JP2014127284A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which, even after repeated battery charges and discharges, can surely actuate a pressure-sensitive current breaking mechanism, for increased safety.SOLUTION: A nonaqueous electrolyte secondary battery 1 comprises: a cathode plate 20 having a cathode active material layer 21; an anode plate 30 having an anode active material layer 31; a separator 40; a nonaqueous electrolyte 50 charged inside a battery case 80; an overcharge additive for generating a gas when overcharged; and a current breaking mechanism 62 which is actuated when the internal pressure of the battery case exceeds a working pressure. In the cathode active material layer 21, a maximum frequency pore diameter is 0.7 μm or greater. In the separator 40, a depth of dent when it is pressed with a force of 0.05 gf is 1.2 μm or less. According to this nonaqueous electrolyte secondary battery 1, separator deformation is small even when the battery is repeatedly charged and discharged, so that a hole, which is a reaction space for the overcharge additive, is not closed up. Therefore, a sufficient amount of gas to actuate the current breaking mechanism can be generated when the battery is overcharged.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. Specifically, the present invention relates to a non-aqueous electrolyte secondary battery provided with a current interruption mechanism that operates when the internal pressure of the battery case exceeds the operating pressure.

  In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been used in various fields such as electronic devices such as mobile phones and personal computers, vehicles such as hybrid cars and electric cars. In particular, a lithium ion secondary battery has a high energy density and is suitable for mounting in various devices.

  Generally, a lithium ion secondary battery includes an electrode body that is laminated or wound with a film-like separator interposed between a positive electrode plate and a negative electrode plate. The positive electrode plate is obtained by forming a positive electrode active material layer on a positive electrode current collector foil. The positive electrode active material layer is formed by applying a positive electrode paste containing a positive electrode active material to a positive electrode current collector foil and drying it. On the other hand, the negative electrode plate is obtained by forming a negative electrode active material layer on a negative electrode current collector foil. The negative electrode active material layer is formed by applying and drying a negative electrode paste containing a negative electrode active material on a negative electrode current collector foil. The electrode body is housed in a battery case and sealed in a state where a terminal member for taking out electric energy is connected. The electrode body in the battery case is impregnated with an electrolytic solution.

  Such lithium ion secondary batteries may generate heat when overcharged due to malfunction or unauthorized use. Therefore, in order to prevent heat generation during overcharge, for example, the overcharge additive added in advance during overcharge reacts to generate gas, thereby increasing the internal pressure of the battery and increasing the internal pressure. It has been proposed to activate the current interrupt mechanism. As a patent document relating to this type of technology, there is the following Patent Document 1. In the technique described in Patent Document 1 below, lithium carbonate is retained on the surface of the conductive material included in the positive electrode active material layer as an overcharge additive (internal pressure increasing agent). During overcharge, the lithium carbonate is electrochemically decomposed to generate carbon dioxide, which increases the internal pressure of the battery.

  However, the technique shown in Patent Document 1 below has the following problems. That is, by repeatedly using (charging / discharging) a lithium ion secondary battery, gaps between the separator and the positive electrode active material layer and between the separator and the negative electrode active material layer (holes, symbols in FIG. 15). The separator is deformed so as to fill in (see S) (see FIG. 16). Specifically, when a lithium ion secondary battery is repeatedly charged and discharged, the negative electrode active material repeatedly expands and contracts. As a result, pressure is applied to the separator. For this reason, the separator is deformed and enters the pores between the separator and the positive electrode active material layer and between the separator and the negative electrode active material layer, thereby closing the pores.

Patent Document 2 listed below describes a lithium ion secondary battery in which the separator is configured with predetermined parameters to increase the flexibility of the separator. The predetermined parameter is “a film thickness measured with an applied load of 36 g / cm ² using a contact-type film thickness meter having a circular contact terminal with a contact bottom surface of 0.5 cm in diameter is L1, and an applied load of 1 When the film thickness measured at ² kg / cm ² is L2, L1−L2 = 2.0 to 10 μm ”. According to the technique described in this document, it is said that the separator can follow the expansion / contraction of the electrode accompanying the charging / discharging of the battery, as the flexibility of the separator is increased. Therefore, even if the battery is repeatedly charged and discharged for about 100 cycles, the separator is not wrinkled or broken, and the cycle characteristics (discharge capacity retention rate) of the battery are not deteriorated.

JP 2010-171020 A JP 2010-218749 A

However, even if the technique described in Patent Document 2 is used, the above-described problem, that is, the problem of pore blocking due to the deformation of the separator cannot be solved. On the contrary, when the technique described in Patent Document 2 is used, since the flexibility of the separator is improved, the separator deformed during the expansion of the electrode is between the separator and the positive electrode active material layer, and the separator. There is a possibility that the air gap between the anode and the negative electrode active material layer enters the gap without any gap and the hole is blocked.

  If the pores are blocked by the separator 40, the reaction space for the overcharge additive is lost. For this reason, even during overcharging, gas cannot be generated sufficiently, and the internal pressure of the battery cannot be increased. If the internal pressure of the battery cannot be increased, the pressure-sensitive current interruption mechanism cannot be operated, and the battery may generate heat. As a result, the safety of the battery cannot be ensured.

  The present invention has been made in view of the above circumstances. That is, the object is to provide a highly safe non-aqueous electrolyte secondary battery that can reliably operate a pressure-sensitive current interrupting mechanism even when the battery is repeatedly charged and discharged.

