JPH08102330A - Rectangular laminated lithium secondary battery - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a highly reliable lithium secondary battery with excellent cycle characteristics. [Structure] In a prismatic laminated lithium secondary battery, when fixing a laminated electrode plate, a fixing surface is a rectangular parallelepiped formed by laminating electrode plates. By doing so, it is possible to reduce the dispersion of the stress between the electrode plates during charging / discharging or between the fixed plate and the electrode plate, thus improving the cycle characteristics. [Effect] Since the cycle characteristics of the lithium secondary battery are improved by the present invention, it is possible to provide a highly reliable lithium secondary battery having excellent cycle characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly comprises a negative electrode and a positive electrode capable of inserting and desorbing lithium and a non-aqueous electrolyte, and has a long life and high energy of a type in which a rectangular plate-shaped negative plate and a positive plate are laminated. The present invention relates to a prismatic laminated lithium secondary battery having a high density.

[0002]

2. Description of the Related Art Conventionally, many proposals have been made for batteries having high energy density using lithium as a negative electrode active material. For example, as a secondary battery using lithium as a negative electrode active material, a battery using a sulfide or oxide of titanium, zirconium, hafnium, niobium, tantalum, vanadium, etc. as a positive electrode active material has been proposed. It cannot be said that the cycle characteristics are sufficient. Particularly, in a prismatic laminated type lithium secondary battery used by stacking a prismatic plate-shaped negative electrode and a positive electrode, deterioration of charge / discharge cycle characteristics becomes a serious problem. It is being studied at various places to solve this problem.
A method of operating by compressing and pressurizing at 0-500 psi
No. 58-73968) has been proposed. However, even with the above proposal, sufficient charge / discharge cycle characteristics have not been obtained,
At present, there is a demand for a drastic improvement in charge / discharge cycle characteristics of a prismatic laminated type lithium secondary battery.

[0003]

Since the technology of the stacking method or the pressing method has not been established, a prismatic stacked lithium secondary battery having sufficient cycle characteristics has not been obtained. An object of the present invention is to provide a novel method for laminating rectangular electrode plates,
It is to improve cycle characteristics.

[0004]

[Means for Solving the Problems] Generally, the electrode plate of a prismatic laminated lithium secondary battery undergoes a volume change due to the insertion and desorption of lithium ions during charge and discharge, which causes stress between the positive and negative electrode plates. However, strain stress remains in the surface of the electrode plate, and the electrode plate is physically destroyed, which adversely affects the cycle life characteristics. On the other hand, between the laminated electrode fixing plate and the electrode plate,
Stress is generated as lithium is inserted and desorbed, and the force that fixes the laminated electrode plates acts directly on each other to rub them against each other, which increases the probability that the electrode plates will be physically destroyed. Becomes

The present invention mainly comprises a negative electrode and a positive electrode capable of inserting and releasing lithium and a non-aqueous electrolyte, and an electrode plate laminated body formed by laminating the rectangular plate-shaped negative electrode plate and the positive electrode plate. And a fixed plate for fixing both ends of the electrode plate laminate to a rectangular laminated lithium secondary battery, the electrode plate laminate having a rectangular parallelepiped shape having dimensions of A cm in length, B cm in width and C cm in height, A × It is characterized in that the layers are stacked in the direction perpendicular to the surface that does not show the maximum value among the values calculated by B, B × C, and A × C.

Further, the electrode plate of the first layer and the electrode plate of the final layer of the electrode plate laminate are characterized in that the volume change due to insertion / desorption of lithium during charge / discharge is small.

The number of electrode plates having a smaller volume change due to lithium insertion / desorption during charging / discharging is N, and the number of electrode plates having a larger volume change due to lithium insertion / desorption during charging / discharging is 2N. It is characterized in that N electrode bodies sandwiching one electrode plate having a smaller volume change and two electrode plates having a larger volume change are stacked with a separator interposed therebetween.

The fixed plate of the electrode plate laminate is characterized by being made of a ceramic material.

