JP2016015298A - Positive electrode active material for lithium secondary battery, electrode for lithium secondary battery, lithium secondary battery and power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for a lithium secondary battery excellent in high rate discharge performance, and a lithium secondary battery using the positive electrode active material.SOLUTION: A positive electrode active material for a lithium secondary battery contains a lithium transition metal composite oxide having an α-NaFeOstructure. In the lithium transition metal composite oxide, transition metal (Me) includes Co, Ni and Mn, a molar ratio Mn/Me of Mn in the transition metal satisfies Mn/Me≥0.5, the half band width of a diffraction peak at 2θ=44±1° in an X-ray diffraction pattern taken by using a CuKα ray source is 0.265° or more, and a P element is contained.

Description

  The present invention relates to a positive electrode active material for a lithium secondary battery containing a novel lithium transition metal composite oxide, an electrode for a lithium secondary battery containing the positive electrode active material, a lithium secondary battery including the electrode, and a battery thereof. The present invention relates to an assembled power storage device.

Conventionally, as a positive electrode active material for a lithium secondary battery, a “LiMeO ₂ type” active material (Me is a transition metal) having an α-NaFeO ₂ type crystal structure has been studied, and lithium secondary batteries using LiCoO ₂ have been widely put into practical use. It was converted. However, the discharge capacity of LiCoO ₂ was about 120 to 130 mAh / g. As Me, it has been desired to use abundant Mn as a global resource. However, the “LiMeO ₂ type” active material containing Mn as Me, when the molar ratio of Mn to Me, Mn / Me exceeds 0.5, the structure changes to spinel type when charged, Since the structure could not be maintained, there was a problem that the charge / discharge cycle performance was extremely inferior.

Accordingly, various “LiMeO ₂ type” active materials having a Mn to Me molar ratio Mn / Me of 0.5 or less and excellent in charge / discharge cycle performance have been proposed and partially put into practical use. For example, LiNi _1/2 Mn _1/2 O ₂ and LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ have a discharge capacity of 150 to 180 mAh / g.

In recent years, there has been proposed an active material that contains Ni, Co, and Mn as Me, has a molar ratio of Mn to Me, Mn / Me of 0.5 or more, and can maintain an α-NaFeO ₂ structure even when charged.

Patent Documents 1 and 2 include 4.3 V (vs) as a battery manufacturing method using an active material containing Ni, Co, and Mn as Me and having a molar ratio Mn to Me of Mn / Me of 0.5 or more. .Li / Li ⁺⁾ of more than 4.8V below (appearing in the positive electrode potential range of vs.Li/Li ^+), by providing a manufacturing step of performing at least throughout charging potential change to a relatively flat region, using Even when a charging method is adopted in which the maximum potential of the positive electrode during charging is 4.3 V (vs. Li / Li ⁺ ) or less or less than 4.4 V (vs. Li ^/ Li ⁺ ) It is described that a battery capable of obtaining a discharge capacity of 200 mAh / g or more can be manufactured.

Thus, unlike the case of the conventional “LiMeO ₂ type” positive electrode active material, the positive electrode active material containing Ni, Co and Mn as Me, and the molar ratio of Mn to Me, Mn / Me is 0.5 or more. In at least the first charge, a relatively high potential exceeding 4.3 V, in particular, a potential of 4.4 V or higher is achieved, whereby a high discharge capacity can be obtained.
In this material, the raw materials are mixed so that the composition ratio Li / Me of lithium (Li) to the ratio of transition metal (Me) is greater than 1, for example, Li / Me is 1.25 to 1.6. Since it is synthesized, it is also called a “lithium-excess type” active material, and the composition after synthesis can be expressed as Li _{1 + α} Me _1-α O ₂ (α> 0). Here, when the composition ratio Li / Me of lithium (Li) with respect to the ratio of the transition metal (Me) is β, β = (1 + α) / (1-α), and thus, for example, Li / Me is 1.5. In this case, α = 0.2.

  It is known to improve various properties of a lithium secondary battery by treating a positive electrode active material containing a lithium transition metal composite oxide with phosphoric acid (see, for example, Patent Documents 3 to 6).

Patent Document 3 discloses that “chemical formula Li _{1 +} xs Mn _{1- xy My} O _2−t (0 <x <0.33, 0 <y <0.66, 0 <s <0.3, 0 <T <0.15, and M is at least one transition metal excluding manganese). First, a first lithium-containing transition metal composite oxide particle is immersed in an aqueous solution containing a first reducing agent. And a second step of performing a heat treatment in a temperature range of 200 to 500 ° C. in a state where the solution containing the first reducing agent is attached to the high lithium-containing transition metal composite oxide particles. The invention according to claim 6 is described. As an object of the present invention, “the present invention is directed to the load characteristics and charge / discharge efficiency while suppressing the decrease in energy density. Dramatically improve various battery characteristics such as improved battery capacity and increased discharge capacity “Providing a positive electrode active material, a method for producing the positive electrode active material, and a battery using the positive electrode active material” (paragraph [0013]).
Patent Document 3 states that “Li ₃ PO ₄ is produced as a residue on the surface of the positive electrode active material particles when phosphate is used as the first reducing agent as in the above configuration. _{Since 3} PO ₄ is not water-soluble, it cannot be easily removed, so that Li ₃ PO ₄ exhibits a function as a protective layer on the surface of the positive electrode active material particles, so that even if charging and discharging are repeated. , It is possible to suppress the elution of transition metal atoms from the positive electrode active material, resulting in improved cycle characteristics, provided that the amount of the first reducing agent relative to the total amount of the high lithium-containing transition metal composite oxide particles (hereinafter simply referred to as (Sometimes referred to as the amount of the first reducing agent) exceeds 5% by mass, the remaining amount of Li ₃ PO ₄ becomes too large, the proportion of the positive electrode active material decreases, and the protective layer becomes thicker. Too much result On the other hand, if the amount of the first reducing agent is less than 1% by mass, it does not change sufficiently to the spinel structure in the vicinity of the surface of the positive electrode active material particles, so Therefore, when phosphate is used as the first reducing agent, the amount of the first reducing agent is preferably regulated to 1 to 5% by mass ”(paragraph [ 0024]).

Patent Document 4 discloses an “active material having a layered structure and represented by the following composition formula (1).
_{Li y Ni a Co b Mn c} M d O x F z1 P z2 (1)
[In the above formula (1), the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba and V, and 1.9 ≦ (a + b + c + d + y) ≦ 2.1, 1.0 ≦ y ≦ 1.3, 0 <a ≦ 0.3, 0 ≦ b ≦ 0.25, 0.3 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.1, 0. 07 ≦ z1 ≦ 0.15, 0.01 ≦ z2 ≦ 0.1, 1.9 ≦ (x + z1) ≦ 2.1. The invention according to claim 1 is described, and as an object of the present invention, “active material having high capacity and excellent charge / discharge cycle durability at high potential, method for producing active material, and lithium ion secondary battery” Is provided "(paragraph [0006]).
Patent Document 4 discloses that “a lithium compound (second precursor) is applied to the positive electrode surface of a lithium ion secondary battery to form a lithium compound layer. The lithium ion secondary battery is used as an electrolyte salt. A non-aqueous electrolyte in which LiPF ₆ is dissolved is provided, and the lithium ion secondary battery is charged and discharged at least once, whereby the lithium compound (second precursor) represented by the composition formula (2) is obtained by this charging and discharging process. P and F derived from LiPF ₆ are diffused inside the crystal structure, and as a result, the active material of this embodiment having a layered structure and represented by the following composition formula (1) is obtained. An active material represented by the following composition formula (1) is obtained by carrying out the charge / discharge process once or more for a lithium ion secondary battery including the layer of the second precursor represented by the composition formula (2). Layer (positive electrode active material layer) Lithium ion secondary battery is completed.
_{Li y Ni a Co b Mn c} M d O x F z1 P z2 (1) "is described as (paragraph [0030]).

