JP2014041799A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery capable of surely inhibiting a battery can from being burst even when it enters the thermorunaway state.SOLUTION: In the outer peripheral part OFa of a shaft core 33A, a recess 55a is formed whose cross-sectional shape in the direction orthogonal to an axis line is a V-character shape and is opened toward the outer side in the radial direction of the shaft core 33A and both sides in the axial direction.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery such as a lithium ion battery.

  Non-aqueous electrolyte secondary batteries such as lithium ion batteries become overcharged when exposed to an abnormally high temperature environment or due to a failure of the charging device, and the temperature inside the battery container rises. A gas may be generated due to decomposition or vaporization of the non-aqueous electrolyte, and the internal pressure in the battery container may increase, and the battery container may be damaged. Therefore, in this type of secondary battery container, in order to prevent an increase in internal pressure in the battery container, when the internal pressure increases due to the generated gas, a gas discharge port provided with a safety valve is provided to discharge the generated gas. ing.

  However, when the temperature rise in the battery container proceeds, the positive electrode plate and the negative electrode plate may come into contact with each other due to meltdown of the separator, breakage of the shaft core, or the like. When a short-circuit occurs, a large current flows through the short-circuited portion, so that the non-aqueous electrolyte may be thermally decomposed or vaporized in a chain, and the non-aqueous electrolyte secondary battery may reach a thermal runaway state. .

  In Japanese Patent No. 4688612 (Patent Document 1), in order to suppress the breakage of the shaft core that causes a short circuit, it can be compressed and deformed so that the distortion of the wound electrode plate group can be absorbed. A non-aqueous electrolyte secondary battery having an axial core made of a flexible material is disclosed.

Japanese Patent No. 4688612

  If the shaft core is configured to be compressible and deformable as in Patent Document 1, the shaft core is prevented from being broken, so that a short circuit is unlikely to occur and the nonaqueous electrolyte secondary battery is prevented from being in a thermal runaway state. There is a certain effect.

  However, in high capacity and high output non-aqueous electrolyte secondary batteries that have been developed in recent years, the energy state in the battery container is high when the internal pressure in the battery container reaches the operating pressure of the safety valve. There is a case. When the non-aqueous electrolyte secondary battery reaches a thermal runaway state when the energy state in the battery container is high, the gas generation speed in the battery container exceeds the gas discharge capacity of the safety valve. The can is filled and the internal pressure in the battery container rises rapidly. For this reason, in high-capacity, high-power non-aqueous electrolyte secondary batteries, even if a safety valve is installed, the speed of gas generation inside the battery exceeds the gas discharge capacity of the safety valve, and the battery contents are violently exhausted from the gas discharge port. The battery can may explode or explode.

  An object of the present invention is to provide a non-aqueous electrolyte secondary battery that can reliably prevent a battery can from bursting even in a thermal runaway state.

  In addition to the above object, another object of the present invention is to provide a non-aqueous electrolyte secondary battery capable of causing a short circuit at an early stage in a state where the energy state in the battery container is low when an abnormality occurs.

  In the present invention, a wound electrode plate group in which a positive electrode plate and a negative electrode plate are wound around a hollow shaft core via a separator is housed in a battery container together with a non-aqueous electrolyte. A non-aqueous electrolyte secondary battery provided with a safety valve is targeted for improvement. The shaft core used in the present invention is compressed and deformed by the internal pressure before the internal pressure in the battery container rises due to the decomposition reaction of the non-aqueous electrolyte and reaches the operating pressure of the safety valve. It is configured to cause a short circuit. In the present invention, the shaft core is first compressed and deformed before gas is generated by the decomposition reaction of the non-aqueous electrolyte and the internal pressure in the battery container rises and the internal pressure reaches the operating pressure of the safety valve. When the shaft core compressively deforms, the electrode plate group also deforms following the deformation, not only the shaft core breakage, but also the separator breakage and electrode plate breakage. A short circuit occurs when the positive electrode plate and the negative electrode plate come into contact with each other. As a result, in the nonaqueous electrolyte secondary battery of the present invention, a short circuit occurs in a state where the energy state in the battery can is lower than that of the conventional nonaqueous electrolyte secondary battery. Even when the non-aqueous electrolyte secondary battery reaches a thermal runaway due to a short circuit, the speed of gas generation inside the battery does not exceed the gas discharge capacity of the safety valve, thus preventing the battery can from bursting. .

