JPH03167766A - Secondary battery - Google Patents

Abstract

PURPOSE:To obtain a low-cost, excellent battery-performance secondary battery by providing a complex negative electrode obtained when a carbonaceous material and a binding agent both treated in advance with a silane coupling agent are mixed with a sodium alloy. CONSTITUTION:A negative electrode comprises a complex of a carbonaceous material and a binding agent, and a complex negative electrode obtained by treating the carbonaceous material and the binding agent with a silane coupling agent in advance, and then mixing them with the sodium alloy is provided. Since the negative electrode thus uses a complex of the sodium alloy, the carbonaceous material and the binding agent, the electrode potential is higher than when using lithium and also higher than when using sodium and so the battery can be charged and discharged at high current without reducing and decomposing the solvent. Further, treatment of the carbonaceous material and the binding agent with a silane coupling agent prevents electrodes from being broken by swelling and contraction due to charge and discharge and enables formation of a battery of long cycle life. A low-cost, good performance secondary battery is thus obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a secondary battery with high energy density, low self-discharge rate, long cycle life, and good performance.

[Conventional technology]

Non-aqueous secondary electrodes using transition metal oxides or sulfides as the positive electrode and alkali metals or their alloys as the negative electrode are well known. Non-aqueous secondary batteries as positive electrodes, JP-A-59-163756, JP-A-59-
163758, secondary batteries using a fusible alloy as the negative electrode material, batteries using an alloy negative electrode produced by melting lithium and metallic aluminum as in U.S. Patent No. 3,607,413, and JP-A No. 58 -73968, which uses a simple alkali metal as a negative electrode, has been reported. On the other hand, the invention of a secondary battery using a conductive polymer doped with alkali metal etc. as a negative electrode was published in Japanese Patent Application Laid-Open No. 1364-1983.
69, and Japanese Patent Laid-Open No. 81-245474 proposes a secondary battery using a mixture of an alkali metal and a conductive polymer as a negative electrode.

In addition, the present inventors also proposed a secondary battery using a mixture of a conductive material and a conductive polymer as an electrode in JP-A-59-112585, and in JP-A-60-72692, a secondary battery using a mixture of a conductive material and a conductive polymer was proposed. He has invented and published a secondary battery that uses a ternary mixed material consisting of aluminum and lithium for the negative electrode.

However, when the above-mentioned square secondary battery using a single alkali metal as the negative electrode is charged and discharged at a high current density, dendrites are formed and the positive and negative electrodes are short-circuited, making subsequent charging and discharging impossible. Furthermore, even when an alkali metal alloy is used for the negative electrode,
Even if the formation of dendrites is suppressed to some extent, repeated charging and discharging will cause the alloy electrode to become finer and collapse. Therefore, unless the amount of electricity per charge and discharge is suppressed, a long cycle life cannot be achieved. In addition, when a conductive polymer doped with alkali metal etc. is used for the negative electrode, although the reversibility of charging and discharging is good, the capacitance density per electrode weight and per electrode volume is low, and a secondary battery with sufficient energy density It cannot be. Therefore, recently, secondary batteries with high capacity and long cycle life have been developed using a mixture of an alkali metal alloy and a conductive polymer as a negative electrode active material (Japanese Patent Laid-Open No. 61-245474). ). However, the conductive polymers used as one of the constituent elements of the negative electrode, such as polyacetylene and polybaraphenylene, are expensive to manufacture, making it difficult to obtain an inexpensive secondary battery.

Furthermore, in high capacity density type electrodes, the reversibility of the alkali metal itself as a negative electrode is not sufficient in lithium metal systems.

As a solution to the above problem, the present inventors previously proposed the use of a negative electrode containing a sodium alloy, carbon black, and/or graphite (Japanese Patent Application No. 1893-1983).
No. 84).

[Problem to be solved by the invention]

However, the negative electrode of the above-mentioned secondary battery has a drawback that the mechanical strength is low and the electrode easily collapses. It was discovered that the cause of this was poor bonding between the carbon material and the binder, and repeated charging and discharging caused the carbon material to separate from the electrode, accelerating its collapse. The problem to be solved by the present invention is to eliminate these drawbacks and provide a secondary battery that is inexpensive and has excellent battery performance.

