JPS62176054A - Lithium battery - Google Patents

Abstract

PURPOSE:To increase charge-discharge capacity to increase battery performance by using a ternary system amorphous oxide to which lithium is added in an amorphous form as a positive active material. CONSTITUTION:An amorphous material of a ternary system oxide comprising amorphous V2O5, Li2O, P2O5 and having a composition of (V2O5)x(Li2O)y(P2O5)z (where, x+y+z=1, 0.1<=y/x<=0.5,0<=z<=0.3) is used as a positive active material 6. This powder is pressed against a supporting member to form a positive electrode. A lithium negative active material is rolled to form a sheet and pressed against a conductive net to form a negative electrode 4. A substance which is chemically stable to positive and negative active materials and allows a lithium ion to move to electrochemically react with the both active materials is used as an electrolyte material. Thereby, Li added in a form of Li2O com pensates the irreversible lithium site in the amorphous V2O5. Therefore, a small, high energy density battery whose loss in charge-discharge capacity is reduce can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a rechargeable and dischargeable lithium secondary battery, and particularly to a lithium battery using an amorphous material as a positive electrode active material that provides a large charge and discharge capacity. be.

[Summary of the Disclosure] The present invention provides V2O5, Li2O. A ternary oxide consisting of P2O5, whose composition is (V2O5)X
(L12O)y (P2 O5)Z (However, x+y+
An amorphous material given by z=1.0.1≦y/x≦0.5゜0≦Z≦0.3) is used as a positive electrode active material, lithium or a lithium alloy is used as a negative electrode active material, and the positive electrode active material is By using as an electrolyte substance a substance that is chemically stable with respect to the substance and the negative electrode active material and that allows lithium ions to move for an electrochemical reaction with the positive electrode active material or the negative electrode active material, Lithium added in advance in the form of Li2O compensates for the irreversible lithium sites in the amorphous 1V2C)5, making it possible to construct a small, high energy density lithium battery with little loss of charge/discharge capacity, and a coin-type battery. It discloses techniques that can be used in various fields such as.

Note that this summary is provided solely for the purpose of quickly accessing the technical content of the present invention, and does not have any influence on the technical scope of the tree invention or the interpretation of rights.

[Prior Art] Conventionally, as a secondary battery using lithium as a negative electrode active material, a battery using V2O5, a crystalline transition metal oxide, as a positive electrode active material (J, Electrochem
, Soc, Meeting, Toronto, M
ayll-16, 1975, NO, 27) has been proposed, but its charge and discharge characteristics were not satisfactory.

Furthermore, regarding the amorphous material obtained by adding P2O5 to ■2O5 and rapidly cooling the melt diameter,
As proposed in No. 9-237778 and Japanese Patent Application No. 80-41213, this material has (1) irreversible lithium sites, and the first discharge capacity (250Ah/
kg) to the second and subsequent charge/discharge capacity (150Ah/k
g) significantly decreases.

(2) Since the initial open-circuit voltage (3.6 V) of the positive electrode active material is high, the electrolyte solvent is easily oxidized and decomposed, causing problems in long-term storage.

[Problems to be Solved by the Invention] Therefore, an object of the present invention is to improve the above-mentioned current problems and provide a lithium battery that is small, has a large charge/discharge capacity, and has excellent battery characteristics. .

[Means for Solving the Problems] In order to achieve the above object, the lithium battery of the present invention uses a ternary oxide (VOS) as a positive electrode active material.
(Li2O)31 (P2OS)2 is used.

In the present invention, it was confirmed that by using a ternary amorphous oxide obtained by adding lithium to v2O5 as a positive electrode active material, a lithium battery with higher charge/discharge capacity and better cycleability than conventional lithium batteries could be constructed. With this recognition, he completed the invention of wood.

That is, the present invention provides V2O5, L i2O.

A ternary oxide consisting of P2O5, whose composition is (
V2 O5)X (Li2O)y(P2OS)2
(However, x+y+z=1.0.1≦y/x≦0.5.0
≦Z≦0.3) as a positive electrode active material, and lithium or a lithium alloy as a negative electrode active material, which is chemically stable with respect to the positive electrode active material and the negative electrode active material, and The present invention is characterized in that a substance capable of causing an electrochemical reaction between lithium ions and the positive electrode active material or the negative electrode active material is used as an electrolyte γ material.

In order to form a positive electrode using this positive electrode active material, this mixed material powder or a mixture of this mixed material powder and a binder powder such as polytetrafluoroethylene is pressure-molded onto a support such as nickel or stainless steel.

Alternatively, a conductive powder such as acetylene black is mixed in order to impart conductivity to the mixed material powder, and a binder powder such as polytetrafluoroethylene is further added thereto as required. put it in a metal container,
Alternatively, the positive electrode can be formed by pressure-molding the above-mentioned mixture onto a support made of nickel, stainless steel, or the like.

