JP2016181500A - Positive electrode active material for nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for a nonaqueous electrolyte secondary battery, which enables the materialization of a nonaqueous electrolyte secondary battery having a high energy density and a high output characteristic.SOLUTION: A positive electrode active material for a nonaqueous electrolyte secondary battery comprises a lithium transition metal composite oxide expressed by the following general formula: Li(NiCr)(MnTi)MgAlMO(where 1.00≤a≤1.30, 0.020≤x≤0.200, 0.006≤y≤0.070, 0.450≤α≤0.550, 0≤β≤0.015, 0≤γ≤0.035, 0≤δ≤0.010, and M represents at least one element selected from a group consisting of Na, K, Ca, Sr, Ba, Ga, Co, Zn, Si, Ge, Zr, Hf, Sn, Ta, Nb, P, Bi, Mo and W).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery.

  In recent years, portable devices such as mobile phones and notebook computers have been reduced in size and functionality, and non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been adopted as drive power sources for these devices. Since the non-aqueous electrolyte secondary battery has a high operating voltage, it has the advantage of higher energy density than other secondary batteries. Based on this advantage, there is a movement to apply non-aqueous electrolyte secondary batteries to larger equipment such as electric vehicles.

As a positive electrode active material for a non-aqueous electrolyte secondary battery, lithium cobaltate (LiCoO ₂ ) is typically put into practical use. The average operating voltage of a non-aqueous electrolyte secondary battery using a lithium transition metal composite oxide having a layered structure such as lithium cobaltate as a positive electrode active material is about 3.5V. On the other hand, when a lithium transition metal composite oxide having a spinel structure such as lithium manganate (LiMn ₂ O ₄ ) is used as the positive electrode active material, a non-aqueous electrolyte secondary battery having an average operating voltage of 4 V or more can be obtained. In particular, when LiNi _0.5 Mn _1.5 O ₄ is used, the average operating voltage is about 4.5V.

  In these lithium transition metal composite oxides having a spinel structure, there is a technique in which a part of manganese is replaced with nickel and another element depending on the purpose.

  Patent Document 1 discloses a technique in which a part of manganese in a spinel structure lithium manganese composite oxide is replaced with nickel or the like and titanium or the like for the purpose of increasing the energy density of the secondary battery.

  Patent Document 2 discloses a technique in which a part of manganese in a spinel structure lithium manganese composite oxide is replaced with nickel, chromium, magnesium, or the like for the purpose of improving the cycle characteristics of a secondary battery.

Patent Document 3 discloses a technique in which lithium nickel manganese oxide having a specific surface area in a specific range is used for a positive electrode for the purpose of preventing a capacity decrease during rapid charging in a secondary battery using lithium titanium oxide as a negative electrode. ing. As an example of the lithium-nickel-manganese _{oxide, LiNi 0.4 Cr 0.05 Al 0.05 Mn} 1.4 Ti 0.1 O 4 is described.

JP 2003-197194 A International Publication No. 2012/077472 JP 2012-033279 A

  High energy density and high output characteristics are required at the same time for the power source of large equipment such as electric vehicles. Since the lithium transition metal composite oxide having a spinel structure has a high average operating voltage, a secondary battery having a high energy density can be realized. On the other hand, a lithium transition metal composite oxide having a spinel structure tends to have insufficient output characteristics because of relatively low lithium ion conductivity and electronic conductivity. This tendency is more remarkable in the lithium nickel manganese composite oxide having a spinel structure.

  The embodiment according to the present invention has been made in view of the above circumstances. An object of an embodiment according to the present invention is a non-aqueous electrolyte secondary battery using a lithium nickel manganese composite oxide having a spinel structure, which has high lithium ion conductivity and high electron conductivity and can improve output characteristics. It is to provide a positive electrode active material for use.

  In order to achieve the above object, the present inventors have conducted intensive studies and have completed an embodiment according to the present invention. The present inventors include chromium and titanium in a lithium nickel manganese composite oxide having a spinel structure, and further limiting the contents of magnesium and aluminum to a certain amount or less, thereby reducing the lithium of the spinel structure lithium nickel manganese composite oxide. It has been found that ion conductivity and electron conductivity can be improved.

The positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention has a general formula Li _a (Ni _1-x Cr _x ) _α (Mn _1-y Ti _y ) _{2-α-β-γ-δ} Mg _β Al _γ M _δ O ₄ (where 1.00 ≦ a ≦ 1.30, 0.020 ≦ x ≦ 0.200, 0.006 ≦ y ≦ 0.070, 0.450 ≦ α ≦ 0.550, 0 ≦ β ≦ 0.015, 0 ≦ γ ≦ 0.035, 0 ≦ δ ≦ 0.010, M is Na, K, Ca, Sr, Ba, Ga, Co, Zn, Si, Ge, Zr, Hf, A lithium transition metal composite oxide represented by at least one element selected from the group consisting of Sn, Ta, Nb, P, Bi, Mo, and W.

  According to the present embodiment, a positive electrode active material using a lithium nickel manganese composite oxide having a spinel structure that has high lithium ion conductivity and high electronic conductivity and can improve output characteristics is provided. Moreover, the non-aqueous electrolyte secondary battery using the positive electrode active material for non-aqueous electrolyte secondary batteries of this embodiment has a high average operating voltage and high output characteristics. Therefore, the nonaqueous electrolyte secondary battery using the positive electrode active material for a nonaqueous electrolyte secondary battery of the present embodiment can achieve both high energy density and high output characteristics.

FIG. 1 shows the relationship between the amount of magnesium contained in a lithium nickel manganese composite oxide having a spinel structure and the characteristics of a non-aqueous electrolyte secondary battery using the lithium nickel manganese composite oxide having the spinel structure as a positive electrode active material. It is a graph showing. FIG. 1 shows the relationship between the amount of aluminum contained in a spinel-structure lithium nickel manganese composite oxide and the characteristics of a non-aqueous electrolyte secondary battery using the spinel-structure lithium nickel manganese composite oxide as a positive electrode active material. It is a graph showing.

  The positive electrode active material for a non-aqueous electrolyte secondary battery of the present embodiment will be described using the embodiments and examples. However, this embodiment is not limited by these embodiments and examples.

[Positive electrode active material for non-aqueous electrolyte secondary battery]
The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present embodiment is mainly composed of a lithium nickel manganese composite oxide having a spinel structure containing chromium and titanium and further containing magnesium and aluminum limited to a certain amount or less. And Hereinafter, the positive electrode active material for a non-aqueous electrolyte secondary battery is also simply referred to as a positive electrode active material. The lithium nickel manganese composite oxide having the spinel structure is also simply referred to as a lithium transition metal composite oxide. In the positive electrode active material, the content of the lithium transition metal composite oxide is greater than 50% by mass. The content of the lithium transition metal composite oxide is preferably 60% by mass or more, and more preferably 80% by mass or more. Hereinafter, the lithium transition metal composite oxide will be described.

(Lithium transition metal composite oxide)
The composition of the lithium transition metal composite oxide is represented by the general formula _{Li a (Ni 1-x Cr} x) α (Mn 1-y Ti y) 2-α-β-γ-δ Mg β Al γ M δ O 4 ( However, 1.00 ≦ a ≦ 1.30, 0.020 ≦ x ≦ 0.200, 0.006 ≦ y ≦ 0.070, 0.450 ≦ α ≦ 0.550, 0 ≦ β ≦ 0.015, 0 ≦ γ ≦ 0.035, 0 ≦ δ ≦ 0.010, M is Na, K, Ca, Sr, Ba, Ga, Co, Zn, Si, Ge, Zr, Hf, Sn, Ta, Nb, P, At least one element selected from the group consisting of Bi, Mo and W).

  The variable a in the general formula satisfies 1.00 ≦ a ≦ 1.30. If the variable a is less than 1.00, the output characteristics of the nonaqueous electrolyte secondary battery are not improved. When the variable a exceeds 1.30, the synthesis of the lithium transition metal composite oxide tends to be difficult. The variable a preferably satisfies 1.10 ≦ a ≦ 1.20.

  The variable α in the above general formula is such that the ratio between the amount of nickel site material occupied by nickel atoms and chromium atoms and the amount of manganese site material occupied by manganese atoms and titanium atoms is close to 1: 3. Adjust so that That is, the variable α satisfies 0.450 ≦ α ≦ 0.550. When the variable α satisfies the above range, the average operating voltage of the non-aqueous electrolyte secondary battery can be about 4.6V. The variable α preferably satisfies 0.480 ≦ α ≦ 0.520.

