JP6010902B2 - Lithium transition metal-based compound powder, method for producing the same, positive electrode for lithium secondary battery and lithium secondary battery using the same - Google Patents

Description

  The present invention relates to a lithium transition metal compound powder used as a lithium secondary battery positive electrode material, a method for producing the same, a positive electrode for a lithium secondary battery using the lithium transition metal compound powder, and the lithium secondary battery. The present invention relates to a lithium secondary battery including a positive electrode for a battery.

  Lithium secondary batteries are excellent in energy density and output density, and are effective in reducing the size and weight. Therefore, the demand for power supplies for portable devices such as notebook computers, mobile phones, and handy video cameras is growing rapidly. ing. Lithium secondary batteries are also attracting attention as power sources for electric vehicles and power load leveling, and in recent years, demand for power sources for hybrid electric vehicles is rapidly expanding. In particular, in electric vehicle applications, it is necessary to be excellent in low cost, safety, life (particularly under high temperature) and load characteristics, and improvements in materials are desired.

Among the materials constituting the lithium secondary battery, as the positive electrode active material, a substance having a function capable of desorbing and inserting lithium ions can be used. There are various types of these positive electrode active material materials, each having its own characteristics. In addition, a common problem for improving performance is to improve load characteristics, and improvements in materials are strongly desired.
Furthermore, there is a demand for a material with a good performance balance that is excellent in low cost, safety, and life (particularly under high temperatures).

  Currently, lithium manganese composite oxides having a spinel structure, layered lithium nickel composite oxides, layered lithium cobalt composite oxides, and the like have been put into practical use as positive electrode active material materials for lithium secondary batteries. All of the lithium secondary batteries using these lithium-containing composite oxides have advantages and disadvantages in terms of characteristics. That is, a lithium manganese composite oxide having a spinel structure is inexpensive and relatively easy to synthesize, and is excellent in safety when used as a battery, but has a low capacity and inferior high-temperature characteristics (cycle and storage). Layered lithium-nickel composite oxides have high capacity and excellent high-temperature characteristics, but are difficult to synthesize, have inferior safety when used as batteries, and have drawbacks such as requiring careful storage. Layered lithium cobalt-based composite oxides are widely used as power sources for portable devices because they are easy to synthesize and have an excellent balance of battery performance. However, they are not sufficient in safety and costly. It is a drawback.

  Under such circumstances, lithium nickel manganese cobalt-based composite oxides with a layered structure have been proposed as promising candidates for active material materials that can overcome or reduce the shortcomings of these positive electrode active material materials and are excellent in battery performance balance. Has been. Particularly, in recent years, demands for lowering costs, higher voltages, and increasing safety demands are promising as positive electrode active material materials that can meet any of the demands.

  However, the degree of cost reduction, higher voltage, and safety will vary depending on the composition ratio. Therefore, for further cost reduction, use with a higher upper limit voltage, and higher safety requirements. Therefore, it is necessary to select and use one having a limited composition range such as a manganese / nickel atomic ratio of approximately 1 or more, or a reduction in the cobalt ratio. However, a lithium secondary battery using a lithium nickel manganese cobalt composite oxide having such a composition range as a positive electrode material deteriorates load characteristics such as rate and output characteristics and low-temperature output characteristics. An improvement was needed.

It is to be noted that conventionally, a known process in which “additive element 1 (Nb, Ta and V)” or “additive element 2 (W, Mo and Re)” as described in the present invention is introduced into a lithium transition metal compound is introduced. Examples of the literature include the following patent documents 1 to 8.
Patent Document 1 describes that a transition metal material is mixed as an aqueous solution and coprecipitated, and then the Li material, W material, and Nb material are mixed and fired in the precipitate.

Patent Document 2 discloses a formula Li _X A _{1 -YM Y} O ₂ (A is at least one transition metal element selected from the group consisting of Mn, Co, and Ni, and M is B, Mg, Ca, which is a positive electrode active material. , Sr, Ba, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, In, Nb, Mo, W, Y, and Rh, at least one element, 0.05 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5).

Patent Document 3 describes Li _a Ni _b Co _c M _d O ₂ (where 0 ≦ a ≦ 1.1, 0.7 ≦ b ≦ 0.9, 0.1 ≦ c ≦ 0.3, 0 ≦ d). ≦ 0.1, b + c + d = 1, M = Al, Mg, Ti, Mo, B, W, at least one element selected from the group consisting of Nb)) An active material is disclosed.
Patent Document _{4, LiNi x M 1-xy} L y O 2 (M as the positive electrode active material is at least one of Co and Mn, L is Al, Sr, Y, Zr, Ta, Mg, Ti , Zn, B, Ca, Cr, Si, Ga, Sn, P, V, Sb, Nb, Mo, W and Fe, at least one selected from the group consisting of 0.1 ≦ x ≦ 1.0, A positive electrode active material whose main component is a composite oxide represented by 0 ≦ y ≦ 0.1) is disclosed.

In Patent Document 5, lithium cobaltate (LiCoO ₂ ) or lithium nickelate (
A part of the transition element Co or Ni in LiNiO ₂ ), Li, Fe, Mn, Ni, Mg, Zn, B, Al, Co, Cr, Si, Ti, Sn, P, V, Sb, Nb, Ta , A positive electrode active material formed by substitution with two or more elements selected from Mo, W (including at least Ti) is disclosed.

Patent Document 6 discloses a positive electrode active material Li _x Ni _1-y M _y Me _z O _{2 + δ} that can contain B, Nb, Ta, W, and Mo.
Patent Documents 7 and 8 disclose elements containing Nb, Ta, W, Mo, and Re as substitution elements of lithium nickel cobalt composite oxide.

JP 2009-140787 A JP-A-8-31408 JP 2003-308880 A JP 2006-351242 A JP 2000-200607 A JP 2006-351379 A WO2007 / 116971 JP 2008-305777 A

Although the combined addition of Nb and W is described for Patent Document 1 described above, Li compound, Nb compound and W compound are added to the transition metal compound co-precipitated with the raw material compound and fired. The Nb compound and the W compound are reacted only on the secondary particle surface of the lithium transition metal compound. That is, the lithium transition metal compound obtained by such a production method is
Nb compound and W compound do not react inside the secondary particles. Accordingly, there remains a problem in terms of improving load characteristics at low temperatures.

Regarding the above-mentioned Patent Documents 2 to 4, there is no description regarding the combined use of Additive 1 and Additive 2 according to the present invention, and there remains a problem in terms of improving load characteristics at low temperatures.
About the above-mentioned patent documents 5-8, although it is the description which can use the additive 1 and additive 2 which concern on this invention together, there is no description of the positive electrode active material actually used together, and the load characteristic improvement at the time of low temperature In that respect, it left a problem.

  Accordingly, it is an object of the present invention to improve powder properties while improving load characteristics such as rate and output characteristics when used as a positive electrode material for a lithium secondary battery, and more preferably to reduce cost and increase voltage resistance. And lithium transition metal-based compound powder for lithium secondary battery positive electrode material capable of achieving high capacity and improving load characteristics especially at low temperatures while achieving both high safety and high safety, and production method thereof An object of the present invention is to provide a positive electrode for a lithium secondary battery using the lithium transition metal-based compound powder and a lithium secondary battery including the positive electrode for a lithium secondary battery.

  In order to solve the problem of improving the physical properties of the powder while improving the load characteristics such as rate and output characteristics, the present inventors have conducted intensive studies to improve the bulk density and optimize the specific surface area. As a result, by causing at least one element (A) selected from the group consisting of Nb, Ta and V and at least one element (B) selected from W, Mo and Re to be present in the particles in a specific manner, Without impairing the aforementioned powder physical property improvement effect, it is possible to obtain a lithium-containing transition metal compound powder that is easy to handle and prepare an electrode, and further, the Li ion mobility near the active material surface and inside the active material. It has been found that lithium transition metal-based compound powders with good load characteristics at low temperatures can be obtained when used as positive electrode materials for batteries. Therefore, the present inventors, as a lithium secondary battery positive electrode material, have excellent powder physical properties, high load characteristics, high voltage resistance, high safety, and are capable of reducing costs and increasing capacity. The present inventors have found that a system compound powder can be obtained and have completed the present invention.

That is, the lithium transition metal based compound powder for a lithium secondary battery positive electrode material of the present invention is as follows.
(1) including at least one element (A) selected from the group consisting of Nb, Ta and V and at least one element (B) selected from W, Mo and Re, and including B and / or Bi elements Consisting of secondary particles of lithium transition metal composite oxide,
The atomic ratio of the total of the element (A) to the total of metallic elements other than Li, the element (A) and the element (B) on the surface portion of the secondary particle is 1 to 50 times the atomic ratio of the entire secondary particle And
The atomic ratio of the total of the element (B) to the total of metallic elements other than Li, the element (A) and the element (B) on the surface portion of the secondary particle is 1 to 100 times the atomic ratio of the entire secondary particle A lithium transition metal compound powder for a lithium secondary battery positive electrode material, characterized in that the concentration of the surface of the element (A) is lower than that of the element (B).
(2) The lithium secondary metal compound powder for a lithium secondary battery positive electrode material is mainly composed of a lithium nickel manganese cobalt composite oxide having a layered structure, and the lithium secondary as described in (1) lithium transition metal based compound powder for a battery positive electrode material.

(3 ) A positive electrode active material layer containing a lithium transition metal compound powder for a lithium secondary battery positive electrode material according to (1) or (2) and a binder, on a current collector, A positive electrode for a lithium secondary battery.
( 4 ) A lithium secondary battery comprising a negative electrode capable of inserting and extracting lithium, a non-aqueous electrolyte containing a lithium salt, and a positive electrode capable of inserting and extracting lithium, wherein the positive electrode is lithium described in ( 3 ) A lithium secondary battery, which is a positive electrode for a secondary battery.

  When the lithium transition metal-based compound powder for a lithium secondary battery positive electrode material of the present invention is used as a positive electrode material for a lithium secondary battery, the cost reduction and safety increase and high load characteristics (particularly, low temperature load characteristics), It is possible to improve both powder handling properties. Therefore, according to the present invention, a lithium secondary battery is provided that is inexpensive, excellent in handleability, high in safety, and excellent in performance even when used at a high charging voltage.

In Example 1, it is a graph which shows the atomic ratio (depth direction) of B, W, and Nb with respect to Ni + Mn + Co obtained by XPS measurement of the lithium nickel manganese cobalt composite oxide powder produced. In Comparative example 1, it is a graph which shows the atomic ratio (depth direction) of B and W with respect to Ni + Mn + Co obtained by XPS measurement of the manufactured lithium nickel manganese cobalt composite oxide powder.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. However, the description of constituent elements described below is an example (representative example) of an embodiment of the present invention, and is not specified by these contents.
[Lithium transition metal compound powder]
The lithium transition metal-based compound of the present invention is characterized by the following (1) or (2). (1) Secondary particles of lithium transition metal composite oxide containing at least one element (A) selected from the group consisting of Nb, Ta and V and at least one element (B) selected from W, Mo and Re Consists of
The atomic ratio of the total of the element (A) to the total of metallic elements other than Li, the element (A) and the element (B) on the surface portion of the secondary particle is 50 times or less of the atomic ratio of the entire secondary particle. ,
The atomic ratio of the total of the element (B) to the total of metallic elements other than Li, the element (A) and the element (B) on the surface portion of the secondary particle is 1 or more times the atomic ratio of the entire secondary particle. A lithium transition metal compound powder for a positive electrode material for a lithium secondary battery.
(2) Lithium transition metal compound powder for a lithium secondary battery positive electrode material having as a main component a lithium transition metal compound having a function capable of insertion / extraction of lithium ions, the raw material compound of the main component , A compound (A ′) having at least one element (A) selected from the group consisting of Nb, Ta and V and a compound (B ′) having at least one element (B) selected from W, Mo and Re A lithium transition metal-based compound powder for a lithium secondary battery positive electrode material, which is obtained by wet-grinding and then firing the mixture.

