JPS6369155A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To lengthen the charge-discharge cycle life and to increase the overdischarge resistant performance by using a substance prepared by quickly cooling a molten mixture of vanadium pentoxide and ammonium phosphate trihydrate in a positive electrode and a molding of a specific carbon powder in a negative electrode. CONSTITUTION:A positve electrode 1 is a molding of amorphous material powder prepared by melting a mixture of V2O5 and (NH4)3PO44.3H2O, and quickly cooling the molten mixture. The mole ratio of (NH4)3PO4.3H2O to V2O5 is specified to 45% or less. A negative electrode is made of carbon having a hydrogen-to-carbon ratio of less than 0.15, an X-ray wide angle diffraction spacing of 3.37Angstrom or more, and a C-axis direction crystallite size of 150Angstrom or less.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a nonaqueous electrolyte secondary battery, and more specifically, a novel nonaqueous electrolyte secondary battery that is small, has a long charge/discharge cycle life, and has excellent overdischarge resistance. It relates to a water electrolyte secondary battery.

(Prior art) The main component of the positive electrode body is TiS2. A nonaqueous electrolyte secondary battery is a transition metal cargogen compound such as MoS2, and the negative electrode body is Li or an alkali metal mainly composed of Li.
Efforts are being made to commercialize it because it has a high energy density.

An example of such a secondary battery is shown in FIG. 3, which is a longitudinal sectional view of a button-type non-aqueous electrolyte secondary battery.

In the figure, ■ is the positive electrode body. The positive electrode body 1 is made by pelletizing or sheeting a mixture of the metallurgical compound powder as described above and a binder such as polytetrafluoroethylene.

The 21i separator 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. In this separator 2, Li is added to an aprotic organic solvent such as
C standing 04.

LEA sentence 04, L 1BF4, Li PFa
.

It is impregnated with a non-aqueous electrolyte of a predetermined concentration in which an electrolyte such as LiASFa is dissolved.

Reference numeral 3 denotes a negative electrode body placed on the positive electrode body l via the separator 2, and is made of Li foil or an alkali metal foil containing Li as a main component.

These positive electrode weight, separator (non-aqueous electrolyte) 2, and 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 backing, and 7 is a current collector interposed between the positive electrode body 1 and the positive electrode can 4. This current collector 7 is usually made of nickel net,
It is composed of a stainless steel wire mesh, punched metal, or foam metal, and is crimped onto one side of the positive electrode body 1 which is formed into pellets or sheets.

(Problems to be Solved by the Invention) In the secondary battery having the conventional structure as described above, the following first-order problems occur, 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 metal Li and are deposited on the negative electrode body again, but if this charge-discharge cycle is repeated, Along with this, the metal Li deposited becomes dendrite-like and grows.

Finally, 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.

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 an amorphous material prepared by melting a mixture of P2O5 and P2O5 and then rapidly cooling the molten metal as the active material of the positive electrode (Japanese Patent Laid-Open No. 61 (Refer to No.-116758) However, since this active material uses P2O5, which has strong hygroscopicity, the following problems occur in the actual battery manufacturing process.

In other words, when blending P2O5 and P2O5 or storing the blend, it is necessary to maintain the surrounding environment at a low temperature and constant humidity.
It is necessary to confirm the presence or absence of deterioration in quality, which requires special equipment and complicated management, leading to an increase in the overall cost of the product.

In addition, in this prior art, the negative electrode body is made of Li as in the prior art.
Since it is a foil or an alkali metal foil mainly composed of Li, the problem of short charge/discharge cycle life remains unsolved.

Since the present invention does not use hygroscopic P2O5, the above-mentioned problems in the positive electrode body are solved, and since the negative electrode body does not use foil, the charge/discharge cycle life is extended, and the present invention is a non-woven fabric with excellent overdischarge resistance. The aim is to provide water electrolyte secondary batteries.

(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 negative electrode body placed on a separator, and an active material (a) 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, are vanadium pentoxide. and ammonium phosphate trihydrate in an amount equivalent to 45 mol% or less based on the vanadium pentoxide, and is an amorphous powder compact prepared by applying a melt quenching method, and (b) a negative electrode. body has a hydrogen/carbon atomic ratio of less than 0.15, x
Interplanar spacing (d002) of (002) plane by MA wide-angle diffraction method
) 3. It is a powder compact of a carbonaceous material with a crystallite size (Lc) of 37 A or more and a C-axis direction crystallite size (Lc) of 150 A or less, and (c) the active material is lithium or an alkali metal mainly composed of lithium. It is characterized by

The battery of the present invention has the above-mentioned (a) and (b).

(c), especially (a) and (b), and the other elements may be the same as the battery illustrated in FIG.

In the battery of the present invention, the active material is Li or an alkali metal mainly composed of Li, and this active material 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 according to the present invention is an amorphous powder prepared by mixing v205 and (NH4) 3Po4.30020, which has low hygroscopicity, melting this mixture, and then preparing the melt by a commonly used melting and quenching method. It is a molded object.

v205, (NH4)3 POn” 30020
When mixing, the molar amount of the latter is set to 45% or less of the molar amount of the former used.

