Cylindrical secondary battery and electric device

Abstract

The invention provides a cylindrical secondary battery and a power utilization device, the cylindrical secondary battery comprises a shell and a roll core, the roll core is accommodated in the shell, the roll core comprises a first pole piece and an isolating membrane, the first pole piece sequentially comprises a first main body part and a first empty foil area, and the first main body part comprises a first current collector and a first active material layer; the first empty foil area comprises a first tab part, and at least part of the first tab part forms a first rubbing part; a first groove is formed in the surface of the first active material layer, extends in the axial direction of the roll core, and penetrates through one end face, in the axial direction of the roll core, of the first active material layer; the cylindrical secondary battery meets the following conditions: 0.53 * 104 < = P1 / S1 < = 6 * 104, the density of the first flattened part is P1 g / cm < 3 >, 0.6 < = P1 < = 3.5, and the cross sectional area of the first groove along the radial direction of the roll core is S1 mm < 2 >. Through the arrangement, electrolyte infiltration is facilitated, and the cycle performance of the cylindrical secondary battery is improved.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a cylindrical secondary battery and an electrical device. Background Art

[0002] A secondary battery is a device that converts external energy into electrical energy and stores it inside, so as to supply power to external electrical devices (such as portable electronic devices, etc.) when needed. At present, secondary batteries are widely used in electrical devices such as unmanned aerial vehicles, mobile phones, tablets, laptop computers, power tools, energy storage, etc. A cylindrical secondary battery is a type of secondary battery, including a housing and a wound core. Among them, the tab of the wound core has a flattened portion, and the flattened portion is likely to cause wetting problems, affecting the performance of the cylindrical secondary battery.

[0003] Application Content

[0004] An embodiment of the present application aims to provide a cylindrical secondary battery and an electrical device to solve the wetting problem caused by the flattened portion of the cylindrical secondary battery in the prior art and improve the cycle performance of the cylindrical secondary battery.

[0005] According to one aspect of the embodiments of the present application, a cylindrical secondary battery is provided, including a housing and a wound core. The wound core is accommodated in the housing. The wound core includes a first electrode plate and a separator. Along the axial direction of the wound core, the first electrode plate sequentially includes a first main body portion and a first bare foil area. The first main body portion includes a first current collector and a first active material layer coated on at least one surface of the first current collector; the first bare foil area includes a first tab portion. Along the axial direction of the wound core, the first tab portion is the part of the first bare foil area that extends beyond the separator, and at least part of the first tab portion forms a first flattened portion; a first groove is formed on the surface of the first active material layer. The first groove extends along the axial direction of the wound core and penetrates one end surface of the first active material layer along the axial direction of the wound core; the cylindrical secondary battery satisfies: 0.53×10 4 ≤P1 / S1≤6×10 4 wherein, the density of the first flattened portion is P1 g / cm 3 , 0.6≤P1≤3.5, and the cross-sectional area of the first groove along the radial direction of the wound core is S1 mm 2 .

[0006] By forming a first groove on the surface of the first active material layer, it is convenient for the electrolyte to infiltrate, improving the cycle performance of the cylindrical secondary battery.

[0007] By limiting the density P1 of the first flattening part, the infiltration problem of the electrolyte is alleviated. Specifically, when P1 < 0.6, when injecting the electrolyte, the electrolyte is not easily distributed evenly, and it is easy to form local accumulation inside the core, and its infiltration effect is not good; when P1 > 3.5, the electrolyte is not easily introduced into the core, and its infiltration effect is lacking. When 0.6 ≤ P1 ≤ 3.5, the capacity retention rate of the cylindrical secondary battery is high, its 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 flow at least partially along the first groove, thereby improving its infiltration effect, and on the other hand, it can reduce the local enrichment of the electrolyte in the first groove and cause side reactions resulting in capacity attenuation. Specifically, when P1 / S1 < 0.53×10 4 , when injecting the electrolyte, the electrolyte is not easily distributed evenly, and it is easy to form local accumulation inside the core, and its infiltration effect is not good; when P1 / S1 > 6×10 4 , the electrolyte is easy to form local enrichment in the first groove and is prone to side reactions. On the one hand, the amount of effective electrolyte that can participate in the charge and discharge 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 regions, resulting in capacity attenuation. When 0.53×10 4 ≤ P1 / S1 ≤ 6×10 4 , the capacity retention rate of the cylindrical secondary battery is high, its 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 facing away from the separator, the separator includes a first end face and a second end face, the first end face is closer to the first surface than the second end face, and the distance between the first surface and the first end face is H1 mm, 0.3 ≤ H1 ≤ 4.

[0010] By limiting the distance H1, the infiltration problem of the electrolyte caused by setting the distance H1 too high is reduced. Specifically, when H1 < 0.3, when injecting the electrolyte, the electrolyte lacks enough time for uniform distribution, and it is easy to form local accumulation inside the core, and its infiltration effect is not good. When H1 > 4, the electrolyte is not easily introduced into the core, and its infiltration effect is lacking. When 0.3 ≤ H1 ≤ 4, the capacity retention rate of the cylindrical secondary battery is high, its infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0011] By defining the proportional relationship between the spacing H1 and the cross-sectional area S1 of the first groove along the radial direction of the core, the wetting effect of the electrolyte is further improved. Specifically, when H1 / S1 < 0.53×10 4 , when injecting the electrolyte, the electrolyte is not easily distributed evenly, and it is easy to form local accumulation inside the core, and its wetting effect is not good. When H1 / S1 > 8×10 4 , the electrolyte is prone to form local enrichment in the first groove and cause side reactions. On the one hand, the amount of effective electrolyte that can participate in the charge and discharge cycle of the cylindrical secondary battery decreases. On the other hand, the local enrichment of the electrolyte in the first groove affects the wetting of other regions, resulting in capacity attenuation. When 0.53×10 4 ≤H1 / S1≤8×10 4 , the capacity retention rate of the cylindrical secondary battery is high, its wetting 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 defining the spacing H1, a preferred solution for improving the wetting problem of the electrolyte is obtained.

[0013] In one or more embodiments, 0.93×10 4 ≤W1 / S1≤80×10 4 , where the coating mass per unit area of the first active material layer on the first electrode sheet is W1 mg / cm 2 , 8 ≤ W1 ≤ 30.

[0014] By defining the coating mass W1 of the first active material layer on the first electrode sheet, the problem of poor wetting of the electrolyte caused by the excessive growth of the diffusion distance of the electrolyte along the radial direction of the core due to the too high setting of the coating mass W1 is reduced, resulting in accelerated cycle decay and lithium deposition. Specifically, when W1 < 8, the coating mass W1 is small, the capacity retention rate of the cylindrical secondary battery is low, and its cycle life and reliability are not good. When W1 > 30, the electrolyte is not easily distributed evenly inside the core, and its wetting effect is lacking. When 8 ≤ W1 ≤ 30, the capacity retention rate of the cylindrical secondary battery is high, its wetting effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0015] By defining the proportional relationship between the coating mass W1 and the cross-sectional area S1 of the first groove along the radial direction of the core, the capacity retention rate of the cylindrical secondary battery and the wetting effect of the electrolyte are further improved. Specifically, when W1 / S1 < 0.93×10 4 , the capacity retention rate of the cylindrical secondary battery is low, and its cycle life and reliability are not good. When W1 / S1 > 80×10 4When the electrolyte is prone to form local enrichment in the first groove and is prone to side reactions, on the one hand, the amount of effective electrolyte that can participate in the charge and discharge cycles of the cylindrical secondary battery decreases. On the other hand, the local enrichment of the electrolyte in the first groove affects the wetting of other regions, thereby leading to capacity attenuation. When 0.93×10 4 ≤W1 / S1≤80×10 4 the capacity retention rate of the cylindrical secondary battery is high, its wetting 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 defining the coating quality W1, a preferred solution for improving the wetting problem of the electrolyte is obtained.

[0017] In one or more embodiments, the cylindrical secondary battery satisfies at least one of the following conditions: (1) 0.3≤f1≤1, where f1 is the ratio of the length of the first groove to the length of the first active material layer along the axial direction of the core; (2) 0.25×10 -4 ≤S1≤1.5×10 -4 . By defining the ratio f1 of the length of the first groove to the length of the first active material layer, or by defining the cross-sectional area S1 of the first groove along the radial direction of the core, on the one hand, the electrolyte can flow at least partially along the first groove, so that the cylindrical secondary battery obtains a wetting effect. On the other hand, it can reduce the local enrichment of the electrolyte in the first groove and the side reactions caused by the local enrichment, resulting in capacity attenuation. Specifically, on the one hand, the amount of effective electrolyte that can participate in the charge and discharge cycles of the cylindrical secondary battery does not decrease due to side reactions. On the other hand, it does not affect the wetting of other regions due to the local enrichment of the electrolyte in the first groove, and does not affect the capacity. That is, whether the ratio f1 of the length of the first groove to the length of the first active material layer is defined, or the cross-sectional area S1 of the first groove along the radial direction of the core is defined, the above two beneficial effects can be achieved. Specifically, when f1<0.3, the length of the first groove is small, and the improvement of the wetting effect of the electrolyte is limited. When 0.3≤f1≤1, the capacity retention rate of the cylindrical secondary battery is high, its wetting effect is good, and the cycle performance of the cylindrical secondary battery can be improved. When S1<0.25×10 -4 the electrolyte is prone to form local enrichment in the first groove and is prone to side reactions. On the one hand, the amount of effective electrolyte that can participate in the charge and discharge cycles of the cylindrical secondary battery decreases. On the other hand, the local enrichment of the electrolyte in the first groove affects the wetting of other regions, thereby leading to capacity attenuation. When S1>1.5×10 -4 the electrolyte is not sufficient to be evenly distributed in the core, and its wetting effect is poor. When 0.25×10 -4 ≤S1≤1.5×10 -4When the time is right, the cylindrical secondary battery has a high capacity retention rate, good infiltration effect, and can improve the cycling performance of the cylindrical secondary battery.

[0018] In one or more embodiments, the cylindrical secondary battery 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 of the first groove to the length of the first active material layer, or further limiting the density P1 of the first flattening portion, or further limiting the cross-sectional area S1 of the first groove along the radial direction of the core, a preferred solution for improving the infiltration 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 satisfies at least one of the following conditions: when n ≤ 0.3N, 2.5 ≤ K ≤ 3.5; when 0.3N < n ≤ 0.8N, 1 ≤ K ≤ 2; when n > 0.8N, 3 ≤ K ≤ 5, where N is the total number of turns of the first pole piece wound in the core, n is the nth turn of the first active material layer wound in the core, and K is the pitch (mm) between two adjacent first grooves in the first active material layer of the nth turn along the circumferential direction of the core. By limiting the distribution of the first grooves on the first active material layer, on the one hand, the electrolyte can flow at least partially along the first grooves to improve the infiltration effect, and on the other hand, the local enrichment of the electrolyte in the first grooves can be reduced. If the electrolyte is locally enriched in the first grooves, side reactions are likely to occur, and the amount of effective electrolyte that can participate in the charge and discharge cycle of the cylindrical secondary battery will decrease. In addition, if the electrolyte is locally enriched in the first grooves, the infiltration of other regions will be affected, resulting in capacity attenuation. 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 infiltration effect of the electrolyte. When 0.3N < n ≤ 0.8N but K < 1, it is easy for the electrolyte to form local enrichment, side reactions are likely to occur, and the infiltration effect of other regions is affected and the processing is difficult. When 0.3N < n ≤ 0.8N but K > 2, it is also easy for the electrolyte to form local enrichment, side reactions are likely to occur, and the infiltration effect of other regions is affected. When n > 0.8N but K < 3, it is easy for the electrolyte to form local enrichment, side reactions are likely to occur, and the infiltration effect of other regions is affected and the processing is difficult. When n > 0.8N but K > 5, it is also easy for the electrolyte to form local enrichment, side reactions are likely to occur, and the infiltration effect of other regions is affected. 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 n value and the K value are matched, the cylindrical secondary battery has a high capacity retention rate, good infiltration effect, and can better improve the cycling performance of the cylindrical secondary battery.

