JP2011253631A - Cathode active material, cathode and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cathode active material with a long life.SOLUTION: A cathode active material includes lithium-containing complex oxide which is expressed by the general formula(1):LiFeQPWO(where Q is at least one selected from a group consisting of Zr, Sn and Y; W is at least one selected from a group consisting of Si and Al; x meets the condition 0<x<1; and y meets the condition 0<y<1) and which shows (200)plane diffraction peak strength of 25-50 in a range of 2θ=16.5-17.5°, (101)plane diffraction peak strength of 70-85 in a range of 2θ=20-21°, (111 and 201)plane diffraction peak strengths of 95-110 in a range of 2θ=25-26°, and (211 and 020)plane diffraction peak strengths of 70-100 in a range of 2θ=29-30°, in the case of assuming the (311) plane diffraction peak strength in a range of 2θ=35-36° in powder X-ray diffraction measurement using Cu-Kα rays as a radiation source to be 100.

Description

  The present invention relates to a positive electrode active material, a positive electrode, and a nonaqueous electrolyte secondary battery. More specifically, the present invention relates to a positive electrode active material for providing a nonaqueous electrolyte secondary battery excellent in cycle characteristics, a positive electrode including the same, and a nonaqueous electrolyte secondary battery.

As secondary batteries for portable electronic devices, non-aqueous electrolyte secondary batteries (hereinafter simply referred to as secondary batteries) such as lithium secondary batteries have been put into practical use and are widely used. Further, in recent years, secondary batteries are attracting attention not only as small-sized batteries for portable electronic devices but also as large-capacity devices for in-vehicle use and power storage. Therefore, demands for safety, cost, life, etc. are higher.
The secondary battery has a positive electrode, a negative electrode, an electrolytic solution, a separator, and an exterior material as main components. The positive electrode includes a positive electrode active material, a conductive material, a current collector, and a binder (binder).

In general, a layered transition metal oxide typified by LiCoO ₂ is used as the positive electrode active material. However, the layered transition metal oxide easily causes oxygen desorption at a relatively low temperature of about 150 ° C. in a fully charged state, and the thermal desorption reaction of the battery can occur due to the oxygen desorption. Therefore, when a secondary battery having such a positive electrode active material is used in a portable electronic device, the secondary battery may generate heat, ignite, or the like.
For this reason, in terms of safety, lithium iron phosphate (LiFePO ₄ ) having an olivine structure that has a stable structure and does not release oxygen when abnormal is expected.

Moreover, since lithium iron phosphate does not contain Co having a low crust abundance, there is an advantage that it is relatively inexpensive. Lithium iron phosphate also has the advantage of being structurally more stable than layered transition metal oxides.
However, when lithium iron phosphate having an olivine type structure is used as a positive electrode active material in a battery, there are problems in charge and discharge characteristics such as insufficient electron conductivity and low average potential.
Therefore, for the purpose of improving the charge / discharge characteristics, the general formula A _a M _b (XY ₄ ) _c Z _d (where A is an alkali metal, M is a transition metal, XY ₄ is PO ₄ , Z is OH, etc.) (For example, refer patent document 1).

Further, the P site represented by the general formula LiMP _1-x A _x O ₄ (wherein M is a transition metal, A is an element having an oxidation number ≦ + 4, and 0 <X <1) is represented by the element A. An active material substituted by the above has also been proposed (see, for example, Patent Document 2).
Further, as a positive electrode active material for excellent non-aqueous electrolyte secondary battery in charge and discharge characteristics at a large current, the general formula _{Li 1-x A x Fe 1} -YZ M y Me z P 1-m X m O 4- _n Z _n (wherein A is Na, K, M is a metal element other than Fe, Li and Al, X is Si, N, As, Z is F, Cl, Br, I, S) , N) (see, for example, Patent Document 3), A _{a + x} M as an electrode active material that is economical, has good charge capacity, and has good rechargeability over many cycles. _{b P 1-x Si x O} 4 ( wherein, a is Ki, Na, or K, M is a metal) material represented by (e.g., see Patent Document 4) have been proposed.

Special table 2005-522009 gazette Special table 2008-506243 gazette JP 2002-198050 A Special table 2005-519451 gazette

However, the active material having the configuration described in Patent Documents 1 to 4 cannot solve the problem that the obtained secondary battery has a short life.
Specifically, in the configuration of the active material described in Patent Documents 1 to 4, the positive electrode active material is greatly expanded or contracted due to insertion / desorption of Li due to charging / discharging. There is a possibility that the active material is physically gradually lost from the current collector or the conductive material, and the structure of the positive electrode active material is destroyed. This is because the internal resistance of the secondary battery increases due to the destruction of the secondary particles and the destruction of the conductive path between the positive electrode active material and the conductive material in a material that has a large expansion or contraction due to charge and discharge. . As a result, the active material that does not contribute to charging / discharging increases, the capacity decreases, and there is a problem that the life of the secondary battery is shortened.

In the present invention thus provides, in general formula (1): LiFe in _{1-x Q x P 1-} y W y O 4 ( wherein, Q is at least one selected Zr, from the group consisting of Sn and Y, W is at least one selected from Si and Al, x is represented by 0 <x <1, y is 0 <y <1, and
When the intensity of a diffraction peak of (311) plane existing between 2θ = 35 to 36 degrees in powder X-ray diffraction measurement using Cu—Kα ray as a radiation source is 100, 2θ of 25-50 = 16. Intensity of diffraction peak of (200) plane between 5 and 17.5 degrees, intensity of diffraction peak of (101) plane between 20 and 21 degrees of 70 to 85, 2θ = 25 of 95 to 110 Lithium-containing composite oxidation showing the intensity of the (111 and 201) plane diffraction peaks between ˜26 degrees and the intensity of the (211 and 020) plane diffraction peaks between 70 and 100 2θ = 29-30 degrees. There is provided a positive electrode active material characterized by containing a material.

