JP2016081800A - Positive electrode active material for nonaqueous secondary battery and manufacturing method thereof, and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a ternary positive electrode active material for a nonaqueous secondary battery, which is improved in low-temperature characteristic; a method for manufacturing such a ternary positive electrode active material; and a nonaqueous secondary battery improved in low-temperature characteristic.SOLUTION: A positive electrode active material for a nonaqueous secondary battery according to the present invention comprises: particles of a complex oxide expressed by the general formula, LiNiCoMnO(a+b+c=1, 0<a<1, 0<b<1 and 0<c<1), of which the average particle diameter is less than 150 nm, and the crystallite size is 25-100% of the average particle diameter.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode active material for a non-aqueous secondary battery, a manufacturing method thereof, and a secondary battery, and more particularly to a positive electrode active material for a non-aqueous secondary battery with improved low-temperature characteristics and a manufacturing method thereof. .

Conventionally, LiCoO ₂ has been mainly used as a positive electrode active material for non-aqueous secondary batteries. However, the non-aqueous secondary battery using LiCoO ₂ as the positive electrode active material has a problem in the thermal stability in the battery in a charged state, and the discharge capacity is small. Therefore, LiCoO ₂ , LiNiO ₂ and LiMnO ₂ are respectively used. A solid solution Li [Co _1-2x Ni _x Mn _x ] O ₂ (0 <x ≦ 1/2) shown on the ternary phase diagram as three components was devised in 2001 (hereinafter referred to as ternary system). A positive electrode active material). LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ is known as an example of such a solid solution, and a non-aqueous secondary battery using this as a positive electrode active material has a discharge capacity and thermal stability. It is superior to LiCoO ₂ .

In recent years, positive electrode active materials for non-aqueous secondary batteries have been required to have higher discharge capacity and improved low-temperature characteristics. As one of the former measures, the particle size of the active material is reduced, that is, the surface area is increased. To reduce the diffusion distance of lithium ions in the solid (Patent Document 1, Non-Patent Document 1). Regarding the latter, for example, it has been reported that the low-temperature characteristics are improved when the microfiber structure is made into a nanofiber structure having a diameter of 70 nm with respect to the V ₂ O ₅ positive electrode active material (Non-patent Document 2).

  Even in the case of a ternary positive electrode active material, there is a possibility that high discharge capacity and low-temperature characteristics may be improved by forming nanoparticles. So far, a ternary positive electrode active material of 100 to 300 nm with improved discharge capacity has been synthesized (Non-patent Document 3). Furthermore, although a ternary positive electrode active material having a smaller primary particle size of 40 to 50 nm has been synthesized, the positive electrode active material has a large particle fusion and cannot be said to be an independent nanoparticle (non-native). Patent Document 4). In this way, smaller independent nanoparticles having an average particle diameter of, for example, 50 nm have not been synthesized yet. In addition, no improvement of the low temperature characteristics has been reported so far.

JP 2013-4401 A

Advanced Functional Materials, 16 (2006) 1904-1912 Advanced Materials, 17125-128 (2005) Electrochimica Acta, 49 (2004) 557-563 Journal of The Electrochemical Society, 156 (2009) A192-A198

  The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a ternary positive electrode active material for a non-aqueous secondary battery with improved low-temperature characteristics. Another object of the present invention is to provide a method for producing a ternary positive electrode active material for non-aqueous secondary batteries with improved low-temperature characteristics and a non-aqueous secondary battery with improved low-temperature characteristics.

As a result of intensive studies by the present inventors, _a ternary positive electrode represented by the general formula LiNi _a Co _b Mn _c O ₂ (a + b + c = 1, 0 <a <1, 0 <b <1, 0 <c <1) The inventors have found that when the ratio of the crystallite size / average particle diameter of the active material nanoparticles is in a specific range, the low temperature characteristics of a non-aqueous secondary battery using the same are improved, and the present invention has been completed.

