JP2013055000A - Lithium transition metal-based compound powder for lithium secondary battery positive electrode material and method for producing the same, lithium secondary battery positive electrode including the same, and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide lithium transition metal-based compound powder for a lithium secondary battery positive electrode material, capable of achieving both improvement of battery performance and all of reduced cost, increased high voltage resistance and enhanced safety.SOLUTION: A lithium transition metal-based compound for a lithium secondary battery positive electrode material is a lithium transition metal-based compound having a function capable of inserting/releasing lithium ions, maintains a secondary particle structure in performing a liquid preparation of electrode coating slurry, and has secondary particles collapsed in pressing a coated electrode.

Description

  The present invention relates to a lithium transition metal-based 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-based compound powder, and the lithium secondary battery. The present invention relates to a lithium secondary battery including a positive electrode for use.

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.
As a positive electrode active material for a lithium secondary battery, a lithium manganese composite oxide, a layered lithium nickel composite oxide, and a layered lithium cobalt composite oxide having a spinel structure have been used. In recent years, iron phosphate has been put to practical use as a lithium nickel manganese cobalt based composite oxide and polyanionic positive electrode material that have an excellent battery performance balance while reducing the cobalt content.

  Improvement of battery energy density is one of the most important issues for commercial lithium secondary batteries. In addition to increasing the capacity per weight of the active material and increasing the average discharge voltage, material design has been performed for the purpose of improving the electrode density. That is, it is generally considered that the higher the Tap density of powder, the higher the packing density of the electrode. Furthermore, the Tap density of the powder tends to increase as the particle diameter increases within a range of 10 μm or less (Non-patent Document 1). Therefore, it is desirable that the particle diameter of the active material is large as long as the battery performance is not adversely affected, and active material particles having a high density and high strength are generally preferred.

However, in recent years, with the expansion of usage of lithium secondary batteries and the development of new active materials, the need to use positive electrode active materials in a finer manner is increasing.
For example, when a lithium secondary battery is used for automobile applications, the use of a refined positive electrode active material is one effective means for improving battery output. That is, the output per active material weight can be improved by making the particles finer and increasing the reaction area. However, when a positive electrode is prepared using a fine active material, generally, the conductivity of the positive electrode material of the Li secondary battery is not sufficiently high, so that the blending amount of the conductive material increases. This is because it is necessary to form a conductive path without any fine active material particles in the electrode plate. Therefore, the finer the active material particles, the lower the ratio of the active material in the composite material. This is not desirable because it means a decrease in the capacity density and energy density of the electrode plate.

On the other hand, when a new compound is put into practical use, miniaturization of the active material is an effective practical means. For example, in recent years, batteries using iron phosphate, which is a polyanion positive electrode, as a positive electrode have been put into practical use. Since this material has a low conductivity and a low Li diffusion coefficient, it was only possible to obtain practical characteristics by making the active material particles finer. As described in the previous section, a substance having low conductivity has a problem that the ratio of the conductive material in the mixture is high and uniform dispersion is difficult. Thus, the iron phosphate positive electrode solves this problem by modifying the active material with a conductive material. However, in addition to the refinement of the active material, surface modification such as carbon coating further reduces the Tap density of the active material. Therefore, the conventional techniques such as carbon coating on fine particles still have problems in improving the composite density of the electrode plate.

Thus, miniaturization of the active material is an effective means for practical use of a positive electrode material having a small Li diffusion coefficient, but a large amount of conductive material is required for forming a conductive path in the electrode plate by miniaturization of the active material. Therefore, it is technically difficult to achieve both high electrode plate densities. However, in recent years, there is an increasing need for miniaturizing the active material. For example, as with iron phosphate, miniaturization of the active material is indispensable for the practical application of a positive electrode material with a small lithium diffusion coefficient, and high capacity positive electrode materials such as lithium silicate are being intensively studied for practical use. . Further, even in a positive electrode material that has already been put into practical use, the output characteristics of the battery can be improved by miniaturizing the active material. For example, lithium ion batteries for automobiles need to improve charge / discharge characteristics at a higher rate compared to consumer batteries, and methods for miniaturizing active materials and optimizing electrode plate structures have been intensively studied. As described above, the miniaturization of active material particles and the method for producing a positive electrode using the fine particles have been increasingly important in recent years.

Introduced heretofore are techniques for refining the primary particle size of the positive electrode active material and methods for producing a plate for a lithium secondary battery using the fine positive electrode active material.
For example, Patent Document 1 uses a coprecipitation method to synthesize lithium-rich nickel manganese cobalt-based composite oxide powder having a fine primary particle size. This lithium rich nickel manganese cobalt based composite oxide powder compound is an attractive material having a discharge capacity of 200 mAh / g or more. However, according to the study by the present inventors, since this substance has a very low Li ⁺ diffusion coefficient at the discharge end, in order to obtain a high capacity at a practical discharge rate,
The diffusion distance of Li ⁺ in the solid needs to be smaller than that of a normal positive electrode active material. From the relationship between the Tap density and the particle size of the powder described above, when a fine positive electrode active material is used, the electrode plate obtained by the conventional technique has a low density. In order to solve this problem, for example, Patent Document 2 proposes dense secondary particles composed of fine primary particles. In addition, Non-Patent Document 2 proposes to improve the rate characteristics by forming a phase excellent in Li ⁺ diffusivity on the surface by surface treatment of an active material made of the substance obtained by a known coprecipitation method. ing.

In recent years, a method for synthesizing a fine active material using a spray pyrolysis method has been proposed. The spray pyrolysis method sprays a metal salt solution as fine droplets in an atmosphere maintained at a temperature higher than the temperature at which pyrolysis occurs, and evaporates the solvent, precipitates the metal salt, and pyrolyzes it in a very short time. This is a method for synthesizing fine powder. Powders obtained by this method have the advantages of compositional uniformity on the atomic scale and uniform dispersibility of trace component elements, and fine particles with good dispersibility can be obtained. Even if there is a composition non-uniformity due to drying or thermal decomposition, the non-uniformity is physically limited within the divided fine particles, so that there is little composition separation due to rearrangement of components. Moreover, since the ratio of the components contained in each sprayed solution is very close to the ratio of the components of the prepared solution, the dispersion of the components can be strictly controlled. Also, spray pyrolysis synthesis using a two-fluid nozzle has been proposed to solve the problem of mass productivity. For example, Patent Document 3 proposes a method for producing lithium manganate powder using a spray pyrolysis method, and Patent Document 4 proposes a method for producing lithium iron phosphate powder. Patent Document 5 also introduces a synthesis example of lithium nickelate using a spray pyrolysis method.

  The technologies for utilizing fine active materials that have been studied in the past are introduced below. Current cathode materials mainly use particles with a diameter of several microns. On the other hand, for example, Patent Document 6 and Patent Document 7 propose a method for producing an electrode plate using fine particles having a diameter of 5 μm or less. Further, Patent Document 8 is characterized in that secondary particles having a mean particle size of 0.5 to 3 μm, which are formed by agglomeration of primary particles, are crushed in an electrode preparation step (coating step). Thereby, the effect which improves the dispersibility of a primary particle was confirmed.

U.S. Pat. No. 7,468,223 U.S. Pat. No. 7,435,402 JP 2005-183004 A JP 2009-070666 A JP 2001-017857 A JP 2007-073344 A JP 2007-109636 A JP 2004-192846 A

Michitaka Suzuki, Chemical Equipment, May 2010 P28-32 Journal of Electrochemical Society, 157 (11) A1177-A1182 (2010)

For example, in the methods of Patent Documents 1 and 2, while the Tap density of the active material is improved, the sintering progresses in the secondary particles and the utilization efficiency decreases, or the utilization efficiency is inferior in the secondary particles. It is assumed that it becomes uniform and leads to a decrease in battery performance. In addition, in the method of surface treatment of an active material made of the material obtained by a known coprecipitation method in Non-Patent Document 2, there is a problem in the life characteristics as estimated from the fact that the surface area of the active material becomes very large. It is thought to produce. That is, in the conventional technique, it is considered that the refinement of the active material particles and the improvement of the electrode density are not always compatible.

On the other hand, conventional techniques such as Patent Document 3 and Patent Document 4 proposed by the spray pyrolysis synthesis method using a two-fluid nozzle to solve the problem of mass productivity while using the spray pyrolysis method include There is no method for obtaining a high energy density electrode plate mixture from the obtained active material, or any properties required for the active material in order to improve the density of the electrode plate mixture.
In Patent Document 6 and Patent Document 7 in which a method for producing an electrode plate using fine particles is proposed, it is necessary to mix more conductive materials than usual or reduce the film thickness of the electrode plate in order to function as an electrode. is there. It is easily imagined that more conductive material is required in a system in which the primary particle size is further reduced. Moreover, in patent document 8 characterized by crushing a secondary particle in an electrode preparation process (application | coating process), when a secondary particle is completely crushed, the effect of reducing a conductive material content It is not allowed. That is, the conventional utilization technique related to an active material having a relatively fine primary particle diameter is packed at a high density from an active material composed of particularly fine primary particles of about 100 to 200 nm proposed in the present invention. It was not intended to form a high-density electrode plate excellent in energy density.

  In view of the above problems, an object of the present invention is to provide a technique for appropriately utilizing a positive electrode active material having a fine primary particle size. Appropriately utilized technology here refers to a method of making an electrode plate that can form a conductive path in an active material with a practical conductive material content while using a fine positive electrode active material, It is to provide a positive electrode active material that makes it possible. According to the present invention, it is possible to produce an electrode plate having a practical composite density while using a fine positive electrode active material.

That is, the present inventors have clarified the characteristics of the active material that enables the active material in which the primary particles are sufficiently refined in the submicron order to be aggregated in the positive electrode mixture in the micron order. The present invention has been completed. The characteristic is that the active material maintains the secondary particle structure during slurry preparation for electrode coating, and the secondary particles are crushed when the coated electrode is pressed. According to the present invention, there is no need to mix the individual primary particles, the conductive additive and the binder, which becomes an obstacle when using fine primary particles, and the electrode plate density is improved. Alternatively, a process of granulating fine primary particles into dense secondary particles prior to slurry preparation is unnecessary, which is extremely advantageous economically. In addition, it is possible to avoid a decrease in the life due to the non-uniformity of the utilization efficiency in the active material secondary particles.

That is, the gist of the present invention is as follows.
(1) A lithium transition metal compound having a function capable of inserting / extracting lithium ions, maintaining a secondary particle structure when preparing a slurry for electrode coating, and crushing secondary particles when pressing a coated electrode A lithium transition metal compound for a positive electrode material of a lithium secondary battery.

(2) The lithium transition metal compound according to (1), wherein the crystal structure of the lithium transition metal compound is layered.
(3) Contains a compound (additive 1 of the present invention) containing at least one element (additive element 1 of the present invention) selected from Group 5 to 7 elements of the fifth or sixth period of the periodic table. The lithium transition metal compound according to (1) or (2), wherein

(4) The lithium transition metal compound according to any one of (1) to (3), wherein the average primary particle size is 0.05 μm or more and 0.3 μm or less.
(5) The lithium transition metal compound according to any one of (1) to (4), wherein the BET specific surface area is 1 m ² / g or more and 20 m ² / g or less.
(6) Having a positive electrode active material layer containing the lithium transition metal compound for a lithium secondary battery positive electrode material according to any one of (1) to (5) and a binder on a current collector. A positive electrode for a lithium secondary battery.

  (7) A lithium secondary battery positive electrode including a lithium transition metal compound, a conductive material, and a binder, wherein the content of the conductive material in the positive electrode mixture is 10 wt% or less with respect to the positive electrode mixture, Secondary particles composed of primary particles having an average particle size of lithium transition metal compound of 0.3 μm or less. In the particle size distribution of the secondary particles in the positive electrode mixture, secondary particles of 1 μm or less pass on a volume basis. A positive electrode for a lithium secondary battery, wherein the positive electrode composite material is present at a rate of 30% or more in terms of partial integration, and the volume resistance value of the positive electrode mixture is 500 Ω · cm or less.

  (8) A lithium secondary battery positive electrode including a lithium transition metal compound, a conductive material, and a binder, wherein the content of the conductive material in the positive electrode mixture is 10 wt% or less with respect to the positive electrode mixture, Secondary particles composed of primary particles having an average particle size of lithium transition metal compound of 0.3 μm or less. In the particle size distribution of the secondary particles in the positive electrode mixture, secondary particles of 1 μm or less pass on a volume basis. A positive electrode for a lithium secondary battery, wherein the positive electrode is present at a rate of 30% or more in terms of partial integration and has a spacing of 5 dB or more at 3 μm in Spacing in a power spectrum obtained from the cross-sectional structure of the positive electrode.

(9) The positive electrode for a lithium secondary battery according to (7) or (8), wherein the crystal structure of the lithium transition metal compound is layered.
(10) A compound in which the lithium transition metal-based compound contains at least one element (additional element 1 of the present invention) selected from Group 5 to 7 elements of the fifth or sixth period of the periodic table (of the present invention) Additive 1) is contained, The positive electrode for lithium secondary batteries of any one of (7)-(9) characterized by the above-mentioned.

(11) The lithium secondary battery according to any one of (7) to (10), wherein the lithium transition metal compound has an average primary particle size of 0.05 μm or more and 0.3 μm or less. Positive electrode.
(12) The lithium transition metal compound has a BET specific surface area of 1 m ² / g or more and 20 m ² /
The positive electrode for a lithium secondary battery according to any one of (7) to (11), wherein the positive electrode is g or less.

(13) A lithium secondary battery including 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 (6) to (12) A lithium secondary battery comprising the positive electrode for a lithium secondary battery described in 1.
(14) A method for producing a lithium transition metal compound having a function capable of inserting / extracting lithium ions and having a composition represented by the general formula (1), wherein the main component material, Mo, W Of a lithium transition metal compound for a lithium secondary battery positive electrode material, characterized by spray pyrolysis of a solution containing a compound having at least one element selected from Nb, Ta, Ca, Mg and Re Method.

(15) The production method according to (14), wherein the heat treatment is performed at 200 ° C. or higher in the spray pyrolysis step.
(16) Secondary particles formed by agglomeration of primary particles having an average particle size of 0.3 μm or less, and a positive electrode using a lithium transition metal compound having a secondary particle bulk density of 2.0 g / cc or less. In the production process, the proportion of secondary particles of 1 μm or less present in the slurry for electrode production is 70% or less in the volume-based cumulative amount of passage, and the secondary particles are crushed by the electrode pressing step. A method for producing a positive electrode for a lithium secondary battery.

  ADVANTAGE OF THE INVENTION According to this invention, the high-density electrode plate excellent in energy density can be formed, and a high energy density lithium secondary battery can be formed.

6 is a graph comparing discharge capacities on the basis of the surface area of the positive electrode active material in Example 10 and Comparative Example 7. It is the graph which compared the power spectrum analysis result of the cross-sectional structure of a positive electrode about Example 1, 2 and the comparative example 2. FIG.

Hereinafter, although embodiment of this invention is described, the range of this invention is not restrict | limited to this embodiment.
[Lithium transition metal compound powder]
The positive electrode active material of the present invention is as follows.
It is a lithium transition metal compound that has a function capable of inserting / extracting lithium ions, and maintains a secondary particle structure during slurry preparation for electrode coating, and secondary particles are crushed when the coated electrode is pressed. A lithium transition metal-based compound powder for a positive electrode material for a lithium secondary battery.