<Lithium-containing transition metal compound>
The lithium transition metal compound of the present invention is a compound having a structure capable of desorbing and inserting Li ions, and examples thereof include sulfides, phosphate compounds, and lithium transition metal composite oxides. . Examples of sulfides include compounds having a two-dimensional layered structure such as TiS ₂ and MoS ₂ , and strong compounds represented by the general formula Me _x Mo ₆ S ₈ (Me is various transition metals including Pb, Ag, and Cu). Examples thereof include a sugar compound having a three-dimensional skeleton structure. Examples of the phosphate compound include those belonging to the olivine structure, and are generally represented by LiMePO ₄ (Me is at least one transition metal), specifically, LiFePO ₄ , LiCoPO ₄ , LiNiPO ₄ , LiMnPO ₄ . ₄ etc. are mentioned. Examples of the lithium transition metal composite oxide include spinel structures capable of three-dimensional diffusion and those belonging to a layered structure capable of two-dimensional diffusion of lithium ions. Those having a spinel structure are generally expressed as LiMe ₂ O ₄ (Me is at least one transition metal), specifically, LiMn ₂ O ₄ , LiCoMnO ₄ , LiNi _0.5 Mn _1.5 O _4. , CoLiVO _{4 and the} like.

Those having a layered structure are generally expressed as LiMeO ₂ (Me is at least one transition metal), specifically, LiCoO ₂ , LiNiO ₂ , LiNi _1-x Co _x O ₂ , LiNi _{1-x—. y} Co _x Mn _y O ₂ , LiNi _0.5 Mn _0.5 O ₂ , Li _1.2 Cr _0.4 Mn _0.4 O ₂ , Li _1.2 Cr _0.4 Ti _0.4 O ₂ , LiMnO ₂ etc. are mentioned.

The lithium transition metal-based compound powder of the present invention preferably includes a crystal structure belonging to an olivine structure, a spinel structure, or a layered structure from the viewpoint of lithium ion diffusion. Among these, those including a crystal structure belonging to a layered structure are particularly preferable.
Further, foreign elements may be introduced into the lithium transition metal-based compound powder of the present invention. Different elements include Na, Mg, Al, Si, K, Ca, Ti, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Ru, Rh, Pd, Ag, In, Sn, Sb. , Te, Ba, Os, Ir, Pt, Au, Pb, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy,
One or more of Ho, Er, Tm, Yb, Lu, N, F, P, S, Cl, Br, and I are selected. These foreign elements may be incorporated into the crystal structure of the lithium transition metal-based composite oxide, or may not be incorporated into the crystal structure of the lithium-nickel-manganese-cobalt-based composite oxide. May be unevenly distributed as a simple substance or a compound.

<Compound (A ′) and Compound (B ′)>
The present invention is characterized in that a compound (A ′) having at least one element (A) selected from the group consisting of Nb, Ta and V is used as the compound (A ′). These elements are elements having a maximum oxidation number of +5 and have a maximum oxidation number lower than that of the element (B), so that they dissolve more into the primary particles. Therefore, the effect of the present invention is exhibited. The additive element 1 is at least one element selected from the group consisting of Nb, Ta, and V. Among these elements (A), the element ( A) is preferably Nb and / or Ta, most preferably Nb.

The type of the compound (A ′) is not particularly limited as long as it exhibits the effects of the present invention, but usually an oxide, halide, lithium salt, alkoxide or the like is used. Among these compounds (A ′), from the viewpoint of chemical stability, oxides and lithium salts are preferable, and oxides are particularly preferable.
Examples of the compound (A ′) usually include Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂ O _{5 and the} like, and preferably Nb ₂ O ₅ , Ta ₂ O from the viewpoint of surface concentration. ₅ is particularly preferable, and Nb ₂ O ₅ is particularly preferable. These compounds (A ′) may be used alone or in a combination of two or more.

  The present invention is characterized in that a compound (B ′) having at least one element (B) selected from W, Mo and Re is used as the compound (B ′). In addition, the element (B) is at least one element selected from W, Mo, and Re. Among these elements (B), the element (B ) Is preferably Mo and / or W, and most preferably W.

The type of compound (B ′) is not particularly limited as long as it exhibits the effects of the present invention, but usually an oxide, a lithium salt, an ammonium salt, an alkoxide, or the like is used. Among these compounds (B ′), lithium salts, ammonium salts, and oxides are preferable and oxides are particularly preferable because they are easily available.
Examples of the compound (B ′) typically include tungsten oxide, ammonium paratungstate, ammonium paramolybdate, molybdenum oxide, lithium tungstate, lithium molybdate, and the like. Includes tungsten oxide, ammonium paratungstate, ammonium paramolybdate, and molybdenum oxide, and particularly preferably tungsten oxide and molybdenum oxide. These compounds (B ′) may be used alone or in a combination of two or more.

  As the range of the total addition amount of the compound (A ′) and the compound (B ′), the value converted into the total molar amount of the element (A) and the element (B) is the total of transition metal elements constituting the main component. With respect to the molar amount, the lower limit is usually 0.01 mol% or more, preferably 0.03 mol% or more, more preferably 0.04 mol% or more, particularly preferably 0.05 mol% or more, Usually, it is less than 2 mol%, preferably 1.9 mol% or less, more preferably 1.8 mol% or less, and particularly preferably 1.6 mol% or less. If the lower limit is not reached, the above effect may not be obtained. If the upper limit is exceeded, battery performance may be reduced.

  The range of the addition ratio of the compound (A ′) and the compound (B ′) is usually 10: 1 or more and 1:40 or less, preferably 5: 1 or more and 1:20 or less, as a molar ratio in terms of additive elements. More preferably, it is 2: 1 or more and 1:20 or less, and particularly preferably 1: 1 or more and 1:10 or less. If it deviates from this range, the effects of the present invention may be difficult to obtain.

<Surface concentration of element (A) or element (B)>
The lithium transition metal-based compound powder of the present invention has an element (A) or element (B) derived from the compound (A ′) or the compound (B ′) on the surface portion of the primary particles, that is, Nb, Ta and V It is characterized in that at least one element (A) selected from the group consisting of and at least one element (B) selected from W, Mo and Re is present in a concentrated state.

  Specifically, the atomic ratio of the total of the element (A) to the total of metallic elements other than Li, the element (A) and the element (B) on the surface portion of the secondary particle is the atomic ratio of the entire secondary particle. It is characterized by being 50 times or less. This ratio is preferably 40 times or less, more preferably 25 times or less, particularly preferably 10 times or less, and most preferably 5 times or less. The lower limit is not particularly limited, but is preferably 1 or more, more preferably 1.1 or more, and particularly preferably 1.2 or more. When this ratio is in the above range, particularly good battery characteristics can be obtained.

  Further, the atomic ratio of the total of the element (B) to the total of the metal elements other than Li, the element (A) and the element (B) on the surface portion of the secondary particle is 1 or more times the atomic ratio of the entire secondary particle It is characterized by being. This ratio is preferably 1.5 times or more, more preferably 2 times or more, and particularly preferably 3 times or more. The upper limit is not particularly limited, but is preferably 100 times or less, more preferably 75 times or less, particularly preferably 50 times or less, and most preferably 25 times or less. If this ratio is too small, the effect of improving powder physical properties is small, while if it is too large, battery performance may be deteriorated.

  The composition of the surface part of the secondary particles of the lithium transition metal compound powder was analyzed by X-ray photoelectron spectroscopy (XPS) using monochromatic light AlKα as an X-ray source, an analysis area of 0.3 mm diameter, and an extraction angle of 45 Perform under the condition of °. Although the range (depth) that can be analyzed varies depending on the composition of the secondary particles, it is usually 0.1 nm to 50 nm, particularly 1 nm to 10 nm for the positive electrode active material. Therefore, in this invention, the surface part of the secondary particle of lithium transition metal type compound powder shows the range which can be measured on these conditions.

In addition, the inside of the secondary particles refers to a portion (depth) in which analysis is possible, particularly a portion having a depth of 10 nm or more and deeper than the surface portion in the positive electrode active material.
Further, in the present invention, a compound having an element of B and / or Bi (hereinafter referred to as “further additive element”) (hereinafter referred to as “further additive”) is used as the further additive. From the viewpoint of improving powder physical properties, it is preferable. Among these additional elements, it is preferable that the additional element is B from the viewpoint that it can be obtained at low cost as an industrial raw material and is a light element.

  As a kind of the compound (further additive) containing a further additive element, the kind is not particularly limited as long as the effect of the present invention is expressed, but usually boric acid, salts of oxo acid, Oxides and hydroxides are used. Among these further additives, boric acid and oxides are preferable, and boric acid is particularly preferable because it can be obtained at low cost as an industrial raw material.

Further exemplary compounds of additive 1 include BO, B ₂ O ₂ , B ₂ O ₃ , B ₄ O ₅ , B ₆ O.
, B ₇ O, B ₁₃ O ₂ , LiBO ₂ , LiB ₅ O ₈ , Li ₂ B ₄ O ₇ , HBO ₂ , H ₃ BO ₃ , B (OH) ₃ , B (OH) ₄ , BiBO ₃ , Bi ₂ O ₃ , Bi ₂ O ₅ , Bi (OH) _{3 and the} like are mentioned, and B ₂ O ₃ , H ₃ BO ₃ , and Bi ₂ O ₃ are preferably mentioned because they are relatively inexpensive and easily available as industrial raw materials. Particularly preferred is H ₃ BO ₃ . These additional additives may be used individually by 1 type, and may mix and use 2 or more types.

<Median diameter and 90% integrated diameter ( _D90 )>
The median diameter of the lithium transition metal-based compound powder of the present invention is usually 4 μm or more, preferably 5 μm or more, more preferably 6 μm or more, most preferably 6.5 μm or more, and usually 20 μm or less, preferably 19 μm or less, more preferably It is 18 μm or less, more preferably 17 μm or less, and most preferably 15 μm or less. When the median diameter is less than this lower limit, there is a possibility that a problem occurs in the coating property at the time of forming the positive electrode active material layer, and when the upper limit is exceeded, battery performance may be deteriorated.

The 90% cumulative diameter (D ₉₀ ) of the secondary particles of the lithium transition metal-based compound powder of the present invention is usually 30 μm or less, preferably 25 μm or less, more preferably 22 μm or less, most preferably 20 μm or less, and usually 10 μm. Above, preferably 11 μm or more, more preferably 12 μm or more, and most preferably 13 μm or more. If the 90% cumulative diameter (D ₉₀ ) exceeds the above upper limit, the battery performance may be deteriorated, and if it is less than the lower limit, there is a possibility of causing a problem in the coating property when forming the positive electrode active material layer.

In the present invention, the median diameter and the 90% cumulative diameter (D ₉₀ ) as the average particle diameter are set to a refractive index of 1.60 by a known laser diffraction / scattering particle size distribution measuring device, and the particle diameter standard is determined. Measured as a volume reference. In the present invention, a 0.1 wt% sodium hexametaphosphate aqueous solution was used as a dispersion medium used in the measurement, and measurement was performed after 5 minutes of ultrasonic dispersion (output 30 W, frequency 22.5 kHz).

