JPS61151975A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To form a battery having a large charge and discharge cycle by specifying the open dimension of the mesh of a metal net. CONSTITUTION:A nonaqueous electrolyte secondary battery consists of a positive electrode 4, nonaqueous electrolyte, and a lithium negative electrode. The lithium negative electrode consists of an alloy negative electrode 3 occluding lithium metal ions at a charging time and ejecting the lithium metal ions at a discharging time, and a metal net 2 integrated with the electrode 3. In this case, the open dimension of the mesh of the metal net is limited to 0.25-0.5mm. According to the above constitution, such a metal negative electrode can be obtained as having a large charge/discharge cycle and a large capacity per unit of volume from view of its performance, being simply manufactured and easily connected to a sealing plate or a case, and capable of occluding lithium.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a rechargeable and dischargeable non-aqueous electrolyte secondary battery, and in particular to improvements in its current collector.

BACKGROUND OF THE INVENTION Non-aqueous electrolyte batteries have high voltage and high energy density, and are therefore widely used as power sources for consumer devices. Recently, there has been active development of rechargeable and dischargeable secondary batteries that take advantage of these characteristics and are lightweight. However, when lithium, which is a negative electrode, is repeatedly charged and discharged, its shape changes, for example, the surface becomes stone-like, dendritic, or spherical, and it becomes suspended in the electrolyte and ceases to function. Therefore, for example, a report was made using polymeric materials such as polyacetylene, which occludes lithium in its pores when charged, and aluminum, which occludes lithium and forms intermetallic compounds (T, O, Besanhar et al.
d, J, Electroa71a1. Chem
, 94°77 (1978)), and recently there has been a report using a fusible alloy such as a wood alloy (Toyoro Noritoku et al., 24th Battery Symposium P, 205 (1983)). In particular, the latter is being considered between the alloy thin plate 't = Tsukernet.

Although it is possible to use a metal or alloy piece for the Li storage substrate of the negative electrode, the problem is current collection. The method is as follows: (1) Any part of the metal or alloy piece for the Li occlusion substrate is spot welded to the case or sealing plate.

(2) Lay a metal grid, such as a metal net or expanded metal, that is slightly larger than this size on top of a metal or alloy piece of a specified size for the Li storage board, and use the protruding part of the grid to cover the case. Or spot weld to the inner surface of the sealing plate.

(3) When the metal or alloy for the Li occlusion substrate is melted in an inert atmosphere, a metal grid such as a metal net or metal expanded metal that will serve as a current collector is immersed in the molten metal and pulled up. First, the molten material is attached to the holes of the metal grid by its surface tension, and the other grid parts are spot-welded together with the lead terminals to the sealing plate or inside the case.

(4) A metal or alloy of a predetermined thickness for the L1 storage board is pressed and buried with a metal grid such as a metal net or expanded metal to integrate it, cut it to a predetermined size, and spot the leads. Weld it or spot weld it directly to the sealing plate or inside the case.

and so on.

Problems to be Solved by the Invention The above method (1) is good as long as the number of charging and discharging is small, but when the number of charging and discharging becomes too large, the spot welds begin to peel off. This results in brittleness when Li t-occlusion occurs to form an intermetallic compound.

Method (2) is good as a current collection method, but the alignment of the alloy and the metal grid when they are stacked in the manufacturing process is extremely complicated and is not suitable for mass production.

In method (3), the melting point varies depending on the type of metal or alloy, the magnitude of surface tension, and the pulling speed.

Since the amount of metal and alloy deposited varies depending on the temperature of the alloy water, the mesh of the current collection net, etc., it is difficult to find the optimum value.

Method (4) is the simplest and allows for reliable current collection, but
During charging, it absorbs lithium and becomes an intermetallic compound, increasing its volume several times, and during discharging, Li is released and it returns to its original shape. In general, if the ratio of the amount of discharged lithium to the amount of charged (=occluded) lithium is small, the change in shape will be small and the charge/discharge cycle will be long. There is a tendency for fatigue to be large and charge/discharge cycles to be shortened.