  As a specific shaft core, a thin part and a thick part thicker than the thin part can be formed. Since the thin-walled portion has lower mechanical strength than the thick-walled portion, when the internal pressure in the battery container increases, the thin-walled portion first compresses and deforms. With this configuration, the shaft core is more easily compressed and deformed than when the shaft core does not have a thin wall portion. Therefore, before the safety valve operates, that is, in a state where the energy state in the battery container is low. In addition, the shaft core can be compressed and deformed to cause a short circuit.

  The thin portion can be formed by a portion corresponding to a recess formed in the outer peripheral portion of the shaft core along the axial direction of the shaft core. Here, the portion corresponding to the recess means a portion where the thickness is reduced as a result of the formation of the recess. Since such a thin part can be formed by processing a part of the outer peripheral part of the shaft core, the thin part can be easily formed on the shaft core. In addition, the corners of the recesses may possibly damage a part of the electrode plate group when the shaft core is compressed and deformed.

  Moreover, you may form a thin part by the part corresponding to the recessed part formed in the inner peripheral part of an axial core along the axial direction of an axial core. Here, the portion corresponding to the recess means a portion where the thickness is reduced as a result of the formation of the recess. When the thin wall portion is formed in this way, no corner portion is particularly formed on the outer peripheral portion of the shaft core, and the corner portion formed at the boundary portion between the thin wall portion and the thick wall portion is the inner portion of the shaft core. It is formed only on the periphery. Therefore, since the positive electrode plate, the negative electrode plate and the separator wound around the shaft core are not damaged by the corners of the recesses, during normal use where no abnormality has occurred in the nonaqueous electrolyte secondary battery, It is possible to prevent a short circuit from occurring due to the corner portion.

  The concave portion can have any shape, and for example, preferably has a cross-sectional shape in which the thickness of the thin portion is constant. When the concave portion has such a cross-sectional shape, since the thickness of the entire thin portion becomes a uniform value, the mechanical strength of the thin portion becomes substantially equal throughout the thin portion, and when the internal pressure in the battery container increases, The entire thin portion is deformed, and the shaft core can be reliably compressed and deformed.

  The concave portion may have a cross-sectional shape in which the thickness of the thin portion is gradually reduced to a minimum value as it goes in one direction in the circumferential direction of the shaft core, and further, the thickness is gradually increased as it goes in one direction. When the concave portion having such a cross-sectional shape is used, the stress generated in the shaft core due to the increase in the internal pressure in the battery container is concentrated on the portion where the thickness becomes the minimum value, so that the shaft core can be reliably compressed and deformed. .

  It is preferable that the ratio of the thickness of the thin portion to the other portion of the shaft core is 5: 100 to 95: 100. When the ratio of the minimum thickness of the thin part to the thickness of the other part of the shaft is in this range, the energy state in the battery container is reliably lower when an abnormality occurs than when the thin part is not formed. A short circuit can occur.

