JPH03225774A - Nonaqueous electrolytic secondary battery - Google Patents

Abstract

PURPOSE:To obtain excellent cycle characteristic with a large capacity and a high potential by using a vanadium oxide containing Li represented by Lii+xV3 O8+y (wherein x and y are specified range values) as the active material of a positive electrode and LiClO4 and Li6 as a nonaqueous electrolyte. CONSTITUTION:A nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode consisting of Li metal or an alloy containing Li, and a nonaqueous electrolyte containing Li ion is provided. As the active material of the positive electrode of this battery, a vanadium oxide containing Li represented by Lii+xV3O8+y (O<=x<=0.6, -0.5<=y<=0.3) is used. As the nonaqueous electrolyte, LiClO4 and LiPF6 are used. Hence, the battery has a large capacity, and a high potential, and is also excellent in cycle characteristics. As a concrete example, the battery has a positive electrode 1, a positive electrode collector 2, a negative electrode 5, and a negative electrode collector 6, and a separator 8 is formed of a porous polypropylene film and impregnated with the electrolyte.

Description

[Detailed Description of the Invention] The present invention relates to a non-aqueous electrolyte secondary battery using lithium metal or a lithium alloy as a negative electrode active material, and more specifically, a high-potential , relates to a non-aqueous electrolyte secondary battery with high energy density and excellent cycle characteristics.

Secondary batteries that use lithium as a negative electrode active material, which is expected to expand in the future, will use chalcogenides (sulfides, selenium compounds, tellurides) of transition metals such as titanium and molybdenum, and oxyhalogens such as iron as positive electrode active materials. Chemical compounds, manganese, cobalt, and vanadium oxides have been studied, but there are still many problems such as battery characteristics and economic efficiency, and there are still few that have been put to practical use.

Among these, lithium secondary batteries using molybdenum sulfide have been put into practical use, but these batteries have drawbacks such as low discharge potential and vulnerability to overcharging.

Therefore, it is desired to develop a lithium secondary battery that has excellent battery performance and high safety.

In such lithium secondary batteries, it is important to select an electrolytic solution containing lithium ions. Conventionally, in order to obtain an electrolytic solution with a good cycle life, improvements in ionic conductivity, reduction in viscosity, etc. type of solvent for the purpose,
Many studies have been made regarding the type and concentration of Norithiram salt as an electrolyte.

Under these circumstances, as a method to reduce the reactivity between lithium and solvent in order to improve cycleability, there is a method of forming a film containing As on the lithium surface by using LiAsF as an electrolyte. Proposed. However, the use of LiAsF as an electrolyte is undesirable from the standpoint of releasing toxic substances into the environment during disposal.

Furthermore, although LiGaO2 and LiBF4 have been conventionally used as electrolytes in lithium batteries, the former has been pointed out to be dangerous as a peroxide, and even the latter does not interact with various inorganic cathode active materials. Not common in terms of compatibility. Furthermore, salts such as LiCF and SO2 have low ionic conductivity and low solubility, and therefore cannot be said to be practical at present. L i P F has also been proposed, but it cannot be said to be sufficient as an electrolyte for batteries used under high potential such as lithium batteries, and it is still not sufficient to fully demonstrate the battery characteristics of lithium secondary batteries. At the same time, research on highly safe electrolytes continues.

The present invention was made in view of the above circumstances, and by optimizing the electrolyte and positive electrode active material in a secondary battery using lithium as a negative electrode active material, it is possible to achieve large capacity, high potential, and cycle characteristics. An object of the present invention is to provide a non-aqueous electrolyte secondary battery that can perform excellent and stable charging and discharging.

To achieve the above object, the present inventor has made extensive studies and found that cycle durability can be improved by simultaneously using LiGaO2 and LiPF5 as electrolytes, and that lithium metal or A negative electrode whose active material is an alloy containing lithium and -L l x+xVs
Om+y (0≦x≦0.6゜-〇, 5≦y≦0.3)
By combining a vanadium oxide containing lithium as a positive electrode to construct a secondary battery, a nonaqueous electrolyte secondary battery with high potential, high energy density, and excellent charge/discharge cycle characteristics can be obtained. This is the heading that led to the completion of the present invention.

Therefore, the present invention provides a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode made of lithium metal or an alloy containing lithium, and a non-aqueous electrolyte containing lithium ions.
As the active material of the positive electrode, Li1+xv30. +y(O≦
x≦0.6. -0.5≦y≦0.3), and uses LiGaO2 and LiPF as the nonaqueous electrolyte. provide.

The present invention will be explained in more detail below.

The non-aqueous electrolyte secondary battery of the present invention uses Li as an electrolyte.
CaO2 and LiPFG coexist, and this electrolyte is combined with a positive electrode and a negative electrode, which will be described later.