<Lithium transition metal compound>
In the present invention, the lithium transition metal compound 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. . As the sulfide, a compound having a two-dimensional layered structure such as TiS ₂ or MoS ₂ or a strong formula represented by a general formula Me _x Mo ₆ S ₈ (Me is various transition metals including Pb, Ag, 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. , LiCoVO _{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.

<Particle strength of secondary particles>
The feature of the present invention is to positively change the shape of the positive electrode secondary particles in the positive electrode mixture during the pressing of the electrode, which will be described in detail later, and improve the performance of the electrode plate. The shape change of the secondary particles is called crushing here. That is, the lithium transition metal-based compound powder of the present invention is characterized by having a specific particle strength.

  The particle strength of the lithium transition metal compound powder required to maintain the secondary particle structure during slurry preparation for electrode coating and to crush the secondary particles during pressing of the coating electrode depends on the slurry preparation method and press method. Although different, in the present invention, the following values are set assuming a general preparation / pressing method. That is, the compressive fracture strength (hereinafter, also simply referred to as “compressive strength”) is desirably 100 MPa or less. The compressive strength is a value obtained by the formula of Hiramatsu et al. Shown in the following formula 1 (“Nippon Mining Kaikai Journal” Vol. 81, No. 932, December 1965, pages 1024 to 1030).

St = 2.8 P / πd ² (d: particle diameter, P: load applied to particles) (Equation 1)
The positive electrode active material used for the non-aqueous electrolyte battery of the present invention is preferably a lithium transition metal composite oxide represented by the following general formula (A).
αLi ₂ MO ₃ · (1-α) LiM′O ₂ (A)
In the general formula, x is a number satisfying 0 <α <1.

M is at least one metallic element average oxidation number of 4 ^+, preferably, Mn, Zr, Ti, at least one metallic element selected from the group consisting of Ru, Re and Pt, more preferably Is at least one metal element selected from the group consisting of Mn, Zr and Ti.
M 'is at least one metallic element average oxidation number of 3 ^+, preferably, V, Mn, Fe, at least one metallic element selected from the group consisting of Co and Ni, more preferably , At least one metal element selected from the group consisting of Mn, Co and Ni.

<Crystal structure>
The lithium transition metal compound used in the present invention preferably has an olivine structure or a layered structure as a crystal structure from the viewpoint of lithium ion diffusion. Among these, those having a layered structure are preferable from the viewpoint of good solid conductivity and remarkable effects of the present invention.

In addition to Mn, Zr, Ti, Ru, Re, Pt, V, Fe, Co, and Ni, other foreign elements may be introduced into the lithium transition metal compound used in the present invention. Different elements include B, Na, Mg, Al, K, Ca, Ti, Cr, Cu, Zn, Sr, Y, Nb, Rh, Pd, Ag, In, Sn, Sb, Te, Ba, Ta, Mo. , W, Os, Ir, Au, Pb, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er,
One or more can be selected from the group consisting of Tm, Yb, Lu, Bi, N, F, Cl, Br and I. These may be incorporated into the crystal structure of the lithium transition metal compound, or may not be incorporated into the crystal structure of the lithium transition metal compound, and are unevenly distributed as a single substance or compound on the particle surface, grain boundary, etc. It may be.

In this specification, a lithium transition metal compound having a layered structure is generally represented by LiMeO ₂ (where Me is a transition metal), and a lithium layer, a transition metal layer, and an oxygen layer are uniaxially oriented. It has a structure equivalent to the laminated lithium transition metal oxide. As typical LiMeO ₂ , 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. Besides 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.

As described above, the layered structure is not necessarily limited to the R (-3) m structure, but it is preferable from the viewpoint of electrochemical performance that it can be attributed to the R (-3) m structure. In order to explain in detail, the following description will be made assuming that the layered structure is an R (-3) m structure.
In the present invention, a lithium transition metal composite oxide represented by the following general formula (A) is used as the positive electrode active material.

αLi ₂ MO ₃ · (1-α) LiM′O ₂ (A)
More preferably, as the positive electrode active material, the ratio of LiNi _a Mn _(1-a) O ₂ having a layered structure is (1-3x) (1-y),
The ratio of Li [Li _1/3 Mn _2/3 ] O ₂ is 3x (1-y),
The ratio of LiCoO ₂ is y
A layered lithium transition metal composite oxide, which is assumed to be solid-solubilized in Step 1, is used.

The lithium transition metal compound has a basic structure represented by the formula (II).
[Li] ^(3a) [(Li _x Ni _{a (1-3x)} Mn _{(3a-1) x + 1-a} ) _(1-y) Co _y ] ^(3b) O ₂ (II)
(Wherein (3a) and (3b) each represent a different metal site in the layered R (-3) m structure)
In the formula (II), the x value is preferably 0.13 ≦ x ≦ 0.26. When the Mn / Ni atomic ratio is in a range larger than 1, when used as a non-aqueous electrolyte battery designed to be charged at a high charging potential, the charge / discharge capacity is improved. This is thought to be because the total amount of Li that can participate in charge / discharge is increased because the ratio of Li existing in the (3b) site also increases as a result of the increase in the Mn / Ni atomic ratio.

The y value is preferably 0 ≦ y ≦ 0.30. When considering the cost of raw materials, the LiCoO ₂ composition does not necessarily need to be dissolved, but the higher the y value, the better the rate characteristics of the battery.
The a value can take any value in the range of 0 ≦ a ≦ 1, but preferably 0.30 ≦ a ≦ 0.80. In this range, the discharge capacity of LiNi _a Mn _(1-a) O ₂ is good,
Structural stability can also be secured.

In the present invention, Li may be added in excess by z mol with respect to the composition of the formula (II) to form a solid solution. In this case, the lithium transition metal compound has a basic structure represented by the formula (I).
[Li] ^(3a) [Li _{z / (2 + z)} {(Li _x Ni _{a (1-3x)} Mn _{(3a-1) x + 1-a} ) _(1-y) Co _y } _{2 / (2 + z)} ] ^(3b) O ₂ (I)
(Where 0.13 ≦ x ≦ 0.26, 0 ≦ y ≦ 0.30, 0.30 ≦ a ≦ 0.80, 0.02 (1-y) (1-3x) ≦ z ≦ 0. 15 (1-y) (1-3x),
(3a) and (3b) represent different metal sites in the layered R (-3) m structure, respectively. ).

In this case, in the layered lithium transition metal composite oxide expressed as LiMeO ₂ (Me is a transition metal), z mol of excess Li is dissolved in the transition metal site (3b site).
[Li] ^(3a) [Li _{z / (2 + z)} Me _{2 / (2 + z)} ] ^(3b) O ₂
It is expressed in the same manner as that expressed.

In order to obtain x, y, and z in the formula (I), each transition metal and Li are analyzed by an inductively coupled plasma emission spectrometer (ICP-AES) to obtain a ratio of Li / Ni / Mn / Co. It is calculated by that.
From a structural point of view, it is considered that both Li related to z and Li related to x are substituted by the same transition metal site. Here, the difference between Li related to x and Li related to z is whether or not the valence of Ni is greater than two (whether or not trivalent Ni is generated). That is, since x is a value linked with the Mn / Ni ratio (Mn rich degree), the Ni valence does not vary only by this x value, and Ni remains divalent. On the other hand, z can be regarded as Li that increases the Ni valence, and z is an index of the Ni valence (the ratio of Ni (III)).

<Compound having the additive element 1 of the present invention in the structural formula>
In the present invention, a compound containing at least one element selected from Group 5 to 7 elements of Periodic Table 5th Period or 6th Period (Additive Element 1 of the present invention) as an additive element (additive of the present invention) It is preferable to use 1). Among these additive elements 1 of the present invention, it is preferable that the additive element 1 of the present invention is at least one element selected from the group consisting of Mo, W, Nb, Ta, and Re because of its great effect. Mo or W is more preferable, and W is most preferable.

The type of the compound containing additive element 1 of the present invention (additive 1 of the present invention) is not particularly limited as long as it exhibits the effects of the present invention. An oxide is used. The additive element 1 is preferably at least one element selected from the group consisting of Mo, W, Nb, Ta, and Re.
Exemplary compounds of the additive 1, the compound having a Mo _{element, MoO, MoO 2, MoO 3} , MoO x, include _{Mo 2 O 3, Mo 2 O} 5, Li 2 MoO 4. Examples of the compound having W element include WO, WO ₂ , WO ₃ , H ₂ WO ₄ , WO _x , W ₂ O ₃ , W ₂ O ₅ , W ₁₈ O ₄₉ , W ₂₀ O ₅₈ , W ₂₄ O ₇₀ , W ₂₅ O ₇₃ , W ₄₀ O ₁₁₈ , Li ₂ WO ₄ , ammonium metatungstate, and ammonium paratungstate. Examples of the compound having an Nb element include NbO, NbO ₂ , Nb ₂ O ₃ , Nb ₂ O ₅ , Nb ₂ O ₅ .nH ₂ O, and LiNbO ₃ . Examples of the compound having Ta element include Ta ₂ O, Ta ₂ O ₅ , and LiTaO ₃ . Examples of the compound having the Re element include ReO ₂ , ReO ₃ , Re ₂ O ₃ , and Re ₂ O ₇ . Among these, MoO ₃ , Li ₂ MoO ₄ , WO ₃ , Li ₂ WO ₄ are preferable, and WO ₃ is particularly preferable because it is relatively easily available as an industrial raw material or includes lithium. It is done. These additives 1 may be used individually by 1 type, and 2 or more types may be mixed and used for them.

<Li conductivity of positive electrode>
The active material powder that can be expected to have the effect of the present invention has an electric conductivity of the powder, although the in-solid diffusion coefficient of lithium determined by the GITT method is usually 10 ⁻⁸ s / cm or less at 50% SOC. 10 ⁻⁸ s / cm or more, preferably 10 ⁻⁷ s / cm or more, more preferably 10 ⁻⁶ s / cm or more, and most preferably 10 ⁻⁵ s / cm or more. The above range indicates that the conductivity of the active material is superior to that of iron phosphate, although the Li diffusion coefficient is smaller than that of general lithium cobaltate, and the effect of the present invention is expected. it can.

<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 usually 5 × 10 ⁵ Ω · cm or less, preferably 2 × 10 ⁵ Ω · cm or less, more preferably 1 × 10 ⁵ Ω · cm or less, particularly preferably 5 × 10 ⁴ Ω · cm or less. If this volume resistivity exceeds this upper limit, the rate characteristics and low-temperature characteristics of the battery may be reduced. The lower limit of the volume resistivity is usually 5 × 10 ¹ Ω · cm or more, preferably 1 × 10 ² Ω · cm or more, more preferably 5 × 10 ² Ω · cm or more, and most preferably 1 × 10 ³ Ω · cm. That's it. 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 is measured by, for example, using a powder resistivity measuring device (eg, manufactured by Dia Instruments Co., Ltd .: Lorester GP powder resistivity measuring system), using a powder probe unit, to form a powder under a predetermined pressure. Can be done against.

<The bulk density>
The bulk density of the lithium transition metal compound powder of the present invention is usually 0.3 g / cc or more, preferably 0.4 g / cc or more, more preferably 0.5 g / cc or more, most preferably 0.7 g / cc or more. It is. Below this lower limit, powder filling properties and electrode preparation are adversely affected, and a positive electrode using this as an active material is not preferable because the capacity density per unit volume becomes too small. Further, the upper limit of the bulk density is usually 2.0 g / cc or less, preferably 1.8 g / cc or less, more preferably 1.5 g / cc or less. While it is preferable for the bulk density to exceed this upper limit, it is preferable for improving powder filling properties and electrode density. On the other hand, the specific surface area may become too low, which is not preferable because battery performance deteriorates.

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 / cc was determined.
<Average primary particle size>
The average primary particle size of the lithium transition metal compound powder of the present invention is usually 0.01 μm or more, preferably 0.03 μm or more, more preferably 0.05 μm or more, and usually 1 μm or less, preferably 0.5 μm or less. More preferably, it is 0.3 μm or less. Since the present invention is intended for a positive electrode having a relatively small Li diffusion coefficient in a solid, exceeding the above upper limit is liable to cause problems such as an increase in Li diffusion resistance and a decrease in charge / discharge characteristics.
On the other hand, when the above lower limit is exceeded, the surface area becomes too large, and an undesirable reaction in the battery may be promoted.

In addition, the average particle diameter of the primary particle in this invention is an average diameter observed with the scanning electron microscope (SEM), and it is about 10-30 primary using the SEM image of 30,000-100,000 times. It can obtain | require as an average value of the particle diameter of particle | grains.
<Median diameter of secondary particles and 90% cumulative diameter (D90)>
The median diameter of the secondary particles of the lithium transition metal compound powder of the present invention is usually 1 μm or more, preferably 2 μm or more, more preferably 3 μm or more, and usually 20 μm or less, preferably 18 μm or less, more preferably 16 μm or less. . If the lower limit is exceeded, the secondary particles themselves become finer, and therefore there is a possibility that the effect of reducing the conductive material content according to the present invention may not be obtained effectively, and if the upper limit is exceeded, the particle strength decreases. Since the generation amount of crushed particles during kneading increases, it is not preferable.

  The 90% cumulative diameter (D90) of the secondary particles of the lithium transition metal-based compound powder of the present invention is usually 30 μm or less, preferably 26 μm or less, more preferably 23 μm or less, usually 5 μm or more, preferably 8 μm or more. More preferably, it is 12 μm or more. If the above upper limit is exceeded, battery performance may be deteriorated, and there may be a problem in applicability when forming the positive electrode active material layer, and if it is below the lower limit, a high bulk density product may not be obtained.

The median diameter as an average particle diameter and the 90% cumulative diameter (D90) can be measured by setting a refractive index of 1.60 using a known laser diffraction / scattering particle size distribution measuring apparatus and using the particle diameter reference as a volume reference. As a dispersion medium used in the measurement, a 0.1% by weight sodium hexametaphosphate aqueous solution can be used.
<BET specific surface area>
The lithium transition metal-based compound powder of the present invention also has a BET specific surface area of usually 0.1 m ² / g or more, preferably 0.3 m ² / g or more, more preferably 0.5 m ² / g or more, most preferably. Is 0.8 m ² / g or more, usually 20 m ² / g or less, preferably 16 m ² / g or less, more preferably 13 m ² / g or less, and most preferably 10 m ² / g or less. If the BET specific surface area is smaller than this range, the battery performance is likely to deteriorate, and if it is large, an undesirable side reaction in the battery may be promoted.

  The BET specific surface area can be measured by a known BET type powder specific surface area measuring device. In the present invention, measurement can be performed by a BET 5-point method using a continuous flow method using a Sysmex NOVA1200 fully automatic powder specific surface area measuring apparatus and using nitrogen as an adsorption gas. Specifically, a powder sample is heated and degassed with a mixed gas at a temperature of 150 ° C., then cooled to liquid nitrogen temperature to adsorb the gas, and then heated to room temperature to adsorb the adsorbed nitrogen gas. By desorbing and quantifying the amount, the specific surface area of the sample can be calculated.

