JP5122169B2 - Electrochemical element - Google Patents

Description

  The present invention relates to a sealed electrochemical device, and more specifically, even if a sudden increase in internal pressure occurs due to gas generation inside the electrochemical device, the exhaust valve is effectively functioned by securing a gas flow path. Regarding technology.

  Electrochemical elements, particularly non-aqueous electrolyte secondary batteries that can be charged and discharged and have a high energy density, are actively studied for the introduction of new high-capacity active materials with the aim of further improving the energy density. As specific examples, the active material is being developed from lithium cobalt oxide to lithium nickel oxide for the positive electrode, and from graphite to an alloy material containing silicon, tin, etc. for the negative electrode.

A non-aqueous electrolyte secondary battery using these active materials is usually formed by laminating a positive electrode and a negative electrode via a separator to form an electrode group, and after housing the electrode group in the case, the opening of the case It is often the case that a sealed structure is formed by sealing with a sealing plate. Thus, when taking a sealed structure, the following two safety mechanisms will be provided. First, an exhaust valve that operates when the internal pressure in the case reaches a predetermined pressure is incorporated in the sealing plate, for example, in order to discharge gas generated inadvertently such as internal short circuit or high temperature storage to the outside of the case. Second, since the terminal provided on the sealing plate is electrically connected to either the positive electrode or the negative electrode, and the case is electrically connected to the other electrode, the sealing plate and the case are electrically connected. In addition to insulation, a perforated plate is disposed between the electrode group and the sealing plate to electrically insulate the two (for example, see Patent Document 1). The perforated plate is made of, for example, polyolefin resin such as polyethylene resin or polypropylene resin, or phenol resin containing glass cloth as a base material and containing an inorganic additive.
JP 2002-231314 A

  However, the above-described high-capacity active material has a high potential, and the amount and generation rate of gas generated unexpectedly are also remarkable. In addition, in non-aqueous electrolyte secondary batteries using these high-capacity active materials, in order to further improve energy density, the excess volume inside the case is often scraped as much as possible, and the gas is generated with a significant momentum. When it occurs, the path of gas to the exhaust valve is restricted, which causes a problem that the gas cannot be smoothly discharged to the outside of the case.

  The present invention has been made in view of the above problems, and when the electrochemical element such as a non-aqueous electrolyte secondary battery having a high energy density is put into practical use in a sealed structure, by optimizing the structure inside the case, The purpose is to operate the safety mechanism normally even when it is unforeseen.

  In order to achieve the above-mentioned object, the inventors tried to analyze in detail the main cause that the safety mechanism does not operate normally when gas is suddenly generated inside the case unexpectedly. As a result, when the internal pressure suddenly increases in the case, the perforated plate randomly provided between the electrode group and the sealing plate is deformed to induce deformation near the exhaust valve built in the sealing plate. As a result, it was clarified that the gas could not reach the exhaust valve efficiently and the exhaust efficiency was lowered. The present invention has been made based on the elucidated results.

Specifically, the present invention is an electrochemical element in which an electrode group in which a positive electrode and a negative electrode are laminated via a separator is housed in a case having an opening, and the opening of the case is sealed by a sealing plate. And an exhaust valve that operates when the internal pressure in the case reaches a predetermined pressure and opens the generated gas in the case to the outside, and has a hole, and is provided between the electrode group and the exhaust valve. a perforated plate, wherein the perforated plate state, and are 20% to 50% of the area of the area except for the hole is the opening, as the hole, located in the center of the perforated plate a second hole portion which includes a first hole portion which is located offset from the second hole, an electrochemical device is characterized that you have been formed.

  In the present invention, since the area of the perforated plate excluding the hole portion is 20 to 50% with respect to the area of the case opening, the perforated plate can be prevented from being damaged even when an impact such as dropping is applied. The generated gas can be appropriately discharged through the section.

  Here, the exhaust valve may be provided on the sealing plate.

  The perforated plate may have a function of electrically insulating the electrode group and the sealing plate. In this aspect, since it is not necessary to provide an insulating part other than the perforated plate, the number of parts can be reduced.

  The perforated plate may have a function of electrically insulating the electrode group and the case.

