JP2015022950A - Positive electrode active material for nonaqueous electrolyte secondary batteries, and nonaqueous electrolyte secondary battery arranged by use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for nonaqueous electrolyte secondary batteries which allows the balance among a low-temperature output characteristic, a cycle characteristic, a load characteristic, other battery characteristics and the cost to be achieved.SOLUTION: A positive electrode active material for nonaqueous electrolyte secondary batteries comprises, as a primary component, secondary particles of a lithium transition metal complex oxide expressed by the following general formula: LiNiMnCoO(where 0.3≤x≤0.6; 0.2≤y≤0.5; 0.5≤x+y≤1.0; 0.0≤z≤0.30; and 1.0≤x/y). The secondary particles has a specific surface area of 2.5-12 m/g, and includes at least one element M selected from a group consisting of boron, silicon, and phosphorus.

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. The present invention also relates to a non-aqueous electrolyte secondary battery using the positive electrode active material.

  In recent years, portable devices such as video cameras, mobile phones, and notebook personal computers have become widespread and downsized, and non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been used for power supplies. Furthermore, it has been attracting attention as a power battery for electric vehicles and the like due to recent environmental problems.

As a positive electrode active material for a lithium ion secondary battery, LiCoO ₂ (lithium cobaltate) is generally widely used as a material capable of constituting a 4V class secondary battery. When LiCoO ₂ is used as the positive electrode active material, it has been put into practical use with a discharge capacity of about 160 mAh / g.

Cobalt, which is a raw material for LiCoO ₂ , is a scarce resource and is unevenly distributed, and thus costs are high and anxiety arises regarding the supply of raw materials.

In response to such circumstances, LiNiO ₂ (lithium nickelate) has also been studied. LiNiO ₂ can practically realize a secondary battery having a discharge capacity of about 200 mAh / g with a 4V class. However, the stability of the crystal structure of the positive electrode active material during charge / discharge is difficult.

In view of these circumstances, there is a technique for replacing cobalt of lithium cobaltate or nickel of lithium nickelate with other elements. The so-called multi-element lithium transition metal composite oxide typified by Li (Ni, Mn, Co) O ₂ (lithium nickel manganese cobaltate) has been proposed, although the element to be substituted and its amount vary depending on the purpose.

  By the way, the lithium transition metal composite oxide used as the positive electrode active material is usually a powder. Since the shape of primary particles, the degree of aggregation of primary particles (that is, the state of secondary particles), and the particle size distribution affect the characteristics of the entire powder and the characteristics of the entire system including the powder, Various characteristics of the body are controlled. Indicators affecting the relationship between the powder and other elements in the system include indicators relating to the specific surface area and the space between particles. One index related to the space between particles is the pore volume.

  Patent Document 1 describes an example of a plurality of composite oxide powders obtained by wet-grinding a slurry containing a raw material compound, spray-drying and then firing, and having different specific surface areas. Moreover, although the range of the preferable specific surface area is described, it is not described how the range is preferable.

  Table 3 of Patent Literature 2 describes examples of lithium transition metal composite oxides having various specific surface areas obtained by mixing and baking a composite carbonate obtained by a so-called coprecipitation method and a lithium compound. Yes. In addition, there is a description of a preferable specific surface area range from the viewpoint of load characteristics and safety, but there is no description of low temperature output characteristics and pores.

  Table 2 of Patent Document 3 describes examples of lithium transition metal composite oxide powders that take various values for the amount of mercury intrusion in a specific pressure range and the pore capacity related to the peak appearing in the specific range in the pore distribution curve. Has been. Moreover, the preferable range is described about several prescription | regulations regarding pore distribution from a viewpoint of a load characteristic and a filling property. Moreover, the description of the range of a specific surface area preferable from a viewpoint of battery performance (specific performance is unknown) and a bulk density is described. However, there is no description regarding the viewpoint of low-temperature output characteristics.

JP 2003-034537 A JP 2009-205893 A JP 2009-158167 A

Among the multi-element lithium transition metal composite oxides described above, lithium nickel cobalt oxide having a ratio of transition metal such as LiNi _1/3 Mn _1/3 Co _1/3 O _{2 in the} vicinity of 1: 1: 1 is low in cost. Although the balance of safety, charge / discharge capacity, etc. is good, output characteristics tend to decrease at low temperatures. In addition, depending on the composition range, the capacity decreases due to large current discharge (deterioration of load characteristics), and the cycle characteristics decrease when the positive electrode active material layer of the positive electrode is thickened. When a non-aqueous electrolyte secondary battery using such a lithium transition metal composite oxide as a positive electrode active material is used as a power source for equipment that is expected to be used in various environments such as electric vehicles, the performance of the equipment is improved. It will vary greatly depending on the usage environment.