  In order to solve this problem, the nonaqueous electrolyte secondary battery of the present invention includes a positive electrode current collector foil, a positive electrode plate having a positive electrode active material layer coated on the positive electrode current collector foil, and a negative electrode current collector. A negative electrode plate having an electric foil and a negative electrode active material layer coated on the negative electrode current collector foil, and a separator interposed between the positive electrode plate and the negative electrode plate to electrically insulate the positive electrode plate and the negative electrode plate A battery case containing an electrode body formed by winding or laminating a positive electrode plate, a negative electrode plate, and a separator, a non-aqueous electrolyte filled in the battery case, and exceeding a normal operating voltage due to overcharging. An overcharge additive that sometimes reacts to generate gas, and a current interrupt mechanism that interrupts the current flowing through the electrode body when the internal pressure of the battery case exceeds the operating pressure. The positive electrode active material layer has a maximum frequency pore diameter of 0.7 μm or more. The separator has a dent amount of 1.2 μm or less when pressed with a force of 0.05 gf.

  As a result of the experiment, the inventors of the present invention have determined that if the maximum frequency pore diameter of the positive electrode active material layer is 0.7 μm or more, the amount of gas generated using the overcharge additive as a gas generation source during overcharge is We found that there is a correlation with the ease of deformation (flexibility). And, the internal pressure (operating pressure) necessary for the operation of the current interrupting mechanism is secured by configuring the separator so that the dent amount (deformation amount) when pressed with a force of 0.05 gf is 1.2 μm or less. It was found that the amount of gas generated was sufficient to do so. Therefore, in the present invention, the positive electrode active material layer is configured so that the maximum frequency pore diameter is 0.7 μm or more, and the separator has a dent amount of 1.2 μm or less when pressed with a force of 0.05 gf. It is configured. Thereby, even if it charges / discharges a battery repeatedly, it can be set as a non-aqueous-electrolyte secondary battery with which a separator deform | transforms and does not block a void | hole. In other words, even if the battery is repeatedly charged and discharged, the deformation of the separator is small and the pores are not blocked. As a result, the reaction space of the overcharge additive can be taken up sufficiently, and the pressure-sensitive current interruption mechanism operates reliably. A highly safe non-aqueous electrolyte secondary battery can be obtained.

Here, in the nonaqueous electrolyte secondary battery of the present invention, the separator preferably has a dent amount of 0.3 μm or more when pressed with a force of 0.05 gf.
As a result of the experiment, the inventor of the present invention has found that when the separator is pressed with a force of 0.05 gf, the dent amount is 0.3 μm or more, but the gas during overcharge is less than 0.3 μm. I found out that there was a lot of generation. Therefore, by configuring in this way, a highly safe non-aqueous electrolyte secondary battery capable of ensuring a sufficient amount of gas generation during overcharge and reliably operating the pressure-sensitive current interrupting mechanism can be obtained. it can.

In the nonaqueous electrolyte secondary battery of the present invention, the separator is made of a porous polyolefin resin and an engineering plastic, and the first layer and the third layer having a content of the engineering plastic of 50 to 80%, and the first layer And a second layer made of a porous polyolefin resin.
Thus, by setting the content of the engineering plastics of the first layer and the third layer to 50 to 80%, the dent amount when pressed with a force of 0.05 gf is 0.3 μm or more and 1.2 μm or less. It is because it can form.
In this case, the first layer and the third layer can be suitably configured by using polyethylene as the porous polyolefin resin and using polyetherketone as the engineering plastic, and the second layer as the porous polyolefin resin. It can be suitably configured by using polyethylene.

In the nonaqueous electrolyte secondary battery of the present invention, the positive electrode active material layer preferably has a maximum frequency pore diameter of 1.2 μm or less.
When the maximum frequency pore diameter of the positive electrode active material layer is larger than 1.2 μm, the internal resistance (IV resistance) of the battery rapidly increases. Thus, the maximum frequency pore diameter of the positive electrode active material layer is 1.2 μm or less. By doing so, it is possible to prevent a battery having an excessively high internal resistance.

  ADVANTAGE OF THE INVENTION According to this invention, even if it charges / discharges a battery repeatedly, the highly safe non-aqueous-electrolyte secondary battery which can operate a pressure-sensitive type electric current interruption mechanism reliably can be provided.

1 is a perspective view of a non-aqueous electrolyte secondary battery according to an embodiment. It is a longitudinal cross-sectional view of the battery. It is a perspective view of the positive electrode plate of the battery. It is a perspective view of the negative electrode plate of the battery. It is the A section enlarged view of FIG. It is the B section enlarged view of FIG. It is a figure explaining an effect | action of an electric current interruption mechanism. It is a graph which shows the relationship between the maximum frequency pore diameter of a positive electrode active material layer, and the gas amount per unit battery capacity which generate | occur | produces at the time of overcharge. It is a graph which shows the relationship between the maximum frequency pore diameter of a positive electrode active material layer, and the internal resistance (IV resistance) of a nonaqueous electrolyte secondary battery. It is the schematic which shows the structure of the separator of the battery. It is a graph which shows the relationship between the thickness of PE + engineering plastic layer, and the deformation amount of a separator. It is a graph which shows the relationship between the thickness of PE layer, and the deformation amount of a separator. It is a graph which shows the relationship between content of an engineering plastic, and the deformation amount of a separator. It is a graph which shows the relationship between the deformation amount of a separator, and the gas amount per unit battery capacity which generate | occur | produces at the time of overcharge. It is a figure which shows the structure of the separator vicinity in the nonaqueous electrolyte secondary battery of an initial state (before going through a charging / discharging cycle). It is a figure which shows the structure of the separator vicinity in the non-aqueous-electrolyte secondary battery after passing through a charging / discharging cycle at the time of using the separator which is easy to deform | transform. It is a figure which shows the structure of the separator vicinity in the non-aqueous-electrolyte secondary battery after passing through a charging / discharging cycle at the time of using the separator which is hard to deform | transform.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIGS. 1 and 2, the non-aqueous electrolyte secondary battery 1 of the present embodiment is a rectangular lithium ion mounted on a vehicle such as a hybrid vehicle or an electric vehicle, or a battery-operated device such as a hammer drill. It is a secondary battery. The lithium ion secondary battery 1 includes an electrode body 10 and a battery case 80 that houses the electrode body 10. Electrode body 10 is impregnated with electrolytic solution 50.

