JPH08162117A - Nonaqueous electrolyte secondary battery and manufacture thereof - Google Patents

Abstract

PURPOSE: To elongate a service life of a positive electrode base plate in a chargeable nonaqueous electrolyte secondary battery. CONSTITUTION: A skin film, having an uneven surface is formed of a core material having three dimensional mesh-like communication pores and using a strong metal such as Ni and flame coated aluminum thereon, is formed on a positive electrode base plate. Accordingly, strength is excellent, high potential errosion resistance utilizing an aluminum characteristic is maintained, and retentivity of active substance is remarkably improved. A sufficiently long service life can be maintained even when discharging and charging are repeated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery having a non-aqueous electrolyte containing rechargeable lithium ions and a method for manufacturing the battery.

[0002]

2. Description of the Related Art Lithium secondary batteries have attracted attention as alkaline batteries and high-capacity batteries for portable electronic devices such as mobile phones, video cameras, and book-type personal computers, as well as for electric vehicles and power storage. It entered the practical stage.

Particularly from the viewpoint of safety, a lithium ion secondary battery provided with an oxide positive electrode, a negative electrode made of a carbon material and a non-aqueous electrolyte containing lithium ions has been put into practical use, and an electrode material,
Development is progressing with regard to separators, manufacturing methods, and structures for ensuring safety. Furthermore, although still in the research stage,
There is also a lithium secondary battery in which an oxide is used as a positive electrode and lithium metal or a lithium alloy is used as a negative electrode.

By the way, since the electric resistance of the non-aqueous electrolyte including the primary battery of the lithium battery is much higher than that of the aqueous solution type, efforts have been made to cope with the high output which accounts for most of the recent applications. . As a means for this, research on materials and compositions for lowering the electrical resistance of the non-aqueous electrolyte has been conducted, and the other is to thin the electrode to increase the apparent area of the reaction and reduce the current density of charge / discharge. . In other words, the primary battery for cameras, which was first put into practical use for high output, has an electrode with a thickness less than half that of electrodes for alkaline batteries, etc., and has a structure in which it is wound in multiple layers together with a thin separator.

In the case of a lithium ion secondary battery, exactly the same idea is inherited. In the case of a secondary battery, since the potential of the positive electrode exceeds 3 V, for example, aluminum foil is used in consideration of oxidation resistance and electrolytic solution resistance, and copper foil or the like is used for the negative electrode. Is LiCoO ₂ or LiN
An electrode in which a complex oxide such as iO ₂ or LiMn ₂ O ₄ is coated with a carbon material together with a binder is used for the negative electrode. (JP-A-60-253157, etc.)

[0006]

However, when the electrode layer is formed by using the currently used aluminum foil or the like as the core material, the output characteristics and There is a demand for a core material that does not decrease in capacity, has high mechanical strength, and has good adhesion to an electrode substance. That is, when charging and discharging are repeated a number of times, the positive electrode gradually expands as a whole, and the contact between the interface between the core material and the electrode active material layer deteriorates, resulting in poor conductivity of the electrode itself and high current density. However, there are problems that the charge and discharge cycle life is shortened, and the fine powder that has fallen off the core material causes a short circuit.

As one of the causes of these, a reaction occurs in which lithium ions penetrate into the crystal lattice during the charge / discharge reaction,
Therefore, due to the expansion and contraction of the crystal lattice of the active material due to lithium ion doping and dedoping, the interface between the electrode active material layer and the current collector, the interface between the active material and the core material, the interface between the active material and the binder resin, etc. The occurrence of defects was considered. There is also a proposal of a metal current collector having a hole that communicates with it in order to prevent the peeling of the active material from the electrode metal foil and the accompanying reduction in battery performance.
(Sanyo Technical Review Vol.20 No.2
Aug. (1988, P60)

Further, in order to prevent the active material from falling off and peeling from the positive electrode and to improve the charge / discharge cycle characteristics of the non-aqueous electrolyte secondary battery, there is a proposal that the current collector is made of a metal foam (special feature). Kaihei 4-28163). In this patent, lithium or a lithium alloy is used for the negative electrode active material, and by making the positive electrode current collector have a foam structure, it is described that the deterioration of the discharge capacity due to repeated charge and discharge cycles does not easily occur. There is. However, only the average pore size is described, and the specific manufacturing method is unknown.
Neither method is a complete solution, and it is hard to say that the cycle life is maintained for practical use.