  The present invention has been made in view of such circumstances. The objective of this invention is providing the positive electrode active material which can implement | achieve the non-aqueous-electrolyte secondary battery which made low-temperature output characteristics, cycling characteristics, load characteristics, and other battery characteristics and cost compatible.

In order to achieve the above object, the inventors of the present application have made extensive studies and have completed the present invention. The inventors of the present invention control the specific surface area of the secondary particles of the lithium transition metal composite oxide having a specific composition, and further include a specific element in the secondary particles to provide low temperature output characteristics, cycle characteristics, load characteristics, and the like. It has been found that it is possible to achieve both characteristics. The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention has a general formula Li _{1 + z} Ni _x Mn _y Co _1-xy O ₂ (0.3 ≦ x ≦ 0.6, 0.2 ≦ y ≦ 0). 0.5, 0.6 ≦ x + y ≦ 1.0, 0.0 ≦ z ≦ 0.30, 1.0 ≦ x / y), and the secondary particles of lithium transition metal composite oxide represented by The secondary particles have a specific surface area of 2.5 m ² / g or more and 12 m ² / g or less, and further contain at least one element M selected from the group consisting of boron, silicon and phosphorus. To do.

  The nonaqueous electrolyte secondary battery of the present invention is characterized in that the positive electrode active material of the present invention is used for the positive electrode.

  Since the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention has the above-described characteristics, the low-temperature output characteristics, cycle characteristics, load characteristics, and other characteristics are compatible, and the cost is low. Becomes a well-balanced positive electrode active material. In addition, the non-aqueous electrolyte secondary battery of the present invention has a good balance of various battery characteristics regardless of the use environment, and can be manufactured at a lower cost.

FIG. 1 is a schematic diagram showing an example of the form of the positive electrode active material of the present invention. FIG. 2 is a ternary diagram showing the relationship between transition metals in the lithium transition metal composite oxide which is the main component of the positive electrode active material of the present invention.

  Hereinafter, the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention will be described in detail using embodiments and examples. However, the present invention is not limited to these embodiments and examples.

  The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention mainly comprises secondary particles having a specific composition, the secondary particles having a specific surface area within a specific range, and further containing a specific element M. Hereinafter, the composition, the specific surface area, and the specific element M will be mainly described.

[composition]
The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention has a general formula of Li _{1 + z} Ni _x Mn _y Co _1-xy O _2.
(0.3 ≦ x ≦ 0.6, 0.2 ≦ y ≦ 0.5, 0.6 ≦ x + y ≦ 1.0, 0.0 ≦ z ≦ 0.30, 1.0 ≦ x / y)
The secondary particles of a lithium transition metal composite oxide represented by A lithium transition metal composite oxide having a composition in this range is low in cost and has a good balance of battery characteristics such as safety and charge / discharge capacity. However, when the operating environment becomes low temperature, the output characteristics tend to deteriorate. In particular, it is insufficient as a power source for electric vehicles and the like. This point will be described later. In addition, when the positive electrode active material layer of the positive electrode is thickened within the above composition range, the cycle characteristics may be deteriorated. In addition, the load characteristics may deteriorate in another certain composition range.

  In transition metals, if the ratio of nickel is high, the charge / discharge capacity tends to increase. However, if the ratio is too high, safety is lowered and costs are increased. In view of this, it is preferable that the range of x is 0.4 ≦ x ≦ 0.6 because the balance of capacity, safety and cost is balanced.

  On the other hand, if the manganese ratio is high, cost reduction and safety improvement can be expected, but if it is too high, other battery characteristics may be adversely affected. In view of this, it is preferable that the range of y is 0.3 ≦ y ≦ 0.5 because various characteristics including cost are balanced.

  On the other hand, if the ratio of cobalt is high, improvement in various battery characteristics can be expected, but if it is too high, safety is lowered and cost is increased. In consideration of these, the range of x + y is preferably 0.8 ≦ x + y ≦ 1.0 because the cost and battery characteristics are balanced.

  When the ratio of lithium to the transition metal element is high, the conductivity tends to improve, and when the ratio is low, the capacity tends to increase. In view of this, it is preferable that the range of z is 0.05 ≦ z ≦ 0.20 because the balance between the capacity and the conductivity is achieved.

