JP4706991B2 - Method for manufacturing lithium secondary battery - Google Patents

Description

The present invention relates to a method for manufacturing a lithium secondary battery .

Conventionally, LiCoO ₂ is mainly used as a positive electrode active material in a lithium secondary battery. However, the lithium secondary battery using LiCoO ₂ as the positive electrode active material has a discharge capacity of only about 120 to 130 mAh / g, and the thermal stability in the battery in a charged state is also inferior.

Therefore, a material obtained by forming a solid solution of LiCoO ₂ with another compound is known as an active material for a lithium secondary battery. That is, as an active material for a lithium secondary battery, LiCoO ₂ , LiNiO ₂ and LiMnO ₂ are each a solid solution having an α-NaFeO ₂ type crystal structure shown on a ternary phase diagram in which three components are arranged. Co _1-2x Ni _x Mn _x ] O ₂ (0 <x ≦ 1/2) was published in 2001. A lithium secondary battery using LiNi _1/2 Mn _1/2 O ₂ or LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ as an example of the solid solution has a discharge capacity of 150 to 180 mAh / better than g and LiCoO _2, it is superior to LiCoO ₂ in terms of thermal stability in the battery in a charged state.

  However, an active material for a lithium secondary battery having a larger discharge capacity has been demanded.

Patent Documents 1 to 4 describe a compound obtained by adding Fe to Li [Li _1/3 Mn _2/3 ] O ₂ as an active material for a lithium secondary battery. Patent Documents 5 to 8 describe compounds obtained by adding Fe or Ni to Li [Li _1/3 Mn _2/3 ] O ₂ as an active material for a lithium secondary battery.

  However, the materials according to the inventions described in Patent Documents 1 to 8 are characterized in that inexpensive iron is used as a raw material. However, lithium secondary batteries using the materials are polarized in comparison with conventional positive electrode active materials. The discharge capacity was not excellent.

Patent Documents 9 and 10 describe a LiNiO ₂ —Li [Li _1/3 Mn _2/3 ] O ₂ -based solid solution as an active material for a lithium secondary battery.

However, the active materials for lithium secondary batteries described in Patent Documents 9 and 10 need to be synthesized in oxygen because the electronic state of Ni is Ni ³⁺ and are difficult to synthesize in air. There was a problem. As described above, an active material for a lithium secondary battery in which Ni is present in a Ni ²⁺ state is also desired from the viewpoint of industrial handling. In addition, with this material, only one electron reaction of Ni ³⁺ → Ni ⁴⁺ can be used, so that it is not expected to improve the discharge capacity of the lithium secondary battery.

Patent Documents 11-12 describe a LiNi _1/2 Mn _1/2 O ₂ —Li [Li _1/3 Mn _2/3 ] O ₂ -based solid solution as an active material for a lithium secondary battery.

However, the discharge capacity of the lithium secondary battery using the materials described in Patent Documents 11 and 12 is inferior to that of LiNi _1/2 Mn _1/2 O ₂ , rather than being improved. Met.

Patent Documents 13-14 describe a material in which Li [Li _1/3 Mn _2/3 ] O ₂ is present on the particle surface of LiMeO ₂ (Me: Co, Ni) as an active material for a lithium secondary battery. ing.

  However, none of the techniques described in Patent Documents 1 to 14 described above and the techniques described in Patent Documents 15 to 18 described below have led to an improvement in discharge capacity, which is an object of the present invention. .

In Patent Documents 15 and 16, “the ratio of Li [Ni _1/2 Mn _1/2 ] O ₂ having a layered structure in the present invention is (1-3x) (1-y),
The ratio of Li [Li _1/3 Mn _2/3 ] O ₂ is 3x (1-y),
The ratio of LiCoO ₂ is y
Layered lithium transition metal composite oxide,
[Li] ^(3a) [(Li _x Ni _{(1-3x) / 2} Mn _{(1 + x) / 2} ) _(1-y) Co _y ] ^(3b) O ₂ (II)
In the basic structure.
Here, (3a) and (3b) represent different metal sites in the layered R (-3) m structure, respectively. However, the important point of the present invention is that Li is added in excess of z mol with respect to the composition of the formula (II) and is dissolved.
[Li] ^(3a) [Li _{z / (2 + z)} {(Li _x Ni _{(1-3x) / 2} Mn _{(1 + x) / 2} ) _(1-y) Co _y } _{2 / (2 + z ^{)] (3b) O 2 ...}} (I)
(However, 0.01 ≦ x ≦ 0.15, 0 ≦ y ≦ 0.35, 0.02 (1-y) (1-3x) ≦ z ≦ 0.15 (1-y) (1-3x) (3a) and (3b) represent different metal sites in the layered R (-3) m structure.)
It is represented by. (Paragraphs 0018 to 0019) and the like, and a solid solution of three components of Li [Ni _1/2 Mn _1/2 ] O ₂ , Li [Li _1/3 Mn _2/3 ] O ₂ and LiCoO ₂ There is a description about the concept adopted as the basic structure. However, even with reference to the comparative example, the Li amount is only specifically described as an excess amount exceeding the amount naturally derived when such a solid solution is assumed, and the Li amount is intended. There is no description that the discharge capacity can be improved by making the ratio of the three components specific within a composition range that is not excessive.

Patent Document 17 describes in claim 1 that “Li [Ni _(xy) Li _{(1 / 3-2x / 3)} Mn _{(2-3-x / 3-y)} Co _2y ] O ₂ (0 < x ≦ 0.5, 0 ≦ y ≦ 1/6, x> y) ”.

Although the composition formula described in claim 1 of Patent Document 17 partially overlaps with the composition range characterized by the present invention as a general concept, Patent Document 17 describes Li [Ni _1/2 Mn _1/2 There is no description suggesting the technical idea of adopting a solid solution of three components of] O ₂ and Li [Li _1/3 Mn _2/3 ] O ₂ and LiCoO _{2. The} range indicated by the above composition formula is Li Except for the composition in the case of a solid solution of three components of [Ni _1/2 Mn _1/2 ] O ₂ , Li [Li _1/3 Mn _2/3 ] O ₂ and LiCoO ₂ , a wide range is included.

Claim 2 of Patent Document 18 states that “Li [Ni _(xy) Li _{(1 / 3-2x / 3)} Mn _{(2 / 3-x / 3-y)} Co _2y ] O ₂ (where x is 0). Greater than 0.5, y is 0 or more and 1/6 or less, and x> y.) ”.

Although the composition formula described in claim 2 of Patent Document 18 partially overlaps with the composition range characterized by the present invention as a superordinate concept, as an example, “composition formula Li [Ni _0.5 Mn _0.5 ] O” ₂ ”and“ compound represented by the composition formula Li [Ni _0.4 Mn _0.4 Co _0.2 ] O ₂ ”are only specifically described, and these are the composition ranges completely characterized by the present invention. It is something that deviates. Patent Document 18 discloses a technical idea that employs a solid solution of three components of Li [Ni _1/2 Mn _1/2 ] O ₂ , Li [Li _1/3 Mn _2/3 ] O ₂ and LiCoO _2. There is no description that suggests.

In Patent Document 19, a hydroxide of a transition metal (Co, Ni, Mn) is prepared by a coprecipitation method, and this is mixed with a lithium compound, and a Li [having an α-NaFeO ₂ type crystal structure through a firing step. A method of synthesizing Co _1-2x Ni _x Mn _x ] O ₂ is described.

JP 2002-068748 A JP 2002-121026 A Japanese Patent No. 03500424 Japanese Patent Laying-Open No. 2005-089279 JP 2006-036620 A JP 2003-048718 A JP 2006-036621 A Japanese Patent No. 0940788 JP 09-055211 A Japanese Patent No. 0359518 JP 2004-158443 A Japanese Patent No. 03946667 Japanese Patent Application Laid-Open No. 08-171935 Japanese Patent No. 03258841 JP 2006-253119 A JP 2007-220475 A JP 2004006267 A JP 2004-152753 A International Publication No. 02/086993 Pamphlet

Non-Patent Document 1, is described for the high Mn content of _{LiCoO 2 -LiNi 0.5 Mn 0.5 O 2} -Li 2 MnO 3 Preparation and electrochemical properties of the solid solutions, specifically, 0.36LiCoO ₂ - 0.2LiNi _1/2 Mn _1/2 O ₂ −0.44Li ₂ MnO ₃ , 0.27LiCoO ₂ −0.2LiNi _1/2 Mn _1/2 O ₂ −0.53Li ₂ MnO ₃ , 0.18LiCoO ₂ − _{0.2LiNi 1/2 Mn 1/2 O 2 -0.62Li 2} MnO 3, but _{0.09LiCoO 2 -0.2LiNi 1/2 Mn 1/2 O 2} -0.71Li 2 MnO 3 is shown When the Li content is as high as 1.4 to 1.5, the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of the diffraction peak of the (003) plane and the (104) plane by X-ray diffraction measurement is 1. About 4 (See FIG. 2), not a 1.56 or more, these solid solutions are clearly different from the active material of the present invention. As for the production method, it is only shown that each acetate salt is decomposed at 400 ° C. using a spray drying method and then fired at 750-950 ° C., and produced using a coprecipitation method. It is not shown to do. Furthermore, although it is shown that the discharge capacity is 200 mAh / g or more in the potential region of 3.0 to 4.6 V, it is not shown that the discharge capacity is increased in the potential region of 4.3 V or less.

Non-Patent Document 2 includes Li [Li _0.182 Ni _0.182 Co _0.091 Mn _0.545 ] O ₂ , that is, 0.545Li [Li _1/3 Mn _2/3 ] O ₂ −0.364 LiNi. For the layered material of _1/2 Mn _1/2 O ₂ -0.091 LiCoO ₂ , the discharge capacity is 200 mAh / g or more in the initial 4.6 to 2.0 V potential region, and 4.6 V to 2.0 V. After the cycle, it is shown that it is about 160 mAh / g in the potential region of 4.3V-2.0V, so this layered material does not have a large discharge capacity in the potential region of 4.3V or less. . In addition, the above layered material is prepared by preparing a slurry of each acetate salt, drying it at 120 ° C., and firing at 900 ° C., and not by using a coprecipitation method. In addition, the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of the diffraction peaks of the (003) plane and the (104) plane by X-ray diffraction measurement is about 1, and the active material of the present invention having 1.56 or more is It is clearly different.

