Secondary batteries, battery packs, and electronic devices

Abstract

The present invention provides a secondary battery, battery pack, and electronic device that improve the uniformity of electrode assembly height. [Solution] The electrode assembly comprises an electrode assembly formed by sequentially stacking and winding a negative electrode sheet, a first separator 12, a positive electrode sheet, and a second separator. The negative electrode sheet includes a negative electrode coating area 211 and a negative electrode tab protruding from the negative electrode coating area. The positive electrode sheet includes a positive electrode coating area 213 and a positive electrode tab protruding from the positive electrode coating area. The negative electrode tab and the positive electrode tab are located on opposite sides of the electrode assembly, respectively. The direction from the negative electrode tab to the positive electrode tab is defined as the height direction H of the electrode assembly. Along the height direction, the distance Lp mm is defined as the distance from the upper end of the negative electrode coating area beyond the upper end of the positive electrode coating area, with a range of Lp values ​​of 0.3-1.7. Along the direction away from the height direction, the distance Ln mm is defined as the distance from the lower end of the negative electrode coating area beyond the lower end of the positive electrode coating area, with a range of Ln values ​​of 0.8-2.2.

Description

Technical Field

[0001] The present invention relates to secondary batteries, battery packs, and electronic devices.

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 vehicles, energy storage, mobile phones, tablet computers, wearable devices, mobile power supplies, electronic cigarettes, digital products, power tools, power devices, energy storage devices, etc. The secondary batteries include cylindrical batteries, which include a casing and an electrode assembly. The electrode assembly includes a positive electrode sheet, a first separator, a negative electrode sheet, and a second separator. After being sequentially laminated with each other, they are wound to form an electrode assembly, and then packaged in a casing. However, existing secondary batteries still need further improvement in some aspects.

Summary of the Invention

Problems to be Solved by the Invention

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

Means for Solving the Problems

[0004] According to one aspect of the present invention, a secondary battery is provided comprising an electrode assembly, the electrode assembly being formed by sequentially stacking and winding a negative electrode sheet, a first separator, a positive electrode sheet, and a second separator, the negative electrode sheet including a negative electrode coating region and a negative electrode tab protruding from the negative electrode coating region, the positive electrode sheet including a positive electrode coating region and a positive electrode tab protruding from the positive electrode coating region, the negative electrode tab and the positive electrode tab being located on opposite sides of the electrode assembly, the direction from the negative electrode tab toward the positive electrode tab being the height direction of the electrode assembly, the distance Lp mm along the height direction from the upper end of the negative electrode coating region to the upper end of the positive electrode coating region being, with the range of Lp being 0.3-1.7, and the distance Ln mm along the direction away from the height direction from the lower end of the negative electrode coating region to the lower end of the positive electrode coating region being, with the range of Ln being 0.8-2.2.

[0005] In the above-described technical solution, the upper edge of the negative electrode coating area exceeds the upper edge of the positive electrode coating area by Lp mm, with Lp being in the range of 0.3-1.7, and the lower edge of the negative electrode coating area exceeds the lower edge of the positive electrode coating area by Ln mm, with Ln being in the range of 0.8-2.2. This improves the height uniformity of at least the entire electrode assembly.

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

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

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

[0009] In some embodiments, the standard deviation of Lp mm in the first 20 volumes is defined as S1 mm, with a range of 0.09-0.15 for S1, and the standard deviation of Lp mm in the remaining volumes is defined as S2 mm, with a range of 0.02-0.04 for S2.

[0010] In some embodiments, G1 mm is defined as the distance along the direction away from the height direction from the lower end of either the first separator or the second separator beyond the lower end of the negative electrode coating area. For 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 defined as S3 mm, with a range of 0.09-0.15. For the remaining turns from the starting position of the 21st turn of the positive electrode sheet to the ending end of the positive electrode sheet, the standard deviation of G1 mm is defined as S4 mm, with a range of 0.08-0.14.

