JPH08236105A - Manufacture of lithium secondary battery positive electrode - Google Patents

Abstract

PURPOSE: To manufacture a lithium secondary battery positive electrode with high film-adhesion property and excellent characteristic of battery by forming a metal oxide film containing lithium on an electrode substrate by jointly using vapor deposition of a lithium containing material and ion beam irradiation. CONSTITUTION: A lithium-containing material is vaporized from a vaporizing source 3 inside a vacuum chamber 1 having an exhaust device 7, and a vaporized material 3a is vapor-deposited on an electrode substrate S mounted on a base holder 2. At the same time, ion beams are irradiated on the substrate S from an ion source 4. A lithium-containing metal oxide film is formed on the substrate S. As the lithium-containing metal oxide, LiMn2 O4 , LiWO3 , LiCoO2 , LiNiCoO, and LiV2 O5 are used. This ion beam is preferably formed by using an inert gas or an oxygen gas as a raw gas, and an accelerating energy of 100eV-500KeV. By using the lithium-containing metal oxide film as the positive electrode of a lithium secondary battery, the mobility of a lithium ion on the inside hardly drops and desirable battery characteristics is easily obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode for a lithium secondary battery, and more particularly to a method for manufacturing a positive electrode for a lithium secondary battery having a high discharge energy density during high-current discharge.

[0002]

2. Description of the Related Art A positive electrode active material for a lithium secondary battery is charged and discharged.
Good reversibility of electricity, that is, lithium ion (Li
⁺) It is desirable that the change in crystal structure with the comings and goings is small.
Be done. Such substances include titanium (Ti) and niobium.
Sulfide such as (Nb) and molybdenum (Mo) and selenization
And metal oxides containing lithium are used. Especially,
Lithium manganese oxide (LiMn₂O_Four) Etc.
Metal oxides containing aluminum can give high energy density
Are known. LiMn₂O_FourThe positive electrode consisting of
Manganese dioxide (MnO₂) And lithium hydroxide (LiO
LiMn obtained by mixing and firing the powder of H)₂O_Fourof
It is manufactured by mixing a binder and a conductive agent into powder and molding it into a plate shape.
Have been. In addition, in recent years, the vacuum evaporation method has been applied to the positive electrode substrate.
LiMn₂O _FourA method of forming a film is also used.

[0003]

However, the LiMn ₂ O ₄ positive electrode manufactured by molding in the plate shape as described above has the following problems.
Since it contains many crystal defects and crystal grain boundaries, LiMn ₂ O
_{4 Since the} binder and the conductive agent mixed in the powder exist as an amorphous region, these portions suppress the movement of lithium ions, and the mobility of lithium ions in the positive electrode decreases. In particular, when a large current discharge is to be performed, crystal defects, crystal grain boundaries, and the amorphous region control the mobility of lithium ions, making a large current discharge difficult.

Further, according to the conventional method for producing a positive electrode using the vacuum evaporation method, a LiMn ₂ O ₄ film having a film thickness of about 100 μm is usually formed on an electrode substrate, but the film is formed by internal stress generated in the film. In fact, it is difficult to put it into practical use because it has a poor adhesion to the substrate and is easily peeled off when the battery is used. Further, according to this method, the crystallinity and crystal grain density of the formed film cannot be controlled. Therefore, in order to obtain desired battery characteristics such as discharge voltage and discharge time, annealing treatment (heat treatment) at high temperature after film formation is performed. However, the material of the substrate is limited in terms of heat resistance.

Therefore, the present invention is a method for producing a positive electrode for a lithium secondary battery by depositing a substance containing lithium on an electrode substrate to form a metal oxide film containing lithium. When used in a battery, the mobility of lithium ions inside is less likely to decrease, and desired battery characteristics such as discharge voltage and discharge time can be easily obtained, and the film adheres to the electrode substrate closely. An object of the present invention is to provide a method capable of forming good properties.

[0006]

The method for producing a positive electrode for a lithium secondary battery of the present invention, which solves the above-mentioned problems, uses a combination of vapor deposition of a substance containing lithium on an electrode substrate and irradiation of the substrate with an ion beam. Then, a film of a metal oxide containing lithium is formed on the substrate. It is conceivable that the irradiation of the substrate with the ion beam is carried out simultaneously with or alternately with the vapor deposition of the substance on the substrate, after the vapor deposition, before or after the vapor deposition, or the like. Irradiation with an ion beam before vapor deposition enables cleaning and modification of the substrate surface.