<BET specific surface area>
The lithium transition metal compound powder of the present invention also has a BET specific surface area of usually 0.3 m ² / g or more, preferably 0.4 m ² / g or more, more preferably 0.45 m ² / g or more, most preferably. Is 0.5 m ² / g or more, usually 3 m ² / g or less, preferably 2.0 m ² / g or less, more preferably 1.5 m ² / g or less, and most preferably 1.3 m ² / g or less. . If the BET specific surface area is smaller than this range, the battery performance is likely to be lowered, and if it is larger, the bulk density is difficult to increase, and there is a possibility that a problem is likely to occur in the coating property at the time of forming the positive electrode active material.

<The bulk density>
The bulk density of the lithium transition metal compound powder of the present invention is usually 1.2 g / cc or more, preferably 1.3 g / cc or more, more preferably 1.4 g / cc or more, most preferably 1.5 g / cc or more. Usually, it is 3.0 g / cc or less, preferably 2.9 g / cc or less, more preferably 2.8 g / cc or less, and most preferably 2.7 g / cc or less. While the bulk density exceeding this upper limit is preferable for improving powder filling properties and electrode density, the specific surface area may become too low, and battery performance may be reduced. If the bulk density is below this lower limit, there is a possibility of adversely affecting the powder filling property and electrode preparation.
In the present invention, the bulk density is 5 to 10 g of lithium transition metal compound powder in a 10 ml glass measuring cylinder and tapped 200 times with a stroke of about 20 mm (tap density) g / Calculate as cc.

<Average primary particle size>
The average diameter (average primary particle diameter) of the lithium transition metal compound powder of the present invention is not particularly limited, but the lower limit is preferably 0.1 μm or more, more preferably 0.2 μm or more, and most preferably 0. Further, the upper limit is preferably 3 μm or less, more preferably 2 μm or less, still more preferably 1.5 μm or less, and most preferably 1.2 μm or less. If the average primary particle size exceeds the above upper limit, it may adversely affect the powder filling property or the specific surface area will decrease, which may increase the possibility that the battery performance such as rate characteristics and output characteristics will decrease. There is sex. If the lower limit is not reached, there is a possibility that problems such as inferior reversibility of charge / discharge due to the undeveloped crystals.

In addition, the average primary particle diameter in this invention is an average diameter observed with the scanning electron microscope (SEM), and the average particle diameter of about 10-30 primary particles using a SEM image of 30,000 times. It can be obtained as a value.
The BET specific surface area can be measured by a known BET type powder specific surface area measuring device. In the present invention, an OMS Riken: AMS8000 type automatic powder specific surface area measuring device was used, nitrogen was used as an adsorption gas, and helium was used as a carrier gas. Specifically, the powder sample was heated and deaerated with a mixed gas at a temperature of 150 ° C., then cooled to liquid nitrogen temperature to adsorb the mixed gas, and then heated to room temperature with water to be adsorbed. Nitrogen gas was desorbed, the amount was detected by a heat conduction detector, and the specific surface area of the sample was calculated therefrom.

<Volume resistivity>
The volume resistivity value when the lithium transition metal-based compound powder of the present invention is compacted at a pressure of 40 MPa is preferably 1 × 10 ³ Ω · cm or more as a lower limit, and preferably 1 × 10 ⁴ Ω · cm or more. More preferably, it is more preferably 1 × 10 ⁵ Ω · cm or more, and most preferably 5 × 10 ⁵ Ω · cm or more. The upper limit is preferably 1 × 10 ⁷ Ω · cm or less, more preferably 8 × 10 ⁶ Ω · cm or less, further preferably 5 × 10 ⁶ Ω · cm or less, and most preferably 3 × 10 ⁶ Ω · cm or less. . If this volume resistivity exceeds this upper limit, the load characteristics when used as a battery may be reduced. On the other hand, if the volume resistivity is below this lower limit, the safety of the battery may be reduced.

  In the present invention, the volume resistivity of the lithium transition metal based compound powder is such that the four probe / ring electrode, the electrode spacing is 5.0 mm, the electrode radius is 1.0 mm, the sample radius is 12.5 mm, and the applied voltage limiter is 90 V. The volume resistivity measured in a state where the lithium transition metal-based compound powder is compacted at a pressure of 40 MPa. The volume resistivity can be measured, for example, by using a powder resistance measuring device (for example, Lorester GP powder resistance measuring system manufactured by Dia Instruments Co., Ltd.) with a powder probe unit on a powder under a predetermined pressure. It can be carried out.

<Crystal structure>
The lithium transition metal-based compound powder of the present invention is preferably composed mainly of a lithium nickel manganese cobalt-based composite oxide including a crystal structure belonging to a layered structure.
Here, the layered structure will be described in more detail. As a typical crystal system having a layered structure, there are those belonging to the α-NaFeO ₂ type such as LiCoO ₂ and LiNiO ₂ , which are hexagonal and have a space group due to their symmetry.

(Hereinafter referred to as “layered R (−3) m structure”).
However, the layered LiMeO ₂ is not limited to the layered R (−3) m structure. In addition to this, LiMnO ₂ called so-called layered Mn is an orthorhombic and space-group Pm2m layered compound, and Li ₂ MnO ₃ called so-called 213 phase is Li [Li _1/3 Mn _2/3 ]. O ₂ , which is a monoclinic space group C2 / m structure, is also a layered compound in which a Li layer, a [Li _1/3 Mn _2/3 ] layer, and an oxygen layer are stacked.

<composition>
The composition of the lithium nickel manganese cobalt composite oxide, which is the main component of the lithium transition metal compound powder of the present invention, is a lithium transition metal composite oxide powder represented by the following composition formula (I). Is preferred.
LiMO ₂ (I)
However, M is an element composed of Li, Ni and Mn, or Li, Ni, Mn and Co, and the Mn / Ni molar ratio is usually 0.1 or more, preferably 0.3 or more, more preferably 0.5 or more, more preferably 0.6 or more, still more preferably 0.7 or more, still more preferably 0.8 or more, most preferably 0.9 or more, usually 5 or less, preferably 4 or less, more preferably 3 or less, more preferably 2.5 or less, and most preferably 1.5 or less. The Co / (Mn + Ni + Co) molar ratio is usually 0 or more, preferably 0.01 or more, more preferably 0.02 or more, still more preferably 0.03 or more, most preferably 0.05 or more, usually 0.35 or less, preferably Is 0.20 or less, more preferably 0.15 or less, still more preferably 0.10 or less, and most preferably 0.099 or less. The Li molar ratio in M is usually 0.001 or more, preferably 0.01 or more, more preferably 0.02 or more, still more preferably 0.03 or more, most preferably 0.05 or more, usually 0.2 or less, Preferably it is 0.19 or less, More preferably, it is 0.18 or less, More preferably, it is 0.17 or less, Most preferably, it is 0.15 or less.

In the above composition formula (I), the atomic ratio of the oxygen amount is described as 2 for convenience, but there may be some non-stoichiometry. In the case of non-stoichiometry, the atomic ratio of oxygen is usually in the range of 2 ± 0.2, preferably in the range of 2 ± 0.15, more preferably in the range of 2 ± 0.12, and even more preferably 2 ± 0.10. And particularly preferably in the range of 2 ± 0.05.
In addition, the lithium transition metal-based compound powder of the present invention is preferably obtained by firing at a high temperature in an oxygen-containing gas atmosphere in order to increase the crystallinity of the positive electrode active material. In particular, the lower limit of the firing temperature is usually 1050 ° C. or higher, preferably 1060 ° C. or higher, more preferably 1070 ° C. or higher, even more preferably in the lithium nickel manganese cobalt-based composite oxide having the composition represented by the above composition formula (I). Is 1080 ° C. or higher, most preferably 1090 ° C. or higher, and the upper limit is 1200 ° C. or lower, preferably 1190 ° C. or lower, more preferably 1180 ° C. or lower, and most preferably 1170 ° C. or lower. If the firing temperature is too low, heterogeneous phases are mixed, and the lattice distortion increases without developing a crystal structure. Moreover, the specific surface area becomes too large. Conversely, if the firing temperature is too high, the primary particles grow excessively, sintering between the particles proceeds too much, and the specific surface area becomes too small.

<Contained carbon concentration C>
The carbon concentration C (wt%) value of the lithium transition metal compound powder of the present invention is usually 0.005 wt% or more, preferably 0.01 wt% or more, more preferably 0.015 wt% or more, most preferably Preferably it is 0.02% by weight or more, usually 0.25% by weight or less, preferably 0.2% by weight or less, more preferably 0.15% by weight or less, still more preferably 0.1% by weight or less, most preferably Is 0.07% by weight or less. If the lower limit is not reached, battery performance may be reduced. If the upper limit is exceeded, swelling due to gas generation when the battery is produced may increase or battery performance may be reduced.

In the present invention, the carbon concentration C of the lithium nickel manganese cobalt-based composite oxide powder is determined by measurement using an oxygen gas combustion (high-frequency heating furnace type) infrared absorption method, as shown in the Examples section below. It is done.
In addition, the carbon component contained in the lithium nickel manganese cobalt composite oxide powder obtained by carbon analysis described later can be regarded as indicating information on the amount of carbonic acid compound, particularly lithium carbonate. This is due to the fact that the carbon amount determined by carbon analysis is assumed to be all derived from carbonate ions, and the carbonate ion concentration analyzed by ion chromatography generally agrees.

  On the other hand, when a composite treatment with conductive carbon is performed as a method for increasing the electron conductivity, a C amount exceeding the specified range may be detected, but such a treatment was performed. The C value in the case is not limited to the specified range.

<Preferred composition>
In the lithium transition metal composite oxide powder for a lithium secondary battery positive electrode material of the present invention, the atomic configuration in the M site in the composition formula (I) is represented by the following formula (II) or the following formula (II ′). Those are particularly preferred.

M = Li _{z / (2 + z)} {(Ni _{(1 + y) / 2} Mn _{(1-y) / 2} ) _1-x Co _x } _{2 / (2 + z)} (II)
(However, in the above formula (II),
0 ≦ x ≦ 0.1,
−0.1 ≦ y ≦ 0.1,
(1-x) (0.05-0.98y) ≤z≤ (1-x) (0.20-0.88y)
It is. )
M = Li _{z ′ / (2 + z ′)} {(Ni _{(1 + y ′) / 2} Mn _{(1-y ′) / 2} ) _{1-x ′} Co _{x ′} } _{2 / (2 + z ′)} (II ′)
(However, in the composition formula (II ′),
0.1 <x ′ ≦ 0.35
−0.1 ≦ y ′ ≦ 0.1
(1-x ′) (0.02-0.98y ′) ≦ z ′ ≦ (1-x ′) (0.20-0.88y ′))
In the above formula (II), the value of x is usually 0 or more, preferably 0.01 or more, more preferably 0.02 or more, still more preferably 0.03 or more, most preferably 0.04 or more, usually 0.1. Hereinafter, it is preferably 0.099 or less, and most preferably 0.098 or less.

