Cylindrical secondary battery and electric device

Abstract

The present application provides a cylindrical secondary battery and an electric device. The cylindrical secondary battery comprises a casing and a wound core; the wound core is accommodated in the casing; the wound core comprises a first electrode sheet and a separator; the first electrode sheet sequentially comprises a first main body portion and a first uncoated foil region; the first main body portion comprises a first current collector and a first active material layer; the first uncoated foil region comprises a first tab portion, and at least part of the first tab portion forms a first flattened portion; the surface of the first active material layer is provided with a first groove, the first groove extends in the axial direction of the wound core, and the first groove passes through one end surface of the first active material layer in the axial direction of the wound core; the cylindrical secondary battery satisfies: 0.53×104≤P1 / S1≤6×104, wherein the density of the first flattened portion is P1g / cm3, wherein 0.6≤P1≤3.5, and the cross-sectional area of the first groove in the radial direction of the wound core is S1mm2. By means of the described configurations, electrolyte infiltration is facilitated, and the cycle performance of the cylindrical secondary battery is improved.

Description

Cylindrical secondary battery and electric device TECHNICAL FIELD

[0001] The present application relates to the technical field of battery, in particular to a cylindrical secondary battery and an electric device. BACKGROUND

[0002] The secondary battery is a device that converts external energy into electrical energy and stores it inside, to power external electric devices (such as portable electronic devices, etc.) at the required time. At present, the secondary battery is widely used in unmanned aerial vehicles, mobile phones, tablets, notebook computers, power tools, energy storage, etc. The cylindrical secondary battery is a kind of secondary battery, which includes a shell and a winding core. The tab of the winding core has a rubbing flat part, which is easy to cause wetting problems and affect the performance of the cylindrical secondary battery.

[0003] SUMMARY

[0004] The embodiments of the present application aim to provide a cylindrical secondary battery and an electric device to solve the wetting problem caused by the rubbing flat part of the cylindrical secondary battery in the prior art, and improve the cycle performance of the cylindrical secondary battery.

[0005] According to an aspect of an embodiment of the present application, a cylindrical secondary battery is provided, which includes a shell and a winding core. The winding core is accommodated in the shell. The winding core includes a first pole piece and a separator. Along the axial direction of the winding core, the first pole piece includes a first main body part and a first empty foil area in sequence. The first main body part includes a first current collector and a first active material layer coated on at least one surface of the first current collector. The first empty foil area includes a first tab part. Along the axial direction of the winding core, the first tab part is the part of the first empty foil area that protrudes beyond the separator, and at least part of the first tab part forms a first rubbing flat part. The surface of the first active material layer is provided with a first groove. The first groove extends along the axial direction of the winding core, and the first groove penetrates one end surface of the first active material layer along the axial direction of the winding core. The cylindrical secondary battery satisfies: 0.53x10 4 ≤P1 / S1≤6x10 4 , wherein the density of the first rubbing flat part is P1g / cm 3 , 0.6≤P1≤3.5, and the cross-sectional area of the first groove along the radial direction of the winding core is S1mm 2 .

[0006] By providing the first groove on the surface of the first active material layer, the electrolyte is facilitated to wet, and the cycle performance of the cylindrical secondary battery is improved.

[0007] By limiting the density P1 of the first flattening part, the problem of electrolyte infiltration is alleviated. Specifically, when P1<0.6, the electrolyte is not easy to be distributed uniformly when injected, and is easy to form local accumulation inside the core, and the infiltration effect is poor; when P1>3.5, the electrolyte is not easy to enter the core, and the infiltration effect is somewhat lacking. When 0.6≤P1≤3.5, the capacity retention rate of the cylindrical secondary battery is high, the infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0008] By limiting the proportional relationship between the density P1 of the first flattening part and the cross-sectional area S1 of the first groove along the radial direction of the core, on the one hand, the electrolyte can at least partially flow along the first groove to improve the infiltration effect, and on the other hand, the local enrichment of the electrolyte in the first groove can be reduced to cause side reactions and lead to capacity attenuation. Specifically, when P1 / S1<0.53×10 4 , the electrolyte is not easy to be distributed uniformly when injected, and is easy to form local accumulation inside the core, and the infiltration effect is poor; when P1 / S1>6×10 4 , the electrolyte is easy to form local enrichment in the first groove, and is easy to cause side reactions, which on the one hand reduces the amount of effective electrolyte participating in the charge-discharge cycle of the cylindrical secondary battery, and on the other hand, the local enrichment of the electrolyte in the first groove affects the infiltration of other areas, thereby leading to capacity attenuation. When 0.53×10 4 ≤P1 / S1≤6×10 4 , the capacity retention rate of the cylindrical secondary battery is high, the infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0009] In one or more embodiments, 0.53×10 4 ≤H1 / S1≤8×10 4 , wherein along the axial direction of the core, the first flattening part includes a first surface away from the separator, the separator includes a first end surface and a second end surface, the first end surface is closer to the first surface than the second end surface, the distance between the first surface and the first end surface is H1 mm, and 0.3≤H1≤4.

[0010] By limiting the distance H1, the problem of electrolyte infiltration caused by excessively high distance H1 is reduced. Specifically, when H1<0.3, the electrolyte lacks sufficient time to be distributed uniformly when injected, and is easy to form local accumulation inside the core, and the infiltration effect is poor; when H1>4, the electrolyte is not easy to enter the core, and the infiltration effect is somewhat lacking. When 0.3≤H1≤4, the capacity retention rate of the cylindrical secondary battery is high, the infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0011] By limiting the proportional relationship between the interval H1 and the cross-sectional area S1 of the first groove along the radial direction of the winding core, the electrolyte infiltration effect is further improved. Specifically, when H1 / S1 < 0.53 x 10 4 , the electrolyte is not easy to distribute uniformly when injected, and is easy to form local accumulation inside the winding core, and the infiltration effect is not good. When H1 / S1 > 8 x 10 4 , the electrolyte is easy to form local enrichment in the first groove and cause side reactions, on the one hand, the amount of effective electrolyte participating in the charging and discharging cycle of the cylindrical secondary battery is reduced, on the other hand, the local enrichment of the electrolyte in the first groove affects the infiltration of other areas, thereby causing capacity attenuation. When 0.53 x 10 4 ≤ H1 / S1 ≤ 8 x 10 4 , the capacity retention rate of the cylindrical secondary battery is high, the infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0012] In one or more embodiments, 0.8 ≤ H1 ≤ 2, by further limiting the interval H1, a preferred solution for improving the infiltration problem of the electrolyte is obtained.

[0013] In one or more embodiments, 0.93 x 10 4 ≤ W1 / S1 ≤ 80 x 10 4 , wherein the unit area coating mass of the first active material layer on the first tab is W1 mg / cm 2 , and 8 ≤ W1 ≤ 30.

[0014] By limiting the unit area coating mass W1 of the first active material layer on the first tab, the problem of poor electrolyte infiltration caused by the increase in the diffusion distance of the electrolyte along the radial direction of the winding core due to the excessively high coating mass W1 is reduced, which causes the cycle attenuation and lithium precipitation. Specifically, when W1 < 8, the coating mass W1 is small, the capacity retention rate of the cylindrical secondary battery is low, and the cycle life and reliability are not good. When W1 > 30, the electrolyte is not easy to distribute uniformly inside the winding core, and the infiltration effect is not good. When 8 ≤ W1 ≤ 30, the capacity retention rate of the cylindrical secondary battery is high, the infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0015] By limiting the proportional relationship between the coating mass W1 and the cross-sectional area S1 of the first groove along the radial direction of the winding core, the capacity retention rate of the cylindrical secondary battery and the electrolyte infiltration effect are further improved. Specifically, when W1 / S1 < 0.93 x 10 4 , the capacity retention rate of the cylindrical secondary battery is low, and the cycle life and reliability are not good. When W1 / S1 > 80 x 10 4When 0.93x10 4 ≤ W1 / S1 ≤ 80x10 4 , the capacity retention rate of the cylindrical secondary battery is high, the impregnation effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0016] In one or more embodiments, 14 ≤ W1 ≤ 20. By further limiting the coating mass W1, a preferred solution for improving the impregnation problem of the electrolyte is obtained.

[0017] In one or more embodiments, the cylindrical secondary battery at least satisfies one of the following conditions: (1) 0.3 ≤ f1 ≤ 1, wherein the ratio of the length of the first groove to the length of the first active material layer along the axial direction of the winding core is f1; (2) 0.25x10 -4 ≤ S1 ≤ 1.5x10 -4 By limiting the ratio f1 of the length of the first groove to the length of the first active material layer, or by limiting the cross-sectional area S1 of the first groove along the radial direction of the winding core, on the one hand, the electrolyte can at least partially flow along the first groove to achieve the impregnation effect of the cylindrical secondary battery, and on the other hand, the electrolyte can be prevented from being locally enriched in the first groove to cause side reactions and capacity decay. Specifically, the amount of effective electrolyte participating in the charge-discharge cycle of the cylindrical secondary battery is not reduced due to side reactions, and the impregnation of other areas is not affected due to the local enrichment of the electrolyte in the first groove, and the capacity is not affected. Whether the ratio f1 of the length of the first groove to the length of the first active material layer is limited or the cross-sectional area S1 of the first groove along the radial direction of the winding core is limited, both can achieve the above-mentioned beneficial effects. Specifically, when f1 < 0.3, the length of the first groove is small, and the improvement of the impregnation effect of the electrolyte is limited, when 0.3 ≤ f1 ≤ 1, the capacity retention rate of the cylindrical secondary battery is high, the impregnation effect is good, and the cycle performance of the cylindrical secondary battery can be improved. -4 When S1 < 0.25x10 -4 , the electrolyte is not sufficient to be uniformly distributed in the winding core, and the impregnation effect is not good. -4 ≤ S1 ≤ 1.5x10 -4At this time, the capacity retention rate of the cylindrical secondary battery is high, the wetting effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0018] In one or more embodiments, the cylindrical secondary battery at least satisfies one of the following conditions: (3) 0.5≤f1≤0.8; (4) 0.8≤P1≤1.5; (5) 1×10 -4 ≤S1≤1.4×10 -4 By further limiting the ratio f1 of the length of the first groove to the length of the first active material layer, or further limiting the density P1 of the first flattening part, or further limiting the cross-sectional area S1 of the first groove along the radial direction of the winding core, a preferred solution for improving the wetting problem of the electrolyte can be obtained.