That is, the positive electrode active material for a non-aqueous secondary battery of the present invention is represented by the general formula LiNi _a Co _b Mn _c O ₂ (a + b + c = 1, 0 <a <1, 0 <b <1, 0 <c <1). A positive electrode active material for a non-aqueous secondary battery comprising composite oxide particles having an average particle diameter of less than 150 nm and a crystallite size of 25 to 100% of the average particle diameter.

In a preferred embodiment, in the general formula LiNi _a Co _b Mn _c O ₂ , a + b + c = 1, 0.2 <a <0.7, 0.1 <b <0.4, 0.1 <c <0. 4.

The method for producing a positive electrode active material for a non-aqueous secondary battery according to the present invention has a general formula LiNi _a Co _b Mn _c O ₂ (a + b + c = 1, 0 <a <1, 0 <b <1, 0 <c <1). A method for producing a positive electrode active material for a non-aqueous secondary battery comprising composite oxide particles represented by the formula: wherein a Li compound, a Ni compound, a Co compound and a Mn compound are dissolved in a polymer compound solution to form a uniform mixed solution A step of obtaining a solid by removing the solvent from the uniform mixed solution, a step of heating the solid at a temperature higher than the decomposition temperature of each metal compound and lower than the decomposition temperature of the polymer compound, and heating at a temperature of 400 ° C. And removing the polymer compound to produce a positive electrode active material for a non-aqueous secondary battery.

  The non-aqueous secondary battery of the present invention uses the positive electrode active material for non-aqueous secondary batteries.

  According to the present invention, it is possible to provide a non-aqueous secondary battery with improved low-temperature characteristics.

It is a figure which shows the initial stage charge / discharge characteristic and capacity transition of the evaluation cell using the positive electrode active material for non-aqueous secondary batteries of an Example. It is a figure which shows the initial stage charge / discharge characteristic and capacity transition of the evaluation cell using the positive electrode active material for non-aqueous secondary batteries of a comparative example.

It is a figure which shows the discharge rate characteristic in the room temperature of the evaluation cell using the positive electrode active material for non-aqueous secondary batteries of an Example. It is a figure which shows the discharge rate characteristic in 0 degreeC of the evaluation cell using the positive electrode active material for non-aqueous secondary batteries of an Example. It is a figure which shows the discharge rate characteristic in the room temperature of the evaluation cell using the positive electrode active material for non-aqueous secondary batteries of a comparative example. It is a figure which shows the discharge rate characteristic in 0 degreeC of the evaluation cell using the positive electrode active material for non-aqueous secondary batteries of a comparative example.

  Hereinafter, although preferable embodiment of this invention is described, this invention is not limited to these embodiment.

The positive electrode active material for a non-aqueous secondary battery of the present invention is a ternary composite oxide particle represented by _a general formula LiNi _a Co _b Mn _c O ₂ . The composition of each metal element is 0 <a <1, 0 <b <1, 0 <c <1, preferably 0.1 <a <0.8, 0.1 <b under the condition of a + b + c = 1. <0.5, 0.1 <c <0.5, more preferably 0.2 <a <0.7, 0.1 <b <0.4, 0.1 <c <0.4 . Examples of such complex oxides include LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2 Mn _{0. 3} O _{2 and the} like can be mentioned. Among these, LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ and LiNi _0.5 Co _0.2 Mn _0.3 O ₂ are preferable in terms of thermal stability.

  The ternary composite oxide particles are single crystal or polycrystal and have any of spherical, polyhedral, ellipsoidal, and cubic shapes. The average particle diameter obtained from the average value of the maximum widths of a plurality of particle cross sections is 150 nm or less, preferably 10 to 100 nm, more preferably 20 to 80 nm. The variation coefficient of the average particle diameter (= 100 × standard deviation / average value) is 70% or less, more preferably 10 to 60%. If it exceeds 70%, the variation in the particle size increases, and the performance as the positive electrode active material decreases. The average particle diameter can be calculated by image analysis of a scanning or transmission electron micrograph. In addition, in this specification, the definition of a particle diameter makes object the particle | grains which exist independently. Therefore, when the fine particles are partially fused to form large particles, the maximum width of the large particles is taken as the particle diameter.