If more than 45 mol % of (NH4) 3PO4* 30020 is mixed with v205, the resulting amorphous material is unsuitable because, when used in a battery, the resulting capacity decreases at an accelerating rate. Preferably, the amount corresponds to 8 to 30 mol% based on v205.

In the present invention, the amorphous substance refers to a substance in which no diffraction peaks due to crystals such as 205 and P2O5 are observed when the substance is identified by X-ray diffraction.

The positive electrode body according to the present invention is manufactured as follows. That is, first, the above-mentioned amorphous material is crushed into a powder having a predetermined particle size, preferably having an average particle size of 3 to 100 particles.Next, a predetermined amount of a binder is added to this powder. Thoroughly knead both. Examples of the binder include polytetrafluoroethylene, chlorosulfonated polyethylene, polyethylene, and polystyrene. If the amount of the binder added is too large, the electrical resistance of the obtained positive electrode body will become high, which is disadvantageous.If the amount of the binder added is too small, the binding effect will not be exhibited. A range of 15% by weight is preferred.

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 methyl 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 an H/C of less than 0.15.

It is a carbonaceous material specified by the parameters of dQ023.37 Å or more and Lc 150 Å or less.

Furthermore, the carbonaceous material of this negative electrode body preferably has an H/C of 0.
．． It is less than 10, more preferably less than 0.07, particularly preferably less than 0.05.

Further, d 002 is preferably 3.39 A or more and 3.75 Å or less, more preferably 3°41 A or more and 3°70 Å or less.

Further, Lc is preferably 8λ or more and 100A or less, more preferably 10A or more and 70A or less.

Here, if H/C is 0.15 or more, "002 is 3
．． If such a carbonaceous material is used as the negative electrode body, whether it is less than 37 people or more than 3 La2S people, the overvoltage during charging and discharging in the negative electrode body will increase, and as a result, the Gas is generated, which significantly impairs the safety of the battery, and 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.

That is, the crystallite size (La) in the a-axis direction determined by wide-angle X-ray diffraction is preferably 10 A or more, more preferably 15 A or more and 150 λ or less, and particularly preferably 18 Å or more and 70 Å or less.

Also, it is also found in X-ray wide-angle diffraction (110)
Face 1? Jf interval dlfO twice the distance aa (=2dl
lO) is preferably 2.38A or more, more preferably 2.
．． The thickness is 39 Å or more and 2.46 Å or less.

A carbonaceous material having such parameters is prepared by carbonizing one or more of the organic polymer compounds, condensed polycyclic hydrocarbon compounds, and polycyclic heterocyclic compounds described below by calcination and thermal decomposition. be able to. 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 to 300
It is set in the range of 0°C.

Examples of starting sources of carbonaceous materials include cellulose resins; phenolic resins; acrylic resins such as polyacrylonitrile and poly(α-halogenated acrylonitrile); halogenated vinyl resins such as polyvinyl chloride, polyvinylidene chloride, and polychlorinated vinyl chloride. ;Polyamideimide resin;
Any organic polymer compound such as conjugated resin such as polyamide resin (polyacetylene, polyCP-phenylene); for example, naphthalene, phenanthrene, anthracene, triphenylene, pyrene, chrysene, naphthacene, bicene, perylene, pentaphene, pentacene, etc. Na 3
A condensed polycyclic hydrocarbon compound formed by condensing two or more monocyclic hydrocarbon compounds with more than one membered ring; for example, indole,
At least two or more heteromonocyclic compounds with three or more members such as isoindole, quinoline, inquinoline, quinoxaline, phthalazine, carbazole, acridine, phenazine, and zenatridine are bonded to each other, or one or more three or more members are bonded to each other. Examples include fused heterocyclic compounds formed by bonding with monocyclic hydrocarbon compounds.

The carbon powder thus prepared is ground into a powder with a predetermined particle size (for example, an average particle size of 10 to 15 particles), and the powder and the binder are mixed in a predetermined ratio (for example, 10 to 15 particles).

A relatively porous negative electrode body is obtained by kneading at a weight to weight ratio of 98 to 80:2 to 20, and molding the kneaded product into pellets or sheets.

The secondary battery of the present invention has 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. Supporting methods include chemical methods, electrochemical methods, and physical methods. For example, the negative electrode body, which is the powder compact, is placed in an electrolytic solution containing a predetermined concentration of Li ions or alkali metal ions. A method can be applied in which the negative electrode body is immersed and electrolytically impregnated using lithium as a counter electrode and the negative electrode body is used as an anode. By doing this, Li ions or alkali metal ions are doped between the layers of the positive or negative electrode and are supported there. It may be applied to both poles or to both poles.