It is a fragmentary sectional view of the lithium ion battery of one embodiment of the present invention. It is a figure which shows the state which winds an electrode group. It is a perspective view of a positive electrode current collector. It is the figure which looked at the positive electrode current collector from the positive electrode battery lid side. (A)-(F) are perspective views of six types of shaft cores that can be used in the present embodiment, and (G) is a perspective view of a conventional shaft core. (A)-(F) is the figure which looked at the axial center shown to FIG. 5 (A)-(F), respectively from the edge part side of the direction where an axis line is extended. It is a table | surface which shows a test result.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of a lithium ion battery according to an embodiment of the present invention cut along the longitudinal direction. In FIG. 1, a part of the cross section of the electrode plate group 9 is not shown. The cylindrical lithium ion battery 1 of the present embodiment includes a battery container body 3, a positive electrode side battery cover 5, a negative electrode side battery cover 7, an electrode plate group 9 infiltrated with an electrolyte, and a positive electrode current collector 11. And a negative electrode current collector 13. The battery container body 3 has a cylindrical shape with both ends opened by a nickel-plated steel material. Openings at both ends of the battery container body 3 are respectively closed by the positive battery cover 5 and the negative battery cover 7. The positive electrode side battery cover 5 and the negative electrode side battery cover 7 are provided with gas discharge ports 5a and 7a, respectively, and terminal through holes 5b and 7b are provided at the center thereof. The gas discharge ports 5a and 7a are closed by the cleavable safety valves 6 and 8, similar to the safety valve structure disclosed in, for example, Japanese Patent Laid-Open No. 11-273650, and the cleavable safety valves 6 and 8 are not shown in FIG. Is held by. The safety valves 6 and 8 generate gas in the battery case main body 3 and release the generated gas when the pressure in the battery case main body 3 becomes equal to or higher than a certain level. An output terminal portion 15 of the positive electrode current collector 11 and an output terminal portion 17 of the negative electrode current collector 13 which will be described later pass through the terminal through holes 5 b and 7 b through a rubber packing 19. Screw portions are formed on the outer peripheral portions of the output terminal portions 15 and 17, and nut members 21 are screwed into the screw portions, respectively. A washer 23 is disposed between the nut member 21 and the positive battery cover 5 and the negative battery cover 7. Note that a screw member 25 as a sealing member is screwed to the positive electrode side battery cover 5 at a liquid injection port for containing an electrolytic solution.

A non-aqueous electrolyte is infiltrated into the electrode plate group 9. In the present embodiment, a solution obtained by dissolving lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate is used as the nonaqueous electrolytic solution.

  FIG. 2 is a diagram showing a state in which the electrode plate group 9 used in the present embodiment is wound. The electrode plate group 9 is configured by winding a belt-like positive electrode plate 27 and a belt-like negative electrode plate 29 in a spiral shape with a hollow cylindrical shaft core 33 as a center through a separator 31. In this specification, the hollow cylindrical shaft core includes a substantially cylindrical shaft core in which a concave portion is provided along the axis on a part of the outer peripheral surface or inner peripheral surface of the shaft core. The positive electrode plate 27 of the present embodiment has a configuration in which a positive electrode mixture containing lithium manganate, which is a lithium transition metal double oxide, is applied almost uniformly on both surfaces of an aluminum foil as a positive electrode current collector plate. On one side extending in the longitudinal direction of the aluminum foil, an uncoated portion 35 that is not coated with the positive electrode mixture is formed. The uncoated part 35 is cut out in a comb-like shape, and a plurality of positive electrode lead pieces 37 are formed by the remaining part cut out. The negative electrode plate 29 has a configuration in which a negative electrode mixture containing carbon powder capable of occluding and releasing lithium ions as a negative electrode active material is applied almost uniformly on both surfaces of a rolled copper foil as a negative electrode current collector plate. On one side extending in the longitudinal direction of the copper foil, an uncoated portion 39 that is not coated with the negative electrode mixture is formed. The uncoated part 39 is notched in a comb-like shape, and a plurality of negative electrode lead pieces 41 are formed by the notched remaining part. In FIG. 1, a plurality of positive electrode lead pieces 37 are located on the positive electrode side battery lid 5 side, and a plurality of negative electrode lead pieces 41 are located on the negative electrode side battery lid 7 side. The separator 31 is formed of a polyethylene porous material through which lithium ions can pass. The separator 31 allows the passage of ions and prevents the positive electrode plate 27 and the negative electrode plate 29 from contacting each other. The shaft core 33 is made of polypropylene resin. A specific configuration of the shaft core 33 will be described in detail later. Note that the detailed configuration of the positive electrode plate 27, the negative electrode plate 29, and the separator 31 is not related to the gist of the present invention, and thus detailed description thereof is omitted.