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

[0012] In some embodiments, the secondary battery further comprises a casing having an opening at one end and a roll groove protruding inward, and a cover member that fits over the opening of the casing, the electrode assembly being housed in the casing, and the roll groove restricting the movement of the electrode assembly in the height direction.

[0013] According to another aspect of the present invention, a battery pack including the secondary battery of any one of the preceding claims of the present invention is also provided.

[0014] In yet another aspect of the present invention, an electronic device comprising a secondary battery according to any one of the above-mentioned claims of the present invention is also provided. [Effects of the Invention]

[0015] The beneficial technical effects of the present invention are as follows: In the above-described 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 range of Lp is 0.3-1.7; the lower end of the negative electrode coating area exceeds the lower end of the positive electrode coating area by Ln mm, and the range of Ln is 0.8-2.2; thereby improving the height uniformity of at least the entire electrode assembly. High height uniformity indicates high capacity uniformity of the battery.

[0016] Furthermore, compared to prismatic and pouch batteries, cylindrical batteries pursue higher energy density, resulting in a higher process window requirement for bare battery cell height uniformity, and the height space for housing the bare battery cells within the casing (to allow each bare battery cell to be placed inside the casing) is also very limited. Therefore, the technical solution of the present invention also improves the capacity uniformity of cylindrical batteries. Moreover, if height uniformity is poor, taller electrode assemblies may not be able to be fitted inside the casing, affecting battery assembly. However, the present invention improves the height uniformity of the electrode assemblies, thereby avoiding situations where taller electrode assemblies cannot be fitted inside the casing during assembly, and thus avoiding the impact of electrode assembly height uniformity on cylindrical battery assembly.

[0017] To more clearly illustrate the embodiments of the present invention or the prior art, the accompanying drawings that may be used in the description of the embodiments or prior art are briefly introduced below. It is clear that the accompanying drawings in the following description represent only a few embodiments of the present invention, and those skilled in the art can obtain other embodiments based on these accompanying drawings without any creative effort. [Brief explanation of the drawing]

[0018] [Figure 1] This is a schematic diagram showing an example of the present invention where the electronic device is in a vehicle. [Figure 2] This is a three-dimensional diagram of a secondary battery according to an embodiment of the present invention. [Figure 3]It is a cross-sectional view of a secondary battery according to an embodiment of the present invention. [Figure 4] It is a schematic view of an electrode assembly of a secondary battery according to an embodiment of the present invention. [Figure 5] It is a schematic developed view before winding of an electrode assembly according to an embodiment of the present invention. [Figure 6] It is a schematic cross-sectional view perpendicular to the height direction of an electrode assembly according to an embodiment of the present invention. [Figure 7] It shows the relationship between the distance by which the negative electrode coating region exceeds the positive electrode coating region on the negative electrode tab side after winding of the electrode assembly of an embodiment of the present invention and the number of winding turns.

Mode for Carrying Out the Invention

[0019] In order to better understand the spirit of the embodiments of the present invention, it will be further described below in combination with some preferred embodiments of the present invention.

[0020] The embodiments of the present invention will be described in detail below. Throughout the present specification, components having the same or similar configurations and components having the same or similar functions are represented by similar reference numerals. The embodiments regarding the drawings described here are of an illustrative nature and are used to provide a basic understanding of the present invention. The embodiments of the present invention should not be construed as a limitation of the present invention.

[0021] As used herein, the terms "substantially", "generally", "substantially" and "about" are used to describe and explain small variations. When used in connection with an event or situation, the terms can refer to examples in which the event or situation occurs exactly and examples in which the event or situation occurs very approximately therein.

[0022] In this specification, unless specifically specified or limited, relative terms such as "central", "vertical", "lateral", "front", "rear", "right", "left", "inner", "outer", "lower", "higher", "horizontal", "vertical", "higher", "lower", "upper", "lower", "top", "bottom" and their derivative terms (such as "horizontally", "downward", "upward", etc.) should be interpreted as referring to the directions described during the discussion or depicted in the drawings. These relative terms are used only for descriptive convenience and do not require the present invention to be constructed or operated in a specific direction.

