JP2005302467A - Lithium ion secondary battery, battery pack thereof and overcharge protection method thereof - Google Patents

Abstract

A lithium-ion secondary battery having a non-returning current interruption function including a resettable safety element that trips when the battery temperature rises and attenuates current, and a safety valve membrane that breaks when the internal pressure of the battery rises, and the like Provided is a battery pack that is highly safe when overcharged.
At the time of overcharging, first, the return-type safety element is activated to attenuate the current value, and further, charging is continued with the attenuated current to increase the internal pressure of the battery to activate the current interruption mechanism. Ensure safety when charging. This return-type safety element is a PTC element or a thermostat, has an operating temperature of 70 ° C. to 100 ° C., a current value is attenuated to 30 mA to 200 mA, and an operating pressure of the current interrupting mechanism is 0.4 MPa to 1 MPa. .6 MPa.
[Selection] Figure 1

Description

  The present invention relates to a lithium ion secondary battery and a battery pack thereof, and more particularly, to a method and apparatus for protecting a battery during overcharge by a suitable current interruption mechanism and a resettable safety element.

  In recent years, along with the cordless and portable use of electronic devices such as AV equipment and personal computers, many small secondary batteries such as high energy density lithium ion secondary batteries equipped with non-aqueous electrolyte and alkaline storage batteries equipped with alkaline electrolyte have been adopted. Has been. As these devices become more sophisticated and functional, high-capacity and safe batteries are desired.

  In the case of non-aqueous secondary batteries such as lithium ion secondary batteries and lithium polymer batteries, an organic solvent may be used in the electrolyte, and the battery temperature rises due to overcharge due to a failure of the charger. The temperature is limited to a certain temperature or less by using a temperature protection element such as a temperature fuse, a thermostat, or a positive temperature coefficient (PTC) element.

  Alternatively, a current cut-off mechanism that cuts off the current by detecting the internal pressure of the battery is provided in the sealing plate so as to be limited to a certain temperature or lower.

  Since the thermal fuse is abnormally charged once and rises to a predetermined temperature, it does not return, so there is an advantage that a battery that has experienced such an abnormal state is not used again. However, there are concerns about malfunctions due to storage at high temperatures and slight external shorts.

  Since the PTC element is a return type, there is no fear of malfunction like a thermal fuse, but conversely, with a general charging current value, for example, a charging current of about 1C that reaches the battery design capacity in one hour. In this overcharge, even when tripping at a predetermined temperature, a current of about 100 mA continues to flow, resulting in a higher voltage state that is more dangerous as a battery. Moreover, there is a concern that the PTC element may fail due to continuous charging at a high voltage such as 20V.

  Further, it has been proposed that the PTC element is backed up with a fuse against a voltage that exceeds the withstand voltage and enters a short mode (see, for example, Patent Document 1).

Conventionally, there is a combination of a current blocking mechanism for a sealing plate and a PTC element that is a resettable safety element, but the current blocking mechanism is activated when overcharged with a charging current of about 1 C, and the PTC element is exclusively short-circuited, etc. This is designed to prevent excessive current from flowing through the battery, making it difficult to operate during overcharging.
JP 2002-150918 A

  However, in recent years, in order to increase the safety of the battery, development to reduce the gas generation of the battery is progressing. For example, in a battery made of an electrolyte such as γ-butyrolactone (GBL), which is a more stable solvent, there is little gas generation in an overcharged state due to the characteristics of GBL, and it is difficult to stop overcharge by the above-described current interruption mechanism. .

  The present invention solves these problems by optimizing the operating temperature and the current interrupting mechanism operating pressure of a PTC element or thermostat that is a resettable safety element even in a battery that generates little gas during overcharging. A cheap and highly reliable non-returnable element is provided.

  In order to achieve the above object, the present invention has a non-returning current interrupting function including a resettable safety element that trips when the temperature of the battery rises and attenuates the current and a safety valve membrane that breaks when the internal pressure of the battery rises. A method for overcharge protection of a lithium ion secondary battery, wherein at the time of overcharge, first the return type safety element is activated to attenuate the current value, and further to continue charging with the attenuated current to increase the battery internal pressure. The current interrupting mechanism is activated to prevent ignition due to overcharging.

  Furthermore, in the lithium ion secondary battery of the present invention, the resettable safety element is a PTC element or a thermostat, the operating temperature is 70 ° C. to 100 ° C., and the current value is tripped to 30 mA to 200 mA. The operating pressure of the shut-off mechanism is 0.4 MPa to 1.6 MPa.

