JPS62186467A - Cylindrical lithium cell - Google Patents

Abstract

PURPOSE:To improve corrosion resistance of a positive electrode collector for improving a high temperature retention property by using a porous body of a stainless steel sheet of a ferrite system containing Cr, Mo, Ti and Nb while having a specified carbon quantity for a sheet-shaped thin positive electrode plate. CONSTITUTION:Graphite powder of 10wt% is added to heat-treated MnO2 powder as a conductive agent while adding polytetrafluoroethylene of 5wt% as a binding agent further adding water to be kneaded. Then, said black mixture is made into a sheet by a rolling roller followed by being press-put into a 0.1mm thick lath-processed porous collector containing Cr of 18-20wt%, Mo of 1.8-2.5wt%, (Ti+Nb) of 0.48wt% and C of 0.007wt% to be made into a positive electrode plate 3. Thereby, especially a spot welding part of a lead plate is prevented from grain field corrosion while improving stability in the high temperature retention.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a current collector material for a positive electrode in a cylindrical lithium battery used as a power source for small electronic devices related to electronics.

Conventional technology Conventionally, this type of cylindrical lithium battery has a structure in which a sheet-like positive electrode plate and a lithium negative electrode plate are wound in a spiral shape with a separator interposed between them, so that the surface area of the positive and negative electrode plates can be reduced to maximize the discharge current. There is something bigger. In order to increase the surface area of the electrode plate as much as possible, a thin electrode plate is used and wound in a spiral shape through a separator, but the material of the positive electrode current collector is an organic electrolyte and an active material MnO2 mixture. Electrolyte resistance and oxidation resistance are required because it comes into direct contact with the current collector. Furthermore, in order to configure the thin electrode plate into a spiral electrode, the positive electrode current collector must be thin and porous.

Generally, when a thin metal plate is lath-processed, processing distortion occurs and corrosion resistance deteriorates. In particular, when a metal plate is welded to the current collector, the welded portion and surrounding areas are likely to be corroded. For this reason, if a battery is stored for a long period of time at high temperatures, the open circuit voltage will decrease.

This phenomenon occurs because the current collector dissolves, and the metal becomes ions, which are dissolved in the electrolyte and deposited on the negative electrode due to the difference in ionization tendency with the negative electrode Li, dissolving Ll and reducing the battery capacity. It is assumed that this occurs in

Problems to be Solved by the Invention In such a conventional configuration, the dye-containing gold 5 molecules are eluted into the organic electrolyte and deposited on the surface of the negative electrode, causing electrochemical local discharge and lowering the voltage. was there.

The present invention solves these problems and aims to improve a positive electrode current collector.

Means for Solving the Problems In order to solve these problems, the present invention includes a current collector of a sheet-like thin positive electrode plate containing Or, Mo, Ti, and Nb.
In addition, a porous body made of a thin ferritic stainless steel plate with a controlled carbon content of 0.007% by weight or less is used. Here, the content of Or is 18-20% by weight, that of Mo is 1.8-2.5% by weight, the total amount of Ti and Wb is Q,
A suitable content was 488% by weight.

Effect If we speculate about the effect of the additive elements here, Cr originally forms a passive layer on the surface and exhibits corrosion resistance, and Mo
Approximately 3 times more corrosion resistant than Ti.

Nb exhibits a strong affinity (bonding force) with C and N and generates Tie and NbN inside the metal crystal.

It is presumed that when C and N precipitate at the grain boundaries of stainless steel, they react with Cr, consume Or, and reduce corrosion resistance. To prevent this consumption of cr, it is necessary to add carbon to the grain boundaries of the crystal.
It is necessary to fix it in a stable form inside the crystal so that it does not precipitate or N.

In ferritic stainless steel, it is better to keep the carbon content as low as possible, but there are limits to the decarburization treatment that reduces carbon in the steel manufacturing process.

Mo is thought to have about three times the corrosion resistance effect of Cr, but if the amount added is too large, workability will deteriorate and costs will increase. There is a range.

The present invention has been developed through experimental studies based on the above speculations,
The present invention significantly improves the corrosion resistance of the current collector of a cylindrical lithium battery using an organic electrolyte, especially the sheet-like MnO2 positive electrode, and improves high-temperature storage characteristics.

Hereinafter, the present invention will be explained in detail with reference to Examples.

The embodiment diagram shows a cylindrical shape M n 02 / as an embodiment of the present invention.
Lx.

A half-sectional view of the battery is shown.

In the figure, 1 is a battery container made of iron plated with Ni, 2 is a Li negative electrode plate, and 3 is a positive electrode plate. 10% graphite powder is added as a conductive agent to heat-treated MnO2 powder, and polytetrafluoride is used as a binder. 5% by weight of ethylene powder was added, and water was further added and kneaded. After forming this mixture into a sheet with a rolling roller, it is made into a sheet with a thickness of 18 to 20 fl.
Weight % Cr -1.8~2.6 Weight % Mo - 0.48
Weight '% (Ti + Nb), C 0.007 weight%
Press-fit into a lath-processed porous current collector. After drying the finished positive electrode plate at 110°C,
After cutting to a predetermined size, the positive electrode lead plate 4 is welded to the positive electrode plate 3. Insulating tape is pasted on both the front and back of the welded portion of the positive electrode lead plate (not shown) to reinforce it. Next, one longitudinal end of the positive electrode plate is used as a winding core, and the positive electrode plate is opposed to the Li negative electrode plate 2 via a separator 6 made of a microporous polypropylene film to form a spiral electrode plate group. After forming the group, the lead plate of the Li negative electrode plate is pushed through the perforated bottom insulating plate so as to be in contact with the inner bottom of the battery container 1, and spot welded.

