Lithium-ion battery module

Abstract

The present invention provides a lithium-ion battery module that can be made smaller by not incorporating a BMU, and that ensures safety during charging and overcharging. [Solution] The lithium-ion battery module of the present invention includes a plurality of electrically connected lithium-ion secondary batteries. The lithium-ion battery module does not have a battery monitoring unit, and is configured so that when the potential of the positive electrode of some of the lithium-ion secondary batteries reaches a predetermined potential during charging, a current of 100 mA or more flows to the some of the lithium-ion secondary batteries without increasing the charge level, and the module maintains a current-carrying state for a certain period of time even if an overvoltage or overcurrent is applied and the battery loses its function.

Description

[Technical Field]

[0001] The present invention relates to a lithium-ion battery module. [Background technology]

[0002] Mobile vehicles such as automobiles, motorcycles, and hybrid drones are equipped with a generator that generates alternating current by using the rotation of an engine, a rectifier that converts alternating current into direct current, and a regulator that converts excess power into heat and dissipates it to supply the battery with regulated voltage direct current (approximately 14V to 14.5V). Also, batteries for mobile devices that include lithium-ion batteries are known (see, for example, Patent Document 1). Lithium-ion batteries have advantages such as being compact due to their high energy density, being lightweight, and having excellent life characteristics. However, lithium-ion batteries have the disadvantage that, when overcharged, gas is generated inside the battery, causing the battery case to expand. In the worst case scenario, the lithium-ion battery may explode or catch fire. For this reason, batteries for mobile devices that include lithium-ion batteries are usually equipped with a battery monitoring unit (BMU). The BMU has a bypass circuit connected to the positive and negative terminals of the lithium-ion battery to prevent the lithium-ion battery from becoming overcharged. Furthermore, the regulator installed in the mobile device converts excess power into heat and dissipates it, so heat dissipation efficiency decreases when the temperature becomes too high, which can lead to failure (puncture). If the regulator fails, high voltage may be supplied to the battery that includes the lithium-ion battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-023258 Summary of the Invention [Problem to be solved by the invention]

[0004] If a high voltage is applied to the battery due to a regulator or charger failure, the BMU will no longer be able to prevent the lithium-ion battery from overcharging, and the BMU will cut off power to the battery. This will prevent power from being supplied from the battery, causing the power supply to suddenly lose power and creating a dangerous situation. The present invention provides a lithium-ion battery module that can be made smaller by not incorporating a BMU, and that ensures safety during charging and overcharging. [Means for solving the problem]

[0005] The present invention provides a lithium-ion battery module comprising a plurality of electrically connected lithium-ion secondary batteries, the lithium-ion battery module having no battery monitoring unit, and configured so that when the potential of the positive electrode of some of the plurality of lithium-ion secondary batteries reaches a predetermined potential during charging, a current of 100 mA or more that does not increase the charge amount flows to some of the lithium-ion secondary batteries, and the lithium-ion battery module maintains a powered state for a certain period of time even when an overvoltage or overcurrent is applied and the battery function is lost. [Effects of the Invention]

[0006] The lithium ion battery module of the present invention does not include a BMU, and therefore can be made smaller and the manufacturing costs can be reduced. The lithium-ion battery module of the present invention does not immediately become non-powered even when an overvoltage or overcurrent is applied and the battery loses its function, but rather maintains a powered state for a certain period of time, thereby preventing the power supply target from suddenly losing power and becoming in a dangerous state. [Brief explanation of the drawings]

[0007] [Figure 1]1 is a schematic perspective view of a lithium-ion battery module according to an embodiment of the present invention; [Figure 2] 1 is an exploded view of a lithium ion battery module according to an embodiment of the present invention; [Figure 3] FIG. 2 is a schematic top view of four lithium ion secondary batteries included in the lithium ion battery module of one embodiment of the present invention. [Figure 4] 1 is a schematic perspective view of a lithium ion secondary battery included in a lithium ion battery module according to one embodiment of the present invention. [Figure 5] 5 is a schematic cross-sectional view of the lithium ion secondary battery taken along dashed line AA in FIG. 4. [Figure 6] 4. FIG. 5(a) is a schematic cross-sectional view of the lithium ion secondary battery taken along the dashed dotted line BB in FIG. 4, and FIG. 5(b) is a schematic cross-sectional view of the lithium ion secondary battery taken along the dashed dotted line CC in FIG. [Figure 7] 6 is a partial cross-sectional view of the lithium ion secondary battery in an area D surrounded by a dashed line in FIG. 5. [Figure 8] 1 is a schematic cross-sectional view of an exterior body included in a lithium ion secondary battery included in a lithium ion battery module according to one embodiment of the present invention. [Figure 9] FIG. 2 is a schematic partial cross-sectional view of a lithium-ion battery module according to one embodiment of the present invention, showing an inner lid, a cell terminal, a first release valve, a cover member, and a second release valve. [Figure 10] FIG. 1 is a schematic diagram of a fabricated lithium ion secondary battery. [Figure 11] 1 is a graph showing measurement results of an overcharge test. DETAILED DESCRIPTION OF THE INVENTION

[0008] The lithium-ion battery module of the present invention includes a plurality of electrically connected lithium-ion secondary batteries. The lithium-ion battery module does not have a battery monitoring unit, and is configured so that when the potential of the positive electrode of some of the lithium-ion secondary batteries reaches a predetermined potential during charging, a current of 100 mA or more flows to the some of the lithium-ion secondary batteries, preventing the battery from increasing its charge level. The module maintains a current-carrying state for a certain period of time even if an overvoltage or overcurrent is applied and the battery loses its function.

[0009] Preferably, each lithium ion secondary battery is a laminate cell in which an electrode assembly is housed in an exterior body having a seal portion formed by overlapping and joining laminate films, The exterior body has a relief valve for releasing the internal pressure. The non-aqueous electrolyte contained in each lithium ion secondary battery preferably contains a redox shuttle agent having a redox potential higher than the potential of the positive electrode of the lithium ion secondary battery when fully charged. The "potential" described herein may be the "open potential." Preferably, the positive electrode has a structure in which positive electrode active material layers are laminated on both sides of a positive electrode current collector sheet, and the negative electrode has a structure in which negative electrode active material layers are laminated on both sides of a negative electrode current collector sheet, and the total area of ​​multiple surfaces of the positive electrode active material layer and the negative electrode active material layer facing each other with the separator sandwiched therebetween in each lithium ion secondary battery is 200 cm 2 This allows the amount of current that flows due to ion conduction of the redox shuttle agent to be increased.

[0010] The concentration of the redox shuttle agent in the non-aqueous electrolyte contained in each lithium ion secondary battery is preferably 0.5 wt % or less, which allows the discharge current of each lithium ion secondary battery to be increased. Preferably, the exterior body included in each lithium-ion secondary battery is a pouch having a seal formed by overlapping and joining a laminate film in which a metal layer, an outer resin layer, and an inner resin layer are stacked, and has grooves formed in the outer resin layer and the metal layer, the grooves being configured to function as release valves. This allows the first release valve to open when the internal pressure exceeds the release pressure, even if gas is generated inside the battery, and allows the gas to be released to the outside of the battery. This prevents the lithium-ion secondary battery from expanding and damaging the battery case, and also prevents nonaqueous electrolyte leaking from the lithium-ion secondary battery from leaking out of the battery case.

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The configurations shown in the drawings and the following description are merely examples, and the scope of the present invention is not limited to those shown in the drawings and the following description.