The value of y is usually −0.1 or more, preferably −0.05 or more, more preferably −0.03 or more, most preferably −0.02 or more, usually 0.1 or less, preferably 0.05 or less, More preferably, it is 0.03 or less, and most preferably 0.02 or less.
The value of z is usually (1-x) (0.05-0.98y) or more, preferably (1-x) (0.06-0.98y) or more, more preferably (1-x) (0. 07-0.98y) or more, more preferably (1-x) (0.08-0.98y) or more, most preferably (1-x) (0.10-0.98y) or more, usually (1- x) (0.20-0.88y) or less, preferably (1-x) (0.18-0.88y) or less, more preferably (1-x) (0.17-0.88y), most Preferably, it is (1-x) (0.16-0.88y) or less. If z is below this lower limit, the conductivity will decrease, and if it exceeds the upper limit, the amount of substitution to transition metal sites will increase so much that the battery capacity will decrease, leading to a decrease in the performance of lithium secondary batteries using this. There is sex. On the other hand, if z is too large, the carbon dioxide absorbability of the active material powder increases, so that it becomes easy to absorb carbon dioxide in the atmosphere. As a result, it is estimated that the concentration of contained carbon increases.

In the above formula (II ′), the value of x ′ is usually larger than 0.1, preferably 0.15 or more, more preferably 0.2 or more, still more preferably 0.25 or more, most preferably 0.30 or more. Usually, it is 0.35 or less, preferably 0.345 or less, and most preferably 0.34 or less.
The value of y ′ is usually −0.1 or more, preferably −0.05 or more, more preferably −0.03 or more, most preferably −0.02 or more, usually 0.1 or less, preferably 0.05 or less. More preferably, it is 0.03 or less, and most preferably 0.02 or less.

  The value of z ′ is usually (1−x ′) (0.02−0.98y ′) or more, preferably (1−x ′) (0.03−0.98y ′) or more, more preferably (1− x ′) (0.04-0.98y ′) or more, most preferably (1-x ′) (0.05-0.98y ′) or more, usually (1-x ′) (0.20-0. 88y ′) or less, preferably (1-x ′) (0.18−0.88y ′) or less, more preferably (1-x ′) (0.17−0.88y ′), most preferably (1 -X ') (0.16-0.88y') or less. If z ′ is less than this lower limit, the conductivity will be reduced, and if it exceeds the upper limit, the amount of substitution to transition metal sites will be too much and the battery capacity will be reduced. there is a possibility. On the other hand, if z ′ is too large, the carbon dioxide absorbability of the active material powder increases, so that it becomes easy to absorb carbon dioxide in the atmosphere. As a result, it is estimated that the concentration of contained carbon increases.

  In the composition range of the above formulas (II) and (II ′), as the z and z ′ values are closer to the lower limit, which is a constant ratio, the battery tends to have lower rate characteristics and output characteristics. The closer the z and z ′ values are to the upper limit, the higher the rate characteristics and output characteristics of the battery, but there is a tendency for the capacity to decrease. In addition, the lower the y, y ′ value, that is, the smaller the manganese / nickel atomic ratio, the lower the charging voltage, the higher the capacity, the lower the cycle characteristics and safety of the battery set with a high charging voltage is seen, Conversely, as the y and y ′ values are closer to the upper limit, the cycle characteristics and safety of the battery set at a higher charge voltage are improved, while the discharge capacity, rate characteristics, and output characteristics tend to decrease. Also, the closer the x and x ′ values are to the lower limit, the lower the load characteristics such as the rate characteristics and the output characteristics of the battery, and conversely, the closer the x and x ′ values are to the upper limit, However, if this upper limit is exceeded, cycle characteristics and safety when set at a high charge voltage will be reduced, and raw material costs will be increased. It is an important component of the present invention that the composition parameters x, x ', y, y', z, and z 'are within a specified range.

Here, the chemical meaning of the Li composition (z, z ′ and x, x ′) in the lithium nickel manganese cobalt composite oxide, which is a preferred composition of the lithium transition metal compound powder of the present invention, will be described in more detail below. explain.
As described above, the layered structure is not necessarily limited to the R (-3) m structure, but is preferably one that can be attributed to the R (-3) m structure from the viewpoint of electrochemical performance.

In order to obtain x, x ′, y, y ′, z, and z ′ of the composition formula of the lithium transition metal compound, each transition metal and Li are analyzed by an inductively coupled plasma emission spectrometer (ICP-AES). Thus, the ratio is calculated by determining the ratio of Li / Ni / Mn / Co.
From a structural point of view, it is considered that Li related to z and z ′ is substituted for the same transition metal site. Here, due to Li relating to z and z ′, the average valence of Ni becomes larger than divalent (trivalent Ni is generated) by the principle of charge neutrality. Since z and z ′ increase the Ni average valence, they are indicators of the Ni valence (the ratio of Ni (III)).

  In addition, when calculating the Ni valence (m) accompanying the change of z and z ′ from the above composition formula, it is assumed that the Co valence is trivalent and the Mn valence is tetravalent.

It becomes. This calculation result means that the Ni valence is not determined only by z and z ', but is a function of x, x' and y, y '. If z, z '= 0 and y, y' = 0, the Ni valence remains divalent regardless of the values of x, x '. When z and z ′ are negative values, it means that the amount of Li contained in the active material is less than the stoichiometric amount, and those having a very large negative value are effective for the present invention. It may not come out. On the other hand, even if the z and z ′ values are the same, the Ni valence increases as the composition is rich in Ni (y, y ′ values are large) and / or Co rich (large in x, x ′ values). This means that when used in a battery, the rate characteristics and output characteristics are improved, but on the other hand, the capacity tends to decrease. From this, it can be said that the upper and lower limits of the z and z 'values are more preferably defined as functions of x, x' and y, y '.

In addition, when the x value is in the range of 0 ≦ x ≦ 0.1 and the amount of Co is small, in addition to reducing the cost, it was used as a lithium secondary battery designed to be charged at a high charging potential. In some cases, charge / discharge capacity, cycle characteristics, and safety are improved.
On the other hand, if the x ′ value is in the range of 0.10 <x ′ ≦ 0.35 and the amount of Co is relatively large, when used as a lithium secondary battery, the charge / discharge capacity, cycle characteristics, load characteristics, safety Improved in a balanced manner.

<Powder X-ray diffraction peak>
In the present invention, the lithium nickel manganese cobalt based composite oxide powder having a composition satisfying the composition formulas (I) and (II) has a diffraction angle 2θ of 64.5 in a powder X-ray diffraction pattern using CuKα rays. When the half width of the (110) diffraction peak existing in the vicinity of ° is FWHM (110), it is preferably in the range of 0.1 ≦ FWHM (110) ≦ 0.3.

In general, since the half width of the X-ray diffraction peak is used as a measure of crystallinity, the present inventors have conducted intensive studies on the correlation between crystallinity and battery performance. As a result, when the half-value width of the (110) diffraction peak having a diffraction angle 2θ of around 64.5 ° is within the specified range, good battery performance is exhibited.
In the present invention, the FWHM (110) is usually 0.01 or more, preferably 0.05 or more, more preferably 0.10 or more, still more preferably 0.12 or more, most preferably 0.14 or more, usually 0.3. Hereinafter, it is preferably 0.28 or less, more preferably 0.26 or less, further preferably 0.24 or less, and most preferably 0.22 or less.

  In the present invention, the lithium nickel manganese cobalt composite oxide powder having a composition satisfying the composition formulas (I) and (II) has a diffraction angle 2θ of 64 in powder X-ray diffraction measurement using CuKα rays. In the (018) diffraction peak existing at around 0 °, the (110) diffraction peak around 64.5 °, and the (113) diffraction peak around 68 °, a different phase is present on the higher angle side than the peak top. In the case of having no diffraction peak derived from or having a diffraction peak derived from a different phase, the integrated intensity ratio of the different phase peak to the diffraction peak of the original crystal phase is preferably in the following range, respectively.

0 ≦ I ₀₁₈ ^* / I ₀₁₈ ≦ 0.20
0 ≦ I ₁₁₀ ^* / I ₁₁₀ ≦ 0.25
0 ≦ I ₁₁₃ ^* / I ₁₁₃ ≦ 0.30
(Here, I ₀₁₈ , I ₁₁₀ , and I ₁₁₃ represent the integrated intensities of the diffraction peaks, respectively (018), (110), and (113), and I ₀₁₈ ^* , I ₁₁₀ ^* , and I ₁₁₃ ^* are (018 ), (110), (113) represents the integrated intensity of a diffraction peak derived from a different phase appearing at a higher angle than the peak top of the diffraction peak.)

By the way, although the details of the causative substance of the diffraction peak derived from this heterogeneous phase are not clear, when a heterogeneous phase is included, the capacity, rate characteristics, cycle characteristics, etc. when it is made into a battery are lowered. For this reason, the diffraction peak may have a diffraction peak that does not adversely affect the battery performance of the present invention, but is preferably a ratio in the above range, and the diffraction peak derived from a different phase with respect to each diffraction peak. The integrated intensity ratio is usually I ₀₁₈ ^* / I ₀₁₈ ≦ 0.20, I ₁₁₀ ^* / I ₁₁₀ ≦ 0.25, I ₁₁₃ ^* / I ₁₁₃ ≦ 0.30, preferably I ₀₁₈ ^* / I ₀₁₈ ≦ 0. 15, I ₁₁₀ ^* / I ₁₁₀ ≦ 0.20, I ₁₁₃ ^* / I ₁₁₃ ≦ 0.25, more preferably I ₀₁₈ ^* / I ₀₁₈ ≦ 0.10, I ₁₁₀ ^* / I ₁₁₀ ≦ 0.15, I ₁₁₃ ^* / _{I 113} ≦ 0.20, more preferably ^{_{I 018 * / I 018 ≦ 0.05}} , I 110 * / I 110 ≦ 0.10, an _{I 113 * / I 113 ≦ 0.15} , It is particularly preferred is also preferably no diffraction peaks derived from heterogeneous phases.

<Reason why the lithium transition metal-based compound powder of the present invention provides the above effects>
The reason why the lithium transition metal-based compound powder of the present invention brings about the above-described effect is presumed as follows.
The lithium transition metal-based compound powder of the present invention has an active material as compared with the single addition because the element (A) of the compound (A ′) is more solid-solved inside the particle than the element (B) of the compound (B ′). The effect of improving the Li movement speed in the vicinity of the surface and inside the active material is increased. As a result, it is presumed that the low-temperature resistance characteristics are improved when the lithium transition metal-based compound powder of the present invention is used as a battery.

[Method for producing lithium transition metal compound powder for positive electrode material of lithium secondary battery]
The method for producing the lithium transition metal-based compound powder of the present invention is not limited to a specific production method, but at least one selected from a lithium compound and Cr, Mn, Fe, Co, Ni, and Cu. The above transition metal compound, the compound (A ′) having at least one element (A) selected from the group consisting of Nb, Ta and V, and at least one element (B) selected from W, Mo and Re A slurry preparation step for pulverizing the compound (B ′) having a liquid in a liquid medium, a spray drying step for spray drying the obtained slurry, and a firing for firing the obtained spray dried body in an oxygen-containing gas atmosphere And a process for producing a lithium transition metal compound powder for a lithium secondary battery positive electrode material.

  Further, in the slurry adjustment step, the median diameter of the lithium compound, the transition metal compound, the compound (A ′) and the compound (B ′) measured in a liquid medium under the following measurement conditions is 0.7 μm. When the slurry supply amount is S (L / min) and the gas supply amount is G (L / min) in the spray drying step, 500 ≦ G / S ≦ 10000. It is preferably produced by a powder production method characterized by spray drying under conditions.

