JP2005259567A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery having higher safety than before.
SOLUTION: A negative electrode using as active material a material capable of electrochemical charge / discharge reaction with lithium, a positive electrode using lithium composite oxide as an active material, a non-aqueous electrolyte, and a separator having a thickness of 20 μm or less. In the case of the wound non-aqueous electrolyte secondary battery, when the battery temperature reaches 70 to 150 ° C., by giving a function of applying pressure from the winding core part to the outer peripheral part, during overcharging It is possible to obtain a highly safe battery that does not buckle and does not cause an internal short circuit.
[Selection] Figure 1

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to improvement of safety.

  Non-aqueous secondary batteries represented by lithium ion batteries and polymer lithium ion secondary batteries have a high voltage and high energy density, and thus the demand thereof is increasing.

  These battery-type cylindrical batteries, prismatic batteries, and the like employ an electrode plate group configuration in which a separator is interposed between positive and negative electrode plates. In general, a metal foil is used as a substrate for an electrode plate of these batteries. For example, a copper foil is used for a negative electrode substrate and an aluminum foil is used for a positive electrode substrate. The body portion of the electrode plate is configured by applying and fixing a mixture layer composed of an active material, a conductive material, and a binder on these substrates. In addition, a porous substrate such as a metal expanded metal or mesh may be used. A metal current collecting piece is connected to the main body portion of these electrode plates to form an electrode plate, and the other end of the current collecting piece is connected to the battery container to conduct to the battery terminal.

  In general, non-aqueous electrolyte secondary batteries are designed to ensure sufficient safety when handled under normal use conditions. However, as a method for evaluating extremely high safety, a severe test is performed in which the battery is further charged from a fully charged state at a high rate such as a current (4C) that reaches the design capacity in a quarter of an hour in an adiabatic state There is a case.

  When such a test is performed, the above-described non-aqueous secondary electrolyte battery continues to be overcharged for a long time, and when it approaches the theoretical capacity of the positive electrode / negative electrode active material, the battery IR rises and Joule heat is generated. And near the theoretical capacity, the thermal stability of the positive and negative electrode active materials has deteriorated, and the generated heat induces self-decomposing heat generation of the active material and oxidation heat generation reaction of the electrolyte, resulting in abnormal heat generation. .

  In order to solve this problem, a commercially available non-aqueous secondary electrolyte battery utilizes a rise in internal pressure of the battery immediately before abnormal heat generation, a mechanism for mechanically interrupting current, and a large current flows. A mechanism that cuts off the current by the PTC element when the battery itself becomes high temperature, a mechanism that cuts off the current by shutting down the separator due to an increase in the temperature inside the battery, and a mechanism that uses a low-melting point porous polyolefin as the separator are attached.

In addition, in order to reduce the injection amount of the flammable organic electrolyte and improve the safety performance of the battery, it has been proposed to provide a filler in the gap inside the battery. (See Patent Document 1)
JP 2000-188133 A

In recent years, with the demand for higher capacity of non-aqueous secondary batteries, in addition to improving performance by improving the active material of the electrode, the volume of members that do not contribute to the electromotive reaction has been reduced, and in limited battery containers There is an urgent need to increase the amount of the substantial active material to be filled. One possible method is to reduce the thickness of the separator.
However, when the thickness of the separator was set to 20 μm or less and overcharge (4 CmA rate in a heat insulation state) was performed, the battery was wound at 70 to 150 ° C. at the time of overcharge even though the safety mechanism was attached. The group cramped and an internal short circuit occurred, causing abnormal heat generation. The short-circuit phenomenon due to the winding of the winding group does not occur in the separator of 20 μm or more, but occurs for the first time when it is 20 μm or less.
Here, the cause of buckling at the time of overcharging includes expansion of positive and negative electrode plates accompanying overcharging and gas generation due to decomposition of the electrolyte.

  The present invention has been made in view of the above circumstances, and its object is to provide a non-aqueous electrolyte secondary battery having a higher level of safety than the conventional one even when a thin separator of 20 μm or less is used. Is to provide.

  The present invention provides a nonaqueous secondary battery having a structure of an electrode body formed by winding a positive electrode, a negative electrode, and a separator existing between these positive and negative electrodes, the separator has a thickness of 20 μm or less, It has a pressurizing means in the direction of the outer periphery where the operating temperature is 70 to 150 ° C.

  By adopting such a configuration, even if gas generation occurs due to expansion of the positive and negative electrode plates or decomposition of the electrolyte during overcharge, a highly safe battery that does not buckle and does not cause an internal short circuit. Can be obtained.

  Furthermore, it is preferable that this pressurizing means is arranged such that a center pin made of a shape memory alloy or a center pin made of a thermoplastic resin and a spring-like metal is arranged in the winding core space. It is also preferable that a foaming agent / microcapsule is disposed.

