Secondary battery, battery pack, and electronic device

Abstract

The utility model provides a secondary battery which comprises an electrode assembly, a negative pole piece, a first diaphragm, a positive pole piece and a second diaphragm which are sequentially stacked and wound to form the electrode assembly, the negative pole piece comprises a negative pole coating area and a negative pole lug protruding out of the negative pole coating area, the positive pole piece comprises a positive pole coating area and a positive pole lug protruding out of the positive pole coating area, the negative pole lug and the positive pole lug are located on the two opposite sides of the electrode assembly respectively, the direction from the negative pole lug to the positive pole lug is the height direction, and the height of the negative pole lug is larger than that of the positive pole lug in the height direction. The distance from the upper end of the negative electrode coating area to the upper end of the positive electrode coating area is Lp mm, the value range of Lp is 0.3-1.7, the distance from the lower end of the negative electrode coating area to the lower end of the positive electrode coating area in the direction deviating from the height direction is Ln mm, and the value range of Ln is 0.8-2.2. The utility model aims to provide a secondary battery, a battery pack and an electronic device so as to at least improve the height uniformity of an electrode assembly.

Description

Technical Field

[0001] The utility model relates to a secondary battery, a battery pack and an electronic device. Background Art

[0002] In the field of new energy power batteries, the application of secondary batteries is becoming increasingly widespread. For example, secondary batteries (such as lithium-ion batteries) can be applied to electronic devices such as cars, energy storage, mobile phones, tablets, wearable devices, mobile power supplies, electronic cigarettes, digital products, power tools, power devices, energy storage devices, etc. Secondary batteries include cylindrical batteries, which include a housing and an electrode assembly. The electrode assembly includes a positive electrode sheet, a first separator, a negative electrode sheet, and a second separator. The electrodes are stacked in sequence and wound into an electrode assembly, which is then encapsulated in a housing. However, existing secondary batteries still need further improvement in some aspects. Utility Model Content

[0003] In view of the problems existing in the related art, the purpose of the present invention is to provide a secondary battery, a battery pack and an electronic device to at least improve the height uniformity of the electrode assembly.

[0004] According to one aspect of the present application, a secondary battery is provided, comprising: an electrode assembly, the electrode assembly comprising: a negative electrode sheet, a first separator, a positive electrode sheet, and a second separator, which are stacked and wound in sequence to form the electrode assembly; the negative electrode sheet comprises a negative electrode coating area and a negative electrode tab protruding from the negative electrode coating area, the positive electrode sheet comprises a positive electrode coating area and a positive electrode tab protruding from the positive electrode coating area, the negative electrode tab and the positive electrode tab are respectively located on opposite sides of the electrode assembly, the direction from the negative electrode tab to the positive electrode tab is the height direction of the electrode assembly, along the height direction, the distance from the upper end of the negative electrode coating area beyond the upper end of the positive electrode coating area is Lp mm, and the value range of Lp is 0.3-1.7, and along the direction away from the height direction, the distance from the lower end of the negative electrode coating area beyond the lower end of the positive electrode coating area is Ln mm, and the value range of Ln is 0.8-2.2.

[0005] In the above technical solution, the upper end of the negative electrode coating area exceeds the upper end of the positive electrode coating area by Lp mm, and the value range of Lp is 0.3-1.7, and the lower end of the negative electrode coating area exceeds the lower end of the positive electrode coating area by Ln mm, and the value range of Ln is 0.8-2.2, which can at least improve the height uniformity of the entire electrode assembly.

[0006] In some embodiments, the following is satisfied: 1.3≤Ln / Lp≤1.7, and within the first 20 turns wound in the winding direction from the starting end of the positive electrode sheet, the range of Ln mm is A1 mm, and within the remaining turns from the starting position of the 21st turn of the positive electrode sheet to the tail end of the positive electrode sheet, the range of Ln mm is A2 mm, and A1 is greater than A2.

[0007] In some embodiments, the value range of A1 is 0.2-0.5, and the value range of A2 is 0-0.2.

[0008] In some embodiments, within the first 20 turns wound in the winding direction from the starting end of the positive electrode sheet, the range of Lp mm is A3 mm, and within the remaining turns from the starting position of the 21st turn of the positive electrode sheet to the tail end of the positive electrode sheet, the range of Lp mm is A4 mm, and A3 is greater than A4.

