JPS6376261A - Secondary cell - Google Patents

Abstract

PURPOSE:To secure such a secondary cell that is high in strength, and even if charging and discharging are repeated, not easily disintegrated and, what is more, excellent in a cell characteristic, by using a negative electrode, made up of alloying lithium electrochemically, on top of aluminum or an aluminum alloy reinforced with fibrous material. CONSTITUTION:This secondary cell is one that uses a negative electrode, made up of alloying lithium electrochemically, on top of aluminum or an aluminum alloy reinforced with fibrous material. It is desirable that the fibrous material is low in reactivity with an electrolyte and excellent in electrical conductivity. As for a method of compoundization with the fibrous material, for example, there are following ways that a method of mixing alloyed powder and a fiber and molding by heating, a method of processing the fiber into sheet form and dipping it in a melted alloy layer, having the alloy impregnated in the sheet inside, and a method of stacking alloyed foil and the fiber alternately and molding it by heating, etc. And, in case of a carbon fiber, it is desirable that such one covering a metal on the carbon fiber as compared with a complex with the carbon fiber itself. In the compounded electrode substrate, the fiber and the metal become entangled with each other so that disintegration of the substrate due to separation and discharge of the lithium is restrained, thus it comes to such one as excellent as a negative electrode.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has a high energy density, small self-discharge,
The present invention relates to a secondary battery with a long cycle life and good charge/discharge efficiency (coupon efficiency).

[Conventional technology]

Currently, the commonly used secondary batteries are lead acid batteries, Ni/C
There are d batteries etc. These secondary batteries are generally aqueous batteries, and the battery voltage of their single cells is about 2.0V at most. In recent years, research and development efforts have been actively conducted on secondary batteries that use 1-i as a negative electrode as secondary batteries capable of achieving high battery voltages.

When 1-i is used as an electrode, water and 1-i do not show high reactivity with each other, so it is necessary to use a non-aqueous electrolyte.

However, when carrying out a secondary battery reaction using Li as a negative electrode active material, dendrites are formed when Li is reduced during charging, causing problems such as a decrease in charge/discharge heart rate and a short circuit between the positive and negative electrodes. .

To solve this problem, a method of preventing l-i dendrites by alloying IIU itself with AJ [
B, M, L, 1st class Niji 11-Naru Or. Electrochemical, Society (B, M, L, R
ao et al: J, E Icctroch
em.

Soc, ) pp. 1490-1492 (1977))
Method using wood alloy [24th Battery Symposium, 18
09 (1983)) etc. have been proposed.

[Problem that the invention seeks to solve]

When using an alloy of 1i and Aj for the negative electrode, l in Aj
The maximum charging/discharging N flow density is limited by the diffusion rate of i, and the L1 diffusion rate of the β phase is fast in the alloy. Therefore,
It is common practice to mold β-type Li-A4 alloy powder and use it for electrodes, but it is difficult to mold β-type 1-i-A1 alloy into a plate shape, and even if it can be molded,
As the electrode is repeatedly charged and discharged, it collapses. In addition, mixing an appropriate binder to prevent collapse will reduce the performance of the bridge.

In addition, when Wood alloy is used as the negative electrode for Li storage and release, the collapse of the substrate is suppressed, and the amount of Li storage is also reduced.
Although it is larger than using 4 alloy, l in Wood alloy
-i diffusion rate is slow, and there is a drawback that the single flow density cannot be increased compared to when a β-type 1-i-A4 alloy is used for the negative electrode.

Further, in a secondary battery in which lithium is absorbed and released electrochemically on an A7 alloy, there are problems such as the alloy substrate disintegrating with cycles, resulting in a decrease in battery performance.

As a result of intensive research to solve the above problems, the present inventors found that at the time of manufacturing A, f, or A1 alloy substrates, the substrates are mixed with III-like substances and mixed with II-like substances.
It was discovered that an excellent negative electrode material can be obtained by manufacturing this material.

The present invention has been made based on the above discovery, and provides a secondary battery that eliminates the conventional drawbacks, has high strength, does not easily collapse even after repeated charging and discharging, and has excellent battery characteristics. The purpose is to

(Means for Solving the Problems) The present invention has been made to achieve the above object, and its gist is to electrochemically alloy lithium on Aj or A1 alloy reinforced with a fibrous material. The secondary battery uses a negative electrode made of

[Specific structure and operation of the invention]

The present invention will be explained in detail below.

It is desirable that the fibrous material used in the present invention has low reactivity with the electrolytic solution and good electrical conductivity. Such fibers include carbon fibers: W, Mo, Ni,
Cu, Fe, Ag, Au, Pt.

CO, TiW metal fiber M: Alloy fiber such as AJ alloy, Fe alloy, Cu alloy, etc.: Inorganic fiber such as alumina, boron, silicon carbide, boron nitride, silica, or carbon fiber coated with metal I! Among them, gold WA fibers or carbon fibers coated with metal are particularly preferred.