The electrolytic solution 50 is prepared by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) with a volume ratio of EC: DMC: EMC = 30: 40: 30 as a solute. This is a non-aqueous electrolyte in which lithium hexafluorophosphate (LiPF ₆ ) is added to adjust the lithium ion concentration to 1 mol / l. Further, the electrolytic solution 50 contains about 4% of an additive (overcharge additive) for generating gas when the lithium ion secondary battery 1 is overcharged. CHB (cyclohexynebenzene) is used as an overcharge additive.

  The battery case 80 includes a case main body member 81 and a sealing lid 82 (see FIGS. 1 and 2). The case body member 81 is made of metal and has a rectangular box shape. The sealing lid 82 is made of metal and has a rectangular plate shape. The sealing lid 82 closes the opening of the case body member 81 and is welded to the case body member 81.

  The electrode body 10 is a wound electrode body in which a belt-like positive electrode plate 20 and a negative electrode plate 30 are wound into a flat shape with a belt-like separator 40 interposed therebetween (see FIG. 1). As shown in FIG. 3, the positive electrode plate 20 includes a strip-shaped positive electrode current collector foil 28 and positive electrode active material layers 21 and 21 formed on both main surfaces of the positive electrode current collector foil 28. The positive electrode active material layer 21 is a layer containing a positive electrode active material, and is disposed along one long side extending in the longitudinal direction DA of the positive electrode current collector foil 28.

  A portion of the positive electrode plate 20 on which the positive electrode active material layer 21 is applied is referred to as a positive electrode active material layer application portion 20b (see FIG. 3). On the other hand, a portion made only of the positive electrode current collector foil 28 without having the positive electrode active material layer 21 is referred to as a positive electrode active material layer uncoated portion 20c. The positive electrode active material layer uncoated portion 20 c extends in a strip shape in the longitudinal direction DA of the positive electrode plate 20 along the other long side of the positive electrode plate 20. The positive electrode active material layer uncoated portion 20c is wound to form a spiral shape, and is located at one end (right end in FIG. 2) in the axial direction (left and right direction in FIG. 2) of the electrode body 10.

In the positive electrode plate 20 of the lithium ion secondary battery 1, an aluminum foil is used as the positive electrode current collector foil 28. The positive electrode active material layer 21 is a layer formed by drying a positive electrode coating liquid (positive electrode paste) applied to the positive electrode current collector foil 28. The positive electrode coating liquid is in a slurry state, and usually contains at least a positive electrode active material, a conductive material, a binder, and a solvent, and further contains a thickener as necessary. It is. The following materials can be used as the positive electrode active material, conductive material, binder, and thickener.
Positive electrode active material: lithium composite oxide such as lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), lithium cobaltate (LiCoO ₂ ), etc. Conductive material: Carbon black such as acetylene black, furnace black, ketjen black , Carbon powder such as graphite powder, etc. Binder: Polytetrafluoroethylene (PTFE), Styrene Butadiene Rubber (SBR), Polyvinylidene Fluoride (PVDF), etc. Thickener: Carboxymethylcellulose (CMC), etc. The following materials can be used as the solvent for preparing the liquid.
Solvent: organic solvent such as toluene, methyl ethyl ketone, N-methyl-2-pyrrolidone or a mixture thereof

  As shown in FIG. 4, the negative electrode plate 30 includes a strip-shaped negative electrode current collector foil 38 and negative electrode active material layers 31 and 31 formed on both main surfaces of the negative electrode current collector foil 38. The negative electrode active material layer 31 is a layer containing a negative electrode active material, and is disposed along one long side extending in the longitudinal direction DA of the negative electrode current collector foil 38.

  A portion of the negative electrode plate 30 where the negative electrode active material layer 31 is coated is referred to as a negative electrode active material layer coating portion 30b (see FIG. 4). On the other hand, a portion made only of the negative electrode current collector foil 38 without having the negative electrode active material layer 31 is referred to as a negative electrode active material layer uncoated portion 30c. The negative electrode active material layer uncoated portion 30 c extends in a strip shape in the longitudinal direction DA of the negative electrode plate 30 along the other long side of the negative electrode plate 30. The negative electrode active material layer uncoated portion 30c is wound to form a spiral shape, and is positioned at one end (left end in FIG. 2) in the axial direction (left and right direction in FIG. 2) of the electrode body 10.

In the negative electrode plate 30 of the lithium ion secondary battery 1, a copper foil is used as the negative electrode current collector foil 38. The negative electrode active material layer 31 is a layer formed by drying a negative electrode coating liquid (negative electrode paste) applied to the negative electrode current collector foil 38. The negative electrode coating liquid is in a slurry form, and usually contains at least a negative electrode active material, a binder, and a solvent, and further contains a conductive material and a thickener as necessary. is there. The following materials can be used as the negative electrode active material. In addition, as the binder, the conductive material, the thickener, and the solvent, the same materials as those for the positive electrode coating liquid described above can be used.
Negative electrode active material: Carbon materials such as amorphous carbon, non-graphitizable carbon, graphitizable carbon, natural graphite

  The positive electrode active material layer uncoated portion 20c of the positive electrode plate 20 in the electrode body 10 is electrically connected by welding the positive electrode terminal structure 60 (see FIG. 2). The positive terminal structure 60 has a positive external terminal member 68 located outside the battery case 80. The negative electrode active material layer uncoated portion 30c of the negative electrode plate 30 is electrically connected to the negative electrode terminal structure 70 by welding. The negative terminal structure 70 has a negative external terminal member 78 located outside the battery case 80.