Examples of the metal oxide containing lithium include LiMn ₂ O ₄ and lithium tungsten oxide (L
ixWO ₃ ), lithium cobalt oxide (LiCo
O ₂ ), lithium nickel cobalt oxide (LiNix
CoyO ₂ ), lithium manganese oxide (LixMnO
₂ ), lithium vanadium oxide (LiV ₂ O ₅ ) and the like.

The vapor deposition of the substance containing lithium is performed by a vacuum vapor deposition method in which the vaporized substance is heated and vaporized by an electron beam, a vacuum vapor deposition method in which the vaporized substance is heated and vaporized by resistance, or the vaporized substance is heated by laser. Vapor deposition method of evaporating and then evaporating the vaporized material by induction heating with a high frequency, or a vapor deposition method of sputtering a target by means of ion beam, magnetron, high frequency or the like. . When there are a plurality of evaporation materials or sputtering target materials for vapor deposition of the lithium-containing material, each material may be evaporated from one evaporation source or may be evaporated from different evaporation sources. It is also possible.

In the ion beam irradiation, usually,
Radicals generated together with ions from the source gas are also irradiated. The ion beam for irradiation is an inert gas (helium (He) gas, neon (Ne) gas, argon (A)
r) gas, krypton (Kr) gas, xenon (Xe)
Gas) or oxygen (O ₂ ) gas or a mixed gas of the above-mentioned inert gas and oxygen gas or the like, which is considered to be an ion beam obtained.

Irradiation with the ion beam is performed simultaneously with, or alternately with, vapor deposition of a substance containing lithium, or after vapor deposition of the substance, or before or after vapor deposition of the substance. The ion beam may be irradiated only at the initial stage of vapor deposition. Further, it is considered that the angle of incidence of the ion beam on the substrate is about 10 ° to 90 ° with respect to the surface of the substrate.

It is considered that the acceleration energy in the ion beam irradiation is about 100 eV to 50 keV. This is because if it is less than 100 eV, a sufficient film adhesion cannot be obtained, and if it is more than 50 keV, the crystal structure is destroyed and defects occur. Also,
The ratio of the number of molecules of the evaporated substance reaching the substrate to the number of irradiated ions (evaporated substance / ion transport ratio) is not limited thereto, but is considered to be about 0.5 to 200. This is because if it is less than 0.5, defects in the film increase and the film growth becomes difficult, and if it is more than 200, the effect of ion irradiation cannot be obtained.

By controlling the acceleration energy of the ion beam and the evaporation material / ion transport ratio within the above range,
The internal stress of the obtained film can be controlled, and the crystallinity and the grain density can be desired. Also, during film formation, by increasing the acceleration energy of the ion beam within the above range, it is possible to amorphize the crystal structure only on the film surface in contact with the electrolytic solution, thereby increasing the fatigue fracture strength of the crystal structure. Can be increased.

The electrode substrate is not particularly limited as long as it is an electrode used in a battery, and the material is nickel (N
i), aluminum (Al), copper (Cu), stainless steel (SUS), carbon (C), and other electrically conductive materials can be mentioned, and their shapes are plate-like, film-like, foam-like, and non-woven fabric-like. Etc., and there is no particular limitation.

[0014]

According to the method for producing a positive electrode for a lithium secondary battery of the present invention, the deposition of a substance containing lithium on an electrode substrate and the irradiation of the substrate with an ion beam are combined to contain lithium on the substrate. A film of metal oxide is formed. By controlling the ion acceleration energy and / or the evaporation material / ion transport ratio at the time of ion beam irradiation, the crystallinity and crystal grain density of the formed positive electrode active material film can be controlled. In the battery using, the desired battery characteristics such as discharge voltage and discharge time can be easily obtained.

Further, in the conventional method for producing a positive electrode by forming a positive electrode active material film using a vapor deposition method, since the obtained film has low crystallinity, the film is annealed at a high temperature after the film is formed to obtain a desired film. Although it was necessary to obtain crystallinity, in the method of the present invention, since the crystallinity can be easily controlled, even when it is necessary to perform an annealing treatment after film formation, it is desirable to perform the treatment at a low temperature. The crystallinity of can be obtained. As a result, it is possible to employ an electrode substrate having a material shape with low heat resistance, and it is possible to select the electrode substrate from a wider range and reduce the cost required for the annealing treatment.

