JP2000223158A - Non-aqueous electrolyte lithium secondary battery - Google Patents

Abstract

(57) [Problem] To provide a non-aqueous electrolyte lithium secondary battery having high energy density and low self-discharge and excellent storage characteristics. SOLUTION: This is a non-aqueous electrolyte lithium secondary battery in which a positive electrode having a negative electrode mixture 1 and a negative electrode having a positive electrode mixture 2 are disposed via a separator 3, wherein a negative electrode active material in the negative electrode mixture 1 is provided. The substance has a layered structure represented by the general formula Li _{(3-n) -m} L _n N (L is one or more transition metals and 0 <n ≦ 0.6, 0 <m ≦ 2.0) The positive electrode active material in the positive electrode mixture 2 is a nitride, and the positive electrode active material in the positive electrode mixture 2 has a general formula Li _x [Ni _{2− y My} O ₄ ] (M is one or more transition metals and elements other than Ni, 0 ≦ x ≦ 2 .1,0.
75 ≦ y ≦ 1.60) is an oxide having a spinel structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte lithium secondary battery, and more particularly, to a non-aqueous electrolyte lithium secondary battery having high energy density, low self-discharge, and excellent storage characteristics. is there.

[0002]

2. Description of the Related Art In recent years, various non-aqueous electrolyte lithium secondary batteries having high electromotive force and high energy density have been used as a power source for electronic equipment, a power source for electric power storage, and a power source for electric vehicles, which have been improved in performance and size. Is attracting attention.

In such a non-aqueous electrolyte lithium secondary battery, metallic lithium, a lithium alloy or a carbon material capable of occluding and releasing lithium at a specific potential level has been used for the negative electrode.

In a battery using lithium metal for the negative electrode,
There is a problem that the dendrite of lithium generated at the time of charging may cause an internal short circuit in the battery and the charge / discharge cycle life cannot be improved.In the case of a battery using a lithium alloy for the negative electrode, the Although there was a problem of powdering and falling off of the active material, the above-mentioned problem was remarkably improved in a battery using a carbon material capable of occluding or releasing lithium at a potential level specific to the negative electrode. However, it has been found that such a battery has a problem that the self-discharge increases due to another cause and the storage characteristics cannot be improved.

[0005] Such a problem is caused by the use of a separator in which a non-aqueous liquid electrolyte is impregnated in a porous polyethylene film as a separator, the use of a polymer gel or a solid electrolyte in place of the separator, The same was true even when the separator and the polymer gel or solid electrolyte were used in combination.

[0006]

The detailed mechanism of the above-mentioned self-discharge is not clear, but is thought to be caused by a side reaction between the carbon material and the electrolyte. The problem was to develop a negative electrode active material that can release, occlude, and release, and is less likely to cause side reactions with the electrolyte.

[0007]

Means for Solving the Problems To solve the above-mentioned problems, the invention according to claim 1 comprises a non-aqueous electrolyte lithium secondary battery in which a positive electrode and a negative electrode are arranged via an isolator. The main component of the negative electrode active material is a general formula Li
_{(3-n) -m} L _n N (L is one or more transition metals, and 0 <n ≦
0.6, 0 <m ≦ 2.0), wherein the main component of the positive electrode active material constituting the positive electrode is a general formula Li _x [Ni _{2− y My} O ₄ ] (M is one or more transition metals, elements other than Ni, 0 ≦ x ≦ 2.1, 0.75 ≦
(y ≦ 1.60), which reduces the activity of lithium occluded in the molecular structure in the charged state by reducing the activity of lithium. The action of reducing the electrolyte can be suppressed, and even if the solvent or the supporting salt constituting the electrolyte is a compound containing oxygen, the active material itself is a nitride, so that the oxide of the oxide is formed at the interface with the electrolyte. The formation of such a film can be suppressed, and the main component of the negative electrode active material has a potential difference of about 1.5 V with respect to the lithium absorption and desorption potential relative to the dissolution and deposition potential of lithium. The main components are lithium absorption and release potential, lithium dissolution,
Since it has a potential difference of about 4.7 to 4.8 V with respect to the deposition potential, a nonaqueous electrolyte lithium secondary battery having a discharge voltage of about 3.2 to 4.8 V can be obtained.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on its embodiments.