  The perforated plate may be made of a hard insulating material.

  The perforated plate may be constituted by a metal plate in which an insulating material is disposed on at least one side. In this aspect, a perforated plate having sufficient strength and insulation can be produced at low cost.

  A lithium nickel composite oxide may be used as the positive electrode active material. In this aspect, even when a lithium nickel composite oxide with a large amount of gas generation is used as the positive electrode active material, by appropriately defining the area of the hole of the perforated plate, it is possible to appropriately release the gas through the exhaust valve. It can be carried out.

  The electrode group may have a wound structure.

  The electrode group is provided with a gap through which the generated gas can pass, and the area of the gap when viewed from the exhaust valve is S0, and the gap when viewed from the exhaust valve is defined by the perforated plate. Assuming that the blocked area is S1, the opening area ratio represented by (S0-S1) / S0 is preferably 0.45 or more. In this aspect, it is possible to prevent the flow of the generated gas from being obstructed by the perforated plate.

  The electrode group is provided with a gas discharger having an inner hole through which the generated gas can pass, and the area of the inner hole when viewed from the exhaust valve is S2, and when viewed from the exhaust valve When the area where the inner hole is blocked by the perforated plate is S3, the opening area ratio represented by (S2-S3) / S2 is preferably 0.3 or more. In this aspect, it is possible to prevent the flow of the generated gas from being obstructed by the perforated plate.

  It is preferable that a protrusion is provided on the periphery of the hole of the perforated plate so as to block a part of the inner hole of the gas discharger as viewed from the exhaust valve. In this aspect, the gas discharger can be prevented from popping out at the time of impact or gas discharge by the protrusion while allowing the generated gas to be discharged by the hole of the perforated plate.

  As described above, according to the present invention, there is provided a high energy density electrochemical device that can smoothly operate an exhaust valve even when gas is suddenly generated inside the case unexpectedly and has strong electrical insulation. it can.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  In one embodiment of the electrochemical device according to the present invention, an electrode group in which a positive electrode and a negative electrode are laminated via a separator is housed in a case, and the opening of the case is sealed with a sealing plate. An exhaust valve having a function of opening the generated gas in the case to the outside by operating when the internal pressure in the case reaches a predetermined pressure, and a perforated plate disposed between the electrode group and the exhaust valve Is provided. Hereinafter, a specific configuration of the electrochemical device according to the present embodiment will be described.

  FIG. 1 is a schematic diagram illustrating an electrochemical device according to the present embodiment, and FIG. 2 is a schematic diagram illustrating an example of a state before sealing with a sealing plate when viewed from an opening of a case. FIG. 3 is a longitudinal sectional view partially showing the electrochemical element.

  The case 4 houses the electrode group 3 and the perforated plate 2. The electrode group 3 is formed by laminating a positive electrode plate and a negative electrode plate via a separator and winding them in a spiral shape. After the electrode group 3 is accommodated in the case 4, the perforated plate 2 is disposed on the electrode group 3, and the opening at the upper end of the case is sealed with the sealing plate 1, whereby the electrochemical device according to the present embodiment is obtained. Composed. As shown in FIG. 3, a positive electrode lead 12 protruding from the upper surface of the electrode group 3 is inserted into a hole 5 b of a perforated plate 2 described later and welded to the sealing plate 1.

  The perforated plate 2 is disposed between the electrode group 3 and the sealing plate 1, and the perforated plate 2 is formed in a disk shape having a slightly smaller diameter than the sealing plate 1 as shown in FIG. 1. Alternatively, as shown in FIG. 2, it may be formed in an elongated plate shape whose both ends are formed in an arc shape. Further, the perforated plate 2 may have other shapes.

  In either type of perforated plate 2, the perforated plate 2 is provided with a hole. In this embodiment, the 1st hole 5a and the 2nd hole 5b are provided as a hole. The second hole 5 b is, for example, a circular through hole, and is formed in the center of the perforated plate 2. The second hole portion 5 b is arranged coaxially with the center of the electrode group 3. The 1st hole 5a consists of a through-hole formed in the both sides of the 2nd hole 5b so that the 2nd hole 5b may be pinched | interposed. Both the first holes 5a are symmetrical to each other.