Moreover, according to this invention, the positive electrode characterized by including the said positive electrode active material, a electrically conductive material, and a binder is provided.
Furthermore, according to the present invention, there is provided a nonaqueous electrolyte secondary battery comprising a positive electrode including the positive electrode active material, a negative electrode, an electrolyte, and a separator.

According to the present invention, it is possible to prevent physical stress (volume shrinkage expansion) of the lithium-containing composite oxide that accompanies repeated charge / discharge (Li insertion / desorption). A water electrolyte secondary battery can be provided.
Further, when the positive electrode active material includes the lithium-containing composite oxide of the general formula (1) that is Q that is Zr and W that is Si, the physical properties of the lithium-containing composite oxide that accompany repeated charge and discharge are further increased. Since stress can be prevented, a positive electrode active material having a longer life can be provided.

Further, when the positive electrode active material includes the lithium-containing composite oxide of the general formula (1), where x is between 0.05 and 0.33 and y is between 0.025 and 0.66, Since the physical stress of the lithium-containing composite oxide that accompanies repeated charge / discharge can be prevented, a positive electrode active material having a longer life can be provided.
Further, when the positive electrode active material contains the lithium-containing composite oxide of the general formula (1) having a half-value width of the diffraction peak of (100) plane of 0.3 to 0.55 degrees, it is accompanied by repeated charge and discharge. Since the physical stress of the lithium-containing composite oxide can be prevented, a positive electrode active material having a longer life can be provided.

  Furthermore, when the positive electrode active material includes the lithium-containing composite oxide of the general formula (1) coated with carbon, the physical stress of the lithium-containing composite oxide that accompanies repeated charge / discharge can be prevented. A positive electrode active material having a long lifetime can be provided.

3 is a powder X-ray diffraction pattern of a positive electrode active material in Production Example 1. FIG. 6 is a powder X-ray diffraction pattern of a positive electrode active material in Production Example 2. FIG. 3 is a powder X-ray diffraction pattern of a positive electrode active material in Comparative Production Example 1. FIG. It is a schematic sectional drawing of a secondary battery.

The present invention will be described in detail below.
(1) the positive electrode active material (1) lithium-containing composite oxide positive electrode active material, the general formula (1): include _{LiFe 1-x Q x P 1} -y W lithium-containing composite oxide represented by _y O ₄ It is out.
Q is at least one selected from the group consisting of Zr, Sn and Y. Therefore, you may select 2 or 3 types simultaneously. By selecting Q from these groups, it is possible to prevent physical stress (volume shrinkage expansion) of the lithium-containing composite oxide that accompanies repeated charge / discharge (Li insertion / desorption), so that the positive electrode active material having a longer lifetime Can provide. Further, among these, it is preferable to select at least Zr that is more ionic than Fe. By selecting Zr, the bond between the metal (Fe and Zr) constituting the lithium-containing composite oxide and oxygen can be strengthened, so that a positive electrode active material that is more resistant to physical stress can be provided. Although Fe and Zr can take various valences, the valence for defining “x” in the general formula (1) means an average value.

  W is at least one selected from Si and Al. Therefore, two types may be selected simultaneously. By selecting W from these groups, it is possible to prevent physical stress (volume shrinkage expansion) of the lithium-containing composite oxide that accompanies repeated charge / discharge (Li insertion / desorption), so that the positive electrode active material having a longer lifetime Can provide. Further, among these, it is preferable to select at least Si having stronger ionicity than P. By selecting Si, since the bond between the metal (Fe and Zr) constituting the lithium-containing composite oxide and oxygen can be strengthened, a positive electrode active material that is more resistant to physical stress can be provided.

Q and W are preferably a combination of Zr and P from the viewpoint of providing a positive electrode active material that is more resistant to physical stress.
x is in the range of 0 <x <1. Within this range, it is possible to provide a positive electrode active material that is more resistant to physical stress than LiFePO ₄ in which Q and W are not substituted. Moreover, it is more preferable that x is in the range of 0.05 to 0.33. Within this range, the crystal structure of the lithium-containing composite oxide can be made dominant in the olivine structure, so that a positive electrode active material that is more resistant to physical stress can be provided. A more preferable range is 0.125 to 0.25.

y is in the range of 0 <y <1. Within this range, it is possible to provide a positive electrode active material that is more resistant to physical stress than LiFePO ₄ in which Q and W are not substituted. Moreover, it is more preferable that y is in the range of 0.025 to 0.66. Within this range, the crystal structure of the lithium-containing composite oxide can be made dominant in the olivine structure, so that a positive electrode active material that is more resistant to physical stress can be provided. A more preferable range is 0.25 to 0.5.
Furthermore, it is particularly preferable that x and y are in the range of 0.125 to 0.25 and 0.25 to 0.5, respectively. By setting from these ranges, a positive electrode active material particularly resistant to physical stress can be provided.

  Here, in the general formula (1), the number of Li atoms is not specified, but is not limited to “1” because it increases or decreases by charging or discharging. The number of atoms of Li is in a range of numbers that can exist in the lithium-containing composite oxide. Usually, it can be adjusted between 0 in the charged state and 1 in the discharged state.

Further, the lithium-containing composite oxide has a (200) plane, (101) plane, (111) plane, (201) plane, (211) in a powder X-ray diffraction measurement result using Cu—Kα rays as a radiation source. There is a specific relationship between the intensity of diffraction peaks of the plane, (020) plane, and (311) plane. Specifically, when the intensity of the diffraction peak of the (311) plane existing between 2θ = 35 to 36 degrees is 100, the specific relationship is as follows:
The intensity of the diffraction peak on the (200) plane between 2θ = 16.5-17.5 degrees is in the range of 25-50,
The intensity of the diffraction peak on the (101) plane between 2θ = 20-21 degrees is in the range of 70-85,
The intensity of diffraction peaks on the (111 and 201) planes between 2θ = 25-26 degrees is in the range of 95-110,
The intensity of diffraction peaks on the (211 and 020) plane between 2θ = 29 and 30 degrees is in the range of 70 to 100. The diffraction peak here means a diffraction peak having the maximum intensity within the range of 2θ. Within these ranges, a positive electrode active material resistant to physical stress can be provided. The reason for this is thought to be that Q, which substitutes Fe such as zirconium, has a strong binding force with oxygen, so that a stronger crystal structure can be obtained by substituting part of iron with Q. Q has more electrons than iron and scatters X-rays more strongly. Therefore, when a part of iron is replaced with Q, the diffraction intensity from the diffraction surface due to iron increases, so that the diffraction intensities of the (101) plane and (211) increase.