The variable β satisfies 0 ≦ β ≦ 0.015. FIG. 1 shows a general formula Li _1.11 (Ni _0.817 Cr _0.183 ) _α (Mn _0.965 Ti _0.035 ) _2-α-β Mg _β O ₄ (in the general formula, a = 1.11, x = 0.183, y = 0.035, γ = 0, δ = 0, and α / (2-α-β-γ-δ) = 0.37). The relationship of variable (beta), energy density (rho) _E, and direct current | flow internal resistance R (25) in 25 degreeC in the nonaqueous electrolyte secondary battery using an oxide is shown. The same tendency is exhibited by lithium transition metal composite oxides having different variables a, x, y, α, γ, and δ. As can be seen from FIG. 1, ρ _E has been drastically reduced from around the variable β exceeding 0.015, and R (25) is 1.20Ω from around the variable β exceeding 0.030. It can be seen that the output characteristics are very deteriorated. The variable β is preferably as small as possible, and more preferably β = 0.

The variable γ satisfies 0 ≦ γ ≦ 0.035. FIG. 2 shows a general formula Li _1.10 (Ni _0.817 Cr _0.183 ) _α (Mn _0.965 Ti _0.035 ) _2-α-γ Al _γ O ₄ (in the general formula, a = 1.10, x = 0.183, y = 0.035, β = 0, δ = 0, and α / (2-α-β-γ-δ) = 0.37). This shows the relationship between the variable γ, the energy density ρ _E and the DC internal resistance R (−25) at −25 ° C. in a non-aqueous electrolyte secondary battery using an oxide. The same tendency is exhibited by lithium transition metal composite oxides having different variables a, x, y, α, β and δ. As can be seen from FIG. 2, ρ _E has fallen drastically from around the variable γ exceeding 0.040, and R (−25) is 8.5Ω from around the variable γ exceeding 0.035. It can be seen that the output characteristics are extremely deteriorated. The smaller the variable γ is, the more preferable it is, it is more preferable to satisfy 0 ≦ γ ≦ 0.010, and it is particularly preferable that γ = 0. Moreover, it is preferable that γ and δ satisfy 0 ≦ γ + δ ≦ 0.010.

  The variable x satisfies 0.020 ≦ x ≦ 0.200. The variable y satisfies 0.006 ≦ y ≦ 0.070. When the variable x and the variable y satisfy the above ranges, the oxidation-reduction reaction at the nickel site is easily performed, and as a result, the output characteristics of the nonaqueous electrolyte secondary battery are improved. When x exceeds 0.200 or y exceeds 0.070, the charge / discharge capacity of the nonaqueous electrolyte secondary battery decreases. In addition, the average operating voltage of the nonaqueous electrolyte secondary battery can be reduced. The variable x preferably satisfies 0.050 ≦ x ≦ 0.150. The variable y preferably satisfies 0.015 ≦ y ≦ 0.045.

  Further, it is preferable to adjust the ratio of the amount of chromium atoms at the nickel site to the amount of titanium atoms at the manganese site to be close to 1: 1 because the mass energy density of the nonaqueous electrolyte secondary battery is improved. That is, it is preferable that the variables α, β, γ, δ, x, and y satisfy 0.85 ≦ (x · α) / {y · (2-α-β-γ-δ)} ≦ 1.15. .

(Element M)
The lithium transition metal composite oxide may contain another element M depending on the purpose. Examples of the element M include Na, K, Ca, Sr, Ba, Ga, Co, Zn, Si, Ge, Zr, Hf, Sn, Ta, Nb, P, Bi, Mo, and W. The element M may be one kind of element or two or more kinds of elements. The variable δ satisfies 0 ≦ δ ≦ 0.010. If δ exceeds 0.010, the output characteristics or the average operating voltage may be reduced.

(Optional component)
In addition to the lithium transition metal composite oxide, the positive electrode active material may contain inevitable impurities mixed in the manufacturing process, a trace amount of additives depending on the purpose, and the like.