  As described above, according to the present invention, it is possible to obtain a non-aqueous electrolyte secondary battery that prevents internal short circuit that occurs during overcharging, has high reliability, and can ensure safety.

  The gist of the present invention is to have a pressurizing means in the direction of the outer peripheral portion in which the operating temperature is 70 to 150 ° C. in the winding core portion.

  Here, the reason why the battery temperature at which pressure is applied from the winding core portion to the outer peripheral portion is set to 70 to 150 ° C. will be described. The reason why the pressure is applied at 70 ° C. or higher is that when pressure is applied from the winding core to the outer periphery at a normal use temperature of less than 70 ° C., there is a margin for deformation of the battery group due to expansion and contraction of the electrode plate during intermittent cycles. There is a phenomenon that the degree of the cycle is reduced and the amount of the electrolytic solution existing between the electrodes is reduced by reducing the distance between the electrodes during the cycle, and the cycle characteristics are deteriorated.

  In addition, when pressure is applied from the winding core to the outer periphery at 150 ° C. or higher, the separator softens from around 150 ° C. and thinning proceeds, so that the battery group easily undergoes shape change, and the outer periphery If pressure is not continuously applied, buckling occurs during overcharge.

  From the above, when the battery temperature reached 70 to 150 ° C., the function of applying pressure from the winding core portion to the outer peripheral portion was provided.

  Examples of means for applying pressure from the core part to the outer peripheral part include means for arranging a shape memory alloy and a spring that cause a volume change at a predetermined temperature in the core space part.

  Shape memory alloy is a shape change when it is processed into a predetermined shape in the austenite phase, which is a crystalline phase at high temperature, and then rapidly cooled and transformed into a different shape in the state of martensite phase at low temperature, and then heated again. This refers to an alloy having a shape memory effect that can be restored to a shape processed in the austenite phase while reverse transformation occurs when the temperature is exceeded.

As a shape memory alloy, specifically, a titanium / nickel alloy having a shape memory characteristic that operates by sensing a subtle temperature difference is useful. Among them, a nickel-titanium alloy having a nickel abundance ratio of 55% by weight or less. Since it has a shape change temperature of 60 ° C. or higher, it can function effectively against the temperature rise of the electrode body during overcharge.

  By using such a shape memory alloy as a material for the center pin, it is possible to cause a shape change under a high temperature environment during overcharge and to apply pressure from the core portion of the battery winding group to the outer peripheral portion.

  The shape of the center pin may be any shape as long as pressure can be applied from the core portion of the battery winding group to the outer peripheral portion. For example, the center pin has a slit portion parallel to the central axis, and the slit The center pin has a shape that is bent in the direction of the central axis so that the diameter of the cross-section of the center pin is small. When the temperature rises, the slit end extends in the outer circumferential direction so that the cross-sectional area increases. The thing of the structure taken up can be illustrated.

  FIGS. 1A and 1B are a sectional view (a) before operation and a sectional view (b) after operation of the pressurizing means. In FIG. 1, the center pin 9 has a slit portion 10, and as can be understood by comparing (a) and (b), pressure can be applied to the outer peripheral portion by increasing the diameter.

  The center pin in the present invention has a structure in which a spring-like metal is compressed in the direction of the central axis and hardened with a thermoplastic resin, and the thermoplastic resin is softened at a certain temperature by a temperature rise, and the metal is original. The shape can be changed to a shape.

  2 (a) and 2 (b) show a sectional view (a) before operation and a sectional view (b) after operation of the pressurizing means. In FIG. 2, the center pin 9 is made of a spring-like metal 11 and a thermoplastic resin 12, and as shown in a comparison between (a) and (b), the diameter increases to apply pressure to the outer peripheral portion. Can do.

  The material used may be any material as long as the shape change temperature is not lower than 70 ° C. and not higher than 150 ° C. Examples of the thermoplastic resin include polyethylene, polypropylene, fluorine-based resin, and polyurethane resin. Moreover, copper, nickel, a copper-zinc alloy, a nickel-copper alloy, a nickel-manganese-iron alloy, a nickel-chromium-iron alloy, or the like is used as the metal. As described above, by using the spring of the present invention as the center pin material, it is possible to effectively change the shape in a high temperature environment during overcharge.

  As another method, a foaming agent / microcapsule that expands in volume at a predetermined temperature may be disposed in the winding core space.

Specifically, examples of the foaming agent include foamable urethane, azo compound, nitroso compound, hydrazine derivative, isocyanate compound, bicarbonate / carbonate, nitrite and the like.
As the microcapsules, gas covered with a partition shell can be used. For the partition shell, it is preferable to use a material that does not affect the battery reaction even if it remains in the battery. Specifically, polyolefin resin such as polyethylene and polypropylene, polyurethane resin, polyvinylidene fluoride, melamine resin Urea resin can be used. As the encapsulated gas, butane, pentane, hexane, dichloroethane, dichloromethane or the like can be used.