[0009] In some embodiments, the standard deviation of Lp mm in the first 20 laps is S1 mm, and the value range of S1 is 0.09-0.15; the standard deviation of Lp mm in the remaining laps is S2 mm, and the value range of S2 is 0.02-0.04.

[0010] In some embodiments, along the direction away from the height direction, the distance that the lower end of either the first diaphragm and the second diaphragm extends beyond the lower end of the negative electrode coating area is G1 mm, and within the first 20 turns wound in the winding direction from the starting end of the positive electrode sheet, the standard deviation of G1 mm is S3 mm, and the value range of S3 is 0.09-0.15. Within the remaining turns from the starting position of the 21st turn of the positive electrode sheet to the end end of the negative electrode sheet, the standard deviation of G1 mm is S4, and the value range of S4 is 0.08-0.14.

[0011] In some embodiments, the secondary battery is a cylindrical battery.

[0012] In some embodiments, the secondary battery further includes a shell having a rolling groove protruding toward the interior of the shell; the electrode assembly is accommodated in the shell, and the rolling groove limits the movement of the electrode assembly in the height direction.

[0013] According to another aspect of the present application, a battery pack is provided, comprising any one of the aforementioned secondary batteries of the present application.

[0014] According to another aspect of the present application, an electronic device is provided, comprising any one of the aforementioned secondary batteries of the present application.

[0015] The beneficial technical effects of the present utility model are:

[0016] In the above technical solution, the upper end of the negative electrode coating region extends beyond the upper end of the positive electrode coating region by Lp mm, with Lp ranging from 0.3 to 1.7. The lower end of the negative electrode coating region extends beyond the lower end of the positive electrode coating region by Ln mm, with Ln ranging from 0.8 to 2.2. This at least improves the height uniformity of the entire electrode assembly. High height uniformity indicates high capacity uniformity of the battery.

[0017] Furthermore, compared to square shell and soft pack batteries, cylindrical batteries pursue higher energy density, so the process window requirements for the height uniformity of bare cells are higher, and the height space inside the shell for accommodating bare cells is also very limited (to ensure that each bare cell can be placed inside the shell). Therefore, the technical solution of this application also improves the capacity uniformity of cylindrical batteries. In addition, if the height uniformity is poor, the taller electrode assembly may not fit into the shell, affecting battery assembly. This application avoids the situation where the taller electrode assembly cannot fit into the shell during assembly by improving the height uniformity of the electrode assembly, thereby preventing the height uniformity of the electrode assembly from affecting the assembly of cylindrical batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0019] Figure 1 A schematic diagram showing an electronic device according to an embodiment of the present application is a vehicle.

[0020] Figure 2 A perspective view of a secondary battery according to an embodiment of the present application is shown.

[0021] Figure 3 A cross-sectional view of a secondary battery according to an embodiment of the present application is shown.

[0022] Figure 4 A schematic diagram of an electrode assembly of a secondary battery according to an embodiment of the present application is shown.

[0023] Figure 5 A schematic diagram of the unfolding of an electrode assembly before winding according to an embodiment of the present application is shown.

[0024] Figure 6 A schematic cross-sectional view perpendicular to the height direction of an electrode assembly according to an embodiment of the present application is shown.

[0025] Figure 7 The figure shows the relationship between the distance that the negative electrode coating area extends beyond the positive electrode coating area and the number of winding turns on the negative electrode tab side of the electrode assembly of the embodiment of the present application after winding. DETAILED DESCRIPTION

[0026] In order to better understand the spirit of the embodiments of the present application, some preferred embodiments of the present application are further described below.

[0027] The embodiments of the present application will be described in detail below. Throughout this specification, identical or similar components and components having identical or similar functions are represented by similar reference numerals. The embodiments described herein with respect to the accompanying drawings are illustrative and diagrammatic and are intended to provide a basic understanding of the present application. The embodiments of the present application should not be construed as limiting the present application.

[0028] As used herein, the terms "substantially," "substantially," and "approximately" are used to describe and illustrate small variations. When used in conjunction with an event or circumstance, the terms may refer to instances where the event or circumstance occurred precisely as well as instances where the event or circumstance occurred very approximately.