[0023] For descriptive convenience, "first", "second", "third", etc. may be used in the text to distinguish different components of one figure or a series of figures. "First", "second", "third", etc. are not intended to describe corresponding components.

[0024] For the convenience of explanation, the following embodiments will be described by taking the electronic device as the vehicle 1000 as an example. The vehicle 1000 may be a gasoline vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle or a range extender vehicle, etc., but is not limited thereto. Referring to FIG. 1, a battery pack 1002 is installed inside the vehicle 1000, and the battery pack 1002 can be installed at the bottom (as shown in FIG. 1) or the head, or the tail, or any other appropriate position of the vehicle body 1001. The battery pack 1002 can be used to supply power to the vehicle 1000. For example, the battery pack 1002 can be used as the operating power source or the driving power source of the vehicle 1000. The battery pack 1002 can include a plurality of secondary batteries (for example, the secondary battery 100 in FIG. 2) and a casing for accommodating the plurality of secondary batteries.

[0025] However, in some other embodiments, the electronic device may be a mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, or power tool. Spacecraft include airplanes, rockets, spacecraft, and spaceships. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric boat toys, and electric airplane toys. Power tools include metal cutting power tools, polishing power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers. Embodiments of the present invention do not impose any special limitations on the electronic device. The electronic device may include a working unit, which may be a unit component that receives power from the battery pack 1002 and performs the corresponding task, such as a fan blade rotation unit or a vacuum cleaner suction unit.

[0026] Figure 2 is a three-dimensional view of a secondary battery 100 according to an embodiment of the present invention, and Figure 3 is a cross-sectional view of a secondary battery 100 according to an embodiment of the present invention. In this embodiment, the secondary battery 100 can be a cylindrical battery.

[0027] In an example of the secondary battery of the present invention, as shown in Figures 2 and 3, the secondary battery 100 includes a casing 200, an opening 205 provided at one end of the casing 200, and a cover member 220 is placed over the opening 205 of the casing 200, closing the housing chamber of the casing 200 and used to package the electrode assembly 120 and electrolyte. The material of the casing 200 can be any of the many usable materials, such as copper, iron, aluminum, steel, aluminum alloy, etc. The casing 200 can be cylindrical, defining a housing chamber, and the electrode assembly 120 is installed inside the housing chamber. The diameter of the casing 200 can be determined based on the specific diameter dimensions of the electrode assembly 120, such as 18 mm, 21 mm, 46 mm, etc. In some embodiments, the secondary battery 100 may be a 4680 cylindrical battery (diameter 46 mm, height 80 mm), or a 4695 cylindrical battery (diameter 46 mm, height 95 mm), or a 46120 cylindrical battery (diameter 46 mm, height 120 mm).

[0028] The electrode assembly 120 is mainly formed by sequentially 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, and the positive electrode tab 313 faces the end wall 111 of the casing 200 opposite the opening 205. The direction from the negative electrode tab 311 to the positive electrode tab 313 is the height direction H of the electrode assembly 120.

[0029] A roll groove 113 projecting inward can be provided on the side wall adjacent to the opening 205 of the casing 200. The electrode assembly 120 is installed between the end wall 111 and the roll groove 113, and the roll groove 113 can restrict the movement of the electrode assembly 120 in the height direction H and the opposite direction between the end wall 111 and the roll groove 113. The end of the casing 200 on the opening 205 side can be configured as a curled edge portion 32, which extends inward along the radial direction of the casing 200. The curled edge portion 32 and the roll groove 113 are spaced apart along the height direction H, and the roll groove 113 and the curled edge portion 32 can jointly clamp the cover member 220.