Patent Document 5 states that “a positive electrode material for a lithium secondary battery having a metal fluoride and a lithium phosphate compound on the surface of a lithium transition metal composite oxide containing at least Mn as a transition metal” (claimed). Item 1) and “The lithium transition metal composite oxide has a hexagonal layered structure and a composition formula LiMn _x M _1-x O ₂ (where 0.3 ≦ x ≦ 0.6. B, Mg, Al, Co, lithium-transition metal composite oxide represented by a one or more elements selected from the group consisting of Ni), or has a cubic spinel structure and the composition formula LiMn _y N _1-y O ₄ (wherein 1.5 ≦ y ≦ 1.9, N is one or more elements selected from the group consisting of Li, Mg, Al, Ni) The lithi according to claim 1, wherein A positive electrode material for a secondary battery.The invention of (Claim 2) is described, and an object of the present invention is “a surface coating that can stably suppress elution of Mn even at high temperature and high voltage without reducing conductivity” "Providing a lithium secondary battery excellent in high-temperature cycle characteristics using lithium manganese composite oxide as a positive electrode material" (paragraph [0010]) is shown.

Patent Document 6 states that “composition formula LiMn _x M _1-x O ₂ (where 0.1 ≦ x ≦ 0.6, M is selected from the group consisting of Li, Mg, Al, Ti, Co, Ni, Mo). In the positive electrode material for a lithium secondary battery having a lithium manganese composite oxide having a layered structure represented by a phosphoric acid compound and A (on the surface of the lithium manganese composite oxide) A is a coating layer containing an oxide or fluoride containing one or more elements selected from the group consisting of Mg, Al, Ti, and Cu, and the atomic concentration of phosphorus in the coating layer is: The positive electrode material for a lithium secondary battery characterized in that the surface layer side is higher than the lithium manganese composite oxide side. "(Claim 1) The invention of (claim 1) is described, and as an object of this invention," lithium manganese having a layered structure " Complex oxide In view of the role of the compound used for coating, it was an object to optimize the arrangement of the coating compound to improve the coating effect, and to use a surface-coated lithium manganese composite oxide having excellent thermal stability in a charged state as a positive electrode material. To provide a lithium secondary battery excellent in safety ”(paragraph [0006]).

WO2012 / 091015 WO2013 / 084923 JP 2011-96626 A JP 2012-38564 A JP2010-23001A JP 2012-38534 A

Although the above-mentioned Me contains Ni, Co and Mn, the discharge capacity of the active material in which the molar ratio of Mn to Me, Mn / Me is 0.5 or more, is generally larger than that of the conventional “LiMeO ₂ type” active material. It is known that the high rate discharge performance is inferior. In recent years, lithium secondary batteries used in the automotive field such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles are required to have a positive electrode active material that not only has a large discharge capacity but also an excellent high-rate discharge performance. Patent Documents 3 and 4 describe that an active material containing Ni, Co, and Mn as Me and having a molar ratio of Mn to Me of Mn / Me of 0.5 or more is subjected to phosphoric acid treatment. The positive electrode active material described in Patent Document 3 has much more P element adhering than that of the present invention (converted to 3100-15000 ppm), and is described in Patent Document 4. The active material is obtained by diffusing P by charge / discharge using a non-aqueous electrolyte in which LiPF ₆ is dissolved, and this P is removed by washing. The phosphoric acid-treated active material described in Patent Documents 5 and 6 is basically a “LiMeO ₂ type” positive electrode active material, which contains Ni, Co and Mn as Me, and the molar ratio of Mn to Me, Mn / Me. Is not an active material having 0.5 or more.
The present invention has been made in view of the above problems, and is an active material containing Ni, Co and Mn as Me, and having a molar ratio of Mn to Me, Mn / Me of 0.5 or more, and high rate discharge performance. It is an object of the present invention to provide a positive electrode active material for a lithium secondary battery, and a lithium secondary battery using the positive electrode active material.

In the present invention, in order to solve the above problems, the following means are adopted.
(1) A positive electrode active material for a lithium secondary battery including a lithium transition metal composite oxide having an α-NaFeO ₂ structure, wherein the transition metal (Me) is Co, Ni, and The Mn molar ratio Mn / Me in the transition metal is Mn / Me ≧ 0.5, and the half width of the diffraction peak at 2θ = 44 ± 1 ° in the X-ray diffraction pattern using the CuKα radiation source is A positive electrode active material for a lithium secondary battery, which is 0.265 ° or more and contains a P element.
(2) The positive electrode active material for a lithium secondary battery according to (1), wherein the amount of the P element is 2000 ppm or less.
(3) The positive electrode active material for a lithium secondary battery according to (1) or (2), wherein the lithium transition metal composite oxide contains P by heat treatment after phosphoric acid treatment.
(4) The positive electrode active material for a lithium secondary battery according to any one of (1) to (3), wherein a molar ratio Li / Me of lithium (Li) to the transition metal is greater than 1.
(5) The electrode for lithium secondary batteries containing the positive electrode active material for lithium secondary batteries of any one of said (1)-(4).
(6) A lithium secondary battery comprising the lithium secondary battery electrode of (5).
(7) A power storage device configured by assembling a plurality of the lithium secondary batteries of (6).

  According to the present invention, by using a positive electrode active material containing a novel lithium transition metal composite oxide, a lithium secondary battery excellent in high-rate discharge performance, particularly high-rate discharge performance after a charge / discharge cycle is provided. be able to.

1 is an external perspective view showing an embodiment of a lithium secondary battery according to the present invention. Schematic showing a power storage device in which a plurality of lithium secondary batteries according to the present invention are assembled

The present inventors include phosphoric acid as an active material (lithium transition metal composite oxide) containing Ni, Co and Mn as transition metals (Me) and having a molar ratio of Mn to Me, Mn / Me of 0.5 or more. When the heat treatment is performed after the treatment, it is found that if the acid pH, the treatment time with the acid, and the heat treatment temperature are in an appropriate range, the high rate discharge performance, particularly the high rate discharge performance after the charge / discharge cycle is improved. Completed the invention. As shown in the above (1), it can be seen that by confirming the Mn / Me ratio, the half width, and the presence or absence of the P element of the lithium transition metal composite oxide, the lithium transition metal composite oxide having the above effect can be obtained.
When Li is chemically desorbed by treating the active material with phosphoric acid, the crystallinity of the active material changes and the pore state changes. Therefore, it is considered that the diffusion of the electrolytic solution in the active material is improved and the electrochemical characteristics of the active material are improved.
By heat treatment after the phosphoric acid treatment, it is considered that a polymerized P layer such as lithium phosphate or metaphosphoric acid (HPO ₃ ) _n is formed on the active material. Since these compounds are not removed by washing and require heating at 1000 ° C. or higher for decomposition and removal, they can be distinguished from P derived from an electrolytic solution and additives (removed by washing).

  The composition of the lithium transition metal composite oxide contained in the active material for lithium secondary battery according to the present invention is that the transition metal (Me) contains Co, Ni and Mn, and the molar ratio Mn / Me is 0.5 or more. The molar ratio Mn / Me is preferably 0.6 or more, and more preferably 0.6 to 0.75.

  In the present invention, in order to improve the initial efficiency and high rate discharge performance of the lithium secondary battery, the molar ratio Co / Me of Co to the transition metal element Me is preferably 0.05 to 0.40, It is more preferable to set it as 0.10-0.30.

In the present invention, the molar ratio Li / Me of lithium (Li) to the transition metal is greater than 1 in order to improve charge / discharge cycle performance. This feature can be expressed as Li _{1 + α} Me _1-α O ₂ ((1 + α) / (1-α)> 1).

In particular, in order to obtain a lithium secondary battery with excellent initial efficiency and high rate discharge performance, the molar ratio Li / Me of Li to the transition metal element Me should be larger than 1.2 and smaller than 1.6. That is, it is preferable that 1.2 <(1 + α) / (1-α) <1.6 in the composition formula Li _{1 + α} Me _1-α O ₂ . In particular, from the viewpoint that a lithium secondary battery having a particularly large discharge capacity and excellent high-rate discharge performance can be obtained, it is preferable to select one having the Li / Me of 1.25 to 1.5.

The lithium transition metal composite oxide according to the present invention has a general formula Li _{1 + α} (Co _a Ni _b Mn _c ) _1-α O ₂ , provided that (1 + α) / (1-α)> 1, a + b + c = 1, a> 0, b> 0, c> 0, which is essentially a composite oxide composed of Li, Co, Ni, and Mn, but contains 1000 ppm or more of Na in order to improve the discharge capacity. It is preferable. As for content of Na, 2000-10000 ppm is more preferable.