  When the ratio of manganese to nickel increases, heterogeneous phases are likely to be generated. On the other hand, if it is too low, the effect of manganese will be insufficient. Considering this, the range of x / y is 1.0 ≦ x / y. Then, as described above, x and y are adjusted.

  These relations regarding the transition metal are represented by a range A within a bold line in FIG. 2, and a preferable range is represented by a range B inside thereof.

  The lithium transition metal composite oxide having the above composition has a good balance of various characteristics including cost, but the low-temperature output characteristics are not satisfactory. In some cases, load characteristics and / or cycle characteristics are also insufficient. Therefore, it is necessary to control the specific surface area of the secondary particles and further contain the element M.

[Specific surface area]
The specific surface area of the secondary particles is 2.5 m ² / g or more and 12 m ² / g or less. If the specific surface area is large, many battery characteristics tend to be improved even if the composition is the same, but if it is too high, it becomes difficult to apply the positive electrode active material on the current collector. Considering these facts, a preferable range of the specific surface area is 3.0 m ² / g or more and 7.0 m ² / g or less. In addition, the value calculated | required by the gas adsorption method represented by BET method is used for a specific surface area. Further, when the specific surface area is increased, the cycle characteristics may be slightly deteriorated. However, if the element M described later is present, the cycle characteristics are sufficiently improved.

[Element M]
At least one element M selected from the group consisting of boron, silicon and phosphorus is further included in the secondary particles of the lithium transition metal composite oxide satisfying the above composition and specific surface area. FIG. 1 is a schematic diagram showing an example of the form of secondary particles containing the element M. FIG. A part of the element M can be dissolved in the lithium transition metal composite oxide, but at least a part thereof is present on the surface of the primary particle 111 of the lithium transition metal composite oxide, and the secondary particle 11 of the lithium transition metal composite oxide. The existence region 12 of the element M is formed as a part. There are several possible forms of the element M. In any case, the compound of the element M is not simply in contact with the primary particle 111 of the lithium transition metal composite oxide as a separate particle, but physically and / or chemically. It is firmly bonded by bonding.

  The existence of the element M existence region 12 is considered to contribute to maintaining the shape of the secondary particles and enhancing the binding force between the positive electrode active material and the current collector. For this reason, although the positive electrode active material of this invention has the large specific surface area, the various characteristic fall by repetition of charging / discharging is suppressed. As a result, various battery characteristics including cycle characteristics can be improved.

  If the content of the element M is too small, the above-described effect is not sufficiently exhibited. If the content is too large, a region unrelated to lithium ion desorption / insertion increases, resulting in a decrease in charge / discharge capacity. If the content of the element M is 0.05% or more in terms of the substance amount ratio with respect to the total transition metals of the lithium transition metal composite oxide, the improvement of the cycle characteristics can be clearly confirmed. If it exceeds a certain level, the effect of improving the cycle characteristics is saturated, so 5% is usually sufficient.

[Particle size distribution of secondary particles]
If the median diameter of the secondary particles is too small, the bulk density of the secondary particles decreases, and if it is too large, it is difficult to apply the positive electrode active material, and the battery performance is adversely affected. A preferable range of the median diameter is 2 μm or more and 25 μm or less. More preferably, they are 7 micrometers or more and 15 micrometers or less. For the median diameter, a volume-based frequency distribution curve (histogram) is obtained as a particle size distribution by laser diffraction, and a value at which the integrated value is 50% is used.

[Method for producing positive electrode active material]
Hereinafter, the manufacturing method of the positive electrode active material of this invention is demonstrated. The manufacturing method is not particularly limited.

<Raw compound>
An oxide, carbonate, sulfate, nitrate, hydroxide or the like containing the target element is appropriately selected. A plurality of target elements may be contained in a single raw material compound, and conversely, a plurality of raw material compounds may be used for a single target element. As the former example, a composite carbonate of nickel and manganese can be selected as a raw material for nickel and manganese. As an example of the latter, what mixed lithium hydroxide and lithium carbonate by a fixed ratio can be selected as a raw material compound of lithium. By adjusting the primary particle size and specific surface area of the raw material compound, the specific surface area of the secondary particles of the lithium transition metal composite oxide particles can be adjusted to some extent.

