JP2003017061A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress drop in capacity attendant in charging/discharging cycles of a lithium secondary battery using a LiCoO2 base positive active material. SOLUTION: In the lithium secondary battery using a lithium metal, a lithium alloy, or a lithium compound in a negative electrode, as a positive active material, Liy (Coy Mnx )O2 (wherein, M is at least one selected from Mn, Ti, Pb, Sn, Fe, Ni, In, and Bi; x+y=1) having a lattice constant c0 in the direction of c axis larger than a lattice constant c0 in the direction of c axis of LiCoO2 is used. The Liy (Coy Mx )O2 is preferable to be synthetisized by baking a mixture LiCoO2 and an oxide of M containing no lithium, and the use of LiCoO2 synthesized at 700 deg.C or lower is preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] [0001] The present invention relates to a lithium secondary battery.
And more specifically, the capacity associated with charge / discharge cycles.
The present invention relates to a lithium secondary battery with little deterioration. [0002] 2. Description of the Related Art As a positive electrode active material of a lithium secondary battery
Has been used for titanium disulfide, vanadium pentoxide,
Gun oxide, lithium manganese oxide, lithium cobalt
Oxides have been proposed, but recently, Li_XCo
O_TwoSuch as lithium cobalt oxide is about 4V
Because they have pressure (e.g.,
U.S. Pat. No. 4,302,518). However, Li_XCoO_TwoX value of about 0.7
In the following areas, Li_XCoO_TwoOxidizes organic electrolyte
It is thought that the reaction proceeds gradually with the charge-discharge cycle.
The capacity deteriorates. [0004] This will be described in detail._XCo
O_TwoLithium secondary batteries using
Li₁CoO_TwoAnd use it as a positive electrode active material.
After assembling the battery, charging the battery₁Co
O_TwoBy electrochemical extraction of Li from
i_XCoO_Two(X <1). However, Li_XCoO_TwoIs an unstable tetravalent
Because of the strong oxidizing power that contains cobalt,
Oxidizes the electrolyte and consequently the capacity with charge-discharge cycles
Is degraded. [0006] SUMMARY OF THE INVENTION The present invention has been described above.
Sea, Li_XCoO_TwoUsing lithium as a positive electrode active material
When a secondary battery is used for charging and discharging to a small value of x,
Solves the problem that the capacity deteriorates with the discharge cycle
Lithium with low capacity deterioration due to charge / discharge cycles
It is intended to provide a secondary battery. [0007] SUMMARY OF THE INVENTION The present invention provides a LiCoO_Two
And MnO_TwoLithium-free manganese oxides such as
Or TiO_Two, PbO_Two, SnO_TwoSuch as lithium
Baking a mixture with a tetravalent metal oxide that does not contain
LiCoO obtained by_TwoLattice constant c in the c-axis direction₀
Lattice constant c greater than₀The compound having
By using it as a positive electrode active material for secondary batteries,
It was found that the problem could be solved. In addition,
Akira says that Fe, Ni, In, Bi, etc.
When used instead, as in the case of Mn, lithium
Compounds useful as positive electrode active materials for secondary batteries
As a result, it has been found that the above problem can be solved.
It is. That is, the present invention relates to lithium metal, lithium
Using lithium alloy or lithium compound for negative electrode
In a secondary battery, LiCoO_Twoof
lattice constant c in the c-axis direction₀Lattice constant in c-axis direction larger than
Number c₀Li having_y(Co _yMn_x) O_Two(However,
M is Mn, Ti, Pb, Sn, Fe, Ni, In and
At least one metal selected from Bi, x +
y = 1) is used for a lithium secondary battery.
Related. [0009] DESCRIPTION OF THE PREFERRED EMBODIMENTS The above-mentioned lithium-free manga
As oxides, MnO_TwoBesides, for example, MnOO
H and the like. In addition, Ti, P other than manganese
b, Sn, Fe, Ni, In, Bi, etc.
Some oxides do not contain lithium and do not contain such lithium.