  In order to contain Na, in the step of preparing a carbonate precursor, which will be described later, a sodium compound such as sodium carbonate is used as a neutralizing agent, and Na is left in the washing step. A method of adding a sodium compound such as sodium can be employed.

  In addition, a small amount of other metals such as alkali metals other than Na, alkaline earth metals such as Mg and Ca, transition metals typified by 3d transition metals such as Fe and Zn, and the like are included as long as the effects of the present invention are not impaired. It does not exclude doing.

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

In the lithium transition metal composite oxide according to the present invention, the half width of the diffraction peak at 2θ = 44 ± 1 ° in the X-ray diffraction pattern using the CuKα radiation source is 0.265 ° or more. By doing so, it becomes possible to improve the high rate discharge performance of the positive electrode active material. The upper limit of the half width of the diffraction peak at 2θ = 44 ± 1 ° is not limited, but can be up to about 0.285. The diffraction peak at 2θ = 44 ± 1 ° is indexed on the (114) plane in the space group P3 ₁ 12 and on the (104) plane in the space group R3-m.

  The lithium transition metal composite oxide according to the present invention is required to satisfy the specific conditions as described above for crystallinity after the phosphoric acid treatment, but in addition to that, it must contain a P element. . This can be confirmed by detecting the P element in high frequency inductively coupled plasma optical emission spectrometry (ICP measurement). The amount of element P is linked to the pH of the treatment liquid and the treatment time, as will be described later. Further, as shown in Examples and Comparative Examples, even if the amount of P element is the same by phosphoric acid treatment, 2θ = 44 ± 1 of the lithium transition metal composite oxide depending on the presence or absence of the subsequent heat treatment and the heat treatment conditions. In some cases, the half-value width of the diffraction peak at 0 ° does not exceed 0.265 °. In the positive electrode active material according to the present invention, when the half-value width of the diffraction peak at 2θ = 44 ± 1 ° is 0.265 ° or more and the P element is detected, the high rate discharge performance is improved. The content of P element is preferably 300 ppm or more, and more preferably 300 to 2000 ppm.

Further, in the lithium transition metal composite oxide, the oxygen position parameter obtained from the crystal structure analysis by the Rietveld method based on the X-ray diffraction pattern may be 0.262 or less at the end of discharge and 0.267 or more at the end of charge. preferable. Thereby, a lithium secondary battery excellent in high rate discharge performance can be obtained. Note that the oxygen positional parameter is Me (transition metal) spatial coordinates (0, 0, 0) for the α-NaFeO ₂ type crystal structure of the lithium transition metal composite oxide belonging to the space group R3-m, This is the value of z when the spatial coordinates of Li (lithium) are defined as (0, 0, 1/2) and the spatial coordinates of O (oxygen) are defined as (0, 0, z). In other words, the oxygen position parameter is a relative index indicating how far the O (oxygen) position is from the Me (transition metal) position (see Patent Documents 1 and 2).

  The lithium transition metal composite oxide and its carbonate precursor according to the present invention preferably have a 50% particle diameter (D50) of 5 to 18 μm in the particle size distribution measurement. When producing a lithium transition metal composite oxide from a hydroxide precursor, excellent performance cannot be obtained unless the particle size is controlled to be smaller, but by producing from a carbonate precursor, 50% in the particle size distribution measurement. Even when the particle diameter (D50) is about 5 to 18 μm, a positive electrode active material having a large discharge capacity can be obtained.

BET specific surface area of the positive electrode active material according to the present invention, the initial efficiency, in order to obtain a lithium secondary battery having excellent high rate discharge performance, preferably at least ^{1m 2 / g, 2~7m 2 /} g is more preferable.
Further, the tap density is preferably 1.25 g / cc or more, and more preferably 1.7 g / cc or more in order to obtain a lithium secondary battery excellent in high rate discharge performance.

  The lithium transition metal composite oxide according to the present invention has a pore region having a pore diameter within a range of up to 60 nm, which indicates the maximum value of the differential pore volume determined by the BJH method from the adsorption isotherm using the nitrogen gas adsorption method ( It is preferable that the pore volume be 0.055 cc / g or more in the pore region (up to 60 nm). Thereby, a lithium secondary battery excellent in initial efficiency and high rate discharge performance can be obtained. In addition, by setting the pore volume to 0.08 cc / g or less, a lithium secondary battery having particularly excellent high rate discharge performance can be obtained. Therefore, the pore volume is 0.055 to 0.08 cc / g. It is preferable that it is g.

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

When preparing a coprecipitation precursor, Mn is easily oxidized among Co, Ni and Mn, and it is not easy to prepare a coprecipitation precursor in which Co, Ni and Mn are uniformly distributed in a divalent state. Uniform mixing at the atomic level of Co, Ni and Mn tends to be insufficient. In particular, in the composition range of the present invention, since the Mn ratio is higher than the Co and Ni ratios, it is particularly important to remove dissolved oxygen in the aqueous solution. Examples of the method for removing dissolved oxygen include a method of bubbling a gas not containing oxygen. The gas not containing oxygen is not limited, but nitrogen gas, argon gas, carbon dioxide (CO ₂ ), or the like can be used. Among these, when preparing a coprecipitated carbonate precursor as in the examples described later, it is preferable to employ carbon dioxide as a gas not containing oxygen because an environment in which carbonate is more easily generated is provided. .

  Although the pH in the step of producing a precursor by co-precipitation of a compound containing Co, Ni and Mn in a solution is not limited, an attempt is made to prepare the co-precipitation precursor as a co-precipitation carbonate precursor. When it does, it can be set to 7.5-11. In order to increase the tap density, it is preferable to control the pH. By setting the pH to 9.4 or less, the tap density can be set to 1.25 g / cc or more, and the high rate discharge performance can be improved. Furthermore, since the particle growth rate can be accelerated by setting the pH to 8.0 or less, the stirring continuation time after completion of dropping of the raw material aqueous solution can be shortened.

  The coprecipitation precursor is preferably a compound in which Mn, Ni, and Co are uniformly mixed. In the present invention, in order to obtain an active material for a lithium secondary battery having a large discharge capacity, the coprecipitation precursor is preferably a carbonate. In addition, a precursor having a larger bulk density can be produced by using a crystallization reaction using a complexing agent. At that time, a higher density active material can be obtained by mixing and firing with a Li source, so that the energy density per electrode area can be improved.

  The raw materials for the coprecipitation precursor include manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese acetate, etc. as the Mn compound, and nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, nickel acetate as the Ni compound. As examples of the Co compound, cobalt sulfate, cobalt nitrate, cobalt acetate, and the like can be given as examples.

  In the present invention, a reaction crystallization method is employed in which a raw material aqueous solution of the coprecipitation precursor is supplied dropwise to a reaction tank maintaining alkalinity to obtain a coprecipitation carbonate precursor. Here, lithium compounds, sodium compounds, potassium compounds, and the like can be used as the neutralizing agent, but it is preferable to use sodium carbonate, sodium carbonate and lithium carbonate, or a mixture of sodium carbonate and potassium carbonate. In order to leave Na at least 1000 ppm, Na / Li, which is the molar ratio of sodium carbonate to lithium carbonate, or Na / K, which is the molar ratio of sodium carbonate to potassium carbonate, is 1/1 [M] or more. Is preferred. By setting Na / Li or Na / K to 1/1 [M] or more, it is possible to reduce the possibility that Na will be excessively removed in the subsequent washing step and become less than 1000 ppm.

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

  In addition, when a complexing agent is present in the reaction tank and a certain convection condition is applied, the particle rotation and revolution in the stirring tank are promoted by continuing the stirring after the dropwise addition of the raw material aqueous solution. In this process, the particles grow concentrically in stages while colliding with each other. That is, the coprecipitation precursor undergoes a reaction in two stages: a metal complex formation reaction when the raw material aqueous solution is dropped into the reaction tank, and a precipitation formation reaction that occurs while the metal complex is retained in the reaction tank. It is formed. Therefore, a coprecipitation precursor having a target particle size can be obtained by appropriately selecting a time for continuing stirring after the dropping of the raw material aqueous solution.