[0019] In one or more embodiments, the number of the first grooves is at least two, and the cylindrical secondary battery at least satisfies one of the following conditions: when n≤0.3N, 2.5≤K≤3.5; when 0.3N By limiting the distribution of the first grooves on the first active material layer, on the one hand, the electrolyte can at least partially flow along the first grooves to improve the wetting effect, and on the other hand, the local enrichment of the electrolyte in the first grooves can be reduced. Local enrichment of the electrolyte in the first grooves is prone to side reactions, which reduces the amount of effective electrolyte participating in the charge-discharge cycle of the cylindrical secondary battery, and in addition, local enrichment of the electrolyte in the first grooves affects the wetting of other areas, thereby leading to capacity decay. On the other hand, it can also alleviate the processing difficulty. Specifically, when n≤0.3N but K<2.5, it is not sufficient to improve the wetting effect of the electrolyte. When 0.3N By limiting the distribution of the first grooves on the first active material layer, on the one hand, the electrolyte can at least partially flow along the first grooves to improve the wetting effect, and on the other hand, the local enrichment of the electrolyte in the first grooves can be reduced. Local enrichment of the electrolyte in the first grooves is prone to side reactions, which reduces the amount of effective electrolyte participating in the charge-discharge cycle of the cylindrical secondary battery, and in addition, local enrichment of the electrolyte in the first grooves affects the wetting of other areas, thereby leading to capacity decay. On the other hand, it can also alleviate the processing difficulty. Specifically, when n≤0.3N but K<2.5, it is not sufficient to improve the wetting effect of the electrolyte. When 0.3N By limiting the distribution of the first grooves on the first active material layer, on the one hand, the electrolyte can at least partially flow along the first grooves to improve the wetting effect, and on the other hand, the local enrichment of the electrolyte in the first grooves can be reduced. Local enrichment of the electrolyte in the first grooves is prone to side reactions, which reduces the amount of effective electrolyte participating in the charge-discharge cycle of the cylindrical secondary battery, and in addition, local enrichment of the electrolyte in the first grooves affects the wetting of other areas, thereby leading to capacity decay. On the other hand, it can also alleviate the processing difficulty. Specifically, when n≤0.3N but K<2.5, it is not sufficient to improve the wetting effect of the electrolyte. When 0.3N When n≤0.3N and 2.5≤K≤3.5, or when 0.3N

[0020] In one or more embodiments, the first recess includes a first sub-recess and a second sub-recess, the first sub-recess extends through the first active material layer along one end surface of the axis of the winding core, and the second sub-recess extends through the first active material layer along the other end surface of the axis of the winding core; in the radial direction of the winding core, the projection of the first sub-recess on the first current collector is separated from the projection of the second sub-recess on the first current collector. By providing the first sub-recess and the second sub-recess extending through the first active material layer along two different end surfaces of the first active material layer, the electrolyte can be infiltrated from two different end surfaces of the first active material layer, which can further improve the infiltration effect of the electrolyte and expand the application scenarios of the cylindrical secondary battery.

[0021] In one or more embodiments, the number of the first tab portions is one, and the portions in the first tab portion are stacked on each other along the winding direction of the winding core from the outer circle to the central axis to form the first flattened portion after being flattened; or the number of the first tab portions is at least two, and each first tab portion is arranged at intervals in the circumferential direction of the winding core, and the at least two first tab portions are overlapped to form the first flattened portion from the outer circle to the central axis of the winding core after being flattened. Thus, the first flattened portion can be formed.

[0022] In one or more embodiments, the winding core includes a second tab, and the winding core is formed by winding the first tab, the second tab, and the separation film located between the first tab and the second tab together; the second tab includes a second main body portion and a second empty foil area in sequence, the second main body portion includes a second current collector and a second active material layer coated on at least one surface of the second current collector, and the second empty foil area includes a second tab portion, along the axis of the winding core, the second tab portion is the part of the second empty foil area beyond the separation film, and at least part of the second tab portion forms a second flattened portion. Thus, not only the first tab portion of the first tab can form the first flattened portion, but also the second tab portion of the second tab arranged apart from the first tab can form the second flattened portion.

[0023] In one or more embodiments, a second recess is provided on the surface of the second active material layer, the second recess extends along the axis of the winding core, and the second recess extends through one end surface of the axis of the winding core; the cylindrical secondary battery satisfies: 0.53×10 4 ≤P2 / S2≤6×10 4 , wherein the density of the second flattened portion is P2 g / cm 3 , 0.6≤P2≤3.5, and the cross-sectional area of the second recess in the radial direction of the winding core is S2 mm 2 .

[0024] By providing the second recess on the surface of the second active material layer, the electrolyte can be infiltrated, and the cycle performance of the cylindrical secondary battery can be improved.

[0025] By limiting the density P2 of the second flattening part, the problem of electrolyte infiltration is alleviated. Specifically, when P2<0.6, during injection of the electrolyte, the electrolyte is not easy to be distributed uniformly, and is easy to form local accumulation inside the core, and the infiltration effect is not good; when P2>3.5, the electrolyte is not easy to enter the inside of the core, and the infiltration effect is somewhat deficient. When 0.6≤P2≤3.5, the capacity retention rate of the cylindrical secondary battery is high, the infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0026] By limiting the proportional relationship between the density P2 of the second flattening part and the cross-sectional area S2 of the second groove along the radial direction of the core, on the one hand, the electrolyte can at least partially flow along the second groove to improve the infiltration effect, and on the other hand, the local accumulation of the electrolyte in the second groove can be reduced, the side reaction can be reduced, and the influence on the infiltration effect of other areas can be reduced. Specifically, when P2 / S2<0.53×10 4 , during injection of the electrolyte, the electrolyte is not easy to be distributed uniformly, and is easy to form local accumulation inside the core, and the infiltration effect is not good; when P2 / S2>6×10 4 , the electrolyte is easy to form local accumulation in the second groove, and is easy to cause side reaction, and affects the infiltration effect of other areas. When 0.53×10 4 ≤P2 / S2≤6×10 4 , the capacity retention rate of the cylindrical secondary battery is high, the infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0027] In one or more embodiments, 0.53×10 4 ≤H2 / S2≤8×10 4 , wherein, along the axial direction of the core, the second flattening part includes a second surface away from the separator, the separator includes a first end surface and a second end surface, the second end surface is close to the second surface relative to the first end surface, the distance between the second surface and the second end surface is H2 mm, and 0.3≤H2≤4.

[0028] By limiting the distance H2, the problem of electrolyte infiltration caused by too high distance H2 is reduced. Specifically, when H2<0.3, during injection of the electrolyte, the electrolyte lacks sufficient time to be distributed uniformly, and is easy to form local accumulation inside the core, and the infiltration effect is not good; when H2>4, the electrolyte is not easy to enter the inside of the core, and the infiltration effect is somewhat deficient. When 0.3≤H2≤4, the capacity retention rate of the cylindrical secondary battery is high, the infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0029] By limiting the proportional relationship between the spacing H2 and the cross-sectional area S1 of the second groove along the radial direction of the core, the impregnation effect of the electrolyte is further improved. Specifically, when H2 / S2<0.53×10 4 , the electrolyte is not easy to be evenly distributed when injected, and is easy to form local accumulation inside the core, and the impregnation effect is not good. When H2 / S2>8×10 4 , the electrolyte is easy to form local enrichment in the first groove, and is easy to cause side reactions and affect the impregnation effect of other areas. When 0.53×10 4 ≤H2 / S2≤8×10 4 , the capacity retention rate of the cylindrical secondary battery is high, the impregnation effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0030] In one or more embodiments, 0.93×10 4 ≤W2 / S2≤80×10 4 , wherein the unit area coating mass of the second active material layer on the second tab is W2 mg / cm 2 , and 8≤W2≤30.

[0031] By limiting the unit area coating mass W2 of the second active material layer on the second tab, the problem of poor impregnation of the electrolyte caused by the increase of the diffusion distance of the electrolyte along the radial direction of the core due to the excessively high coating mass W2 is reduced, which leads to accelerated cycle attenuation and lithium precipitation. Specifically, when W2<8, the coating mass W2 is small, the capacity retention rate of the cylindrical secondary battery is low, and the cycle life and reliability are not good. When W2>30, the electrolyte is not easy to be evenly distributed inside the core, and the impregnation effect is not good. Specifically, the diffusion distance of the electrolyte along the radial direction of the core is increased, which causes poor impregnation of the electrolyte, leading to accelerated cycle attenuation and lithium precipitation. When 8≤W2≤30, the capacity retention rate of the cylindrical secondary battery is high, the impregnation effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0032] By limiting the proportional relationship between the coating mass W2 and the cross-sectional area S2 of the second groove along the radial direction of the core, the impregnation effect of the electrolyte is further improved. Specifically, when W2 / S2<0.93×10 4 , the capacity retention rate of the cylindrical secondary battery is low, and the cycle life and reliability are not good. When W2 / S2>80×10 4 , the electrolyte is easy to form local enrichment in the second groove, and is easy to cause side reactions and affect the impregnation effect of other areas. When 0.93×10 4 ≤W2 / S2≤80×10 4At this time, the capacity retention rate of the cylindrical secondary battery is high, the wetting effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0033] In one or more embodiments, the cross-sectional shape of the first groove is semicircular, triangular or rectangular; and / or, the cross-sectional shape of the second groove is semicircular, triangular or rectangular. Thus, the electrolyte is facilitated to flow at least partially along the first groove and / or the second groove to improve the wetting effect thereof.

[0034] In one or more embodiments, the first electrode tab is a negative electrode tab. Generally, the poor wetting of the negative electrode has a great impact on the performance of the cylindrical secondary battery, and by providing the first groove on the negative electrode tab, the impact of the wetting problem of the electrolyte on the overall performance of the cylindrical secondary battery can be effectively alleviated.

[0035] According to another aspect of the embodiments of the present application, a power utilization device is provided, which includes the cylindrical secondary battery described above. BRIEF DESCRIPTION OF DRAWINGS

[0036] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, which are schematic and not intended to be limiting of the embodiments, and in which like reference numerals refer to like elements in the various figures, unless otherwise specified. The sizes of the elements in the figures are intended to be not limiting, and are provided for the purpose of illustration.

[0037] FIG. 1 is a schematic view of a cylindrical secondary battery according to an embodiment of the present application;

[0038] FIG. 2 is a sectional view along A-A in FIG. 1 according to an embodiment of the present application;

[0039] FIG. 3 is a schematic view of a jellyroll without a first flattening portion and a second flattening portion according to an embodiment of the present application;

[0040] FIG. 4 is a schematic view of an unfolded first electrode tab provided with one first groove according to an embodiment of the present application;

[0041] FIG. 5 is a schematic view of an unfolded first electrode tab provided with a plurality of first grooves according to an embodiment of the present application;

[0042] FIG. 6 is a schematic view of a jellyroll formed with a first flattening portion and a second flattening portion according to an embodiment of the present application;

[0043] FIG. 7 is a sectional view along B-B1 in FIG. 4 according to an embodiment of the present application;

[0044] FIG. 8 is a sectional view along B-B in FIG. 5 according to an embodiment of the present application;

[0045] FIG. 9 is a schematic view of another implementation of an unfolded first electrode tab according to an embodiment of the present application;

[0046] FIG. 10 is a schematic view of another implementation of the first tab in an unfolded state according to an embodiment of the present application;

[0047] FIG. 11 is a schematic view of the second tab provided with a second groove in an unfolded state according to an embodiment of the present application;

[0048] FIG. 12 is a schematic view of the second tab provided with a plurality of second grooves in an unfolded state according to an embodiment of the present application;

[0049] FIG. 13 is a sectional view taken along line C-C1 in FIG. 11 according to an embodiment of the present application;

[0050] FIG. 14 is a sectional view taken along line C-C in FIG. 12 according to an embodiment of the present application.

