JPS62256369A - Composite negative electrode for secondary batteries - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a novel composite negative electrode for secondary batteries, and more specifically to a composite negative electrode used in high capacity, high output secondary batteries. be.

Currently, the commonly used secondary batteries are lead acid batteries, Ni/C
There are d batteries etc. These secondary batteries have a single cell battery voltage of about 2.0V at most, and -a is an aqueous battery. BACKGROUND ART In recent years, research and development efforts have been actively conducted to develop secondary batteries that use Li as a negative electrode as secondary batteries that can achieve high battery voltage.

When Li is used for electric scraping, it is necessary to use a non-aqueous electrolyte because of the high reactivity between water and Li.

However, when Li metal is used as the negative electrode active material, its electroplating reaction potential is very low, so there is no electrolytic solution that can continue the battery reaction reversibly in combination with the positive electrode that can provide sufficient battery voltage. Sometimes, dendrites are formed on the Li electrode side, causing problems such as a decrease in charging and discharging efficiency and a short circuit between the positive and negative electrodes. One way to prevent the formation of dendrites is to use an alloy of Li and other metals, such as AI, as the negative electrode to increase the deposition potential of Li. Not enough to prevent it.

Therefore, by adding a small amount of an inhibitor to prevent side reactions, such as hexamethylene phosphoramide or polyethylene oxide, to the electrolyte solution, an ion-conductive protective film is formed at the interface between the negative electrode and the electrolyte solution, thereby preventing side reactions with the electrolyte solution. Although there are attempts to prevent this, it is difficult to completely cover it with a protective film, and new problems such as the stability of the inhibitor itself arise, which poses practical problems.

[Problem that the invention seeks to solve]

An object of the present invention is to solve the problems of the prior art as described above, to be able to store a large amount of alkali metal ions as guest ions as a negative electrode active material, and to perform a stable reversible reaction in a known non-aqueous electrolyte. It is an object of the present invention to provide a negative electrode that has an electrode reaction potential capable of performing the following steps, has a high energy density, and can constitute a high-performance secondary battery that can be repeatedly charged and discharged stably.

(Means to solve the problem) The above purpose is α type AI! ! 03+Crg03. is the type MnO2゜Ti, 0. ,V,0. , a-type Ga, O,
This is achieved by a composite negative electrode for secondary batteries, which is made of a corundum-type metal oxide selected from among the above and a conductive polymer, and also contains an alkali metal.

Among the corundum metal oxides used in the present invention, those particularly preferred as electrode materials are V2O1 and α type^120.
and TizOs. Of course, by mixing only corundum metal oxide with a conductive agent and using it for the negative electrode, alkali metal ions can be sufficiently introduced and extracted electrochemically.
However, in the present invention, in order to make charging and discharging more efficient, faster, prevent deterioration of the electrode and electrolyte due to overcharging, and extend the cycle life, the above-mentioned A composite of a corundum-type metal oxide and a conductive polymer is used.

In the present invention, the term "conductive polymer" refers to a polymer having electron conductivity, and specific examples thereof include polymers having a conjugated double bond chain such as polyacetylene, polyvaraphenylene, polythenylene, etc. , polyacetylene-
Examples include isoprene block copolymers and polyacetylene-ethylene oxide graft copolymers. The bending polymer has considerable electrical conductivity in the state obtained by polymerization, but the electrical conductivity is further improved by adding an alkali metal ion dopant as in the present invention.

A particularly preferred alkali metal ion dopant is lithium metal ion.

Among the above-mentioned conductive polymers, polyacetylene and polyvaraphenylene are particularly preferred.Polyacetylene and polyvaraphenylene themselves have a large amount of electrochemically capable of introducing and extracting alkali metal ions, and they can be repeatedly inserted and removed relatively stably. This is because it can be used as a negative electrode, and by combining it with a corundum metal oxide, the performance as a negative electrode is significantly improved.

The process in which corundum metal oxide (MesOJ) electrochemically charges and discharges with alkali metal ions (M') is shown by the following equation.

(However, in the formula, 0 < x 6.5. It is shown by the following formula.

(However, in the formula, M: alkali metal, O<x<1.0゜y
Sx) The electrode potential of the composite negative electrode for secondary batteries of the present invention is that of the conductive polymer! ! Types, types of alkali metal dopants, and electrolytes! Class I, the electrode potential reflects the electrode potential of each individual system, although it varies depending on the composite ratio of the composite conductive polymer and corundum metal oxide.