  The preferable stirring duration after completion of dropping of the raw material aqueous solution is influenced by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but 0.5 h or more is required to grow the particles as uniform spherical particles. Preferably, 1 h or more is more preferable. Further, in order to reduce the possibility that the output performance in the low SOC region of the battery is not sufficient due to the particle size becoming too large, 30 h or less is preferable, 25 h or less is more preferable, and 20 h or less is most preferable.

  In addition, the preferable stirring duration for setting D50, which is a particle diameter at which the cumulative volume in the particle size distribution of the secondary particles of the carbonate precursor and the lithium transition metal composite oxide is 50%, to 5 to 18 μm is controlled by pH It depends on. For example, when the pH is controlled to 7.5 to 8.2, the stirring duration is preferably 1 to 15 h, and when the pH is controlled to 8.3 to 9.4, the stirring duration is 3 to 3. 20h is preferred.

  When the carbonate precursor particles are prepared using a sodium compound such as sodium carbonate as a neutralizing agent, sodium ions adhering to the particles are washed away in the subsequent washing step. It is preferable to wash and remove under conditions such that Na remains at 1000 ppm or more. For example, when the produced carbonate precursor is removed by suction filtration, a condition that the number of washings with 200 ml of ion-exchanged water is 5 times can be employed.

The carbonate precursor is preferably dried at 80 ° C. to less than 100 ° C. in an air atmosphere under normal pressure. By drying at 100 ° C. or higher, more water can be removed in a short time, but by drying at 80 ° C. for a long time, an active material having more excellent electrode characteristics can be obtained. Although the reason is not necessarily clear, since the carbonate precursor is a porous body having a specific surface area of 50 to 100 m ² / g, it has a structure that easily adsorbs moisture. Therefore, by drying at a low temperature, a state in which a certain amount of adsorbed water remains in the pores in the state of the precursor is removed from the pores in the firing step of mixing with the Li salt and firing. The invention may be because molten Li can enter the pores so as to replace the adsorbed water, and thereby, an active material having a more uniform composition can be obtained compared with the case of drying at 100 ° C. Have guessed. In addition, although the carbonate precursor obtained by drying at 100 ° C. exhibits a black brown color, the carbonate precursor obtained by drying at 80 ° C. exhibits a skin color, so depending on the color of the precursor Can be distinguished.

Therefore, in order to quantitatively evaluate the difference in the precursors found above, the hues of the respective precursors are measured, and standard colors for paints (JPMA Standard Paint Colors) issued by the Japan Paint Manufacturers Association in accordance with JIS Z 8721. ) Compared with the 2011 F version. For measuring the hue, a color reader CR10 manufactured by Konica Minolta Co., Ltd. was used. According to this measuring method, the value of dL * representing lightness is larger in white and smaller in black. Further, the value of da * representing the hue is larger when red is stronger and smaller when green is stronger (red is weaker). In addition, the value of db * representing the hue becomes larger when yellow is stronger and larger when blue is stronger (yellow is weaker).
The hue of the dried product at 100 ° C. is in the range reaching the standard color F05-40D in the red direction as compared with the standard color F05-20B, and the standard color FN− in the white direction as compared with the standard color FN-10. It was found to be in the range up to 25. Among these, it was recognized that the color difference from the hue exhibited by the standard color F05-20B was the smallest.
On the other hand, the hue of the dried product at 80 ° C. is within the range reaching the standard color F19-70F in the white direction compared to the standard color F19-50F, and the standard color in the black direction compared to the standard color F09-80D. It was found to be in the range up to F09-60H. Especially, it was recognized that the color difference with the hue which standard color F19-50F exhibits is the smallest.
From the above knowledge, the hue of the carbonate precursor is preferably positive in all of dL, da and db as compared with the standard color F05-20B, dL is +5 or more, da is +2 or more, and db is It can be said that +5 or more is more preferable.

  The active material for a lithium secondary battery of the present invention can be suitably prepared by mixing the carbonate precursor and the Li compound and then heat-treating them. As a Li compound, it can manufacture suitably by using lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, etc. However, with respect to the amount of the Li compound, it is preferable to add an excess of about 1 to 5% in view of the disappearance of a part of the Li compound during firing.

  In the present invention, in order to make the content of Na in the lithium transition metal composite oxide 1000 ppm or more, even if Na contained in the carbonate precursor is 1000 ppm or less, the Na compound is added together with the Li compound in the firing step. By mixing with the carbonate precursor, the amount of Na contained in the active material can be 1000 ppm or more. As the Na compound, sodium carbonate is preferable.

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

On the other hand, if the firing temperature is too low, crystallization does not proceed sufficiently and the electrode characteristics tend to deteriorate. In the present invention, the firing temperature is preferably at least 800 ° C. or higher. By sufficiently crystallizing, the resistance of the crystal grain boundary can be reduced and smooth lithium ion transport can be promoted.
In addition, the inventors have analyzed the half width of the diffraction peak of the active material of the present invention in detail, and in the sample synthesized at a temperature up to 750 ° C., strain remains in the lattice, and at a temperature higher than that, It was confirmed that almost all strains could be removed by synthesis. The crystallite size was increased in proportion to the increase in the synthesis temperature. Therefore, even in the composition of the active material of the present invention, a favorable discharge capacity can be obtained by aiming at a particle having almost no lattice distortion in the system and having a sufficiently grown crystallite size. Specifically, it is preferable to employ a synthesis temperature (firing temperature) and a Li / Me ratio composition in which the strain amount affecting the lattice constant is 2% or less and the crystallite size is grown to 50 nm or more. all right. Although changes due to expansion and contraction are observed by charging and discharging by molding these as electrodes, it is preferable as an effect that the crystallite size is maintained at 30 nm or more in the charging and discharging process.

As described above, the firing temperature is related to the oxygen release temperature of the active material. However, even if the firing temperature does not reach the firing temperature at which oxygen is released from the active material, the crystal due to large growth of primary particles above 900 ° C. A phenomenological phenomenon is observed. This can be confirmed by observing the fired active material with a scanning electron microscope (SEM). The active material synthesized through a synthesis temperature exceeding 900 ° C. has primary particles grown to 0.5 μm or more, which is disadvantageous for Li ⁺ movement in the active material during the charge / discharge reaction, and has a high rate discharge performance. descend. The size of the primary particles is preferably less than 0.5 μm, and more preferably 0.3 μm or less. Further, at a synthesis temperature exceeding 900 ° C., the pore volume of the active material is less than 0.055 cc / g in the pore region up to 60 nm, and the initial efficiency and high rate discharge performance are lowered.
Therefore, in order to improve initial efficiency and high rate discharge performance, when the lithium transition metal composite oxide according to the present invention of 1.2 <molar ratio Li / Me <1.6 is used as the positive electrode active material, the firing temperature is It is preferable to set it as 800-900 degreeC.

In the present invention, the lithium transition metal composite oxide produced as described above is subjected to phosphoric acid treatment, and after the phosphoric acid treatment, heat treatment is performed. If the pH of the acid (hydrogen ion concentration) and the treatment time are in an appropriate range, and the temperature range of the heat treatment is appropriate, the lithium transition metal composite oxide subjected to the phosphoric acid treatment is subjected to X-ray diffraction using a CuKα radiation source. Compared with the pattern in which the half width of the diffraction peak at 2θ = 44 ° in the pattern is 0.265 ° or more and P element is detected in the high frequency inductively coupled plasma optical emission spectrometry and the phosphoric acid treatment is not performed. The high rate discharge performance when used as a substance is improved. The hydrogen ion concentration in the phosphoric acid treatment is preferably 0.05 to 1.0 M, and the acid treatment time is preferably 30 to 10800 seconds. The heat treatment temperature after the phosphoric acid treatment is more than 200 ° C, preferably less than 800 ° C, more preferably 250 to 550 ° C.
As described above, a lithium transition metal composite oxide used as a positive electrode active material was produced.

