Nonaqueous electrolyte secondary battery and secondary battery module

Abstract

A secondary cell module according to the present invention has: at least one nonaqueous electrolyte secondary cell; and an elastic body that is arranged together with the nonaqueous electrolyte secondary cell and that receives a load from the nonaqueous electrolyte secondary cell in the direction of arrangement. The nonaqueous electrolyte secondary cell comprises: an electrode body in which a positive pole, a negative pole, and a separator disposed between the positive pole and the negative pole are laminated; and a housing which contains the electrode body, wherein the modulus of elastic compression of the elastic body is 5 MPa to 120 MPa, the positive pole has a positive pole collector containing Al and an element other than Al, and the thermal conductivity of the positive pole collector is 65 W / (m·K) to 150 W / (m·K).

Description

[Technical field]

[0001] The present disclosure relates to techniques for non-aqueous electrolyte secondary batteries and secondary battery modules. [Background technology]

[0002] A non-aqueous electrolyte secondary battery such as a lithium ion secondary battery typically includes an electrode body in which a positive electrode having a positive electrode active material layer and a negative electrode having a negative electrode active material layer are laminated with a separator interposed therebetween, and an electrolyte. Such a non-aqueous electrolyte secondary battery is, for example, a battery that performs charging and discharging by moving charge carriers (e.g., lithium ions) in the electrolyte back and forth between both electrodes. When charging a non-aqueous electrolyte secondary battery, charge carriers are released from the positive electrode active material constituting the positive electrode active material layer, and charge carriers are absorbed in the negative electrode active material constituting the negative electrode active material layer. Conversely, when discharging, charge carriers are released from the negative electrode active material, and charge carriers are absorbed in the positive electrode active material. In this way, when charge carriers are absorbed and released into the active material as the non-aqueous electrolyte secondary battery is charged and discharged, the electrode body expands and contracts.

[0003] Incidentally, a nail penetration test is a safety evaluation test for checking the resistance of a battery to an internal short circuit. The nail penetration test is a test in which, for example, a nail is inserted into a battery to simulate an internal short circuit, and the degree of heat generation is examined to check the safety of the battery.

[0004] For example, Patent Document 1 discloses a nonaqueous electrolyte secondary battery having a positive electrode that reversibly absorbs lithium ions, the positive electrode including an active material layer and a sheet-like current collector supporting the active material layer, the current collector including aluminum and at least one element other than aluminum, and an average composition obtained by averaging the ratio of elements constituting the current collector in the thickness direction of the current collector is equal to the composition of an alloy having a liquidus temperature of 630° C. or less. According to Patent Document 1, the melting point of the positive electrode current collector is kept low, and the time until the positive electrode current collector melts during a nail penetration test is shortened, thereby suppressing heat generation in the battery during the nail penetration test. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2005 / 076392 Summary of the Invention

[0006] In order to further ensure the safety of non-aqueous electrolyte secondary batteries, it is important to further reduce the amount of heat generated by the battery during a nail penetration test.

[0007] A secondary battery module according to one aspect of the present disclosure includes at least one nonaqueous electrolyte secondary battery, and an elastic body arranged together with the nonaqueous electrolyte secondary battery and receiving a load from the nonaqueous electrolyte secondary battery in the arrangement direction, the nonaqueous electrolyte secondary battery includes an electrode assembly including a positive electrode, a negative electrode, and a separator arranged between the positive electrode and the negative electrode stacked together, and a case accommodating the electrode assembly, the elastic body having a compressive elastic modulus of 5 MPa to 120 MPa, the positive electrode having a positive electrode current collector containing Al and an element other than Al, and the positive electrode current collector having a thermal conductivity of 65 W / (m·K) to 150 W / (m·K).

[0008] Further, a nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure is a nonaqueous electrolyte secondary battery comprising: an electrode assembly obtained by stacking a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; an elastic body that receives a load from the electrode assembly in a stacking direction of the electrode assembly; and a case that accommodates the electrode assembly and the elastic body, wherein the compressive elastic modulus of the elastic body is 5 MPa to 120 MPa, the positive electrode has a positive electrode current collector containing Al and an element other than Al, and the positive electrode current collector has a thermal conductivity of 65 W / (m·K) to 150 W / (m·K).

[0009] According to one aspect of the present disclosure, it is possible to suppress the amount of heat generated by a battery during a nail penetration test. [Brief description of the drawings]

[0010] [Figure 1]FIG. 1 is a perspective view of a secondary battery module according to an embodiment. [Diagram 2] FIG. 2 is an exploded perspective view of the secondary battery module according to the embodiment. [Diagram 3] FIG. 3 is a cross-sectional view that illustrates a schematic state in which a nonaqueous electrolyte secondary battery expands. [Figure 4] FIG. 4 is a schematic cross-sectional view showing the state of the electrode body during a nail penetration test. [Diagram 5] FIG. 5 is a schematic cross-sectional view showing a state in which the elastic body is disposed in the housing. [Figure 6] FIG. 6 is a schematic perspective view of a cylindrically wound electrode body. [Figure 7] FIG. 7 is a schematic perspective view showing an example of an elastic body. [Figure 8] FIG. 8 is a schematic cross-sectional view of a portion of the elastic body sandwiched between the electrode body and the housing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An example of an embodiment will be described in detail below. The drawings referred to in the description of the embodiment are schematic, and the dimensional ratios of components depicted in the drawings may differ from those of the actual products.

[0012] Fig. 1 is a perspective view of a secondary battery module according to an embodiment. Fig. 2 is an exploded perspective view of the secondary battery module according to an embodiment. The secondary battery module 1 includes, as an example, a stack 2, a pair of binding members 6, and a cooling plate 8. The stack 2 includes a plurality of nonaqueous electrolyte secondary batteries 10, a plurality of insulating spacers 12, a plurality of elastic bodies 40, and a pair of end plates 4.

