JP7520561B2 - Energy storage element - Google Patents

Description

The present invention relates to an energy storage element equipped with a wound electrode body.

Conventionally, a wound electrode body is known as an electrode body used in a secondary battery (see, for example, Patent Document 1). In this electrode body 102, as shown in FIG. 14, a long sheet-shaped positive electrode 123 and a negative electrode 124 are stacked and wound with two long sheet-shaped separators 126 and 127 in between. When viewed from the direction of the winding axis, the electrode body 102 is elliptical with a major axis and a minor axis. The electrode body 102 also has R portions located at both ends in the major axis direction.

When the electrode body 102 is viewed from the direction of the winding axis, the positive electrode winding end 1230 and the negative electrode winding end 1240 are arranged at one end in the long diameter direction of the electrode body 102, with the R portion located on this side sandwiched between them. Also, when the electrode body 102 is viewed from the direction of the winding axis, the separator winding ends 1260, 1270 are arranged at the other end in the long diameter direction of the electrode body 102.

Patent No. 6202347

In the above electrode body, a step may be formed at the portion where the positive electrode winding end, the negative electrode winding end, or the separator winding end is located due to these ends. As a result, when the electrode body is housed in a case and pressure is applied from the outside to the portion of the electrode body where the step is formed, the pressure received by the step portion and the portion surrounding the step portion may differ. The bias in the pressure applied to the electrode body may reduce the battery performance.

Therefore, the present embodiment aims to provide an energy storage element that includes a wound electrode body and suppresses uneven pressure applied to the electrode body.

The energy storage element of this embodiment is
an electrode assembly in which a strip-shaped first electrode and a second electrode having mutually different polarities are wound in a state where they overlap with a strip-shaped separator;
A case that houses the electrode body,
a length of the separator in the winding direction is longer than a length of the second electrode in the winding direction;
the electrode body is a wound body having a major axis and a minor axis when viewed from a direction of a winding axis of the electrode body,
a terminal end portion of the first electrode located at the end of the winding direction is located closer to the start of the winding direction than a terminal end portion of the second electrode located at the end of the winding direction,
In the winding direction, a terminal edge of the terminal portion of the second electrode is located between a position overlapping with a terminal edge of the terminal portion of the first electrode and a position on the opposite side of the terminal edge of the terminal portion of the first electrode in the minor diameter direction of the electrode body across the winding axis,
When viewed from the short diameter direction of the electrode body, the terminal edge of the terminal portion located at the end of the winding direction of the separator is located between the terminal edge of the terminal portion of the first electrode and the terminal edge of the terminal portion of the second electrode.

With this configuration, the separator's end portion reduces the difference in thickness of the electrode body in the short diameter direction caused by the difference in the position of the end portion of each electrode, improving the uniformity of the width of the electrode body, thereby suppressing uneven pressure applied to the electrode body.

In the energy storage element,
the separator is provided so as to sandwich the first electrode or the second electrode therebetween,
When the electrode body is viewed from the winding axis direction,
In the winding direction, the terminal edges of both end portions of the separator sandwiching the first electrode or the second electrode are aligned in the same position and positioned toward the end of the winding than the second electrode, and when viewed from the short diameter direction of the electrode body, may be located between the terminal edge of the terminal portion of the first electrode and the terminal edge of the terminal portion of the second electrode.

With this configuration, the end portions of both separators sandwiching the first and second electrodes can suppress the difference in thickness of the electrode body in the short diameter direction caused by the difference in the position of the end portions of each electrode.

In addition, in the energy storage element,
the first electrode and the second electrode each have a sheet-like conductive portion and an active material layer overlapping the conductive portion;
When the electrode body is viewed from the winding axis direction,
the active material layer of the first electrode is disposed at an end portion of the first electrode;
The active material layer of the second electrode may be disposed in a portion of the second electrode overlapping with an end portion of the first electrode in the winding direction.

In the energy storage element,
The second electrode may be disposed outwardly of the first electrode and may be thinner than the first electrode.

With this configuration, the difference in thickness of the electrode body in the short diameter direction due to the difference in the position of the end of each electrode tends to become large, so the effect of the separator's end portion suppressing this difference in thickness becomes more pronounced.

In the energy storage element,
When the electrode body is viewed from the winding axis direction,
an end portion of the second electrode and an end portion of the first electrode are disposed on one side in the minor axis direction;
The end portion of the separator may be disposed on an opposite side of the end portion of the second electrode across the winding axis in the minor diameter direction.

With this configuration, the separator extends from the position where it overlaps with the end of the second electrode to the opposite side of the winding axis in the short diameter direction, so that the step caused by the end of the second electrode can be filled.

The energy storage element of this embodiment has a wound electrode body, and can provide an energy storage element that suppresses uneven pressure applied to the electrode body.

FIG. 1 is a perspective view of an energy storage element according to the present embodiment. FIG. 2 is a side view of the energy storage element. FIG. 3 is a plan view of the energy storage element. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. FIG. 5 is a perspective view for explaining an electrode body of the energy storage element. FIG. 6 is a schematic diagram for explaining an electrode body of the electricity storage element. FIG. 7 is an enlarged view for explaining an electrode body of the energy storage element. FIG. 8 is a schematic diagram for explaining an electrode body of an energy storage element according to a comparative example. FIG. 9 is a schematic diagram for explaining an electrode body of an energy storage element according to a comparative example. FIG. 10 is a schematic diagram for explaining an electrode body of an energy storage element according to a comparative example. FIG. 11 is a schematic diagram for explaining an electrode body of an energy storage element according to a modified example. FIG. 12 is a schematic diagram for explaining an electrode body of an energy storage element according to a modified example. FIG. 13 is a perspective view of an electricity storage device including the electricity storage element. FIG. 14 is a schematic diagram for explaining an electrode body of a conventional energy storage element.

One embodiment of the present invention will be described below with reference to Figures 1 to 7. In this embodiment, a chargeable and dischargeable secondary battery will be described as an example of an energy storage element. Note that the names of the components (elementary components) in this embodiment are those used in this embodiment and may differ from the names of the components (elementary components) in the background art.

The storage element of this embodiment is a non-aqueous electrolyte secondary battery. More specifically, the storage element is a lithium ion secondary battery that utilizes electron transfer that occurs with the transfer of lithium ions. This type of storage element supplies electrical energy. Storage elements are used singly or in multiples. Specifically, a storage element is used singly when the required output and the required voltage are small. On the other hand, when at least one of the required output and the required voltage is large, the storage element is used in combination with other storage elements in a storage device. In the storage device, the storage element used in the storage device supplies electrical energy.

As shown in Figs. 1 to 4, the energy storage element includes an electrode body 2 and a case 3 that houses the electrode body 2. In addition to the electrode body 2 and the case 3, the energy storage element 1 of this embodiment includes an external terminal 4 that is disposed on the outside of the case 3 and is electrically connected to the electrode body 2, and a current collector 5 that electrically connects the electrode body 2 and the external terminal 4.

As shown in FIG. 5, the electrode body 2 has a configuration in which a strip-shaped first electrode and a second electrode having different polarities are wound in a state of overlapping with a strip-shaped separator 25. The electrode body 2 of this embodiment includes a laminate 22 in which a positive electrode 23 as a first electrode and a negative electrode 24 as a second electrode are stacked in a state of being insulated from each other, and the laminate 22 is wound. In this electrode body 2, a separator 25 is wrapped around the outer periphery of the electrode body 2. The energy storage element 1 is charged and discharged by the movement of lithium ions between the positive electrode 23 and the negative electrode 24 in the electrode body 2.

When viewed from the direction of the winding axis, the electrode body 2 is a wound body having a long diameter and a short diameter. The electrode body 2 in this embodiment has a flat cylindrical shape. The electrode body 2 has R portions as folded portions at both ends in the long diameter direction.

The laminate 22 is formed by winding a positive electrode 23 and a negative electrode 24 in a stacked (overlapping) state. In the laminate 22, each electrode has a sheet-shaped conductive portion and an active material layer that overlaps the conductive portion.

As shown in FIG. 7, the positive electrode 23 has a metal foil 230, which is a sheet-shaped conductive part, and a positive electrode active material layer 231 overlapping the metal foil. The metal foil 230 is strip-shaped. In this embodiment, the metal foil 230 is, for example, aluminum foil. The positive electrode 23 also has a positive electrode non-covered part (a part where the positive electrode active material layer 231 is not formed) 232 of the positive electrode active material layer 231 at one edge in the width direction, which is the short side direction of the strip shape (see FIG. 5). The part of the positive electrode 23 where the positive electrode active material layer 231 is formed is referred to as the positive electrode covered part 233.

The positive electrode active material layer 231 contains a positive electrode active material and a binder.

The positive electrode active material is, for example, a lithium metal oxide. Specifically, the positive _electrode active material is, for example, _a composite oxide represented by _LiaMebOc ( _{Me represents one or more transition metals) (LiaCoyO2, LiaNiwO2, LiaMnzO4, LiaNiwCoyMnzO2, etc.), or a polyanion compound represented by LilMem ( XOn ) p ( Me represents one or more transition metals , and} X represents _, for _{example ,} P, Si, B _{, or V} ) ( _{LiaFebPO4 , LiaMnbPO4 , LiaMnbSiO4 , LiaCobPO4F , etc.} ). The positive electrode active material in this embodiment is LiNi1 _/ 3Co1 _/ 3Mn1 _{/ 3O2} .

The binder used in the positive electrode active material layer 231 is, for example, polyvinylidene fluoride (PVdF), a copolymer of ethylene and vinyl alcohol, polymethylmethacrylate, polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, and styrene butadiene rubber (SBR). The binder in this embodiment is polyvinylidene fluoride.

The positive electrode active material layer 231 may further contain a conductive additive such as Ketjen Black (registered trademark), acetylene black, graphite, etc. The positive electrode active material layer 231 of this embodiment contains acetylene black as a conductive additive.

The negative electrode 24 has a metal foil 240, which is a sheet-like conductive part, and a negative electrode active material layer 241 overlapping the metal foil 240 (see FIG. 7). The thickness of the negative electrode 24 is approximately the same as the thickness of the positive electrode 23. The metal foil 240 is strip-shaped. The metal foil 240 in this embodiment is, for example, copper foil. The negative electrode 24 has a negative electrode non-covered part (a part where the negative electrode active material layer is not formed) 242 of the negative electrode active material layer at the edge part (opposite to the positive electrode non-covered part 232 in the width direction, which is the short direction of the strip shape) (see FIG. 5). The width of the negative electrode covered part (a part where the negative electrode active material layer is formed) 243 of the negative electrode 24 is larger than the width of the positive electrode covered part 233.

The negative electrode active material layer 241 contains a negative electrode active material and a binder.

The negative electrode active material is, for example, a carbon material such as graphite, non-graphitizable carbon, or easily graphitizable carbon, lithium titanate, or a material such as silicon (Si) and tin (Sn) that undergoes an alloying reaction with lithium ions. The negative electrode active material in this embodiment is non-graphitizable carbon.

The binder used in the negative electrode active material layer 241 is the same as the binder used in the positive electrode active material layer 231. In this embodiment, the binder is polyvinylidene fluoride.

The negative electrode active material layer 241 may further contain a conductive additive such as Ketjen Black (registered trademark), acetylene black, graphite, etc. The negative electrode active material layer 241 of this embodiment does not contain a conductive additive.

In the electrode body 2 of this embodiment, the positive electrode 23 and the negative electrode 24 configured as described above are wound in a state insulated by the separator 25. That is, in the electrode body 2 of this embodiment, a laminate 22 of the positive electrode 23, the negative electrode 24, and the separator 25 is wound. In addition, in the electrode body 2 of this embodiment, the negative electrode 24 is disposed outside the positive electrode 23. Specifically, the negative electrode 24 is disposed outside the positive electrode 23 in the stacking direction.

The separator 25 is an insulating member. The separator 25 is disposed between the positive electrode 23 and the negative electrode 24. This insulates the positive electrode 23 and the negative electrode 24 from each other in the electrode body 2 (specifically, the laminate 22). Furthermore, the separator 25 holds the electrolyte in the case 3. This allows lithium ions to move between the positive electrodes 23 and the negative electrodes 24 that are alternately stacked with the separator 25 in between when the energy storage element 1 is charged or discharged.

As shown in FIG. 6, the length of the separator 25 in the winding direction is longer than the length of the negative electrode 24 in the winding direction. The separator 25 in this embodiment is arranged to sandwich the positive electrode 23 or the negative electrode 24 therebetween. More specifically, the separator 25 includes a first separator 26 and a second separator 27 that sandwich the positive electrode 23 or the negative electrode 24 therebetween. The first separator 26 and the second separator 27 are separate bodies.

In addition, the separator 25 in this embodiment is formed, for example, from polyethylene. The hardness of the separator 25 is softer than the hardness of the positive electrode 23 and the negative electrode 24.

The width of the separator (the dimension in the short direction of the band shape) is slightly larger than the width of the negative electrode covering portion 243 (see FIG. 5). The separator 25 is placed between the positive electrode 23 and the negative electrode 24, which are stacked in a state where the covering portions 233, 243 are misaligned in the width direction so that they overlap each other. At this time, the positive electrode uncovered portion 232 and the negative electrode uncovered portion 242 do not overlap. That is, the positive electrode uncovered portion 232 protrudes in the width direction from the overlapping region of the positive electrode 23 and the negative electrode 24, and the negative electrode uncovered portion 242 protrudes in the width direction (the direction opposite to the protruding direction of the positive electrode uncovered portion 232) from the overlapping region of the positive electrode 23 and the negative electrode 24. The electrode body 2 is formed by winding the stacked positive electrode 23, negative electrode 24, and separator 25, i.e., the laminate 22.

The separator 25 of this embodiment has a base layer 250 and an inorganic layer 251 that is provided on one side of the base layer 250 and is harder than the base layer 250 (see FIG. 7). Furthermore, each base layer 250 of the pair of separators 25 that sandwich the negative electrode 24 faces the negative electrode 24. The base layer 250 that sandwiches the negative electrode 24 while facing it has a shape that matches the shape of the negative electrode 24, so that the insulation between the positive electrode 23 and the negative electrode 24 can be improved.

The base layer 250 is formed of a porous film of, for example, polyethylene, polypropylene, _{cellulose, polyamide, etc. The inorganic layer 251 is an inorganic layer containing inorganic particles such as SiO2 particles, Al2O3 particles ,} and boehmite (alumina hydrate).

The case 3 houses the electrode body 2 (see FIG. 4). In this embodiment, the case 3 has a case body 31 with an opening and a cover plate 32 that covers (closes) the opening of the case body 31. In addition to the electrode body 2, the case 3 houses an electrolyte, a current collector 5, etc. in the internal space 33.

The case 3 is also made of a metal that is resistant to the electrolyte. In this embodiment, the case 3 is made of, for example, aluminum or an aluminum-based metal material such as an aluminum alloy. The case 3 may also be made of a metal material such as stainless steel or nickel, or a composite material in which a resin such as nylon is bonded to aluminum.

The electrolyte is a non-aqueous electrolyte. The electrolyte is obtained by dissolving an electrolyte salt in an organic solvent. The organic solvent is, for example, a cyclic carbonate such as propylene carbonate or ethylene carbonate, or a chain carbonate such as dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate. The electrolyte salt is, for example, LiClO ₄ , LiBF ₄ , or LiPF ₆ .

The case body 31 includes a plate-shaped blocking portion 311 having an inner surface facing the inside of the case 3 and an outer surface facing the outside of the case 3, and a body portion 312 connected to the periphery of the blocking portion 311, the body portion 312 being cylindrical and extending toward the inner surface of the blocking portion 311 and surrounding the inner surface.

The blocking portion 311 is a portion that is located at the lower end of the case body 31 when the case body 31 is placed so that the opening faces upward (i.e., it becomes the bottom wall of the case body 31 when the opening faces upward). The blocking portion 311 is rectangular when viewed in the normal direction of the blocking portion 311. The four corners of the blocking portion 311 are arc-shaped.

In the following, as shown in FIG. 1, the long side direction of the blocking portion 311 is defined as the X-axis direction, the short side direction of the blocking portion 311 is defined as the Y-axis direction, and the normal direction of the blocking portion 311 is defined as the Z-axis direction.

The body 312 of this embodiment has a square tube shape. More specifically, the body 312 has a flattened square tube shape. The body 312 has a pair of long wall portions 313 extending from the long sides at the periphery of the blocking portion 311, and a pair of short wall portions 314 extending from the short sides at the periphery of the blocking portion 311. That is, the pair of long wall portions 313 face each other at a distance in the Y axis direction (more specifically, a distance corresponding to the short sides at the periphery of the blocking portion 311), and the pair of short wall portions 314 face each other at a distance in the X axis direction (more specifically, a distance corresponding to the long sides at the periphery of the blocking portion 311). The short wall portions 314 connect the corresponding ends of the pair of long wall portions 313 (more specifically, facing each other in the Y axis direction), thereby forming the square tube-shaped body 312.

As described above, the case body 31 has a rectangular cylindrical shape (i.e., a bottomed rectangular cylindrical shape) with one end in the opening direction (Z-axis direction) closed.

The cover plate 32 is a plate-shaped member that closes the opening of the case body 31. Specifically, the cover plate 32 abuts against the case body 31 so as to close the opening of the case body 31. When viewed in the Z-axis direction, the cover plate 32 is a rectangular plate that is long in the X-axis direction. Furthermore, the four corners of the cover plate 32 are arc-shaped.

The cover plate 32 has a gas exhaust valve 321 that can exhaust gas inside the case 3 to the outside. The gas exhaust valve 321 exhausts gas from inside the case 3 to the outside when the internal pressure of the case 3 rises to a predetermined pressure. In this embodiment, the gas exhaust valve 321 is provided in the center of the cover plate 32 in the X-axis direction.

The external terminal 4 is a portion that is electrically connected to an external device or an external terminal of another storage element. The external terminal 4 is formed of a conductive material. For example, the external terminal 4 is formed of aluminum, copper, iron, stainless steel, steel such as chromium molybdenum steel, or other high-strength conductive metal.

The current collector 5 is disposed within the case 3 and is directly or indirectly connected to the electrode body 2 so that it can be electrically connected thereto (see FIG. 4).

In the storage element 1 having the above configuration, the terminal portion 234 located at the end of the winding direction of the positive electrode 23 is located closer to the beginning of the winding direction than the terminal portion 244 located at the end of the winding direction of the negative electrode 24 (see FIG. 6). In addition, in the winding direction, the terminal edge 245 of the terminal portion 244 of the negative electrode 24 is located between a position where it overlaps with the terminal edge 235 of the terminal portion 234 of the positive electrode 23 and a position P on the opposite side of the winding axis in the short diameter direction (Y axis direction) of the electrode body 2 with respect to the terminal edge 235 of the terminal portion 234 of the positive electrode 23 (if a virtual plane is assumed that connects the vertices of the curved folded portions (R portions) located at both ends of the electrode body in the long diameter direction (Z axis direction) from the winding axis and extends in the winding axis direction (X axis direction), the position P is symmetrical to the terminal edge 235 of the terminal portion 234 of the positive electrode 23 with respect to this virtual plane). The position where the terminal edge 235 of the terminal portion 234 of the positive electrode 23 overlaps with the terminal edge 235 of the positive electrode 23 when viewed from the short side direction. In the energy storage element 1 of this embodiment, the terminal edge 245 of the negative electrode 24 is located between the position where the terminal edge 235 of the terminal portion 234 of the positive electrode 23 overlaps with the folded portion (R portion) of the electrode.

The base material layer 250 sandwiching the negative electrode 24 in a state facing the negative electrode 24 has a shape (a shape having a step) that conforms to the step of the electrode caused by the terminal end 244 of the negative electrode 24 when viewed from the winding axis direction, for example. Note that this sandwiching base material layer 250 has a shape (a shape having a step) that conforms to the step between the negative electrode non-covered portion 242 and the negative electrode covered portion 243 when viewed from the short diameter direction (Y-axis direction) of the electrode body 2.

Furthermore, when viewed from the short diameter direction (Y-axis direction) of the electrode body 2, the end edge 255 of the end portion 254 located at the end of the winding direction of the separator 25 is located between the end edge 235 of the end portion 234 of the positive electrode 23 and the end edge 245 of the end portion 244 of the negative electrode 24. In the energy storage element 1 of this embodiment, when the electrode body 2 is viewed from the winding axis direction, the end edges 255 of both end portions 254 of the separators 25 sandwiching the negative electrode 24 in the winding direction (specifically, the end edge 265 of the end portion 264 of the first separator 26 and the end edge 275 of the end portion 274 of the second separator 27) are aligned in the same position and are positioned closer to the end of the winding than the negative electrode 24, and are located between the end edge 235 of the positive electrode 23 and the end edge 245 of the negative electrode 24 when viewed from the short diameter direction (Y-axis direction) of the electrode body 2.

In the electrode body 2 of this embodiment, when the electrode body 2 is viewed from the winding axis direction, the positive electrode active material layer 231 is disposed at the terminal end 234 of the positive electrode 23 (see FIG. 7). When viewed from the winding axis direction, the negative electrode active material layer 241 is disposed at a portion that overlaps with the terminal end 234 of the positive electrode 23 in the winding direction of the negative electrode 24.

Furthermore, when the electrode body 2 is viewed from the direction of the winding axis, the terminal end 244 of the negative electrode 24 and the terminal end 234 of the positive electrode 23 are disposed on one side in the minor axis direction (see FIG. 6). Furthermore, when the electrode body 2 is viewed from the direction of the winding axis, the terminal end 254 of the separator 25 is disposed on the opposite side of the winding axis in the minor axis direction from the terminal end 244 of the negative electrode 24.

In the energy storage element 1 of this embodiment, when the electrode body 2 is viewed from the winding axis direction, the start edge 257 of the start end 256 located at the most start side in the winding direction of the separator 25 (specifically, the start edge 267 of the start end 266 of the first separator 26 and the start edge 277 of the start end 276 of the second separator 27) are located at different positions in the winding direction from the start edge 237 of the start end 236 located at the most start side in the winding direction of the positive electrode 23 and the start edge 247 of the start end 246 located at the most start side in the winding direction of the negative electrode 24. The length of the negative electrode 24 in the winding direction is longer than the length of the positive electrode 23 in the winding direction and shorter than the length of the separator 25 in the winding direction. Therefore, the separator 25 can reliably insulate the positive electrode 23 and the negative electrode 24.

In the energy storage element 1 of this embodiment, the positive electrode active material layer 231 is disposed over the entire area in the winding direction of the positive electrode 23. That is, the positive electrode active material layer 231 is disposed over the entire area from the starting end 236 to the terminal end 234 of the positive electrode 23. In addition, the negative electrode active material layer 241 is disposed over the entire area in the winding direction of the negative electrode 24. That is, the negative electrode active material layer 241 is disposed over the entire area from the starting end 246 to the terminal end 244 of the negative electrode 24.

In the energy storage element 1 of this embodiment, when the amount of change in thickness when the negative electrode 24 expands is ΔT1, the number of separators arranged at the position of the terminal end 234 of the positive electrode 23 outside the terminal end 234 in the short diameter direction (Y-axis direction) of the electrode body 2 is N, and the amount of change in thickness when the separator 25 is compressed is ΔT2, then ΔT1 < N × ΔT2. Therefore, the separator 25 can absorb the amount of change in thickness when the negative electrode 24 located at the outermost position of the electrode body 2 expands, and as a result, the current distribution of the electrode body 2 becomes more uniform, improving the output characteristics.

The change in thickness ΔT2 of the separator 25 when compressed is calculated by measuring the compression ratio by performing a creep test on the separator 25 taken out of the product cell after disassembling it and washing and drying it, and then using the compression ratio. The change in thickness ΔT1 of the negative electrode 24 when it expands corresponds to the difference between the thickness of the negative electrode 24 in the discharged state (SOC = 0%) of the energy storage element 1 (product cell) and the thickness of the negative electrode 24 in the charged state (SOC = 100%) of the product cell.

For example, in a configuration in which the negative electrode 24 is located outside the positive electrode 23, the thickness change amount ΔT1 of the negative electrode 24 when it expands is measured as follows. After discharging the product cell to a discharged state (SOC = 0%), the product cell is disassembled to remove the positive electrode 23 and the negative electrode 24, and each electrode is washed and dried. The thickness of the negative electrode 24 is then measured. Next, a small test cell is made using the removed electrodes, and the test cell is charged to a charged state (SOC = 100%). Furthermore, the test cell is disassembled, each electrode is washed and dried, and the thickness of the negative electrode 24 is measured, and the difference in thickness of the negative electrode 24 is taken as the thickness change amount ΔT1 of the negative electrode 24 when it expands. Note that the charge and discharge of the test cell is performed with the upper limit of the nominal voltage (recommended voltage range) of the product cell being SOC = 100% and the lower limit being SOC = 0%.

As shown in Figures 8 to 10, in a conventional electrode body 2, when the electrode body 2 is viewed from the short diameter direction (Y-axis direction), the terminal edge 255 of the separator 25 is not located anywhere except between the terminal edge 235 of the positive electrode 23 and the terminal edge 245 of the negative electrode 24. Therefore, in a conventional energy storage element, the difference in thickness of the electrode body 2 in the short diameter direction caused by the difference in the position of the terminal end 234 of the positive electrode 23 and the terminal end 244 of the negative electrode 24 results in large variation in the width of the electrode body 2, and the pressure applied to the electrode body 2 is uneven.

In contrast, in the energy storage element 1, the terminal edge 255 of the separator 25 is located between the terminal edge 235 of the positive electrode 23 and the terminal edge 245 of the negative electrode 24 (see FIG. 6). As a result, the terminal portion 254 of the separator 25 reduces the difference in thickness of the electrode body 2 in the short diameter direction caused by the difference in the position of the terminal portion 234 of the positive electrode 23 and the terminal portion 244 of the negative electrode 24, improving the uniformity of the width of the electrode body 2 and suppressing bias in the pressure applied to the electrode body 2.

Specifically, the thickness in the short diameter direction of the portion of the electrode body 2 located closer to the end of the winding in the winding direction than the terminal end 234 of the positive electrode 23 (for example, the thickness of the portion indicated by β in FIG. 6) is thinner than the thickness in the short diameter direction of the normal portion of the electrode body 2 (for example, the thickness of the portion indicated by α in FIG. 6) by the thickness of the positive electrode 23. In this energy storage element 1, the terminal end 254 of the separator 25 fills in this thickness difference, thereby suppressing the difference in thickness of the electrode body 2 in the short diameter direction caused by the difference in the position of the terminal end 234 of the positive electrode 23 and the terminal end 244 of the negative electrode 24.

According to the energy storage element 1 of this embodiment, the terminal edges 235 of both separators 25 sandwiching the positive electrode 23 and the negative electrode 24 are aligned in the same position and positioned outside the negative electrode 24, and when viewed from the short diameter direction of the electrode body 2, are located between the terminal edge 235 of the positive electrode 23 and the terminal edge 245 of the negative electrode 24. Therefore, the terminal parts 254 of both separators 25 sandwiching the positive electrode 23 and the negative electrode 24 can suppress the difference in thickness of the electrode body 2 in the short diameter direction caused by the difference in the position of the terminal part 234 of the positive electrode 23 and the terminal part 244 of the negative electrode 24.

In addition, in the energy storage element 1 of this embodiment, when viewed from the winding axis direction, the terminal end 244 of the negative electrode 24 and the terminal end 234 of the positive electrode 23 are arranged on one side in the short diameter direction, and the terminal end 254 of the separator 25 is arranged on the opposite side of the winding axis in the radial direction from the terminal end 244 of the negative electrode 24. In other words, the separator 25 extends from the position where it overlaps with the terminal end 244 of the negative electrode 24 to the opposite side of the winding axis in the short diameter direction, so that the step caused by the terminal end 244 of the negative electrode 24 can be filled.

The energy storage element of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and part of the configuration of one embodiment can be replaced with the configuration of another embodiment. Furthermore, part of the configuration of one embodiment can be deleted.

For example, when the electrode body 2 is viewed from the winding axis direction, the starting edge 267 of the starting end 266 of the first separator 26 and the starting edge 277 of the starting end 276 of the second separator 27 may be aligned in the same position and positioned closer to the winding start side than the starting edge 237 of the positive electrode 23 and the starting edge 247 of the negative electrode 24. Also, in this electrode body 2, when the electrode body 2 is viewed from the winding axis direction, the starting edge 237 of the positive electrode 23 and the starting edge 247 of the negative electrode 24 are positioned at different positions. Specifically, the starting edge 247 of the negative electrode 24 is positioned closer to the winding start side than the starting edge 237 of the positive electrode 23 when the electrode body 2 is viewed from the winding axis direction.

The starting end 236 of the positive electrode active material layer 231 and the starting end 246 of the negative electrode active material layer 241 are aligned with the starting end 256 of the separator 25 when viewed from the short diameter direction (Y-axis direction) of the electrode body 2. Furthermore, when viewed from the short diameter direction (Y-axis direction) of the electrode body 2, the starting end of the positive electrode active material layer 231 and the starting end of the negative electrode active material layer 241 are aligned.

In this energy storage element 1, the end portion 234 of the positive electrode 23, the end portion 244 of the negative electrode 24, and the end portion 254 of the separator 25 are all located closer to the winding axis than the center of curvature of the R portion of the electrode body 2. In addition, the start portion 236 of the positive electrode 23, the start portion 246 of the negative electrode 24, and the start portion 256 of the separator 25 are all located closer to the winding axis than the center of curvature of the R portion of the electrode body 2.

In the above embodiment, the separator 25 is wound around the outer periphery of the electrode body 2 once, but the separator may be wound around multiple times. For example, as shown in FIG. 11, the separator 25 may be wound around the outer periphery of the electrode body 2 two times.

In the above embodiment, the thickness of the positive electrode 23 and the thickness of the negative electrode 24 are approximately the same, but they may be different. For example, it is possible that the thickness of the negative electrode 24 is thinner than the thickness of the positive electrode 23. In this case, the difference in thickness of the electrode body 2 in the short diameter direction due to the difference in position between the terminal end 234 of the positive electrode 23 and the terminal end 244 of the negative electrode 24 tends to become large, so the effect of the terminal end 254 of the separator 25 suppressing this thickness difference becomes more pronounced.

In the above embodiment, the terminal edge 265 of the first separator 26 and the terminal edge 275 of the second separator 27 are aligned at the same position in the winding direction, but they do not have to be aligned at the same position. In this case, it is sufficient that the terminal edge 265 of the first separator 26 or the terminal edge 275 of the second separator 27 is located between the terminal edge 235 of the positive electrode 23 and the terminal edge 245 of the negative electrode 24.

In the above embodiment, the negative electrode active material layer 241 is disposed over the entire area of the negative electrode 24 in the winding direction, but may be disposed over a portion of the negative electrode 24 in the winding direction. For example, it is conceivable that the negative electrode active material layer 241 is not disposed at the terminal portion 244 of the negative electrode 24. That is, when viewed from the short diameter direction of the electrode body, the end portion of the negative electrode active material layer 241 in the winding direction may overlap the end portion of the positive electrode active material layer 231 in the winding direction. In this case, since the thickness of the terminal portion 244 of the negative electrode 24 is thin, the difference in thickness between the terminal portion 234 of the positive electrode 23 and the terminal portion 244 of the negative electrode 24 is likely to be large, but this difference can be suppressed by the separator 25.

In the above embodiment, the terminal edge 245 of the negative electrode 24 is located between the position where it overlaps with the terminal edge 235 of the terminal portion 234 of the positive electrode 23 (the position where it overlaps when viewed from the short diameter direction) and the R portion (the folded position of the electrode), but as shown in FIG. 12, it may be located between the R portion and a position on the opposite side of the winding axis from the terminal edge 235 of the positive electrode 23 in the short diameter direction (Y axis direction) of the electrode body 2. That is, the terminal edge 245 of the negative electrode 24 and the terminal edge 255 of the separator 25 may both be located on the opposite side of the winding axis from the terminal edge 235 of the positive electrode 23 in the Y axis direction of the electrode body 2.

In the above embodiment, the terminal edge 265 of the first separator 26 and the terminal edge 275 of the second separator 27 are aligned at the same position in the winding direction, but they may be located at different positions. In this case, only one of the terminal edge 265 of the first separator 26 and the terminal edge 275 of the second separator 27 may be located between the terminal edge 235 of the positive electrode 23 and the terminal edge 245 of the negative electrode 24 when viewed from the short diameter direction of the electrode body 2. Note that the starting edge 267 of the first separator 26 and the starting edge 277 of the second separator 27 are aligned at the same position in the winding direction, but they may be located at different positions.

In the above embodiment, the first separator 26 and the second separator 27 that sandwich the positive electrode 23 or the negative electrode 24 between them are separate bodies, but they may be integrated (a single continuous separator).

In the above embodiment, the inorganic layer 251 is provided on one side of the base layer 250 in the separator 25, but the inorganic layer 251 may be provided on both sides of the base layer 250. Note that the separator 25 does not need to have the inorganic layer 251, and may be composed of, for example, only the base layer 250.

The starting edge 237 of the positive electrode 23 and the starting edge 247 of the negative electrode 24 may be located at different positions in the short diameter direction of the electrode body 2.

In addition, in the above embodiment, the storage element is described as being used as a chargeable and dischargeable non-aqueous electrolyte secondary battery (e.g., a lithium ion secondary battery), but the type and size (capacity) of the storage element are arbitrary. Also, in the above embodiment, a lithium ion secondary battery is described as an example of a storage element, but this is not limiting. For example, the present invention can be applied to storage elements of various secondary batteries, as well as other primary batteries and capacitors such as electric double layer capacitors.

The energy storage element (e.g., a battery) may be used in an energy storage device 11 (a battery module when the energy storage element is a battery) as shown in FIG. 13. The energy storage device 11 has at least two energy storage elements 1 and a bus bar member 12 that electrically connects the two (different) energy storage elements 1 to each other. In this case, the technology of the present invention may be applied to at least one energy storage element 1.

1...energy storage element, 2...electrode body, 3...case, 4...external terminal, 5...current collector, 11...energy storage device, 12...busbar member, 22...laminated body, 23...positive electrode, 24...negative electrode, 25...separator, 26...first separator, 27...second separator, 31...case body, 32...cover plate, 33...internal space, 102...electrode body, 123...positive electrode, 124...negative electrode, 126...separator, 127...separator, 230...metal foil, 231...positive electrode active material layer, 232...positive electrode uncoated portion, 233...positive electrode coated portion, 234...terminal portion, 235...terminal edge, 236...starting end, 237...starting edge, 240...metal foil, 241...negative electrode active material 242: negative electrode non-coated portion; 243: negative electrode coated portion; 244: end portion; 245: end edge; 246: beginning edge; 247: beginning edge; 250: substrate layer; 251: inorganic layer; 254: end portion; 255: end edge; 256: beginning edge; 257: beginning edge; 264: end portion; 265: end edge; 266: beginning edge; 267: beginning edge; 274: end portion; 275: end edge; 276: beginning edge; 277: beginning edge; 311: blocking portion; 312: body portion; 313: long wall portion; 314: short wall portion; 321: gas exhaust valve; 1230: positive electrode winding end; 1240: negative electrode winding end; 1260, 1270: separator winding end

Claims (5)

an electrode assembly in which a strip-shaped first electrode and a second electrode having mutually different polarities are wound in a state where they overlap with a strip-shaped separator;
A case that houses the electrode body,
a length of the separator in the winding direction is longer than a length of the second electrode in the winding direction;
The electrode body is a wound body having a major axis and a minor axis when viewed from a direction of a winding axis of the electrode body,
a terminal end portion of the first electrode located at the end of the winding direction is located closer to the start of the winding direction than a terminal end portion of the second electrode located at the end of the winding direction,
In the winding direction, a terminal edge of the terminal portion of the second electrode is located between a position overlapping with a terminal edge of the terminal portion of the first electrode and a position on the opposite side of the terminal edge of the terminal portion of the first electrode in the minor diameter direction of the electrode body across the winding axis,
When viewed from the short diameter direction of the electrode body, a terminal edge of a terminal portion located at the end of the winding direction of the separator is located between a terminal edge of the terminal portion of the first electrode and a terminal edge of the terminal portion of the second electrode,
When viewed from the short diameter direction of the electrode body, a starting edge of a starting end of the first electrode and a starting edge of a starting end of the second electrode are located at a position other than between a terminal edge of a terminal end of the first electrode and a terminal edge of a terminal end of the second electrode,
The innermost periphery of the electrode body is constituted by the second electrode, and the second electrode is one turn longer than the first electrode in the winding direction at a starting end side of the first electrode and the second electrode in the electrode body .
A storage element characterized by: the separator is provided so as to sandwich the first electrode or the second electrode therebetween,
When the electrode body is viewed from the winding axis direction,
2. The energy storage element of claim 1, wherein, in the winding direction, the terminal edges of both terminal portions of the separator sandwiching the first electrode or the second electrode are aligned in the same position and positioned toward the end of the winding than the second electrode, and when viewed from the short diameter direction of the electrode body, are located between the terminal edge of the terminal portion of the first electrode and the terminal edge of the terminal portion of the second electrode. the first electrode and the second electrode each have a sheet-like conductive portion and an active material layer overlapping the conductive portion;
When the electrode body is viewed from the winding axis direction,
the active material layer of the first electrode is disposed at an end portion of the first electrode;
3 . The energy storage element according to claim 1 , wherein the active material layer of the second electrode is disposed in a portion of the second electrode that overlaps with an end portion of the first electrode in a winding direction of the second electrode. The energy storage element according to any one of claims 1 to 3, wherein the second electrode is disposed outside the first electrode and is thinner than the first electrode. When the electrode body is viewed from the winding axis direction,
an end portion of the second electrode and an end portion of the first electrode are disposed on one side in the minor axis direction;
The energy storage element according to any one of claims 1 to 4, wherein the end portion of the separator is disposed on the opposite side of the winding axis in the minor axis direction from the end portion of the second electrode.