JP2015026449A - Lithium secondary battery device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery device capable of, at the time of temperature rise due to overcharging, being safely stopped by shutting down a current in a short time.SOLUTION: A low temperature shutdown separator, whose shutdown temperature is lower than that of a standard shutdown separator, is produced by further providing a low melting point material layer for a structure of the standard shutdown separator. A lithium secondary battery device 20 has a structure where a unit cell 10a, to which the standard shutdown separator is applied, is disposed in a center part, in which temperature tends to become relatively high, and a unit cell 10b, to which the low temperature shutdown separator is applied, is disposed in an outer peripheral part, in which relatively low temperature is maintained.

Description

  The present invention relates to a lithium secondary battery device including a highly safe separator.

  The usage form of the battery is generally called an “assembled battery” in which up to several tens of unit cells are combined in addition to the unit cells. The assembled battery is used for electronic devices, electric tools, in-vehicle use, and the like. Another type of battery use is generally called a “battery module” in which up to several hundred unit cells are combined. Battery modules are used for building backup power supplies, wind power storage devices, mobile phone base station power supplies, and the like. As used herein, the term “battery device” includes both the above “assembled battery” and “battery module”.

  In the lithium secondary cell, a separator is inserted between the positive electrode and the negative electrode in order to maintain electrical insulation of both electrodes. As the separator, a polyolefin microporous film such as polyethylene or polypropylene having a shutdown function is mainly used. The shutdown function is a function that suppresses thermal runaway by stopping the current in the battery by blocking the movement of Li ions when the battery is overheated to block the internal hole. Hereinafter, the fact that the shutdown function is exhibited is also referred to as “shut down”.

  When the lithium secondary cell is charged and discharged, the battery temperature rises due to Joule heat generation according to the current value. In charge and discharge in a lithium secondary battery device (hereinafter, also simply referred to as a battery device) composed of a plurality of lithium secondary cells, the temperature distribution occurs in the battery device because the heat dissipation state differs between the central portion and the outer peripheral portion. . Similarly, even in a laminate type single cell having an electrode group (hereinafter also simply referred to as an electrode group) composed of a plurality of positive electrodes, negative electrodes, and separators, temperature distribution occurs in the electrode group in the central portion and the peripheral portion.

  When a battery unit having a temperature distribution or a laminated unit cell having an electrode group having a temperature distribution overheats due to overcharging or other reasons and the temperature rises, the temperature at which the separator shuts down (hereinafter also referred to as the shutdown temperature) If they are the same, the center portion is shut down at a high temperature, but the current continues to flow without shutting down at the outer peripheral portion at a low temperature, and the battery temperature further rises to increase the risk of thermal runaway of the battery.

  Therefore, in Patent Document 1, a unit cell is constituted by an electrode group using a separator of polyethylene (PE) having a low shutdown temperature in the outer peripheral portion having a low temperature and a polypropylene (PP) having a high shutdown temperature in the central portion having a high temperature. If the temperature of the battery rises due to abnormalities such as overcharge, the PE and PP separators are shut down according to the temperature distribution in the electrode group, so that the entire battery is shut down in a short time It has been proposed to stop.

JP 2006-331922 A

  However, in particular, when the scale of the power supply is increased, such as a battery device (a battery pack or a battery module), a temperature distribution is generated in the battery device that cannot be dealt with by the difference in shutdown temperature inherent in PE or PP. Sometimes. Therefore, in order to shut down the entire battery device in a short time, the difference between the shutdown temperature of the separator used in the high temperature region and the shutdown temperature of the separator used in the low temperature region is further increased. There was a need.

  A lithium secondary battery device according to a first aspect of the present invention is a lithium secondary battery device including a positive electrode, a negative electrode, a separator provided with a single layer or a plurality of layers of microporous membranes, and an electrolyte. In the lithium secondary battery device in which a plurality of lithium secondary cells are arranged on the outer periphery surrounding the lithium secondary cells arranged in the center, and a separator for the lithium secondary cells arranged in the center The shutdown temperature is higher than the shutdown temperature of the separator of the lithium secondary cell disposed on the outer periphery.

  According to the present invention, when the temperature of the lithium secondary battery device rises and a temperature distribution is generated between the central portion and the outer peripheral portion of the device, the entire battery device can be shut down in a short time, and extra The battery can be safely stopped without causing an increase in battery temperature.

