Secondary battery

Abstract

The invention relates to the technical field of batteries, and discloses a secondary battery, which comprises a battery cell; the packaging film forms a first accommodating groove; the packaging film comprises a protection layer, a metal layer and a heat sealing layer which are sequentially stacked. The first accommodating groove comprises a first wall body and a second wall body surrounding the first wall body, and a heat sealing layer of the first wall body faces the battery cell; the first wall body comprises a first area, and the thickness of the heat sealing layer of the first area is smaller than that of the heat sealing layer of other areas except the first area of the packaging film; the battery cell comprises a first pole piece, a second area without a paste layer is arranged on the outermost circle of the battery cell and on the surface, facing the first containing groove, of the first pole piece, and the dynamic friction coefficient between the heat sealing layer of the second area and the heat sealing layer of the first area is larger than that between the heat sealing layer of the second area and the heat sealing layer of other areas, except the first area, of the packaging film. According to the secondary battery provided by the invention, the contact thermal resistance of the battery can be reduced, the thermal uniformity of the battery is improved, and the cycling stability of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a secondary battery. Background Art

[0002] With the rapid development of new energy vehicles and consumer electronics, the energy density and charge and discharge rate of lithium batteries continue to increase, which puts higher requirements on the thermal management performance of batteries. As the core packaging material of soft-pack lithium batteries, the structural design of aluminum-plastic film directly affects the heat dissipation efficiency and temperature uniformity of the battery cells.

[0003] However, the thermal uniformity and cyclic expansion of existing batteries still need to be improved. Summary of the invention

[0004] In view of this, the present invention provides a secondary battery to solve the problem that thermal uniformity and cyclic expansion of batteries in the prior art still need to be improved.

[0005] In a first aspect, the present invention provides a secondary battery, comprising:

[0006] Battery cells;

[0007] The packaging film is formed with a first receiving groove for receiving the battery cell; the packaging film comprises a protective layer, a metal layer and a heat-sealing layer which are stacked in sequence, the heat-sealing layer is arranged on a side of the metal layer facing the first receiving groove, and the protective layer is arranged on a side of the metal layer facing away from the first receiving groove;

[0008] The first receiving groove includes a first wall body and a second wall body surrounding the first wall body, wherein the heat sealing layer of the first wall body is arranged facing the battery core; the first wall body includes a first region, and the thickness of the heat sealing layer of the first region is smaller than the thickness of the heat sealing layer of other regions of the packaging film except the first region;

[0009] The battery cell includes a first pole piece. At the outermost circle of the battery cell, the surface of the first pole piece facing the first receiving groove has a second area without a coating layer, and the dynamic friction coefficient between the second area and the heat sealing layer of the first area is greater than the dynamic friction coefficient between the second area and the heat sealing layer of other areas of the packaging film except the first area.

[0010] Beneficial effects: For the secondary battery provided by the present invention, by forming a first accommodation groove in the encapsulation film, the thickness of the heat-sealing layer in the first region is controlled to be smaller than that of the heat-sealing layer in other regions of the encapsulation film except the first region. At the same time, the dynamic friction coefficient between the second region of the first electrode tab at the outermost circle of the battery cell and the heat-sealing layer in other regions of the encapsulation film except the first region is relatively large, so that the frictional force between the second region of the first electrode tab at the outermost circle of the battery cell and the heat-sealing layer in the first region is increased. Firstly, it can make the battery cell fit more closely with the encapsulation film, thereby reducing the air gap between the battery cell and the encapsulation film, reducing the contact thermal resistance, improving the overall heat dissipation efficiency of the battery, improving the thermal uniformity, and increasing the furnace temperature passing rate. Secondly, during the charge and discharge process of the battery, expansion will occur (especially for high-energy-density batteries such as high-nickel ternary or silicon-based systems, the expansion is more intense). When there is a certain frictional force between the battery cell and the encapsulation film, the existence of the frictional force can enable the encapsulation film to absorb stress more flexibly through micro-deformations. At the same time, the increase in the frictional force can limit the deformation amplitude, avoid excessive stretching and rupture of the encapsulation film, help reduce the internal stress during the charge and discharge process of the battery, improve the cyclic expansion of the battery cell, improve the performance stability of the battery, and reduce the decline in battery performance caused by internal expansion. Thirdly, the increase in the frictional force between the second region of the battery cell and the heat-sealing layer in the first region of the encapsulation film can prevent the battery cell from undergoing micro-displacements in the first accommodation groove during vibration, impact or long-term cycling, reducing the risk of internal short circuits such as electrode tab scratching and separator damage caused by mechanical friction. Fourthly, the reduction in the thickness of the heat-sealing layer in the first accommodation groove can shorten the heat conduction path between the encapsulation film and the battery cell, accelerate the transfer of heat from the inside of the battery cell to the outer layer of the encapsulation film, improve the overall heat dissipation efficiency of the battery, increase the furnace temperature passing rate, and reduce the risk of battery failure caused by local overheating of the battery cell in high-temperature or fast-charging scenarios. In addition, the reduction in the thickness of the heat-sealing layer in the first accommodation groove leaves more accommodation space for the battery cell, which is beneficial to reducing the overall thickness of the battery and increasing the volume energy density of the battery cell.