[0030] The secondary battery 100 further includes an electrode column 160 that penetrates the end wall 111. The electrode column 160 can be electrically connected to the positive electrode tab 313 of the electrode assembly 120 via a positive electrode collector, thereby positively charging the electrode column 160. The negative electrode tab 311 can be electrically connected to the casing 200 via a negative electrode collector, thereby negatively charging the casing 200.

[0031] Figure 4 is a schematic diagram of an electrode assembly 120 of a secondary battery 100 according to an embodiment of the present invention. Referring to Figure 4, the electrode assembly 120 is formed by sequentially stacking and winding a negative electrode sheet 11, a first separator 12, a positive electrode sheet 13, and a second separator 14. The wound electrode assembly 120 has a winding center hole 120c.

[0032] The positive electrode sheet 13 may include a positive electrode current collector 136 and a positive electrode coated area 213, the positive electrode coated area 213 being coated on a portion of the surface of the positive electrode current collector 136. The positive electrode coated area 213 is a positive electrode active material layer formed by coating a positive electrode active material. The portion of the positive electrode current collector 136 not covered by the positive electrode coated area 213 constitutes the positive electrode tab 313. The negative electrode sheet 11 may include a negative electrode current collector 118 and a negative electrode coated area 211, the negative electrode coated area 211 being coated on a portion of the surface of the negative electrode current collector 118. The negative electrode coated area 211 is a negative electrode active material layer formed by coating a negative electrode active material. The portion of the negative electrode current collector 118 not covered by the negative electrode coated area 211 constitutes the negative electrode tab 311.

[0033] Taking a lithium-ion battery as an example, the material of the positive electrode current collector 136 can be aluminum, and the positive electrode coating area 213 can contain a positive electrode active substance, which can be lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide, etc. The material of the negative electrode current collector 118 can be copper. The negative electrode coating area 211 can contain a negative electrode active substance, which can be carbon or silicon, etc. The materials of the first separator 12 and the second separator 14 can be PP (polypropylene) or PE (polyethylene), etc.

[0034] In one example of the secondary battery 100 of the present invention, the method for manufacturing the secondary battery 100 according to the present invention includes the following steps.

[0035] Winding: The negative electrode sheet 11, the first separator 12, the positive electrode sheet 13, and the second separator 14 are stacked and wound together to form a wound structure, and the uncoated portions of the positive electrode current collector 136 of the positive electrode sheet 13 and the negative electrode tab 311 of the negative electrode sheet 11 are formed. The positive electrode tab 313 and the negative electrode tab 311 are bent along the radial direction of the electrode assembly 120.

[0036] Welding of the current collector and electrode assembly 120: Specifically, the positive electrode current collector and the negative electrode current collector are welded to the surface areas of the bent positive electrode tab 313 and negative electrode tab 311, respectively.

[0037] Installation into the casing: The electrode assembly 120, with the positive and negative electrode collectors welded to it, is installed into the casing 200 through the opening 205. The method of installation of the electrode assembly 120 in this step is not limited and may be done manually or by a mechanical arm.

[0038] Install the 160mm polar column.

[0039] Electrolyte injection: The method of electrolyte injection is not limited; injection may be performed through the opening 205, or injection may be performed by installing an injection hole in the end wall 111. Preferably, in this embodiment, the electrolyte is injected through the opening 205, eliminating the step of creating an injection hole in the end wall 111, and allowing injection to be performed by directly utilizing the existing opening 205, thereby simplifying the process and reducing costs.

[0040] Sealing: The cover member 220 is sealed and attached to the opening 205. There are various packaging methods, but this is not limited to them. In some embodiments, first, the outer circumference of the casing 200 is roll-pressed to form a roll groove 113 that is recessed toward the center of the casing 200, thereby restricting the movement of the electrode assembly 120 in the height direction H. Furthermore, a mechanical sealing process is employed to crimp and seal the cover member 220 to form a curled edge portion 32, thereby sealing and attaching the cover member 220 to the opening 205 of the casing 200. This step is a mature process, low-cost and highly efficient.