Schematic diagram of cylindrical lithium secondary battery Model diagram of standard shutdown separator Low temperature shutdown separator schematic diagram Outline diagram of a small cylindrical lithium secondary battery device Schematic diagram of another configuration of low-temperature shutdown separator Schematic diagram of another configuration of low-temperature shutdown separator Outline diagram of a large-scale lithium secondary battery device Overview of laminated lithium secondary battery

-First embodiment-
A secondary cylindrical lithium secondary cell 10 (hereinafter also referred to as a cell 10) constituting the lithium secondary battery device of this embodiment is shown in FIG. The model 18650 type was used. The unit cell 10 is wound in a state in which the positive electrode 5 and the negative electrode 8 and the separator 7 for electrically insulating the positive electrode 5 and the negative electrode 8 are sandwiched between the two electrodes and placed in the battery container 6. It is produced by injecting and sealing a functional electrolyte. The positive electrode 5 is electrically connected to the positive electrode terminal 4, and the negative electrode 8 is electrically connected to the negative electrode terminal 9, and the cell 10 is charged and discharged via the positive electrode terminal 4 and the negative electrode terminal 9.

  The positive electrode 5 can be produced by applying a paste obtained by kneading a positive electrode active material, a conductive agent, a binder, and an organic solvent to a current collector. As the positive electrode active material, a material capable of adsorbing and releasing lithium ions is used, and examples thereof include Ni-based, Co-based, and Mn-based active materials. As the conductive agent, a carbon-based material such as acetylene black or ketjen black is used. For example, polyvinylidene fluoride can be used as the binder. N-methyl-2-pyrrolidone can be used as the organic solvent. For the current collector for the positive electrode, an aluminum foil which is a conductive metal can be used. The negative electrode 8 can be produced by applying a paste obtained by kneading a negative electrode active material, a conductive agent, a binder, and an organic solvent to a current collector. As the negative electrode active material, for example, graphite, carbon fiber, or the like can be used as a material that can insert and desorb lithium ions. The same material as the positive electrode can be used for the conductive agent, the binder, and the organic solvent. For the current collector, for example, a copper foil can be used as a conductive material. As the electrolyte solution, for example, lithium hexafluorophosphate can be used as a water-insoluble electrolyte solution obtained by dissolving an electrolyte salt in an organic solvent.

  As the separator 7, the standard shutdown separator 7a shown in FIG. 2 (hereinafter also referred to as separator 7a) or the low-temperature shutdown separator 7b shown in FIG. 3 (hereinafter also referred to as separator 7b) was used. As will be described later, the shutdown temperature of the low temperature shutdown separator 7b is set lower than the shutdown temperature of the standard shutdown separator 7a.

  FIG. 2 is a diagram schematically showing a cross section of the standard shutdown separator 7a. The standard shutdown separator 7a is obtained by coating the heat-resistant material layer 1 on one side of the microporous membrane 2. The thickness of the microporous membrane 2 of this embodiment is 16 μm. The heat-resistant material layer 1 is formed by applying a solution obtained by adding a surfactant and a binder to a boehmite dispersion on the surface of the microporous film 2 and then drying it. The thickness of the heat-resistant material layer 1 is 5 μm. The solvent used in the dispersion is not limited as long as a heat-resistant material such as water or alcohol can be dispersed.

  As the microporous film 2, a three-layer structure (not shown) having a polyethylene film sandwiched between polypropylene films was used. Each of the polyethylene film and the polypropylene film constituting the microporous film 2 has a hole for movement of Li ions. The temperature at which the hole is closed, that is, the shutdown temperature is 125 to 140 ° C. for the polyethylene film and 160 to 170 ° C. for the polypropylene film. Thus, the member used for the microporous membrane 2 is selected with a shutdown temperature of 100 ° C. or higher in consideration of the general usage situation of the unit cell 10 that is used at 100 ° C. or lower. This is because if a temperature of 100 ° C. or lower is selected, the battery may be shut down under normal battery use conditions.

  Further, each of the polyethylene film and the polypropylene film constituting the microporous film 2 is subjected to uniaxial stretching or biaxial stretching at the time of production in order to improve mechanical strength. Due to the above stretching, strain remains in each of the polyethylene film and the polypropylene film. When each film is used alone, this distortion is caused at a high temperature and heat shrinkage is likely to occur. The temperature at which the thermal shrinkage of the polyethylene film is higher than the shutdown temperature of the polyethylene film, but is in the vicinity. Similarly, the temperature at which the thermal contraction of the polypropylene film is higher than the shutdown temperature of the polypropylene film, but is in the vicinity.

  When this heat shrinkage proceeds to some extent, it may break. When the film breaks, a short circuit between the positive electrode and the negative electrode occurs, which may cause a thermal runaway. Therefore, in the microporous film 2 of the present embodiment, the polyethylene film is sandwiched between polypropylene films so that the film is not easily broken even if the shutdown temperature of the polyethylene film is slightly exceeded. Furthermore, since the separator 7 is provided with the heat-resistant material layer 1, the heat-resistant material layer 1 can reinforce the microporous membrane 2 and further prevent the microporous membrane 2 from being broken. The heat-resistant material layer 1 can prevent thermal shrinkage even when the temperature rises higher than the shutdown temperature of the polypropylene film.