[0051] Reference Signs:

[0052] Cylindrical secondary battery 100;

[0053] Housing 1, jelly-roll 2, first tab 21, separator 22, second tab 23;

[0054] First main portion 211, first empty foil region 212, first current collector 2111, first active material layer 2112;

[0055] First groove 21121, one of the end faces 2112a of the first active material layer in the axial direction of the jelly-roll, the other end face 2112b;

[0056] First sub-groove 21121a, second sub-groove 21121b, first tab portion 2121, first flattened portion 21211, first surface 21211a;

[0057] First end face 22a, second end face 22b;

[0058] Second main portion 231, second empty foil region 232, second current collector 2311, second active material layer 2312, second groove 23121, one of the end faces 2312a of the second active material layer in the axial direction of the jelly-roll;

[0059] Second tab portion 2321, second flattened portion 23211, second surface 23211a;

[0060] Center axis O, axial direction X, circumferential direction Z1, winding direction Z2, radial direction Y, length direction Z. DETAILED DESCRIPTION

[0061] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will be combined with the accompanying drawings for the embodiments of the present application to make a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0062] It should be noted that when an element is described as "fixed" to another element, it can be directly on the other element or one or more intervening elements can be present therebetween. When an element is described as "connected" to another element, it can be directly connected to the other element or one or more intervening elements can be present therebetween. The terms "vertical", "horizontal", "left", "right", and similar expressions used in the specification are for illustrative purposes only.

[0063] In the description of the present application, it should be noted that the use of the terms "first", "second", and the like to describe components should be understood as only for the convenience of distinguishing the corresponding components, and the above terms have no special meaning unless otherwise stated, and therefore should not be understood as limiting the scope of protection of the present application.

[0064] In addition, the technical features involved in each of the embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0065] Referring to FIGS. 1 and 2, the present application provides a cylindrical secondary battery 100 including a case 1 and a jelly-roll 2, the jelly-roll 2 being housed in the case 1. The cylindrical secondary battery 100 is configured to be connected to an external circuit. The external circuit refers to a circuit portion connected between the cylindrical secondary battery 100 and the outside, and can be a load circuit in an electric device, such that the secondary battery 100 can output the electric energy stored in the jelly-roll 2 to the outside, or can be a power input circuit of the electric device, such that the external electric energy is input to the inside to supply the jelly-roll 2 with power.

[0066] The cylindrical secondary battery 100 of the present application is not particularly limited, and can include any device in which an electrochemical reaction occurs. In some embodiments, the cylindrical secondary battery 100 can include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery, etc.

[0067] In addition, the cylindrical secondary battery 100 should also include an electrolyte (not shown in the figure), which is stored in the inside of the case 1 and is used to soak the jelly-roll 2.

[0068] The specific configuration of the shell 1 is not specifically limited here, as long as the space for accommodating the core 2 defined by the shell 1 itself is isolated from the external environment outside the shell 1 and meets the use requirements of stable storage of electrolyte.

[0069] For the above-mentioned core 2, referring to FIG. 3, the core 2 includes the first tab 21 and the separator 22, and the first tab 21 and the separator 22 are wound to form the core 2. The direction of the center axis O of the core 2 is defined as the axial direction X of the core 2. The winding direction Z2 of the first tab 21 and the separator 22 is the winding direction Z2 of the core 2. For one of the windings of the first tab 21, the winding direction Z2 thereof is defined as the circumferential direction Z1 of the core 2. The direction from the center axis O of the core 2 to the shell 1 is defined as the radial direction Y of the core 2, and the radial direction Y is perpendicular to the axial direction X.

[0070] Referring to FIGS. 4, 5 and 6, along the axial direction X of the core 2, the first tab 21 includes the first main body part 211 and the first empty foil area 212 in sequence. The first main body part 211 includes the first current collector 2111 and the first active material layer 2112 coated on at least one surface of the first current collector 2111. The first empty foil area 212 includes the first tab part 2121. Along the axial direction X of the core 2, the first tab part 2121 is the part of the first empty foil area 212 beyond the separator 22, and at least part of the first tab part 2121 forms the first flattened part 21211.

[0071] In some embodiments, the number of the first tab part 2121 is one, and the parts in the first tab part 2121 are overlapped with each other after being flattened to form the first flattened part 21211 from the outer circle to the center axis O along the winding direction Z2 of the core 2; or the number of the first tab part 2121 is at least two, and each of the first tab parts 2121 is arranged in the circumferential direction Z1 of the core 2, and the at least two first tab parts 2121 are overlapped with each other after being flattened to form the first flattened part 21211 from the outer circle to the center axis O of the core 2.

[0072] For the above-mentioned first active material layer 2112, referring to FIGS. 4, 5, 7 and 8, the surface of the first active material layer 2112 is provided with the first groove 21121, the first groove 21121 extends along the axial direction X of the core 2, and the first groove 21121 penetrates the first active material layer 2112 along one end surface 2112a of the axial direction X of the core 2; the cylindrical secondary battery 100 satisfies: 0.53x10 4 ≤P1 / S1≤6x10 4 , the density of the first flattened part 21211 is P1g / cm 3 , 0.6≤P1≤3.5, and the cross-sectional area of the first groove 21121 along the radial direction Y of the core 2 is S1mm 2It can be understood that S1 refers to the sum of the cross-sectional areas of all the first grooves 21121 on the first active material layer 2112.

[0073] The density of the first flattening part 21211 is the ratio between the mass and the volume of the first flattening part 21211. The specific explanation and test method of the density of the first flattening part 21211 will be described in detail in the test method below.

[0074] The area of the part missing in the projection of the first active material layer 2112 at the first groove 21121 along the axial direction X of the core 2 is the cross-sectional area of the first groove 21121 along the radial direction Y of the core 2.

[0075] In some embodiments, the number of first grooves 21121 is multiple, and the multiple first grooves 21121 are distributed along the length direction Z of the first electrode tab 21. It can be understood that when the number of first grooves 21121 is multiple, the sum of the cross-sectional areas of all the first grooves 21121 makes the cylindrical secondary battery 100 meet the above condition (i.e. 0.53x10 4 ≤P1 / S1≤6x10 4 ).

[0076] It can be understood that the first grooves 21121 can be formed in various ways, for example, when the first active material layer 2112 is coated on the first current collector 2111, some areas are skipped to form the first grooves 21121; for example, when the first active material layer 2112 is formed, the first grooves 21121 are formed by laser drilling technology, or the first active material layer 2112 is coated first and then rolled to form the first grooves 21121, which is not limited in the present application.

[0077] In the embodiments of the present application, by opening the first grooves 21121 on the surface of the first active material layer 2112, the electrolyte is infiltrated, and the cycle performance of the cylindrical secondary battery 100 is improved. By limiting the density P1 of the first flattening part 21211, the infiltration problem of the electrolyte is alleviated. Specifically, when P1<0.6, the electrolyte is not easy to distribute uniformly when injected, and local accumulation is easy to form inside the core, and the infiltration effect is not good, when P1>3.5, the electrolyte is not easy to enter the inside of the core 2, and the infiltration effect is lacking. When 0.6≤P1≤3.5, the capacity retention rate of the cylindrical secondary battery 100 is high, the infiltration effect is good, and the cycle performance of the cylindrical secondary battery 100 can be improved.

[0078] In addition, the inventors have found that, in order to achieve a good wettability, the density P1 of the first flattening portion 21211 directly affects the setting of the cross-sectional area S1 of the first groove 21121, and therefore, by limiting the proportional relationship between the density P1 of the first flattening portion 21211 and the cross-sectional area S1 of the first groove 21121 along the radial direction Y of the winding core 2 (i.e. 0.53x10 4 ≤ P1 / S1 ≤ 6x10 4 ), on the one hand, the electrolyte can at least partially flow along the first groove 21121 to improve the wettability, and on the other hand, the local enrichment of the electrolyte in the first groove 21121 can be reduced to affect the wettability. Specifically, when P1 / S1 < 0.53x10 4 , during the injection of the electrolyte, the electrolyte is not easy to be uniformly distributed, and local accumulation is easy to form inside the winding core 2, and side reactions are easy to occur, on the one hand, the amount of effective electrolyte participating in the charge-discharge cycle of the cylindrical secondary battery 100 is reduced, and on the other hand, the local enrichment of the electrolyte inside the winding core 2 affects the wettability of other areas, thereby leading to capacity attenuation, when P1 / S1 > 6x10 4 , the electrolyte is easy to form local enrichment in the first groove 21121, and side reactions are easy to occur, on the one hand, the amount of effective electrolyte participating in the charge-discharge cycle of the cylindrical secondary battery 100 is reduced, and on the other hand, the local enrichment of the electrolyte inside the first groove 21121 affects the wettability of other areas, thereby leading to capacity attenuation. When 0.53x10 4 ≤ P1 / S1 ≤ 6x10 4 , the capacity retention rate of the cylindrical secondary battery 100 is high, the wettability is good, and the cycle performance of the cylindrical secondary battery 100 can be improved. Preferably, when 2x10 4 ≤ P1 / S1 ≤ 4.5x10 4 , the capacity retention rate of the cylindrical secondary battery 100 is higher, the wettability is better, and the cycle performance of the cylindrical secondary battery 100 can be better improved.

[0079] In some embodiments, along the axial direction X of the winding core 2, the first flattening portion 21211 is away from the first surface 21211a of the separator 22, the separator 22 includes a first end surface 22a and a second end surface 22b, the first end surface 22a is closer to the first surface 21211a than the second end surface 22b, the distance between the first surface 21211a and the first end surface 22a is H1 mm, 0.3 ≤ H1 ≤ 4, and 0.53x10 4 ≤ H1 / S1 ≤ 8x10 4 .

[0080] By limiting the distance H1, the problem of electrolyte infiltration caused by the distance H1 being set too high is reduced. Specifically, when H1 < 0.3, the electrolyte does not have enough time to be evenly distributed when the electrolyte is injected, and local accumulation is easily formed inside the jelly-roll 2, and the infiltration effect is poor. When H1 > 4, the electrolyte does not easily enter the jelly-roll 2, and the infiltration effect is somewhat lacking. When 0.3 ≤ H1 ≤ 4, the capacity retention rate of the cylindrical secondary battery 100 is high, the infiltration effect is good, and the cycle performance of the cylindrical secondary battery 100 can be improved.

[0081] In addition, the inventor has found that, in order to obtain a good infiltration effect, the size of the distance H1 directly affects the setting of the cross-sectional area S1 of the first groove 21121, and therefore, by limiting the proportional relationship between the distance H1 and the cross-sectional area S1 of the first groove 21121 along the radial direction Y of the jelly-roll 2 (i.e., 0.53 x 10 4 ≤ H1 / S1 ≤ 8 x 10 4 ), the infiltration effect of the electrolyte is further improved. Specifically, when H1 / S1 < 0.53 x 10 4 , the electrolyte does not easily distribute evenly when the electrolyte is injected, and local accumulation is easily formed inside the jelly-roll 2, and the infiltration effect is poor. When H1 / S1 > 8 x 10 4 , the electrolyte is easily locally enriched in the first groove 21121, and side reactions are easily generated. On the one hand, the amount of effective electrolyte participating in the charge-discharge cycle of the cylindrical secondary battery 100 is reduced, and on the other hand, the local enrichment of the electrolyte in the first groove 21121 affects the infiltration of other areas, thereby causing capacity decay. When 0.53 x 10 4 ≤ H1 / S1 ≤ 8 x 10 4 , the capacity retention rate of the cylindrical secondary battery 100 is high, the infiltration effect is good, and the cycle performance of the cylindrical secondary battery 100 can be improved.

[0082] Preferably, when 3 x 10 4 ≤ H1 / S1 ≤ 5 x 10 4 , the capacity retention rate of the cylindrical secondary battery 100 is higher, the infiltration effect is better, and the cycle performance of the cylindrical secondary battery 100 can be better improved.

