JPH04267074A - Lithium secondary battery - Google Patents

Abstract

PURPOSE:To aim at the safety of assembly work and safety of maintenance under the discharge condition, and obtain even and homogeneous negative electrode by forming negative electrode without using lithium, and eliminating existence of metal lithium after concluding discharge. CONSTITUTION:The mixture which is mainly composed of lithium thiolate compound, which has sulfur - lithium ion bond for generating sulfur - sulfur bond with electrolytic oxidation, and electronic ion mixed conductive high polymer is used for positive electrode. Solid lithium ion conductive electrolyte including lithium ion is used for electrolyte. Composite, which is mainly composed of metal aluminium and carbon material, is used for negative electrode. Assembly work is thereby performed safely without treating active metal lithium. Furthermore, under the discharge condition, since metal lithium does not exist practically, even if a battery is broken, danger of ignition is eliminated. Electrode area of negative electrode is enlarged without processing it into sheet- shape, and even and homogeneous negative electrode is obtained easily.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery using a solid or solid lithium ion conductive electrolyte.

0002

[Prior art] High voltage of 3 to 4 volts and 100Wh/
As a lithium secondary battery that is expected to have a high energy density of more than 1 kg, the negative electrode uses metallic lithium or a lithium alloy, and the positive electrode uses materials such as titanium disulfide, molybdenum disulfide, vanadium oxide, cobalt oxide, etc., which can reversibly insert and remove lithium ions. Batteries using inorganic materials have been proposed.

As the electrolyte, a liquid electrolyte in which a lithium salt such as lithium perchlorate or lithium fluoroborate is dissolved in an aprotic organic solvent such as propylene carbonate or dimethoxyethane is used. The ionic conductivity of this liquid electrolyte is two to three orders of magnitude lower than the aqueous electrolyte used in nickel-cadmium secondary batteries or lead-acid batteries, so in order to obtain a large current comparable to those of these batteries, the electrode area must be increased. In addition, it is necessary to make the separator thinner.

[0004] The positive electrode is used by processing a composition obtained by mixing a powdered positive electrode active material, a conductive material, and a binder into a sheet shape. In addition to processing into a sheet, the electrode area of the positive electrode can be increased by reducing the particle size of the powder or using porous powder. However, metal lithium or lithium alloys are soft and difficult to process into powder, and the only way to obtain a large electrode area is to rely on processing them into thin foils. The positive electrode processed into a thin sheet shape and the negative electrode are stacked with a separator such as a polypropylene nonwoven fabric interposed therebetween, wound into a spiral shape, placed in a battery container, and assembled by pouring an electrolytic solution. All operations are carried out under dry, inert gas.

[0005]

[Problems to be Solved by the Invention] When assembling a lithium secondary battery, it is important to make the electrodes that come into contact with the electrolyte uniform and homogeneous over the entire surface. A positive electrode is usually provided with a composition of a positive electrode active material, a conductive material, and a binder, and a relatively homogeneous material can be obtained by selecting a chemically stable positive electrode active material and uniformly mixing the positive electrode active material.

However, it is difficult to uniformly and uniformly process lithium metal or lithium alloy foil, which has a thickness of several micrometers to several tens of micrometers, through a multi-stage rolling process for the negative electrode. Difficult to assemble uniformly due to tension. During battery charging and discharging, the dissolution and precipitation reaction of lithium progresses non-uniformly within the surface of the negative electrode, and as the charge and discharge cycles are repeated, the non-uniformity increases until the current concentrates locally, causing lithium to precipitate in a dendritic manner. occurs, breaking through the separator and connecting with the positive electrode, causing an internal short circuit. When an internal short circuit occurs, a large current flows, heating up the battery, increasing the vapor pressure of the organic solvent, and causing the battery to burst. Metallic lithium is exposed to the atmosphere and reacts with water, generating hydrogen and igniting. Extremely dangerous. The present invention solves these problems and aims to provide a highly safe lithium secondary battery.

[0007]

[Means for Solving the Problem] In order to solve this problem, the lithium secondary battery of the present invention can be assembled without using metallic lithium or a lithium alloy for the negative electrode, and also has a structure in which metallic lithium is substantially removed after discharging. In order to create a lithium secondary battery that does not currently exist, we created a mixture mainly consisting of a lithium thiolate compound having a sulfur-lithium ion bond that generates a sulfur-sulfur bond through electrolytic oxidation, and an ion-electronic mixed conductive polymer. The positive electrode active material used,
A negative electrode using a composition mainly composed of metal aluminum or its alloy and a carbon material and a soluble lithium thiolate compound are fixed to the positive electrode so that lithium ions from the lithium thiolate compound are uniformly deposited when the battery is charged. Therefore, the normal battery operating temperature range (-20 to 60
℃), and preferably, at least one of the positive electrode active material or the negative electrode composition contains a solid or solid lithium ion containing lithium ion. It is a mixture of conductive electrolytes.