Therefore, from the standpoint of performance and manufacturing, method (4) is the most advantageous, but there are still problems. Also,
Expanded metal is weaker than metal net and cannot be put to practical use.

Therefore, the present invention uses a metal net to solve the above-mentioned problems in the method (4), and provides a battery that has a long charge/discharge cycle even if the ratio of the amount of discharged lithium is large.

Means for Solving the Problem In order to solve this problem, the present invention limits the opening size of the metal net to 0.25 to 0.50 m.

Function: According to this configuration, a metal negative electrode body capable of occluding lithium can be obtained, which has a long charge/discharge cycle, a high capacity per unit volume in terms of performance, is easy to manufacture, and is easy to connect to a sealing plate or case. .

Example There are many metal elements that can absorb metallic lithium, that is, form intermetallic compounds with lithium, but metals that can be used as negative electrodes for batteries, that is, can absorb large amounts of lithium, will collapse and shatter when used alone. I end up. This is a process in which a thin plate of aluminum or lead is exposed to a large amount of lithium (Li >
You can tell right away if you come in contact with it. In other words, it is difficult to use alone, and it is necessary to add a metal element such as cadmium or zinc that acts as a binder to hold these intermetallic compounds together, in other words, it is necessary to form an alloy in advance.

Naturally, if a large amount of a metal element such as cadmium is added, the amount of Li occlusion per unit weight and volume of the alloy, that is, the electric capacity, will decrease, but the charge/discharge cycle will be lengthened accordingly.

Therefore, in this example, in order to determine the effect of the aperture size of the current collecting metal net, the Li f occluding alloy was an alloy consisting of 20wtqb cadmium and 80wt% lead (hereinafter referred to as Cd(20)-Pb( 80) was selected. 0 of this Cd(20)-Pb(80) alloy
．． A 1 m thick thin plate was lightly held between nickel nets, and short-circuited with a lithium plate serving as a counter electrode in a 1 mol/2 lithium perchlorate/propylene carbonate electrolyte at 20°C.
When a time-quiet device is used, the Li f-absorbed alloy (hereinafter referred to as Li
alloy).

This Li alloy has a capacity of approximately 1,700 m per unit volume.
Ah / cc, Li 2,060 m of single metal
It can be seen that there is no grandson color compared to Ah /CC. Incidentally, this alloy stores 400 mAh of Lit-per unit weight. Moreover, the shape of this LL alloy in liquid is greatly deformed, and it is quite brittle in terms of strength. In other words, the Li storage capacity is large and close to that of Li metal, and LL
The mechanical strength of the alloy is low, and the aperture size of the current collector net is selected to have the most significant effect.

This Cdlo)-Pb(go) alloy contains metal Cd2!
Of and metal pbsoP2 were melted in a vacuum melting furnace to form an alloy, which was then rolled into a 100 μm thin plate.

The metal net is made of 5US3o4 stainless steel wire with 80 meshes (sieve mesh opening size 0.
18m + 1.60 mesh (same <0.25mm), 4
0 mesh (same (o, 3e mm), 32 mesh (
The same (0,50 tram) and 24 meshes (same < 0,70 am) were used.

Next, this alloy thin plate (soxsow) and each metal net were stacked and pressed under a pressure of 5 tons, and then
This was punched out into a disk shape with a diameter of 16. Table 1 shows the amount of alloy retained in this disk and the amount of Li occluded. In Table 1, the amount of Li to be stored is 86% of the maximum storage amount of this alloy. This will be explained below with reference to the drawings.

of Table 1 FIG. 1 is a cross-sectional view of the battery used in the example.

Figure 2 is a disk-shaped punched-out piece of an integrated metal net and Li storage alloy, where a is a plan view and b is a plan view.
C shows a cross-sectional view, and C shows an enlarged view of the mesh portion of the metal net.

In FIG. 1, 1 is the thickness o, 2. oSUSso, *This is a sealing plate made of stainless steel, and the alloy body punched into the disk shape described above is spot welded to the inside of this sealing plate. 2 is a metal net in the punched alloy.