  The PTC element or thermostat in these cases exhibits the same actions and effects even when attached in close contact with the outside of the battery surface as in the case of a battery pack.

  As described above, in the present invention, in the overcharge, after the PTC element or thermostat as the resettable safety element operates to attenuate the current, the current interrupting mechanism built in the sealing plate is operated, Reliable lithium-ion secondary battery that can prevent malfunctions caused by non-recoverable problems such as thermal fuses, high-temperature storage malfunctions, and operation due to a slight external short-circuit, making it unusable. And a battery pack thereof.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  In FIG. 1, reference numeral 1 denotes a flat rectangular battery pack, which includes a battery 2 made of a lithium ion secondary battery. One end of the battery 2 is covered with the terminal unit 13. The terminal unit 13 has a configuration in which an insulating cover made of an insulating resin, a first external connection terminal 15 and a second external connection terminal 16 are integrated by insert molding. The first external connection terminal 15 has a substantially gate shape in cross section, and extends downward from the terminal unit 13 so that the connection legs 17 on both sides thereof overlap the outer surface of one end of the battery case 3. In addition, a window portion 19 that exposes the first and second external connection terminals 15 and 16 to the outside is opened on the end surface of the terminal unit 13. The connection leg 17 of the first external connection terminal 15 is connected to the outer surface of the battery case 3 by welding 24.

  Hereinafter, two preferred embodiments will be described based on the battery pack of FIG.

  FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1, and shows a rectangular battery having an overcharge protection function according to the present invention having a resettable safety element and a current interruption function in a sealing plate, and a battery pack using this battery. is there.

  In FIG. 2, the battery 2 is configured to house a power generation element 4 made of an electrode plate group in which a positive electrode plate and a negative electrode plate are laminated via a separator in a battery case 3 and an electrolyte. One end opening of the battery case 3 is sealed through an insulating gasket 8 with a sealing plate 7 having a cap 6 provided with a protrusion 5, the cap 6 being one polarity connection electrode, and the battery case 3 being the other. A polar connection electrode is formed. The sealing plate 7 is configured by housing and arranging a safety valve mechanism 11, a resettable safety element 12 and a cap 6 through an inner gasket 10 in the filter 9, and the filter 9 is connected to the power generation element 4. Are connected to the safety valve mechanism 11 via the return-type safety element 12.

  An annular protrusion (not shown) protrudes from the outer periphery of the lower surface of the terminal unit 13 to form an accommodation space in which the lead plate 22 is accommodated. An elastic body 23 is interposed between the annular protrusion and the crimped portion at the opening end of the battery case 3. As the elastic body 23, foamed polyethylene, butyl rubber or the like having resistance to electrolytic solution is preferably used.

  As described in FIG. 1, the connection leg 17 of the first external connection terminal 15 is connected to the outer surface of the battery case 3 by welding 24. As shown in FIG. 2, the weld 24 between the connection leg portion 17 and the battery case 3 is disposed at the position where the reinforcing plate 27 at one end of the battery case 3 is disposed. Further, one end of the second external connection terminal 16 and the lead plate 22 is connected by welding (not shown), and the other end of the lead plate 22 is connected to the protruding portion 5 of the cap 6 of the sealing plate by welding 25b. ing.

  On the other hand, FIG. 3 is a cross-sectional view taken along the line AA of FIG. 1, and a lithium ion secondary battery having a current blocking mechanism in the sealing plate and a battery attached in close contact with the battery surface. It is a lithium ion secondary battery pack comprising a resettable safety element that trips when the temperature rises and attenuates the current.

  On the other hand, in FIG. 3, instead of providing a stainless steel spacer 14 inside the battery and not providing the return type safety element, a return type safety element 26 is provided between the first lead plate 22a and the second lead plate 22b. The lead plate 22, which is configured to be interposed and has a function of cutting off current when the resistance of the lead plate 22 is rapidly increased when the temperature is higher than a predetermined temperature, is attached in close contact with the battery surface.

  Thus, the return type element comprising the PTC element or thermostat, which is a return type safety element attached in close contact with the current blocking mechanism of the seal plate of the present invention and the inside of the seal plate or the outside of the battery surface, is a non-return type element. It is possible to prevent malfunction caused by high-temperature storage, which is a problem of a certain thermal fuse, and that it cannot be used due to a slight external short circuit.

  Also, PTC elements and thermostats continue to flow at a current of about 100 mA in the case of PTC elements even after being operated by overcharging at a current of 1 ItA, and the thermostat returns and recharges when the battery temperature drops after operation. As a result, there is a problem that a dangerous high voltage state occurs.