[0029] In this specification, unless otherwise specified or limited, relative terms such as "central", "longitudinal", "lateral", "front", "rear", "right", "left", "inner", "outer", "lower", "higher", "horizontal", "vertical", "above", "below", "above", "below", "top", "bottom" and their derivatives (such as "horizontally", "downwardly", "upwardly", etc.) should be interpreted as referring to the directions described in the discussion or depicted in the drawings. These relative terms are only used for convenience of description and do not require that the present application be constructed or operated in a specific orientation.

[0030] For ease of description, “first,” “second,” “third,” etc. may be used herein to distinguish different components in a figure or a series of figures. “First,” “second,” “third,” etc. are not intended to describe the corresponding components.

[0031] For the convenience of explanation, the following embodiments are described by taking the electronic device as a vehicle 1000. The vehicle 1000 can be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended range vehicle, etc., but is not limited thereto. Figure 1 The vehicle 1000 is provided with a battery pack 1002 inside, and the battery pack 1002 can be provided at the bottom of the vehicle body 1001 (eg Figure 1 As shown) or head, or tail, or any other appropriate position. The battery pack 1002 can be used to power the vehicle 1000. For example, the battery pack 1002 can be used as an operating power source or a driving power source for the vehicle 1000. The battery pack 1002 may include a plurality of secondary batteries (such as Figure 2 The secondary battery 100) and a housing for accommodating a plurality of secondary batteries.

[0032] However, in some other embodiments, the electronic device may also be a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, and the like. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, and the like. Electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, and the like; electric tools include metal cutting electric tools, grinding electric tools, assembly electric tools, and railway electric tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, and the like. The embodiments of the present application do not impose any special restrictions on electronic devices. The electronic device may include a working part, which is a unit component that can obtain electrical energy from the battery pack 1002 and perform corresponding work, such as a fan blade rotation unit, a vacuum cleaner dust collection unit, and the like.

[0033] Figure 2 1 shows a perspective view of a secondary battery 100 according to an embodiment of the present application, Figure 3 FIG2 shows a cross-sectional view of a secondary battery 100 according to an embodiment of the present application. In this embodiment, the secondary battery 100 may be a cylindrical battery.

[0034] In one example of the secondary battery of the present invention, Figure 2 and Figure 3 As shown, the secondary battery 100 includes a housing 200, one end of which is provided with an opening 205. The cover assembly 220 covers the opening 205 of the housing 200 and blocks the housing cavity of the housing 200 for encapsulating the electrode assembly 120 and the electrolyte. The housing 200 can be made of any of a variety of available materials, such as copper, iron, aluminum, steel, aluminum alloy, etc. The housing 200 can be cylindrical and define a housing cavity, and the electrode assembly 120 is disposed in the housing cavity. The diameter of the housing 200 can be determined according to the specific diameter size of the electrode assembly 120, such as 18 mm, 21 mm, 46 mm, etc. In some embodiments, the secondary battery 100 can be a 4680 cylindrical battery (diameter 46 mm, height 80 mm), or the secondary battery 100 can be a 4695 cylindrical battery (diameter 46 mm, height 95 mm), or the secondary battery 100 can be a 46120 cylindrical battery (diameter 46 mm, height 120 mm).

[0035] The electrode assembly 120 is primarily formed by stacking and winding a negative electrode sheet, a first separator, a positive electrode sheet, and a second separator. The electrode assembly 120 has a positive electrode tab 313 and a negative electrode tab 311 on opposite sides. The negative electrode tab 311 faces the opening 205, while the positive electrode tab 313 faces the end wall 111 of the housing 200 opposite the opening 205. The direction from the negative electrode tab 311 toward the positive electrode tab 313 is the height direction H of the electrode assembly 120.

[0036] An inwardly protruding rolling groove 113 may be provided on the sidewall of the housing 200 adjacent to the opening 205. The electrode assembly 120 is disposed between the end wall 111 and the rolling groove 113, and the rolling groove 113 is capable of limiting movement of the electrode assembly 120 in the height direction H and the opposite direction between the end wall 111 and the rolling groove 113. The end of the housing 200 on the side of the opening 205 may be configured as a curling portion 32, which extends radially inwardly of the housing 200. The curling portion 32 is spaced apart from the rolling groove 113 along the height direction H, and the rolling groove 113 and the curling portion 32 can jointly clamp the cover plate assembly 220.