Here, LiGaO2 and LiPFG are usually dissolved in a solvent and used as an electrolyte, but in this case, the blending ratio of both (L 1CQO4: L 1PFs) is 1:9 to 9:1.
(molar ratio), particularly preferably from 2:8 to 6:4. In addition, the concentration needs to be high enough to exhibit high ionic conductivity, but if we take into account the increase in viscosity due to the interaction between ions and solvent at high concentrations, the lithium concentration should be 0.5~ It is preferably 3 mol/Q, particularly 1 to 2 mol/Q.

The solvent for dissolving this electrolyte is not particularly limited, but a solvent with a relatively high dielectric constant is preferably used. Specifically, propylene carbonate.

Cyclic carbonates such as ethylene carbonate and butylene carbonate, diethyl carbonate.

Acyclic carbonates such as dibutyl carbonate, glymes such as tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, dioxane, dimethoxyethane, diethylene glycol dimethyl ether, lactones such as γ-butyrolactone, phosphoric acid esters such as triethyl phosphate, boric acid One or more of boric acid esters such as triethyl, sulfur compounds such as sulfolane and methyl sulfoxide, nitriles such as acetonitrile, amides such as dimethylformamide and dimethylacetamide, dimethyl sulfate, nitromethane, nitrobenzene, and digloloethane. Mixtures may be mentioned. Among these, one or more mixed solvents selected from cyclic carbonates such as ethylene carbonate and propylene carbonate, and acyclic carbonates such as diethyl carbonate are particularly preferred. These solvents also contain 1 to 10% by weight of aromatic hydrocarbons (
benzene, toluene, etc.). Moreover, a polymerization inhibitor can be added if necessary.

In the non-aqueous electrolyte secondary battery of the present invention, the electrolyte solution is impregnated into a polymer such as polyethylene oxide, polypropylene oxide, an isocyanate crosslinked product of polypropylene oxide, or a phosazene polymer having an ethylene oxide oligomer in its side chain. , it can also be used as a solid electrolyte.

As the positive electrode active material constituting the secondary battery of the present invention, L
l z+xV, Os+F (0≦x≦0.6.-0.5
≦y≦0.3) is used. This is usually vanadium pentoxide (V2
It is obtained by mixing a vanadium compound such as O5) or ammonium metavanadate (NH4VO, ) with a lithium salt and heating and baking the mixture at a predetermined temperature. In this case, the lithium salts include lithium carbonate (L12cO3), lithium oxide (Li20), lithium nitrate (L i No3),
Inorganic salts such as lithium hydroxide (LiOH) and organic salts such as lithium acetate (CH, CO0Li) are used, and Li and Go□ are particularly preferably used.

The firing temperature is a temperature at which the heated mixture becomes molten, for example 600°C to 800°C, particularly 720°C.
There are two methods: a method of firing at ~770° C. and a method of synthesizing the powder as it is by in-phase reaction at 600° C. or lower, and the method is appropriately selected depending on the subsequent powder treatment process. The firing time at that time is not particularly limited, but in the former case, it is preferably 1 hour or more.

In the latter case, it is desirable to take measures so that the solid phase reaction proceeds uniformly, but a longer firing time is required. Further, the firing atmosphere is preferably air or oxygen atmosphere. The mixing ratio is not particularly limited, but the V:Li ratio is 3:o,
The ratio is preferably 8 to 3:1.4, particularly 3:0.9 to 3:1.15.

Note that X in Li +, V3O, + is a value that increases with discharge, and the conductivity also decreases, so it is desirable that it be close to O at the time of synthesis, but it is not particularly limited. Although y changes depending on the firing conditions and raw material mixing ratio, it is preferably 0 to -0.3.

When producing a positive electrode using this positive electrode active material, the powder particle size of the positive electrode material is not necessarily limited, but the average particle size is 3p.
A high-performance positive electrode can be produced by using a material having a diameter of m or less. This powder is mixed with a conductive agent such as acetylene black and a binder such as fluororesin powder, mixed with an organic solvent, etc., passed between rolls to a desired thickness, and further dried. A positive electrode sheet can be produced by combining the following methods. The amount of the conductive agent mixed can be 3 to 25 parts by weight, particularly 5 to 15 parts by weight, based on 100 parts by weight of the active material, but in the present invention, the conductivity of the positive electrode active material is relatively good. Therefore, it is possible to reduce the amount of conductive agent used. The amount of the binder is 100% of the above positive electrode active material.
The amount is preferably 2 to 25 parts by weight.

As the negative electrode active material constituting the secondary battery of the present invention, lithium metal or a lithium alloy capable of intercalating and deintercalating lithium is used. In this case, the lithium alloys include Ila and Ilb containing lithium.

Ha, IVa, Va group metals or alloys of two or more thereof can be used, especially Afl, In containing lithium.
, Sn, Pb, Bi, Cd, Zn, or an alloy of two or more of these are suitable.