  FIG. 3 is a schematic diagram of the low-temperature shutdown separator 7b. The low temperature shutdown separator 7b is formed by coating the same heat-resistant material layer 1 as that of the standard shutdown separator 7a on one side of the microporous membrane 2 and the low melting point material layer 3 on the opposite side. That is, the low temperature shutdown separator 7b has a configuration in which the low melting point material layer 3 is further provided in addition to the configuration of the standard shutdown separator 7a.

  The low melting point material used for the low melting point material layer 3 is selected for the following reason. The normal battery operating temperature is often 100 ° C. or lower. Furthermore, since the significance of the low melting point material layer 3 is to lower the shutdown temperature of the separator, the low melting point material of the low melting point material layer 3 is the lowest shutdown temperature among those constituting the microporous membrane 2 of the present invention. It is required to melt at a temperature lower than the shutdown temperature (125 to 140 ° C.) of the polyethylene film to close the pores of the microporous film 2. From the above, the low melting point material of the low melting point material layer 3 is selected to have a melting point of 100 to 125 ° C. In particular, it is preferable to set the shutdown temperature to 100 to 115 ° C. in order to provide a sufficient difference from the shutdown temperature with the standard shutdown separator 7a and improve the safety when the module temperature rises. In addition, when the lithium secondary battery device is operated, the temperature difference in the lithium secondary battery device is too large, which may make the operation unstable. Therefore, it is preferable to design the lithium secondary battery device so that the temperature difference is 5 to 40 ° C. Accordingly, the difference in shutdown temperature between the low temperature shutdown separator 7b and the standard shutdown separator 7a is preferably 5 to 40 ° C. in accordance with the design temperature of the lithium secondary battery device.

  Since the manufacturing method of the microporous film 2 and the heat-resistant material layer 1 in the low temperature shutdown separator 7b is the same as that of the standard shutdown separator 7a, the description is omitted and the manufacturing method of the low melting point material layer 3 will be described. A surfactant is added to an aqueous solvent suspension of polyolefin containing polyethylene by adding 0.6% by volume of the surfactant to the solvent volume and 2% by weight of the binder based on the weight of the polyethylene. After adjusting the concentration to a 30% by mass solution (including a surfactant), it is applied to the surface of the microporous membrane 2 opposite to the surface on which the heat-resistant material layer 1 is formed, and dried. A melting point material layer 3 was formed. The film thickness of the low melting point material layer 3 was 9 μm. The solvent used for the suspension is not limited as long as a low melting point material such as water or alcohol can be dispersed.

  When the low melting point material is formed by coating, the weight ratio in the solution is 6% by mass or more of the low melting point material, the surfactant is 0.05% by volume or more with respect to the solvent, and the binder is 0% with respect to the low melting point material. It is preferable to form a film under a condition of 5% by mass or more. When the low melting point material is less than 7% by mass, the weight of the low melting point material per unit area decreases, and the shutdown performance when melted becomes insufficient. When the surfactant is less than 0.05% by volume, the low melting point material is not sufficiently dispersed, and the compatibility with the microporous film 2 is poor, so that the low melting point material cannot be uniformly applied. When the binder is less than 0.5% by mass, the low melting point material and the microporous membrane 2 are not sufficiently bound, and the low melting point material peels off from the microporous membrane 2 after drying.

  Other methods for providing the heat-resistant material layer 1 and the low melting point material layer 3 on the microporous film 2 include a spray method and a CVD method. The coating method is simple because it is a method for obtaining a uniform film at low cost.

  As the binder, EVA (with a structural unit derived from vinyl acetate of 20 to 35 mol%), ethylene-acrylic acid copolymer such as ethylene-ethyl acrylate copolymer (EEA), fluorine-based rubber, styrene butadiene Rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), polyethylene oxide (PEO), poly-N-vinylacetamide (PNVA) Butyl acrylate-acrylic acid copolymer, cross-linked acrylic resin, polyurethane, epoxy resin and the like can be used.

  The air permeability and thermal contraction rate of the low-temperature shutdown separator 7b were evaluated. The air permeability was 330 s / 100 cc at room temperature, but increased to 110 s / 100 cc at 110 ° C. Moreover, the heat shrinkage rate at a temperature of 150 ° C. was 3%, which was within the target of 10%. From the above evaluation, when the low-temperature shutdown separator 7b in which the heat-resistant material layer 1 and the low melting point material layer 3 are provided on the microporous film 2 is overheated, the short circuit between the positive electrode 5 and the negative electrode 8 due to thermal shrinkage can be prevented and 110 ° C. Confirmed that it is possible to shut down nearby. The target of the heat shrinkage rate is selected as a value that does not cause a short circuit between the positive electrode 5 and the negative electrode 8 during heat shrinkage in consideration of the following circumstances and the dimensions of the positive electrode, the negative electrode, and the separator. The separator is thermally shrunk at a high temperature, but if the shrinkage rate is increased, the insulation between the positive electrode and the negative electrode may be broken and a short circuit may occur. Since short circuiting under high temperature conditions is very dangerous, it is necessary to take measures such as increasing the area of the separator relative to the electrode. The thermal contraction rate of the separator is preferably 10% or less at 150 ° C., and particularly preferably 8% or less.