Lithium or a lithium alloy is used as the negative electrode active material. Such lithium or lithium alloy can be formed into a negative electrode by being spread into a sheet or by pressing the sheet onto a conductive net made of nickel, stainless steel, etc., as in the case of general lithium.

Further, as the electrolyte, a substance is used that is chemically stable with respect to the positive electrode active material and the negative electrode active material, and is capable of moving lithium ions for electrochemical reaction with the positive electrode active material. For example, propylene carbonate, 2-
Methyltetrahydrofuran, dioxolene, tetrahydrofuran, 1,2-dimethoxyethane, ethylene carbonate, γ-butyrolactone, dimethyl sulfoxide,
one or more aprotic organic solvents such as acetonitrile, formamide, dimethylformamide, nitromethane and LiCf104, LiAJZC1! , 4.

Li[]F4, LiCu, LiPF6, LiA
Known electrolytes generally used in batteries using lithium as a negative electrode active material, such as a combination with a lithium salt such as sF6, or a solid electrolyte or molten salt using lithium ions as a conductor, can be used as the electrolyte in the present invention. I can do it.

The aforementioned amorphous material as a positive electrode active material has the compositional formula (V2OS) x (Li2O)y (P2OS
)z (However, in )(+y+z=1), o, i
Preferably, the materials are mixed in the range of ≦y/x≦0.5.0≦z<0.3, then melted and rapidly cooled. It has been confirmed that it is difficult for a positive electrode active material having a composition outside this range to exhibit excellent characteristics.

[Function]According to the present invention, lithium added in advance in the form of Li2O compensates for irreversible lithium sites in the amorphous The battery of the present invention can be used in various fields such as a coin type battery.

The above-mentioned ternary amorphous oxide is different from the conventional binary amorphous oxide, (V2OS)x (P2OS)y (where x+y=1.y≦0.3) (Patent application 1982- 2
(Refer to No. 37778) The reasons why the battery exhibits better battery characteristics than those of 37778 are as follows: (1) By adding Li2O(7), the irreversible lithium sites in v2O5 are reduced or eliminated, and the amount of lithium that is trapped there and dies is reduced. Therefore, the utilization efficiency of lithium in the negative electrode increases.

(2) By adding Li2O, the initial open circuit voltage is 366■
The voltage dropped to 63.3v, preventing oxidation and decomposition of the electrolyte solvent.

Two points can be considered.

Note that the method for producing the ternary amorphous material is not limited to the method described above.

For example, L i2O. It is also possible to use a method in which a mixture of V2O5 and P2O5 in a predetermined ratio is placed in a platinum crucible, heated in an electric furnace at 750°C for 1 hour, and then the platinum crucible is quickly immersed in water for quenching.

Alternatively, a similar amorphous material can be obtained by a roll quenching method which has a higher quenching rate.

[Examples] The present invention will be explained in detail by examples below with reference to the drawings.

Note that the present invention is not limited only to the following examples. In the following examples, all battery preparations and measurements were performed in an argon atmosphere.

Example 1 In this example, the amorphous material as the positive electrode active material is ■2O5
Mix a predetermined amount of Li2O and P2O5 and heat to 750°C.
It was prepared by melting it in a platinum crucible for one hour and then rapidly cooling it in water. Here, amorphization was confirmed by X-ray diffraction. As a specific example, (V2OS)09y(P2O5)o
,og(L12O)0026(V2Os)0. ga
u(P2Os)0. or(L i2 0) o, zt
(V20S)0.73 (P2OS)5. o
, (L 12O) 0.32 (V2OS ) 6j?
(Figure 1 shows the X-ray diffraction patterns of four amorphous substances with P2 O5>a, or.

As can be seen from Figure 1, these X-ray diffraction patterns are
The K line shows an X-ray amorphous pattern with a very broad peak around 27°, indicating that it has become amorphous. Results similar to those shown in FIG. 1 were obtained with other mixing ratios.

In addition to the underwater quenching method, methods such as the twin roll method, splat cooling, vacuum evaporation, electron beam evaporation, and sputtering can also be used to amorphize this substance group.

FIG. 2 is a cross-sectional view of a coin-type battery that is a specific example of a lithium battery according to the present invention. In the figure, 1 is a stainless steel sealing plate, 2 is a polypropylene gasket, 3 is a stainless steel positive electrode case, 4 is a lithium battery, 5 is a polypropylene separator, and 6 is a positive electrode mixture pellet.