[0037] The secondary battery 100 further includes a post 160 extending through the end wall 111. The post 160 can be electrically connected to the positive electrode tab 313 of the electrode assembly 120 via a positive current collecting disc, thereby making the post 160 positively charged. The negative electrode tab 311 can be electrically connected to the housing 200 via a negative current collecting disc, thereby making the housing 200 negatively charged.

[0038] Figure 4 FIG1 shows a schematic diagram of an electrode assembly 120 of a secondary battery 100 according to an embodiment of the present application. Figure 4 The electrode assembly 120 is formed by stacking and winding the negative electrode sheet 11, the first separator 12, the positive electrode sheet 13, and the second separator 14 in sequence. The wound electrode assembly 120 has a winding center hole 120c.

[0039] The positive electrode sheet 13 may include a positive electrode current collector 136 and a positive electrode coating region 213, which is coated on a portion of the surface of the positive electrode current collector 136. The positive electrode coating region 213 is a positive electrode active material layer formed by coating the positive electrode active material. The portion of the positive electrode current collector 136 not covered by the positive electrode coating region 213 constitutes a positive electrode tab 313. The negative electrode sheet 11 may include a negative electrode current collector 118 and a negative electrode coating region 211, which is coated on a portion of the surface of the negative electrode current collector 118. The negative electrode coating region 211 is a negative electrode active material layer formed by coating the negative electrode active material. The portion of the negative electrode current collector 118 not covered by the negative electrode coating region 211 constitutes a negative electrode tab 311.

[0040] Taking a lithium-ion battery as an example, the positive electrode current collector 136 can be made of aluminum, and the positive electrode coating region 213 can include a positive electrode active material, such as lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide. The negative electrode current collector 118 can be made of copper. The negative electrode coating region 211 can include a negative electrode active material, such as carbon or silicon. The first and second separators 12 and 14 can be made of polypropylene (PP) or polyethylene (PE).

[0041] In an example of the secondary battery 100 of the present invention, the manufacturing method of the secondary battery 100 of the present invention includes the following steps:

[0042] Winding: The negative electrode sheet 11, the first separator 12, the positive electrode sheet 13, and the second separator 14 are stacked and wound to form a wound structure. The positive electrode tab 313 and the negative electrode tab 311 are formed by the uncoated portion of the positive electrode collector 136 of the positive electrode sheet 13 and the negative electrode collector 118 of the negative electrode sheet 11. The positive electrode tab 313 and the negative electrode tab 311 are bent in the radial direction of the electrode assembly 120.

[0043] The current collecting disc is welded to the electrode assembly 120 : Specifically, the positive electrode current collecting disc and the negative electrode current collecting disc are welded to the surface areas of the bent positive electrode tab 313 and the bent negative electrode tab 311 , respectively.

[0044] Inserting into the shell: The electrode assembly 120 welded with the positive electrode collecting disc and the negative electrode collecting disc is installed into the shell 200 through the opening 205. The method of installing the electrode assembly 120 in this step is not limited, for example, it can be installed manually or by a robot.

[0045] Install pole 160.

[0046] Injecting electrolyte: There is no limitation on the method of injecting the electrolyte. The electrolyte can be injected through the opening 205 or through an injection hole provided on the end wall 111. Preferably, in this embodiment, the electrolyte is injected through the opening 205, which reduces the process of providing an injection hole on the end wall 111 and allows the electrolyte to be directly injected through the existing opening 205, thereby simplifying the process and reducing costs.

[0047] Sealing: The cover plate assembly 220 is sealed and mounted on the opening 205. Various sealing methods are available, and are not limited thereto. In some embodiments, the outer periphery of the housing 200 is first rolled to form a groove 113 recessed toward the center of the housing 200 to restrict movement of the electrode assembly 120 in the height direction H. A mechanical sealing process is then used to seal the cover plate assembly 220 to form a crimped edge 32, thereby sealing the cover plate assembly 220 to the opening 205 of the housing 200. This step is a mature, low-cost, and highly efficient process.