  The negative terminal structure 70 includes a negative internal terminal member 71, a negative external terminal member 78, and a gasket 79 (see FIG. 2). The negative electrode internal terminal member 71 is made of copper and is mainly located inside the battery case 80. The negative electrode internal terminal member 71 is bonded to the negative electrode active material layer uncoated portion 30c of the negative electrode plate 30 in the battery case 80, and passes through the sealing lid 82 of the battery case 80 to be connected to the negative electrode external terminal member. 78 and the gasket 79 are caulked to the sealing lid 82 and are electrically connected to the negative external terminal member 78.

  The negative external terminal member 78 is made of copper, is bent in a crank shape, and is located outside the battery case 80. The negative external terminal member 78 has a through-hole 78H for fastening a bus bar or the like with a bolt on the tip side. The gasket 79 is made of an electrically insulating resin and is interposed between the negative electrode external terminal member 78 and the negative electrode internal terminal member 71 and the battery case 80 to electrically insulate them.

  On the other hand, the positive terminal structure 60 includes a positive internal terminal structure 61, a positive external terminal member 68, and a gasket 69 (see FIG. 2). The positive electrode internal terminal structure 61 is mainly located inside the battery case 80. The positive electrode internal terminal structure 61 includes a current interruption mechanism 62. The current interrupt mechanism 62 is a mechanism that interrupts the current flowing through the electrode body 10 when the internal pressure of the battery case 80 exceeds the operating pressure.

  The positive external terminal member 68 is made of aluminum, has a shape bent in a crank shape, and is located outside the battery case 80. The positive external terminal member 68 has a through hole 68H on the front end side for fastening a bus bar or the like with a bolt. The gasket 69 is made of an electrically insulating resin. The gasket 69 includes a first insulating member 69 </ b> A disposed outside the sealing lid 82 and a second insulating member 69 </ b> B disposed inside the sealing lid 82. The gasket 69 is interposed between the positive electrode external terminal member 68 and the positive electrode internal terminal structure 61 and the battery case 80, and electrically insulates them.

  2 and 5, the positive electrode internal terminal structure 61 includes a positive electrode current collecting terminal member 63, an enclosing member 66, a flat plate diaphragm 64, a rectangular concave relay member 65, and a caulking member. 67. The positive current collecting terminal member 63, the diaphragm 64, the relay member 65, and the caulking member 67 are all made of aluminum. The surrounding member 66 is made of an electrically insulating resin and surrounds the breaking member 63X of the positive electrode current collecting terminal member 63.

  The caulking member 67 is caulked and deformed through the through hole 82H of the sealing lid 82, and couples the relay member 65, the positive external terminal member 68, and the gasket 69 to the sealing lid 82 (see FIG. 5). Through the caulking member 67, the relay member 65 and the positive external terminal member 68 are electrically connected. Further, the diaphragm 64 connected to the relay member 65 is electrically connected to the positive external terminal member 68.

  Further, as shown in FIG. 5, the positive electrode current collecting terminal member 63 includes a rectangular plate-shaped breaking member 63X parallel to the sealing lid 82, and an elongated plate-shaped current collecting connection extending downward from the breaking member 63X. The member 63Y is integrally formed. Among these, the current collector connection member 63Y is joined to the positive electrode active material layer uncoated portion 20c of the positive electrode plate 20 (see FIG. 2). Thereby, the breaking member 63X is electrically connected to the electrode body 10 (specifically, the positive electrode plate 20). The breaking member 63X is formed with a through hole 63G that penetrates the center of the breaking member 63X along the vertical direction, and two through holes 63H and 63H that are located on both sides of the through hole 63G along the vertical direction. Has been.

  Moreover, the fracture | rupture member 63X has the welding part 63F welded to the diaphragm 64 in the position of the periphery of the through-hole 63G, as shown in FIG. The overall shape of the welded portion 63F is a ring shape along the periphery of the through hole 63G when viewed in plan. Furthermore, a ring-shaped notch 63E is formed in the fracture member 63X at a position radially outside the weld 63F (see FIG. 6). The notch 63E is a fragile portion (a rupture portion) in the rupture member 63X.

  The surrounding member 66 includes a plate-like insulating resin member 66A and a plate-like insulating resin member 66B (see FIG. 5). The surrounding member 66 is formed with a through hole 66G penetrating the central portion of the surrounding member 66 and two through holes 66H and 66H located on both sides of the through hole 66G.

  As shown in FIG. 5, in a state where the surrounding member 66 surrounds the breaking member 63X, the through hole 63H of the breaking member 63X overlaps the through hole 66H of the surrounding member 66, and further, the through hole of the breaking member 63X. 63G and the through-hole 66G of the surrounding member 66 overlap. Further, as shown in FIG. 6, the welded portion 63 </ b> F and the cutout portion 63 </ b> E of the breaking member 63 </ b> X are exposed in the through hole 66 </ b> G of the surrounding member 66, and the through hole 63 </ b> G of the breaking member 63 </ b> X It communicates with the through hole 66G.