Further, there is a possibility that the annealing process can be omitted by optimizing the film forming temperature, the ion irradiation conditions, the processing time and the like. Further, by increasing the acceleration energy at the time of ion beam irradiation, the crystal structure can be made amorphous only on the film surface that comes into contact with the electrolytic solution, and thereby the fatigue fracture strength of the crystal structure can be increased.

Further, since the ion beam irradiation forms a mixed layer composed of the constituent atoms of the film and the substrate to be formed, the adhesion of the film is improved. In addition, the crystallinity of the film can be controlled by controlling the acceleration energy at the time of ion beam irradiation, whereby the internal stress of the film can be relaxed, and also in this respect, the adhesion of the film to the substrate can be improved. . Furthermore, since the internal stress of the film can be relaxed, even when the electrode substrate is a conductive film, the positive electrode active material film can be formed on the film.

Further, there is no amorphous region composed of impurities such as a binder and a conductive agent, which is found in the case of manufacturing a positive electrode by molding a positive electrode active material into a plate shape in the related art, and As compared with the conventional method, crystal defects and crystal grain boundaries can be reduced by controlling the crystal growth, so that the decrease in the mobility of lithium ions can be suppressed when used as a battery.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a film forming apparatus used for carrying out the method for producing a lithium secondary battery positive electrode of the present invention. This apparatus has a vacuum container 1, in which a holder 2 for supporting a film-forming electrode substrate S, and an evaporation source 3 and an ion source 4 are installed at positions facing the holder 2. Further, a film thickness monitor 5 such as a crystal oscillator type film thickness monitor and an ion current measuring device 6 such as a Faraday cup are arranged near the substrate holder 2. Further, an exhaust device 7 is attached to the container 1 so that the inside of the container 1 can have a predetermined degree of vacuum.

In carrying out the method for producing a lithium secondary battery positive electrode of the present invention using this apparatus, after the electrode substrate S is supported by the holder 2, the inside of the vacuum container 1 is brought to a predetermined vacuum degree. Then, the evaporation material 3a containing the constituent atoms of the target film is vacuum-deposited from the evaporation source 3 toward the substrate S, and simultaneously with or alternately with the evaporation material 3a, after the evaporation, or before or after the evaporation, from the ion source 4. The deposition surface is irradiated with an ion beam obtained from an inert gas, an oxygen gas, or a mixed gas of an inert gas and an oxygen gas to form a metal oxide film containing lithium.

In the film forming operation, the ion beam irradiation may be performed only at the initial stage of the vacuum deposition of the substance 3a.
Further, the ion beam acceleration energy is 100 eV to 50 k.
eV, the incident angle of the ion beam on the substrate S is 1
The angle is 0 ° to 90 °. Further, the evaporation material / ion transport ratio is 0.5 to 200. The transport ratio is controlled by measuring the deposition amount of the evaporation material 3a on the substrate S by the film thickness monitor 5 and measuring the number of ions with which the substrate S is irradiated by the ion current measuring device 6.

According to this method, the crystallinity and the grain density of the film formed can be controlled by controlling the acceleration energy of the ion beam by the ion source 4 and / or the evaporation material / ion transport ratio. Therefore, the battery using the film-formed positive electrode has desired battery characteristics, and in this respect, the battery design becomes easy. Similarly, since it is easy to control the crystallinity of the formed film, the processing temperature can be lowered even when the annealing treatment is performed after the film formation, and the selection allowable range of the electrode substrate is widened. The cost required for annealing can be reduced.

Further, the film and the substrate S are irradiated with the ion beam.
The formation of the mixed layer at the interface improves the adhesion of the film. Further, since the crystallinity of the formed film can be controlled, the internal stress of the film can be relieved. Also in this respect, the adhesion of the film to the substrate can be improved. In addition, there is no amorphous region consisting of impurities such as a binder or a conductive agent, which is seen in the case of manufacturing a positive electrode by molding a conventional positive electrode active material into a plate, and controlling the crystal growth. By doing so, crystal defects and crystal grain boundaries can be reduced, so that the mobility of lithium ions when the positive electrode is used can be improved, and the discharge energy density at the time of large current discharge can be increased accordingly.