Specifically, the above-mentioned problems can be solved by satisfying either or both of the following two items. The stress between the laminated electrode fixing plate and the electrode plates or between the electrode plates caused by the volume change of the electrode plates during charge / discharge is reduced. Disperses the generated stress.

[0010]

[Operation] Items are solved by the following methods. In order to reduce and uniformly generate as much as possible the stress caused by the volume change of the plate-shaped electrode plates during charge / discharge in a prismatic laminated lithium secondary battery of the same capacity, the electrode plates should be laminated in the direction of lamination. It is preferable to stack the rectangular parallelepiped formed by the method on the rectangular surface having the smallest area in the vertical direction. Since the area of the fixed plate is inevitably small when the electrode plate is laminated on a smaller surface, the pressure applied to the electrode plate by the fixed plate becomes more uniform, and the capacity density as a battery and the cycle characteristics can be improved. . Furthermore, by selecting a material that is harder than any of the materials that make up the electrode plate as the material for the electrode plate fixing plate, the stress generated between the laminated electrode fixing plate and the electrode plate can be made uniform. Become. The hardest material among the materials forming the electrode plate is an oxide of a transition metal, which is a positive electrode active material, and is significantly harder than a metal or a resin material. Therefore, when a laminated electrode plate is fixed, for example, a metal plate is easily deformed. In order to avoid this and achieve a long service life, it is preferable that the fixed plate of the laminated electrode is made of a ceramic material that is hard and is not easily plastically deformed. When a ceramic material is used as the electrode fixing plate, the fixing plate does not undergo plastic deformation during pressure fixing, so the electrode surface can be fixed with a uniform force, increasing the capacity density of the battery. Is also expected. Furthermore, among the metal plates, fixing with a steel plate increases the battery voltage during charge / discharge, especially during charging, causing the elution of iron and lowering the capacity density, but with a fixing plate made using a ceramic material, There is an advantage that nothing happens, and a long life can be achieved with a high capacity.

On the other hand, it is possible to disperse the generated stress of the item by the following method. By making the electrode plate in contact with the fixed plate an electrode plate having a smaller volume change during charge / discharge, the amount of wear of the electrode plate in contact with the fixed plate during charge / discharge can be reduced and the service life can be extended. In addition, as the structure of the electrode plate laminate, one electrode plate having a smaller volume change during charging / discharging is sandwiched by electrode plates having a larger volume change during charging / discharging, and the method of stacking them also has a long service life. Has an effect on. This is because it is possible to disperse the strain stress generated in the electrode plate and reduce the strain remaining in the electrode plate by thinning the electrode plate side having a large volume change and increasing the number of components. That is, by thinning the electrode having a large volume change, the distance of the active material from the current collector is shortened, so that the electrode reaction becomes more uniform, the local volume expansion is avoided, and the strain stress generated in the electrode plate is reduced. Can be made uniform and relaxed. The above prismatic laminated type lithium secondary battery electrode plate is prepared by adding and kneading a binder and a conductive agent powder such as acetylene black to a predetermined active material powder, and kneading the mixture on an electrode substrate made of stainless steel or the like. After coating, it is dried and prepared.

Further, as the electrolyte, propylene carbonate, 2-methyltetrahydrofuran, dioxolene,
One or more aprotic polar organic solvents such as tetrahydrofuran, 1,2-dimethoxyethane, ethylene carbonate, γ-butyl lactone, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dimethyl sulfoxide, acetonitrile, formamide, dimethylformamide, nitromethane. LiAsF ₆ ,
LiClO ₄ , LiAlCl ₄ , LiBF ₄ , LiPF ₆
It is possible to use a known electrolyte that is generally used in a battery that uses lithium as a negative electrode active material, such as an organic electrolyte solution in which a lithium salt such as is dissolved as a solute, or a solid electrolyte or a molten salt that uses lithium ions as a conductor. it can.
Further, the effect of the present invention does not change at all even if a separator is used if necessary in view of the structure of the battery.

[0013]

The present invention will be described below in detail with reference to examples. The invention is not limited to the following examples. The production of evaluation cells and the measurement and evaluation thereof in the following examples were all performed in an argon atmosphere.