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

  It is desirable that the positive electrode active material powder and the negative electrode material powder have an average particle size of 100 μm or less. In particular, the positive electrode active material powder is desirably 10 μm or less for the purpose of improving the high output characteristics of the non-aqueous electrolyte battery. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill or a sieve is used. At the time of pulverization, wet pulverization in the presence of water or an organic solvent such as hexane may be used. There is no particular limitation on the classification method, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

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

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

  Among these, as the conductive agent, acetylene black is desirable from the viewpoints of electron conductivity and coatability. The addition amount of the conductive agent is preferably 0.1% by weight to 50% by weight, and particularly preferably 0.5% by weight to 30% by weight with respect to the total weight of the positive electrode or the negative electrode. In particular, it is desirable to use acetylene black by pulverizing into ultrafine particles of 0.1 to 0.5 μm because the required carbon amount can be reduced. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet.

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

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

  The positive electrode and the negative electrode are prepared by mixing the main constituents (positive electrode active material in the positive electrode, negative electrode material in the negative electrode) and other materials into a mixture and mixing with an organic solvent such as N-methylpyrrolidone or toluene or water. After that, the obtained mixed solution is applied on a current collector such as an aluminum foil, or is pressure-bonded and heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. About the application method, for example, it is desirable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. It is not limited.

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

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

Furthermore, by mixing and using LiPF ₆ or LiBF ₄ and a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ , the viscosity of the electrolyte can be further reduced. The low temperature characteristics can be further improved, and self-discharge can be suppressed, which is more desirable.

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

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

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

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

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

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

  Examples of the solvophilic polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a polymer having a monomer having an isocyanate group, and the like crosslinked. The monomer can be subjected to a crosslinking reaction using a radical initiator in combination with heating or ultraviolet rays (UV), or using an actinic ray such as an electron beam (EB).

  Other battery components include a terminal, an insulating plate, a battery case, and the like, but these components may be used as they are.

  FIG. 1 shows an external perspective view of a rectangular lithium secondary battery 1 which is an embodiment of a lithium secondary battery according to the present invention. In the figure, the inside of the container is seen through. In the lithium secondary battery 1 shown in FIG. 1, an electrode group 2 is housed in a battery container 3. The electrode group 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material via a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4 ′, and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5 ′.

  The shape of the lithium secondary battery according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), a flat battery, and the like. The present invention can also be realized as a power storage device in which a plurality of the lithium secondary batteries are assembled. One embodiment of a power storage device is shown in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of lithium secondary batteries 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV).

Both the conventional positive electrode active material and the active material of the present invention can be charged / discharged when the positive electrode potential reaches around 4.5 V (vs. Li ^/ Li ⁺ ). However, depending on the type of nonaqueous electrolyte used, if the positive electrode potential during charging is too high, the nonaqueous electrolyte may be oxidized and decomposed, resulting in a decrease in battery performance. Therefore, in use, a lithium secondary battery capable of obtaining a sufficient discharge capacity even when a charging method is adopted in which the maximum potential of the positive electrode during charging is 4.3 V (vs. Li ^/ Li ⁺ ) or less. May be required. When the active material of the present invention is used, for example, 4.4 V (vs. Li ^/ Li) such that the maximum potential of the positive electrode during charging is lower than 4.5 V (vs. Li ^/ Li ⁺ ) during use. ⁺ ) Or less and 4.3 V (vs. Li ^/ Li ⁺ ) or less, even if a charging method is adopted, it is possible to take out a discharge electric quantity exceeding the capacity of the conventional positive electrode active material of about 200 mAh / g or more. Is possible.

In order for the positive electrode active material according to the present invention to have a high discharge capacity, the transition metal element constituting the lithium transition metal composite oxide is present in a portion other than the transition metal site of the layered rock salt type crystal structure. It is preferable that the ratio is small. This is because, in the precursor to be subjected to the firing step, the transition metal elements such as Co, Ni, and Mn in the precursor core particles are sufficiently uniformly distributed, and appropriate for promoting the crystallization of the active material sample. This can be achieved by selecting the conditions for the firing process. If the distribution of the transition metal in the precursor core particles subjected to the firing step is not uniform, a sufficient discharge capacity cannot be obtained. Although the reason for this is not necessarily clear, when the distribution of the transition metal in the precursor core particles to be subjected to the firing step is not uniform, the resulting lithium transition metal composite oxide has a layered rock salt type crystal structure other than the transition metal site. The present inventors speculate that this is due to the occurrence of so-called cation mixing, in which a part of the transition metal element is present at the lithium site. The same inference can be applied to the crystallization process in the firing step. If the crystallization of the active material sample is insufficient, cation mixing in the layered rock salt type crystal structure is likely to occur. When the transition metal element has a high uniformity of distribution, the intensity ratio of the diffraction peaks of the (003) plane and the (104) plane tends to be large when the X-ray diffraction measurement result belongs to the space group R3-m. There is. In the present invention, the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of diffraction peaks of the (003) plane and the (104) plane by X-ray diffraction measurement is 1.0 or more at the end of discharge and 1.75 or more at the end of charging. It is preferable that If the precursor synthesis conditions and procedure are inadequate, the peak intensity ratio will be smaller and often less than 1.

By adopting the synthesis conditions and synthesis procedures described in this specification, a high-performance positive electrode active material as described above can be obtained. In particular, when the charging upper limit potential is set lower than 4.5 V (vs. Li ^/ Li ⁺ ), for example, it is set lower than 4.4 V (vs. Li ^/ Li ⁺ ) or 4.3 V (vs. Li ^/ Li ⁺ ). In this case, a positive electrode active material for a lithium secondary battery capable of obtaining a high discharge capacity can be obtained.

Example 1
<Sample synthesis>
Cobalt sulfate heptahydrate (14.08 g), nickel sulfate hexahydrate (21.00 g) and manganese sulfate pentahydrate (65.27 g) were weighed, and all of these were dissolved in 200 ml of ion-exchanged water, and Co: Ni: Mn A 2.0 M aqueous sulfate solution having a molar ratio of 12.50: 19.94: 67.56 was prepared. On the other hand, 750 ml of ion exchange water was poured into a ₂ L reaction tank, and CO ₂ gas was bubbled for 30 minutes to dissolve CO _{2 in the} ion exchange water. The temperature of the reaction vessel was set to 50 ° C. (± 2 ° C.), and the aqueous sulfate solution was stirred at a rate of 3 ml / min while stirring the inside of the reaction vessel at a rotational speed of 700 rpm using a paddle blade equipped with a stirring motor. It was dripped. Here, during the period from the start to the end of the dropwise addition, an aqueous solution containing 2.0 M sodium carbonate and 0.4 M ammonia is appropriately dropped, so that the pH in the reaction tank is always 7.9 (± 0. 05). After completion of the dropping, stirring in the reaction vessel was further continued for 5 hours. After the stirring was stopped, the mixture was allowed to stand for 12 hours or more.
Next, using a suction filtration device, the coprecipitated carbonate particles produced in the reaction vessel are separated, and sodium ions adhering to the particles are washed away using ion-exchanged water, and an electric furnace is used. Then, it was dried at 100 ° C. for 20 hours in an air atmosphere under normal pressure. Then, in order to arrange | equalize a particle size, it grind | pulverized for several minutes with the smoked automatic mortar. In this way, a coprecipitated carbonate precursor was produced.

Lithium carbonate is added to 2.278 g of the coprecipitated carbonate precursor so that the molar ratio of Li: (Co, Ni, Mn) is 1.44 and mixed well using a smoked automatic mortar. The body was prepared. Using a pellet molding machine, molding was performed at a pressure of 6 MPa to obtain pellets having a diameter of 25 mm. The amount of the mixed powder subjected to pellet molding was determined by conversion so that the mass of the assumed final product was 2 g. One pellet was placed on an alumina boat having a total length of about 100 mm, placed in a box-type electric furnace (model number: AMF20), and heated in an air atmosphere at normal pressure to a temperature of 900 ° C. over 10 hours. And calcined for 10 hours at the temperature after the temperature elevation. The box-type electric furnace has internal dimensions of 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was turned off and allowed to cool naturally with the alumina boat placed in the furnace. As a result, the temperature of the furnace decreases to about 200 ° C. after 5 hours, but the subsequent temperature decrease rate is somewhat moderate. After the passage of day and night, it was confirmed that the furnace temperature was 100 ° C. or lower, and then the pellets were taken out and pulverized for several minutes in a smoked automatic mortar in order to make the particle diameter uniform. Thus, the starting lithium transition metal composite oxide Li _1.18 Co _0.10 Ni _0.17 Mn _0.55 O ₂ (Li / Me = 1.44) containing 2100 ppm of Na and having a D50 of 13 μm. ) Was produced.