  In addition, the diaphragm 64 has a protruding portion 64 </ b> A that protrudes toward the breaking member 63 </ b> X side of the positive electrode current collecting terminal member 63 at the center position of the diaphragm 64. As shown in FIG. 6, a ring-shaped (annular) welded portion 63F of the fracture member 63X is welded to the lower surface side of the protruding portion 64A of the diaphragm 64. Thereby, the breaking member 63X and the diaphragm 64 are electrically connected. In FIG. 6, a portion where the welded portion 63 </ b> F of the fracture member 63 </ b> X and the protruding portion 64 </ b> A of the diaphragm 64 are welded is indicated by cross hatching as a welding conduction portion W.

  Further, as shown in FIG. 5, the peripheral edge portion 64 </ b> E of the diaphragm 64 is airtightly joined to the peripheral edge portion 65 </ b> E of the relay member 65. Thus, a space C (see FIG. 5) is formed by the relay member 65, the diaphragm 64, and the caulking member 67. In the present embodiment, the space C communicates with the outside of the battery case 80 through the through hole 67H of the caulking member 67, so that the pressure in the space C is atmospheric pressure.

  In the lithium ion secondary battery 1 according to the present embodiment configured as described above, in the positive electrode internal terminal structure 61 described above, the positive electrode current collecting terminal member 63, the diaphragm 64, the relay member 65, and the surrounding member 66 are: A current interruption mechanism 62 is provided (see FIG. 2). The current interruption mechanism 62 interrupts the current flowing through the electrode body 10 when the internal pressure of the battery case 80 exceeds the operating pressure.

  Specifically, for example, due to overcharging of the lithium ion secondary battery 1, a reaction voltage (that is, an abnormal high voltage larger than a normal operation voltage) greater than a predetermined maximum operation voltage (for example, 4.1 V) and As a result, the electrolytic solution 50 starts to decompose, the temperature of the battery increases, and CHB added to the electrolytic solution 50 is oxidized and decomposed to release a large amount of gas. When the internal pressure of the battery case 80 rises due to a large amount of released gas and exceeds the operating pressure of the current interrupt mechanism 62 (for example, 750 kPa), the current interrupt mechanism 62 operates as follows. The current flowing through the electrode body 10 is cut off.

  That is, when a large amount of gas is released, as shown in FIG. 5, the diaphragm 64 passes through the through holes 66H and 66H of the surrounding member 66, the through hole 66G of the surrounding member 66, and the through hole 63G of the breaking member 63X. The internal pressure F (see FIG. 5) of the battery case 80 is applied from the lower side to the upper side in FIG. Then, as the internal pressure F of the battery case 80 increases, the diaphragm 64 is pushed outward (upward in FIG. 5) from the battery case 80 due to a pressure difference with the space C and deforms. At this time, of the breaking member 63X welded to the projecting portion 64A of the diaphragm 64, a portion exposed in the through hole 66G of the surrounding member 66 (a portion including the welded portion 63F and the notch portion 63E) is also included. Together with the protrusion 64A of the diaphragm 64, the battery case 80 is pushed outward (upward in FIG. 5) to be deformed.

  When the internal pressure F of the battery case 80 exceeds the operating pressure of the current interrupt mechanism 62, as shown in FIG. 7, the breaking member 63X breaks at the position of the notch 63E, and the diaphragm 64 and the positive current collecting terminal member 63 And are separated. Thereby, the energization between the diaphragm 64 and the electrode body 10 is interrupted. Specifically, the current flowing through the electrode body 10 is cut off through the path of “positive electrode external terminal member 68” → “caulking member 67” → “relay member 65” → “diaphragm 64” → “positive electrode current collector terminal member 63”. . Thereby, the charging (overcharge) of the lithium ion secondary battery 1 is stopped.

  Here, in the lithium ion secondary battery 1 of the present embodiment, the positive electrode active material layer 21 has a maximum frequency pore diameter of 0.7 μm or more and 1.2 μm or less. This is due to the following reason. That is, as shown in FIG. 8, when the maximum frequency pore diameter of the positive electrode active material layer 21 is smaller than 0.7 μm, the amount of gas generated per unit capacity during overcharge is as small as about 20 cc / Ah or less. On the other hand, when the maximum frequency pore diameter of the positive electrode active material layer 21 is 0.7 μm or more, the amount of gas per unit capacity generated at the time of overcharging is as high as about 60 cc / Ah or more. Accordingly, it is desirable that the maximum frequency pore diameter of the positive electrode active material layer 21 be 0.7 μm or more in order to prevent the amount of gas generated during overcharging from becoming too small.

  Further, as shown in FIG. 9, when the maximum frequency pore diameter of the positive electrode active material layer 21 is larger than 1.2 μm, the internal resistance (IV resistance) of the lithium ion secondary battery 1 rapidly increases from about 70 mΩ. On the other hand, when the maximum frequency pore diameter of the positive electrode active material layer 21 is 1.2 μm or less, the internal resistance (IV resistance) of the lithium ion secondary battery 1 is distributed up to about 70 mΩ. Therefore, in order to prevent the internal resistance (IV resistance) of the lithium ion secondary battery 1 from becoming too large, it is desirable that the maximum frequency pore diameter of the positive electrode active material layer 21 be 1.2 μm or less.

  In the lithium ion secondary battery 1 of the present embodiment, the separator 40 is a microporous film made of a strip-shaped synthetic resin. Specifically, as shown in FIG. 10, the separator 40 includes a first layer 41 and a third layer 43 in which polyethylene (PE), which is a porous polyolefin resin, is mixed with an engineering plastic having high heat resistance, and the first layer 41 and the third layer 43. The second layer 42 is sandwiched between the first layer 41 and the third layer 43. The second layer 42 is a layer made of polyethylene (PE). In the present embodiment, the engineering plastic mixed in the first layer 41 and the third layer 43 is polyether ketone (PEK).