(200) plane diffraction peak intensity is less than 25, (101) plane diffraction peak intensity is less than 70, (111) (201) plane diffraction peak intensity is less than 95, (211) (020) plane When the intensity of the diffraction peak is less than 70, iron is not sufficiently substituted with Q, so that the crystal structure becomes brittle and the cycle characteristics may be deteriorated.
(200) plane diffraction peak intensity is greater than 50, (101) plane diffraction peak intensity is greater than 85, (111) (201) plane diffraction peak intensity is greater than 110, (211) (020) ) When the intensity of the diffraction peak on the surface is greater than 100, the amount of substitution of Q for iron is too large, and as a result, the capacity may decrease.

When the intensity of the diffraction peak of the (311) plane existing between 2θ = 35 to 36 degrees is 100,
The intensity of the diffraction peak on the (200) plane is more preferably in the range of 30 to 45.
Further, the intensity of diffraction peaks on the (111 and 201) planes is more preferably in the range of 100 to 105.
Further, the intensity of the diffraction peak on the (211 and 020) plane is more preferably in the range of 75 to 95.

As a specific lithium-containing composite oxide that can satisfy the relationship of the diffraction peak,
LiFe _1-x Zr _x P _1-y Si _y O ₄ (0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.66)
_{LiFe 1-x Zr x P 1} -y Al y O 4 (0.05 ≦ x ≦ 0.33,0.05 ≦ y ≦ 0.33)
LiFe _1-x Sn _x P _1-y Si _y O ₄ (0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.66)
_{LiFe 1-x Sn x P 1} -y Al y O 4 (0.05 ≦ x ≦ 0.33,0.05 ≦ y ≦ 0.33)
LiFe _1-x Y _x P _1-y Si _y O ₄ (0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.33)
_{LiFe 1-x Y x P 1} -y Al y O 4 (0.05 ≦ x ≦ 0.33,0.025 ≦ y ≦ 0.16)

LiFe _1-x (Zr, Sn) _x P _1-y Si _y O ₄
(0.05 ≦ x ≦ 0.33, 0.1 ≦ y ≦ 0.66, atomic ratio of Zr and Sn 1: 0.99: 0.01 to 0.01: 0.99)
_{LiFe 1-x (Zr, Sn} ) x P 1-y Al y O 4
(0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.33, atomic ratio of Zr and Sn 10.99: 0.01 to 0.01: 0.99)
LiFe _1-x (Zr, Y) _x P _1-y Si _y O ₄
(0.05 ≦ x ≦ 0.66, 0.05 ≦ y ≦ 0.66, atomic ratio of Zr and Y 1: 0.99: 0.01 to 0.01: 0.99)
_{LiFe 1-x (Zr, Y} ) x P 1-y Al y O 4
(0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.33, atomic ratio of Zr and Y 1: 0.99: 0.01 to 0.01: 0.99)
LiFe _1-x (Sn, Y) _x P _1-y Si _y O ₄
(0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.66, atomic ratio of Sn and Y 1: 0.99: 0.01 to 0.01: 0.99)
_{LiFe 1-x (Sn, Y} ) x P 1-y Al y O 4
(0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.33, atomic ratio of Sn and Y 1: 0.99: 0.01 to 0.01: 0.99)

LiFe _1-x (Zr, Sn, Y) _x P _1-y Si _y O ₄
(0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.66, atomic ratio of Zr, Sn, and Y 0.01: 0.01: 0.98 to 0.01: 0.98: 0 .01-0.98: 0.01: 0.01)
LiFe _1-x (Zr, Sn, Y) _x P _1-y Al _y O ₄
(0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.66, atomic ratio of Zr, Sn, and Y 0.01: 0.01: 0.98 to 0.01: 0.98: 0 .01-0.98: 0.01: 0.01)
LiFe _1-x Zr _x P _1-y (Si, Al) _y O ₄
(0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.66, atomic ratio of Si and Al 1: 0.99: 0.01 to 0.01: 0.99)
LiFe _1-x Sn _x P _1-y (Si, Al) _y O ₄
(0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.66, atomic ratio of Si and Al 0.99: 0.01 to 0.01: 0.99)
LiFe _1-x Y _x P _1-y (Si, Al) _y O ₄
(0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.66, atomic ratio of Si and Al 0.99: 0.01 to 0.01: 0.99)

LiFe _1-x (Zr, Sn) _x P _1-y (Si, Al) _y O ₄
(0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.66, atomic ratio of Zr and Sn 0.99: 0.01 to 0.01: 0.99, atomic ratio of Si and Al 0 .99: 0.01-0.01: 0.99)
LiFe _1-x (Zr, Y) _x P _1-y (Si, Al) _y O ₄
(0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.66, atomic ratio of Zr to Y: 0.99: 0.01 to 0.01: 0.99, atomic ratio of Si to Al: 0 .99: 0.01-0.01: 0.99)
LiFe _1-x (Sn, Y) _x P _1-y (Si, Al) _y O ₄
(0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.66, atomic ratio of Sn to Y 0.99: 0.01 to 0.01: 0.99, atomic ratio of Si to Al 0 .99: 0.01-0.01: 0.99)
LiFe _1-x (Zr, Sn, Y) _x P _1-y (Si, Al) _y O ₄
(0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.66, atomic ratio of Zr, Sn, and Y 0.01: 0.01: 0.98 to 0.01: 0.98: 0 0.01 to 0.98: 0.01: 0.01, atomic ratio of Si and Al 0.99: 0.01 to 0.01: 0.99)
Etc.