[0009]

The present invention has been made on the basis of such findings, and its main purpose is to prevent the positive electrode material from falling off during the assembly process and to remove the active material during repeated charge / discharge cycles. The present invention provides a non-aqueous electrolyte secondary battery in which the capacity is less likely to decrease due to factors such as the above, and a method for manufacturing the same. Another object of the present invention is to prevent the dissolution of the electrode substrate core material accompanying a charge / discharge cycle, and further improve the retention of the active material, thereby providing a non-aqueous electrolyte secondary battery having stable and high capacity charge / discharge characteristics, and The manufacturing method is provided.

That is, in a non-aqueous electrolyte secondary battery including a non-aqueous electrolyte containing rechargeable lithium ions,
This can be achieved by using, as a core material, a continuous metal porous body having three-dimensional net-like communicating pores made of nickel as a core material, and using a metal porous body coated with aluminum by thermal spraying as a positive electrode substrate.

Further, the present invention can be achieved by spraying aluminum and then heat-treating it in a non-oxidizing atmosphere. As another means for forming an aluminum film, a vacuum vapor deposition method or a plating method can be considered, but there are drawbacks such as a high cost of a vacuum device and a waste liquid treatment facility of a plating solution, and a slow film forming speed, which are not practical. Absent. The thermal spraying method used in the present invention is industrial because it can be processed in the atmosphere and has a high film formation rate. Among the aluminum metal spraying methods, acetylene using an aluminum rod that can form a film in an atmosphere that can suppress the oxidation of the aluminum film.
Gas spraying with an oxygen flame is preferred.

Nickel and aluminum are easy to combine,
Excessive heat treatment easily forms a brittle intermetallic compound that deteriorates workability even inside the skeleton, and therefore it is necessary to optimize heat treatment conditions. The conditions are not particularly limited, but by a short time treatment in an inert atmosphere or in a non-oxidizing atmosphere such as a reducing atmosphere, aluminum on the surface of the nickel skeleton diffuses below the surface of the core skeleton, and The heat treatment conditions may be such that a compound is slightly formed between the aluminum layer and the aluminum layer.

The thickness of the sprayed aluminum layer that exerts these effects is not particularly limited, but pinholes occur if it is too thin, so the average thickness is preferably about 1 μm or more. On the other hand, if the thickness is too large, the porous metal skeleton of the core material becomes thicker, the pore diameter becomes narrower, and finally the space volume decreases, so that the amount of the active material that can be filled decreases, so that the average thickness is preferably 50 μm or less.

A continuous metal porous body having three-dimensional mesh-like communicating pores has a porosity of 90% or more and a uniform pore diameter.
Utilizing the feature that the active material can be filled in the three-dimensional communication space, it is used for the electrodes of alkaline storage batteries and contributes to higher capacity of the batteries. INDUSTRIAL APPLICABILITY The present invention is to apply this continuous metal porous body having three-dimensional mesh-like communicating pores, which has already been proven in alkaline storage batteries, to an electrode substrate of a non-aqueous electrolyte battery.

The continuous metal porous body having the three-dimensional network pores used in the present invention is a resin core material having three-dimensional pores and having a porosity of 90% or more. For example, urethane foam resin is used as the core material. Or, or a non-woven fabric core integrally bonded to an organic fiber aggregate with an epoxy resin as a binder, the electroless plating of the resin skeleton, carbon coating or conductive treatment of nickel or the like by sputtering or vacuum deposition, Porous metal obtained by electroplating and heating in a reducing atmosphere for decomposition and annealing of resin (Japanese Patent Publication No. 47-10524, Japanese Patent Publication No. 61-76686, Japanese Patent Publication No. 4-284360), or urethane foam resin. A paste containing nickel metal powder and a binder as main components, and sintered in a reducing atmosphere (Japanese Patent Publication No. 38-17).
554), without limitation.

As one specific example of such a continuous metal porous body having three-dimensional mesh-like communicating pores, the trade name "Celmet" relating to the manufacture of the present applicant can be mentioned. In this case, graphite is applied to urethane foam resin in the form of slurry, excess slurry is removed, and then nickel is electroplated. Then, it is obtained by decomposing and removing the resin and annealing by heating in a hydrogen reducing atmosphere. Since the space of the metal porous body having the three-dimensional network pores can be filled with the active material, it is not necessary to make it thin like a metal foil, and the thickness of the metal porous body is 0.
There is no particular limitation as long as it is in the range of 3 mm to 2 mm.