[0041] Figure 5 is a schematic diagram of the electrode assembly 120 before winding according to an embodiment of the present invention. According to the embodiment of the present invention, both the upper and lower ends of the negative electrode coating area 211 exceed the upper and lower ends of the positive electrode coating area 213 (overhang, OH) along the height direction H and the direction away from the height direction H. Specifically, referring to Figures 4 and 5, on the positive electrode tab 313 side, the distance along the height direction H from the upper end of the negative electrode coating area 211 to the upper end of the positive electrode coating area 213 is Lp mm. In some embodiments, the range of the value of Lp can be 0.3-1.7. On the negative electrode tab 311 side, the distance along the direction away from the height direction H from the lower end of the negative electrode coating area 211 of the negative electrode sheet 11 to the lower end of the positive electrode coating area 213 of the positive electrode sheet 13 is Ln mm.

[0042] On the negative electrode tab 311 side, the negative electrode coating area 211 has a negative electrode thinning area 3111 at one end away from the height direction H. However, if the negative electrode thinning area 3111 and the positive electrode coating area 213 overlap excessively in the radial direction, it is easy to cause the positive and negative electrode balance (Cell Balance, abbreviated as CB value) of the battery cell to be less than 1.0, leading to the lithium deposition phenomenon during full charge. On the positive electrode tab 313 side, 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 and the negative electrode coating area 211 overlap radially, and by making the positive and negative electrode balance of the battery cell greater than the design value, the lithium deposition phenomenon does not occur during the charging process, improving safety. It can be understood that designing the negative electrode coating area 211 so that both the upper and lower ends exceed the positive electrode coating area 213 is effective in preventing lithium deposition.

[0043] In the above-described 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 range of Lp is 0.3-1.7. 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 range of Ln is 0.8-2.2. As a result, at least the height uniformity of the entire electrode assembly 120 is good. Since high height uniformity indicates high capacity uniformity of the battery, the technical solution of the present invention also improves the capacity uniformity of cylindrical batteries. On the other hand, in the assembly of current secondary batteries, when it is necessary to adapt multiple electrode assemblies to a casing of the same standard, the height of each winding within the electrode assembly is uneven during winding, resulting in poor height uniformity of the electrode assembly, and the height of the multiple electrode assemblies produced is not uniform, i.e., poor height uniformity. If the height uniformity of multiple electrode assemblies is poor, it may not be possible to insert a taller electrode assembly into the casing, which affects the assembly of the battery. This invention improves the uniformity of electrode assembly height, thereby avoiding situations where taller electrode assemblies cannot be inserted into the casing during assembly, and preventing the uniformity of electrode assembly height from affecting the assembly of cylindrical batteries.

[0044] In several other situations, a casing of the same standard is adaptable to the tallest electrode assembly, and a battery formed by assembling the shortest electrode assembly in a casing of the same standard has a lower energy density in the height direction after the shortest electrode assembly is adapted to the casing, compared to a battery formed by assembling the tallest battery cell in a casing of the same standard. In the case of the electrode assembly 120 of the embodiment of the present invention, if the height uniformity of a single electrode assembly in one batch of electrode assemblies 120 is relatively good, the heights of multiple electrode assemblies 120 produced in batch are more consistent compared to the heights of multiple electrode assemblies produced in current batches. As a result, after packaging multiple electrode assemblies 120 in a casing 200 adapted to the tallest electrode assembly 120, the shorter 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 effect obtained when the electrode assembly 120 of the embodiment of the present invention is adapted to a cylindrical battery is better because it has good height uniformity and high space utilization rate in the height direction.