[0083] It can be understood that the above-mentioned distance H1 is the height of the first flattening portion 21211 along the axial direction X of the jelly-roll 2.

[0084] In some embodiments, 0.8 ≤ H1 ≤ 2, by further limiting the distance H1, a preferred solution for improving the infiltration problem of the electrolyte is obtained.

[0085] In some embodiments, the coating mass per unit area of ​​the first active material layer 2112 on the first electrode 21 is W1 mg / cm². 2 Where 8≤W1≤30, 0.93×10 4 ≤W1 / S1≤80×10 4 .

[0086] By limiting the coating mass W1 per unit area of ​​the first active material layer 2112 on the first electrode 21, the problem of poor electrolyte wetting caused by an excessively high coating mass W1 per unit area, leading to increased diffusion distance of the electrolyte along the radial Y direction of the core 2 on the first electrode 21, is reduced. This reduces the risk of accelerated cycle decay and lithium plating. Specifically, when W1 < 8, the coating mass W1 is low, resulting in low capacity retention of the cylindrical secondary battery 100 and poor cycle life and reliability. When W1 > 30, the electrolyte is not easily distributed evenly inside the core 2, and the wetting effect is somewhat lacking. When 8 ≤ W1 ≤ 30, the capacity retention of the cylindrical secondary battery 100 is high, and the wetting effect is good, which can improve the cycle performance of the cylindrical secondary battery 100.

[0087] Furthermore, the inventors discovered that, in order to obtain a better wetting effect, the coating quality W1 directly affects the setting of the cross-sectional area S1 of the first groove 21121. Therefore, by limiting the proportional relationship between the coating quality W1 and the cross-sectional area S1 of the first groove 21121 along the radial Y direction of the core 2 (i.e., 0.93 × 10⁻⁶), the following method is used: 4 ≤W1 / S1≤80×10 4 This further improves the capacity retention and electrolyte wetting effect of the cylindrical secondary battery 100. Specifically, when W1 / S1 < 0.93 × 10 4 At this time, the cylindrical secondary battery 100 exhibits low capacity retention, poor cycle life, and low reliability. When W1 / S1 > 80 × 10⁻⁶, the capacity retention of the secondary battery 100 is low. 4 When electrolyte accumulates locally within the first groove 21121, side reactions are likely to occur. This reduces the amount of effective electrolyte available for charge-discharge cycles of the cylindrical secondary battery 100. Furthermore, the localized accumulation of electrolyte within the first groove 21121 affects wetting of other areas, leading to capacity decay. When 0.93 × 10⁻⁶... 4 ≤W1 / S1≤80×10 4 At this time, the cylindrical secondary battery 100 exhibits high capacity retention and good wetting effect, which improves its cycle performance. In some embodiments, when 9×10 4 ≤W1 / S1≤50×10 4At this time, the capacity retention rate of the cylindrical secondary battery 100 is higher, the wicking effect is better, and the cycle performance of the cylindrical secondary battery 100 can be better improved.

[0088] In some embodiments, 14≤W1≤20. By further limiting the unit area coating mass W1 of the first active material layer 2112 on the first tab 21, a preferred solution for improving the wicking problem of the electrolyte is obtained.

[0089] In some embodiments, referring to FIG. 5 or FIG. 9, along the axial direction X of the winding core 2, the ratio of the length L1 of the first groove 21121 to the length L2 of the first active material layer 2112 is f1. The difference between FIG. 5 and FIG. 9 is that the length L1 of the first groove 21121 in FIG. 9 is close to the length L2 of the first active material layer 2112, that is, the ratio f1 of the length L1 of the first groove 21121 to the length L2 of the first active material layer 2112 is close to 1. The cylindrical secondary battery 100 at least meets one of the following conditions: (1) 0.3≤f1≤1; (2) 0.25×10 -4 ≤ S1≤1.5×10 -4 By limiting the ratio f1 of the length L1 of the first groove 21121 to the length L2 of the first active material layer 2112, or by limiting the cross-sectional area S1 of the first groove 21121 along the radial direction Y of the winding core 2, on the one hand, the electrolyte can at least partially flow along the first groove 21121 to obtain a wicking effect, and on the other hand, the local enrichment of the electrolyte in the first groove 21121 can be reduced to reduce side reactions, without affecting the amount of effective electrolyte that can participate in the charge-discharge cycle of the cylindrical secondary battery 100, and without affecting the wicking of other areas due to the local enrichment of the electrolyte in the first groove 21121, without affecting the capacity. That is, whether the ratio f1 of the length L1 of the first groove 21121 to the length L2 of the first active material layer 2112 is limited or the cross-sectional area S1 of the first groove 21121 along the radial direction Y of the winding core 2 is limited, both can achieve the above-mentioned two beneficial effects. Specifically, when f1<0.3, the length L1 of the first groove 21121 is small, and the improvement of the wicking effect of the electrolyte is limited, when 0.3≤f1≤1, the capacity retention rate of the cylindrical secondary battery 100 is high, the wicking effect is good, and the cycle performance of the cylindrical secondary battery 100 can be improved. -4 When S1<0.25×10 -4At that time, the electrolyte was not evenly distributed inside the core 2, resulting in poor wetting effect. When 0.25×10 -4 ≤S1≤1.5×10 -4 At that time, the cylindrical secondary battery 100 has a high capacity retention rate and a good wetting effect, which can improve the cycle performance of the cylindrical secondary battery 100.

[0090] In some embodiments, the cylindrical secondary battery 100 satisfies at least one of the following conditions: (3) 0.5 ≤ f1 ≤ 0.8; (4) 0.8 ≤ P1 ≤ 1.5; (5) 1 × 10 -4 ≤S1≤1.4×10 -4 By further limiting the ratio f1 of the length L1 of the first groove 21121 to the length L2 of the first active material layer 2112, or by further limiting the density P1 of the first flattened portion 21211, or by further limiting the cross-sectional area S1 of the first groove 21121 along the radial Y of the core 2, a preferred solution to improve the electrolyte wetting problem can be obtained.

[0091] In some embodiments, the number of the first grooves 21121 is at least two, and the cylindrical secondary battery 100 at least satisfies one of the following conditions: when n≤0.3N, 2.5≤K≤3.5; when 0.3N

[0092] In addition, the inventor has found that, in order to obtain a better infiltration effect, the value of n directly affects the setting of the value of K. When n≤0.3N and 2.5≤K≤3.5, or when 0.3N

[0093] For example, when N is 10, when n≤3, 2.5≤K≤3.5; when 3

[0094] In some embodiments, referring to FIG. 10, the first groove 21121 includes a first sub-groove 21121a and a second sub-groove 21121b. The first sub-groove 21121a penetrates the first active material layer 2112 along one end surface 2112a of the core 2 in the axial direction X of the core 2. The second sub-groove 21121b penetrates the first active material layer 2112 along the other end surface 2112b of the core 2 in the axial direction X of the core 2. In the radial direction Y of the core 2, the projection of the first sub-groove 21121a on the first current collector 2111 is separated from the projection of the second sub-groove 21121b on the first current collector 2111. That is, the first sub-groove 21121a and the second sub-groove 21121b are arranged at intervals on the first active material layer 2112. By arranging the first sub-groove 21121a and the second sub-groove 21121b penetrating the first active material layer 2112 along two different end surfaces of the first active material layer 2112, the electrolyte can be infiltrated from two different end surfaces of the first active material layer 2112, which can further improve the infiltration effect of the electrolyte and expand the application scenarios of the cylindrical secondary battery 100.

[0095] In some embodiments, the first electrode tab 21 is a negative electrode tab. Generally, poor negative electrode infiltration has a great impact on the performance of the cylindrical secondary battery 100. By arranging the first groove 21121 on the negative electrode tab, the influence of the electrolyte infiltration problem on the overall performance of the cylindrical secondary battery 100 can be effectively alleviated.

[0096] It can be understood that, when the first electrode tab 21 is a negative electrode tab, the first current collector 2111 includes, but is not limited to, one or both of a conductive metal sheet such as a copper foil or a nickel foil. As an example, the first current collector 2111 is made of a copper foil. The first active material layer 2112 includes, but is not limited to, one or more of artificial graphite, natural graphite, soft carbon, hard carbon, graphene, mesocarbon microbeads, silicon-based materials, tin-based materials, lithium carbonate, or other metals that can form alloys with lithium.

[0097] In some embodiments, referring to FIGS. 2, 3, 6, 11 and 12, the winding core 2 comprises a second tab 23, and the winding core 2 is formed by co-winding the first tab 21, the separator 22, the second tab 23 and another separator 22 (not shown in the figure). The first tab 21 and the second tab 23 have opposite polarities. The second tab 23 comprises a second main body 231 and a second hollow foil area 232 in sequence. The second main body 231 comprises a second current collector 2311 and a second active material layer 2312 coated on at least one surface of the second current collector 2311. The second hollow foil area 232 comprises a second lug 2321. In the axial direction X of the winding core 2, the second lug 2321 is a part of the second hollow foil area 232 that protrudes out of the separator 22, and at least a part of the second lug 2321 forms a second flattened part 23211. Thus, not only can the first lug 2121 of the first tab 21 form a first flattened part 21211, but also the second lug 2321 of the second tab 23 disposed apart from the first tab 21 can form a second flattened part 23211.

[0098] The surface of the second active material layer 2312 is provided with a second groove 23121. The second groove 23121 extends in the axial direction X of the winding core 2 and penetrates through the second active material layer 2312 along one end surface 2312a of the second active material layer 2312 in the axial direction X of the winding core 2. The cylindrical secondary battery 100 satisfies: 0.53x10 4 ≤P2 / S2≤6x10 4 The density of the second flattened part 23211 is P2 g / cm 3 , 0.6≤P2≤3.5, and the cross-sectional area of the second groove 23121 in the radial direction Y of the winding core 2 is S2 mm 2 It can be understood that, in some embodiments, the number of the second grooves 23121 on the second active material layer 2312 is one (as shown in FIG. 11 or FIG. 13), and S2 refers to the cross-sectional area of the one second groove 23121; in some embodiments, the number of the second grooves 23121 on the second active material layer 2312 is a plurality (as shown in FIG. 12 or FIG. 14), and S2 refers to the sum of the cross-sectional areas of all the second grooves 23121 on the second active material layer 2312.

[0099] By providing the second groove 23121 on the surface of the second active material layer 2312, the electrolyte is facilitated to infiltrate, and the cycle performance of the cylindrical secondary battery 100 is improved.

[0100] By limiting the density P2 of the second flattening part 23211, the problem of electrolyte infiltration is alleviated. Specifically, when P2<0.6, the electrolyte is not easy to distribute uniformly when injected, and is easy to form local accumulation inside the core, and the infiltration effect is poor, and when P2>3.5, the electrolyte is not easy to enter the inside of the core 2, and the infiltration effect is deficient. When 0.6≤P2≤3.5, the capacity retention rate of the cylindrical secondary battery 100 is high, the infiltration effect is good, and the cycle performance of the cylindrical secondary battery 100 can be improved.