  FIG. 4 is a diagram showing an outline of a small-scale cylindrical lithium secondary battery device 20 (hereinafter also referred to as battery device 20) configured using the single battery 10 shown in FIG. In addition, although not shown in the drawing, a packing of these unit cells 10 is a general battery device 20. A battery device of this scale is generally called an assembled battery. The number of batteries is up to about several tens, and the use includes electronic equipment, power tools, and in-vehicle use. The battery device 20 is configured using 25 unit cells 10. Among them, nine of the central portions of the battery device 20 that are relatively hot due to charging / discharging shown by the dotted frame in FIG. 4 are standard cell separators 10a (hereinafter, Unit cell 10a). On the other hand, 16 of the outer peripheral portions that are relatively low in temperature are single cells 10b (hereinafter also referred to as single cells 10b) using the low temperature shutdown separator 7b. The configurations other than the separators of the standard shutdown separator-applied unit cell 10a and the low-temperature shutdown separator-applied unit cell 10b were the same, the positive electrode active material of the positive electrode 5 was an Mn-based material, and the negative electrode active material of the negative electrode 8 was a graphite-based material. The battery capacity was 1.25 Ah. When the temperatures of the two types of batteries were examined under the above conditions, the average temperature of the standard shutdown separator-applied cell 10a when the battery device 20 was charged was 10 compared to the average temperature of the low-temperature shutdown separator-applied cell 10b. It was about 20 ° C higher.

  In order to confirm the safety in overcharging of the battery apparatus 20 of FIG. 4, the overcharge characteristic was evaluated. Charging was further continued from the state where the battery device 20 was fully charged (SOC 100%), and characteristics of voltage, current, and battery temperature were confirmed. The test conditions were a charge rate of 2C, a constant current constant voltage (CCCV) mode, and an upper limit voltage of 8.4V.

  When the battery device 20 is overcharged at a constant current of 2.5 A, the temperature of each unit cell 10 starts to rise, and the unit cell 10 a applied with the standard shutdown separator at the center and the low temperature shutdown at the outer periphery in the vicinity of SOC 200% Both the separator-applied cell 10b were shut down. When the separator 7 of each unit cell 10 is shut down, the resistance (DCR) of the battery device 20 increases and the battery voltage rises to the upper limit value. Then, the charging mode is switched from constant current (CC) to constant voltage (CV). The current value gradually decreased. As the current value decreased, the heat generation stopped, the battery temperature gradually decreased, and each unit cell 10 of the battery device 20 safely stopped.

  In the constant current constant voltage (CCCV) mode, the upper limit voltage is 8.4 V, and the overcharge characteristics in each condition where the charge rate is 5 C (6.25 A) or 8 C (10 A) are confirmed. Each unit cell 10 of the battery device 20 stopped safely.

  The secondary battery device according to the first embodiment described above includes a positive electrode 14, a negative electrode 15, separators 7 a and 7 b provided with a single layer or a plurality of layers of microporous membranes 2, and an electrolyte. A plurality of secondary unit cells 10 are arranged at the center, and a plurality of lithium secondary cells 10 are further arranged on the outer periphery surrounding the lithium secondary unit cell 10 arranged at the center. The shutdown temperature of the separator (first separator) of the lithium secondary cell 10 disposed in the center is higher than the shutdown temperature of the separator (second separator) of the lithium secondary cell 10 disposed in the outer periphery.

  In other words, in the battery device 20 of the present embodiment, the standard shutdown separator-applied cell 10a is disposed in the central portion where the temperature tends to be high, and the low-temperature shutdown separator-applied cell 10b is disposed in the outer peripheral portion that is relatively low in temperature. As a result, when the temperature of the battery device 20 rises due to overcharging, even the battery device 20 having a temperature distribution larger than that of the single battery can be shut down sufficiently, and the charging current is cut off in a short time, and the battery temperature is reduced. The rise can be prevented and the single cells 10a and 10b of the battery device 20 can be safely stopped. Further, since the standard shutdown separator 7a and the low-temperature shutdown separator 7b are provided with the heat-resistant material layer 1, even if the battery temperature reaches a temperature at which the microporous membrane 2 undergoes thermal shrinkage, it does not thermally shrink. Can be.

  In the present embodiment, the microporous membrane 2 has a three-layer structure composed of polyethylene and polypropylene, but may be a single-layer structure of polypropylene. Since the heat-resistant material layer 1 is provided in the separator 7 of the present invention, the membrane does not break even if the microporous film 2 is a single layer of polypropylene. The same applies to the following embodiments and modifications.

  In the present embodiment, polyolefin containing polyethylene is used as the material of the low melting point material layer 3, but polyethylene can be used alone or a synthetic wax agent can be used. The same applies to the following embodiments and modifications.