  The 1st hole 5a and the 2nd hole 5b become a passage of the gas which generate | occur | produced suddenly in the case 4 unexpectedly. For this reason, it becomes easy to guide gas smoothly toward the exhaust valve 11 provided in the sealing plate 1. Furthermore, since the area of the perforated plate 2 excluding the first hole part 5a and the second hole part 5b is 20% or more and 50% or less with respect to the area of the opening part of the case 4, it suddenly occurs suddenly. The electric insulation between the electrode group 3 and the sealing plate 1 can be firmly maintained with a certain mechanical strength while steadily guiding the gas to the exhaust valve 11.

  Here, the ratio of the area of the perforated plate 2 excluding the holes 5a and 5b to the area of the case opening is defined as the perforated plate area ratio. That is, the perforated plate area ratio means the ratio of the area that blocks the gas to the area of the opening. If the perforated plate area ratio is less than 20%, the perforated plate 2 may be damaged when an impact such as dropping is applied to the electrochemical element. For this reason, if the perforated plate area ratio is less than 20%, the electrical insulation between the electrode group 3 and the sealing plate 1 may not be maintained. On the other hand, if the perforated plate area ratio exceeds 50%, the path for steadily guiding the suddenly generated gas to the exhaust valve 11 is insufficient, so that the perforated plate 2 is deformed.

  In addition to the perforated plate 2, an insulating part can be disposed between the electrode group 3 and the sealing plate 1. However, in this case, the insulating gas must not accidentally block the path of the generated gas, so that its mechanical strength is much lower than that of the perforated plate 2, or the same area as the perforated plate 2. It is necessary to have a hole having a gap.

The positions and shapes of the first hole 5a and the second hole 5b in the perforated plate 2 can be arbitrarily selected. Also that shows both provided arrangement of FIG. In the two first hole 5a and the second hole 5b. It is not always necessary to form two first holes 5a. For example, only one first hole 5a is provided, and the first hole 5a extends in the circumferential direction around the second hole 5b. It may be. In this case, it is preferable that the 1st hole 5a is formed more than about a half circumference. Three or more first hole portions 5a may be formed.

  The thickness of the perforated plate 2 is preferably such that the thickness itself does not cause a decrease in energy density while having sufficient mechanical strength. Specifically, in the electrochemical element having a capacity of 3.0 Ah or less, the thickness of the perforated plate 2 is preferably in the range of 0.2 to 1.0 mm. This preferred range changes appropriately in proportion to the capacity of the electrochemical element.

  The “opening” is substantially the same as the inner diameter of the case 4. Specifically, after the electrode group 3 and the perforated plate 2 are stored in the case 4, the diameter near the upper portion of the case 4 is reduced as a pre-processing, and then the sealing plate 1 is arranged to perform the caulking and sealing. The term “opening” refers to a portion before reduction but not reduction near the upper portion of the case, and is the same as the inner diameter of the case 4 at a place other than the upper portion of the case 4.

  In the present embodiment, an example in which the exhaust valve 11 is built in the sealing plate 1 is shown, but the present invention is not limited to this. For example, in a battery in which the axis of the electrode group 3 is oriented in a direction different from the direction of the sealing plate 1, the exhaust valve may not be incorporated in the sealing plate. Even in this case, the perforated plate 2 is disposed between the electrode group and the exhaust valve.

  The perforated plate 2 has a function of electrically insulating the electrode group 3 and the sealing plate 1. This eliminates the need for the insulating parts described above. In order to give the perforated plate 2 an insulating function, for example, the perforated plate 2 can be made of a hard insulating material. Examples of the insulating material include a heat resistant resin such as bakelite, a glass fiber reinforced resin such as glass phenol, and a reinforced plastic.

  Further, in order to give the perforated plate 2 an insulating function, the perforated plate 2 can be constituted by a metal plate in which an insulating material is disposed on at least one side. When the perforated plate 2 is made of a hard insulating material, it is difficult and expensive to mold the perforated plate 2. For this reason, if it is set as the structure which arrange | positions an insulating material to at least one side of a metal plate, the perforated plate 2 which has sufficient intensity | strength and insulation can be produced cheaply.