[0011] In an optional embodiment, the dynamic friction coefficient between the second region and the heat-sealing layer in the first region is μ1, and the dynamic friction coefficient between the second region and the heat-sealing layer in other regions of the encapsulation film except the first region is μ2, and μ1 and μ2 satisfy 1.1 ≤ μ1 / μ2 ≤ 5.

[0012] Beneficial effects: By satisfying μ1 / μ2≥1.1, μ1 and μ2 can not only effectively increase the friction between the battery cell and the heat-sealing layer in the first receiving groove, making the battery cell fit more closely with the packaging film, reducing the air gap between the battery cell and the packaging film, lowering the contact thermal resistance, thereby improving the overall heat dissipation efficiency of the battery, enhancing the thermal uniformity, and increasing the furnace temperature passing rate of the battery cell; but also ensure that the packaging film can more flexibly absorb stress through minute deformation, while the increase in friction can limit the deformation amplitude, preventing the packaging film from being overstretched and ruptured, which helps to reduce the internal stress of the battery during charge and discharge, thus improving the performance stability of the battery and reducing the degradation of battery performance caused by internal stress; at the same time, during vibration, impact or long-term cycling, it can effectively prevent the battery cell from undergoing minute displacement in the first receiving groove, reducing the risk of internal short circuits such as pole piece scratching and separator damage caused by mechanical friction. By satisfying μ1 / μ2≤5, μ1 and μ2 can reduce the material requirements and process requirements, lower the preparation difficulty and production cost, while avoiding cleaning the metal layer under the heat-sealing layer, ensuring the mechanical properties of the packaging film, and ensuring that the battery cell can pass the drop test.

[0013] In an optional embodiment, in the first receiving groove, on at least a part of the surface of the packaging film of the first wall body facing the battery cell, a first groove is provided, and the first groove is provided on at least a part of the heat-sealing layer; at least a part of the battery cell is placed in the first groove;

[0014] The depth of the first groove is less than or equal to the thickness of the heat-sealing layer;

[0015] And / or, the depth of the first groove is H1 mm, and the thickness of the heat-sealing layer in the first groove is H2 mm, and H1 and H2 satisfy 30%≤H1 / (H1 + H2)≤100%;

[0016] And / or, the area of the first wall body is S1 mm2, and the projected area of the first groove is S2 mm2, and S1 and S2 satisfy 0.7≤S2 / S1≤0.98.

[0017] Beneficial effects: By providing a first groove on the surface of the packaging film of the first wall body facing the battery cell, and the first groove is provided on at least a part of the heat-sealing layer, this can not only accommodate at least a part of the battery cell through the first groove, thereby increasing the energy density of the battery; but also shorten the heat conduction path between the metal layer of the packaging film and the battery cell, accelerating the transfer of heat from the inside of the battery cell to the outer layer of the packaging film, especially in high-temperature or fast-charging scenarios, which helps to reduce the risk of local overheating; by forming a first groove on the heat-sealing layer, the dynamic friction coefficient between the battery cell and the heat-sealing layer corresponding to the first groove increases, thereby effectively increasing the friction between the battery cell and the heat-sealing layer in the first receiving groove.

[0018] The depth of the first groove is less than or equal to the thickness of the heat-sealing layer to avoid damaging the metal layer during cleaning and ensure the encapsulation effect of the encapsulation film on the battery cell.