Non-Patent Document 3 includes 0.7Li ₂ MnO ₃ .0.3LiMn _0.33 Ni _0.33 Co _0.33 O ₂ , 0.5Li ₂ MnO ₃ .0.5LiMn _{0. 33} Ni _0.33 Co _0.33 O ₂ is shown, and for the former, the discharge capacity is 261 mAh / g at 50 ° C. and 4.8 V charge, and 200 mAh / g at 50 ° C. and 4.6 V charge. Although shown, increasing the discharge capacity in a potential region of 4.3 V or less is not shown. The positive electrode active material is prepared by mixing co-precipitated hydroxides of Co, Ni, and Mn and LiOH and calcining at 300 or 500 ° C. and calcining at 800 or 1000 ° C. However, the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of the diffraction peaks of the (003) plane and the (104) plane by X-ray diffraction measurement is about 1, and the active material of the present invention having 1.56 or more is It is clearly different.

Non-Patent Document 4 describes Li [Li _1/5 Ni _1/10 Co _1/5 Mn _1/2 ] O ₂ , that is, 0.6Li [Li _1/3 Mn _2/3 ] O ₂ -0.2LiNi. _1/2 Mn _1/2 O ₂ is a solid solution having a layered crystal structure of -0.2LiCoO ₂ is shown, by X-ray diffraction measurement (003) plane and (104) intensity ratio of the diffraction peaks of surface _{I ( 003)} / I ₍₁₀₄₎ is about 1.4 (see FIG. 3) and not 1.56 or more, so this solid solution is clearly different from the active material of the present invention. Moreover, about the manufacturing method, only the sol-gel method using each acetate is shown, It does not show manufacturing using a coprecipitation method. Furthermore, the discharge capacity is shown to be 229 mAh / g at 4.5 V charge, but it is not shown to increase the discharge capacity in a potential region of 4.3 V or less.

Non-Patent Document 5 describes the activity of (1-2x) LiNi _1/2 Mn _1/2 O ₂ .xLi [Li _1/3 Mn _2/3 ] O ₂ .xLiCoO ₂ (0 ≦ x ≦ 0.5). 0.2LiNi _1/2 Mn _1/2 O ₂ .0.4Li [Li _1/3 Mn _2/3 ] O ₂ .0.4LiCoO ₂ , 0.5Li [ Li _1/3 Mn _2/3 ] O ₂ .0.5LiCoO ₂ or the like has a composition close to that of the present invention, but is outside the range of the composition of the present invention. Moreover, about the manufacturing method, only the solid-phase method using each acetate is shown, It does not show manufacturing using a coprecipitation method. Furthermore, since the discharge capacity is about 190 mAh / g at 4.6 V charge (x = 0.4), the discharge capacity in the potential region of 4.3 V or less is not large.

Non-Patent Document 6 describes LiNi _0.20 Li _0.20 Mn _0.60 O ₂ , that is, 0.6Li [Li _1/3 Mn _2/3 ] O ₂ −0.4LiNi _1/2 Mn _1/2. Although the positive electrode active material of O ₂ is shown, the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of the diffraction peaks of the (003) plane and the (104) plane by X-ray diffraction measurement is 1. Although the intensity of the diffraction peak on the (104) plane is greater than that on the (003) plane after discharge, this positive electrode active material is the active material of the present invention. Is clearly different. Moreover, about the manufacturing method, only the method of baking the powder which heat-decomposed each acetate or nitrate is shown, and manufacturing using a coprecipitation method is not shown. Furthermore, it is shown that the discharge capacity is 288 mAh / g in the initial stage at 4.8 V charge and 220 mAh / g after 20 cycles, but it is shown that the discharge capacity in the potential region below 4.3 V is increased. It has not been.

Non-Patent Document 7 discloses layered (1-xy) LiNi _1/2 Mn _1/2 O ₂ .xLi [Li _1/3 Mn _2/3 ] O ₂ .yLiCoO ₂ (0 ≦ x = y ≦ 0.3 and x + y = 0.5) positive electrode active material, 0.5LiNi _1/2 Mn _1/2 O ₂ .0.5Li [Li _1/3 Mn _{2 / 3} ] O ₂ has an intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of the diffraction peaks of the (003) plane and the (104) plane measured by X-ray diffraction measurement of about 1.4, and is not 1.56 or more. This positive electrode active material is clearly different from the active material of the present invention. Moreover, about the manufacturing method, only the solid-phase method using each acetate is shown, It does not show manufacturing using a coprecipitation method. Furthermore, since the discharge capacity is 180 mAh / g at 4.6 V charge, the discharge capacity in the potential region of 4.3 V or less is not large.

Non-Patent Document 8 shows a 0.5Li (Ni _0.5 Mn _0.5 ) O ₂ -0.5Li (Li _1/3 Mn _2/3 ) O ₂ solid solution having a layered structure. Q24 which is a solid solution of a lithium transition metal complex oxide having a —NaFeO ₂ type crystal structure has an intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of diffraction peaks of (003) plane and (104) plane by X-ray diffraction measurement Is about 1.2 and not more than 1.56, this solid solution is clearly different from the active material of the present invention. In S24 and VS24, the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of the diffraction peaks of the (003) plane and the (104) plane by X-ray diffraction measurement is 1.56 or more, but many impurity peaks are observed. It is not specified as a solid solution of a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure. Moreover, about the manufacturing method, only the method of baking the precursor from each acetate is shown, and manufacturing using a coprecipitation method is not shown. Further, regarding Q24, it is shown that the discharge capacity is about 210 mAh / g at 4.6 V charge, but it is not shown that the discharge capacity in the potential region of 4.3 V or less is increased. S24 and VS24 have a small discharge capacity.

Non-Patent Document 9 shows the electrochemical properties of Li (Li _{(1-x) / 3} Co _x Mn _{(2-2x) / 3} O ₂ ) (0 ≦ x ≦ 1) solid solution, Li (Li _{0.7 / 3} Co _0.3 Mn _{1.4 / 3} O ₂ satisfying this composition formula, that is, 0.7Li [Li _1/3 Mn _2/3 ] O ₂ -0.3LiCoO ₂ , Li (Li _{0.6 / 3} Co _0.4 Mn _{1.2 / 3} O ₂ , ie, 0.6Li [Li _1/3 Mn _2/3 ] O ₂ -0.4LiCoO ₂ is obtained by X-ray diffraction measurement ( The intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of the diffraction peak between the (003) plane and the (104) plane is about 1.3 and is not 1.56 or more. Therefore, this solid solution is the active material of the present invention. Obviously, the production method is different from that of each nitrate. Only the method of firing the body is shown, it is not shown that it is manufactured using the coprecipitation method, and the discharge capacity is about 250 mAh / g at 4.6 V charge. However, increasing the discharge capacity in a potential region of 4.3 V or less is not shown.

Non-Patent Document 10 shows the synthesis, structure, and electrochemical behavior of Li [Ni _x Li _{1 / 3-2x / 3} Mn _{2 / 3-x / 3} ] O ₂ , and the production method is coprecipitation. Li [Ni _0.25 Li _1/6 Mn _7/12 ] O ₂ satisfying this composition formula, that is, 0.5Li [Li _1/3 Mn _2/3 ] A solid solution such as O ₂ -0.5LiNi _1/2 Mn _1/2 O ₂ has an intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of diffraction peaks of (003) plane and (104) plane by X-ray diffraction measurement. Is about 1 and not greater than 1.56, so these solid solutions are clearly different from the active material of the present invention. Furthermore, it is shown that the discharge capacity is about 220 mAh / g at 4.8 V charge, but it is not shown that the discharge capacity in the potential region of 4.3 V or less is increased (from the charge / discharge curve). Seen, it is about 150 mAh / g in terms of 4.3 V).

Non-Patent Document 11 shows the synthesis and electrochemical characteristics of Li [Co _x Li _{(1 / 3-x / 3)} Mn _{(2 / 3-2x / 3)} ] O ₂ compound. _{Li [Co 0.33 Li 0.67 / 3} Mn 1.34 / 3 O 2 satisfying the composition formula, that _is, 0.67Li _{[Li 1/3} Mn 2/3] compounds of the O ₂ -0.33LiCoO 2 is Since the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of the diffraction peak of the (003) plane and the (104) plane measured by X-ray diffraction measurement is about 1.4 and not 1.56 or more, this compound is This is clearly different from the active material of the present invention. Moreover, about the manufacturing method, only the method of baking the powder which heat-decomposed each acetate or nitrate is shown, and manufacturing using a coprecipitation method is not shown. Furthermore, although the discharge capacity is shown to be about 200 mAh / g at 4.6 V charge, it has not been shown to increase the discharge capacity in a potential region of 4.3 V or less (from the charge / discharge curve). Seen, it is about 150-160 mAh / g in 4.3V conversion).

Non-Patent Document 12 describes a Li (Li _0.2 Ni _0.2 Mn _0.6 ) O ₂ positive electrode active material for lithium secondary batteries, ie, 0.6Li [Li _1/3 Mn _2/3 ] O. _It shows about the result of X-ray diffraction measurement of a 2-0.4LiNi _1/2 Mn _1/2 O ₂ positive electrode active material, and the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄ of the diffraction peak of the (003) plane and the (104) plane. ₎ Is about 1.6 after discharge, and about 1.7, but after synthesis, it is about 1.2 before discharge and not 1.56 or more. The material is clearly different from the active material of the present invention. Moreover, about the manufacturing method, only the sol-gel method using each acetate is shown, It does not show manufacturing using a coprecipitation method. Further, the discharge capacity is about 200 mAh / g in the potential region of 2.0-4.6V, but after charging of 4.6V, it is about 110 mAh / g in the cycle of the potential region of 2.0-4.3V. Therefore, the discharge capacity in the potential region of 4.3 V or less is not large.