For example, TiO 2 may be TiO 2_Two, Pb
O_Two, SnO _TwoAnd the like. Hereinafter, the above Mn, Ti, Pb, Sn, F
oxides containing no lithium, such as e, Ni, In, Bi
Of these, lithium-free manganese oxide is taken as an example.
To explain, LiCoO_TwoAnd man without lithium
The compound obtained by calcining the mixture with the gun oxide is L
i_y(Co_yMn_x) O_TwoExpressed by the chemical formula of (x + y = 1)
Is done. This Li_y(Co_yMn_x) O_TwoRepresented by
The characteristics of the compound, for example, Mn was added at 20 mol%
Explaining the case as an example, adding 20 mol% of Mn
In this case, the compound is Li_0.8(Co_0.8Mn_0.2)
O_Twobecome. LiMO known so far_Two(M is C
o, Mn, Ni, Fe, V and two or more metals)
Is 1, but the Li used in the present invention is_y(Co_yMn_x)
O_TwoIn this case, Li becomes smaller than 1 by the added amount of Mn. Ma
This Li_y(Co_yMn _x) O_TwoThen, later in FIG.
As described on the basis of the above, the lattice constant c in the c-axis direction₀Is L
iCoO_TwoLattice constant c in the c-axis direction₀Greater than. Soshi
Therefore, Li is smaller than 1 only when the amount of Mn is added.
This means that Ti, Pb, Sn, Fe, Ni, I
The same applies to the case of n and Bi.
Is less than 1 and their lithium-containing compounds
Lattice constant c in the c-axis direction of the composite oxide₀Also LiCoO_TwoOf c
Axial lattice constant c₀Be larger. Then, as described above, Li is smaller than 1.
Therefore, Li vacancies already exist in the crystal structure from the time of synthesis.
It is presumed that it exists, and it is Li⁺Expansion of ion
It is supposed to smooth the scattering. Also Li sky
That Mn is tetravalent as described below.
To insert Li into the sample at the time of synthesis by discharge reaction
Characteristic of conventional Li
MO_TwoIt is thought to be different. As mentioned above, Li is smaller than 1.
Is due to solid solution of Mn, which is tetravalent stable.
Is unstable as described above.⁴⁺Organic electrolysis
Suppresses the oxidation of the solution to prevent capacity deterioration due to charge / discharge cycles.
It is considered to be a small positive electrode active material. Also, c-axis
Lattice constant c₀Is LiCoO_TwoLattice constant in the c-axis direction
Number c₀Being larger also contributes to the above-mentioned improvement in characteristics.
It is thought that it is. The above Li_y(Co_yMn_x) O_TwoIs that
In the synthesis, LiCoO_TwoAnd MnO_TwoLichiu etc.
Bake by heating a mixture with manganese oxide containing no
LiCoO synthesized around 1100 ° C_TwoUsing
Then, a single-phase Li_y(Co _yMn_x) O_TwoIs obtained
, LiCoO_Two, Co_ThreeO_Four, Li_TwoMnO_ThreeEtc.
Phase separation occurs. However, it was synthesized at a relatively low temperature of 700 ° C.
LiCoO_Two, A single-phase Li_y(Co_yMn
_x) O_TwoIs obtained. Further, according to ESCA (X-ray photoelectron spectroscopy),
When the valences of Co and Mn were examined, Mn was tetravalent and Co
Was trivalent. Conventional LiMnO_TwoSo, M is all
Trivalent and tetravalent are not mixed. LiCoO synthesized at low temperature_Two(375-5
Synthesized at 00 ° C.) is a LiCoO having a conventional layered structure.
_Two(Synthesized at 900-1100 ° C) and X-ray diffraction image is slightly different
Are considered to have different crystal structures.
