim 9, wherein the concentration of the complexing agent is 0.6M or more.
The method for producing a transition metal hydroxide precursor according to claim 9 or 10, wherein the concentration of the reducing agent is 0.05 M or more.
A transition metal hydroxide precursor according to any one of claims 6 to 8 and a lithium compound are mixed and baked at 750 to 900 ° C, having an α-NaFeO 2 type crystal structure, transitioning with Li A method for producing a positive electrode active material for a nonaqueous electrolyte battery, comprising a lithium transition metal composite oxide having a metal (Me) molar ratio (Li / Me) of greater than 1.
An electrode for a nonaqueous electrolyte secondary battery containing the positive electrode active material according to any one of claims 1 to 5.
A nonaqueous electrolyte secondary battery comprising the electrode for a nonaqueous electrolyte secondary battery according to claim 13.
A power storage device in which a plurality of the nonaqueous electrolyte secondary batteries according to claim 14 are assembled.