JPH0412589B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is a lithium secondary battery that is small in size and has a large charge/discharge capacity. Specifically, lithium or a lithium alloy is used as a negative electrode active material, additives are added to Cu ₂ V ₂ O ₇ , and the battery is melted. The present invention relates to a lithium secondary battery that can be charged and discharged using a material obtained by post-quenching as a positive electrode active material. [Prior Art] Many proposals regarding high energy density batteries using lithium as a negative electrode active material have been made. For example, a battery is known in which an intercalation compound of graphite and fluorine is used as a positive electrode active material, and lithium metal is used as a negative electrode active material (for example, see US Pat. No. 3,514,337). Furthermore, lithium batteries using graphite fluoride as a positive electrode active material and lithium batteries using manganese dioxide as a positive electrode active material are already commercially available. However, these batteries were primary batteries and had the disadvantage that they could not be recharged. Regarding secondary batteries using lithium as a negative electrode active material, batteries using titanium, zirconium, hafnium, niobium, tantalum, vanadium sulfides, selenium compounds, and tellurium compounds as positive electrode active materials (for example, US Pat. No. 4,009,052) ) or batteries using chromium oxide, niobium selenide, copper vanadate, etc.
of the Electrochemical Society (J.Electrochem.Soc.) Vol. 124 (7) No. 968 and No.
325 (1977), Japanese Patent Application No. 55-25217), etc., but these batteries could not necessarily be said to have sufficient battery characteristics and economical efficiency. [Problems to be solved by the invention] In addition, regarding lithium batteries using amorphous materials as positive electrode active materials, in the case of MoS ₂ , MoS ₃ , and V ₂ S ₅ [Journal of Electroanalytical
Chemistry (J.Electroanal.Chem.) Volume 118 No.
229 (1981)] and LiV ₃ O ₃ [Journal
Of Non-Crystalline Solites (J.Non-
Crystalline Solids, Vol. 44, p. 297 (1981), etc. have been proposed. However, there were problems with discharge at high current density and charge/discharge characteristics. An object of the present invention is to improve the above-mentioned current situation and provide a lithium secondary battery that is small in size, has a large charge/discharge capacity, and has excellent characteristics. [Means for Solving the Problems] To summarize the present invention, the present invention relates to a lithium secondary battery, in which P ₂ O ₅ , TeO ₂ , GeO 2 are added to Cu ₂ V ₂ O ₇ as additives. ₂ , Sb ₂ O ₃ , BiO ₃ and
An amorphous material obtained by adding at least one oxide selected from the group consisting of B ₂ O ₃ , melting and rapid cooling 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 chemically stable with respect to the substance and the negative electrode active material;
In addition, the electrolyte material is characterized in that a substance capable of allowing lithium ions to move for an electrochemical reaction with the positive electrode active material or the negative electrode active material is used as the electrolyte material. To explain the present invention in more detail, the positive electrode active material used in the lithium secondary battery according to the present invention includes the aforementioned Cu ₂ V ₂ O ₇ and P ₂ O ₃ , TeO ₂ , GeO ₂ , Sb ₂ O ₃ ,
It is an amorphous material obtained by melting and rapidly cooling with at least one oxide of Bi ₂ O ₃ and B ₂ O ₃ . The amount of the oxide used is preferably 50 mol % or less, particularly preferably 10 to 25 mol %, based on Cu ₂ V ₂ O ₇ . To form a positive electrode using this positive electrode active material,
This amorphous material powder or a mixture of the amorphous material powder and a binder powder such as polytetrafluoroethylene is pressure-molded into a film on a support such as nickel or stainless steel. Alternatively, a conductive powder such as acetylene black may be mixed with the amorphous substance powder to impart conductivity, and a binder powder such as polytetrafluoroethylene may be added thereto as required. It can be formed by placing it in a metal container or by pressure-molding the above-mentioned mixture on a support such as nickel or stainless steel. Lithium or lithium alloy, which is the negative electrode active material, can be formed into a negative electrode by spreading it into a sheet or by pressing the sheet onto a conductor network such as nickel or stainless steel, as in the case of general lithium batteries. can. Further, as the electrolyte, one or more aprotons such as propylene carbonate, 2-methyltetrahydrofuran, dioxolane, tetrahydrofuran, 1,2-dimethoxyethane, ethylene carbonate, γ-butyrolactone, dimethyl sulfoxide, acetonitrile, formamide, dimethylformamide, nitromethane, etc. organic solvent and