[0017]

[Function] When a continuous metal porous body having nickel three-dimensional continuous pores is used as the positive electrode core material of a non-aqueous liquid electrolyte secondary battery, the porosity of the three-dimensional continuous pores is 90% or more. In addition, there is an advantage that the space can be filled with the active material and the active material retention property in the bag-shaped space is good. However, it cannot be used as it is because the chargeable oxide used for the positive electrode active material dissolves at a high potential exceeding 3 V. In the present invention, since the surface of the nickel porous metal skeleton is coated with the aluminum layer having a noble potential by thermal spraying, it does not dissolve even when the charge potential exceeds 3 V, and the charge / discharge cycle life is improved. Can be made.

Further, according to the present invention, since the sprayed aluminum layer is formed on the surface of the porous metal skeleton with a thickness of preferably 1 μm to 50 μm with unevenness of the order of several hundred nm (nanometer) to several tens μm, this is the active material. It is possible to increase the contact area with and improve the adhesion, and to suppress the detachment of the active material from the core material due to the charge / discharge cycle.

The conventional porous metal body obtained by any of the manufacturing methods is usually subjected to a heat treatment in a sufficient reducing atmosphere in the final step to improve the mechanical strength required for filling the active material. Has a smooth three-dimensional skeleton. By coating the surface of such a metal porous body skeleton with a sprayed film, the surface texture can be made uneven, so that it is more closely attached to the active material and the conductive material than the metal porous body having a smooth surface. It is possible to improve the property.

By doing so, it is possible to prevent the active material, the conductive material, and the like from falling off the surface of the core material when the charge / discharge cycle is repeated, so that the output characteristics and the capacity decrease are suppressed, and the charge / discharge cycle life is greatly improved. it can. Further, after the aluminum is sprayed onto the core material, the aluminum is diffused by heat treatment in a non-oxidizing atmosphere, whereby the sprayed aluminum layer and the base material are integrated near the interface to form a diffusion layer, thus forming the sprayed layer. It is possible to obtain an electrode plate in which the adhesion between the film and the core material is increased and there is no fear of film peeling during electrode formation processing. Furthermore, the charging potential is improved by the aluminum film present on the surface, and the dissolution of the core material is prevented more reliably.

[0021]

【Example】

(Example 1) <Fabrication of Positive Electrode> A positive electrode was fabricated using a commercially available continuous metal porous body having nickel three-dimensional mesh-like communicating pores (trade name "Celmet" manufactured by Sumitomo Electric Industries, Ltd.). Thickness 1.0 mm, average pore diameter of communicating pores 300μ
m, and nickel cermet having a weight of 350 g / m ² was used as a core material, and after cleaning treatment by acid treatment, aluminum spraying was performed. Using an acetylene / oxygen flame using an aluminum rod with a purity of 99.8%, so that the average thickness of the sprayed coating layer on the three-dimensional continuous metal skeleton constituting the metal porous body is 10 μm under a protective atmosphere of argon gas. It was adjusted. LiCoO ₂ was used for the positive electrode. After mixing 8% by weight of acetylene black as a conductive agent, 5% by weight of an aqueous dispersion of polytetrafluoroethylene resin was kneaded as a binder to prepare a paste-like mixture.
After filling the three-dimensional pores of the porous metal core material, the thickness was 0.4 mm by compression molding.

<Preparation of Negative Electrode> A kneaded material of graphite powder and polyethylene terephthalate was used as a negative electrode material and had a thickness of 15 μm.
m copper foil on both sides, dried and then compression molded to a thickness of 0.
A negative electrode having a thickness of 4 mm was prepared.

<Preparation of Non-Aqueous Electrolyte Solution> Ethylene carbonate (EC) as a solvent and LiPF ₆ as a solute
(Lithium hexafluorophosphate) was dissolved at 1 mol / liter to prepare a non-aqueous electrolyte solution.