Non-Patent Document 13 includes nanocrystalline Li [Li _0.2 Ni _0.2 Mn _0.6 ] O ₂ , that is, 0.6Li [Li _1/3 Mn _2/3 ] O ₂ −0.4LiNi _{1 / 2} Mn _1/2 O ₂ is shown, but the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of the diffraction peak between the (003) plane and the (104) plane by X-ray diffraction measurement is about 1.3. Since it is not 1.56 or more, this nanocrystal is clearly different from the active material of the present invention. Moreover, about the manufacturing method, only the method of baking the powder which heat-decomposed each acetate or nitrate is shown, and manufacturing using a coprecipitation method is not shown. Furthermore, it is shown that the discharge capacity is about 210 mAh / g at 4.8 V charge, but it is not shown that the discharge capacity in the potential region of 4.3 V or less is increased.

Non-Patent Document 14 describes the preparation of LiCoO ₂ —Li ₂ MnO ₃ (Li [Li _{(x / 3)} Co _1-x Mn _{(2x / 3)} ] O ₂ ) solid solution as a positive electrode active material for lithium ion batteries and Li [Li _0.2 Co _0.4 Mn _0.4 ] O ₂ that is shown for electrochemical behavior and satisfies this composition formula, ie, 0.6Li [Li _1/3 Mn _2/3 ] O ₂ -0. .4 LiCoO ₂ solid solution, Li [Li _0.23 Co _0.31 Mn _0.46 ] O ₂ , ie, 0.69Li [Li _1/3 Mn _2/3 ] O ₂ -0.31 LiCoO ₂ solid solution is an X-ray The diffraction peak intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ between the (003) plane and the (104) plane by diffraction measurement is about 2.3 and 1.9, respectively, before charging and discharging. 56 or more (FIG. 2 However, at the end of charging with a charging capacity of 160 mAh or more, the strength ratio is extremely reduced (1.4 to 1.7 for the former solid solution, see FIG. 10), and the strength ratio is extremely reduced. Since the intensity ratio at the end of discharge when the active material (solid solution) is discharged is not clear, it cannot be said that these active materials are the same as the active material of the present invention. As for the production method, it is only shown that each acetate salt is decomposed at 400 ° C. using a spray drying method and then fired at 750-950 ° C., and produced using a coprecipitation method. It is not shown to do. Furthermore, the discharge capacity is about 100 mAh / g at 4.5 V charge and is not large.

Non-Patent Document 15 shows a layered 0.6LiNi _0.5 Mn _0.5 O ₂ .xLi ₂ MnO ₃ .yLiCoO ₂ (x + y = 0.4) positive electrode active material, which satisfies this composition formula. 0.6LiNi _0.5 Mn _0.5 O ₂ .0.4Li ₂ MnO ₃ is an intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of diffraction peaks of (003) plane and (104) plane by X-ray diffraction measurement. Is about 1.4 and not more than 1.56. Therefore, this positive electrode active material is clearly different from the active material of the present invention. Moreover, about the manufacturing method, only the method of baking the powder which heat-decomposed each acetate salt is shown, It does not show manufacturing using a coprecipitation method. Furthermore, it is shown that the discharge capacity is about 210 mAh / g at 4.6 V charge, but it is not shown that the discharge capacity in the potential region below 4.3 V is increased (4.3 V conversion). About 150 mAh / g).

Non-Patent Document 16 describes a Li [Li _0.15 Ni _0.275 Mn _0.575 ] O ₂ positive electrode active material for a lithium secondary battery, that is, 0.45Li [Li _1/3 Mn _2/3 ] O _2. -0.55LiNi _1/2 Mn _1/2 O ₂ positive electrode active material is shown, but the intensity ratio I ₍₀₀₃₎ / I ₍ of diffraction peaks of (003) plane and (104) plane by X-ray diffraction measurement. ₁₀₄₎ is about 1 and not 1.56 or more, so this positive electrode active material is clearly different from the active material of the present invention. Moreover, about the manufacturing method, only the sol-gel method using each acetate is shown, It does not show manufacturing using a coprecipitation method. Furthermore, it is shown that the discharge capacity is about 180 mAh / g at 4.6 V charge, but it is not shown that the discharge capacity in the potential region of 4.3 V or less is increased (4.3 V conversion). About 140 mAh / g).

Non-Patent Document 17 shows the synthesis and electrochemical properties of Li [Li _{(1-2x) / 3} Ni _x Mn _{(2-x) / 3} ] O ₂ as a positive electrode active material for lithium secondary batteries. and that _{although, Li [Li 0.15 Ni 0.275 Mn} 0.575] O 2 satisfying the composition formula, that _{is, 0.45Li [Li 1/3 Mn 2/3]} O 2 -0.55LiNi 1 / The positive electrode active material of ₂ Mn _1/2 O ₂ has a diffraction peak intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of about (003) plane and (104) plane by X-ray diffraction measurement, which is about 1. Since it is not more than .56, these positive electrode active materials are clearly different from the active materials of the present invention. Moreover, about the manufacturing method, only the sol-gel method using each acetate is shown, It does not show manufacturing using a coprecipitation method. Furthermore, it is shown that the discharge capacity is about 190 mAh / g at 4.6 V charge, but it is not shown that the discharge capacity in the potential region below 4.3 V is increased (4.3 V conversion). About 140 mAh / g).

Electrochimica Acta 51 (2006) 5581-5586 Electrochemistry Communications 7 (2005) 1318-1322 Electrochemistry Communications 9 (2007) 787-795 Journal of Power Sources 146 (2005) 281-286 Journal of Power Sources 146 (2005) 598-601 Solid State Ionics 176 (2005) 1035-1042 Journal of The Electrochemical Society, 152 (1) A171-A178 (2005) Journal of Power Sources 124 (2003) 533-537 Electrochemistry Communications 9 (2007) 103-108 Journal of The Electrochemical Society, 149 (6) A777-A791 (2002) Journal of The Electrochemical Society, 151 (5) A720-A727 (2004) Electrochemical and Solid-State Letters, 6 (9) A183-A186 (2003) Electrochemical and Solid-State Letters, 6 (8) A166-A169 (2003) Journal of Power Sources 159 (2006) 1353-1359 Materials Letters 58 (2004) 3197-3200 Journal of Materials Chemistry, 2003,13,319-322 Journal of Power Sources 112 (2002) 634-638

The present invention has been made in view of the above problems, and is a method of manufacturing a lithium secondary battery having a large discharge capacity, particularly a lithium secondary battery capable of increasing the discharge capacity in a potential region of 4.3 V or less . An object is to provide a manufacturing method .

  The present invention will be described with a technical idea. However, the action mechanism includes estimation, and the correctness does not limit the present invention. It should be noted that the present invention can be implemented in various other forms without departing from the spirit or main features thereof. Therefore, the above-described embodiment or experimental example is merely an example in all respects and should not be interpreted in a limited manner. The scope of the present invention is indicated by the scope of claims, and is not restricted to the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

When known LiMnO ₂ is used as an active material for a lithium secondary battery, Yarn-Teller distortion caused by a redox reaction of Mn ⁴⁺ / Mn ³⁺ occurs in the charge / discharge process, so that a stable discharge capacity cannot be obtained.

Further, Li [Co _1-2x Ni _x, which is a known solid solution having an α-NaFeO ₂ type crystal structure shown on a ternary phase diagram in which LiCoO ₂ , LiNiO ₂ and LiMnO ₂ are arranged as three components, respectively. In the material of Mn _x ] O ₂ (0 <x ≦ 1/2), the valence of the transition metal element when synthesized is not only Co and Ni, but also the valence of Mn with charge / discharge. fluctuate. However, only in special cases where Ni and Mn are present in the same ratio, it is empirically possible to take the electronic states of Ni ²⁺ , Mn ⁴⁺ , and Co ^3+. Even if chemical oxidation-reduction (lithium insertion / extraction) is performed, the valence of Mn remains tetravalent, and it is considered that good reversible characteristics can be obtained. At this time, with electrochemical oxidation, the valence of Ni changes from divalent to trivalent, and further to tetravalent, and the valence of Co changes from trivalent to tetravalent. Here, the special case in which Ni and Mn are present in the same ratio is shown in a ternary phase diagram in which LiCoO ₂ , LiNiO ₂ and LiMnO ₂ are arranged as three components, respectively, as shown in FIG. Corresponds to a point on a straight line. However, if it deviates from this straight line, the electronic states of Ni ²⁺ , Mn ⁴⁺ , and Co ³⁺ cannot be taken, resulting in poor discharge capacity and charge / discharge cycle performance.

A part of materials considered to have valences of each metal element of Li ⁺ , Co ³⁺ , Ni ²⁺ and Mn ⁴⁺ can also be found in Patent Documents 15 to 18.
However, as described above, even with reference to the descriptions in Patent Documents 15 to 18, a battery having a discharge capacity that exceeds the conventional material as a secondary battery has not been obtained.

As a typical layered structure including Li ⁺ and Mn ⁴⁺ , there is monoclinic Li [Li _1/3 Mn _2/3 ] O ₂ . The various compounds based on this Li [Li _1/3 Mn _2/3 ] O ₂ have been studied so far, as described in Patent Documents 1-14. However, it is known that Li [Li _1/3 Mn _2/3 ] O ₂ can hardly obtain a charge / discharge capacity when used alone. This is ^{presumably because} the oxidation-reduction reaction of Mn ⁴⁺ → Mn ⁵⁺ does not occur in the stable region of a normal organic electrolyte.

The inventors focused on the fact that the Li [Li _1/3 Mn _2/3 ] O ₂ has a valence of Mn of 4 and studied to form a solid solution with other compounds. By doing so, Li [Li _1/3 Mn _2/3 ] O ₂ and the solid solution can be obtained without changing the valence of Mn from 4 even when electrochemical oxidation-reduction (charge / discharge) is performed. It is possible that the valence of the transition metal element constituting the other compound that is formed can be changed, which can result in high discharge capacity and stable charge / discharge cycle performance. It was.

The present inventors further provide a ternary solid solution of LiCoO ₂ —LiNi _1/2 Mn _1/2 O ₂ —Li [Li _1/3 Mn _2/3 ] O ₂ including LiCoO _{2 in} this binary system. It was investigated. Since LiCoO ₂ is excellent in initial charge / discharge efficiency and excellent in high rate charge / discharge characteristics, it was thought that this feature could be utilized.