  In order to improve such a problem, a thermostat with a holding function has been developed in which a thermostat and a PTC element are combined to prevent the thermostat from returning during charging by using the heat generated by the PTC element. The thermostat is used and it is an expensive part. Moreover, it has the subject that size reduction is difficult.

  In the case of the present invention, it is a current interruption mechanism composed of two welded metal foils incorporated in a PTC element and a sealing plate, and can be manufactured with a material that is much cheaper than a thermostat using a bimetal. Is possible.

  In addition, when an electrolytic solution mainly composed of a solvent that generates little gas in an overcharged state such as GBL is used, in the conventional method in which overcharge is first stopped by a current interruption mechanism, SOC = 140% to 180% The internal pressure in% was important, and ignition could occur if the timing of shut-off was delayed. Therefore, the isolation pressure is designed to be very low, and higher accuracy is required, making manufacturing difficult.

  In the case of the present invention, the PTC element is first activated to attenuate the current to suppress the temperature rise of the battery, and then the overcharge is continued with the attenuated current to decompose the electrolyte and generate gas. The timing of is not as important as before. Therefore, it is suitable for a battery that generates a small amount of gas during overcharge.

  Therefore, the operating temperature of the PTC element or thermostat that is the resettable safety element is a temperature that does not reach the thermal runaway start temperature of the battery, and is 100 ° C. or less in view of the maximum temperature of the battery surface (anxiety of burns) during abnormal charging. However, 70 ° C. or higher is desirable from the viewpoint of discharge characteristics at a high temperature.

  In addition, the current interruption mechanism is desirably 0.4 MPa or more from malfunction due to high temperature storage and productivity, and 1.6 MPa or less from reliable operation by overcharge.

  Hereinafter, embodiments of the present invention will be described in detail using a pack using a prismatic lithium ion secondary battery.

  In the positive electrode plate, lithium cobaltate is used as a positive electrode active material, acetylene black as a conductivity-imparting agent, polytetrafluoroethylene (PTFE) as a binder, CMC as a thickener, and water as a dispersion medium. A slurry-like positive electrode mixture was prepared. An aluminum foil was used as the current collector, and the positive electrode mixture was applied to produce a positive electrode plate sheet. After drying, the sheet was rolled to a predetermined thickness to produce a positive electrode plate. A tab type lead was ultrasonically welded to the electrode plate according to the purpose.

  In the negative electrode plate, graphitized mesocarbon microbeads (MCMB) as an active material, styrene-butadiene copolymer rubber (SBR) as a binder, CMC as a thickener, and a slurry negative electrode using water as a dispersion medium A preparation for use was prepared. A copper foil was used as a current collector, and a negative electrode mixture was applied to both surfaces of the current collector to prepare a negative electrode sheet. Next, the negative electrode plate sheet was dried, rolled to a predetermined thickness, and cut into predetermined dimensions to produce a negative electrode plate. A tab-type lead made of nickel was welded to a part of the negative electrode plate with ultrasonic waves.

  The positive electrode plate and the negative electrode plate were wound through a separator that is a microporous film of polyethylene to prepare an electrode plate group.

  The electrode plate group was inserted into a case and a non-aqueous electrolyte was injected. As the electrolyte, a non-aqueous electrolyte solution in which 1.0 mol / l of lithium hexafluorophosphate was dissolved in a solvent in which ethylene carbonate and γ-butyrolactone (GBL) were mixed at a volume ratio of 2: 3 was used. The positive tab type lead was in contact with the inner wall of the case. The tab lead of the negative electrode was connected to the terminal portion of the sealing plate, sealed with the sealing plate, activated and discharged several cycles, and a prismatic lithium ion secondary battery with a battery capacity of 850 mAh was produced.

  When the charging current is 850 mA (1 ItA (It: time, A: current)), the sealing plate has a PTC element operating at 60 ° C., 70 ° C., 80 ° C., 100 ° C., and 110 ° C. and a battery internal pressure of 1.0 MPa, respectively. Batteries produced using a battery having a function of detecting current and blocking current are referred to as batteries of Comparative Example 1, Example 1, Example 2, Example 3, and Comparative Example 2, respectively.

  In the case of a charging current of 1 ItA on the sealing plate, the battery of Comparative Example 3 is obtained in the same manner as above except that only the PTC element operating at 80 ° C. is provided.