[0101] In addition, the inventor has found that in order to obtain a good infiltration effect, the size of the density P1 of the first flattening part 21211 will directly affect the setting of the cross-sectional area S1 of the first groove 21121, and therefore by limiting the proportional relationship (i.e. 0.53×10 4 ≤P2 / S2≤6×10 4 ) between the density P2 of the second flattening part 23211 and the cross-sectional area S2 of the second groove 23121 along the radial direction Y of the core 2, on the one hand, the electrolyte can at least partially flow along the second groove 23121 to improve the infiltration effect, and on the other hand, the local enrichment of the electrolyte in the second groove 23121 can be reduced to produce a side reaction. Specifically, when P2 / S2<0.53×10 4 , the electrolyte is not easy to distribute uniformly when injected, and is easy to form local accumulation inside the core 2, and is easy to produce a side reaction, on the one hand, the amount of effective electrolyte participating in the charge-discharge cycle of the cylindrical secondary battery 100 is reduced, and on the other hand, the local enrichment of the electrolyte inside the second groove 23121 affects the infiltration of other areas, thereby causing capacity decay, and when P2 / S2>6×10 4 , the electrolyte is easy to form local enrichment in the second groove 21121, and is easy to produce a side reaction to cause capacity decay. When 0.53×10 4 ≤P2 / S2≤6×10 4 , the capacity retention rate of the cylindrical secondary battery 100 is high, the infiltration effect is good, and the cycle performance of the cylindrical secondary battery 100 can be improved.

[0102] Preferably, when 2×10 4 ≤P2 / S2≤4.5×10 4 , the capacity retention rate of the cylindrical secondary battery 100 is higher, the infiltration effect is better, and the cycle performance of the cylindrical secondary battery 100 can be better improved.

[0103] In some embodiments, along the axial direction X of the jelly-roll 2, the second flattened portion 23211 comprises a second surface 23211a facing away from the separator 22, the separator 22 comprising a first end surface 22a and a second end surface 22b, the second end surface 22b being closer to the second surface 23211a than the first end surface 22a, the distance between the second surface 23211a and the second end surface 22b being H2 mm, 0.3≤H2≤4, and 0.53×10 4 ≤H2 / S2≤8×10 4 .

[0104] By limiting the distance H2, the problem of electrolyte infiltration caused by too high distance H2 is reduced. Specifically, when H2<0.3, the electrolyte lacks sufficient time to be uniformly distributed when injected, and is prone to form local accumulation inside the jelly-roll 2, which is not good for the infiltration effect. When H2>4, the electrolyte is not easy to enter the inside of the jelly-roll 2, and the infiltration effect is not good. When 0.3≤H2≤4, the capacity retention rate of the cylindrical secondary battery 100 is high, the infiltration effect is good, and the cycle performance of the cylindrical secondary battery 100 can be improved.

[0105] In addition, the inventors have found that, in order to obtain a good infiltration effect, the size of the distance H2 directly affects the setting of the cross-sectional area S2 of the second groove 23121, and therefore, by limiting the proportional relationship between the distance H2 and the cross-sectional area S2 of the second groove 23121 along the radial direction Y of the jelly-roll 2 (i.e. 0.53×10 4 ≤H2 / S2≤8×10 4 ), the infiltration effect of the electrolyte is further improved. Specifically, when H2 / S2<0.53×10 4 , the electrolyte is not easy to be uniformly distributed when injected, and is prone to form local accumulation inside the jelly-roll 2, which is not good for the infiltration effect. When H2 / S2>8×10 4 , the electrolyte is prone to form local accumulation in the second groove 23121, and side reactions are prone to occur, which on the one hand reduces the amount of effective electrolyte participating in the charge-discharge cycle of the cylindrical secondary battery 100, and on the other hand, the local accumulation of electrolyte in the second groove 23121 affects the infiltration of other areas, thereby causing capacity decay. When 0.53×10 4 ≤H2 / S2≤8×10 4 , the capacity retention rate of the cylindrical secondary battery 100 is high, the infiltration effect is good, and the cycle performance of the cylindrical secondary battery 100 can be improved.

[0106] It can be understood that the above-mentioned distance H2 is the height of the second flattened portion 23211 along the axial direction X of the jelly-roll 2.

[0107] Preferably, 3×104 ≤H2 / S2≤5×10 4 At that time, the cylindrical secondary battery 100 has a higher capacity retention rate, better wetting effect, and can better improve the cycle performance of the cylindrical secondary battery 100.

[0108] In some embodiments, the coating mass per unit area of ​​the second active material layer 2312 on the second electrode 23 is W2 mg / cm². 2 8≤W2≤30, and 0.93×10 4 ≤W2 / S2≤80×10 4 .

[0109] By limiting the coating mass W2 per unit area of ​​the second active material layer 2312 on the second electrode 23, the problem of poor electrolyte wetting caused by an excessively high coating mass W2, which leads to an increased diffusion distance of the electrolyte along the radial Y direction of the core 2 on the second electrode 23, is reduced. This reduces the risk of accelerated cycle decay and lithium plating. Specifically, when W2 < 8, the coating mass W2 is low, resulting in low capacity retention of the cylindrical secondary battery 100 and poor cycle life and reliability. When W2 > 30, the electrolyte is not easily distributed evenly inside the core 2, and the wetting effect is somewhat lacking. When 8 ≤ W2 ≤ 30, the capacity retention of the cylindrical secondary battery 100 is high, and the wetting effect is good, which can improve the cycle performance of the cylindrical secondary battery 100.

[0110] Furthermore, the inventors discovered that, in order to obtain a better wetting effect, the coating quality W2 directly affects the setting of the cross-sectional area S2 of the second groove 23121. Therefore, by limiting the proportional relationship between the coating quality W2 and the cross-sectional area S2 of the second groove 23121 along the radial Y direction of the core 2 (i.e., 0.93 × 10⁻⁶), the following method is used: 4 ≤W2 / S2≤80×10 4 This further improves the capacity retention and electrolyte wetting effect of the cylindrical secondary battery 100. Specifically, when W2 / S2 < 0.93 × 10 4 At this time, the cylindrical secondary battery 100 exhibits low capacity retention, poor cycle life, and poor reliability. When W2 / S2 > 80 × 10⁻⁶, the capacity retention of the secondary battery is low. 4 When the electrolyte is locally enriched within the second groove 23121, side reactions are likely to occur. This reduces the amount of effective electrolyte that can participate in the charge-discharge cycle of the cylindrical secondary battery 100. Furthermore, the localized enrichment of electrolyte within the second groove 23121 affects the wetting of other areas, leading to capacity decay. When 0.93 × 10⁻⁶... 4 ≤W2 / S2≤80×10 4 At that time, the cylindrical secondary battery 100 has a high capacity retention rate and a good wetting effect, which can improve the cycle performance of the cylindrical secondary battery 100.

[0111] In some embodiments, when 9x10 4 ≤W2 / S2≤50x10 4 The capacity retention rate of the cylindrical secondary battery 100 is higher, the wettability is better, and the cycle performance of the cylindrical secondary battery 100 can be better improved.

[0112] In some embodiments, the cross-sectional shape of the first groove 21121 is semicircular, triangular, or rectangular; and / or, the cross-sectional shape of the second groove 23121 is semicircular, triangular, or rectangular. Thus, the electrolyte can flow at least partially along the first groove 21121 and / or the second groove 23121 to improve the wettability.

[0113] It can be understood that the cross-sectional shape of the first groove 21121 or the second groove 23121 is not limited to the above-mentioned semicircular, triangular, or rectangular shape, and can also be trapezoidal or the like. Regardless of the cross-sectional shape of the first groove 21121 or the second groove 23121, the beneficial effects of improving the wettability of the electrolyte can be achieved by setting the first groove 21121 and / or the second groove 23121.

[0114] It can be understood that other structural features of the second groove 23121 can also be set as the first groove 21121, which will not be described here.

[0115] In some embodiments, the first electrode tab 21 is a negative electrode tab, and the second electrode tab 23 is a positive electrode tab. Generally, the poor wettability of the negative electrode has a great impact on the performance of the cylindrical secondary battery 100. By setting the first groove 21121 on the negative electrode tab, the impact of the wettability of the electrolyte on the overall performance of the cylindrical secondary battery 100 can be effectively alleviated. When the second groove 23121 is also set on the positive electrode tab, the impact of the wettability of the electrolyte on the overall performance of the cylindrical secondary battery 100 can be further alleviated.

[0116] It can be understood that the first tab 21 is a negative electrode tab, and the second tab 23 is a positive electrode tab, and the first current collector 2111 includes but is not limited to one of a conductive metal sheet such as a copper foil, a nickel foil, etc. As an example, the first current collector 2111 is made of a copper foil. The first active material layer 2112 includes but is not limited to one or more of artificial graphite, natural graphite, soft carbon, hard carbon, graphene, mesocarbon microbeads, silicon-based materials, tin-based materials, lithium carbonate, or other metals capable of forming alloys with lithium. The second current collector 2311 includes but is not limited to one of a conductive metal sheet such as an aluminum mesh, an aluminum foil, a copper foil, etc. As an example, the second current collector 2311 is made of an aluminum foil. The second active material layer 2312 includes but is not limited to one or more of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganate, lithium nickelate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium iron phosphate, and a lithium-rich manganese-based material.

[0117] In order to evaluate the beneficial effects of the cylindrical secondary battery 100 of the present application, relevant tests and analysis were performed on the cylindrical secondary batteries 100 in the examples and comparative examples.

[0118]

Test Method

[0119] Density measurement of the first flattening portion 21211 / second flattening portion 23211

[0120] For the convenience of the reader and for the convenience of description, the method of density measurement of the first flattening portion 21211 is described by taking the first flattening portion 21211 as an example, and the method of density measurement of the second flattening portion 23211 can refer to the method of density measurement of the first flattening portion 21211. Please refer to FIGS. 3, 5 and 6, the highest point of the first surface 21211a of the first flattening portion 21211 facing away from the separator 22 is taken as the plane reference, and the microscope is used to measure downward to the separator 22, recorded as the first flattening portion 21211 height H1 mm; the diameter D mm of the jelly-roll 2 in the cylindrical secondary battery 100 and the diameter d mm of the center hole are measured by using a microscope; the cylindrical secondary battery 100 is disassembled, the length L of the first tab 21 after being unfolded and the height H of the first tab portion 2121 after being unfolded are measured by using a flexible ruler, and the thickness T1 of the first tab portion 2121 after being unfolded is measured by using a microscope. Among them, since FIG. 3 is a schematic diagram of the jelly-roll 2 without the first flattening portion 21211 and the second flattening portion 23211 provided by the present application, the height H of the first tab portion 2121 after being unfolded is actually equivalent to the H marked in FIG. 3, and the volume of the first flattening portion 21211 is calculated by using the following formula: V = [(π × (D / 2) × (D / 2)) - (π × (d / 2) × (d / 2))] × H1; the mass of the first flattening portion 21211 is calculated: M = T1 × L × H × ρ, ρ = 8.96 g / cm 3(Density of the first current collector 2111 (copper foil)); calculate the density of the first flattening part 21211: P1 = M / V.

[0121] The first groove 21121 / second groove 23121 is measured along the cross-sectional area of the radial direction Y of the winding core 2

[0122] For the convenience of the reader to understand, and for the convenience of description, taking the first groove 21121 as an example, the measurement method of the cross-sectional area of the first groove 21121 along the radial direction Y of the winding core 2, and the measurement method of the cross-sectional area of the second groove 23121 along the radial direction Y of the winding core 2 can be referred to the measurement method of the cross-sectional area of the first groove 21121 along the radial direction Y of the winding core 2. After the first pole piece 21 with the first groove 21121 is prepared into a sample by liquid nitrogen brittle fracture or ion polishing, the maximum width W and the maximum depth T of the first groove 21121 are measured by SEM (scanning electron microscope), please refer to FIG. 8, the maximum width W and the maximum depth T of the first groove 21121 are measured for 5 times and the average value is taken; when the W and T of each first groove are the same, the cross-sectional area of all the first grooves 21121 along the radial direction Y of the winding core 2 is calculated: S1 = q x W x T mm 2 , wherein q is the number of the first grooves 21121; when the W and T of the first grooves are different, the cross-sectional area S0 of each first groove is calculated in turn, and then all S0 are added up to obtain the total cross-sectional area S1.