Example 1 First, the battery structure is shown in FIGS. FIG. 1 shows the structure of the electrode plate and the electrode fixing plate when the electrode plate is laminated on the surface of the smallest area, FIG. 2 is the case of laminating it on the second largest surface, and FIG. 3 is the structure of the electrode plate and the electrode fixing plate when laminated on the surface of the largest area. Is shown.
The electrode plates in contact with the fixed plate 2 in FIGS. 1 to 3 are all positive electrode plates 3 whose volume change during charge / discharge is small. The volume of the electrode plate laminated portion of each of the batteries shown in FIGS. 1 to 3 is 84.
It is the same as cm ³ (7 cm × 5 cm × 2.4 cm), but the area of the electrode plate is different because the stacking directions of the electrode plates are different. That is,
Although it is 35 cm ² in FIG. 3, it is as small as 16.8 cm ² in FIG. ² and 12.0 cm ² in FIG. 1, and the number of constituents increases accordingly.

Next, a method for manufacturing the secondary battery manufactured in this embodiment will be described below. First, 4.0 wt% of EPDM (abbreviation of ethylene-propylene-diene copolymer) as a binder and 9.0 wt% of acetylene black powder as a conductive agent powder were added to positive electrode active material LiV ₃ O ₈ powder, and xylene was added. Was kneaded and prepared as a positive electrode paste. Figure 1
As shown in 1-A of FIG. 3 (1-B for negative electrode), the rectangle of the terminal portion (1.0 × 3.0 cm) and the rectangle of the electrode portion (5 × 7c)
m, 2.4 x 7 cm, 5 x 2.4 cm), the prepared paste was applied to an aluminum expanded metal electrode substrate, and the product was kept at room temperature in vacuum for 5 hours and dried, and then wrapped with polypropylene non-woven fabric. It was used as the positive electrode plate 3. The negative electrode plate 4 was also prepared and used in the same manner as the positive electrode plate. The negative electrode was made of Li-Pb-L as the active material.
A alloy powder is used, and EPDM as a binder is 3.0 wt.
%, And 7.0 wt% of acetylene black powder was added as a conductive agent powder. Expanded metal material is SUS
Made from 304. The thickness of the electrode thus manufactured is 0.06 cm for the negative electrode and 0.03 cm for the positive electrode. The number of electrodes in the evaluation cell depends on the installation direction of the electrode plate, but 3.
The amount of the positive electrode active material that gives an output of 0 Ah was calculated, and the amount was calculated based on this. As shown in FIGS. 1 to 3, the electrode plates are alternately laminated so that the outermost electrodes (first and last layer electrodes) become the positive electrode plate 3 having a small volume change, and the laminated body has a thickness of 0. It was clamped by a fixing plate 2 made of a steel plate of 5 cm and fixed with eight bolts (5-1 to 5-8 in the figure).

As the electrolytic solution, a mixed solvent solution of 1.0 M LiPF ₆ propylene carbonate (PC) and 1,2-dimethoxyethane (DME) was used. After fixing the electrode plate laminated body with a steel plate, it was wrapped with an electrolytic solution resistant synthetic resin, and after checking that there was no liquid leakage by injecting an electrolytic solution into this, thermocompression sealing was performed and the battery was evaluated. .

The charge-discharge cycle test and a constant current test, the discharge started at a current density of 1.0 mA / cm ^2, termination voltage was charged at 4.0V, discharging at 2.0 V. Positive electrode active material LiV ₃
The cycle life of the battery was defined as the number of cycles when the capacity density of O ₈ was 100 Ah / kg or less.

Table 1 shows the cycle life evaluation results of the prototype cell made of the electrode plate and the fixed plate shown in FIGS. Comparing cells 1, 2, and 3, the battery life increases as the area of the stacking surface decreases,
It can be seen that the cycle characteristics are improved. This is considered to be because the stress was effectively reduced by stacking the electrode plates on the surface of the minimum area.