[Method for producing positive electrode active material]
As a method for producing the positive electrode active material, a known method for producing a positive electrode active material can be appropriately used. For example, a raw material compound that decomposes into an oxide at high temperature is mixed in accordance with the target composition, a raw material compound that is soluble in a solvent is dissolved in the solvent, and the precursor is precipitated by adjusting the temperature, adjusting the pH, adding a complexing agent, etc. Can be obtained by a method including a step of appropriately adjusting a raw material mixture, and a step of firing the obtained raw material mixture at an appropriate temperature. Hereinafter, the step of adjusting the raw material mixture is also referred to as “mixing step”, and the step of baking is also referred to as “baking step”.

<Mixing process>
In the mixing step, a raw material compound that decomposes into an oxide at a high temperature is mixed in accordance with the target composition to obtain a raw material mixture, or a raw material compound that is soluble in a solvent is dissolved in a solvent to adjust temperature and pH. In this step, the precursor is precipitated by adding a complexing agent to obtain a raw material mixture. The raw material component of the positive electrode active material of this embodiment is obtained by the mixing step.

  A raw material compound will not be specifically limited if it is a compound decomposed | disassembled into an oxide at high temperature. Examples of the raw material compound include a lithium compound, a nickel compound, a manganese compound, a chromium compound, and a titanium compound, and these can be oxides, carbonates, hydroxides, nitrates, sulfates, and the like.

  The mixing ratio of the raw material compounds is not particularly limited, but is preferably a mixing ratio that satisfies the content of each element in the general formula.

<Baking process>
The firing step is a step of firing the raw material mixture to obtain a fired product. Moreover, the baked product which is a positive electrode active material of this embodiment is obtained by a baking process.

  Although the firing time varies depending on the firing temperature, there is usually no problem if it is 5 hours or longer. Although there is no particular problem if the firing time is long, usually 48 hours is sufficient.

  The firing atmosphere is not particularly limited, but an oxidizing atmosphere is preferable. Examples of the oxidizing atmosphere include an air atmosphere and an oxygen-containing atmosphere.

  Hereinafter, the present embodiment will be described more specifically using examples. However, the present embodiment is not limited to these examples. In addition, when expressing the ratio of an element, it represents with a substance amount ratio.

Example 1
A composite oxide of Ni: Mn = 23.7: 76.3 was obtained by the coprecipitation method. This composite oxide is mixed with lithium carbonate, chromium oxide (III) and titanium oxide (IV) so that Li: (Ni + Mn): Cr: Ti = 1.10: 1.900: 0.050: 0.050. To obtain a mixed raw material. The obtained mixed raw material was fired at 900 ° C. for 11 hours in the atmosphere to obtain a sintered body. The obtained sintered body was pulverized and passed through a dry sieve to obtain a lithium transition metal composite oxide represented by the general formula Li _1.10 Ni _0.450 Cr _0.050 Mn _1.450 Ti _0.050 O _4. It was.

(Comparative Example 1)
Ni: Mn = 25.0: using a composite oxide of 75.0, a mixed raw material chromium oxide (III), in the same manner as in Example 1 except for not mixing titanium oxide (IV) is performed, the general formula _{Li 1.10} A lithium transition metal composite oxide represented by Ni _0.500 Mn _1.500 O ₄ was obtained.

(Comparative Example 2)
This was performed in the same manner as in Example 1 except that a composite oxide of Ni: Mn = 23.1: 76.9 was used, and titanium oxide (IV) was not mixed into the mixed raw material, and the general formula Li _1.10 Ni _0.450 Cr ₀ A lithium transition metal composite oxide represented by _0.050 Mn _1.500 O ₄ was obtained.

(Comparative Example 3)
Using a composite oxide of Ni: Mn = 25.6: 74.4 and performing the same procedure as in Example 1 except that chromium (III) oxide is not mixed into the mixed raw material, the general formula Li _1.10 Ni _0.500 Mn ₁ A lithium transition metal composite oxide represented by _.450 Ti _0.050 O ₄ was obtained.