  Table 1 shows the results of a continuous overcharge test and a high temperature storage test using 10 cells of each of the prismatic lithium ion batteries of Examples 1 to 3 and Comparative Examples 1 to 3.

  In addition, the continuous overcharge test is a continuous overcharge test at a charging voltage of 20 V and a charging current of 0.85 A (equivalent to 1 ItA) after remaining discharge at a constant current of 0.85 A (1.0 ItA) up to a final voltage of 3.0 V. The presence or absence of ignition when 120 hours was performed was confirmed.

  In the high temperature storage test, after a residual discharge at a constant current of 0.85 A (1.0 ItA) to a final voltage of 3.0 V, a constant current of 1400 mA (0.7 ItA) until the battery voltage reaches 4.2 V. Whether or not the current interruption mechanism malfunctions when a fully charged battery is charged and then charged until the current value decays to 100 mA (0.05 ItA) is stored in a 60 ° C. environment for 20 days. It was confirmed.

  As is clear from Table 1, in the battery of the example, the PTC element was activated, the charging current was attenuated to 0.1 A, the overcharge in that state continued, and the internal pressure of the battery increased after 24 hours to 30 hours As a result, the current interrupting mechanism was activated and charging was impossible. That is, it was found that even when an abnormal state such as overcharging occurs, the battery is not restored and can be prevented from being used further as a battery.

  On the other hand, in the case of Comparative Example 1, when the high temperature storage was performed at 60 ° C., the PTC element malfunctioned, and a problem that could not be discharged occurred. Moreover, in the case of the comparative example 2, the operating temperature of PTC was as high as 110 degreeC, the temperature rose to the thermal runaway area | region of a battery, and the thing leading to ignition generate | occur | produced.

  In the case of Comparative Example 3, as in Example 2, the PTC element operates at 80 ° C., the charging current decays to 0.1 A, charging continues in that state, and the charging current value suddenly becomes 0 after 5 days. .Returned to 85A, and then fired. The reason why the current value returned to 0.85 A is presumed that the withstand voltage of the PTC element reached its limit due to long-term charging at 20 V and was destroyed. Thus, in the case of only the PTC element, there is a case where the PTC element breaks down due to a high voltage such as 20 V and long-time charging, resulting in ignition.

  Next, when the charging current is 1 ItA on the sealing plate, the PTC element operating at 80 ° C. and the function of detecting the internal pressure of the battery of 0.2 MPa, 0.4 MPa, 1.6 MPa, and 2.0 MPa to cut off the current, respectively. Batteries manufactured using the batteries having the above-described characteristics are batteries of Comparative Example 4, Example 4, Example 5, and Comparative Example 5, respectively.

  Table 2 shows the results of a continuous overcharge test and a high temperature storage test using the prismatic lithium ion batteries of Examples 4 to 5 and Comparative Examples 4 to 5.

  As is clear from Table 2, in the battery of the example, the PTC element was activated, the charging current was attenuated to 0.1 A, the overcharge in that state continued, and the internal pressure of the battery increased after 24 hours to 30 hours As a result, the current interrupting mechanism was activated and charging was impossible. That is, it was found that even when an abnormal state such as overcharging occurs, the battery is not restored and can be prevented from being used further as a battery.

  On the other hand, in the case of Comparative Example 4, when the battery was stored at a high temperature of 60 ° C., the battery internal pressure reached 0.2 MPa, and the current interruption mechanism malfunctioned, causing a problem that the battery could not function. Moreover, in the case of the comparative example 5, since it did not reach the battery internal pressure which a current interruption mechanism act | operates, the charging current continued flowing, and what led to ignition generate | occur | produced by the short circuit between local positive and negative electrodes.

  Further, an embodiment in which the PTC element is mounted in the battery pack will be described. In FIG. 3, a positive electrode plate, a negative electrode plate, and a separator were made into an electrode plate group by the same method as described above, inserted into a case, and an electrolyte solution was injected. A prismatic lithium ion battery was produced in the same manner as in Example 2 except that the sealing plate was equipped with only a current interrupting mechanism that detects the internal pressure of the battery of 1.0 MPa and interrupted the current.

  A battery pack in which the PTC element operating at 80 ° C. is attached in close contact with the outside of the battery surface to form a pack is a battery pack of Example 6, and a battery pack having a PTC element operating at 110 ° C. is comparative example 6. Battery pack.

  Table 3 shows the results of performing a continuous overcharge test and a high temperature storage test on these battery packs in the same manner as described above.