[0012] Fig. 1 is a schematic perspective view of a lithium-ion battery module 60 of this embodiment, Fig. 2 is an exploded three-dimensional view of the lithium-ion battery module 60 of this embodiment, Fig. 3 is a schematic top view of four lithium-ion secondary batteries 30a to 30d included in the lithium-ion battery module 60 of this embodiment, and Fig. 4 is a schematic perspective view of a lithium-ion secondary battery 30a included in the lithium-ion battery module of this embodiment. Also, Fig. 5 is a schematic cross-sectional view of the lithium-ion secondary battery 30a taken along dashed line AA in Fig. 4, Fig. 6(a) is a schematic cross-sectional view of the lithium-ion secondary battery 30a taken along dashed line BB in Fig. 4, Fig. 6(b) is a schematic cross-sectional view of the lithium-ion secondary battery 30a taken along dashed line CC in Fig. 4, and Fig. 7 is a partial cross-sectional view of the lithium-ion secondary battery 30a taken within an area D enclosed by a dashed line in Fig. 5.

[0013] The lithium-ion battery module 60 of this embodiment includes a plurality of lithium-ion secondary batteries 30a-30d connected in series. Each of the lithium-ion secondary batteries 30a-30d includes a positive electrode 3, a negative electrode 4, a separator 6 sandwiched between the positive electrode 3 and the negative electrode 4, a non-aqueous electrolyte 12, and an exterior housing that houses the positive electrode 3, the negative electrode 4, the separator 6, and the non-aqueous electrolyte 12. The lithium-ion battery module 60 does not include a battery monitoring unit having a bypass circuit electrically connected to the positive electrode 3 and the negative electrode 4 of each of the lithium-ion secondary batteries 30a-30d. When the potential of the positive electrode 3 of one of the plurality of lithium-ion secondary batteries 30a-30d reaches a predetermined potential during charging of the lithium-ion battery module 60, a current of 100 mA or more and 1800 mA or less flows through the one of the lithium-ion secondary batteries, preventing an increase in the charge level.

[0014] For example, as shown in FIG. 2, a lithium ion battery module 60 includes four lithium ion secondary batteries 30a to 30d, which are connected in series as shown in FIG. The lithium-ion battery module 60 may be a lithium-ion battery module for a mobile object mounted on a mobile object such as an automobile, motorcycle, or hybrid drone, or may be a lithium-ion battery module configured to be charged while the mobile object is moving. The mobile object may include a generator configured to generate AC current using the rotation of an engine or the like, a rectifier, and a regulator configured to supply DC current to the battery. The lithium-ion battery module 60 may also be an engine-starting lithium-ion battery module. The engine-starting lithium-ion battery module is a lithium-ion battery module configured to supply power to rotate a starter motor for starting an engine mounted on an automobile, motorcycle, hybrid drone, or the like. The lithium-ion battery module 60 may be configured without a battery monitoring unit having a bypass circuit electrically connected to the positive electrode 3 and negative electrode 4 of each lithium-ion secondary battery 30a-30d. The lithium-ion battery module 60 maintains a current-carrying state for a certain period of time even when it loses its battery function due to the application of an overvoltage or an overcurrent. An example of a case where the battery function is lost is when the groove serving as the first release valve 15 of the exterior body 13 ruptures. The certain period of time is, for example, 40 seconds or more, preferably 60 seconds or more, and more preferably 75 seconds or more. Furthermore, the current flowing through the lithium-ion battery module 60 may gradually decrease during this certain period.

[0015] The lithium ion secondary batteries 30a to 30d included in the lithium ion battery module 60 include a positive electrode 3 containing a positive electrode active material, a negative electrode 4 containing a negative electrode active material, a separator 6 sandwiched between the positive electrode 3 and the negative electrode 4, a non-aqueous electrolyte 12, and an exterior body 13 that houses the positive electrode 3, the negative electrode 4, the separator 6, and the non-aqueous electrolyte 12. The exterior body 13 can have a first open valve with an opening pressure of 150 kPa or less. The non-aqueous electrolyte 12 can contain a redox shuttle agent. The lithium ion secondary batteries 30a to 30d can have the same configuration except for the direction in which the first conductive plate 9 is bent, the direction in which the second conductive plate 10 is bent, the length of the first conductive plate 9, the length of the second conductive plate 10, and the position of the first open valve 15.

[0016] The number of lithium-ion secondary batteries 30a to 30d included in the lithium-ion battery module 60 is not particularly limited. The lithium-ion secondary batteries 30a to 30d may have, for example, substantially rectangular front and back surfaces, and are stacked so that the front and back surfaces of the batteries 30a to 30d face each other. The lower end of a first side of the substantially rectangular shape is located at the bottom of a battery case 31 that houses the lithium-ion secondary batteries 30a to 30d, and the upper end of a second side opposite the first side of the substantially rectangular shape is located at the opening of the battery case 31. The first side of the batteries 30a to 30d (the end of the third side of the substantially rectangular shape) is the side where the positive electrode current collector sheet 16 extends from the electrode assembly 2 inside the exterior body 13, and the second side (the end of the fourth side opposite the third side of the substantially rectangular shape) is the side where the negative electrode current collector sheet 17 extends from the electrode assembly 2 inside the exterior body 13. The front and back surfaces are parallel to the positive electrode 3 , negative electrode 4 , and separator 6 that constitute the electrode assembly 2 .

[0017] The exterior body 13 is a container that houses the electrode assembly 2 and the non-aqueous electrolyte 12. The material of the exterior body 13 is, for example, a laminate film. For example, the exterior body 13 is a laminate film pouch. FIG. 8 is a schematic cross-sectional view of the laminate film included in the exterior body 13. The laminate film is, for example, formed by laminating an outer resin layer 50 on the outer surface of a metal layer 49 and laminating an inner resin layer 48 on the inner surface of the metal layer 49. Here, the "inside" refers to the interior side of the exterior body 13, and the "outside" refers to the outside of the exterior body 13. The thickness of the laminate film can be, for example, 50 to 200 μm.

[0018] The exterior body 13 can be provided to form an internally sealed space for accommodating the electrode assembly 2 and the nonaqueous electrolyte 12. When the exterior body 13 is made of a laminate film, the lithium-ion secondary batteries 30a to 30d of this embodiment are pouch-type batteries. In this case, the exterior body 13 can have a seal portion 25 formed by overlapping and joining (e.g., welding) a laminate film around its periphery. The seal portion 25 can also include a portion where a laminate film is bonded to both sides of the first conductive plate 9 and a portion where a laminate film is bonded to both sides of the second conductive plate 10. For example, the exterior body 13 can have a structure in which the upper, lower, first side, and second side of two rectangular laminate films are bonded together by the seal portion 25. In this case, the lithium-ion secondary batteries 30a to 30d have the seal portions 25 at the upper end, lower end, first side, and second side. The width of the seal portion 25 at the upper end of each of the lithium-ion secondary batteries 30a to 30d may be narrower than the width of the seal portion 25 at the lower end, the width of the seal portion 25 at the first side, and the width of the seal portion 25 at the second side. This allows the upper portion of the exterior body 13 to be opened preferentially when the internal pressure of the exterior body 13 increases, allowing the gas inside the exterior body 13 to be quickly released to the outside of the exterior body 13. This prevents the exterior body 13 from expanding and cracking the battery case 31. If the battery case 31 cracks, the nonaqueous electrolyte 12 leaking from the lithium-ion secondary batteries 30a to 30d may also leak from the battery case 39, potentially igniting the nonaqueous electrolyte 12.