  Between the positive electrode side battery cover 5 and the end portion of the electrode plate group 9, a positive electrode current collector 11 to which a plurality of positive electrode lead pieces 37 are connected is disposed adjacent to the end portion of the electrode plate group 9. . A negative electrode current collector 13 to which a plurality of negative electrode lead pieces 41 are connected is disposed adjacent to the end of the electrode plate group 9 between the negative electrode side battery cover 7 and the end of the electrode plate group 9. ing. In the present embodiment, the positive electrode current collector 11 and the negative electrode current collector 13 have substantially the same shape.

  3 is a perspective view of the positive electrode current collector 11 used in the present embodiment, and FIG. 4 is a view of the positive electrode current collector 11 viewed from the positive electrode battery lid 5 side. The positive electrode current collector 11 includes an output terminal portion 15 at the center of an annular current collector body 43. The output terminal portion 15 is configured to penetrate the positive electrode side battery lid 5 and extend to the outside. The current collector body 43 is formed with an annular recess 45 centered on the output terminal portion 15. The annular recess 45 opens toward the direction in which the output terminal portion 15 extends. A plurality of ventilation through holes 46 are provided at the bottom of the annular recess 45. It is not necessary to provide a plurality of ventilation through holes 46, and only one ventilation through hole 46 may be provided. The positive electrode current collector 11 includes a columnar portion 47 that is inserted into the shaft core 33 of the electrode plate group 9 on the side opposite to the side on which the output terminal portion 15 of the current collector body 43 is provided. By inserting the columnar portion 47 into one end portion of the shaft core 33, the positional relationship between the positive electrode current collector 11 and the electrode plate group 9 is established. The ends of the plurality of positive electrode lead pieces 37 are ultrasonically welded to the outer peripheral portion of the current collector body 43 of the positive electrode current collector 11.

  In the present embodiment, as shown in FIG. 1, the negative electrode current collector 13 has substantially the same shape as the positive electrode current collector 11, and the current collector main body 49, the output terminal portion 17, , A concave portion 51 and a columnar portion 53. Also in the negative electrode current collector 13, the columnar portion 53 is inserted into the shaft core 33 of the electrode plate group 9, and the positional relationship between the negative electrode current collector 13 and the electrode plate group 9 is determined. The ends of the plurality of negative electrode lead pieces 41 are ultrasonically welded to the outer peripheral portion of the current collector body 49 of the negative electrode current collector 13. Since the negative electrode current collector 13 has substantially the same shape as the positive electrode current collector 11, in FIG. 3 and FIG. Illustration of the electric body is omitted.

  FIGS. 5A to 5F are perspective views of six types of shaft cores 33 that can be used in this embodiment, and FIG. 5G is a perspective view of a conventional shaft core. FIGS. 6A to 6F are views of the shaft cores shown in FIGS. 5A to 5F viewed from the end side in the direction in which the axis extends.

  In the shaft cores 33A to 33C shown in FIGS. 5A to 5C and FIGS. 6A to 6C, the outer peripheral portions OFa to OFc of the shaft cores 33A to 33C are arranged in the axial direction of the shaft cores 33A to 33C. Concave portions 55a to 55c extending along the surface are formed.

  The shaft core 33A shown in FIGS. 5 (A) and 6 (A) has a V-shaped cross section in a direction perpendicular to the axis, and opens toward the radially outer side of the shaft core 33A and both sides in the axial direction. A concave portion 55a is formed in the outer peripheral portion OFa. The shaft core 33B shown in FIGS. 5B and 6B has a circular cross section in a direction perpendicular to the axis, and opens toward the radially outer side of the shaft core 33B and both sides in the axial direction. A recess 55b is formed in the outer periphery OFb. Therefore, in the shaft core 33A shown in FIGS. 5A and 6A and the shaft core 33B shown in FIGS. 5B and 6B, the recesses 55a and 55b formed in the outer peripheral portions OFa and OFb. Has a cross-sectional shape in which the thickness gradually decreases to a minimum value as it goes in one circumferential direction of the shaft cores 33A and 33B, and further, the thickness gradually increases in one direction.

