JPS63298963A - Nonaqueous solvent secondary battery - Google Patents

Abstract

PURPOSE:To retard self discharge and to lengthen charge-discharge cycle life by forming a negative electrode with lithium or alkali metal mainly comprising lithium supported, so as to be reduced on the side facing a separator on carbon obtained by baking organic compounds. CONSTITUTION:Phenol resin is baked in an atmosphere of nitrogen to carbonize it, and carbon powder obtained is mixed with polytetrafluoroethylene powder, then a mixture is pressed to form a pellet. The pellet is immersed in an electrolyte prepared by dissolving LiClO4 in propylene carbonate, then electrolysis is conducted using the pellet as an anode and metallic lithium as a cathode. In the electrolysis, current density in the early stage is reduced, then gradually increased with the advance of electrolysis. A large amount of lithium is supported on the side facing the metallic lithium compared with the back side. By forming a negative electrode 5 in which the content of active material is larger on the side facing a separator 4, self discharge is retarded and charge- discharge cycle life is lengthened.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a non-aqueous solvent secondary battery, and more specifically, it is capable of suppressing a decrease in discharge capacity due to self-discharge during storage, The present invention also relates to a non-aqueous solvent secondary battery having a long charge/discharge cycle life.

(Prior Art) Conventionally, non-aqueous solvent secondary batteries have, for example, a sheet made of lithium (Li) or an alkali metal mainly composed of Li as a negative electrode body, and a transition metal chalcogen compound as an active material as a positive electrode body. There is a structure in which a powder compact is laminated with a separator in between, and a negative electrode body is attached to each negative electrode that also serves as a negative electrode terminal, and a positive electrode body is attached to a positive electrode can that also serves as a positive electrode terminal. Efforts are being made to commercialize it because of its energy density.

However, in such non-aqueous solvent secondary batteries, problems arise due to the fact that the negative electrode body is a Li foil or an alkali metal foil containing Li as a main component itself.

In other words, when the battery is discharged, Li from the negative electrode body becomes Li ions and moves to the electrolyte, and during charging, these Li ions become gold EAL+ and are deposited on the negative electrode body again, but if this charge-discharge cycle is repeated, Accordingly, the metal L+ deposited becomes 'dendritic'. This dendrite-like L
Since i is an extremely active substance, it decomposes the electrolyte, resulting in the disadvantage that the charge/discharge cycle characteristics of the battery deteriorate. As we continue to grow, in the end,
The problem is that this dendrite-shaped metal Li deposit penetrates the separator and reaches the positive electrode body, causing a short circuit phenomenon. In other words, the problem is that the charge/discharge cycle life is short.

In order to avoid such problems, attempts have been made to construct the negative electrode by using a carbonaceous material obtained by calcining various organic compounds as a carrier, and supporting Li or an alkali metal mainly composed of Li. For example, Japanese Patent Application Laid-open No. 1986-
No. 235372 discloses such a negative electrode body.

In the case of this negative electrode body, it has a structure in which a carbonaceous material obtained by firing an organic compound and a metal Li foil are integrally laminated.
It is used by being assembled into a battery with the foil facing the separator side. After the battery is manufactured, metal L is
The i-foil turns into Li ions, and the more the i-foil is supported in the porous carbonaceous material, the closer it is to the separator.

(Problems to be Solved by the Invention) However, in such non-aqueous solvent secondary batteries, Li in the negative electrode body
A problem arises due to the fact that the amount supported is greater on the separator side.

That is, in the negative electrode body, a doping phenomenon of Li ions occurs during charging, and a dedoping phenomenon of Li ions supported on the negative electrode body occurs during discharging.

However, since the amount of Li supported in the negative electrode body is larger toward the separator side, the current distribution on the surface of the negative electrode body becomes uneven during charging and discharging, and doping and dedoping phenomena of Li ions occur in a part of the surface of the negative electrode body. . As a result, as the charge/discharge cycle is repeated, the amount of Li supported on that part of the negative electrode surface increases, and eventually dendrite-like Li is deposited, which reduces the charge/discharge cycle life as described above. The problem arises that the length becomes shorter.