[0019] In the exterior body 13, the seal portion 25 may be folded from the base of the seal portion 25 at the upper end, first side, second side, or lower end of the lithium-ion secondary batteries 30a to 30d. This increases the volume ratio of the lithium-ion secondary batteries 30a to 30d in the battery case 39, making it possible to reduce the size of the lithium-ion battery module 60. The folded portion can also be fixed with tape or the like.

[0020] The exterior body 13 may have a first open valve 15 with an opening pressure of 150 kPa or less. The first open valve 15 is a valve that opens to discharge gas inside the exterior body 13 to the outside when the pressure inside the exterior body 13 exceeds the opening pressure. The first open valve 15 includes, for example, a groove formed in the outer resin layer 50 and the metal layer 49. The opening pressure of the first open valve 15 can be adjusted by changing the material and thickness of the inner resin layer 48, the material and thickness of the metal layer 49, the depth, width, length, etc. of the groove. The groove may have a depth that reaches the inner resin layer 48. The opening pressure of the first open valve 15 may be 100 kPa or more and 150 kPa or less. The first open valve 15 may be disposed at the upper end of each of the lithium-ion secondary batteries 30a to 30d so as to extend from the first side to the second side. The length of the first open valve 15 can be between one-third and nine-tenths of the length from the edge on the first side of the upper end to the edge on the second side. This allows gas inside the exterior body 13 to be efficiently discharged to the outside of the battery. The first open valve 15 can be provided in a portion of the upper end of the lithium-ion secondary batteries 30a to 30d where the seal portion 25 is not disposed. The first open valve 15 can be disposed adjacent to a space 52 formed between the inner lid 32 and the lithium-ion secondary batteries 30a to 30d by a recess in the inner lid 32 included in the battery case 39.

[0021] The electrode assembly 2 has a structure in which at least one positive electrode 3, at least one negative electrode 4, and at least one separator 6 are stacked. The electrode assembly 2 may have a stacked structure in which a plurality of positive electrodes 3, a plurality of negative electrodes 4, and separators 6 are stacked. When the electrode assembly 2 has a stacked structure, the electrode assembly 2 has a structure in which sheet-shaped positive electrodes 3 and sheet-shaped negative electrodes 4 are alternately stacked with separators 6 interposed therebetween. The number of stacked positive electrodes 3 or negative electrodes 4 included in the electrode assembly 2 can be appropriately designed according to the required battery capacity. The electrode assembly 2 may also have a wound structure in which the positive electrodes 3, negative electrodes 4, and separators 6 are stacked and wound.

[0022] The electrode assembly 2 has a positive electrode extension portion in which a positive electrode current collector sheet 16 overlaps and extends from a laminated structure in which a positive electrode 3, a negative electrode 4, and a separator 6 are stacked. The positive electrode current collector sheet 16 constituting the positive electrode extension portion is bundled by a first clip 7. The electrode assembly 2 has a negative electrode extension portion in which a negative electrode current collector sheet 17 overlaps and extends from a laminated structure in which a positive electrode 3, a negative electrode 4, and a separator 6 are stacked. The negative electrode current collector sheet 17 constituting the negative electrode extension portion is bundled by a second clip 8.

[0023] The separator 6 is in the form of a sheet and is disposed between the positive electrode 3 and the negative electrode 4. The separator 6 is not particularly limited as long as it can prevent a short-circuit current from flowing between the positive electrode 3 and the negative electrode 4 and is permeable to an electrolyte, but can be, for example, a microporous film of polyolefin or polyethylene.

[0024] The positive electrode 3 includes a positive electrode current collector sheet 16 and a positive electrode active material layer 21 provided on the positive electrode current collector sheet 16. The positive electrode 3 may have a square or rectangular sheet shape. For example, the positive electrode 3 may have a structure in which the positive electrode active material layers 21 are laminated on both sides of the square positive electrode current collector sheet 16. The positive electrode current collector sheet 16 is not particularly limited as long as it has electrical conductivity and can have the positive electrode active material layer 21 on its surface, but is, for example, a metal foil. Aluminum foil is preferred. The thickness of the positive electrode current collector sheet 16 is, for example, 10 μm to 40 μm.

[0025] The positive electrode active material layer 21 can be formed on the positive electrode current collector sheet 16 by adding a conductive agent, a binder, etc. to the positive electrode active material and applying a coating method or the like. The positive electrode active material is, for example, a lithium transition metal composite oxide capable of reversibly absorbing and releasing lithium ions. Specifically, the positive electrode active material is LiFePO4, Li x Fe 1-y M y An olivine-type compound such as PO4 (where 0.05≦x≦1.2, 0≦y≦0.8, and M is at least one of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, and Nb). The positive electrode active material, an olivine-type compound (e.g., lithium iron phosphate), has a positive electrode potential of 3.6 V vs. Li / Li. + At about this voltage, all the lithium atoms in the positive electrode active material are released as lithium ions into the non-aqueous electrolyte. Therefore, if charging is continued after the positive electrode active material has released all the lithium atoms, the potential of the positive electrode will rise sharply. Furthermore, if the potential of the positive electrode becomes higher than 4.3 V to 4.5 V, the non-aqueous electrolyte will decompose in the positive electrode and generate gas. The non-aqueous electrolyte contained in the lithium ion secondary battery of the present invention has a potential of 3.8 V vs. Li / Li + Higher than 4.3 vs. Li / Li + Because the battery contains a redox shuttle agent with a redox potential lower than the redox potential of the redox shuttle agent, even if charging continues after the positive electrode active material has released all of its lithium atoms, current can flow between the positive electrode and the negative electrode due to ionic conduction of the redox shuttle agent, preventing the positive electrode potential from rising above the redox potential of the redox shuttle agent. This prevents the positive electrode potential from rising to a potential that would decompose the non-aqueous electrolyte, thereby preventing gas generation inside the battery. Furthermore, because the voltage change is rapid, the redox shuttle agent can operate within a narrow SOC range, making it easier for the SOC adjustment function as a balancer to function.

[0026] The negative electrode 4 includes a negative electrode current collector sheet 17 and a negative electrode active material layer 22 provided on the negative electrode current collector sheet 17. The negative electrode 4 may have a square or rectangular sheet shape. For example, the negative electrode 4 may have a structure in which the negative electrode active material layers 22 are laminated on both sides of the rectangular negative electrode current collector sheet 17.

[0027] The negative electrode current collector sheet 17 is not particularly limited as long as it has electrical conductivity and can have the negative electrode active material layer 22 on its surface, but is, for example, a metal foil. Copper foil is preferable. The thickness of the negative electrode current collector sheet 17 is, for example, 10 μm to 40 μm. The negative electrode active material layer 22 can be formed on the negative electrode current collector sheet 17 by adding a conductive agent, a binder, etc. to the negative electrode active material and then applying the resulting mixture by a coating method or the like. Examples of the negative electrode active material include carbon such as graphite, partially graphitized carbon, amorphous carbon, hard carbon, and soft carbon, LiTiO4, and Sn alloys.