[0008]

[Function] With this configuration, the lithium secondary battery of the present invention has
Since metallic lithium or its alloy, which must be handled in an inert gas, is not required when constructing the battery, assembly work can be performed safely. When storing a battery, if it is stored in a discharged state, there is virtually no metallic lithium in the battery in the discharged state, so even if the battery is destroyed, it will not catch fire.

Furthermore, by using a composition mainly composed of metal aluminum or its alloy and carbon material for the negative electrode, it is possible to form an electrode using materials such as powder, fiber, or porous material without having to process it into a thin sheet. The area can be increased, and a uniform and homogeneous negative electrode with a large area can be produced relatively easily.

[0010] Metallic lithium is uniformly and homogeneously formed on at least one of the surfaces or insides of metal aluminum, its alloy, or carbon material within the battery by charging. Since lithium ions are directly deposited from the electrolyte, metallic lithium is formed without contamination with impurities such as oxygen. Therefore, during repeated charging and discharging, concentration of current is less likely to occur, and internal short circuits can be effectively prevented.

[0011] Furthermore, since the metallic lithium produced by electrolysis (charging) and the electrolyte are very well connected, polarization can be reduced during discharging and a large current can be obtained. This effect becomes more effective by adding and mixing a lithium ion conductive solid or solid electrolyte to at least one of the positive electrode and the negative electrode. Among these, addition and mixing of a specific lithium ion conductive electrolyte composition mainly consisting of a polyether compound, a layered compound, and a lithium salt is particularly effective.

0012

[Embodiment] A lithium secondary battery according to an embodiment of the present invention will be described below with reference to the drawings. As the lithium thiolate in this example, it is possible to use a lithium salt of a reduced product of a disulfide compound represented by the general formula (R(S)y)n described in U.S. Pat. No. 4,833,048. can. R is an aliphatic group or an aromatic group, S is sulfur, y is an integer of 1 or more, and n is an integer of 2 or more. For example, C2N2S
2,5-dimercapto-1,3 represented by (SLi)2
, 4-lithium thiolate, etc., which liberate lithium ions through electrolytic oxidation and generate sulfur-sulfur bonds, thereby forming polymers.

[0013] As the ion-electronic mixed conductive polymer in this example, polythiophene or polypyrrole having ethylene oxide in the side chain, or a polymer compound of these doped with an anion such as iodine, etc. can be effectively used. . Further, it is more preferable to use a material that can have a porous fibril structure and retain a disulfide compound in its pores.

[0014] As the carbon material, natural graphite, artificial graphite,
Any of amorphous carbon, fibrous, powder, petroleum pitch type, and coal coke type can be used. The particles or fibers preferably have a diameter or fiber diameter of 0.01 to 10 microns and a fiber length of several micrometers to several mm.

Metal aluminum or its alloys include Al, Al-Fe, Al-Si, Al-Zn, Al
-Flake-like materials obtained by ultra-quenching such as -Li, spherical or amorphous powders obtained by mechanical pulverization in air or inert gas such as nitrogen, etc. are used. The particle size is preferably 1 μm to 100 μm in diameter.

The mixing ratio of carbon material and aluminum or aluminum alloy powder is 0.01 to 1 part of carbon material powder to 1 part of aluminum or aluminum alloy powder.
5 parts, preferably 0.05 to 0.5 parts. If the amount of carbon material is less than 0.01 part, it will be difficult to uniformly disperse the aluminum or aluminum alloy powder, the carbon powder will agglomerate, and the conductivity between the aluminum or aluminum alloy particles will be poor, making it ineffective as an electrode. If the amount exceeds 5 parts, the aluminum or aluminum alloy powder particles will be thickly covered with carbon particles, and contact with the electrolyte will be cut off, resulting in unstable potential and increased polarization.

