JPH0467751B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention provides a lithium secondary battery that is small in size and has a large charge/discharge capacity, in particular, uses lithium or a lithium alloy as a negative electrode active material, and uses MoO ₃ or WO ₃ as a negative electrode active material.
This invention relates to a lithium secondary battery that can be charged and discharged using a material obtained by adding additives to the material, melting it, and then rapidly cooling it 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 sulfide, 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, etc. [J.Electrochem.
Soc.) Vol. 124 (7), pages 968 and 325 (1977)], but these batteries could not necessarily be said to have sufficient battery characteristics and economic 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.) No. 118
Volume 229 (1981)] and the case of 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, and the present invention relates to _a lithium secondary battery _.
In addition, P ₂ O ₅ , TeO ₂ , GeO ₂ , Sb ₂ O ₃ ,
An amorphous material obtained by adding at least one oxide selected from the group consisting of Bi ₂ O ₃ and B ₂ O ₃ and rapidly cooling after melting is used as a positive electrode active material, and lithium or a lithium alloy is used as a negative electrode active material. An electrolyte material is a substance that is chemically stable with respect to the positive electrode active material and the negative electrode active material and that allows lithium ions to migrate for an electrochemical reaction with the positive electrode active material or the negative electrode active material. It is characterized by the following. 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 above-mentioned MoO ₃ or WO ₃ and P ₂ O ₅ , TeO ₂ ,
It is an amorphous material obtained by melting and rapidly cooling an oxide of at least one of GeO ₂ , Sb ₂ O ₃ , Bi ₂ O ₃ , and B ₂ O ₃ . The amount of the oxide used is 50% for MoO ₃ or WO ₃
It is preferably mol% or less, particularly preferably 10 to 25 mol%. 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, propylene carbonate, 2-methyltetrahydrofuran, dioxysolane, tetrahydrofuran, 1,2-dimethoxyethane, ethylene carbonate, γ-butyrolactone, dimethyl sulfoxide, acetonitrile,
one or more non-pyrotic organic solvents such as formamide, dimethylformamide, nitromethane, etc.
Combinations with lithium salts such as LiClO ₄ , LiAlCl ₄ , LiBF ₄ , LiCl, LiPF ₆ or LiAsF ₄ 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 olipropylene 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. In other words, a network former such as P ₂ O ₅ which is melted and cooled together with MoO ₃ or WO ₃ forms a random network consisting of Mo(W)-O-P bonds, resulting in highly reactive properties. It supplies many unpaired dangling bonds. Since this bond does not directly contribute to the crystal structure of the lattice meter, it is thought that the consumption of dangling bonds during charging and discharging does not involve lattice destruction or element precipitation, which is why conventional crystalline cathode materials This is presumed to be the cause of deeper and better 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 achieve amorphousization with a smaller amount of network formers such as P ₂ O ₅ and MoO ₃ or This is advantageous in increasing the filling amount of WO ₃ as a positive electrode active material. For example, in the case of the twin roll quenching method, an amorphous material is produced using an apparatus as shown in FIG. FIG. 1 is a schematic cross-sectional view of a twin-roll quenching device for amorphizing metal oxides.
MoO ₃ or WO ₃ with P ₂ O ₅ , TeO ₂ , GeO ₂ ,
A mixture of a predetermined amount of at least one of 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 and heated by a silicon carbide heater 2.
Heat and melt at 800℃ (15000℃ for WO ₃ ).
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. A pair of rolls 6 that rotates the melt 5 at high speed from 2000 to 4000 rpm.
A thin strip-shaped amorphous material 7 is ejected during the
Manufacture. 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 preparation and measurements were performed in an argon atmosphere. Example 1 The amorphous material as the positive electrode active material is MoO ₃
After mixing a predetermined amount _{of P2O5} and melting at about 800℃,
It was produced by rapidly cooling the roll. As an example, 90 mol%
The X-ray diffraction pattern of an amorphous material consisting of MoO ₃ -10 mol % P ₂ O ₅ is shown in FIG. That is, FIG. 2 is a graph showing the X-ray diffraction results of the positive electrode active material in the present invention in terms of the relationship between Bragg angle 2θ (degrees, horizontal axis) and reflection intensity (CPS, vertical axis). As can be seen from Figure 2, the CuCα ray shows an amorphous pattern in X-rays with a very broad peak around 2θ of about 26 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, 33 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 15N LiAsF ₄ /
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 MoO ₃ 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. However, the one containing 0% P ₂ O ₅ is crystalline MoO ₃ alone and is not amorphous. The prepared cathode active material was crushed using a mixing pulverizer to approx.
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 a typical example of 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 1mA. Shown below.