The advantage of the composite negative electrode is that it can be charged and discharged with high current density and high efficiency within the stable range of the electrolyte, making full use of the features of the corundum metal oxide, which has a high capacity density. It is possible.

In other words, corundum-type metal oxides have a thick lattice constant (
, 800^H/kg or more of alkali metal, of which 130AI/hg or more can be fully reversibly taken in and out. However, corundum type metal oxide electrodes have a relatively high current density, 3mA/c
If charging/discharging is performed at a temperature higher than d, the overvoltage will be large, and
If large discharges are repeated, the voltage flatness during charging and discharging deteriorates, making it difficult to operate the battery efficiently.Therefore, excessive carbon black, a conductive agent, is added to increase the porosity of the electrodes. Although it is necessary to take measures such as increasing the specific surface area, carbon black has a very small amount of lithium metal that can be reversibly taken out and taken out, or can hardly accommodate it, so it itself is just a conductive agent and an electrode. Its only function is to increase the porosity.

However, when a conductive polymer is used instead of a carbon blank as in the present invention, the conductive polymer itself not only acts as an excellent conductive agent;
It has a potential that includes the substantially constant electrode potential of IVvsLi/Li'' of a corundum metal oxide electrode, and can prevent dendritic electrodeposition of Li and decomposition due to side reactions of the electrolytic solution in the event of overcharging.

On the other hand, when only a conductive polymer is used as the negative electrode material,
For example, polyacetylene and polyparaphenylene are 1
50^) It is possible to reversibly insert and remove alkali metal ions at a rate of 1/2 or more, making it useful as an excellent negative electrode material, but when the doping amount is increased to achieve high capacity, the electrode potential becomes extremely low. By combining a tetraelectric polymer with a corundum-type metal oxide, an appropriate electrode potential can be achieved. The negative electrode for secondary batteries can be easily charged and discharged within the battery, and has high capacity and high energy density.

Note that the electrical conductivity of the undoped conductive polymer and the corundum metal oxide itself is very low, so for the purpose of improving initial electric shock, carbon plastic or corundum metal oxide may be mixed. There is no problem in adding high valence metal oxides etc. that can control the valence of the material.

Next, a specific example of a method for combining a conductive polymer and a corundum metal oxide will be described.

(1) A method in which a conductive polymer and a corundum metal oxide are mixed and then pressurized and molded.

That is, a pre-polymerized conductive polymer in the form of powder or granules and a corundum-type metal oxide are mechanically mixed and molded to produce a pellet-like or film-like electrode. Note that this electrode may be molded to include a current collecting substrate, that is, Ni, Fe, stainless steel, AN plate, or the like.

(2) After synthesizing the desired conductive polymer in a polymerization solution containing an appropriate amount of corundum metal oxide powder so that the conductive polymer after polymerization and the corundum metal oxide have the desired ratio. , a method of molding and making composite electrodes.

(3) A method in which the synthesized conductive polymer is molded into a film or pellet, and then a corundum-type metal oxide is further applied and pressure molded to form a composite. Or, conversely, a conductive polymer is placed on a molded corundum-type metal oxide and re-molded to form a composite. According to this method,
It is possible to produce a composite electrode in which two or more layers are laminated.

The present invention may use any method other than the above method.

In addition, it goes without saying that a current collector may be included in the electrode.
A conductive agent such as a binder or carbon black, or a substance such as TiO2 that can control the valence of the corundum metal oxide may be further mixed or added.

Furthermore, in order to actually incorporate and use the negative electrode of the present invention in a battery, it is necessary to previously contain an alkali metal at least one discharge capacity into the composite negative electrode. The most common method for incorporating an alkali metal is to electrochemically reduce alkali metal ions from an electrolytic solution in which an alkali metal salt is dissolved, and to accommodate the alkali metal in the composite electrode.

Furthermore, there is a method of forcibly electrolyzing using an external power source, and a method of causing contact and short circuit between the alkali metal and the composite electrode due to a voltaic potential difference to accommodate the alkali metal. Also,
It is also possible to adopt a method of chemically reacting with an alkali metal compound.

The method of accommodating the alkali metal is not necessarily limited to these methods. Further, these treatments may be performed before configuring the battery, or may be performed after the battery is assembled.

Next, the composite ratio of the corundum metal oxide and the conductive polymer will be explained.