Next, a specific example of carrying out the method of the present invention by the apparatus shown in FIG. 1 will be described. Experimental Example An electrode substrate S made of stainless steel (SUS) was installed in a holder 2, and the inside of the vacuum container 1 was initially set at 1 × 10 ⁻⁶ Tor.
The degree of vacuum was set to r or less. Then, lithium oxide (Li ₂
O) and manganese monoxide (MnO) were mixed to vaporize the vaporized substance 3a using the electron beam vaporization source 3 to form a film on the substrate S. At the same time, the Ar ion beam from the ion source 4 is perpendicular to the substrate S and the acceleration energy is 1 keV.
Irradiation was performed at -10 keV. At this time, the oxygen partial pressure in the container 1 was maintained at 1 × 10 ⁻⁶ Torr to 5 × 10 ⁻⁴ Torr. A for the deposition amount (number of molecules) of Li ₂ O and MnO
The ratio of the number of r ions (Li ₂ O + MnO / Ar) is 5 to 70.
And The temperature of the substrate S during film formation is room temperature to 500 ° C.
Kept at.

As a result, the film thickness on the substrate S is 1 μm to 50 μm.
LiMn ₂ O ₄ film having a thickness of 1 μm to 5 μm was formed at the interface between the substrate S and the LiMn ₂ O ₄ film. No peeling was observed when the positive electrode obtained by annealing the electrode substrate S on which the LiMn ₂ O ₄ film was formed at 500 ° C. for 10 hours was used as a battery.
In addition, the formed LiMn ₂ O ₄ film has a cubic crystal structure, and the crystallinity is controlled within the range of the ion beam acceleration energy and the Li ₂ O + MnO / Ar transport ratio, and as a result, it is obtained. The lithium secondary battery using the positive electrode has a discharge capacity of 200 V in a discharge voltage range of 2.5 V to 4.5 V.
The battery characteristic was mA · h / g.

[0026]

According to the present invention, a method for producing a positive electrode of a lithium secondary battery by depositing a substance containing lithium on an electrode substrate to form a metal oxide film containing lithium is obtained. When the positive electrode is used as a battery, the internal mobility of lithium ions is unlikely to decrease, and desired battery characteristics such as discharge voltage and discharge time can be easily obtained, and the film is formed on the electrode substrate. It is possible to provide a method capable of forming good adhesion.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an example of a film forming apparatus used for carrying out a method of the present invention.

[Explanation of symbols]

 1 Vacuum Container 2 Substrate Holder 3 Evaporation Source 3a Evaporation Material Containing Lithium 4 Ion Source 5 Film Thickness Monitor 6 Ion Current Measuring Device 7 Exhaust Device S Substrate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasushi Iwamoto 47 Umezu Takaune-cho, Ukyo-ku, Kyoto City Nissin Electric Co., Ltd. (72) Inventor Satoshi Nishiyama 47 Umezu Takaune-cho, Ukyo-ku, Kyoto City Nissin Electric Co., Ltd.

Claims (5)

[Claims] 1. A method for forming a metal oxide film containing lithium on the substrate by using vapor deposition of a substance containing lithium on an electrode substrate and irradiation of the substrate with an ion beam. Method for manufacturing positive electrode of lithium secondary battery. 2. The metal oxide containing lithium is lithium manganese oxide, lithium tungsten oxide,
The method for producing a lithium secondary battery positive electrode according to claim 1, wherein the material is a material selected from the group consisting of lithium cobalt oxide, lithium nickel cobalt oxide, and lithium vanadium oxide. 3. The positive electrode for a lithium secondary battery according to claim 1, wherein the ion beam for irradiation is an ion beam obtained by using an inert gas or oxygen gas or a mixed gas of an inert gas and oxygen gas as a source gas. Manufacturing method. 4. The method for producing a lithium secondary battery positive electrode according to claim 1, wherein the acceleration energy of the ion beam for irradiation is in the range of 100 eV to 50 keV. 5. The vapor deposition of a substance containing lithium as described above, a vacuum vapor deposition method of heating and vaporizing a vaporized substance by an electron beam, a vacuum vapor deposition method of heating and vaporizing a vaporized substance by resistance, or a vaporized substance by a laser. 5. A lithium secondary battery positive electrode according to any one of claims 1 to 4, which is carried out by a vacuum vapor deposition method of heating and evaporating a vaporized material, a vacuum vapor deposition method of inductively heating and vaporizing a vaporized material by high frequency, or a sputter vapor deposition method. Method.