<Median diameter measurement conditions>
Using a laser diffraction / scattering particle size distribution measuring device, the refractive index is set to 1.24, and the measurement is performed after 5 minutes of ultrasonic dispersion (output 30 W, frequency 22.5 kHz) with the particle diameter reference as the volume reference.
For example, a lithium nickel manganese cobalt composite oxide powder will be described as an example. A lithium compound, a nickel compound, a manganese compound, a cobalt compound, and a compound (A ′) and a compound (B ′) are dispersed in a liquid medium. The spray-dried body obtained by spray-drying the slurry thus produced can be produced by firing in an oxygen-containing gas atmosphere.
Hereinafter, the method for producing a lithium transition metal-based compound powder of the present invention will be described in detail by taking as an example the method for producing a lithium nickel manganese cobalt-based composite oxide powder which is a preferred embodiment of the present invention.

<Slurry preparation process>
Among the raw material compounds used in the preparation of the slurry in producing the lithium transition metal-based compound powder by the method of the present invention, the lithium compounds include Li ₂ CO ₃ , LiNO ₃ , LiNO ₂ , LiOH, LiOH · H _2. Examples include O, LiH, LiF, LiCl, LiBr, LiI, CH ₃ OOLi, Li ₂ O, Li ₂ SO ₄ , dicarboxylic acid Li, citric acid Li, fatty acid Li, and alkyl lithium. Among these lithium compounds, lithium compounds that do not contain nitrogen, sulfur, or halogen atoms are preferred because they do not generate harmful substances such as SO _x and NO _x during the firing treatment. It is a compound that easily forms voids by generating cracked gas in the secondary particles of the spray-dried powder by generating cracked gas. Taking these points into consideration, Li ₂ CO ₃ , LiOH, LiOH.H ₂ O is preferable, and Li ₂ CO ₃ is particularly preferable. These lithium compounds may be used individually by 1 type, and may use 2 or more types together.

Moreover, as a nickel compound, Ni (OH) ₂ , NiO, NiOOH, NiCO ₃ , 2NiCO ₃ .3Ni (OH) ₂ .4H ₂ O, NiC ₂ O ₄ .2H ₂ O, Ni (NO ₃ ) ₂ .6H ₂ O, NiSO ₄ , NiSO ₄ .6H ₂ O, nickel fatty acid, nickel halide and the like. Among these, Ni (OH) ₂ , NiO, NiOOH, NiCO ₃ , 2NiCO ₃ .3Ni (OH) ₂ .4H ₂ O, and the like do not generate harmful substances such as SO _X and NO _X during the firing treatment. Nickel compounds such as NiC ₂ O ₄ .2H ₂ O are preferred. Further, from the viewpoint that it can be obtained as an industrial raw material at a low cost and from the viewpoint of high reactivity, Ni (OH) ₂ , NiO, NiOOH, NiCO ₃ , and further, a decomposition gas is generated at the time of firing. Ni (OH) ₂ , NiOOH, and NiCO ₃ are particularly preferable from the viewpoint of easily forming voids in the secondary particles. These nickel compounds may be used individually by 1 type, and may use 2 or more types together.

In addition, manganese compounds such as Mn ₂ O ₃ , MnO ₂ , Mn ₃ O ₄ , manganese oxide, MnCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganese dicarboxylate, manganese citrate, fatty acid manganese And manganese salts such as oxyhydroxide, manganese chloride and the like. Among these manganese compounds, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ , and MnCO ₃ do not generate gases such as SO _X and NO _X during firing, and can be obtained at low cost as industrial raw materials. Therefore, it is preferable. These manganese compounds may be used individually by 1 type, and may use 2 or more types together.

Further, as the cobalt compound, Co (OH) ₂ , CoOOH, CoO, Co ₂ O ₃ , Co ₃ O ₄ , Co (OCOCH ₃ ) ₂ .4H ₂ O, CoCl ₂ , Co (NO ₃ ) ₂ .6H ₂ O, Co (SO ₄ ) ₂ · 7H ₂ O, CoCO _{3 and the} like. Among them, Co (OH) ₂ , CoOOH, CoO, Co ₂ O ₃ , Co ₃ O ₄ , and CoCO ₃ are preferable, and more preferably, from the viewpoint that no harmful substances such as SO _X and NO _X are generated during the firing process. Co (OH) ₂ and CoOOH are industrially inexpensively available and highly reactive. In addition, Co (OH) ₂ , CoOOH, and CoCO ₃ are particularly preferable from the viewpoint of easily forming voids in the secondary particles of the spray-dried powder due to generation of decomposition gas during firing. These cobalt compounds may be used individually by 1 type, and may use 2 or more types together.

  In addition to the above Li, Ni, Mn, and Co raw material compounds, other elements are substituted to introduce the above-mentioned foreign elements, and voids in secondary particles formed by spray drying described later are efficiently formed. It is possible to use a group of compounds intended to be used. In addition, the addition stage of the compound used for the purpose of efficiently forming the voids of the secondary particles used here can be selected either before or after mixing the raw materials depending on the property. It is. In particular, it is preferable to add a compound that is easily decomposed due to mechanical shear stress applied by the mixing step after the mixing step.

The compound (A ′) is as described above. The compound (B ′) is as described above.
The method for mixing the raw materials is not particularly limited, and may be wet or dry. For example, a method using an apparatus such as a ball mill, a vibration mill, or a bead mill can be used. Wet mixing in which the raw material compound is mixed in a liquid medium such as water or alcohol is preferable because more uniform mixing is possible and the reactivity of the mixture can be increased in the firing step.

The mixing time varies depending on the mixing method, but it is sufficient that the raw materials are uniformly mixed at the particle level. For example, in a ball mill (wet or dry type), usually about 1 to 2 days, and in a bead mill (wet continuous method), a residence time. Is usually about 0.1 to 6 hours.
In the raw material mixing stage, it is preferable that the raw material is pulverized in parallel. As the degree of pulverization, the particle diameter of the raw material particles after pulverization is an index, but the average particle diameter (median diameter) is usually 0.7 μm or less, preferably 0.6 μm or less, more preferably 0.55 μm or less, most preferably Preferably, it is 0.5 μm or less. If the average particle size of the pulverized raw material particles is too large, the reactivity in the firing process is lowered, and the composition is difficult to homogenize. However, making particles smaller than necessary leads to an increase in the cost of pulverization, so that the average particle size is usually 0.01 μm or more, preferably 0.02 μm or more, more preferably 0.05 μm or more. It ’s fine. A means for realizing such a degree of pulverization is not particularly limited, but a wet pulverization method is preferable. Specific examples include dyno mill.

  In the present invention, the median diameter of the pulverized particles in the slurry was measured with a known laser diffraction / scattering type particle size distribution measuring apparatus with a refractive index of 1.24 and a particle diameter standard set as a volume standard. Is. In the present invention, a 0.1 wt% sodium hexametaphosphate aqueous solution was used as a dispersion medium used in the measurement, and measurement was performed after 5 minutes of ultrasonic dispersion (output 30 W, frequency 22.5 kHz).

<Spray drying process>
After wet mixing, the resulting slurry is then subjected to a normal drying step. The drying method is not particularly limited, but spray drying is preferable from the viewpoints of uniformity of the generated particulate matter, powder fluidity, powder handling performance, and efficient production of dry particles.

(Spray-dried powder)
In the method for producing a lithium transition metal-based compound powder such as lithium nickel manganese cobalt-based composite oxide powder of the present invention, a slurry obtained by wet-grinding a raw material compound, additive 1 and additive 2 is sprayed. By drying, a powder composed of secondary particles obtained by agglomerating primary particles is obtained. The spray-dried powder formed by agglomerating primary particles to form secondary particles is a geometric feature of the spray-dried powder of the present invention. Examples of the shape confirmation method include SEM observation and cross-sectional SEM observation.

The median diameter of the powder obtained by spray drying, which is also a firing precursor of lithium transition metal based compound powder such as lithium nickel manganese cobalt based composite oxide powder of the present invention (in this case, measured without applying ultrasonic dispersion) The value is usually 35 μm or less, more preferably 30 μm or less, still more preferably 25 μm or less, and most preferably 20 μm or less. However, since it tends to be difficult to obtain a too small particle size, it is usually 3 μm or more, preferably 4 μm or more, more preferably 5 μm or more. In the case of producing a particulate material by the spray drying method, the particle size can be controlled by appropriately selecting the spray format, the pressurized gas flow supply rate, the slurry supply rate, the drying temperature, and the like.

  That is, for example, a lithium compound, a nickel compound, a manganese compound, and a slurry in which a cobalt compound, additive 1 and additive 2 are dispersed in a liquid medium are spray-dried, and the obtained powder is fired to obtain lithium nickel. In producing the manganese cobalt-based composite oxide powder, when the slurry viscosity during spray drying is V (cp), the slurry supply amount is S (L / min), and the gas supply amount is G (L / min), Spray drying is performed under conditions where the slurry viscosity V is 50 cp ≦ V ≦ 10000 cp and the gas-liquid ratio G / S is 500 ≦ G / S ≦ 10000.

  If the slurry viscosity V (cp) is too low, it may be difficult to obtain a powder obtained by agglomerating primary particles to form secondary particles. If the slurry viscosity V (cp) is too high, the supply pump may fail or the nozzle may be blocked. is there. Therefore, the slurry viscosity V (cp) is usually 50 cp or more as a lower limit, preferably 100 cp or more, more preferably 300 cp or more, most preferably 500 cp, and the upper limit is usually 12000 cp or less, preferably 10000 cp or less, more preferably. Is 9000 cp or less, and most preferably 8000 cp or less.

  Further, when the gas-liquid ratio G / S is lower than the lower limit, the secondary particle size is coarsened or the drying property is liable to be lowered. When the upper limit is exceeded, the productivity may be lowered. Therefore, the gas-liquid ratio G / S is usually 500 or more, preferably 600 or more, more preferably 700 or more, most preferably 800 or more as a lower limit, and usually 10,000 or less, preferably 9000 or less, as an upper limit. Preferably it is 8000 or less, most preferably 7500 or less.

The slurry supply amount S and the gas supply amount G are appropriately set according to the viscosity of the slurry used for spray drying, the specifications of the spray drying apparatus used, and the like.
In the method of the present invention, the above-mentioned gas-liquid ratio G / S is satisfied by controlling the slurry supply amount and gas supply amount that meet the above-mentioned slurry viscosity V (cp) and that are suitable for the specifications of the spray drying apparatus to be used. Spray drying may be performed within a range, and other conditions are appropriately set according to the type of apparatus to be used, but it is preferable to select the following conditions.

  That is, spray drying of the slurry is usually 50 ° C. or higher, preferably 70 ° C. or higher, more preferably 120 ° C. or higher, most preferably 140 ° C. or higher, usually 300 ° C. or lower, preferably 250 ° C. or lower, more preferably 230. It is preferable to carry out the reaction at a temperature of ℃ or less, most preferably 210 ℃ or less. If this temperature is too high, the resulting granulated particles may have a lot of hollow structures, which may reduce the packing density of the powder. On the other hand, if it is too low, problems such as powder sticking and blockage due to moisture condensation at the powder outlet may occur.

<Baking process>
The fired precursor thus obtained is then fired.
Here, in the present invention, the “firing precursor” means a precursor of a lithium transition metal compound such as a lithium nickel manganese cobalt composite oxide before firing obtained by spray drying. For example, a compound that generates or sublimates decomposition gas during firing to form voids in secondary particles may be included in the above-mentioned spray-dried powder to form a firing precursor.

