JPH0580791B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a nonaqueous electrolyte secondary battery, and more particularly, to a novel nonaqueous electrolyte secondary battery that is small, has a long charge/discharge cycle life, and has excellent overdischarge resistance. . (Prior art) The main component of the positive electrode body is a cargogen compound of a transition metal such as MoS ₂ or TiS ₂ , and the negative electrode body is made of Li or
BACKGROUND ART Efforts are being made to commercialize nonaqueous electrolyte secondary batteries, which are mainly made of alkali metals such as Li, and have a high energy density. An example of such a secondary battery is shown in FIG. The figure is a longitudinal cross-sectional view of a button-shaped non-aqueous electrolyte secondary battery. In the figure, 1 is a positive electrode body. The positive electrode body 1 is
A mixture of the metal chalcogen compound powder as described above and a binder such as polytetrafluoroethylene is formed into pellets or sheets. A separator 2 is made of a liquid-retaining material such as a porous polypropylene thin film or a polypropylene nonwoven fabric, and is placed on the positive electrode body 1 . This separator 2 contains LiClO 4 , LiAl O 4 , LiClO ₄ , LiAl ^O ₄ ,
It is impregnated with a nonaqueous electrolyte solution of a predetermined concentration in which an electrolyte such as LiBF ₄ , LiPF ₆ , or LiAsF ₆ is dissolved. Reference numeral 3 denotes a negative electrode body placed on the positive electrode body 1 with a separator 2 in between, and is made of Li foil or an alkali metal foil containing Li as a main component. These positive electrode body 1, separator (non-aqueous electrolyte)
2 and the negative electrode body 3 constitute a power generation element as a whole. Then, this power generation element is housed in a battery container consisting of a positive electrode can 4 and a negative electrode can 5, and a battery is assembled. 6 is an insulating packing, 7 is a positive electrode body 1
This is a current collector interposed between the positive electrode can 4 and the positive electrode can 4. The current collector 7 is usually made of nickel, stainless steel metal wire mesh, punched metal, or foam metal, and is crimped onto one side of the pelletized or sheeted positive electrode body 1. (Problems to be Solved by the Invention) In the secondary battery having the conventional structure as described above, the following problems have occurred, and improvement thereof is required. The first problem is based on the fact that the negative electrode body is a Li foil or an alkali metal foil mainly composed of Li. 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 metallic Li and are deposited on the negative electrode body again, but if this charge-discharge cycle is repeated, As a result, the metal Li deposited becomes dendrite-like and grows, and eventually the dendrite-shaped metal Li deposits penetrate the separator and reach the positive electrode body, causing a short circuit phenomenon. . In other words, the problem is that the charge/discharge cycle life is short. The second problem is based on the fact that the positive electrode body contains a metal chalcogen compound as a main component. That is, in general, as the depth of discharge during charging and discharging of a battery becomes deeper, the metal chalcogen compound becomes inactivated more rapidly. As a result, the battery capacity decreases significantly after several charge/discharge cycles, making it unusable for practical use. In order to solve this second problem, it has been proposed to use a solid solution of V ₂ O ₅ and P ₂ O ₅ as the active material of the positive electrode body (see JP-A-59-134561). However, the battery proposed here cannot be said to have completely solved all of the above-mentioned problems, and furthermore, the negative electrode body is Li foil or an alkali metal foil mainly composed of Li, so it cannot be recharged. The problem of short discharge cycle life remains unsolved. The present invention aims to solve the above-mentioned problems and provide a nonaqueous electrolyte secondary battery that has a long charge/discharge cycle life and also has excellent overdischarge resistance. (Means for Solving the Problems) The nonaqueous electrolyte secondary battery of the present invention includes a positive electrode body, a separator placed on the positive electrode body, a nonaqueous electrolyte held in the separator, and a nonaqueous electrolyte secondary battery of the present invention. A non-contact device with a built-in power generation element consisting of a negative electrode body placed on a separator, and an active material included in the positive electrode body and/or the negative electrode body and moving between the positive and negative electrode bodies in response to charge/discharge reactions. In an aqueous electrolyte secondary battery, (a) the positive electrode body is made by melting and rapidly cooling a mixture of V ₂ O ₅ and P ₂ O ₅ in an amount equivalent to 30 mol% or less with respect to the V ₂ O ₅ ; (b) the negative electrode body has a hydrogen/carbon atomic ratio of 0.04 or more;
less than 0.10, the interplanar spacing (d ₀₀₂ ) of the (002) plane by X-ray wide-angle diffraction method is 3.41 Å or more and 3.70 Å or less, and the crystallite size in the c-axis direction (Lc) is 10 Å or more and 70 Å
Below, and the crystallite size in the a-axis direction (La)
(c) The active material is lithium or an alkali metal mainly composed of lithium. The battery of the present invention is characterized by having the above-mentioned (a), (b), and (c), especially (a) and (b), and other elements are illustrated in FIG. It may be the same as a battery. In the battery of the present invention, the active material is Li or an alkali metal mainly composed of Li;
It moves back and forth between the positive electrode body and the negative electrode body in response to charging and discharging of the battery. First, the positive electrode body is a powder compact of an amorphous material, which will be described later. This amorphous substance consists of V ₂ O ₅ and P ₂ O ₅ , and their quantitative ratio is as follows with respect to the number of moles of V ₂ O ₅ .