You. Therefore, as described above, the low-temperature synthesized product L
iCoO_TwoAnd conventional high temperature synthetic LiCoO_TwoAnd
MnO_TwoWhen firing the mixture with
It is considered to be. And it is the boundary where the difference occurs
LiCoO_TwoThe synthesis temperature of Li_y(Co_yMn_x) O
_TwoIt is thought that it changes depending on the conditions when synthesizing
But approaches 375 ° C, which is considered the lower limit of low temperature
The more the layered structure becomes more disordered. In addition, LiC
oO_TwoThe change in the turbulence of the layered structure of
It is considered to be close to the low temperature type described above. Next, Li_y(Co_yMn_x) O_TwoResult
The crystal structure will be described. FIG. 2 shows LiCoO synthesized at 700 ° C._Two
And MnO_TwoTo Co / Mn = 9/1, 8/2, 7/3, 6
/ 4 (molar ratio) and mix the resulting mixture
X-ray diffraction patterns of samples synthesized by firing at 900 ° C respectively
It is. FIG. 3 shows LiCoO synthesized at 1100 ° C.
_TwoAnd MnO_TwoSimilarly, Co / Mn = 9/1, 8/2, 7
/ 3, 6/4 (molar ratio)
X-ray rotation of a sample synthesized by firing each material at 900 ° C
It is a folding pattern. FIGS. 2 and 3 both show MnO_TwoDue to the increase in volume
Lattice constant (a₀, C₀) Changes, the peak position changes
I do. However, in the latter case, as shown in FIG.
The shift is, for example, around 2θ = 31 °_ThreeO_FourThe pea
(Indicated by crosses) were observed and were not a single phase. On the other hand, in the former, as shown in FIG.
In addition, Co / Mn = 8/2 (molar ratio) and Co / Mn = 9 /
At 1 (molar ratio), there was no peak near 2θ = 31 ° C.
It was one compound. Co / Mn = 8/2 in FIG.
(Molar ratio) and the pattern of Co / Mn = 9/1 (molar ratio)
And LiCoO (not shown in FIG. 2)_TwoPutter
Lattice constant a₀, C₀Is shown in FIG. As shown in FIG. 4, the addition of Mn (FIG.
4, the lattice constant a due to the decrease in the y value on the horizontal axis)₀But slightly
Decrease and the lattice constant c₀Is increasing. From this, Mn is
It turns out that it is a solid solution in Co and is not a mixture. This
As described above, the solid solution of Mn, which is tetravalent stable,
Unstable Co⁴⁺Suppresses the oxidation of the organic electrolyte by
Positive electrode active material with less capacity deterioration due to charge / discharge cycles
It is considered to be. As described above, LiCoO_TwoAs 7
Less than 00 ° C, especially 375-700 ° C
If present, single-phase Li_y(Co_yMn_x) O_TwoIs obtained
You. LiCoO_TwoAnd MnO_TwoSuch as lithium
The calcination of the mixture with the manganese oxide not containing
It is performed at 00 to 1100 ° C. for 1 to 48 hours. Li_y(Co_yMn_x) O_TwoX in
y is x + y = 1, but x is 0.05 to 0.20.
Among them, those having particularly good characteristics can be obtained. Li_y(Co_yMn_x) O_TwoRaw material for
LiCoO_TwoIs, for example, Co_ThreeO _FourAnd LiOH ・ H_Two
It is obtained by heat-treating a mixture with O. Up
Note Co_ThreeO_FourIs cobalt carbonate (CoCO_ThreeIn oxygen
Is obtained by the heat treatment of_Three
O_FourInstead of CoCO_ThreeAnd 2CoCO_Three・ Co (OH)
_TwoOr LiOH.H_TwoInstead of O
Li_TwoCO_ThreeOther lithium salts may be used. The positive electrode is made of the above Li_y(Co_yMn_x) O_Two
If necessary, for example, graphite, acetylene black
And electron conduction aids such as polytetrafluoroe
Add binder such as styrene and mix to prepare positive mix
Then, the obtained positive electrode mixture is subjected to, for example, pressure molding.