  Specific examples of a configuration in which an insulating material is disposed on at least one surface of a metal plate include a configuration in which a resin material such as polypropylene or polyethylene is fixed to at least one surface of a metal plate such as SUS or iron by adhesion or the like, and an insulating property on the metal plate The structure etc. which apply | coat and coat a coating material can be mentioned. Examples of the coating method include spray coating and dipping. From the viewpoint of maintaining strong electrical insulation between the electrode group 3 and the sealing plate 1, the insulating material is most preferably disposed on both surfaces of the metal plate. In the case where an insulating material is provided only on one side of the metal plate, the lower surface of the sealing plate 1 that may come into contact with the positive electrode and the insulating material are considered in consideration of the possibility that the metal plate is eluted under the positive electrode potential. It is preferable to face the arranged surface. Further, since the holes 5a and 5b of the perforated plate 2 may be used as holes for passing the positive or negative current collecting lead, it is preferable that an insulating material is also disposed on the perforated section of the metal plate.

  For example, in a battery in which the axis of the electrode group 3 is oriented in a direction different from the direction of the sealing plate 1, the perforated plate 2 may have a function of electrically insulating the electrode group 3 and the case 4. Good. Specific configurations of the perforated plate in this case include those in which the perforated plate 2 itself is configured by a hard insulating material, and those in which the perforated plate 2 is configured by a metal plate in which the insulating material is disposed on at least one side.

The positive electrode uses a lithium nickel composite oxide as an active material. When a non-aqueous electrolyte secondary battery is selected as the electrochemical element, the active material of the positive electrode includes lithium cobalt composite oxide (LiCo _1-X M _X O ₂ , M is an arbitrary metal element, 0 ≦ x <1), Lithium manganese composite oxide (LiMn _1-X M _X O ₂ or LiMn _{2 -X} M _X O ₄ , M is an arbitrary metal element, 0 ≦ x <1) can be used, among which lithium nickel composite oxidation The product (LiNi _1-X M _X O ₂ , M is an arbitrary metal element, 0 ≦ x <1) has an extremely large amount of unexpected gas generation. However, the provision of the perforated plate 2 makes it possible to steadily guide the gas generated in the case unexpectedly to the exhaust valve.

  The electrode group 3 has a wound structure as described above. The electrode group 3 may be a wound structure in which a strip-like positive electrode and a negative electrode are wound with a separator interposed therebetween, or a multilayer laminated structure in which strip-like positive and negative electrodes are stacked via a separator. I do not care. However, since the gap inside the electrode group 3 is formed only in the vertical direction of the case 4 in the case of the wound structure, the gas generated unexpectedly goes to the sealing plate 1 without diffusing in the lateral direction. For this reason, it becomes easy to exhibit the effect by the perforated board 2 by setting it as a winding structure. The wound electrode group 3 may be cylindrical or rectangular. In either configuration, the same effect can be obtained.

  It is preferable that the perforated plate 2 does not shield the gas flow path that is assumed to have the highest flow rate among the flow paths of the gas discharged from the electrode group 3. The smaller the ratio of shielding the flow path, the more efficiently the gas is discharged. In the case of a cylindrical wound battery, this flow path is formed by extracting the core used when winding the electrode plate after winding the electrode plate, or this winding. This corresponds to the inner core hole (gas discharge means) inserted into the core hole. Note that the center core is inserted into the core hole so as to cope with a case where clogging of a separator or the like occurs when gas is discharged. Due to the presence of the core, clogging can be suppressed and gas can be discharged reliably. In addition, the flow path in the case of a square battery corresponds to a gap between the core and the electrode group, a gap between the corner of the case and the electrode group, and the like.

  Hereinafter, the relationship between the flow path for discharging the gas and the perforated plate when the core is disposed inside the electrode group will be described with reference to FIG. FIG. 4 is a view of the perforated plate 5A as viewed from the exhaust valve side. As shown in FIG. 4, a core hole 5B after the core is removed is formed inside the electrode group 3, and a core 5C is disposed in the core hole 5B. The middle core 5C is a gas discharger that is formed of a cylindrical member and has an inner hole. For this reason, the gas discharged | emitted from the bottom part of the electrode group 3 goes up through the inner hole of the core 5C, and is guide | induced to an exhaust valve.