  This firing condition depends on the composition and the lithium compound raw material used, but as a tendency, if the firing temperature is too high, primary particles grow excessively, sintering between the particles proceeds too much, and the specific surface area becomes small. Pass. On the other hand, if it is too low, heterogeneous phases are mixed, and the lattice distortion increases without developing the crystal structure. Moreover, the specific surface area becomes too large. The firing temperature is usually 1050 ° C. or higher, preferably 1060 ° C. or higher, more preferably 1070 ° C. or higher, further preferably 1080 ° C. or higher, most preferably 1090 ° C. or higher, and the upper limit is 1200 ° C. or lower, preferably 1190 ° C. or lower. More preferably, it is 1180 ° C. or less, and most preferably 1170 ° C. or less.

  For firing, for example, a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln or the like can be used. The firing process is usually divided into three parts: temperature increase, maximum temperature retention, and temperature decrease. The second maximum temperature holding portion is not necessarily limited to one time, and may include two or more stages depending on the purpose, which means that aggregation is eliminated to the extent that secondary particles are not destroyed. The temperature raising, maximum temperature holding, and temperature lowering steps may be repeated twice or more with a crushing step or a crushing step meaning crushing to primary particles or even fine powder.

  When firing is performed in two stages, the first stage is preferably maintained at a temperature not lower than the temperature at which the Li raw material begins to decompose and below the melting temperature. For example, when lithium carbonate is used, the first stage is preferably maintained at 400 ° C. or higher. More preferably, it is 450 ° C. or higher, more preferably 500 ° C. or higher, most preferably 550 ° C. or higher, usually 850 ° C. or lower, more preferably 800 ° C. or lower, more preferably 780 ° C. or lower, most preferably 750 ° C. or lower. is there.

  In the temperature raising step leading to the maximum temperature holding step, the temperature in the furnace is usually raised at a temperature raising rate of 1 ° C./min to 15 ° C./min. Even if this rate of temperature rise is too slow, it takes time and is industrially disadvantageous. However, if it is too fast, the furnace temperature does not follow the set temperature depending on the furnace. The heating rate is preferably 2 ° C./min or more, more preferably 3 ° C./min or more, preferably 10 ° C./min or less, more preferably 8 ° C./min or less.

  Although the holding time in the maximum temperature holding step varies depending on the temperature, it is usually 30 minutes or longer, preferably 1 hour or longer, more preferably 2 hours or longer, most preferably 3 hours or longer within the above-mentioned temperature range. Time or less, preferably 25 hours or less, more preferably 20 hours or less, and most preferably 15 hours or less. If the firing time is too short, it becomes difficult to obtain a lithium transition metal-based compound powder with good crystallinity, and it is not practical to be too long. If the firing time is too long, it will be disadvantageous because it will be necessary to crush afterwards or it will be difficult to crush.

  In the temperature lowering step, the temperature in the furnace is usually decreased at a temperature decreasing rate of 0.1 ° C./min to 15 ° C./min. If the temperature lowering rate is too slow, it takes time and is industrially disadvantageous, but if it is too fast, the uniformity of the target product tends to be lost or the deterioration of the container tends to be accelerated. The temperature lowering rate is preferably 1 ° C./min or more, more preferably 3 ° C./min or more, preferably 10 ° C./min or less, more preferably 8 ° C./min or less.

  Since the firing atmosphere has an appropriate oxygen partial pressure region depending on the composition of the lithium transition metal-based compound powder to be obtained, appropriate various gas atmospheres for satisfying the oxygen partial pressure region are used. Examples of the gas atmosphere include oxygen, air, nitrogen, argon, hydrogen, carbon dioxide, and a mixed gas thereof. An oxygen-containing gas atmosphere such as air can be used for the lithium nickel manganese cobalt based composite oxide powder specifically implemented in the present invention. Usually, the atmosphere has an oxygen concentration of 1% by volume or more, preferably 10% by volume or more, more preferably 15% by volume or more, and 100% by volume or less, preferably 50% by volume or less, more preferably 25% by volume or less.

In such a production method, in order to produce the lithium transition metal-based compound powder of the present invention, for example, the lithium nickel manganese cobalt-based composite oxide powder having the specific composition, the production conditions are constant. When preparing a slurry in which a lithium compound, a nickel compound, a manganese compound, and a cobalt compound, and additive 1 and additive 2 are dispersed in a liquid medium, by adjusting the mixing ratio of each compound, It is possible to control the molar ratio of Li / Ni / Mn / Co.
According to the lithium transition metal-based compound powder of the present invention such as lithium nickel manganese cobalt-based composite oxide powder thus obtained, the capacity is high, the low-temperature output characteristics and the storage characteristics are excellent, and the performance balance is high. A positive electrode material for a lithium secondary battery is provided.

[Positive electrode for lithium secondary battery]
The positive electrode for a lithium secondary battery of the present invention is obtained by forming a positive electrode active material layer containing a lithium transition metal compound powder for a lithium secondary battery positive electrode material of the present invention and a binder on a current collector. It is.
The positive electrode active material layer is usually formed by mixing a positive electrode material, a binder, and a conductive material and a thickener, which are used if necessary, in a dry form into a sheet shape, and then pressing the positive electrode current collector on the positive electrode current collector. Alternatively, these materials are dissolved or dispersed in a liquid medium to form a slurry, which is applied to the positive electrode current collector and dried.

  As the material for the positive electrode current collector, metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, and carbon materials such as carbon cloth and carbon paper are usually used. Of these, metal materials are preferable, and aluminum is particularly preferable. As for the shape, in the case of a metal material, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punch metal, a foam metal, etc., and in the case of a carbon material, a carbon plate, a carbon thin film, a carbon cylinder Etc. Among these, metal thin films are preferable because they are currently used in industrialized products. In addition, you may form a thin film suitably in mesh shape.

  When a thin film is used as the positive electrode current collector, its thickness is arbitrary, but it is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 100 mm or less, preferably 1 mm or less, more preferably 50 μm or less. The range of is preferable. If it is thinner than the above range, the strength required for the current collector may be insufficient. On the other hand, if it is thicker than the above range, the handleability may be impaired.

  The binder used in the production of the positive electrode active material layer is not particularly limited, and in the case of a coating method, any material that is stable with respect to the liquid medium used during electrode production may be used. Specific examples include polyethylene, Resin polymers such as polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, nitrocellulose, SBR (styrene butadiene rubber), NBR (acrylonitrile butadiene rubber), fluorine rubber, isoprene rubber, butadiene rubber, ethylene・ Rubber polymers such as propylene rubber, styrene / butadiene / styrene block copolymers and hydrogenated products thereof, EPDM (ethylene / propylene / diene terpolymers), styrene / ethylene / butadiene / ethylene copolymers, Styrene / isoprene styrene bromide Copolymer and its hydrogenated thermoplastic elastomeric polymer, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinyl acetate copolymer, propylene / α-olefin copolymer, etc. Fluorine polymers such as soft resinous polymers, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymers, ion conductivity of alkali metal ions (especially lithium ions) And a polymer composition having the same. In addition, these substances may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

The ratio of the binder in the positive electrode active material layer is usually 0.1% by weight or more, preferably 1% by weight or more,
More preferably, it is 3% by weight or more, usually 80% by weight or less, preferably 60% by weight or less, more preferably 40% by weight or less, and most preferably 10% by weight or less. If the proportion of the binder is too low, the positive electrode active material cannot be sufficiently retained and the positive electrode has insufficient mechanical strength, which may deteriorate battery performance such as cycle characteristics. Battery capacity and conductivity may be reduced.

  The positive electrode active material layer usually contains a conductive material in order to increase conductivity. There are no particular restrictions on the type, but specific examples include metal materials such as copper and nickel, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, and amorphous carbon such as needle coke. And carbon materials. In addition, these substances may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios. The proportion of the conductive material in the positive electrode active material layer is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 1% by weight or more, and usually 50% by weight or less, preferably 30%. % By weight or less, more preferably 20% by weight or less. If the proportion of the conductive material is too low, the conductivity may be insufficient, and conversely if it is too high, the battery capacity may be reduced.

  As a liquid medium for forming a slurry, it is possible to dissolve or disperse a lithium transition metal compound powder as a positive electrode material, a binder, and a conductive material and a thickener used as necessary. If it is a solvent, there is no restriction | limiting in particular in the kind, You may use either an aqueous solvent or an organic solvent. Examples of the aqueous solvent include water and alcohol. Examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N , N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran (THF), toluene, acetone, dimethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane, etc. be able to. In particular, when an aqueous solvent is used, a dispersant is added together with the thickener, and a slurry such as SBR is slurried. In addition, these solvents may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

  The content of the lithium transition metal-based compound powder of the present invention as the positive electrode material in the positive electrode active material layer is usually 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more, and usually 99%. .9% by weight or less, preferably 99% by weight or less. If the proportion of the lithium transition metal compound powder in the positive electrode active material layer is too large, the strength of the positive electrode tends to be insufficient, and if it is too small, the capacity may be insufficient.

Further, the thickness of the positive electrode active material layer is usually about 20 to 200 μm.
As the electrode density after pressing the positive electrode, the lower limit is usually 3.1 g / cm ³ or more, preferably 3.2 g / cm ³ or more, particularly preferably 3.3 g / cm ³ or more, and the upper limit is usually , 4.2 g / cm ³ or less, preferably 4.0 g / cm ³ or less, particularly preferably 3.8 g / cm ³ or less.
The positive electrode active material layer obtained by coating and drying is preferably consolidated by a roller press or the like in order to increase the packing density of the positive electrode active material.
Thus, the positive electrode for a lithium secondary battery of the present invention can be prepared.

[Lithium secondary battery]
The lithium secondary battery of the present invention includes the above-described positive electrode for a lithium secondary battery of the present invention capable of occluding and releasing lithium, a negative electrode capable of occluding and releasing lithium, and a non-aqueous electrolyte using a lithium salt as an electrolytic salt, Is provided. Further, a separator for holding a nonaqueous electrolyte may be provided between the positive electrode and the negative electrode. In order to effectively prevent a short circuit due to contact between the positive electrode and the negative electrode, it is desirable to interpose a separator in this way.

<Negative electrode>
The negative electrode is usually configured by forming a negative electrode active material layer on a negative electrode current collector, similarly to the positive electrode.
As a material of the negative electrode current collector, a metal material such as copper, nickel, stainless steel, nickel-plated steel, or a carbon material such as carbon cloth or carbon paper is used. Among these, in the case of a metal material, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, etc., and in the case of a carbon material, a carbon plate, a carbon thin film, a carbon cylinder, etc. are mentioned. Among these, metal thin films are preferable because they are currently used in industrialized products. In addition, you may form a thin film suitably in mesh shape. When a metal thin film is used as the negative electrode current collector, the preferred thickness range is the same as the range described above for the positive electrode current collector.

The negative electrode active material layer includes a negative electrode active material. The negative electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions, but it can usually occlude and release lithium from the viewpoint of high safety. A carbon material is used.
Although there is no restriction | limiting in particular as a carbon material, Graphite (graphite), such as artificial graphite and natural graphite, and the thermal decomposition thing of organic substance on various thermal decomposition conditions are mentioned. Examples of pyrolysis products of organic matter include coal-based coke, petroleum-based coke, coal-based pitch carbide, petroleum-based pitch carbide, or carbide obtained by oxidizing these pitches, needle coke, pitch coke, phenol resin, crystalline cellulose, etc. And carbon materials obtained by partially graphitizing these, furnace black, acetylene black, pitch-based carbon fibers, and the like. Among them, graphite is preferable, and particularly preferable is artificial graphite, purified natural graphite, or graphite material containing pitch in these graphites, which is manufactured by subjecting easy-graphite pitch obtained from various raw materials to high-temperature heat treatment. Therefore, those subjected to various surface treatments are mainly used. One of these carbon materials may be used alone, or two or more thereof may be used in combination.