  The crystallite size of the ternary composite oxide particles is 25 to 100%, preferably 30 to 100%, more preferably 35 to 100% of the average particle diameter. If it is less than 25%, the number of crystal interfaces increases, so the movement of Li ions slows down, and the low-temperature characteristics tend to deteriorate. The crystallite size can be calculated from the X-ray diffraction using Scherrer's equation. In this specification, an average value of the (003) plane and the (104) plane is adopted as the crystallite size.

The ternary composite oxide particles may include a doping component D as necessary. In this case, the general formula LiNi _a Co _b Mn _c D _d O ₂ ((D is Al, Mg, Ti, Sn, At least one selected from Zn, W, Zr, Mo, Fe and Na, a + b + c + d = 1, 0 <a <1, 0 <b <1, 0 <c <1, 0 ≦ d ≦ 0.1) Can be represented.

  The production of such ternary composite oxide particles is not particularly limited as long as it is a method capable of suppressing mass transfer of a metal element that causes particle growth under high-temperature reaction conditions. An example of such a method is a method in which a metal compound as a raw material and a polymer compound are uniformly mixed, and then the metal compound is decomposed at a temperature lower than the melting temperature or decomposition temperature of the polymer compound.

  As an example of a method for producing ternary composite oxide particles, a method using a polymer compound will be described. The polymer compound is preferably a polymer compound that is soluble in a solvent in which the metal compound is soluble and is not easily carbonized. For example, if the metal compound is water-soluble, polyvinyl alcohol, a water-soluble cellulose derivative, a water-soluble polypeptide, And water-soluble polymerizable unsaturated compounds such as water-soluble polysaccharides, polyvinylpyrrolidone, polyacrylic acid and polyacrylic acid copolymers, or copolymers thereof. If it is water-insoluble, a polymer compound that is difficult to be carbonized by thermal decomposition, such as polymethacrylate, polyoxymethylene, ethyl cellulose, or the like can be used.

  The metal compound is not particularly limited as long as it decomposes at a temperature lower than the melting temperature or decomposition temperature of the polymer compound, and examples thereof include metal nitrates and metal acetates. In particular, metal nitrate is preferable because it is easily decomposed at a relatively low temperature. In addition, the metal compound in this specification is limited to the metal compound contained in the said general formula.

  The concentration of the metal compound in the polymer compound affects the particle size of the generated particles. When the concentration is high, the generated particles are likely to be close to each other, so that particle growth occurs and the particle diameter is likely to increase. As an appropriate concentration, 0.0004 to 0.02 mol (in terms of ternary complex oxide), preferably 0.0006 to 0.0016 mol, and more preferably 0.0008 to 0.012 per 1 g of the polymer compound. Is a mole. When the amount is more than 0.02 mol per 1 g of the polymer compound, the particle diameter of the generated particles tends to increase.

  Uniform mixing of the metal compound with the polymer compound can be carried out by dissolving both in a soluble solvent and mixing with a stirrer or the like. The solvent is not particularly limited as long as it is a liquid that dissolves both the metal compound and the polymer compound and can be removed at a temperature lower than the decomposition temperature of the metal compound. For example, water, lower alcohols such as methanol and ethanol, Mention may be made of ketones such as acetone, esters such as ethyl acetate, tetrahydrofuran and methylene chloride. Next, the solvent is removed from the obtained mixed solution under heating or reduced pressure to obtain a polymer compound solid in which the metal compound is uniformly mixed, and this is heat-treated in the air or, if necessary, in an inert atmosphere. Thus, ternary composite oxide particles can be produced.

  When heat is used for solvent removal, the temperature is preferably a temperature at which the metal compound does not decompose, for example, 100 ° C. or less. The heating time is not particularly limited until the solvent is removed from the solution of the metal compound and the polymer compound to solidify.