  At the peripheral edge of the hole formed in the central portion of the perforated plate 5A, a protrusion 5D is provided so that the center core 5C does not jump out during impact or gas discharge. The protrusion 5D desirably has an area as small as possible in order to partially shield the flow of gas discharged from the inner hole of the core 5C or the core hole 5B. However, if the protrusion 5D is too small, sufficient strength to hold down the core 5C cannot be secured. For this reason, it is necessary to regulate the dimension of the protrusion 5D to some extent.

The area of the inner circumference calculated by the inner diameter of the core hole 5B, that is, the cross-sectional area of the core hole 5B is S0, and the protrusion 5D of the perforated plate 5A existing in the core hole 5B when viewed from the exhaust valve side. Let the area be S1. That is, the area S1 is an area of the core hole 5B that is blocked by the protrusion 5D. Here, the core opening area ratio R1 is expressed by the following formula (1):
R1 = (S0−S1) / S0 (1)
It is defined as Further, the area of the inner circumference calculated by the inner diameter of the core 5C, that is, the cross-sectional area of the inner hole is S2, and the area of the protrusion 5D of the perforated plate existing inside the core 5C when viewed from the exhaust valve side. Is S3. That is, the area S3 is an area of the cross-sectional area of the inner hole that is blocked by the protrusion 5D. Here, the core opening area ratio R2 is expressed by the following formula (2):
R2 = (S2-S3) / S2 (2)
It is defined as The core opening area ratio R1 is preferably 0.45 or more. On the other hand, it is preferable that the center core opening area ratio R2 is 0.3 or more. If it is in this range, the gas can be easily discharged from the exhaust valve.

  A specific configuration in the case where the electrochemical element is configured by a nonaqueous electrolyte secondary battery will be described in more detail.

  The positive electrode has a structure in which a mixture layer is provided on a core material such as an aluminum foil. The mixture layer is made of, for example, a conductive agent such as graphite or carbon black, a binder such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene, and, if necessary, carboxymethylcellulose (CMC). It is a layer formed by adding a thickener.

  The negative electrode has a structure in which a mixture layer is provided on a core material such as copper foil. The mixture layer is made of an active material such as graphite or a material that can be alloyed with lithium, a conductive agent such as carbon nanofiber or carbon black, or a binder such as PVDF styrene-butadiene copolymer (SBR), if necessary. A layer formed by adding a thickener such as CMC as necessary.

As the separator, a microporous film made of polyolefin such as polyethylene or polypropylene can be used. As the electrolytic solution (non-aqueous electrolyte), a solution obtained by dissolving an electrolyte such as LiPF ₆ or LiBF ₄ in a solvent which is a simple substance or a mixture of a chain carbonate and / or a cyclic carbonate can be used. As the battery case, a molded product made of cylindrical or square iron or aluminum can be used.

  Examples of the nonaqueous electrolyte secondary battery are shown below, but the electrochemical device of the present invention is not limited to these examples.

(Negative electrode)
96 parts by weight of massive artificial graphite (MAG-D / trade name, manufactured by Hitachi Chemical Co., Ltd.) as active material, 3 parts by weight of SBR as binder, and CMC (Daiichi Kogyo) as thickener 1 part by weight of Pharmaceutical Co., Ltd. and an appropriate amount of water were mixed using a planetary mixer to prepare a negative electrode mixture paste. This paste was applied to both surfaces of a current collector (thickness 10 μm) made of copper foil, dried, rolled and cut to obtain a negative electrode (58 mm × 600 mm, thickness 170 μm).

(Positive electrode)
93 parts by weight of LiCoO ₂ powder as an active material and 4 parts by weight of acetylene black (AB) as a conductive agent were mixed. To the obtained powder, an N-methyl-2-pyrrolidone (NMP) solution of PVDF as a binder (# 1320 / trade name, manufactured by Kureha Chemical Industry Co., Ltd.) so that the solid content ratio is 3 parts by weight. Mixed. An appropriate amount of NMP was added to the obtained mixture to prepare a positive electrode mixture paste. This paste is applied to both surfaces of a current collector (thickness 15 μm) made of aluminum foil, dried and rolled, and further dehydrated and cut at 85 ° C. to obtain positive electrode A (57 mm × 550 mm, thickness 180 μm) was obtained.