When a graphite material is used as the negative electrode active material, the d value (interlayer distance: d ₀₀₂ ) of the lattice plane (002 plane) determined by X-ray diffraction by the Gakushin method is usually 0.335 nm or more, and usually 0.34 nm. In the following, it is preferable that the thickness is 0.337 nm or less.
Further, the ash content of the graphite material is usually 1% by weight or less, particularly 0.5% by weight or less, and particularly preferably 0.1% by weight or less, based on the weight of the graphite material.

Further, the crystallite size (Lc) of the graphite material determined by X-ray diffraction by the Gakushin method is usually 30 nm or more, preferably 50 nm or more, and particularly preferably 100 nm or more.
The median diameter of the graphite material determined by the laser diffraction / scattering method is usually 1 μm or more, especially 3 μm or more, more preferably 5 μm or more, especially 7 μm or more, and usually 100 μm or less, especially 50 μm or less, more preferably 40 μm or less, especially 40 μm or less. It is preferable that it is 30 micrometers or less.

Moreover, the BET specific surface area of the graphite material is usually 0.5 m ² / g or more, preferably 0.7 m ² / g or more, more preferably 1.0 m ² / g or more, and further preferably 1.5 m ² / g. or more, and usually 25.0 m ² / g or less, preferably 20.0 m ² / g, more preferably 15.0 m ² / g or less, still more preferably 10.0 m ² / g or less.
Further, when performing Raman spectroscopy using argon laser light for graphite material, and strength _{I A} of the peak _{P A} is detected in the range of 1580～1620Cm ^-1, it is detected in the range of 1350 ^-1 that intensity ratio _I a / _{I B} of the intensity _{I B} of a peak _{P B} is what is preferably 0 to 0.5. Further, the half width of the peak _{P A} is preferably 26cm ^-1 or less, 25 cm ^-1 or less is more preferable.

In addition to the above-mentioned various carbon materials, it can also be used as a negative electrode active material of other materials capable of inserting and extracting lithium. Specific examples of negative electrode active materials other than carbon materials include metal oxides such as tin oxide and silicon oxide, nitrides such as Li _2.6 Co _0.4 N, and lithium alloys such as lithium alone and lithium aluminum alloys. Can be mentioned. One of these materials other than the carbon material may be used alone, or two or more thereof may be used in combination. Moreover, you may use in combination with the above-mentioned carbon material.

  As in the case of the positive electrode active material layer, the negative electrode active material layer is usually prepared by slurrying the above-described negative electrode active material, a binder, and optionally a conductive material and a thickener in a liquid medium. It can manufacture by apply | coating to a negative electrode electrical power collector, and drying. As the liquid medium, the binder, the thickener, the conductive material, and the like that form the slurry, the same materials as those described above for the positive electrode active material layer can be used.

<Nonaqueous electrolyte>
As the non-aqueous electrolyte, for example, known organic electrolytes, polymer solid electrolytes, gel electrolytes, inorganic solid electrolytes, and the like can be used. Of these, organic electrolytes are preferable. The organic electrolytic solution is configured by dissolving a solute (electrolyte) in an organic solvent.
Here, the type of the organic solvent is not particularly limited. For example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, ethers, amines, esters, amides. A phosphoric acid ester compound or the like can be used. Typical examples include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 4-methyl-2- Pentanone, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile Benzonitrile, butyronitrile, valeronitrile, 1,2-dichloroethane, dimethylformamide, dimethyl sulfoxide, trimethyl phosphate, triethyl phosphate, etc. Et compounds, hydrogen atoms may be partially substituted with a halogen atom. Moreover, these single or 2 or more types of mixed solvents can be used.

  The organic solvent described above preferably contains a high dielectric constant solvent in order to dissociate the electrolytic salt. Here, the high dielectric constant solvent means a compound having a relative dielectric constant of 20 or more at 25 ° C. Among the high dielectric constant solvents, it is preferable that ethylene carbonate, propylene carbonate, and compounds in which hydrogen atoms thereof are substituted with other elements such as halogen or alkyl groups are contained in the electrolytic solution. The proportion of the high dielectric constant solvent in the electrolyte is preferably 20% by weight or more, more preferably 25% by weight or more, and most preferably 30% by weight or more. If the content of the high dielectric constant solvent is less than the above range, desired battery characteristics may not be obtained.

In addition, in the organic electrolyte, a gas such as CO ₂ , N ₂ O, CO, and SO ₂ , vinylene carbonate, polysulfide S _x ^{2−, and the} like that enables efficient charge and discharge of lithium ions on the negative electrode surface You may add the additive which forms a film in arbitrary ratios. Among these additives, vinylene carbonate is particularly preferable.
Furthermore, in organic electrolytes, additives such as lithium difluorophosphate that are effective in improving cycle life and output characteristics, and additives that are effective in suppressing high-temperature storage gases such as propane sultone and propene sultone May be added at an arbitrary ratio.

The type of the electrolytic salt is not particularly limited, and any conventionally known solute can be used. Specific examples include LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiBOB, LiCl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₃ CF ₃ ) _{2 and the} like. Any one of these electrolytic salts may be used alone, or two or more thereof may be used in any combination and ratio.

  The lithium salt of the electrolytic salt is usually contained in the electrolytic solution so as to have a concentration of 0.5 mol / L to 1.5 mol / L. Even if the lithium salt concentration in the electrolytic solution is less than 0.5 mol / L or more than 1.5 mol / L, the electric conductivity may be lowered, and the battery characteristics may be adversely affected. The lower limit of this concentration is preferably 0.75 mol / L or more and the upper limit is 1.25 mol / L or less.

Even when a polymer solid electrolyte is used, the type thereof is not particularly limited, and any known crystalline / amorphous inorganic substance can be used as the solid electrolyte. Examples of the crystalline inorganic solid electrolyte include LiI, Li ₃ N, Li _{1 + x} J _x Ti _2-x (PO ₄ ) ₃ (J = Al, Sc, Y, La), Li _0.5-3x RE _{0. .5 + x} TiO ₃ (RE = La, Pr, Nd, Sm) and the like. Examples of the amorphous inorganic solid electrolyte include oxide glasses such as 4.9LiI-34.1Li ₂ O-61B ₂ O ₅ and 33.3Li ₂ O-66.7SiO ₂ . Any one of these may be used alone, or two or more may be used in any combination and ratio.

<Separator>
When the above-described organic electrolyte is used as the electrolyte, a separator is interposed between the positive electrode and the negative electrode in order to prevent a short circuit between the electrodes. The material and shape of the separator are not particularly limited, but those that are stable with respect to the organic electrolyte used, have excellent liquid retention properties, and can reliably prevent short-circuiting between electrodes are preferable. Preferable examples include microporous films, sheets, nonwoven fabrics and the like made of various polymer materials. Specific examples of the polymer material include polyolefin polymers such as nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, and polybutene. In particular, from the viewpoint of chemical and electrochemical stability, which is an important factor for separators, polyolefin polymers are preferable. From the viewpoint of self-occluding temperature, which is one of the purposes of use of separators in batteries, polyethylene is preferred. Is particularly desirable.

  When using a separator made of polyethylene, it is preferable to use ultra-high molecular weight polyethylene from the viewpoint of maintaining high-temperature shape, and the lower limit of the molecular weight is preferably 500,000, more preferably 1,000,000, and most preferably 1,500,000. On the other hand, the upper limit of the molecular weight is preferably 5 million, more preferably 4 million, and most preferably 3 million. This is because if the molecular weight is too large, the fluidity becomes too low, and the pores of the separator may not close when heated.

<Battery shape>
The lithium secondary battery of the present invention is produced by assembling the above-described positive electrode for a lithium secondary battery of the present invention, a negative electrode, an electrolyte, and a separator used as necessary into an appropriate shape. Furthermore, other components such as an outer case can be used as necessary.

  The shape of the lithium secondary battery of the present invention is not particularly limited, and can be appropriately selected from various commonly employed shapes according to the application. Examples of commonly used shapes include a cylinder type with a sheet electrode and separator in a spiral shape, a cylinder type with an inside-out structure combining a pellet electrode and a separator, and a coin type with stacked pellet electrodes and a separator. Can be mentioned. The method for assembling the battery is not particularly limited, and can be appropriately selected from various commonly used methods according to the shape of the target battery.

<Charge potential of the positive electrode when fully charged>
In the following examples, the lithium secondary battery of the present invention is used at a charging potential of the positive electrode in a fully charged state of less than 4.4 V, but becomes 4.4 V (vs. Li ^/ Li ⁺ ) or more. It is also possible to use with a battery that is designed in such a way. That is, even when the lithium nickel manganese cobalt based composite oxide powder for a lithium secondary battery positive electrode material of the present invention is used as a lithium secondary battery designed to be charged at a high charging potential, the effect of the present invention is achieved. Should be effective.

  The general embodiment of the lithium secondary battery of the present invention has been described above. However, the lithium secondary battery of the present invention is not limited to the above-described embodiment, and various modifications are possible as long as the gist thereof is not exceeded. Can be implemented.

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples as long as the gist of the present invention is not exceeded.
[Measurement method of physical properties]
The physical properties and the like of lithium transition metal-based compound powders produced in each Example and Comparative Example described below were measured as follows.

<Median diameter of pulverized particles in slurry>
Using a known laser diffraction / scattering particle size distribution measuring device, the refractive index was set to 1.24, and the particle diameter standard was measured as the volume standard. Further, a 0.1 wt% aqueous solution of sodium hexametaphosphate was used as a dispersion medium, and measurement was performed after 5 minutes of ultrasonic dispersion (output 30 W, frequency 22.5 kHz).

<Median diameter of secondary particles>
Using a known laser diffraction / scattering particle size distribution measuring apparatus, the refractive index was set to 1.60, and the particle diameter standard was measured as a volume standard. Further, a 0.1 wt% aqueous solution of sodium hexametaphosphate was used as a dispersion medium, and measurement was performed after 5 minutes of ultrasonic dispersion (output 30 W, frequency 22.5 kHz).

<Composition analysis of primary particle surface by X-ray photoelectron spectroscopy (XPS)>
An X-ray photoelectron spectrometer “Quantum 2000” manufactured by PHI was used under the following conditions.
X-ray source: Monochromatic AlKα
Analysis area: 0.3 mm square Extraction angle: 45 °
<Specific surface area>
Obtained by BET method.

<Bulk density>
4 to 10 g of the sample powder was put into a 10 ml glass graduated cylinder, and the powder packing density when tapped 200 times with a stroke of about 20 mm was obtained.
<Average primary particle size>
It calculated | required from the SEM image of 30,000 times.

[Production of Lithium Transition Metal Compound Powder (Examples and Comparative Examples)]
Example 1
Li ₂ CO ₃ , NiCO ₃ , Mn ₃ O ₄ , CoOOH, H ₃ BO ₃ , WO _3, Nb ₂ O ₅ are mixed with Li: Ni: Mn: Co: B: W: Nb = 1.15: 0.45. : 0.45: 0.1
After weighing and mixing to a molar ratio of 0: 0.0025: 0.015: 0.005,
Pure water was added thereto to prepare a slurry. While stirring the slurry, the solid content in the slurry was pulverized to a median diameter of 0.5 μm using a circulating medium agitation type wet pulverizer.