  Although boehmite was used for the heat-resistant material layer 1 of the present embodiment, any one of Al, Al oxide (alumina), aluminum hydroxide, boehmite, Si, Si oxide, magnesium oxide, magnesium hydroxide or 2 Mixtures of more than one type may be used.

  In the present embodiment, the heat-resistant material layer 1 is provided only on one side of the microporous membrane 2, but it can also be provided on both sides of the microporous membrane 2. In this embodiment, the low melting point material layer 3 is also provided only on one side of the microporous membrane 2, but it can also be provided on both sides of the microporous membrane 2. The same applies to the following embodiments and modifications.

  In this embodiment, a cylindrical lithium secondary battery (18650 type) is used as a single battery, but other types of cylindrical lithium secondary batteries have the same effects. In addition, a laminated lithium secondary battery or the like may be used as the single battery.

-Modification 1 of the first embodiment-
A low-temperature shutdown separator 7c shown in FIG. 5 can be used instead of the low-temperature shutdown separator 7b used in the low-temperature shutdown separator-applied cell 10b of the battery device 20 of the first embodiment. The low-temperature shutdown separator 7c is obtained by providing the heat-resistant material layer 1 on the microporous film 2 and the low melting point material layer 3 thereon. When the shutdown temperature of the low temperature shutdown separator 7c is reached, the low melting point material of the low melting point material layer 3 of the low temperature shutdown separator 7c melts, passes through the heat resistant material layer 1, and closes the pores of the microporous membrane 2. Since the low-temperature shutdown separator 7c has the above-described effects, the shutdown effect similar to that of the low-temperature shutdown separator 7b of the low-temperature shutdown separator application cell 10b of the battery device 20 of the first embodiment is achieved. Therefore, the battery device 20 of the present modification also has the same operational effects as the first embodiment. Furthermore, since the heat-resistant material layer 1 and the low-melting-point material layer 3 are formed on one surface of the microporous film 2, the application process can be simplified.

-Modification 2 of the first embodiment-
A low-temperature shutdown separator 7d shown in FIG. 6 can be used instead of the low-temperature shutdown separator 7b used in the low-temperature shutdown separator-applied cell 10b of the battery device 20 of the first embodiment. In the low-temperature shutdown separator 7d, a mixed layer 13 is provided by applying a mixture of a heat-resistant material and a low-melting-point material on one surface of the microporous membrane 2, and the heat-resistant material layer 1 is provided on the other surface of the microporous membrane 2. It was. When the shutdown temperature of the low temperature shutdown separator 7d is reached, the low melting point material contained in the mixed layer 13 melts and closes the pores of the microporous membrane 2. Since the low-temperature shutdown separator 7d has the above-described effects, the shutdown effect similar to that of the low-temperature shutdown separator 7b of the low-temperature shutdown separator application cell 10b of the battery device 20 of the first embodiment is achieved. Therefore, the battery device 20 of the present modification also has the same operational effects as the first embodiment. In addition, the work process can be simplified and the production cost can be reduced as compared with the method of laminating different material layers.

  The standard shutdown separator 7a and the low-temperature shutdown separators 7b, 7c, and 7d described in the first embodiment and the modifications thereof are provided with the heat-resistant material layer 1, but the heat-resistant material layer 1 may not be provided. is there. The standard shutdown separator has a configuration of only the microporous membrane 2, and the low temperature shutdown separator has a configuration in which the low melting point material layer 3 is provided on the microporous membrane 2, but such a separator can also be manufactured. .

-Second embodiment-
FIG. 7 is a schematic diagram of a large-scale lithium secondary battery device 40 (hereinafter also referred to as a battery device 40). This is a battery device combined on a larger scale than the battery device 20 shown in the first embodiment, and is generally called a battery module. As for the scale, the number of batteries is about several hundreds, and the use is for building backup power source, mobile phone base station, wind power storage device and the like. As the battery type, a cylindrical lithium secondary cell 10 or a laminated lithium secondary battery can be applied.

  In the battery device 40, a standard shutdown separator application battery unit 30 composed of a battery to which the standard shutdown separator 7 a is applied is disposed in the central portion where the temperature tends to be high, and the low temperature shutdown separator 7 b is applied to a relatively low temperature outer peripheral portion. The battery unit 31 is applied with a low-temperature shutdown separator constituted by a battery, and by performing a shutdown corresponding to the temperature distribution of the battery device 40 at the time of overcharge, the first embodiment, the second embodiment and Similarly, the battery device 40 can be safely stopped in a short time during overcharging.

  In this embodiment, the low temperature shutdown separators 7c and 7d shown in the first and second modifications of the first embodiment can be applied instead of the low temperature shutdown separator 7b.