Furthermore, since the amount of Li supported is larger on the separator side of the negative electrode body, the supported Li becomes Li ions and is more likely to move into the electrolyte, that is, there is a problem that the discharge capacity is significantly reduced due to self-discharge.

An object of the present invention is to solve the above-mentioned problems and provide a non-aqueous solvent secondary battery that can suppress a decrease in discharge capacity due to self-discharge during battery storage and has a long charge-discharge cycle life.

[Structure of the Invention] (Means for Solving the Problems) As a result of intensive studies to achieve the above object, the present inventors have determined that the amount of active material supported on the carbonaceous material as described below They discovered that it is sufficient to reduce the amount toward the separator, and have completed the present invention.

That is, the non-aqueous solvent secondary battery of the present invention includes a non-aqueous solvent secondary battery including a power generating element formed by integrally laminating a positive electrode body, a separator, and a negative electrode body in this order. In the pond, the negative electrode body is composed of a carbonaceous material which is a fired body of an organic compound and Li or an alkali metal mainly composed of Li supported on the carbonaceous material, and It is characterized in that the amount supported is smaller toward the separator.

The non-aqueous solvent secondary battery of the present invention is characterized by a negative electrode body, and other structures are the same as conventional batteries.

The negative electrode body according to the present invention has Li or an alkali metal mainly composed of Li supported on a carbonaceous material obtained by firing an organic compound as described above so that the amount decreases toward the separator side.

The organic compound that serves as the raw material for this carbonaceous material is not particularly limited as long as it is commonly used, such as epoxy resin; phenol resin; polyacrylonitrile, poly(α-halogenated acrylonitrile).
Acrylic resins such as; halogenated vinyl resins such as polyvinyl chloride, polyvinylidene chloride, and polychlorinated vinyl chloride; polyamideimide vA resins; polyamide resins; conjugated resins such as polyacetylene, poly(p-phenylene), etc. organic polymer compounds; for example, naphthalene,
A condensed polycyclic hydrocarbon compound formed by condensing two or more monocyclic hydrocarbon compounds with three or more members, such as phenanthrene, anthracene, triphenylene, pyrene, chrysene, naphthacene, picene, perylene, pentaphene, and pentacene, or Various pitches based on derivatives of the above compounds such as carboxylic acids, carboxylic acid anhydrides, and carboxylic acid imides, and mixtures of the above compounds; for example, indole, isoindole, quinoline, inquinoline, quinoxaline, phthalazine, carbazole , acridine,
A fused heterocyclic compound formed by at least two or more 3-membered ring or more heterocyclic compounds such as phenazine or zenatridine bonded to each other or bonded to one or more 3-membered or more monocyclic hydrocarbon compounds; Examples include derivatives of each compound such as carboxylic acid, carboxylic acid anhydride, and carboxylic acid imide, as well as 1,2,4,5-tetracarboxylic acid of benzene, its dianhydride, or its diimide.

This carbonaceous material is prepared by combining one or more of the above-mentioned organic compounds in a non-oxidizing atmosphere at a temperature of 1,100 to 1,300° C.
It can be prepared by calcination e pyrolysis and carbonization for 2 to 3 hours.

The carbonaceous material thus prepared is pulverized to a predetermined particle size (for example, an average particle size of 20 to 50 u) to form a powder, and this powder and a binder are mixed in a predetermined quantitative ratio (for example, a weight ratio of 80 to 90 μm).
: 20 to 10), and the kneaded product is compressed and molded into pellets or sheets, resulting in a relatively porous carrier.

The negative electrode body according to the present invention can be manufactured, for example, as follows.

That is, methods for supporting the active material on the carbonaceous material include chemical methods, physical methods, and electrochemical methods. It is possible to apply a method of electrolytically impregnating a carbonaceous material such as that described above as an anode and metal Li as a cathode by immersing it.

As for the electrolysis conditions at this time, the current density may be set low during the electrolysis stage, and the current density may be increased successively as the electrolysis progresses.

By doing so, a large amount of the active material is supported on the carbonaceous material facing the metal Li.