<Phosphoric acid treatment to lithium transition metal composite oxide>
A 300 ml Erlenmeyer flask was mixed with 85 wt% phosphoric acid and ion-exchanged water to prepare a phosphoric acid aqueous solution having a hydrogen ion concentration (calculated as phosphoric acid concentration × 3) of 0.1M. 5.0 g of the above lithium transition metal composite oxide was added to the above phosphoric acid aqueous solution stirred at 25 ° C. and 400 rpm using a stirrer. The lithium transition metal composite oxide was collected on the filter paper by suction filtration after 30 seconds from the introduction of the lithium transition metal composite oxide.
This lithium transition metal composite oxide was dried for 16 to 18 hours at 80 ° C. in air at normal pressure using a dryer (manufactured by Yamato Kagaku Co., Ltd.) to obtain a lithium transition metal composite oxide treated with phosphoric acid. .

<Heat treatment of phosphoric acid-treated lithium transition metal composite oxide>
The above-mentioned phosphoric acid-treated lithium transition metal composite oxide (5.0 g) is added to an alumina crucible lid and placed in a box-type electric furnace (model number: AMF20). In the air, the heating rate is 5 ° C./min. Was subjected to a heat treatment under the conditions of 400 ° C. and a holding time of 4 hours to obtain a lithium transition metal composite oxide that had been subjected to a phosphoric acid treatment and a heat treatment.
This lithium transition metal complex oxide was Li / Me = 1.40.

(Example 2)
Instead of using 5.0 g of the lithium transition metal composite oxide treated with phosphoric acid and heat treated, 5.0 g of a mixture of the lithium transition metal composite oxide treated with phosphoric acid and heat treated and LiOH.H ₂ O was used. In the same manner as in Example 1, a lithium transition metal composite oxide according to Example 2 was produced.
The method of determining the mixing amount of LiOH.H ₂ O was performed as follows. The ICP measurement described later for the phosphoric acid-treated active material was performed to determine the amount of P in the active material. The mixed amount was LiOH.H ₂ O having a mole number three times the mole number of P in the active material.
This lithium transition metal complex oxide was Li / Me = 1.42.

(Example 3)
Example 3 is the same as Example 1 except that the time (acid treatment time) from introduction of the lithium transition metal composite oxide into the phosphoric acid aqueous solution until suction filtration is changed from 30 sec to 60 sec. A lithium transition metal composite oxide was prepared.
This lithium transition metal complex oxide was Li / Me = 1.42.

Example 4
4. A mixture of phosphoric acid-treated and heat-treated lithium transition metal composite oxide and LiOH.H ₂ O in a mortar made of agate instead of 5.0 g of phosphoric acid-treated and heat-treated lithium transition metal composite oxide A lithium transition metal composite oxide according to Example 4 was produced in the same manner as Example 3 except that 0 g was used.
This lithium transition metal composite oxide was Li / Me = 1.45.

(Example 5)
Example 5 is the same as Example 1 except that the time (acid treatment time) from the introduction of the lithium transition metal composite oxide into the phosphoric acid aqueous solution until the suction filtration is changed from 30 sec to 600 sec. A lithium transition metal composite oxide was prepared.
This lithium transition metal complex oxide was Li / Me = 1.41.

(Example 6)
Example 6 is the same as Example 1 except that the time (acid treatment time) from when the lithium transition metal composite oxide was added to the phosphoric acid aqueous solution until suction filtration was changed from 30 sec to 1800 sec. A lithium transition metal composite oxide was prepared.
This lithium transition metal complex oxide was Li / Me = 1.42.

(Example 7)
Example 7 is the same as Example 1 except that the time (acid treatment time) from when the lithium transition metal composite oxide was added to the phosphoric acid aqueous solution until suction filtration was changed from 30 sec to 3600 sec. A lithium transition metal composite oxide was prepared.
This lithium transition metal complex oxide was Li / Me = 1.40.

(Example 8)
Example 8 is the same as Example 1 except that the time (acid treatment time) from charging the lithium transition metal composite oxide into the phosphoric acid aqueous solution until suction filtration was changed from 30 sec to 10800 sec. A lithium transition metal composite oxide was prepared.
This lithium transition metal composite oxide was Li / Me = 1.38.

(Comparative Example 1)
A lithium transition metal composite oxide according to Comparative Example 1 was produced in the same manner as in Example 1 except that the phosphoric acid treatment was not performed.

(Comparative Example 2)
The lithium transition metal according to Comparative Example 2 was the same as Example 1 except that the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment was changed from 0.1 M to 0.05 M and the heat treatment after the phosphoric acid treatment was not performed. A composite oxide was produced.

(Comparative Example 3)
The lithium transition metal according to Comparative Example 3 was the same as Example 3 except that the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment was changed from 0.1 M to 0.05 M and the heat treatment after the phosphoric acid treatment was not performed. A composite oxide was produced.

(Comparative Example 4)
A lithium transition metal composite oxide according to Comparative Example 4 was produced in the same manner as in Example 1 except that the heat treatment after the phosphoric acid treatment was not performed.

(Comparative Example 5)
A lithium transition metal composite oxide according to Comparative Example 5 was produced in the same manner as in Example 3 except that the heat treatment after the phosphoric acid treatment was not performed.

(Comparative Examples 6-11)
Comparative Example 4 except that the time (acid treatment time) from the introduction of the lithium transition metal composite oxide into the phosphoric acid aqueous solution until the suction filtration was changed from 30 sec to 180, 300, 600, 1800, 3600 and 10800 sec. In the same manner, lithium transition metal composite oxides according to Comparative Examples 6 to 11 were produced.

(Comparative Example 12)
The lithium transition metal according to Comparative Example 12 was the same as Example 1 except that the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment was changed from 0.1 M to 0.2 M and no heat treatment after the phosphoric acid treatment was performed. A composite oxide was produced.

(Comparative Example 13)
The lithium transition metal according to Comparative Example 13 was the same as Example 3 except that the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment was changed from 0.1 M to 0.2 M and the heat treatment after the phosphoric acid treatment was not performed. A composite oxide was produced.

(Comparative Example 14)
The lithium transition metal according to Comparative Example 14 was the same as Example 1 except that the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment was changed from 0.1 M to 0.3 M and the heat treatment after the phosphoric acid treatment was not performed. A composite oxide was produced.

(Comparative Example 15)
The lithium transition metal according to Comparative Example 15 was the same as Example 3 except that the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment was changed from 0.1 M to 0.3 M and no heat treatment after the phosphoric acid treatment was performed. A composite oxide was produced.

(Comparative Example 16)
The lithium transition metal according to Comparative Example 16 was the same as Example 1 except that the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment was changed from 0.1 M to 0.5 M and the heat treatment after the phosphoric acid treatment was not performed. A composite oxide was produced.

(Comparative Example 17)
The lithium transition metal according to Comparative Example 17 was the same as Example 3 except that the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment was changed from 0.1 M to 0.5 M and the heat treatment after the phosphoric acid treatment was not performed. A composite oxide was produced.

(Comparative Example 18)
The lithium transition metal according to Comparative Example 18 was the same as Example 1 except that the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment was changed from 0.1 M to 1.0 M and the heat treatment after the phosphoric acid treatment was not performed. A composite oxide was produced.

(Comparative Example 19)
The lithium transition metal according to Comparative Example 19 was the same as Example 3 except that the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment was changed from 0.1 M to 1.0 M and the heat treatment after the phosphoric acid treatment was not performed. A composite oxide was produced.

(Comparative Example 20)
Except that the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment was changed from 0.1 M to 0.05 M and the heat treatment temperature after the phosphoric acid treatment was changed from 400 ° C. to 200 ° C., the same as in Example 1, A lithium transition metal composite oxide according to Comparative Example 20 was produced.