Combinations with lithium salts such as LiClO ₄ , LiAlCl ₄ , LiBF ₄ , LiCl, LiPF ₆ or LiAsF ₈ or solid electrolytes or molten salts with Li ⁺ as the conductor, generally used in batteries using lithium as the negative electrode active material. Any known electrolyte can be used. Further, when a microporous separator is used as necessary in the battery configuration, a thin film made of porous polypropylene or the like may be used. The reason why the positive electrode active material has excellent charge and discharge characteristics as described above is not necessarily clear, but one reason is
One reason is that the positive electrode active material in the present invention is almost completely amorphous. That is, melted and cooled with Cu ₂ V ₂ O ₇
Random networks are formed by network formers such as P ₂ O ₅ and supply many unpaired dangling bonds with high reactivity.
Since this bond does not directly contribute to the structure of the crystalline lattice system, it is thought that the consumption of dangling bonds during charging and discharging does not involve lattice destruction or element precipitation, which makes it better than conventional crystalline cathode materials. This is presumed to be the cause of deep and good charge/discharge characteristics. The method for producing the metal oxide amorphous material as described above is basically not limited. However, the roll quenching method, which has a better quenching speed than the simple underwater quenching method, can make the Cu ₂ V ₂ O ₇ cathode amorphous with a smaller amount of network formers such as P ₂ O ₅ . This is advantageous in increasing the amount of active material filled.
For example, in the case of the twin roll quenching method, an amorphous material is produced using an apparatus as shown in FIG. That is, FIG. 1 is a schematic cross-sectional view of a twin-roll quenching apparatus for amorphizing metal oxides. Cu ₂ V ₂ O ₇
A mixture of a predetermined amount of at least one of P ₂ O ₅ , TeO ₂ , GeO ₂ , Sb ₂ O ₃ , Bi ₂ O ₃ , and B ₂ O ₃ is put into a quartz nozzle 1 with a small hole diameter of 0.3 mmφ at the tip; Heat and melt at 700°C using silicon carbide heater 2. After confirming that the base material is completely melted, the nozzle hole is moved closer to the contact area between the rolls using the air piston 3, and at the same time, the internal pressure of the nozzle is rapidly increased to 150 kg/cm ³ using argon gas 4. Melt 5
is ejected between a pair of rolls 6 rotating at a high speed of 2,000 to 4,000 rpm to produce a thin strip-shaped amorphous material 7 that is ultra-quenched and solidified. In addition, the network former is
No matter which of P ₂ O ₅ , TeO ₂ , GeO ₂ , Sb ₂ O ₃ , Bi ₂ O ₃ , and B ₂ O ₃ was used, there was no significant difference in the degree of amorphism and battery characteristics. [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 The amorphous material as the positive electrode active material is
A predetermined amount of P ₂ O ₃ was mixed with Cu ₂ V ₂ O ₇ , melted at about 700°C, and then rapidly cooled with a roll. As an example,
FIG. 2 shows the X-ray diffraction pattern of an amorphous material consisting of 90 mol % Cu ₂ V ₂ O ₇ -10 mol % P ₂ O ₅ . In other words, Figure 2 shows the X-ray diffraction results at the Plagg angle 2θ (degrees, horizontal axis).
This is a graph showing the relationship between Cps and reflection intensity (Cps, vertical axis). As can be seen from Figure 2, CuKα radiation
It shows an amorphous pattern in X-rays with a very broad peak around 2θ of about 32 degrees, indicating that it has become amorphous. Results similar to those shown in FIG. 2 were obtained with other mixing ratios. FIG. 3 is a sectional view showing the structure of a coin-type battery, which is a specific example of the battery according to the present invention, and in the figure,
31 is a stainless steel sealing plate, 32 is a polypropylene gasket, 33 is a stainless steel positive electrode case, 34 is a lithium negative electrode, 35 is a polypropylene microporous separator, and 36 is a positive electrode mixture pellet. First, a metal lithium negative electrode 4 placed under pressure on a sealing plate 1 is inserted into the recess of the gasket 2, and a separator 5 and a positive electrode mixture pellet 6 are placed on the metal lithium negative electrode 4 in this order. as an electrolyte
1N LiClO ₄ /propylene carbonate (PC) +
1,2-dimethoxyethane (DME) [1:1 volume ratio] (equal volume solvent of propylene carbonate and 1,2-dimethoxyethane) or 1.5N LiAsF ₆ /
After injecting and impregnating an appropriate amount of 2-methyltetrahydrofuran (2MeTHF), the cathode case 3 is covered and caulked, resulting in a diameter of 23 mm and a thickness of 2 mm.
A coin-type battery was fabricated. The positive electrode active material was prepared by mixing Cu ₂ V ₂ O ₇ and P ₂ O ₅ so that the mole % of P ₂ O ₅ was in the range of 0 to 50, and according to the method described above. The prepared positive electrode active material was crushed using a mixing pulverizer.
After pulverizing for 70 minutes, it was mixed with Kettchen Black EC and tetrafluoroethylene in a weight ratio.
They were weighed and mixed at a ratio of 70:25:5. This mixed powder was spread into a sheet with a thickness of 0.5 mm using a roll.
A positive electrode mixture pellet 6 having a diameter of 20 mm was prepared. Table 1 shows the discharge characteristics (2V termination) of the lithium secondary battery produced as described above (using 1N LiClO ₄ /PC-DME as the electrolyte) at a constant current of 1 mA.