<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 considered as follows. An active material that can be expected to be particularly effective in the present invention is a positive electrode active material having a feature that the electrical conductivity is relatively excellent, although the diffusibility of Li ions in the solid is relatively inferior. The present invention improves the energy density of the electrode plate mixture by controlling the dispersion state of the cathode active material having such characteristics in the cathode mixture. Specifically, the above-mentioned active material in which primary particles are sufficiently refined in the submicron order is aggregated in the micron order in the positive electrode mixture so that a conductive path is passed to each particle with a small conductive material content. Can be formed. This is because the active material exhibiting more effects in the present invention has a relatively high electrical conductivity, so that electrons are supplied by contact between the particles in the aggregate of primary particles. Therefore, it is not necessary to form a conductive path for each primary particle by contact with the conductive material, so that the content of the conductive material can be effectively reduced while being a positive electrode using fine particles. .

  In order for the lithium transition metal-based compound powder of the present invention to exhibit the above-described effects, it is necessary to cause a significant structural change when the electrode is pressed. In order for the particles to undergo shape change during pressing, the lithium transition metal compound powder must have a specific particle strength, and the lithium transition metal compound powder has a bulk density suitable for shape change. There is a need. Furthermore, in order for the lithium transition metal-based compound powder to form an optimal dispersion state in the positive electrode after the structural change, the powder is a secondary particle having a specific size composed of fine primary particles. There must be. By combining these various requirements, the lithium transition metal-based compound powder of the present invention can exhibit the above-described effects.

[Method for producing lithium transition metal-based compound powder of the present invention]
The method for producing the lithium transition metal-based compound powder of the present invention is not particularly limited as long as the gist of the present invention is satisfied. Usually, the coprecipitation method, spray drying method, spray pyrolysis method, solid phase A reaction method or a hydrothermal reaction method is used. Among these, the coprecipitation method, the spray drying method, and the spray pyrolysis method are preferable from the viewpoint of high composition uniformity. Among them, the coprecipitation method and the spray pyrolysis method are preferable from the viewpoint that the particle size of the precursor is smaller. Further, in order to suppress the crystal diameter of the primary particles while increasing the crystal regularity, a heat treatment for increasing the crystal regularity may be performed in a state where the primary particles are sparsely packed, and then granulation may be performed. From this point of view, the coprecipitation method is preferable to the method of precipitating as a carbonate and the like to form a porous aggregate after decomposition, rather than the method of precipitating as a hydroxide that is easily dehydrated and condensed. A spray pyrolysis method that can form particles is more preferred.

Here, the spray pyrolysis method will be described in more detail.
The spray pyrolysis method sprays a metal salt solution as fine droplets in an atmosphere maintained at a temperature higher than the temperature at which pyrolysis occurs, and evaporates the solvent, precipitates the metal salt, and pyrolyzes it in a very short time. This is a method of synthesizing fine oxide (or non-oxide) fine powder. Powders obtained by this method have the advantages of compositional uniformity on the atomic scale and uniform dispersibility of trace component elements, and fine particles with good dispersibility can be obtained. Even if there is a compositional non-uniformity due to drying or thermal decomposition, it is physically limited within the divided fine particles, so that there is little composition separation due to rearrangement of components. Moreover, since the ratio of the component contained in each sprayed solution is very close to that of the adjusted solution, the dispersion of the component can be strictly controlled.

Further, an additive element that inhibits crystal growth may be added to suppress the growth of primary particles. Such an element may be added simultaneously with the elements constituting the active material or may be added to the precursor. However, from the viewpoint of dispersing the element more uniformly and obtaining finer primary particles, It is preferable to add a dispersion or solution to the solution containing the constituent elements.
When producing the lithium transition metal-based compound powder of the present invention by spray pyrolysis, for example, a slurry in which a nickel compound, a manganese compound, and a cobalt compound are dispersed in a liquid medium is spray-dried and / or Or after spray pyrolysis, it may be mixed with a lithium compound and the mixture may be fired to produce a slurry or solution in which a nickel compound, a manganese compound, a cobalt compound, and a lithium compound are dispersed or dissolved. It may be produced by drying or spray pyrolysis, and firing if necessary.

Hereinafter, the method for producing the lithium transition metal compound powder of the present invention will be described in detail.
Among the raw material compounds used for the preparation of the slurry in producing the lithium transition metal-based compound powder by the method of the present invention, the nickel compounds include Ni (OH) ₂ , NiO, N
iOOH, NiCO ₃ , 2Ni (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 acetate, fatty acid nickel, nickel halide and the like. Among these, Ni (NO ₃₎ is highly soluble in water.
) ₂ · 6H ₂ O, NiSO ₄ · 6H ₂ O and nickel acetate are preferred. Ni (NO ₃ ) ₂ .6H ₂ O and nickel acetate are particularly preferred from the viewpoint that the primary particle size can be reduced in spray pyrolysis. These nickel compounds may be used individually by 1 type, and may use 2 or more types together.

Further, as the manganese compound, manganese oxides such as Mn ₂ O ₃ , MnO ₂ , Mn ₃ O ₄ , M
Examples thereof include manganese salts such as nCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganese dicarboxylate, manganese citrate and fatty acid manganese, halides such as oxyhydroxide and manganese chloride. Among these, Mn (NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganese dicarboxylate, manganese citrate, and fatty acid manganese, which are highly soluble in water, are preferable. Mn (NO ₃ ) ₂ and manganese acetate are particularly preferable from the viewpoint that the primary particle size can be reduced in spray pyrolysis. These manganese compounds may be used individually by 1 type, and may use 2 or more types together.

Cobalt compounds include Co (OH) ₂ , CoOOH, CoO, Co ₂ O ₃ , C
o 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 and the like. Among these, Co (N
O ₃ ) ₂ · 6H ₂ O, Co (OCOCH ₃ ) ₂ · 4H ₂ O, CoCl ₂ , and Co (SO ₄ ) ₂ · 7H ₂ O are preferable. From the viewpoint that the primary particle size can be reduced in spray pyrolysis, Co (NO ₃ ) ₂ .6H ₂ O and Co (OCOCH ₃ ) ₂ .4H ₂ O are particularly preferable. These cobalt compounds may be used individually by 1 type, and may use 2 or more types together.

As the lithium _{compound, Li 2 CO 3, LiNO 3} , LiNO 2, LiOH, LiOH · H 2 O, LiH, LiF, LiCl, LiBr, LiI, CH 3 OOLi, Li 2 O, Li 2 SO 4, dicarboxylic Acid Li, citrate Li, fatty acid Li, alkyl lithium, etc. are mentioned. These lithium compounds may be used individually by 1 type, and may use 2 or more types together.

The method for mixing the raw materials is not particularly limited, and may be wet or dry. As a result, it is desirable that the mixed salt is completely dissolved. As the dispersion medium, either an organic solvent or water can be used, but it is preferable to use water. The solution in which the raw material salt is dissolved may be directly subjected to a drying and / or pyrolysis process, or converted to hydroxide, carbonate, etc. by a coprecipitation method in order to avoid the problem of exhaust gas treatment in the subsequent process. The mixed solution mixed with the Li raw material by washing with water or the like may be subjected to a drying and / or pyrolysis step.

The mixed solution is then subjected to a drying and / or pyrolysis step. The drying method is not particularly limited, but the spray pyrolysis method is preferable from the viewpoint of making primary particles fine and forming substantially spherical secondary particles efficiently. In addition to being substantially spherical, the secondary particles composed of fine primary particles are preferably hollow or have many voids inside. The reason why the density after press compression can be improved by the substantially spherical secondary particle shape is not sufficiently clear, but is estimated as follows. When a composite material containing a hollow active material aggregate is compressed, the compressive stress energy is concentrated on the hollow composite oxide particle powder having a low compressive fracture strength. At this time, the secondary particles are destroyed and become ultrafine to near the particle size of the primary particles. And since a secondary particle is a substantially spherical shape, it compresses more uniformly. In this process, the ultrafine powder is press-fitted into the gaps inside the secondary particles and filled with a high density, so that the positive electrode active material as a whole is highly filled. As a result, it is assumed that a positive electrode with a large volumetric capacity density is obtained.

The particle shape of the powder obtained by spray drying and / or pyrolysis is appropriately selected from spray type, pressurized gas flow supply rate, raw material solution supply rate, raw material solution concentration, drying and / or pyrolysis temperature, heating method, etc. Can be controlled.
<Spray type>
Either an ultrasonic atomizer or a two-fluid nozzle can be used, but a two-fluid nozzle is used for mass production from the viewpoint of productivity. The nozzle diameter is usually from 0.1 mm to 5 mm, preferably from 0.2 mm to 3 mm, more preferably from 0.4 mm to 2 mm. If the nozzle diameter is too small, clogging tends to occur and stable production tends to be difficult. If it is too large, the particle diameter tends to be too large or the particle size distribution tends to be too wide.

<Raw material solution concentration>
Usually, the concentration of transition metal such as Ni, Mn, Co is 0.1 mol / l or more and 10 mol / l or less, preferably 0.2 mol / l or more, 5 mol / l or less, more preferably 0.3 mol / l or more, 4 mol / l or less. If the concentration is too low, the productivity is lowered, and if it is too high, the particle size distribution of the secondary particles is too wide, the average particle size is too large, or the strength of the secondary particles tends to be lowered.

<Thermal decomposition temperature>
Although it depends on the type of raw material and the device type, it is usually 200 ° C. or higher and 1100 ° C. or lower, preferably 250 ° C. or higher and 900 ° C. or lower, more preferably 300 ° C. or higher and 800 ° C. or lower. If the temperature is too low, it takes time for firing in the subsequent step. If the temperature is too high, the particle strength tends to decrease, the composition becomes uneven, or a single phase tends to be difficult to obtain.

<Residence time>
The residence time during spray pyrolysis is usually 0.01 to 60 seconds, preferably 0.1 to 30 seconds. Here, the residence time refers to the time for the droplets to pass through the heated portion. If it is too short, the decomposition will be insufficient, and if it is too long, the economy tends to decrease.
<Heating method>
There are no restrictions on the heating method for obtaining an atmosphere maintained at a temperature higher than the temperature at which thermal decomposition occurs in the reaction chamber, and a method in which a furnace body made of metal or refractory is heated from the outside and sprayed into the furnace body (indirect Heating method) or a method of supplying hot air with combustion gas (high temperature gas direct heating method) may be used. Electromagnetic heating such as microwaves can also be used to heat the furnace body and / or droplets. The indirect heating method relies on radiant heat transfer from the furnace body and conduction heat transfer from the gas heated by radiation to supply heat to the spray droplets, resulting in poor thermal efficiency and a temperature distribution in the furnace body radial direction. While there is a problem that it is large, it has a feature that it is easy to control the thermal history during the flight time. On the other hand, the high-temperature gas direct heating method directly heats the droplets by heat transfer from the high-temperature gas, so it is excellent in thermal efficiency and mass productivity, and can also reduce the temperature distribution in the furnace body radial direction. In order to control the heat history, it is necessary to devise a method such as supplying a high-temperature gas in multiple stages.

<Temperature distribution>
The particle properties can also be controlled by controlling the thermal history that the droplets undergo when passing through the heated portion (reaction chamber).
By making the temperature in the vicinity of the atomizer outlet relatively high, it is possible to obtain secondary particles with more developed cavities. Conversely, more solid secondary particles can be obtained by relatively lowering the temperature in the vicinity of the atomizer outlet. In general, in the indirect heating method, since it is heated by radiation, the temperature near the atomizer tends to be relatively low due to the influence of the latent heat of vaporization of the solvent, and the evaporation rate tends to be relatively small. The density of the secondary particles tends to increase. On the other hand, in the high-temperature gas direct heating method, since the high-temperature gas is directly introduced in the vicinity of the spray droplets, generally, the vicinity of the atomizer tends to be higher than the indirect heating method. However, even when meeting with the high-temperature gas direct heating method, secondary particles having desired properties can be obtained by adjusting the temperature distribution, for example, by supplying combustion exhaust gas in multiple stages. In this way, the sprayed stock solution is solidified in a very short time and then thermally decomposed to produce fine powder.

<Separation method>
The generated fine powder may be separated by an air classifier such as a cyclone, or may be separated by a synthetic resin filter such as PTFE, or may be separated by a ceramic filter. At least a part of the exhaust gas from which the solid has been separated can be recycled as spray gas or burner auxiliary gas. Or you may use as a heat source for a heating of a spray pyrolysis apparatus.

<Average particle diameter of powder obtained by spray drying and / or pyrolysis>
The average particle size of the powder obtained by spray drying and / or pyrolysis is usually 1 μm or more, preferably 2 μm or more, more preferably 3 μm or more, and usually 20 μm or less, preferably 18 μm or less, more preferably 16 μm or less. If the lower limit is exceeded, the secondary particles themselves become finer, and therefore there is a possibility that the effect of reducing the conductive material content according to the present invention may not be obtained effectively, and if the upper limit is exceeded, the particle strength decreases. The amount of crushed particles generated during kneading may increase.

The powder obtained in this manner is adjusted to physical properties suitable for subsequent processes by classification or the like. Here, pulverization, pulverization, or the like may be performed, or pulverization and dispersion in a medium may be performed, and granulation may be performed by spray drying or the like.
<Baking treatment>
The mixed powder thus obtained is then fired. 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, the primary particles grow too much. Too much. The firing temperature is usually 700 ° C. or higher, preferably 800 ° C. or higher, more preferably 850 ° C. or higher, usually 1100 ° C. or lower, preferably 1075 ° C. or lower, more preferably 1050 ° C. or lower.

  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.

  In the temperature raising step, the temperature in the furnace is usually raised at a temperature raising rate of 1 ° C./min to 10 ° 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 temperature rising rate is preferably 2 ° C./min or more, more preferably 3 ° C./min or more, preferably 10 ° C./min or less, more preferably 5 ° 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 2 hours or longer, more preferably 5 hours or longer, 50 hours or shorter, preferably 25 hours within the aforementioned temperature range. Hereinafter, it is more preferably 20 hours or less. If the firing time is too short, it becomes difficult to obtain a lithium nickel manganese cobalt composite oxide powder having 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 normally decreased at a temperature decreasing rate of 0.1 ° C./min to 10 ° C./min. If the temperature drop is too slow, it takes time and is industrially disadvantageous, but if it is too fast, it tends to lack uniformity of the target product or accelerate deterioration of the container. 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 5 ° C./min or less.

As an atmosphere during firing, an oxygen-containing gas atmosphere such as air can be used. 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.
The lithium transition metal-based compound powder thus obtained has a secondary particle shape aggregated in the micron order while having a fine primary particle diameter in the submicron order. Can be used effectively.

[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.
According to another aspect of the present invention, there is provided a method for producing an electrode in which the ratio of crushed particles of 1 μm or less generated by pulverization of secondary particles in the production process of preparing a slurry for producing an electrode is 70 in volume-based cumulative accumulation. % Or less. From the viewpoint of efficiently forming a conductive path to the active material, it is preferably 60% or less, and more preferably 50% or less. The lower limit is 0.1% or more, more preferably 0.5% or more. Within this range, the secondary particle structure of the lithium transition metal compound is maintained in the slurry, which is preferable.

  The electrode manufacturing method of the present invention is characterized in that the electrode material density is 2.0 g / cc or more, and preferably 2.2 g / cc or more from the viewpoint of improving battery energy density. More preferably, it is 2.4 g / cc or more. The upper limit is usually 4.0 g / cc or less, and is preferably 3.6 g / cc or less from the viewpoint of securing an electrolyte solution holding amount that does not adversely affect rate characteristics. More preferably, it is cc or less.