  Moreover, although the heat-resistant material layer 1 is provided in the standard shutdown separator 7a and the low-temperature shutdown separators 7b, 7c, and 7d, the heat-resistant material layer 1 can be omitted. In that case, the standard shutdown separator has a configuration of only the microporous membrane 2, and the low-temperature shutdown separator has a configuration in which the low melting point material layer 3 is provided on the microporous membrane 2, but such a separator may be manufactured. Is possible.

-Third embodiment-
FIG. 8 shows an internal structure of a laminated lithium secondary battery 21 (hereinafter referred to as battery 21) using a laminated battery. Although the battery 21 is a single battery, since it has a plurality of electrode groups, that is, battery constituent bodies, a temperature distribution is generated from the center to the outer periphery of the electrode group. The battery 21 was composed of a positive electrode 14, a negative electrode 15, a standard shutdown separator 7a, and a low temperature shutdown separator 7b. The configurations of the standard shutdown separator 7a and the low temperature shutdown separator 7b are the same as those in the first embodiment. A standard shutdown separator 7a was used in the central portion having a relatively high temperature, and a low temperature shutdown separator 7b was used in the outer peripheral portion having a low temperature.

  In the present embodiment, the thickness of the microporous film 2 is 16 μm, the thickness of the heat-resistant material layer 1 is 3 μm, and the thickness of the low melting point material layer 3 is 4 μm. When the characteristics of the low-temperature shutdown separator 7b in the present embodiment under the above conditions were evaluated, the heat shrinkage rate was 8% at 150 ° C., the air permeability at room temperature was 414 s / 100 cc, and the air permeability at 110 ° C. was a low melting point. Measurement was not possible because the pores of the separator were closed due to melting of the material. It was confirmed that the low-temperature shutdown separator 7b used in the second embodiment can achieve both the suppression of thermal contraction that does not cause an electrode short circuit and the shutdown effect at the time of temperature increase.

  The characteristics at the time of overcharging of the battery 21 were confirmed by an overcharge test. As in the first embodiment, the positive electrode active material was Mn-based material, the negative electrode active material was graphite-based material, and the battery capacity was 1.25 Ah. The test conditions were a constant current and constant voltage (CCCV) mode, an upper limit voltage of 8.4 V, and a charge rate of 2C and 5C. The overcharge characteristic of the battery 21 of the present embodiment is similar to the battery device 20 of the first embodiment. When the separators 7a and 7b having different shutdown temperatures are shut down according to the temperature distribution, the battery resistance increases and the current is increased. The battery 21 stopped safely.

  In the battery 21 of the present embodiment as well, as in the first embodiment, the standard shutdown 7a is disposed in the central portion where the temperature tends to be high, and the low-temperature shutdown separator 7b is disposed in the outer peripheral portion where the temperature is relatively low. As a result, when the temperature of the battery 21 rises due to overcharging, shutdown according to the temperature distribution of the battery 21 is possible, the charging current is cut off in a short time, the battery temperature rise is prevented, and the entire battery 21 is It can be stopped safely. Since the standard shutdown separator 7a and the low temperature shutdown separator 7b are provided with the heat-resistant material layer 1, even if the battery temperature reaches the temperature at which the microporous membrane 2 undergoes thermal contraction, the standard shutdown separator 7a and the low-temperature shutdown separator 7b do not heat shrink.

  In this embodiment, the low temperature shutdown separators 7c and 7d shown in the first and second modifications of the first embodiment can be applied instead of the low temperature shutdown separator 7b.

  Moreover, although the heat-resistant material layer 1 is provided in the standard shutdown separator 7a and the low-temperature shutdown separators 7b, 7c, and 7d, the heat-resistant material layer 1 can be omitted. In that case, the standard shutdown separator has a configuration of only the microporous membrane 2, and the low-temperature shutdown separator has a configuration in which the low melting point material layer 3 is provided on the microporous membrane 2, but such a separator may be manufactured. Is possible.

  Note that a laminated battery including a standard shutdown separator 7a (hereinafter referred to as separator 7a in this paragraph) and a low-temperature shutdown separator 7b (hereinafter referred to as separator 7b in this paragraph) is used for the lithium secondary battery device of the present invention. It is also possible. As a specific example, a laminated battery using only the separator 7a in the standard shutdown separator-applied battery unit 30 (hereinafter, unit 30 in FIG. 7), a low-temperature shutdown separator applied battery unit 31 (hereinafter, unit in the present paragraph). It is also possible to use the laminated battery 21 of the present embodiment (hereinafter referred to as the battery 21 in this paragraph) for 31). By doing so, all the separators of the batteries constituting the unit 30 and the separators 7b of the batteries constituting the unit 31 are shut down almost simultaneously. Although it is conceivable that the battery separator 7a constituting the unit 31 does not shut down, the power generation performance is sufficiently suppressed in the above-described shutdown situation, and it is possible to sufficiently suppress thermal runaway. Alternatively, a laminated battery in which the battery 21 is used for the unit 30 and some of the separators 7a of the battery 21 are replaced with the separator 7b and more separators 7b are arranged than the battery 21 can be used for the unit 31. By doing so, the separator 7b of the battery 21 constituting the unit 30 is shut down first, and then the separator 7a of the battery 21 constituting the unit 30 and the battery separator 7b constituting the unit 31 are shut down almost simultaneously. Even in this case, it is conceivable that the battery separator 7a constituting the unit 31 does not shut down. However, the power generation performance is sufficiently suppressed in the above-described shutdown situation, and it is sufficiently possible to suppress thermal runaway. .