Generally, the weight ratio of corundum metal oxide and conductive polymer is 1:0.01 to t:to, preferably 1:0.
02-1:1, more preferably 1:0.05-1:0.
It is compounded in the range of 5.

The thus obtained composite of the present invention exhibits extremely excellent performance as a page turner for secondary batteries, and as mentioned above, not only has a high capacitance per electrode weight, but also has a high capacitance of 3 wA/1 in a general-purpose organic solvent electrolyte. Even at a high current density of c+J or higher, charging and discharging can be repeated with high efficiency.

Here, as the organic solvent constituting the electrolytic solution, male carbonates such as propylene carbonate and ethylene carbonate, phosphoric acid esters such as trimethyl phosphate and triethyl phosphate, tetrahydrofuran, 1.
Examples include ether compounds such as 2-dimethoxyethane, sulfolanes such as sulfolane and 3-methyl-sulfolane, and lactones such as γ-butyrolactone and δ-butyrolactone. - Specifically, a single system of propylene carbonate or sulfolane, a mixed system of propylene carbonate and an ether compound, or a mixed system of sulfolane and an ether compound are preferable.

On the other hand, as electrolytes, L+CI Oa, LiBF4
+LiPFa + LiAsFi I LiBPh4
．． LiBBu, , LiBPh3Bu rLiBE
Lithium salt such as t3Bu or Na or K instead of the above Li0
Examples include sodium salt and potassium salt using . Among these, preferred alkali metal salts are lithium salts.

The positive electrode material used in the secondary battery is not particularly limited, but includes Ti5g, VzOs, Cr30s,
Metal chalcogenide compounds such as Co0g and amorphous compounds thereof, carbon-based compounds such as graphite and carbon fluoride, or P-type polyaniline, P-type polypyrrole, P-type polythiophene, and P-type polyacetylene. , so-called conductive polymers, and the like. Among these, preferred positive electrode materials include Vz
Examples include amorphous type a oxides typified by OsPzOs type oxides and conductive polymers having N atoms in the main chain typified by polyaniline.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Polyacetylene slurry obtained by slurry polymerization of monodentate acetylene (solvent toluene, solid content 5% by weight) 100
g and 20 g of commercially available α-type A f gos powder were mixed and stirred, and then 2 g of polytetrafluoroethylene was added as a binder and Ketjen Black EC2 was added as a conductive agent.
g was mixed. Take 20 μ out of the mixture and make a diameter of 15 μm.
It was pressure molded into a disk shape of tsφ.

Next, using temporary nickel as a current collector, lithium metal was set at the bottom of an experimental cell having the structure shown in Figure 1, with a concentration of 1 mol/l between them! While impregnated with a propylene carbonate electrolyte of LiC10a subjected to IIM, a glass porous separator was sandwiched, and the composite electrode prepared by the above method was placed on top.

A current was passed through this composite electrode at a current density of 1.0 mA/aj in a direction that reduced the lithium metal ions in the electrolytic solution, and electrolysis was performed until the amount of electricity reached 45 coulombs.

Next, the experimental cell was disassembled, and a composite electrode containing lithium metal was used as a negative electrode using a cell having a structure similar to that shown in FIG. For the positive electrode, polyaniline was chemically polymerized using ammonium persulfate salt as an oxidizing agent in a 1N HBF4 aqueous solution, and after further filtration and separation,
10 g of polyaniline powder was neutralized with aqueous ammonia, further reduced with hydrazine, and dried under reduced pressure at 100°C for a long time to make the structure of the repeating unit in the polyaniline as benzenoid-rich as possible. After mixing Ketjen Black as an auxiliary agent with Ig and 0.6 g of polytetrafluoroethylene as a binder, 20
The sample was separated and pressure-molded into a diameter of 15 mm and used. A battery experimental cell was assembled using a 2 molar ZltH LiCl 04 propylene carbonate solution as the electrolyte.

The cell was discharged at a current density of 5.0 tsA/c until the cell voltage dropped to 1.5v. Next, 3.0
A charge/discharge cycle test was performed in which the battery was charged at a current density of mA/- until the battery voltage reached 3.5V, then discharged to 1.5V at a constant current density of 5mA/aJ, and then charged to 3.5V at a constant current density of 3+wA/aJ. Ta.

As a result, the charge/discharge efficiency was almost 100%, with 47 cycles.
This high level was maintained until 0 cycles, and the charge/discharge efficiency gradually decreased after 470 cycles.