The positive electrode active material layer usually contains a conductive material in order to increase conductivity. There are no particular restrictions on the type of conductive material, 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 such as needle coke. Examples thereof include carbon materials such as carbon. Moreover, since the positive electrode active material used for this invention is a fine primary particle, there exists a tendency for a surface area to become large. For the purpose of forming a conductive path for such an active material with a relatively small amount of conductive material, the conductive material also preferably has a high surface area, specifically, carbon black having a surface area of 100 m ² / g or more. Is desirable. 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 15% by weight or less, preferably 10%. % 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.

When the lithium transition metal compound in the composite material is a secondary particle, and the particle size distribution of the secondary particle in the positive electrode composite material is measured, the secondary particle of 1 μm or less is 30% or more in the volume-based cumulative amount of passage. The ratio is preferably 50% or more, more preferably 70% or more. The upper limit is 99.9% or less. This range is desirable because the lithium transition metal compound is sufficiently pulverized by the electrode pressing step. As the ratio of the crushed particles generated by pressing the electrode increases, the active material becomes denser by pressing, and thus the density of the composite material tends to improve. The secondary particles are usually composed of primary particles having an average particle size of 0.5 μm or less. The average particle size of the primary particles is preferably 0.4 μm or less, more preferably 0.3 μm or less. As a minimum, it is 0.01 micrometer or more normally, Preferably it is 0.03 micrometer or more, More preferably, it is 0.05 micrometer or more. If it is this range, since the fall of a charge / discharge characteristic can be suppressed and the undesirable reaction in a battery can also be suppressed, it is preferable.

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 foil, 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 foil is preferable because it is excellent in mass productivity and is currently used in industrialized products. The metal foil may be appropriately formed in a mesh shape. Also, in order to improve the adhesion between the metal foil and the positive electrode mixture, or to reduce the interface resistance between the metal foil and the positive electrode mixture, the surface of the metal foil is roughened or coated with a conductive material. It is preferable to apply. This resistance is attributed to the electronic conductive resistance in the boundary region between the electrode and the current collector. Therefore, the electrical conductive resistance, and the electrical contact between the active material and the final body through the passive layer on the surface of the metal foil is taken, or the adhesion between the metal foil surface and the positive electrode mixture is increased. It is preferable to reduce variation in electric resistance in the surface direction of the electrode.

  When a metal foil is used as the positive electrode current collector, the thickness thereof is arbitrary, but 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. The following ranges are preferred. If the thickness 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 copolymer and hydrogenated products thereof, EPDM (ethylene-propylene-diene terpolymer), styrene / ethylene / butadiene / ethylene copolymer, 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, PVDF (fluorinated polyvinylidene fluoride), polytetrafluoroethylene / ethylene copolymers, ions of alkali metal ions (especially lithium ions) Examples thereof include a polymer composition having conductivity. Moreover, since the positive electrode active material used for this invention is a fine primary particle, there exists a tendency for a surface area to become large. For the purpose of firmly binding such an active material, specifically, among PVDFs having strong oxidation resistance, those having a weight average molecular weight of 500,000 or more and a strong binding force are desirable. These substances may be used alone or in combination of two or more in any combination and ratio.

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 5% by weight or more, and usually 80% by weight or less, preferably 60% by weight or less. More preferably, it is 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 mechanical strength of the positive electrode may be insufficient, and the battery performance such as cycle characteristics may be deteriorated. There is a possibility that it may lead to a decrease in capacity and conductivity.

  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, hexamethylphosphamide, 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.

The thickness of the positive electrode active material layer is usually about 10 to 200 μm. If this range is exceeded and the film is too thin, the energy density of the battery will decrease, and if it is too thick, the output characteristics and cycle life will tend to decrease.
As the electrode density after pressing the positive electrode, the lower limit is usually 2.0 g / cm ³ or more, preferably 2.2 g / cm ³ or more, particularly preferably 2.4 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.

Note that the positive electrode active material layer obtained by applying the slurry to the positive electrode current collector and drying is consolidated by a roller press or the like in order to increase the packing density of the positive electrode active material. In the case of this study, the pressure applied to the electrode during consolidation is 0.8 ton / cm ² or more, more desirably 1.2 ton / cm ² or more, particularly preferably. 1.5 ton / cm ² or more.
<Conductivity of positive electrode mixture>
The content of the conductive material in the positive electrode mixture is usually 1 wt% or more and 10 wt% or less with respect to the positive electrode mixture. If it is less than this range, the resistivity of the electrode is too high, and the output tends to decrease. On the other hand, if the amount is too large, the density of the electrode tends to decrease, and the safety during an internal short circuit tends to decrease. The resistance of the positive electrode mixture is a volume resistance value, and the lower limit is usually 5 Ω · cm or more, preferably 10 Ω · cm or more, more preferably 20 Ω · cm or more, and the upper limit is usually 500 Ω · cm or less, preferably 400 Ω. · Cm or less, more preferably 300 Ω · cm or less. If the resistivity is too low, the safety at the time of internal short circuit tends to be lowered. Conversely, if the resistivity is too large, the capacity tends to be lowered or the output tends to be lowered.

<Particle size distribution of active material in electrode plate>
When the particle size distribution of the coated electrode plate after pressing is measured, D50 is usually 5 μm or less, preferably 4 μm or less, and more preferably 3 μm or less. Moreover, a minimum is 0.01 micrometer or more normally, Preferably it is 0.05 micrometer or more, More preferably, it is 0.1 micrometer or more.
The proportion of fine particles of 1 μm or less in the volume-based cumulative amount of the coated electrode plate after pressing is usually 30% or more, preferably 50% or more, and more preferably 70% or more. As the ratio of the crushed particles generated by pressing the electrode increases, the active material is densified by pressing, so that the density of the composite material tends to improve, which is preferable. The secondary particles are usually composed of primary particles having an average particle size of 0.5 μm or less. The average particle size of the primary particles is preferably 0.4 μm or less, more preferably 0.3 μm or less. As a minimum, it is 0.01 micrometer or more normally, Preferably it is 0.03 micrometer or more, More preferably, it is 0.05 micrometer or more. If it is this range, since the fall of a charge / discharge characteristic can be suppressed and the undesirable reaction in a battery can also be suppressed, it is preferable.

<Reason why the positive electrode for a lithium secondary battery of the present invention exhibits the above-mentioned effect>
The reason why the positive electrode for a lithium secondary battery of the present invention brings about the above-described effect is considered as follows. The present invention can improve the energy density of the electrode plate mixture by controlling the dispersion state of the cathode active material in the cathode mixture. Specifically, the above-mentioned active material in which primary particles are sufficiently refined in the submicron order is aggregated in the micron order in the positive electrode mixture so that a conductive path is passed to each particle with a small conductive material content. Can be formed. This is because the active material exhibiting more effects in the present invention has a relatively high electrical conductivity, so that electrons are supplied by contact between the particles in the aggregate of primary particles. Therefore, it is not necessary to form a conductive path for each primary particle by contact with the conductive material, so that the content of the conductive material can be effectively reduced while being a positive electrode using fine particles. . Moreover, the positive electrode which has the characteristic mentioned above can express the outstanding discharge rate characteristic by forming such an electrode plate structure.

[Positive electrode of the present invention]
Another gist of the present invention is characterized by a specific positive electrode.
More specifically, it has the following features.
A positive electrode for a lithium secondary battery including a lithium transition metal compound, a conductive material, and a binder, wherein the content of the conductive material in the positive electrode mixture is 10 wt% or less with respect to the positive electrode mixture, and the lithium transition metal The system compound is a secondary particle composed of primary particles having an average particle diameter of 0.3 μm or less, and in the particle size distribution of the secondary particles in the positive electrode mixture, the secondary particles of 1 μm or less are integrated in the volume-based passage amount accumulation. A positive electrode for a lithium secondary battery, wherein the positive electrode mixture is present at a ratio of 30% or more and has a volume resistance value of 500 Ω · cm or less.

  A positive electrode for a lithium secondary battery including a lithium transition metal compound, a conductive material, and a binder, wherein the content of the conductive material in the positive electrode mixture is 10 wt% or less with respect to the positive electrode mixture, and the lithium transition metal The system compound is a secondary particle composed of primary particles having an average particle diameter of 0.3 μm or less, and in the particle size distribution of the secondary particles in the positive electrode mixture, the secondary particles of 1 μm or less are integrated in the volume-based passage amount accumulation. A positive electrode for a lithium secondary battery, which is present at a ratio of 30% or more and has a spacing of 5 dB or more at a spacing of 3 μm in a power spectrum obtained from a cross-sectional structure of the positive electrode.

[Lithium transition metal compounds]
The lithium transition metal compound used for the positive electrode of the present invention is not particularly limited as long as it has the above-described configuration. Specifically, among the lithium transition metal-based compounds described above, the particle strength of the secondary particles may or may not satisfy the above-mentioned regulation, but preferably the particle strength of the secondary particles. The strength is as defined above.

[Conductive material]
The conductive material used for the positive electrode of the present invention is the same as the above conductive material.
[Binder]
The binder used for the positive electrode of the present invention is the same as the above binder.
[Particle size distribution of secondary particles in positive electrode mixture]
The positive electrode of the present invention is characterized in that secondary particles of 1 μm or less in the particle size distribution of secondary particles in the positive electrode mixture are present in a proportion of 30% or more in the volume-based cumulative amount of passage. The proportion of fine particles of 1 μm or less in the volume-based cumulative amount of the coated electrode plate after pressing is usually 30% or more, preferably 50% or more, and more preferably 70% or more. As the ratio of the crushed particles generated by pressing the electrode increases, the active material is densified by pressing, so that the density of the composite material tends to improve, which is preferable.

The particle size distribution of the secondary particles in the positive electrode mixture is generally D50 of 5 μm or less, preferably 4 μm or less, and more preferably 3 μm or less. The lower limit is usually 0.01 μm
The thickness is preferably 0.05 μm or more, more preferably 0.1 μm or more. The secondary particles are usually composed of primary particles having an average particle size of 0.5 μm or less. The average particle size of the primary particles is preferably 0.4 μm or less, more preferably 0.3 μm or less. As a minimum, it is 0.01 micrometer or more normally, Preferably it is 0.03 micrometer or more, More preferably, it is 0.05 micrometer or more. If it is this range, since the fall of a charge / discharge characteristic can be suppressed and the undesirable reaction in a battery can also be suppressed, it is preferable.

<Crushing of secondary particles in press>
The secondary particle structure is maintained during slurry preparation for electrode coating, and the secondary particles are crushed during pressing of the coating electrode. This means that the lithium transition metal compound powder in the positive electrode mixture changes in structure before and after pressing. It means to wake up. That is, in the electrode plate prepared according to the method presented in the present invention, although the transition metal compound powder exists in the form of secondary particles in the positive electrode, the particles are crushed by crushing during pressing. Therefore, the actual condition is an aggregate of primary particles, and by measuring the particle size distribution of the positive electrode mixture, it can be determined whether or not it is the electrode manufacturing method according to this patent.
For example, an electrode produced by the method defined by this patent is 1 μm generated by crushing secondary particles when the particle size distribution of the positive electrode mixture is measured while satisfying the size of the primary particles and the conductive material content. The following crushed pieces are characterized by being 30% or more in accumulated passage, preferably 50% or more, more preferably 70% or more.

[Power spectrum obtained from the cross-sectional structure of the positive electrode]
The present invention is characterized in that, in the power spectrum obtained from the cross-sectional structure of the positive electrode, the spacing is 5 dB or more in intensity at 3 μm. From the point that it is desirable that the composition distribution in the electrode is non-uniform, it is preferably 6 dB or more, more preferably 7 dB or more, and particularly preferably 8 dB or more. As an upper limit, it is 100 dB or less, More preferably, it is 90 dB or less, Most preferably, it is 80 dB or less.

In the present application, the power spectrum analysis is a power spectrum analysis based on the cross-sectional structure of the positive electrode. First, an image of 1024 × 1024 pixels is extracted from the cross-sectional SEM image of the positive electrode photographed at a magnification of 2000, and a hamming window process is performed on the image to remove discontinuities at the boundaries of the four sides of the image. Next, a power spectrum is obtained by performing Fourier transform using image software ImageJ. Further, the obtained power spectrum is integrated in the rotation direction with respect to the center of the spectrum to obtain spectrum data. Here, the distance from the center of the power spectrum is defined as Spacing (μm), and the spectrum intensity is defined as Intensity. Finally, dB (10 log (base data / average value)) of the entire data is obtained on the basis of an average value of 0.2 to 0.5 μm of the spectrum data, and Insensitivity is converted to dB.
In this power spectrum analysis, the uniformity of the composition distribution in the electrode can be evaluated.

[Production method of positive electrode]
As a manufacturing method of the positive electrode of this invention, it can manufacture using the above-mentioned manufacturing method.
<Reason why the positive electrode of the present invention provides the above-mentioned effect>
The reason why the positive electrode for a lithium secondary battery of the present invention brings about the above-described effect is considered as follows. The present invention can improve the energy density of the positive electrode mixture by controlling the dispersion state of the positive electrode active material in the positive electrode mixture. Specifically, the above-mentioned active material in which primary particles are sufficiently refined in the submicron order is aggregated in the micron order in the positive electrode mixture so that a conductive path is passed to each particle with a small conductive material content. Can be formed. This is because the active material exhibiting more effects in the present invention has a relatively high electrical conductivity, so that electrons are supplied by contact between the particles in the aggregate of primary particles. Therefore, it is not necessary to form a conductive path for each primary particle by contact with the conductive material, so that the content of the conductive material can be effectively reduced while being a positive electrode using fine particles. . Moreover, the positive electrode which has the characteristic mentioned above can express the outstanding discharge rate characteristic by forming such an electrode plate structure.

  The meaning of the power spectrum in the present invention is explained as follows. When the primary particles are 1 μm or less, a particularly remarkable difference occurs when the spacing is 1 μm, depending on the dispersion state in the positive electrode plate. This is because the periodicity in the vicinity of 1 μm varies greatly depending on whether or not the primary particles form aggregates. That is, when the primary particles form aggregates, the mixing of the positive electrode active material particles and the conductive material particles is not uniform in this Spacing, and the periodicity in the region where the Spacing is 1 μm or less is low. Intensity of the image becomes relatively low. In the present invention, the Intensity is indexed by performing dB conversion with a spacing of 0.2 to 0.5 μm as a reference (zero) in the power spectrum. Therefore, in the embodiment of the present invention, Intensity at 1 μm or more takes a positive value, which is higher than when no aggregate is formed.

[Production method of positive electrode]
<Slurry adjustment conditions>
Still another subject matter of the present invention is characterized by a method for producing a specific positive electrode.
Specifically, it is characterized by the following.
A process for producing a positive electrode using a lithium transition metal compound having secondary particles formed by agglomeration of primary particles having an average particle size of 0.3 μm or less and a bulk density of the secondary particles of 2.0 g / cc or less. In which the ratio of secondary particles of 1 μm or less present in the electrode-forming slurry is 70% or less in the volume-based cumulative amount of passage, and the secondary particles are crushed by the electrode pressing step. Manufacturing method of secondary battery positive electrode.

