JPH0359964A - Non-water solvent medium secondary battery - Google Patents

Abstract

PURPOSE:To maintain high energy density at the time of high current discharging whereas pollution problems are eliminated with safety maintained against explosion by specifying the quantity of water contained in a positive electrode active material. CONSTITUTION:A battery is made up out of a positive electrode 6 including a positive electrode active material mainly composed of spinel type Li-Mn2-O4 wherein the quantity of water is specified within a range of 0.01 to 0.2%, a negative electrode 4 made of a light metal and of a separator 5 interposed between the positive electrode 6 and the negative electrode 4 wherein electrolyte solution including the electrolyte of Li-PF6 is contained. In this case, even if inner temperature is increased due to short circuit when it gets to on or about 80 deg.C in inner temperature, LiF is quickly produced so that inner resistance is increased to a great extent while the dielectric strength thereof becomes high. This constitution can prevent the battery from being deformed, bursted, exploded, for example.

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 particularly to a non-aqueous solvent secondary battery with an improved positive electrode.

(Prior Art) In recent years, non-aqueous solvent secondary batteries using lithium as a negative electrode active material have attracted attention as high energy density batteries. In such nonaqueous solvent secondary batteries, the positive electrode active materials used in combination with the lithium negative electrode include metal oxides such as manganese, titanium, molybdenum, vanadium, hafnium, chromium, zirconium, tantalum, and niobium, sulfide, and selenium. compounds or tellurides have been proposed. In particular, progress is being made in the development of lithium-based non-aqueous solvent secondary batteries that use a lithium-manganese composite oxide containing lithium as a positive electrode, which is obtained by firing manganese dioxide and a lithium salt such as lithium carbonate.

In the above-mentioned nonaqueous solvent battery, the electrolytic solution impregnated into the separator interposed between the positive electrode and the negative electrode is an organic solvent such as propylene carbonate, ethylene carbonate, jetoxyethane, γ-butyrolactone, tetrahydrofuran, sulfolane, or 1,3-dioxolane. niLiBF
4. LiAsFb.

LiCρ04 and LiCF3SO3 dissolved electrolytes are used.

However, LiBF4LiCF, SO as electrolyte
Since the electrolytic solution using No. 3 has low conductivity, there is a problem in that it increases the internal resistance of the battery and makes it difficult to perform large current discharge. Furthermore, an electrolytic solution using LiAsF, . However, LiAsF6 is a source of pollution, and Li CR04 is not completely safe against explosions when a large amount of lithium is used in the negative electrode, so it cannot be installed in consumer devices that require large secondary batteries. There was a problem.

For this reason, a battery using lithium hexafluorophosphate (L i P F 6 ) as an electrolyte has been proposed (Japanese Patent Application Laid-Open No. 81-20 (I1B3)).

When using an electrolytic solution containing such an electrolyte, LiC,
Similar to 904, the electrolyte has high conductivity and a battery capable of discharging a large current can be manufactured, but there is a problem of safety against explosion.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned conventional problems. The aim is to provide a non-aqueous solvent secondary battery that is problem-free and highly reliable.

[Structure of the Invention (Means for Solving the Problem) The present invention provides a positive electrode containing a positive electrode active material mainly composed of spinel-type LiMn2O4, a negative electrode made of a light metal, and a negative electrode interposed between the positive electrode and the negative electrode, In a non-aqueous solvent secondary battery equipped with a power generation element comprising a separator holding an electrolyte containing an electrolyte of lithium hexafluorophosphate, the water content in the positive electrode active material is set to 0.01 to 0.2. % range.

The spinel type LiMn2O4 constituting the positive electrode active material is, for example, 2Mn02M n 2O3
．． 7 M n 00 H and other manganese oxides and Li2
After mixing lithium salts such as CO3 and LiOH, 400
It is obtained by firing in the range of ~900°C.