  In the above embodiment and modification, the battery device is configured by a battery using one of two types of separators, that is, a standard shutdown separator and a low temperature shutdown separator. As a more preferable form, by changing the material and application method of the low melting point material layer 3, the number of types of low temperature shutdown separators is increased, and any of the three or more types of separators having different shutdown temperatures including the standard shutdown separator is used. It is also possible to configure a battery device with a battery using these. By doing in this way, it can respond more finely with respect to the temperature distribution in a battery apparatus, and it becomes possible to perform the shutdown of the whole battery apparatus in a short time.

The lithium secondary battery device according to the above-described embodiments and modifications has the following operational effects.
(1) The lithium secondary battery device of the present invention has a lithium secondary battery unit including a positive electrode, a negative electrode, a separator provided with a single layer or a plurality of layers of microporous films, and an electrolytic solution at the center. A plurality of lithium secondary cells are further arranged on the outer peripheral portion surrounding the lithium secondary cells arranged in the central portion. The shutdown temperature of the lithium secondary cell separator (hereinafter referred to as the first separator) disposed in the central portion is lower than the shutdown temperature of the lithium secondary cell separator (hereinafter referred to as the second separator) disposed in the outer peripheral portion. It is high. That is, the first separator is a standard shutdown separator, and the second separator is a low temperature shutdown separator that shuts down at a lower temperature than the standard shutdown separator.
Thereby, the separator can be shut down according to the temperature distribution of the battery device. Therefore, when the battery device is overheated due to overcharging or the like and the battery temperature rises, the charging current can be cut off in a short time in the entire battery device, and the battery device can be safely stopped without causing an excessive increase in battery temperature.

(2) The separator of the lithium single secondary battery arranged on the outer peripheral portion of the lithium secondary battery device of the present invention may be provided with a low melting point material layer on the low temperature shutdown separator. By providing the low melting point material layer only in the low temperature shutdown separator, a shutdown temperature lower than the shutdown temperature of the microporous membrane can be provided.

(3) In the lithium secondary battery device of the present invention, it is preferable to further set the shutdown temperature range of the separator to 100 to 160 ° C. By setting the lower limit of the shutdown temperature range to 100 ° C., normal use of the battery device can be prevented from being hindered. In addition, by setting the upper limit of the shutdown temperature range to 160 ° C., it is possible to achieve both suppression of thermal shrinkage of the microporous film and shutdown.

(4) In the lithium secondary battery device of the present invention, the shutdown temperature that the standard shutdown separator can have is 125 to 140 ° C., the shutdown temperature that the low-temperature shutdown separator can have 100 to 125, and the standard shutdown separator The difference between the shutdown temperature and the shutdown temperature of the low temperature shutdown separator is preferably set to 5 to 40 ° C. Considering the actual temperature condition of the battery device, the respective shutdown temperatures of the two types of separators are set more finely, so that the entire battery device can be safely shut down in a shorter time.

(5) In the lithium secondary battery device of the present invention, it is preferable to further provide a heat-resistant material layer on the separator. By providing the heat-resistant material layer, the shape of the microporous membrane is stabilized, and even if the battery temperature becomes equal to or higher than the shutdown temperature of the microporous membrane, the microporous membrane can suppress thermal shrinkage.

(6) In the lithium secondary battery device of the present invention, it is preferable that the thermal shrinkage rate of the separator at 150 ° C. is set within 8%. Thereby, the short circuit of the positive electrode and the negative electrode due to the thermal contraction of the separator can be prevented, and the safety of the battery can be improved.

(7) In the lithium secondary battery device of the present invention, the low-melting-point material layer is formed using a low-melting-point material made of any one kind or a mixture of two or more kinds of polyethylene, synthetic wax, and polyolefin resin. Is preferred. Thereby, it melts at a temperature lower than that of the microporous membrane and the pores of the microporous membrane can be blocked, the movement of Li ions is blocked, the rise in battery temperature is stopped, and the battery can be safely stopped.

(8) In the lithium secondary battery device of the present invention, the low melting point material layer may be formed using a solution containing a surfactant, a binder, and a low melting point material that has been emulsified in water. preferable. As a result, the low-melting-point material can easily become compatible with the separator, and a uniform low-melting-point material layer can be formed on the surface.