Naturally, it is preferable that the above-mentioned fiber has low reactivity with the electrolytic solution and good electrical conductivity.The fiber can have various shapes depending on the method of preparation, but it is particularly preferable to have a cylindrical shape. preferable. The diameter is preferably ~50 μm or less, but the thickness of the negative electrode made by this is 100 μm or less.
Considering that the thickness is ~200 μm, 1 to 10 μm is appropriate.

The A1 alloy used includes Aj of 5Qwt% or more,
MO, Mn, Si, Cu, Ti, Fe.

An alloy containing 5Qwt% or less of one or more components selected from the group consisting of Zn, pb, Cr, Ca, Sn, and In is used, and in particular, MO.

Multicomponent alloys with Ca, Pb and In are preferred.

In addition, there are no particular restrictions on the method of compounding with the fibrous material, but examples include a method of mixing alloy powder and fibers and heat molding, processing the fibers into a sheet shape, and immersing the fibers in a molten alloy layer. Method of impregnating alloy inside sheet, alloy foil and l
There is a method in which I-fibers are alternately formed into Vi layers and then heated and molded, and any method may be used.

Furthermore, in the case of carbon fibers, carbon fibers coated with metal are preferable to composites with carbon and miscellaneous materials.

Composite electrode substrates are created using these methods! ! Since the fibers and metal are entangled, collapse of the substrate due to precipitation and release of Ll is suppressed, making it an excellent negative electrode.

Next, the Li
The method for electrodepositing is explained below.

In a non-aqueous electrolyte containing salt or in a molten salt,
The above-mentioned substrate is used for negative contamination, and in general, lithium metal is used as a positive electrode, and electricity corresponding to a set electric power source is passed at a constant current or constant voltage to alloy the substrate.

In this case, the alloying electricity () needs to be suppressed to an amount of electricity equivalent to electrodepositing 0.6 atoms or less of li per 1 atom of aluminum contained in the substrate.

If the amount of 1-i deposited exceeds 0.6 atoms, the amount of electricity ω that can be charged and discharged in each cycle is greatly limited, and the battery performance deteriorates. -i
It is preferable to alloy it initially. Within this range,
The amount of electricity that can be charged and discharged in each cycle and the charging and discharging efficiency are 6
The number of cycles that can be repeatedly charged and discharged until the voltage drops to 0% is large, and the electrode performance is extremely good.

When alloying with a constant current, the current density is 10m^/C
A value of 1i or less is preferable; if it exceeds this, dendrites will precipitate on the substrate surface. A particularly preferred current density is 3a+
^/cd or less. On the other hand, when alloying is carried out at a constant voltage, the potential of the substrate is 0 compared to the oxidation-reduction potential of Li/Li9.
．． 2■ to 0.4V is good.

At a potential lower than 0.2■, li dendrites occur,
At potentials higher than 0.4 ■, the alloying time takes very long.

The active material that can be used for the positive electrode in the secondary battery of the present invention is not particularly limited as long as it can electrochemically react reversibly with a non-aqueous electrolyte at a higher potential than the negative electrode.

For example, it is also possible to use a material that forms a living room compound with L;9, such as TiS2, or an inorganic amorphous oxide that can reversibly take in and take out li+. Further, conductive polymers such as polyacetylene, polypyrrole, polythiophene, polyaniline, polyparaphenylene, etc., which can reversibly take in and out anions, can also be used. These 3Jlft
Among i-type polymers, polyaniline is the positive electrode material that makes the most of the performance of the battery of the present invention. This is because polyaniline has an extremely high limit concentration for doping with anions per active material weight a among conductive polymers, has high stability against air, moisture, etc., and has an extremely low self-discharge rate.

The electrolytic solution that can be used in the secondary battery of the present invention is Li
8F4, Li BPh4. LiBBtl<.

LiClO2,L! PFs, L! At least one type of 1i salt such as AsFs is dissolved or mixed in a non-aqueous solvent.

Examples of the nonaqueous solvent include carbonates such as propylene carbonate and ethylene carbonate: sulfolane, 3-
Sulfolanes such as methyl-sulfolane: Ethers such as 1,2-dimethoxyethane, 1,1-dimethoxyethane, tetrahydrofuran, 2-methyl-tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioquinrane: Lactones such as γ-butyrolactone and δ-butyrolactone, phosphoric esters such as trimethyl diphosphate and triethyl phosphate, and other esters can be used. However, it is not necessarily limited to these. Moreover, these solvents can also be used as a mixed solvent in which two or more types are mixed.