The feature of the non-aqueous electrolyte lithium secondary battery according to the embodiment of the present invention is that a non-aqueous electrolyte lithium secondary battery in which a positive electrode and a negative electrode are disposed via an isolator is a negative electrode constituting the negative electrode. The main component of the active material is represented by the general formula Li _{(3-n) -m}
L _n N (L is one or more transition metals, 0 <n ≦ 0.6,
0 <m ≦ 2.0) and has a layered structure represented by the general formula Li:
_x [Ni _2-y M y O _4] (M is one or more transition metals,
Elements other than Ni, 0 ≦ x ≦ 2.1, 0.75 ≦ y ≦ 1.
An oxide having a spinel structure represented by the formula (60).

The general formula Li which is a main component of the negative electrode active material
_{In the} nitride represented by _{(3-n) -m} L _n N, n is 0 <n ≦ 0.
6, m is 0 <m ≦ 2.0 (preferably 0.2 ≦ m ≦ 2.
0), which has a layered structure, can smoothly transfer ions and electrons between particles, and reduce the electrolyte due to lithium occluded in the molecular structure in a charged state. And a side reaction of the negative electrode active material itself with a solvent or a supporting salt constituting the electrolyte can be suppressed. This also makes it possible to use aluminum for the current collector of the negative electrode. Note that L
V, Cr, Mn, Fe, Co, Ni, Cu, Z
n, preferably Co, Ni, Cu.

The oxide represented by the general formula Li _x [Ni _{2 -y My} O ₄ ], which is the main component of the positive electrode active material, has x
Is 0 ≦ x ≦ 2.1, y is 0.75 ≦ n ≦ 1.60, and has a spinel structure, a stable crystal structure can be obtained. By combining substances, a non-aqueous electrolyte lithium secondary battery having high storage voltage, high energy density, and low self-discharge and excellent storage characteristics can be obtained. Note that M is a transition metal other than Ni, preferably Mn, Co, Z
n, Fe, and V are preferable.

The separator may be a separator in which a non-aqueous liquid electrolyte is impregnated in a porous polyethylene film and / or a polymer gel or solid electrolyte.

Examples of the non-aqueous liquid electrolyte include esters such as propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate and γ-butyrolactone; substituted tetrahydrofurans such as tetrahydrofuran and 2-methyltetrahydrofuran; and dioxolanes. , Diethyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, and other ethers, dimethylsulfoxide, sulfolane, methylsulfolane, acetonitrile, methyl formate, methyl acetate, methyl acetate, N
-Lithium tetrafluoroborate (LiB) in an organic solvent such as methylpyrrolidone and dimethylformamide.
F ₄ ), lithium hexafluorophosphate (LiP
F ₆ ), lithium perchlorate (LiClO ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ),
Inorganic salts such as lithium hexafluoroarsenate (LiAsF ₆ ), LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ SO
₂ ) An imide salt such as (C ₄ F ₉ SO ₂ ) or LiC (C
A solution in which an organic salt such as a methide salt such as F ₃ SO ₂ ) ₃ is dissolved is used.

The polymer gel or solid electrolyte includes a polyethylene oxide derivative or a polymer containing at least the derivative, a polypropylene oxide derivative or a polymer containing at least the derivative,
Polyphosphazene or a polymer containing at least the derivative thereof, a polymer containing an ion-dissociating group, a phosphate ester polymer derivative, a polyvinylpyridine derivative, a bisphenol A derivative, polyacrylonitrile, polyvinylidene fluoride, a fluoroelastomer, etc. A polymer matrix is used.

Furthermore, the above-mentioned polymer gel or solid electrolyte is an organic electrolyte, but lithium nitride, halide, oxyacid salt, phosphorus sulfide compound such as Li ₃ N, LiI, Li ₅ NI ₂ ,
Li ₃ N—LiI—LiOH, Li ₄ SiO ₄ , Li ₄
SiO ₄ —LiI—LiOH, xLi ₃ PO ₄ — (1-
x) Li ₄ SiO ₄ , Li ₂ SiS ₃ , LiLaTiO
₃ , LiTi ₂ (PO ₄ ) _{3 and the} like can be used alone or in combination with the organic electrolyte.

