JP2606632B2 - Lithium secondary battery - Google Patents

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 comprising a solid or solid lithium ion conductive electrolyte.

[0002]

2. Description of the Related Art A high voltage of 3 to 4 volts and 100 Wh /
As a lithium secondary battery that can be expected to have a high energy density of over kg, use lithium metal or lithium alloy for the negative electrode, and titanium dioxide, molybdenum disulfide, vanadium oxide, cobalt oxide, etc. A battery using an inorganic material has been proposed. As the electrolyte, a liquid electrolyte in which a lithium salt such as lithium perchlorate or lithium borofluoride is dissolved in an aprotic organic solvent such as propylene carbonate or dimethoxyethane is exclusively used. Since the ionic conductivity of this liquid electrolyte is two to three orders of magnitude lower than the aqueous electrolyte used for nickel cadmium secondary batteries or lead-acid batteries, the electrode area must be reduced to obtain a large current comparable to these batteries. It is necessary to make the separator larger and make the separator thinner. The positive electrode is used by processing a composition obtained by mixing a powdery positive electrode active material, a conductive material, and a binder into a sheet. In addition to processing into a sheet,
By reducing the particle size of the powder or using a porous powder, the electrode area of the positive electrode can be increased. However, lithium metal or lithium alloy which is soft and difficult to process powder has to rely on thin foil processing to obtain a large electrode area. The negative electrode formed by processing lithium into a thin sheet is joined to the positive electrode via a separator such as a polypropylene nonwoven fabric, spirally wound, placed in a battery container, and poured with an electrolyte to be assembled. All the assembly operations are performed in a dry inert gas.

[0003]

An important factor in assembling a lithium secondary battery is to make the electrodes in contact with the electrolyte uniform and uniform over the entire surface. In general,
The positive electrode is composed of a composition of a positive electrode active material, a conductive material, and a binder. A relatively homogeneous positive electrode can be obtained as long as a chemically stable positive electrode active material is selected and uniformly mixed. However, for the negative electrode, it is difficult to uniformly and uniformly process metallic lithium or lithium alloy foil having a thickness of several μm to several tens of μm through a multi-stage rolling process. Further, it is difficult to uniformly assemble the battery due to local tension in the battery assembly process. Then, when the battery is charged and discharged, the dissolution and deposition reaction of lithium proceeds unevenly in the negative electrode surface, and the unevenness is amplified as the charge / discharge cycle is repeated. Deposition occurs, breaks through the separator and connects to the positive electrode, causing an internal short circuit. When an internal short circuit occurs, a large current flows and the battery is heated, the vapor pressure of the organic solvent increases, and the battery ruptures, metallic lithium is exposed to the atmosphere, reacts with water, generates hydrogen, and leads to ignition. Thus, the conventional lithium secondary battery has an extremely dangerous configuration.

The present invention has been made to solve such a problem, and comprises a homogeneous lithium anode, a safe lithium secondary battery that does not deposit resinous lithium and short-circuit the battery even after repeated charge / discharge cycles. It is intended to provide a secondary battery.

[0005]

According to the present invention, a battery can be assembled without using lithium metal or a lithium alloy for a negative electrode.
In order to obtain a lithium secondary battery in which substantially no metallic lithium is present in the battery after the discharge, an ionic electron containing a lithium thiolate group having a sulfur-lithium ion bond that generates a sulfur-sulfur bond by electrolytic oxidation A mixed conductive polymer is used for the positive electrode. Then, for the negative electrode, a composition mainly composed of metallic aluminum or an alloy thereof and a carbon material is used so that lithium ions from the lithium thiolate compound are uniformly deposited by battery charging. In order to fix a soluble lithium thiolate compound to the positive electrode,
A solid or solid lithium ion conductive electrolyte is used in a normal battery operating temperature range (−20 to 60 ° C.). More preferably, one or both of the positive electrode and the negative electrode are mixed with a solid or solid lithium ion conductive electrolyte.