[Table] Also, 1mA constant current, per positive electrode active material
Table 2 shows the charge/discharge characteristics (number of cycles) resulting from charging/discharging at a capacity of 150 Ah/Kg.

[Table] From Table 2, as a representative example, P ₂ O ₅ is 10
FIG. 4 shows a charge-discharge curve when a solid solution containing mol % is used as a positive electrode active material. In other words, Figure 4 shows the charge/discharge capacity (Ah/Kg, horizontal axis) and cell voltage (V,
It is a graph showing the relationship with the vertical axis). The numbers in the figure indicate the number of charge/discharge cycles. Here, the electrolyte is
1.5N.LiAsF ₆ /2MeTHF was used. As can be seen from this result, the melted and cooled M ₂ O ₃ −P ₂ O ₅ containing 10 to 25 mol% of P ₂ O ₅ is Cu ₂ V ₂ O ₇
It shows superior charge-discharge characteristics compared to P ₂ O ₅ alone or a molten cooled product containing more than 50 mol % of P 2 O 5 . Example 2 Using a lithium secondary battery produced in the same manner as in Example 1 (Figure 3), a 2V-
Figure 5 shows the results of voltage-regulated charging and discharging between 3.5V and the same relationship as Figure 4. Here the electrolyte is
1.5N LiAsF ₆ /2MeTHF was used. The initial discharge capacity reached 270Ah/Kg and continued
It maintained a capacity of 200Ah/Kg up to 50 times. Example 3 Using a lithium secondary battery produced in the same manner as in Example 1, 1 mA (0.5 mA/cm ² ) and 2 mA (1 mA/cm 2 ) were used.
Figure 6 shows the results of discharging at constant currents of 4 mA (2 mA/cm ² ), 8 mA (4 mA/cm ² ) ^, and 8 mA (4 mA/cm 2 ). That is, the sixth
The figure shows Li/Cu ₂ V ₂ O ₇ (units, horizontal axis) and cell voltage (V,
It is a graph showing the relationship with the vertical axis). Here, 1.5N LiAsF ₆ /2MeTHF was used as the electrolyte. If the positive electrode utilization rate at 2V final capacity during 1mA (0.5mA/cm ² ) discharge is 100%, the capacity retention rate is:
84%, 67%, 26% at 2mA, 4mA, 8mA respectively
showed a good value. Example 4 Cu ₂ V ₂ O ₇ and TeO ₂ , GeO ₂ , Sb ₂ O ₃ , Bi ₂ O ₃ ,
An oxide of one type of B ₂ O ₃ was weighed out so that the proportion of Cu ₂ V ₂ O ₇ was 90 mol %, and a positive electrode active material was prepared in the same manner as in Example 1. Using this positive electrode active material, a positive electrode mixture pellet was prepared in the same manner as in Example 1, and a coin-type lithium secondary battery was further manufactured. 1mA using this battery,
Table 3 shows the discharge characteristics (number of cycles) obtained by conducting a charge/discharge test under the condition of 160 Ah/Kg.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to construct a small, high-energy density lithium secondary battery with a large charge/discharge capacity, and the battery of the present invention has the advantage that it can be used in various fields such as coin-type batteries. has.

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional view of a twin-roll quenching device for amorphizing metal oxides, and Figure 2 shows the X-ray diffraction results of the positive electrode active material in the present invention in terms of the relationship between the plug angle and the reflection intensity. The graph, FIG. 3 is one of the present invention.
A cross-sectional view showing the configuration of a coin-type battery as an example,
FIGS. 4 to 6 are characteristic diagrams showing the charging and discharging characteristics of a battery in one embodiment of the present invention. 1: Quartz nozzle, 2: Silicon carbide heater,
3: air piston, 4: argon gas, 5: melt, 6: roll pair, 7: ribbon-shaped amorphous material, 3
1: Sealing plate, 32: Gasket, 33: Positive electrode case, 34: Lithium negative electrode, 35: Separator, 3
6: Positive electrode mixture pellet.

Claims (1)

[Claims] 1 Cu ₂ V ₂ O ₇ with additives such as P ₂ O ₅ , TeO ₂ ,
An amorphous material obtained by adding at least one oxide selected from the group consisting of GeO ₂ , Sb ₂ O ₃ , Bi ₂ O ₃ and B ₂ O ₃ and rapidly cooling after melting is used as a positive electrode active material, Lithium or a lithium alloy is used 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 for lithium ions to undergo an electrochemical reaction with the positive electrode active material or the negative electrode active material. A lithium secondary battery characterized in that an electrolyte material is a substance capable of movement.