The number of moles of P ₂ O ₅ is set to 30% or less. P ₂ O ₅
If the content is more than 30 mol%, it is not suitable because the capacity obtained when used in a battery will be very small. The amount of P ₂ O ₅ is 3 to V ₂ O ₅
Preferably, the amount corresponds to 15 mol%. In addition, the specific crystalline substance in the present invention refers to this
It refers to a state in which no diffraction peaks based on crystals such as V ₂ O ₅ or P ₂ O ₅ are observed when identified by a line diffraction method. Such an amorphous material can be prepared by applying a commonly used melt quenching method. That is, P ₂ O ₅ ,
V ₂ O ₅ powders are mixed in a predetermined ratio, the resulting mixture is melted, and the melt is brought into contact with, for example, a cooled copper plate or copper drum to be rapidly cooled.
It is preferable to set the cooling rate at this time to 10 ⁴ to 10 ⁸ ° C./sec., since a good quality amorphous material can be obtained. The positive electrode body according to the present invention is manufactured as follows. That is, first, the above-mentioned amorphous material is ground into powder having a predetermined particle size. Average particle size is 3-100μm
It is. When the average particle size is less than 3 μm, the surface area of the amorphous material is large, but the bulk density is small. Therefore, the filling amount in the positive electrode body decreases, which is undesirable because the capacity retention rate decreases and the charge/discharge cycle life decreases. In addition, the average particle size of the amorphous material is
If it exceeds 100 μm, the surface area of the amorphous material becomes small, the discharge utilization rate decreases, and the charge/discharge cycle life decreases, which is not preferable. Next, a predetermined amount of a binder is added to this powder and the two are sufficiently kneaded. Examples of the binder include polytetrafluoroethylene, polyethylene, chlorosulfonated polyethylene, and polystyrene. If the amount of binder added is too large, the electrical resistance of the resulting positive electrode body will increase, which is disadvantageous.
It is preferably in the range of 0 to 15% by weight based on the powder weight of the amorphous material. The obtained kneaded product is formed into a pallet or sheet of a predetermined thickness and attached to a metal wire mesh made of stainless steel, nickel, etc. or punched metal to form a relatively porous positive electrode body. Next, the negative electrode body will be explained. The negative electrode body is a powder compact of a carbonaceous material, which will be described later. This carbonaceous material has H/C of 0.04 or more and less than 0.10, d ₀₀₂ of 3.41 Å or more and 3.70 Å or less, and Lc of 10 Å or more.
It is a carbonaceous material specified by the parameters of 70 Å or less and La of 18 Å or more and 70 Å or less. Further, the carbon material of this negative electrode body preferably has an H/C of less than 0.07, particularly preferably less than 0.05. Here, if H/C is 0.10 or more, d ₀₀₂ is 3.41
If such a carbonaceous material is used as a negative electrode body, whether it is less than Å or Lc is greater than 70Å, the overvoltage during charging and discharging in the negative electrode body will increase, and as a result, the Gas may be generated and the safety of the battery is compromised. Furthermore, the charge/discharge cycle characteristics are also unsatisfactory. Further, it is preferable that the carbonaceous material of the negative electrode body of the present invention satisfies the following conditions in addition to the above conditions. In other words, the distance a ₀ (=2d ₁₀₀ ) is twice the interplanar spacing d ₁₀₀ of the (110) plane found in X-ray wide-angle diffraction.
is preferably 2.38 Å or more, more preferably 2.39 Å
2.46 Å or less. Carbonaceous materials having such parameters can be produced by carbonizing one or more of the following organic polymer compounds, condensed polycyclic hydrocarbon compounds, and polycyclic heterocyclic compounds by firing and thermally decomposing them. It can be prepared. An important factor in this carbonization process is the heat treatment temperature; if this temperature is too low, carbonization will not proceed, and if it is too high, the carbonaceous state will be added to graphite. Although it varies depending on the starting source used, the heat treatment temperature is usually 800~800℃.