Solid or solid lithium ion conductive electrolytes containing lithium ions include LiI, Li3
N-LiI-B2O3, LiI-H2O, Li-βAl
A polymer electrolyte made of polyethylene oxide in which an inorganic ion conductor such as 2O3 and an inorganic lithium salt are dissolved, L
A solid electrolyte membrane made of a polyacrylonitrile membrane containing propylene carbonate in which iClO4 is dissolved can be used. Among these, when mixing an electrolyte in at least one of the positive electrode or the negative electrode, a solid electrolyte composition consisting of a polyether compound obtained by adding ethylene oxide and butylene oxide to a polyamine compound, an ion exchange layered compound, and a lithium salt is preferably used. It will be done. In this solid electrolyte composition, the polyether compound, which is one of the constituent components, has a surface-active effect, and acts to uniformly disperse and mix the composition in at least one of the positive electrode and the negative electrode, reducing polarization. .

A polyether compound obtained by adding ethylene oxide and butylene oxide to a polyamine compound is a polyether compound obtained by adding ethylene oxide and butylene oxide to a polyamine compound.
It can be obtained by addition reaction of ethylene oxide and butylene oxide at 0°C and 1 to 10 atm. Polyamine compounds include polyethyleneimine,
Polyalkylene polyamines or derivatives thereof can be used. As a polyalkylene polyamine,
Examples include diethylenetriamine, triethylenetetramine, hexamethylenetetramine, dipropylenetriamine, and the like.

The number of moles of ethylene oxide and butylene oxide added is 2 to 150 moles per active hydrogen of the polyamine compound. Adding ethylene oxide (
The ratio of EO) to butylene oxide (BO) is 80/
20 to 10/90 (=EO/BO). The average molecular weight of the polyether thus obtained is 1000-5
It is 0,000,000. The amount of the polyether compound added is preferably 0.5 to 20% based on the total amount of the solid electrode composition.

Examples of ion-exchangeable layered compounds include clay minerals containing silicates such as montmorillonite, hectorite, saponite, and smectite, zirconium phosphate,
Phosphate esters such as titanium phosphate, vanadate, antimonic acid, tungstic acid, or quaternary
Examples include those modified with organic cations such as ammonium salts or organic polar compounds such as ethylene oxide and butylene oxide.

(Example 1) Ethylene oxide (E
O) and butylene oxide (BO) were added in such a way that the ratio of EO to BO was 30/70, and the average molecular weight was 1.
A 20% by weight polyether solution was prepared by dissolving 80,000 polyether compounds in acetonitrile. Furthermore, γ-zirconium phosphate powder with an average particle size of 15 μm was added to a polyether solution containing 10% LiCF3SO3 as a lithium salt so that the solid content was 30% by weight, and the mixture was stirred at 40°C for 24 hours. An electrolyte slurry was obtained.

After applying the electrolyte slurry on a smooth Teflon plate using a doctor blade, the electrolyte slurry was heated to 130°C.
By drying in an argon stream for 1 hour and vacuum drying for an additional 5 hours, the size was 80 x 80 mm and the thickness was 85 μm.
A sheet-like electrolyte composition of m was obtained.

Next, to 1 part by weight of the electrolyte slurry, 0.1 part by weight of artificial graphite powder with a degree of graphitization of 48% and an average particle size of 2 μm, 2,5-dimercapto-1,3,4-lithium 2 parts by weight of thiolate and 1 part by weight of polypyrrole doped with iodine and having ethylene oxide in the side chain were added and mixed to obtain a positive electrode slurry.

Polypyrrole having ethylene oxide in its side chain and doped with iodine (hereinafter abbreviated as PPEOI) was synthesized according to the production method shown below.

After dissolving 0.1 mol of 2-pyrrolecarboxylic acid in acetonitrile and cooling it to 0°C, 0.1 mol of bromine was added dropwise, followed by stirring, neutralization with a 20% aqueous sodium carbonate solution, and the aqueous layer was Extracted with ether. After drying this ether layer, the ether was removed to obtain a mixture in which bromine was substituted twice and once at the 3, 4, and 5 substitution positions of 2-pyrrolecarboxylic acid. This mixture was dissolved in a mixed solution of xylene and ethanolamine at a volume fraction of 20:1 and refluxed. After heating, the mixture was washed with a 30% acetic acid aqueous solution, and the organic layer was separated and dried. After removing xylene, a mixture of 2-substituted and 1-substituted bromo-2-pyrroles of bromine was obtained. This mixture was redissolved in xylene and fractionated using a silica gel column to obtain 3-bromopyrrole. 1 mol of 3-bromopyrrole obtained in this way is reacted with 1 mol of tetraethylene glycol to perform debromic acid, resulting in polypyrrole having ethylene oxide in the side chain.
An ether compound of tetraethylene glycol and pyrrole was obtained. Thereafter, the ether compound of tetraethylene glycol and pyrrole was mixed with iodine in an amount of 0.001 mol/
The desired PPEOI was obtained by infiltrating an ethanol solution containing 1 hour at 20° C. for 1 hour and then drying.