  Here, the above-mentioned predetermined temperature is preferably between 70 and 150 ° C. from the viewpoint of ensuring safety.

In addition, a conventionally well-known thing can be used for other members, such as a negative electrode active material or a positive electrode active material of this invention.

Hereinafter, the present invention will be described in more detail with reference to examples.
(Example 1)
A method for manufacturing a cylindrical battery will be described below.

  FIG. 3 shows a longitudinal sectional view of a cylindrical battery according to the present invention. In FIG. 3, a lithium ion secondary battery 1 has a positive electrode 2, a negative electrode 3, and a separator 4 wound to form an electrode body, and has a space 8 at the center of the electrode body. And an electrolyte solution (not shown) in which an electrolyte salt is dissolved in a non-aqueous solvent, and is sealed with a sealing plate 6.

  In a general commercial battery, a safety element such as a safety valve or a PTC element is incorporated in the sealing plate. However, in the battery of the embodiment, for the safety test, the sealing plate 6 has no safety mechanism. Not incorporated.

  And after arrange | positioning the nickel-titanium alloy which is 54.5 weight% of nickel as the center pin 9 in the electrode body center space part 8, electrolyte solution was inject | poured and the battery can was formed using the sealing board.

  The center pin using the nickel-titanium alloy having a nickel abundance ratio of 54.5% by weight was processed into the shape shown in FIG. 1, and the shape recovery temperature was 85 ° C. This volume expansion coefficient is about twice at 100 ° C.

  In this case, the shape recovery temperature was measured from the temperature at which the center pin was placed in the oven, the temperature was raised at 2 ° C./min, and the shape change was visually confirmed.

  A method for producing a negative electrode / positive electrode plate is described below.

  Prepared by mixing 95% by weight of graphite powder, 4% by weight of styrene butadiene rubber aqueous dispersion (binder) and 1% by weight of carboxymethylcellulose (thickener), and kneading with water as a medium. The negative electrode slurry was applied, dried and rolled to obtain a negative electrode. When the active material is a lithium alloy, 85% by weight thereof, 14% by weight of an aqueous dispersion of styrene butadiene rubber (binder) and 1% by weight of carboxymethylcellulose (thickener) are mixed, and water is used as a medium. A negative electrode slurry prepared by kneading was applied, dried and rolled to obtain a negative electrode. In this example, the results of the graphite material will be described, but the effects of the invention were the same in the case of other lithium aluminum alloys, lithium silicon alloys, lithium tin alloys, lithium zinc alloys, lithium magnesium alloys and the like.

The positive electrode plate was prepared by mixing 10% by weight of carbon powder as a conductive material and 5% by weight of polyvinylidene fluoride resin as a binder with 85% by weight of LiCoO ₂ powder, and kneading them using dehydrated N-methylpyrrolidinone as a medium. The produced slurry was applied onto a positive electrode current collector made of aluminum foil, dried and rolled. In this example, for the sake of brevity, the results of lithium-containing transition metal oxides, especially LiCoO ₂ , will be described, but the effects of the invention are the same in the case of other transition metal oxides, transition metal chalcogenides, vanadium oxides, etc. there were.
As the organic electrolyte, a solution obtained by dissolving 1.5 mol / liter of LiPF ₆ in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 1 was used.
The battery 1 was produced as described above.
(Example 2)
The electrode body central space 8 was filled with a center pin made of a spring-like metal and a thermoplastic resin, and then an electrolyte solution was injected to form a battery can using a sealing plate.

The center pin used in this example is a spring-like nickel-chromium-iron alloy with a thickness of 500 μm, compressed in the direction of the central axis, immersed in polyethylene dissolved in hot xylene, and rapidly cooled. did. This volume expansion is about double at 120 ° C.
A battery 2 was produced in the same manner as in Example 1 except that the center pin was replaced with the center pin 9 in the electrode body central space 8.
(Example 3)
After filling the electrode body central space 8 with a foaming agent, an electrolyte was injected, and a battery can was formed using a sealing plate.

The foaming agent used in this example used 20 g of p-toluenesulfonyl hydrazide. A battery 3 was produced in the same manner as in Example 1 except that the electrode body central space 8 was filled with a foaming agent.
Example 4
After filling the electrode body center space part 8 with a thermal expansion microcapsule, electrolyte solution was inject | poured and the battery can was formed using the sealing board.

The thermal expansion microcapsule used in the present example used 20 g of L320 manufactured by Dainichi Seika Kogyo Co., Ltd., which causes volume expansion several tens of times at about 90 ° C. or more.
A battery 4 was produced in the same manner as in Example 1 except that the electrode body central space 8 was filled with thermally expanded microcapsules.
(Comparative Example 1)
After filling the electrode body center space part 8 with the center pin 9 which does not thermally expand, electrolyte solution was inject | poured and the battery can was formed using the sealing board.