[Lithium transition metal compounds]
The lithium transition metal compound used for the positive electrode of the present invention is the same as the above lithium transition metal compound.
[Conductive material]
The conductive material used for the positive electrode of the present invention is the same as the above conductive material.

[Binder]
The binder used for the positive electrode of the present invention is the same as the above binder.
[Production method of positive electrode]
As a manufacturing method of the positive electrode of this invention, it can manufacture using the above-mentioned manufacturing method.
[Proportion of crushed particles of 1 μm or less generated by crushing of secondary particles in the production process of preparing slurry for electrode preparation]
The electrode manufacturing method of the present invention is such that the ratio of crushed particles of 1 μm or less generated by crushing of secondary particles in the manufacturing process of preparing the electrode forming slurry is 70% or less in the volume-based cumulative amount of passage. It is characterized by. From the viewpoint of efficiently forming a conductive path to the active material, it is preferably 60% or less, and more preferably 50% or less. The lower limit is 0.1% or more, more preferably 0.5% or more. Within this range, the secondary particle structure of the lithium transition metal compound is maintained in the slurry, which is preferable.

<Reason for Producing Method of Positive Electrode of the Present Invention>
The reason why the positive electrode for a lithium secondary battery of the present invention brings about the above-described effect is considered as follows. The present invention can improve the energy density of the positive electrode mixture by controlling the dispersion state of the positive electrode active material in the positive electrode mixture. Specifically, the above-mentioned active material in which primary particles are sufficiently refined in the submicron order is aggregated in the micron order in the positive electrode mixture so that a conductive path is passed to each particle with a small conductive material content. Can be formed. Such an electrode uses the transition metal compound powder having the characteristics defined in the present invention, and the above-described manufacturing method that promotes the structural change of the transition metal compound powder in the composite during pressing of the positive electrode plate. It can be created by using it.

[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. Examples of the shape include a metal foil, a metal cylinder, a metal coil, a metal plate, and a metal thin film in the case of a metal material, and a carbon plate, a carbon thin film, and a carbon cylinder in the case of a carbon material. 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) 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 or less, preferably Is preferably 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 Raman spectrum analysis using an argon laser beam is performed on the graphite material, the intensity IA of the peak PA detected in the range of 1580 to 1620 cm −1 and the peak detected in the range of 1350 to 1370 cm −1. The strength ratio IA / IB of the PB to the strength IB is preferably 0 or more and 0.5 or less. Further, the half width of the peak PA is preferably 26 cm −1 or less, and more preferably 25 cm −1 or less.

In addition to the various carbon materials described above, other materials capable of inserting and extracting lithium can be used as the negative electrode active material. As a specific example of the negative electrode active material other than the carbon material,
Examples include metal oxides such as tin oxide and silicon oxide, sulfides and nitrides, lithium alloys such as lithium alone and lithium aluminum alloys, composite oxides of lithium and titanium, and compounds of silicon, carbon, and carbon. . As for materials other than these carbon materials, one kind may be used alone, or two or more kinds 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 forming the slurry, the same materials as those described above for the positive electrode active material layer can be used at the same ratio.

<Non-aqueous electrolyte>
1-1. Electrolyte <Lithium salt>
As the electrolyte, a lithium salt is usually used. The lithium salt is not particularly limited as long as it is known to be used for this purpose, and any lithium salt can be used. Specific examples include the following.

LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiTaF ₆ , LiPO ₂ F ₂ , FSO ₃ Li, CF ₃ SO ₃ Li, LiN (FSO ₂ ) ₂ , LiN (FSO ₂ ) (CF ₃ SO ₂ ), LiN (CF _{3 SO 2) 2, LiN (C} 2 F 5 SO 2) 2, lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic _{1,3-perfluoropropanedisulfonylimide, LiC (FSO 2) 3,} LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluorooxalatophosphate, lithium difluorobisoxalatophosphate, LiBF ₃ CF _{3 , LiBF 3 C 2 F 5,} LiPF 3 _{CF 3) 3, LiPF 3 (} C 2 F 5) 3 or the like is output characteristics and high-rate discharge characteristics, high-temperature storage characteristics, particularly preferred from the viewpoint that an effect of improving the cycle characteristics and the like.

These lithium salts may be used alone or in combination of two or more. A preferable example in the case of using two or more types in combination is a combination of LiPF ₆ and LiBF ₄ , LiPF ₆ and FSO ₃ Li, LiPF ₆ and LiPO ₂ F _{2 and the} like, and has an effect of improving load characteristics and cycle characteristics. . Among these, the combined use of LiPF ₆ and FSO ₃ Li, LiPF ₆ and LiPO ₂ F ₂ is preferable because the effect is remarkable, and among them, the combined use of LiPF ₆ and LiPO ₂ F ₂ is a remarkable effect with a small amount of addition. Is particularly preferred because

When LiPF ₆ and LiBF ₄ , LiPF ₆ and FSO ₃ Li are used in combination, the concentration of LiBF ₄ or FSO ₃ Li with respect to 100% by weight of the total amount of the non-aqueous electrolyte is not limited, and the effect of the present invention is not significantly impaired. As long as it is optional, it is usually 0.01% by weight or more, preferably 0.1% by weight or more, based on the non-aqueous electrolyte of the present invention, while its upper limit is usually 30% by weight or less, preferably 20%. % By weight or less. On the other hand, even when LiPF ₆ and LiPO ₂ F ₂ are used in combination, the concentration of LiPO ₂ F ₂ with respect to 100% by weight of the total amount of the non-aqueous electrolyte is not limited as long as the effect of the present invention is not significantly impaired. However, with respect to the non-aqueous electrolyte of the present invention, it is usually 0.001% by weight or more, preferably 0.01% by weight or more, while the upper limit is usually 10% by weight or less, preferably 5% by weight or less. is there. Within this range, effects such as output characteristics, load characteristics, low temperature characteristics, cycle characteristics, and high temperature characteristics are improved. On the other hand, if it is too much, it may be deposited at low temperature to deteriorate the battery characteristics, and if it is too little, the effect of improving the low temperature characteristics, cycle characteristics, high temperature storage characteristics, etc. may be reduced.

Here, the active material prepared in the electrolyte solution in the case of incorporating the LiPO ₂ F ₂ in the electrolyte solution, the LiPO ₂ F ₂ which is separately synthesized by a known method, described later method or be added to the electrolytic solution containing LiPF ₆ In the present invention, there is a method of generating LiPO ₂ F ₂ in the system when water is allowed to coexist in battery components such as a positive electrode plate and a positive electrode plate and assembling a battery using an electrolyte containing LiPF ₆ . Any method may be used.

The method for measuring the content of LiPO ₂ F ₂ in the non-aqueous electrolyte and the non-aqueous electrolyte battery is not particularly limited, and any known method can be used. Examples include ion chromatography and F nuclear magnetic resonance spectroscopy (hereinafter sometimes abbreviated as NMR).
Another example is the combined use of an inorganic lithium salt and an organic lithium salt, and the combined use of both has the effect of suppressing deterioration due to high-temperature storage. As the organic lithium salt, CF ₃ SO ₃ Li, LiN (FSO ₂ ) ₂ , LiN (FSO ₂ ) (CF ₃ SO ₂ ), LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , Lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropane disulfonylimide, LiC (FSO ₂ ) ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluorooxalate phosphate, lithium difluorobisoxalatophosphate, LiBF ₃ CF ₃ , LiBF ₃ C ₂ F ₅ , LiPF ₃ (CF ₃ ) ₃ LiPF ₃ (C ₂ F ₅ ) ₃ or the like is preferable. In this case, the ratio of the organic lithium salt to 100% by weight of the whole non-aqueous electrolyte is preferably 0.1% by weight or more, particularly preferably 0.5% by weight or more, preferably 30% by weight or less, particularly preferably. 20% by weight or less.

The concentration of these lithium salts in the non-aqueous electrolyte solution is not particularly limited as long as the effects of the present invention are not impaired, but the electric conductivity of the electrolyte solution is in a good range, and good battery performance is ensured. Therefore, the total molar concentration of lithium in the non-aqueous electrolyte is preferably 0.3 mol / L or more, more preferably 0.4 mol / L or more, and further preferably 0.5 mol / L or more. Preferably it is 3 mol / L or less, More preferably, it is 2.5 mol / L or less, More preferably, it is 2.0 mol / L or less. If the total molar concentration of lithium is too low, the electrical conductivity of the electrolyte may be insufficient. On the other hand, if the concentration is too high, the electrical conductivity may decrease due to an increase in viscosity, resulting in decreased battery performance. There is a case.

1-2. Solvent As the non-aqueous solvent, a saturated cyclic carbonate, a cyclic carbonate having a fluorine atom, a chain carbonate, a cyclic and chain carboxylic acid ester, an ether compound, a sulfone compound, and the like can be used.

<Saturated cyclic carbonate>
Examples of the saturated cyclic carbonate include those having an alkylene group having 2 to 4 carbon atoms.
Specifically, examples of the saturated cyclic carbonate having 2 to 4 carbon atoms include ethylene carbonate, propylene carbonate, and butylene carbonate. Among these, ethylene carbonate and propylene carbonate are particularly preferable from the viewpoint of improving battery characteristics resulting from an improvement in the degree of lithium ion dissociation.
A saturated cyclic carbonate may be used individually by 1 type, and may have 2 or more types together by arbitrary combinations and ratios.

  The blending amount of the saturated cyclic carbonate is not particularly limited and is arbitrary as long as the effects of the present invention are not significantly impaired. The lower limit of the blending amount when one kind is used alone is 5% in 100% by volume of the non-aqueous solvent. Volume% or more, more preferably 10 volume% or more. By setting this range, the decrease in electrical conductivity resulting from the decrease in the dielectric constant of the non-aqueous electrolyte is avoided, and the large current discharge characteristics, negative electrode stability, and cycle characteristics of the non-aqueous electrolyte secondary battery are good. It becomes easy to be in a range. Moreover, an upper limit is 95 volume% or less, More preferably, it is 90 volume% or less, More preferably, it is 85 volume% or less. By setting it as this range, the viscosity of the non-aqueous electrolyte solution is set to an appropriate range, a decrease in ionic conductivity is suppressed, and as a result, the load characteristics of the non-aqueous electrolyte secondary battery are easily set in a favorable range.

  Moreover, one of the preferable combinations in the case of using 2 or more types of saturated cyclic carbonates by arbitrary combinations is a combination of ethylene carbonate and propylene carbonate. In this case, the volume ratio of ethylene carbonate to propylene carbonate is preferably 99: 1 to 40:60, and particularly preferably 95: 5 to 50:50. Furthermore, the amount of propylene carbonate in the entire non-aqueous solvent is 0.1% by volume or more, preferably 1% by volume or more, more preferably 2% by volume or more, and the upper limit is usually 20% by volume or less, preferably 8% by volume. % Or less, more preferably 5% by volume or less.

<Cyclic carbonate having a fluorine atom>
The cyclic carbonate having a fluorine atom (hereinafter sometimes abbreviated as “fluorinated cyclic carbonate”) is not particularly limited as long as it is a cyclic carbonate having a fluorine atom.
Examples of the fluorinated cyclic carbonate include derivatives of cyclic carbonates having an alkylene group having 2 to 6 carbon atoms, such as ethylene carbonate derivatives. Examples of the ethylene carbonate derivative include fluorinated products of ethylene carbonate or ethylene carbonate substituted with an alkyl group (for example, an alkyl group having 1 to 4 carbon atoms), and particularly those having 1 to 8 fluorine atoms. Is preferred.

Specifically, monofluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4-fluoro-4-methylethylene carbonate, 4,5-difluoro-4-methylethylene carbonate, 4- Fluoro-5-methylethylene carbonate, 4,4-difluoro-5-methylethylene carbonate, 4- (fluoromethyl) -ethylene carbonate, 4- (difluoromethyl) -ethylene carbonate, 4- (trifluoromethyl) -ethylene carbonate 4- (fluoromethyl) -4-fluoroethylene carbonate, 4- (fluoromethyl) -5-fluoroethylene carbonate, 4-fluoro-4,5-dimethylethylene carbonate, 4,5-difluoro-4,5-dimethyl Le ethylene carbonate, 4,4-difluoro-5,5-dimethylethylene carbonate.

Among them, at least one selected from the group consisting of monofluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, and 4,5-difluoro-4,5-dimethylethylene carbonate has high ionic conductivity. It is more preferable in terms of imparting properties and suitably forming an interface protective film.
A fluorinated cyclic carbonate may be used individually by 1 type, and may have 2 or more types together by arbitrary combinations and ratios. The blending amount of the fluorinated cyclic carbonate is not particularly limited and may be arbitrary as long as the effects of the present invention are not significantly impaired, but in 100% by volume of the non-aqueous solvent, preferably 0.01% by volume or more, more preferably 0.8%. It is 1 volume% or more, More preferably, it is 0.2 volume% or more, Preferably it is 95 volume% or less, More preferably, it is 90 volume% or less. Within this range, the non-aqueous electrolyte secondary battery tends to exhibit a sufficient cycle characteristic improvement effect, and avoids a decrease in discharge capacity maintenance rate due to a decrease in high-temperature storage characteristics or an increase in the amount of gas generated. Cheap.

  In addition, the cyclic carbonate which has a fluorine atom expresses an effective function not only as a solvent but also as an auxiliary agent described in 1-4 below. There is no clear boundary in the blending amount when used as a cyclic carbonate solvent / auxiliary having a fluorine atom, and the blending amount described in the previous paragraph can be followed as it is.

<Chain carbonate>
As a chain carbonate, a C3-C7 thing is preferable.
Specifically, as the chain carbonate having 3 to 7 carbon atoms, dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n-propyl isopropyl carbonate, ethyl methyl carbonate, methyl-n-propyl carbonate, Examples include n-butyl methyl carbonate, isobutyl methyl carbonate, t-butyl methyl carbonate, ethyl-n-propyl carbonate, n-butyl ethyl carbonate, isobutyl ethyl carbonate, t-butyl ethyl carbonate.

Among them, dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n-propyl isopropyl carbonate, ethyl methyl carbonate, and methyl n-propyl carbonate are preferable, and dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are particularly preferable. is there.
Further, a chain carbonate having a fluorine atom (hereinafter sometimes abbreviated as “fluorinated chain carbonate”) can also be suitably used. The number of fluorine atoms contained in the fluorinated chain carbonate is not particularly limited as long as it is 1 or more, but is usually 6 or less, preferably 4 or less. When the fluorinated chain carbonate has a plurality of fluorine atoms, they may be bonded to the same carbon or may be bonded to different carbons. Examples of the fluorinated chain carbonate include a fluorinated dimethyl carbonate derivative, a fluorinated ethyl methyl carbonate derivative, and a fluorinated diethyl carbonate derivative.

Examples of the fluorinated dimethyl carbonate derivative include fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate, bis (fluoromethyl) carbonate, bis (difluoro) methyl carbonate, bis (trifluoromethyl) carbonate, and the like.
Fluorinated ethyl methyl carbonate derivatives include 2-fluoroethyl methyl carbonate, ethyl fluoromethyl carbonate, 2,2-difluoroethyl methyl carbonate, 2-fluoroethyl fluoromethyl carbonate, ethyl difluoromethyl carbonate, 2,2,2-trimethyl Examples include fluoroethyl methyl carbonate, 2,2-difluoroethyl fluoromethyl carbonate, 2-fluoroethyl difluoromethyl carbonate, and ethyl trifluoromethyl carbonate.