[0026] After applying the positive electrode slurry on a smooth Teflon plate using a doctor blade, it was dried in a dry argon stream at 130°C for 1 hour, and then vacuum-dried for 5 hours to obtain a size of 80 x 80 mm. A sheet-like positive electrode composition having a thickness of 160 μm was obtained.

Furthermore, if the polyether solution has an average particle size of 1
A mixed powder of 1 part by weight of 8 μm metal aluminum powder with a purity of 99.98% and 0.1 part by weight of artificial graphite powder with a degree of graphitization of 48% and an average particle size of 2 μm was prepared so that the solid content was 50%. and mixed at 40° C. for 24 hours to obtain a negative electrode slurry. The solid content ratio of the negative electrode slurry and the electrode slurry is 1.
:2 in an alumina ball mill for 24 hours to obtain an electrode composition slurry. After applying the electrode composition slurry on a smooth Teflon plate using a doctor blade, it was dried in a dry argon stream at 130°C for 1 hour, and then vacuum-dried for 5 hours to form a sheet with a size of 80 x 8.
A negative electrode composition in the form of a sheet having a diameter of 0 mm and a thickness of 180 μm was obtained.

Subsequently, a carbon sheet with a thickness of 50 μm formed from a mixture mainly composed of fluorocarbon resin and carbon powder, a positive electrode composition, an electrolyte composition, a negative electrode composition, and a carbon sheet were stacked in this order, and the temperature was increased. 150℃, pressure 200k
After heat-pressing under conditions of g/cm2, the material was cut into a size of 28 x 28 mm to form a unit cell.

Finally, a heat-adhesive conductive film with a thickness of 10 μm mainly made of synthetic rubber and carbon fiber is interposed, and a film with a thickness of 30 μm is inserted.
After thermally bonding copper foil that also serves as μm electrode leads to both sides of the cell, the entire cell is made up of a 38 μm thick polyethylene terephthalate film, a 50 μm thick aluminum foil, and a 50 μm thick polyethylene film. Battery A was produced by sealing with a laminate film.

(Comparative Example 1) 2,5-dimercapto-1,
Instead of 3,4-lithium thiolate, this was replaced with LiBF.
Ag/AgCl in acetonitrile in which 1 mol of 4 was dissolved.
Same as Example 1, except that a disulfide compound containing no lithium ions that was electrolytically oxidized at a potential of 1.0 V was used for the electrode, and a lithium alloy plate with a thickness of 200 μm and an aluminum content of 30 at% was used for the negative electrode. and battery B
was created.

(Example 2) 2,5-dimercapto-1,
1 part by weight of 3,4-lithium thiolate powder, 0.2 part by weight of polythiophene doped with iodine and having ethylene oxide in the side chain of a porous fibril structure with an average particle size of 0.3 microns, carbon Black 0.
1 part by weight, LiI-Li3N-B2O3 (mol = 1:1
:1) 1 part by weight of the powder was mixed with a toluene solution containing 6% by weight of low-density polyethylene (Exelen VL-200, density=0.9, manufactured by Sumitomo Chemical Industries, Ltd.) dissolved in the low-density polyethylene in the dried positive electrode composition. After mixing to a content of 5% by volume, the mixture was coated on a 200-mesh nylon net and dried to produce a positive electrode composition with a size of 80 x 80 mm and a thickness of about 155 μm.

[0032] Also, after mixing LiI-Li3N-B2O3 powder and a 6% by weight low density polyethylene toluene solution so that the content of low density polyethylene in the dry electrolyte composition was 35% by volume, a 200 mesh It was coated on a nylon net and dried to obtain an electrolyte composition with a size of 80 x 80 mm and a thickness of about 90 μm. Furthermore, 1 part by weight of metallic aluminum powder with a purity of 99.98% and an average particle size of 18 μm, 0.1 part by weight of an artificial graphite powder with a degree of graphitization of 90% and an average particle size of 0.6 μm, and LiI-Li3N- B2
The content of low density polyethylene in the negative electrode composition obtained by drying 0.5 parts by weight of O3 powder and a similar toluene solution was 7.5 parts by weight.
After mixing to give the same volume percentage, apply it on a 200 mesh nylon net and dry it to a size of 80 x 80 mm.
A negative electrode composition having a thickness of about 190 μm was obtained. Battery C was manufactured in the same manner as in Example 1 using a positive electrode composition, an electrolyte composition, and a negative electrode composition.