[0020] In one or more embodiments, the first groove includes a first sub-groove and a second sub-groove. The first sub-groove penetrates one end face of the first active material layer along the axial direction of the core, and the second sub-groove penetrates the other end face of the first active material layer along the axial direction of the core. In the radial direction of the core, the projection of the first sub-groove on the first current collector is separated from the projection of the second sub-groove on the first current collector. By providing the first sub-groove and the second sub-groove that penetrate the first active material layer through two different end faces of the first active material layer, the electrolyte can be infiltrated from two different end faces 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 ears is one, and each part of the first tab ears overlaps with each other from the outer circle to the central axis along the winding direction of the core after being flattened to form a first flattened part; or the number of the first tab ears is at least two, and each first tab ear is arranged at intervals along the circumferential direction of the core, and at least two first tab ears overlap from the outer circle to the central axis of the core after being flattened to form a first flattened part. Thus, the first flattened part can be formed.

[0022] In one or more embodiments, the core includes a second pole piece, and the core is formed by coiling the first pole piece, the second pole piece, and the separator located between the first pole piece and the second pole piece. The second pole piece sequentially includes a second main body part and a second empty foil area. The second main body part includes a second current collector and a second active material layer coated on at least one surface of the second current collector. The second empty foil area includes a second tab ear. Along the axial direction of the core, the second tab ear is the part where the second empty foil area extends beyond the separator, and at least part of the second tab ear forms a second flattened part. Thus, not only the first tab ear of the first pole piece can form a first flattened part, but also the second tab ear of the second pole piece spaced from the first pole piece can form a second flattened part.

[0023] In one or more embodiments, a second groove is formed on the surface of the second active material layer. The second groove extends along the axial direction of the core and penetrates one end face of the second active material layer along the axial direction of the core. The cylindrical secondary battery satisfies: 0.53×10 4 ≤P2 / S2≤6×10 4 , where the density of the second flattened part is P2 g / cm 3 , 0.6≤P2≤3.5, and the cross-sectional area of the second groove along the radial direction of the core is S2mm 2 .

[0024] By forming the second groove on the surface of the second active material layer, it is convenient for the electrolyte to infiltrate and improves the cycling performance of the cylindrical secondary battery.

[0025] By limiting the density P2 of the second flattening portion, the electrolyte infiltration problem is alleviated. Specifically, when P2 < 0.6, when injecting the electrolyte, the electrolyte is not easily distributed evenly, and it is easy to form local accumulation inside the core, and its infiltration effect is not good. When P2 > 3.5, the electrolyte is not easily introduced into the core, and its infiltration effect is lacking. When 0.6 ≤ P2 ≤ 3.5, the capacity retention rate of the cylindrical secondary battery is high, its 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 portion and the cross-sectional area S2 of the second groove along the radial direction of the core, on the one hand, the electrolyte can flow at least partially along the second groove to improve its infiltration effect, and on the other hand, it can reduce the local enrichment of the electrolyte in the second groove, reduce the occurrence of side reactions, and reduce the influence on the infiltration effect of other regions. Specifically, when P2 / S2 < 0.53×10 4 When injecting the electrolyte, the electrolyte is not easily distributed evenly, and it is easy to form local accumulation inside the core, and its infiltration effect is not good. When P2 / S2 > 6×10 4 When injecting the electrolyte, the electrolyte is easy to form local enrichment in the second groove, is prone to side reactions, and affects the infiltration effect of other regions. When 0.53×10 4 ≤ P2 / S2 ≤ 6×10 4 When injecting the electrolyte, the electrolyte is not easily distributed evenly, and it is easy to form local accumulation inside the core, and its infiltration effect is not good. When P2 / S2 > 6×10

[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 portion includes a second surface facing away from the separator, the separator includes a first end face and a second end face, the second end face is closer to the second surface than the first end face, and the distance between the second surface and the second end face is H2 mm, 0.3 ≤ H2 ≤ 4.

[0028] By limiting the distance H2, the electrolyte infiltration problem caused by setting the distance H2 too high is reduced. Specifically, when H2 < 0.3, when injecting the electrolyte, the electrolyte lacks enough time to be evenly distributed, and it is easy to form local accumulation inside the core, and its infiltration effect is not good. When H2 > 4, the electrolyte is not easily introduced into the core, and its infiltration effect is lacking. When 0.3 ≤ H2 ≤ 4, the capacity retention rate of the cylindrical secondary battery is high, its infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0029] By defining 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 wetting effect of the electrolyte is further improved. Specifically, when H2 / S2 < 0.53×10 4 , when injecting the electrolyte, the electrolyte is not easily distributed evenly, and it is easy to form local accumulation inside the core, and its wetting effect is not good. When H2 / S2 > 8×10 4 , the electrolyte is likely to form local enrichment in the first groove, and side reactions are likely to occur, and it affects the wetting effect of other regions. When 0.53×10 4 ≤H2 / S2≤8×10 4 , the capacity retention rate of the cylindrical secondary battery is high, its wetting 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 , where the coating mass per unit area of the second active material layer on the second electrode is W2 mg / cm 2 , 8≤W2≤30.

[0031] By defining the coating mass W2 per unit area of the second active material layer on the second electrode, the problem of poor wetting of the electrolyte caused by the excessive growth of the diffusion distance of the electrolyte along the radial direction of the core due to the too high setting of the coating mass W2, resulting in accelerated cycle decay and lithium plating, is reduced. Specifically, when W2 < 8, the coating mass W2 is small, the capacity retention rate of the cylindrical secondary battery is low, and its cycle life and reliability are not good. When W2 > 30, the electrolyte is not easily distributed evenly inside the core, and its wetting effect is lacking. Specifically, the problem of poor wetting of the electrolyte caused by the increase in the diffusion distance of the electrolyte along the radial direction of the core of the second electrode, resulting in accelerated cycle decay and lithium plating. When 8≤W2≤30, the capacity retention rate of the cylindrical secondary battery is high, its wetting effect is good, and the cycle performance of the cylindrical secondary battery can be improved.

[0032] By defining 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 wetting 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 its cycle life and reliability are not good. When W2 / S2 > 80×10 4 , the electrolyte is likely to form local enrichment in the second groove, and side reactions are likely to occur, and it affects the wetting effect of other regions. When 0.93×10 4 ≤W2 / S2≤80×10 4When the time is right, the cylindrical secondary battery has a high capacity retention rate, good infiltration effect, and can improve the cycling performance of the cylindrical secondary battery.

[0033] In one or more embodiments, the cross-sectional shape of the first groove is semi-circular, triangular or rectangular; and / or, the cross-sectional shape of the second groove is semi-circular, triangular or rectangular. This facilitates the electrolyte to flow at least partially along the first groove and / or the second groove, thereby improving its infiltration effect.

[0034] In one or more embodiments, the first electrode sheet is a negative electrode sheet. Generally, poor infiltration of the negative electrode has a great impact on the performance of the cylindrical secondary battery. By providing the above-mentioned first groove on the negative electrode sheet, the influence of the electrolyte infiltration problem 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, an electrical device is provided, including the above-mentioned cylindrical secondary battery. Description of the Drawings

[0036] One or more embodiments are exemplarily illustrated by corresponding drawings. These exemplary illustrations do not limit the embodiments. Elements with the same reference numerals in the drawings represent similar elements, unless otherwise stated, the dimensions in the drawings do not constitute a proportional limitation.

[0037] Figure 1 is a schematic diagram of the cylindrical secondary battery provided by the embodiments of the present application;

[0038] Figure 2 is along the Figure 1 A-A cross-sectional view in

[0039] Figure 3 is a schematic diagram of the winding core without the first flattening portion and the second flattening portion provided by the embodiments of the present application;

[0040] Figure 4 is a schematic diagram of the unfolded first electrode sheet with one first groove provided by the embodiments of the present application;

[0041] Figure 5 is a schematic diagram of the unfolded first electrode sheet with multiple first grooves provided by the embodiments of the present application;

[0042] Figure 6 is a schematic diagram of the winding core with the first flattening portion and the second flattening portion formed provided by the embodiments of the present application;

[0043] Figure 7 is along the Figure 4 B-B1 cross-sectional view in

[0044] Figure 8is a cross-sectional view taken along B-B in Figure 5 ;

[0045] Fig. 9 is a schematic diagram of another implementation of the unfolded first pole piece provided by an embodiment of the present application;

[0046] Fig.10 is a schematic diagram of another implementation of the unfolded first pole piece provided by an embodiment of the present application;

[0047] Fig.11 is a schematic diagram of the unfolded second pole piece provided by an embodiment of the present application with a second groove provided;

[0048] Fig.12 is a schematic diagram of the unfolded second pole piece provided by an embodiment of the present application with a plurality of second grooves provided;

[0049] Fig.13 is a cross-sectional view taken along C-C1 in Fig.11 ;

[0050] Fig.14 is a cross-sectional view taken along C-C in Fig.12 ;

[0051] Reference numerals:

[0052] Cylindrical secondary battery 100;

[0053] Shell 1, winding core 2, first pole piece 21, separator 22, second pole piece 23;

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

[0055] First groove 21121, one end face 2112a of the first active material layer along the axial direction of the winding core, the other end face 2112b;

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

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

[0058] Second main body portion 231, second empty foil region 232, second current collector 2311, second active material layer 2312, second groove 23121, one end face 2312a of the second active material layer along the axial direction of the winding core;

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

[0060] Central axis O, axial direction X, circumferential direction Z1, winding direction Z2, radial direction Y, and longitudinal direction Z. Specific embodiments

[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Apparently, the described embodiments are 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 are not 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 efforts shall fall within the protection scope of the present application.

[0062] It should be noted that when an element is expressed as "fixed to" another element, it can be directly on the other element, or there can be one or more intermediate elements therebetween. When an element is expressed as "connected to" another element, it can be directly connected to the other element, or there can be one or more intermediate elements therebetween. The terms "vertical", "horizontal", "left", "right" and similar expressions used in this specification are only for the purpose of illustration.

[0063] In the description of the present application, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Without further statement, the above terms have no special meaning, and thus cannot be construed as limiting the protection scope of the present application.

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

[0065] Please refer to Figure 1 and Figure 2 , the present application provides a cylindrical secondary battery 100, including a housing 1 and a wound core 2, and the wound core 2 is accommodated in the housing 1. The cylindrical secondary battery 100 is used to connect to an external circuit. The above external circuit refers to the circuit part connected between the cylindrical secondary battery 100 and the outside world. The external circuit can be a load circuit in an electrical device, so that the secondary battery 100 can output the electrical energy stored in the wound core 2 to the outside, or it can be a power input circuit of an electrical device, so that external electrical energy is input inward to replenish energy for the wound core 2.

[0066] The cylindrical secondary battery 100 of the present application is not particularly limited and may include any device that undergoes an electrochemical reaction. In some embodiments, the cylindrical secondary battery 100 may 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 inside the housing 1 and is used to infiltrate the wound core 2.

[0068] Regarding the specific structure of the housing 1, no specific limitation is made here. It only needs to meet the usage requirements that the space defined by the housing 1 itself for accommodating the wound core 2 is isolated from the external environment outside the housing 1 and can stably store the electrolyte.