On the other hand, LiCo _0.2 Ni _0.8 O ₂ is used as the active material, the amount applied to the aluminum foil is reduced and rolling is performed gently, and the same as the positive electrode A, except that the theoretical capacity and thickness per unit area are uniform. A positive electrode B was prepared according to the following formulation.

(Electrode group)
The positive electrode A and the negative electrode described above were wound into a cylindrical shape around the core through a separator (# 2320 manufactured by Celgard / trade name, thickness 0.02 mm). Thereafter, the winding core was extracted from the electrode group to form an electrode group A (theoretical capacity 2550 mAh) having a diameter of 17.6 mm and a height of 60 mm. Thereby, the core hole exists in the center of the electrode group. On the other hand, an electrode group B was configured in the same manner as the electrode group A except that the positive electrode A was changed to the positive electrode B.

(Perforated plate)
A perforated plate 2 having a design shown in FIG. 2 was prepared by processing a glass phenol plate (thickness 0.5 mm) having a diameter of 18 mm. Then, seven types of perforated plates 2 were produced by changing the holes in a similar manner. In these seven types of perforated plates 2, the areas excluding the holes are 0.38 cm ² (perforated plate A), 0.50 cm ² (perforated plate B), 0.75 cm ² (perforated plate C), and 0.87 cm, respectively. ² (perforated plate D), 1.00 cm ² (perforated plate E), 1.25 cm ² and has a (perforated plate F) and 1.38Cm ² (perforated plate G). Further, with respect to the perforated plate D, perforated plates I, J, and K were produced in which the area of the first hole 5a was kept as it was and only the area of the second hole 5b was reduced. The areas of the perforated plates I, J, and K excluding the holes are 0.87 cm ² , 0.99 cm ² , and 1.00 cm ² , respectively.

  Further, an iron plate (thickness 0.5 mm) having a diameter of 18 mm was punched and processed into the same shape and area as sample D. A perforated plate H was prepared by spray-coating a fluororesin as an insulating material on the plate so as to have a thickness of 15 μm.

(Non-aqueous electrolyte secondary battery)
Negative electrode lead protruded from the lower surface of electrode group A after housing electrode group A in a cylindrical case made of iron with a diameter of 18.30 mm, an inner diameter of 17.85 mm (opening area: 2.50 cm ² ), and a height of 68 mm Was welded to the bottom of the case. Thereafter, a core as a gas discharger was inserted into the core hole of the electrode group. At this time, the inner diameter of the core hole of the electrode group was 3.5 mm, and the inner diameter of the center core was 2.8 mm. Note that the thickness of the core is 0.25 mm. Further, on the upper side of the electrode group A, a perforated plate A (battery AA), a perforated plate B (battery AB), a perforated plate C (battery AC), a perforated plate D (battery AD), a perforated plate E (battery AE), and a perforated plate F (Battery AF), perforated plate G (battery AG), perforated plate H (battery AH), perforated plate I (battery AI), perforated plate J (battery AJ), and perforated plate K (battery AK) The positive electrode lead protruding from the upper surface of group A was welded to the sealing plate through the holes of these perforated plates. An exhaust valve having an operating pressure of 14.7 MPa is incorporated in the sealing plate.

  On the other hand, after housing the electrode group B in the same case as the batteries AA to AG, the negative electrode lead protruded from the lower surface of the electrode group B was welded to the bottom surface of the case. Further, above the electrode group B, a perforated plate A (battery BA), a perforated plate B (battery BB), a perforated plate C (battery BC), a perforated plate D (battery BD), a perforated plate E (battery BE), and a perforated plate F (Battery BF), perforated plate G (battery BG), perforated plate H (battery BH), perforated plate I (battery BI), perforated plate J (battery BJ), and perforated plate K (battery BK) The positive electrode lead protruded from the upper surface of the group B was inserted into the holes of these perforated plates and welded to the sealing plate. An exhaust valve having an operating pressure of 14.7 MPa is incorporated in the sealing plate.