Note that such active material may be supported not only on the carbonaceous material but also on the positive electrode body.

The non-aqueous solvent secondary battery of the present invention will be explained based on FIG. 1. In the figure, 1 is a positive electrode can that also serves as a positive electrode terminal, and is made of, for example, a stainless steel plate. 2 is a positive electrode body. The positive electrode body 2 is made of V2O5, MoO3, V6O13, Cr301
2. Oxides such as WO2; Ti2S, MoS2, V
2 S5, MOSs, CuS, CrO, 5V
Transition metal chalcogen compounds such as sulfides such as O and 5S2; selenides such as VSe2 and NbS2 are used as positive electrode active materials, and the powder of this positive electrode active material, carbon book, acetylene black, and DBP oil absorption amount is 160 to 500 cm3.
/100g, a surface area of 800 to 1300rn2/g, and a hollow shell-like conductive furnace black with a thin graphite layer on the surface (trade name: Ketjen Black: Lion Akzo Co., Ltd.) and other conductive agents and binding of polytetrafluoroethylene, polyethylene, etc. The mixture with the agent is made into pellets or sheets.

3 is a positive electrode current collector, and the positive electrode current collector 3 is made of a net made of nickel, stainless steel, etc., expanded metal, punched metal sheet, etc., and is crimped to the positive electrode can 1 side of the positive electrode body 2 to be integrated. It is attached and stored at the bottom of the positive electrode can.

4 is a separator, which is a porous polypropylene thin film;
It is made of a material with liquid retention properties, such as a porous thin film of polyethylene. Separator 44m is LiCJ1
04. LiPF6, LiBF4. It is impregnated with an electrolytic solution in which an electrolyte such as LiAsF6 is dissolved in an aprotic organic solvent such as propylene carbonate, 1,2-dimethoxyethane, γ-butyrolactone, dioxolane, ethylene carbonate, or 2-methyltetrahydrofuran.

Reference numeral 5 denotes the negative electrode body as described above, and the negative electrode body 5 is placed on the separator 4 such that the surface on which the amount of supported active material is small faces the separator 4 side.

Each negative electrode 6 also serves as a negative electrode terminal, and a negative electrode body 5 is attached to each negative electrode 6. Each negative electrode 6 is fitted into a positive electrode can 1 via an insulating backing 7, and the opening peripheral portion of the positive electrode can 1 is bent inward to seal the entire battery.

Note that the shape of the non-aqueous solvent secondary battery of the present invention is not limited to the button shape as shown in FIG. 1, but may be cylindrical,
It may be flat, square, or the like.

(Function) In the secondary battery of the present invention, since the amount of active material supported in the carbonaceous material of the negative electrode body is made smaller toward the separator side, movement of the active material into the electrolyte can be suppressed. Can be done. In addition, the current distribution on the surface of the negative electrode during charging and discharging becomes uniform, and Li ion doping and dedoping phenomena on a part of the surface of the negative electrode disappear. The formation of dendrite-like deposits that occurred when the amount of active material supported was larger toward the separator side is eliminated. Therefore, a decrease in discharge capacity due to self-discharge during battery storage can be significantly suppressed, and the charge/discharge cycle life can be extended.

(Example) Example (1) Production of positive electrode body 4 g of V2O5 powder, 1 g of acetylene black, and 0.5 g of polytetrafluoroethylene powder were kneaded, and the resulting kneaded product was roll-formed to a thickness of 0.5 mm. It was made into a sheet. One side of this sheet is a positive electrode current collector with a wire diameter of 9+u+,
It was crimped onto a 60 mesh stainless steel net.

(2) Manufacture of negative electrode body The phenol resin was carbonized by firing at 1100° C. for 3 hours in nitrogen gas. The obtained carbonaceous material was pulverized, 4 g of this powder was mixed with 1 g of polytetrafluoroethylene powder, and 5 g of this mixture was press-molded to a thickness of 0.
．． It was made into pellets of 5 mm and 9 cm in diameter.