[0048] Figure 5 Schematic diagram of the electrode assembly 120 before winding according to an embodiment of the present application is shown. According to an embodiment of the present application, the upper end and the lower end of the negative electrode coating area 211 are both overhang (OH) the upper end and the lower end of the positive electrode coating area 213 along the height direction H and the direction away from the height direction H. Figure 4 and Figure 5On the positive electrode tab 313 side, along the height direction H, the upper end of the negative electrode coating region 211 extends beyond the upper end of the positive electrode coating region 213 by a distance Lp mm. In some embodiments, the value of Lp can range from 0.3 to 1.7. On the negative electrode tab 311 side, along a direction away from the height direction H, the lower end of the negative electrode coating region 211 of the negative electrode sheet 11 extends beyond the lower end of the positive electrode coating region 213 of the positive electrode sheet 13 by a distance Ln mm.

[0049] On one side of the negative electrode tab 311, the negative electrode coating area 211 has a negative electrode thinning area 3111 at one end in the direction away from the height direction H. If the negative electrode thinning area 3111 overlaps too much with the positive electrode coating area 213 in the radial direction, it is easy to cause the positive and negative electrode ratio of the battery cell (Cell Balance, referred to as CB value) to be less than 1.0, resulting in lithium deposition when fully charged. On the side of the positive electrode tab 313, the positive electrode coating area 213 of the positive electrode sheet 13 has a positive electrode thinning area 3131 at one end in the height direction H. The positive electrode thinning area 3131 overlaps with the negative electrode coating area 211 in the radial direction. The positive and negative electrode ratio of the battery cell is greater than the design value, and there will be no lithium deposition during the charging process, thereby improving safety. It can be understood that in order to prevent lithium deposition, it is feasible to design the upper and lower ends of the negative electrode coating area 211 to extend beyond the positive electrode coating area 213 respectively.

[0050] In the above technical solution, the upper end of the negative electrode coating area 211 exceeds the upper end of the positive electrode coating area 213 by Lp mm, and the value range of Lp is 0.3-1.7, and the lower end of the negative electrode coating area 211 exceeds the lower end of the positive electrode coating area 213 by Ln mm, and the value range of Ln is 0.8-2.2, which at least makes the height uniformity of the entire electrode assembly 120 better. High height uniformity means high capacity uniformity of the battery, so the technical solution of the present application also improves the capacity uniformity of the cylindrical battery. On the other hand, for the current secondary battery assembly, when it is necessary to select a shell of the same specification to accommodate multiple electrode assemblies, the current electrode assembly is wound, and the height of each winding in the electrode assembly is uneven, the height uniformity of the electrode assembly is poor, and the height of the multiple electrode assemblies produced is not uniform, that is, the height uniformity is poor. If the height uniformity of multiple electrode assemblies is poor, the higher electrode assemblies may not be installed inside the shell, affecting the battery assembly. The present application avoids the situation where the higher electrode assemblies cannot be installed inside the shell during assembly by improving the height uniformity of the electrode assemblies, thereby preventing the height uniformity of the electrode assemblies from affecting the assembly of cylindrical batteries.

[0051] In other cases, a shell of the same specification can be adapted to the highest electrode assembly, and the battery formed by assembling the lowest electrode assembly into the shell of the same specification, compared to the battery formed by assembling the highest cell into the shell of the same specification, the space utilization rate in the height direction after the lowest electrode assembly is adapted to the shell is compared to the space utilization rate in the height direction after the highest electrode assembly is adapted to the above shell. Obviously, the former has a lower energy density than the latter. According to the electrode assembly 120 of the embodiment of the present application, if the height uniformity of the single electrode assembly of the batch electrode assembly 120 is relatively good, then the height of the multiple electrode assemblies 120 produced in batches is more consistent than the height of the current batch production of multiple electrode assemblies. Thus, after the multiple electrode assemblies 120 are assembled into the shell 200 adapted to the highest electrode assembly 120, the lower electrode assemblies 120 can also obtain a higher energy density. Preferably, when the secondary battery 100 is a cylindrical battery, since cylindrical batteries pursue higher energy density, the electrode assembly 120 of the embodiment of the present application, when adapted to a cylindrical battery, has good height uniformity and high space utilization in the height direction. When adapted to a cylindrical battery, the electrode assembly 120 of the embodiment of the present application can achieve better results.