[0123] Test of cycle performance (capacity retention rate)

[0124] The cylindrical secondary batteries 100 in each example and the comparative example are subjected to charge-discharge cycle tests in a 25°C thermostat, the charge-discharge voltage range is 2.5V to 4.2V, 0.5C constant current charging is performed to 4.2V, then 4.2V constant voltage charging is performed to 0.05C and standing for 5min, then 0.5C constant current discharging is performed to 2.5V, the above charge-discharge process is cycled for 600 times, and the initial capacity C1 and the capacity C after the 600th cycle are recorded. 600 , thereby calculating the capacity retention rate: capacity retention rate (%) = C 600 / C1 x 100%. The higher the capacity retention rate is, the better the wettability of the winding core 2 is, and the better the cycle performance of the cylindrical secondary battery 100 is.

[0125] Test of lithium precipitation performance

[0126] After the cylindrical secondary batteries in each example and the comparative example are subjected to charge-discharge according to the following test procedure, they are disassembled, and the lithium precipitation state on the surface of the pole piece is observed. The area on the surface of the pole piece where lithium is not precipitated is golden yellow, and the area where lithium is precipitated is grayish white.

[0127] The degree of lithium precipitation is determined according to the ratio between the lithium precipitation area and the active material layer area: area = 0%, no lithium precipitation; slight lithium precipitation: area less than 5%; moderate lithium precipitation: area between 5%-20%; severe lithium precipitation: area greater than 20%.

[0128] Lithium precipitation test procedure:

[0129] 1) The ambient temperature for testing is 25°C;

[0130] 2) Stand for 30 minutes;

[0131] 3) Constant current charge the battery at a charge rate of 1C until the voltage reaches 4.2V, and then constant voltage charge the prepared cylindrical secondary battery until the current decreases to 0.05C (C: rated capacity of the battery);

[0132] 4) Stand for 5 minutes;

[0133] 5) Discharge the battery using direct current at a charge rate of 0.2C until the voltage reaches 2.5V;

[0134] 6) Adjust the ambient temperature to 10°C;

[0135] 7) Stand for 120 minutes;

[0136] 8) Constant current charge the battery at a charge rate of 2C until the voltage reaches 4.2V, and then constant voltage charge the secondary battery until the current decreases to 0.05C;

[0137] 9) Stand for 5 minutes;

[0138] 10) Discharge the battery using direct current at a discharge rate of 0.5C until the voltage reaches 2.5V;

[0139] 11) Stand for 60 minutes;

[0140] 12) Repeat steps 8-11 for 10 times;

[0141] 13) Constant current charge the battery at a charge rate of 2C until the voltage reaches 4.2V, and then constant voltage charge the secondary battery until the current decreases to 0.05C;

[0142] 14) Stand for 15 minutes.

[0143] Example 1:

[0144] <Preparation of the negative electrode sheet>

[0145] The negative active material artificial graphite, carboxymethyl cellulose sodium (CMC-Na) and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 97.3:1.7:1.0, then deionized water was added as a solvent, and stirred and mixed uniformly to obtain a negative electrode slurry with a solid content of 50wt%. The negative electrode slurry was uniformly coated on a copper foil with a thickness of 10μm, and dried at 100℃ to obtain a negative electrode tab with a single-sided coated negative electrode material layer (i.e. a first active material layer). Then, the above steps were repeated on the other surface of the negative electrode current collector to obtain a negative electrode tab with a double-sided coated negative electrode material layer. Then, after cold pressing, cutting and slitting, a first groove was set on the negative electrode material layer on both surfaces of the negative electrode current collector by laser, to obtain a negative electrode tab with a specification of 62mm×1455mm for use. As shown in FIGS.5 and 8, the width W of the first groove is 10μm, the depth T of the first groove is 20μm, the length L1 of the first groove is 60mm, the width L2 of the first active material layer is 62mm, f1=L1 / L2=0.97, the spacing K between adjacent first grooves is 2.5mm, the unit coating mass W1 of the negative electrode material layer is 8.6mg / cm 2 , and the compacted density of the negative electrode material layer is 1.6g / cm 3 .

[0146] <Preparation of a positive electrode tab>

[0147] An aluminum foil with a thickness of 16μm was selected as a positive electrode current collector. The positive active material lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2), the binder polyvinylidene fluoride (PVDF) and the conductive carbon black were dispersed in N-methyl pyrrolidone (NMP) solvent in a mass ratio of 94.8:2.8:2.4, and fully stirred and mixed to obtain a positive electrode slurry with a solid content of 72wt%. The positive electrode slurry was uniformly coated on the surface of the above positive electrode current collector, and dried at 100℃ to obtain a positive electrode tab with a single-sided coated positive electrode material layer (i.e. a second active material layer). Then, the above steps were repeated on the other surface of the positive electrode current collector to obtain a positive electrode tab with a double-sided coated positive electrode material layer. Then, after cold pressing, cutting and slitting, the positive electrode tab was dried under vacuum at 100℃ for 4 hours to obtain a positive electrode tab with a specification of 60mm×1407mm for use. The unit coating mass of the positive electrode material layer was 15mg / cm 2 , and the compacted density of the positive electrode material layer was 3.4g / cm 3 .

[0148] <Separator>

[0149] A polyethylene (PE) film with a thickness of 12μm was used as a separator.

[0150] <Preparation of an electrolyte>

[0151] In a glove box under dry argon atmosphere, organic solvents ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC) were mixed in a mass ratio of 30:50:20 to obtain a base solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the above base solvent. After being mixed uniformly, an electrolyte was obtained. The mass percentage of LiPF6 based on the mass of the electrolyte was 12.5%, and the balance was the base solvent.

[0152] <Preparation of cylindrical secondary battery>

[0153] The separator film, the positive electrode sheet, the separator film, and the negative electrode sheet prepared above were sequentially stacked in order, and the separator film was arranged between the positive electrode and the negative electrode to play a role of isolation. After winding, rubbing, welding of the current collector plate, entering the shell, code spraying, vacuum drying, injecting electrolyte, plugging, and high-temperature standing, formation capacity and the like were performed, and a cylindrical secondary battery was obtained. The density P1 of the first rubbing part was 1.2 g / cm 3 , and H1 was 1.2 mm. The upper limit voltage of formation was 3.6 V, the formation temperature was 45°C, and the high-temperature standing time after formation was 24 h.

[0154] Specific examples and comparative examples are provided in the present application, and relevant performance tests are performed, and the test results are analyzed.

[0155] Regarding P1 / S1 and the influence of P1 on the performance of the cylindrical secondary battery

[0156] The cylindrical secondary batteries of Examples A1 to A7, Examples A8 to A14, Comparative Examples A1 to A4 were prepared based on the method of Example 1; the differences between Examples A1 to A7 and Comparative Examples A1 and A2 and Example 1 (P1 was 1.2 mg / cm 2 ) were that, first, P1 was 1 mg / cm 2 , and second, the parameters were adjusted according to the proportions in Table 1. The only difference between Examples A8 to A14, Comparative Example A3, and Comparative Example A4 was that the parameters were adjusted according to Table 2. For details, please refer to Table 1 and Table 2, Table 1 shows the influence of P1 / S1 on the performance of the cylindrical secondary battery 100, and Table 2 shows the influence of P1 on the performance of the cylindrical secondary battery 100.

[0157] Table 1

[0158] From Table 1, it can be seen that when 0.53x10 4 ≤P1 / S1≤6x10 4When P1 / S1<0.53x10 4 or P1 / S1>6x10 4 , the capacity retention rate of the cylindrical secondary battery is low, the wetting effect is somewhat deficient, and the cylindrical secondary battery has moderate or even severe lithium precipitation.

[0159] Preferably, when 2x10 4 ≤P1 / S1≤4.5x10 4 , the capacity retention rate of the cylindrical secondary battery is higher, the wetting effect is better, and the lithium precipitation performance is better, i.e., the cycle performance of the cylindrical secondary battery can be improved better.

[0160] Table 2

[0161] As can be seen from Table 2, when 0.6≤P1≤3.5, the capacity retention rate of the cylindrical secondary battery is higher, the wetting effect is better, and the lithium precipitation performance is better, i.e., the cycle performance of the cylindrical secondary battery can be improved better. When P1<0.6 or P1>3.5, the capacity retention rate of the cylindrical secondary battery is low, the wetting effect is somewhat deficient, and the cylindrical secondary battery has moderate or even severe lithium precipitation.

[0162] Preferably, when 0.8≤P1≤1.5, the capacity retention rate of the cylindrical secondary battery is higher, the wetting effect is better, and the lithium precipitation performance is better, i.e., the cycle performance of the cylindrical secondary battery can be improved better.

[0163] Regarding H1 / S1 and the influence of H1 on the performance of the cylindrical secondary battery

[0164] The cylindrical secondary batteries of Examples B1 to B7, Examples B8 to B14, and Comparative Examples B1 to B4 were prepared based on the method of Example 1. The difference between Examples B1 to B7 and Comparative Examples B1 and B2 and Example 1 (H1 is 1.2 mg / cm 2 ) is that, first, H1 is 1.2 mg / cm 2 , and second, the parameters are adjusted according to the proportions in Table 3. The only difference between Examples B8 to B14 and Comparative Examples B3 and B4 is that the parameters are adjusted according to Table 4. For details, please refer to Table 3 and Table 4. Table 3 shows the influence of H1 / S1 on the performance of the cylindrical secondary battery 100, and Table 4 shows the influence of H1 on the performance of the cylindrical secondary battery 100.

[0165] Table 3

[0166] As can be seen from Table 3, when 0.53x10 4≤ H1 / S1≤ 8 x 10 4 When H1 / S1≥ 0.53 x 10 4 or H1 / S1> 8 x 10 4 , the capacity retention rate of the cylindrical secondary battery is low, the wetting effect is insufficient, and the cylindrical secondary battery has moderate or even severe lithium precipitation.

[0167] Preferably, when 3 x 10 4 ≤ H1 / S1≤ 5 x 10 4 , the capacity retention rate of the cylindrical secondary battery is higher, the wetting effect is better, and the cycle performance of the cylindrical secondary battery can be improved better.

[0168] Table 4

[0169] As can be seen from Table 4, when 0.3≤ H1≤ 4, the capacity retention rate of the cylindrical secondary battery is high, the wetting effect is good, and the cycle performance of the cylindrical secondary battery can be improved. When H1< 0.3 or H1> 4, the capacity retention rate of the cylindrical secondary battery is low, the wetting effect is insufficient, and the cylindrical secondary battery has moderate or even severe lithium precipitation.

[0170] Preferably, when 0.8≤ H1≤ 2, the capacity retention rate of the cylindrical secondary battery is higher, the wetting effect is better, and the cycle performance of the cylindrical secondary battery can be improved better.