  Furthermore, a lithium-containing composite oxide satisfying 0.05 ≦ x ≦ 0.33 and 0.05 ≦ y ≦ 0.66 as the ranges of x and y is preferable. In particular, in the lithium-containing composite oxide in this range, x and y are preferably in the following ranges depending on the valence of Q and the type of W.

When Q is a tetravalent element and W is Si, the ranges of x and y are 0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.66, and 2x = y It is preferable that
When Q is a trivalent element and W is Si, the ranges of x and y are 0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.33, and x = y It is preferable that
When Q is a tetravalent element and W is Al, the ranges of x and y are 0.05 ≦ x ≦ 0.33, 0.05 ≦ y ≦ 0.33, and x = y It is preferable that
When Q is a trivalent element and W is Al, the ranges of x and y are 0.05 ≦ x ≦ 0.33, 0.025 ≦ y ≦ 0.16, and x = 2y It is preferable that

When the intensity of the diffraction peak of the (311) plane existing between 2θ = 35 to 36 degrees is 100,
The intensity of the diffraction peak on the (200) plane between 2θ = 16.5-17.5 degrees is in the range of 25-50,
The intensity of the diffraction peak on the (101) plane between 2θ = 20-21 degrees is in the range of 70-85,
The intensity of diffraction peaks on the (111 and 201) planes between 2θ = 25-26 degrees is in the range of 95-110,
When the intensity of the diffraction peak on the (211 and 020) plane between 2θ = 29 to 30 degrees is in the range of 70 to 100, a positive electrode active material that is more resistant to physical stress can be provided.

Next, it is preferable that the half width of the diffraction peak on the (311) plane is in the range of 0.3 to 0.55 degrees. By having a half width within this range, a positive electrode active material that is more resistant to physical stress can be provided. The reason is considered to depend on the crystallinity of the primary particles. When the full width at half maximum is less than 0.3, it means that the crystallinity is high, and the size of the primary particles increases and the discharge characteristics may deteriorate. If it is larger than 0.55, it is considered that the crystallinity is poor or the substitution of Fe with Q (especially zirconium) is not performed uniformly, so that the cycle characteristics may be deteriorated. A more preferable range of the half width is 0.35 to 0.5 degrees.
In addition, the half width of the diffraction peak of the (200) plane, the half width of the diffraction peak of the (101) plane, the half width of the diffraction peak of the (111 and 201) plane, and the half of the diffraction peak of the ((211 and 020) plane If the value ranges are in the range of 0.3 to 0.6 degrees, a positive electrode active material that is more resistant to physical stress can be provided.

  The lithium-containing composite oxide is usually used in the form of particles. In the case of having a particle shape, it is preferable that the particle size is as small as possible because the efficiency of lithium ion insertion / desorption can be increased. The particle size is preferably 10 μm or less. The lower limit of the particle size is about 50 nm, which is realistic from the balance between the efficiency of insertion / desorption and the manufacturing cost. The particle diameter is a value measured with a laser diffraction particle size distribution device manufactured by Nikkiso Co., Ltd., Microtrack MT3000II.

(2) Carbon coating The lithium-containing composite oxide may be coated with carbon. By covering with carbon, the conductivity of electrons to the lithium-containing composite oxide can be increased, so that the efficiency of insertion / extraction of lithium ions can be increased. The coating with carbon may be the entire surface or a part of the surface of the lithium-containing composite oxide. The entire surface is preferable because the conductivity of electrons to the lithium-containing composite oxide can be further increased.
The coating amount of carbon is about 1 to 10 parts by weight with respect to 100 parts by weight of the lithium-containing composite oxide. When the amount is less than 1 part by weight, the effect of the carbon coating may not be sufficiently obtained. When the amount is more than 10 parts by weight, the film made of carbon covering the lithium-containing composite oxide becomes too thick, and on the contrary, the efficiency of insertion / extraction of lithium ions may be hindered. A more preferable coating amount of carbon is about 2 to 5 parts by weight.

(3) Other positive electrode active material, to the extent that does not impair the effects of the present _{invention, LiCoO 2, LiNiO 2, LiFeO} 2, LiMnO 2, LiMn 2 O 4, LiCoPO 4, LiNiPO 4, LiMnPO 4, LiFePO 4 , etc. Other oxides may be included.

(4) Manufacturing method The positive electrode active material can be manufactured by using any combination of carbonates, hydroxides, chlorides, sulfates, acetates, oxides, oxalates, nitrates, and the like as raw materials. . These raw materials may contain crystal water. As a production method, a solid phase method, a sol-gel method, a melt quench method, a mechanochemical method, a coprecipitation method, a hydrothermal method, a spray pyrolysis method, or the like can be used.

In addition, as a method of coating the lithium-containing composite oxide with carbon, a method of mixing carbon and a lithium-containing composite oxide, which is generally performed in olivine type lithium iron phosphate, or an organic compound and lithium A method of carbonizing an organic compound and then mixing a raw material of the lithium-containing composite oxide and an organic compound, and simultaneously forming a lithium-containing composite oxide and coating it with carbon Etc. In addition to this method, the following method is also exemplified. That is, a complex oxide (Fe _1-x Q _x P _{1 -y} W _y O ₄ ) containing no Li is produced in a solution containing a polymerizable organic compound (for example, aniline). In this manufacturing process, the organic compound is oxidized and polymerized by trivalent iron in Fe, and a shell made of a polymer of the organic compound can be formed on the surface of the composite oxide. By heat-treating the obtained composite oxide and the lithium compound in a reducing atmosphere, a lithium-containing composite oxide having a carbon film derived from a polymer can be obtained. In this method, the surface of the lithium-containing composite oxide can be coated more uniformly with carbon.

(II) Nonaqueous electrolyte secondary battery A secondary battery has a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator. Hereinafter, each constituent material will be described.
(A) Positive Electrode The positive electrode includes a positive electrode active material, a conductive material, a binder, and a current collector. For example, a known mixture of an active material, a conductive material, and a binder mixed with an organic solvent is applied to the current collector. It can produce by the method of. If the lithium-containing composite oxide is covered with carbon and its conductivity is sufficient, the use of a conductive material may be omitted.