<Mixed>
Raw material compounds are mixed to obtain a raw material mixture. A known mixing method such as dry mixing in which the raw material compound is mixed with a blade-type stirrer, etc., or wet mixing in which the raw material compound is slurried and mixed also for pulverization such as a bead mill may be appropriately employed. When wet mixing is employed, a known drying method such as spray drying is appropriately employed to dry the slurry to obtain a final raw material mixture.

<Baking>
The obtained raw material mixture is fired. If the firing temperature is too low, the reaction with the lithium compound will be insufficient, or sufficient crystallinity will not be obtained, and if it is too high, the particle shape of the present invention will not be obtained. is necessary. Although it depends on the composition, approximately 700 ° C. or higher and 1000 ° C. or lower is preferable. More preferably, it is 800 degreeC or more and 950 degrees C or less. It is sufficient that the firing time is 3 hours or more as the time for maintaining the maximum temperature. An air atmosphere or an oxygen atmosphere can be appropriately used as the firing atmosphere.

  Based on the above, the firing temperature is adjusted, and the specific surface area of the secondary particles of the obtained lithium transition metal composite oxide is adjusted. If the firing temperature is lowered, the specific surface area is high, and if the firing temperature is raised, the specific surface area tends to be low. Therefore, the specific surface area of the adjusted raw material compound slurry is adjusted as appropriate.

<Post-processing>
After firing, if necessary, treatments such as crushing, pulverization, and dry sieving are performed to obtain the positive electrode active material of the present invention.

  Hereinafter, it demonstrates more concretely using an Example and a comparative example.

Lithium carbonate, an oxide raw material having a median diameter of 8.9 μm and a composition of Ni / Mn = 5/5 and boric acid, the mass ratio of Li: Ni: Mn: B = 1.05: 0.5: 0.5: 2.6 × 10 ⁻² Weighed so as to be dispersed in pure water to prepare a slurry. This slurry was wet pulverized with zirconia balls, and the median diameter of the solid content in the slurry was adjusted to 0.19 μm. Next, this slurry (solid content 12.5% by weight) was spray-dried using a three-fluid nozzle type spray dryer to obtain a raw material mixture. Air was used as the dry gas, the dry gas introduction amount was 74 L / min, and the slurry introduction amount was 18 × 10 ⁻³ L / min. The drying inlet temperature was 240 ° C. About 40 g of the obtained raw material mixture was charged into an alumina crucible and fired at 875 ° C. for 9 hours in an air atmosphere (heating rate 3.33 ° C./min) to obtain a general formula Li _1.05 (Ni _0.5 Mn _0.005 ) _{. 5} ) Secondary particles containing 2.6 mol% of boron in the lithium transition metal composite oxide represented by O ₂ were obtained.

Silicon dioxide is used instead of boric acid, and the mass ratio is Li: Ni: Mn: Si = 1.11: Ni: Mn: Si = 1.05: 0.5: 0.5: 1.7 × 10. ^A raw material mixture was obtained in the same manner as in Example 1 except that the weight was adjusted to ⁻² . The obtained raw material mixture was fired in the same manner as in Example 1 except that the firing temperature was 990 ° C., and the lithium transition metal composite represented by the general formula Li _1.05 (Ni _0.5 Mn _0.5 ) O ₂ Secondary particles containing 1.7 mol% of silicon in the oxide were obtained.

Lithium phosphate is used instead of boric acid, and the mass ratio is Li: Ni: Mn: P = 1.11: Ni: Mn: Si = 1.05: 0.5: 0.5: 1.8 × A raw material mixture was obtained in the same manner as in Example 1 except for weighing to 10 ⁻² . The obtained raw material mixture was fired in the same manner as in Example 1 except that the firing temperature was 980 ° C., and the lithium transition metal composite represented by the general formula Li _1.05 (Ni _0.5 Mn _0.5 ) O ₂ Secondary particles containing 1.7 mol% of phosphorus in the oxide were obtained.

[Comparative Example 1]
In the same manner as in Example 1 except that the firing temperature is 930 ° C., 2.6 mol% of boron is added to the lithium transition metal composite oxide represented by the general formula Li _1.05 (Ni _0.5 Mn _0.5 ) O _2. Secondary particles contained were obtained.

[Comparative Example 2]
In the same manner as in Example 2 except that the firing temperature is 1045 ° C., 1.7 mol% of silicon is added to the lithium transition metal composite oxide represented by the general formula Li _1.05 (Ni _0.5 Mn _0.5 ) O _2. Secondary particles contained were obtained.