[Table] Also, 1mA constant current, per positive electrode active material
Table 2 shows typical examples of discharge characteristics (number of cycles) resulting from charging and discharging at a capacity of 150Ah/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. That is, FIG. 4 is a graph showing the charging/discharging characteristics of a battery in one embodiment of the present invention in terms of the relationship between charging/discharging capacity (Ah/Kg, horizontal axis) and cell voltage (V, vertical axis). The numbers in the figure indicate the number of charge/discharge cycles. Here, the electrolyte is
15N LiAsF ₆ /2MeTHF was used. As can be seen from this result, the molten and cooled product of MoO ₃ - P ₂ O ₅ containing 10 to 25 mol% of P 2 O ₅ is different from _{MoO 3} alone or the molten and cooled product containing more than 50 mol% of P ₂ O ₅ . It shows superior charge-discharge characteristics compared to other batteries. Furthermore, it is possible to similarly amorphize the WO ₃ -P ₂ O ₅ system, which is a group transition metal oxide of the same periodic table as MoO ₃ , in the composition range of 10 to 25 mol% P ₂ O ₅ . The mixture, melted and rapidly cooled showed suitable battery characteristics. Example 2 90 mol% MoO ₃ -10 mol% as positive electrode active material
An amorphous substance of P ₂ O ₅ was used. Other than that, lithium secondary batteries produced in the same manner as in Example 1 were used at 1 mA (0.5 mA/cm 2 ) and 10 mA (5 mA/cm ² ).
Table 3 shows the results of discharging at a constant current of cm ² ).

[Table] The cathode material utilization rate does not decrease even under large current discharge, and the cathode utilization rate when discharging at 1mA (0.5mA/cm ² )
When set to 100%, the positive electrode utilization rate at 10 mA (5 mA/cm ² ) discharge was 80%, which showed a high capacity retention rate. Example 3 A predetermined amount of WO ₃ and P ₂ O ₅ was weighed out so that P ₂ O ₅ was in the range of 0 to 50 mol %, and a positive electrode active material was prepared in the same manner as in Example 1. A positive electrode mixture pellet was produced using the following method. Furthermore, a coin-type lithium battery was produced in the same manner as in Example 1. Here, the electrolyte is 1N LiClO ₄ /PC−
For the lithium secondary battery of the present invention constructed using both DME and 1.5N LiAsF ₆ /2MeTHF,
A charge/discharge test was conducted under the conditions of mA and 106Ah/Kg.
The resulting charge/discharge characteristics (number of cycles) are shown in Table 4.

[Table] As seen in this result, in a lithium secondary battery using the positive electrode active material shown in Table 4, the electrolyte contains 1N
Approximately 50 times when using LiClO ₄ /PC-DME,
It was found that more than 100 cycles could be obtained when 1.5N LiAsF ₆ /2MeTHF was used. Example 4 MoO ₃ or WO ₃ and TeO ₂ , GeO ₂ , Sb ₂ O ₃ ,
A positive electrode active material was prepared in the same manner as in Example 1 by weighing Bi ₂ O ₃ and one oxide of B ₂ O ₃ so that the proportion of MoO ₃ or WO ₃ was 90 mol%. did. 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. Using this battery, 1m
A. The discharge characteristics (number of cycles) as a result of a charge/discharge test conducted under the condition of 160 Ah/Kg are as shown in Tables 5 and 6.

【table】

〔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 cross-sectional schematic diagram 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 Bragg angle and 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,
FIG. 4 is a characteristic diagram 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 MoO ₃ or WO ₃ with P ₂ O ₅ as an additive,
adding at least one oxide selected from the group consisting of TeO ₂ , GeO ₂ , Sb ₂ O ₃ , Bi ₂ O ₃ and B ₂ O ₃ ;
An amorphous material obtained by rapid cooling after melting 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 ions. A lithium secondary battery characterized in that an electrolyte material is a substance that can move to perform an electrochemical reaction with the positive electrode active material or the negative electrode active material.