[Means to solve the problem]

As a result of intensive research to solve the above-mentioned problems, the present inventors have discovered that the reversibility of the negative electrode can be significantly improved by using a composite that has been subjected to a specific treatment as the negative electrode. Based on this knowledge, we have completed the present invention.

That is, the present invention provides a secondary electrode comprising a positive electrode, a negative electrode, and an electrolytic material, in which the negative electrode is made of a composite of a sodium alloy, a carbon material, and a binder, and the carbon material and the binder are preliminarily bonded by silane coupling. The present invention provides a secondary battery comprising a composite negative electrode obtained by treating the composite negative electrode with a sodium alloy and then mixing it with a sodium alloy.

The present invention will be explained in detail below.

First, the structural materials used for the negative electrode of the battery of the present invention will be sequentially explained.

Sodium alloys are preferably alloys of sodium and lead or sodium and tin, but particularly preferred are alloys that are easy to form and that can electrochemically and reversibly transfer large amounts of alkali metal ions. It is an alloy of sodium and lead that can be formed.

As for the composition of the above-mentioned alloy, the molar ratio of sodium to lead is preferably within the range of 10:1 to 1:2 when the battery is being charged. The reason for this is that sodium and the FO metal can maintain an alloy state from the charging state to the discharging state of the battery, or the open circuit potential is higher than the potential of sodium alone, and the sodium dendrites This is because it is within a range where generation can be suppressed, and at the same time, the amount of electricity charged and discharged in each cycle can be as large as possible, and within a range where sodium does not enter an anti-exhaustion state in the negative electrode before the specified discharge state.

The carbon material refers to graphite, activated carbon, and carbon black, and may be in the form of powder, granules, or mW.

In particular, there are many types of carbon black, but they are not particularly limited. Each may be used alone or in combination.

The binder may be one based mainly on polyethylene or polypropylene, or an olefin copolymer rubber (E
Although it is possible to use materials such as PR, EPDM) and polytetrafluoroethylene, polyethylene, polypropylene, or olefin copolymer rubber is preferable for the negative electrode of the battery of the present invention, and the most preferred is EPDM. .

On the other hand, the silane-based coupling agent, which is used as a drug to combine carbon materials and binders, is either fM-inclusive type or R S l (O R
') Represented by a, R represents an organic functional group R t
indicates an alkyl group.

Specific examples include γ-aminobrobyltriethoxysilane, N-β-aminoethyl-γ-aminoprobyltrimethoxysilane, γ-ureidopropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, and vinyltrimethoxysilane. etc. can be mentioned.

As a coupling method, for example, the above coupling agent is added to a mixture of a carbon material and a binder, a catalyst such as butyltin acetate is further added, and after heating at a temperature of about 50 to 200°C or higher, impurities are removed. After adding a solution of the above-mentioned coupling agent to the carbon material and adding a binder, the mixture is washed and removed at a temperature of about 100°C or higher for several hours.
There are methods such as heat treatment to bond the carbon material and the binder. There is no particular restriction on the amount of the coupling agent added, but 0.5 to 20% by weight based on the carbon material is usually suitably used.

To mold an electrode using these constituent materials, add a predetermined amount of sodium alloy powder, a predetermined amount of carbon material that has been coupled, and a binder, and then mix well. After uniformly dispersing the mixture on top of TEPCO, etc., it is pressurized with a roll press machine or a hydraulic press machine to form an electrode. There is a method in which an electrode is obtained by adding an organic solvent to form a wet paste, coating it on a substrate, and then press-molding it.

There are no particular restrictions on the positive electrode material used in the battery of the present invention, but it can release and occlude sodium ions by charging and discharging, and
Cobalt oxide is optimal as an active material having a potential difference of several volts with respect to the negative electrode. In particular, the most preferable positive electrode is one in which a certain amount of sodium ions are occluded, that is, in the form of an intercalation compound of sodium and cobalt oxide.

As the electrolytic solution, a solution of Na salt in a non-aqueous solvent is used, but as the Na salt, Na P Fe,
NaBF NaCN O NaCF3So3,
P 4″ NaAsF NaB (CHa) 4 etc.
In addition to propylene carbonate and sulfolane, examples of non-aqueous solvents include tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and 4-dimethyltetrahydrofuran.
Methyl-1,3-dioxolane, 1,3-dioxolane, dioxane, 2-methoxy-1,3-dioxolane,
Anisole, m-trifluoromethylanisole, 1.
Examples include 2-dimethoxyethane, 1,1-dimethoxyethane, tiglyme, 12-crown-4, and the like.