[0069] For the above-mentioned wound core 2, please refer to Figure 3 , the wound core 2 includes a first electrode tab 21 and a separator 22. The first electrode tab 21 and the separator 22 are wound to form the wound core 2. The direction where the central axis O of the wound core 2 is located is defined as the axial direction X of the wound core 2. The winding direction Z2 of the first electrode tab 21 and the separator 22 is the winding direction Z2 of the wound core 2. Among them, for one turn of the winding of the first electrode tab 21, its winding direction Z2 is defined as the circumferential direction Z1 of the wound core 2. The direction from the central axis O of the wound core 2 towards the housing 1 is defined as the radial direction Y of the wound core 2, and the radial direction Y is perpendicular to the axial direction X.

[0070] Please refer to Figure 4 , Figure 5 and Figure 6 , along the axial direction X of the wound core 2, the first electrode tab 21 sequentially includes a first main body portion 211 and a first empty foil area 212. The first main body portion 211 includes 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 area 212 includes a first pole ear 2121. Along the axial direction X of the wound core 2, the first pole ear 2121 is the part of the first empty foil area 212 that extends beyond the separator 22, and at least part of the first pole ear 2121 forms a first flattened portion 21211.

[0071] In some embodiments, the number of the first pole ears 2121 is one, and each part of the first pole ear 2121 is superposed on each other from the outer circle towards the central axis O along the winding direction Z2 of the wound core 2 after being flattened to form the first flattened portion 21211; or the number of the first pole ears 2121 is at least two, each first pole ear 2121 is arranged at intervals along the circumferential direction Z1 of the wound core 2, and at least two of the first pole ears overlap from the outer circle of the wound core 2 towards the central axis O after being flattened to form the first flattened portion 21211.

[0072] For the above-mentioned first active material layer 2112, please refer to Figure 4 , Figure 5 , Figure 7 and Figure 8 , a first groove 21121 is formed on the surface of the first active material layer 2112. The first groove 21121 extends along the axial direction X of the core 2, and the first groove 21121 penetrates one end surface 2112a of the first active material layer 2112 along the axial direction X of the core 2; the cylindrical secondary battery 100 satisfies: 0.53×10 4 ≤P1 / S1≤6×10 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 along the radial direction Y of the core 2 is S1 mm 2 . It 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] Wherein, the density of the first flattening portion 21211 is the ratio of the mass of the first flattening portion 21211 to its volume. The specific explanation and test method for the density of the first flattening portion 21211 will be specifically introduced in the following test method.

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

[0075] Wherein, in some embodiments, the number of the first grooves 21121 is multiple, and along the length direction Z after the first pole piece 21 is unfolded, the multiple first grooves 21121 are spaced apart and distributed on the first active material layer 2112. It can be understood that when the number of the first grooves 21121 is multiple, the sum of the cross-sectional areas of all the first grooves 21121 enables the cylindrical secondary battery 100 to satisfy the above conditions (i.e., 0.53×10 4 ≤P1 / S1≤6×10 4 ).

[0076] It can be understood that the processing method of the first groove 21121 can be in various forms. For example, when coating the first active material layer 2112 on the first current collector 2111, some areas are skipped to form the first groove 21121; or when forming the first active material layer 2112, the above first groove 21121 is formed by laser drilling technology, or alternatively, the first active material layer 2112 is coated first and then roll-pressed to form the first groove 21121. The present application is not limited thereto.

[0077] In the embodiment of the present application, by providing a first groove 21121 on the surface of the first active material layer 2112, it is convenient for the electrolyte to infiltrate, thereby improving the cycling performance of the cylindrical secondary battery 100. By defining the density P1 of the first flattening portion 21211, the infiltration problem of the electrolyte is alleviated. Specifically, when P1 < 0.6, when injecting the electrolyte, the electrolyte is not easily distributed evenly, and it is easy to form local accumulation inside the core, and its infiltration effect is poor. When P1 > 3.5, the electrolyte is not easily introduced into the core 2, and its infiltration effect is somewhat lacking. When 0.6 ≤ P1 ≤ 3.5, the cylindrical secondary battery 100 has a high capacity retention rate, its infiltration effect is good, and it can improve the cycling performance of the cylindrical secondary battery 100.

[0078] In addition, through the research of the inventor, it is found that in order to obtain a good infiltration effect, the size of the density P1 of the first flattening portion 21211 will directly affect the setting of the cross-sectional area S1 of the first groove 21121. Therefore, by defining 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 core 2 (i.e., 0.53×10 4 ≤ P1 / S1 ≤ 6×10 4 ), on the one hand, the electrolyte can flow at least partially along the first groove 21121 to improve its infiltration effect, and on the other hand, it can reduce the local enrichment of the electrolyte in the first groove 21121 and affect the infiltration effect. Specifically, when P1 / S1 < 0.53×10 4 , when injecting the electrolyte, the electrolyte is not easily distributed evenly, and it is easy to form local accumulation inside the core 2, and side reactions are likely to occur. Then, on the one hand, the amount of effective electrolyte that can participate in the charge and discharge cycle of the cylindrical secondary battery 100 is reduced, and on the other hand, the electrolyte is locally enriched inside the core 2, which affects the infiltration of other regions, resulting in capacity attenuation. When P1 / S1 > 6×10 4 , the electrolyte is easily locally enriched in the first groove 21121, and side reactions are likely to occur. Then, on the one hand, the amount of effective electrolyte that can participate in the charge and discharge cycle of the cylindrical secondary battery 100 is reduced, and on the other hand, the electrolyte is locally enriched inside the first groove 21121, which affects the infiltration of other regions, resulting in capacity attenuation. When 0.53×10 4 ≤ P1 / S1 ≤ 6×10 4 , the cylindrical secondary battery 100 has a high capacity retention rate, its infiltration effect is good, and it can improve the cycling performance of the cylindrical secondary battery 100. Preferably, when 2×10 4 ≤ P1 / S1 ≤ 4.5×10 4 , the cylindrical secondary battery 100 has an even higher capacity retention rate, its infiltration effect is better and it can better improve the cycling performance of the cylindrical secondary battery 100.

[0079] In some embodiments, along the axial direction X of the core 2, the first flattening portion 21211 faces away from the first surface 21211a of the separator 22. The separator 22 includes a first end face 22a and a second end face 22b. The first end face 22a is closer to the first surface 21211a than the second end face 22b. The distance between the first surface 21211a and the first end face 22a is H1 mm, where 0.3 ≤ H1 ≤ 4, and 0.53×10 4 ≤ H1 / S1 ≤ 8×10 4 .

[0080] By limiting the distance H1, the problem of electrolyte infiltration caused by an overly high setting of the distance H1 is reduced. Specifically, when H1 < 0.3, when injecting the electrolyte, the electrolyte does not have enough time to be evenly distributed, and it is easy to form local accumulation inside the core 2, and its infiltration effect is not good. When H1 > 4, the electrolyte is not easy to enter the inside of the core 2, and its infiltration effect is lacking. When 0.3 ≤ H1 ≤ 4, the capacity retention rate of the cylindrical secondary battery 100 is high, its infiltration effect is good, and the cycle performance of the cylindrical secondary battery 100 can be improved.

[0081] In addition, the inventors have found through research that in order to obtain a good infiltration effect, the size of the distance H1 will directly affect the setting of the cross-sectional area S1 of the first groove 21121. 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 core 2 (i.e., 0.53×10 4 ≤ H1 / S1 ≤ 8×10 4 ), the infiltration effect of the electrolyte is further improved. Specifically, when H1 / S1 < 0.53×10 4 , when injecting the electrolyte, the electrolyte is not easy to be evenly distributed, and it is easy to form local accumulation inside the core 2, and its infiltration effect is not good. When H1 / S1 > 8×10 4 , the electrolyte is easy to form local enrichment in the first groove 21121, and side reactions are likely to occur. On the one hand, the amount of effective electrolyte that can participate in the charge and discharge cycle of the cylindrical secondary battery 100 is reduced. On the other hand, the electrolyte is locally enriched inside the first groove 21121, which affects the infiltration of other regions, resulting in capacity decay. When 0.53×10 4 ≤ H1 / S1 ≤ 8×10 4 , the capacity retention rate of the cylindrical secondary battery 100 is high, its infiltration effect is good, and the cycle performance of the cylindrical secondary battery 100 can be improved.

[0082] Preferably, when 3×10 4 ≤ H1 / S1 ≤ 5×10 4When the time is right, the capacity retention rate of the cylindrical secondary battery 100 is higher, its infiltration effect is better, and it can better improve the cycling performance of the cylindrical secondary battery 100.

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

[0084] In some embodiments, 0.8 ≤ H1 ≤ 2. By further limiting the spacing 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 sheet 21 is W1 mg / cm 2 , where 8 ≤ W1 ≤ 30, 0.93×10 4 ≤ W1 / S1 ≤ 80×10 4 .

[0086] By limiting the coating mass per unit area W1 of the first active material layer 2112 on the first electrode sheet 21, the problem of poor infiltration of the electrolyte caused by the excessive growth of the diffusion distance of the electrolyte along the radial direction Y of the core 2 due to the too high coating mass per unit area W1 of the first active material layer 2112 on the first electrode sheet 21 is reduced, resulting in accelerated cycle decay and lithium deposition. Specifically, when W1 < 8, the coating mass W1 is small, the capacity retention rate of the cylindrical secondary battery 100 is low, and its cycle life and reliability are poor. When W1 > 30, the electrolyte is not easily distributed evenly inside the core 2, and its infiltration effect is lacking. When 8 ≤ W1 ≤ 30, the capacity retention rate of the cylindrical secondary battery 100 is high, its infiltration effect is good, and it can improve the cycling performance of the cylindrical secondary battery 100.

[0087] In addition, the inventors have found through research that in order to obtain a better infiltration effect, the size of the coating mass W1 will directly affect the setting of the cross-sectional area S1 of the first groove 21121. Therefore, by limiting the proportional relationship between the coating mass W1 and the cross-sectional area S1 of the first groove 21121 along the radial direction Y of the core 2 (that is, 0.93×10 4 ≤ W1 / S1 ≤ 80×10 4 ), the capacity retention rate of the cylindrical secondary battery 100 and the infiltration effect of the electrolyte are further improved. Specifically, when W1 / S1 < 0.93×10 4 , the capacity retention rate of the cylindrical secondary battery 100 is low, and its cycle life and reliability are poor. When W1 / S1 > 80×10 4When this occurs, the electrolyte is prone to form local enrichment in the first groove 21121, and side reactions are likely to occur. On the one hand, the amount of effective electrolyte that can participate in the charge-discharge cycle of the cylindrical secondary battery 100 decreases. On the other hand, the local enrichment of the electrolyte inside the first groove 21121 affects the wetting of other regions, thereby leading to capacity decay. When 0.93×10 4 ≤W1 / S1≤80×10 4 When this is the case, the cylindrical secondary battery 100 has a high capacity retention rate, good wetting effect, and can improve the cycling performance of the cylindrical secondary battery 100. In some embodiments, when 9×10 4 ≤W1 / S1≤50×10 4 When this is the case, the cylindrical secondary battery 100 has an even higher capacity retention rate, better wetting effect, and can better improve the cycling performance of the cylindrical secondary battery 100.