  Fluorinated diethyl carbonate derivatives include ethyl- (2-fluoroethyl) carbonate, ethyl- (2,2-difluoroethyl) carbonate, bis (2-fluoroethyl) carbonate, ethyl- (2,2,2-trifluoro). Ethyl) carbonate, 2,2-difluoroethyl-2′-fluoroethyl carbonate, bis (2,2-difluoroethyl) carbonate, 2,2,2-trifluoroethyl-2′-fluoroethyl carbonate, 2,2, Examples include 2-trifluoroethyl-2 ′, 2′-difluoroethyl carbonate, bis (2,2,2-trifluoroethyl) carbonate, and the like.

A chain carbonate may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.
The amount of the chain carbonate is preferably 5% by volume or more, more preferably 10% by volume or more, and further preferably 15% by volume or more in 100% by volume of the non-aqueous solvent. By setting the lower limit in this way, the viscosity of the non-aqueous electrolyte solution is set to an appropriate range, the decrease in ionic conductivity is suppressed, and consequently the large current discharge characteristics of the non-aqueous electrolyte secondary battery are easily set to a favorable range. Become. Further, the chain carbonate is preferably 90% by volume or less, more preferably 85% by volume or less, in 100% by volume of the nonaqueous solvent. By setting the upper limit in this way, it is easy to avoid a decrease in electrical conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte and to make the large current discharge characteristics of the non-aqueous electrolyte secondary battery in a favorable range. .

The battery performance can be remarkably improved by combining ethylene carbonate at a specific blending amount with respect to the specific chain carbonate.
For example, when dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate is selected as the specific chain carbonate, the blending amount of ethylene carbonate is 10% by volume or more and 80% by volume or less, dimethyl carbonate, ethyl methyl carbonate, or diethyl It is preferable that the blending amount of carbonate is 20% by volume or more and 90% by volume or less. By selecting such a blending amount, the low-temperature deposition temperature of the electrolyte is lowered, the viscosity of the nonaqueous electrolytic solution is also lowered to improve the ionic conductivity, and a high output can be obtained even at a low temperature.

  It is also preferable to use two or more types of specific chain carbonates in combination. When dimethyl carbonate and ethyl methyl carbonate are used in combination with a specific chain carbonate, the blending amount of ethylene carbonate is 10% by volume or more and 60% by volume or less, and the blending amount of dimethyl carbonate is 10% by volume or more and 70% by volume or less. Particularly preferred are those in which the amount of ethyl methyl carbonate is 10% by volume or more and 80% by volume or less. When a specific chain carbonate is used in combination with dimethyl carbonate and diethyl carbonate, the blending amount of ethylene carbonate is 10% by volume or more and 60% by volume or less, and the blending amount of dimethyl carbonate is 10% by volume or more and 70% by volume. Hereinafter, it is particularly preferable that the amount of diethyl carbonate is 10% by volume or more and 70% by volume or less. Further, when ethyl methyl carbonate and diethyl carbonate are used in combination with a specific chain carbonate, the blending amount of ethylene carbonate is 10% by volume or more and 60% by volume or less, the blending amount of ethyl methyl carbonate is 10% by volume or more, 80% Those having a volume% or less and a blending amount of diethyl carbonate of 10 vol% or more and 70 vol% or less are particularly preferable.

<Cyclic carboxylic acid ester>
Examples of the cyclic carboxylic acid ester include those having 3 to 12 total carbon atoms in the structural formula.
Specific examples include gamma butyrolactone, gamma valerolactone, gamma caprolactone, epsilon caprolactone, and the like. Among these, gamma butyrolactone is particularly preferable from the viewpoint of improving battery characteristics resulting from an improvement in the degree of lithium ion dissociation.

  The amount of the cyclic carboxylic acid ester is usually 5% by volume or more, more preferably 10% by volume or more, in 100% by volume of the non-aqueous solvent. By setting the lower limit in this manner, the electrical conductivity of the non-aqueous electrolyte solution is improved, and the large current discharge characteristics of the non-aqueous electrolyte secondary battery are easily improved. Moreover, the compounding quantity of cyclic carboxylic acid ester becomes like this. Preferably it is 50 volume% or less, More preferably, it is 40 volume% or less. By setting the upper limit in this way, the viscosity of the non-aqueous electrolyte solution is set to an appropriate range, a decrease in electrical conductivity is avoided, an increase in negative electrode resistance is suppressed, and a large current discharge of the non-aqueous electrolyte secondary battery is performed. It becomes easy to make the characteristic a good range.

<Chain carboxylic acid ester>
Examples of the chain carboxylic acid ester include those having 3 to 7 carbon atoms in the structural formula.
The compounding amount of the chain carboxylic acid ester is usually 10% by volume or more, more preferably 15% by volume or more, in 100% by volume of the non-aqueous solvent. By setting the lower limit in this way, the electrical conductivity of the non-aqueous electrolyte solution is improved, and the large current discharge characteristics of the non-aqueous electrolyte secondary battery are easily improved. Moreover, the compounding quantity of chain | strand-shaped carboxylic acid ester is 60 volume% or less preferably in 100 volume% of nonaqueous solvents, More preferably, it is 50 volume% or less. By setting the upper limit in this manner, an increase in negative electrode resistance is suppressed, and the large current discharge characteristics and cycle characteristics of the non-aqueous electrolyte secondary battery are easily set in a favorable range.

<Ether compound>
As the ether compound, a chain ether having 3 to 10 carbon atoms in which part of hydrogen may be substituted with fluorine, and a cyclic ether having 3 to 6 carbon atoms are preferable.
Among them, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether have high solvating ability to lithium ions and improve ion dissociation. Of these, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are preferable because they have low viscosity and give high ionic conductivity.

  The compounding amount of the ether compound is usually in 100% by volume of the non-aqueous solvent, preferably 5% by volume or more, more preferably 10% by volume or more, further preferably 15% by volume or more, and preferably 70% by volume or less. More preferably, it is 60 volume% or less, More preferably, it is 50 volume% or less. If it is this range, it is easy to ensure the improvement effect of the lithium ion dissociation degree of chain ether, and the improvement of the ionic conductivity derived from a viscosity fall, and when a negative electrode active material is a carbonaceous material, a chain ether with lithium ion It is easy to avoid a situation where the capacity is reduced due to co-insertion.

<Sulfone compounds>
As the sulfone compound, a cyclic sulfone having 3 to 6 carbon atoms and a chain sulfone having 2 to 6 carbon atoms are preferable. The number of sulfonyl groups in one molecule is preferably 1 or 2.
Examples of the cyclic sulfone include trimethylene sulfones, tetramethylene sulfones, and hexamethylene sulfones that are monosulfone compounds; trimethylene disulfones, tetramethylene disulfones, and hexamethylene disulfones that are disulfone compounds.

Among these, from the viewpoint of dielectric constant and viscosity, tetramethylene sulfones, tetramethylene disulfones, hexamethylene sulfones, and hexamethylene disulfones are more preferable, and tetramethylene sulfones (sulfolanes) are particularly preferable.
The sulfolane is preferably sulfolane and / or a sulfolane derivative (hereinafter sometimes abbreviated as “sulfolane” including sulfolane). As the sulfolane derivative, one in which one or more hydrogen atoms bonded to the carbon atom constituting the sulfolane ring are substituted with a fluorine atom or an alkyl group is preferable.

  The compounding amount of the sulfone compound is usually 0.3% by volume or more, more preferably 0.5% by volume or more, and further preferably 1% by volume or more in 100% by volume of the nonaqueous solvent. Is 40% by volume or less, more preferably 35% by volume or less, and still more preferably 30% by volume or less. Within this range, durability improvement effects such as cycle characteristics and storage characteristics can be easily obtained, and the viscosity of the non-aqueous electrolyte can be set to an appropriate range to avoid a decrease in electrical conductivity. When charging / discharging an aqueous electrolyte secondary battery at a high current density, it is easy to avoid a situation in which the charge / discharge capacity retention rate decreases.

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 manufactured by assembling the above-described positive electrode for a lithium secondary battery of the present invention, a negative electrode, a nonaqueous 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, an inside-out cylinder type with a combination of pellet electrode and separator, and a coin type with a stack of pellet electrode and 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>
The lithium secondary battery of the present invention is preferably designed so that the charging potential of the positive electrode in a fully charged state is 4.4 V (vs. Li ^/ Li ⁺ ) or higher. That is, when the lithium transition metal-based compound 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 charge potential according to the specific composition described above, Effectively enhances properties and safety. However, it is also possible to use this charging potential as less than 4.4V.

  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 unless it exceeds the gist.
[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.

Composition (Li / Ni / Mn / Co):
It was determined by ICP-AES analysis.
Crystal phase:
It calculated | required by the powder X-ray-diffraction pattern using a CuK alpha ray.
(Powder X-ray diffraction measurement device) PANalytical X'Pert Pro MPD
(Measurement conditions) X-ray output: 40 kV, 30 mA, scanning axis: θ / 2θ
Scanning range (2θ): 10.0-70.0 °, 10.0-155.0 ° (precision measurement)
Measurement mode: Continuous
Reading width: 0.016 °
Counting time: 29.8 seconds, 99.7 seconds (precision measurement)
Slit: Automatic variable slit, 10.0mm fixed
Specific surface area:
The BET specific surface area was measured by a BET 5-point system using a Sysmex NOVA 1200 type fully automatic powder specific surface area measuring apparatus, using nitrogen as an adsorption gas.

Average primary particle size:
Using an SEM image of 30,000-100,000 times, the average particle size of about 10 to 30 primary particles was obtained.
Secondary median diameter and 90% cumulative diameter (D90):
The laser diffraction / scattering type particle size distribution measuring apparatus used was HORIBA LA-920, the refractive index was set to 1.24, and the particle diameter standard was measured as the volume standard. As a dispersion medium used in the measurement, a 0.1% by weight sodium hexametaphosphate aqueous solution was used for measurement.

The bulk density:
10 to 11 g of the sample powder was put in a 10 ml glass graduated cylinder, and the powder packing density when tapped 200 times with a stroke of about 20 mm was obtained.
Volume resistivity:
Using a powder resistivity measurement device (Dia Instruments: Lorester GP powder low efficiency measurement system PD-41), the sample weight is 3 g, and a powder probe unit (four probe / ring electrode, electrode spacing 5.0 mm) The electrode resistivity is 1.0 mm, the sample radius is 12.5 mm, and the applied voltage limiter is 90 V. The volume resistivity [Ω · cm] of the powder under various pressures is measured, and the volume resistivity under a pressure of 40 MPa is measured. The values were compared.

Physical properties of particulate powder:
The form was confirmed by confirmation through SEM observation and cross-sectional SEM observation. The median diameter as an average particle diameter was measured using a laser diffraction / scattering particle size distribution measuring device (HORIBA LA-920), a refractive index of 1.60, and a particle diameter standard as a volume standard. As a dispersion medium, a 0.1 wt% sodium hexametaphosphate aqueous solution was used for measurement. The specific surface area was determined by the BET method.

Measurement of compressive fracture strength of particulate powder:
The compressive strength of the particles was measured using a micro compression tester MCT-W500 manufactured by Shimadzu Corporation. That is, with a test load of 100 mN, a load speed of 3.874 mN / sec, and using a flat type indenter having a diameter of 10 μm, measurement was performed on arbitrary XX particles having a known particle size, and the compressive strength was obtained. Arbitrary lithium transition metal compound particles of 5-50 μm were selected with an optical microscope attached to the apparatus, and the compression fracture strength was measured. The compressive fracture strength of a plurality of particles per sample was measured.

Measurement of various physical properties by mercury intrusion method:
As a measuring device by the mercury intrusion method, Autopore III9420 manufactured by Micromeritics was used. Moreover, as measurement conditions of the mercury intrusion method, measurement was performed while increasing the pressure from 3.86 kPa to 413 MPa at room temperature. The mercury surface tension value was 480 dyn / cm, and the contact angle value was 141.3 °.

Median diameter of active material particles in slurry:
Using a laser diffraction / scattering particle size distribution measuring apparatus (LA-920 manufactured by HORIBA), the refractive index was set to 1.60, and the particle diameter standard was measured as a volume standard. The slurry was dispersed using NMP (N-methyl-2-pyrrolidone) as a dispersion medium, and measurement was performed while stirring with a stirrer in a batch cell.

Median diameter of active material particles in positive electrode mixture:
Using a laser diffraction / scattering particle size distribution measuring apparatus (LA-920 manufactured by HORIBA), the refractive index was set to 1.60, and the particle diameter standard was measured as a volume standard. The coated electrode was impregnated with NMP (N-methyl-2-pyrrolidone) solvent, and the positive electrode mixture layer was sampled with a spatula. This sample was dispersed in an NMP solvent, and measurement was performed while stirring with a stirrer in a batch type cell.

[Production of Lithium Transition Metal Compound Powder (Examples and Comparative Examples)]
The powder physical properties of the conductive material and binder used in the present invention are shown below.
Conductive material (Mitsubishi Carbon Black # 3400B):
Particle size ^{21nm, SSA: 165m 2 / g} , DBP adsorption of 175cm ³ / 100g.
Binder (Kureha KF Polymer # 7208):
Weight average molecular weight 630,000, inherent viscosity 2.1 dl · g, melting point 173 ° C., crystallization temperature 136 ° C., 8 wt% NMP solution, solution viscosity 2100 mPa · s, moisture 0.1% or less.

Example 1
LiNO ₃ : Ni (NO ₃ ) ₂ .6H ₂ O: Mn (NO ₃ ) ₂ .6H ₂ O: Co (N
O _{3) 2} · 6H ₂ O and 0.1667: 0.2200: 0.4883 were weighed so as to be 0.1250 molar ratio, into an aqueous solution of 0.5M dissolved in water. The _Li 2 WO ₄ in this respect the lithium transition metal-based compound produced after baking, was added so as to be 2 wt%. Using this as a raw material solution, a spray pyrolysis treatment was performed under the following conditions using an indirect heating type spray pyrolysis apparatus. Using a two-fluid nozzle, the nozzle gas pressure was 0.2 MPa, the carrier gas pressure was 0.01 MPa, the furnace temperature was 500 ° C., and the residence time was 1 second. The composite oxide powder obtained by spray pyrolysis is charged into an alumina crucible, fired at 900 ° C. for 8 hours at a heating / cooling rate of 5 ° C./min under air flow, crushed, and lithium transition metal system Compound powder was obtained.

From the XRD (powder X-ray diffraction) pattern using CuKα rays of this lithium transition metal-based compound powder, it was confirmed that the crystal structure included a layered R (-3) m structure. Moreover, the peak resulting from a superlattice structure was observed between 20 ° and 30 °. As a result of SEM measurement, the primary particles of the powder were present in the range of about 0.05 to 0.15 μm, and the average primary particle size was 0.1 μm. The median diameter of the secondary particles was 1.86 μm, the bulk density was 0.85 g / cc, and the BET specific surface area was 7.25 m ² / g.