  The layer thickness of the first layer 41 and the third layer 43 is about 7 μm. The layer thickness of the second layer 42 is about 6 μm. The thicknesses of the first layer 41, the second layer 42, and the third layer 43 are set to such a thickness in order to balance the shutdown function, strength, and battery characteristics of the separator 40.

  When the relationship between the thickness of the first layer 41 and the third layer 43 and the amount of deformation of the separator 40 was examined, the thickness of the first layer 41 and the third layer 43 was changed from 3 μm as shown in FIG. It was found that even when the thickness was increased by 1 μm up to 9 μm, the deformation amount of the separator 40 was not changed to about 0.80 μm. Here, the deformation amount of the separator 40 means that the separator 40 was pressed with a force of 0.05 gf (gram weight) with a triangular pyramid indenter using a dynamic ultra-micro hardness meter DUH-W201 manufactured by Shimadzu Corporation. Is the amount of depression (push-in depth, unit is μm), and is an index indicating the ease of deformation of the separator 40.

  Further, when the relationship between the thickness of the second layer 42 and the deformation amount of the separator 40 was examined, as shown in FIG. 12, even if the thickness of the second layer 42 was increased from 3 μm to 9 μm by 1 μm, the separator It was found that the deformation amount of 40 was not changed from about 0.80 μm. Therefore, it was found that the layer thicknesses of the first layer 41, the second layer 42, and the third layer 43 hardly affect the deformation amount of the separator 40.

  On the other hand, when the relationship between the content of the engineering plastic contained in the first layer 41 and the third layer 43 and the deformation amount of the separator 40 was examined, as shown in FIG. It was found that the amount of deformation of the separator 40 becomes smaller (harder to deform) as it is increased. It was found that by setting the content of the engineering plastic to about 50 to 80%, a separator 40 having a desirable hardness described later, that is, a separator 40 having a deformation amount of 0.3 μm or more and 1.2 μm or less can be configured. The amount of deformation of the separator 40 is changed by changing the content of engineering plastic (in this embodiment, polyetherketone) because engineering plastic (polyetherketone) is harder than polyethylene, which is a polyolefin resin. It is.

  Next, the relationship between the amount of deformation (ease of deformation) of the separator 40 and the amount of gas generated during overcharging will be described with reference to FIGS. FIG. 14 is a graph showing the results of examining the relationship between the amount of deformation (ease of deformation) of the separator 40 and the amount of gas generated during overcharging. In the graph shown in FIG. 14, the horizontal axis indicates the deformation amount of the separator 40, and the vertical axis indicates the amount of gas per unit volume generated during overcharge. The ● plot in the graph shows the case where the maximum frequency pore diameter of the positive electrode active material layer 21 is 0.20 μm, and the * plot shows the case where the maximum frequency pore diameter of the positive electrode active material layer 21 is 0.35 μm. , X plot shows the case where the maximum frequency pore diameter of the positive electrode active material layer 21 is 0.56 μm, Δ plot shows the case where the maximum frequency pore diameter of the positive electrode active material layer 21 is 0.73 μm, The plot shows the case where the maximum frequency pore diameter of the positive electrode active material layer 21 is 0.78 μm, and the ♦ plot shows the case where the maximum frequency pore diameter of the positive electrode active material layer 21 is 0.96 μm.

  As shown in FIG. 14, if the maximum frequency pore diameter of the positive electrode active material layer 21 is not about 0.70 μm or more, the amount of gas generated during overcharge even if the deformation amount (ease of deformation) of the separator 40 is changed. Does not change much. Further, it can be seen from the graph shown in FIG. 14 that when the deformation amount (ease of deformation) of the separator 40 is 1.2 μm or less, the amount of gas generated during overcharge can be increased. In addition, although it repeats, the deformation amount of the separator 40 means that the separator 40 was pushed with a force of 0.05 gf with a triangular pyramid indenter using Shimadzu Corporation's dynamic ultra micro hardness tester DUH-W201. Is the amount of depression (push-in depth, unit is μm), and is an index indicating the ease of deformation of the separator 40.

  As described above, the amount of gas generated during overcharge differs depending on whether the deformation amount of the separator 40 is greater than 1.2 μm or less than 1.2 μm. That is, in the lithium ion secondary battery 1 in an initial state (before passing through a charge / discharge cycle described later), as shown in FIG. 15, between the positive electrode active material layer 21 and the separator 40 and between the negative electrode active material layer 31 and A gap (hole) S exists between the separator 40. This gap S is a space necessary for the overcharge additive to react under high temperature and high voltage during overcharge.

  However, when the amount of deformation of the separator 40 is larger than 1.2 μm, that is, when the separator 40 is easily deformed, the holes S are deformed through a charge / discharge cycle as shown in FIG. It is blocked by the separator 40. That is, as the lithium ion secondary battery 1 is charged / discharged, the negative electrode active material included in the negative electrode active material layer 31 expands or contracts. The separator 40 is pushed by the expanding negative electrode active material, and is deformed so as to fill the void S. When the holes S are thus blocked by the separator 40, the reaction site for the overcharge additive is reduced. Therefore, the overcharge additive cannot react sufficiently, and as a result, the amount of gas generated during overcharge decreases. If the amount of gas generated during overcharging decreases, the internal pressure does not rise above a predetermined operating pressure even during overcharging, and the current interrupt mechanism 62 does not operate. With this, the thermal runaway of the lithium ion secondary battery 1 cannot be stopped.

  On the other hand, when the deformation amount of the separator 40 is 1.2 μm or less, that is, when the separator 40 is not easily deformed, as shown in FIG. 17, the charging / discharging of the lithium ion secondary battery 1 is performed. Even after the cycle, the separator 40 is not deformed so much that the pores S are not blocked, and a sufficient space remains for the overcharge additive to react. Accordingly, since a sufficient amount of gas generation can be ensured during overcharge (see FIG. 14), the internal pressure of the lithium ion secondary battery 1 rises to a predetermined operating pressure or higher. Operates. Therefore, the thermal runaway of the lithium ion secondary battery 1 can be stopped.