Specifically, except for the center pin 9 made of stainless steel (SUS304) and having the structure shown in FIG. Produced.
(Comparative Example 2)
After placing a copper-zinc-aluminum (zinc 26 wt%, aluminum 4 wt%) alloy as the center pin 9 in the electrode body central space 8, an electrolyte was injected and a battery can was formed using a sealing plate. .

The center pin using this copper-zinc-aluminum (26% by weight zinc, 4% by weight aluminum) alloy is processed into the shape before recovery (a) and after recovery (b) shown in FIG. The shape recovery temperature was 25 ° C. This volume expansion coefficient is about twice at 25 ° C.
A battery 6 was produced in the same manner as in Example 1 except that a center pin 9 made of a copper-zinc-aluminum (26 wt% zinc, 4 wt% aluminum) alloy was disposed in the electrode body central space 8.

  The cylindrical battery produced above has a diameter of 18 mm and a height of 65 mm.

As described above, the above-described implementation batteries 1 to 4 and the cylindrical batteries of the comparative batteries 5 and 6 were manufactured and subjected to safety evaluation.
The configurations of the batteries in Examples 1 to 4 are all the thicknesses and lengths of the positive and negative electrode plates so that the battery capacity, the positive electrode discharge utilization factor, and the negative electrode discharge utilization factor are equal to the batteries 5 and 6 of the comparative example. Made the same. The dimensions are shown below.

The dimensions of the positive electrode plate body of Examples 1 to 4 and Comparative Examples 5 and 6 are 37 mm wide and 380 m long.
m, thickness 0.150 mm, the dimensions of the negative electrode plate main body were 39 mm wide, 415.0 mm long, and 0.150 mm thick. Table 1 shows the discharge capacity and safety test results of the second cycle obtained in the charge / discharge tests of the batteries 1 to 5 of the example and the battery 6 of the comparative example. The discharge capacity was confirmed by performing constant voltage charging at 4.2 V for 2 hours and discharging to 3.0 V at 0.2 CmA.

  As can be seen from Table 1, it can be seen that the batteries 1 to 4 and the battery 6 of the present invention have the same battery capacity as the battery 5 using the conventional center pin shown in the comparative example.

As can be seen from (Table 1), the battery 6 of the present invention has an intermittent cycle of 45 ° C. (1 C charge / discharge, 24 hour charge suspension), as compared with the batteries 1 to 4 and the battery 5 using the conventional center pin. It can be seen that the characteristics are very inferior.
The center pin used in this battery 6 is a copper-zinc-aluminum (26% by weight zinc, 4% by weight aluminum) alloy, and its shape recovery temperature is 25 ° C. As described above, during the 45 ° C. intermittent cycle, It is considered that the characteristics deteriorated when pressure is applied from the winding core portion to the outer peripheral portion.

  Table 10 shows the maximum heat generation temperature of each of the batteries 1 to 4 of the example and the batteries 5 and 6 of the comparative example when overcharged at 2 CmA for 4 hours together with the presence or absence of group buckling. Here, the presence or absence of group buckling was confirmed by X-ray CT image analysis of the battery after the test.

  From Table 1, it can be seen that the batteries 1 to 4 or the battery 6 of the present invention have no abnormal heat generation due to an internal short circuit caused by group buckling during an overcharge test, and for the conventional center pin shown in the comparative example. It can be seen that the safety is improved as compared with the battery 5.

  The nonaqueous electrolyte secondary battery of the present invention is useful as a power source for use in portable information terminals, portable electronic devices, and the like.

(A) sectional drawing before operation of pressurizing means concerning one embodiment of the present invention, (b) sectional view after operation (A) sectional view before operation, (b) sectional view after operation of the pressurizing means according to another embodiment of the present invention External perspective view (partially sectional view) of a non-aqueous electrolyte secondary battery used in an example of the present invention Cross-sectional view of the center pin used in the comparative example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Positive electrode 3 Negative electrode 4 Separator 5 Case 6 Sealing port 7 Electrode body 8 Space part 9 Center pin 10 Slit part 11 Spring-like metal 12 Thermoplastic resin

Claims (3)

In a non-aqueous secondary battery having a structure of an electrode body formed by winding a positive electrode, a negative electrode, and a separator present between these positive and negative electrodes,
A non-aqueous electrolyte secondary battery, wherein the separator has a thickness of 20 μm or less, and has a means for pressurizing the winding core in the direction of the outer periphery with an operating temperature of 70 to 150 ° C. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the pressurizing unit includes a center pin made of a shape memory alloy or a center pin made of a thermoplastic resin and a spring-like metal in the winding core space. . 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the pressurizing unit includes a foaming agent / microcapsule disposed in a winding core space.