Using the lithium transition metal compound powder produced by the above method, a slurry was prepared by the following method.
Slurry preparation method (1):
5 wt% conductive material (# 3400B) and 88 wt% active material were added to the solid content of the positive electrode mixture to be prepared, and dry kneading was performed at 2000 rpm for 3 min in a kneader. 7 wt% binder PVDF (# 7208 (8.1 wt%, NMP solution)) was added to the above mixed powder in three portions, and kneading was performed at 2000 rpm for 3 min in a kneader. NMP solvent was added to adjust the viscosity of the slurry. NMP was added so that the solid content concentration of the slurry was 40 to 50 wt%. After adding a predetermined amount of NMP, kneading was performed at 2000 rpm for 3 minutes in a kneader to obtain a slurry for coating.

(Example 2)
A raw material solution having a concentration of 1 M was prepared by the same preparation procedure as in Example 1. Using this as a raw material solution, the composite oxide powder obtained by spray pyrolysis in the same manner as in Example 1 was charged into an alumina crucible, and heated at 980 ° C. for 8 hours at a heating / cooling rate of 5 ° C./min. After firing, it was crushed to obtain lithium transition metal compound powder.

From the XRD (powder X-ray diffraction) pattern using CuKα rays of this lithium transition metal-based compound powder, it was confirmed that the crystal structure included a layered R (-3) m structure. Moreover, the peak resulting from a superlattice structure was observed between 20 ° and 30 °. As a result of SEM measurement, the primary particles of this powder were present in the range of about 0.1 to 0.2 μm, and the average primary particle size was 0.1 μm. The median diameter of the secondary particles was 6.52 μm, the bulk density was 0.79 g / cc, and the BET specific surface area was 4.95 m ² / g.

Using the lithium transition metal compound powder produced by the above method, a slurry was prepared by the following method.
Slurry preparation method (1):
5 wt% of the conductive material (# 3400B) with respect to the solid content of the positive electrode mixture to be prepared, 88w
A t% active material was added, and dry kneading was performed with a kneader at 2000 rpm for 3 min. 7 wt% of PVDF # 7208 (8.1 wt%, NMP solution) was added to the above mixed powder in three portions, and kneading was performed at 2000 rpm for 3 min in each kneader. NMP solvent was added to adjust the viscosity of the slurry. NMP was added so that the solid content concentration of the slurry was 40 to 50 wt%. After adding a predetermined amount of NMP, kneading was performed at 2000 rpm for 3 minutes in a kneader to obtain a slurry for coating.

(Example 3)
A raw material solution having a concentration of 3.6 M was prepared by the same preparation procedure as in Example 1. Using this as a raw material solution, spray pyrolysis was performed at 400 ° C. and a residence time of 1 second using a high temperature gas direct heating type spray pyrolysis apparatus to obtain a composite oxide. The obtained composite oxide powder was charged into an alumina crucible, fired at 1000 ° C. for 8 hours at a temperature increase / decrease rate of 5 ° C./min under air flow, and then crushed to obtain a lithium transition metal compound powder. Obtained.

From the XRD (powder X-ray diffraction) pattern using CuKα rays of this lithium transition metal-based compound powder, it was confirmed that the crystal structure included a layered R (-3) m structure. Moreover, the peak resulting from a superlattice structure was observed between 20 ° and 30 °. As a result of SEM measurement, the primary particles of this powder were present in the range of about 0.1 to 0.2 μm, and the average primary particle size was 0.1 μm. The median diameter of the secondary particles was 20.9 μm, the bulk density was 0.65 g / cc, and the BET specific surface area was 5.42 m ² / g.

Using the lithium transition metal compound powder produced by the above method, a slurry was prepared by the following method.
Slurry preparation method (1):
5 wt% conductive material (# 3400B) and 88 wt% active material were added to the solid content of the positive electrode mixture to be prepared, and dry kneading was performed at 2000 rpm for 3 min in a kneader. 7 wt% of PVDF # 7208 (8.1 wt%, NMP solution) was added to the above mixed powder in three portions, and kneading was performed at 2000 rpm for 3 min in each kneader. NMP solvent was added to adjust the viscosity of the slurry. NMP was added so that the solid content concentration of the slurry was 40 to 50 wt%. After adding a predetermined amount of NMP, kneading was performed at 2000 rpm for 3 minutes in a kneader to obtain a slurry for coating.

Example 4
A positive electrode precursor was obtained in the same manner as in Example 3 except that Li ₂ WO ₄ was not added and the spray pyrolysis temperature was 600 ° C. Next, the obtained positive electrode precursor was charged into an alumina crucible, fired at 1000 ° C. for 8 hours under air flow (temperature raising / lowering rate 5 ° C./min.), Crushed, and lithium transition metal compound powder. Got.

From the XRD (powder X-ray diffraction) pattern using CuKα rays of this lithium transition metal-based compound powder, it was confirmed that the crystal structure included a layered R (-3) m structure. Moreover, the peak resulting from a superlattice structure was observed between 20 ° and 30 °. As a result of SEM measurement, the primary particles of this powder were present in the range of about 0.1 to 0.3 μm, and the average primary particle size was 0.1 μm. The median diameter of the secondary particles was 12.6 μm, the bulk density was 0.71 g / cc, and the BET specific surface area was 2.93 m ² / g.

Using the lithium transition metal compound powder produced by the above method, a slurry was prepared by the following method. Slurry preparation method (1): 5 wt% of conductive material (# 3400B) and 88 wt% of active material are added to the solid content of the positive electrode mixture to be prepared, and 2000 rpm, 3 min, Dry kneading was performed. 7 wt% PVDF # 7208 (8.1 wt%, NMP solution) was added to the above mixed powder in three portions, and each was mixed with a kneader at 2000 rpm, 3 min,
Kneaded. NMP solvent was added to adjust the viscosity of the slurry. NMP was added so that the solid content concentration of the slurry was 40 to 50 wt%. After adding a predetermined amount of NMP, kneading was performed at 2000 rpm for 3 minutes in a kneader to obtain a slurry for coating.

(Example 5)
A positive electrode precursor was obtained in the same manner as in Example 3 except that the spray pyrolysis temperature was 600 ° C. Next, the obtained positive electrode precursor was charged into an alumina crucible, fired at 1000 ° C. for 8 hours under air flow (temperature raising / lowering rate 5 ° C./min.), Crushed, and lithium transition metal compound powder. Got.

From the XRD (powder X-ray diffraction) pattern using CuKα rays of this lithium transition metal-based compound powder, it was confirmed that the crystal structure included a layered R (-3) m structure. Moreover, the peak resulting from a superlattice structure was observed between 20 ° and 30 °. As a result of SEM measurement, the primary particles of this powder were present in the range of about 0.1 to 0.3 μm, and the average primary particle size was 0.1 μm. The median diameter of the secondary particles was 15.0 μm, the bulk density was 0.77 g / cc, and the BET specific surface area was 6.81 m ² / g.
Using the lithium transition metal compound powder produced by the above method, a slurry was prepared by the following method.

Preparation of slurry (2):
5 wt% of the conductive material (# 3400B) and 7 wt% of PVDF # 7208 (8.1 wt%, NMP solution) are mixed with the solid content of the positive electrode mixture to be prepared, and the mixture is mixed at 2000 rpm for 3 min. Kneaded. 88 wt% active material was added to the slurry, and kneading was performed at 2000 rpm for 3 min in a kneader. NMP solvent was added to adjust the viscosity of the slurry. NMP was added so that the solid content concentration of the slurry was 40 to 50 wt%. After adding a predetermined amount of NMP, kneading was performed at 2000 rpm for 3 minutes in a kneader to obtain a slurry for coating.

(Comparative Example 1)
Li ₂ CO ₃ , NiCO ₃ , Mn ₃ O ₄ , CoOOH are weighed and mixed so that the molar ratio of Li: Ni: Mn: Co = 1.1917: 0.2200: 0.4883: 0.1250 is obtained. After that, 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 or less using a circulating medium agitation type wet pulverizer. Two-fluid nozzle type spray dryer (Okawara Kako Co., Ltd .: L
(T-8 type). At this time, air was used as the dry gas, the dry gas introduction amount was 60 L / min, and the slurry supply amount was 11 g / min. The drying inlet temperature was 150 ° C. This particulate powder was charged into an alumina crucible, calcined at 1000 ° C. for 8 hours under air flow (heating rate 5 ° C./min.), And then pulverized to obtain a lithium transition metal compound powder.

From the XRD (powder X-ray diffraction) pattern using CuKα rays of this lithium transition metal-based compound powder, it was confirmed that the crystal structure included a layered R (-3) m structure. Moreover, the peak resulting from a superlattice structure was observed between 20 ° and 30 °. As a result of SEM measurement, the primary particles of this powder were present in the range of about 0.5 to 1.5 μm, and the average primary particle size was 1.0 μm. The median diameter of the secondary particles was 8.18 μm, the bulk density was 0.82 g / cc, and the BET specific surface area was 1.03 m ² / g.

Table 1 summarizes the physical properties of the lithium transition metal-based compound powders obtained in Examples 1 to 5 and Comparative Example 1.
From Table 1, the following is clear.
The primary particle size of the lithium transition metal-based compound powder of Example 1-5 prepared using the spray pyrolysis method was as fine as about 1/10 compared to Comparative Example 1 prepared using the spray drying method. . It can be seen that the primary particles of the lithium transition metal compound powder can be refined by the spray pyrolysis method. Moreover, when Example 1-5 is compared, it turns out that a secondary particle diameter becomes large, so that the density | concentration of a raw material solution is high. That is, in the spray pyrolysis method, by adjusting the concentration of the raw material solution, the secondary particle diameter can be controlled while keeping the primary particle shape fine. In addition, in the comparison of Examples 4 and 5, it is understood that the particle strength and the surface area (primary particle diameter) can be controlled by adding a crystal growth inhibitor such as Li ₂ WO ₄ .

  The strength of the secondary particles or the particle size of the primary particles can also be controlled by the temperature during firing. The fog pyrolysis method has a feature that a smaller primary particle diameter can be maintained at a higher firing temperature as compared with a coprecipitation method, a solid phase reaction method and the like.

(Comparative Example 2)
Secondary particles of the lithium transition metal compound powder synthesized in Example 5 were pulverized by a wet ball mill (Asahi Science AV type ball mill). In a PFA 100 ml container, 100 g of alumina balls (bulk density 3.6 g / cm ³ , diameter 1 mm) were filled with 10.0 g of a sample and 20 g of ethanol and crushed (40 rpm for 3 hours). After crushing, the alumina balls were separated, and ethanol was evaporated and removed using a rotary evaporator. Next, it was dried at 120 ° C. for 12 hours with a dryer. As a result of the particle size distribution measurement, the median diameter of the secondary particles was crushed to 0.41 μm.
Using the lithium transition metal compound powder produced by the above method, a slurry was prepared by the following method.

Slurry preparation method (1):
5 wt% conductive material (# 3400B) and 88 wt% active material were added to the solid content of the positive electrode mixture to be prepared, and dry kneading was performed at 2000 rpm for 3 min in a kneader. 7 wt% PVDF # 7208 (8.1 wt%, NMP solution) was added to the above mixed powder in three portions, and kneading was performed at 2000 rpm for 3 min in each kneader. NMP solvent was added to adjust the viscosity of the slurry. NMP was added so that the solid content concentration of the slurry was 40 to 50 wt%. After adding a predetermined amount of NMP, kneading was performed at 2000 rpm for 3 minutes in a kneader to obtain a slurry for coating.

(Comparative example 3) t2x-milled (# 3400, 20 wt%)
Using the lithium transition metal compound powder produced in Comparative Example 2, a slurry was prepared by the following method.
Slurry preparation method (1):
A conductive material (# 3400B) of 20 wt% with respect to the solid content of the positive electrode mixture to be prepared;
A wt% active material was added, and dry kneading was performed at 2000 rpm for 3 min in a kneader. 15 wt% PVDF # 7208 (8.1 wt%, NMP solution) was added to the above mixed powder in three portions, and kneading was performed at 2000 rpm for 3 min in each kneader. NMP solvent was added to adjust the viscosity of the slurry. NMP was added so that the solid content concentration of the slurry was 40 to 50 wt%. After adding a predetermined amount of NMP, kneading was performed at 2000 rpm for 3 minutes in a kneader to obtain a slurry for coating.

The slurry for electrode coating prepared in Examples 1 to 5 and Comparative Examples 1 to 4 is dried after coating on an Al foil, and pressed to a plate density of 2.0 g / cm ³ or more by a roll press, A positive electrode plate for a lithium secondary battery was obtained. In this study, an electrode plate was prepared by applying a pressure of 0.8 ton / cm ² or more during pressing.
Table 2 summarizes the physical properties of the slurry and the positive electrode using the lithium transition metal compound powder obtained in Examples 1 to 5 and Comparative Examples 1 to 3.

From Table 2, the following is clear.
In Table 2, the shape change of the positive electrode secondary particles in the positive electrode preparation step is shown. The change in the particle size distribution in the electrode coating slurry and in the positive electrode mixture after pressing indicates the collapse of the positive electrode secondary particles during pressing. In Example 1-5, the proportion of crushed pieces of 1 μm or less in the electrode plate is greatly increased, and it can be seen that the particle shape of the positive electrode has changed greatly when the electrode is pressed. On the other hand, in Comparative Example 1-3, there is little change in the particle shape in the electrode preparation process.

[Production and evaluation of battery]
Using the lithium transition metal-based compound powders produced in Examples 1 to 5 and Comparative Examples 1 to 4 as positive electrode materials (positive electrode active materials), lithium secondary batteries were produced by the following method.
A positive electrode plate for a lithium secondary battery punched to 12.5 mmφ is used as a test electrode, and a lithium metal plate is used as a counter electrode. EC (ethylene carbonate): DMC (dimethyl carbonate): EMC (ethyl methyl carbonate) = 3: 3: 4 Using an electrolytic solution in which LiPF ₆ was dissolved in a solvent of (volume ratio) at 1 mol / L, using a porous polypropylene film with a thickness of 25 μm as a separator, a coin-type cell was used in an environment where the humidity was −40 ° C. or lower. Assembled.

The produced coin cell was evaluated as follows.
Rate test:
About each coin-type cell, CC-CV charge was carried out to the charging upper limit voltage to 4.8V with the constant current of 20 mAh / g. The cut-off current during CV charging was 4 mAh / g. Subsequently, CC discharge was performed at a discharge lower limit voltage of 2.0V. For each cycle, the discharge current was sequentially changed to 20 mAh / g, 100 mAh / g, and 200 mAh / g, and the discharge capacity at each discharge rate was measured. After measuring the 100 mAh / g discharge capacity, the battery was discharged again at 20 mAh / g until reaching the lower limit potential of 2.0 V, then charged at 20 mAh / gC, and the subsequent 200 mAh / g discharge capacity was measured. The

Positive power spectrum analysis:
Power spectrum analysis was performed based on the cross-sectional structure of the positive electrode. First, an image of 1024 × 1024 pixels was extracted from the cross-sectional SEM image of the positive electrode taken at a magnification of 2000, and the image was subjected to Hamming window processing to remove discontinuities at the boundaries of the four sides of the image. Next, a power spectrum was obtained by performing Fourier transform using image software ImageJ. Further, the obtained power spectrum was integrated in the rotation direction with respect to the center of the spectrum to obtain spectrum data. Here, the distance from the center of the power spectrum is defined as Spacing (μm), and the spectrum intensity is defined as Intensity. Finally, dB (10 log (basic data / average value)) of the entire data was obtained based on the average value of 0.2 to 0.5 μm of the spectrum data, and Inrenity was converted to dB.