<Production of Non-Aqueous Electrolyte Secondary Battery> A cylindrical battery BA1 of the present invention was produced using the positive and negative electrodes and the non-aqueous electrolyte described above. (Battery size: diameter 14.2 mm, length 50.0 mm). As the separator, a microporous film made of polypropylene having a three-dimensional pore structure (trade name "Celgard 3401" manufactured by Polyplastics Co., Ltd.) was used and impregnated with the non-aqueous electrolyte solution described above.

A battery having the structure shown in FIG. 1 was produced. The electrode body is formed by spirally winding the whole body with a positive electrode 1 and a negative electrode 2 and a strip-shaped separator 3 wider than these bipolar plates interposed. Further, polypropylene insulating plates 6 and 7 are arranged on the upper and lower sides of the electrode body, respectively, and are inserted into the case.
After forming a step on the upper part of the above, an electrolytic solution was injected and sealed with a sealing plate 9 to manufacture.

(Example 2) Similar to Example 1, the same as Example 1 except that a nickel cermet was used as the positive electrode core material and a sprayed aluminum layer having an average thickness of 2 μm was formed to form a positive electrode plate substrate. Then, a battery BA2 was constructed.

Example 3 The same celmet as in Example was used as the core material, and the average thickness of the sprayed aluminum coating layer was 15
A battery BA3 was formed in the same manner as in Example 1 except that the positive electrode substrate was heat-treated at 400 ° C. for 10 minutes in a hydrogen gas (dew point −60 ° C.) air flow in an atmosphere having a pressure of 50 μm and a pressure of 50 Torr. .

Comparative Example 1 A battery BC1 using an aluminum foil having a thickness of 20 μm was manufactured as a positive electrode plate substrate by a conventional manufacturing method. LiCoO ₂ as the positive electrode active material
And 7% by weight of acetylene black as a conductive agent and 5% by weight of an aqueous dispersion of a polytetrafluoroethylene resin as a binder, and a mixture in the form of a paste is evenly applied on both sides of the aluminum foil, After drying, the positive electrode having a thickness of 0.3 mm was obtained by compression molding using a roller press. Except for the positive electrode, the same structure as in Example 1 of the present invention was used.

(Comparative Example 2) A battery BC2 having the same structure as in Example 1 was prepared except that a nickel cermet having no aluminum sprayed film was used as the core material.

(Comparative Example 3) A battery having the same configuration as in Example 1 except that a nickel cermet having a sprayed aluminum layer coated with an average thickness of 0.8 μm was used as the positive electrode core material in the same manner as in Example 1. BC3 was prepared. In the battery evaluation test, after charging to a charge end voltage of 4.2 V with a charge current of 100 mA, a discharge end voltage of 3.
A charge / discharge cycle test in which the process of discharging to 0 V was defined as one cycle was performed, and the change in capacity of each battery when the charge / discharge cycles were repeated was examined. The test was performed for each of 10 cells, and the average value was compared. The test results are shown in FIG.

FIG. 2 shows the charge / discharge cycle characteristics of each battery.
6 is a graph showing the change in battery capacity with the change in the number of cycles, with the vertical axis as the reference on the vertical axis. From the figure, although the battery BC1 using the conventional aluminum foil shown as Comparative Example 1 maintains the initial 85% even after 500 cycles, the present invention BA1, BA
It can be seen that in both the batteries of No. 2 and BA3, 90% or more of the initial battery capacity was maintained even after 500 cycles, and the cycle life was even longer. Also, BA2
Has a slightly smaller capacity than BA1, but
It remains at 91%. Furthermore, BA3 using a positive electrode substrate that has been heat treated after thermal spraying has a capacity retention rate of 95%.
The results show that the decrease in capacity is smaller than 93% of BA1 that has not been heat-treated, and that heat treatment after aluminum spraying is more effective for increasing the life.

On the other hand, comparative battery BC2 having no thermal spray coating
Or in BC3 which has a spray coating of 0.8 μm on average,
Deterioration is large with the passage of cycles, and even at the 100th cycle, it is as low as 60% of the initial battery capacity. In the case of BA1 to BA3 using a continuous metal porous body having continuous pores with a three-dimensional network structure as the core material, from the charge / discharge cycle characteristic evaluation results, nickel rapidly melts due to repeated charge / discharge cycles. Capacity will decrease,
It seems that one of the factors is that the thermal spraying of aluminum having a noble potential reduced the dissolution of the core material in the electrolytic solution.

