JPH0322366A - Secondary battery - Google Patents

Abstract

PURPOSE:To concurrently obtain high energy density, high charging/discharging efficiency and a long life by using a mix dispersed with Li or Li alloy or Li- mixed metal in an ion conducting polymer material for a negative electrode. CONSTITUTION:When lithium or lithium alloy or lithium-mixed metal is dispersed in an ion conducting polymer material, the surface of a negative electrode is not deteriorated, the active material of the negative electrode is dispersed, and the specific surface area is increased. The energy density, cycle life, and charging/discharging efficiency are improved, the negative electrode surface is not deteriorated, a large current can be extracted, and the generation of moss-shaped lithium or dendrites can be prevented.

Description

[Detailed Description of the Invention] [Prior Art] Conventionally, secondary batteries using conductive polymer materials as electrodes have been proposed. Conductive polymer materials have the property of taking in and releasing electrolyte ions through an electrochemically reversible REDOX reaction. It is explained that this is due to a phenomenon called doping, in which a complex is formed. Among conductive polymers, materials such as polyvirol and polyaniline are suitable for positive electrode materials for non-aqueous secondary batteries because they can be stably doped with anions in non-aqueous solutions, and polymers are lightweight. , it is possible to increase the energy density of the battery. In particular, non-aqueous electrolyte secondary batteries that use lithium as the negative electrode and conductive polymers such as boriananiline as the positive electrode active material have high battery voltage and are expected to have high energy density, and are expected to be the next generation. FT is widely viewed as a secondary battery.

[Problems to be solved by the invention] However, when this type of secondary battery is put into practical use, there are problems such as deterioration of the negative electrode and decomposition of the electrolyte. The length has only been increased for a limited number of uses.

That is, by repeated charging and discharging, especially charging and discharging at a large current, protrusions such as dendrites are deposited, and these protrusions penetrate through the separator and cause a short circuit between the electrodes, which shortens the cycle life. In addition, water entering the battery makes the surface of the lithium negative electrode passivated, increasing the electrical resistance of the electrode and making it impossible to pass a large current.In addition, the dissolution and precipitation of Li on the negative electrode surface becomes non-uniform, causing dendrites, etc. It also causes the precipitation of protrusions. Furthermore, since the electrolytic solution is also exposed to a harsh environment where the potential difference between the positive and negative electrodes is 3V or more, it decomposes over several hundred charge/discharge cycles.

Conventionally, countermeasures have been taken to solve the above problems, such as alloying the lithium negative electrode and using a mixed solvent as the electrolytic solvent. However, when Li negative electrodes are alloyed, although the generation of dendrites can be suppressed, repeated charge/discharge cycles cause the negative electrodes to become brittle and fall off from the current collector, shortening the cycle life. . Furthermore, even when a mixed solvent is used as the electrolyte solvent, dendrites may occur to some extent and the surface of the lithium negative electrode may be damaged. ! Although it is possible to prevent the transition to three countries, the current situation is that sufficient impact has not been achieved.

In addition, the lithium produced during charging and discharging is highly active,
Due to the reaction with the solvent or impurities in the solvent, it becomes moss-like lithium, which causes problems with cycle life, especially when a large current is applied.

For the above reasons, at present, secondary batteries using conductive polymer materials as positive electrode active materials are only put into practical use for limited low-power applications such as backup power sources for semiconductor memories.

[Problems to be Solved by the Invention] In view of these circumstances, the present inventors have developed a method that satisfies high energy density, high charge/discharge efficiency, and long life at the same time, and is also capable of drawing out a large current. In addition, the aim is to realize a battery system using a negative electrode that does not generate moss-like lithium or dendrites, and can be used in cylindrical large-capacity batteries, etc., and is safe, flexible, and can be made into a large area. It is.

[Means for Solving the Problems] In view of these facts, the present inventors have conducted intensive studies, and found that when lithium, lithium alloy, or lithium mixed metal is dispersed in viscous or ion-conductive polymer materials, negative electrodes can be formed. The surface does not deteriorate, the active material of the negative electrode is dispersed, and the specific surface area is large, making it possible to extract a large current, and depending on the type of polymer material used for the negative electrode mixture. A flexible negative electrode with a large area is also possible, and by further dispersing a metal that can be alloyed with lithium in the negative electrode mixture, the component ratio in the lithium alloy or lithium mixed metal can be easily adjusted. Discovered that by dispersing a conductive material that does not form a lithium alloy in the negative electrode mixture, in particular a fibrous conductive material, the conductivity of the negative electrode mixture is improved and the cycle life of the battery is improved,
This led to the present invention.

In addition, in the present invention, an ion-conducting polymer material is used for the negative electrode mixture231 (this allows the movement of lithium ions without making it porous, etc.).
Another effect of the invention is that lithium is not directly exposed to the air even when the battery is disassembled, making it possible to create a safe battery negative electrode.

That is, the present invention provides a non-aqueous secondary battery having a positive electrode made of a conductive or semiconducting polymeric material, in which the negative electrode of the secondary battery contains Li, Li alloy, or Li mixed in an ion-conductive polymeric material. This is a secondary battery characterized by being made of a mixture containing metals dispersed therein.