Further, the separator is preferably an insulating thin film having excellent ion permeability and mechanical strength, is resistant to organic solvents, and is an olefin polymer such as polypropylene or polyethylene, glass fiber, polyvinylidene fluoride, or the like. Sheets, microporous membranes, and nonwoven fabrics made of polytetrafluoroethylene or the like are used. The separator has a pore diameter of 0.01 to about the same as that used for other batteries.
The thickness of the separator is preferably 10 μm, and the thickness of the separator is also preferably 5 to 300 μm.

The above-mentioned positive and negative electrode active materials are preferably powders having an average particle diameter of 0.1 to 100 μm. To obtain this powder, a mortar, ball mill, sand mill, vibrating ball mill, planetary ball mill, jet Mills, counter jet mills, swirling air jet mills, sieves, pulverizers such as air classifiers, classifiers, granulators can be used,
At the time of pulverization, wet pulverization may be carried out by coexisting with an organic solvent such as water or hexane. At the time of classification, either a dry method or a wet method may be used.

The positive and negative electrode active materials include a conductive agent,
Binders, fillers and the like can also be added.

Examples of the conductive agent include natural graphite (flaky graphite, earthy graphite, etc.) which does not adversely affect battery performance.
Artificial graphite, carbon black, acetylene black, ketjen black, carbon whiskers, carbon fiber, metal (copper, nickel, iron, silver, gold, etc.) powder, metal fiber,
Electron conductive materials such as metal deposits and conductive ceramics can be used alone or in combination, and the added amount is 1 to 50% by weight, preferably 2 to 30% by weight.

Examples of the binder include tetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, ethylene-propylene diene terpolymer (E
PDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororesin, thermoplastic resin such as carbomethoxycellulose, polymer having rubber elasticity, polysaccharide can be used as one kind or a mixture of two or more kinds, The addition amount is 1 to 50% by weight, preferably 2 to 30%.
% By weight. Since the polysaccharide has a functional group which reacts with lithium, it is better to inactivate the functional group by a method such as methylation in advance.

As the filler, an olefin-based polymer such as polypropylene or polyethylene, aerosil, alumina, carbon, or the like, which does not adversely affect the battery performance, can be used, and its addition amount is preferably 0 to 30% by weight.

Further, positive and negative electrode current collectors are used as the positive and negative electrode active materials, and the material thereof is aluminum, titanium, stainless steel, nickel, calcined carbon,
In addition to conductive polymers, conductive glass, etc., those with aluminum, copper, etc. surface treated with carbon, nickel, titanium, silver, etc. for the purpose of improving adhesiveness, conductivity, and oxidation resistance can be used. , Negative electrode as copper, stainless steel, nickel, aluminum, titanium, calcined carbon, conductive polymer,
In addition to conductive glass, aluminum-cadmium alloy, etc., those obtained by applying a treatment of carbon, nickel, titanium, silver, etc. to the surface of copper or aluminum for the purpose of improving adhesiveness, conductivity, and reduction resistance can be used. . Further, these materials may be subjected to oxidation treatment on the surface. The positive and negative electrode current collectors may be films, sheets, nets, punched metals, expanded metals, laths, porous bodies, foams, and formed bodies of fiber groups other than foils. ~ 5
The thickness is preferably set to 00 μm.

The shape of the non-aqueous electrolyte lithium secondary battery according to the present invention is cylindrical, square, coin, button,
Flat and film-shaped ones are conceivable, but in order to obtain a high energy density, it is preferable to use a polymer-based gel or a film-shaped one using a solid electrolyte.

Examples of the battery exterior material include metals such as iron, nickel, copper, aluminum, titanium, and stainless steel, alloys of these metals, polypropylene, polyethylene, polystyrene, ABS, acrylic resin, polyethylene terephthalate, polyimide, and the like. A high energy density can be realized by using a resin such as polyurethane, the above-mentioned metal, or a laminate of the above-mentioned resin and an alloy composed of these metals, particularly an aluminum laminate.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

FIG. 1 is a cross-sectional view of a non-aqueous electrolyte lithium secondary battery according to an example of the present invention and a comparative example.