The reason why the amount of water contained in the positive electrode active material is limited is as follows. If the water content is less than 0.01%, the amount of LiF produced, which will be described later, will be too small and will not contribute to explosion prevention.On the other hand, if the water content exceeds 0.2%, a positive electrode containing the positive electrode active material will not be incorporated. When a battery is repeatedly charged and discharged, water is extracted from the positive electrode active material into the electrolyte and reacts with the metal such as lithium, which is the negative electrode active material, to generate hydrogen gas, which can cause problems such as leakage. This causes an increase in battery internal pressure. More preferable water content is 0.03 to 0.15%, still more preferable water content is 0.
．． It is in the range of 0.05 to 0.1%.

The positive electrode is obtained by mixing the spinel-type L i M n 2 O4 active material with a conductive material such as carbon black and a binder such as polytetrafluoroethylene and molding the mixture.

The above-mentioned negative electrode uses an alkali metal such as lithium as an active material, and the active material is formed into a foil or plate shape.
Examples include those having a structure in which the active material is supported on a carrier made of a carbonaceous material or the like.

As the electrolytic solution, one in which the lithium hexafluorophosphate (LiPF) as an electrolyte is dissolved in a mechanical solvent can be used. Examples of such organic solvents include propylene carbonate, ethylene carbonate, dimethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1.3
-Dioxolane, sulfolane, etc. can be mentioned.

(Function) According to the present invention, a positive electrode includes a positive electrode active material mainly composed of spinel-type LiMn2O4 with a moisture content specified in the range of 0.01 to 0.2%, a negative electrode made of a light metal, and the positive electrode, By comprising a separator interposed between the negative electrode and holding an electrolyte containing LiPF2 electrolyte, it is highly safe against ruptures and explosions, has a long charge/discharge cycle life, and has a high energy density. A non-aqueous solvent secondary battery can be obtained.

That is, spinel type LiMn2O4 can be charged and discharged in a wide potential range, and has a capacity density of 148mA.
h/g and has good properties as a positive electrode, and the LiMn2O. By containing a small amount of water in the electrolyte, even if the battery generates heat due to a short circuit, the water will be extracted into the electrolyte, and the electrolyte LiPF6 in the electrolyte will be extracted.
The following reactions can easily occur and ensure safety against explosions.

2L i PF, +5H2O → 2L i F + 1OHF + P2O5 The LiF generated in the above reaction can be released on the surfaces of the positive and negative electrodes or in the gaps between the separators, etc.
Since F is a highly resistive substance, it has high insulation properties and functions to increase the internal resistance of the battery.

Therefore, in the secondary battery of the present invention, even if the internal temperature rises due to a short circuit, if the internal temperature reaches around 80°C, the L
iF is rapidly generated, greatly increases the internal resistance, and transforms the battery into an insulator, thereby preventing accidents such as deformation, rupture, and explosion of the battery. In addition, the water content in the positive electrode active material is 1.
If it is within the above range, it is firmly held in the active material, so it is usually not easily extracted from the positive electrode, does not react with negative electrode lithium, etc., and is therefore safe.

(Example) Hereinafter, an example in which the present invention is applied to a cylindrical lithium secondary battery will be described in detail with reference to FIG. 1 and FIGS. 2(a) and (b).

Embodiment 1 Reference numeral 1 in the figure is a bottomed cylindrical metal container that also serves as a negative electrode terminal and has insulating paper 2 disposed on the inner surface except for the bottom and near the top end A.1. Inside the container l is a cylindrical power generating element 3.
is stored. This power generation element 3 has a negative electrode 4 made of metallic lithium impregnated with an electrolytic solution in which 1 mol/D of Li PF6 is dissolved in a solvent containing a mixture of pro"pyrene carbonate and 2-methyltetrahydrofuran at a ratio of 1:1. A separator 5 made of a microporous polypropylene film and a positive electrode 6 to be described later are laminated in this order 4;
It is constructed by forming a strip-like material and winding this strip-like material in a spiral shape.

