JPS62195853A - Lithium cell - Google Patents

Abstract

PURPOSE:To improve the charge and discharge characteristics by constructing a cell with a positive electrode active material composed of ultra fine particles of V2O5 of under 0.1mum in mean particle diameter and a negative electrode active material made of lithium and an electrolyte composed of specified materials. CONSTITUTION:A lithium cell is constructed with a positive electrode active material composed of ultra fine particles of V2O5 of under 0.1mum in mean particle diameter and a negative electrode active material made of lithium and an electrolyte composed of materials chemically stale to the positive electrode active material and lithium and in which lithium ions are movable for electrochemical reaction with the position electrode active material. As for the electrolyte, a conventional electrolyte commonly used for a cell using lithium as the negative electrode active material e.g. a combination of more than one kind of non-protonic organic solvent such as propylene carbonate, 2- methyltetrahydrofuran and a lithium salt such as LiClO4 and so on or a solid electrolyte having carriers of electricity of lithium ions or a fused salt and so on can be used. Thereby it is possible to obtain a high current and the cell can be used as a lithium secondary cell of good discharge constancy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lithium secondary battery that is small in size and has a large charge/discharge capacity.

[Summary of the Disclosure] The present invention provides V! with an average particle size of 01 μm or less. The ultrafine particles of 1105 are used as a positive electrode active material, and lithium is used as a negative electrode active material, which is chemically stable with respect to the positive electrode active material and lithium, and allows lithium ions to move for an electrochemical reaction with the positive electrode active material. By using substances as electrolytes,
This invention discloses a technology that can be used in various fields as a lithium secondary battery that can obtain a large current and has good discharge uniformity because the effective reaction surface area is expanded.

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] Many proposals have been made regarding high energy density batteries using lithium as a negative electrode active material. For example, a battery is known that uses graphite and a fluorine intercalation compound as a positive electrode active material, and a lithium alloy as a negative electrode active material (for example, see US Pat. No. 3,514,337). Furthermore, lithium batteries using fluorinated graphite 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 are primary batteries and have the disadvantage that they cannot be recharged.

Regarding secondary batteries using lithium as a negative electrode active material, batteries using titanium, hafnium, niobium, tantalum, vanadium sulfides, selenides, and tellurides as positive electrode active materials (for example, U.S. Pat. No. 4,009,
052 specification), or batteries using chromium oxide, niobium selenide, etc. (J, EIelectroche)
m, Soc,, 124(7), 9fi8 and325
, (+977) ), etc. have been proposed, but these batteries have not necessarily been satisfactory in terms of their battery characteristics and economic efficiency.

Regarding lithium batteries using amorphous materials as positive electrode active materials, MoS2, Mo53. In the case of v2ss (
J,EI electroanal,Chem,, 118,
229 (+981)) or LiV308 (J, N
on-Crystalline 5olids, 44°297 (1981)), etc. have been proposed.

However, both proposals had problems in terms of discharge at high current density and charge/discharge characteristics.

Using crystalline P2O5 as a positive electrode active material
J, EIectrochem, Soc, Meetin
g, Toronto, Mayll-16, 1975, N.
o, 27). Also, P2O5 and P2O
An amorphous material obtained by adding 5 and rapidly cooling after melting is proposed in Japanese Patent Application No. 59-237778.

However, all of them had small capacities and unsatisfactory charge/discharge characteristics.

[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 ultrafine particles of V and O5 as the positive electrode active material. The average particle size is preferably 0.1 μm or less. That is, the present invention uses vQ05 ultrafine particles with an average particle size of 0.1 μm or less as a positive electrode active material, lithium as a negative electrode active material, and is chemically stable with respect to the positive electrode active material and lithium, and lithium ions are used as a positive electrode active material. It is characterized in that an electrolyte is composed of a substance that can move to perform an electrochemical reaction with the active material.

[Function] Such ultrafine particle formation is a particularly effective means for improving the battery characteristics of positive electrode active materials with low electronic conductivity, such as P2O5, and increases the obtained current and charging time by expanding the reaction surface area. This makes it possible to shorten the time and make the battery reaction more uniform by reducing the particle size.