[0045] Furthermore, it is clearly understandable that when assembling electrode assemblies and positive and negative electrode collectors in batches, it is necessary to weld multiple positive and negative electrode collectors to multiple electrode assemblies in a one-to-one correspondence. If the heights of the electrode assemblies in one batch are not uniform, the welding positions of one pair of positive and negative electrode collectors and electrode assemblies will have less agreement with each other compared to the welding positions of another electrode assembly and another pair of positive and negative electrode collectors during batch assembly. However, if the heights are relatively consistent with each other, as in the electrode assembly 120 of the embodiment of the present invention, the agreement of the welding positions of the positive and negative electrode collectors and electrode assembly 120 will be better, meaning that the selection of welding positions will be better.

[0046] In some embodiments, the above-mentioned Ln and Lp satisfy: 1.3 ≤ Ln / Lp ≤ 1.7. In other words, the distance Ln mm that the negative electrode coating area 211 extends toward the negative electrode tab 311 is 1.3 to 1.7 times the distance Lp mm that it extends toward the positive electrode tab 313. In this embodiment, by controlling the positive electrode and negative electrode tab sides to Ln and Lp respectively, safety can be improved while simultaneously meeting the energy density requirements and improving the energy density of the battery cell. Furthermore, for cylindrical batteries, since the negative electrode thinning area 3111 of the negative electrode coating area 211 is located toward the negative electrode tab 311, lithium deposition can be avoided by controlling the distance Ln mm that the negative electrode coating area 211 extends toward the negative electrode tab 311 to be relatively large.

[0047] In some embodiments, the tab tape 316 can be installed adjacent to the positive electrode coating area 213 of the positive electrode tab 313 (specifically, at the edge of the positive electrode thinning area 3131). The tab tape 316 is an insulating material and provides insulation, thus avoiding risks on the positive electrode side. The main composition of the tab tape 316 can be boehmite and PVDF (polyvinylidene fluoride). Therefore, with the above ratio of 1.3 ≤ Ln / Lp ≤ 1.7, it is possible to improve energy density and ensure safety under the conditions of the extreme energy density of the cylindrical battery.

[0048] Referring to Figure 5, in some embodiments, along the height direction H, the width of the negative electrode coating area 211 is b mm, with a range of b values ​​from 110.5 to 111.5. The width of the positive electrode coating area 213 is c mm, with a range of c values ​​from 108 to 109. In some embodiments, the width of the negative electrode current collector 118 of the negative electrode sheet 11 is a mm, with a range of a values ​​from 116.8 to 118.2. The width of the positive electrode current collector 136 is e mm, with a range of e values ​​from 116.3 to 117.7. The width of the first separator 12 is d mm, with a range of d values ​​from 112 to 114. Preferably, the widths of the first separator 12 and the second separator 14 are the same. In Figure 5, the total width of the laminate of the stacked negative electrode sheet 11, first separator 12, positive electrode sheet 13, and second separator 14 is f mm, and the range of the value of f is 124-126, for example, f is 125.

[0049] Figure 6 is a schematic cross-sectional view perpendicular to the height direction H of an electrode assembly 120 according to an embodiment of the present invention. In the winding direction R of the electrode assembly 120, the end end 11e of the negative electrode sheet 11 extends beyond the end end 13e of the positive electrode sheet 13. In the direction opposite to the winding direction R, the start end 11s of the negative electrode sheet 11 extends beyond the start end 13s of the positive electrode sheet 13. In this way, lithium ions detached from the positive electrode coating region 213 of the positive electrode sheet 13 can smoothly fit into the negative electrode coating region 211 of the negative electrode sheet 11, thereby preventing the occurrence of lithium deposition. Furthermore, in the winding direction R and the direction opposite to it, both the first separator 12 and the second separator 14 extend beyond the positive electrode sheet 13 and the negative electrode sheet 11, respectively, and perform an electrical insulating effect. Therefore, it should be understood that the positive electrode sheet 13, the negative electrode sheet 11, the first separator 12, and the second separator 14 all overlap from the beginning of the starting end 13s of the positive electrode sheet 13, and in this specification, the starting end 13s of the positive electrode sheet 13 is defined as the starting position for calculating the number of turns.