[0028] The negative electrode active material is preferably amorphous carbon. When a lithium ion secondary battery having an olivine-type compound (for example, lithium iron phosphate) as the positive electrode active material and graphite as the negative electrode active material is fully charged (battery voltage 3.45 V to 3.6 V), the potential of the negative electrode is 0.1 V vs. Li / Li + Charging is continued in this state until the potential of the positive electrode reaches the redox shuttle agent's redox potential (3.8 V vs. Li / Li + Higher than 4.3 vs. Li / Li + If charging is continued until the potential of the negative electrode reaches 0 V vs. Li / Li + The potential of the negative electrode is 0V vs. Li / Li + If the negative electrode potential is smaller than 0V, metallic lithium may be deposited on the negative electrode, which may have a negative impact on safety (for example, metallic lithium may be deposited as dendrite, causing a short circuit between the negative electrode and the positive electrode). Also, when a battery with graphite as the negative electrode active material is further charged from a fully charged state, the potential of the negative electrode drops relatively quickly to 0V vs. Li / Li. + The potential drops to a level lower than Since the negative electrode active material of the lithium ion secondary battery of the present invention is amorphous carbon, the rate of decrease in the negative electrode potential during charging is slower than that of a secondary battery using graphite as the negative electrode active material. Therefore, even when the secondary battery of the present invention is charged to the redox potential of the redox shuttle agent, the negative electrode potential remains at 0 V vs. Li / Li. + Furthermore, by reducing the available capacity of the negative electrode active material, the rate of decrease in the potential of the negative electrode during charging can be further slowed down, and even when the secondary battery of the present invention is charged up to the redox potential of the redox shuttle agent, the potential of the negative electrode can be kept at 0 V vs. Li / Li. +Therefore, it is possible to suppress the electrodeposition of metallic lithium on the negative electrode, and it is possible to improve the resistance to electrodeposition compared to a battery using graphite as the negative electrode active material.

[0029] The nonaqueous electrolyte 12 can be made of a solvent such as carbonates, lactones, ethers, or esters, or a mixture of two or more of these solvents. Among these, a mixture of cyclic carbonates and chain carbonates is particularly preferred. The electrolyte 12 is a solution in which a lithium salt solute, such as LiCF3SO3, LiAsF6, LiClO4, LiBF4, LiPF6, LiBOB, LiN(CF3SO2)2, or LiN(C2F5SO2), is dissolved in an organic solvent. If necessary, additives such as VC (vinylene carbonate), PS (propane sultone), VEC (vinyl ethyl carbonate), PRS (propene sultone), or a flame retardant may be added alone or in combination.

[0030] The non-aqueous electrolyte 12 contains a redox shuttle agent. The redox shuttle agent has a redox potential higher than the potential of the positive electrode 3 when the lithium-ion secondary batteries 30a to 30d are fully charged. As a result, when the lithium-ion secondary battery is fully charged or overcharged, a current flows between the positive electrode 3 and the negative electrode 4 due to ionic conduction of the redox shuttle agent, preventing the non-aqueous electrolyte 12 from being decomposed and generating gas inside the battery. The potential of the positive electrode 3 when fully charged is determined by the positive electrode active material contained in the positive electrode 3 and the negative electrode active material contained in the negative electrode 4. For example, if the positive electrode active material contained in the positive electrode 3 is LiFePO4 and the negative electrode active material contained in the negative electrode 4 is carbon, the potential of the positive electrode 3 when fully charged is 3.65 V to 3.7 V vs. Li / Li + is.

[0031] The redox shuttle agent contained in the non-aqueous electrolyte 12 is 3.8 V vs. Li / Li + and can have a redox potential higher than 3.80 V vs. Li / Li+ More than 4.0V vs. Li / Li + It is preferred that the redox potential is: The concentration of the redox shuttle agent in non-aqueous electrolyte 12 is, for example, 0.5 wt% or less, preferably 0.1 wt% to 0.5 wt%, and more preferably 0.1 wt% to 0.4 wt%. This allows current to flow between positive electrode 3 and negative electrode 4 during overcharge and increases the discharge current of lithium-ion secondary batteries 30a to 30d. If the concentration of the redox shuttle agent in non-aqueous electrolyte 12 is too high, the discharge current of lithium-ion secondary batteries 30a to 30d may decrease. The redox shuttle agent contained in the non-aqueous electrolyte 12 is, for example, 2,5-di-tert-butyl-1,4-dimethoxybenzene (approximately 3.9 V vs. Li / Li + ), 2,5-di-tert-butoxy-1,4-dimethoxybenzene (approximately 3.9 V vs. Li / Li + These redox shuttle agents are capable of maintaining the ionic conduction current of the redox shuttle agent even after repeated charge-discharge cycles (they are durable).

[0032] During charging, lithium-ion secondary batteries 30a-30d are configured to allow a current of 100 mA to 3000 mA (preferably 200 mA to 2500 mA), and more preferably 600 mA to 1800 mA (preferably 600 mA to 1800 mA), to flow through them so as not to increase the charge level when the potential of positive electrode 3 reaches the redox potential of the redox shuttle agent. This prevents lithium-ion secondary batteries 30a-30d from becoming overcharged. The amount of current can be adjusted by varying the concentration of the redox shuttle agent in nonaqueous electrolyte 12 and the total area of ​​multiple opposing surfaces of positive electrode active material layer 21 and negative electrode active material layer 22 across separator 6. The higher the concentration of the redox shuttle agent, the greater the amount of redox shuttle agent conducting through nonaqueous electrolyte 12 between positive electrode 3 and negative electrode 4, and therefore the greater the amount of current. Furthermore, the larger the total area, the more conduction paths there are for the redox shuttle agent that conducts between the positive electrode 3 and the negative electrode 4, and the greater the amount of current. The total area is 200 cm 2 Wider than 400cm, preferably 2 Wider than 600cm, preferably 2 This makes it possible to sufficiently increase the amount of current that flows due to ion conduction of the redox shuttle agent, even when the concentration of the redox shuttle agent is 0.5 wt % or less. In lithium ion secondary batteries 30a to 30d, the state in which the potential of positive electrode 3 reaches the redox potential of the redox shuttle agent can be considered to be a 100% state of charge (SOC).

[0033] The positive electrode 3, the negative electrode 4, and the non-aqueous electrolyte 12 are in a state where the potential of the positive electrode 3 reaches the redox potential of the redox shuttle agent, and the potential of the negative electrode 4 is 0 V vs. Li / Li +The negative electrode 4 may be provided so that the positive electrode 3 has a larger capacity than the negative electrode 4. This can suppress the deposition of metallic lithium on the negative electrode 4 at low temperatures, thereby preventing a short circuit between the positive electrode 3 and the negative electrode 4 due to the deposition of metallic lithium. For example, when the positive electrode active material is lithium iron phosphate and the negative electrode active material is amorphous carbon, the negative electrode 4 can be provided so that the usable capacity of the negative electrode active material is 190 mAh / g or less. In this case, the potential of the negative electrode 4 gradually decreases as charging progresses, so that even when the potential of the positive electrode 3 reaches the redox potential of the redox shuttle agent, the potential of the negative electrode 4 can be kept at 0 V vs. Li / Li. + The usable capacity of the negative electrode active material can be adjusted by changing the ratio between the amount of the negative electrode active material contained in the negative electrode 4 and the amount of the positive electrode active material contained in the positive electrode 3.

