JP4591012B2 - Sealed lithium secondary battery - Google Patents

Description

  The present invention relates to a sealed lithium secondary battery, and in particular, a bottomed battery container containing positive and negative electrodes and a non-aqueous electrolyte is sealed with an upper lid, and the upper lid includes a current interruption mechanism having a conductive diaphragm. The present invention relates to a sealed lithium secondary battery.

  Conventionally, sealed batteries have been widely used in home appliances, and recently, lithium secondary batteries have been used in particular, among sealed batteries. In addition, since the lithium secondary battery has a high energy density, development is being promoted as an in-vehicle power source for electric vehicles (EV) and hybrid vehicles (HEV). However, in a sealed battery, when it falls into an overcharged state due to a failure of the charging device or the like, an internal short circuit occurs between the positive and negative electrodes, and gas is generated due to decomposition of the electrolytic solution, so the internal pressure of the battery may increase extremely. . In order to solve this problem, for example, a battery having an explosion-proof device in which a protruding portion in which a central portion of a thin metal plate protrudes downward is welded to a thick metal plate, and a peripheral portion of these metal plates is fixed by caulking. Is disclosed (see Patent Document 1). In particular, a lithium battery using an organic (non-aqueous) solvent as an electrolyte solution has higher battery performance than a battery using an aqueous electrolyte solution, and thus a more reliable explosion-proof operation (ensure safety) is required. The

  As shown in FIG. 3, the present inventors have previously proposed a sealed cylindrical lithium secondary battery 50 having an upper lid 40 with a built-in explosion-proof device (see Patent Document 2). In the sealed cylindrical lithium secondary battery 50, the electrode winding group 11 is accommodated in a bottomed cylindrical battery can 10. An annular positive current collecting ring 14 is disposed on the upper part of the electrode winding group 11. The positive electrode current collecting ring 14 is connected to the bottom surface of the splitter 24 constituting the upper lid 40 via the positive electrode lead plate 32. The upper lid 40 is caulked and fixed to the battery can 10.

  As shown in FIG. 4, the upper lid 40 has a disk-shaped upper lid cap 21. The peripheral edge portion of the upper lid cap 21 is caulked and fixed by the peripheral edge portion of the dish-shaped diaphragm 22 having a bottom portion formed below. In the diaphragm 22, a cleavage groove 18 is formed between the center portion and the peripheral portion, which is cleaved when the battery internal pressure increases. The bottom portion of the diaphragm 22 has a flat central portion, and the bottom surface of the central portion and the upper surface of the connecting plate 6 protruding upward in a flat shape are electrically and mechanically joined by resistance welding. . Between the diaphragm 22 and the peripheral edge of the connecting plate 6, a flat plate-like splitter 24 having a through hole formed in the center is sandwiched. A peripheral portion of the splitter 24 is locked by an insulating ring 23 having a substantially T-shaped cross section. In the lithium secondary battery 50, when the battery internal pressure increases, the diaphragm 22 is reversed and the connection with the connection plate 6 is broken, so that the current is cut off and the battery can be disabled.

JP-A-8-7866 JP 2004-134204 A

  However, in the techniques of Patent Document 1 and Patent Document 2, when overcharging due to low rate charging, the battery is disabled by the operation of the current interrupt mechanism (explosion-proof device), so safety can be ensured. During overcharge due to high rate charging of 1C or more (large current), the decomposition of the non-aqueous electrolyte proceeds at an accelerated rate due to a rapid temperature rise, and a large amount of gas is generated, so the battery internal pressure rises rapidly. Therefore, it is difficult to ensure safety. In addition, when the battery container is suddenly deformed by external force to the battery, an internal short circuit occurs between the positive and negative electrodes due to the deformation, causing gas generation and the internal pressure of the battery rapidly increases. Cleavage may cause gas to escape. In this case, since the current is not interrupted, the decomposition reaction of the nonaqueous electrolyte is promoted, and the battery internal pressure further increases. Naturally, the behavior of the lithium secondary battery does not cause physical damage to humans when the battery is abnormal, such as when overcharged, deformed by external force, or pierced with a foreign object. Ensuring safety by minimizing it is a very important battery characteristic.

  In view of the above cases, an object of the present invention is to provide a sealed lithium secondary battery that can ensure safety when the battery is abnormal.