[0006]

Since lithium metal or its alloy, which needs to be handled in an inert gas, is not required at the time of battery construction, the battery can be safely assembled. When storing the battery, the battery may be stored in a discharged state. In the discharged state, there is substantially no metallic lithium in the battery, so that even if the battery is destroyed, it will not ignite. Furthermore, by using a composition mainly composed of metal aluminum or its alloy and a carbon material for the negative electrode, it can be formed into a powdery, fibrous, or porous material without processing into a thin sheet to increase the reaction area. By doing so, the electrode area can be enlarged, and a large-area, uniform and homogeneous negative electrode can be formed relatively easily. Lithium metal is formed uniformly and uniformly on the surface of metal aluminum or its alloy or carbon material or in the inside of the battery by charging. Since lithium ions are deposited directly from the electrolyte,
Metal lithium is formed without mixing impurities such as oxygen. Therefore, even if the charge and discharge are repeatedly performed, current concentration at the negative electrode hardly occurs, and an internal short circuit of the battery due to deposition of lithium can be effectively prevented. In addition, since the lithium metal and the electrolyte generated by the electrolysis (charging) are connected in an extremely good state, the polarization can be reduced at the time of discharging, and a large current can be obtained. This function is more effective when one or both of the positive electrode and the negative electrode are mixed with a lithium ion conductive solid or solid electrolyte. Among them, addition and mixing of a specific lithium ion conductive electrolyte composition comprising a polyether compound, a layered compound and a lithium salt is particularly effective.

[0007]

The lithium thiolate group of the present invention includes a compound represented by the general formula (R) disclosed in U.S. Pat. No. 4,833,048.
(S) _y ) A lithium salt of a reduced form of a disulfide compound represented by _n can be used. Wherein R represents an aliphatic group or
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, such as 2,5-dimercapto-1,3,4-lithium thiolate represented by the formula (1) and lithium diethyldithiocarbamate represented by the formula (2) release lithium ions by electrolytic oxidation, -A polymer that forms a polymer by the formation of a sulfur bond is used.

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In the present invention, monomers composing the ionic-electron mixed conductive polymer include aniline, pyrrole, thiophene, etc., which polymerize to give electron conductivity, and ethylene.
A derivative in which a salt represented by an oxide chain is ionized and dissolved to introduce ion-conducting groups is used. Among the mixed ionic electronic conducting polymer obtained by polymerizing these derivatives
Also , an ionic / electron mixed conductive polymer which causes a highly reversible oxidation-reduction reaction at 0 to ± 1.0 volt with respect to an Ag / AgCl electrode is effectively used. In the present invention, the ion-electron mixed conductive polymer is prepared by preliminarily charging a salt to a monomer, such as aniline, pyrrole, or thiophene, which gives electron conductivity by polymerization.
It can be obtained by adding a group that gives away ion conductivity by dissolving away and a lithium thiolate group, and then polymerizing the added monomer by electrolytic oxidation or chemical oxidation. Depending on the polymerization conditions, the lithium thiolate group added to the monomer forms a sulfur-sulfur bond to form an ion-electron mixed conductive polymer in a polymerized form, or the lithium thiolate group does not polymerize. Can be used to obtain an ion-electron mixed conductive polymer.

As the carbon material, natural graphite, artificial graphite,
Any of amorphous carbon, fibrous, powdery, petroleum pitch type, and coal coke type can be used. Particle or fiber size, diameter or fiber diameter 0.01 to 10μ
m, the fiber length is preferably from several μm to several mm.

[0010] Metal aluminum or its alloys include flakes obtained by ultra-quenching such as Al, Al-Fe, Al-Si, Al-Zn, Al-Li, Al-Zn-Si, in air or Spherical or amorphous powder obtained by mechanical pulverization in an inert gas such as nitrogen is used. The particle size is preferably 1 μm to 100 μm in diameter. The mixing ratio of the carbon material and the aluminum or aluminum alloy powder is 0.01 to 5 parts, preferably 0.05 to 0.5 part, of the carbon material powder per 1 part of the aluminum or aluminum alloy powder. If the amount of the carbon material is less than 0.01 part, it is difficult to uniformly disperse the aluminum or aluminum alloy powder, and the carbon powder is agglomerated, the electric conduction between the aluminum or aluminum alloy particles becomes poor, and the electrode does not work effectively. In addition, when the content is 5 parts or more, the aluminum or aluminum alloy powder particles are thickly covered with carbon particles, and the contact with the electrolyte is cut off.
Potential becomes unstable or polarization increases.