The positive electrode 6 was manufactured by the following method.

First, a mixture of manganese dioxide (MnO2) powder and lithium carbonate (Li2CO3) powder at a predetermined ratio was mixed with 80%
The mixture was heated and allowed to cool at 0° C. for 4 hours to produce a spinel-type LiMn2O4 (active material) with a moisture content of 0.08%. Subsequently, 482 parts by weight of this spinel-type LiMn2O and 15 parts by weight of acetylene black were mixed to form a mixture, and then an adhesive solution was prepared by dissolving 3 parts by weight of an ethylene-propylene-cyclopentadiene terpolymer in toluene in advance. 1
00 parts by weight were kneaded together with 97 parts by weight of the above mixture.

Next, this kneaded product is applied to a metal core made of stainless steel with a thickness of 10 μm, dried, and then pressure molded while heating at a temperature of 90°C for 30 seconds, and further cut into desired dimensions. A positive electrode was manufactured.

Further, an insulating sealing plate 7 is provided in the vicinity of the opening of the container l in a liquid-tight manner by caulking, and a positive electrode terminal 8 is fitted into the sealing plate 7. A lead terminal 9 of the positive electrode 6 is connected to this positive electrode terminal 8 by spot welding. A nickel foil lead terminal 10 is crimped onto the negative electrode 4, and the lead terminal 10 is connected to the inner surface of the container 1 by sporer welding.

Comparative Example 1 A cylindrical lithium secondary battery having the same structure as in Example 1 was assembled, except that a positive electrode having an active material with a water content of 0.003% was used.

Comparative Example 2 Except for using a positive electrode having an active material with a water content of 0.8%.
A cylindrical lithium secondary battery with the same disaster resistance as in Example 1 was assembled.

Therefore, a short circuit test was conducted on 50 lithium secondary batteries of Example 1 and Comparative Example 1.2 under a temperature condition of 0 to 60°C. In addition, the total battery height is 1. Items exceeding the OI were determined to be frequently manipulated items with deformation. The results are shown in Table 1 below.

Table 1 - In addition, the lithium secondary batteries of Example 1 and Comparative Example 1.2 were discharged to an external load 10 at Ω to 3V to 2V, and then
The operation of charging up to V was repeated, and the capacity deterioration rate was determined from the amount of electricity in each cycle. Add the ooze to the third layer.
The characteristic diagram shown in the figure was obtained.

As is clear from the characteristic diagrams shown in Table 1 and FIG. 3, the secondary battery of this example is less prone to abnormalities such as deformation than the secondary battery of Comparative Example 1.2. It can be seen that it can maintain a high capacity even after repeated use and has excellent performance.

[Effects of the Invention] As detailed above, the non-aqueous solvent secondary battery of the present invention is small in size, has a long charge/discharge cycle life, has high energy density, has high explosion safety, and can be used in various applications. It has remarkable effects, such as being able to be effectively applied as a power source for consumer equipment.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a well water solvent secondary battery showing one embodiment of the present invention, FIG. 2 is a partial cross-sectional view of the non-aqueous solvent secondary battery of FIG. 1, and FIG. Comparison 1 It is a characteristic diagram showing the capacity deterioration rate with respect to the number of charge/discharge cycles in the non-aqueous solvent secondary battery of Example 1.2. i... Container, 2... Power generation element, 4... Negative electrode, 5...
-Separator, 6...Positive electrode, 7...Sealing plate.

Claims (1)

[Claims] Consisting of a positive electrode containing a positive active material mainly composed of spinel-type LiMn_2O_4, a negative electrode made of a light metal, and a separator interposed between the positive electrode and the negative electrode and holding an electrolytic solution containing an electrolyte of lithium hexafluorophosphate. What is claimed is: 1. A non-aqueous solvent secondary battery comprising a power generation element comprising: a non-aqueous solvent secondary battery, characterized in that the amount of water in the positive electrode active material is in the range of 0.01 to 0.2%;