The maximum energy density per weight of positive and negative electrodes of this battery is 14
2wh/kg, maximum capacitance density is 59^H/k
It was g. Further, the discharge capacity at the 500th cycle was 40^H/kg.

Actual observation ■l In practice N1, α type A j? Instead of setting the mixing ratio of go3 and polyacetylene to 1:0.25, α-type Al was added to the polymerization solution so that the mixing ratio was 1:0.4.
! (h) was added in advance, and acetylene was polymerized under an inert atmosphere using a solution of tetrabutoxytitanium and triethylaluminum catalyst in toluene with stirring.

α-type A 1.03 is incorporated into the polymer, and after separating it from the polymerization solution by filtration, drying under reduced pressure is performed, and further, 10 weight each of Ketjen Black EC as a conductive aid and polyethylene as a binder is added. Mixed by %. A 20-inch portion was taken out of the mixture and pressure-molded into a diameter of 15 mm. Similar to Example 1, a cell having the structure shown in FIG. 1 was used for this electrode, and 45 chlorides of lithium ions were reduced in advance to prepare a composite negative electrode.

The positive electrode was produced as follows. VzO5 manufactured by Wako Pure Chemical Industries
and P! 0. After mixing in a molar ratio of 9:l, 1,00
The temperature was raised to 0° C., held for 30 minutes, and then rapidly cooled to produce an amorphous material, which was pulverized. Gentien black ECl0 as a conductive aid! % and 5% of polytetrafluoroethylene as a binder were added and mixed well. The above mixture 22cm was placed on a platinum wire mesh cut out to a diameter of 1511φ and molded under pressure to form an electrode with a diameter of 15fsφ. did.

A battery experiment was conducted using a battery cell having the structure shown in FIG. The electrolyte contains 2 mol/l of LiCI in a mixed solvent of sulfolane and tetrahydrofuran in a volume ratio of 2:1.
Using a solution of O, a positive electrode, a negative electrode, and a separator were set, and a battery was assembled.

First, discharge at a constant current of 4 m^/d until the final voltage reaches 1.8 V, then discharge at the same current density until the final voltage reaches 3.5 V.
The battery was charged until the voltage reached V, and charging and discharging were repeated in the same manner.

As a result, the maximum discharge capacity is 69^H per weight of both poles.
/kg, and the maximum energy density is 14 per weight of both poles.
6wh/kg was recorded. As the cycles were repeated, the capacitance gradually decreased, but at the 500th cycle, the capacitance showed 41^H/kg. Further, the charge/discharge efficiency showed 98% or more up to 500 cycles.

Implementation ■ Dissolve aluminum chloride and titanium tetrachloride in a molar ratio of 100:5 in an acidic aqueous solution of hydrochloric acid, then gradually add aqueous ammonia to co-precipitate aluminum hydroxide and titanium hydroxide, which are separated by filtration. After that, preliminary drying was performed at 100°C. 20% by weight of polyacetylene and 10% by weight of polyethylene prepared in the same manner as in Example 1 were added and mixed, and then pressure molded into a disk shape with a diameter of 15 mφ to prepare an electrode.

Hereinafter, the production of the positive electrode and the brain intercalation of the negative electrode Li were carried out in the same manner as in Example 1, and the battery performance was examined in exactly the same manner as in Example 1.

Maximum energy density per pole weight is 148% wh/k
It was g. Also, the maximum capacitance density is 1 to 70^H/
Met. The number of repetitions until the discharge capacity of this battery decreased to half of the maximum capacity was 572 times.

Lithium metal 1 g s htox 5 g, polyparaphenylene 2 g 1 powdered polytetrafluoroethylene 0
．． After stirring and mixing 5g of Ketjenblack EC and 0.6g of Ketjenblack EC well under an inert atmosphere, 20cm of the liquid was taken out and a diameter of 1.
A composite electrode was produced by pressure molding to a size of 5 wφ.

As a positive electrode, amorphous chromium chloride 15■, Ketjen black 1■ and polytetrafluoroethyl ethyl solution were used.
An experimental cell was assembled using a cell having the structure shown in the figure.

A repeated charging and discharging test was conducted in which this battery was discharged from the discharge direction at 4 sAIaj until the voltage reached 1.5V, and then charged at 4sA/aj until the voltage reached 3.5V.

As a result, the maximum discharge capacitance density was 61AH/kg,
The maximum energy density was 139wh/kg.