[0019]

[Table 1]

Example 2 FIGS. 4 to 7 show the structure of the evaluation cell manufactured in this example and the method of manufacturing the electrodes. In this embodiment, the electrode plate stacking surface is 3
Both cells have a surface of 5 cm x 2.4 cm, and the electrode fixing plate has a thickness of 0.
A 5 cm steel plate is used. The features of each evaluation cell will be described below in the order of the drawing numbers. The cell of FIG. 4 has the same laminated surface area as the cell 1 of Example 1, but the outermost electrode plate (electrodes of the first layer and the last layer) is used as the negative electrode plate 4 contrary to the cell 1 and the negative electrode is used. And cell number 4 is a cell in which positive electrodes and positive electrodes are alternately laminated. FIG. 5 shows a cell number 5 in which one positive electrode plate 3 having a small volume change during charge / discharge is sandwiched between two negative electrode plates 4 having a large volume change to form a set and laminated. FIG. 6 is the reverse of FIG. 5, in which one negative electrode plate 4 having a large volume change is sandwiched between two positive electrode plates 3 having a small volume change, and one set is sandwiched. FIG. 7 shows the structure of the electrode plate used in the cell 5. The cell 5 is characterized in that two negative electrode plates 4 each having a thickness half that of the negative electrode plate of the cell 4 are used and one positive electrode plate 3 having a small volume change is sandwiched. Specifically, the negative electrode plate 4 as shown on the left side of FIG. 7 is manufactured. This was wrapped with a non-woven fabric made of polypropylene, folded in two in the center where there was no electrode mixture, and the positive electrode plate 3 was placed between them to form one set. This is laminated and assembled as a battery. In contrast to FIG. 5, FIG. 6 is characterized in that it is configured such that two positive electrode plates 3 having a small volume change at the time of charging / discharging and two negative electrode plates 4 having a large volume change are sandwiched. The other battery manufacturing conditions and evaluation conditions were the same as in Example 1. Table 2 summarizes the evaluation results of these batteries. The results of the cell 1 of Example 1 are also shown for comparison.

[0021]

[Table 2]

The cell 1 in which the positive and negative electrodes having the small volume change are placed on the outermost side and the positive and negative electrodes are alternately laminated has a life of 390 cycles, while the cell 4 having the negative electrode having the large volume change as the outermost has a life of 98 cycles. Remarkably decreased. The cell 5 of the method in which two negative electrodes with a large volume change are made thin and the positive electrode plate with a small volume change is assembled between them, the cell 5 has significantly improved cycle characteristics compared to the cell 6 with the opposite laminated structure. Was done. It is considered that this is because the stress between the electrode plates caused by the volume change of the electrodes during charge / discharge is dispersed and relaxed. Example 3 Table 3 shows cell 1 shown in Example 1 and cell 8 of FIG.
The electrode plate structure and fixing method are exactly the same, and the material of the fixing plate is different from the 1 cm thick alumina plate (cell 8) and the 0.5 cm thick steel plate (cell 1). And the discharge capacity.

[0023]

[Table 3]

From Table 3, in the steel plate pressing, the discharge capacity has already dropped to about 70% of the initial value after 100 cycles.
When fixed using an alumina plate, the discharge capacity was 190 Ah / kg or more even after 200 cycles, and the life was 400 cycles or more. Thus, it is understood that the cycle characteristics can be improved by using alumina, which is a ceramic, for the fixing plate. It is considered that this is due to the uniform pressing of the electrode plate.

[0025]

EFFECTS OF THE INVENTION In the prismatic type battery, the volume change of the electrode plates occurs during charging and discharging, so that stress is generated between the electrode plates and between the electrode plate and the fixing plate, and the electrode plates are prevented from collapsing. It was difficult to obtain sufficient cycle characteristics.
According to the present invention, it is possible to reduce the stress by dispersing the stress between the electrode plates or between the electrode plate and the fixing plate, and further, by fixing with the ceramics plate, it is possible to perform uniform pressure fixation, so that cycle characteristics are improved. Not only is it possible to improve the discharge capacity density, but it is possible to provide a highly reliable secondary battery.

[Brief description of drawings]

[Fig. 1] Schematic shape of a lithium secondary battery with 5 cm x 7 cm x 2.4 cm square electrode plate stacking dimensions, with a 5 cm x 2.4 cm surface as a pressure fixing surface (the outermost electrode plate is the positive electrode plate) Stacked so that).