This ternary solid solution is represented as a triangular phase diagram shown in FIG. All compounds on this matrix will exist as Co ³⁺ , Ni ²⁺ , Mn ⁴⁺ . That is, in the LiCoO ₂ -LiNiO ₂ -LiMnO ₂ system described above, as shown in FIG. 2, only ^Ni 2+ on the line where Ni and Mn are present in the same proportion, while can not exist as ^{Mn 4+,} LiCoO if _{2 -LiNi 1/2 Mn 1/2 O 2 -Li} [Li 1/3 Mn 2/3] a ternary solid solution of _{O 2,} ^Co 3+ at all points in the ^system, Ni ^{2+, Mn 4+} It can exist as

Therefore, the ternary solid solution that forms the basis of the present invention is x {Li [Li _1/3 Mn _2/3 ] O ₂ } · y {LiNi _1/2 Mn _1/2 O ₂ } · (z = 1 −xy) {LiCoO ₂ }. By transforming this, the following equation is derived: Li _{1 + x / 3} Co _1-xy Ni _{y / 2} Mn _{2x / 3 + y / 2} O ₂ Here, from the definition, 0 ≦ x, 0 ≦ y, and x + y ≦ 1.

  The present inventors have used this material as an active material when the value of x is in a specific range within the range of 1/3 <x in the ternary solid solution and satisfies specific properties. It has been found that the lithium secondary battery exhibits a large discharge capacity, particularly a large discharge capacity in a potential region of 4.3 V or less.

As can be seen from the above compositional formula, the active material composition characterized by the present invention is one of the characteristics that the content ratio of Li is higher than that of the conventional active material. Even considering only this point, the active material composition of the present invention cannot be plotted on the composition diagram of FIG. 2 describing the prior art. In addition, the composition diagram of FIG. 2 cannot represent a material that does not satisfy the relationship of a + b + c = 1 in the composition formula Li _q Co _a Ni _b Mn _c O _d like the material according to the present invention.

Here, the present invention provides a lithium secondary battery for manufacturing a lithium secondary battery in which a charging method in which the maximum potential of the positive electrode during charging is 4.3 V (vs. Li / Li +) or less is employed. A method comprising a solid solution of a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, wherein the composition ratio of Li, Co, Ni and Mn contained in the solid solution is Li _{1+ (1/3) x} Co _1-xy Ni _{(1/2) y} Mn _{(2/3) x + (1/2) y} (x + y ≦ 1, 0 ≦ y) is satisfied, and Li [Li _1/3 Mn _2/3 ] O _{In the 2} (x) -LiNi _1/2 Mn _1/2 O ₂ (y) -LiCoO ₂ (z) system triangular phase diagram, (x, y, z) is a point A (0.45, 0.55). 0), point B (0.63, 0.37, 0), point C (0.7, 0.25, 0.05), point D (0.67, .18, 0.15), point E (0.75, 0, 0.25), point F (0.55, 0, 0.45), and point G (0.45, 0.2, 0. 35) 4.3 V (vs. Li) for a lithium secondary battery using an active material represented by a value in a range existing on or inside a heptagon ABCDEFG having an apex at 35) and a positive electrode containing the active material / Li +) and 4.8 V or less (vs. Li / Li +) in the positive electrode potential range, including a step of charging the potential change appearing with respect to the charge amount to reach at least a relatively flat region. To do. The active material has an intensity ratio of diffraction peaks of the (003) plane and the (104) plane as measured by X-ray diffraction measurement of I ₍₀₀₃₎ / I ₍₁₀₄₎ ≧ 1.56 before charge and discharge, and at the end of discharge. It is preferable that I ₍₀₀₃₎ / I ₍₁₀₄₎ > 1.

Here, “before charging / discharging” in the present invention refers to the period from the synthesis of the active material until the first electrochemical energization.
In addition, “discharge end” means after discharge of 160 mAh / g or more (in the examples, after discharge of 177 mAh / g or more). Specifically, as shown in the examples, the battery was charged to 4.3 V (vs. Li / Li +), a constant current discharge with a current of 0.1 ItA was performed, and the end point of 2.0 V was reached. Discharged at the end.

In general, when a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure is synthesized through a firing step, the composition of the compound actually obtained varies slightly compared to the composition calculated from the raw material composition ratio. It is known as a fact to do. The present invention can be carried out without departing from the technical idea or the main features thereof, and the composition of the product obtained by synthesis does not exactly match the above composition formula, and is within the scope of the present invention. It goes without saying that it should not be interpreted as not belonging. In particular, it is known that the amount of Li is easily volatilized in the firing step. In addition, the coefficient of oxygen atoms may vary depending on the synthesis conditions. Note that the composition formula of claim 1 of the present application does not prescribe the coefficient of oxygen atoms. O in Li [Li _1/3 Mn _2/3 ] O ₂ (x) -LiNi _1/2 Mn _1/2 O ₂ (y) -LiCoO ₂ (z) in the triangular phase diagram is strictly 2 only Instead, the missing ones are also included.
Further, the active material of the present invention may contain an element other than Li, Co, Ni, Mn, and O, and even when it contains an element other than Li, Co, Ni, Mn, and O, the solid solution As long as Li, Co, Ni and Mn are taken out of the elements constituting the composition and the composition ratio satisfies the provisions of the present application and the effects of the present invention are exhibited, such elements are also within the technical scope of the present invention. Belonging to. As elements other than Li, Co, Ni, Mn, and O, transition metal elements other than Co, Ni, and Mn may be used.

The active material for a lithium secondary battery according to the present invention can be charged and discharged by reaching a positive electrode potential of around 4.5 V (vs. Li ^/ Li ⁺ ). However, depending on the type of nonaqueous electrolyte used, if the positive electrode potential during charging is too high, the nonaqueous electrolyte may be oxidized and decomposed, resulting in a decrease in battery performance. Accordingly, in use, a lithium secondary battery capable of obtaining a sufficient discharge capacity even if a charging method is adopted in which the maximum potential of the positive electrode during charging is 4.3 V (vs. Li ^/ Li ⁺ ) or less. May be required. When an active material for a lithium secondary battery in which (x, y, z) is in the above range and the intensity ratio of the diffraction peak between the (003) plane and the (104) plane by X-ray diffraction measurement satisfies the above conditions is used. Even when a charging method is adopted such that the maximum potential of the positive electrode during charging is 4.3 V (vs. Li / Li ⁺ ) or less in use, 177 mAh / g or more (mostly 180 mAh / g or more) It is possible to take out the amount of discharge electricity exceeding the capacity of the conventional positive electrode active material.
Therefore, the present invention provides a method for manufacturing a lithium secondary battery for manufacturing a lithium secondary battery in which a charging method in which the maximum potential of the positive electrode during charging is 4.3 V (vs. Li / Li +) or less is employed. And a solid solution of a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, wherein the composition ratio of Li, Co, Ni and Mn contained in the solid solution is Li _{1+ (1/3) x} Co _1-xy Ni _{(1/2) y} Mn _{(2/3) x + (1/2) y} (x + y ≦ 1, 0 ≦ y, 1-xy = z) is satisfied, and Li [Li _{1 / 3} Mn _2/3] in _{O 2 (x) -LiNi 1/2 Mn} 1/2 O 2 (y) -LiCoO 2 (z) based triangular phase diagram, (x, y, z) is a point A (0 .45, 0.55, 0), point B (0.63, 0.37, 0), point C (0.7, 0.25, 0.05) , Point D (0.67, 0.18, 0.15), point E (0.75, 0, 0.25), point F (0.55, 0, 0.45), and point G (0 Lithium secondary containing an active material represented by a value in a range existing on or inside a heptagon ABCDEFG having a vertex of .45, 0.2, 0.35) and a positive electrode containing the active material Charging of a battery that exceeds 4.3V (vs.Li/Li+) and is less than 4.8V (vs.Li/Li+) in the positive electrode potential range, and the potential change that appears with respect to the amount of charge reaches at least a relatively flat region. And the lithium secondary battery has a dischargeable amount of electricity of 177 mAh / g or more in a potential region of 4.3 V (vs. Li / Li +) or less. The active material preferably has an intensity ratio of diffraction peaks of the (003) plane and the (104) plane measured by X-ray diffraction measurement such that I ₍₀₀₃₎ / I ₍₁₀₄₎ > 1 at the end of discharge.

  In the active material for a lithium secondary battery, the (x, y, z) is a point H (0.6, 0.4, 0), a point I (0.67, 0.13, 0.2), It is represented by a value in a range existing on or in the line of a quadrilateral HIJK with the point J (0.7, 0, 0.3) and the point K (0.55, 0.05, 0.4) as vertices. It is preferable.

In this range, 198 mAh / g or more (mostly 200 mAh / g) even when a charging method is adopted in which the maximum potential of the positive electrode during charging is 4.3 V (vs. Li / Li ⁺ ) or less. g or more), it is possible to take out the amount of discharge electricity greatly exceeding the capacity of the conventional positive electrode active material.

  Moreover, this invention is a lithium secondary battery containing the above active materials for lithium secondary batteries.

Here, LiCoO ₂ powder and _LiNi 1/2 _Mn 1/2 _{O 2} powder and _{Li [Li 1/3 Mn 2/3] O} 2 made of simple mixture only with powder, lithium secondary according to the present invention It is not included in the “solid solution” contained in the battery active material. Each of these three materials has a different peak position corresponding to each lattice constant observed when X-ray diffraction measurement is performed. Therefore, when X-ray diffraction measurement is performed on these simple mixtures, each single item corresponds. A diffraction pattern is obtained. However, in the solid solution of the lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure according to the present invention, at least a part of Li [Li _1/3 Mn _2/3 ] O ₂ is LiCoO ₂ and / or LiNi _{1. / 2} It is in solid solution with Mn _1/2 O ₂ . Even if the above (x, y, z) is within the above range, Li [Li _1/3 Mn _2/3 ] O ₂ is completely solid with LiCoO ₂ and / or LiNi _1/2 Mn _1/2 O _2. If not dissolved, the effect of the present invention that a lithium battery having a large discharge capacity can be obtained is not achieved.