(Example 2)
A composite oxide of Ni: Mn = 23.7: 76.3 was obtained by the coprecipitation method. This composite oxide is mixed with lithium carbonate, chromium oxide (III) and titanium oxide (IV) so that Li: (Ni + Mn): Cr: Ti = 1.09: 1.850: 0.099: 0.050 To obtain a mixed raw material. The obtained mixed raw material was fired at 900 ° C. for 11 hours in the atmosphere to obtain a sintered body. The obtained sintered body is pulverized and subjected to dry sieving to obtain a lithium transition metal composite oxide represented by the general formula Li _1.09 Ni _0.439 Cr _0.099 Mn _1.411 Ti _0.050 O _4. It was.

Example 3
A composite oxide of Ni: Mn = 23.8: 76.2 was obtained by the coprecipitation method. Lithium carbonate, chromium oxide (III), titanium oxide (IV) and magnesium carbonate were mixed with this composite oxide, Li: (Ni + Mn): Cr: Ti: Mg = 1.12: 1.838: 0.097: 0. .050: 0.015 to obtain a mixed raw material. The obtained mixed raw material was fired at 900 ° C. for 11 hours in the atmosphere to obtain a sintered body. The obtained sintered body was pulverized, passed through a dry sieve, and a lithium transition metal composite represented by the general formula Li _1.12 Ni _0.438 Cr _0.097 Mn _1.400 Ti _0.050 Mg _0.015 O ₄ An oxide was obtained.

(Comparative Example 4)
A composite oxide of Ni: Mn = 23.7: 76.3 was obtained by the coprecipitation method. Lithium carbonate, chromium oxide (III), titanium oxide (IV), and magnesium carbonate were mixed with this composite oxide, and Li: (Ni + Mn): Cr: Ti: Mg = 1.10: 1.832: 0.098: 0. .050: 0.020 to obtain a mixed raw material. The obtained mixed raw material was fired at 900 ° C. for 11 hours in the atmosphere to obtain a sintered body. The obtained sintered body was pulverized, passed through a dry sieve, and a lithium transition metal composite represented by the general formula Li _1.10 Ni _0.435 Cr _0.098 Mn _1.397 Ti _0.050 Mg _0.020 O ₄ An oxide was obtained.

(Comparative Example 5)
A composite oxide of Ni: Mn = 23.7: 76.3 was obtained by the coprecipitation method. Lithium carbonate, chromium oxide (III), titanium oxide (IV) and magnesium carbonate were mixed with this composite oxide, Li: (Ni + Mn): Cr: Ti: Mg = 1.10: 1.828: 0.098: 0. .050: 0.024 to obtain a mixed raw material. The obtained mixed raw material was fired at 900 ° C. for 11 hours in the atmosphere to obtain a sintered body. The obtained sintered body was pulverized, passed through a dry sieve, and a lithium transition metal composite represented by the general formula Li _1.10 Ni _0.434 Cr _0.098 Mn _1.394 Ti _0.050 Mg _0.024 O ₄ An oxide was obtained.

(Comparative Example 6)
A composite oxide of Ni: Mn = 23.9: 76.1 was obtained by the coprecipitation method. Lithium carbonate, chromium oxide (III), titanium oxide (IV) and magnesium carbonate were mixed with this composite oxide, Li: (Ni + Mn): Cr: Ti: Mg = 1.11: 1.815: 0.098: 0. .051: 0.036 to obtain a mixed raw material. The obtained mixed raw material was fired at 900 ° C. for 11 hours in the atmosphere to obtain a sintered body. The obtained sintered body was pulverized, passed through a dry sieve, and a lithium transition metal composite represented by the general formula Li _1.11 Ni _0.434 Cr _0.098 Mn _1.381 Ti _0.051 Mg _0.036 O ₄ An oxide was obtained.

Example 4
A composite oxide of Ni: Mn = 23.6: 76.4 was obtained by the coprecipitation method. Lithium carbonate, chromium oxide (III), titanium oxide (IV) and aluminum oxide were mixed with this composite oxide, Li: (Ni + Mn): Cr: Ti: Al = 1.10: 1.833: 0.097: 0. .050: 0.020 to obtain a mixed raw material. The obtained mixed raw material was fired at 900 ° C. for 11 hours in the atmosphere to obtain a sintered body. The obtained sintered body was pulverized, passed through a dry sieve, and a lithium transition metal composite represented by the general formula Li _1.10 Ni _0.433 Cr _0.097 Mn _1.400 Ti _0.050 Al _0.020 O ₄ An oxide was obtained.