Methods for producing the ultrafine particles of VU05 as described above include an evaporation method in a gas or an alkoxide hydrolysis method, but the present invention is not fundamentally limited to these methods.

For example, when using the in-gas evaporation method, ultrafine particles are produced using an apparatus as shown in FIG.

That is, in the vacuum chamber 21, an ultrafine particle collector 22 and an ember 21 are connected to an inert gas (for example) gas cylinder 26 via a regulator 25. In addition, in the figure, 27
is a window for observing the inside of the vacuum chamber 1; 28 is a manometer;
29 is a Pirani vacuum gauge.

Inert gas is introduced into the vacuum chamber 1 from an inert gas cylinder 6 via the regulator 5 to create an inert gas diluted atmosphere inside the vacuum chamber 1, and at the same time, the voltage is increased by the power source 4.
1O, the raw material evaporation groove 3 is heated to evaporate the raw material. The evaporated raw material 3 collides with the inert gas and is rapidly cooled, becoming supersaturated and producing ultrafine particles.

The concentration of inert gas at this time is preferably 1O-100T.
It is orr. This is because if the pressure exceeds 100 Torr, the particle size of the particles becomes too large. On the other hand, I O'I' o
This is because if it is less than r r, particles will be difficult to generate.

Moreover, it is preferable that the temperature of evaporation is 1000-1200°C. This is because if the temperature exceeds 1,200°C, the particle size becomes too large, and if the temperature is below 1,000°C, the raw material becomes difficult to evaporate.

In this way, crystals with an average grain size of 0.1 μm or less +!
fV, 05 ultrafine particles can be obtained.

In addition, in the case of alkoxide hydrolysis method, vo(c
Water is added dropwise to an alkoxide such as OYI+5)3, stirred to hydrolyze it, and the resultant is centrifuged to obtain a dry powder. By drying and dehydrating this powder at 100 to 300°C,
Ultrafine particles of VU05 can be obtained.

To form a positive electrode using these v905 ultrafine particles, the mixed material powder or a mixture thereof with 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 (=J) to the mixed substance powder, and a binder powder such as polytetrafluoroethylene is further added thereto as required. The positive electrode can be formed by placing this mixture in a metal 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 spreading it into a sheet or by pressing the sheet onto a conductive mesh 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. An example is propylene carbonate, 2-
Medyltetrahydrofuran, dioxolene, tetrahydrofuran, 1,2-dimethoxyethane, ethylene carbonate, γ-butyrolactone, dimethyl sulfoxide,
flI14°LiBF4 to Li CaO2,1,i with one or more aprotic organic solvents such as acetonitrile, porumamide, dimethylformamide, nitromethane, etc.
In the present invention, known electrolytes generally used in batteries using lithium as a negative electrode active material, such as a combination with a lithium salt such as , LtCu, 1fPF6, LiAsF6, or a solid electrolyte or molten salt using lithium ions as a conductor, are used. can also be used as an electrolyte.

Further, when a microporous separator is used as required in the battery configuration, a thin film made of porous polypropylene or the like may be used.

[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, cell preparation and measurements were performed in an argon atmosphere.

Example 1 FIG. 2 is a sectional view of a coin-type battery which is an example of a lithium battery according to the present invention. In the figure, 1 is a stainless steel sealing plate, 2 is a polypropylene casket], 3 is a stainless steel positive electrode case, 4 is a lithium negative electrode, 5 is a polypropylene separator, and 6 is a positive electrode mixture bellet I.

First, the metal lithium negative electrode 4 placed under pressure on the sealing plate 1 is inserted into the four parts of the gasket 2, and the separator 5 and the positive electrode mixture are placed on the lithium negative electrode 4 at the opening of the sealing plate 1. 1.5N-LiAsF6/2-Megilte) as an electrolyte.
- After pouring and impregnating an appropriate amount of Rahi 1 to Rofuran (2Me THF), a positive electrode case 3 was placed on and caulked to create a coin-type battery with a diameter of 23n+n+ and a thickness of 2mm.