In order to solve the above problems, the present invention is such that a bottomed battery container containing positive and negative electrodes and a non-aqueous electrolyte is sealed with an upper lid, and the upper lid is provided with a current interruption mechanism having a conductive diaphragm. In the sealed lithium secondary battery, the diaphragm is formed with a first cleaving groove that cleaves at a predetermined pressure, and the bottom of the battery container can be cleaved at least after the cleaving of the first cleaving groove. 2 is formed , the reverse pressure of the diaphragm is A (MPa), the cleavage pressure of the first cleavage groove is B (MPa), and the cleavage pressure of the second cleavage groove is C (MPa). ), The reverse pressure A, the cleavage pressure B, and the cleavage pressure C satisfy the following formula (1) and the following formula (2) .

In the present invention, even if an internal short circuit occurs between the positive and negative electrodes when a battery abnormality occurs and gas is generated due to decomposition of the nonaqueous electrolyte, the first cleavage groove formed in the diaphragm is cleaved at a predetermined pressure so that the inside of the battery container Thus, the battery internal pressure can be reduced, and even if the decomposition of the nonaqueous electrolyte proceeds at an accelerated rate and the battery internal pressure further increases, at least after the first cleavage groove is opened, the battery container Since the second cleaving groove formed at the bottom of the gas can be cleaved, the second cleaving groove is cleaved and the non-aqueous electrolyte of the gas generation source is discharged. Therefore, safety can be ensured , and the formula ( By satisfying 1), since the electric current is interrupted before the first cleavage groove is cleaved and gas generation is suppressed, gas discharge from the first cleavage groove can be made gentle, and the first When the internal pressure of the battery is reduced by cleaving the cleaving groove, the second cleaving groove is cleaved. Therefore, the discharge of the non-aqueous electrolyte can be prevented, and by satisfying the formula (2), even if the internal pressure of the battery suddenly increases, the first cleavage groove is surely cleaved after the current is interrupted. reliably gas, and Ru can be smoothly discharged.

In this case, a dish-shaped having a planar portion da Iyafuramu is in the center, the flat portion, the flat surface portion of the conductive connection plate having a flat portion in the center projection is formed above the electrically and mechanically If a conductive splitter with a through hole is sandwiched between the diaphragm and the connection plate, the current is interrupted by the reversal of the diaphragm accompanying the rise in the battery internal pressure during overcharge. Therefore, promotion of gas generation can be suppressed. The reverse pressure A may be in the range of 0.8 MPa to 1.2 MPa, and the cleavage pressure B may be in the range of 1.2 MPa to 1.8 MPa. In addition, the second cleavage groove can be formed by an arcuate groove and a radial groove.

According to the present invention, even when an internal short circuit occurs between the positive and negative electrodes when a battery abnormality occurs and gas is generated due to decomposition of the nonaqueous electrolyte, the gas in the battery container is released by the first cleavage groove being cleaved at a predetermined pressure. Since the battery is discharged, the internal pressure of the battery can be reduced, and even if the decomposition of the non-aqueous electrolyte proceeds at an accelerated rate and the internal pressure of the battery further increases, the second cleavage groove at least after the first cleavage groove is opened. Since the second cleavage groove is cleaved and the non-aqueous electrolyte of the gas generation source is discharged, safety can be ensured , and the first cleavage can be achieved by satisfying equation (1). Since the electric current is interrupted before the groove is cleaved to suppress gas generation, the gas discharge can be made gentle, and the second crevice groove when the battery internal pressure is reduced by cleaving the first crevice groove. Does not cleave, so it is possible to prevent the discharge of the non-aqueous electrolyte and satisfy the formula (2) And, even if the battery internal pressure rises rapidly, so the first cleavage groove is reliably cleaved after current interruption, to ensure gas and Ru can be smoothly discharged, in addition to the advantage it can.

  Hereinafter, embodiments of a sealed cylindrical lithium ion secondary battery to which the present invention can be applied will be described with reference to the drawings.

(Constitution)
As shown in FIG. 1A, the sealed cylindrical lithium ion secondary battery 30 of this embodiment has an electrode winding group 11. In the electrode winding group 11, a positive electrode plate and a negative electrode plate are wound around a glass resin core with a polyethylene microporous thin film separator interposed therebetween, and a bottomed cylindrical battery can also serves as a negative electrode terminal 10 is accommodated in the approximate center. The battery can 10 is sealed with an upper lid 20 provided with a current interruption mechanism.