After reducing the upper diameter of these cases by machining, 1.2M LiPF ₆ was dissolved in a mixture of non-aqueous solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1: 3. The non-aqueous electrolyte was poured and sealed by placing a sealing plate on the reduced portion of the upper part of the case and caulking. Thereby, a nonaqueous electrolyte secondary battery is completed. Among these, batteries AB to AF, AH to AJ, BA to BF, and BH to BJ are examples, and batteries AA, AG, AK, BA, BG, and BK are comparative examples.

  These nonaqueous electrolyte secondary batteries were subjected to the following evaluation after repeating a constant current charge of 500 V at a final voltage of 4.1 V and a constant current discharge of 500 mA at a final voltage of 3.0 V twice. It was.

(Drop test)
After removing 20 batteries and measuring the open circuit voltage, the battery was dropped 10 times from a height of 150 cm, and the open circuit voltage was measured again. A voltage difference of 20 mV or more before and after dropping was recognized as “voltage abnormality”. Table 1 shows the occurrence rate of voltage abnormality.

(Confirmation of gas generation behavior difference)
Remove one battery AD and one BD, and perform constant current charging with a termination voltage of 4.2 V at 1500 mA in an atmosphere of 25 ° C., then perform constant voltage charging with a termination current of 100 mA at 4.2 V. It was. This battery was stored in a pressure vessel shown in FIG. Under this forced condition, gas is rapidly generated. And the change of the temperature and pressure in a pressure vessel was measured.

  The specific measurement method is as follows. That is, the battery 6 is installed in a chamber 7 equipped with a heater 8, a pressure gauge 9 and a thermometer 10, and the battery 6 is heated by the heater 8, and when the temperature reaches 250 ° C., the temperature is kept constant. . The gas generated in the battery 6 by being exposed to a high temperature of 250 ° C. is released to the outside of the battery 6 (that is, in the chamber 7) through the exhaust valve. Here, the pressure gauge 9 and the thermometer 10 Is the ideal gas equation of state (PV = nRT, P is pressure, V is volume, n is the number of moles of gas molecules, R is a constant, and T is temperature). Was converted into the displacement of gas at 20 ° C. FIG. 6 shows the integrated amount of the exhaust amount of the gas on the vertical axis and the elapsed time on the horizontal axis.

(Confirmation of exhaust valve operation when gas is generated)
Twenty batteries were extracted and charged in the same manner as in “Confirmation of gas generation behavior difference”, and then stored in a pressure vessel shown in FIG. 5 and then heated to 250 ° C. Since gas was rapidly generated under this forced condition, the battery was taken out from the pressure vessel after the gas was released to the outside of the case, and the appearance of the battery was inspected. Gases released through the exhaust valve were recognized as “pass”. The results are shown in Table 1.

  As can be seen from Table 1, the occurrence of voltage abnormality (internal short circuit) increases rapidly when the perforated plate area ratio is less than 20%. As a result of disassembling and analyzing the corresponding batteries AA and BA, it was confirmed that the perforated plate was damaged due to an impact caused by dropping, and electrical insulation between the electrode group and the sealing plate could not be maintained.

  Table 1 shows the core area opening area ratio and the core area opening area ratio, and this core area opening area ratio is R1 derived from the equation (1). The opening area ratio is R2 derived from the equation (2).

  When the center core opening area ratio R2 is lower than 45% and the core opening area ratio R1 is lower than 30%, the exhaust valve operation pass rate decreases. This exhaust valve operation pass rate is low, the area of the second hole 5b located just above the gas discharge port is small, the cause of the decrease in the pass rate, the flow rate is the most among the gas flow path It is presumed that the path assumed to be many was blocked by the perforated plate. It can be seen that the smaller the rate at which this channel is shielded, the more efficiently the gas is discharged.

  On the other hand, it can be seen from the result of confirming the operation of the exhaust valve when the gas is generated that if the perforated plate area ratio exceeds 50%, the pass rate at which the exhaust valve operates normally is extremely reduced. When the corresponding batteries AG and BG were disassembled and analyzed, it was confirmed that the perforated plate was deformed to block the path between the electrode group and the exhaust valve.