[0050] In some embodiments, in the winding direction R, the above-mentioned Ln mm has a range of A1 mm for the first 20 turns starting from the beginning end 13s of the positive electrode sheet 13. That is, the difference between the maximum and minimum values ​​of Ln mm measured in the first 20 turns is A1 mm. For the remaining turns from the starting position of the 21st turn of the positive electrode sheet 13 to the end end 13e of the positive electrode sheet 13, the above-mentioned range of Ln mm is A2 mm. Typically, the range of the number of turns in the remaining turns is 25-35. In some embodiments, A1 is greater than A2. That is, the range A1 of Ln for the first 20 turns is greater than the range A2 of Ln for the remaining turns.

[0051] Please refer to Figure 7 for understanding. Figure 7 shows the relationship between the distance Ln at which the negative electrode coating area 211 exceeds the positive electrode coating area 213 on the negative electrode tab 311 side of the electrode assembly 120 according to an embodiment of the present invention, and the number of turns of the electrode assembly 120. Specifically, in Figure 7, the horizontal coordinate represents the number of turns, and the vertical coordinate is Ln, which is the measured value (in mm) at which the negative electrode coating area 211 exceeds the positive electrode coating area 213 at a selected measurement point of each turn. In the actual production of the electrode assembly, the distance at which the negative electrode coating area exceeds the positive electrode coating area is set as a theoretical value, but in the winding process of the electrode assembly, there is a deviation between the actual distance at which the negative electrode coating area exceeds the positive electrode coating area and the theoretical value. As can be seen from Figure 7, in the first 20 turns, the variation of Ln is larger, range A1 is also larger, and range A1 is larger than range A2 of Ln in the remaining turns (all turns from the 20th turn onwards). In other words, the range of Ln for the outer winding of the electrode assembly 120 is smaller than the range of Ln for the inner winding. Through winding correction, the range A2 of the outer winding's Ln can be controlled to be smaller than the range A1 of the inner winding's Ln, allowing the outer winding's Ln to have a smaller range, resulting in better height uniformity in the electrode assembly and making the battery safer.

[0052] In some embodiments, the range of Ln in the first 20 turns can be 0.2-0.5. In some embodiments, the range of Ln in the remaining turns can be 0-0.2. Such ranges can effectively improve the height consistency of the electrode assembly 120 and are achievable and controllable under existing process conditions.

[0053] Similar to Ln, in the first 20 turns, the Lp mm range is A3 mm. In the remaining turns, the Lp mm range is A4 mm, where A3 can be greater than A4. That is, the Lp range of the outer windings of the electrode assembly 120 is smaller than the Lp range of the inner windings. Through winding correction, the Lp range A4 of the outer windings can be controlled to be smaller than the Lp range A3 of the inner windings, allowing the outer windings to have a smaller Lp range, thereby providing good height uniformity to the electrode assembly and making the battery safer.

[0054] The width of the negative electrode coating area 211 that exceeds the positive electrode coating area 213 along the height direction H is Lp mm. Furthermore, in some embodiments, for the first 20 turns, the standard deviation of Lp mm is S1 mm, and the range of S1 can be 0.09-0.15. For the remaining turns, the standard deviation of Lp mm is S2 mm, and the range of S2 can be 0.02-0.04.

[0055] The standard deviations S1 and S2 of Lp mentioned above can be measured in the following way: Select several measurement points in the electrode assembly, measure Lp at these points, and then calculate the standard deviation based on the standard deviation formula. The standard deviation formula is as follows: JPEG2026047234000002.jpg18160