[0013] Each nonaqueous electrolyte secondary battery 10 is a chargeable and dischargeable secondary battery such as a lithium ion secondary battery. The nonaqueous electrolyte secondary battery 10 of this embodiment is a so-called prismatic battery, and includes an electrode body 38 (see FIG. 3), an electrolyte, and a flat rectangular parallelepiped housing 13. The housing 13 is composed of an exterior can 14 and a sealing plate 16. The exterior can 14 has a substantially rectangular opening on one side, and the electrode body 38, the electrolyte, and the like are accommodated in the exterior can 14 through this opening. The exterior can 14 is preferably covered with an insulating film such as a shrink tube. The opening of the exterior can 14 is provided with a sealing plate 16 that closes the opening and seals the exterior can 14. The sealing plate 16 constitutes a first surface 13a of the housing 13. The sealing plate 16 and the exterior can 14 are joined together, for example, by laser, friction stir welding, brazing, or the like.

[0014] The housing 13 may be, for example, a cylindrical case, or may be an exterior body made of a laminate sheet including a metal layer and a resin layer.

[0015] The electrode body 38 has a structure in which a plurality of sheet-like positive electrodes 38a and a plurality of sheet-like negative electrodes 38b are alternately stacked with separators 38d interposed therebetween (see FIG. 3). The positive electrodes 38a, the negative electrodes 38b, and the separators 38d are stacked along a first direction X. That is, the first direction X is the stacking direction of the electrode body 38. The electrodes located at both ends in this stacking direction face a long side surface of the housing 13, which will be described later. The first direction X, second direction Y, and third direction Z shown in the figure are perpendicular to each other.

[0016] The electrode body 38 may be a cylindrically wound electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are laminated with a separator interposed therebetween and then wound, or a flat-wound electrode body in which a cylindrically wound electrode body is formed into a flat shape. In the case of a flat-wound electrode body, a rectangular exterior can is applicable, whereas in the case of a cylindrically wound electrode body, a cylindrical exterior can is applied.

[0017] An output terminal 18 electrically connected to the positive electrode 38a of the electrode body 38 is provided on the sealing plate 16, i.e., the first surface 13a of the housing 13, near one end in the longitudinal direction, and an output terminal 18 electrically connected to the negative electrode 38b of the electrode body 38 is provided on the other end. Hereinafter, the output terminal 18 connected to the positive electrode 38a will be referred to as the positive electrode terminal 18a, and the output terminal 18 connected to the negative electrode 38b will be referred to as the negative electrode terminal 18b. In addition, when it is not necessary to distinguish the polarity of the pair of output terminals 18, the positive electrode terminal 18a and the negative electrode terminal 18b will be collectively referred to as the output terminals 18.

[0018] The exterior can 14 has a bottom surface facing the sealing plate 16. The exterior can 14 also has four side surfaces connecting the opening and the bottom surface. Two of the four side surfaces are a pair of long side surfaces connected to two opposing long sides of the opening. Each long side surface is the surface with the largest area among the surfaces of the exterior can 14, i.e., the main surface. Each long side surface is a side surface that extends in a direction intersecting (for example, perpendicular to) the first direction X. The remaining two side surfaces excluding the two long side surfaces are a pair of short side surfaces connected to the short sides of the opening and bottom surface of the exterior can 14. The bottom surface, long side surfaces, and short side surfaces of the exterior can 14 correspond to the bottom surface, long side surfaces, and short side surfaces of the housing 13, respectively.

[0019] In the description of this embodiment, for convenience, the first surface 13a of the housing 13 is the upper surface of the nonaqueous electrolyte secondary battery 10. The bottom surface of the housing 13 is the bottom surface of the nonaqueous electrolyte secondary battery 10, the long side surface of the housing 13 is the long side surface of the nonaqueous electrolyte secondary battery 10, and the short side surface of the housing 13 is the short side surface of the nonaqueous electrolyte secondary battery 10. In the secondary battery module 1, the surface on the upper side of the nonaqueous electrolyte secondary battery 10 is the upper surface of the secondary battery module 1, the surface on the bottom side of the nonaqueous electrolyte secondary battery 10 is the bottom surface of the secondary battery module 1, and the surface on the short side of the nonaqueous electrolyte secondary battery 10 is the side surface of the secondary battery module 1. The upper surface side of the secondary battery module 1 is the vertically upward, and the bottom surface side of the secondary battery module 1 is the vertically downward.

[0020] The multiple nonaqueous electrolyte secondary batteries 10 are arranged side by side at a predetermined interval so that the long sides of adjacent nonaqueous electrolyte secondary batteries 10 face each other. In this embodiment, the output terminals 18 of each nonaqueous electrolyte secondary battery 10 are arranged to face in the same direction, but may be arranged to face in different directions.

[0021] Two adjacent nonaqueous electrolyte secondary batteries 10 are arranged (stacked) so that the positive electrode terminal 18a of one nonaqueous electrolyte secondary battery 10 and the negative electrode terminal 18b of the other nonaqueous electrolyte secondary battery 10 are adjacent to each other. The positive electrode terminal 18a and the negative electrode terminal 18b are connected in series via a bus bar. Note that the output terminals 18 of the same polarity of multiple adjacent nonaqueous electrolyte secondary batteries 10 may be connected in parallel with each other via a bus bar to form a nonaqueous electrolyte secondary battery block, and the nonaqueous electrolyte secondary battery blocks may be connected in series with each other.

[0022] The insulating spacer 12 is disposed between two adjacent nonaqueous electrolyte secondary batteries 10 to electrically insulate the two nonaqueous electrolyte secondary batteries 10. The insulating spacer 12 is made of, for example, a resin having insulating properties. Examples of the resin constituting the insulating spacer 12 include polypropylene, polybutylene terephthalate, and polycarbonate. The multiple nonaqueous electrolyte secondary batteries 10 and the multiple insulating spacers 12 are stacked alternately. In addition, the insulating spacer 12 is also disposed between the nonaqueous electrolyte secondary battery 10 and the end plate 4.