(Example 5)
A composite oxide of Ni: Mn = 23.7: 76.3 was obtained by the coprecipitation method. Lithium carbonate, chromium oxide (III), titanium oxide (IV) and aluminum oxide were mixed with this composite oxide, Li: (Ni + Mn): Cr: Ti: Al = 1.10: 1.825: 0.097: 0. .050: 0.028 to obtain a mixed raw material. The obtained mixed raw material was fired at 900 ° C. for 11 hours in the atmosphere to obtain a sintered body. The obtained sintered body was pulverized, passed through a dry sieve, and a lithium transition metal composite represented by the general formula Li _1.10 Ni _0.433 Cr _0.097 Mn _1.392 Ti _0.050 Al _0.028 O ₄ An oxide was obtained.

(Example 6)
A composite oxide of Ni: Mn = 23.7: 76.3 was obtained by the coprecipitation method. Lithium carbonate, chromium oxide (III), titanium oxide (IV), and aluminum oxide were mixed with this composite oxide, Li: (Ni + Mn): Cr: Ti: Al = 1.10: 1.721: 0.097: 0. .050: 0.032 to obtain a mixed raw material. The obtained mixed raw material was fired at 900 ° C. for 11 hours in the atmosphere to obtain a sintered body. The obtained sintered body was pulverized, passed through a dry sieve, and a lithium transition metal composite represented by the general formula Li _1.10 Ni _0.432 Cr _0.097 Mn _1.389 Ti _0.050 Al _0.032 O ₄ An oxide was obtained.

(Comparative Example 7)
A composite oxide of Ni: Mn = 23.7: 76.3 was obtained by the coprecipitation method. Lithium carbonate, chromium oxide (III), titanium oxide (IV) and aluminum oxide were mixed with this composite oxide, Li: (Ni + Mn): Cr: Ti: Al = 1.10: 1.817: 0.097: 0. 049: 0.037 to obtain a mixed raw material. The obtained mixed raw material was fired at 900 ° C. for 11 hours in the atmosphere to obtain a sintered body. The resulting pulverized sintered body, subjected to dry sieving, the lithium transition metal composite represented by the general formula _{Li 1.10 Ni 0.431 Cr 0.097 Mn 1.386} Ti 0.049 Al 0.037 O 4 An oxide was obtained.

(Comparative Example 8)
A composite oxide of Ni: Mn = 23.7: 76.3 was obtained by the coprecipitation method. Lithium carbonate, chromium oxide (III), titanium oxide (IV), and aluminum oxide were mixed with this composite oxide. Li: (Ni + Mn): Cr: Ti: Al = 1.10: 1.810: 0.097: 0 049: 0.044 to obtain a mixed raw material. The obtained mixed raw material was fired at 900 ° C. for 11 hours in the atmosphere to obtain a sintered body. The obtained sintered body was pulverized, passed through a dry sieve, and a lithium transition metal composite represented by the general formula Li _1.10 Ni _0.429 Cr _0.097 Mn _1.381 Ti _0.049 Al _0.044 O ₄ An oxide was obtained.

(Comparative Example 9)
A composite oxide of Ni: Mn = 23.7: 76.3 was obtained by the coprecipitation method. Lithium carbonate, chromium oxide (III), titanium oxide (IV) and aluminum oxide were mixed with this composite oxide, Li: (Ni + Mn): Cr: Ti: Al = 1.10: 1.789: 0.096: 0. 049: 0.066 to obtain a mixed raw material. The obtained mixed raw material was fired at 900 ° C. for 11 hours in the atmosphere to obtain a sintered body. The obtained sintered body was pulverized, passed through a dry sieve, and a lithium transition metal composite represented by the general formula Li _1.10 Ni _0.424 Cr _0.096 Mn _1.365 Ti _0.049 Al _0.066 O ₄ An oxide was obtained.