  Heat treatment of a polymer compound solid in which a metal compound is uniformly mixed is constant in a temperature range above the decomposition temperature of the metal compound and below the decomposition temperature of the polymer compound when the decomposition of the metal compound occurs below the decomposition temperature of the polymer compound. After the heat treatment for a time, it is preferable that the heat treatment is performed by raising the temperature to the firing temperature. By performing heat treatment for a certain period of time in a temperature range higher than the decomposition temperature of the metal compound and lower than the decomposition temperature of the polymer compound, fine particles that are the basis of the ternary composite oxide particles are generated, and this is the ternary centered on this. Since the formation of system complex oxide particles occurs, the particle size distribution is not wide and particles having a small particle size are easily obtained. The temperature range above the decomposition temperature of the metal compound and below the decomposition temperature of the polymer compound is not particularly limited because it varies depending on the type of the metal compound and the polymer compound, but is, for example, 130 to 360 ° C, preferably 150 to 320 ° C. Preferably it is 170-280 degreeC. Above 360 ° C., many polymer compounds start to decompose or carbonize. The time for heat treatment in this temperature range is 5 minutes to 4 hours, preferably 10 minutes to 3 hours, and more preferably 15 minutes to 2 hours. When the heat treatment is performed for longer than 4 hours, the particle size after firing tends to increase. As a calcination temperature, it is 400-1000 degreeC, Preferably it is 500-950 degreeC, More preferably, it is 550-900 degreeC. When the temperature is lower than 400 ° C., the polymer compound tends to remain. If it is higher than 1000 ° C., the particle size tends to be large. The rate of temperature increase up to the firing temperature is not particularly limited, but a rate lower than 1 ° C./min is not preferable because the particle diameter tends to increase.

  In addition, when decomposition | disassembly of a metal compound does not occur below the decomposition temperature of a high molecular compound, it is preferable to heat up by raising rapidly to a calcination temperature. By doing so, the particle size distribution is widened, but particles having a small particle diameter are easily obtained. The rate of temperature increase up to the firing temperature is not particularly limited, but a rate lower than 1 ° C./min is not preferable because the particle diameter tends to increase.

  The positive electrode active material for a non-aqueous secondary battery according to the present invention can be used as a positive electrode active material for a lithium secondary battery comprising at least a positive electrode, a negative electrode, and a non-aqueous electrolyte containing a lithium salt.

  The negative electrode active material used in the present invention is not particularly limited as long as it is a lithium-based negative electrode material, and a lithium-doped and dedopeable material improves safety and reliability such as cycle life. preferable. Examples of materials that can be lithium-doped and dedope include graphite-based materials, carbon-based materials, tin oxide-based, silicon-based oxides and the like, which are used as known negative electrode materials for lithium secondary batteries, silicon And tin-based alloys.

  The method for forming the positive electrode active material and the negative electrode active material of the present invention into an electrode can be appropriately selected from known methods according to the desired characteristics of the nonaqueous secondary battery. For example, a positive electrode active material (or negative electrode active material), a binder, and optionally a solvent such as N-methyl-2-pyrrolidone (NMP) are mixed to obtain a slurry, which is then applied to a current collector. Examples thereof include a coating method in which the mixture is dried and then compressed and a sheet method in which a mixture of an active material and polytetrafluoroethylene is kneaded and formed into a sheet using a rolling roll.

  When forming the positive electrode and the negative electrode used in the non-aqueous secondary battery of the present invention, a conductive material and a binder are used as necessary. The type of the binder is not particularly limited, and examples thereof include fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene, fluorine rubber, SBR, acrylic resin, polyolefins such as polyethylene and polypropylene, and the like. The The amount of the binder can be appropriately determined in consideration of the type of binder and the intended electrode strength.

The type of the conductive material is not particularly limited, and examples thereof include carbon black, acetylene black, and vapor grown carbon fiber. The amount of the conductive material is not particularly limited as long as sufficient electronic conductivity can be secured in the electrode.
When the positive electrode and the negative electrode are formed on the current collector, the material of the current collector can be selected in consideration of the voltage resistance of the material, such as copper foil, stainless steel foil, titanium foil, and aluminum foil. Is done.