Is obtained. For the negative electrode, lithium metal, lithium-Al
Lithium alloys such as minium alloys, lithium-carbon materials
A lithium compound such as (eg, graphite) is used. For the electrolyte, for example, LiClO_Four, L
iPF₆, LiBF_Four, LiCF_ThreeSO_Three, LiC_FourF
₉SO_ThreeOne or more electrolytes such as
-Dimethoxyethane, 1,2-diethoxyethane, pro
Pyrene carbonate, ethylene carbonate, γ-butyl
Lolactone, tetrahydrofuran, 1,3-dioxola
Organic solvents dissolved in single or mixed solvents such as
An electrolyte is used. When a lithium-carbon material is used for the negative electrode,
However, when assembling the battery, only the carbon material is used.
Lithium-carbon material using electrochemical reaction in
In this case, it becomes a lithium (Li) source for the positive electrode active material.
It is preferable to mix a substance. For example, Li_y
(Co_yMn_x) O_TwoAnd Li_TwoMoO_Three, Li_TwoNi
O_TwoOr Nb with Li_TwoO_FiveAnd Li
i_y(Co_yMn_x) O_TwoLi is extracted at lower potential
And the material into which Li is inserted into the carbon material
Method. Further, the reaction between the positive electrode active material and the organic electrolyte is performed.
Li to prevent_y(Co_yMn_x) O_TwoThe surface of the particle is L
i_FourSiO_Four・ Li_ThreePO_FourWith a solid electrolyte such as
May be In order to increase overvoltage, PbO_Two
And In_TwoO_Three, Bi_TwoO_ThreeOxides such as
No. In the above, Li_y(Co_yM_x) O_TwoBaby
Although the case where M is Mn has been described, this M is Mn.
Has been described for the case where M is Ti other than Mn,
Suitable for Pb, Sn, Fe, Ni, In, Bi, etc.
Can be used. For example, the above Li_y(Co
_yM_x) O_TwoWhen M is to synthesize other than Mn,
LiCoO_TwoOf lithium and oxides of lithium-free M
It is suitable to synthesize by firing
You. [0036] The present invention will now be described in more detail with reference to the following examples.
explain. However, the present invention is limited to only those examples.
It is not done. Embodiment 1 First, as shown below, Li at a lower temperature than before.
CoO_TwoWas synthesized. Cobalt carbonate (CoCO)_Three) At 375 ° C
Heat in oxygen for 20 hours,_ThreeO _FourGot. This Co
_ThreeO_FourAnd LiOH ・ H_TwoO is converted to Li / Co = 1/1 (mol
Ratio) and the resulting mixture is acidified at 700 ° C. for 20 hours.
Heated in water to produce LiCoO _TwoWas synthesized. The LiCoO synthesized as described above_TwoWhen
MnO_TwoAre mixed at Co / Mn = 9/1 (molar ratio) to obtain
The resulting mixture was calcined at 900 ° C. for 24 hours to obtain Li_0.9
(Co_0.9Mn_0.1) O_TwoWas synthesized. The Li synthesized as described above_0.9(C
o_0.9Mn_0.1) O_TwoIs used as the positive electrode active material.
Acetylene black and a binder as electron conduction aids
To make polytetrafluoroethylene 80: 15: 5 (weight
(Amount ratio) to prepare a positive electrode mixture. A mold was filled with 40 mg of this positive electrode mixture,
1t / cm^TwoPress-formed into a 10mm diameter disc
Then, heat treatment was performed at 200 ° C. to obtain a positive electrode. Use this positive electrode
First, a button-type lithium secondary battery shown in FIG.
Was. In FIG. 1, reference numeral 1 denotes the above positive electrode;
Is a disc-shaped negative electrode made of lithium having a diameter of 14 mm.
You. 3 is a separator made of microporous polypropylene film
4 is an electrolyte absorption made of polypropylene non-woven fabric
Body. 5 is a stainless steel positive electrode can, 6 is
Positive current collector made of stainless steel mesh, 7 is stainless steel
This is a negative electrode can made of stainless steel and nickel plated on the surface.