Polythiophene having ethylene oxide in its side chain and doped with iodine (hereinafter abbreviated as PTEOI) was synthesized according to the production method shown below.

First, polythiophene acetic acid was synthesized by electrolytically polymerizing thiophene acetic acid in acetonitrile with tetran-butylammonium perchlorate as a supporting electrolyte on a graphite electrode, and the resulting black polymer was electrochemically dedoped. Thereafter, the mixture was acid chloridated with thionyl chloride, and a dichloroethane solution of polyethylene glycol monomethyl ether was added, followed by heating under reflux to obtain a polythiophene acetic acid-polyethylene oxide graft polymer. Then, the polythiophene acetic acid-polyethylene oxide graft polymer was added with 0.0 iodine.
The desired PTE is obtained by soaking in an ethanol solution containing 0.01 mol/l at 20°C for 1 hour and then drying.
Obtained OI.

(Comparative Example 2) 2,5-dimercapto-1,
Instead of 3,4-lithium thiolate, this was replaced with LiBF.
Ag/AgCl in acetonitrile in which 1 mol of 4 was dissolved.
Example 2 was carried out in the same manner as in Example 2, except that a disulfide compound containing no lithium ions was electrolytically oxidized at a potential of 1.0 V to the electrode, and a 200 μm thick lithium alloy plate with an aluminum content of 30 at% was used as the negative electrode. I made Battery D.

[0036] Battery A of Example 1 produced in this manner,
Battery B of Comparative Example 1, Battery C of Example 2, and Battery B of Comparative Example 2 were subjected to a constant voltage of 3.6 volts at 65°C for 17
After time application, at 65℃, 1μA, 10μA, 100μA
, 500 μA, and 1 mA for 3 seconds each, and the current-voltage characteristics were evaluated by recording the battery voltage at that time. The results are shown in Figure 1. Example battery A and battery C
In comparison with Battery B and Battery D of Comparative Examples, the drop in voltage is smaller and a larger current can be obtained.

[0037]

[Effects of the Invention] As is clear from the above description of the embodiments,
According to the lithium secondary battery of the present invention, a positive electrode mainly composed of a mixture of a lithium thiolate compound having a sulfur-lithium ion bond that generates a sulfur-sulfur bond through electrolytic oxidation and an electron-ion mixed conductive polymer is used. By using a composition mainly composed of metallic aluminum or its alloy and carbon material for the negative electrode, it is possible to safely assemble a lithium secondary battery without handling chemically active metallic lithium or its alloy during battery assembly. can. The lithium secondary battery assembled in this way has the advantage that if it is stored in a discharged state, there is virtually no metallic lithium in the battery in the discharged state, so it will not catch fire even if the battery is destroyed. have. Furthermore, compared to conventional batteries that use metallic lithium or its alloy as a negative electrode, a larger current can be extracted.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the battery current-voltage characteristics of a lithium secondary battery according to an example of the present invention and a lithium secondary battery according to a comparative example.

Claims (3)

[Claims] Claim 1: A positive electrode active material using a mixture mainly consisting of a lithium thiolate compound having a sulfur-lithium ion bond that generates a sulfur-sulfur bond through electrolytic oxidation, and an ion-electronic mixed conductive polymer; A lithium secondary battery comprising an electrolyte using a solid or solid lithium ion conductive electrolyte containing aluminum, and a negative electrode using a composition mainly composed of metal aluminum or its alloy and a carbon material. 2. The lithium secondary battery according to claim 1, wherein a solid or solid lithium ion conductive electrolyte containing lithium ions is mixed into at least one of the positive electrode active material and the negative electrode composition. 3. A solid or solid lithium ion conductive electrolyte containing lithium ions comprises a polyether compound obtained by adding at least one of ethylene oxide or propylene oxide to a polyamine compound, an ion exchange layered compound, and a compound having the formula LiX. The represented lithium salt (X
The lithium secondary battery according to claim 1 or 2, wherein the lithium secondary battery is a solid composition containing at least an anion of a strong acid.