Next, this pellet was dissolved in propylene carbonate with Li.
The pellets were immersed in an electrolytic solution in which C-Fun 04 was dissolved to a concentration of 1 mol/ml, and subjected to electrolytic treatment using the pellet as an anode and metal Li as a cathode. The electrolysis conditions are: first, the bath temperature is 20
°C, current density 0, 1-mA/cs2. The electrolysis time was 8 hours. Next, the current density was reduced to 0 while keeping the bath temperature at 20°C.
．． 5+*A/cm2. The electrolysis time was 8 hours, and the current density was 1.0 mA/cm2. The electrolysis time was 8 hours.

Due to this treatment, in the pellet, Li is concentrated closer to the cathode side.
The amount of supported was increased. The discharge capacity of this negative electrode body is 3.5
It was mAh.

(3) Assembly of the battery The above-mentioned positive electrode body was installed in a stainless steel positive electrode can with the current collector facing down, and a porous polypropylene thin film was placed on top of it as a separator.
It was impregnated with a non-aqueous electrolyte prepared by dissolving 1 mol/aq in propylene carbonate. Then, the negative electrode body was placed thereon with the surface having a smaller amount of active material facing the separator side to form a power generation element.

In addition, the positive electrode body should also be prepared at a concentration of 1 mol/min before being incorporated into the battery.
Immerse it in a Li-ion electrolyte solution, and use the positive electrode body as an anode.
It was subjected to electrolytic treatment using metal Li as a cathode. The electrolytic conditions are
Bath temperature 20℃, "FrL flow density 0, 5+ 1, 0+1
, 5 mA/cm2', and electrolysis time were 8 hours each. Through such treatment, the positive electrode body has a discharge capacity of 2.5 mAh.
This means that Li is supported.

Thereafter, each negative electrode was fitted into a positive electrode can via an insulating backing, and the entire battery was sealed.

For comparison, a negative electrode body with a thickness of 0.5 mm and a diameter of 9
mm pellet and thickness 0, 5mm, straight PA9fflf
A cell battery was manufactured in the same manner as in the example except that the metal Li foil of fi was integrated into the battery so that the metal Li foil was placed on the separator side.

(4) Characteristics of each battery The evaluation tests described below were conducted on the non-aqueous solvent secondary batteries thus obtained.

Charging and discharging from 3V to 2V with a constant resistance load of 10Ω
A charge/discharge cycle test was conducted, and the discharge capacity retention rate (%) in each cycle was measured when the initial discharge capacity was taken as 100%. The results are shown in FIG.

In addition, the discharge capacity was measured after repeating 3 cycles of charging and discharging from 3V to 2V under a constant resistance load of 1OkΩ.Next, these batteries were stored at a temperature of 20℃, and the storage period was The discharge capacity was measured for each ffff, and the discharge capacity retention rate with respect to the discharge capacity before storage was determined. The results are shown in Figure 3.

[Effects of the Invention] As is clear from the above description, the non-aqueous solvent secondary battery of the present invention can suppress a decrease in discharge capacity due to self-discharge during storage, and has a long charge-discharge cycle life. Therefore, its industrial value is a dog.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a button-type non-aqueous solvent secondary battery which is an example of the present invention, and Fig. 2 shows the relationship between charge/discharge cycle and discharge capacity retention rate of the battery in the example of the present invention and a comparative example. FIG. 3 is a diagram showing storage days vs. discharge capacity retention rate of batteries in Examples and Comparative Examples of the present invention. 1... Positive electrode can 2... Positive electrode body 3... Positive electrode current collector 4... Separator 5... Negative electrode body 6... ... Negative electrode can 7 ... Insulating backing Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] In a non-aqueous solvent secondary battery equipped with a power generation element formed by integrally laminating a positive electrode body, a separator, and a negative electrode body in this order, the negative electrode body is composed of a carbonaceous material that is a fired body of an organic compound, and a carbonaceous material that is a fired body of an organic compound. A non-aqueous solvent secondary battery comprising lithium or an alkali metal mainly composed of lithium supported on a carbonaceous material, and characterized in that the amount of the lithium or the alkali metal mainly composed of lithium supported is smaller toward the separator side. .