Reference numeral 8 denotes a negative electrode current collector made of a stainless steel mesh,
The negative electrode 2 is spot-welded to the inner surface of the
Is pressed against the negative electrode current collector 8 made of this stainless steel net.
Have been. 9 is an annular gasket made of polypropylene.
This battery has propylene carbonate and 1,2-
LiCl in a mixed solvent of 1: 1 by volume with dimethoxyethane
F_ThreeSO_Three0.6mol / l dissolved electrolyte was injected
Have been. Comparative Example 1 Co_ThreeO_FourAnd LiOH ・ H_TwoO is Li / Co = 1/1
(Molar ratio) and the resulting mixture was treated at 900 ° C. for 24 hours.
Firing for LiCoO_TwoWas synthesized. The LiCoO synthesized as described above_Two
Was used as a positive electrode active material, and otherwise the same as in Example 1.
Thus, a button-type lithium secondary battery was manufactured. Toes
Thus, the battery of Comparative Example 1 contained Mn as the positive electrode active material.
LiCoO_Two(However, this synthesis is
Synthesized at 900 ° C according to the synthesis method)
The other parts have the same configuration as the battery of Example 1. The battery of Example 1 and the battery of Comparative Example 1
With a charge / discharge current of 0.785 mA (1 mA / cm^Two) And 4.
The battery was charged and discharged between a voltage of 3 to 3.0 V. Table 1 shows the charging of both batteries.
4 shows the relationship between the number of discharge cycles and the charge / discharge capacity. [0048] [Table 1]As shown in Table 1, the charge / discharge cycle was 10 cycles.
Up to the point, the battery of Comparative Example 1 was more charged and discharged than the battery of Example 1.
Although the electric capacity was large, the example became effective at the 20th cycle.
Battery 1 has a larger charge / discharge capacity than battery of Comparative Example 1.
40 cycles with more charge / discharge cycles
The difference increases at the 80th cycle and the
The battery of Example 1 has a small capacity deterioration due to the charge / discharge cycle.
And had been revealed. [0050] As described above, according to the present invention,
Lithium secondary with less capacity deterioration due to charge / discharge cycles
A battery can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an example of a lithium secondary battery according to the present invention. FIG. 2 is a view showing an X-ray diffraction pattern of a sample synthesized by firing a mixture of LiCoO ₂ and MnO ₂ synthesized at 700 ° C. at 900 ° C. FIG. 3 LiCoO ₂ and MnO ₂ synthesized at 1100 ° C.
FIG. 6 is a view showing an X-ray diffraction pattern of a sample synthesized by firing a mixture of the above at 900 ° C. FIG. 4 shows Li _y (Co _y) obtained from the pattern shown in FIG.
Is a diagram showing a relationship between Mn _x) O ₂ of the y values and the lattice constant. [Description of Signs] 1 Positive electrode 2 Negative electrode 3 Separator

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Shoji Yamanaka             1-335 Minamikaniya, Minami-ku, Hiroshima-shi, Hiroshima             Room 1105 F-term (reference) 4G048 AA04 AB01 AC06 AD03 AE05                 5H029 AJ03 AJ05 AK02 AL01 AL12                       AM05 AM07 BJ03 BJ12 EJ01                       EJ04 EJ12 HJ02                 5H050 AA07 AA08 BA17 CA08 CB12                       EA02 EA10 EA11 EA22 EA23                       EA24 HA02 HA13

Claims (1)

Claims 1. A lithium secondary battery using a lithium metal, a lithium alloy or a lithium compound for a negative electrode,
Li having a lattice constant c ₀ in the c-axis direction larger than the lattice constant c _{0 in} the c-axis direction of LiCoO ₂ as the positive electrode active material.
_{y (Co y Mn x) O} 2 ( however, M is Mn, Ti, P
A lithium secondary battery using at least one metal selected from b, Sn, Fe, Ni, In and Bi, and using x + y = 1).