[0052] Furthermore, it is obvious that when assembling electrode assemblies and positive and negative current collector plates in batches, it is necessary to weld multiple positive and negative current collector plates to multiple electrode assemblies in a one-to-one correspondence. If the height uniformity of the batch electrode assemblies is poor, the welding positions of one set of positive and negative current collector plates and the electrode assemblies will be less consistent than the welding positions of another electrode assembly and another set of positive and negative current collector plates during batch assembly. However, if the height consistency of the electrode assemblies 120, similar to the embodiments of the present application, is relatively good, the welding positions of the positive and negative current collector plates and the electrode assemblies 120 will be more consistent, that is, the selection of welding positions will be better.

[0053] In some embodiments, the above Ln and Lp satisfy: 1.3≤Ln / Lp≤1.7. In other words, the distance Ln mm that the negative electrode coating area 211 exceeds on the negative electrode tab 311 side is 1.3-1.7 times the distance Lp mm that the positive electrode tab 313 exceeds on the side. In this embodiment, while controlling the positive and negative electrode tab sides to have Ln and Lp respectively to improve safety, it is also possible to meet energy density requirements and improve the energy density of the battery cell. In addition, for cylindrical batteries, the negative electrode thinning area 3111 of the negative electrode coating area 211 is set on the side of the negative electrode tab 311, so the distance Ln mm that the negative electrode coating area 211 exceeds on the side of the negative electrode tab 311 is controlled to be larger, which can avoid lithium electrolysis.

[0054] In some embodiments, a tab glue 316 may be provided at the location of the positive electrode tab 313 adjacent to the positive electrode coating region 213 (specifically, at the edge of the positive electrode thinning region 3131). The tab glue 316 is an insulating material to provide insulation and avoid positive electrode side risks. The main components of the tab glue 316 may be boehmite and PVDF (polyvinylidene fluoride). Therefore, by achieving the above ratio of 1.3 ≤ Ln / Lp ≤ 1.7, the energy density can be increased while ensuring safety under the conditions of the extreme energy density of the cylindrical battery.

[0055] refer to Figure 5 In some embodiments, along the height direction H, the width of the negative electrode coating area 211 is b mm, and the value of b can range from 110.5 to 111.5. The width of the positive electrode coating area 213 is c mm, and the value of c can range from 108 to 109. In some embodiments, the width of the negative electrode current collector 118 of the negative electrode plate 11 is a mm, and the value of a can range from 116.8 to 118.2. The width of the positive electrode current collector 136 is e mm, and the value of e can range from 116.3 to 117.7. The width of the first separator 12 is d mm, and the value of d can range from 112 to 114. Preferably, the widths of the first separator 12 and the second separator 14 can be the same. Figure 5 In the figure, the total width of the stacked negative electrode sheet 11, the first separator 12, the positive electrode sheet 13, and the second separator 14 is f mm, and the value range of f can be 124-126, for example, f can be 125.

[0056] Figure 6 A schematic cross-sectional view perpendicular to the height direction H of the electrode assembly 120 according to an embodiment of the present application is shown. In the winding direction R of the electrode assembly 120, the tail end 11e of the negative electrode sheet 11 exceeds the tail end 13e of the positive electrode sheet 13. In the direction opposite to the winding direction R, the starting end 11s of the negative electrode sheet 11 exceeds the starting end 13s of the positive electrode sheet 13. In this way, the lithium ions separated from the positive electrode coating area 213 of the positive electrode sheet 13 can be smoothly embedded in the negative electrode coating area 211 of the negative electrode sheet 11, thereby avoiding the occurrence of lithium plating. In addition, in the winding direction R and the opposite direction thereof, the first diaphragm 12 and the second diaphragm 14 both exceed the positive electrode sheet 13 and the negative electrode sheet 11 to play an electrical insulating role. Therefore, it should be understood that the positive electrode sheet 13 and the negative electrode sheet 11 as well as the first separator 12 and the second separator 14 are all overlapped starting from the starting end 13s of the positive electrode sheet 13. In this specification, the starting end 13s of the positive electrode sheet 13 is used as the starting position for calculating the number of turns.