As a solid or solid lithium ion conductive electrolyte containing lithium ions, LiI, Li ₃ N—LiI—
Contains inorganic ion conductors such as B ₂ O ₃ , LiI ・ H ₂ O, Li-β-Al ₂ O ₃ , polymer electrolyte composed of polyethylene oxide in which inorganic lithium salt is dissolved, and propylene carbonate in which LiClO ₄ is dissolved For example, a solid electrolyte membrane made of a polyacrylonitrile film can be used. Among them,
When mixing the electrolyte into one or both of the positive electrode and the negative electrode, use a solid electrolyte composition comprising a polyether compound obtained by adding ethylene oxide and butylene oxide to a polyamine compound, an ion-exchangeable layered compound, and a lithium salt. Is desirable. In this solid electrolyte composition, a polyether compound, which is one of the constituent components, has a surface-active action, and acts to uniformly disperse and mix the composition on either or both of the positive electrode and the negative electrode, Reduce polarization. The polyether compound obtained by adding ethylene oxide and butylene oxide to the polyamine compound can be obtained by subjecting the polyamine compound to addition reaction of ethylene oxide and butylene oxide at 100 to 180 ° C. and 1 to 10 atm under an alkali catalyst. As the polyamine compound, polyethyleneimine, polyalkylenepolyamine or a derivative thereof can be used. Examples of the polyalkylene polyamine include diethylene triamine, triethylene tetramine, hexamethylene tetramine, dipropylene triamine and the like. The addition mole number of ethylene oxide and butylene oxide is 2 to 150 moles per active hydrogen of the polyamine compound.
The ratio of ethylene oxide (EO) and butylene oxide (BO) to be added is 80/20 to 10/90 (= EO / BO)
It is. The polyether thus obtained has an average molecular weight of 1,000 to 5,000,000. The addition amount of this polyether compound is preferably 0.5 to 20% based on the total amount of the solid electrode composition. Examples of the ion-exchangeable layered compound include montmorillonite, hectorite, saponite, clay minerals including silicates such as smectite, zirconium phosphate, phosphates such as titanium phosphate, vanadic acid, antimonic acid, tungstic acid, or ,
Those modified with an organic cation such as a quaternary ammonium salt or an organic polar compound such as ethylene oxide or butylene oxide may be mentioned.

Example 1 84 g (1 mol) of thiophene and 100
ml of carbon tetrachloride were mixed and cooled to 0 ° C. In addition, 500
A solution of g (3.1 mol) of bromine in 300 ml of carbon tetrachloride was gradually added. After all were mixed, carbon tetrachloride was distilled off, 15 g of sodium hydroxide was added, and the mixture was heated on a steam bath for 4 hours. After the product was separated from the alkali layer and dried, a mixture of monosubstituted, disubstituted and trisubstituted thiophene bromides was obtained by distillation. Dissolve this mixture in xylene,
Separation was performed using a silica gel column to obtain 30 g of 2,3,5-tribromothiophene.

The thus obtained 32 g (0.1 mol) of 2,2
3,5-tribromothiophene and 6.5 g (0.2 mol) of metallic zinc
6 g (0.2 mol) of acetic acid was reacted to obtain 3-bromothiophene.

The thus obtained 3-bromothiophene 0.5 m
ol was reacted with 0.5 mol of tetraethylene glycol to remove debrominated acid, thereby obtaining an ether compound of tetraethylene glycol and thiophene represented by the formula (3) (hereinafter referred to as thiophene derivative 1).

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Further , the thiophene derivative 1 was subjected to another bromination to obtain a 4-bromo-substituted thiophene derivative 1 . 4 g was added to 0.05 mol of the 4-bromo- substituted product thus obtained.
Of thiourea in acetonitrile to give thiophene
0.01 mol of the 4-mercapto- substituted derivative of derivative 1 was obtained. This 4-
Substituted mercapto in chlorine is 2,5-dimercapto-1,3,4-
Is reacted with a thiadiazole 0.01 mol, to obtain a tetraethylene glycol ether derivatives of thiophene was introduced disulfide (hereinafter referred to as thiophene derivative 2). this
The structure of the thiophene derivative 2 is represented by the formula (4). Thiophene derivative 2 thus obtained (1 mol / l)
As a monomer in propylene carbonate, with lithium perchlorate as the supporting electrolyte, relative to the saturated calomel reference electrode
Electrostatic oxidation at 1.2 to 1.5 V was performed to obtain an ion-ion mixed conductive polymer containing a lithium thiolate group. this
The structure of the ion-electron mixed conductive polymer is expressed by equation (5).
It is. N in the formula (5) is an integer of 1 or more;
m is 0 or an integer of 1 or more.