Further, the electric capacity of this battery at the 500th cycle was 288 H/kg.

α type A l used in Ura boat construction example 1, 0. Ti2 instead of
A battery was prepared and tested in the same manner as in Example 1, except that O3 was used.

:・The maximum discharge capacity of this battery is 67AH/kg,
The maximum energy density was 143wh/kg. Further, the cycle life until the discharge capacity decreased to half of the maximum value was 523 times.

1” Luniy Example! Cr2 instead of α type A 1 , O, used in
A battery was prepared in the same manner as in Example 1, except that O2 was used, and a battery experiment was conducted (Example 6).

Also, instead of α-type Al1tO-t, ε-type 1'lnO□
A similar experiment was conducted using (Example 7).

α type Al, 0. instead of v! A similar experiment was conducted using 03 (Example 8).

A similar experiment was conducted using α-type Ga103 instead of α-type allzo* (Example 9).

The experimental results are shown in the table below.

Example 6 138 64 38〃
8140 66 35〃9 1,3
3 62 30 tm 10% polyethylene was mixed with 20 cm of a commercially available alloy powder with an atomic ratio of Li and AI of 50:50, and the mixture was pressure-molded and used as the negative electrode, and the same polyaniline electrode as in Example 1 was used as the positive electrode. The experimental cell was assembled using the same electrolyte as used in Example 1.

A repeated charging and discharging test was conducted in which this battery was discharged from the discharge direction at 5 sAIaj until the voltage reached 1.5V, and then charged at 3IIIA/aJ until the voltage reached 3.5V. As a result, the maximum discharge capacity was 39 AH/kg per weight of both poles, and the maximum energy density was 89 wh/kg. However, the capacity decreased with each cycle, and at the 112th cycle, the capacity became 1/2 of the maximum value.

1 Comparison 1 Assemble the exact same experimental cell as that made in Comparative Example 1,
After discharging to 1.5 V at a current density of 5 A/- from the discharging direction, charging was performed at a current density of 3 s+A/aJ until the voltage reached 4.3 V, and thereafter a repeated charging and discharging test was conducted. The maximum discharge capacity density of this battery was 694 FI/kg, and the maximum energy density was recorded as 173 wh/kg, but the capacity gradually decreased and by the 27th cycle, it was almost impossible to discharge.

The negative electrode was exactly the same as in Comparative Example 1, the positive electrode and electrolyte were the same as in Example 2, the final discharge voltage was set to 1.8 V, and the final charge voltage was set to 3. .5■,
Charging and discharging were repeated at a constant current density of 4-AI-.

As a result, the maximum discharge capacity density was 51 AH/kg, and the maximum energy density was 102 wh/ksr. However, the capacity gradually decreases with each cycle, and at the 97th cycle, the discharge capacity is reached! After showing 21 AI/Nigi, it became almost impossible to discharge at the 98th time.

Comparative cell: An experimental cell exactly the same as Comparative Example 3 was constructed, and the battery voltage was set to 1.
Charging and discharging were performed at a constant current density of 4-AI- in the range of 8V to 4°3V. As a result, the maximum discharge capacity is 59AH
/Nigi, maximum energy density is 165wh/kg
However, the capacity gradually decreased, and at the 24th cycle, it became almost impossible to discharge.

〔Effect of the invention〕

A secondary battery incorporating the composite negative electrode of the present invention can be repeatedly charged and discharged with high charge/discharge efficiency while maintaining a high capacitance density as described above, has a long cycle life, and is lightweight. This secondary battery is used as a power source for small electronic devices, load leveling, solar and wind power generation electrical energy storage systems,
It is extremely useful as a power source for electric vehicles, etc.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of the configuration of a secondary battery using the negative electrode of the present invention. Reference numbers in FIG. 1 are as follows. DESCRIPTION OF SYMBOLS 1... Lead wire, 2... Piton O-ring, 3... Current collector, 4... Third electrode, 5...
porous diaphragm, 6... second electrode, 7... current collector,
8...Lead wire, 9...Teflon container. 10th 1...Lead wire 6...Second electrode 2...
・Paiton O-ring 7..., current collector 5...porous diaphragm

Claims (1)

[Claims] 1, α type Al_2O_3, Cr_2O_3, ε type MnO
_2, Ti_2O_3, V_2O_3, α-type Ga_2O
A composite negative electrode for a secondary battery, comprising a corundum metal oxide selected from _3 and a conductive polymer, and containing an alkali metal.