  As shown in FIG. 2, the upper lid 20 is a disc-shaped upper lid cap 1 made of iron and nickel-plated that also serves as a positive electrode terminal. A diaphragm 2, a flat donut-shaped splitter 4 made of an aluminum alloy and having an opening at the center, and a connecting plate 6 made of aluminum alloy and having a central portion protruding upward in a planar shape. The diaphragm 2, the splitter 4 and the connection plate 6 constitute a current interruption mechanism.

  A cylindrical protrusion protruding upward is formed at the center of the upper lid cap 1. An opening is formed on the upper surface of the protrusion. The peripheral edge of the upper lid cap 1 is fixed by caulking at the peripheral edge of the diaphragm 2. The bottom of the diaphragm 2 forms a flat central portion. A cleavage groove 8 (first cleavage groove) is formed between the center portion and the peripheral edge portion of the diaphragm 2. The cleaving groove 8 is thinned and has a groove width and a groove depth so that the cleaving groove 8 is cleaved when the internal pressure of the battery reaches a cleaving pressure B (unit MPa, detailed later). The bottom surface of the center portion of the diaphragm 2 and the top surface of the center portion of the connection plate 6 are joined electrically and mechanically by resistance welding (hereinafter, this resistance welding portion is referred to as a joint portion 7). The diaphragm 2 operates when the internal pressure of the lithium ion secondary battery 30 reaches the reverse pressure A (unit MPa, detailed later), that is, the current cutoff pressure of the current cutoff mechanism (the diaphragm 2 is reversed to the upper lid cap 1 side). Thus, the joint strength of the joint part 7 is set. A splitter 4 is sandwiched between the diaphragm 2 and the connection plate 6 via a bush 5 made of an annular and polypropylene resin with a flange portion in contact with the bottom surface of the diaphragm 2. The splitter 4 is disposed along the bottom of the diaphragm 2. The central portion of the connection plate 6 passes through the opening formed in the center of the splitter 4. A through hole 9 is formed between the central portion and the peripheral portion of the splitter 4 for discharging the gas in the battery can 10 to the outside of the battery.

  The outer periphery of the splitter 4 is locked with a predetermined interval from the bottom surface of the diaphragm 2 by a resin insulating ring 3 having a substantially T-shaped cross section. The insulating ring 3 is provided with three or more claws 15 that support the outer peripheral portion of the splitter 4 on the inner surface side, and the insulating ring 3 and the claws 15 are integrally formed. The diaphragm 2, the splitter 4, the upper lid cap 1, and the connection plate 6 are formed by pressing.

  As shown in FIG. 1B, the bottom surface of the battery can 10 is formed with two arc-shaped grooves 17a having a diameter smaller than the diameter of the bottom surface and symmetrical with respect to the center of the bottom surface. Radial radial grooves 17b are formed on the outer peripheral side of the bottom surface at both ends and the center of the cleavage groove 17a. The arc-shaped groove 17a and the radiation groove 17b are combined to form a cleavage groove 17 (second cleavage groove). The cleaving groove 17 is thinned, and the groove width and the groove depth are set so that the cleaving groove 17 is cleaved when the battery internal pressure reaches the cleaving pressure C (unit MPa).

The reverse pressure A of the diaphragm 2, the cleavage pressure B of the cleavage groove 8, and the cleavage pressure C of the cleavage groove 17 are set so as to satisfy the following expressions (1) and (2). That is, the cleavage pressure B is set larger than the reverse pressure A, and the cleavage pressure C is set larger than the cleavage pressure B. The pressure difference between the cleavage pressure B and the reverse pressure A is set to be 0.2 MPa or more and less than 0.8 MPa.

  As shown in FIG. 1 (A), a negative electrode current collecting ring for current collection is fixed to the lower end of the shaft core of the electrode winding group 11, and an electrode winding group is provided at the periphery of the negative electrode current collecting ring. The negative electrode tab derived from 11 is ultrasonically welded. The negative electrode current collecting ring is resistance welded to the inner bottom portion of the battery can 10. On the other hand, a positive electrode current collecting ring 14 for current collection is fixed to the upper end of the shaft core, and a positive electrode tab is ultrasonically welded to the peripheral portion of the positive electrode current collecting ring 14. One end of a strip-shaped positive electrode lead plate 16 is welded to the positive electrode current collecting ring 14. The other end of the positive electrode lead plate 16 is connected to one end of a strip-like positive electrode lead plate 12, and the other end of the positive electrode lead plate 12 is a splitter that constitutes an upper lid 20 disposed above the electrode winding group 11. 4 is welded to the lower surface. A portion along the splitter 4 of the diaphragm 2 and the splitter 4 are accommodated in the positive electrode current collecting ring 14. In the space S defined by the bottom surface of the splitter 4 and the inner surface of the positive electrode current collecting ring 14, the positive electrode lead piece 16 is bent and accommodated near the periphery of the space S.