It is set in the range of 3000℃. Examples of starting sources of carbonaceous materials include cellulose resin; phenolic resin; polyacrylonitrile,
Acrylic resins such as poly(α-halogenated acrylonitrile); halogenated vinyl resins such as polyvinyl chloride, polyvinylidene chloride, and polychlorinated vinyl chloride; polyamideimide resins; polyamide resins; polyacetylene, poly(p-phenylene), etc. Any organic polymer compound such as conjugated resin; for example, naphthalene, phenanthrene, anthracene, triphenylene, pyrene, chrysene,
naphthacene, picene, perylene, pentaphene,
Condensed polycyclic hydrocarbon compounds formed by condensing two or more monocyclic hydrocarbon compounds with three or more members, such as pentacene; for example, indole, isoindole, quinoline, isoquinoline, quinoxaline, phthalazine, carbazole, acridine, phenazine , a fused heterocyclic compound formed by at least two heteromonocyclic compounds having 3 or more members, such as phenanthridine, bonded to each other or to one or more monocyclic hydrocarbon compounds having 3 or more members. can be given. The carbonaceous material thus prepared is pulverized to a predetermined particle size (e.g., average particle size of 5 to 10 μm) to form a powder, and the powder and binder are mixed in a predetermined ratio of amounts (e.g., 95 to 80 μm in weight ratio). :5 to 20), and the kneaded product is formed into pellets or sheets to obtain a relatively porous negative electrode body. The secondary battery of the present invention includes a positive electrode body as described above,
The negative electrode body can be assembled and manufactured with other elements in a conventional manner. At this time, before this negative electrode body is assembled into a battery, Li or an alkali metal mainly composed of Li, which is an active material, is supported on this negative electrode body. As a method of supporting, for example, the above-mentioned negative electrode body, which is a powder compact, is immersed in an electrolytic solution containing Li ions or alkali metal ions at a predetermined concentration, and lithium is used as a counter electrode, and this negative electrode body is used as an anode for electrolysis. An impregnating method can be applied. By doing so, Li ions or alkali metal ions are doped between the layers of the negative electrode body and supported therein. Note that such active material may be supported not only on the negative electrode body but also on the positive electrode body or both electrodes. Thus, in the secondary battery of the present invention, the following reaction proceeds. That is, during charging: In the positive electrode body, V ₂ O ₅ (Li)→V ₂ O ₅ +Li ⁺ +e In the negative electrode body, C+Li ⁺ +e→C・Li During discharging: In the positive electrode body, V ₂ O ₅ +Le ⁺ +e→ In the V ₂ O ₅ (Li) negative electrode body, the reaction is C.Li→C+Li ⁺ +e. That is, in the secondary battery of the present invention, for example, a doping phenomenon of Li ions occurs in the negative electrode body during charging, and a dedoping phenomenon of Li ions supported on the negative electrode body occurs during discharging, resulting in reversible electrochemical As the oxidation-reduction reaction progresses with charging and discharging, the formation of dendrite-shaped deposits that occur on the surface of the negative electrode when it is made of Li foil disappears. [Examples of the Invention] Examples, Comparative Examples 1 and 2 (1) Manufacture of positive electrode body 9 g of V ₂ O ₅ powder was mixed with 1.3 g of P ₂ O ₅ powder (8 mol % based on V ₂ O ₅ ), This mixture was melted at 800°C. The resulting melt was rapidly cooled by flowing down onto a copper plate cooled with dry ice, and then ground to an average particle size of 100 μm. The obtained powder was identified by X-ray diffraction and was found to be amorphous. 5 g of this amorphous powder and 0.5 g of powdered polytetrafluoroethylene were kneaded, and the resulting kneaded product was roll-formed to form a sheet with a thickness of 0.4 mm. One side of this sheet is a current collector with a wire diameter of 0.1 mm.
The positive electrode was crimped onto a 60 mesh stainless steel net. (2) Manufacture of negative electrode body Phenol resin powder is placed in nitrogen gas.
It was baked at 1700°C for 2 hours. The obtained carbonaceous material powder was pulverized to obtain a powder with an average particle size of 5 μm.
The structural parameters of this thing are H/C 0.04,
d ₀₀₂ was 3.68 Å and Lc was 14 Å. Next, 9.5g of this powder and 0.5g of polyethylene powder
50 mg of this mixture was pressure-molded into pellets with a thickness of 0.5 mm. (3) Battery assembly The above-mentioned cathode body was placed in a stainless steel cathode can with the current collector facing down, a polypropylene nonwoven fabric was placed on top of it, and then LiClO ₄
It was impregnated with a non-aqueous electrolytic solution prepared by dissolving the following in propylene carbonate at a concentration of 1 mol/mol. Then, the negative electrode body was placed thereon to form a power generation element. Note that, before being incorporated, the positive electrode body was immersed in a Li ion electrolyte solution having a concentration of 1 mol/min, and subjected to an electrolytic treatment using the positive electrode body as an anode and lithium as a cathode. Electrolysis conditions are bath temperature 20℃, current density
The electrolysis time was 0.5A/cm ² and 15 hours. Through such treatment, Li with a capacity of 6.0 mAh was supported on the positive electrode body. In this way, a button-shaped secondary battery as shown in FIG. 3 was manufactured. For comparison, the negative electrode body was a Li foil itself, and the positive electrode body was a molded body of crystalline V ₂ O ₅ powder and polytetrafluoroethylene.