  In both electrode groups A and B, when the perforated plate G has a perforated plate area ratio exceeding 50%, the acceptance rate is extremely low, but among them, the acceptance rate of the battery BG using the electrode group B is extremely low. . This is considered to be due to the difference in gas generation behavior measured using the batteries AD and BD. That is, since the lithium nickel composite oxide employed in the electrode group B generates a large amount of gas after pyrolysis, the use of a perforated plate with an inappropriate perforated plate area ratio is considered to cause a problem. From this result, when a non-aqueous electrolyte secondary battery is selected as the electrochemical element and lithium nickel composite oxide is used as the positive electrode active material, the effect of using an appropriate perforated plate is more prominently exhibited. I understand that

  According to the present invention, it is possible to provide a high energy density electrochemical element that is excellent in safety at high temperatures and has strong electrical insulation, so that the industrial applicability is high and the effect is remarkable.

It is the schematic showing an example of the structure of the electrochemical element by embodiment of this invention. It is the schematic showing an example of the opening part of the case before sealing with a sealing board. It is a longitudinal cross-sectional view which shows the said electrochemical element partially. It is a figure which shows the perforated board observed from the exhaust-valve side, and the core hole and center core of an electrode group. It is the schematic for demonstrating the measuring method which confirms the behavior of the gas generation under high temperature. It is a characteristic view which shows the difference in the gas generation | occurrence | production behavior under the high temperature by the difference in a positive electrode active material.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sealing plate 2 Perforated plate 3 Electrode group 4 Case 5a Hole part 5b Hole part 6 Battery 7 Chamber 8 Heater 9 Pressure gauge 10 Thermometer 11 Exhaust valve 12 Positive electrode lead 5A Perforated board 5B Core hole 5C Middle core 5D Protrusion part

Claims (11)

An electrode group in which a positive electrode and a negative electrode are stacked via a separator is housed in a case having an opening, and the opening of the case is an electrochemical element sealed by a sealing plate,
An exhaust valve that operates when the internal pressure in the case reaches a predetermined pressure, and releases the generated gas in the case to the outside;
A perforated plate having a hole and provided between the electrode group and the exhaust valve,
The perforated plate state, and are 20% to 50% of the area of the area except for the hole is the opening,
As the hole and the second hole portion located at the center of the perforated plate, a first hole portion which is located offset from the second hole portion, characterized that you have been formed Electrochemical element.   The electrochemical device according to claim 1, wherein the exhaust valve is provided on the sealing plate.   The electrochemical element according to claim 2, wherein the perforated plate has a function of electrically insulating the electrode group and the sealing plate.   The electrochemical element according to claim 1, wherein the perforated plate has a function of electrically insulating the electrode group and the case.   The electrochemical element according to claim 3 or 4, wherein the perforated plate is made of a hard insulating material.   The electrochemical element according to claim 3 or 4, wherein the perforated plate is constituted by a metal plate having an insulating material disposed on at least one side.   2. The electrochemical element according to claim 1, wherein a lithium nickel composite oxide is used as an active material of the positive electrode.   The electrochemical device according to claim 1, wherein the electrode group has a wound structure. The electrode group is provided with a gap through which the generated gas can pass,
When the area of the gap when viewed from the exhaust valve is S0 and the area where the gap is closed by the perforated plate when viewed from the exhaust valve is S1, (S0−S1) / S0 The electrochemical device according to claim 1, wherein the opening area ratio is 0.45 or more. The electrode group is provided with a gas discharger having an inner hole through which the generated gas can pass,
When the area of the inner hole when viewed from the exhaust valve is S2, and the area where the inner hole when viewed from the exhaust valve is blocked by the perforated plate is S3, (S2-S3) / The electrochemical device according to claim 1, wherein an opening area ratio represented by S <b> 2 is 0.3 or more. 11. The electricity according to claim 10, wherein a projection is provided at a peripheral edge of the hole of the perforated plate so as to block a part of the inner hole of the gas discharger as viewed from the exhaust valve. Chemical element.

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