[Fig.2] Schematic shape of a lithium secondary battery with a 5 cm x 7 cm x 2.4 cm square electrode plate stacking section, with a 7 cm x 2.4 cm surface as a pressure fixing surface (the outermost electrode plate is the positive electrode plate). Stacked so that).

[Fig. 3] Schematic shape of a lithium secondary battery with 5 cm x 7 cm x 2.4 cm square electrode plate stacking part, with a 7 cm x 5 cm surface as a pressure fixing surface (the outermost electrode plate is the positive electrode plate). Laminated so that).

[Fig. 4] Schematic shape of a lithium secondary battery with square electrode plate stacking dimensions of 5 cm x 7 cm x 2.4 cm, with a 5 cm x 2.4 cm surface as a pressure fixing surface (the outermost electrode plate is the negative electrode plate). Stacked so that).

[Fig. 5] A lithium secondary battery with 5 cm x 7 cm x 2.4 cm square electrode plate stacking section, the 5 cm x 2.4 cm surface is the pressure fixing surface, and one positive electrode plate is sandwiched between two negative electrode plates. Schematic shape of a stacked battery (the outermost electrode plate is the negative electrode plate).

[Figure 6] Rectangular electrode plate stacking section: A lithium secondary battery with dimensions of 5 cm x 7 cm x 2.4 cm, a 5 cm x 2.4 cm surface is the pressure fixing surface, and one negative electrode plate is sandwiched between two positive electrode plates. Schematic shape of a stacked battery (the outermost electrode plate is the positive electrode plate).

FIG. 7 is a schematic shape of the negative electrode plate of FIG.

[Fig. 8] Schematic shape of a lithium secondary battery with rectangular electrode plate stacking dimensions of 5 cm x 7 cm x 2.4 cm, with a 5 cm x 2.4 cm surface as a pressure fixing surface, and a pressure fixing plate made of ceramics. (The outermost electrode plate is the positive electrode plate).

[Explanation of symbols]

1-A ... Positive electrode plate terminal, 1-B ... Negative electrode plate terminal, 1-C ... Negative electrode substrate exposed part, 2 ... Electrode plate fixing steel plate, 3 ... Positive electrode plate covered with separator, 4 ... Negative electrode covered with separator Plates, 5-1 to 5-8 ... Bolts and nuts for fixing electrode plates, 8 ...
Separator for positive electrode plate, 9 ... Separator for negative electrode plate, 10 ...
Alumina plate for fixing electrodes.

Claims (4)

[Claims] 1. An electrode plate laminate comprising a negative electrode and a positive electrode capable of inserting and releasing lithium and a non-aqueous electrolyte as main constituent elements, and an electrode plate laminate formed by stacking the rectangular plate-shaped negative electrode plate and the positive electrode plate. In a prismatic laminated lithium secondary battery composed of fixing plates for fixing both ends of the electrode plate laminated body, in the electrode plate laminated body having a rectangular parallelepiped shape having dimensions of Acm in length, Bcm in width and Ccm in height, A × B, A prismatic laminated lithium secondary battery characterized by being laminated in a direction perpendicular to a surface which does not show the maximum value among the values calculated by B × C and A × C. 2. The electrode plate of the first layer and the electrode plate of the final layer of the electrode plate laminated body are electrode plates having a smaller volume change due to insertion and desorption of lithium during charge and discharge. Item 2. A prismatic laminated lithium secondary battery according to item 1. 3. The number of electrode plates whose volume change due to lithium insertion / desorption during charging / discharging is N, and the number of electrode plates whose volume change due to lithium insertion / desorption during charging / discharging is greater is 2N. 2. The rectangular laminated lithium battery according to claim 1, wherein N electrode bodies sandwiching one electrode plate having a smaller volume change and two electrode plates having a larger volume change are stacked with a separator interposed therebetween. Next battery. 4. The prismatic laminated lithium secondary battery according to claim 1, wherein the fixing plate of the electrode plate laminated body is made of a ceramic material.