  The composition of the positive electrode using the lithium transition metal-based compound powders obtained in Examples 1 to 5 and Comparative Examples 1 to 3 and the rate measurement results are summarized in Table 3.

From Table 3, the following is clear.
Compared with Comparative Example 1-2, the discharge rate characteristics of Example 1-5 were very good.
This is because the active material keeps the secondary particle structure during slurry preparation for electrode application, and the secondary particles are crushed during pressing of the application electrode. In this example, since there is no need to mix the individual primary particles, the conductive additive and the binder, which is an obstacle when using fine primary particles, the fine primary particles are used. Therefore, it was possible to achieve both high electrode plate density and high discharge rate characteristics.

Comparative Example 1 is a lithium transition metal-based compound powder prepared using a spray drying method, and the primary particle diameter is about 10 times larger than that of the lithium transition metal-based compound powder of Example 1-5. Therefore, it is considered that the overvoltage at the discharge end is large and as a result, the discharge rate characteristic is deteriorated.
Further, Comparative Example 2 has extremely poor conductivity of the electrode plate as compared with Example 1-5. That is, a favorable conductive path for the lithium transition metal-based compound powder in the positive electrode mixture cannot be formed, and the discharge rate is deteriorated. As shown in Table 1, in Comparative Example 2, the secondary particles are crushed in advance, and there is little change in the shape of the secondary particles between the slurry and the positive electrode mixture. That is, the active material is kept in the secondary particle form in the mixture slurry, so that mixing of the individual primary particles, the conductive additive, and the binder can be avoided. Since the particle structure is destroyed prior to the preparation of the mixed material, in Comparative Example 2, the mixing of the individual primary particles and the conductive additive occurs, and a sufficient network of conductive material cannot be formed in the electrode plate. It is thought that the conductivity was lowered.

  In Comparative Example 3, the same fine lithium transition metal-based compound powder as in Comparative Example 2 is used. However, by significantly increasing the conductive material content, the same discharge characteristics as in Example 1-5 were developed. ing. In other words, Example 1-5 uses the small amount of conductive material present in the positive electrode mixture extremely effectively, and the minimum amount of conductive material despite the use of fine lithium transition metal compound powder. Thus, a conductive path can be formed.

(Example 6)
70% by weight of the lithium transition metal compound powder prepared in Example 5, 20% by weight of acetylene black, and 10% by weight of polytetrafluoroethylene powder were thoroughly mixed in a mortar to form a thin sheet. This was punched out using a 9 mmφ punch. At this time, the total weight was adjusted to about 10 mg.

(Example 7)
70% by weight of the lithium transition metal compound powder prepared in Example 3, 20% by weight of acetylene black, and 10% by weight of polytetrafluoroethylene powder were thoroughly mixed in a mortar to form a thin sheet. This was punched out using a 9 mmφ punch. At this time, the total weight was adjusted to about 10 mg.

(Example 8)
The raw material solution prepared in Example 1 was evaporated and dried to solidify in an evaporating dish using a hot stirrer. The obtained composite oxide powder was charged into an alumina crucible, fired at 1000 ° C. for 8 hours at a temperature increase / decrease rate of 5 ° C./min under air flow, and then crushed to obtain a lithium transition metal compound powder. Obtained. This lithium transition metal compound powder 70%, acetylene black 20% by weight, polytetrafluoroethylene powder 10% by weight, weighed together in a mortar and made into a thin sheet, 9mmφ punch Punched using. At this time, the total weight was adjusted to about 10 mg.

Example 9
Li (OCOCH ₃ ): Ni (OCOCH ₃ ) ₂ : Mn (OCOCH ₃ ) ₂ : Co
(OCOCH ₃ ) ₂ was weighed to a molar ratio of 0.1667: 0.2200: 0.4883: 0.1250 and dissolved in water to give a 0.5 M aqueous solution. Li2WO4 was added to this so that it might become 2 wt% with respect to the lithium transition metal type compound produced | generated after baking. This raw material solution was evaporated and dried in an evaporating dish with stirring using a hot stirrer. The obtained composite oxide powder was charged into an alumina crucible, fired at 1000 ° C. for 8 hours at a temperature increase / decrease rate of 5 ° C./min under air flow, and then crushed to obtain a lithium transition metal compound powder. Obtained. This lithium transition metal compound powder 70%, acetylene black 20% by weight, polytetrafluoroethylene powder 10% by weight, weighed together in a mortar and made into a thin sheet, 9mmφ punch Punched using. At this time, the total weight was adjusted to about 10 mg.

(Comparative Example 4)
The spray pyrolysis precursor prepared in Example 4 was charged into an alumina crucible,
After calcination at 30 ° C. for 8 hours (temperature increase / decrease rate of 5 ° C./min.), Pulverization was performed to obtain a lithium transition metal compound powder. This lithium transition metal compound powder 70%, acetylene black 20% by weight, polytetrafluoroethylene powder 10% by weight, weighed together in a mortar and made into a thin sheet, 9mmφ punch Punched using. At this time, the total weight was adjusted to about 10 mg.

(Comparative Example 5)
The raw material solution prepared in the same manner as in Example 1 except that Li ₂ WO ₄ was not contained was evaporated and dried in an evaporating dish with stirring using a hot stirrer. The obtained composite oxide powder was charged into an alumina crucible, fired at 1000 ° C. for 8 hours at a temperature increase / decrease rate of 5 ° C./min under air flow, and then crushed to obtain a lithium transition metal compound powder. Obtained. This lithium transition metal compound powder 70%, acetylene black 20% by weight, polytetrafluoroethylene powder 10% by weight, weighed together in a mortar and made into a thin sheet, 9mmφ punch Punched using. At this time, the total weight was adjusted to about 10 mg.

(Comparative Example 6)
A raw material solution prepared in the same manner as in Example 9 except that Li ₂ WO ₄ was not contained was evaporated and dried in an evaporating dish while stirring with a hot stirrer. The obtained composite oxide powder was charged into an alumina crucible, fired at 1000 ° C. for 8 hours at a temperature increase / decrease rate of 5 ° C./min under air flow, and then crushed to obtain a lithium transition metal compound powder. Obtained. This lithium transition metal compound powder 70%, acetylene black 20% by weight, polytetrafluoroethylene powder 10% by weight, weighed together in a mortar and made into a thin sheet, 9mmφ punch Punched using. At this time, the total weight was adjusted to about 10 mg.

From Table 4, the following is clear.
When Examples 6-7 and Comparative Example 4 are compared, it is clear that the discharge rate characteristics are improved by the presence of Li2WO4, and it is found that the improvement of the discharge capacity becomes remarkable particularly when the rate is increased. did. In addition, the same tendency was confirmed in Examples 8-9 and Comparative Example 5-6 prepared by a production method other than the spray pyrolysis method, and by adding an additive element defined in the present invention, lithium transition It is possible to improve the rate characteristics of the metal compound powder.

(Example 10)
A spray pyrolysis treatment was performed in the same manner as in Example 5 to obtain a composite oxide powder. The powder was charged into an alumina crucible and fired at different temperatures at a heating / lowering rate of 5 ° C./min under air flow. Specifically, after firing for 8 hours at temperatures of 950 ° C., 1000 ° C., 1025 ° C., and 1100 ° C., respectively, pulverization was performed to obtain a lithium transition metal compound powder. Each BET specific surface area of the lithium transition metal based compound powder 10.15m ² /g(950℃),6.81m ² /g(1000℃),5.45m ² /g(1025℃),2.06m ² / g (1100 ° C.).

(Comparative Example 7)
A composite oxide powder was obtained in the same manner as in Example 10 except that Li ₂ WO ₄ was not added.
Next, the obtained positive electrode precursor was charged into an alumina crucible and fired at different temperatures at a temperature rising / falling rate of 5 ° C./min under air flow. Specifically, after baking for 8 hours at temperatures of 880 ° C., 930 ° C., 950 ° C., 1000 ° C., and 1100 ° C., respectively, pulverization was performed to obtain a lithium transition metal compound powder. Each BET specific surface area of the lithium transition metal based compound powder 8.12m ² /g(880℃),5.59m ² /g(930℃),4.39m ² /g(950℃),2.93m ² / g (1000 ° C.) and 0.698 m ² / g (1100 ° C.).

  Table 5 summarizes the relationship between the surface area of the lithium transition metal-based compound powder obtained in Example 10 and Comparative Example 7 and the firing temperature.

From Table 5, the following is clear.
When firing under the same conditions, it is apparent that the surface area of Example 10 containing Li ₂ WO ₄ is larger than Comparative Example 7 not containing. This is considered to be because the surface area of the lithium transition metal compound powder increased because the primary particle size of the lithium transition metal compound powder became fine because the additive had an effect of preventing sintering.

70% by weight of each lithium transition metal compound powder produced in Example 10 and Comparative Example 7, 20% by weight of acetylene black, and 10% by weight of polytetrafluoroethylene powder were thoroughly mixed in a mortar. The thin sheet was punched out using a 9 mmφ punch. At this time, the total weight was adjusted to about 10 mg.
This 9 mmφ positive electrode is used as a test electrode, a lithium metal plate is used as a counter electrode, and LiPF ₆ is added to 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 an electrolytic solution dissolved at 1 mol / L and using a porous polyethylene film having a thickness of 25 μm as a separator.

The produced coin cell was evaluated as follows.
For each coin cell, CC-C up to 4.8V with a constant current of 0.1C
V charged. The cut-off current during CV charging was 0.02C. Subsequently, CC discharge was performed at a low current of 1.0 C and a discharge lower limit voltage of 2.0 V.

  The measurement results of the 1.0 C discharge capacity of the coin-type cell using the lithium transition metal compound powder obtained in Example 10 and Comparative Example 7 are collectively shown in Table 6 and FIG.

The following is clear from Table 6 and FIG.
When comparing 1.0C discharge capacity at the same surface area, the discharge capacity of Example 10 containing _Li 2 WO ₄ were found to be greater than that of Comparative Example 7 containing no _Li 2 WO _4. The expression mechanism of this phenomenon is not yet clear, but Li ₂ WO ₄ not only refines the primary particle diameter of the lithium transition metal compound powder as a sintering inhibitor, but also has the same surface area as the lithium transition metal. When the discharge capacities of the system compound powders were compared, it was revealed that the discharge capacities were improved.

The following is clear from FIG.
When the power spectrum analysis of Examples 1 and 2 and Comparative Example 2 was performed, the spectrum shapes of both were greatly different. Intensities are widened in the Spacing region of the spectra of Examples 1 and 2 and Comparative Example 2 having a spectrum of 0.5 μm or more. This indicates that the deviation in composition distribution (distribution between the active material and the conductive material) in the positive electrode is larger in the examples. The positive electrode produced by using the manufacturing method proposed in this patent is characterized in that fine active material particles are aggregated in an electrode plate to form a domain structure. This bias in the composition in the electrode can be quantitatively discriminated using a power spectrum. For example, it is characterized that the intensity is 5 dB or more when the spacing is 3 μm.

  The use of the lithium secondary battery 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 notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, lighting equipment, toys, game machines, watches, strobes, cameras, power tools, automotive power sources, and the like.

Claims (16)

  Lithium transition metal compound that has a function capable of inserting / extracting lithium ions, maintains a secondary particle structure during slurry preparation for electrode coating, and crushes secondary particles during coating electrode pressing A lithium transition metal compound for a positive electrode material of a lithium secondary battery.   The lithium transition metal-based compound according to claim 1, wherein the crystal structure of the lithium transition metal-based compound is layered.   It contains a compound (additive 1 of the present invention) containing at least one element (additive element 1 of the present invention) selected from Group 5 to 7 elements of the 5th or 6th period of the periodic table. The lithium transition metal compound according to claim 1 or 2.   4. The lithium transition metal-based compound according to claim 1, wherein the average primary particle diameter is 0.05 μm or more and 0.3 μm or less. BET specific surface area of ^{1 m} 2 / g or more, the lithium transition metal based compound according to any one of claims 1 to 4, characterized in that not more than ^{20 m} 2 / g.   Lithium comprising a positive electrode active material layer containing a lithium transition metal compound for a lithium secondary battery positive electrode material according to any one of claims 1 to 5 and a binder on a current collector. Secondary battery positive electrode.   A positive electrode for a lithium secondary battery including a lithium transition metal compound, a conductive material, and a binder, wherein the content of the conductive material in the positive electrode mixture is 10 wt% or less with respect to the positive electrode mixture, and the lithium transition metal Secondary particles composed of primary particles having an average particle diameter of 0.3 μm or less in the system compound, and in the particle size distribution of the secondary particles in the positive electrode mixture, the secondary particles of 1 μm or less are accumulated in the volume-based passage amount accumulation. A positive electrode for a lithium secondary battery, wherein the positive electrode mixture is present at a ratio of 30% or more and has a volume resistance value of 500 Ω · cm or less.   A positive electrode for a lithium secondary battery including a lithium transition metal compound, a conductive material, and a binder, wherein the content of the conductive material in the positive electrode mixture is 10 wt% or less with respect to the positive electrode mixture, and the lithium transition metal Secondary particles composed of primary particles having an average particle diameter of 0.3 μm or less in the system compound, and in the particle size distribution of the secondary particles in the positive electrode mixture, the secondary particles of 1 μm or less are accumulated in the volume-based passage amount accumulation. A positive electrode for a lithium secondary battery, which is present at a ratio of 30% or more and has a spacing of 5 dB or more at a spacing of 3 μm in a power spectrum obtained from a cross-sectional structure of the positive electrode.   The positive electrode for a lithium secondary battery according to claim 7 or 8, wherein the crystal structure of the lithium transition metal-based compound is a layered structure.   A compound in which the lithium transition metal-based compound contains at least one element (additive element 1 of the present invention) selected from Group 5 to 7 elements of the fifth or sixth period of the periodic table (additive 1 of the present invention) 10) The positive electrode for a lithium secondary battery according to any one of claims 7 to 9, wherein the positive electrode is a lithium secondary battery.   11. The positive electrode for a lithium secondary battery according to claim 7, wherein the lithium transition metal compound has an average primary particle diameter of 0.05 μm or more and 0.3 μm or less. 12. The positive electrode for a lithium secondary battery according to claim 7, wherein the lithium transition metal-based compound has a BET specific surface area of 1 m ² / g or more and 20 m ² / g or less.   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 lithium secondary battery according to claim 6-12 is used as a positive electrode. A lithium secondary battery using a positive electrode for a secondary battery.   A method for producing a lithium transition metal compound having a function capable of inserting / extracting lithium ions and having a composition represented by the general formula (1), wherein the main component material, Mo, W, Nb, A method for producing a lithium transition metal compound for a positive electrode material for a lithium secondary battery, comprising spray pyrolyzing a solution containing a compound having at least one element selected from Ta, Ca, Mg and Re.   The manufacturing method according to claim 14, wherein the heat treatment is performed at 200 ° C. or higher in the spray pyrolysis step.   A process for producing a positive electrode using a lithium transition metal compound having secondary particles formed by agglomeration of primary particles having an average particle size of 0.3 μm or less and a bulk density of the secondary particles of 2.0 g / cc or less. In which the ratio of secondary particles of 1 μm or less present in the electrode-forming slurry is 70% or less in the volume-based cumulative amount of passage, and the secondary particles are crushed by the electrode pressing step. Manufacturing method of secondary battery positive electrode.

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