As binders (binders), polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, ethylene propylene diene polymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluoro rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, Nitrocellulose or the like can be used.
As the conductive material, acetylene black, carbon, graphite, natural graphite, artificial graphite, needle coke, or the like can be used.
As the current collector, foamed (porous) metal having continuous pores, metal formed in a honeycomb shape, sintered metal, expanded metal, non-woven fabric, plate, foil, perforated plate, foil, and the like can be used. .

As the organic solvent, N-methyl-2-pyrrolidone, toluene, cyclohexane, dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. are used. be able to.
The thickness of the positive electrode is preferably about 0.01 to 20 mm. If it is too thick, the conductivity is lowered, and if it is too thin, the capacity per unit area is lowered. The positive electrode obtained by coating and drying may be compacted by a roller press or the like in order to increase the packing density of the active material.

(B) Negative electrode A negative electrode can be produced by a known method. Specifically, it can be manufactured in the same manner as described in the method for manufacturing the positive electrode. That is, after mixing the known binder described in the method for producing the positive electrode, the known conductive material, and the negative electrode active material, the mixed powder is formed into a sheet shape, and the formed body is made of a conductor such as stainless steel or copper. What is necessary is just to crimp | bond to a net | network (current collector). Moreover, it can also produce by apply | coating the slurry obtained by mixing the said mixed powder with the well-known organic solvent demonstrated by the positive electrode preparation method on metal substrates, such as copper.
A known material can be used as the negative electrode active material. In order to constitute a high energy density battery, it is preferable that the potential at which lithium is inserted / desorbed is close to the deposition / dissolution potential of metallic lithium. A typical example is a carbon material such as natural or artificial graphite in the form of particles (scale-like, lump-like, fibrous, whisker-like, spherical, pulverized particles, etc.).

Examples of the artificial graphite include graphite obtained by graphitizing mesocarbon microbeads, mesophase pitch powder, isotropic pitch powder, and the like. Also, graphite particles having amorphous carbon attached to the surface can be used. Among these, natural graphite is more preferable because it is inexpensive, close to the redox potential of lithium, and can constitute a high energy density battery.
Further, lithium transition metal oxide, lithium transition metal nitride, transition metal oxide, silicon oxide, and the like can be used as the negative electrode active material. Among these, Li ₄ Ti ₅ O ₁₂ is more preferable because it has high potential flatness and a small volume change due to charge and discharge.

(C) Nonaqueous electrolyte As the nonaqueous electrolyte, for example, an organic electrolyte, a gel electrolyte, a polymer solid electrolyte, an inorganic solid electrolyte, a molten salt, or the like can be used. After injecting the nonaqueous electrolyte, the opening of the secondary battery container is sealed. Gas generated by energization before sealing may be removed.
Examples of the organic solvent constituting the organic electrolyte include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC) and butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate, and dipropyl carbonate. Chain carbonates such as γ-butyrolactone (GBL), lactones such as γ-valerolactone, furans such as tetrahydrofuran and 2-methyltetrahydrofuran, diethyl ether, 1,2-dimethoxyethane, 1,2-diethoxy Examples include ethers such as ethane, ethoxymethoxyethane, dioxane, dimethyl sulfoxide, sulfolane, methyl sulfolane, acetonitrile, methyl formate, methyl acetate, and the like. it can.
Moreover, since cyclic carbonates such as PC, EC and butylene carbonate are high-boiling solvents, they are suitable as solvents to be mixed with GBL.

Examples of the electrolyte salt constituting the organic electrolyte include lithium borofluoride (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium trifluoroacetate (LiCF ₃ COO) ), Lithium salts such as lithium bis (trifluoromethanesulfone) imide (LiN (CF ₃ SO ₂ ) ₂ ), and one or more of these may be used in combination. The salt concentration of the electrolytic solution is preferably 0.5 to 3 mol / l.

(D) Separator Examples of the separator include porous materials and nonwoven fabrics. As the material of the separator, the above-described one that does not dissolve or swell in the organic solvent contained in the electrolyte is preferable. Specific examples include polyester polymers, polyolefin polymers (for example, polyethylene and polypropylene), ether polymers, and inorganic materials such as glass.

(E) Other members Various materials used for conventionally known nonaqueous electrolyte secondary batteries can be used for other members such as battery containers, and there is no particular limitation.

(F) Manufacturing method of secondary battery The secondary battery includes a laminate including, for example, a positive electrode, a negative electrode, and a separator sandwiched therebetween. The laminate may have, for example, a strip-like planar shape. Moreover, when producing a cylindrical or flat battery, the laminate may be wound.
One or more of the laminates are inserted into the battery container. Usually, the positive electrode and the negative electrode are connected to the external conductive terminal of the battery. Thereafter, the battery container is sealed to block the positive electrode, the negative electrode, and the separator from the outside air.

  In the case of a cylindrical battery, the sealing method is generally a method in which a lid having a resin packing is fitted into the opening of the battery container and the battery container and the lid are caulked. In the case of a square battery, a method of attaching a lid called a metallic sealing plate to the opening and performing welding can be used. In addition to these methods, a method of sealing with a binder and a method of fixing with a bolt via a gasket can also be used. Furthermore, a method of sealing with a laminate film in which a thermoplastic resin is attached to a metal foil can also be used. An opening for electrolyte injection may be provided at the time of sealing.

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to a following example. The reagents used in the production examples were special grade reagents manufactured by Kishida Chemical Co. unless otherwise specified.
Production Example 1
First, 30 ml of ethanol was weighed into a sample bottle as a solvent. As a starting material, 1.3196 g of LiCH ₃ COO as a lithium source was weighed, Fe (NO ₃ ) ₃ · 9H ₂ O as an iron source, ZrCl ₄ as a zirconium source, H ₃ PO ₄ (purity 85%) as a phosphorus source, silicon Si (OC ₂ H ₅ ) ₄ as a source was weighed in a molar ratio of Li: Fe: Zr: P: Si = 1: 0.75: 0.25: 0.5: 0.5, and the solvent It was dissolved in order. After all the raw materials are dissolved in a solvent, the mixture is stirred for 1 week at room temperature with a stirrer, and then left in a constant temperature bath at 40 ° C. for 24 hours to evaporate ethanol to obtain a brown powder. It was.