Furthermore, the active material for a lithium secondary battery according to the present invention is an active material existing in a region where x> 1/3, and in the vicinity of 2θ = 20 to 30 ° of an X-ray diffraction diagram using CuKα rays, Li A diffraction peak observed in a [Li _1/3 Mn _2/3 ] O ₂ type monoclinic crystal was observed. This is presumed to be a superlattice line observed when Li ⁺ and Mn ⁴⁺ are regularly arranged. In the present invention, the discharge capacity is particularly excellent in the case where the intensity of the monoclinic diffraction peak seen in the vicinity of 21 ° is 4 to 7% of the diffraction peak intensity of the hexagonal (003) plane, which is the main phase. It was about. As the Li [Li _1/3 Mn _2/3 ] O ₂ ratio in the solid solution increases, the intensity of the monoclinic diffraction peak seen near 21 ° increases. As a result, it is difficult to obtain a sufficient discharge capacity for an active material in which the intensity of the monoclinic diffraction peak seen near 21 ° with respect to the diffraction peak intensity of the hexagonal (003) plane of the main phase exceeds 7%. Become.

Here, according to the present invention, the solid solution of the lithium transition metal composite oxide is Li [Li _1/3 Mn _2/3 ] O in the vicinity of 20 to 30 ° when X-ray diffraction measurement using CuKα ray is performed. It is characterized by observing diffraction peaks observed in type ₂ monoclinic crystals.

  In addition, when the present inventors mix a precursor containing a transition metal element and a lithium compound to obtain a solid solution of a lithium transition metal composite oxide through a firing step, they contain Co, Ni, and Mn in a solvent. It has been found that when a precursor is prepared by coprecipitation of a hydroxide, an active material for a lithium secondary battery that can be a lithium battery having a large discharge capacity can be reliably synthesized. This is related to the fact that the transition metal (Co, Ni, Mn) can be uniformly distributed in the precursor by obtaining the transition metal hydroxide as a precursor by the coprecipitation method. The present inventors are thinking. In addition, the description in Patent Document 19 is a reference for a preferable method for producing such a precursor.

  Here, the present invention provides a precursor by co-precipitation of a hydroxide containing Co, Ni and Mn in a solvent, and the lithium transition metal is subjected to a process of mixing and firing the precursor and a lithium compound. A method for producing an active material for a lithium secondary battery, comprising producing a solid solution of a composite oxide.

Even when the active material for a lithium secondary battery according to the present invention is used and a charging method is employed such that the maximum potential of the positive electrode during charging is 4.3 V (vs. Li ^/ Li ⁺ ) or less during use. In order to manufacture a lithium secondary battery capable of taking out a sufficient discharge capacity, a charging process in consideration of the characteristic behavior of the active material for a lithium secondary battery according to the present invention described below is performed. It is important to provide it during the manufacturing process of the secondary battery. That is, when constant current charging is continued using the active material for a lithium secondary battery according to the present invention for the positive electrode, a region where the potential change is relatively flat is relatively long in the positive electrode potential range of 4.3 V to 4.8 V. Observed over time. FIG. 9 shows a comparison of positive electrode potential behavior when the positive electrodes using the active materials for lithium secondary batteries of Example 6 (AT17) and Comparative Example 4 (AT11) are charged for the first time. The curve described as “1st charge” corresponds to this. As shown in FIG. 9 (a) (Embodiment 6), at the time of the first charge, a region where the potential change is relatively flat at a potential of around 4.45V from the vicinity where the amount of charge exceeds 100 mAh / g is long. Observed over time. On the other hand, in FIG. 9B (Comparative Example 4), such a flat region is hardly observed. The charging conditions adopted here are constant current and constant voltage charging with a current of 0.1 ItA and a voltage (positive electrode potential) of 4.5 V (vs. Li ^/ Li ⁺ ). A potential flat region over a relatively long period is hardly observed when a material having an x value of 1/3 or less is used. On the other hand, a material having a value of x exceeding 2/3 is short even when a region where the potential change is relatively flat is observed. Further, this behavior is not observed even in a conventional Li [Co _1-2x Ni _x Mn _x ] O ₂ (0 ≦ x ≦ 1/2) material. This behavior is characteristic of the active material for a lithium secondary battery according to the present invention.

Here, the present invention is a manufacturing method for manufacturing the lithium secondary battery in which a charging method in which the maximum potential of the positive electrode during charging is 4.3 V (vs. Li ^/ Li ⁺ ) or less is employed. In the positive potential range of 4.3 V (vs. Li ^/ Li ⁺ ) and 4.8 V or less (vs. Li ^/ Li ⁺ ), the potential change that appears with respect to the charge amount is at least in a relatively flat region. It is the manufacturing method of the lithium secondary battery characterized by including the process of performing the charge to reach | attain.

  Here, it is necessary to perform the charge in the initial charge / discharge step before completion of the battery at least until the potential flat region is reached. Since the potential flat region lasts relatively long (for example, 100 mAh / g or more), it is preferable to continue charging so as to pass through this process as much as possible. Here, when the end point of the potential flat region is observed due to a potential rise or the like, this may be used as a charge termination condition, and charging is performed when the current value is attenuated to the set value by employing constant current and constant voltage charging. It may be a termination condition.

ADVANTAGE OF THE INVENTION According to this invention, the lithium secondary battery with a large discharge capacity, especially the lithium secondary battery which can enlarge the discharge capacity in the electric potential area | region of 4.3 V or less can be provided.

It is a figure which shows the technical idea and technical scope of this invention. It is a figure for demonstrating the technical idea of a prior art. Crystal of active material of composition formula Li _{1+ (1/3) x} Co _1-xy Ni _{(1/2) y} Mn _{(2/3) x + (1/2) y} (x + y ≦ 1, 0 ≦ y) It is a figure which shows a structure. FIG. ₂ is an X-ray diffraction pattern of an active material assuming LiNiO ₂ (a simulation result close to the measurement result of the present invention was obtained) . _(Li 0.8 _{Ni 0.2)} is _{[Ni 0.8 Li 0.2] O 2} X -ray diffraction diagram of the assumed active material (which simulation results close to the literature was obtained). X-ray diffractogram before and after charge and discharge and after discharge of a conventional active material comprising LiNi _0.20 Co _0.20 Mn _0.60 O ₂ and LiNi _0.20 Co _0.27 Mn _0.53 O ₂ It is. It is an X-ray diffraction pattern of the active material of Example 1 (AT06). It is a figure which shows the XAFS measurement result of the active material of Examples 1-4 and the comparative example 41. FIG. It is an X-ray diffraction pattern of the active material of Comparative Example 3 (AT09). It is a figure which shows the electric potential behavior at the time of the initial stage charging / discharging process performed in the lithium secondary battery manufacturing process of the active material of Example 6 (AT17) and Comparative Example 4 (AT11). It is a figure which shows the charging / discharging behavior of the lithium secondary battery using the active material of Example 6, Comparative Example 4 and Comparative Example 42. It is the X-ray-diffraction figure before charging / discharging (synthetic sample) of the active material of Example 7 (AT18), after charge, and after discharge. It is an X-ray diffraction pattern before charge / discharge (synthetic sample), after charge and after discharge of the active material of Example 16 (AT33). Li [Li _1/3 Mn _2/3 ] O ₂ (x) -LiNi _1/2 Mn _1/2 O ₂ (Plotted values of discharge capacity for the active materials of Examples 1 to 44 and Comparative Examples 1 to 40 y) is a -LiCoO ₂ (z) based triangular phase diagram.

As described above, the manufacturing method of the lithium secondary battery of the present invention, as a cathode active material for a lithium secondary _{battery, Li [Li 1/3 Mn 2/3]} O 2 (x) -LiNi 1/2 Mn 1 _{/ 2} O ₂ (y) -LiCoO ₂ (z) In the triangular phase diagram, (x, y, z) are point A (0.45, 0.55, 0) and point B (0.63, 0). .37,0), point C (0.7,0.25,0.05), point D (0.67,0.18,0.15), point E (0.75,0,0.25) ), F (0.55, 0, 0.45), and a value in a range existing on or inside the heptagon ABCDEFG having the point G (0.45, 0.2, 0.35) as a vertex. It is characterized by using the active material represented . The active material has an intensity ratio of diffraction peaks of the (003) plane and the (104) plane as measured by X-ray diffraction measurement of I ₍₀₀₃₎ / I ₍₁₀₄₎ ≧ 1.56 before charge and discharge, and at the end of discharge. It is preferable that I ₍₀₀₃₎ / I ₍₁₀₄₎ > 1.
As shown in FIG. 13 and Tables 1 and 2 below, when the above (x, y, z) is a value in the above range, the discharge capacity in a potential region of 4.3 V or less is 177 mAh / g. As described above, if the value is out of the above range, only a discharge capacity of 176 mAh / g or less can be obtained. Thus, in order to obtain an active material capable of increasing the discharge capacity, the above (x, y, z) Needs to be in a specific range.
Further, the above (x, y, z) is a point H (0.6, 0.4, 0), a point I (0.67, 0.13, 0.2) among the insides of the heptagon ABCDEFG. , The point J (0.7, 0, 0.3) and the point K (0.55, 0.05, 0.4) are in a range existing on or in the line of the quadrilateral HIJK. It was found that a particularly high discharge capacity (198 mAh / g or more) can be obtained.

Moreover, the following is estimated about the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of the diffraction peak of the (003) plane and the (104) plane by X-ray diffraction measurement.
The active material of the composition formula Li _{1+ (1/3) x} Co _1-xy Ni _{(1/2) y} Mn _{(2/3) x + (1/2) y} (x + y ≦ 1, 0 ≦ y) is It has a layered structure as shown in FIG. 3, and the Me ³⁺ layer is considered to be composed of Li ⁺ , Co ³⁺ , Ni ²⁺ , and Mn ⁴⁺ . Further, in the active material having a layered structure as shown in FIG. 3, ^{Ni 3+} in a part of the Li ⁺ layer found the intensity of the Li ⁺ is contaminated in a portion of the ^{Ni 3+} layer _{I (104)} It is thought to grow. Therefore, a representative layered oxide LiNiO ₂ ^{(Me 3+} layer is ^{Ni 3+} only) taken up, ^{Ni 3+} in a part of the Li ⁺ layer, a so-called disorder phase Li ⁺ is contaminated in a portion of the ^{Ni 3+} layer Assuming that (Li _0.8 Ni _0.2 ) [Ni _0.8 Li _0.2 ] O ₂ is obtained, an X-ray diffraction pattern simulated by theoretical calculation is shown in FIG.
As shown in FIG. 4A, LiNiO ₂ has an intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ = 1.10, and the (003) diffraction peak is sufficiently large. As shown in the figure, a transition phase (Co, Ni, Mn) is mixed into the disorder phase in the Li layer, so that the intensity ratio of both changes greatly, and I ₍₀₀₃₎ / I ₍₁₀₄₎ ≦ 1.
In the conventional active material, it is considered that the formation of such a disorder phase does not cause a smooth movement of Li ions from the Li layer, and also affects the reversible capacity.
On the other hand, in the active material of the present invention, since I ₍₀₀₃₎ / I ₍₁₀₄₎ ≧ 1.56, the generation of the disorder phase is very small, and it is considered that an excellent discharge capacity was obtained. .