[0057] In some embodiments, in the winding direction R, within the first 20 turns of winding starting from the starting end 13s of the positive electrode sheet 13, the above-mentioned Ln mm has a range A1 mm. That is, among the multiple Ln mm measured in the first 20 turns, the difference between the maximum and minimum values ​​is A1 mm. Within the remaining turns from the starting position of the 21st turn of the positive electrode sheet 13 to the tail end 13e of the positive electrode sheet 13, the above-mentioned Ln mm has a range A2 mm. Generally, the number of remaining turns ranges from 25 to 35. In some embodiments, A1 is greater than A2. That is, the range A1 of Ln in the first 20 turns is greater than the range A2 of Ln in the remaining turns.

[0058] See Figure 7 understand. Figure 7 The figure shows the relationship between the distance Ln between the negative electrode coating area 211 and the positive electrode coating area 213 and the number of windings of the electrode assembly 120 on the negative electrode tab 311 side according to the embodiment of the present application. Figure 7 In the figure, the horizontal axis represents the number of turns, and the vertical axis represents the measured value (in mm) of the negative electrode coating area 211 extending beyond the positive electrode coating area 213 at the selected test point of each turn. In the actual production of the electrode assembly, the distance of the negative electrode coating area extending beyond the positive electrode coating area is set as a theoretical value. However, during the winding process of the electrode assembly, the actual distance of the negative electrode coating area extending beyond the positive electrode coating area may deviate from the theoretical value. Figure 7 As can be seen in the figure, Ln fluctuates more significantly within the first 20 turns, resulting in a greater range A1. Range A1 is greater than the range A2 of Ln in the remaining turns (all turns after the 20th turn). In other words, the range of Ln in the outer turns of electrode assembly 120 is smaller than that of the inner turns. Winding correction can be used to control the range A2 of Ln in the outer turns to be smaller than the range A1 of Ln in the inner turns, resulting in a smaller range of Ln in the outer turns, ensuring good height uniformity in the electrode assembly and a safer battery.

[0059] In some embodiments, the range A1 of Ln within the first 20 turns can be 0.2-0.5. In some embodiments, the range A2 of Ln within the remaining turns can be 0-0.2. This range can effectively improve the height consistency of the electrode assembly 120 and is achievable and controllable under existing process conditions.

[0060] Similar to Ln, within the first 20 turns, the range of Lp mm is A3 mm; within the remaining turns, the range of Lp mm is A4 mm, where A3 can be greater than A4. That is, the range of Lp in the outer turns of electrode assembly 120 is smaller than the range of Lp in the inner turns. Winding correction can be used to control the range of Lp in the outer turns (A4) to be smaller than the range of Lp in the inner turns (A3). This results in a smaller range of Lp in the outer turns, ensuring good height uniformity in the electrode assembly and a safer battery.

[0061] The width of the negative electrode coating area 211 exceeding the positive electrode coating area 213 along the height direction H is Lp mm. Furthermore, in some embodiments, within the first 20 circles, the standard deviation of Lp mm is S1 mm, and the value range of S1 can be 0.09-0.15; in the remaining circles, the standard deviation of Lp mm is S2 mm, and the value range of S2 can be 0.02-0.04.

[0062] The standard deviations S1 and S2 of Lp mentioned above can be tested in the following way: select several test points in the electrode assembly, measure Lp at these test points, and then calculate according to the standard deviation formula. The standard deviation formula is as follows:

[0063]

[0064] Where S represents the standard deviation, It represents the arithmetic mean of the Lp measurement values ​​at each test point, x i represents the Lp value at the i-th test point, and n represents the number of test points. For example, select multiple test points within the remaining laps, measure the Lp values ​​at these test points, and calculate the standard deviation of Lp using the above formula to obtain S2. By controlling the standard deviations S1 and S2 of Lp for the first 20 laps and the remaining laps within the above range, the electrode assembly can achieve better height uniformity.