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The average molecular weight obtained by adding ethylene oxide (EO) and butylene oxide (BO) to polyethyleneimine containing 10 N atoms in the molecule so that the ratio of EO to BO is 30/70 is obtained. 180000 polyether compounds were dissolved in acetonitrile to prepare a 20% by weight polyether solution. Further, γ-zirconium phosphate powder having an average particle diameter of 15 μm was added to a polyether solution in which 10% of LiCF ₃ SO ₃ was dissolved as a lithium salt so as to have a solid content of 30% by weight. to obtain a time撹拌 mixed electrolyte slurry. The electrolyte slurry is applied on a smooth Teflon plate using a doctor blade, dried for 1 hour in a dry argon gas stream at 130 ° C., and further vacuum-dried for 5 hours to obtain a size of 80 × 8.
A sheet-shaped electrolyte composition having a thickness of 0 mm and a thickness of 85 μm was obtained. Next, a graphitization degree of 4 was added to 1 part by weight of the electrolyte slurry.
8%, 0.1 part by weight of artificial graphite powder having an average particle size of 2 μm, and 2 parts by weight of the ion-electron mixed conductive polymer containing a lithium thiolate group were mixed to obtain a positive electrode slurry. The positive electrode slurry was applied on a smooth Teflon plate using a doctor blade, dried for 1 hour in a dry argon gas stream at 130 ° C., and further vacuum-dried for 5 hours to obtain a size of 80 × 80 mm and a thickness of 160 μm. Thus, a sheet-shaped positive electrode composition was obtained. Further, a mixed powder of 1 part by weight of a metal aluminum powder having an average particle size of 18 μm and a purity of 99.98% and 0.1 part by weight of an artificial graphite powder having a graphitization degree of 48% and an average particle size of 2 μm was added to the polyether solution. 5 solids content
The mixture was added at 0% and mixed at 40 ° C. for 24 hours to obtain a negative electrode slurry. The negative electrode slurry and the electrolyte slurry were mixed in an alumina ball mill for 24 hours so that the solid content ratio was 1: 2, to obtain an electrode composition slurry. The electrode composition slurry was applied on a smooth Teflon plate using a doctor blade, dried in a dry argon gas stream at 130 ° C. for 1 hour, and further vacuum-dried for 5 hours to obtain a size of 80%.
A sheet-shaped negative electrode composition having a size of × 80 mm and a thickness of 180 μm was obtained.

The carbon sheet having a thickness of 50μm comprising a mixture of fluorocarbon resin and carbon powder, the positive electrode composition, electrolyte composition, the anode composition, one on top of the carbon sheet, temperature 1
After hot pressing under the condition of 50 ° C. and a pressure of 200 kg / cm ² , 28
A cell was cut into a size of × 28 mm. A copper foil serving also as a 30 μm-thick electrode lead is thermally bonded to both sides of the unit cell via a 10 μm-thick heat-conductive conductive film made of synthetic rubber and carbon fiber, and then the entire unit cell is 38 μm in thickness.
And a 50 μm-thick aluminum foil and a 50 μm-thick polyethylene film to form a battery A.

(Comparative Example 1) A thiophene derivative 1 was replaced with LiBF by replacing the ion-electron mixed conductive polymer containing a lithium thiolate group with LiBF.
Ag / AgCl ₄ with 1 mole dissolved in acetonitrile
Same as Example 1 except that a lithium electrode-free disulfide compound electrolytically oxidized at a potential of 1.0 V with respect to the electrode was used, and a lithium alloy plate having a thickness of 200 μm and an aluminum content of 30 atom% was used for the negative electrode. And battery B
Was prepared.