  The shaft core 33C shown in FIGS. 5 (C) and 6 (C) has a substantially U-shaped cross section and has a recess 55c that opens toward the radially outer side and both axial sides of the shaft core 33C. Formed in the part OFc. Specifically, it has two surfaces F1 and F2 extending so as to approach each other from the outer peripheral portion OFc of the shaft core 33C toward the center of the shaft core 33C, and a curved surface F3 connecting the two surfaces F1 and F2. A recess 55c is formed. The curved surface F3 is a circular arc surface formed so that the distance from the inner peripheral part IFc of the shaft core 33C is constant.

  In the shaft cores 33D to 33F shown in FIGS. 5D to 5F and FIGS. 6D to 6F, the axial directions of the shaft cores 33D to 33F are arranged on the inner peripheral portions IFd to IFf of the shaft cores 33D to 33F. Concave portions 55d to 55f extending along the line are formed. The shaft core 33D shown in FIGS. 5 (D) and 6 (D) has a V-shaped cross-sectional shape, and a recess 55d that opens toward the radially inner side and both axial sides of the shaft core 33D. It is formed in the part IFd. The shaft core 33E shown in FIGS. 5 (E) and 6 (E) has a recess 55e that has a circular cross section and opens toward the radially inner side and both axial sides of the shaft core 33E. Is formed. Therefore, in the shaft core 33D shown in FIGS. 5 (D) and 6 (D) and the shaft core 33E shown in FIGS. 5 (E) and 6 (E), the recesses 55d formed in the inner peripheral portions IFd and IFe and 55e has a cross-sectional shape in which the thickness gradually decreases to a minimum value as it goes in one direction in the circumferential direction of the shaft core 33, and the thickness gradually increases as it goes in one direction.

  The shaft core 33F shown in FIG. 5 (F) and FIG. 6 (F) has a substantially U-shaped cross section, and has a recess 33f that opens toward the radially inner side and both axial sides of the shaft core 33F. Is formed. Specifically, it has two surfaces F4 and F5 that extend from the inner peripheral portion IFf of the shaft core 33 toward the radially outer side of the shaft core 33F, and a curved surface F6 that connects the two surfaces. A recess 55f is formed. The curved surface F6 is an arc surface formed so that the distance from the outer peripheral portion OFf of the shaft core 33F is constant.

  In order to verify the effect of the thermal runaway countermeasure according to the present invention, the inventor uses the shaft cores 33A to 33F to which the thermal runaway countermeasure shown in FIGS. 5 (A) to (F) and FIGS. 6 (A) to (F) is applied. Charging at the start of thermal runaway when overcharged for the adopted lithium ion battery and the lithium ion battery (comparative example) employing a conventional shaft core that does not take measures against thermal runaway shown in FIG. 5 (G) And the presence or absence of can rupture after thermal runaway occurred.

  In this test, with respect to the shaft cores 33A to 33F shown in FIGS. 5A to 5F and FIGS. 6A to 6F, the thickness of the shaft cores 33A to 33F where the recesses 55a to 55f are not formed. Dimension (dimension a in FIGS. 6A to 6F) and the minimum thickness dimension of the shaft cores 33A to 33F in the recesses 55a to 55f (in FIGS. 6A to 6F) 11 axes having a ratio of (b) to 100: 5 to 100: 95 were prepared, and lithium ion batteries of Examples 1 to 11 were produced. Each of the manufactured lithium ion batteries and the conventional lithium ion battery that does not have a recess (ie, the ratio of a: b is 100: 100) is charged until it becomes overcharged, and lithium ions at the start of thermal runaway The battery charge rate SOC (%) and the presence or absence of rupture of the battery container body 3 due to the occurrence of thermal runaway were confirmed.