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

[0089] In some embodiments, please refer to Figure 5 or Fig. 9 , along the axial direction X of the 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, Figure 5 and Fig. 9 The difference is Fig. 9 In -4 ≤S1≤1.5×10 -4By defining 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 defining the cross-sectional area S1 of the first groove 21121 along the radial direction Y of the core 2, on the one hand, the electrolyte can flow at least partially along the first groove 21121 to obtain a wetting 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 and discharge cycles of the cylindrical secondary battery 100. In addition, it does not affect the wetting of other regions due to the local enrichment of the electrolyte in the first groove 21121, and does not affect 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 defined, or the cross-sectional area S1 of the first groove 21121 along the radial direction Y of the core 2 is defined, the above two beneficial effects can be achieved. Specifically, when f1 < 0.3, the length L1 of the first groove 21121 is small, and the improvement of the wetting effect of the electrolyte is limited. When 0.3 ≤ f1 ≤ 1, the capacity retention rate of the cylindrical secondary battery 100 is high, its wetting effect is good, and the cycle performance of the cylindrical secondary battery 100 can be improved. When S1 < 0.25×10 -4 When, the electrolyte is likely to form local enrichment in the first groove 21121, and side reactions are likely to occur. Then, on the one hand, the amount of effective electrolyte that can participate in the charge and discharge cycles 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 wetting of other regions, resulting in capacity attenuation. When S1 > 1.5×10 -4 When, the electrolyte is not sufficient to be evenly distributed inside the core 2, and its wetting effect is not good. When 0.25×10 -4 ≤ S1 ≤ 1.5×10 -4 When, the capacity retention rate of the cylindrical secondary battery 100 is high, its wetting effect is good, and the cycle performance of the cylindrical secondary battery 100 can be improved.

[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 defining the ratio f1 of the length L1 of the first groove 21121 to the length L2 of the first active material layer 2112, or further defining the density P1 of the first flattening portion 21211, or further defining the cross-sectional area S1 of the first groove 21121 along the radial direction Y of the core 2, a preferred solution for improving the wetting problem of the electrolyte can be obtained.

[0091] In some embodiments, the number of the first grooves 21121 is 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 < n ≤ 0.8N, 1 ≤ K ≤ 2; when n > 0.8N, 3 ≤ K ≤ 5, where N is the total number of turns of the winding of the first pole piece 21 in the winding core 2, n is the nth turn of the winding of the first active material layer 2112 in the winding core 2, and K is the spacing (mm) between two adjacent first grooves 21121 in the first active material layer 2112 of the nth turn along the circumferential direction Z1 of the winding core 2. By defining the distribution of the first grooves 21121 on the first active material layer 2112, on the one hand, the electrolyte can flow at least partially along the first grooves 21121, thereby improving its wetting effect; on the other hand, the local enrichment of the electrolyte in the first grooves 21121 can be reduced, and the probability of side reactions can be reduced, without affecting the amount of effective electrolyte that can participate in the charge and discharge cycles of the cylindrical secondary battery 100. In addition, it does not affect the wetting of the electrolyte in other regions, and on the other hand, it alleviates 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 < n ≤ 0.8N but K < 1, it is easy to cause local enrichment of the electrolyte and side reactions to occur. On the one hand, the amount of effective electrolyte that can participate in the charge and discharge cycles of the cylindrical secondary battery 100 is reduced. On the other hand, the electrolyte is locally enriched inside the first grooves 21121, which affects the wetting of other regions, resulting in capacity attenuation. When 0.3N < n ≤ 0.8N but K > 2, it is also easy to cause local enrichment of the electrolyte and side reactions to occur. On the one hand, the amount of effective electrolyte that can participate in the charge and discharge cycles of the cylindrical secondary battery 100 is reduced. On the other hand, the electrolyte is locally enriched inside the first grooves 21121, which affects the wetting of other regions, resulting in capacity attenuation. When n > 0.8N but K < 3, it is easy to cause local enrichment of the electrolyte and side reactions to occur. On the one hand, the amount of effective electrolyte that can participate in the charge and discharge cycles of the cylindrical secondary battery 100 is reduced. On the other hand, the electrolyte is locally enriched inside the first grooves 21121, which affects the wetting of other regions, resulting in capacity attenuation and difficult processing. When n > 0.8N but K > 5, it is also easy to cause local enrichment of the electrolyte and side reactions to occur. On the one hand, the amount of effective electrolyte that can participate in the charge and discharge cycles of the cylindrical secondary battery 100 is reduced. On the other hand, the electrolyte is locally enriched inside the first grooves 21121, which affects the wetting of other regions, resulting in capacity attenuation.

[0092] In addition, through the research of the inventor, it is found that in order to obtain a better wetting 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 < n ≤ 0.8N and 1 ≤ K ≤ 2, or when n > 0.8N and 3 ≤ K ≤ 5, the values of n and K match, the capacity retention rate of the cylindrical secondary battery 100 is high, its wetting effect is good, and the cycle performance of the cylindrical secondary battery 100 can be better improved.

[0093] For example, when N is 10, when n ≤ 3, 2.5 ≤ K ≤ 3.5; when 3 < n ≤ 8, 1 ≤ K ≤ 2; when n > 8, 3 ≤ K ≤ 5.

[0094] In some embodiments, please refer 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 one end face 2112a of the first active material layer 2112 along the axial direction X of the core 2, and the second sub-groove 21121b penetrates the other end face 2112b of the first active material layer 2112 along the axial direction X of the core 2; along 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 providing the first sub-groove 21121a and the second sub-groove 21121b that penetrate the first active material layer 2112 through two different end faces of the first active material layer 2112, the electrolyte can be infiltrated from two different end faces of the first active material layer 2112, the wetting effect of the electrolyte can be further improved, and the application scenario of the cylindrical secondary battery 100 can be expanded.

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

[0096] It can be understood that if the first electrode plate 21 is a negative electrode plate, the first current collector 2111 includes but is not limited to one or two of conductive metal thin plates such as copper foil and nickel foil. As an example, the first current collector 2111 is made of 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, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium carbonate, or other metals that can form alloys with lithium.

[0097] In some embodiments, please refer to Figure 2 , Figure 3 , Figure 6 , Fig.11 and Fig.12 , the core 2 includes a second pole piece 23. The core 2 is formed by winding together the first pole piece 21, the separator 22, the second pole piece 23, and another separator 22 (not shown in the figure) after they are stacked. Among them, the polarities of the first pole piece 21 and the second pole piece 23 are opposite. The second pole piece 23 sequentially includes a second main body portion 231 and a second empty foil region 232. The second main body portion 231 includes 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 empty foil region 232 includes a second pole ear 2321. Along the axial direction X of the core 2, the second pole ear 2321 is the part of the second empty foil region 232 that extends beyond the separator 22, and at least a part of the second pole ear 2321 forms a second flattened portion 23211. Thus, not only can the first pole ear 2121 of the first pole piece 21 form a first flattened portion 21211, but also the second pole ear 2321 of the second pole piece 23 spaced apart from the first pole piece 21 can form a second flattened portion 23211.

[0098] Among them, a second groove 23121 is formed on the surface of the second active material layer 2312. The second groove 23121 extends along the axial direction X of the core 2, and the second groove 23121 penetrates one end face 2312a of the second active material layer 2312 along the axial direction X of the core 2; the cylindrical secondary battery 100 satisfies: 0.53×10 4 ≤P2 / S2≤6×10 4 , where the density of the second flattened portion 23211 is P2 g / cm 3 , 0.6≤P2≤3.5, and the cross-sectional area of the second groove 23121 along the radial direction Y of the 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 this one second groove 23121; in some embodiments, the number of the second grooves 23121 on the second active material layer 2312 is multiple (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 forming the second groove 23121 on the surface of the second active material layer 2312, it is convenient for the electrolyte 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, when injecting the electrolyte, the electrolyte is not easily distributed evenly, and it is easy to form local accumulation inside the core, and its infiltration effect is not good. When P2 > 3.5, the electrolyte is not easily introduced into the core 2, and its infiltration effect is somewhat lacking. When 0.6 ≤ P2 ≤ 3.5, the capacity retention rate of the cylindrical secondary battery 100 is high, its infiltration effect is good, and the cycle performance of the cylindrical secondary battery 100 can be improved.

[0101] In addition, through the inventor's research, it is found that in order to obtain a better 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. Therefore, by limiting the proportional relationship 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 (i.e., 0.53×10 4 ≤ P2 / S2 ≤ 6×10 4 ), on the one hand, the electrolyte can flow at least partially along the second groove 23121 to improve its infiltration effect, and on the other hand, it can reduce the local enrichment of the electrolyte in the second groove 23121 and generate side reactions. Specifically, when P2 / S2 < 0.53×10 4 , when injecting the electrolyte, the electrolyte is not easily distributed evenly, and it is easy to form local accumulation inside the core 2, and side reactions are likely to occur. Then, on the one hand, the amount of effective electrolyte that can participate in the charge and discharge cycle of the cylindrical secondary battery 100 is reduced, and on the other hand, the electrolyte is locally enriched inside the second groove 23121, which affects the infiltration of other regions, resulting in capacity attenuation. When P2 / S2 > 6×10 4 , the electrolyte is easily locally enriched in the second groove 21121, and side reactions are likely to occur, leading to capacity attenuation. When 0.53×10 4 ≤ P2 / S2 ≤ 6×10 4 , the capacity retention rate of the cylindrical secondary battery 100 is high, its 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, its infiltration effect is better, and the cycle performance of the cylindrical secondary battery 100 can be improved better.

[0103] In some embodiments, along the axial direction X of the core 2, the second flattening portion 23211 includes a second surface 23211a facing away from the separator 22. The separator 22 includes a first end face 22a and a second end face 22b. The second end face 22b is closer to the second surface 23211a than the first end face 22a. The distance between the second surface 23211a and the second end face 22b is H2 mm, where 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 an overly high setting of the distance H2 is reduced. Specifically, when H2 < 0.3, when injecting the electrolyte, the electrolyte lacks sufficient time for uniform distribution and is likely to form local accumulation inside the core 2, and its infiltration effect is poor. When H2 > 4, the electrolyte is not easily introduced into the core 2, and its infiltration effect is lacking. When 0.3 ≤ H2 ≤ 4, the capacity retention rate of the cylindrical secondary battery 100 is high, its infiltration effect is good, and the cycle performance of the cylindrical secondary battery 100 can be improved.

[0105] In addition, through research by the inventors, it is found that in order to obtain a good infiltration effect, the size of the distance H2 will directly affect the setting of the cross-sectional area S2 of the second groove 23121. 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 core 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 , when injecting the electrolyte, the electrolyte is not easily distributed evenly and is likely to form local accumulation inside the core 2, and its infiltration effect is poor. When H2 / S2 > 8×10 4 , the electrolyte is likely to form local enrichment in the second groove 23121, and side reactions are likely to occur. On the one hand, the amount of effective electrolyte that can participate in the charge and discharge cycle of the cylindrical secondary battery 100 is reduced. On the other hand, the electrolyte is locally enriched inside the second groove 23121, which affects the infiltration of other regions, resulting in capacity decay. When 0.53×10 4 ≤ H2 / S2 ≤ 8×10 4 , the capacity retention rate of the cylindrical secondary battery 100 is high, its 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 distance H2 is also the height of the second flattening portion 23211 along the axial direction X of the core 2.

[0107] Preferably, when 3×104 ≤H2 / S2≤5×10 4 When ≤H2 / S2≤5×10, the capacity retention rate of the prismatic secondary battery 100 is higher, its infiltration effect is better, and the cycle performance of the prismatic secondary battery 100 can be better improved.

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

[0109] By limiting the coating mass per unit area W2 of the second active material layer 2312 on the second electrode sheet 23, the problem of poor infiltration of the electrolyte caused by the excessive growth of the diffusion distance of the electrolyte along the radial direction Y of the core 2 on the second electrode sheet 23 due to the excessive setting of the coating mass W2, resulting in accelerated cycle decay and lithium deposition, is reduced. Specifically, when W2 < 8, the coating mass W2 is small, the capacity retention rate of the prismatic secondary battery 100 is low, and its cycle life and reliability are poor. When W2 > 30, it is not easy for the electrolyte to be evenly distributed inside the core 2, and its infiltration effect is lacking. When 8≤W2≤30, the capacity retention rate of the prismatic secondary battery 100 is high, its infiltration effect is good, and the cycle performance of the prismatic secondary battery 100 can be improved.