[0023] The insulating spacer 12 has a flat portion 20 and a wall portion 22. The flat portion 20 is interposed between the opposing long side surfaces of two adjacent nonaqueous electrolyte secondary batteries 10. This ensures insulation between the outer casings 14 of the adjacent nonaqueous electrolyte secondary batteries 10.

[0024] The wall portion 22 extends from the outer edge of the flat portion 20 in the direction in which the nonaqueous electrolyte secondary batteries 10 are arranged, and covers part of the top surface, side surface, and bottom surface of the nonaqueous electrolyte secondary batteries 10. This makes it possible to ensure, for example, a side distance between adjacent nonaqueous electrolyte secondary batteries 10 or between the nonaqueous electrolyte secondary batteries 10 and the end plates 4. The wall portion 22 has a notch 24 through which the bottom surface of the nonaqueous electrolyte secondary battery 10 is exposed. In addition, the insulating spacer 12 has upwardly facing biasing receiving portions 26 at both ends in the second direction Y.

[0025] The elastic body 40 is arranged along the first direction X together with the multiple nonaqueous electrolyte secondary batteries 10. That is, the first direction X is not only the stacking direction of the electrode body 38 as described above, but also the arrangement direction of the nonaqueous electrolyte secondary batteries 10 and the elastic body 40. The elastic body 40 is sheet-shaped and is interposed, for example, between the long side surface of each nonaqueous electrolyte secondary battery 10 and the flat surface portion 20 of each insulating spacer 12. The elastic body 40 arranged between two adjacent nonaqueous electrolyte secondary batteries 10 may be a single sheet or a laminate of multiple sheets. The elastic body 40 may be fixed to the surface of the flat surface portion 20 by adhesion or the like. Alternatively, a recess may be provided in the flat surface portion 20, and the elastic body 40 may be fitted into the recess. Alternatively, the elastic body 40 and the insulating spacer 12 may be integrally molded. Alternatively, the elastic body 40 may also serve as the flat surface portion 20.

[0026] The multiple nonaqueous electrolyte secondary batteries 10, the multiple insulating spacers 12, and the multiple elastic bodies 40 arranged in parallel are sandwiched in the first direction X between a pair of end plates 4. The end plates 4 are made of, for example, a metal plate or a resin plate. The end plates 4 are provided with screw holes 4a that penetrate the end plates 4 in the first direction X and into which screws 28 are screwed.

[0027] The pair of restraining members 6 are elongated members with the longitudinal direction being the first direction X. The pair of restraining members 6 are arranged to face each other in the second direction Y. The laminate 2 is interposed between the pair of restraining members 6. Each of the restraining members 6 includes a main body portion 30, a support portion 32, a plurality of biasing portions 34, and a pair of fixing portions 36.

[0028] The main body portion 30 is a rectangular portion extending in the first direction X. The main body portion 30 extends parallel to the side surfaces of each nonaqueous electrolyte secondary battery 10. The support portion 32 extends in the first direction X and protrudes in the second direction Y from the lower end of the main body portion 30. The support portion 32 is a plate-like body that is continuous in the first direction X and supports the stack 2.

[0029] The multiple urging portions 34 are connected to the upper end of the main body portion 30 and protrude in the second direction Y. The support portion 32 and the urging portions 34 face each other in the third direction Z. The multiple urging portions 34 are arranged in the first direction X at predetermined intervals. Each urging portion 34 is, for example, in the shape of a leaf spring, and urges each nonaqueous electrolyte secondary battery 10 toward the support portion 32.

[0030] The pair of fixing portions 36 are plate-like bodies protruding in the second direction Y from both ends of the main body 30 in the first direction X. The pair of fixing portions 36 face each other in the first direction X. Each fixing portion 36 is provided with a through hole 36a through which the screw 28 is inserted. The pair of fixing portions 36 fix the restraining member 6 to the laminate 2.

[0031] The cooling plate 8 is a mechanism for cooling a plurality of nonaqueous electrolyte secondary batteries 10. The stack 2 is placed on a main surface of the cooling plate 8 while being restrained by a pair of restraining members 6, and is fixed to the cooling plate 8 by inserting fastening members such as screws into the through holes 32a of the support parts 32 and the through holes 8a of the cooling plate 8.

[0032] FIG. 3 is a cross-sectional view showing a schematic state of expansion of a nonaqueous electrolyte secondary battery. In FIG. 3, the number of nonaqueous electrolyte secondary batteries 10 is thinned out. Also, the internal structure of the nonaqueous electrolyte secondary batteries 10 is simplified, and the insulating spacer 12 is omitted. As shown in FIG. 3, an electrode body 38 (a positive electrode 38a, a negative electrode 38b, and a separator 38d) is housed inside each nonaqueous electrolyte secondary battery 10. In the nonaqueous electrolyte secondary battery 10, the exterior can 14 expands and contracts due to the expansion and contraction of the electrode body 38 accompanying charging and discharging. When the exterior can 14 of each nonaqueous electrolyte secondary battery 10 expands, a load G1 toward the outside in the first direction X is generated in the stack 2. That is, the elastic body 40 arranged together with the nonaqueous electrolyte secondary battery 10 receives a load from the nonaqueous electrolyte secondary battery 10 in the first direction X (the arrangement direction of the nonaqueous electrolyte secondary battery 10 and the elastic body 40, and the stacking direction of the electrode body 38). On the other hand, a load G2 corresponding to the load G1 is applied to the laminate 2 by the restraining member 6.

[0033] Fig. 4 is a schematic cross-sectional view showing the state of the electrode assembly during the nail penetration test. As shown in Fig. 4, the positive electrode 38a includes a positive electrode current collector 50 and a positive electrode active material layer 52 formed on the positive electrode current collector 50, and the negative electrode 38b includes a negative electrode current collector 54 and a negative electrode active material layer 56 formed on the negative electrode current collector 54. When a nail is pierced into the nonaqueous electrolyte secondary battery by the nail penetration test, and the nail 58 penetrates the positive electrode 38a and the separator 38d and reaches the negative electrode 38b as shown in Fig. 4, and the positive electrode current collector 50 and the negative electrode current collector 54 directly contact the nail 58, an internal short circuit occurs, a short circuit current flows, and the nonaqueous electrolyte secondary battery generates heat.