The positive electrode active material was able to evaporate V, -O5 in gas at about 1100° C. under an argon atmosphere of about 20 Torr.

The obtained positive electrode active material was mixed with acetylene black AB and tetrafluoroethylene at a weight ratio of 70+25:5. The mixture was roll-molded to a thickness of o, 6.
The mn+ bound material was punched out with a punch to obtain a positive electrode mixture pellet 6.

Using the lithium battery created as described above, 0.
The results of constant current discharge at various current densities of 5 to 8 mA/cm2 are shown in Table 1 together with commercially available crystalline V2O5 reagents (particle size: 1 to 10 m).

Table 1 Simple discharge capacity at each discharge current density (2V ending) Unit - Lung/kg As shown in Table 1, the commercially available crystalline VOO5 reagent exhibits a higher capacity with respect to low discharge current capacity. However, as the discharge current density increases, V, O, which has a large effective reaction surface area,
5. The effectiveness of the ultrafine particle sample is remarkable. As a representative example from Table 1, simple discharge profiles of a commercially available crystalline V2O5 reagent and a VΩ05 ultrafine particle sample at a large discharge current density of 8 mA/cm2 are shown in FIG.

Example 2 Using a lithium battery prepared in the same manner as Example 1,
0.5-8 m after constant current discharge of 0.5 mA 7 cm2
Voltage parent-controlled charging and discharging tests between 2v and 3.5V were conducted at each charging current of A/cm2. The discharge capacity in the second cycle was measured using commercially available crystalline V! Table 2 shows each of the 0L05 reagent and Vλ05 ultrafine particle sample.

Table 2 Discharge capacity of the second cycle at each charging current density (2V end) Unit: Ah / kg V2O5 not only for simple discharge but also for cycle capacity
It can be seen that the ultrafine particle sample is more effective at rapid charging and exhibits better characteristics.

Example 3 Using a lithium battery prepared in the same manner as Example 1,
A voltage regulated charge/discharge test between 2V and 3.5V was conducted at a constant current density of 2mA/cm2. Commercially available crystalline v! FIG. 4 shows the cycle characteristics of the 205 reagent and the VU05 ultrafine particle sample. It can be seen that the VU05 ultrafine particle sample has excellent profile hysteresis during both charging and discharging, and as a reflection of this, the capacity decrease due to charging and discharging cycles is small.

Example 4 A lithium battery was produced in the same manner as in Example 1 using v4205 ultrafine particles produced by an alkoxide hydrolysis method. 2v to 3.5V at constant current density of 2mA/cm2
A voltage regulated charge/discharge test was conducted between the two. The discharge capacity in the second cycle was 130Ah/g, and the V
The capacity is approximately the same as that of ultrafine particles (Table 2 of Example 2). Further, as in Example 3, the cycle characteristics show good characteristics, with little capacity reduction due to charge/discharge cycles.

[Effects of the Invention] As explained above, according to the present invention, the effective reaction surface area is expanded by the ultrafine particles of the positive electrode active material. It has the advantage that it can be used in various fields as a secondary battery.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of an evaporation device in waste for ultrafine V and O5 particles, Fig. 2 is a cross-sectional view showing the structure of a coin-type battery that is an embodiment of the present invention, and Fig. 3 4 is a characteristic diagram showing the discharge characteristics of a battery according to an embodiment of the present invention, and FIG. 4 is a characteristic diagram showing the charge and discharge characteristics of a battery according to an embodiment of the present invention. 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 , 21... Vacuum chamber, 22... Ultrafine particle sample collection container, 23... Evaporation source, 24... Power source for evaporation source, 25... Regulator, 26... To helium caspon, 27... Observation window, 28... Manometer, 29... Vacuum cage.

Claims (1)

[Claims] Ultrafine particles of V_2O_5 with an average particle size of 0.1 μm or less are used as the positive electrode active material, and lithium is used as the negative electrode active material. 1. A lithium battery characterized by comprising, as an electrolyte, a substance capable of movement for the purpose of .