A battery similar to that of the example was manufactured, and this was used as Comparative Example 1.
It was used as a battery. In addition, a battery similar to that of the example was manufactured, except that the negative electrode body was made of Li foil itself, and this was used as a comparative example 2 battery. (4) Characteristics of each battery For these batteries, constant voltage charging and 20KΩ constant resistance discharging were repeated between 3 and 2V, and the capacity retention rate of the battery in each cycle (%: initial capacity is 100) ) was measured. The results are shown in Figure 1. In addition, deep discharge evaluation was performed by repeating constant voltage charging and 20 KΩ constant resistance discharging between 3 V and 0.9 V, and measuring the capacity retention rate of the battery in each cycle. The results are shown in Figure 2. As is clear from the figure, it was found that the battery of the present invention has a low capacity retention rate and a significantly long charge/discharge cycle life regardless of the depth of discharge. Comparative Examples 3 and 4 (1) Manufacture of negative electrode body Polyacrylonitrile powder was fired in nitrogen gas at a temperature of 1000°C (Comparative Example 3) or 2500°C (Comparative Example 4) for 2 hours. The obtained carbonaceous materials were each ground to obtain powders with an average particle size of 5 μm. The structural parameters of these powders are the first
It was as shown in the table. (2) Battery assembly The negative electrode body obtained as described above was combined with the positive electrode body used in the example to produce a button-shaped secondary battery according to the example. (3) Characteristics of each battery For these batteries, constant voltage charging and 20kΩ constant resistance discharging were repeated between 3 and 2V, and the battery capacity retention rate (%: initial capacity is 100) at 100 cycles and 200 cycles. ) was measured. The results are shown in Table 1 along with the measurement results for the batteries of Examples.

[Table] [Effects of the Invention] As is clear from the above explanation, the secondary battery of the present invention has a long charge/discharge cycle life without being affected by the depth of discharge, and has excellent overdischarge resistance.
It is a highly reliable battery. Although the explanation has been given regarding a secondary battery having a button-shaped structure, the technical idea of the present invention is not limited to this structure, and for example, non-aqueous solvents having a cylindrical, flat, or square shape may be used. It can also be applied to secondary batteries.

[Brief explanation of the drawing]

Both FIG. 1 and FIG. 2 are diagrams showing the relationship between battery charge/discharge cycles and capacity retention rate, and FIG. 3 is a longitudinal cross-sectional view of a nonaqueous solvent battery having a button-shaped structure. 1... Positive electrode body, 2... Separator (non-aqueous electrolyte), 3... Negative electrode body, 4... Positive electrode can, 5... Negative electrode can, 6... Insulating packing, 7... Current collector.

Claims (1)

[Claims] 1. A positive electrode body, a separator placed on the positive electrode body, a nonaqueous electrolyte held in the separator, a negative electrode body placed on the separator, and the positive electrode body and/or the separator. Or, in a non-aqueous electrolyte secondary battery with a built-in power generation element comprising an active material that is included in the negative electrode body and moves between the positive and negative electrode bodies in response to charging and discharging reactions, (a) the positive electrode body is , an amorphous powder with an average particle size of 3 to 100 μm prepared by melting and quenching a mixture of vanadium pentoxide and phosphorus pentoxide in an amount equivalent to 30 mol% or less of the vanadium pentoxide. (b) the negative electrode body has a hydrogen/carbon atomic ratio of 0.04 or more;
less than 0.10, the interplanar spacing (d ₀₀₂ ) of the (002) plane by X-ray wide-angle diffraction method is 3.41 Å or more and 3.70 Å or more, and the crystallite size in the c-axis direction (Lc) is 10 Å or more and 70 Å
Below, and the crystallite size in the a-axis direction (La)
18 Å or more and 70 Å or less, and (c) the active material is lithium or an alkali metal mainly composed of lithium. 2. The non-aqueous electrolysis according to claim 1, wherein the carbonaceous material is carbonized at least one selected from the group of organic molecular compounds, fused polycyclic hydrocarbon compounds, and polycyclic heterocyclic compounds. Liquid secondary battery.