The positive electrode plate constituting the electrode winding group 11 has an aluminum foil as a positive electrode current collector. A positive electrode mixture containing a lithium manganese composite oxide (LiMnO ₂ ) powder as a positive electrode active material is applied to both surfaces of the aluminum foil substantially uniformly. The positive electrode mixture is mixed with a conductive carbon material and a binder polyvinylidene fluoride (hereinafter abbreviated as PVDF). The positive electrode mixture is mixed with N-methylpyrrolidone (hereinafter abbreviated as NMP) as a viscosity adjusting solvent at the time of coating, and is dispersed and kneaded substantially uniformly by Cornell Despa. An uncoated portion of the positive electrode mixture is left on the side edge on one side in the longitudinal direction of the aluminum foil. The positive electrode plate is dried and then pressed and cut into strips. A positive electrode tab is formed on an uncoated portion of the positive electrode mixture. On the other hand, the negative electrode plate has a copper foil of a negative electrode current collector. On both surfaces of the copper foil, a negative electrode mixture containing graphite as a negative electrode active material is applied substantially uniformly. The negative electrode mixture is mixed with PVDF as a binder. The negative electrode mixture is mixed with the viscosity adjusting solvent NMP at the time of coating, and is dispersed and kneaded substantially uniformly by Cornell Despa. An uncoated portion of the negative electrode mixture is left on one side edge of the copper foil in the longitudinal direction. The negative electrode plate is dried and then pressed and cut into strips. A negative electrode tab is formed on an uncoated portion of the negative electrode mixture. The positive electrode tab and the negative electrode tab are disposed on the opposite end surfaces of the electrode winding group 11.

  A non-aqueous electrolyte (not shown) is injected into the battery can 10. As the non-aqueous electrolyte, for example, an electrolyte obtained by dissolving 1 mol / liter of lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and dimethyl carbonate is used. The peripheral edge portion of the upper lid 20 is fixed by caulking to the upper portion of the battery can 10 via the gasket 13, and the lithium ion secondary battery 30 is sealed.

(Action etc.)
Next, the operation and the like of the lithium ion secondary battery 30 of the present embodiment will be described.

  The lithium ion secondary battery 30 according to the present embodiment includes a current interruption mechanism having the diaphragm 2 in the upper lid 20. When the battery is abnormal such as overcharge, an internal short circuit occurs between the positive and negative electrodes, and the non-aqueous electrolyte is decomposed, so that gas is generated and the battery internal pressure rises. When the battery internal pressure reaches the reverse pressure A, the diaphragm 2 is reversed. At this time, since the movement of the connecting plate 6 is suppressed by the splitter 4, the junction 7 is broken and the current is interrupted. Further, since the reversal pressure A of the diaphragm 2 is larger than the atmospheric pressure, once the diaphragm 2 is reversed, the diaphragm 2 does not return to its original shape at the atmospheric pressure, and the connection plate 6 comes into electrical contact with the diaphragm 2 again. There is nothing. Therefore, decomposition of the non-aqueous electrolyte is suppressed and gas generation is not promoted, so that an increase in battery internal pressure can be suppressed and excellent safety can be ensured.

  Further, in the lithium ion secondary battery 30 of the present embodiment, the cleavage groove 8 is formed in the diaphragm 2. When the battery internal pressure further rises and exceeds the cleavage pressure B when the battery is abnormal, the cleavage groove 8 is cleaved. The gas in the battery can 10 is discharged to the outside through the through hole 9 formed in the splitter 4, the cleavage location of the cleavage groove 8, and the opening formed in the upper lid cap 1. Since the cleavage pressure B is set higher than the reverse pressure A, the current is interrupted when the cleavage groove 8 is cleaved. For this reason, since gas generation is no longer promoted, the gas in the battery can 10 can be quickly discharged.