  Further, it can be seen from the graph shown in FIG. 14 that the amount of deformation (ease of deformation) of the separator 40 is desirably 0.3 μm or more. When the deformation amount of the separator 40 is smaller than 0.3 μm, that is, when it is difficult to deform the separator 40, the deformation amount of the separator 40 is set to 0.3 μm or more and 1.2 μm or less. This is because the amount of generated gas is reduced.

  In addition, the experimental result shown in FIG. 14 shows the result when an overcharge test under the following conditions is performed on the lithium ion secondary battery 1 that has been charged and discharged under the following cycle test conditions. It is a thing. The charge / discharge cycle was performed as follows. That is, with respect to the lithium ion secondary battery 1, CC charging (Constant Current charging) is performed at a charging rate of 2C until the SOC becomes 0% to 100%, and the environmental temperature is changed from 100% to 0%. Until then, CC discharge (Constant Current discharge) at a discharge rate of 2 C was taken as one cycle, and 1000 cycles of charge / discharge were performed.

  Here, 1C indicating the charge / discharge rate is a current value at which discharge is completed in 1 hour after a battery having a rated capacity value (nominal capacity value) is discharged at a constant current. For example, when the rated capacity (nominal capacity) of the lithium ion secondary battery is 1.0 Ah, 1C = 1.0 A. Also, SOC is an abbreviation for State Of Charge (charging state, charging rate).

  The overcharge test was performed as follows. That is, first, the positive electrode plate 20, the negative electrode plate 30, and the separator 40 of the lithium ion secondary battery 1 subjected to the charge / discharge cycle were reassembled into a laminate cell. The laminate cell was CCCV charged (Constant Current / Constant Voltage charge) for 2.5 hours at a charge rate of 1 C until the SOC reached 100% (4.1 V). Thereafter, CC charging was performed at a charging rate of 1C (1A) until the SOC became 160% at an environmental temperature of 25 ° C.

  The amount of gas generated was determined from the volume change before and after the overcharge test by measuring the volume of the laminate cell before the overcharge test and the volume of the laminate cell after the overcharge test by the Archimedes method. The gas generation amount (cc / Ah) per unit battery capacity was determined by dividing the measured gas amount (cc or ml) by the battery capacity (Ah) of the laminate cell. Note that the gas amount shown in FIG. 8 is obtained by the same method.

  Further, in the lithium ion secondary battery 1 used in this experiment, the negative electrode plate 30 uses a copper foil as the negative electrode current collector foil 38 and is a negative electrode active material as a negative electrode coating liquid that becomes the negative electrode active material layer 31. A mixture of natural graphite, CMC as a thickener, and SBR as a binder in a weight ratio of 98: 1: 1 was used. As the electrolytic solution 50, one having the conditions shown in paragraph [0019] was used.

  As described in detail above, the lithium ion secondary battery 1 of this embodiment includes a positive electrode plate 20 having a positive electrode current collector foil 28 and a positive electrode active material layer 21 coated on the positive electrode current collector foil 28. , A negative electrode plate 30 having a negative electrode current collector foil 38 and a negative electrode active material layer 31 coated on the negative electrode current collector foil 38, and a positive electrode plate 20 interposed between the positive electrode plate 20 and the negative electrode plate 30. A separator 40 that electrically insulates the negative electrode plate 30, a battery case 80 that houses the positive electrode plate 20, the negative electrode plate 30, and the electrode body 10 that is formed by winding the separator 40, and an electrolytic solution that is filled in the battery case 80 The liquid 50, an overcharge additive that reacts to generate gas when it exceeds a normal operating voltage during overcharging, and a current interruption mechanism 62 that operates when the internal pressure of the battery case 80 exceeds a predetermined operating pressure. And. The positive electrode active material layer 21 has a maximum frequency pore diameter of 0.7 μm or more. The separator 40 has a dent amount (deformation amount) of 1.2 μm or less when pressed with a force of 0.05 gf.

  In the lithium ion secondary battery 1 of this embodiment, since the maximum frequency pore diameter of the positive electrode active material layer 21 is 0.7 μm or more, the amount of gas generated using the overcharge additive as a gas generation source during overcharge is: The separator 40 is affected by ease of deformation (flexibility) (see FIGS. 8 and 14). Since the dent amount (deformation amount) of the separator 40 when pressed with a force of 0.05 gf is 1.2 μm or less, the separator 40 is deformed even when the lithium ion secondary battery 1 is repeatedly charged and discharged. The air holes S are not blocked (see FIG. 17). That is, even when the lithium ion secondary battery 1 is repeatedly charged and discharged, the separator 40 is not deformed so much that the holes S are not blocked, and as a result, a sufficient reaction space for the overcharge additive can be obtained. Therefore, it is possible to obtain a highly safe battery that can reliably operate the pressure-sensitive current interrupting mechanism 62.

  Further, in the lithium ion secondary battery 1 of the present embodiment, the separator 40 has a dent amount (deformation amount) of 0.3 μm or more when pressed with a force of 0.05 gf. For this reason, it is possible to prevent the amount of gas generated from returning by making the separator 40 difficult to deform (a separator having a dent amount of less than 0.3 μm) (see FIG. 14).