[0110] In addition, the inventors have found through research that in order to obtain a better infiltration effect, the size of the coating mass W2 will directly affect the setting of the cross-sectional area S2 of the second groove 23121. Therefore, by limiting the proportional relationship between the coating mass W2 and the cross-sectional area S2 of the second groove 23121 along the radial direction Y of the core 2 (i.e., 0.93×10 4 ≤W2 / S2≤80×10 4 ), the capacity retention rate of the prismatic secondary battery 100 and the infiltration effect of the electrolyte are further improved. Specifically, when W2 / S2 < 0.93×10 4 , the capacity retention rate of the prismatic secondary battery 100 is low, and its cycle life and reliability are poor. When W2 / S2 > 80×10 4 , the electrolyte is likely to form local enrichment in the second groove 23121, and side reactions are likely to occur. On the one hand, the amount of effective electrolyte that can participate in the charge and discharge cycle of the prismatic secondary battery 100 is reduced. On the other hand, the electrolyte is locally enriched inside the second groove 23121, which affects the infiltration of other regions, thereby resulting in capacity decay. When 0.93×10 4 ≤W2 / S2≤80×10 4 , the capacity retention rate of the prismatic secondary battery 100 is high, its infiltration effect is good, and the cycle performance of the prismatic secondary battery 100 can be improved.

[0111] In some embodiments, when 9×10 4 ≤W2 / S2≤50×10 4 the capacity retention rate of the cylindrical secondary battery 100 is higher, its infiltration effect 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. Thereby facilitating the electrolyte to flow at least partially along the first groove 21121 and / or the second groove 23121 to improve its infiltration effect.

[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 shapes, and can also be trapezoidal, etc. No matter what the cross-section of the first groove 21121 or the second groove 23121 is, the beneficial effect of improving the infiltration problem of the electrolyte brought by the first groove 21121 and / or the second groove 23121 set in the embodiments of the present application can be achieved.

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

[0115] In some embodiments, the first electrode sheet 21 is a negative electrode sheet, and the second electrode sheet 23 is a positive electrode sheet. Generally, poor infiltration of the negative electrode has a great impact on the performance of the cylindrical secondary battery 100. By providing the above-mentioned first groove 21121 on the negative electrode sheet, the influence of the electrolyte infiltration problem on the overall performance of the cylindrical secondary battery 100 can be effectively alleviated. When the above-mentioned second groove 23121 is provided on the positive electrode sheet at the same time, the influence of the electrolyte infiltration problem on the overall performance of the cylindrical secondary battery 100 can be further alleviated.

[0116] It is understandable that if the first electrode sheet 21 is a negative electrode sheet and the second electrode sheet 23 is a positive electrode sheet, the first current collector 2111 includes but is not limited to one of conductive metal thin sheets such as copper foil and nickel foil. As an example, the first current collector 2111 is made of 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, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium carbonate, or other metals that can form alloys with lithium. The second current collector 2311 includes but is not limited to one of conductive metal thin sheets such as aluminum mesh, aluminum foil, and copper foil. As an example, the second current collector 2311 is made of aluminum foil. The second active material layer 2312 includes but is not limited to one or more of lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium manganate, lithium nickelate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium iron phosphate, and lithium-rich manganese-based materials.

[0117] To evaluate the beneficial effects of the cylindrical secondary battery 100 of the present application, relevant tests and analyses were carried out on the cylindrical secondary batteries 100 in the examples and comparative examples.

[0118]

Test Method

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

[0120] For the convenience of readers' understanding and for ease of description, taking the first flattening portion 21211 as an example, the method for measuring the density of the first flattening portion 21211 is described. The method for measuring the density of the second flattening portion 23211 can refer to the method for measuring the density of the first flattening portion 21211. Please refer to Figure 3 、 Figure 5 and Figure 6 , the highest point of the first surface 21211a of the first flattening portion 21211 facing away from the separator 22 is used as a planar reference, and the distance is measured downward to the separator 22 using a microscope, denoted as the height H1 mm of the first flattening portion 21211; the diameter D mm of the wound core 2 and the diameter d mm of the central hole in the cylindrical secondary battery 100 are measured using a microscope; the cylindrical secondary battery 100 is disassembled, and the length L after the first electrode sheet 21 is unfolded and the height H after the first electrode tab 2121 is unfolded are measured using a flexible ruler, and the thickness T1 after the first electrode tab 2121 is unfolded is measured using a microscope. Among them, since Figure 3 is a schematic diagram of the wound core 2 provided in the embodiment of the present application without the first flattening portion 21211 and the second flattening portion 23211, the height H after the first electrode tab 2121 is unfolded is actually equivalent to Figure 3For the H marked herein, the volume of the first flattening part 21211 is calculated using the following formula: V = [(π×(D / 2)×(D / 2))-(π×(d / 2)×(d / 2))]×H1; calculate the mass of the first flattening part 21211: 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] Measurement of the cross-sectional area of the first groove 21121 / second groove 23121 along the radial direction Y of the core 2

[0122] For the convenience of readers' understanding and for descriptive purposes, taking the first groove 21121 as an example, the method for measuring the cross-sectional area of the first groove 21121 along the radial direction Y of the core 2 is described. The method for measuring the cross-sectional area of the second groove 23121 along the radial direction Y of the core 2 can refer to the method for measuring the cross-sectional area of the first groove 21121 along the radial direction Y of the core 2. Prepare a sample by subjecting the first pole piece 21 with the first groove 21121 to liquid nitrogen embrittlement or ion polishing, and use SEM (scanning electron microscope) to measure the maximum width W and maximum depth T of the first groove 21121. Please refer to Figure 8 , and after measuring the maximum width W and maximum depth T of the first groove 21121 5 times each, take the average value; when the W and T of each first groove are the same, calculate the cross-sectional area of all the first grooves 21121 along the radial direction Y of the core 2: S1 = q×W×T mm 2 , where q is the number of the first grooves 21121; when the W and T of the first grooves are different, calculate the cross-sectional area S0 of each first groove in turn, and then add up all the S0 to obtain the total cross-sectional area S1.

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

[0124] Perform charge-discharge cycling tests on the cylindrical secondary batteries 100 in the examples and comparative examples in an incubator at 25°C. The charge-discharge voltage range is 2.5V to 4.2V. Charge at a constant current of 0.5C to 4.2V, then charge at a constant voltage of 4.2V to 0.05C and let it stand for 5 minutes, and then discharge at a constant current of 0.5C to 2.5V. Repeat the above charge-discharge process 600 cycles, and record the initial capacity C1 and the capacity C after the 600th cycle 600 , and thus calculate the capacity retention rate: Capacity retention rate (%) = C 600 / C1×100%. Among them, the higher the capacity retention rate, the better the wetting effect of the core 2 and the better the cycling performance of the cylindrical secondary battery 100.

[0125] Test of lithium plating performance

[0126] After charging and discharging the cylindrical secondary batteries in each example and comparative example according to the following test process, disassemble them and observe the lithium deposition state on the surface of the electrode sheet. The area without lithium deposition on the electrode sheet surface is golden yellow, and the area with lithium deposition is grayish white.

[0127] Confirm the degree of lithium deposition according to the ratio between the lithium deposition area and the active material layer area: Area = 0%, no lithium deposition; Slight lithium deposition: Area less than 5%; Moderate lithium deposition: Area between 5% - 20%; Severe lithium deposition: Area greater than 20%.

[0128] Lithium deposition test process:

[0129] 1) The environmental temperature for the test is 25°C;

[0130] 2) Stand still for 30 minutes;

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

[0132] 4) Stand still for 5 minutes;

[0133] 5) Use direct current to discharge the battery at a discharging rate of 0.2C until the voltage reaches 2.5V;

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

[0135] 7) Stand still for 120 minutes;

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

[0137] 9) Stand still for 5 minutes;

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

[0139] 11) Stand still for 60 minutes;

[0140] 12) Repeat steps 8 to 11 for 10 cycles;

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

[0142] 14) Stand still for 15 minutes.

[0143] Example 1:

[0144] <Preparation of negative electrode plate>

[0145] Mix artificial graphite as the negative active material, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) in a mass ratio of 97.3:1.7:1.0, then add deionized water as a solvent and stir to mix evenly to obtain a negative electrode slurry with a solid content of 50 wt%. Uniformly coat the negative electrode slurry on a copper foil with a thickness of 10 μm and dry it at 100 °C to obtain a negative electrode plate with a single-sided coated negative electrode material layer (i.e., the first active material layer). Then, repeat the above steps on the other surface of the negative electrode current collector to obtain a negative electrode plate with a double-sided coated negative electrode material layer. Then, after cold pressing, cutting, and slitting, set the first groove on the negative electrode material layers on both sides of the negative electrode current collector by laser to obtain a negative electrode plate with a specification of 62 mm × 1455 mm for use. Among them, reference can be made to Figure 5 and Figure 8 , the width W of the first groove is 10 μm, the depth T of the first groove is 20 μm, the length L1 of the first groove is 60 mm, the width L2 of the first active material layer is 62 mm, f1 = L1 / L2 = 0.97, the spacing K between adjacent first grooves is 2.5 mm, the unit coating mass W1 of the negative electrode material layer is 8.6 mg / cm 2 , and the compaction density of the negative electrode material layer is 1.6 g / cm 3 .

[0146] <Preparation of positive electrode plate>

[0147] Select an aluminum foil with a thickness of 16 μm as the positive electrode current collector, and disperse lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2), binder polyvinylidene fluoride (PVDF), and conductive carbon black in a mass ratio of 94.8:2.8:2.4 in an N-methylpyrrolidone (NMP) solvent, stir and mix well to obtain a positive electrode slurry with a solid content of 72 wt%. Uniformly coat the positive electrode slurry on the surface of the above positive electrode current collector and dry it at 100 °C to obtain a positive electrode plate with a single-sided coated positive electrode material layer (i.e., the second active material layer). Then, repeat the above steps on the other surface of the positive electrode current collector to obtain a positive electrode plate with a double-sided coated positive electrode material layer. Then, after cold pressing, cutting, and slitting, dry it in a vacuum at 100 °C for 4 hours to obtain a positive electrode plate with a specification of 60 mm × 1407 mm for use. Among them, the unit coating mass of the positive electrode material layer is 15 mg / cm 2 , and the compaction density of the positive electrode material layer is 3.4 g / cm 3 .

[0148] <Separator>

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

[0150] <Preparation of Electrolyte>

[0151] In a dry argon atmosphere glove box, organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and 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 base solvent, and the electrolyte was obtained after being fully mixed. Based on the mass of the electrolyte, the mass percentage of LiPF6 is 12.5%, and the balance is the base solvent.

[0152] <Preparation of cylindrical secondary battery>

[0153] The prepared separator, positive electrode sheet, separator, and negative electrode sheet are stacked in order, so that the separator is between the positive electrode and the negative electrode to play an isolating role. After winding, flattening, current collector welding, shelling, coding, vacuum drying, electrolyte injection, sealing, high temperature standing, and then forming capacity, a cylindrical secondary battery can be obtained. Among them, the density P1 of the first flattened part is 1.2g / cm 3 , H1 is 1.2mm. The upper limit voltage of the formation is 3.6V, the formation temperature is 45℃, and the high temperature standing time after formation is 24h.

[0154] This application provides specific embodiments and comparative examples, conducts relevant performance tests, and analyzes the test results.