  FIG. 7 is a table showing the test results. According to the results shown in FIG. 7, all the lithium-ion ions in Examples 1 to 11 were formed in any of the concave shapes in FIGS. 5 (A) to (F) and FIGS. 6 (A) to (F). In the secondary battery, thermal runaway occurs at a lower charging rate than a conventional lithium ion secondary battery in which no concave portion is formed due to the fracture of the concave portion. In particular, thermal runaway occurs at a lower charging rate as the numerical value of b with respect to a is smaller, that is, as the minimum value of the thickness dimension of the shaft core 33 in the recess 55 is smaller. Moreover, in all the lithium ion secondary batteries of Examples 1 to 11, no rupture of the battery container due to the occurrence of thermal runaway was confirmed. The higher the charging rate, the higher the energy state in the battery container. Therefore, the test results shown in FIG. 7 show that all the lithium ion secondary batteries of Examples 1 to 11 have thermal runaway in a state where the energy state in the battery container is lower than that of the conventional lithium ion secondary battery. It shows that. On the other hand, in the conventional lithium ion secondary battery in which no recess was formed, the battery container was confirmed to be ruptured due to the occurrence of thermal runaway.

  In the above embodiment, the cross-sectional shape of the recess formed in the shaft core is the same along the direction in which the axis extends, but the recess is formed so that the cross-sectional shape changes toward the direction in which the axis extends. May be. For example, the depth of the concave portion may be deeper toward the central position in the axial direction, and the depth of the concave portion may be shallower away from the central position. The reverse is also possible. Furthermore, you may form the part where the depth of a recessed part becomes deep at predetermined intervals in an axial direction.

  In the above embodiment, the lithium ion battery has been described. However, the present invention can of course be applied to other non-aqueous electrolyte secondary batteries.

  According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery that can reliably prevent a battery can from bursting even when a thermal runaway state is reached.

DESCRIPTION OF SYMBOLS 1 Lithium ion battery 3 Battery container main body 5 Positive electrode side battery cover 5a Gas discharge port 5b Terminal through-hole 6 Safety valve 7 Negative electrode side battery cover 7a Gas discharge port 7b Terminal through hole 8 Safety valve 9 Electrode plate group 11 Positive electrode collector 13 Negative electrode collection Electrical body 15 Output terminal portion 17 Output terminal portion 19 Rubber packing 21 Nut member 23 Washer 25 Screw member 27 Positive electrode plate 29 Negative electrode plate 31 Separator 33 Axle core 35 Uncoated portion 37 Positive electrode lead piece 39 Uncoated portion 41 Negative electrode lead piece 43 current collector body 45 recess 46 through-hole 47 columnar portion 49 current collector body 51 recess 53 columnar portion 55 recess

Claims (7)

A wound electrode plate group in which a positive electrode plate and a negative electrode plate are wound around a hollow shaft core via a separator is housed in a battery container together with a non-aqueous electrolyte, and a safety valve is provided in the battery container. Non-aqueous electrolyte secondary battery,
The wound electrode plate is compressed and deformed by the internal pressure before the internal pressure rises due to the decomposition reaction of the non-aqueous electrolyte and the internal pressure reaches the operating pressure of the safety valve. A non-aqueous electrolyte secondary battery characterized by being configured to cause a short circuit within a group.   2. The non-aqueous electrolysis according to claim 1, wherein a thin portion and a thick portion having a thickness larger than the thin portion are formed on the shaft core, and the thin portion is first compressed and deformed. Liquid secondary battery.   The non-aqueous electrolyte secondary battery according to claim 2, wherein the thin portion is formed by a portion corresponding to a recess formed in an outer peripheral portion of the shaft core along an axial direction of the shaft core.   The non-aqueous electrolyte secondary battery according to claim 2, wherein the thin portion is formed by a portion corresponding to a recess formed in an inner peripheral portion of the shaft core along an axial direction of the shaft core.   The non-aqueous electrolyte secondary battery according to claim 3, wherein the recess has a cross-sectional shape in which the thickness of the thin portion is constant.   The concave portion has a cross-sectional shape in which the thickness of the thin portion gradually decreases to a minimum value as it goes in one direction in the circumferential direction of the shaft core, and further, the thickness gradually increases as it goes in one direction. The nonaqueous electrolyte secondary battery according to claim 3 or 4.   7. The non-aqueous electrolyte 2 according to claim 2, wherein the ratio of the minimum thickness of the thin portion to the thickness of the other portion of the shaft is 5: 100 to 95: 100. Next battery.