15 wt% sucrose was added to the obtained powder, mixed well in an agate mortar, and then pressed into a pellet. The obtained pellet-like mixture was baked at 600 ° C. for 12 hours in a nitrogen atmosphere to obtain a sample made of Li _a Fe _0.75 Zr _0.25 P _0.5 Si _0.5 O ₄ . On the surface of this sample, 2.4 parts by weight of carbon adhered to 100 parts by weight of the sample, and it was confirmed that the average particle diameter was about 5 μm. The obtained sample is designated as A1.

Production Example 2
First, 30 ml of ethanol was weighed into a sample bottle as a solvent. As a starting material, 1.3196 g of LiCH ₃ COO as a lithium source was weighed, Fe (NO ₃ ) ₃ · 9H ₂ O as an iron source, ZrCl ₄ as a zirconium source, H ₃ PO ₄ (purity 85%) as a phosphorus source, silicon Si (OC ₂ H ₅ ) ₄ as a source was weighed in a molar ratio of Li: Fe: Zr: P: Si = 1: 0.85: 0.15: 0.7: 0.3, and the solvent It was dissolved in order. After all the raw materials are dissolved in a solvent, the mixture is stirred for 1 week at room temperature with a stirrer, and then left in a constant temperature bath at 40 ° C. for 24 hours to evaporate ethanol to obtain a brown powder. It was.

15 wt% sucrose was added to the obtained powder, mixed well in an agate mortar, and then pressed into a pellet. The obtained pellet-like mixture was baked at 600 ° C. for 12 hours in a nitrogen atmosphere to obtain a sample made of Li _a Fe _0.85 Zr _0.15 P _0.7 Si _0.3 O ₄ . On the surface of this sample, 2.4 parts by weight of carbon adhered to 100 parts by weight of the sample, and it was confirmed that the average particle diameter was about 5 μm. The obtained sample is designated as A2.

Production Example 3
First, 30 ml of ethanol was weighed into a sample bottle as a solvent. As a starting material, 1.3196 g of LiCH ₃ COO as a lithium source was weighed, Fe (NO ₃ ) ₃ · 9H ₂ O as an iron source, ZrCl ₄ as a zirconium source, H ₃ PO ₄ (purity 85%) as a phosphorus source, silicon Si (OC ₂ H ₅ ) ₄ as a source was weighed in a molar ratio of Li: Fe: Zr: P: Si = 1: 0.875: 0.125: 0.75: 0.25, and the solvent It was dissolved in order. After all the raw materials are dissolved in a solvent, the mixture is stirred for 1 week at room temperature with a stirrer, and then left in a constant temperature bath at 40 ° C. for 24 hours to evaporate ethanol to obtain a brown powder. It was.

15 wt% sucrose was added to the obtained powder, mixed well in an agate mortar, and then pressed into a pellet. The obtained pellet-like mixture was baked in a nitrogen atmosphere at 600 ° C. for 12 hours to obtain a sample made of Li _a Fe _0.875 Zr _0.125 P _0.75 Si _0.25 O ₄ . On the surface of this sample, 2.4 parts by weight of carbon was attached to 100 parts by weight of the sample, and it was confirmed that the average particle diameter was about 9 μm. The obtained sample is designated as A3.

Production Example 4
First, 30 ml of methanol was weighed as a solvent in a sample bottle. As a starting material, 1.3196 g of LiCH ₃ COO as a lithium source was weighed, Fe (NO ₃ ) ₃ · 9H ₂ O as an iron source, ZrCl ₄ as a zirconium source, H ₃ PO ₄ (purity 85%) as a phosphorus source, silicon Si (OC ₂ H ₅ ) ₄ as a source was weighed in a molar ratio of Li: Fe: Zr: P: Si = 1: 0.9: 0.1: 0.8: 0.2, and the solvent It was dissolved in order. After all the raw materials are dissolved in a solvent, the mixture is stirred for 1 week at room temperature with a stirrer, and then left in a constant temperature bath at 40 ° C. for 24 hours to evaporate ethanol to obtain a brown powder. It was.

15 wt% sucrose was added to the obtained powder, mixed well in an agate mortar, and then pressed into a pellet. The obtained pellet-like mixture was baked at 600 ° C. for 12 hours in a nitrogen atmosphere to obtain a sample made of Li _a Fe _0.9 Zr _0.1 P _0.8 Si _0.2 O ₄ . On the surface of this sample, 2.4 parts by weight of carbon was attached to 100 parts by weight of the sample, and it was confirmed that the average particle diameter was about 9 μm. The obtained sample is designated as A4.

Production Example 5
First, 30 ml of methanol was weighed as a solvent in a sample bottle. As a starting material, 1.3196 g of LiCH ₃ COO as a lithium source was weighed, Fe (NO ₃ ) ₃ · 9H ₂ O as an iron source, ZrCl ₄ as a zirconium source, H ₃ PO ₄ (purity 85%) as a phosphorus source, silicon Si (OC ₂ H ₅ ) ₄ as a source was weighed in a molar ratio of Li: Fe: Zr: P: Si = 1: 0.925: 0.075: 0.85: 0.15, and the solvent It was dissolved in order. After all the raw materials are dissolved in a solvent, the mixture is stirred for 1 week at room temperature with a stirrer, and then left in a constant temperature bath at 40 ° C. for 24 hours to evaporate ethanol to obtain a brown powder. It was.

15 wt% sucrose was added to the obtained powder, mixed well in an agate mortar, and then pressed into a pellet. The obtained pellet-like mixture was baked at 600 ° C. for 12 hours in a nitrogen atmosphere to obtain a sample made of Li _a Fe _0.925 Zr _0.075 P _0.85 Si _0.15 O ₄ . On the surface of this sample, 2.4 parts by weight of carbon was attached to 100 parts by weight of the sample, and it was confirmed that the average particle diameter was about 9 μm. The obtained sample is designated as A5.