After storing the electrode plate group in the battery container as described above, the charcoal fl
& Propylene (P-C) and 1,2-dimethoxyethane (
LiGe was added to the mixed melt of DME (DME) at a concentration of 1 mol/l.
A predetermined amount of electrolyte solution containing O4 is injected.

After placing the upper insulating plate 7, the positive electrode lead plate 4 is welded to the human e-rivet 9 crimped to the sealing gasket 8. 1
0 is the positive terminal.

The effects of the present invention were compared for positive electrode current collectors having various alloy components in a %A size cylindrical lithium battery.

Table 1 shows the composition of the positive electrode current collector of the prototype battery, the change in open circuit voltage of the battery when stored at 80'C, and the comprehensive evaluation of corrosion resistance, workability, and cost.

From the experimental results in Table 1, 45.11 austenitic (
It is clear that stainless steel (containing Ni) has extremely poor corrosion resistance in organic electrolytes. As a result of disassembling the battery and cutting off the contents, we found that the lead plate and contact area of the current collector in the positive image and the surrounding area were severely corroded, and the surface of the opposing L1 negative electrode plate was discolored. This current flux corrodes the current collector and dissolves into metal ions, which pass through the micropores of the separator, are attracted to the surface of the L1 negative electrode plate, and are deposited, electrochemically generated on the negative electrode surface. It is thought that this occurred due to local discharge.From electron microscopy observation,
In particular, it is assumed that intergranular corrosion occurs in the welded parts of the lead plates. No. 1 in Table 1 is the composition of the present invention, and it can be seen that corrosion resistance and workability are particularly poor.

Further, in the case of N13, even if the carbon content is regulated to 0.007%, the corrosion resistance is poor if Ti and Nb are not added. This is considered to be because the precipitation of C and N at grain boundaries cannot be suppressed. Na, 3 is Ti.

Although Nb is added, the reason why the corrosion resistance is not improved as much as in the present invention is considered to be because the amount of C is as high as 0.03 weight factor. Or
NO,4, in which twice the amount of MO, which is said to have three times better corrosion resistance than that of the present invention, has the same corrosion resistance as the present invention, but has the disadvantage of poor workability and high cost.

In addition, in No. 6, in which only Ti was added, and in Nn, 7, in which only Nb was added, even if the amount of C was suppressed to 0.007%, the corrosion resistance was lower than that when both Ti-1-Nb were added simultaneously. It was found to be less effective compared to Also, even if the amount of Or added is increased to 21 to 26% by weight like Na and 6, C
If the amount is large, corrosion resistance will not improve, processability will deteriorate, and costs will increase. In the case of No. 10, when the carbon content is low and Ti and Nb are added twice as much as in the present invention, the corrosion resistance is equivalent to the Nn of the present invention, 1, but the workability is slightly worse and the cost is high. Become. It was found that the corrosion resistance was not improved even if the amount of Ti-1-Nb added was larger than necessary.

Reducing the amount of C in the steel material to the Q,007 weight ratio has the effect of suppressing intergranular corrosion, so it is desirable to reduce the carbon even further, but to achieve this, the decarburization treatment process must be repeated. There is a need. This process takes time and increases costs, so instead we use Ti, which has a strong affinity with C and N.

A small amount of Nb is added to create N, Nf:Ti- inside the metal crystal.
C, Nb-N mold is fixed and stabilized to form C at grain boundaries.
, N is prevented from precipitating.

The total addition amount of Ti and Nb may be 0.48 weight, which is larger than the C and N contents in the steel material (0.03 weight in total).

If more than this is added, the '44 material becomes brittle, causing a problem of poor sheet processing and lath processing.

Effects of the Invention As described above, according to the present invention, the assembly of the positive electrode plate of a cylindrical lithium battery having a group of spiral steep plates oriented toward high-rate discharge is improved, and in particular, the lead plate is welded at the grooves and 7 points. The purpose is to provide a cylindrical lithium battery that prevents intergranular corrosion in the parts and has excellent stability during storage.

[Brief explanation of drawings]

The figure is a cross-sectional view of a cylindrical lithium battery constructed using a positive electrode plate having a current collector in an embodiment of the present invention. 1...Battery container, 2...L1 negative electrode plate, 3
...Positive electrode plate, 4...Temporary positive electrode lead, 6
...Separator. Name of agent: Patent attorney Toshio Nakao and one other person (-
List of each 2 --- Li # Extremely Obscene 3 -- Positive electrode plate 4 --- q Ward class g --- E / \゛ Shiichig 7 --- K part Zakumai Meshi 8 --- ° Main door η"again't 9 --- Akμs miumri Ntsu L io --- Right and wrong i place

Claims (2)

[Claims] (1) A battery in which a sheet-like positive electrode plate and a Li negative electrode plate are arranged in a spiral shape with a separator in between, and the positive electrode current collector has a
A cylindrical lithium battery using a ferritic porous stainless steel thin plate containing chromium, molybdenum, titanium, and niobium, and with a carbon content limited to 0.007% by weight or less. (2) The stainless steel that makes up the positive electrode current collector contains 18 to 18% chromium.
The cylindrical lithium battery according to claim 1, comprising 20% by weight, 1.8 to 2.5% by weight of molybdenum, 0.48% by weight of titanium and niobium in total, and the balance being iron.