Example 2 The thiophene derivative 2 synthesized in Example 1 was replaced with lithium iodide.
The average particle size was 0.3 μm synthesized by a chemical polymerization method using cupric borofluoride as an oxidizing agent in an acidic aqueous solution in which
Thiophene derivative 2 having a fibril structure 2
0.2 parts by weight of a polymer powder, 0.1 carbon black
6 parts by weight of low-density polyethylene (Excellen VL-200, density = 0.9, manufactured by Sumitomo Chemical Co., Ltd.) was dissolved in 1 part by weight of LiI-Li ₃ NB ₂ O ₃ (molar ratio = 1: 1: 1) powder by weight. After mixing the toluene solution with the dried low-density polyethylene in the positive electrode composition so that the content of the low-density polyethylene is 5% by volume, the mixture is coated on a 200-mesh nylon net, dried, and dried to a size of 80 × 8.
A positive electrode composition having a thickness of 0 mm and a thickness of about 155 μm was produced. Moreover, after the content of LiI-Li ₃ NB ₂ O ₃ powder and 6 wt% of low density polyethylene of the electrolyte composition was dried toluene solution of the low density polyethylene was mixed in a 35 volume%, 200 mesh And dried on a nylon net to obtain an electrolyte composition having a size of 80 × 80 mm and a thickness of about 90 μm. Further, a purity of 99.98 having an average particle size of 18 μm.
% Of metallic aluminum powder and a degree of graphitization of 90
%, An artificial graphite powder having an average particle diameter of 0.6 μm, 0.1 part by weight, a LiI-Li ₃ NB ₂ O ₃ powder, 0.5 part by weight, and a similar toluene solution in a dried negative electrode composition. After mixing so that the content of high density polyethylene is 7.5% by volume, 200
Apply on mesh nylon net, dry and size 80
A negative electrode composition having a size of × 80 mm and a thickness of about 190 μm was obtained. Battery C was prepared in the same manner as in Example 1 using the positive composition, the electrolyte composition, and the negative electrode composition.

Comparative Example 2 The thiophene derivative 1 was replaced with an acidic aqueous solution in place of the ion-electron mixed conductive polymer containing a lithium thiolate group.
Chemical polymerization method using cupric borofluoride as an oxidizing agent in liquid
Lithium ion containing no lithium thiolate group
Battery D was produced in the same manner as in Example 2, except that a mixed conductive polymer was used as a positive electrode and a lithium alloy plate having a thickness of 200 μm and an aluminum content of 30 atomic% was used as a negative electrode.

(Evaluation of Battery Characteristics) The battery A of Example 1, the battery B of Comparative Example 1, the battery C of Example 2, and the battery B of Comparative Example 2 thus manufactured at 3.6 ° C. at 3.6 ° C. After applying a constant voltage of _V for 17 hours, at 65 ° C, 1 μA, 10 μA
A, 100 μA, 500 μA, and 1 mA were respectively discharged for 3 seconds, and the battery voltage at that time was recorded to evaluate the current-voltage characteristics. The results are shown in FIG. The batteries A and C of the example have a smaller voltage drop and a larger current than the batteries B and D of the comparative example.

[0022]

As is apparent from the above description of the embodiments, according to the present invention, the ionic electron containing a lithium thiolate group having a sulfur-lithium ion bond which forms a sulfur-sulfur bond by electrolytic oxidation. By using a positive electrode mainly composed of a mixed conductive polymer and a negative electrode composed of a composition mainly composed of metal aluminum or its alloy and a carbon material as a negative electrode, chemically active metallic lithium or its alloy can be used in a battery. The lithium secondary battery can be safely assembled without handling during assembly. The lithium secondary battery assembled in this manner has an advantage that when stored in the discharged state, the battery does not ignite even when the battery is destroyed, since substantially no metallic lithium is present in the battery in the discharged state. doing. Furthermore, compared with a conventional battery using metal lithium or an alloy thereof as a negative electrode, the battery can be charged and discharged with a larger current. Furthermore, even if charging with a large current is repeated, resinous lithium does not precipitate, and the battery does not short-circuit.

[Brief description of the drawings]

FIG. 1 is a diagram showing current-voltage characteristics of a battery of an example of the present invention and a battery of a comparative example.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Tadashi Soson 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. In-company (56) References JP-A-4-267707 (JP, A) JP-A-4-267074 (JP, A)

Claims (3)

(57) [Claims] An ion-electron mixed conductive polymer containing a lithium thiolate group having a sulfur-lithium ion bond, which forms a sulfur-sulfur bond by electrolytic oxidation, is used as a positive electrode active material, and a solid or solid containing lithium ions is used. A lithium secondary battery in which an electrolyte mainly composed of a lithium ion conductive composition is used as a battery electrolyte, and a composition mainly composed of metal aluminum or an alloy thereof and a carbon material is used as a negative electrode. 2. The lithium secondary battery according to claim 1, wherein a solid or solid lithium ion conductive electrolyte containing lithium ions is mixed with the positive electrode active material and the negative electrode composition. 3. A polyether compound in which a solid or solid lithium ion conductive electrolyte containing lithium ions has a polyamine compound added with one or both of ethylene oxide and propylene oxide, and
3. The lithium secondary battery according to claim 1, which is a solid composition mainly composed of an ion-exchangeable layered compound and a lithium salt represented by the formula LiX (X is an anion of a strong acid). Next battery.