[0034] The first clip 7 is provided so as to overlap and clamp the portion (positive electrode extension portion) of the positive electrode current collector sheet 16 where the positive electrode active material layer 21 is not provided, and the second clip 8 is provided so as to overlap and clamp and bundle the portion (connection portion, negative electrode extension portion) of the negative electrode current collector sheet 17 where the negative electrode active material layer 22 is not provided. The first clip 7 or the second clip 8 may be welded and integrated with the overlapping and sandwiched positive electrode current collector sheet 16 or negative electrode current collector sheet 17. For example, the first clip 7 or the second clip 8 and the overlapping and sandwiched positive electrode current collector sheet 16 or negative electrode current collector sheet 17 can be integrated by ultrasonic welding. The first clip 7 or the second clip 8 is made of a conductive material. If the positive electrode current collector sheet 16 is made of aluminum foil, the first clip 7 that binds the positive electrode current collector sheet 16 can be made of an aluminum plate. If the negative electrode current collector sheet 17 is made of copper foil, the second clip 8 that binds the negative electrode current collector sheet 17 can be made of a copper plate.

[0035] The first conductive plate 9 is joined to the first clip 7. The first conductive plate 9 can be joined to the first clip 7 by overlapping the first conductive plate 9 and the first clip 7 and welding them together. When the positive electrode current collecting sheet 16 and the first clip 7 are made of aluminum, the first conductive plate 9 can be an aluminum plate. The thickness of the first conductive plate 9 can be, for example, 100 μm to 500 μm.

[0036] First conductive plate 9 and exterior body 13 can form a seal portion 25 where exterior body 13 is bonded to first conductive plate 9. The first conductive plate 9 can have positive electrode cell terminals 23a-23d. The positive electrode cell terminals 23a-23d are positive electrode terminals of the lithium ion secondary batteries 30a-30d, respectively, and are connected to the negative electrode cell terminals 24a-24d of the other lithium ion secondary batteries 30a-30d and the connection terminal 37a of the inner lid 32. The positive electrode cell terminals 23a-23d can be provided, for example, on the lugs of the first conductive plate 9. The positive electrode cell terminals 23a-23d can be arranged so as to protrude upward from the upper end (upper surface) of the lithium ion secondary batteries 30a-30d. For example, the positive electrode cell terminal 23a can be arranged as in the batteries shown in FIGS. 4 and 6(a).

[0037] The lithium-ion secondary batteries 30a to 30d are provided so that the positive electrode extension and the exterior body 13 can be folded so that the first clip 7 is substantially parallel to the first side (side surface) of the lithium-ion secondary batteries 30a to 30d. At this time, the folded exterior body 13 is positioned between the first clip 7 and the electrode assembly 2. The first conductive plate 9 may also be folded so that it is substantially parallel to the front or back surface of the lithium-ion secondary batteries 30a to 30d. By changing the folding direction, it is possible to select whether the positive electrode cell terminals 23a to 23d are disposed on the front side or the back side. For example, as in the battery 30a shown in FIGS. 4, 5, and 7, the positive electrode extension and the exterior body 13 can be folded, and the first conductive plate 9 can be folded.

[0038] The second conductive plate 10 is joined to the second clip 8. The second conductive plate 10 can be joined to the second clip 8 by overlapping the second conductive plate 10 and the second clip 8 and welding them together. When the negative electrode current collecting sheet 17 and the second clip 8 are made of copper, the second conductive plate 10 can be a copper plate. The thickness of the second conductive plate 10 can be, for example, 100 μm to 500 μm.

[0039] The second conductive plate 10 and the exterior body 13 can form a seal portion 25 where the exterior body 13 is adhered to the second conductive plate 10 . The second conductive plate 10 may have negative cell terminals 24a-24d. The negative cell terminals 24a-24d are negative terminals of the lithium ion secondary batteries 30a-30d, respectively, and are connected to the positive cell terminals 23a-23d of the other lithium ion secondary batteries 30a-30d and the connection terminal 37b of the inner lid 32. The negative cell terminals 24a-24d may be provided, for example, on the lugs of the second conductive plate 10. The negative cell terminals 24a-24d may be arranged so as to protrude upward from the upper ends (upper surfaces) of the lithium ion secondary batteries 30a-30d. For example, the negative cell terminal 24a may be arranged as in the batteries shown in FIGS. 4 and 6(b).

[0040] The lithium-ion secondary batteries 30a to 30d are provided so that the negative electrode extension and the exterior body 13 can be folded so that the second clip 8 is substantially parallel to the second side (side surface) of the lithium-ion secondary batteries 30a to 30d. At this time, the folded exterior body 13 is positioned between the second clip 8 and the electrode assembly 2. The second conductive plate 10 may also be folded so that it is substantially parallel to the front or back surface of the lithium-ion secondary batteries 30a to 30d. By changing the folding direction, it is possible to select whether the negative electrode cell terminals 24a to 24d are disposed on the front side or the back side. For example, as in the battery 30a shown in FIGS. 4 and 5, the negative electrode extension and the exterior body 13 can be folded, and the second conductive plate 10 can be folded.

[0041] A plurality of such lithium ion secondary batteries 30a to 30d can be combined to form a battery pack connected in series. Here, the battery pack shown in Fig. 3 will be used for explanation. The lithium ion secondary batteries 30a to 30d are stacked so that their wide surfaces (front or back) face each other. The lithium ion secondary battery 30a is arranged so that the first side is on the left side and the second side is on the right side, and the first conductive plate 9, the second conductive plate 10, the positive electrode extension, the negative electrode extension, and the exterior body 13 are bent so that the positive electrode cell terminal 23a and the negative electrode cell terminal 24a are located on the lower surfaces. The negative electrode cell terminal 24a serves as the negative electrode terminal of this assembled battery.

[0042] The lithium-ion secondary battery 30b is positioned so that its first side is on the right and its second side is on the left. The first conductive plate 9, the second conductive plate 10, the positive electrode extension, the negative electrode extension, and the exterior body 13 are folded so that the positive electrode cell terminal 23b is located on the lower surface and the negative electrode cell terminal 24b is located on the upper surface. This folding allows the positive electrode cell terminal 23a of the battery 30a and the negative electrode cell terminal 24b of the battery 30b to overlap. The positive electrode cell terminal 23a and the negative electrode cell terminal 24b are joined and electrically connected by ultrasonic welding or the like. This joined portion is located in an upper space 52 formed between the inner lid 32 and the lithium-ion secondary batteries 30a-30d by a recess having an opening on the battery side of the inner lid 32. This configuration suppresses leakage current.

[0043] The lithium-ion secondary battery 30c is positioned so that its first side is on the left and its second side is on the right. The first conductive plate 9, the second conductive plate 10, the positive electrode extension, the negative electrode extension, and the exterior body 13 are folded so that the positive electrode cell terminal 23c is located on the lower surface and the negative electrode cell terminal 24c is located on the upper surface. By folding the battery 30c in this manner, the positive electrode cell terminal 23b of the battery 30b and the negative electrode cell terminal 24c of the battery 30c are arranged to overlap. The positive electrode cell terminal 23b and the negative electrode cell terminal 24c are joined and electrically connected by ultrasonic welding or the like. This joined portion is located in an upper space 52 formed between the inner lid 32 and the lithium-ion secondary batteries 30a to 30d by a recess in the inner lid 32 that has an opening on the battery side.

[0044] The lithium-ion secondary battery 30d is positioned so that its first side is on the right and its second side is on the left. The first conductive plate 9, the second conductive plate 10, the positive electrode extension, the negative electrode extension, and the outer casing 13 are folded so that the positive electrode cell terminal 23d and the negative electrode cell terminal 24d are located on the upper surface. This folding allows the positive electrode cell terminal 23c of the battery 30c and the negative electrode cell terminal 24d of the battery 30d to overlap. The positive electrode cell terminal 23c and the negative electrode cell terminal 24d are joined and electrically connected by ultrasonic welding or the like. This joined portion is located in an upper space 52 formed by a recess having an opening on the battery side of the inner lid 32. This prevents leakage current from flowing. The positive electrode cell terminal 23d serves as the positive electrode terminal of this assembled battery. Although an example of a battery pack in which four batteries 30a to 30d are connected in series is shown here, the number of batteries connected in series is not particularly limited. Also, the battery pack may be a battery pack in which a plurality of series-connected batteries are connected in parallel, with a plurality of batteries being connected in series.

[0045] The battery case 39 of the lithium-ion battery module 60 includes a battery case 31 that houses multiple lithium-ion secondary batteries 30a to 30d, an inner lid 32 that is provided to close the opening of the battery case 31, and an upper lid 33. The inner lid 32 is disposed between the battery case 31 and the upper lid 33. The material of the battery case 31, the material of the inner lid 32, and the material of the upper lid 33 may be plastic. FIG. 9 is a schematic partial cross-sectional view of a lithium-ion battery module 60, showing the inner lid 32, the positive electrode cell terminal 23d, the negative electrode cell terminal 24d, the first release valve 15, the cover member 43, and the second release valve 46. 2, a positive electrode external terminal 34, a negative electrode external terminal 35, a fuse 38, connection terminals 37a, 37b, etc. are provided on the upper surface of the inner lid 32. The inner lid 32 also has slits 36a, 36b penetrating the inner lid 32, a wall portion that forms a fuse chamber 40 on the upper surface of the inner lid 32, a recessed portion having an opening on the lower surface side of the inner lid 32, etc. The inner lid 32 is adhered to the battery case 31 with an adhesive or the like so that the inside of the battery case 31 is an airtight space except for the slits 36a and 36b.

[0046] The positive cell terminal 23d, which is the positive terminal of the battery assembly described above, is inserted into the slit 36a so as to pass through, and the positive cell terminal 23d is joined to a connection terminal 37a on the upper surface of the inner lid 32 (for example, by ultrasonic welding). The connection terminal 37a is also electrically connected to the positive external terminal 34 by wiring. Therefore, the positive cell terminal 23d, which is the positive terminal of the battery assembly described above, is electrically connected to the positive external terminal 34, and it becomes possible to charge and discharge the battery assembly described above via the positive external terminal 34. The wiring may be integrated with the inner lid 32 by insert molding or the like.

[0047] The negative cell terminal 24a, which is the negative terminal of the battery pack described above, is inserted through the slit 36b and joined to the connection terminal 37b on the upper surface of the inner lid 32 (e.g., by ultrasonic welding). The connection terminal 37b is electrically connected to the negative external terminal 35 via wiring and a fuse 38. Therefore, the negative cell terminal 24a, which is the negative terminal of the battery pack described above, is electrically connected to the negative external terminal 35, enabling the battery pack to be charged and discharged via the negative external terminal 35. In addition, if an overcurrent flows through the lithium-ion battery module 60 due to a failure of the regulator supplying power to the lithium-ion battery module 60, a short circuit between the positive electrode 3 and the negative electrode 4, or the occurrence of a leak current, the fuse 38 melts and cuts off the electrical connection between the negative cell terminal 24a and the negative external terminal 35, thereby preventing a dangerous condition for the lithium-ion battery module 60 or a vehicle equipped with the lithium-ion battery module 60. The wiring may be integrated with the inner lid 32 by insert molding or the like. In this example, the fuse 38 is configured to be part of the wiring between the negative electrode 4 and the negative electrode external terminal 35, but the fuse 38 may also be configured to be part of the wiring between the positive electrode 3 and the positive electrode external terminal 34.

[0048] The fuse 38 is replaceably fixed in a fuse chamber 40 surrounded by a wall on the top surface of the inner lid 32. For example, the fuse 38 is fixed inside the chamber 40 by screws 42c, 42b, etc. This allows the fuse 38 to be easily replaced with a new one when it blows. In addition, a seal member 41 is sandwiched between the upper end of the wall of the inner lid 32 and the top lid 33, or between the fuse 38 and the top lid 33, so that the fuse chamber 40 becomes an airtight space. This prevents water from entering the chamber 40 and prevents corrosion of the fuse 38, poor contact at the connection between the fuse 38 and the wiring, and the occurrence of leak current.

[0049] The lithium-ion battery module 60 includes a cover member 43 adhered to the upper surface of the inner lid 32 so as to cover the slits 36a, 36b and the connection terminals 37a, 37b. Furthermore, as shown in FIG. 9 , the cover member 43 is adhered to the inner lid 32 so that the electrical connection chamber 51 between the inner lid 32 and the cover member 43 is an airtight space except for the slits 36a, 36b. Therefore, the interior of the battery case 31, which is connected by the slits 36a, 36b, and the electrical connection chamber 51 form an airtight space. This prevents water from entering the electrical connection chamber 51 and the interior of the battery case 31, thereby preventing corrosion of the connection terminals 37a, 37b, the positive cell terminals 23a to 23d, and the negative cell terminals 24a to 24d, as well as leakage current.

[0050] As shown in FIG. 9 , the cover member 43 has a gas vent 44 extending from the electrical connection chamber 51. The gas vent 44 is covered with a cap 45, and the gas vent 44 and the cap 45 are configured to function as a second release valve 46 that releases gas in the chamber 51 to the outside when the pressure inside the chamber 51 and the battery case 31 increases. The release pressure of the second release valve 46 can be set to 30 kPa or more and 60 kPa or less. The release pressure can be adjusted by changing the material, size, etc. of the cap 45.

[0051] As shown in FIG. 9 , the inner lid 32 has a recess with an opening on the back side. This recess forms an upper space 52 located above the lithium-ion secondary batteries 30a to 30d. The joined portions of the positive cell terminal 23a and the negative cell terminal 24b, the joined portions of the positive cell terminal 23b and the negative cell terminal 24c, and the joined portions of the positive cell terminal 23c and the negative cell terminal 24d can be disposed in this upper space 52. This allows these joined portions to be disposed below the inner lid 32 without being bent, thereby preventing leakage current. Furthermore, this recess can have a depth such that the upper ends of the joined, unbent positive and negative cell terminals do not come into contact with the inner lid 32.

[0052] The first open valves 15 of the lithium-ion secondary batteries 30a to 30d can be disposed adjacent to the upper spaces 52. This allows the gas inside the exterior body 13 to quickly move to the upper spaces 52 when the internal pressure of the exterior body 13 increases due to gas generation and the first open valves 15 open. This allows the internal pressure of the exterior body 13 to quickly decrease when the internal pressure of the exterior body 13 exceeds the opening pressure of the first open valves 15, preventing the exterior body 13 from swelling and the battery case 31 from cracking. In addition, the gas inside the battery case 31 moves through the slits 36a and 36b to the electrical connection chamber 51, and when the pressure in the chamber 51 increases, the second release valve 46 opens and the gas is released into the space between the inner lid 32 and the top lid 33.

[0053] The battery case 31 has claws 53a-53c, and the inner lid 32 has sockets 54a-54c. The claws 53a-53c and sockets 54a-54c are arranged so that the claws 53a-53c and sockets 54a-54c engage with each other when the battery case 31 and inner lid 32 are assembled. The claws 53a-53c and sockets 54a-54c can be arranged so that the inner lid 32 detaches from the battery case 31 when the internal pressure of the battery case 31 exceeds a predetermined pressure. This allows gas inside the battery case 31 to be released to the outside when the first open valves 15 of the lithium-ion secondary batteries 30a-30d open and the internal pressure of the battery case 31 suddenly increases. This prevents the exterior body 13 from swelling and cracking the battery case 31. In this example, the battery case 31 has the claws and the inner lid 32 has the sockets, but the inner lid 32 may have the claws and the battery case 31 has the sockets. The predetermined pressure can be set to a pressure greater than the opening pressure of the second opening valve, and can be set to, for example, 200 kPa or more and 400 kPa or less.

[0054] The top lid 33 is fixed to the inner lid 32 so that the positive external terminal 34 and the negative external terminal 35 are located outside the battery case 39, and the cover member 43, the fuse chamber 40, and the like are located between the inner lid 32 and the top lid 33. By fixing the top lid 33 in this manner, the battery pack can be charged and discharged via the positive external terminal 34 and the negative external terminal 35, and the waterproof performance of the lithium-ion battery module 60 can be improved. The top cover 33 can be fixed to the inner cover 32 using, for example, screws 42a. This makes it possible to remove the top cover 33 from the inner cover 32, allowing the fuse 38 to be replaced. An opening may be provided in the top cover 33 or between the top cover 33 and the inner cover 32, through which gas in the space between the inner cover 32 and the top cover 33 can be released to the outside.

[0055] When the lithium-ion battery module 60 is mounted on a vehicle such as an automobile or motorcycle, the positive terminal of the regulator is connected to the positive external terminal 34 of the lithium-ion battery module 60 by wiring, and the negative terminal of the regulator is connected to the negative external terminal 35 of the lithium-ion battery module 60 by wiring. When the generator generates electricity using the rotation of the engine, a DC voltage (approximately 14 V to 14.5 V) adjusted by the regulator is applied between the positive electrode external terminal 34 and the negative electrode external terminal 35. This causes an ionic conduction current to flow between the positive electrode 3 and the negative electrode 4, charging each of the secondary batteries 30 a to 30 d, and the voltage between the positive electrode external terminal 34 and the negative electrode external terminal 35 gradually increases. Since the lithium-ion battery module 60 has four lithium-ion secondary batteries 30 a to 30 d connected in series, if each battery 30 a to 30 d has the same remaining battery capacity, each of the lithium-ion secondary batteries 30 a to 30 d is charged until the voltage between the positive electrode cell terminals 23 a to 23 d and the negative electrode cell terminals 24 a to 24 d (hereinafter also referred to as inter-terminal voltage) reaches approximately 3.5 V to 3.6 V. When the inter-terminal voltage is 3.6 V, the potential of the negative electrode cell terminals 24 a to 24 d is 0 V vs. Li / Li + ~0.1VLi / Li +The potential of the positive cell terminals 23a to 23d is about 3.6 V vs. Li / Li + ~3.7VLi / Li + That's about it.

[0056] When the remaining battery power levels of the lithium-ion secondary batteries 30a to 30d become unbalanced due to self-discharge of the lithium-ion secondary batteries 30a to 30d, the terminal voltage of some of the lithium-ion secondary batteries may be higher than that of the other lithium-ion secondary batteries. For example, if the voltage applied between the positive electrode external terminal 34 and the negative electrode external terminal 35 by the regulator is 14.5 V, and the terminal voltage of battery 30a, the terminal voltage of battery 30b, the terminal voltage of battery 30c, the terminal voltage of battery 30d, and the terminal voltage of battery 30d at the start of charging are 2.8 V, 3.2 V, 2.7 V, and 2.8 V, respectively, as charging progresses, the terminal voltage of battery 30b may exceed 3.9 V, and the potential of the positive electrode cell terminal 23b and the positive electrode 3 of battery 30b may reach the redox potential of the redox shuttle agent (e.g., 2,5-di-tert-butyl-1,4-dimethoxybenzene). In this case, an ionic conduction current of the redox shuttle agent flows between the positive electrode 3 and the negative electrode 4 of battery 30b, preventing the charging of battery 30b and preventing the potential of the positive electrode 3 from increasing. This suppresses the decomposition of nonaqueous electrolyte 12 inside battery 30b and the generation of gas, thereby preventing battery 30b from expanding. Meanwhile, batteries 30a, 30c, and 30d continue charging until the voltage between the positive electrode external terminal 34 and the negative electrode external terminal 35 reaches 14.5 V. Thus, even when a voltage is applied between the positive electrode external terminal 34 and the negative electrode external terminal 35, charging stops only in battery 30b, where the potential of the positive electrode 3 has reached the redox potential of the redox shuttle agent.

[0057] If a high voltage (e.g., 34.5 V) is applied between the positive electrode external terminal 34 and the negative electrode external terminal 35 of the lithium-ion battery module 60 due to a malfunction of the regulator installed in the vehicle, a large current will flow to the batteries 30a-30d. This will cause the potential of the positive electrode cell terminals 23a-23d and the positive electrode 3 of the batteries 30a-30d to reach the redox potential of the redox shuttle agent (e.g., 2,5-di-tert-butyl-1,4-dimethoxybenzene), and the charging of the batteries 30a-30d will likely stop or slow down. In a battery whose charging has stopped or slowed down, an ionic conduction current of the redox shuttle agent will flow between the positive electrode 3 and the negative electrode 4. If the current flowing through the batteries 30a-30d exceeds the upper limit of the ionic conduction current of the redox shuttle agent, the charging of the batteries 30a-30d will resume. If further current continues to flow, the batteries 30a-30d will likely become overcharged. In this way, even if a high voltage is applied between the positive electrode external terminal 34 and the negative electrode external terminal 35 due to a regulator failure, the ionic conduction current of the redox shuttle agent flows, making it possible to temporarily stop or slow down the charging of the batteries 30a to 30d. Therefore, if the application of high voltage due to the regulator failure is short, the ionic conduction current of the redox shuttle agent can be prevented from flowing and causing the batteries 30a to 30d to enter an overcharged state.

[0058] If a high voltage is repeatedly or for a long time applied between the positive electrode external terminal 34 and the negative electrode external terminal 35 of the lithium-ion battery module 60 due to a regulator failure, the capacity of the redox shuttle agent may be exceeded, causing the batteries 30a-30d to become overcharged, resulting in the generation of gas inside the batteries 30a-30d. Because the batteries 30a-30d each have a first release valve 15 with an open pressure of 150 kPa or less, even if gas is generated inside the battery, the first release valve 15 opens when the internal pressure exceeds the open pressure, allowing the gas to be released outside the battery. This prevents the batteries 30a-30d from expanding and damaging the battery case 39, and also prevents the nonaqueous electrolyte 12 from leaking from the exterior body 13 of the batteries 30a-30d or the battery case 39. If the nonaqueous electrolyte 12 is present inside the exterior body 13, even if the first release valve 15 opens, the current supplied from the mobile vehicle battery 60 to the mobile vehicle gradually decreases rather than suddenly stopping. This makes it possible to prevent the mobile body from suddenly losing power, and to take measures before the mobile body loses power.

[0059] Fabrication of lithium-ion secondary batteries and lithium-ion secondary battery modules A paste was prepared by kneading lithium iron phosphate powder (positive electrode active material), acetylene black (conductive additive), and polyvinylidene fluoride (PVdF) (binder). This paste was applied to one side of aluminum foil (positive electrode current collector) and dried to produce a positive electrode with a layer of positive electrode active material on one side of the aluminum foil. A paste was prepared by kneading soft carbon (anode active material), styrene-butadiene copolymer (SBR) (binder), and carboxymethyl cellulose (CMC) (thickener). This paste was applied to one side of copper foil (anode current collector), dried, and pressed to produce a cathode with a layer of anode active material on one side of the copper foil. The amounts of cathode active material in the cathode and anode active material in the anode were adjusted so that the usable capacity of the anode active material was 190 mAh / g or less.

[0060] A positive electrode, a separator, and a negative electrode were stacked so that the positive electrode active material layer and the negative electrode active material layer faced each other with a separator made of a polyolefin material sandwiched between them, and the positive and negative electrodes were covered with a single separator. One reference electrode (metallic lithium electrode) was placed on the outer surface of the positive electrode via the separator, and the other reference electrode (metallic lithium electrode) was placed on the outer surface of the negative electrode via the separator. This laminate was placed in a laminate film exterior, and all openings in the exterior were sealed except for the inlet. Then, an electrolyte solution (non-aqueous solvent: EC / DEC / EMC, lithium salt: LiPF6, 1,4-t-butyl-2,5-dimethoxybenzene: 0.5 wt% or less as a redox shuttle agent) was injected into the exterior through the inlet to impregnate the laminate with the electrolyte. After that, the interior of the exterior was degassed, and the inlet was sealed. Furthermore, a groove that would become the first open valve 15 as shown in Figures 8 and 10 was formed in the exterior body to produce a lithium ion secondary battery. A total of four similar lithium ion secondary batteries were produced, and these four lithium ion secondary batteries were housed in a plastic case and connected in series to produce a lithium ion secondary battery module.

[0061] Low temperature cycle test A cycle test was conducted using the fabricated lithium-ion secondary battery. The cycle test was conducted in a thermostatic chamber at -10°C in accordance with the standard for lead-acid starter batteries. The upper limit charge voltage was 3.9 V, the operating voltage of the redox shuttle agent, and the battery was charged by CCCV at 5 ItA to 100% SOC. After charging, the sample cell was rested for 10 minutes and then discharged at 1 ItA until the voltage reached 2.0 V. After discharging, the sample cell was rested for 10 minutes and then charged again. This charge-discharge cycle was repeated 20 times. The lithium-ion secondary battery was then disassembled and the negative electrode active material layer was observed. No metallic lithium was found to be electrolytically deposited. Note that due to the high operating voltage (3.9 V) of the redox shuttle agent, when graphite is used as the negative electrode active material, metallic lithium is likely to be electrolytically deposited on the negative electrode during low-temperature charging. However, even when the upper limit charging voltage was set to 3.9 V, by using amorphous carbon as the negative electrode active material and setting the usable capacity of the negative electrode active material to 190 mAh / g or less, it was possible to suppress the deposition of metallic lithium at the negative electrode during low-temperature charging.

[0062] Overcharge test Assuming a malfunction of the regulator / rectifier (REG / RECT) of a motorcycle equipped with a lithium-ion secondary battery module, the fabricated lithium-ion secondary battery module was charged using a constant current / constant voltage (CCCV) method (current: 17 A, voltage: 34.5 V) (however, voltage application was terminated when 34.5 V was reached, at a temperature of 25°C). Figure 11 shows the changes in voltage, current, cell temperature, and ambient temperature (temperature outside the cell) during this test. Approximately 30 seconds after the start of the test, a voltage of approximately 20 V was applied to the secondary battery module, and a current of approximately 20 V and 17 A continued to flow for approximately 240 seconds until approximately 270 seconds after the start of the test. After approximately 270 seconds from the start of the test, the voltage applied to the secondary battery module began to increase, and when it reached the upper limit of 34.5 V, current gradually stopped flowing to the secondary battery module. This increase in voltage and decrease in current are thought to be due to the pores in the separator closing due to the temperature rise of the secondary battery, blocking the ionic conduction path between the positive and negative electrodes. The groove in the outer casing (first release valve 15) ruptured approximately 280 seconds after the start of the test. Even after the groove ruptured, current continued to flow for approximately 80 seconds.

[0063] When a voltage of 20 V was applied to the secondary battery module, a voltage of approximately 5 V was applied to each secondary battery, which greatly exceeded the operating voltage (3.9 V) of the redox shuttle agent. Even in this case, current continued to flow through the secondary battery module for approximately 240 seconds. As can be seen, even when a voltage significantly exceeding the rated voltage is applied to the secondary battery module from the motorcycle, the secondary battery module does not immediately become non-powered, but rather the current value gradually decreases. Furthermore, the groove (first release valve 15) in the lithium-ion secondary battery ruptures, allowing gas to escape from the exterior, and the plastic case housing the lithium-ion secondary battery is not damaged. In other words, even if an abnormality occurs in the device (mobile object) in which the secondary battery module of the present invention is mounted, causing an overvoltage or large current beyond what is expected to flow through the secondary battery module of the present invention, the device (mobile object) can remain powered for a while, so there is no risk of immediately losing control of the device (mobile object), and there is no risk of liquid leakage due to damage to the case, thereby avoiding fire accidents. [Explanation of symbols]

[0064] 2: Electrode assembly 3: Positive electrode 4: Negative electrode 6: Separator 7: First clip 8: Second clip 9: First conductive plate 10: Second conductive plate 12: Non-aqueous electrolyte 13: Exterior body 15: First release valve 16: Positive electrode current collector sheet 17: Negative electrode current collector sheet 21: Positive electrode active material layer 22: Negative electrode active material layer 23a-23d: Positive electrode cell terminal 24a-24d: Negative electrode cell terminal 25: Seal portion 30a-30d: Lithium ion secondary battery 31: Battery case 32: Inner lid 33: Top lid 34: Positive electrode external terminal 35: Negative electrode external terminal 36a, 36b: Slits 37a, 37b: Connection terminals 38: Fuse 39: Battery case 40: Fuse chamber 41: Seal member 42a-42c: Screws 43: Cover member 44: Gas vent 45: Cap 46: Second release valve 48: Inner resin layer 49: Metal layer 50: Outer resin layer 51: Electrical connection chamber 52: Upper space 53a to 53c: Claws 54a to 54c: Sockets 60: Lithium-ion battery module

Claims

1. A lithium ion battery module including a plurality of electrically connected lithium ion secondary batteries, Each lithium ion secondary battery has a non-aqueous electrolyte containing a redox shuttle agent; The lithium ion battery module does not have a battery monitoring unit, and is configured so that when the potential of the positive electrode of some of the plurality of lithium ion secondary batteries reaches a predetermined potential during charging, a current of 100 mA or more that does not increase the charge amount flows to the some of the lithium ion secondary batteries, and the lithium ion battery module maintains a powered state for a certain period of time even if an overvoltage or overcurrent is applied and the battery function is lost.

2. Each lithium-ion secondary battery is a laminate cell in which an electrode assembly is housed in an exterior body having a seal formed by overlapping and joining laminate films, The lithium ion battery module according to claim 1 , wherein the exterior body has a release valve for releasing internal pressure.

3. The laminate film has a laminated structure in which a metal layer, an outer resin layer, and an inner resin layer are laminated, The lithium ion battery module according to claim 2 , wherein the exterior body has a groove formed in the outer resin layer and the metal layer, the groove functioning as the release valve.

Images