Furthermore, the following is estimated about the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of the diffraction peak before charge / discharge after the active material preparation and the change in the intensity ratio after charge / discharge.
Even if the intensity ratio of the diffraction peaks before charging / discharging is I ₍₀₀₃₎ / I ₍₁₀₄₎ ≧ 1.56, if there is a transition metal mixed into the Li layer during charging / discharging, the diffraction on the (003) plane As the peak becomes broader, the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ becomes remarkably small, and in the conventional active material, as shown in FIG. , (004) plane diffraction peak and its intensity may be reversed.
On the other hand, in the active material of the present invention, as shown in Table 1, FIG. 11 and FIG. 12, I ₍₀₀₃₎ / I ₍₁₀₄₎ ≧ 1.56 before charging and discharging, I ₍₀₀₃₎ / I ₍₁₀₄₎ > 1 (in the embodiment, I ₍₀₀₃₎ / I ₍₁₀₄₎ > 1.3), and the (003) plane diffraction peak is the (004) plane diffraction peak. Therefore, it is suggested that no transition metal is mixed into the Li layer during charging / discharging, and a stable large reversible capacity can be obtained. At the end of discharge, the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ may be larger than before charging / discharging. When the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ becomes smaller at the end of the discharge than before the charge / discharge, the change in the intensity ratio is preferably small and should be within 30% before the charge / discharge. More preferably, it is within 26% in the examples.

Next, a method for producing the active material for a lithium secondary battery of the present invention will be described.
The active material for a lithium secondary battery of the present invention basically includes a raw material containing a metal element (Li, Mn, Co, Ni) constituting the active material according to the composition of the active material (oxide). It can be obtained by adjusting and baking this. However, with respect to the amount of the Li raw material, it is preferable to add an excess of about 1 to 5% in view of the disappearance of a part of the Li raw material during firing.
In producing an oxide having a desired composition, a so-called “solid phase method” in which salts of Li, Co, Ni, and Mn are mixed and fired, or Co, Ni, and Mn were previously present in one particle. A “coprecipitation method” is known in which a coprecipitation precursor is prepared, and a Li salt is mixed and fired therein. In the synthesis process by the “solid phase method”, especially Mn is difficult to uniformly dissolve in Co and Ni, so it is difficult to obtain a sample in which each element is uniformly distributed in one particle. In literatures and the like, many attempts have been made to dissolve Mn in a part of Ni or Co by a solid phase method (LiNi _1-x Mn _x O ₂ etc.), but the “coprecipitation method” is selected. It is easier to obtain a homogeneous phase at the atomic level. Therefore, the “coprecipitation method” is employed in the examples described later.

  In preparing the coprecipitation precursor, it is extremely important to make the solution in which the coprecipitation precursor is obtained have an inert atmosphere. This is because Co, Ni, and Mn are easily oxidized, and it is not easy to produce a coprecipitated hydroxide in which Co, Ni, and Mn are uniformly distributed in a divalent state. Uniform mixing at the atomic level tends to be insufficient. Particularly in the composition range of the present invention, since the Mn ratio is higher than the Co and Ni ratios, it is even more important to make the solution in an inert atmosphere. In Examples described later, an inert gas was bubbled into an aqueous solution to remove dissolved oxygen, and a reducing agent was added dropwise at the same time.

  It does not limit about the preparation method of the precursor with which the said baking is provided. A Li compound, a Mn compound, a Ni compound, and a Co compound may be simply mixed, or a hydroxide containing a transition metal element may be coprecipitated in a solution and mixed with the Li compound. In order to produce a uniform composite oxide, a method in which a co-precipitated hydroxide of Mn, Ni, and Co and a Li compound are mixed and fired is preferable.

  The preparation of the coprecipitated hydroxide precursor is preferably a compound in which Mn, Ni and Co are uniformly mixed. However, the precursor is not limited to hydroxides, and any other poorly soluble salt in which other elements such as carbonates and citrates exist uniformly at the atomic level should be used in the same way as hydroxides. Can do. In addition, a precursor having a larger bulk density can be produced by using a crystallization reaction using a complexing agent. At that time, an active material having a higher density and a smaller specific surface area can be obtained by mixing and firing with a Li source, so that the energy density per electrode area can be improved.

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

  As a raw material used for the preparation of the coprecipitated hydroxide precursor, any form can be used as long as it forms a precipitation reaction with an alkaline aqueous solution, but preferably a highly soluble metal salt is used. Good.

  The active material for a lithium secondary battery in the present invention can be suitably produced by mixing the coprecipitated hydroxide precursor and the Li compound and then heat-treating them. As a Li compound, it can manufacture suitably by using lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, etc.

In obtaining an active material having a large reversible capacity, the selection of the firing temperature is extremely important.
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 prescribed phase tends to be observed as a phase separation rather than as a solid solution phase, and such materials are not preferred because the reversible capacity of the active material is greatly reduced. In such materials, impurity peaks are observed around 35 ° and 45 ° on the X-ray diffraction pattern. Therefore, it is important that the firing temperature is lower 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 invention. However, there is a slight difference in the oxygen release temperature depending on the composition of the active material. It is preferable to keep it. In particular, it is confirmed that the oxygen release temperature of the precursor shifts to the 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 coprecipitation precursor and LiOH.H ₂ O is 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 the crystallization proceeds to some extent by adopting a firing temperature of about 500 ° C in advance. The composition thus obtained is preferably subjected to thermogravimetric analysis.

On the other hand, if the firing temperature is too low, crystallization does not proceed sufficiently and the electrode characteristics are also greatly deteriorated. The firing temperature needs to be at least 800 ° C. or higher. Sufficient crystallization is important for reducing the resistance of the grain boundaries and promoting smooth lithium ion transport. Visual observation using a scanning electron microscope is mentioned as a method of determining the degree of crystallization. When the positive electrode active material of the present invention was observed with a scanning electron microscope, the sample synthesis temperature was 800 ° C. or less, and it was formed from nano-order primary particles. By further increasing the sample synthesis temperature, It was crystallized to a submicron level, and large primary particles that lead to improved electrode characteristics were obtained.
On the other hand, there is the half width of the X-ray diffraction peak described above as another indication of the degree of crystallization. However, simply selecting a synthesis temperature at which the half-value width of the diffraction peak of the main phase is small is not always sufficient to obtain an active material having a large reversible capacity. This is because the half-width of the diffraction peak is governed by two factors: the amount of strain that represents the degree of crystal lattice mismatch and the size of the crystallite that is the smallest domain. It is necessary to separate these in order to determine the degree of the problem. The inventors have analyzed the half-value width of the active material of the present invention in detail, and in the sample synthesized at a temperature up to 800 ° C., strain remains in the lattice, and almost no synthesis is performed at a temperature higher than that. It was confirmed that the strain could be removed. The crystallite size was increased in proportion to the increase in the synthesis temperature. Therefore, even in the composition of the active material of the present invention, a favorable discharge capacity can be obtained by aiming at a particle having almost no lattice distortion in the system and having a sufficiently grown crystallite size. Specifically, it has been found that it is preferable to employ a synthesis temperature (firing temperature) such that the strain amount affecting the lattice constant is 1% or less and the crystallite size is grown to 150 nm or more. Although changes due to expansion and contraction are observed by charging and discharging by forming these as electrodes, it is preferable as an effect that the crystallite size is maintained at 130 nm or more in the charging and discharging process. 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 preferably 900 to 1100 ° C, more preferably 950 to 1050 ° C. If there is, high characteristics can be exhibited.

  The nonaqueous electrolyte used for the lithium secondary battery according to the present invention 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 nonaqueous 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, 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 , (n-C _{4 H 9) 4 NI, (} C 2 H 5) 4 N-mal _{ate, (C 2 H 5)} 4 N-benzoate, (C 2 H 5) 4 N-phtalate, lithium stearyl sulfonate, lithium octyl sulfonate, organic ion salts of lithium dodecyl benzene sulfonate, and the like. These These ionic compounds can be used alone or in admixture of two or more.

Furthermore, by using a mixture of 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, so that the low temperature characteristics are further improved. It can be increased and self-discharge can be suppressed, which is more desirable.

  Moreover, you may use normal temperature molten salt and an ionic liquid as a nonaqueous electrolyte.

  The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, more preferably 0.5 mol / l to 2 in order to reliably obtain a non-aqueous electrolyte battery having high battery characteristics. .5 mol / l.

The negative electrode material is not limited, and any negative electrode material 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.

  It is desirable that the positive electrode active material powder and the negative electrode material powder have an average particle size of 100 μm or less. In particular, the positive electrode active material powder is desirably 10 μm or less for the purpose of improving the high output characteristics of the non-aqueous electrolyte battery. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. 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 or a sieve 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.

  The positive electrode active material and the negative electrode material, which are the main components of the positive electrode and the negative electrode, have been described in detail above. In addition to the main components, the positive electrode and the negative electrode include a conductive agent, a binder, a thickener, and a filler. Etc. may be contained as other constituents.

  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 desirable from the viewpoints of electron 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, it is desirable to use acetylene black by pulverizing into ultrafine particles of 0.1 to 0.5 μm because the required carbon amount can be reduced. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet.

  Examples of the binder include thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, and polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, and 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 addition amount of the binder is preferably 1 to 50% by weight, particularly preferably 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 the 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.