[0034] Here, the positive electrode current collector 50 of this embodiment is a low thermal conductivity Al-containing positive electrode current collector that contains Al and elements other than Al and has a thermal conductivity of 65 W / (m·K) to 150 W / (m·K). In such a low thermal conductivity Al-containing positive electrode current collector, heat is likely to concentrate at the short circuit portion (the portion of the positive electrode current collector that is in direct contact with the nail), and therefore melting of the positive electrode current collector 50 at the short circuit portion is accelerated. In other words, the time from when an internal short circuit occurs in a nail penetration test until the positive electrode current collector 50 melts is accelerated.

[0035] The elastic body 40 of this embodiment has a compressive elastic modulus of 5 MPa to 120 MPa. The load G1 toward the outside in the first direction X and the load G2 corresponding to the load G1 are alleviated by the elastic body having a compressive elastic modulus of 5 MPa to 120 MPa, so that excessive proximity between the positive electrode 38a and the negative electrode 38b is suppressed. As a result, the increase in the area of ​​the short-circuited portion of the positive electrode collector 50 in the nail penetration test is suppressed compared to the case where the above-mentioned low thermal conductivity Al-containing positive electrode collector is used but an elastic body having a compressive elastic modulus of 5 MPa to 120 MPa is not arranged or an elastic body having a compressive elastic modulus of more than 120 MPa is arranged, so that the time from the occurrence of an internal short circuit in the nail penetration test to the melting of the positive electrode collector 50 is shortened, and the amount of heat generated by the battery in the nail penetration test is suppressed.

[0036] Fig. 5 is a schematic cross-sectional view showing a state in which an elastic body is disposed in a housing. The elastic body 40 is not limited to being arranged together with the nonaqueous electrolyte secondary battery 10 as described above, i.e., being disposed outside the housing 13, but may be disposed inside the housing 13. The elastic bodies 40 shown in Fig. 5 are disposed on both ends of the electrode body 38 in the stacking direction (first direction X) of the electrode body 38. The elastic bodies 40 are also sandwiched between the inner wall of the housing 13 and the electrode body 38.

[0037] When the electrode body 38 expands due to charging / discharging of the nonaqueous electrolyte secondary battery 10, a load is generated on the electrode body 38 toward the outside in the first direction X. That is, the elastic body 40 disposed inside the housing 13 receives a load from the electrode body 38 in the first direction X (the stacking direction of the electrode body 38). If the elastic body 40 has a compressive elastic modulus of 5 MPa to 120 MPa and the positive electrode current collector 50 is a low-thermal conductivity Al-containing positive electrode current collector that contains Al and elements other than Al and has a thermal conductivity of 65 W / (m·K) to 150 W / (m·K), the same effects as those described above can be obtained.

[0038] The elastic body 40 in the housing 13 may be disposed anywhere as long as it can receive a load from the electrode body 38 in the stacking direction of the electrode body 38. For example, if the electrode body 38 is a cylindrically wound electrode body 38 as shown in FIG. 6, the elastic body 40 may be disposed in the winding core 39 of the cylindrically wound electrode body 38. The stacking direction of the cylindrically wound electrode body 38 is the radial direction (R) of the electrode body 38. As the electrode body 38 expands and contracts, a load is generated in the electrode body 38 in the stacking direction of the electrode body 38 (the radial direction (R) of the electrode body 38), and the elastic body 40 in the winding core 39 receives the load in the stacking direction of the electrode body 38. Although not illustrated in the drawings, when a plurality of electrode bodies 38 are arranged in the housing 13, the elastic body 40 may be disposed between adjacent electrode bodies 38. In addition, in the case of a flat-wound type, the elastic body may be disposed in the center of the electrode body in the same manner.

[0039] The positive electrode 38a, the negative electrode 38b, the separator 38d, the elastic body 40, and the electrolyte will be described in detail below.

[0040] The positive electrode 38a has a positive electrode current collector 50 and a positive electrode active material layer 52 formed on the positive electrode current collector 50. The positive electrode current collector 50 may contain Al and an element other than Al, and may have a thermal conductivity in the range of 65 W / (m·K) to 150 W / (m·K). Note that the Al and the element other than Al may or may not be alloyed.

[0041] The Al content in the positive electrode current collector 50 is preferably more than 50 mass%, more preferably 75 mass% or more, and even more preferably 90 mass% or more, for example, from the viewpoint of suppressing an increase in the resistance value of the positive electrode current collector 50. The upper limit of the Al content in the positive electrode current collector 50 is, for example, 98 mass% or less.

[0042] The elements other than Al contained in the positive electrode current collector 50 are not particularly limited as long as they can adjust the thermal conductivity to the above range, and examples thereof include Mg, Si, Sn, Cu, Zn, and Ge. Among these, Mg is preferred in terms of ease of adjusting the thermal conductivity of the positive electrode current collector 50. The content of Mg in the positive electrode current collector 50 is preferably 1.5% by mass or more, and more preferably 3% by mass or more, in terms of adjusting the thermal conductivity of the positive electrode current collector 50 to 150 W / (m·K) or less. The higher the content of Mg in the positive electrode current collector 50, the harder the positive electrode current collector 50 becomes. In general, when the positive electrode current collector becomes hard, for example, in a nonaqueous electrolyte secondary battery using a flat-wound electrode body, stress is applied to the corners (where the electrodes and separator are curved) of the flat-wound electrode body due to expansion and contraction of the electrode body caused by charging and discharging, and the positive electrode current collector at the corners of the electrode body may break. However, in this embodiment, the elastic body 40 of 5 MPa to 120 MPa also relieves the stress applied to the corners of the flat wound electrode body, so that breakage of the positive electrode current collector 50 is suppressed even if the Mg content in the positive electrode current collector 50 is increased. The Mg content in the positive electrode current collector 50 is, for example, less than 50 mass %, and taking into consideration the resistance value of the positive electrode current collector 50, it is preferably 10 mass % or less, and more preferably 6 mass % or less.