  Furthermore, in the lithium ion secondary battery 30 of the present embodiment, the cleavage groove 17 is formed on the bottom surface of the battery can 10. When the battery is abnormal, such as overcharge due to high rate charging or sudden deformation of the battery can 10 due to external force, heat generation due to an internal short circuit between the positive and negative electrodes increases, and the decomposition of the non-aqueous electrolyte proceeds at an accelerated rate. As a result, the internal pressure of the battery rises rapidly. Even if the gas is discharged through the cleavage site of the cleavage groove 8, if the internal pressure of the battery further increases and exceeds the cleavage pressure C, the cleavage groove 17 is cleaved. For this reason, the non-aqueous electrolyte in the battery can 10 is discharged to the outside through the cleavage location of the cleavage groove 17 and the non-aqueous electrolyte of the gas generation source disappears, so that gas generation is suppressed. In addition, after the non-aqueous electrolyte is discharged, the gas in the battery can 10 is discharged from both the cleavage groove 8 and the cleavage groove 17. Therefore, since the non-aqueous electrolyte and gas are quickly discharged, the lithium ion secondary battery 30 can be safely made unusable.

Furthermore, in the lithium ion secondary battery 30 of the present embodiment, since the cleavage pressure C is set higher than the cleavage pressure B, when the gas is discharged by the cleavage of the cleavage groove 8 and the internal pressure of the battery decreases, the cleavage pressure C Since the groove 17 is not cleaved, safety can be ensured without discharging the non-aqueous electrolyte.

Furthermore, if the pressure difference (B−A) between the reverse pressure A and the cleavage pressure B is less than 0.2 MPa, when the battery internal pressure suddenly increases when the battery is abnormal, the cleavage groove before the operation of the current interruption mechanism Since 8 may be cleaved, gas generation is continued without interrupting the current, and the battery internal pressure rises. Conversely, the pressure difference when ing more than 0.8 MPa, since the gas without rupturing groove 8 also interrupt the current cleavage is not discharged, the battery internal pressure rises. For this reason, in the lithium ion secondary battery 30 of this embodiment, the pressure difference is set to 0.2 MPa or more and less than 0.8 MPa. As a result, even if the internal pressure of the battery suddenly increases, the cleavage groove 8 is reliably cleaved after the current is interrupted, so that the gas can be reliably and smoothly discharged.

  Further, in the lithium ion secondary battery 30 of the present embodiment, the cleavage groove 8 and the cleavage groove 17 are formed in the diaphragm 2 and the bottom surface of the battery can 10, respectively. For this reason, for example, even when the diaphragm 2 does not reverse due to the action of an external force, the two cleavage grooves 8 and 17 are cleaved by the rise of the battery internal pressure, and the gas and the non-aqueous electrolyte of the gas generation source are discharged. Sex can be secured.

  In the conventional lithium ion secondary battery, when the battery internal pressure rises when the battery is abnormal, the current is cut off by the current cut-off mechanism, and the gas in the battery can is released by the cleavage of the cleavage groove formed in the battery lid. It is possible to ensure safety when overcharging by charging. However, when the battery can be overcharged by charging at a high rate of 1C or more, or when the battery can suddenly deforms due to external force, the internal pressure of the battery rises rapidly. There are times when you can't. In addition, since the battery internal pressure rises rapidly, the cleavage groove may be broken before the current interrupt mechanism is activated. In this case, since the current is not cut off even when gas discharge is started, the battery temperature rapidly rises and gas is continuously generated. You will lose. The lithium ion secondary battery 30 of the present embodiment solves these problems.

  In the lithium ion secondary battery 30 of the present embodiment, an example in which the arc-shaped grooves 17a and the radial grooves 17b are formed as the cleavage grooves 17 at two locations on the bottom surface of the battery can 10 has been shown, but the present invention is not limited thereto. It is not something. The cleavage groove 17 may be, for example, an arc-shaped groove, a radial groove, or an annular groove. Further, the cleavage groove 8 is not particularly limited. Furthermore, in this embodiment, although the example which sets the reverse pressure of the diaphragm 2 with the welding strength of the junction part 7 was shown, this invention is not limited to this, For example, the thickness and intensity | strength of the diaphragm 2 are changed. You may set it.

  Moreover, in the lithium ion secondary battery 30 of this embodiment, although the example which used the aluminum alloy for the material of the diaphragm 2, the connection board 6, and the splitter 4 was shown, this invention is not limited to this, Aluminum Other conductive materials such as nickel alloys and conductive plastics may be used.