  The positive electrode and the negative electrode are obtained by kneading the main components (positive electrode active material for the positive electrode, negative electrode material for the negative electrode) and other materials into a mixture and mixing them in an organic solvent such as N-methylpyrrolidone or toluene. The obtained mixed liquid is applied on a current collector described in detail below, or is pressure-bonded 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 desirable 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 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 nonaqueous electrolyte batteries include polyolefin resins typified by polyethylene, polypropylene, etc., polyester resins typified by polyethylene terephthalate, polybutylene terephthalate, etc., polyvinylidene fluoride, 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 desirable that the separator be used in combination with the above-described porous film, non-woven 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 using a radical initiator in combination with heating or ultraviolet rays (UV), or using an actinic ray such as an electron beam (EB).

  The configuration of the lithium secondary battery is not particularly limited, and examples thereof include a cylindrical battery having a positive electrode, a negative electrode, and a roll separator, a square battery, a flat battery, and the like.

Table 1 shows the composition of the positive electrode active material used in the lithium secondary batteries according to Examples and Comparative Examples. Here, the compositions of Examples 1 to 44 are represented by the composition formula Li _{1+ (1/3) x} Co _1-xy Ni _{(1/2) y} Mn _{(2/3) x + (1/2) y} (x + y ≦ 1, 0 ≦ y, z = 1−xy), and (x, y, z) satisfies the range of claim 1. Although the composition formula is satisfied, the value of (x, y, z) deviates from the range described in claim 1, and Comparative Examples 41 to 43 do not satisfy even the composition formula. That is, in FIG. 1, the compositions of Examples 1 to 44 are present on or inside the heptagon ABCDEFG, and the compositions of Comparative Examples 1 to 40 are present outside the heptagon ABCDEFG.

Example 1
Manganese sulfate pentahydrate, nickel sulfate hexahydrate, and cobalt sulfate heptahydrate are added to ion-exchanged water so that each element of Co, Ni, and Mn has a ratio of 0.25: 0.17: 0.45. A mixed aqueous solution was prepared by dissolution. At that time, the total concentration was 0.667M and the volume was 180 ml. Next, 600 ml of ion-exchanged water was prepared in a 1-liter beaker, maintained at 50 ° C. using a hot water bath, and 8N NaOH was added dropwise to adjust the pH to 11.5. In this state, Ar gas was bubbled for 30 minutes to sufficiently remove dissolved oxygen in the solution. The inside of the beaker was stirred at 700 rpm, and the mixed aqueous solution of the previous sulfate was dropped at a speed of 3 ml / min. Meanwhile, the temperature was kept constant in a hot water bath, and the pH was kept constant by intermittently dropping 8N NaOH. At the same time, 50 ml of a 2.0 M hydrazine aqueous solution as a reducing agent was added dropwise at a speed of 0.83 ml / min. After both droppings were completed, the coprecipitated hydroxide was sufficiently grown by standing still for 12 hours or more with stirring stopped.
Here, in the above procedure, if the dropping speed of each solution is too fast, a uniform precursor at the elemental level cannot be obtained. For example, when the dropping speed is 10 times the above, it has become clear from the results of EPMA measurement that the element distribution in the precursor is clearly non-uniform. In addition, when an active material was synthesized using such a non-uniform precursor, it was confirmed that the distribution of elements after firing was non-uniform, and sufficient electrode characteristics could not be exhibited. By the way, it can be seen from the results of EPMA measurement that LiOH.H ₂ O, Co (OH) ₂ , Ni (OH) ₂ , and MnOOH are used as raw material powders by the solid phase method, which makes it even more non-uniform. It was.

Next, the coprecipitation product was taken out by suction filtration and dried in an oven at 100 ° C. under normal pressure in an air atmosphere. After drying, the powder was pulverized for several minutes in a mortar having a diameter of about 120 mmφ so as to obtain a uniform particle size, thereby obtaining a dry powder.
This dry powder was confirmed to be a β-Ni (OH) ₂ type single phase by X-ray diffraction measurement. Moreover, it was confirmed by the EPMA measurement that Co, Ni, and Mn are uniformly distributed.

Lithium hydroxide monohydrate powder (LiOH.H ₂ O) was weighed so that the amount of Li with respect to the transition metal (Ni + Mn + Co) satisfied the composition formula of Example 1 in Table 1, and mixed to obtain a mixed powder. .
Next, the mixed powder was pellet-molded at a pressure of 6 MPa. The amount of the precursor powder subjected to pellet molding was determined by conversion so that the mass as a product after synthesis was 3 g. As a result, the molded pellets had a diameter of 25 mmφ and a thickness of about 10-12 mm. The pellets were placed on an alumina boat having a total length of about 100 mm, placed in a box-type electric furnace, and baked in an air atmosphere at 1000 ° C. for 12 hours. 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 temperature of the furnace was 100 ° C. or less, and then the pellets were taken out and pulverized to the same particle size using a mortar.

As a result of powder X-ray diffraction measurement using a Cu (Kα) tube, the crystal structure of the obtained active material is confirmed to be an α-NaFeO ₂ type hexagonal crystal structure as a main phase and partially Li [Li _{1 / 3} Mn _2/3 ] O ₂ type monoclinic crystals, a diffraction peak around 20-30 ° was observed. FIG. 6 shows an X-ray diffraction diagram for the active material of Example 1 (AT06). The intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of the diffraction peak between the (003) plane and the (104) plane of the active material before charge and discharge was 1.69. Further, when the count number of a peak near 18 ° indicating the maximum intensity is 100, the count number of a diffraction peak at 21 ° found in a monoclinic crystal of Li [Li _1/3 Mn _2/3 ] O ₂ type is 7.

Furthermore, XAFS measurement was performed as a valence evaluation of the transition metal element. When the spectrum of the XANES region was analyzed, it was confirmed that the electronic states of Co ³⁺ , Ni ²⁺ and Mn ⁴⁺ were taken. The XANES measurement results are shown in FIG.

(Examples 2-44)
The composition of the transition metal element contained in the coprecipitated hydroxide precursor and the mixed amount of lithium hydroxide were changed in accordance with the composition formula shown in Tables 1 to 44 in Table 1, and were the same as in Example 1. The active material according to the present invention was synthesized.

As a result of X-ray diffraction measurement, a hexagonal structure of α-NaFeO ₂ type was confirmed as the main phase as in Example 1, and a part of Li [Li _1/3 Mn _2/3 ] O ₂ type monoclinic was confirmed. A diffraction peak around 20-30 ° seen in the crystal was observed. In addition, as shown in Table 1, the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of the diffraction peak between the (003) plane and the (104) plane of the active material before charging / discharging is 1.56 or more. there were.

(Comparative Examples 1-40)
About the composition of the transition metal element which the coprecipitation hydroxide precursor contains, and the mixing amount of lithium hydroxide, it changed according to the compositional formula shown in Table 1 to Comparative Examples 1-40, and it carried out similarly to Example 1. Then, an active material according to a comparative example was synthesized.

FIG. 8 shows an X-ray diffraction diagram for the active material of Comparative Example 3 (AT09) as a representative. As for Comparative Examples 12 to 18 and 33 to 40 in which the value of x is 2/3 or more, the α-NaFeO ₂ type hexagonal crystal structure is confirmed as the main phase as in Example 1, and a part of Li A diffraction peak in the vicinity of 20 to 30 ° as observed in the [Li _1/3 Mn _2/3 ] O ₂ type monoclinic crystal was observed. However, in Comparative Examples 1 to 11 and 19 to 32 in which the value of x is 1/3 or less, an α-NaFeO ₂ type hexagonal crystal structure was confirmed, but the peak height of the maximum intensity on the X-ray diffraction diagram. As long as is made full scale, a diffraction peak observed in a monoclinic crystal of Li [Li _1/3 Mn _2/3 ] O ₂ type was not clearly observed. Further, as shown in Table 1, the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of the diffraction peak between the (003) plane and the (104) plane of the active material before charging and discharging was 1.43 or more. However, some of them were 1.56 or less.

(Comparative Examples 41 and 42)
Implementation was performed except that the composition of the transition metal element contained in the coprecipitated hydroxide precursor and the amount of lithium hydroxide mixed were changed in accordance with the composition formula shown in LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ In the same manner as in Example 1, active materials according to Comparative Examples 41 and 42 were synthesized.
Here, Comparative Example 41 and Comparative Example 42 differ only in the setting values of the charging voltage under the test conditions described later (Comparative Example 41: 4.6 V, Comparative Example 42: 4.3 V), and are the same as the active material. It is.

(Comparative Example 43)
In place of the coprecipitated hydroxide precursor powder, the element ratio of each powder of LiOH.H ₂ O, Co (OH) ₂ , Ni (OH) ₂ and MnOOH is Li: Co: Ni: Co = 1: 0. .33: 0.33: The active material according to Comparative Example 43 was synthesized in the same manner as in Example 1 except that the powder obtained by mixing so as to be 0.33: 0.33 was used. The obtained X-ray diffraction pattern was indistinguishable from Comparative Examples 1 and 42. However, as a result of EPMA observation, Co, Ni, and Mn were not uniformly distributed.

(Production and evaluation of lithium secondary battery)
Using each of the active materials of Examples 1 to 44 and Comparative Examples 1 to 43 as a positive electrode active material for a lithium secondary battery, lithium secondary batteries were produced by the following procedure, and battery characteristics were evaluated.

  An active material, acetylene black (AB) and polyvinylidene fluoride (PVdF) were mixed at a weight ratio of 85: 8: 7, and N-methylpyrrolidone was added as a dispersion medium and kneaded and dispersed to prepare a coating solution. In addition, PVdF converted into solid weight using the liquid by which solid content was melt | dissolved and disperse | distributed. The coating solution was applied to an aluminum foil current collector having a thickness of 20 μm to produce a positive electrode plate. In addition, the electrode weight and thickness were standardized so that it might become the same test conditions in all the batteries.

  As the counter electrode, lithium metal was used as the negative electrode for the purpose of observing the single behavior of the positive electrode. Lithium metal was adhered to the nickel foil current collector. However, the lithium secondary battery was prepared so that the capacity of the lithium secondary battery was sufficiently regulated.