Thus, in the secondary battery of the present invention, the following reaction proceeds. That is, during charging: In the positive electrode body, V205 (Li) + V205 +Li” +e In the negative electrode body, C+Li” +e+C working Li During discharging: In the positive electrode body, V205 +Lf” +e−+V2O5(
Li) In the negative electrode body, the reaction is CsLi+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 Since the target oxidation-reduction reaction progresses with charging and discharging, the formation of dendrite-shaped deposits that occur on the surface of the negative electrode body when it is a Li foil disappears.

(Embodiments of the invention) (1) Production of positive electrode body 9 g of V2O5 powder and 2.5 g of (NH4)3PO4.3002O powder (24 mol% vs. V20s) were mixed, and this mixture was melted at 800°C for 4 hours. . The resulting melt was cooled with dry ice and poured onto a copper plate for rapid cooling, and then ground to an average particle size of 100%. 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 0.41.

One side of the dust sheet was crimped to a current collector, a stainless steel net with a wire diameter of 0.1 mm and a mesh size of 60, to form a positive electrode.

(2) Manufacture of negative electrode body Phenol resin powder was heated at 1700° in nitrogen gas.
It was baked at C for 2 hours. The obtained carbonaceous material powder was pulverized to obtain a powder having an average particle size of 5 doors. The structural parameters of this are: H/C 0.04, d 002 3.68, L
c was 14A.

Next, 9.5 g of this powder and 0.5 g of polyethylene powder were mixed, and 50 mg of this mixture was pressure-molded to a thickness of 0.5.
I chose m+w beret.

(3) Assembly of the battery The above-mentioned positive electrode body was mounted on a stainless steel positive electrode can with the current collector facing down, and a polypropylene nonwoven fabric was placed on top of it. First, it was impregnated with a non-aqueous electrolyte dissolved in propylene carbonate. Then, the negative electrode body was placed thereon to form a power generation element.

In addition, before incorporating the positive electrode body, the concentration is 1 mol/L.
It was immersed in an i-ion electrolytic solution and subjected to electrolytic treatment using the positive electrode body as an anode and lithium as a cathode. The electrolysis conditions are bath temperature 2
0°C, current density 0.5mA/crn2. The electrolysis time was 15 hours. Through such treatment, the positive electrode body has a capacity of 6.
This means that 0mAh of Li was supported.

In this way, a button-shaped secondary battery as shown in FIG. 3 was manufactured. When this battery is charged, a portion of the lithium present in the positive electrode is filled into the negative electrode according to the above formula, and the battery charging is completed, but the proportion is proportional to the lithium present in the positive electrode body in the discharged state. The range is 30-80%.

For comparison, a battery similar to that of Example was fabricated, except that the negative electrode body was Li foil itself, the positive electrode body was a crystalline ■2O, and a molded body of powder and polytetrafluoroethylene. This was designated as Comparative Example 1 battery.

In addition, a battery similar to that of the example was fabricated, except that the negative electrode body was made of Li foil itself, and the positive electrode body was made of an amorphous material containing 12 mol% of P2O5 with respect to v205 as an active material, and this was used as a comparative example. Two batteries were used.

(4) Characteristics of each battery For these batteries, constant voltage charging between 3 and 2V -20
Ω constant resistance discharge was repeated, and the capacity retention rate (%: initial capacity is taken as 100) of the battery in each cycle was measured. The results are shown in Figure 1.

In addition, deep discharge evaluation was performed by repeating constant voltage charging at -20 Ω and constant resistance discharging between 3 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.

(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.
It also has excellent overdischarge resistance and is a highly reliable battery.

In addition, in the manufacturing process, especially in the manufacturing process of the positive electrode body, it has low hygroscopicity and does not decompose (NHa).
Since 3POa-30020 is used, there is no need for equipment or complicated management for maintaining low temperature and humidity, which is required when P2O5 is used.

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 drawings]

Both FIG. 1 and FIG. 2 are diagrams showing the relationship between charge/discharge cycles and capacity retention rate of a battery, and FIG. 3 is a longitudinal sectional view of a non-aqueous 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... Each negative electrode. 6... Insulating backing, 7... Current collector. Figure 1 Cycle O (- Figure 2 Figure 3

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, the positive electrode body, and In a non-aqueous electrolyte secondary battery with a built-in power generation element consisting of 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 compact prepared by applying a melt quenching method to a mixture of vanadium pentoxide and ammonium phosphate trihydrate in an amount equivalent to 45 mol% or less to the vanadium pentoxide, (b) The negative electrode body has a hydrogen/carbon atomic ratio of less than 0.15,
Interplanar spacing (d_0_0) of (002) plane by line wide-angle diffraction method
_2) It is a powder compact of a carbonaceous material with a crystallite size (Lc) of 3.37 Å or more and a crystallite size (Lc) in the C-axis direction of 150 Å or less, and (c) the active material is lithium or an alkali metal mainly composed of lithium. A non-aqueous electrolyte secondary battery characterized by: 2. The non-carbon material according to claim 1, wherein the carbonaceous material is carbonized at least one selected from the group of organic polymer compounds, fused polycyclic hydrocarbon compounds, and polycyclic heterocyclic compounds. Water electrolyte secondary battery.