Further, it is considered that the peeling and dropping of the active material from the core material due to the charge / discharge cycle were alleviated and the life was extended. The reason for this is that the surface of the sprayed film has irregularities on the order of several hundred nm to several tens of μm on average, and therefore it is considered that the adhesion to the positive electrode active material was better due to the anchor effect than the smooth base material. Therefore, it is considered that peeling from the core material due to expansion and contraction of the active material accompanying the charge / discharge cycle can be prevented, the life can be extended, and the charge / discharge cycle life can be improved.

In the above examples, the positive electrode LiCoO ₂ , the negative electrode graphite, and the ethylene carbonate solution in which 1 mol / liter of lithium hexafluorophosphate was dissolved were used as the electrolytic solution, but the non-aqueous electrolytic solution secondary battery of the present invention was used. The positive electrode, the negative electrode, and the electrolytic solution are not limited to those in the examples. LiC for the positive electrode
Those containing oO ₂ and LiMn ₂ O ₄ or LiNiO ₂ can be used, and the negative electrode can be made of lithium metal, lithium alloy,
It is possible to use a material containing any of carbon materials that can be doped or dedoped with lithium ions.

In the example, the case where a continuous metal porous body (trade name: Celmet) having nickel three-dimensional reticulated pores was used was used.
Metals such as Fe-Cr and Fe-Cr-Ni are also possible. Furthermore, in the embodiment, the specific example of the case where the present invention is applied to the cylindrical non-aqueous electrolyte secondary battery has been described.
The shape of the battery is not particularly limited, and the present invention can be applied to non-aqueous electrolyte secondary batteries of various shapes such as flat type and rectangular type.

[0036]

In the battery of the present invention, the positive electrode is LiCo
A positive electrode active material containing O ₂ , LiNiO ₂ , LiMn ₂ O _4, etc.,
Since the core material sprayed with aluminum is used as the positive electrode core material, in the battery of this structure, even if the charging voltage becomes high due to overcharging, the aluminum ions contacting the electrolytic solution may dissolve as ions. Absent. The reason is that the melting voltage of aluminum is high.

By using a metal porous body having three-dimensional mesh-like communicating pores having a layer sprayed with aluminum,
A long life can be achieved by the synergistic effect of retaining the active material, which has a three-dimensional bag-like structure, and the corrosion resistance at a high potential due to the aluminum film having a noble potential.

The surface of the sprayed film has an average of several hundred nm to several tens μ.
Due to the presence of m-order irregularities, it has better adhesion to the positive electrode active material due to the anchor effect than a smooth core material, and can prevent peeling from the core material due to expansion and contraction of the active material during charge / discharge cycles. Life can be extended. Furthermore, by using an aluminum film, the present invention has excellent unique effects such as a low contact resistance between the positive electrode active material and the positive electrode core material and an excellent charge / discharge cycle.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a cylindrical battery of the present invention.

FIG. 2 is a charge / discharge cycle characteristic diagram of the present invention battery and a comparative battery.

[Explanation of symbols]

 1: Positive electrode 2: Negative electrode 3: Separator 4: Negative electrode lead plate 5: Positive electrode lead plate 6: Insulating plate 7: Insulating plate 8: Case 9: Sealing plate

Claims (7)

[Claims] 1. A battery provided with a non-aqueous electrolyte containing rechargeable lithium ions, wherein the positive electrode substrate is a continuous metal porous core material having three-dimensional mesh-like communicating pores, and aluminum formed by thermal spraying on the core material. A non-aqueous electrolyte secondary battery having a layer. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein a diffusion layer is present between the core material and an aluminum layer formed thereon. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the core material comprises Ni and inevitable impurities. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the core material has a communicating porosity of 90% or more. 5. The aluminum layer has an average thickness of 1 to 5
The thickness is 0 μm.
The non-aqueous electrolyte secondary battery described. 6. A battery provided with a non-aqueous electrolyte solution containing rechargeable lithium ions, wherein a positive electrode substrate having an aluminum layer formed by thermal spraying on a metal porous core material having three-dimensional mesh-like communicating pores is used. And a method for manufacturing a non-aqueous electrolyte secondary battery. 7. The porous metal core material is thermally sprayed with aluminum and then heat-treated in a non-oxidizing atmosphere to provide a diffusion layer between the core material and the aluminum layer formed thereon. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 6.