  The battery pack of Example 6 in which a current blocking mechanism that detects a battery internal pressure of 1.0 MPa is cut off on the sealing plate inside the battery and a PTC element that is in close contact with the outside of the battery surface and operates at 80 ° C. are attached. In the case, the PTC element operates on the sealing plate shown in Table 1 in the same manner as in Example 2 having a PTC element that operates at 80 ° C. and a function of detecting a battery internal pressure of 1.0 MPa to cut off the current. The charging current decayed to 0.1 A, overcharging in that state continued, and after 24 hours to 26 hours, the internal pressure of the battery increased and the current interruption mechanism was activated, making charging impossible.

  The battery pack of Comparative Example 6 is provided with a current blocking mechanism that detects an internal pressure of 1.0 MPa on the sealing plate inside the battery and interrupts the current, and a PTC element that adheres to the outside of the battery surface and operates at 110 ° C. In this case, the operating temperature of the PTC was as high as 110 ° C., and the temperature rose to the thermal runaway region of the battery, which led to ignition.

  In other words, it can be seen that the present invention can exert the same effect even in a structure in which the PTC element is adhered to the outside of the battery surface, and the same result can be obtained even if a thermostat is used instead of the PTC.

  As described above, in the overcharge, after the PTC element or the thermostat as the resettable safety element is activated and the current is attenuated, the current interruption mechanism built in the sealing plate is activated, so that A highly reliable lithium ion secondary battery and its battery pack can be prevented from malfunctioning when stored at high temperatures, which was a non-returnable problem, and being unable to operate due to a slight external short circuit. Can be provided.

  The lithium ion secondary battery and its battery pack of the present invention are useful as a portable power source having excellent safety.

The perspective view which showed the battery pack of one Embodiment of this invention. 1 is a schematic longitudinal cross-sectional view of the battery according to the embodiment of the present invention, taken along the line AA in FIG. 1 is a schematic longitudinal sectional view taken along the line AA of FIG. 1 of a battery pack according to another embodiment of the present invention.

Explanation of symbols

1 battery pack 2 battery 3 battery case (connection electrode)
5 Cap protrusion (connection electrode)
6 Cap 13 Terminal Unit 15 First External Connection Terminal 16 Second External Connection Terminal 17 Connection Leg 22 Lead Plate 23 Elastic Body 24 Welding 26 Resettable Safety Element 27 Reinforcing Plate

Claims (4)

Overcharge protection method for a lithium ion secondary battery having a non-returning current interruption function having a return type safety element that trips when the battery temperature rises and attenuates the current, and a safety valve membrane that breaks when the internal pressure of the battery rises Because
At the time of overcharge, first, the resettable safety element is actuated to attenuate the current value, and further charging is continued with the attenuated current, thereby increasing the internal pressure of the battery and operating the current interrupt mechanism to cause ignition due to overcharge. How to prevent overcharge protection of lithium ion secondary battery. Trips when the temperature of the lithium ion secondary battery with a non-returning current interruption function equipped with a safety valve membrane that breaks when the internal pressure of the battery rises and when the temperature of the battery attached in close contact with the battery surface rises An overcharge protection method for a lithium ion secondary battery pack comprising a resettable safety element that attenuates current,
At the time of overcharge, first, the resettable safety element is actuated to attenuate the current value, and further charging is continued with the attenuated current, thereby increasing the internal pressure of the battery and operating the current interrupt mechanism to cause ignition due to overcharge. How to prevent overcharge protection of lithium ion secondary battery pack. A lithium ion secondary battery having a non-returning current interruption function comprising a resettable safety element that trips when the battery temperature rises and attenuates the current, and a safety valve membrane that breaks when the internal pressure of the battery rises,
The return-type safety element is a PTC element or a thermostat, whose operating temperature is 70 ° C. to 100 ° C., the current value is attenuated to 30 mA to 200 mA, and the operating pressure of the current interrupting mechanism is 0.4 MPa to A lithium ion secondary battery having a pressure of 1.6 MPa. Trips when the temperature of the lithium ion secondary battery with a non-returning current interruption function equipped with a safety valve membrane that breaks when the internal pressure of the battery rises and when the temperature of the battery attached in close contact with the battery surface rises A lithium ion secondary battery pack comprising a resettable safety element that attenuates current,
The return-type safety element is a PTC element or a thermostat, whose operating temperature is 70 ° C. to 100 ° C., the current value is attenuated to 30 mA to 200 mA, and the operating pressure of the current interrupting mechanism is 0.4 MPa to A lithium ion secondary battery pack having a pressure of 1.6 MPa.

Images