JPH047070B2 - - Google Patents

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. [Summary of the Disclosure] The present invention provides a ternary oxide consisting of V ₂ O ₅ , Li ₂ O, and P ₂ O ₅ , the composition of which is (V ₂ O ₅ ) _x (Li ₂ O) _y ( P ₂ O ₅ ) _z (However, x+y+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 is chemically stable with respect to the positive electrode active material and the negative electrode active material, and lithium By using as an electrolyte material a substance that allows 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 Li ₂ O becomes amorphous V ₂ O. In order to compensate for the irreversible lithium sites in ₅ , it is possible to construct a small, high energy density lithium battery with little loss of charge/discharge capacity, and discloses a technology that can be used in various fields such as coin-type batteries. . 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 present invention or the interpretation of rights. [Prior Art] Conventionally, secondary batteries that use lithium as a negative electrode active material include batteries that use V ₂ O ₅ , a crystalline transition metal oxide, as a positive electrode active material (J.
Electrochem.Soc.Meeting, Toronto, May11−
16, 1975, No. 27), but its charge and discharge characteristics were not satisfactory. Furthermore, regarding an amorphous material obtained by adding P ₂ O ₅ to V ₂ O ₅ and rapidly cooling it after melting,
As proposed in Japanese Patent Application No. 59-237778 and Japanese Patent Application No. 60-41213, this material has (1) irreversible lithium sites, and compared to the first discharge capacity (250Ah/Kg), The charge/discharge capacity (150Ah/Kg) from the second time onwards will be significantly reduced. (2) Because the initial open circuit voltage (3.6V) of the positive electrode active material is high, the electrolyte solvent is easily oxidized and decomposed.
There were problems such as problems with 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 in size, 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 (V ₂ O ₅ ) _x (Li ₂ O) _y (P ₂ O ₅ ) _z is used. In the present invention, by using a ternary amorphous oxide in which lithium is added to V ₂ O ₅ as a positive electrode active material, a lithium battery with higher charge/discharge capacity and superior cycleability than conventional lithium batteries can be constructed. The present invention was completed based on this knowledge. That is, the present invention provides a ternary oxide consisting of V ₂ O ₅ , Li ₂ O, and P ₂ O ₅ , the composition of which is (V ₂ O ₅ ) _x (Li ₂ O) _y (P ₂ O ₅ ) _z (However, x+y+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 is chemically stable with respect to the positive electrode active material and the negative electrode active material, and lithium The present invention is characterized in that an electrolyte material is a substance that allows ions to move for an electrochemical reaction with the positive electrode active material or the negative electrode active material. To form a positive electrode using this positive electrode active material,
This mixed substance powder or a mixture of this 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 such a mixed material powder, and a binder powder such as polytetrafluoroethylene is added as required, and this mixture is mixed with a The positive electrode can be formed by placing the mixture in a container or by pressure-molding the above-mentioned mixture onto a support such as nickel or stainless steel. 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 that allows lithium ions to move for electrochemical reaction with the positive electrode active material. For example, propylene carbonate, 2-methyltetrahydrofuran, dioxolene, tetrahydrofuran,
One or more aprotic organic solvents such as 1,2-dimethoxyethane, ethylene carbonate, γ-butyrolactone, dimethyl sulfoxide, acetonitrile, formamide, dimethylformamide, nitromethane and LiClO ₄ , LiAlCl ₄ , LiBF ₄ ,
The present invention uses known electrolytes that are generally used in batteries that use lithium as a negative electrode active material, such as combinations with lithium salts such as LiCl, LiPF ₆ , LiAsF _{6 ,} or solid electrolytes or molten salts that use lithium ions as conductors. It can also be used as an electrolyte. The aforementioned amorphous material as a positive electrode active material has the compositional formula (V ₂ O ₅ ) _x (Li ₂ O) _y (P ₂ O ₅ ) _z (where x
+y+z=1), 0.1≦y/x≦0.5, 0
Preferably, the materials are mixed in a range of 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 Li ₂ O compensates for irreversible lithium sites in amorphous V ₂ O ₅ , so a compact high-energy battery with little loss of charge/discharge capacity is produced. A high density lithium battery can be constructed, and 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 the conventional binary amorphous oxide, (V ₂ O ₅ ) _x (P ₂ O ₅ ) _y (where x+y=
1, _y ≦0.3) (see Japanese Patent Application _{No. 59-237778} ). Otherwise, the amount of lithium that is trapped and dies is reduced, increasing the efficiency of using lithium in the negative electrode. (2) Due to the addition of Li ₂ O, the initial open circuit voltage decreased from 3.6 V to 3.3 V, and the oxidation of the electrolyte solvent
Decomposition was prevented. 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, a mixture of Li ₂ O, V ₂ O ₅ and P ₂ O ₅ 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 heated. A method of quickly immersing it in water and rapidly cooling it can also be used. 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 cell preparations and measurements were performed in an argon atmosphere. Example 1 In this example, the amorphous material as the positive electrode active material is
Mix a predetermined amount of Li ₂ O and P ₂ O ₅ with V ₂ O ₅ , and add 750
It was prepared by melting it in a platinum crucible at ℃ for about 1 hour and then rapidly cooling it in water. Here, amorphization was confirmed by X-ray diffraction. As a specific example, (V ₂ O ₅ ) _0.95 (P ₂ O ₅ ) _0.05 (Li ₂ O) _0.086 (V ₂ O ₅ ) _0.864 (P ₂ O ₅ ) _0.05 (Li ₂ O) _0.22 (V ₂ O ₅ ) The X-ray diffraction patterns of four amorphous substances of _0.73 (P ₂ O ₅ ) _0.05 (Li ₂ O) _0.32 (V ₂ O ₅ ) _0.63 (P ₂ O ₅ ) _0.05 are shown in FIG. As can be seen from Figure 1, these X-ray diffraction patterns show an X-ray amorphous pattern with a very broad peak around 2θ27° in the CuK line, indicating that it has become amorphous. I understand. 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, sprat 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 negative electrode, 5 is a polypropylene separator,
6 indicates 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 1.5N−LiAsF ₆ /2− as an electrolyte.
After injecting and impregnating an appropriate amount of 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 were mixed in a weight ratio of 70:20:5 using a crusher. The mixture was roll-formed to a thickness of 0.6 mm and punched out with a punch to obtain a disc-shaped positive electrode (area: 2 cm ² ) with a diameter of 16 mm. FIG. 3 shows the results of discharging the lithium battery thus prepared at a constant current density of 0.5 mA/cm ² . Furthermore, Table 1 shows the comparison results between the first circuit and the second discharge capacity (2V termination).