In the non-aqueous electrolyte lithium secondary battery shown in FIG. 1, a negative electrode mixture 1 containing a negative electrode active material, graphite as a conductive agent, and polyvinylidene fluoride as a binder is formed into a slurry, and this is mixed with a negative electrode. A slurry is prepared by applying a negative electrode obtained by coating on a copper foil as an electric body, drying and pressing, and a positive electrode mixture 2 containing a positive electrode active material, graphite as a conductive agent, and polyvinylidene fluoride as a binder. This is coated on an aluminum foil as a positive electrode current collector, dried, and pressed to form a positive electrode in a large number with a separator as a separator 3 made of a polyolefin film microporous film interposed therebetween. The spirally wound electrode body is fixed by taping to form a spiral electrode body. Insulating plates 4 are disposed on the upper and lower surfaces of the spiral electrode body, and the spirally wound electrode body is housed in a battery case 5 made of aluminum. From the current collector The extracted aluminum positive electrode lead wire 10 is welded to the projection of the safety valve 8, and the copper negative electrode lead wire 11 drawn from the negative electrode current collector is welded to the bottom of the battery container 5. The lid 7 is fixed by caulking the battery container 5 through the sealing gasket 6 after injecting the electrolytic solution into the
mm and a height of 65 mm.

The lid 7 is provided with a PTC element 9 in addition to the safety valve 8 as a current cutoff mechanism.

The electrolytic solution is obtained by dissolving 1 mol of lithium hexafluorophosphate (LiPF ₆ ) as a supporting electrolyte salt in ethylene carbonate and diethyl carbonate having a mixing ratio of 1: 1 as a solvent.

(Example 1) A nonaqueous electrolyte lithium secondary battery A1 according to Example 1 contains 900 parts of a mixture of lithium nitride (Li ₃ N) and cobalt (Co) as a negative electrode active material.
Li _2.6 heat-treated for 20 hours in an inert gas atmosphere at
Co _0.4 N is obtained from Li _1.0 Co _0.4 obtained by extracting Li with iodine (I ₂ ) in propylene carbonate.
N is prepared and nickel hydroxide (Ni
(OH) ₂₎ and Li _1.0 Mn _1.5 The mixture was heat-treated for 20 hours under a dry air atmosphere at 750 ° C. of manganese carbonate and (MnCO ₃₎ and lithium hydroxide (LiOH · H ₂ O)
Ni _0.5 O ₄ was prepared, and the negative electrode active material was 87% by weight.
A negative electrode mixture 1 in which a conductive agent was mixed at a ratio of 10% by weight and a binder at a ratio of 3% by weight was dispersed in N-methyl-2-pyrrolidone to form a slurry, which was uniformly applied to a copper foil having a thickness of 10 μm. And dried and pressed to form a negative electrode. The positive electrode mixture 2 obtained by mixing 87% by weight of the positive electrode active material, 10% by weight of the conductive agent, and 3% by weight of the binder was N- Methyl-
Dispersed in 2-pyrrolidone to form a slurry, having a thickness of 1
The positive electrode was uniformly coated on a 0 μm aluminum foil, dried, and pressed to form a positive electrode.

Example 2 A non-aqueous electrolyte lithium secondary battery A2 according to Example 2 has nickel hydroxide (Ni (OH) ₂ ) and manganese carbonate (MnCO ₃ ) as positive electrode active materials.
And a mixture of lithium hydroxide (LiOH.H ₂ O)
Li heat-treated in a dry air atmosphere at 50 ° C for 20 hours
_1.0 Mn _1.5 Ni _0.5 O ₄ is obtained by extracting Li with iodine (I ₂ ) in propylene carbonate to obtain Li _0.05
Same as Example 1 except that Mn _1.5 O ₄ was used.

Comparative Example 1 The non-aqueous electrolyte lithium secondary battery B1 according to Comparative Example 1 is the same as Example 1 except that graphite was used as the negative electrode active material.

Comparative Example 2 A nonaqueous electrolyte lithium secondary battery B2 according to Comparative Example 2 is the same as Comparative Example 1 except that lithium manganate (LiMn ₂ O ₄ ) was used as a positive electrode active material.

The non-aqueous electrolyte lithium secondary batteries A1 and A2 according to Examples 1 and 2 and the non-aqueous electrolyte lithium secondary batteries B1 and B2 according to Comparative Examples 1 and 2 were stored using the self-discharge rate as an index. The test was performed. As test conditions,
The nonaqueous electrolyte lithium secondary batteries A1 and A2 have a charge end voltage of 5.0 V and a discharge end voltage of 3.0 V, and the nonaqueous electrolyte lithium secondary battery B1 has a charge end voltage of 4.9 V and a discharge end voltage of 3 V. The non-aqueous electrolyte lithium secondary battery B2 had a charge end voltage of 4.2 V and a discharge end voltage of 2.0 V.
2 charge / discharge cycles at a 10-hour rate
The battery after the third cycle is stored at room temperature for 30 days,
The discharge capacity after storage was measured, the self-discharge rate was calculated by the formula shown in Chemical formula 1, the discharge voltage and the weight energy density were measured, and the results are shown in Table 1.