[Comparative Example 3]
In the same manner as in Example 3 except that the firing temperature was 1020 ° C., 1.8 mol% of phosphorus was added to the lithium transition metal composite oxide represented by the general formula Li _1.05 (Ni _0.5 Mn _0.5 ) O _2. Secondary particles contained were obtained.

[Comparative Example 4]
An oxide raw material having lithium carbonate and a median diameter of 8.9 μm and a composition of Ni / Mn = 5/5 has a mass ratio of Li: Ni: Mn = 1.05: 0.5: 0.5. Thus, the raw material mixture was obtained like Example 1 except weighing. The obtained raw material mixture was fired in the same manner as in Example 1 except that the firing temperature was 950 ° C., and the lithium transition metal composite represented by the general formula Li _1.05 (Ni _0.5 Mn _0.5 ) O ₂ Oxide secondary particles were obtained.

[Comparative Example 5]
Secondary particles of lithium transition metal composite oxide represented by the general formula Li _1.05 (Ni _0.50 Mn _0.50 ) O ₂ were obtained in the same manner as in Comparative Example 4 except that the firing temperature was 1010 ° C. .

[Production of secondary battery]
Secondary batteries for various evaluations were produced in the following manner.

[For output characteristics evaluation]
A paste was prepared by dispersing and dissolving 90% by weight of the positive electrode active material powder, 5% by weight of carbon powder to be a conductive material and 5% by weight of polyvinylidene fluoride (PVDF) in normal methylpyrrolidone (NMP), and kneading. This was applied to a current collector made of aluminum foil, dried, and rolled to obtain a positive electrode plate. The density of the positive electrode mixture film after rolling was set to 2.7 g / cm ³ .

  A graphite material was used as the negative electrode active material. A paste was prepared by dispersing 97.5% by weight of negative electrode active material powder, 1.5% by weight of carboxymethyl cellulose (CMC) and 1.0% by weight of styrene butadiene rubber (SBR) in water and kneading. This was applied to a current collector made of copper foil, dried, and rolled to obtain a negative electrode plate.

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

  A porous polyethylene film was used as a separator.

  Lead electrodes were attached to the positive electrode plate and the negative electrode plate, and the positive electrode, the separator, and the negative electrode were stacked in this order. These were stored in a laminate pack, an electrolyte solution was injected, and the laminate pack was sealed to obtain a laminate type secondary battery. This was used for output characteristic evaluation.

[For load characteristics evaluation]
A positive electrode plate, a non-aqueous electrolyte, and a separator were prepared in the same manner as the output characteristic evaluation battery. Moreover, the negative electrode which consists of lithium foil was prepared.

  A lead electrode was attached to the positive electrode plate and the negative electrode plate, and the negative electrode, the separator, and the positive 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 is fixed by the side of the container made of Teflon (registered trademark). The tip of the positive lead electrode is led out of the container and becomes a positive terminal. The positive and negative terminals are electrically insulated by the container side. After storage, the electrolyte was poured and sealed with a stainless steel container lid to obtain a sealed secondary battery. This was used for load characteristic evaluation.

[For cycle characteristics evaluation]
A carbon material was used as the negative electrode active material. A paste was prepared by kneading 97.5% by weight of negative electrode active material powder, 1.0% by weight of styrene butadiene rubber and 1.5% by weight of carboxymethylcellulose (CMC) aqueous solution, and this was collected from a copper foil. It was applied to the body, dried and molded into a plate shape to obtain a negative electrode plate.

  A positive electrode plate, a non-aqueous electrolyte, and a separator were prepared in the same manner as the output characteristic evaluation battery.

  Lead electrodes were attached to the positive electrode plate and the negative electrode plate, and a laminate type secondary battery was obtained in the same manner as the output characteristic evaluation battery. This was used for cycle characteristic evaluation.

[Evaluation of battery characteristics]
Various battery characteristics were evaluated in the following manner.

[Output characteristics]
Under an environment of 25 ° C., a full charge voltage was set to 4.2 V, and constant current charging was performed to a charge depth of 50%, and then pulse discharge / charge was performed at a specific current value i. After applying the pulse for 10 seconds, discharging and charging were repeated in 3 minutes. The pulse discharge / charge current values i were 0.04A, 0.08A, 0.12A, 0.16A and 0.20A. The current value i is plotted on the horizontal axis of the graph, the voltage value V after 10 seconds of pulse discharge is plotted on the vertical axis of the graph, and the absolute value of the slope is obtained in the current range in which linear linearity is maintained in the i-V plot. R (25).

  Under an environment of −25 ° C., the full charge voltage was set to 4.2 V, and constant current charging was performed until the charge depth was 50%, and then pulse discharge was performed at a specific current value. The pulse was discharged only for 10 minutes after the application for 10 seconds. The pulse discharge current value i was set to 0.04 A, 0.06 A, 0.08 A, and 0.10 A. Thereafter, the battery resistance was determined in the same manner as R (25), and was set to R (-25). Low R means high output characteristics.

[Load characteristic evaluation]
The battery was charged at a constant current and a constant voltage at a full charge voltage of 4.3 V and a charge load of 0.2 C (1 C: a current value at which discharge was completed in 1 hour from a fully charged state). Thereafter, constant current discharge was performed at a discharge voltage of 2.75 V and a discharge load of 0.2 C, and the charge released up to the discharge voltage was defined as a normal discharge capacity Q _d (0.2 C). On the other hand, the charge voltage 4.3 V, discharge voltage 2.75 V, discharge load 0.2 C, 1C, in the order of 3C, respectively performs charging and discharging, the load discharge capacity and the discharge capacity when the 3C _Q d and (3C) did. Load ratio for normal discharge capacity of the discharge capacity _{(≡Q d (3C) / Q} d (0.2C) .Q d (3C that the load efficiency _{P r} a) and the load discharge capacity and that the load efficiency is high, the load Means good characteristics.

[Cycle characteristic evaluation]
In an environment of 25 ° C., constant current and constant voltage charging and constant current discharging are repeated 200 times at a full charge voltage of 4.2 V, a discharge voltage of 2.75 V, and a current density of 1.35 mA / cm ² with respect to the positive electrode. The ratio of the discharge capacity at the 200th time to the discharge capacity at the 1st time is defined as a capacity retention rate P _s (200). A high capacity retention rate means good cycle characteristics.

  About Examples 1-3 and Comparative Examples 1-5, the manufacturing conditions and characteristics of a positive electrode active material are shown in Table 1, and battery characteristics are shown in Table 2.

  In Tables 1 and 2, the output characteristics (especially low temperature) due to the higher specific surface area than Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, Example 3 and Comparative Example 3, and Comparative Example 4 and Comparative Example 5. It can be seen that the output characteristics) and the load characteristics are improved. On the other hand, from Examples 1 to 3 and Comparative Example 4, it can be seen that the presence of the element M significantly improves the cycle characteristics.

  By using the positive electrode active material of the present invention as a positive electrode, it is possible to realize a non-aqueous electrolyte secondary battery capable of taking out a large output regardless of the use environment. Such a non-aqueous electrolyte secondary battery can be suitably used as a power source for devices that are expected to be used in various environments such as electric vehicles and hybrid electric vehicles.

DESCRIPTION OF SYMBOLS 1 Positive electrode active material 11 Secondary particle of lithium transition metal complex oxide 111 Primary particle of lithium transition metal complex oxide 12 Existence area of element M

Claims (7)

General formula Li _{1 + z} Ni _x Mn _y Co _1-xy O ₂
(0.3 ≦ x ≦ 0.6, 0.2 ≦ y ≦ 0.5, 0.6 ≦ x + y ≦ 1.0, 0.0 ≦ z ≦ 0.30, 1.0 ≦ x / y)
And the secondary particles have a specific surface area of 2.5 m ² / g to 12 m ² / g, and boron, silicon and phosphorus A positive electrode active material for a nonaqueous electrolyte secondary battery, comprising at least one element M selected from the group consisting of:   The positive electrode active material according to claim 1, wherein 0.4 ≦ x ≦ 0.6 for the lithium transition metal composite oxide.   The positive electrode active material according to claim 1, wherein the lithium transition metal composite oxide satisfies 0.3 ≦ y ≦ 0.5.   The positive electrode active material according to claim 1, wherein the lithium transition metal composite oxide satisfies 0.8 ≦ x + y ≦ 1.0.   5. The element M according to claim 1, wherein the content of the element M is 0.05% or more and 5% or less in a substance amount ratio with respect to all transition metals of the lithium transition metal composite oxide. Positive electrode active material.   The positive electrode active material according to claim 1, wherein a median diameter of the secondary particles is 2 μm or more and 25 μm or less.   A non-aqueous electrolyte secondary battery using the positive electrode active material according to claim 1 as a positive electrode.

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