[0065] See also Figure 4, on the side of the negative electrode tab 311, along the direction away from the height direction H, the lower end of the first diaphragm 12 or the second diaphragm 14 may extend beyond the lower end of the negative electrode coating area 211, and the distance outward is G1 mm. In some embodiments, the value range of G1 may be 0.9-1.4. In some embodiments, the standard deviation of G1 mm in the first 20 circles is S3 mm, and the value range of S3 may be 0.09-0.15. In the remaining circles, the standard deviation of G1 is S4 mm, and the value range of S4 may be 0.08-0.14. The standard deviations S3 and S4 of G1 are calculated using the above standard deviation formula. By controlling the standard deviations S1 and S2 of G1 of the first diaphragm 12 and / or the second diaphragm 14 to have the above value range, the electrode assembly can have better height uniformity. Furthermore, compared with square shell and soft-pack batteries, cylindrical batteries pursue higher energy density, and the process window requirements for the height uniformity of bare cells are higher. In addition, the height space inside the shell for accommodating bare cells is also very limited (so that each bare cell can be placed inside the shell). Therefore, the technical solution of this application also improves the capacity uniformity of cylindrical batteries.

[0066] The embodiments of the present application further provide a battery pack, including any of the above-mentioned secondary batteries 100, and the battery pack can have the beneficial effects described above with respect to the secondary batteries 100. The embodiments of the present application further provide an electronic device 1000, including any of the above-mentioned secondary batteries 100, and the electronic device can have the beneficial effects described above with respect to the secondary batteries 100.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A secondary battery, characterized in that: The electrode assembly comprises: a negative electrode sheet, a first separator, a positive electrode sheet, and a second separator, which are stacked and wound in sequence to form the electrode assembly; The negative electrode plate includes a negative electrode coating area and a negative electrode tab protruding from the negative electrode coating area. The positive electrode plate includes a positive electrode coating area and a positive electrode tab protruding from the positive electrode coating area. The negative electrode tab and the positive electrode tab are respectively located on opposite sides of the electrode assembly. The direction from the negative electrode tab to the positive electrode tab is the height direction of the electrode assembly. Along the height direction, the distance that the upper end of the negative electrode coating area exceeds the upper end of the positive electrode coating area is Lp mm, and the value range of Lp is 0.3-1.

7. Along the direction away from the height direction, the distance that the lower end of the negative electrode coating area exceeds the lower end of the positive electrode coating area is Ln mm, and the value range of Ln is 0.8-2.

2.

2. The secondary battery according to claim 1, wherein Meet: 1.3≤Ln / Lp≤1.7; In the first 20 turns of winding in the winding direction from the starting end of the positive electrode sheet, the range of Ln mm is A1 mm, In the remaining turns from the starting position of the 21st turn of the positive electrode sheet to the end of the positive electrode sheet, the range of Lnmm is A2 mm, and A1 is greater than A2.

3. The secondary battery according to claim 2, wherein The value range of A1 is 0.2-0.5, and the value range of A2 is 0-0.

2.

4. The secondary battery according to claim 1, wherein The range of Lp mm is A3 mm within the first 20 turns of winding in the winding direction from the starting end of the positive electrode sheet. In the remaining turns from the starting position of the 21st turn of the positive electrode sheet to the end of the positive electrode sheet, the range of Lpmm is A4 mm, and A3 is greater than A4.

5. The secondary battery according to claim 4, wherein The standard deviation of Lp mm in the first 20 cycles is S1 mm, and the value range of S1 is 0.09-0.

15. The standard deviation of Lp mm in the remaining circles is S2 mm, and the value range of S2 is 0.02-0.

04.

6. The secondary battery according to claim 1, wherein In a direction away from the height direction, the lower end of any one of the first separator and the second separator exceeds the lower end of the negative electrode coating region by a distance of G1 mm, In the first 20 turns of winding in the winding direction from the starting end of the positive electrode sheet, the standard deviation of G1mm is S3mm, and the value range of S3 is 0.09-0.

15. In the remaining turns from the starting position of the 21st turn of the positive electrode sheet to the end of the negative electrode sheet, the standard deviation of G1mm is S4, and the value range of S4 is 0.08-0.

14.

7. The secondary battery according to claim 1, wherein The secondary battery is a cylindrical battery.

8. The secondary battery according to claim 1, wherein Also includes: a housing, wherein the housing is provided with a rolling groove protruding toward the interior of the housing; The electrode assembly is accommodated in the housing, and the rolling groove limits the movement of the electrode assembly in the height direction.

9. A battery pack, characterized in that: A secondary battery according to any one of claims 1 to 8.

10. An electronic device, characterized in that: A secondary battery according to any one of claims 1 to 8.

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