  In the above cell, when a separator is disposed between the positive electrode and the negative electrode for the purpose of insulation and electrolyte solution retention, the separator is not particularly limited, and is a polyethylene microporous film, a polypropylene microporous film, or polyethylene. There are polypropylene laminated film, cellulose paper, woven fabric or nonwoven fabric made of glass fiber, aramid fiber, polyacrylonitrile fiber, etc., which can be appropriately determined according to the purpose and situation.

In the non-aqueous secondary battery of the present invention, for example, a non-aqueous electrolyte solution, a gel electrolyte, or a solid electrolyte can be used as an electrolyte. As the non-aqueous electrolyte, a non-aqueous electrolyte containing a lithium salt can be used, and is appropriately determined according to the use conditions such as the type of the positive electrode material, the properties of the negative electrode material, and the charging voltage. Examples of the non-aqueous electrolyte containing a lithium salt include lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dimethoxyethane, γ-butyrolactone, acetic acid. What was melt | dissolved in the organic solvent which consists of 1 type, or 2 or more types, such as methyl and methyl formate, can be used. The concentration of the electrolytic solution is not particularly limited, but generally about 0.5 to 2 mol / l is practical. As a matter of course, it is preferable to use an electrolytic solution having a water content of 100 ppm or less.

The non-aqueous secondary battery of the present invention is represented by the general formula LiNi _a Co _b Mn _c O ₂ described above (a + b + c = 1, 0 <a <1, 0 <b <1, 0 <c <1). A positive electrode active material for a non-aqueous secondary battery comprising a composite oxide particle, wherein the average particle size is less than 150 nm and the crystallite size is 25 to 100% of the average particle size. A positive electrode, a negative electrode, a separator, an electrolyte and the like using a substance are housed in a battery container.

  The shape of the non-aqueous secondary battery of the present invention is not particularly limited, and can be appropriately determined according to the purpose, such as a coin type, a cylindrical type, a square type, and a film type.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

[Synthesis of ternary complex oxide particles]
(Example)
Mn (NO ₃ ) ₂ .6H ₂ O 6.76 g (decomposition temperature 129 ° C.), Co (NO ₃ ) ₂ .6H ₂ O 6.96 g (decomposition temperature 100-105 ° C.), Ni (NO ₃ ) ₂ · 6H 6.96 g of ₂ O (decomposition temperature: 137 ° C.) and 7.28 g of Li (CH ₃ COO) .2H ₂ O were dissolved in 400 ml of 5% aqueous polyvinyl alcohol solution. This was put in a ceramic container and dried at 100 ° C. for 2 hours to obtain a wine red transparent solid. When this was heated at 200 ° C. for 2 hours, it became an ocher opaque solid. When this solid was observed with a transmission electron microscope, a particulate structure of about several nm to several tens of nm was observed. Next, the ocherous solid was ground with a mortar and placed in a ceramic container, and heat-treated at 800 ° C. for 4 hours in an electric furnace in the atmosphere.
From the elemental analysis and transmission electron microscope observation of the product, the product has a composition of LiNi _0.31 Co _0.33 Mn _0.36 O _{2 and} a composite oxide nanoparticle having an average particle diameter of 62 nm (variation coefficient 52%). Confirmed to be particles. Further, X-ray diffraction measurement showed a diffraction pattern of the ternary composite oxide, and it was found that the crystallite size was 31 nm (50% of the average particle diameter).

(Comparative example)
Mn (NO ₃ ) ₂ · 6H ₂ O 6.76 g, Co (NO ₃ ) ₂ · 6H ₂ O 6.96 g, Ni (NO ₃ ) ₂ · 6H ₂ O 6.96 g and Li (CH ₃ COO) · 2H After dissolving 7.28 g of ₂ O in 50 ml of distilled water, it was placed in a ceramic container, heated at 120 ° C. for 2 hours to remove water, and then heat-treated at 200 ° C. for 1 hour. Next, the produced brown liquid was put in a ceramic container and heat-treated in an electric furnace at 800 ° C. for 5 hours in the atmosphere.
Scanning electron microscope observation of the product revealed that the product was an amorphous particle having a distribution of about several hundred nm to 5 μm. From the X-ray diffraction measurement, the product showed a diffraction pattern of the ternary composite oxide, and the crystallite size was 103 nm.