Next, this slurry was spray-dried by using a two-fluid nozzle type spray dryer (manufactured by Okawara Chemical Co., Ltd.) at an air supply rate of 60 L / min and a slurry supply rate of 8 mL / min (gas / liquid = 7500). Particulate powder obtained by spray drying with a spray dryer is placed in an alumina crucible and fired at 650 ° C. for 5 hours in an air atmosphere (heating rate 5 ° C./min.), And further fired at 1100 ° C. for 2 hours. (The temperature raising / lowering speed was 10 ° C./min.). Thereafter, pulverization classification is performed, and a lithium nickel manganese cobalt composite having a layered structure of Li _1.05 Ni _0.45 Mn _0.45 Co _0.1 B _0.0025 W _0.015 Nb _0.005 O ₂ An oxide was obtained.
The median diameter of this composite oxide was 6.5 μm, the BET specific surface area was 0.9 m ² / g, the bulk density was 1.7 g / cc, and the average primary particle size was 0.5 μm.

(Example 2)
The composition is Li ₂ CO ₃ , NiCO ₃ , Mn ₃ O ₄ , CoOOH, H ₃ BO ₃ , WO _3, Nb ₂ O ₅ , Li: Ni: Mn: Co: B: W: Nb = 1.15: 0 .45: 0.45: 0.10: 0.0025: 0.015: 0.01 This was prepared in the same manner as in Example 1 except that the molar ratio was changed.
The obtained composite oxide had a median diameter of 8.9 μm, a BET specific surface area of 0.7 m ² / g, a bulk density of 1.9 g / cc, and an average primary particle size of 0.5 μm.

(Comparative Example 1)
Li ₂ CO ₃ , Ni (OH) ₂ , Mn ₃ O ₄ , CoOOH, H ₃ BO ₃ , WO ₃ are replaced with Li: Ni: Mn: Co: B: W = 1.15: 0.45: 0.45. : Weighed and mixed so that the molar ratio was 0.10: 0.0025: 0.015, and then added pure water to prepare a slurry. While stirring the slurry, the solid content in the slurry was pulverized to a median diameter of 0.5 μm using a circulating medium agitation type wet pulverizer.

Next, this slurry was spray-dried using a four-fluid nozzle type spray dryer (manufactured by Fujisaki Electric Co., Ltd .: MDP-50 type). Air was used as the drying gas at this time, the drying gas introduction amount G was 1600 L / min, and the slurry introduction amount S was 7.8 × 10 ⁻¹ L / min (gas-liquid ratio G / S = 2050). The drying inlet temperature was 200 ° C. The particulate powder obtained by spray drying with a spray dryer was charged into an alumina crucible, fired at 1100 ° C. for 2 hours in an air atmosphere, and then pulverized to have a composition of Li _1.12 (Ni _0.45 Mn A lithium nickel manganese cobalt composite oxide (x = 0.1, y = 0.00, z = 0.12) of _0.45 Co _0.1 ) O ₂ was obtained. The obtained composite oxide had a median diameter of 10.1 μm, a BET specific surface area of 0.8 m ² / g, a bulk density of 1.8 g / cc, and an average primary particle size of 0.5 μm.

Example 3
It was produced in the same manner as in Example 1 except that the air supply rate during spray drying was 30 L / min, the slurry supply rate was 23 mL / min (gas / liquid = 1300), and the firing temperature was 1150 ° C.
The obtained composite oxide had a median diameter of 13.9 μm, a BET specific surface area of 0.8 m ² / g, a bulk density of 2.5 g / cc, and an average primary particle size of 0.5 μm.

(Comparative Example 2)
Manufactured in the same manner as Comparative Example 1 except that the air supply rate during spray drying was 1200 L / min, the slurry supply rate was 7.8 × 10 ⁻¹ L / min (gas / liquid = 1540), and the firing temperature was 1150 ° C. did.
The obtained composite oxide had a median diameter of 15.0 μm, a BET specific surface area of 0.4 m ² / g, a bulk density of 2.3 g / cc, and an average primary particle size of 0.5 μm.

[Production and evaluation of batteries]
Using the lithium transition metal-based compound powders produced in the above Examples and Comparative Examples as positive electrode materials (positive electrode active materials), lithium secondary batteries were produced and evaluated by the following methods.
[Production of positive electrode]
74% by mass of the produced lithium transition metal composite oxide powder, 20% by mass of acetylene black, 5% by mass of polytetrafluoroethylene powder, and 1% by mass of lithium difluorophosphate were thoroughly mixed in a mortar, The thin sheet was punched out using 9 mmφ and 12 mmφ punches. At this time, the total weight was adjusted to about 7.5 mg for 9 mmφ and about 17.5 mg for 12 mmφ, respectively. This was pressure-bonded to an aluminum mesh to obtain 9 mmφ and 12 mmφ positive electrodes.

A 9 mmφ positive electrode was used as a test electrode, a lithium metal plate as a counter electrode, and 1 mol of LiPF ₆ in a solvent of EC (ethylene carbonate): DMC (dimethyl carbonate): EMC (ethyl methyl carbonate) = 3: 3: 4 (volume ratio). A coin-type cell was assembled using a 25 μm-thick porous polyethylene film as a separator using an electrolytic solution dissolved at / L.
The obtained coin-type cell was subjected to a constant current / constant voltage charge of 0.2 mA / cm ² , that is, a reaction for releasing lithium ions from the positive electrode at an upper limit of 4.2 V. Subsequently, the initial charge capacity per unit weight of the positive electrode active material when a constant current discharge of 0.2 mA / cm ² , that is, a reaction of occluding lithium ions in the positive electrode was performed at a lower limit of 3.0 V was Qs (C) [mAh / g], and the initial discharge capacity was Qs (D) [mAh / g].

[Production of negative electrode]
Graphite powder having an average particle size of 8 to 10 μm (d ₀₀₂ = 3.35 Å) was used as the negative electrode active material, and polyvinylidene fluoride was used as the binder, and these were weighed at a weight ratio of 92.5: 7.5. Were mixed in an N-methylpyrrolidone solution to obtain a negative electrode mixture slurry. The slurry was applied to one side of a 20 μm thick copper foil, dried to evaporate the solvent, punched to 12 mmφ, and pressed at 0.5 ton / cm ² to form a negative electrode. At this time, the amount of the negative electrode active material on the electrode was adjusted to be about 6 to 8 mg.

A test in which a negative electrode is used as a test electrode, a battery cell is assembled using lithium metal as a counter electrode, and lithium ions are occluded in the negative electrode by a constant current-constant voltage method (cut current 0.05 mA) of 0.2 mA / cm ² -3 mV. The initial occlusion capacity per unit weight of the negative electrode active material at a lower limit of 0 V was defined as Qf [mAh / g].

[Production of battery for performance test]
The above-mentioned 12 mmφ positive electrode and negative electrode were combined, a test battery was assembled using a coin cell, and the battery performance was evaluated. That is, the above-described positive electrode prepared is placed on the positive electrode can of the coin cell, a porous polyethylene film having a thickness of 25 μm is placed thereon as a separator, pressed with a polypropylene gasket, and then EC ( An electrolytic solution in which LiPF ₆ was dissolved at a rate of 1 mol / L in a solvent of ethylene carbonate): DMC (dimethyl carbonate): EMC (ethyl methyl carbonate) = 3: 3: 4 (volume ratio) was added to the can. After fully infiltrating the separator, the above-described negative electrode was placed, a negative electrode can was placed and sealed, and a coin-type lithium secondary battery was produced. At this time, the balance between the weight of the positive electrode active material and the weight of the negative electrode active material was set so as to satisfy the following expression.
(Weight of negative electrode active material [g] × Qf [mAh / g]) / (Weight of positive electrode active material [g] × Qs (C)
[MAh / g]) = 1.2

[Battery characteristics test]
In order to measure the low temperature load characteristics of the battery thus obtained, the 1 hour rate current value of the battery, that is, 1C, was set as shown in the following equation, and the following tests were performed.
1C [mA] = Qs (D) × positive electrode active material weight [g] / h
First, a constant current 0.2C charge / discharge cycle and a constant current 1C charge / discharge cycle were performed at room temperature. The upper limit of charging was 4.1 V, and the lower limit voltage was 3.0 V. Next, when a coin cell adjusted to a charging depth of 40% is held in a low temperature atmosphere of −30 ° C. for 1 hour or longer by 1/3 C constant current charging / discharging and then discharged for 10 seconds at a constant current of 0.5 C [mA]. Assuming that the voltage after 10 seconds is V [mV] and the voltage before discharge is V ₀ [mV], the resistance value R [Ω] is calculated from the following equation as ΔV = V−V ₀ .

    R [Ω] = ΔV [mV] /0.5C [mA]

From Examples 1 and 2 and Comparative Example 1 in Table 1, lowering of the low temperature resistance is observed by adding an element (A) such as Nb. In addition, from Example 3 and Comparative Example 2, even when the firing temperature was raised and the specific surface area was lowered, a low temperature resistance decrease due to an element (A) such as Nb was observed.
The results of depth direction analysis by XPS for Example 1 and Comparative Example 1 are shown in Table 2, FIG. 1 and FIG. From Table 2, it can be seen that the concentration degree of the Nb surface is lower than that of W. From this, it is considered that the element (A) such as Nb is further substituted to the inside of the particle to facilitate Li diffusion inside the particle, thereby improving the low temperature resistance.

  Combining the results shown in Tables 1 and 2, a combination of an element that enriches the surface, such as W, and an additive element that forms a solid solution, such as Nb, reduces low-temperature resistance without impairing powder characteristics. I understood that I could do it. Therefore, according to the lithium transition metal-based compound powder for a lithium secondary battery positive electrode material of the present invention, it can be seen that a lithium secondary battery excellent in initial resistance at low temperature can be realized.

  The use of the lithium secondary battery using the lithium transition metal-based composite oxide powder of the present invention is not particularly limited, and can be used for various known uses. Specific examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidiscs, and transceivers. , Electronic notebook, calculator, memory card, portable tape recorder, radio, backup power supply, motor, lighting equipment, toy, game machine, clock, strobe, camera, pacemaker, electric tool, automotive power source, track vehicle power source, artificial Examples include a power source for satellites.

Claims (4)

Lithium transition metal containing at least one element (A) selected from the group consisting of Nb, Ta and V and at least one element (B) selected from W, Mo and Re and containing B and / or Bi elements Consisting of secondary particles of complex oxide,
The atomic ratio of the total of the element (A) to the total of metallic elements other than Li, the element (A) and the element (B) on the surface portion of the secondary particle is 1 to 50 times the atomic ratio of the entire secondary particle The atomic ratio of the total of the element (B) to the total of metallic elements other than Li, the element (A) and the element (B) on the surface portion of the secondary particle is 1 of the atomic ratio of the entire secondary particle. A lithium transition metal compound powder for a lithium secondary battery positive electrode material, characterized in that the concentration of the surface of the element (A) is lower than that of the element (B) by 100 to 100 times.   2. The lithium secondary battery positive electrode material according to claim 1, wherein the lithium transition metal-based compound powder for a lithium secondary battery positive electrode material contains a lithium nickel manganese cobalt-based composite oxide having a layered structure as a main component. Lithium transition metal compound powder. A lithium secondary battery comprising a positive electrode active material layer containing the lithium transition metal compound powder for a lithium secondary battery positive electrode material according to claim 1 or 2 and a binder on a current collector. Positive electrode. A lithium secondary battery comprising a negative electrode capable of inserting and extracting lithium, a non-aqueous electrolyte containing a lithium salt, and a positive electrode capable of inserting and extracting lithium, wherein the positive electrode is a lithium secondary battery according to claim 3. A lithium secondary battery characterized by being a positive electrode for use.

Images