[0155] About P1 / S1 and the influence of P1 on the performance of cylindrical secondary batteries

[0156] Based on the method of Example 1, cylindrical secondary batteries of Examples A1 to A7, Examples A8 to A14, and Comparative Examples A1 to A4 were prepared; Examples A1 to A7, and Comparative Examples A1, A2 and Example 1 (P1 was 1.2 mg / cm 2 ) are as follows: First, P1 is 1 mg / cm 2 , and secondly, adjusting the parameters according to the ratio in Table 1. The difference between Examples A8 to A14, Comparative Examples A3 and A4 is that the parameters in Table 2 are adjusted. Please refer to Tables 1 and 2 for details. Table 1 shows the effect of P1 / S1 on the performance of the cylindrical secondary battery 100, and Table 2 shows the effect of P1 on the performance of the cylindrical secondary battery 100.

[0157] Table 1

[0158] <![CDATA[P1 / S1]]> <![CDATA[P1 / g / cm 3 > <![CDATA[S1 / mm 2 > Capacity retention rate / % Lithium Separation Performance Comparative Example A1 <![CDATA[0.51×10 4 > 1 <![CDATA[1.961×10 -4 > 62.5 Moderate lithium precipitation Example A1 <![CDATA[0.53×10 4 > 1 <![CDATA[1.887×10 -4 > 82.4 No lithium precipitation Example A2 <![CDATA[1×10 4 > 1 <![CDATA[1×10 -4 > 83.2 No lithium precipitation Example A3 <![CDATA[2×10 4 > 1 <![CDATA[0.5×10 -4 > 84.1 No lithium precipitation Example A4 <![CDATA[3.5×10 4 > 1 <![CDATA[0.286×10 -4 > 85.2 No lithium precipitation Example A5 <![CDATA[4.5×10 4 > 1 <![CDATA[0.222×10 -4 > 85.7 No lithium precipitation Example A6 <![CDATA[5×10 4 > 1 <![CDATA[0.2×10 -4 > 81.9 Mild lithium deposition Example A7 <![CDATA[6×10 4 > 1 <![CDATA[0.167×10 -4 > 81.4 Mild lithium deposition Comparative Example A2 <![CDATA[6.2×10 4 > 1 <![CDATA[0.161×10 -4 > 71.2 Severe lithium evolution

[0159] From Table 1, we can see that when 0.53×104 When 0.53×10 ≤ P1 / S1 ≤ 6×10 4 the cylindrical secondary battery has a high capacity retention rate, good infiltration effect, good lithium deposition performance, and can improve the cycle performance of the cylindrical secondary battery. When P1 / S1 < 0.53×10 4 or P1 / S1 > 6×10 4 the cylindrical secondary battery has a low capacity retention rate, lacks infiltration effect, and shows moderate or even severe lithium deposition in the cylindrical secondary battery.

[0160] Preferably, when 2×10 4 ≤ P1 / S1 ≤ 4.5×10 4 the cylindrical secondary battery has a higher capacity retention rate, better infiltration effect and better lithium deposition performance, that is, it can better improve the cycle performance of the cylindrical secondary battery.

[0161] Table 2

[0162] <![CDATA[P1 / S1]]> <![CDATA[P1 / g / cm 3 > <![CDATA[S1 / mm 2 > Capacity retention rate / % Lithium Separation Performance Comparative Example A3 <![CDATA[1×10 4 > 0.4 <![CDATA[0.4×10 -4 > 63.5 Moderate lithium precipitation Example A8 <![CDATA[1×10 4 > 0.6 <![CDATA[0.6×10 -4 > 81.4 No lithium precipitation Embodiment A9 <![CDATA[1×10 4 > 0.7 <![CDATA[0.7×10 -4 > 82.2 No lithium precipitation Embodiment A10 <![CDATA[1×10 4 > 0.8 <![CDATA[0.8×10 -4 > 82.9 No lithium precipitation Embodiment A11 <![CDATA[1×10 4 > 1.2 <![CDATA[1.2×10 -4 > 85.2 No lithium precipitation Example A12 <![CDATA[1×10 4 > 1.5 <![CDATA[1.5×10 -4 > 85.7 No lithium precipitation Embodiment A13 <![CDATA[1×10 4 > 3 <![CDATA[3×10 -4 > 84.9 Mild lithium deposition Embodiment A14 <![CDATA[1×10 4 > 3.5 <![CDATA[3.5×10 -4 > 84.4 Mild lithium deposition Comparative Example A4 <![CDATA[1×10 4 > 3.7 <![CDATA[3.7×10 -4 > 75.2 Severe lithium evolution

[0163] As can be seen from Table 2, when 0.6 ≤ P1 ≤ 3.5, the cylindrical secondary battery has a relatively high capacity retention rate, good infiltration effect, good lithium deposition performance, and can improve the cycle performance of the cylindrical secondary battery. When P1 < 0.6 or P1 > 3.5, the cylindrical secondary battery has a low capacity retention rate, lacks infiltration effect, and shows moderate or even severe lithium deposition in the cylindrical secondary battery.

[0164] Preferably, when 0.8 ≤ P1 ≤ 1.5, the cylindrical secondary battery has a higher capacity retention rate, better infiltration effect and better lithium deposition performance, that is, it can better improve the cycle performance of the cylindrical secondary battery.

[0165] Regarding the influence of H1 / S1 and H1 on the performance of the cylindrical secondary battery

[0166] Cylindrical secondary batteries of Examples B1 to B7, Examples B8 to B14, 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, firstly, H1 is 1.2 mg / cm 2 , and secondly, the parameters are adjusted according to the ratio in Table 3. The difference points between Examples B8 to B14, Comparative Examples B3 and B4 are only in the parameter adjustment 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.

[0167] Table 3

[0168] <![CDATA[H1 / S1]]> <![CDATA[H1 / mm]]> <![CDATA[S1 / mm 2 > Capacity retention rate / % Lithium Separation Performance Comparative Example B1 <![CDATA[5.1×10 3 > 1 <![CDATA[0.197×10 -4 > 66.5 Moderate lithium precipitation Example B1 <![CDATA[0.53×10 4 > 1 <![CDATA[0.189×10 -4 > 80.4 No lithium precipitation Example B2 <![CDATA[1×10 4 > 1 <![CDATA[1×10 -4 > 82.2 No lithium precipitation Example B3 <![CDATA[3×10 4 > 1 <![CDATA[0.333×10 -4 > 84.9 No lithium precipitation Example B4 <![CDATA[4×10 4 > 1 <![CDATA[0.25×10 -4 > 85.6 No lithium precipitation Example B5 <![CDATA[5×10 4 > 1 <![CDATA[0.2×10 -4 > 85.8 No lithium precipitation Example B6 <![CDATA[6×10 4 > 1 <![CDATA[0.167×10 -4 > 84.1 Mild lithium deposition Example B7 <![CDATA[8×10 4 > 1 <![CDATA[0.125×10 -4 > 83.4 Mild lithium deposition Comparative Example B2 <![CDATA[8.2×10 4 > 1 <![CDATA[0.122×10 -4 > 68.2 Severe lithium evolution

[0169] As can be seen from Table 3, when 0.53×10 4 ≤H1 / S1≤8×10 4 the capacity retention rate of the cylindrical secondary battery is high, its infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved. When H1 / S1 < 0.53×10 4 or H1 / S1 > 8×10 4 the capacity retention rate of the cylindrical secondary battery is low, its infiltration effect is lacking, and moderate or even severe lithium deposition occurs in the cylindrical secondary battery.

[0170] Preferably, when 3×10 4 ≤H1 / S1≤5×10 4 the capacity retention rate of the cylindrical secondary battery is higher, its infiltration effect is better, and the cycle performance of the cylindrical secondary battery can be better improved.

[0171] Table 4

[0172] <![CDATA[H1 / S1]]> <![CDATA[H1 / mm]]> <![CDATA[S1 / mm 2 > Capacity retention rate / % Lithium Separation Performance Comparative Example B3 <![CDATA[1×10 4 > 0.1 <![CDATA[0.1×10 -4 > 63.5 Moderate lithium precipitation Example B8 <![CDATA[1×10 4 > 0.3 <![CDATA[0.3×10 -4 > 79.4 No lithium precipitation Example B9 <![CDATA[1×10 4 > 0.5 <![CDATA[0.5×10 -4 > 80.2 No lithium precipitation Example B10 <![CDATA[1×10 4 > 0.8 <![CDATA[0.8×10 -4 > 81.9 No lithium precipitation Example B11 <![CDATA[1×10 4 > 1.5 <![CDATA[1.5×10 -4 > 82.6 No lithium precipitation Example B12 <![CDATA[1×10 4 > 2 <![CDATA[2×10 -4 > 82.8 No lithium precipitation Example B13 <![CDATA[1×10 4 > 3 <![CDATA[3×10 -4 > 81.1 Mild lithium deposition Example B14 <![CDATA[1×10 4 > 4 <![CDATA[4×10 -4 > 80.4 Mild lithium deposition Comparative Example B4 <![CDATA[1×10 4 > 4.2 <![CDATA[4.2×10 -4 > 65.2 Severe lithium evolution

[0173] As can be seen from Table 4, when 0.3≤H1≤4, the capacity retention rate of the cylindrical secondary battery is high, its infiltration 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, its infiltration effect is lacking, and moderate or even severe lithium deposition occurs in the cylindrical secondary battery.

[0174] Preferably, when 0.8≤H1≤2, the capacity retention rate of the cylindrical secondary battery is higher, its infiltration effect is better, and the cycle performance of the cylindrical secondary battery can be better improved.

[0175] Regarding the influence of W1 / S1 and W1 on the performance of the cylindrical secondary battery

[0176] 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, the differences between Examples C1 to C6 and Comparative Examples C1 and C2 compared with Example 1 (W1 was 8.6 mg / cm 2 ) were as follows: First, W1 was 10 mg / cm 2 , and second, the parameters were adjusted according to the ratios in Table 5. Among them, the differences between Examples C7 to C12 and Comparative Examples C3 and C4 compared with Example 1 were that the parameters were adjusted according to the ratios in Table 6. 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.

[0177] Table 5

[0178] <![CDATA[W1 / S1]]> <![CDATA[W1 / mg / cm 2 > Capacity retention rate / % Lithium Separation Performance Comparative Example C1 <![CDATA[0.91×10 3 > 10 67.2 Mild lithium deposition Example C1 <![CDATA[0.93×10 4 > 10 81.1 No lithium precipitation Example C2 <![CDATA[9×10 4 > 10 83.6 No lithium precipitation Example C3 <![CDATA[30×10 4 > 10 84.3 No lithium precipitation Example C4 <![CDATA[50×10 4 > 10 84.5 No lithium precipitation Example C5 <![CDATA[60×10 4 > 10 82.8 Mild lithium deposition Example C6 <![CDATA[80×10 4 > 10 82.1 Mild lithium deposition Comparative Example C2 <![CDATA[95×10 4 > 10 65.9 Severe lithium evolution

[0179] As can be seen from Table 5, when 0.93×10 4 ≤W1 / S1≤80×10 4 the capacity retention rate of the cylindrical secondary battery is high, its infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved. When 0.93×10 4 >W1 / S1 or W1 / S1>80×10 4 the capacity retention rate of the cylindrical secondary battery is low, its infiltration effect is somewhat lacking, and moderate or even severe lithium deposition occurs in the cylindrical secondary battery.

[0180] Preferably, when 9×10 4 ≤W1 / S1≤50×10 4 the capacity retention rate of the cylindrical secondary battery is higher, its infiltration effect is better, and the cycle performance of the cylindrical secondary battery can be better improved.