Furthermore, in the present embodiment, lithium manganese composite oxide (LiMnO ₂ ) powder is exemplified as the positive electrode active material, but the present invention is not limited to this. Examples of the positive electrode active material that can be used other than the present embodiment include lithium manganese composite oxides represented by the chemical formula LiMn ₂ O ₄ , lithium sites or manganese sites of these lithium manganese composite oxides other than Fe, Co, etc. And lithium manganese transition metal composite oxides substituted or doped with the above metal elements. Such lithium manganese transition metal complex oxide has the formula _{LiMn 1-x M x O 2} , LiMn 2-x M x O 4 (M is a transition Mn, Fe, Co, one or more selected from Ni, etc. Metal). It is also possible to use a lithium-nickel composite oxide (LiNiO _2), lithium cobalt complex oxide (LiCoO ₂₎ or the like. In the present embodiment, graphite is exemplified as the negative electrode active material, but the present invention is not limited to this, and for example, a carbonaceous material such as amorphous carbon can be used.

  Furthermore, in the present embodiment, the non-aqueous electrolyte was prepared by dissolving 1 mol / liter of lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and dimethyl carbonate, but the present invention is limited to this. Is not to be done. For example, as an organic solvent, what is normally used for a lithium ion secondary battery may be used, and lithium hexafluorophosphate, lithium tetrafluoroborate, etc. can be mentioned also as lithium salt. Further, the mixing ratio of the organic solvent and the content of the lithium salt are not particularly limited.

  Furthermore, in the present embodiment, the cylindrical lithium ion secondary battery 30 is exemplified, but the present invention is not limited to this, and may be, for example, a square shape or a polygonal shape. Also, the battery capacity, size, etc. are not particularly limited.

Next, an example of the lithium ion secondary battery 30 produced by changing the reverse pressure A, the cleavage pressure B, and the cleavage pressure C according to the present embodiment will be described. In addition, it describes together about the lithium ion secondary battery of the comparative example produced for the comparison. Moreover, about each Example and the comparative example, the battery capacity was 9 Ah. Of the following examples, Examples 3 and 7 are shown for reference.

Example 1
As shown in Table 1 below, in Example 1, the current breaking pressure A was set to 0.8 MPa, the cleavage pressure B was set to 1.2 MPa, and the cleavage pressure C was set to 4.2 MPa. The pressure difference (B−A) between the reverse pressure A and the cleavage pressure B is 0.4 MPa. In Table 1, an electric current breaking pressure A, an upper lid cleavage pressure B, and a can bottom cleavage pressure C indicate a reverse pressure A, a cleavage pressure B, and a cleavage pressure C, respectively.

(Example 2 to Example 3)
As shown in Table 1, Examples 2 to 3 were the same as Example 1 except that the upper lid cleavage pressure B and the can bottom cleavage pressure C were changed. In Example 2, the upper lid cleavage pressure B was 1.4 MPa and the can bottom cleavage pressure C was 4.0 MPa. In Example 3, the upper lid cleavage pressure B was 1.6 MPa, and the can bottom cleavage pressure C was 4.5 MPa. . The pressure difference (B−A) is 0.6 MPa in Example 2 and 0.8 MPa in Example 3.

Example 4
As shown in Table 1, Example 4 was the same as Example 1 except that the current interruption pressure A was 1.0 MPa. The pressure difference (B−A) is 0.2 MPa.

(Example 5 to Example 7)
As shown in Table 1, Examples 5 to 7 were the same as Example 4 except that the upper lid cleavage pressure B and the can bottom cleavage pressure C were changed. In Example 5, the upper lid cleavage pressure B was 1.4 MPa and the can bottom cleavage pressure C was 4.0 MPa. In Example 6, the upper lid cleavage pressure B was 1.6 MPa and the can bottom cleavage pressure C was 4.5 MPa. In No. 7, the upper lid cleavage pressure B was 1.8 MPa and the can bottom cleavage pressure C was 4.1 MPa. The pressure difference (B−A) is 0.4 MPa in Example 5, 0.6 MPa in Example 6, and 0.8 MPa in Example 7.

(Example 8)
As shown in Table 1, in Example 8, the current breaking pressure A was set to 1.2 MPa, the cleavage pressure B was set to 1.4 MPa, and the cleavage pressure C was set to 4.0 MPa. The pressure difference (B−A) is 0.2 MPa.