(Comparative Example 21)
Except that the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment was changed from 0.1 M to 0.05 M and the heat treatment temperature after the phosphoric acid treatment was changed from 400 ° C. to 200 ° C., the same as in Example 3, A lithium transition metal composite oxide according to Comparative Example 21 was produced.

(Comparative Example 22)
A lithium transition metal composite oxide according to Comparative Example 22 was produced in the same manner as in Example 1 except that the heat treatment temperature after the phosphoric acid treatment was changed from 400 ° C. to 200 ° C.

(Comparative Example 23)
A lithium transition metal composite oxide according to Comparative Example 23 was produced in the same manner as in Example 3 except that the heat treatment temperature after the phosphoric acid treatment was changed from 400 ° C. to 200 ° C.

(Comparative Example 24)
In the same manner as in Example 1, except that the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment was changed from 0.1 M to 0.2 M, and the heat treatment temperature after the phosphoric acid treatment was changed from 400 ° C. to 200 ° C. A lithium transition metal composite oxide according to Comparative Example 24 was produced.

(Comparative Example 25)
Except for changing the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment from 0.1 M to 0.2 M and changing the heat treatment temperature after the phosphoric acid treatment from 400 ° C. to 200 ° C., as in Example 3, A lithium transition metal composite oxide according to Comparative Example 25 was produced.

(Comparative Example 26)
Except that the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment was changed from 0.1 M to 0.3 M and the heat treatment temperature after the phosphoric acid treatment was changed from 400 ° C. to 200 ° C., the same as in Example 1, A lithium transition metal composite oxide according to Comparative Example 26 was produced.

(Comparative Example 27)
Except for changing the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment from 0.1 M to 0.3 M and changing the heat treatment temperature after the phosphoric acid treatment from 400 ° C. to 200 ° C., as in Example 3, A lithium transition metal composite oxide according to Comparative Example 27 was produced.

(Comparative Example 28)
Except that the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment was changed from 0.1 M to 0.5 M and the heat treatment temperature after the phosphoric acid treatment was changed from 400 ° C. to 200 ° C., the same as in Example 1, A lithium transition metal composite oxide according to Comparative Example 28 was produced.

(Comparative Example 29)
In the same manner as in Example 3 except that the hydrogen ion concentration of the phosphoric acid aqueous solution in the phosphoric acid treatment was changed from 0.1 M to 0.5 M, and the heat treatment temperature after the phosphoric acid treatment was changed from 400 ° C. to 200 ° C. A lithium transition metal composite oxide according to Comparative Example 29 was produced.

(Comparative Example 30)
A lithium transition metal composite oxide according to Comparative Example 30 was produced in the same manner as in Example 1 except that the heat treatment temperature after the phosphoric acid treatment was changed from 400 ° C. to 150 ° C.

(Comparative Example 31)
A lithium transition metal composite oxide according to Comparative Example 31 was produced in the same manner as in Example 2 except that the heat treatment temperature after the phosphoric acid treatment was changed from 400 ° C. to 150 ° C.

(Comparative Example 32)
A lithium transition metal composite oxide according to Comparative Example 32 was produced in the same manner as in Example 3 except that the heat treatment temperature after the phosphoric acid treatment was changed from 400 ° C. to 150 ° C.

(Comparative Example 33)
A lithium transition metal composite oxide according to Comparative Example 33 was produced in the same manner as in Example 4 except that the heat treatment temperature after the phosphoric acid treatment was changed from 400 ° C. to 150 ° C.

(Comparative Example 34)
A lithium transition metal composite oxide according to Comparative Example 34 was produced in the same manner as in Example 1 except that the heat treatment temperature after the phosphoric acid treatment was changed from 400 ° C. to 800 ° C.

(Comparative Example 35)
A lithium transition metal composite oxide according to Comparative Example 35 was produced in the same manner as in Example 2 except that the heat treatment temperature after the phosphoric acid treatment was changed from 400 ° C. to 800 ° C.

(Comparative Example 36)
A lithium transition metal composite oxide according to Comparative Example 36 was produced in the same manner as in Example 3 except that the heat treatment temperature after the phosphoric acid treatment was changed from 400 ° C. to 800 ° C.

(Comparative Example 37)
A lithium transition metal composite oxide according to Comparative Example 37 was produced in the same manner as in Example 4 except that the heat treatment temperature after the phosphoric acid treatment was changed from 400 ° C. to 800 ° C.

(Comparative Example 38)
The lithium according to Comparative Example 38 was replaced with the boric acid treatment under the following conditions instead of the phosphoric acid treatment of the lithium transition metal composite oxide, and the heat treatment after the boric acid treatment was not performed. A transition metal composite oxide was produced.
To a 300 ml Erlenmeyer flask, 1.2428 g of boric acid powder was added, ion-exchanged water was added, and an aqueous boric acid solution having a hydrogen ion concentration of 0.1 M was prepared. 5.0 g of the above lithium transition metal composite oxide was added to the stirring solution of the aqueous boric acid solution at 25 ° C. and 400 rpm using a stirrer. The lithium transition metal composite oxide was collected on the filter paper by suction filtration after 30 seconds from the introduction of the lithium transition metal composite oxide.
The lithium transition metal composite oxide was dried in air at normal pressure and 80 ° C. for 16 to 18 hours to obtain a boric acid-treated lithium transition metal composite oxide.

(Comparative Example 39)
Comparative Example 39 is the same as Comparative Example 38 except that the time (acid treatment time) from when the lithium transition metal composite oxide was added to the boric acid aqueous solution until suction filtration was changed from 30 sec to 60 sec. A lithium transition metal composite oxide was prepared.

(Comparative Example 40)
After completion of the dropwise addition of the sulfuric acid aqueous solution, the time for further stirring in the reaction vessel was changed from 5 h to 3 h, and the molar ratio of Li: (Co, Ni, Mn) during firing was changed from 1.44 to 1.3. The lithium transition metal composite oxidation according to Comparative Example 40 was performed in the same manner as in Example 1 except that the firing temperature was changed from 900 ° C. to 915 ° C. and the phosphoric acid treatment and the subsequent heat treatment were not performed. A product was made.

<Measurement of half width>
The lithium transition metal composite oxides according to all Examples and Comparative Examples were subjected to X-ray diffraction measurement in accordance with the following conditions and procedures, and the half width was determined. Powder X-ray diffraction measurement was performed using an X-ray diffractometer (manufactured by Rigaku, model name: MiniFlex II). The radiation source was CuKα, and the acceleration voltage and current were 30 kV and 15 mA, respectively. The sampling width is 0.01 deg, the scanning time is 14 minutes (scanning speed is 5.0), the divergence slit width is 0.625 deg, the light receiving slit width is open, and the scattering slit is 8.0 mm. With respect to the obtained X-ray diffraction data, the peak derived from Kα2 is not removed, and “PDXL”, which is the software attached to the X-ray diffractometer, is used to determine the diffraction peak existing at 2θ = 44 ± 1 ° on the X-ray diffraction diagram. The full width at half maximum was determined.
Further, it was confirmed by X-ray diffraction measurement that all the lithium transition metal composite oxides have an α-NaFeO ₂ structure.

<Quantification of elements>
Lithium transition metal composite oxides according to all examples and comparative examples were subjected to high frequency inductively coupled plasma emission spectroscopy analysis (ICP measurement) according to the following conditions and procedures to detect P element and determine the amount of P. .
50 mg of lithium transition metal composite oxide was put into a 30 ml beaker, 10 ml of 5 mol / l hydrochloric acid aqueous solution was added, and the mixture was heated on a hot plate at 150 ° C. for 15 minutes to be dissolved. This solution was filtered and diluted to 1000 ml with ion exchange water to prepare a sample solution for measurement.
A standard solution for preparing a calibration curve is prepared by diluting each standard solution (manufactured by Nacalai Tesque, 1000 ppm) to a predetermined concentration using ion-exchanged water for each element of Li, Ni, Co, Mn and P. did.
Using a Shimadzu sequential plasma emission spectrometer (ICPS-8100, manufactured by Shimadzu Corporation), 20 to 40 ml each of the above sample solution and standard solution were used to quantify each element of Li, Ni, Co, Mn, and P. did. The measurement conditions were a plasma output of 1.2 kW, a carrier gas flow rate of 1.0 ml / min, and a measurement count of 3 times.