[0043] The thermal conductivity of the positive electrode current collector 50 may be in the range of 65 W / (m·K) to 150 W / (m·K). In order to further suppress the amount of heat generated by the battery during a nail penetration test, the thermal conductivity is preferably in the range of 85 W / (m·K) to 130 W / (m·K), and more preferably in the range of 95 W / (m·K) to 120 W / (m·K).

[0044] <Method of measuring thermal conductivity> The thermal diffusivity, specific heat, and density of the positive electrode current collector 50 are measured by the following methods, and then substituted into the following formula (1) to determine the thermal conductivity (W / m·K) of the positive electrode current collector 50. Thermal diffusivity: Measured at 25°C using a xenon flash analyzer (registered trademark: LFA 467HT HyperFlash, manufactured by Netsch Japan Co., Ltd.). Specific heat: Measured using a differential scanning calorimeter (DSC) by comparison with a sapphire standard. · Density: Measured using Archimedes' principle. Thermal conductivity = (thermal diffusivity) × (specific heat) × (density) (1) The positive electrode current collector 50 has a resistance of 45 kN / mm 2 ~73.5kN / mm 2 The Young's modulus is measured by a tensile test (for example, a tensile / compression tester Technograph TG-2kN manufactured by MinebeaMitsumi) at a temperature of 25°C.

[0045] The positive electrode current collector 50 preferably has a liquidus temperature of 650° C. or less in order to melt quickly during a nail penetration test and effectively suppress the amount of heat generated by the battery. The lower limit of the liquidus temperature of the positive electrode current collector 50 is, for example, 450° C. or more. The liquidus temperature is the temperature at which a solid phase begins to form from a liquid phase. The liquidus temperature is obtained by differential scanning calorimetry (DSC).

[0046] The positive electrode active material layer 52 includes a positive electrode active material. The positive electrode active material layer 52 preferably includes a conductive material and a binder in addition to the positive electrode active material. The positive electrode active material layer 52 is preferably provided on both sides of the positive electrode current collector 50.

[0047] The positive electrode active material may be, for example, a lithium transition metal composite oxide. Metal elements contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. Among them, it is preferable to contain at least one of Ni, Co, and Mn. Examples of suitable composite oxides include lithium transition metal composite oxides containing Ni, Co, and Mn, and lithium transition metal composite oxides containing Ni, Co, and Al.

[0048] Examples of the conductive material include carbon materials such as carbon black, acetylene black, ketjen black, graphite, etc. Examples of the binder include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. Furthermore, these resins may be used in combination with cellulose derivatives such as carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0049] The positive electrode 38a can be produced, for example, by applying a positive electrode composite slurry containing a positive electrode active material, a conductive material, a binder, and the like onto the positive electrode current collector 50, drying the coating, and then rolling the coating to form the positive electrode active material layer 52 on the positive electrode current collector 50.

[0050] The negative electrode 38b has a negative electrode current collector 54 and a negative electrode active material layer 56 formed on the negative electrode current collector 54. For the negative electrode current collector 54, a foil of a metal that is stable in the potential range of the negative electrode 38b, a film having such a metal disposed on a surface layer, or the like is used, and examples thereof include copper.

[0051] The negative electrode active material layer 56 includes a negative electrode active material. The negative electrode active material layer 56 preferably includes a binder and the like. Examples of the binder include the same binder as that included in the positive electrode active material layer 52. The negative electrode active material layer 56 is preferably formed on both sides of the negative electrode current collector 54.

[0052] Examples of the negative electrode active material include those capable of reversibly absorbing and releasing lithium ions, and specific examples thereof include carbon materials such as natural graphite, artificial graphite, non-graphitizable carbon, and easily graphitizable carbon, surface-modified carbon materials in which the surface of the carbon materials is covered with an amorphous carbon film, metals that can be alloyed with lithium, such as silicon (Si) and tin (Sn), or alloys containing metal elements such as Si and Sn, and oxides containing metal elements such as Si and Sn. These may be used alone or in combination of two or more.

[0053] The negative electrode 38b can be produced, for example, by applying a negative electrode composite slurry containing a negative electrode active material, a binder, and the like onto the negative electrode current collector 54, drying the coating, and then rolling it to form the negative electrode active material layer 56 on the negative electrode current collector 54.

[0054] The separator 38d may be, for example, a porous sheet having ion permeability and insulation. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. The material of the separator 38d is preferably an olefin resin such as polyethylene or polypropylene, or cellulose. The separator 38d may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. The separator 38d may also be a multilayer separator including a polyethylene layer and a polypropylene layer, and may have a material such as an aramid resin or ceramic applied to the surface of the separator 38d.

[0055] Examples of materials constituting the elastic body 40 include thermosetting elastomers such as natural rubber, urethane rubber, silicone rubber, and fluororubber, and thermoplastic elastomers such as polystyrene, olefin, polyurethane, polyester, and polyamide. These materials may be foamed. Another example is a heat insulating material carrying a porous material such as silica xerogel.

[0056] In this embodiment, it is preferable to define the compressive elastic modulus of the negative electrode active material layer 56, the separator 38d, and the elastic body 40 as follows. It is preferable that the compressive elastic modulus of the separator 38d is smaller than that of the negative electrode active material layer 56, and that the compressive elastic modulus of the elastic body 40 is smaller than that of the separator 38d. That is, the compressive elastic modulus is in the order of the negative electrode active material layer 56>separator 38d>elastic body 40. Therefore, among the above, the negative electrode active material layer 56 is the least deformable, and the elastic body 40 is the most deformable. By defining the compressive elastic modulus of each member as above, for example, the retention of the electrolyte in the electrode body 38 is improved, so that it is possible to suppress the increase in resistance during high-rate charging and discharging. The compressive elastic modulus of the separator 38d is preferably 0.3 to 0.7 times, and more preferably 0.4 to 0.6 times, the compressive elastic modulus of the negative electrode active material layer 56, in terms of effectively suppressing the increase in resistance during high-rate charging and discharging. The compressive elastic modulus of the elastic body 40 may be in the range of 5 MPa to 120 MPa, and is preferably in the range of 25 MPa to 100 MPa.