[Electrochemical evaluation of positive electrode active materials for secondary batteries]
An evaluation cell was prepared by the following procedure using the ternary composite oxide particles of the above example as a positive electrode active material for a secondary battery and a commercially available ternary composite oxide as a comparative example. The discharge characteristics under current density conditions were evaluated. The commercially available ternary composite oxide used as a comparative example this time had an average particle size of 5 μm.

Using acetylene black as the conductive material and polytetrafluoroethylene (PTFE) as the binder, an active material: 45 parts by weight, a conductive material: 40 parts by weight, and a binder: 15 parts by weight were mixed to prepare an electrode sheet. A 20 × 14 mm size electrode sheet was adhered to a 20 μm Al foil using a conductive paste and vacuum dried at 170 ° C. for 10 hours to obtain a positive electrode for battery characteristics evaluation. The physical properties of the prepared electrodes are shown in Table 1.

  The prepared electrode is a positive electrode, the negative electrode is a metal lithium foil having a thickness of 200 μm, the electrolyte is 1 mol / l LiPF6, ethylene carbonate and ethyl methyl carbonate (volume ratio 30:70), and the separator is a polyethylene microporous membrane ( An evaluation cell was fabricated using a superposed layer having a thickness of 25 μm.

  In the evaluation of the evaluation cell, initial charge / discharge characteristics, 25 ° C. rate characteristics, and 0 ° C. rate characteristics were performed by the methods described below.

[Initial charge / discharge characteristics]
Under a 25 ° C. environment, a constant current / constant voltage charge with a charge current of 0.2 CA (30 mA / g) and a charge voltage of 4.30 V was performed, and the charge was terminated when the current value reached C / 20. After the completion of charging, discharging was performed under the conditions of a discharge current of 0.2 CA (30 mA / g) and a final voltage of 3.0 V.
The above charge / discharge was repeated 5 times to evaluate initial charge / discharge characteristics.
[Rate characteristics at room temperature (25 ° C)]
Using the above cell, the discharge characteristics at a high current density in a 100% SOC, 25 ° C. environment were confirmed. Charging is performed under the condition that the charging is performed at a constant current and constant voltage with a charging current of 0.2 CA (30 mA / g) and a charging voltage of 4.30 V in a 25 ° C. environment and the charging is terminated when the current value reaches C / 20. The discharge was performed under the conditions of 0.2 CA (30 mA / g), 0.5 CA (70 mA / g), 1 CA (150 mA / g), 2 CA (300 mA / g) current density, and a final voltage of 3.0 V. Was done.
[Rate characteristics at 0 ° C]
Using the above cell, the discharge characteristics at a high current density in a 100% SOC, 0 ° C. environment were confirmed. Charging is performed under the condition that the charging is performed at a constant current and constant voltage with a charging current of 0.2 CA (30 mA / g) and a charging voltage of 4.30 V in a 25 ° C. environment and the charging is terminated when the current value reaches C / 20. For discharge and discharge, in a 0 ° C. environment, a current density of 0.2 CA (30 mA / g), 0.5 CA (70 mA / g), 1 CA (150 mA / g), 2 CA (300 mA / g), final voltage 3. Discharge was performed under the condition of 0V.

FIG. 1 shows initial charge / discharge characteristics and capacity transition of an evaluation cell using the positive electrode active material of the example.
FIG. 2 shows initial charge / discharge characteristics / capacity transition of an evaluation cell using a commercially available positive electrode active material.

FIG. 3 shows the discharge rate characteristics at room temperature of an evaluation cell using the positive electrode active material of the example.
FIG. 4 shows the discharge rate characteristics at 0 ° C. of the evaluation cell using the positive electrode active material of the example.
FIG. 5 shows the discharge rate characteristics at room temperature of an evaluation cell using a commercially available positive electrode active material.
FIG. 6 shows the discharge rate characteristics at 0 ° C. of an evaluation cell using a commercially available positive electrode active material.