  In the lithium ion secondary battery 1 of the present embodiment, the separator 40 is made of polyethylene, which is a porous polyolefin resin, and polyetherketone, which is an engineered plastic, and the content of engineering plastic (polyetherketone) is 50 to 80. % Of the first layer 41 and the third layer 43, and the second layer 42 made of polyethylene and disposed between the first layer 41 and the third layer 43. As a result, the separator 40 having the optimum hardness to ensure a sufficient amount of gas generated during overcharge, that is, the dent amount (deformation amount) when pressed with a force of 0.05 gf is 0.3 μm or more. A separator 40 of 2 μm or less can be suitably formed (see FIGS. 13 and 14).

  Moreover, in the lithium ion secondary battery 1 of this embodiment, the positive electrode active material layer 21 has a maximum frequency pore diameter of 1.2 μm or less. When the maximum frequency pore diameter of the positive electrode active material layer 21 is made larger than 1.2 μm, the internal resistance (IV resistance) of the lithium ion secondary battery 1 suddenly increases (see FIG. 9). Further, since the maximum frequency pore diameter of the positive electrode active material layer 21 is set to 1.2 μm or less, the battery does not have an excessively large internal resistance.

  Although the present invention has been described above with reference to the embodiments, it is needless to say that the present invention is not limited to the above-described embodiments, and can be appropriately modified and applied without departing from the gist thereof. For example, in the embodiment, the lithium ion secondary battery 1 having the wound electrode body 10 is exemplified, but the technical idea of the present invention is also applied to a non-aqueous electrolyte secondary battery having a stacked electrode body. Can be applied. In the above embodiment, the lithium ion secondary battery 1 having the square battery case 80 is exemplified. However, the technical idea of the present invention is applied to a non-aqueous electrolyte secondary battery having a cylindrical battery case. Applicable.

  In the embodiment, polyethylene is used as the porous polyolefin resin, but other porous polyolefin resins such as polypropylene may be used. In the embodiment, polyether ketone is used as the engineering plastic, but other aromatic polyether ketones such as polyether ether ketone (PEEK) and other engineering plastics may be used.

  In the embodiment, CHB is used as the overcurrent additive, but other additives may be used. For example, a monomer additive such as an aromatic monomer such as biphenyl or thiophene may be used. Even when these monomer additives are included in the electrolyte solution, when the lithium ion secondary battery exceeds the maximum operating voltage and reaches the reaction voltage of the additive, the monomer additive undergoes a polymerization reaction to cause a gas reaction. Will occur. The positive electrode active material layer 21 may contain lithium carbonate as an overcurrent additive. In this case, when the lithium ion secondary battery is overcharged, as the potential of the positive electrode plate increases, the decomposition reaction of lithium carbonate proceeds and carbon dioxide gas is generated.

  In the embodiment, the current interrupting mechanism 62 is configured as a part of the positive electrode terminal structure 60, and the electrical connection between the positive electrode current collector terminal member 63 and the positive electrode external terminal member 68 is cut off due to the deformation of the diaphragm 64 during overcharge. However, the current interrupting mechanism is appropriately configured as long as the electrical connection between the positive current collecting terminal member 63 and the positive external terminal member 68 is cut off as the internal pressure increases during overcharging. May be changed.

1 ... Lithium ion secondary battery (non-aqueous electrolyte secondary battery)
DESCRIPTION OF SYMBOLS 10 ... Electrode body 28 ... Positive electrode collector foil 21 ... Positive electrode active material layer 20 ... Positive electrode plate 38 ... Negative electrode collector foil 31 ... Negative electrode active material layer 30 ... Negative electrode plate 40 ... Separator 41 ... First layer 42 ... Second layer 43 ... 3rd layer 50 ... Electrolyte solution 62 ... Current interruption mechanism 80 ... Battery case S ... Hole

Claims (5)

A positive electrode plate having a positive electrode current collector foil and a positive electrode active material layer coated on the positive electrode current collector foil;
A negative electrode plate having a negative electrode current collector foil and a negative electrode active material layer coated on the negative electrode current collector foil;
A separator interposed between the positive electrode plate and the negative electrode plate to electrically insulate the positive electrode plate and the negative electrode plate;
A battery case containing an electrode body formed by winding or laminating the positive electrode plate, the negative electrode plate, and the separator;
A non-aqueous electrolyte filled in the battery case;
An overcharge additive that reacts to generate gas when it exceeds normal operating voltage due to overcharge;
A non-aqueous electrolyte secondary battery comprising a current interruption mechanism for interrupting a current flowing through the electrode body when an internal pressure of the battery case exceeds an operating pressure,
The positive electrode active material layer has a maximum frequency pore diameter of 0.7 μm or more,
The nonaqueous electrolyte secondary battery, wherein the separator has a dent amount of 1.2 μm or less when pressed with a force of 0.05 gf. The nonaqueous electrolyte secondary battery according to claim 1,
The non-aqueous electrolyte secondary battery, wherein the separator has a dent amount of 0.3 μm or more when pressed with a force of 0.05 gf. The nonaqueous electrolyte secondary battery according to claim 2,
The separator is
A first layer and a third layer comprising a porous polyolefin resin and an engineering plastic, wherein the content of the engineering plastic is 50 to 80%;
A non-aqueous electrolyte secondary battery comprising a second layer made of a porous polyolefin resin and disposed between the first layer and the third layer. The nonaqueous electrolyte secondary battery according to claim 3,
The first layer and the third layer are made of polyethylene as the porous polyolefin resin and polyether ketone as the engineering plastic.
The non-aqueous electrolyte secondary battery, wherein the second layer uses polyethylene as a porous polyolefin resin. A non-aqueous electrolyte secondary battery according to any one of claims 1 to 4,
The non-aqueous electrolyte secondary battery, wherein the positive electrode active material layer has a maximum frequency pore diameter of 1.2 μm or less.

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