(Example 7)
A composite oxide of Ni: Mn = 23.7: 76.3 was obtained by the coprecipitation method. Lithium carbonate, chromium oxide (III), titanium oxide (IV) and zirconium oxide were mixed with this composite oxide, Li: (Ni + Mn): Cr: Ti: Zr = 1.10: 1.894: 0.050: 0 .050: 0.006 to obtain a mixed raw material. The obtained mixed raw material was fired at 900 ° C. for 11 hours in the atmosphere to obtain a sintered body. The obtained sintered body was pulverized, passed through a dry sieve, and a lithium transition metal composite represented by the general formula Li _1.10 Ni _0.449 Cr _0.050 Mn _1.445 Ti _0.050 Zr _0.006 O ₄ An oxide was obtained.

[Output characteristics evaluation]
The internal resistances of the nonaqueous electrolyte secondary batteries using the lithium transition metal composite oxides obtained in Examples 1 to 7 and Comparative Examples 1 to 9 as the positive electrode active materials were determined. Low internal resistance means good output characteristics.

(1. Production of positive electrode)
A positive electrode paste was obtained by kneading 90% by mass of a positive electrode active material, 5% by mass of carbon powder, and 5% by mass of an N-methylpyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF) (5% by mass as PVDF). The obtained positive electrode paste was applied to a current collector made of an aluminum foil, dried and rolled to obtain a positive electrode.

(2. Production of negative electrode)
Lithium titanate was used as the negative electrode active material. A negative electrode active material 97.5% by mass, carboxymethylcellulose (CMC) 1.5% by mass, and styrene butadiene rubber (SBR) 1.0% by mass were dispersed in pure water and kneaded to obtain a negative electrode paste. The obtained negative electrode paste was applied to a current collector made of copper foil, dried and rolled to obtain a negative electrode.

(3. Preparation of non-aqueous electrolyte)
Ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed at a volume ratio of 3: 7 to obtain a mixed solvent. Lithium hexafluorophosphate (LiPF ₆ ) was dissolved in the obtained mixed solvent so as to have a concentration of 1 mol / L to obtain a nonaqueous electrolytic solution.

(4. Separator)
A porous polyethylene film was used as a separator.

(5. Production of secondary battery)
Lead electrodes were attached to the positive and negative electrode current collectors, respectively, and vacuum-dried at 120 ° C. After drying, a separator was placed between the positive electrode and the negative electrode, and these were stored in a bag-like laminate pack. After storing, vacuum drying was performed at 60 ° C. to remove moisture adsorbed on each member. After drying, a non-aqueous electrolyte was poured into the laminate pack and sealed to obtain a non-aqueous electrolyte secondary battery for evaluation. The obtained secondary battery was aged with a weak current, and the electrolyte was sufficiently applied to the positive electrode and the negative electrode. After aging, the secondary battery was placed in an environment at 25 ° C. and −25 ° C., and the DC internal resistance was measured.

(6. DC internal resistance measurement)
Constant current charging was performed up to a charge depth of 50% at a full charge voltage of 3.5V. After charging, pulse discharge with a specific current i was performed, and the voltage V at that time was measured. The pulse was 10 seconds and the interval between pulses was 3 minutes. V used the final value of each pulse. Each voltage V at i = 0.04A, 0.08A, 0.12A, 0.16A, 0.20A is plotted with current i on the horizontal axis and voltage V on the vertical axis, and approximate lines connecting the plots. Was the internal resistance R (T) at T ° C.

[Energy density evaluation]
The lithium transition metal composite oxides obtained in Examples 1 to 7 and Comparative Examples 1 to 9 were each used as the positive electrode active material, and the energy density of the secondary battery was evaluated in the following manner.

(1. Production of positive electrode)
A positive electrode was obtained in the same procedure as the secondary battery for output characteristic evaluation.

(2. Production of negative electrode)
Metallic lithium was molded into a thin sheet to obtain a negative electrode.

(3. Preparation of non-aqueous electrolyte)
An electrolytic solution was obtained in the same procedure as the secondary battery for output characteristic evaluation except that MEC was diethyl carbonate.

(4. Separator)
The same separator as the secondary battery for output characteristic evaluation was used.

(5. Production of secondary battery)
A lead electrode was attached to the positive electrode, and the positive electrode, the separator, and the negative electrode were sequentially accommodated in a container. The negative electrode is electrically connected to a stainless steel container bottom, and the container bottom serves as a negative electrode terminal. The separator was fixed by a container side made of Teflon (registered trademark). The tip of the positive lead electrode was led out of the container and used as a positive terminal. The positive and negative terminals were electrically insulated by the container side. After storage, the electrolyte was poured and sealed with a stainless steel container lid to obtain a sealed test battery. This was used for energy density evaluation.