(Example 9 to Example 10)
As shown in Table 1, Examples 9 to 10 were the same as Example 8 except that the upper lid cleavage pressure B and the can bottom cleavage pressure C were changed. In Example 9, the upper lid cleavage pressure B was 1.6 MPa and the can bottom cleavage pressure C was 4.2 MPa. In Example 10, the upper lid cleavage pressure B was 1.8 MPa, and the can bottom cleavage pressure C was 4.5 MPa. The pressure difference (B−A) is 0.4 MPa in Example 9 and 0.6 MPa in Example 10.

(Comparative Examples 1 to 2)
As shown in Table 1, Comparative Example 1 and Comparative Example 2 were the same as Example 1 except that the upper lid cleavage pressure B and the can bottom cleavage pressure C were changed. In Comparative Example 1, the upper lid cleavage pressure B was 1.8 MPa and the can bottom cleavage pressure C was 4.0 MPa. In Comparative Example 2, the upper lid cleavage pressure B was 2.0 MPa and the can bottom cleavage pressure C was 2.0 MPa. . The pressure difference (B−A) is 1.0 MPa in Comparative Example 1 and 1.2 MPa in Comparative Example 2.

(Comparative Example 3)
As shown in Table 1, Comparative Example 3 was the same as Example 4 except that the upper lid cleavage pressure B was 2.0 MPa and the can bottom cleavage pressure C was 4.0 MPa. The pressure difference (B−A) is 1.0 MPa.

(Comparative Example 4)
As shown in Table 1, Comparative Example 4 was the same as Example 8 except that the upper lid cleavage pressure B was 1.2 MPa and the can bottom cleavage pressure C was 4.5 MPa. The pressure difference (B−A) is 0.2 MPa.

(Comparative Example 5)
As shown in Table 1, in Comparative Example 5, the current interruption pressure A was 0.8 MPa, the upper lid cleavage pressure B was 2.0 MPa, and the can bottom cleavage pressure C was 4.2 MPa. The pressure difference (B−A) is 1.2 MPa.

(Comparative Example 6)
As shown in Table 1, in Comparative Example 6, the current breaking pressure A was 4.0 MPa, the upper lid cleavage pressure B was 2.0 MPa, and the bottom cleavage pressure C was 3.8 MPa. The pressure difference (B−A) is −2.0 MPa.

(Comparative Example 7)
As shown in Table 1, in Comparative Example 7, the current interruption pressure A was 2.0 MPa, the upper lid cleavage pressure B was 4.0 MPa, and the can bottom cleavage pressure C was 3.8 MPa. The pressure difference (B−A) is 2.0 MPa.

(Comparative Example 8)
As shown in Table 1, in Comparative Example 8, the current interruption pressure A was 2.0 MPa, the upper lid cleavage pressure B was 2.0 MPa, and the can bottom cleavage pressure C was 4.0 MPa. The pressure difference (B−A) is 0.0 MPa.

(Comparative Example 9)
As shown in Table 1, in Comparative Example 9, the current interruption pressure A was 2.2 MPa, the upper lid cleavage pressure B was 2.1 MPa, and the can bottom cleavage pressure C was 4.0 MPa. The pressure difference (B−A) is −0.1 MPa.

(Comparative Example 10)
As shown in Table 1, in Comparative Example 10, the current breaking pressure A was 1.1 MPa, the upper lid cleavage pressure B was 1.2 MPa, and the can bottom cleavage pressure C was 3.2 MPa. The pressure difference (B−A) is 0.1 MPa.

<Test>
About the battery of each Example and the comparative example, the overcharge test and the crush test were done as follows. In the overcharge test, the behavior of the battery was observed when the battery was continuously charged at a current value of 1C, 3C, and 5C. In the crushing test, after charging the battery to 100% SOC (fully charged), the battery was placed on its side so that the winding axis would be in the horizontal direction, and the crushing treatment with a radius of 1.75 mm was made perpendicular to the battery longitudinal direction. The behavior of the battery was observed when the tool was lowered at a speed of 1.6 m / min from the upper side in the vertical direction to the center in the longitudinal direction of the battery and subjected to a destructive test by external pressure. The observation results in each test are shown in Table 2 below.