Comparative production example 1
First, 30 ml of ethanol was weighed into a sample bottle as a solvent. As a starting material, 1.3788 g of LiNO ₃ as a lithium source was weighed, FeCl ₃ .6H ₂ O as an iron source, ZrCl ₄ as a zirconium source, H ₃ PO ₄ (purity 85%) as a phosphorus source, Si (OC as a silicon source) ₂ H ₅ ) ₄ is weighed in a molar ratio of Li: Fe: Zr: P: Si = 1: 0.75: 0.25: 0.5: 0.5 and dissolved in the solvent in order. I went. After all the raw materials were dissolved in the solvent, the mixture was stirred with a stirrer at room temperature for 1 week, and then left in a constant temperature bath at 40 ° C. for 24 hours to obtain a brown powder.

15 wt% sucrose was added to the obtained powder, mixed well in an agate mortar, and then pressed into a pellet. The obtained pellet-like mixture was baked at 600 ° C. for 12 hours in a nitrogen atmosphere to obtain a sample made of Li _a Fe _0.75 Zr _0.25 P _0.5 Si _0.5 O ₄ . It was confirmed that 2.4 parts by weight of carbon adhered to 100 parts by weight of the sample on the surface of the sample. The obtained sample is designated as B1.

Comparative production example 2
First, 30 ml of ethanol was weighed into a sample bottle as a solvent. As a starting material, 0.4789 g of LiOH was weighed as a lithium source, FeCl ₃ .6H ₂ O as an iron source, ZrCl ₄ as a zirconium source, H ₃ PO ₄ (purity 85%) as a phosphorus source, and Si (OC ₂ as a silicon source). H ₅ ) ₄ was weighed in a molar ratio of Li: Fe: Zr: P: Si = 1: 0.875: 0.125: 0.75: 0.25 and dissolved in the solvent in order. It was. After all the raw materials were dissolved in the solvent, the mixture was stirred with a stirrer at room temperature for 1 week, and then left in a constant temperature bath at 40 ° C. for 24 hours to obtain a brown powder.

15 wt% sucrose was added to the obtained powder, mixed well in an agate mortar, and then pressed into a pellet. The obtained pellet-like mixture was baked in a nitrogen atmosphere at 600 ° C. for 12 hours to obtain a sample made of Li _a Fe _0.875 Zr _0.125 P _0.75 Si _0.25 O ₄ . It was confirmed that 2.4 parts by weight of carbon adhered to 100 parts by weight of the sample on the surface of the sample. The obtained sample is designated as B2.

Comparative production example 3
First, 30 ml of methanol was weighed as a solvent in a sample bottle. 0.4789 g of LiOH as a lithium source was weighed as a starting material, FeCl ₃ · 6H ₂ O as an iron source, ZrOCl ₂ · 8H ₂ O as a zirconium source, H ₃ PO ₄ (purity 85%) as a phosphorus source, and a silicon source Si (OC ₂ H ₅ ) ₄ was weighed in a molar ratio of Li: Fe: Zr: P: Si = 1: 0.9: 0.1: 0.8: 0.2, It was dissolved in order. After all the raw materials were dissolved in the solvent, the mixture was stirred with a stirrer at room temperature for 1 week, and then left in a constant temperature bath at 40 ° C. for 24 hours to obtain a brown powder.

15 wt% sucrose was added to the obtained powder, mixed well in an agate mortar, and then pressed into a pellet. The obtained pellet-like mixture was baked at 600 ° C. for 12 hours in a nitrogen atmosphere to obtain a sample made of Li _a Fe _0.9 Zr _0.1 P _0.8 Si _0.2 O ₄ . It was confirmed that 2.5 parts by weight of carbon adhered to 100 parts by weight of the sample on the surface of the sample. The obtained sample is designated as B3.

Comparative production example 4
First, 30 ml of ethanol was weighed into a sample bottle as a solvent. As a starting material, 1.3196 g of LiCH ₃ COO as a lithium source was weighed, Fe (NO ₃ ) ₃ · 9H ₂ O as an iron source, ZrCl ₄ as a zirconium source, H ₃ PO ₄ (purity 85%) as a phosphorus source, silicon Si (OC ₂ H ₅ ) ₄ as a source was weighed in a molar ratio of Li: Fe: Zr: P: Si = 1: 0.98: 0.02: 0.96: 0.04 to obtain a solvent. It was dissolved in order. After all the raw materials were dissolved in the solvent, the mixture was stirred with a stirrer at room temperature for 1 week, and then left in a constant temperature bath at 40 ° C. for 24 hours to obtain a brown powder.

15 wt% sucrose was added to the obtained powder, mixed well in an agate mortar, and then pressed into a pellet. The obtained pellet-like mixture was baked at 600 ° C. for 12 hours in a nitrogen atmosphere to obtain a sample made of Li _a Fe _0.98 Zr _0.02 P _0.96 Si _0.04 O ₄ . It was confirmed that 2.4 parts by weight of carbon adhered to 100 parts by weight of the sample on the surface of the sample. The obtained sample is designated as B4.

  With respect to these positive electrode active materials, powder X-ray diffraction measurement was performed using an X-ray analyzer MiniFlexII manufactured by Rigaku Corporation using Cu-Kα rays as an X-ray source. 1-3 show powder X-ray diffraction patterns of A1, A2 and B1. Table 1 shows the intensities and half-value widths of the diffraction peaks at 17.1, 20.6, 25.5, 29.6, and 35.6 ° 2θ obtained from the measurement results.

From Table 1, all the samples of production examples
There is a specific relationship between the intensity of diffraction peaks on the (200) plane, (101) plane, (111) plane, (201) plane, (211) plane, (020) plane, and (311) plane. Specifically, when the intensity of the diffraction peak of the (311) plane existing between 2θ = 35 to 36 degrees is 100, the specific relationship is as follows:
The intensity of the diffraction peak on the (200) plane between 2θ = 16.5-17.5 degrees is in the range of 30-45,
The intensity of the diffraction peak on the (101) plane between 2θ = 20-21 degrees is in the range of 70-85,
The intensity of diffraction peaks on the (111 and 201) planes between 2θ = 25-26 degrees is in the range of 100-105,
The intensity of diffraction peaks on the (211 and 020) plane between 2θ = 29 to 30 degrees has a plurality of peak intensities in the range of 75 to 95.