(9) In the lithium secondary battery device of the present invention, the weight ratio of the low melting point material in the solution is 6% by mass or more, and the volume ratio of the surfactant in the solution is 0.05% by volume with respect to the solvent. The weight ratio of the binder in the solution is preferably 0.5% by mass or more with respect to the low melting point material. Thereby, the amount of the low melting point material per unit area necessary for shutdown can be ensured, and a more uniform low melting point material layer can be obtained.

(10) In the lithium secondary battery device of the present invention, the heat-resistant material layer is any one of Al, Al oxide (alumina), aluminum hydroxide, boehmite, Si, Si oxide, magnesium oxide, and magnesium hydroxide. One type or a mixture of two or more types can be used. As a result, even if the battery temperature exceeds the upper melting limit temperature of the microporous membrane, the heat-resistant material layer does not deteriorate and the shape is maintained, so that the microporous membrane of the separator can suppress thermal shrinkage and prevent a short circuit between the positive electrode and the negative electrode it can.

(11) In the lithium secondary battery device of the present invention, it is preferable that the heat-resistant material layer and the low melting point material layer are further provided by being applied to a microporous film. Thereby, a uniform layer can be provided more simply than other methods (for example, a spray method etc.).

  It is also possible to combine one or more of the above-described embodiments and modifications. It is also possible to combine modifications.

  The above description is merely an example, and the present invention is not limited to the above embodiment.

DESCRIPTION OF SYMBOLS 1 ... Heat-resistant material layer, 2 ... Microporous film, 3 ... Low melting-point material layer, 4 ... Positive electrode terminal, 5 ... Positive electrode,
6 ... Battery container, 7 ... Separator, 7a ... Standard shutdown separator,
7b, 7c, 7d ... low temperature shutdown separator, 8 ... negative electrode, 9 ... negative electrode terminal,
10 ... lithium secondary cell, 10a ... standard shutdown separator battery,
10b ... Low temperature shutdown separator application battery, 13 ... Mixed layer,
14 ... Positive electrode, 15 ... Negative electrode, 20 ... Small-scale lithium secondary battery device,
21 ... Lithium secondary cell 30 ... Standard shutdown separator battery unit,
31 ... Low-temperature shutdown separator application battery unit,
40. Large-scale lithium secondary battery device

Claims (11)

A plurality of lithium secondary cells each having a positive electrode, a negative electrode, a separator provided with a single layer or a plurality of layers of microporous membranes, and an electrolytic solution are disposed in the central portion, and the lithium secondary cells disposed in the central portion are disposed. In the lithium secondary battery device in which a plurality of the lithium secondary cells are further arranged on the outer periphery surrounding the secondary cell,
The shutdown temperature of the separator (hereinafter referred to as a first separator) of the lithium secondary cell disposed in the central portion is the same as the separator of the lithium secondary cell (hereinafter referred to as a second separator) disposed in the outer peripheral portion. The lithium secondary battery device is characterized by being higher than the shutdown temperature. The lithium secondary battery device according to claim 1,
The lithium secondary battery device, wherein the second separator includes a low melting point material layer. The lithium secondary battery device according to claim 1 or 2,
The separator has a shutdown temperature range of 100 to 160 ° C. In the lithium secondary battery device according to any one of claims 1 to 3,
The shutdown temperature of the first separator is 125 to 140 ° C.,
The shutdown temperature of the second separator is 100 to 125 ° C.
The lithium secondary battery device, wherein a difference between a shutdown temperature of the first separator and a shutdown temperature of the second separator is 5 to 40 ° C. In the lithium secondary battery device according to any one of claims 1 to 4,
The separator is further provided with a heat-resistant material layer, and the lithium secondary battery device. The lithium secondary battery device according to claim 5,
The lithium secondary battery device, wherein the thermal shrinkage rate of the separator at 150 ° C. is within 8%. In the lithium secondary battery device according to any one of claims 2 to 6,
The low-melting-point material layer is formed using a low-melting-point material made of any one kind or a mixture of two or more kinds of polyethylene, synthetic wax, and polyolefin resin. The lithium secondary battery device according to claim 7,
The low-melting-point material layer is formed using a surfactant, a binder, and a solution containing the low-melting-point material that has been made into an aqueous emulsion. The lithium secondary battery device according to claim 8,
The weight ratio of the low melting point material in the solution is 6 mass% or more,
The volume ratio of the surfactant in the solution is 0.05% by volume or more with respect to the solvent,
The lithium secondary battery device, wherein a weight ratio of the binder in the solution is 0.5% by mass or more based on a low melting point material. The lithium secondary battery device according to claim 5 or 6,
The heat-resistant material layer is formed using any one kind or a mixture of two or more kinds of Al, Al oxide (alumina), aluminum hydroxide, boehmite, Si, Si oxide, magnesium oxide, and magnesium hydroxide. A lithium secondary battery device. The lithium secondary battery device according to any one of claims 5 to 10,
The lithium secondary battery device, wherein the heat-resistant material layer and the low-melting-point material layer are provided by being applied to the microporous film.

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