Among the above solvents, propylene carbonate, 1.2
-Dimethoxyethane, tetrahydrofuran, 2-methyl-tetrahydrofuran, sulfolane, or a mixed solvent of propylene carbonate and ethers are preferred. The reason for this is that these solvents can exist relatively stably in both the positive electrode active material and the negative electrode active material, and do not significantly impede reversible charging and discharging of the battery.

〔Example〕

Next, the secondary battery according to the present invention will be described with reference to Examples and Comparative Examples.

Example 1 (Manufacture of negative electrode) Carbon li! with a diameter of 8 μm and a length of 20 m+. The cloth was immersed in a copper electroless plating solution (manufactured by Takaracho Kagaku Kogyo Co., Ltd., Cuposite Copper Mix #328) for 2 minutes and then pulled up to coat the surface with 0.2 to 0.5 μm of copper. After thoroughly mixing 1 allt of carbon, 0.027 g, and 0.2458 g of A1 alloy powder (JIS NQ5052), it was filled into a 10 cj Iφ carbon mold,
While creating a vacuum using a vacuum pump, it was heated to 600°C and pressurized to 30 K9/ci using hydraulic pressure. 600℃
After holding for 30 minutes, the heating was stopped and the mixture was slowly cooled while still being pressurized. After the temperature reached room temperature, pressurization was stopped, the carbon fiber reinforced I'4 alloy was taken out from the mold, and the plate fPJ
150μm, bulk rfi2.3t 9/cd 10αφ
I made a board for this.

This substrate was cut into a diameter of 15 mm to obtain a negative electrode substrate with a t-meter of 14.6 mm.

(Manufacture of positive electrode) Aniline was polymerized while stirring a solution in which 0.5 mol/J of aniline was dissolved in a 1N aqueous hydrochloric acid solution and gradually adding ammonium persulfate as an oxidizing agent. The per[Q ammonium used was 1% per aniline monomer.
:1 molar ratio, and the reaction solution was kept at approximately 40° C. from the start of the reaction until the end of the reaction, and the reaction was allowed to proceed for 3 hours.

After the synthesized polyaniline was separated by filtration, it was neutralized with an excess aqueous ammonia solution, further washed with water, and then thoroughly dried under reduced pressure at 220°C.

This polyaniline was mixed with 7 wt% each of a polytetrafluoroethylene binder and acetylene black.
A pellet having a diameter of 15 sφ was produced. Thereafter, polyaniline was reduced in the pellet in a 5 wt % aqueous hydrazine solution, and the pellet was dried under reduced pressure at 220° C. to obtain a positive electrode.

(Battery Performance Test) The negative electrode and positive electrode prepared as described above were assembled into a battery container, and a battery test was conducted. FIG. 1 is a longitudinal cross-sectional view of the battery used in the battery test, and in the figure, reference numeral 1 indicates the negative electrode.

A negative electrode 1 is in contact with a nickel current collector 2, a glass fiber porous separator 3 impregnated with an electrolytic solution is stacked, a positive electrode 4 and a platinum current collector 5 are stacked, and the stack is assembled into a screw-type polytetrafluoroethylene container 6. The leads Ij17, 7 connected to the current collector 2.5 were pulled out from the container 6 to form a battery.

In the above battery, the thickness of the separator 3 is set to 1 mm to ensure that sufficient electrolyte exists, and the electrolyte contains LtBF4.
was prepared by dissolving it in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane in a volume ratio of 1:1 so as to have a concentration of 1 mol/j'fA degrees.

The assembled battery was connected to a charging/discharging device, and the first charging was started slowly at a current density of 0.51 A/cd. The amount of electricity charged is 20m0.
f%, and 60m0J% was the limit for positive electrode aniline.

After 1 p of the first charging, the current density was increased to 2.5 m^/d, and the test was repeated by discharging and charging. In this case, the battery voltage was adjusted to be maintained between 4.0 and 2.0V. Hereinafter, repeated charging and discharging tests were conducted until the coulombic efficiency during charging and discharging decreased to 50%, and that point was defined as the life span.

As a result, the cycle life was 525 times, and the self-discharge rate was 5.6%/month. The energy density at that time is 28
It was 0wh/kg.

Example 2 (Manufacture of negative electrode) 4.5μm tungsten! ! A sheet was manufactured by processing the rough material to have a porosity of 80% and a thickness of 150 μm. This sheet was immersed in a JIS Nα3004 A1 alloy bath to contain A1 alloy in the pores, and then pulled out of the molten bath. Before the sheet cooled down, it was placed between rolls with a spacing of 120 μm. A uniform foil was pressure-molded and subjected to H14, and a portion thereof was cut out to a size of 151Mφ and used as an electrode substrate for battery testing.

The manufacturing method of the positive electrode and the battery testing method were carried out in the same manner as in Example 1.

As a result, the cycle life was 510 times, the self-discharge rate at J3 at the 300th cycle was 4.2% per month, and the energy density was 224 wh/ko.