[0181] Table 6

[0182]

[0183]

[0184] As can be seen from Table 6, when 8≤W1≤30, the capacity retention rate of the cylindrical secondary battery is high, its infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved. 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, its infiltration effect is somewhat lacking, and moderate or even severe lithium deposition occurs in the cylindrical secondary battery.

[0185] Preferably, when 14≤W1≤20, the capacity retention rate of the cylindrical secondary battery is higher, its infiltration effect is better, and the cycle performance of the cylindrical secondary battery can be better improved.

[0186] Regarding the influence of f1 or S1 on the performance of the cylindrical secondary battery

[0187] Based on the method of Example 1, Examples D1 to D5, Examples D6 to D12, and Comparative Examples D1 to D3 of the cylindrical secondary battery were prepared. The only difference between them is that the parameters are adjusted according to the ratios in Table 7 and Table 8. For details, please refer to Table 7 and Table 8. Table 7 shows the influence of f1 on the performance of the cylindrical secondary battery 100, and Table 8 shows the influence of S1 on the performance of the cylindrical secondary battery 100.

[0188] Table 7

[0189] <![CDATA[f1]]> Capacity retention rate / % Lithium Separation Performance Comparative Example D1 0.1 68.5 Mild lithium deposition Example D1 0.3 84.5 No lithium precipitation Example D2 0.5 85.3 No lithium precipitation Example D3 0.7 87.2 No lithium precipitation Example D4 0.8 87.9 No lithium precipitation Example D5 1 88.1 No lithium precipitation

[0190] As can be seen from Table 7, when 0.3 ≤ f1 ≤ 1, the capacity retention rate of the cylindrical secondary battery is high, its infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved. When f1 < 0.3 or f1 > 1, the capacity retention rate of the cylindrical secondary battery is low, and its infiltration effect is somewhat lacking.

[0191] Preferably, when 0.5 ≤ f1 ≤ 0.8, the capacity retention rate of the cylindrical secondary battery is higher, its infiltration effect is better, and the cycle performance of the cylindrical secondary battery can be improved better.

[0192] Table 8

[0193] <![CDATA[S1 / mm 2 > Capacity retention rate / % Lithium Separation Performance Comparative Example D2 <![CDATA[1×10 -5 > 66.5 Mild lithium deposition Example D6 <![CDATA[0.25×10 -4 > 82.0 No lithium precipitation Example D7 <![CDATA[0.5×10 -4 > 82.8 No lithium precipitation Example D8 <![CDATA[1×10 -4 > 84.6 No lithium precipitation Example D9 <![CDATA[1.2×10 -4 > 85.3 No lithium precipitation Example D10 <![CDATA[1.4×10 -4 > 85.5 No lithium precipitation Example D11 <![CDATA[1.45×10 -4 > 83.8 No lithium precipitation Example D12 <![CDATA[1.5×10 -4 > 83.1 No lithium precipitation Comparative Example D3 <![CDATA[1.7×10 -4 > 60.2 Moderate lithium precipitation

[0194] 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, its infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved. When S1 < 0.25×10 -4 or S1 > 1.5×10 -4 , the capacity retention rate of the cylindrical secondary battery is low, its infiltration effect is somewhat lacking and mild lithium deposition or even moderate lithium deposition occurs.

[0195] Preferably, when 1×10 -4 ≤ S1 ≤ 1.4×10 -4 , the capacity retention rate of the cylindrical secondary battery is higher, its infiltration effect is better, and the cycle performance of the cylindrical secondary battery can be improved better.

[0196] Regarding the influence of n and K on the performance of the cylindrical secondary battery

[0197] Based on the preparation method of Example 1 and adjusted according to the parameters in Table 9 to obtain Comparative Examples E1 to E6 and Examples E1 to E13. Among them, the number of winding turns N of the negative electrode material layer is 30 turns, and n is the nth turn of the negative electrode material layer in the winding core.

[0198] In Comparative Examples E1 and E2 and Examples E1 to E3, the K value of each turn was adjusted to be 1 to 9 according to Table 9, and the first groove was not provided in other turns.

[0199] In Comparative Examples E3 and E4 and Examples E4 to E6, the K value of each turn was adjusted to be 10 to 24 according to Table 9, and the first groove was not provided in other turns.

[0200] In Comparative Examples E5 and E6 and Examples E7 to E9, the K value of each turn was adjusted to be 25 to 30 according to Table 9, and the first groove was not provided in other turns.

[0201] In Example E10, when n ranges from 1 to 9, K = 3; when n ranges from 10 to 24, K = 1.5; no first groove is provided for other turns.

[0202] In Example E11, when n ranges from 1 to 9, K = 3; when n ranges from 25 to 30, K = 4; no first groove is provided for other turns.

[0203] In Example E12, when n ranges from 10 to 24, K = 1.5; when n ranges from 25 to 30, K = 4; no first groove is provided for other turns.

[0204] In Example E10, when n ranges from 1 to 9, K = 3; when n ranges from 10 to 24, K = 1.5; when n ranges from 25 to 30, K = 4.

[0205] Please refer to Table 9, which shows the influence of n and K on the performance of the cylindrical secondary battery 100.

[0206] Table 9

[0207]

[0208]

[0209] 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, its infiltration effect is poor, and it is prone to mild lithium plating. When 0.3N < n ≤ 0.8N but K < 1 or K > 2, the capacity retention rate of the cylindrical secondary battery is not high, its infiltration effect is poor, and it is prone to mild lithium plating. When n > 0.8N but K < 3 or K > 5, the capacity retention rate of the cylindrical secondary battery is not high, its infiltration effect is poor, and it is prone to mild lithium plating. 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, its infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved. In addition, it can be seen from Examples E10 to E13 that as the number of first grooves increases, the infiltration effect of the cylindrical secondary battery is better and its capacity retention rate is higher.

[0210] Regarding the influence of P2 / S2 and P2 on the performance of the cylindrical secondary battery

[0211] Example 3 is obtained by adjusting the definition of the positive electrode sheet based on Example 1. In Example 3, along the length direction after unfolding the positive electrode current collector, and on the positive electrode material layers on both sides of the positive electrode current collector, second grooves are formed by laser. Among them, 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.

[0212] Examples F1 (i.e., Example 3) to Example F7, Example F8 to Example F14 and Comparative Examples F1 to Comparative Example F4 of the cylindrical secondary battery are prepared based on Example 3. Among them, the differences between Examples F1 to Example F7, Example F8 to Example F14, and Comparative Examples F1 to Comparative Example F4 are only in adjusting the parameters according to the ratios in Table 10 and Table 11. Please refer to Table 10 and Table 11. Table 10 shows the influence of P2 / S2 on the performance of the cylindrical secondary battery 100, and Table 11 shows the influence of P2 on the performance of the cylindrical secondary battery 100.

[0213] Table 10

[0214]

[0215]

[0216] As can be seen from Table 10, when 0.53×10 4 ≤P2 / S2≤6×10 4 , the capacity retention rate of the cylindrical secondary battery is high, its infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved. When P2 / S2 < 0.53×10 4 or P2 / S2 > 6×10 4 , the capacity retention rate of the cylindrical secondary battery is low, its infiltration effect is somewhat lacking, and moderate or even severe lithium deposition occurs in the cylindrical secondary battery.

[0217] Preferably, when 2×10 4 ≤P2 / S2≤4.5×10 4 , the capacity retention rate of the cylindrical secondary battery is higher, its infiltration effect is better, and the cycle performance of the cylindrical secondary battery can be better improved.

[0218] Table 11

[0219] <![CDATA[P2 / S2]]> <![CDATA[P2 / g / cm 3 > Capacity retention rate / % Lithium Separation Performance Comparative Example F3 <![CDATA[1×10 4 > 0.4 65.4 Moderate lithium precipitation Example F8 <![CDATA[1×10 4 > 0.6 83.8 No lithium precipitation Example F9 <![CDATA[1×10 4 > 0.7 84.7 No lithium precipitation Example F10 <![CDATA[1×10 4 > 0.8 85.3 No lithium precipitation Example F11 <![CDATA[1×10 4 > 1.2 87.8 No lithium precipitation Example F12 <![CDATA[1×10 4 > 1.5 88.3 No lithium precipitation Example F13 <![CDATA[1×10 4 > 3 87.4 Mild lithium deposition Example F14 <![CDATA[1×10 4 > 3.5 86.9 Mild lithium deposition Comparative Example F4 <![CDATA[1×10 4 > 3.7 77.5 Severe lithium evolution

[0220] As can be seen from Table 11, when 0.6 ≤ P1 ≤ 3.5, the capacity retention rate of the cylindrical secondary battery is high, its infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved. When P2 < 0.6 or P2 > 3.5, the capacity retention rate of the cylindrical secondary battery is low, its infiltration effect is somewhat lacking, and moderate or even severe lithium plating occurs in the cylindrical secondary battery.

[0221] Preferably, when 0.8 ≤ P2 ≤ 1.5, the capacity retention rate of the cylindrical secondary battery is higher, its infiltration effect is better, and the cycle performance of the cylindrical secondary battery can be improved better.

[0222] Regarding the influence of H2 / S2 and H2 on the performance of the cylindrical secondary battery

[0223] Based on Example 3, cylindrical secondary battery Examples G1 to G7, Examples G8 to G14, and Comparative Examples G1 to G4 were prepared. Among them, the differences between Examples G1 to G7, Examples G8 to G14, and Comparative Examples G1 to G4 are only that the parameters are adjusted according to the ratios 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 the cylindrical secondary battery 100, and Table 13 shows the influence of H2 on the performance of the cylindrical secondary battery 100.

[0224] Table 12

[0225] <![CDATA[H2 / S2]]> <![CDATA[H2 / mm]]> Capacity retention rate / % Lithium Separation Performance Comparative Example G1 <![CDATA[5.1×10 3 > 1 68.5 Moderate lithium precipitation Example G1 <![CDATA[0.53×10 4 > 1 83.9 No lithium precipitation Example G2 <![CDATA[1×10 4 > 1 84.7 No lithium precipitation Example G3 <![CDATA[3×10 4 > 1 87.4 No lithium precipitation Example G4 <![CDATA[4×10 4 > 1 88.2 No lithium precipitation Example G5 <![CDATA[5×10 4 > 1 88.4 No lithium precipitation Example G6 <![CDATA[6×10 4 > 1 86.6 Mild lithium deposition Example G7 <![CDATA[8×10 4 > 1 85.9 Mild lithium deposition Comparative Example G2 <![CDATA[8.2×10 4 > 1 70.2 Severe lithium evolution

[0226] As can be seen from Table 12, when 0.53×10 4 ≤ H2 / S2 ≤ 8×10 4 , the capacity retention rate of the cylindrical secondary battery is high, its infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved. When H2 / S2 < 0.53×10 4 or H2 / S2 > 8×10 4 , the capacity retention rate of the cylindrical secondary battery is low, its infiltration effect is somewhat lacking, and moderate or even severe lithium plating occurs in the cylindrical secondary battery.

[0227] Preferably, when 3×10 4 ≤ H2 / S2 ≤ 5×10 4 , the capacity retention rate of the cylindrical secondary battery is higher, its infiltration effect is better, and the cycle performance of the cylindrical secondary battery can be improved better.