As shown in Table 2 below, in each of the batteries of Examples 1 to 10 where the current breaking pressure A, the upper lid cleavage pressure B, and the can bottom cleavage pressure C satisfy the condition of A <B <C (Equation 1), 1C In the overcharge test, the reversal of the diaphragm 2 occurred smoothly, and the current interruption mechanism worked to stop the charging current without causing bursting ignition. On the other hand, in the battery of Comparative Example 6 that does not satisfy the condition of Equation 1, the cleavage groove 8 was cleaved and the gas was discharged from the cleavage groove 8 before the current was interrupted (before reaching the current interruption pressure). The current could not be interrupted and a bursting fire occurred.

  Further, from the result of the overcharge test at a large current and high rate of 3C and 5C, a battery in which the pressure difference (BA) between the current breaking pressure A and the upper lid cleavage pressure B is smaller than 0.2 MPa, that is, the formula (2) In each battery of Comparative Example 4, Comparative Example 6, Comparative Example 6 to Comparative Example 8 to Comparative Example 10 in which 0.2> (B−A) is not satisfied, the reversal of the diaphragm 2 is smoothly performed with a rapid pressure rise and a temperature rise. Since the cleavage groove 8 was cleaved before the current was interrupted without occurring, the current could not be interrupted and a burst ignition occurred.

Furthermore, from the result of the crush test, a battery having a pressure difference (BA) of 0.8 MPa or more , that is, Comparative Example 1 to Comparative Example 3 that does not satisfy the formula (2) (BA) ≧ 0.8 MPa , In each battery of Comparative Example 5 and Comparative Example 7, the cleavage of the cleavage groove 8 was not in time for the rapid pressure increase at the time of the collapse, and the caulking sealing portion of the upper lid 20 was damaged. From this, a battery that satisfies Equation 1 and also satisfies Equation (2) can reliably cut off the charging current by operating the current interruption mechanism reliably for large current charging at a high rate, and is sufficiently safe. It has been found that a sealed lithium ion secondary battery can be provided.

  The present invention contributes to the manufacture and sale of lithium secondary batteries in order to provide a sealed lithium secondary battery that can ensure safety when the battery is abnormal, and thus has industrial applicability.

1 shows a sealed cylindrical lithium ion secondary battery according to an embodiment to which the present invention is applicable, in which (A) is a cross-sectional view and (B) is a bottom view. It is sectional drawing which shows the upper cover of the sealed cylindrical lithium ion secondary battery of embodiment. It is sectional drawing which shows the conventional sealed cylindrical lithium ion secondary battery in which the cleavage groove | channel is not formed in the battery can bottom. It is sectional drawing which shows the upper cover of the conventional sealed cylindrical lithium ion secondary battery.

Explanation of symbols

2 Diaphragm (a part of current interruption mechanism)
4 Splitter (part of current interruption mechanism)
6 Connection board (part of current interruption mechanism)
8 cleavage groove (first cleavage groove)
10 Battery can (bottomed battery container)
17 Cleavage groove (second cleavage groove)
20 Upper lid 30 Sealed cylindrical lithium ion secondary battery (sealed lithium secondary battery)

Claims (4)

In a sealed lithium secondary battery in which a bottomed battery container containing positive and negative electrodes and a non-aqueous electrolyte is sealed with an upper lid, and the upper lid is provided with a current interruption mechanism having a conductive diaphragm, the diaphragm includes A first cleaving groove that is cleaved at a predetermined pressure is formed, and at the bottom of the battery container, a second cleaving groove that can be cleaved at least after cleaving the first cleaving groove is formed , and When the reverse pressure of the diaphragm is A (MPa), the cleavage pressure of the first cleavage groove is B (MPa), and the cleavage pressure of the second cleavage groove is C (MPa), the reverse pressure A, the cleavage The sealed lithium secondary battery , wherein the pressure B and the cleavage pressure C satisfy the following formula (1) and the following formula (2) .

The diaphragm has a plate-like shape having a flat portion at the center, and the flat portion of the conductive connecting plate having a protrusion formed at the top and the flat portion at the center is electrically and mechanically connected to the flat portion. 2. The sealed lithium secondary battery according to claim 1 , wherein a conductive splitter having a through hole is sandwiched between the diaphragm and the connection plate. The sealed pressure according to claim 1 or 2, wherein the reverse pressure A is in a range of 0.8 MPa to 1.2 MPa, and the cleavage pressure B is in a range of 1.2 MPa to 1.8 MPa. Lithium secondary battery. 4. The sealed lithium secondary battery according to claim 1, wherein the second cleavage groove is formed by an arc-shaped groove and a radial groove. 5.

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