<Production and evaluation of lithium secondary battery>
Using the lithium transition metal composite oxides according to all Examples and Comparative Examples as the positive electrode active materials for lithium secondary batteries, lithium secondary batteries were prepared according to the following procedure, and the battery characteristics were evaluated.

  Using N-methylpyrrolidone as a dispersion medium, an active material, acetylene black (AB), and polyvinylidene fluoride (PVdF) were kneaded and dispersed at a mass ratio of 90: 4: 6. The coating paste was applied to one side of an aluminum foil current collector having a thickness of 20 μm to produce a positive electrode plate. In addition, the mass and coating thickness of the active material applied per fixed area were standardized so that the test conditions were the same among the lithium secondary batteries according to all the examples and comparative examples.

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

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

  The lithium secondary battery produced by the above procedure was subjected to an initial charge / discharge process at 25 ° C. Charging was performed at a constant current and a constant voltage with a current of 0.1 CA and a voltage of 4.6 V, and the charge termination condition was when the current value attenuated to 1/6. The discharge was a constant current discharge with a current of 0.05 CA and a final voltage of 2.0 V. This charge / discharge was performed for two cycles. Here, a pause process of 10 minutes was provided after charging and discharging, respectively.

  Next, the charge voltage was changed and a 30-cycle charge / discharge test was performed. All voltage control was performed on the positive electrode potential. The charging / discharging test was performed at a constant current and constant voltage with a current of 0.2 CA and a voltage of 4.3 V, and the charge termination condition was when the current value was attenuated to 1/6. The discharge was a constant current discharge with a current of 0.5 CA and a final voltage of 2.0 V. In this 30-cycle charge / discharge test, the discharge capacity at the 30th cycle was recorded as the 0.5C discharge capacity at the 30th cycle.

Table 1 shows the powder physical properties of lithium transition metal composite oxides according to all examples and comparative examples, and the test results of lithium secondary batteries using the lithium transition metal composite oxides as positive electrode active materials for lithium secondary batteries.
The description in Table 1 means the following matters.
“Before Li / Me acid treatment”: Li / Me molar ratio of lithium transition metal composite oxide before phosphoric acid treatment “Heat treatment temperature”: Temperature of heat treatment performed after phosphoric acid treatment. The blank is not heat-treated.
“After Li / Me acid treatment”: the heat treatment was performed after the heat treatment, and the heat treatment was not performed is the Li / Me molar ratio of the lithium transition metal composite oxide after the phosphoric acid treatment. Neither was washed prior to measurement.
“P amount”: the amount of P element detected by high-frequency inductively coupled plasma emission spectroscopy (ICP measurement) “FWHM (104)”: 2θ = 44 ± 1 ° in an X-ray diffraction pattern using a CuKα radiation source FWHM of diffraction peak of

From Tables 1 and 2, the transition metal (Me) contains Co, Ni and Mn, the molar ratio Li / Me of lithium (Li) to the transition metal is greater than 1, and the molar ratio Mn of Mn in the transition metal. / Me is Mn / Me ≧ 0.5, FWHM (104) (half-value width of diffraction peak of 2θ = 44 ± 1 ° in X-ray diffraction pattern using CuKα radiation source) is 0.265 ° or more, and The positive electrode active material containing a lithium transition metal composite oxide in which element P is detected in high frequency inductively coupled plasma optical emission spectrometry has a high 0.5C discharge capacity at the 30th cycle of 160 mAh / g or more, and the high after charging / discharging cycle. It turns out that rate discharge performance is excellent (refer Examples 1-8). Further, as in Examples 2 and 4, the P in the active material after the phosphoric acid treatment is reacted with LiOH to change to a P compound having high Li ion conductivity such as Li ₃ PO _4. Then, mixing of LiOH.H ₂ O was attempted after the acid treatment, but from the result, the improvement in high-rate discharge performance was comparable regardless of whether or not LiOH was mixed.

On the other hand, the lithium transition metal composite oxide having the same composition as that of the example not subjected to the phosphoric acid treatment has a FWHM (104) of less than 0.265 °, and the positive electrode active material containing this has a high rate discharge performance. Low (see Comparative Example 1). By changing the firing temperature, the FWHM (104) may be 0.265 ° or more, but when the phosphoric acid treatment is not performed, the high rate discharge performance is low (see Comparative Example 40). Even when the phosphoric acid treatment is performed, if the heat treatment is not performed, or if the heat treatment temperature is too low or too high, the lithium transition metal composite oxide has a FWHM (104) of less than 0.265 °, and the positive electrode The substance does not improve the high rate discharge performance (see Comparative Examples 2-37).
When a weak acid such as boric acid was used for the acid treatment, the acid treatment solution changed to neutral or alkaline during the treatment, so that the acid treatment was insufficient and Li was hardly eliminated. Further, the FWHM (104) is less than 0.265 °, and the positive electrode active material containing the FWHM (104) does not improve the high rate discharge performance (see Comparative Examples 38 and 39).
In Comparative Example 40, the value of Li / Me is different from those of other Examples and Comparative Examples, but the value of Li / Me has little influence on FWHM (104).

  In Table 3, among Examples 1 to 8, Examples 1, 3, and 5 to 8 having the same conditions other than the acid treatment time, the average discharge potential at the time of 0.5C discharge at the 30th cycle, and the initial charge and discharge The value of hourly coulomb efficiency (hereinafter also referred to as “initial coulomb efficiency”) is shown. From the results of Examples 1 to 8 shown in Table 1, compared with Examples 1 to 4 in which the P amount is 300 ppm, Examples 5 to 8 in which the P amount is 500 to 1400 ppm has 30 cycles. The value of 0.5C discharge capacity (mAh / g) is large. However, as can be seen from Table 3, the average discharge potential tends to decrease as the P amount increases. This means that the energy density of the battery decreases as the amount of P increases.

  The initial coulomb efficiency approached 100% as the P content increased, but exceeded 100 in Example 8 where the P content was 1400 ppm. When the Coulomb efficiency exceeds 100, the amount of Li desorbed by acid treatment increases, and since the metal Li is used for the negative electrode, lithium exceeding the amount of lithium released by the first charge is discharged during the first discharge. It means being occluded. In the lithium secondary battery using a negative electrode active material that does not contain lithium, such as graphite, for the negative electrode, the initial Coulomb efficiency does not exceed 100. Therefore, even if the positive electrode active material according to Example 8 is used, A large discharge capacity as shown in Table 1 cannot be obtained.

  From these perspectives. The amount of P is preferably 2000 ppm or less, more preferably 1000 ppm or less, further preferably 500 ppm or less, and most preferably 300 ppm or less.

(Explanation of symbols)
DESCRIPTION OF SYMBOLS 1 Lithium secondary battery 2 Electrode group 3 Battery container 4 Positive electrode terminal 4 'Positive electrode lead 5 Negative electrode terminal 5' Negative electrode lead 20 Power storage unit 30 Power storage device

  By using the positive electrode active material containing the novel lithium transition metal composite oxide of the present invention, it is possible to provide a lithium secondary battery with excellent high-rate discharge performance. It is useful as a lithium secondary battery for electric vehicles.

Claims (7)

A positive electrode active material for a lithium secondary battery including a lithium transition metal composite oxide having an α-NaFeO ₂ structure, wherein the transition metal (Me) includes Co, Ni, and Mn. The molar ratio of Mn in the transition metal Mn / Me is Mn / Me ≧ 0.5, and the half width of the diffraction peak at 2θ = 44 ± 1 ° in the X-ray diffraction pattern using the CuKα radiation source is 0.265. A positive electrode active material for a lithium secondary battery, which is at least ° and contains a P element.   2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the amount of the P element is 2000 ppm or less.   3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the lithium transition metal composite oxide contains P by heat treatment after phosphoric acid treatment. 4.   The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 3, wherein a molar ratio Li / Me of lithium (Li) to the transition metal is greater than 1.   The electrode for lithium secondary batteries containing the positive electrode active material for lithium secondary batteries of any one of Claims 1-4.   A lithium secondary battery comprising the electrode for a lithium secondary battery according to claim 5.   A power storage device configured by assembling a plurality of lithium secondary batteries according to claim 6.

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