Example 1
Using the obtained positive electrode active material, a secondary battery was produced by the following method.
A1 was pulverized in an agate mortar. About 80% by weight of the pulverized product obtained, about 10% by weight of acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, and about 10% by weight of Teflon (registered trademark) resin powder (Kureha) as a binder Kureha KF polymer made by Kagaku Co.).
The mixture was dissolved and dispersed in N-methyl-2-pyrrolidone (manufactured by Kishida Chemical Co., Ltd.) to form a slurry, which was applied to both surfaces of an aluminum foil having a thickness of 20 μm by a doctor blade method. The coating amount was about 5 mg / cm ² . After the coating film was dried, it was cut so that the electrode application surface was 2 cm × 2 cm and pressed to produce a positive electrode (total thickness 30 μm).

As the negative electrode active material, natural graphite powder (lithium ion battery negative electrode material MAG manufactured by Hitachi Chemical Co., Ltd.) was used. About 10% by weight of Teflon (registered trademark) resin powder was mixed with this negative electrode active material as a binder. This mixture is dissolved and dispersed in N-methyl-2-pyrrolidone to form a slurry, which is applied to both sides of a 20 μm thick copper foil, dried and then pressed to produce a negative electrode (total thickness 30 μm). did.
The positive electrode and the negative electrode produced as described above were cut out to a size of 30 mm × 30 mm, respectively, and an aluminum tab having a width of 3 mm and a length of 50 mm as a current introduction terminal of the secondary battery, a width of 3 mm for the negative electrode, A copper tab having a length of 50 mm was welded to prepare a positive electrode and a negative electrode.

A separator made of a polyolefin resin microporous membrane (Hypore manufactured by Asahi Kasei Co., Ltd.) was sandwiched between the positive electrode and the negative electrode. The obtained laminate is sandwiched between two laminated metal foils laminated with a thermoplastic resin as a battery exterior, and then the surroundings are thermally welded except for the electrolyte injection opening. Sealed.
An electrolyte in which 1 mol / liter LiPF ₆ was dissolved in 50% by volume of ethylene carbonate and 50% by volume of diethyl carbonate was introduced into the battery casing from the opening, thereby impregnating the electrolyte in the laminate.
After the impregnation, the secondary battery shown in FIG. 4 was obtained by sealing the opening. In FIG. 4, 1 is a positive electrode, 2 is a negative electrode, 3 is a separator, 4 is a positive electrode and a negative electrode tab, and 5 is a laminate.

Examples 2 and 3
A secondary battery was obtained in the same manner as in Example 1 except that A2 and A3 were used as shown in Table 2 instead of A1.
Examples 4 and 5
A secondary battery as in Example 1 except that A4 and A5 are used as shown in Table 2 instead of A1, and lithium titanate (Li ₄ Ti ₅ O ₁₂ ) is used instead of natural graphite powder. Got.

Comparative Examples 1-4
A secondary battery was obtained in the same manner as in Example 1 except that any of B1 to B4 was used as shown in Table 2 instead of A1.

The battery thus produced was charged and discharged in an environment at 25 ° C. The charging current was 0.3 mA, and the charging was terminated when the battery potential reached 4V. After charging was completed, discharging was performed at 0.3 mA, and discharging was completed when the battery potential reached 2.0V. Furthermore, charging / discharging was repeated at a current of 0.3 mA, the discharge capacity at the 100th time was measured, and the capacity retention rate was obtained by the following formula. The results are shown in Table 2.
Capacity retention = 100th discharge capacity / first discharge capacity

From Table 2, the secondary batteries of Examples 1 to 5 exhibited a high capacity retention rate of 90% or more when the negative electrode active material was a natural sunspot and 97% or more when Li ₄ Ti ₅ O ₁₂ was used.

1: positive electrode, 2: negative electrode, 3: separator, 4: positive electrode and negative electrode tab, 5: laminate

Claims (7)

General formula (1): LiFe _1-x Q _x P _1-y W _y O ₄ (wherein Q is at least one selected from the group consisting of Zr, Sn and Y, and W represents Si and At least one selected from Al, x is 0 <x <1, y is 0 <y <1, and
When the intensity of a diffraction peak of (311) plane existing between 2θ = 35 to 36 degrees in powder X-ray diffraction measurement using Cu—Kα ray as a radiation source is 100, 2θ of 25-50 = 16. Intensity of diffraction peak of (200) plane between 5 and 17.5 degrees, intensity of diffraction peak of (101) plane between 20 and 21 degrees of 70 to 85, 2θ = 25 of 95 to 110 Lithium-containing composite oxidation showing the intensity of the (111 and 201) plane diffraction peaks between ˜26 degrees and the intensity of the (211 and 020) plane diffraction peaks between 70 and 100 2θ = 29-30 degrees. A positive electrode active material comprising a material.   The positive electrode active material according to claim 1, wherein the positive electrode active material includes the lithium-containing composite oxide of the general formula (1) that is the Q that is Zr and the W that is Si.   The said positive electrode active material contains the lithium containing complex oxide of the said General formula (1) which is the said x between 0.05-0.33 and the said y between 0.025-0.66. The positive electrode active material according to 1 or 2.   The said positive electrode active material contains the lithium containing complex oxide of the said General formula (1) which has the half value width of the diffraction peak of (100) plane of 0.3-0.55 degree | times. The positive electrode active material described in 1.   The positive electrode active material according to claim 1, wherein the positive electrode active material includes a lithium-containing composite oxide of the general formula (1) coated with carbon.   A positive electrode comprising the positive electrode active material according to claim 1, a conductive material, and a binder.   A non-aqueous electrolyte secondary battery comprising a positive electrode including the positive electrode active material according to claim 1, a negative electrode, an electrolyte, and a separator.

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