  Looking at the initial charge / discharge characteristics and capacity transition of the evaluation cell, the evaluation cell using the positive electrode active material of the example has a characteristic that the decrease in the initial charge / discharge capacity is small compared to the evaluation cell using the commercially available positive electrode active material. Was seen.

  When the discharge rate characteristics at room temperature and 0 ° C. of the evaluation cell using the positive electrode active material of the example were examined, the discharge capacity at a discharge rate of 0.2 C was reduced to 90.5% of the room temperature at 0 ° C. Looking at the change in discharge capacity when the discharge rate increases with the discharge rate of 0.2 C as a reference (capacity maintenance rate), 91.6% is maintained at room temperature at the discharge rate of 2 C where the current density is the highest. On the other hand, it decreased to 81.4% at 0 ° C.

  Similarly, looking at the discharge rate characteristics at room temperature and 0 ° C. of an evaluation cell using a commercially available positive electrode active material, the discharge capacity decreased to 81.9% of the room temperature at 0 ° C. The capacity retention rate at the discharge rate of 2C with the highest current density was maintained at 81.7% at room temperature, but decreased to 74.3% at 0 ° C.

  The evaluation cell using a commercially available positive electrode active material has a lower capacity retention rate due to a larger decrease in discharge capacity with respect to current density than the evaluation cell using the positive electrode active material of the example. Looking at the ratio of the capacity retention rate at 0 ° C. to the room temperature at the discharge rate 2C having the highest density, the evaluation cell using the commercial positive electrode active material was 0.909, and the evaluation cell using the positive electrode active material of the example Is almost the same as 0.889. That is, it is considered that there is no difference between the two in terms of the change in the capacity retention ratio with respect to the temperature change from room temperature to 0 ° C. From the above, it can be said that the feature of the evaluation cell using the positive electrode active material of the example is that the decrease in discharge capacity at 0 ° C. is small. This result suggests that the positive electrode active material of the example has improved low-temperature characteristics as compared with the conventional positive electrode active material.

Cathode active for non-aqueous secondary battery comprising composite oxide particles represented by the general formula LiNi _a Co _b Mn _c O ₂ (a + b + c = 1, 0 <a <1, 0 <b <1, 0 <c <1) By using a positive electrode active material for a non-aqueous secondary battery that is a substance and has an average particle size of less than 150 nm and a crystallite size of 25 to 100% of the average particle size, A non-aqueous secondary battery for electric vehicles can be obtained.

Claims (4)

Cathode active for non-aqueous secondary battery comprising composite oxide particles represented by the general formula LiNi _a Co _b Mn _c O ₂ (a + b + c = 1, 0 <a <1, 0 <b <1, 0 <c <1) A positive electrode active material for a non-aqueous secondary battery, which is a substance and has an average particle diameter of less than 150 nm and a crystallite size of 25 to 100% of the average particle diameter. In the general formula LiNi _a Co _b Mn _c O ₂ , a + b + c = 1, 0.2 <a <0.7, 0.1 <b <0.4, 0.1 <c <0.4. The positive electrode active material for nonaqueous secondary batteries according to 1. Cathode active for non-aqueous secondary battery comprising composite oxide particles represented by the general formula LiNi _a Co _b Mn _c O ₂ (a + b + c = 1, 0 <a <1, 0 <b <1, 0 <c <1) A method for producing a substance, a step of dissolving a Li compound, a Ni compound, a Co compound and a Mn compound in a polymer compound solution to obtain a uniform mixed solution, a step of removing a solvent from the uniform mixed solution to obtain a solid, A step of heating the solid above the decomposition temperature of each metal compound and below the decomposition temperature of the polymer compound to produce fine particles, heating at 400 ° C. or more to remove the polymer compound, and positive electrode active material for non-aqueous secondary battery The manufacturing method of the positive electrode active material for non-aqueous secondary batteries consisting of the process of producing | generating. A non-aqueous secondary battery using the positive electrode active material for a non-aqueous secondary battery according to claim 1.

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