A metal lithium negative electrode 4 placed under pressure on the sealing plate 1 is inserted into the recess of the gasket 2, and a separator 5 and positive electrode mixture pellets 6 are placed on the lithium negative electrode 4 at the opening of the sealing plate 1. Place it in this order and use 1 as an electrolyte.
．． After injecting and impregnating an appropriate amount of 5 N LiAsF6/2-methyltetrahydrofuran (2Me THF), a positive electrode case 3 was placed and caulked to create a coin-shaped battery with a diameter of 23 mm and a thickness of 2 mm.

In forming the positive electrode mixture pellet 6, the above four types of amorphous materials as positive electrode active materials, acetylene black AB and polytetrafluoroethylene are mixed in a weight ratio of 7.
They were mixed using a sand crusher at a ratio of 0:2O=5. The mixture was roll-formed to a thickness of 0.6 mm and punched out to obtain a disk-shaped positive electrode (area: 2 cm2) with a diameter of 16 mm.

Using the lithium battery created in this way, 0.5
FIG. 3 shows the results of discharging at a constant current density of m/cm 2 . Furthermore, the first and second discharge capacities (2V
Table 1 shows the results of the comparison.

These results show that the system with a large amount of lithium added has a low discharge potential and a small first discharge capacity, but the doped lithium efficiently compensates for the irreversible sites in the amorphous material, and the second The difference with the discharge capacity, that is, the amount of irreversible lithium is reduced.

Furthermore, in Figure 4, the amount of lithium that can go in and out through charging and discharging per mole of positive electrode active material is set at 0.5 mA/cm.
The results are shown below, which were traced and plotted up to the 10th cycle at a charge/discharge current density of 2.

(V2 O5) (P2 O5) Teha, positive electrode active material 0, qso, 0! ; For every mol of lithium, 0.7 mol of lithium is trapped in irreversible sites and cannot be charged, whereas (Li2O
) It can be seen that in the system to which x is added, the irreversible sites of lithium are filled efficiently depending on the amount added.

Example 2 Using a lithium battery prepared in the same manner as Example 1,
(At a charge/discharge current density of 1.5mA/ca+2,
Voltage regulated charging and discharging between 3.5V and 3.5V was performed. The relationship between the number of charge/discharge cycles and the discharge capacity of each amorphous material obtained as a result is shown in Figure 5.-4-0 In the system to which (Li2O)X was added, the cycle life and stability were improved. observed, especially (Li2O)(lo1
6(V2 o5)ilJj4 (P2Os >6.6g
In the system, approximately 180Ah/k per (V2O3) weight
It is still continuing even after 2(1(l) cycles have passed, while showing a charge/discharge capacity of 1.3 g.

Example 3 It was created in the same manner as in Example 1 (Li2O). ,0. .

(V2 O5)5. Hz4 (P2O5)a, r using a lithium battery with an amorphous material as the positive electrode active material,
．． 5 mA/c+n 2.2mA/cm 2.4mA/
The results of charging and discharging at various discharge current densities of cm 2°8 mA/cm 2 are shown in FIG. In both cases, charging is a charge-discharge cycle with a voltage regulation between 2 and 3.5 V at a current density of 0.5 mA/cm2.

[Effects of the Invention] As explained above, according to the present invention, Li
Since the lithium added in the form of 2O compensates for the irreversible lithium sites in the amorphous V2O3, it is possible to construct a small, high energy density lithium battery with little loss of charge/discharge capacity, and the battery of the present invention has the following features: It has the advantage that it can be used in various fields such as coin-type batteries.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the X-ray diffraction pattern of the positive electrode active material in an example of the present invention, FIG. 2 is a cross-sectional view showing an example of the structure of a coin-type battery that is an example of the present invention, and FIG. A characteristic diagram showing the discharge characteristics of the battery in the example of the present invention. Figures 4 and 5 are characteristic diagrams showing the charge and discharge characteristics of the battery in the example of the present invention. Figure 6 is a characteristic diagram showing the discharge characteristics of the battery in the example of the present invention. FIG. 1... Stainless steel sealing plate, 2... Polypropylene gasket, 3... Stainless steel positive electrode case, 4... Lithium negative electrode, 5... Polypropylene separator, 6... Positive electrode mixture bezel. nt.

Claims (1)

[Claims] A ternary oxide consisting of V_2O_5, Li_2O, and P_2O_5, the composition of which is (V_2O_5)x(Li_2O)y(P_2O_5)
z (however, x+y+z=1, 0.1≦y/x≦0.5,
0≦z≦0.3) as a positive electrode active material, and lithium or a lithium alloy as a negative electrode active material, which is chemically stable with respect to the positive electrode active material and the negative electrode active material, A lithium battery characterized in that the electrolyte material is a substance that allows lithium ions to move for an electrochemical reaction with the positive electrode active material or the negative electrode active material.