The electrolytic solution used was LiPF ₆ dissolved in a mixed solvent having an EC / EMC / DMC volume ratio of 6: 7: 7 to a concentration of 1 mol / l. As the separator, a microporous membrane made of polypropylene whose surface was modified with polyacrylate to improve electrolyte retention was used. Moreover, what attached lithium metal foil to the nickel plate was used as a reference electrode. A metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) is used for the exterior body, and the open ends of the positive electrode terminal, the negative electrode terminal, and the reference electrode terminal are exposed externally. The electrodes were housed in such a way that the fusion allowance where the inner surfaces of the metal resin composite film faced each other was hermetically sealed except for the portions to be the injection holes.

  The lithium secondary battery produced as described above was subjected to an initial charge / discharge process of 5 cycles at 20 ° C. All voltage control was performed on the positive electrode potential. Charging was performed at a constant current and a constant voltage with a current of 0.1 ItA and a voltage of 4.5 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 ItA and a final voltage of 2.0V. In all cycles, a 30 minute rest period was set after charging and discharging. FIG. 9 shows the behavior of the first two cycles in this initial charge / discharge process. FIGS. 9A and 9B correspond to Example 6 (AT17) and Comparative Example 4 (AT11), respectively.

  Subsequently, a charge / discharge cycle test was performed. All voltage control was performed on the positive electrode potential. The conditions of the charge / discharge cycle test are the same as the conditions of the initial charge / discharge step except that the charge voltage is 4.3 V (vs. Li / Li +) (only Comparative Example 41 is 4.6 V). In all cycles, a 30 minute rest period was set after charging and discharging. The amount of electricity discharged at the fifth cycle in this charge / discharge cycle test was recorded as “discharge capacity (mAh / g)”. A representative charge / discharge curve at the fifth cycle in this charge / discharge cycle test is shown in FIG.

  In addition, the percentage of the discharge electricity amount at the 10th cycle in this charge / discharge cycle test with respect to the “discharge capacity (mAh / g)” was determined and used as “capacity maintenance ratio (%)”.

  About the active material of Examples 1-44 and Comparative Examples 1-40, the powder X-ray-diffraction measurement using a Cu (K (alpha)) tube was performed after charging / discharging similarly to before charging / discharging. The X-ray diffraction patterns of the active material of Example 7 (AT18) and the active material of Example 16 (AT33) before charging / discharging (synthetic sample), at the end of charging and at the end of charging are shown in FIGS. 11 and 12, respectively.

Tables 1 and 2 show the results of battery tests on the active materials of Examples 1 to 44 and Comparative Examples 1 to 40 (excluding the capacity retention rate). Moreover, the value of the discharge capacity is plotted on a Li [Li _1/3 Mn _2/3 ] O ₂ (x) -LiNi _1/2 Mn _1/2 O ₂ (y) -LiCoO ₂ (z) system triangular phase diagram. As shown in FIG.

As can be seen from the results of Tables 1 and 2, and (x, y, z), point A (0.45, 0.55, 0: corresponding to the composition of AT66), point B (0.63) , 0.37,0: corresponding to the composition of AT58), point C (0.7, 0.25, 0.05: corresponding to the composition of AT81), point D (0.67, 0.18, 0.15) : Corresponding to the composition of AT30), point E (0.75, 0, 0.25: corresponding to the composition of AT73), point F (0.55, 0, 0.45: corresponding to the composition of AT78), and point Use the active material of Examples 1 to 44 satisfying the value of the range existing on or inside the heptagon ABCDEFG with G (0.45, 0.2, 0.35: corresponding to the composition of AT14) as the apex To provide a lithium secondary battery having a large discharge capacity of 177 mAh / g or more in a potential region of 4.3 V or less. It could be. What used the active material of Comparative Examples 1-40 which is outside said range was 176 mAh / g or less. In particular, the more specific range (x, y, z) corresponds to point H (0.6, 0.4, 0: corresponding to the composition of AT19), point I (0.67, 0.13, 0). .2: corresponding to the composition of AT28), point J (0.7, 0, 0.3: corresponding to the composition of AT33), and point K (0.55, 0.05, 0.4: corresponding to the composition of AT71) In the case of using an active material that satisfies the value of the range existing on or inside the quadrilateral HIJK with the vertex (corresponding) (Examples 5 to 8, Examples 11, 12, 16, 25 to 30, 36), A lithium secondary battery having a large discharge capacity of 198 mAh / g or more in a potential region of 4.3 V or less could be obtained.
Further, for LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , when the charging potential was 4.6 V as in Comparative Example 41, the discharge capacity was 181 mAh / g. When the charging potential is 4.3 V as in 42, the discharge capacity is 149 mAh / g. Therefore, the value of the discharge capacity of the active material of the present invention is Li [Co _1-2x Ni _x Mn _x ] O ₂ (0 ≦ x ≦ 1/2) and higher than the LiNiO ₂ system, which has been represented as a high capacity system.

As shown in Table 1, the active material of the present invention has a diffraction peak intensity ratio of I ₍₀₀₃₎ / I ₍₁₀₄₎ ≧ 1.56 before charge / discharge, and I ₍₀₀₃₎ at the end of discharge. Since / I ₍₁₀₄₎ > 1 is greater than I ₍₀₀₃₎ / I ₍₁₀₄₎ > 1.3, and the change in the intensity ratio at the end of discharge is within 26% before charge and discharge, It is suggested that the transition metal is not mixed into the Li layer during charge / discharge, and in this respect, conventional Li [Li _1/3 Mn _2/3 ] O ₂ (x) -LiNi _1/2 Mn _1/2 O _This is clearly distinguished from a ₂ (y) -LiCoO ₂ (z) -based active material.

  Moreover, about the capacity | capacitance maintenance factor, although the lithium secondary battery using the active material of Examples 1-44 was almost 100%, the lithium secondary battery using the active material of Comparative Examples 41, 42, and 43 was , 89%, 98% and 80%, respectively, the lithium secondary battery according to the present invention is extremely excellent in terms of charge / discharge cycle performance.

Claims (10)

A manufacturing method for manufacturing a lithium secondary battery employing a charging method in which the maximum potential of the positive electrode during charging is 4.3 V (vs. Li ^/ Li ⁺ ) or less, comprising α-NaFeO ₂ type crystals The composition ratio of Li, Co, Ni, and Mn contained in the solid solution includes a solid solution of a lithium transition metal composite oxide having a structure, and Li _{1+ (1/3) x} Co _1-xy Ni _{(1/2 ) Y} Mn _{(2/3) x + (1/2) y} (x + y ≦ 1, 0 ≦ y, 1-xy = z), Li [Li _1/3 Mn _2/3 ] O ₂ (x ) -LiNi _1/2 Mn _1/2 O ₂ (y) -LiCoO ₂ (z) In the triangular phase diagram, (x, y, z) is a point A (0.45, 0.55, 0), Point B (0.63, 0.37, 0), Point C (0.7, 0.25, 0.05), Point D (0.67, 0.18, 0.15) ), Point E (0.75, 0, 0.25), point F (0.55, 0, 0.45), and point G (0.45, 0.2, 0.35) as vertices A lithium secondary battery using an active material represented by a value in a range existing on or inside the heptagon ABCDEFG and having a positive electrode exceeding 4.3 V (vs. Li ^/ Li ⁺ ) Lithium secondary characterized in that it includes a step of charging at least to a relatively flat region in which a potential change that appears with respect to the amount of charge is in a positive electrode potential range of 4.8 V or less (vs. Li ^/ Li ⁺ ). Battery manufacturing method. The potential change that appears with respect to the amount of charge in the positive electrode potential range of above 4.3 V (vs. Li ^/ Li ⁺ ) and below 4.8 V (vs. Li ^/ Li ⁺ ) reaches at least a relatively flat region. The method for manufacturing a lithium secondary battery according to claim 1, wherein the charging is charging in an initial charging / discharging process. 3. The lithium secondary battery according to claim 1, wherein the lithium secondary battery has a dischargeable amount of electricity of 177 mAh / g or more in a potential region of 4.3 V (vs. Li / Li ⁺ ) or less. A method for manufacturing a secondary battery.   In the active material, the above (x, y, z) is point H (0.6, 0.4, 0), point I (0.67, 0.13, 0.2), point J (0. (7, 0, 0.3) and a point K (0.55, 0.05, 0.4), which is represented by a value in a range existing on or inside a quadrilateral HIJK having a vertex. Item 4. The method for producing a lithium secondary battery according to any one of Items 1 to 3. 5. The lithium secondary battery according to claim 4, wherein the lithium secondary battery has a dischargeable electric capacity of 200 mAh / g or more in a potential region of 4.3 V (vs. Li / Li ⁺ ) or less. Manufacturing method. When the solid solution of the lithium transition metal composite oxide was subjected to X-ray diffraction measurement using CuKα rays, the Li [Li _1/3 Mn _2/3 ] O ₂ type was formed in the vicinity of 20 to 30 ° before charging and discharging. A diffraction peak observed in a monoclinic crystal is observed, and the intensity of the diffraction peak is about 4 to 7% with respect to the intensity of the diffraction peak of the (003) plane. The manufacturing method of the lithium secondary battery of any one of these. In the solid solution of the lithium transition metal composite oxide, the intensity ratio of the diffraction peaks of the (003) plane and the (104) plane by X-ray diffraction measurement is I ₍₀₀₃₎ / I ₍₁₀₄₎ ≧ 1.56 before charge / discharge. The method for producing a lithium secondary battery according to claim 1, wherein I ₍₀₀₃₎ / I ₍₁₀₄₎ > 1 at the end of discharge. 8. The solid solution of the lithium transition metal composite oxide according to any one of claims 1 to 7, wherein the valence of each of the constituent elements is Li1 ⁺ , Co3 ⁺ , Ni2 ⁺ , Mn4 ^+. The manufacturing method of the lithium secondary battery as described.   The manufacturing method of the lithium secondary battery of any one of Claims 1-8 including the process of manufacturing the solid solution of the said lithium transition metal complex oxide using a coprecipitation method.   The step of producing a solid solution of the lithium transition metal composite oxide using a coprecipitation method comprises the step of producing a precursor by coprecipitation of a compound containing Co, Ni and Mn in a solution, and the precursor, The manufacturing method of the lithium secondary battery of Claim 9 including the process of mixing and baking a lithium compound.