(6. Discharge capacity measurement)
A unit that is discharged from the start to the end of discharge after a constant current and constant voltage charge at a full charge voltage of 5.0 V and a charge rate of 0.1 C, followed by a constant current discharge at a discharge voltage of 3.0 V and a discharge rate of 0.1 C. the charge per mass discharge capacity Q _d. Here, 1C means a current density at which discharge is completed in 1 hour from a fully charged state.

(7. Calculation of average operating voltage)
The time average of the operating voltage of the secondary battery at the time of discharge was calculated | required, and this was made into average operating voltage <E>.

(8. Calculation of energy density)
From Q _d and the product of <E>, calculates the energy [rho _E per unit mass taken out of the secondary battery, which was used as the energy density of the secondary battery.

  Table 1 shows the composition of the main component of the positive electrode active material and various battery characteristics for Examples 1 to 8 and Comparative Examples 1 to 10.

  Table 1 shows the following.

  The secondary battery using the positive electrode active material of Comparative Example 2 containing only chromium in the main component composition has output characteristics compared to the secondary battery using the positive electrode active material of Comparative Example 1 not containing chromium in the main component composition. Although improved, since R (25) exceeds 1.20Ω, it cannot be said that the output characteristics of the secondary battery using the positive electrode active material of Comparative Example 2 are still sufficiently good.

  The secondary battery using the positive electrode active material of Comparative Example 3 containing only titanium in the main component composition has deteriorated output characteristics as compared with the secondary battery using the positive electrode active material of Comparative Example 1.

  The secondary battery using the positive electrode active material of Example 1 containing both chromium and titanium in the main component composition has sufficiently improved output characteristics.

Cathode active material secondary battery using the comparative examples 4-6 to excessive containing magnesium as a main component composition, the energy density [rho _E is below the 620mWh / g, it can not be said that the energy density is good enough. Since the secondary battery using the positive electrode active material of Comparative Example 6 has R (25) exceeding 1.20Ω, it cannot be said that the output characteristics are sufficiently good. The range of the variable β with sufficiently good output characteristics and energy density of the secondary battery is about β = 0.015 or less. Further, the smaller the variable β, the better, and β = 0 is the best.

The secondary batteries using the positive electrode active materials of Comparative Examples 7 to 9 containing excess aluminum in the main component composition have sufficiently high output characteristics because R (−25) exceeds 8.5Ω. Absent. Cathode active material secondary battery using the comparative examples 8 and 9, [rho _E is below the 620mWh / g, an energy density not be also sufficiently good. The range of the variable γ with sufficiently good output characteristics and energy density of the secondary battery is about γ = 0.035 or less. Further, the smaller the variable γ is, the better, and γ = 0 is the best.

When the positive electrode active material for a non-aqueous electrolyte secondary battery of this embodiment is used, a non-aqueous electrolyte secondary battery having both high energy density and output characteristics can be obtained. The resulting nonaqueous electrolyte secondary battery is
It can be suitably used as a power source for large equipment such as electric vehicles.

Claims (4)

Formula _{Li a (Ni 1-x Cr} x) α (Mn 1-y Ti y) 2-α-β-γ-δ Mg β Al γ M δ O 4 ( where, 1.00 ≦ a ≦ 1.30 0.020 ≦ x ≦ 0.200, 0.006 ≦ y ≦ 0.070, 0.450 ≦ α ≦ 0.550, 0 ≦ β ≦ 0.015, 0 ≦ γ ≦ 0.035, 0 ≦ δ ≦ 0.010, M is selected from the group consisting of Na, K, Ca, Sr, Ba, Ga, Co, Zn, Si, Ge, Zr, Hf, Sn, Ta, Nb, P, Bi, Mo and W A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium transition metal composite oxide represented by:   2. The positive electrode active material according to claim 1, wherein 0.85 ≦ (x · α) / {y · (2-α-β-γ-δ)} ≦ 1.15 in the general formula.   The positive electrode active material according to claim 1, wherein β = 0 in the general formula.   The positive electrode active material according to claim 1, wherein γ = 0 in the general formula.

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