[0056] JPEG2026047234000003.jpg46160

[0057] Referring to 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 separator 12 or the second separator 14 can extend beyond the lower end of the negative electrode coating area 211, and the protruding distance is G1 mm. In some embodiments, the range of the value of G1 can be 0.9-1.4. In some embodiments, the standard deviation of G1 mm within the first 20 turns is S3 mm, and the range of the value of S3 can be 0.09-0.15. Within the remaining turns, the standard deviation of G1 is S4 mm, and the range of the value of S4 can be 0.08-0.14. The standard deviations of G1 S3 and S4 are calculated using the standard deviation formulas described above. By controlling the standard deviations of G1 S3 and S4 of the first separator 12 and / or the second separator 14 to have the above-described ranges, the electrode assembly can be made to have better height uniformity. Furthermore, compared to prismatic and pouch batteries, cylindrical batteries pursue higher energy density, thus requiring a higher process window for height uniformity of bare battery cells, and the height space for housing the bare battery cells inside the casing (to allow each bare battery cell to be placed inside the casing) is also very limited. Therefore, the technical solution of the present invention also improves the capacity uniformity of cylindrical batteries.

[0058] Embodiments of the present invention further provide a battery pack comprising any one of the secondary batteries 100 described above, and the battery pack may have the beneficial effects described above for the secondary battery 100. Embodiments of the present invention further provide an electronic device comprising any one of the secondary batteries 100 described above, and the electronic device may have the beneficial effects described above for the secondary battery 100.

[0059] The foregoing describes only preferred embodiments of the present invention and is not intended to limit it. The present invention can have various modifications and changes for those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention. [Industrial applicability]

[0060] The secondary battery, battery pack, and electronic device of the present invention can be applied to the field of new energy power battery technology. [Explanation of symbols]

[0061] 1000: Vehicle 1001: Vehicle body 1002: Battery pack 11: Negative electrode sheet 11e, 13e: Termination 11s, 13s: Starting end 12: First Separator 13: Positive electrode sheet 13s:Starting end 14: Second separator 32: Curl edge section 100: Secondary battery 111: End wall 113: Roll groove 118:Negative electrode current collector 136: Positive electrode current collector 120: Electrode Assembly 120c: Winding center hole 160: Polar column 200: Casing 211: Negative electrode coating area 213: Positive electrode coating area 205:Aperture 220: Cover component 311: Negative electrode tab 3111: Negative electrode thinning area 313: Positive Tab 3131:Positive thinning region 316: Tab Tape ae:width f: Total width G1, Ln, Lp: Distance H: Height direction R: Winding direction

Claims

1. The electrode assembly is formed by sequentially stacking and winding a negative electrode sheet, a first separator, a positive electrode sheet, and a second separator. The negative electrode sheet includes a negative electrode coating area and a negative electrode tab protruding from the negative electrode coating area, the positive electrode sheet 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 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 aforementioned height direction, the distance Lp mm is defined as the distance at which the upper end of the negative electrode coating area exceeds the upper end of the positive electrode coating area, and the range of Lp is 0.3-1.

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

2. A secondary battery characterized by the following features.

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

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

2.

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

5. Let S1 mm be the standard deviation of Lp mm in the aforementioned 20 volumes, and the range of S1 is 0.09-0.

15. The secondary battery according to claim 4, wherein the standard deviation of Lp mm in the remaining winding is S2 mm, and the range of the value of S2 is 0.02-0.

04.

6. Along the direction away from the height direction, G1 mm is defined as the distance at which the lower end of either the first separator or the second separator exceeds the lower end of the negative electrode coating area. In 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 range of S3 is 0.09-0.

15. The secondary battery according to claim 1, wherein in the remaining turns from the starting position of the 21st turn of the positive electrode sheet to the ending end of the positive electrode sheet, the standard deviation of G1 mm is S4 mm, and the range of the value of S4 is 0.08-0.

14.

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

8. A casing having an opening at one end and a roll groove protruding inward, The casing further comprises a cover member that is placed over the opening, The secondary battery according to claim 1, wherein the electrode assembly is housed in the casing, and the roll groove restricts the movement of the electrode assembly in the height direction.

9. A battery pack characterized by including a secondary battery according to any one of claims 1 to 8.

10. An electronic device characterized by including a secondary battery according to any one of claims 1 to 8.

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