[0171] Regarding W1 / S1 and the influence of W1 on the performance of the cylindrical secondary battery

[0172] The cylindrical secondary batteries of Examples C1 to C7, Examples C8 to C14, and Comparative Examples C1 to C4 were prepared based on the method of Example 1. Among them, Examples C1 to C6 and Comparative Examples C1 and C2 are different from Example 1 (W1 is 8.6 mg / cm 2 ) in that, first, W1 is 10 mg / cm 2 , and second, the proportion adjustment parameters in Table 5 are adjusted. Among them, Examples C7 to C12 and Comparative Examples C3 and C4 are different from Example 1 in that the proportion adjustment parameters in Table 6 are adjusted. For details, please refer to Table 5 and Table 6, Table 5 shows the influence of W1 / S1 on the performance of the cylindrical secondary battery 100, and Table 6 shows the influence of W1 on the performance of the cylindrical secondary battery 100.

[0173] Table 5

[0174] As can be seen from Table 5, when 0.93 x 10 4≤W1 / S1≤80×10 4 At this time, the cylindrical secondary battery exhibits high capacity retention and good wetting effect, which can improve the cycle performance of the cylindrical secondary battery. However, when the wettability is 0.93 × 10⁻⁶, the cylindrical secondary battery shows good capacity retention and good wetting effect. 4 >W1 / S1 or W1 / S1>80×10 4 At that time, the capacity retention rate of cylindrical secondary batteries was low, their wetting effect was somewhat lacking, and the cylindrical secondary batteries exhibited moderate to severe lithium plating.

[0175] Preferably, when 9×10 4 ≤W1 / S1≤50×10 4 At that time, cylindrical secondary batteries have a higher capacity retention rate, better wetting effect, and can better improve the cycle performance of cylindrical secondary batteries.

[0176] Table 6

[0177] As shown in Table 6, when 8≤W1≤30, the cylindrical secondary battery has a high capacity retention rate and a good wetting effect, which can improve the cycle performance of the cylindrical secondary battery. However, when W1<8, the capacity retention rate of the cylindrical secondary battery is low. When W1>30, the capacity retention rate of the cylindrical secondary battery is low, the wetting effect is somewhat lacking, and the cylindrical secondary battery exhibits moderate or even severe lithium plating.

[0178] Preferably, when 14≤W1≤20, the cylindrical secondary battery has a higher capacity retention rate, better wetting effect, and can better improve the cycle performance of the cylindrical secondary battery.

[0179] The impact of f1 or S1 on the performance of cylindrical secondary batteries

[0180] Based on the method of Example 1, cylindrical secondary batteries were prepared in Examples D1 to D5, Examples D6 to D12, and Comparative Examples D1 to D3. The only difference between them is that the parameters were adjusted according to the proportions in Tables 7 and 8. Please refer to Tables 7 and 8 for details. Table 7 shows the effect of f1 on the performance of cylindrical secondary battery 100, and Table 8 shows the effect of S1 on the performance of cylindrical secondary battery 100.

[0181] Table 7

[0182] As shown in Table 7, when 0.3≤f1≤1, the cylindrical secondary battery has a high capacity retention rate and a good wetting effect, which can improve the cycle performance of the cylindrical secondary battery. However, when f1<0.3 or f1>1, the capacity retention rate of the cylindrical secondary battery is low and the wetting effect is somewhat lacking.

[0183] Preferably, when 0.5≤f1≤0.8, the capacity retention rate of the cylindrical secondary battery is higher, the wetting effect is better, and the cycle performance of the cylindrical secondary battery can be better improved.

[0184] Table 8

[0185] As can be seen from Table 8, when 0.25×10 -4 ≤S1≤1.5×10 -4 , the capacity retention rate of the cylindrical secondary battery is high, the wetting effect is good, and the cycle performance of the cylindrical secondary battery can be improved, while when S1<0.25×10 -4 or S1>1.5×10 -4 , the capacity retention rate of the cylindrical secondary battery is low, the wetting effect is insufficient, and there is slight lithium precipitation or even moderate lithium precipitation.

[0186] Preferably, when 1×10 -4 ≤S1≤1.4×10 -4 , the capacity retention rate of the cylindrical secondary battery is higher, the wetting effect is better, and the cycle performance of the cylindrical secondary battery can be better improved.

[0187] Influence of n and K on the performance of the cylindrical secondary battery

[0188] Based on the preparation method of Example 1 and adjusted according to the parameters in Table 9, Comparative Examples E1 to E6 and Examples E1 to E13 were obtained. Among them, the winding number N of the negative electrode material layer was 30 turns, and n was the nthturn of the negative electrode material layer in the winding core.

[0189] In Comparative Examples E1 and E2 and Examples E1 to E3, the K value of each turn when n was 1 to 9 was adjusted according to Table 9, and the first groove was not provided in the other turns.

[0190] In Comparative Examples E3 and E4 and Examples E4 to E6, the K value of each turn when n was 10 to 24 was adjusted according to Table 9, and the first groove was not provided in the other turns.

[0191] In Comparative Examples E5 and E6 and Examples E7 to E9, the K value of each turn when n was 25 to 30 was adjusted according to Table 9, and the first groove was not provided in the other turns.

[0192] In Example E10, when n was 1 to 9, K=3; when n was 10 to 24, K=1.5; and the first groove was not provided in the other turns.

[0193] In Example E11, when n was 1 to 9, K=3; when n was 25 to 30, K=4; and the first groove was not provided in the other turns.

[0194] In embodiment E12, when n is 10 to 24, K = 1.5; when n is 25 to 30, K = 4; and no first grooves are provided for other numbers of turns.

[0195] In embodiment E10, when n is 1 to 9, K = 3; when n is 10 to 24, K = 1.5; and when n is 25 to 30, K = 4.

[0196] Please refer to Table 9, which shows the influence of n and K on the performance of the cylindrical secondary battery 100.

[0197] Table 9

[0198] As can be seen from Table 9, when n ≤ 0.3N but K < 2.5 or K > 3.5, the capacity retention rate of the cylindrical secondary battery is not high, the wetting effect is not good, and the battery is prone to mild lithium precipitation. When 0.3N < n ≤ 0.8N but K < 1 or K > 2, the capacity retention rate of the cylindrical secondary battery is not high, the wetting effect is not good, and the battery is prone to mild lithium precipitation. When n > 0.8N but K < 3 or K > 5, the capacity retention rate of the cylindrical secondary battery is not high, the wetting effect is not good, and the battery is prone to mild lithium precipitation. When n ≤ 0.3N and 2.5 ≤ K ≤ 3.5, or when 0.3N < n ≤ 0.8N and 1 ≤ K ≤ 2, or when n > 0.8N and 3 ≤ K ≤ 5, the capacity retention rate of the cylindrical secondary battery is high, the wetting effect is good, and the cycle performance of the cylindrical secondary battery can be improved. In addition, as can be seen from embodiments E10 to E13, the more the number of first grooves provided, the better the wetting effect of the cylindrical secondary battery, and the higher the capacity retention rate.

[0199] Influence of P2 / S2 and P2 on the performance of the cylindrical secondary battery

[0200] Based on the adjustment of the positive electrode tab in embodiment 1, embodiment 3 is obtained, in which a second groove is provided on the positive electrode material layer on both sides of the positive electrode current collector along the length direction of the positive electrode current collector after being spread out by laser. The width of the second groove is 10 μm, the depth of the second groove is 4 μm, the length of the second groove is 60 mm, the width of the second active material layer is 60 mm, and the spacing K between adjacent second grooves is 2.5 mm. The density P2 of the second flattening part is 1 g / cm 3 , and H2 is 1 mm.

[0201] Examples F1 (i.e. Example 3) to F7, Examples F8 to F14 and Comparative Examples F1 to F4 of cylindrical secondary batteries were prepared based on Example 3. Among them, the difference of Examples F1 to F7, Examples F8 to F14, Comparative Examples F1 to F4 is only that the proportion adjustment parameters in Table 10 and Table 11 are adjusted, please refer to Table 10 and Table 11, Table 10 shows the influence of P2 / S2 on the performance of cylindrical secondary battery 100, and Table 11 shows the influence of P2 on the performance of cylindrical secondary battery 100.

[0202] Table 10

[0203] From Table 10, when 0.53x10 4 ≤P2 / S2≤6x10 4 , the capacity retention rate of the cylindrical secondary battery is high, the wetting effect is good, and the cycle performance of the cylindrical secondary battery can be improved, while when P2 / S2<0.53x10 4 or P2 / S2>6x10 4 , the capacity retention rate of the cylindrical secondary battery is low, the wetting effect is lacking, and the cylindrical secondary battery appears moderate or even severe lithium precipitation.

[0204] Preferably, when 2x10 4 ≤P2 / S2≤4.5x10 4 , the capacity retention rate of the cylindrical secondary battery is higher, the wetting effect is better and the cycle performance of the cylindrical secondary battery can be better improved.

[0205] Table 11

[0206] From Table 11, when 0.6≤P2≤3.5, the capacity retention rate of the cylindrical secondary battery is high, the wetting effect is good, and the cycle performance of the cylindrical secondary battery can be improved, while when P2<0.6 or P2>3.5, the capacity retention rate of the cylindrical secondary battery is low, the wetting effect is lacking, and the cylindrical secondary battery appears moderate or even severe lithium precipitation.

[0207] Preferably, when 0.8≤P2≤1.5, the capacity retention rate of the cylindrical secondary battery is higher, the wetting effect is better and the cycle performance of the cylindrical secondary battery can be better improved.

[0208] Regarding H2 / S2 and the influence of H2 on the performance of the cylindrical secondary battery

[0209] Cylindrical secondary batteries of Examples G1 to G7, Examples G8 to G14 and Comparative Examples G1 to G4 were prepared based on Example 3. Among them, the only difference of Examples G1 to G7, Examples G8 to G14, Comparative Examples G1 to G4 is the proportion adjustment parameter in Table 12 and Table 13, please refer to Table 12 and Table 13, Table 12 shows the influence of H2 / S2 on the performance of cylindrical secondary battery 100, Table 13 shows the influence of H2 on the performance of cylindrical secondary battery 100.

[0210] Table 12

[0211] As can be seen from Table 12, when 0.53x10 4 ≤ H2 / S2 ≤ 8x10 4 , the capacity retention rate of the cylindrical secondary battery is high, its infiltration effect is good, and it can improve the cycle performance of the cylindrical secondary battery, while when H2 / S2 < 0.53x10 4 or H2 / S2 > 8x10 4 , the capacity retention rate of the cylindrical secondary battery is low, its infiltration effect is lacking, and the cylindrical secondary battery appears moderate or even severe lithium precipitation.

[0212] Preferably, when 3x10 4 ≤ H2 / S2 ≤ 5x10 4 , the capacity retention rate of the cylindrical secondary battery is higher, its infiltration effect is better and it can better improve the cycle performance of the cylindrical secondary battery.

[0213] Table 13

[0214] As can be seen from Table 13, when 0.3 ≤ H2 ≤ 4, the capacity retention rate of the cylindrical secondary battery is high, its infiltration effect is good, and it can improve the cycle performance of the cylindrical secondary battery, while when H2 < 0.3 or H2 > 4, the capacity retention rate of the cylindrical secondary battery is low, its infiltration effect is lacking, and the cylindrical secondary battery appears moderate or even severe lithium precipitation.