The present invention will be explained in more detail below.

Examples of the polymer material for the positive electrode in the present invention include conductive polymer materials such as polyacetylene, polythiophene, and polyaniline, and REDOX active polymer materials such as polydiphenylbenzidine, polyvinylcarbazole, and polytriphenylamine. As an electrode material,
Shows electrical conductivity of 10'S/c or more! II and high ionic conductivity in terms of ion diffusivity, all of the polymer materials listed above exhibit high electrical conductivity through electrochemical doping.

Examples of the electrolyte solvent include carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, ethers such as 2,2-dimethoxyethane, ethoxymethoxyethane, methyl diglyme, and dioxolane. esters, cyclic esters such as γ-butyrolactone, etc. can be used alone or in combination, and in particular, carbonates and/or cyclic esters can be used as main components, ethers,
Mixtures with other solvents, such as non-polar solvents, show excellent performance. Furthermore, a solid polymer electrolyte can also be used in place of the electrolyte. In particular, when a polymer solid electrolyte is also used as the polymer material in the negative electrode mixture, the non-surface area at the interface between the lithium negative electrode and the polymer solid electrolyte is large, making it possible to create a polymer solid electrolyte battery with low internal impedance. Become.

A solid polymer electrolyte is composed of at least a polymer as a matrix and an electrolyte salt as a carrier. Examples of the polymer matrix include polyethylene oxide, polypropylene oxide, or ether polymers having copolymers thereof in the main chain or side chain, esters such as β-probiolactone and γ-butyrolactone, ethylene carbonate, Examples include polymers having carbonates such as brobylene carbonate in the main chain or side chain. In particular, polyethers whose terminal ends are substituted with atomic groups inert to L1 and crosslinked polyethers are excellent in that they have low reactivity with Li.
Among these, crosslinked polyether is excellent in terms of strength.

As the electrolyte salt used for the non-aqueous electrolyte and the polymer solid electrolyte, SCN''' CI-Br I
BF4″″ PF&CF3SO3″″ SbF6-
AsF&CI04 ″″ B (CsHs) 4
Lithium salts with anions such as CF3 503 may be mentioned.

As a separator, it passes the electrolyte and holds the electrolyte.
In addition, a material that does not cause a harmful reaction with the electrolytic solution, such as a nonwoven fabric, a woven fabric, a net, or a porous membrane made of synthetic resin such as polyethylene or polypropylene, is used.

The ion-conductive polymer material for the negative electrode mixture in the present invention is a resin that has binding properties, is insoluble in the electrolytic solution, and is not decomposed by reaction with lithium, such as a polyether solid polymer electrolyte, etc. Examples include composite materials made of a combination of a resin such as polyvinylidene fluoride or polyacrylonitrile, a solvent having a high dielectric constant such as brobylene carbonate or γ-butyrolactone, and an electrolyte salt. These polymer materials preferably have a crosslinked structure. When using an ion-conducting polymer material that does not have sufficient binding properties, it is used by mixing it with a material that has binding properties.

These materials can conduct lithium ions without becoming porous, and since there is no direct contact between lithium and the electrolyte, they can
It is superior to resins that do not have ion conductivity in that it can avoid various problems caused by impurities in the No. 14 solution and electrolyte reacting with the lithium surface. Furthermore, compared to negative electrode mixtures using polymeric materials that do not have ion conductivity, this method is superior in that the conductivity of the negative electrode can be maintained even with a small amount of lithium and conductive agent.

The negative electrode active material used in the negative electrode mixture in the present invention is lithium, which is used in the form of lithium alone, lithium alloy, or lithium mixed metal, and the amount of these metal materials used in the negative electrode mixture is 60 to 60% by weight. 98%,
Particularly preferred is 75 to 96%. In addition, as for the shape, powder or fibrous ones are suitable. Metals that can be alloyed with lithium include aluminum, sodium, potassium, calcium, silver, lead, tin, bismuth, antimony, zinc, magnesium, thallium, silicon, etc., and alloys of one or more of these and lithium Alloyed or mixed, if not completely alloyed, with the polymeric material and dispersed within the polymeric material. Alternatively, the metal material capable of being alloyed with lithium is previously dispersed in a polymeric material, and lithium is introduced into the negative electrode mixture by an electrochemical method.

Suitable conductive materials for use in the negative electrode mixture as needed include materials that do not form an alloy with lithium and have high electrical conductivity, such as carbon, platinum, gold, stainless steel, and conductive polymers.

Among them, carbon is particularly good because lithium can be incorporated into the material by doping. Powder or fibrous materials are suitable as the shape of the conductive material, and fibrous materials are particularly excellent because they can provide a good current collecting effect with a small amount added. In the negative electrode mixture, it is preferable to add the conductive material in the smallest possible amount without reducing the current collection effect of the negative electrode.

In other words, when the conductive agent is in the form of powder, the ffljl fraction is preferably 5 to 20%, particularly 7 to 15%, and when the conductive agent is in the form of fibers, the weight fraction is preferably 2 to 15%. %, particularly preferably 3 to 10%.