Comparative Example 1 The production of the positive electrode and the battery testing method were the same, except that a commercially available JIS Nα5052 A1 alloy foil was cut into 15 #φ and washed with alkali, water, and dried for surface treatment as the negative electrode substrate. was carried out in the same manner as in Example 1.

As a result, the cycle time was as low as 0,420 times, and the self-discharge rate was 6.7%/month.

Comparative Example 2 JIS Nfi3QO4 A1 alloy foil was obtained from Takeuchi Metal Foil Co., Ltd. This one has a thickness of 120AITn,
, width 100a*. A part of it was cut to 15φM and used for battery testing. Further, the manufacturing of the positive electrode and the battery testing method were the same as in Example 1.

As a result, the number of cycles at which the coulombic efficiency reached 50% was 4.
00 times, and the self-discharge rate measured at the 300th time was 10
．． It was 5%/month.

Example 3 (Manufacture of negative electrode) Carbon fibers with a diameter of 8 μm were assembled to a thickness of 150 μm.
A sheet with a width of 20 m, a length of 50 m, and a length of 50 m was prepared. This material had a porosity of 75%.

This sheet is immersed in a copper plating solution, and the surface is coated with a thickness of 0.
A copper layer of 2 to 0.5 μm was deposited.

A plated carbon fiber sheet is immersed in a furnace in which Aj gold alloy of JISNα5052 is melted, pulled up and Aj gold alloy is melted into the holes.
1 alloy.

In order to electrodeposit lithium into the reinforced aluminum alloy, the above alloy was placed in an immersion cell, lithium metal was used as the counter electrode, and pc'-DME (polycarbonate and 1,2- dimethoxyethane) was used to electrodeposit Ll by passing a current at a current density of 0.5m to a current density of 45% with respect to this alloy.Then, it was washed with a DME solvent and 15 It was cut into φ pieces for battery testing.

(TI construction of positive electrode) Using titanium disulfide powder, polytetrafluoroethylene as a binder, acetylene black as a conductive agent, and dimethylbenzoquinone as a sublimable substance, these
After mixing thoroughly at a ratio of 5:5:5:45,
77 mg was filled into a mold and molded at a pressure of 2t/CIi to create an electric Jll+.

Next, it was placed in a glass tube and heated to 320°C while being evacuated in an electric furnace to create a porous titanium di(silyl)ide electrode. This electrode had a thickness of 360 g, m and a weight of 3
8r#9, the bulk density was 0.6g/c+n'te.

(M Pond Test) The electrode material prepared by the above method was set in the battery shown in FIG. 1. The π1 electrolyte was LiASF6/2 with a concentration of 17 l/J.
-Stratiform compound-C using methyltetrahydrofuran solution
A secondary battery using titanium disulfide as a positive electrode has T as shown in the following formula; S2 + xLi + +xc -al 1xT
i To perform charging and discharging by S2 reaction, the first time started with releasing lithium in the negative electrode at a current density of 11IIA/Cd,
A charge/discharge cycle test was conducted.

As a result, the cycle life was 350, the self-discharge rate at the 200th cycle was 4.2%, and the energy density was 250wh.
/kg.

Comparative Example 3 Negative (foil made of Li94AJ6 was used for 15s
The test was conducted in the same manner as in Example 3 except that the sample was cut into φ.

As a result, the battery voltage stopped rising from the 152nd time.
It was presumed that andrite was occurring. The 100th self-discharge rate was 9.5%, and the energy density was 250w.
It was h/ka.

〔effect〕

As described above, in the secondary battery according to the present invention, carbon fibers, metal fibers, inorganic fibers, etc. are used when manufacturing the negative electrode base material.
By mixing H-like substances to form a composite with A or A' alloy, mechanical strength is improved, electrode collapse due to l-i electrodeposition and release is suppressed, and cycle life is extended. Furthermore, it has all the characteristics required of a battery, such as high energy density, low self-discharge, and good charging and discharging efficiency.

[Brief explanation of the drawing]

FIG. 1 is a schematic longitudinal sectional view showing an example of a battery for measuring characteristics of a secondary battery of the present invention. 1... Negative electrode, 2... Nickel current collector,
3...Hiberator-14...Positive electrode, 5
...Platinum current collector, 6...Polytetrafluoroethylene container, 7
······Lead.

Claims (3)

[Claims] (1) A secondary battery characterized by using a negative electrode in which lithium is electrochemically alloyed on aluminum or aluminum alloy reinforced with a fibrous material. (2) The secondary battery according to claim 1, wherein the fibrous material is a fiber made of carbon, an inorganic substance, a metal, or an alloy. (3) The secondary battery according to claim 1, wherein the fibrous material is a carbon fiber coated with a metal or an alloy.