[Table] From these results, the higher the amount of lithium added, the lower the discharge potential and the smaller the first discharge capacity, but the doped lithium efficiently compensates for irreversible sites in the amorphous material, The difference with the second discharge capacity, that is, the amount of irreversible lithium is reduced. Furthermore, Figure 4 shows the amount of lithium that can be taken in and out through charging and discharging per mole of positive electrode active material.
The results were plotted at a charge/discharge current density of 0.5 mA/cm ² up to the 10th cycle. (V ₂ O ₅ ) _0.95 (P ₂ O ₅ ) _0.05 , 0.7 mol of lithium per 1 mol of positive electrode active material is trapped in irreversible sites and cannot be charged.
It can be seen that in the system to which (Li ₂ O) _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 in Example 1, a charge-discharge current density of 0.5 mA/cm ² was used, and a voltage of 2V to
Voltage regulated charging and discharging between 3.5V and 3.5V was performed. FIG. 5 shows the relationship between the number of charge/discharge cycles and the discharge capacity of each amorphous material obtained as a result. In the system containing (Li ₂ O) _x , the cycle life and stability were improved, _especially when (Li ₂ O)
₆ (V ₂ O ₅ ) _0.864 (P ₂ O ₅ ) _0.05 system shows a charge/discharge capacity of approximately 180Ah/Kg per (V ₂ O ₅ ) weight,
Still continuing after 200 cycles. Example 3 Created in the same manner as Example 1 (Li ₂ O) _0.086
(V ₂ O ₅ ) _0.864 (P ₂ O ₅ ) _0.05 using a lithium battery with an amorphous material as the positive electrode active material, 0.5 mA/cm ² ,
FIG. 6 shows the results of charging and discharging at discharge current densities of 2 mA/cm ² , 4 mA/cm ² and 8 mA/cm ² . In all cases, charging is carried out at a current density of 0.5 mA/cm ² and
This is a charge/discharge cycle with voltage regulation between 3.5V. [Effects of the Invention] As explained above, according to the present invention, lithium added in advance in the form of Li ₂ O becomes amorphous.
By compensating for the irreversible lithium sites in V ₂ O ₅ , it is possible to construct a compact high energy density lithium battery with little loss of charge/discharge capacity, and the battery of the present invention can be used in various fields such as coin-type batteries. It has the advantage of being able to

[Brief explanation of drawings]

FIG. 1 is a diagram showing an X-ray diffraction pattern of a positive electrode active material in an example of the present invention, and FIG. 2 is a cross-sectional view showing an example of the configuration of a coin-type battery according to an example of the present invention.
FIG. 3 is a characteristic diagram showing the discharge characteristics of the battery in the example of the present invention, FIGS. 4 and 5 are characteristic diagrams showing the charge and discharge characteristics of the battery in the example of the present invention, and FIG. FIG. 3 is a characteristic diagram showing current characteristics of a battery in an example. 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 pellet.

Claims (1)

[Claims] 1 A ternary oxide consisting of V ₂ O ₅ , Li ₂ O, and P ₂ O ₅ , whose composition is (V ₂ O ₅ ) _x (Li ₂ O) _y (P ₂ O ₅ ) _z (However, x+y+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 is chemically stable with respect to the positive electrode active material and the negative electrode active material, and lithium A lithium battery characterized in that an electrolyte material is a substance that allows ions to move for an electrochemical reaction with the positive electrode active material or the negative electrode active material.