As the current collector supporting the negative electrode mixture in the present invention, a material that does not form an alloy with lithium and has high electrical conductivity is suitable, similar to the conductive material described above, and these shapes include plate-like, Alternatively, net-like, cloth-like, or cotton-like materials are suitable.

The nonaqueous secondary battery system in the present invention is basically composed of these conductive or semiconductive positive electrode active materials, a nonaqueous electrolyte, a separator or a solid polymer electrolyte, a negative electrode, and a negative electrode current collector. .

EXAMPLES The present invention will be specifically explained below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Examples Negative Electrode Production Example 1 A negative electrode was produced using the following recipe on a current collector substrate obtained by polishing a glassy carbon substrate with emery paper (No. 200).

Polyethylene oxide (PEO) / polypropylene oxide (PPO) copolymerized triol (EO/PO-6/l MV-8
000) 10vt% Tolylene-2,4-diisocyanate 0.27vt% Dibutyltin dilaurate 0. A dichloromethane solution of Olwt% was prepared, 20vt% of aluminum powder was dispersed therein, and the solution was cured at 80° C. for 2 hours in vacuum. 1 mol L of this
An electric field of 0.5 V was applied for 10 minutes using Lf as a counter electrode in a L B F 4 /PC solution to deposit a lithium layer on the aluminum/crosslinked polyether interface to produce a negative electrode.

Negative Electrode Production Example 2 A negative electrode was produced in the same manner as in Negative Electrode Production Example 1, except that 5 vt% of carbon fiber + 5 vL% of Ketjen Black + 20 vt% of aluminum powder were used instead of 20 vL% of aluminum powder.

Negative Electrode Production Example 3 Equimolar moles of cinnamoyl chloride were added dropwise to the polyether triol used in Negative Electrode Production Example 1 under an inert atmosphere, and the mixture was reacted to obtain cinnamoylated PEO/PPO. Based on the obtained cinnamoylated PEO/PPO, a negative electrode was manufactured on the same aluminum foil as in negative electrode production example 1 using the following recipe.

Cinnamoylated polyether 10wt% 5-nitroacenaphthene 0.01wt% methyl ethyl ketone solution was prepared, and L i /A I (!rc1
a ratio 3/2) 85 vt% of alloy powder + 5 wt% of carbon fibers were dispersed and applied on a glassy carbon substrate, and irradiated for 10 minutes at 10+W/c+a2 using a high-pressure mercury lamp to cause crosslinking, thereby producing a negative electrode.

Negative electrode production example 4 0.25 g of poly(γ-methyl-L-glutamate) and 94.7 g of the following block type polyether: CI+2
- Cll-COO[ (CI12 CI12 0)+
2 (Cllz Cll (CI3)01 3)
3(Cl12 CI+2 0) u it and further 1.05 g of valatoluenesulfonic acid to 100 l of 1,2-dichloroethane! The mixture was dissolved in water and reacted for 72 hours while passing nitrogen through the solution. After dialysis and purification of this, the substitution rate was 100.
The same operation was repeated until it reached %.

The obtained polymer was mixed with 5% by volume of penzoyl peroxide as a reaction initiator and 0% of LiBF4 as an electrolyte salt per unit of ethylene oxide and propylene oxide.
．． Li/AlCf was added at a ratio of 0.4 mol.
fl amount ratio 3l2> Alloy powder 85wt% 10 carbon fibers 5vt
% was dispersed and applied onto the same glassy carbon substrate as in Negative Electrode Production Example 1 to form a film. Next, this was heated at 100° C. for 1 hour to cause crosslinking, thereby producing a negative electrode.

Negative Electrode Comparative Example 1 The same current collector glassy carbon plate as in Negative Electrode Production Example 1 was used as it was as a negative electrode.

Negative electrode comparison example 2 A pure lithium plate was used as the negative electrode.

Using the negative electrode prepared according to the above negative electrode manufacturing example, the positive electrode made of a conductive polymer material (polyaniline), and 1 mol LiBF4/DME(3)/PC(7) as the electrolyte solution, 0.2llA/c+e' was produced. Charging and discharging were repeated at a constant current, and the battery characteristics and the surface condition of the negative electrode were examined at the 300th cycle.

The battery performance of the negative electrode obtained in the above negative electrode manufacturing example is shown below.

[Effects of the Invention] As explained above, according to some aspects of the present invention, it is excellent in energy density, cycle life, and charging/discharging efficiency, the negative electrode surface does not deteriorate, and it is possible to extract a large current. In addition, we did not see the presence of moss-like lithium or dendrites,
In addition, it is possible to obtain a secondary battery having a negative electrode that is safe and can be made to have a large area.

Claims (1)

[Claims] (1) In a non-aqueous secondary battery that uses a conductive or semiconducting polymer material as a positive electrode active material, the negative electrode of the secondary battery contains Li, Li alloy, or Li mixed metal in the ion-conductive polymer material. A secondary battery characterized by being a dispersed mixture.