The secondary battery of the present invention is usually constructed by interposing an electrolyte between the positive and negative electrodes, but in this case, a separator may be interposed between the positive and negative electrodes to prevent current short-circuiting due to contact between the two electrodes. .

The separator may be made of a porous material that allows ions in the electrolyte solution to pass through and that can contain the electrolyte, such as nonwoven fabric, woven fabric, or mesh made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene. etc. can be used.

There is no particular restriction on the form of the secondary battery of the present invention, and specifically, it may be in any form such as a spiral-structured cylindrical battery, a box-type, a coin-type, a button-type, a paper-type battery, etc.

The non-aqueous electrolyte secondary battery of the present invention has a large capacity, a high potential, excellent cycle characteristics, and is capable of stable charging and discharging.

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

[Example 1] Vanadium pentoxide and lithium carbonate were mixed at a predetermined ratio, heated and cooled, and then pulverized to obtain powdered Li1. .

*Using vzoe as a positive electrode active material, 15 parts by weight of conductive carbon and 15 parts by weight of fluororesin powder as a binder were added to 10 parts by weight of this powder, mixed thoroughly, and mixed with an organic solvent to determine the thickness. It was rolled to a thickness of 100-.

After that, it was vacuum dried at 150℃ and punched out to a predetermined diameter.
A battery positive electrode was produced.

Using the above battery positive electrode, a lithium foil punched to a predetermined size was used as a negative electrode, and LiCQQ was added to a mixed solvent of propylene carbonate and ethylene carbonate (volume mixing ratio 1:1).
The battery shown in FIG. 1 was assembled using an equimolar solution of 4 and LiPF so that the total lithium concentration was 1 mol as an electrolyte solution.

Here, in FIG. 1, 1 is a positive electrode, 2 is a stainless steel positive electrode collector, and an electric body, and the positive electrode l and the current collector 2 are integrated, and the current collector 2 is a spacer made of a metal plate. 3
The spacer 3 is spot welded to the inner surface of the positive electrode can 4. 5 is the negative electrode, 6
is a negative electrode current collector, and the negative electrode 5 is spot welded to the negative electrode current collector 6 fixed to the inner bottom surface of the negative electrode can 7. Furthermore, 8 is a separator made of a porous polypropylene film, which is impregnated with the electrolytic solution. 9 is an insulating backing. The dimensions of the battery are 20.0 cm in diameter and 1.6 m in thickness.

This battery was charged at a charge/discharge current of 1 mA and at a discharge end voltage of 2. Charging and discharging were repeated at OV and a charge end voltage of 3.5V. Figure 2 shows the cycle characteristics until the discharge capacity is halved.

[Comparative Example 1] LiCQQ was added to a mixed solvent of propylene carbonate and ethylene carbonate (volume mixing ratio 1:l) as an electrolyte.
A battery was assembled in the same manner as in Example 1, except that only 1 mol of lithium was used.

A charge/discharge test was conducted on this battery under the same conditions as in Example 1. The results are shown in Figure 2.

[Comparative Example 2] LiPF was added to a mixed solvent of propylene carbonate and ethylene carbonate (volume mixing ratio 1:1) as an electrolyte.
A battery was assembled in the same manner as in Example 1, except that lithium was dissolved so that the lithium concentration was 1 mol.

A charge/discharge test was conducted on this battery under the same conditions as in Example 1. The results are shown in Figure 2.

[Comparative Example 3] Li B was added to a mixed solvent of propylene carbonate and ethylene carbonate (volume mixing ratio 1:1) as an electrolyte.
A battery was assembled in the same manner as in Example 1, except that only F was dissolved so that the lithium concentration was 1 mol.

A charge/discharge test was conducted on this battery under the same conditions as in Example 1. The results are shown in Figure 2.

From the results shown in FIG. 2, LiCQQ4 and LiPF.

It has become clear that the battery of the present invention using an electrolyte solution containing a mixture of these solutes has superior cycle characteristics compared to a battery using each solute alone. Furthermore, the battery of the present invention shows no abnormality during charging, performs stable charging and discharging, and is a secondary battery that has excellent performance that meets the above-mentioned objectives in addition to its large capacity and high potential. This was confirmed.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a battery used in carrying out Examples and Comparative Examples of the present invention, and FIG. 2 is a graph showing the charge-discharge cycle characteristics of the batteries of Examples and Comparative Examples. 1... Positive electrode 3... Spacer 5... Negative electrode 7... Each negative electrode 9... Backing 2... Positive electrode current collector 4... Positive electrode can 6... Negative electrode current collector 8...Separator

Claims (1)

[Claims] 1. In a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode made of lithium metal or an alloy containing lithium, and a non-aqueous electrolyte containing lithium ions, the active material of the positive electrode is Li_1_+_xV_3O_8_+_y (0≦
x≦0.6, -0.5≦y≦0.3), and LiClO_4 and LiPF_6 are used as the nonaqueous electrolyte. Electrolyte secondary battery.