In No. 3, Li disks (diameter 15 m) in the amount shown in Table 1 are crimped onto the spot-welded alloy body, and lithium perchlorate is added to the same volume mixed solvent of propylene carbonate and 1,2-dimethoxyethane over the disks. It is a Li alloy that spontaneously forms when a predetermined amount of an electrolytic solution containing 1 mol/2 of Li is injected.

In Figure 2, 11 is metal net, 12 is LL storage alloy, 1
3 indicates the opening size of the net. 4 is a positive electrode, which is made from a mixture of 100 parts by weight of amorphous chromium oxide 01308, 8 parts by weight of artificial graphite with a specific surface area of 300 m'/P, and 12 parts by weight of a filler-like fluororesin binder. This is a diameter 13+11 spot welded to the inner surface of the case 6 made of corrosion-resistant stainless steel with a thickness of 0.2 mm.
It is molded inside the case to a diameter of 16 cm and a thickness of 1.11011 mm on a current collector 6 made of expanded titanium metal of ffl. In this battery, the positive electrode capacity is at least 1.4 times the negative electrode capacity. 7 and 8 are a separator and an impregnating material made of a polypropylene nonwoven fabric, and after injecting a predetermined amount of electrolyte into the positive electrode side, the separator and the impregnating material are caulked together with a polypropylene gasket 9.

The maximum outer diameter of this battery is 20.0mm, and the maximum total height is 2.6mm.
− is.

Next, these batteries are charged and discharged at a constant current of A-Eft of 2.5 mA. Charging and discharging are performed at the discharge lower limit voltage 1. OV, charging upper limit voltage 3
．． The battery was charged and discharged at a voltage of 8V within this range. The third index is the index when the capacity change due to the charge/discharge cycle at this time, that is, the capacity retention rate of the negative electrode is set as 100 for the capacity of the first cycle.
As shown in the figure. In addition, the discharge capacity accompanying the charge/discharge cycle of the negative electrode substrate made of the Li storage alloy and the buried metal net at this time is integrated up to the 80% point in Figure 3, and the cumulative cycle capacity is calculated by dividing this by the volume of the negative electrode substrate. The density is shown in Figure 4.

Effects of the Invention In the above explanation, it can be seen from FIG. 3 that the deterioration of the negative electrode due to charge/discharge cycles decreases rapidly as the opening size of the metal net increases. However, it would be a mistake to make a judgment based solely on the degree of capacity deterioration, and it is necessary to evaluate the filling capacity and cycle characteristics as well. This is shown in Figure 4, and if you reduce the opening size of the metal net, the amount of metal wires that make up the net will get in the way and the capacity will decrease as shown in Table 1. , it can be seen that the cumulative cycle capacity density is decreasing overall.

Comprehensively judging from these Figures 3 and 4, it is good for batteries to have an opening size of 0.25 to 0.50 wm (B-D for metal wires), and is more preferable. It is optimal for the current collector of the negative electrode alloy for lithium secondary batteries to have an opening size of 0.25 to 0.36 rran.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a battery according to an embodiment of the present invention, and FIG. 2 is an explanatory view of a lithium storage alloy negative electrode body, where a is a plan view, b is a cross-sectional view, and C is an eye of the metal net current collector. Fig. 3 is an enlarged view showing the opening size of metal nets with various opening sizes; FIG. 4 is a diagram showing the integrated cycle capacity density. 1...Sealing plate, 2...Metal net, 3
...Lithium alloy, 4...Positive electrode, 6.
...Case, 6...Current collector, 7...
...Separator, 8...Impregnating material, 9...
·gasket. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 8 Contains J 4th cannon 2nd diagram 1 Ime, 4 rate (shi) gu 澾

Claims (1)

[Claims] A nonaqueous electrolyte secondary battery consisting of a positive electrode, a nonaqueous electrolyte, and a lithium negative electrode. It consists of a metal net integrated with the metal net, and the opening size of the metal net is 0.25~
A non-aqueous electrolyte secondary battery with a thickness of 0.50 mm.