[0057] The compressive elastic modulus is calculated by dividing the deformation amount in the thickness direction of the sample when a predetermined load is applied to the sample in the thickness direction by the compressed area and multiplying the result by the sample thickness. That is, the compressive elastic modulus (MPa)=load (N) / compressed area (mm 2 )×(deformation amount of sample (mm) / thickness of sample (mm)). However, when measuring the compressive elastic modulus of the negative electrode active material layer 56, the compressive elastic modulus of the negative electrode current collector 54 is measured, and the compressive elastic modulus of the negative electrode 38b in which the negative electrode active material layer 56 is formed on the negative electrode current collector 54 is measured. Then, the compressive elastic modulus of the negative electrode active material layer 56 is calculated based on the compressive elastic modulus of the negative electrode current collector 54 and the negative electrode 38b. When determining the compressive elastic modulus of the negative electrode active material layer 56 from the produced negative electrode 38b, the compressive elastic modulus of the negative electrode 38b is measured, and the compressive elastic modulus of the negative electrode current collector 54 obtained by scraping off the negative electrode active material layer 56 from the negative electrode 38b is measured, and the compressive elastic modulus of the negative electrode active material layer 56 is calculated based on the measured compressive elastic modulus.

[0058] The compressive elastic modulus of the negative electrode active material layer 56 can be adjusted, for example, by adjusting the rolling force applied to the negative electrode composite slurry formed on the negative electrode current collector 54. The compressive elastic modulus of the negative electrode active material layer 56 can also be adjusted, for example, by changing the material or physical properties of the negative electrode active material. Note that the adjustment of the pressure elastic modulus of the negative electrode active material layer 56 is not limited to the above. The compressive elastic modulus of the separator 38d is adjusted, for example, by selecting the material, controlling the porosity, pore size, etc. The compressive elastic modulus of the elastic body 40 is adjusted, for example, by selecting the material, shape, etc.

[0059] The elastic body 40 may have a uniform compressive elastic modulus on one surface, but may also have a structure in which the ease of deformation varies within the surface, as described below.

[0060] FIG. 7 is a schematic perspective view showing an example of an elastic body. The elastic body 40 shown in FIG. 7 has a soft part 44 and a hard part 42. The hard part 42 is located closer to the outer edge of the elastic body 40 than the soft part 44. The elastic body 40 shown in FIG. 7 has a structure in which the hard parts 42 are arranged on both ends in the second direction Y, and the soft part 44 is arranged between the two hard parts 42. It is preferable that the soft part 44 is arranged so as to overlap with the center of the long side of the housing 13 and the center of the electrode body 38 when viewed from the first direction X. In addition, it is preferable that the hard part 42 is arranged so as to overlap with the outer edge of the long side of the housing 13 and the outer edge of the electrode body 38 when viewed from the first direction X.

[0061] As described above, the expansion of the nonaqueous electrolyte secondary battery 10 is mainly caused by the expansion of the electrode body 38. The electrode body 38 expands more toward the center. That is, the electrode body 38 displaces more in the first direction X toward the center, and displaces less toward the outer edge from the center. In addition, with the displacement of the electrode body 38, the nonaqueous electrolyte secondary battery 10 displaces more in the first direction X toward the center of the long side of the housing 13, and displaces less toward the outer edge from the center of the long side of the housing 13. Therefore, when the elastic body 40 shown in FIG. 7 is disposed in the housing 13, the elastic body 40 can receive a large load caused by a large displacement of the electrode body 38 at the soft portion 44 and a small load caused by a small displacement of the electrode body 38 at the hard portion 42. Furthermore, when the elastic body 40 shown in FIG. 7 is disposed outside the housing 13, the elastic body 40 can bear a large load caused by a large displacement of the nonaqueous electrolyte secondary battery 10 at the soft portion 44, and can bear a small load caused by a small displacement of the nonaqueous electrolyte secondary battery 10 at the hard portion 42.

[0062] The elastic body 40 shown in FIG. 7 has a recess 46 recessed in the first direction X. A portion of the non-recessed portion adjacent to the recess 46 can be displaced toward the recess 46 when a load is applied from the non-aqueous electrolyte secondary battery 10 or the electrode body 38. Therefore, by providing the recess 46, the non-recessed portion can be easily deformed. Here, in order to make the soft portion 44 more easily deformable than the hard portion 42, it is preferable to make the ratio of the area of ​​the recess 46 to the area of ​​the soft portion 44 larger than the ratio of the area of ​​the recess 46 to the area of ​​the hard portion 42 when viewed from the first direction X. Note that, in the elastic body 40 shown in FIG. 7, the recess 46 is arranged only in the soft portion 44, but the recess 46 may be arranged in the hard portion 42.

[0063] The recess 46 includes a core portion 46a and multiple line portions 46b. The core portion 46a is circular and is disposed at the center of the elastic body 40 when viewed from the first direction X. The multiple line portions 46b extend radially from the core portion 46a. As the line portions 46b extend radially, the proportion of the line portions 46b increases closer to the core portion 46a, and the non-recessed portion decreases. Therefore, the non-recessed portion is more likely to deform in the region closer to the core portion 46a.

[0064] Although not illustrated in the drawings, the elastic body 40 may have a plurality of through holes penetrating the elastic body 40 in the first direction X, instead of or in addition to the recesses 46 described above. By providing the through holes, the non-through hole portion can be made easier to deform. Therefore, in order to make the soft portion 44 easier to deform than the hard portion 42, it is preferable to make the ratio of the area of ​​the through holes to the area of ​​the soft portion 44 larger than the ratio of the area of ​​the through holes to the area of ​​the hard portion 42, as viewed from the first direction X.