[0035]

Embedded image

[0036]

[Table 1]

From Table 1, it can be seen that the non-aqueous electrolyte lithium secondary batteries A1 and A2 according to Examples 1 and 2 and the non-aqueous electrolyte lithium secondary battery B2 according to Comparative Example 2 correspond to the non-aqueous electrolyte lithium secondary battery B according to Comparative Example 1. It can be seen that the self-discharge rate is improved compared to the secondary battery B1. The reason is not clear, by using a general formula _{Li (3-n) -m L} n N represented nitrides as the main component of the negative electrode active material, dissolved occluding lithium, the potential of release of lithium About 1.5 with respect to the potential of deposition
The potential difference of V can be set to a low value, the activity of lithium occluded in the molecular structure in the charged state is reduced, the reduction of the electrolyte is reduced, and the solvent and the supporting electrolyte salt constituting the electrolyte contain oxygen. Even if it is a compound, it is considered that since the negative electrode active material is a nitride, the action of these reacting to form a film such as an oxide at the interface of the electrolyte can be reduced.

Further, from Table 1, the self-discharge rate of the non-aqueous electrolyte lithium secondary battery B2 according to Comparative Example 2 is improved, but the discharge voltage is 3.4 V, so that the energy density of the battery is lowered. You can see that This is because the main component of the negative electrode active material is the same as that of the nonaqueous electrolyte lithium secondary battery A1 according to the first embodiment, but the main component of the positive electrode active material has a potential of absorbing and releasing lithium that dissolves lithium. This is because a potential difference of about 4.7 to 4.8 V with respect to the potential for deposition was not achieved.

In the above embodiment, Co was used as the substitution element of the negative electrode active material.
V, Cr, Mn, Fe, Ni, Cu, preferably N
i or Cu may be used. Further, although the substitution element of the positive electrode active material is Mn, other transition metals other than Ni may be Co, Zn, Fe, and V.

Further, the starting materials of the active material, the production method, the shapes of the positive electrode, the negative electrode, the electrolyte, the separator, and the battery described in Examples 1 and 2 are not limited thereto.
The shape of the battery is not limited to a cylindrical shape.

Since the potential of the main component of the negative electrode active material with respect to lithium is about 1.5 V, it is needless to say that the weight energy density can be further improved by replacing the current collector with copper with aluminum.

[0042]

As described above, the present invention can provide a non-aqueous electrolyte lithium secondary battery having high energy density, low self-discharge and excellent storage characteristics, and requires high electromotive force and high energy density. It greatly contributes to the use.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a non-aqueous electrolyte lithium secondary battery according to an example of the present invention and a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Negative electrode mixture 2 Positive electrode mixture 3 Separator 4 Insulating plate 5 Battery container 6 Sealing gasket 7 Lid 8 Safety valve 9 PTC element 10 Positive electrode lead wire 11 Negative electrode lead wire

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H003 AA02 AA03 AA04 BB01 BB05 BC06 BD00 5H014 AA02 EE10 HH00 5H029 AJ03 AJ04 AJ05 AK03 AL01 AM00 AM02 AM03 AM04 AM05 AM07 AM16 BJ02 BJ14 DJ04 DJ17 HJ02

Claims (1)

[Claims] 1. A non-aqueous electrolyte lithium secondary battery in which a positive electrode and a negative electrode are disposed via an isolator, wherein a main component of a negative electrode active material constituting the negative electrode is represented by a general formula Li _{(3-n) -m} L _n N
(L is one or more transition metals, 0 <n ≦ 0.6, 0 <m
≦ 2.0) a nitride having a layered structure represented by
The main component of the positive electrode active material constituting the positive electrode is represented by the general formula Li _x [N
i _2-y M y O _4] (M is at least one transition metal element other than Ni, 0 ≦ x ≦ 2.1,0.75 ≦ y ≦ 1.60)
A non-aqueous electrolyte lithium secondary battery characterized by being an oxide having a spinel structure represented by the following formula: