Battery cell and mylar film thereof

Abstract

The invention provides a battery cell and a mylar film thereof. The mylar film is used for wrapping the periphery of the core package and comprises a first piece, second pieces and a surrounding piece, the first piece corresponds to the bottom face of the core package, the edge of the first piece is divided into a first section connected with the second pieces and a second section connected with the surrounding piece, and the second pieces can be folded along the second sections and connected end to end to correspondingly wrap the side face of the core package. The enclosure sheet can be folded relative to the first sheet and is connected to one side, facing the core package, of the second sheet so as to block a gap between the first sheet and the second sheet. The enclosure sheet can be connected to the side, facing the core package, of the second sheet after being folded relative to the first sheet, and the gap between the first sheet and the second sheet is blocked, so that the folded mylar film forms complete isolation between the core package and the shell within the height range corresponding to the enclosure sheet; and the powder in the core package can be blocked in the height range and cannot fall on the shell, so that the risk that the shell is corroded is avoided, and the safety performance of the battery core is improved.

Description

Technical Field

[0001] The present application relates to the technical field of battery manufacturing, and more specifically, to a battery cell and its Mylar film. Background Art

[0002] Conventional battery cells are usually wrapped with a layer of Mylar film around the core package and then placed in a shell. In order to facilitate the smooth flow and penetration of the electrolyte inside and outside the Mylar film, a gap or opening is set on the Mylar film at the position corresponding to the bottom of the core package, and the powder in the core package will also fall from the inside of the Mylar film through the gap or opening on the Mylar film to the shell, which makes the metal shell corroded, and thus poses a safety hazard to the battery cell. Summary of the invention

[0003] The purpose of the embodiments of the present application is to provide a battery cell and its Mylar film with improved safety performance.

[0004] In a first aspect, an embodiment of the present application provides a Mylar film, which is used to wrap around the periphery of a core package, and the Mylar film includes a first sheet, a second sheet and a surrounding sheet, the first sheet corresponds to the bottom surface of the core package, the edge of the first sheet is divided into a first section connected to the second sheet and a second section connected to the surrounding sheet, the second sheet can be folded along the second section and connected end to end to correspond to wrapping the side of the core package, the surrounding sheet can be folded relative to the first sheet and connected to the side of the second sheet facing the core package to block the gap between the first sheet and the second sheet.

[0005] In one embodiment, the second sheet is provided with openings for allowing electrolyte to pass through.

[0006] In one embodiment, the first sheet is rectangular and has two long sides and two short sides, and the length of the long sides is greater than the length of the short sides;

[0007] After the second sheet is folded along the second section, its head and tail connecting seams correspond to one of the two long sides; and / or, the opening is located in the area of ​​the second sheet corresponding to the short side after the second sheet is folded along the second section.

[0008] In one of the embodiments, a direction perpendicular to the first sheet is defined as a height direction of the second sheet, and there are a plurality of openings, which are arranged in sequence along the height direction.

[0009] In one embodiment, the plurality of openings are divided into a plurality of first holes and a plurality of second holes, and the distance from any second hole to the first sheet is greater than the distance from any first hole to the first sheet; the first hole is a blind hole surrounded by indentations and capable of being punched open under a set pressure, and the second hole is a through hole penetrating the second sheet; the liquid level of the electrolyte when the first hole closest to the first sheet is punched open under a set pressure is set as a critical liquid level, and the critical liquid level is higher than at least one of the second holes.

[0010] In one embodiment, the areas of the plurality of first holes are equal and the indentation depths are the same; and the areas of the plurality of second holes gradually increase as they gradually move away from the first sheet.

[0011] In one embodiment, there are three first holes, and the areas of the three first holes are S; there are three second holes, and the three second holes are annular and have an inner circle and an outer circle, and the areas of the areas enclosed by the outer circles of the three second holes are S. Along the direction gradually away from the first sheet, the areas of the areas enclosed by the inner circles of the three second holes are 3S / 4, 2S / 4, and S / 4 respectively.

[0012] In a second aspect, an embodiment of the present application provides a battery cell, comprising a core package and the above-mentioned Mylar film, wherein the Mylar film is wrapped around the outer surface of the core package.

[0013] In one embodiment, the battery cell includes a base support having a groove, and one end of the core package where the bottom surface is located is accommodated in the groove, and the base support is supported between the core package and the Mylar film; the enclosure sheet is hot-melt between the base support and the second sheet.

[0014] In one embodiment, the battery cell includes an outer shell and a cover plate, the cover plate is connected to the outer shell to jointly form a first accommodation space, the Mylar film and the core package are both located in the first accommodation space, the edge of the second sheet away from the first sheet is connected to the cover plate, and the core package is confined in the second accommodation space surrounded by the Mylar film and the cover plate.

[0015] The beneficial effect of the Mylar film provided in the embodiment of the present application is that when the Mylar film is folded to wrap the core package, the first sheet corresponds to the bottom surface of the core package and constitutes the bottom surface of the Mylar film, and the second sheet corresponds to the side surface of the core package and constitutes the side surface of the Mylar film. After being folded relative to the first sheet, the enclosure sheet can be connected to the side of the second sheet facing the core package, and the gap between the first sheet and the second sheet is blocked, so that the folded Mylar film completely isolates the core package from the outer shell within the height range corresponding to the enclosure sheet, and the powder in the core package will also be blocked within this height range and will not fall on the outer shell, thereby avoiding the risk of corrosion of the outer shell and improving the safety performance of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0017] Figure 1 A schematic diagram of the structure of the Mylar film in the battery cell provided in an embodiment of the present application when it is not folded;

[0018] Figure 2 for Figure 1 The schematic diagram of the structure of the Mylar film after folding is shown;

[0019] Figure 3 It is a schematic diagram of the enlarged structure of the second hole in the Mylar membrane shown in Figure 2;

[0020] Figure 4 A schematic diagram of the structure of the bottom support of the battery cell provided in an embodiment of the present application;

[0021] Figure 5 for Figure 4 The base shown is Figure 2 The schematic diagram of the structure of the Mylar membrane connection shown;

[0022] Among them, the reference numerals in the figure are:

[0023] 10. Mylar film; 110. first sheet; 111. first section; 112. second section; 113. long side; 114. short side; 130. second sheet; 131. first area; 132. second area; 133. third area; 150. enclosure sheet; 151. sub-sheet; 160. opening; 170. opening; 171. first hole; 172. second hole; 173. inner ring; 174. outer ring; 175. connecting bridge; 20. base; 210. groove. DETAILED DESCRIPTION

[0024] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0025] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0026] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0027] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0028] Please also read Figures 1 to 5 , the battery cell provided by the embodiment of the present application is now described. The battery cell includes a Mylar film 10, a core package, an outer shell and a cover plate, the cover plate is connected to the outer shell to jointly enclose a first accommodation space, the Mylar film 10 and the core package are both located in the first accommodation space, the Mylar film 10 is wrapped around the outer periphery of the core package and has an opening 160, the edge of the opening 160 of the Mylar film 10 is connected to the cover plate, so that the Mylar film 10 and the cover plate jointly enclose a second accommodation space, the core package is confined in the second accommodation space, so that the Mylar film 10 can separate the core package from the outer shell.

[0029] For the shell, Mylar film 10 and core package, the surfaces away from the cover plate are all bottom surfaces, and the surfaces between the bottom surface and the cover plate are all side surfaces, so the bottom surface of the Mylar film 10, the bottom surface of the core package and the bottom surface of the shell correspond to each other, and the side surfaces of the Mylar film 10, the side surfaces of the core package and the side surfaces of the shell correspond to each other. Specifically, the shell and the Mylar film 10 are cylindrical in shape, and both can be cylindrical to obtain a cylindrical battery cell, or both can be cubic to obtain a square battery cell.

[0030] The Mylar film 10 includes a first sheet 110, a second sheet 130 and a surrounding sheet 150. The first sheet 110 corresponds to the bottom surface of the core package. The edge of the first sheet 110 is divided into a first section 111 connected to the second sheet 130 and a second section 112 connected to the surrounding sheet 150. The second sheet 130 can be folded along the second section 112 and connected end to end to correspond to the side of the wrapped core package. The surrounding sheet 150 can be folded relative to the first sheet 110 and connected to the side of the second sheet 130 facing the core package to block the gap between the first sheet 110 and the second sheet 130.

[0031] It can be understood that when the Mylar film 10 is not folded (such as Figure 1As shown in FIG. 1 , the Mylar film 10 is in sheet form and is divided into three parts: a first sheet 110, a second sheet 130 and a baffle sheet 150. After the Mylar film 10 is folded and wrapped around the core package (as shown in FIG. Figure 2 As shown in FIG. 1 , the first sheet 110 corresponds to the bottom surface of the core package and constitutes the bottom surface of the Mylar film 10, and the second sheet 130 corresponds to the side surface of the core package and constitutes the side surface of the Mylar film 10. Further, after being folded relative to the first sheet 110, the enclosure sheet 150 can be connected to the side of the second sheet 130 facing the core package, and the gap between the first sheet 110 and the second sheet 130 is blocked, so that the folded Mylar film 10 completely isolates the core package from the shell within the height range corresponding to the enclosure sheet 150, and the powder in the core package will also be blocked within the height range and will not fall on the shell, thereby avoiding the risk of corrosion of the shell and improving the safety performance of the battery cell.

[0032] It should be noted that the edge of the second sheet 130 away from the first sheet 110 forms an opening 160 of the folded Mylar film 10 and is connected to the cover plate.

[0033] Furthermore, combined with Figure 2 and Figure 3 As shown, the second sheet 130 is provided with an opening 170 for electrolyte to pass through. Electrolyte is injected into the inner side of the Mylar film 10 through the opening 160, and excess electrolyte can flow to the outer side of the Mylar film 10 through the opening 170. After the electrolyte in the core package is consumed, the electrolyte on the outer side of the Mylar film 10 will also enter the inner side of the Mylar film 10 through the opening 170 and replenish the core package. In addition, since the position of the opening 170 corresponds to the side of the core package rather than the bottom of the core package, the speed of the electrolyte flowing out from the inner side of the Mylar film 10 to the outer side will also be slowed down, and the time for the electrolyte to soak the core package during injection will be extended, thereby increasing the wettability of the core package.

[0034] In the present application, the first sheet 110 is rectangular and has two long sides 113 and two short sides 114, and the length of the long side 113 is greater than the length of the short side 114. After the second sheet 130 is folded along the second section 112, its head and tail connection seam corresponds to one of the two long sides 113. It can be understood that since the first sheet 110 is rectangular, the overall shape will be a cube after the Mylar film 10 is folded to wrap the core package, and the battery cell is a square battery cell. The area of ​​the area corresponding to the long side 113 on the second sheet 130 will be greater than the area corresponding to the short side 114. By connecting the second sheet 130 head to tail in the area corresponding to the long side 113 and with a larger area, the connection operation can be made easier and the connection more stable.

[0035] In the present application, the second sheet 130 is connected to one of the long sides 113, so that the long side 113 constitutes the first section 111 of the edge of the first sheet 110, and the two short sides 114 and the remaining long side 113 together constitute the second section 112 of the edge of the first sheet 110. When the second sheet 130 is folded along the second section 112 and connected end to end, the end-to-end connecting seam of the second sheet 130 corresponds to the other long side 113.

[0036] Furthermore, the second sheet 130 is stably connected end to end by hot melting. The enclosure sheet 150 includes three sub-sheets 151 , and one sub-sheet 151 is connected to each of the two short sides 114 and the remaining long side 113 constituting the second section 112 .

[0037] Combination Figure 2 and Figure 3 As shown, specifically, when the Mylar film 10 is not folded, the second sheet 130 includes a first area 131, two second areas 132 and two third areas 133, one third area 133, one second area 132, the first area 131, another second area 132, and another third area 133 are connected in sequence, and the first area 131 is connected to one of the long sides 113 of the first sheet 110. After the Mylar film 10 is folded to wrap the core package, the two second areas 132 correspond to the two short sides 114 of the first sheet 110, and the two third areas 133 are the first and last two sheets on the second sheet 130, and the two are partially overlapped and connected together, so as to obtain a side wall that is opposite to the first area 131 and has the same area and corresponds to the other long side 113 of the first sheet 110, so that the connection seam of the two third areas 133 corresponds to one long side 113.

[0038] In other embodiments, the second sheet 130 may be connected to one of the short sides 114. Specifically, one of the second regions 132 may be connected to a short side 114 of the first sheet 110. The short side 114 constitutes the first section 111 of the edge of the first sheet 110. The two long sides 113 and the remaining short side 114 together constitute the second section 112 of the edge of the first sheet 110. In this case, the connecting seam of the two third regions 133 may correspond to a long side 113.

[0039] It can be understood that since the length of the long side 113 is greater than that of the short side 114 , the area of ​​the first region 131 is greater than that of the second region 132 , so the two third regions 133 can be stably connected in a larger area opposite to the first region 131 .

[0040] Further, the opening 170 is located in the area corresponding to the short side 114 after the second sheet 130 is folded along the second section 112. It can be understood that the opening 170 is located in the second area 132. Considering that the second sheet 130 needs to be connected end to end in an area corresponding to the long side 113 and with a larger area, in order to avoid covering each other and blocking the opening 170 when connected end to end, the opening 170 is selected to be set in the second area 132 corresponding to the short side 114. In this embodiment, the two second areas 132 are opposite and are each provided with six openings 170, which can help to evenly distribute the electrolyte on the opposite sides of the core package.

[0041] In other embodiments, the opening 170 may be provided in only one second region 132, while no opening 170 may be provided in the other second region 132. In addition, the number of openings 170 in the two second regions 132 may be different. In other embodiments, the opening 170 may be provided in the region corresponding to the long side 113 after the second sheet 130 is folded along the second section 112, that is, the opening 170 is provided in the first region 131 and / or the third region 133.

[0042] In the present application, the direction perpendicular to the first sheet 110 is defined as the height direction of the second sheet 130 (i.e. Figure 2 There are multiple openings 170, and the multiple openings 170 are arranged in sequence along the height direction. It can be understood that after the Mylar film 10 is folded to wrap the core package, the second sheet 130 is perpendicular to the first sheet 110. As the electrolyte level inside the Mylar film 10 gradually rises, the multiple openings 170 can cooperate with each other to allow the electrolyte to flow out to avoid deformation of the part of the Mylar film 10 below the liquid level due to excessive local pressure. Specifically, the multiple openings 170 are distributed linearly in the height direction. In addition, the centers of the multiple openings 170 divide the second sheet 130 into equal intervals in the height direction.

[0043] Specifically, there are six openings 170 in the height direction of the second sheet 130. Along the direction gradually away from the first sheet 110, the six openings 170 are set to be 1#, 2#, 3#, 4#, 5# and 6#, and the height of the second sheet 130 is set to be c. Then, the distance between the centers of any two adjacent openings 170 is c / 7.

[0044] Furthermore, the plurality of openings 170 are divided into a plurality of first holes 171 and a plurality of the second holes 172, and the distance from any second hole 172 to the first sheet 110 is greater than the distance from any first hole 171 to the first sheet 110. The first hole 171 is a blind hole surrounded by indentations and can be punched open under a set pressure, and the second hole 172 is a through hole that penetrates the second sheet 130. The liquid level of the electrolyte when the first hole 171 closest to the first sheet 110 is punched open under a set pressure is set as a critical liquid level, and the critical liquid level is higher than at least one second hole 172.

[0045] It is understood that the number of the first holes 171 and the number of the second holes 172 may be equal or different. However, the plurality of second holes 172 are all located at a position farther from the first sheet 110, while the plurality of first holes 171 are all located at a position closer to the first sheet 110, so that the plurality of second holes 172 are all located at a side of the first hole 171 farthest from the first sheet 110, away from the first sheet 110.

[0046] Specifically, among the six openings 170 , 1#, 2#, 3#, 4#, 5#, and 6#, the openings 170 , 1#, 2#, and 3# are first holes 171 , and the openings 170 , 4#, 5#, and 6# are second holes 172 .

[0047] It can be understood that in the initial stage of injecting the electrolyte, since the multiple first holes 171 are close to the first sheet 110 and are closed blind holes, the outflow of the electrolyte can be blocked, so the injected electrolyte is held by the Mylar film 10, and the time for the electrolyte to soak the core will be extended, which is beneficial to increase the wettability of the core package. As the liquid level of the electrolyte gradually rises, the pressure on the first hole 171 gradually increases. When the pressure on the 1# opening 170 closest to the first sheet 110 reaches the set pressure, the 1# opening 170 is opened, and the electrolyte can flow out through the 1# opening 170. The liquid level of the electrolyte is set to the critical level when the pressure on the 1# opening 170 closest to the first sheet 110 reaches the set pressure, and the critical level must be at least higher than the 4# opening 170.

[0048] It can be understood that by adjusting the set pressure at which the first hole 171 is flushed, the critical liquid level can be adjusted to be higher than at least one second hole 172, so that before the first hole 171 is flushed, the electrolyte can flow out through the second hole 172 below the critical liquid level, and the liquid level continues to gradually rise until it reaches the critical liquid level. In this way, the setting of the second hole 172 can extend the time when the electrolyte reaches the critical liquid level, and further extend the time for the electrolyte to soak the core package.

[0049] In the present application, the areas of the multiple first holes 171 are equal and the indentation depth is the same. Thus, as the electrolyte level gradually rises, the multiple first holes 171 will be flushed open by the electrolyte one by one under the equal set pressure. The areas of the multiple second holes 172 gradually increase as they gradually move away from the first sheet 110, so the area of ​​the second hole 172 farther from the first sheet 110 is larger. In this way, when the liquid level of the electrolyte rises to the second hole 172 with a larger area, the second hole 172 can accelerate the outflow of the electrolyte when the electrolyte level is too high.

[0050] Further, there are three first holes 171, and the areas of the three first holes 171 are all S. There are three second holes 172, and the three second holes 172 are annular and have an inner circle 173 and an outer circle 174. The areas of the areas surrounded by the outer circles 174 of the three second holes 172 are all S. Along the direction gradually away from the first sheet 110, the areas of the areas surrounded by the inner circles 173 of the three second holes 172 are 3S / 4, 2S / 4, and S / 4 respectively. By setting the areas of the multiple first holes 171 and the multiple second holes 172, the outflow speed of the electrolyte can be adjusted, thereby achieving the adjustment of the electrolyte level rising speed. In other embodiments, the areas of the three first holes 171 can be different, and the areas of the three second holes 172 can also be set to other values.

[0051] Specifically, the thickness of the second sheet 130 is set to d, and the speed of electrolyte injection is set to V (mm 3 / s), under the condition that the electrolyte flow rate is V / 4 when the 1# opening 170 is opened, the area of ​​the 1# opening 170 is S=V / (4d). The electrolyte density is set to ρ, and when the liquid level of the electrolyte reaches the critical liquid level h=5c / 7, the 1# opening 170 will be opened by pressure, and the pressure is set to F=Sρg4c / 7. At this time, since the liquid level of the electrolyte has submerged all of the 4# opening 170 and half of the 5# opening 170, the electrolyte will flow out through the 4# and 5# openings 170. Before the liquid level reaches 5c / 7, the electrolyte will first flow out through the 4# opening, and then through the 4# and 5# openings 170. The setting of the 4# and 5# openings 170 prolongs the time for the electrolyte to reach the critical liquid level and prolongs the time for the electrolyte to soak the core package.

[0052] Combination Figure 2 and Figure 3 As shown, the second hole 172 is annular and has an inner ring 173, an outer ring 174 and a connecting bridge 175 connected between the inner ring 173 and the outer ring 174. There are multiple connecting bridges 175, and the multiple connecting bridges 175 stably connect the inner ring 173 to the inside of the outer ring 174. The area surrounded by the inner ring 173 blocks the passage of electrolyte, and a channel for electrolyte to flow through is formed between the inner ring 173 and the outer ring 174. Therefore, the area of ​​the area between the inner ring 173 and the outer ring 174 is the area of ​​the second hole 172.

[0053] In the present application, the 1#, 2#, and 3# openings 170 are all circular and have equal areas of S, the 4#, 5#, and 6# openings 170 are all annular, and the areas of the areas enclosed by the outer rings 174 of the 4#, 5#, and 6# openings 170 are all S, and the areas of the areas enclosed by the inner rings 173 of the 4#, 5#, and 6# openings 170 are 3S / 4, 2S / 4, and S / 4, respectively. Therefore, the areas of the 4#, 5#, and 6# openings 170 are S / 4, 2S / 4, and 3S / 4, respectively.

[0054] When the liquid level reaches 5c / 7, the 1# opening 170 is opened, and the electrolyte flows out of the 4# opening 170 and the 5# opening 170. At this time, the net injection speed inside the Mylar membrane 10 is 5V / 8, and the liquid level rise speed slows down. When the liquid level reaches 6c / 7, the 2# opening 170 is opened, and the 1# and 2# openings 170 can both allow the electrolyte to flow out. The speed of the electrolyte flowing out of the Mylar membrane 10 is greater than the injection speed, and the liquid level will gradually drop to 4c / 7. When the injection is not completed, the liquid level will remain at this height. When the injection is completed, the electrolyte inside the Mylar membrane 10 will continue to flow out, causing the liquid level to continue to drop.

[0055] In the present application, the area of ​​each opening 170 is set according to the electrolyte injection speed. In other embodiments, the area of ​​the opening 170 also needs to be changed at different injection speeds.

[0056] Combination Figure 2 , Figure 4 and Figure 5 As shown, in the present application, the battery cell further includes a base 20, the base 20 is provided with a groove 210, one end of the upper bottom surface of the core package is accommodated in the groove 210, the base 20 is supported between the core package and the Mylar film 10, and the enclosure sheet 150 is hot-melted between the base 20 and the second sheet 130. It can be understood that since the base 20 is supported between the core package and the Mylar film 10, the base 20 can provide support when the second sheet 130 is hot-melted to the enclosure sheet 150, and the enclosure sheet 150 can also be hot-melted to the base 20, so that the base 20 can further block the gap between the second sheet 130 and the first sheet 110, so as to further reduce the possibility of the powder in the core package falling on the shell and corroding the shell, thereby improving the safety performance of the battery cell. Since the base 20 is provided with a groove 210, part of the electrolyte can be stored in the groove 210, so as to provide electrolyte for the core package during the operation of the core package.

[0057] Specifically, the overall shape of the base 20 is a cube, and the four edges of the base 20 can provide a fulcrum for the second sheet 130 when the enclosure sheet 150 is hot-melted between the base 20 and the second sheet 130 .

[0058] Specifically in the present application, the height h of the base 20 is equal to the height of the enclosure sheet 150 , and both are c / 8, so the upper surface of the base 20 is lower than the 1# opening 170 closest to the first sheet 110 to avoid interference with the opening 170 .

[0059] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A Mylar film, characterized in that: The Mylar film is used to wrap around the core package, and the Mylar film includes a first sheet, a second sheet and a surrounding sheet. The first sheet corresponds to the bottom surface of the core package, and the edge of the first sheet is divided into a first section connected to the second sheet and a second section connected to the surrounding sheet. The second sheet can be folded along the second section and connected end to end to wrap the side of the core package accordingly. The surrounding sheet can be folded relative to the first sheet and connected to the side of the second sheet facing the core package to block the gap between the first sheet and the second sheet.

2. The Mylar film according to claim 1, characterized in that: The second sheet is provided with openings for allowing electrolyte to pass through.

3. The Mylar film according to claim 2, characterized in that: The first sheet is rectangular and has two long sides and two short sides, and the length of the long sides is greater than the length of the short sides; After the second sheet is folded along the second section, its head and tail connecting seams correspond to one of the two long sides; and / or, the opening is located in the area of ​​the second sheet corresponding to the short side after the second sheet is folded along the second section.

4. The Mylar film according to claim 2, characterized in that: A direction perpendicular to the first sheet is defined as a height direction of the second sheet. There are a plurality of openings, and the plurality of openings are sequentially arranged along the height direction.

5. The Mylar film according to claim 4, characterized in that: The multiple openings are divided into multiple first holes and multiple second holes, and the distance from any second hole to the first sheet is greater than the distance from any first hole to the first sheet; the first hole is a blind hole surrounded by indentations and can be punched open under a set pressure, and the second hole is a through hole that penetrates the second sheet; the liquid level of the electrolyte when the first hole closest to the first sheet is punched open under a set pressure is set as a critical liquid level, and the critical liquid level is higher than at least one of the second holes.

6. The Mylar film according to claim 5, characterized in that: The areas of the plurality of first holes are equal and the indentation depths are the same; the areas of the plurality of second holes gradually increase as they gradually move away from the first sheet.

7. The Mylar film according to claim 6, characterized in that: There are three first holes, and the areas of the three first holes are S; there are three second holes, and the three second holes are annular and have an inner circle and an outer circle. The areas of the areas enclosed by the outer circles of the three second holes are S. Along the direction gradually away from the first sheet, the areas of the areas enclosed by the inner circles of the three second holes are 3S / 4, 2S / 4, and S / 4 respectively.

8. A battery cell, characterized in that: It comprises a core package and the Mylar film according to any one of claims 1 to 7, wherein the Mylar film is wrapped around the outer surface of the core package.

9. The battery cell according to claim 8, characterized in that: The battery core includes a base, which is provided with a groove. One end of the core package where the bottom surface is located is accommodated in the groove. The base is supported between the core package and the Mylar film; the enclosure sheet is hot-melted between the base and the second sheet.

10. The battery cell according to claim 8, characterized in that: The battery cell includes an outer shell and a cover plate, the cover plate is connected to the outer shell to jointly form a first accommodation space, the Mylar film and the core package are both located in the first accommodation space, the edge of the second sheet away from the first sheet is connected to the cover plate, and the core package is confined in the second accommodation space surrounded by the Mylar film and the cover plate.

Images