[0065] Other examples of the elastic body will be described below.

[0066] FIG. 8 is a schematic cross-sectional view of a portion of the elastic body sandwiched between the electrode body and the housing. The elastic body 40 receives a load from the electrode body 38 in the stacking direction (first direction X) of the electrode body 38. The elastic body 40 has a base material 42a on which a hard portion 42 having a predetermined hardness is formed, and a soft portion 44 softer than the hard portion 42. The hard portion 42 is a protruding portion that protrudes from the base material 42a toward the electrode body 38, and breaks or undergoes plastic deformation when subjected to a load equal to or greater than a predetermined load. The soft portion 44 is sheet-shaped and is disposed closer to the electrode body 38 than the base material 42a on which the hard portion 42 is formed. However, the soft portion 44 is separated from the electrode body 38. The soft portion 44 has a through hole 44a at a position overlapping with the hard portion 42 when viewed from the first direction X, and the hard portion 42 is inserted into the through hole 44a, and the tip of the hard portion 42 protrudes from the soft portion 44.

[0067] As the shape of the hard portion 42 changes, the elastic body 40 transitions from a first state in which the load from the electrode body 38 is received by the hard portion 42 to a second state in which the load is received by the soft portion 44. That is, the elastic body 40 first receives the load in the stacking direction of the electrode body 38 due to the expansion of the electrode body 38 by the hard portion 42 (first state). If the amount of expansion of the electrode body 38 increases for some reason and a load that cannot be received by the hard portion 42 is applied to the hard portion 42, the hard portion 42 breaks or plastically deforms, the electrode body 38 comes into contact with the soft portion 44, and the load in the stacking direction of the electrode body 38 is received by the soft portion 44 (second state).

[0068] In the case of an elastic body having an uneven shape, the compressive elastic modulus is calculated as follows: Compressive elastic modulus (MPa) = Load (N) / Projected area of ​​elastic body in the surface direction (mm 2 ) × (deformation amount of elastic body (mm) / thickness to the protrusion of the elastic body (mm)).

[0069] The electrolyte is, for example, a non-aqueous electrolyte containing a supporting salt in an organic solvent (non-aqueous solvent). For the non-aqueous solvent, for example, esters, ethers, nitriles, amides, and mixed solvents of two or more of these are used. For the supporting salt, for example, a lithium salt such as LiPF6 is used.

[0070] <Example> The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0071] <Example 1> [Preparation of positive electrode] The positive electrode active material is LiNi 0.82 Co 0.15 Al 0.03 A lithium transition metal composite oxide represented by O2 was used. This positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a solid mass ratio of 97:2:1, and N-methyl-2-pyrrolidone (NMP) was used as a dispersion medium to prepare a positive electrode composite slurry.

[0072] The positive electrode current collector has a thermal conductivity of 150 W / (m K), a Mg content of 1.5 mass%, a liquidus temperature of 651°C, and a Young's modulus of 68.6 kN / mm 2 An Al-Mg alloy foil having the above structure was prepared.

[0073] The positive electrode composite slurry was applied to both sides of the Al-Mg alloy foil, and the coating was dried and rolled, and then cut to a predetermined electrode size to obtain a positive electrode in which a positive electrode active material layer was formed on both sides of the positive electrode current collector.

[0074] [Preparation of negative electrode] Graphite particles as the negative electrode active material, a dispersion of SBR, and CMC-Na were mixed in a solid content mass ratio of 100:1:1.5, and water was used as a dispersion medium to prepare a negative electrode composite slurry. This negative electrode composite slurry was applied to both sides of a negative electrode current collector made of copper foil, the coating was dried, rolled, and then cut into a predetermined electrode size to obtain a negative electrode in which a negative electrode active material layer was formed on both sides of the negative electrode current collector. When the negative electrode was produced, the compressive elastic modulus of the negative electrode active material layer was measured and found to be 660 MPa.

[0075] [Preparation of electrolyte] Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4. LiPF6 was dissolved in the mixed solvent to a concentration of 1.4 mol / L to prepare an electrolyte solution.

[0076] [Preparation of non-aqueous electrolyte secondary battery] The negative electrode, a separator having a compressive elastic modulus of 120 MPa, and the positive electrode were laminated in this order, wound, and then molded into a flat shape to prepare a flat-wound electrode body. The negative electrode and the positive electrode were connected to a positive electrode terminal and a negative electrode terminal, and the electrode body was housed in an exterior body made of an aluminum laminate. After the electrolyte solution was injected, the opening of the exterior body was sealed to prepare a nonaqueous electrolyte secondary battery.

[0077] The fabricated nonaqueous electrolyte secondary battery was sandwiched between a pair of elastic bodies (urethane foam having a compressive elastic modulus of 60 MPa), which were then sandwiched and fixed between a pair of end plates to fabricate a secondary battery module.

[0078] <Example 2> The positive electrode current collector has a thermal conductivity of 138 W / (m K), a Mg content of 2.4 mass%, a liquidus temperature of 653°C, and a Young's modulus of 70.6 kN / mm 2 A secondary battery module was fabricated in the same manner as in Example 1, except that an Al-Mg alloy foil was used.

[0079] <Example 3> The positive electrode current collector has a thermal conductivity of 117 W / (m K), a Mg content of 4.7 mass%, a liquidus temperature of 640°C, and a Young's modulus of 70.6 kN / mm 2 A secondary battery module was fabricated in the same manner as in Example 1, except that an Al-Mg alloy foil was used.

[0080] <Example 4> The positive electrode current collector has a thermal conductivity of 65 W / (m K), a Mg content of 93 mass%, a liquidus temperature of 595°C, and a Young's modulus of 45 kN / mm 2 A secondary battery module was fabricated in the same manner as in Example 1, except that an Al-Mg alloy foil was used.

[0081] <Example 5> A secondary battery module was produced in the same manner as in Example 1, except that the Al-Mg alloy foil of Example 3 was used as the positive electrode current collector, and urethane foam having a compressive elastic modulus of 5 MPa was used as the elastic body.