[0228] Table 13

[0229] <![CDATA[H2 / S2]]> <![CDATA[H2 / mm]]> Capacity retention rate / % Lithium Separation Performance Comparative Example G3 <![CDATA[1×10 4 > 0.1 65.4 Moderate lithium precipitation Example G8 <![CDATA[1×10 4 > 0.3 81.8 No lithium precipitation Example G9 <![CDATA[1×10 4 > 0.5 82.6 No lithium precipitation Example G10 <![CDATA[1×10 4 > 0.8 84.4 No lithium precipitation Example G11 <![CDATA[1×10 4 > 1.5 85.1 No lithium precipitation Example G12 <![CDATA[1×10 4 > 2 85.3 No lithium precipitation Example G13 <![CDATA[1×10 4 > 3 83.5 Mild lithium deposition Example G14 <![CDATA[1×10 4 > 4 82.8 Mild lithium deposition Comparative Example G4 <![CDATA[1×10 4 > 4.2 67.2 Severe lithium evolution

[0230] 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 the cycle performance of the cylindrical secondary battery can be improved. When H2 < 0.3 or H2 > 4, the capacity retention rate of the cylindrical secondary battery is low, its infiltration effect is somewhat lacking, and moderate or even severe lithium plating occurs in the cylindrical secondary battery.

[0231] Preferably, when 0.8 ≤ H2 ≤ 2, the capacity retention rate of the cylindrical secondary battery is higher, its infiltration effect is better, and the cycle performance of the cylindrical secondary battery can be improved better.

[0232] Regarding the influence of W2 / S2 and W2 on the performance of the cylindrical secondary battery

[0233] Based on Example 3, cylindrical secondary battery Examples M1 to M6, Examples M7 to M12, and Comparative Examples M1 to M4 were prepared. Among them, the differences between Examples M1 to M6 and Comparative Examples M1 and M2 with respect to Example 3 (W2 was 8.6 mg / cm 2 ) were as follows: First, W2 was 10 mg / cm 2 ; second, the parameters were adjusted according to the ratio in Table 14. The differences between Examples M7 to M12, Comparative Examples M3, and Comparative Examples M4 with respect to Example 3 were that the parameters were adjusted according to the ratio 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.

[0234] Table 14

[0235]

[0236]

[0237] As can be seen from Table 14, when 0.93×10 4 ≤ W2 / S2 ≤ 80×10 4 , the capacity retention rate of the cylindrical secondary battery is high, its infiltration effect is good, and the cycle performance of the cylindrical secondary battery can be improved. When W2 / S2 < 0.93×10 4 or W2 / S2 > 80×10 4 , the capacity retention rate of the cylindrical secondary battery is low, its infiltration effect is somewhat lacking, and moderate or even severe lithium plating occurs in the cylindrical secondary battery.

[0238] Preferably, when 9×10 4 ≤ W2 / S2 ≤ 50×10 4 , the capacity retention rate of the cylindrical secondary battery is higher, its infiltration effect is better, and the cycle performance of the cylindrical secondary battery can be improved better.

[0239] Table 15

[0240] <![CDATA[W2 / S2]]> <![CDATA[W2 / mg / cm 2 > Capacity retention rate / % Lithium Separation Performance Comparative Example M3 <![CDATA[5×10 4 > 6 70.5 Mild lithium deposition Embodiment M7 <![CDATA[5×10 4 > 8 87.7 No lithium deposition Example M8 <![CDATA[5×10 4 > 14 90.4 No lithium deposition Example M9 <![CDATA[5×10 4 > 16 91.1 No lithium deposition Example M10 <![CDATA[5×10 4 > 20 91.3 No lithium deposition Example M11 <![CDATA[5×10 4 > 25 89.5 Slight lithium deposition Example M12 <![CDATA[5×10 4 > 30 88.7 Slight lithium deposition Comparative example M4 <![CDATA[5×10 4 > 32 72.3 Severe lithium deposition

[0241] As can be seen from Table 15, when 8 ≤ W2 ≤ 30, the columnar secondary battery has a high capacity retention rate, good infiltration effect, and can improve the cycle performance of the columnar secondary battery. When W2 < 8 or W2 > 30, the columnar secondary battery has a low capacity retention rate, the infiltration effect is lacking, and moderate or even severe lithium plating occurs in the columnar secondary battery.

[0242] Preferably, when 14 ≤ W2 ≤ 20, the columnar secondary battery has a higher capacity retention rate, better infiltration effect, and can better improve the cycle performance of the columnar secondary battery.

[0243] The embodiment of the present application also provides an example of an electrical device. The electrical device includes a load and the above-mentioned columnar secondary battery 100. The columnar secondary battery 100 is connected to the load, and the columnar secondary battery 100 is used to supply power to the load.

[0244] The electrical device can be an energy storage product, a mobile phone, a tablet, a drone, an electric vehicle with one wheel or two or more wheels, or an electric cleaning tool, etc.

[0245] For example, for the above-mentioned drone, the battery pack is carried on the drone, and the battery pack is used to supply power to the load on the drone, including the flight system, control system, camera system, etc.

[0246] It should be noted that the specification and drawings of the present application give preferred embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described in this specification. These embodiments do not serve as additional limitations to the content of the present application. The purpose of providing these embodiments is to make the understanding of the disclosed content of the present application more thorough and comprehensive. Further, the above technical features continue to be combined with each other to form various embodiments not listed above, which are all regarded as the scope described in the specification of the present application; furthermore, for those of ordinary skill in the art, improvements or changes can be made according to the above description, and all such improvements and changes should fall 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 winding core (2), wherein the winding core (2) is accommodated in the housing (1), the winding core (2) comprises a first pole piece (21) and a separator (22), and along the axial direction of the winding core (2), the first pole piece (21) comprises a first main body (211) and a first empty foil area (212) in sequence, the first main body (211) comprises 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 area (212) comprises a first pole ear portion (2121), and along the axial direction of the winding core (2), the first pole ear portion (2121) is the portion of the first empty foil area (212) that exceeds the isolation film (22), and at least part of the first pole ear portion (2121) forms a first flattened portion (21211); characterized in that: A first groove (21121) is provided on the surface of the first active material layer (2112), the first groove (21121) extends along the axial direction of the winding core (2), and the first groove (21121) passes through one end surface (2112a) of the first active material layer (2112) along the axial direction of the winding core (2); The cylindrical secondary battery (100) satisfies: 0.53×10 4 ≤P1 / S1≤6×10 4 , wherein the density of the first flattened portion (21211) is P1g / cm 3 , 0.6≤P1≤3.5, the cross-sectional area of ​​the first groove (21121) along the radial direction of the winding core (2) is S1mm 2 .

2. The cylindrical secondary battery (100) according to claim 1, characterized in that: 0.53×10 4 ≤H1 / S1≤8×10 4 , wherein, along the axial direction of the winding core (2), the first flattened portion (21211) includes a first surface (21211a) facing away from the isolation film (22), the isolation film (22) includes a first end face (22a) and a second end face (22b), the first end face (22a) is close to the first surface (21211a) relative to the second end face (22b), and the distance between the first surface (21211a) and the first end face (22a) is H1 mm, 0.3≤H1≤4.

3. The cylindrical secondary battery (100) according to claim 2, characterized in that: 0.8≤H1≤2。 4. The cylindrical secondary battery (100) according to any one of claims 1 to 3, characterized in that: 0.93×10 4 ≤W1 / S1≤80×10 4 , wherein the coating mass per unit area of ​​the first active material layer (2112) on the first pole piece (21) is W1 mg / cm 2 , 8≤W1≤30.

5. The cylindrical secondary battery (100) according to claim 4, characterized in that: 14≤W1≤20。 6. The cylindrical secondary battery (100) according to any one of claims 1 to 5, characterized in that: The cylindrical secondary battery (100) satisfies at least one of the following conditions: (1) 0.3≤f1≤1, wherein, along the axial direction of the winding core (2), the ratio of the length of the first groove (21121) to the length of the first active material layer (2112) is f1; (2)0.25×10 -4 ≤S1≤1.5×10 -4 。 7. The cylindrical secondary battery (100) according to claim 6, characterized in that: 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 。 8. The cylindrical secondary battery (100) according to any one of claims 1 to 7, characterized in that: The number of the first grooves (21121) is 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<n≤0.8N, 1≤K≤2; When n>0.8N, 3≤K≤5; Wherein, N is the total number of turns of the first pole piece (21) in the winding core (2), n is the nth turn of the first active material layer (2112) in the winding core (2), K is the distance between two adjacent first grooves (21121) in the first active material layer (2112) of the nth turn along the circumferential direction of the winding core (2), and the unit of K is mm.

9. The cylindrical secondary battery (100) according to any one of claims 1 to 8, characterized in that: The first groove (21121) comprises a first sub-groove (21121a) and a second sub-groove (21121b), the first sub-groove (21121a) penetrating one end surface (2112a) of the first active material layer (2112) along the axial direction of the winding core (2), and the second sub-groove (21121b) penetrating the other end surface (2112b) of the first active material layer (2112) along the axial direction of the winding core (2); Along the radial direction of the winding core (2), a projection of the first sub-groove (21121a) on the first current collector (2111) is separated from a projection of the second sub-groove (21121b) on the first current collector (2111).

10. The cylindrical secondary battery (100) according to any one of claims 1 to 9, characterized in that: The number of the first pole ear portion (2121) is one, and the various parts of the first pole ear portion (2121) are overlapped with each other from the outer ring to the central axis along the winding direction of the winding core (2) after being flattened to form the first flattened portion (21211); or The number of the first pole ear portions (2121) is at least two, each of the first pole ear portions (2121) is arranged at intervals along the circumferential direction of the winding core (2), and at least two of the first pole ear portions (2121) overlap from the outer ring of the winding core (2) to the central axis to form the first flattened portion (21211).

11. The cylindrical secondary battery (100) according to any one of claims 1 to 10, characterized in that: The winding core (2) comprises a second pole piece (23), and the winding core (2) is formed by winding the first pole piece (21), the second pole piece (23), and an isolation film (22) located between the first pole piece (21) and the second pole piece (23); The second pole piece (23) comprises a second main body (231) and a second hollow foil area (232) in sequence, the second main body (231) comprising 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) comprising a second pole ear (2321), along the axial direction of the winding core (2), the second pole ear (2321) is the portion of the second hollow foil area (232) that exceeds the isolation film (22), and at least a portion of the second pole ear (2321) forms a second flattened portion (23211).

12. The cylindrical secondary battery (100) according to claim 11, characterized in that: A second groove (23121) is provided on the surface of the second active material layer (2312), the second groove (23121) extends along the axial direction of the winding core (2), and the second groove (23121) passes through one end surface (2312a) of the second active material layer (2312) along the axial direction of the winding core (2); The cylindrical secondary battery (100) satisfies: 0.53×10 4 ≤P2 / S2≤6×10 4 , wherein the density of the second flattened portion (23211) is P2 g / cm 3 , 0.6≤P2≤3.5, the cross-sectional area of ​​the second groove (23121) along the radial direction of the winding core (2) is S2 mm 2 .

13. The cylindrical secondary battery (100) according to claim 12, characterized in that: 0.53×10 4 ≤H2 / S2≤8×10 4 , wherein, along the axial direction of the winding core (2), the second flattened portion (23211) includes a second surface (23211a) facing away from the isolation film (22), the isolation film (22) includes a first end face (22a) and a second end face (22b), the second end face (22b) is closer to the second surface (23211a) relative to the first end face (22a), and the distance between the second surface (23211a) and the second end face (22b) is H2 mm, 0.3≤H2≤4.

14. The cylindrical secondary battery (100) according to claim 12, characterized in that: 0.93×10 4 ≤W2 / S2≤80×10 4 , wherein the coating mass per unit area of ​​the second active material layer (2312) on the second pole piece (23) is W2 mg / cm 2 , 8≤W2≤30.

15. The cylindrical secondary battery (100) according to claim 12, characterized in that: 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.

16. The cylindrical secondary battery (100) according to any one of claims 1 to 15, characterized in that: The first pole piece (21) is a negative pole piece.

17. An electrical device, characterized in that: The invention comprises a cylindrical secondary battery (100) as claimed in any one of claims 1 to 16.

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