Among them, ether compounds are particularly excellent in terms of stability.

[For production]

In the battery of the present invention, since the negative electrode uses a composite of a sodium alloy, a carbon material, and a binder, the electrode potential is higher than lithium and higher than sodium, so that the solvent is not reductively decomposed. Can be charged and discharged with high current. Furthermore, by treating the carbon material and the binder with a silane coupling agent, it is possible to suppress electrode collapse due to swelling and shrinkage of the electrode during charging and discharging, thereby making it possible to construct a battery with a long cycle life.

〔Example〕

Next, the secondary battery of the present invention will be specifically explained with reference to Examples.

Example 1 Vinyltrimethoxysilane was added dropwise in an aqueous solution to a mixture of acetylene black and graphitic carbon fiber synthesized by a gas phase method at a weight ratio of 3:1 in an amount of 10% by weight relative to acetylene black. and kneaded well.

Further, EPDM dissolved in xylene was added to the above kneaded material at a weight ratio of 3=1 to acetylene black and mixed. Next, the temperature was raised to 100° C., and heat treatment was performed for about 4 hours. To this, the weight ratio of acetylene black is 10
Double the amount of powder of a sodium-lead alloy (an alloy in which the atomic ratio of sodium is 2.5 times that of lead) was added and mixed.

A plate-shaped negative electrode was obtained by scattering the mixed powder described above on a stainless steel wire mesh current collector and press-molding it with a hydraulic press.

The positive electrode contains Na COO2, sodium co0.7, balt oxide, 96 weight, 06, and carbon black, 3 weight 9.
6. A mixture of 1% by weight of polytetrafluoroethylene and pressure molded on a current collector was used.

A polypropylene microporous film was used for the separator, and 1 mol 1D of NaPFe was used for the electrolysis.
Using 1,2-dimethoxyethane melted to ifa degree,
Assembled an AA type battery.

The open circuit voltage of this battery was 266V. When this battery was repeatedly charged and discharged between 2.0V and 3.5V,
The maximum amount of discharged electricity was 625+eAh, and the cycle life until the discharge capacity was halved was 720 times.

Also, when this battery was charged and discharged for the 20th time,
When a self-discharge test was conducted at 20B at ℃, the self-discharge rate was 12%. After the self-discharge test, the original capacity was completely restored.

Example 2 To acetylene black, 10% by weight of γ-aminobrobyl triethquin silane was added to the acetylene black, and 1% by weight of butyltin acetate was added to the acetylene black, and on top of that, EPDM was added to the acetylene black. Added 30% by weight.

The mixture was heated to 200°C and left for about 4 hours. Next, an alloy powder having an atomic ratio of sodium and lead of 2.7:1 was added in an amount ten times that of acetylene black, and the mixture was further mixed well. A small amount of xylene was added to this mixture to form a paste, which was then applied onto a stainless steel Tokyo Electric body and pressure molded to produce a negative electrode.

An AA type battery was assembled in the same manner as in Example 1, using the same positive electrode, separator, and electrolyzer as in Example 1.

When this battery was repeatedly charged and discharged between 2.0 V and 3.5 V, the maximum amount of discharged electricity was 605 rahAh, and the cycle life was 840 times. Also, the self-discharge rate is lO,
It was 5%.

Comparative Example Using the same constituent materials as in Example 1 and omitting only the coupling treatment, a battery was assembled and its performance was examined.

As a result, the maximum amount of discharged electricity was 625 mAh, but the cycle life was as short as 304 times. Furthermore, the self-discharge rate was 17%, which was somewhat large.

〔Effect of the invention〕

As described above, the secondary power supply of the present invention has high capacity and high energy density, is highly reversible, has a low self-discharge rate, and can be used at low cost. Large, large-scale power supplies that can be used as power supplies, power supplies for household electrical appliances, drive power supplies for electric vehicles, load leveling, and power supplies for identification cards.
Alternatively, it can be used as a small and excellent secondary electric propulsion.

Claims (1)

[Claims] In a secondary battery consisting of a positive electrode, a negative electrode, and an electrolyte, the negative electrode is made of a composite of a sodium alloy, a carbon material, and a binder. A secondary battery comprising a composite negative electrode obtained by mixing with an alloy.