[0215] Preferably, when 0.8 ≤ H2 ≤ 2, the capacity retention rate of the cylindrical secondary battery is higher, its infiltration effect is better and it can better improve the cycle performance of the cylindrical secondary battery.

[0216] Regarding W2 / S2 and the influence of W2 on the performance of the cylindrical secondary battery

[0217] Cylindrical secondary batteries of Examples M1 to M6, Examples M7 to M12 and Comparative Examples M1 to M4 were prepared based on Example 3. Among them, Examples M1 to M6 and Comparative Examples M1, M2 are relative to Example 3 (W2 is 8.6 mg / cm 2The difference between the cylindrical secondary battery of the embodiment M1 and the cylindrical secondary battery of the embodiment M2 is that: first, W2 is 10 mg / cm2 2 ; second, the parameters are adjusted according to the proportion in Table 14. The difference between the cylindrical secondary battery of the embodiment M7 to the cylindrical secondary battery of the embodiment M12, the comparative example M3, the comparative example M4 and the cylindrical secondary battery of the embodiment 3 is that the parameters are adjusted according to the proportion in Table 15. Please refer to Table 14 and Table 15, Table 14 shows the influence of W2 / S2 on the performance of the cylindrical secondary battery 100, and Table 15 shows the influence of W2 on the performance of the cylindrical secondary battery 100.

[0218] Table 14

[0219] As shown in Table 14, when 0.93x10 4 ≤W2 / S2≤80x10 4 , the capacity retention rate of the cylindrical secondary battery is high, the wetting effect is good, and the cycle performance of the cylindrical secondary battery can be improved, and when W2 / S2<0.93x10 4 or W2 / S2>80x10 4 , the capacity retention rate of the cylindrical secondary battery is low, the wetting effect is poor, and the cylindrical secondary battery appears moderate or even severe lithium precipitation.

[0220] Preferably, when 9x10 4 ≤W2 / S2≤50x10 4 , the capacity retention rate of the cylindrical secondary battery is higher, the wetting effect is better, and the cycle performance of the cylindrical secondary battery can be better improved.

[0221] Table 15

[0222] As shown in Table 15, when 8≤W2≤30, the capacity retention rate of the cylindrical secondary battery is high, the wetting effect is good, and the cycle performance of the cylindrical secondary battery can be improved, and when W2<8 or W2>30, the capacity retention rate of the cylindrical secondary battery is low, the wetting effect is poor, and the cylindrical secondary battery appears moderate or even severe lithium precipitation.

[0223] Preferably, when 14≤W2≤20, the capacity retention rate of the cylindrical secondary battery is higher, the wetting effect is better, and the cycle performance of the cylindrical secondary battery can be better improved.

[0224] The embodiment of the present application also provides an example of a power consuming device, which comprises a load and the cylindrical secondary battery 100 described above. The cylindrical secondary battery 100 is connected to the load, and the cylindrical secondary battery 100 is used to supply power to the load.

[0225] The power consuming device can be an energy storage product, a mobile phone, a tablet, a drone, an electric vehicle with one wheel or more than two wheels, or an electric cleaning tool, etc.

[0226] For example, for the unmanned aerial vehicle described above, the battery pack is carried on the unmanned aerial vehicle, and the battery pack is used to supply power to the load on the unmanned aerial vehicle, including the flight system, the control system, the camera system and the like.

[0227] It should be noted that the preferred embodiments of the present application are given in the specification and drawings of the present application, but the present application can be realized in many different forms, and is not limited to the embodiments described in the specification. These embodiments are not additional limitations on the content of the present application, and the purpose of providing these embodiments is to make the understanding of the disclosed content of the present application more thorough and comprehensive. Furthermore, the above technical features continue to combine with each other to form various embodiments not listed above, which are all considered to be within the scope of the present application. Furthermore, for those skilled in the art, the above description can be improved or transformed, and all these improvements and transformations should be within the protection scope of the appended claims of the present application.

Claims

1. A cylindrical secondary battery (100) comprising a housing (1) and a jelly-roll (2) accommodated in the housing (1), the jelly-roll (2) comprising a first electrode plate (21) and a separator (22), the first electrode plate (21) comprising a first main body portion (211) and a first empty-foil portion (212) in sequence along an axial direction of the jelly-roll (2), the first main body portion (211) comprising a first current collector (2111) and a first active material layer (2112) coated on at least one surface of the first current collector (2111), the first empty-foil portion (212) comprising a first tab portion (2121), the first tab portion (2121) being a portion of the first empty-foil portion (212) protruding beyond the separator (22) along the axial direction of the jelly-roll (2), and at least a portion of the first tab portion (2121) forming a first flattened portion (21211), characterized in that a first groove (21121) is formed on a surface of the first active material layer (2112), the first groove (21121) extending along the axial direction of the jelly-roll (2) and penetrating through one end surface (2112a) of the first active material layer (2112) along the axial direction of the jelly-roll (2), wherein the cylindrical secondary battery (100) satisfies at least one of the following conditions: (1) 0.3≤f1≤1, wherein a ratio of a length of the first groove (21121) to a length of the first active material layer (2112) along the axial direction of the jelly-roll (2) is f1; (2) the first groove (21121) has a number of at least two, and the cylindrical secondary battery (100) satisfies at least one of the following conditions: when n≤0.3N, 2.5≤K≤3.5; when 0.3N wherein N is a total number of winding turns of the first electrode plate (21) in the jelly-roll (2), n is the n th winding turn of the first active material layer (2112) in the jelly-roll (2), and K is a distance between two adjacent first grooves (21121) in the n th winding turn of the first active material layer (2112) along a circumferential direction of the jelly-roll (2), and the unit of K is mm. The first groove (21121) comprises a first sub-groove (21121a) and a second sub-groove (21121b), the first sub-groove (21121a) penetrating through one end surface (2112a) of the first active material layer (2112) along the axial direction of the jelly-roll (2), and the second sub-groove (21121b) penetrating through the other end surface (2112b) of the first active material layer (2112) along the axial direction of the jelly-roll (2) ; and The cylindrical secondary battery (100) satisfies: 0.53 x 10 4 ≤ P1 / S1 ≤ 6 x 10 4 , where the density of the first flattening portion (21211) is P1 g / cm 3 , 0.6 ≤ P1 ≤ 3.5, and the cross-sectional area of the first groove (21121) in the radial direction of the jelly-roll (2) is S1 mm 2 .

2. The cylindrical secondary battery (100) according to claim 1, characterized by 0.53 x 10 4 ≤ H1 / S1 ≤ 8 x 10 4 In the axial direction of the core (2), the first flattening portion (21211) includes a first surface (21211a) facing away from the separator film (22), the separator film (22) includes a first end surface (22a) and a second end surface (22b), the first end surface (22a) is closer to the first surface (21211a) than the second end surface (22b), the distance between the first surface (21211a) and the first end surface (22a) is H1 mm, and 0.3 ≤ H1 ≤ 4.

3. The cylindrical secondary battery (100) according to claim 2, characterized by 0.8≤H1≤2。 4. The cylindrical secondary battery (100) according to any one of claims 1 to 3, characterized by 0.93 x 10 4 ≤ W1 / S1 ≤ 80 x 10 4 wherein the first active material layer (2112) on the first electrode tab (21) has a coating mass per unit area of W1 mg / cm 2 8 ≤ W1 ≤ 30.

5. The cylindrical secondary battery (100) according to claim 4, characterized by 14≤W1≤20。 6. The cylindrical secondary battery (100) according to any one of claims 1 to 5, characterized by a projection of the first sub-groove (21121a) on the first current collector (2111) along a radial direction of the jelly-roll (2) is separated from a projection of the second sub-groove (21121b) on the first current collector (2111) along the radial direction of the jelly-roll (2). ​ (2)0.25×10 -4 ≤S1≤1.5×10 -4 。 7. The cylindrical secondary battery (100) according to claim 6, characterized by ​ (3)0.5≤f1≤0.8； (4)0.8≤P1≤1.5； (5)1×10 -4 ≤S1≤1.4×10 -4 。 8. The cylindrical secondary battery (100) according to any one of claims 1 to 7, characterized by, ​ ​ ​ ​ ​ 9. The cylindrical secondary battery (100) according to any one of claims 1 to 8, characterized by, ​ ​ 10. The cylindrical secondary battery (100) according to any one of claims 1 to 9, characterized by, The number of the first tab portions (2121) is one, and portions of the first tab portions (2121) are mutually superposed from an outer periphery to a central axis in a winding direction of the winding core (2) after being flattened to form the first flattened portion (21211); or The number of the first tab portions (2121) is at least two, and each of the first tab portions (2121) is arranged at intervals in a circumferential direction of the winding core (2), and at least two of the first tab portions (2121) are overlapped from an outer periphery to a central axis of the winding core (2) to form the first flattened portion (21211).

11. The cylindrical secondary battery (100) according to any one of claims 1 to 10, characterized by, The winding core (2) comprises a second tab (23), and the winding core (2) is formed by jointly winding the first tab (21), the second tab (23), and a separation film (22) between the first tab (21) and the second tab (23); The second tab (23) comprises a second main body portion (231) and a second empty foil area (232) in sequence, the second main body portion (231) comprises a second current collector (2311) and a second active material layer (2312) coated on at least one surface of the second current collector (2311), and the second empty foil area (232) comprises a second tab portion (2321), along an axial direction of the winding core (2), the second tab portion (2321) is a part of the second empty foil area (232) beyond the separation film (22), and at least a part of the second tab portion (2321) forms a second flattened portion (23211).

12. The cylindrical secondary battery (100) according to claim 11, characterized by A surface of the second active material layer (2312) is provided with a second groove (23121), the second groove (23121) extends along an axial direction of the winding core (2), and the second groove (23121) penetrates through the second active material layer (2312) along one end surface (2312a) of the axial direction of the winding core (2); The cylindrical secondary battery (100) satisfies: 0.53 x 10 4 ≤ P2 / S2 ≤ 6 x 10 4 , where the density of the second flattening part (23211) is P2 g / cm 3 , 0.6 ≤ P2 ≤ 3.5, and the cross-sectional area of the second groove (23121) in the radial direction of the jelly-roll (2) is S2 mm 2 .

13. The cylindrical secondary battery (100) according to claim 12, characterized by 0.53 x 10 4 ≤ H2 / S2 ≤ 8 x 10 4 In the axial direction of the core (2), the second flattening portion (23211) includes a second surface (23211a) facing away from the separator film (22), the separator film (22) includes a first end surface (22a) and a second end surface (22b), the second end surface (22b) is closer to the second surface (23211a) than the first end surface (22a), the distance between the second surface (23211a) and the second end surface (22b) is H2 mm, and 0.3 ≤ H2 ≤ 4.

14. The cylindrical secondary battery (100) according to claim 12, characterized by 0.93 x 10 4 ≤ W2 / S2≤ 80 x 10 4 wherein a coating weight per unit area of the second active material layer (2312) on the second electrode plate (23) is W2 mg / cm 2 8 ≤ W2 ≤ 30.

15. The cylindrical secondary battery (100) according to claim 12, characterized by A cross-sectional shape of the first groove (21121) is semicircular, triangular, or rectangular; And / or, A cross-sectional shape of the second groove (23121) is semicircular, triangular, or rectangular.

16. The cylindrical secondary battery (100) according to any one of claims 1 to 15, characterized by, The first tab (21) is a negative tab.

17. An electrical device, comprising: The cylindrical secondary battery (100) according to any one of claims 1-16.

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