[0082] <Example 6> A secondary battery module was produced in the same manner as in Example 1, except that the Al-Mg alloy foil of Example 3 was used as the positive electrode current collector, and urethane foam having a compressive elastic modulus of 120 MPa was used as the elastic body.

[0083] <Comparative Example 1> The positive electrode current collector has a thermal conductivity of 190 W / (m K), a magnesium content of 0 mass%, a liquidus temperature of 650°C, and a Young's modulus of 68.6 kN / mm 2 A secondary battery module was fabricated in the same manner as in Example 1, except that an Al foil was used.

[0084] <Comparative Example 2> The positive electrode current collector has a thermal conductivity of 180 W / (m K), a magnesium content of 0 mass%, a liquidus temperature of 610°C, and a Young's modulus of 73.5 kN / mm 2 A secondary battery module was fabricated in the same manner as in Example 1, except that an Al foil was used.

[0085] <Comparative Example 3> A secondary battery module was produced in the same manner as in Example 1, except that the Al-Mg alloy foil of Example 3 was used as the positive electrode current collector, a separator having a compressive elastic modulus of 230 MPa was used, and a urethane foam having a compressive elastic modulus of 200 MPa was used as the elastomer.

[0086] [Measurement of battery internal resistance] The battery internal resistance was measured for the secondary battery modules of each Example and Comparative Example under the following conditions. The secondary battery modules were adjusted to a state of charge of SOC 60%, and were subjected to constant current discharge at a rate of 5C for 10 seconds under a temperature condition of 25°C, and the voltage drop amount (V) was calculated. The voltage drop amount (V) was then divided by the corresponding current value (I) to calculate the battery internal resistance (Ω).

[0087] [Measurement of heat generation from batteries using nail penetration tests] The secondary battery modules of each Example and Comparative Example were adjusted to a state of charge of SOC 100% under a temperature condition of 25° C. Then, a needle with a radius of 0.5 mm and a tip curvature of φ0.9 mm was pierced at a speed of 0.1 mm / sec in the thickness direction of the nonaqueous electrolyte secondary battery so as to connect the positive electrode and the negative electrode, thereby generating an internal short circuit. An ammeter was then connected between the positive and negative electrodes, and the amount of current flowing to an external load during the short circuit was measured to calculate the amount of heat generated.

[0088] Table 1 shows the physical properties of the positive electrode current collector, elastomer, separator, and negative electrode active material layer used in each Example and Comparative Example, as well as the test results of each Example and Comparative Example.

[0089] [Table 1]

[0090] In all of Examples 1 to 6, which used positive electrode current collectors in which the compressive modulus of the elastic body was 5 MPa to 120 MPa, which contained Al and elements other than Al, and which had thermal conductivity in the range of 65 W / (m K) to 150 W / (m K), the amount of heat generated by the batteries in the nail penetration test was suppressed compared to Comparative Examples 1 to 3, which did not satisfy the above requirements.

[0091] The secondary battery modules of each Example and Comparative Example were charged at a constant current of 0.33 C until the voltage reached 4.2 V under a temperature condition of 25° C., and then discharged at a constant current of 0.33 C until the voltage reached 3.0 V. This charge / discharge cycle was repeated 1000 times. Then, the secondary battery module was disassembled, the flat-wound electrode body was taken out, and it was confirmed whether or not the positive electrode current collector at the corner of the electrode body had been broken. As a result, only in Comparative Example 3, the positive electrode current collector at the corner had been broken. [Explanation of symbols]

[0092] 1 Secondary battery module 2. Laminate 4 End Plate 6 Restraint member 8 Cooling plate 10 Nonaqueous electrolyte secondary battery 12 Insulating spacer 13. Cabinet 14 Outer can 16 Sealing plate 18 Output terminal 38 Electrode body 38a Positive electrode 38b negative electrode 38d Separator 39 Winding core 40 Elastic Body 42 Hard part 42a Base material 44 Soft part 44a through hole 46 Recess 46a core 46b Line part 50 Positive electrode current collector 52 Cathode active material layer 54 Negative electrode current collector 56 Negative electrode active material layer 58 Nail

Claims

1. A secondary battery module including at least one nonaqueous electrolyte secondary battery and an elastic body arranged together with the nonaqueous electrolyte secondary battery and receiving a load from the nonaqueous electrolyte secondary battery in the arrangement direction, The nonaqueous electrolyte secondary battery includes an electrode assembly in which a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode are laminated, and a case that houses the electrode assembly, The elastic body has a compressive elastic modulus of 60 MPa to 120 MPa; the positive electrode has a positive electrode current collector containing Al and an element other than Al, and the positive electrode current collector has a thermal conductivity of 65 W / (m·K) to 150 W / (m·K).

2. The Young's modulus of the positive electrode current collector is 45 kN / mm ２ ~73.5kN / mm ２ The secondary battery module according to claim 1 ,

3. 3 . The secondary battery module according to claim 1 , wherein the elements other than Al include Mg, and the content of Mg in the positive electrode current collector is 1.5 mass % or more.

4. 4. The secondary battery module according to claim 1, wherein the positive electrode current collector has a liquidus temperature of 650° C. or lower.

5. the separator has a compressive elastic modulus smaller than that of the negative electrode active material layer constituting the negative electrode, 5. The secondary battery module according to claim 1, wherein the elastic body has a compressive elastic modulus smaller than that of the separator.

6. A nonaqueous electrolyte secondary battery comprising: an electrode assembly in which a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode are laminated; an elastic body that receives a load from the electrode assembly in a lamination direction of the electrode assembly; and a case that contains the electrode assembly and the elastic body, The elastic body has a compressive elastic modulus of 60 MPa to 120 MPa; the positive electrode has a positive electrode current collector containing Al and an element other than Al, and the thermal conductivity of the positive electrode current collector is 65 W / (m·K) to 150 W / (m·K).

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