[0019] By satisfying H1 / (H1 + H2) ≥ 30%, H1 and H2 can not only effectively shorten the heat conduction path between the metal layer of the encapsulation film and the battery cell, accelerate the heat transfer from the inside of the battery cell to the outer layer of the encapsulation film, especially in high-temperature or fast-charging scenarios, which helps reduce the risk of local overheating and improve the furnace temperature passing rate of the battery cell; at the same time, it can effectively increase the dynamic friction coefficient μ1 of the heat-sealing layer in the first groove, ensure μ1 / μ2 ≥ 1.1, make the battery cell fit more closely with the encapsulation film, reduce the air gap between the battery cell and the encapsulation film, lower the contact thermal resistance, thereby improving the overall heat dissipation efficiency of the battery, improving the thermal uniformity, and increasing the furnace temperature passing rate of the battery cell; moreover, it can leave more accommodation space for the battery cell, which is beneficial to reducing the overall thickness of the battery and increasing the volume energy density. By satisfying H1 / (H1 + H2) ≤ 100%, H1 and H2 can effectively avoid damaging the metal layer during cleaning, ensure the encapsulation effect of the encapsulation film on the battery cell, ensure the mechanical properties of the encapsulation film, and ensure that the battery cell can pass the drop test.

[0020] By satisfying S2 / S1 ≥ 0.7, S1 and S2 can not only provide a larger accommodation space for the battery cell in the first groove, thereby increasing the energy density of the battery, but also ensure sufficient contact area between the battery cell and the heat-sealing layer in the first groove, thus ensuring sufficient frictional force between the battery cell and the heat-sealing layer in the first groove. By satisfying S2 / S1 ≤ 0.98, S1 and S2 can ensure the mechanical strength of the transition area of the encapsulation film cavity, ensure the encapsulation performance of the encapsulation film, and avoid corner breakage caused by subsequent cyclic expansion of the battery cell.

[0021] In an optional implementation manner, within the range of the orthographic projection area of the first groove, the thickness of the metal layer is H3 mm;

[0022] Outside the range of the orthographic projection area of the first groove, the thickness of the metal layer is H4 mm;

[0023] H3 and H4 satisfy 0.9 ≤ H3 / H4 ≤ 1.1.

[0024] Beneficial effects: By satisfying 0.9 ≤ H3 / H4 ≤ 1.1, H3 and H4 can ensure that the metal layer exposed in the first groove is not damaged, thereby ensuring the encapsulation effect of the encapsulation film on the battery cell while increasing the energy density of the battery.

[0025] In an optional implementation manner, a transition area is formed at the junction of the first wall and the second wall;

[0026] The distance between the edge of the first groove and the transition area is W1 mm, and W1 satisfies 0 ≤ W1 ≤ 10.

[0027] Beneficial effects: By satisfying 0 ≤ W1 ≤ 10, W1 can not only ensure the mechanical strength of the transition zone of the encapsulation film, guarantee the encapsulation performance of the encapsulation film, avoid corner breakage caused by subsequent cyclic expansion of the battery cell, and ensure that the battery cell passes the drop test; but also ensure the contact area between the heat-sealing layer in the first groove and the battery cell, guarantee sufficient frictional force between the heat-sealing layer in the first groove and the battery cell, make the battery cell fit more closely with the encapsulation film, reduce the air gap between the battery cell and the encapsulation film, lower the contact thermal resistance, thereby improving the overall heat dissipation efficiency of the battery, improving the thermal uniformity, increasing the furnace temperature passing rate of the battery cell, and improving the cyclic expansion of the battery cell. At the same time, it ensures that more battery cells can be accommodated in the first groove, improving the volumetric energy density of the battery.

[0028] In an alternative embodiment, the battery cell further includes a second pole piece, the second pole piece has the opposite polarity to the first pole piece, and the second pole piece is a negative pole piece; along the second direction, the edge of the first groove is disposed between the first pole piece and the second pole piece;

[0029] And / or, along the second direction, the distance between the edge of the first groove and the edge of the second pole piece is L mm, and L satisfies L ≥ 0.2.

[0030] Beneficial effects: By adopting the above design, the heat-sealing layer retained by the encapsulation film can effectively block the second pole piece and the metal layer, reducing the risk of electrochemical corrosion or short circuit of the battery.

[0031] In an alternative embodiment, a tab is disposed on one side of the battery cell along the second direction;

[0032] The encapsulation film further includes a first encapsulation area, a second encapsulation area, and a third encapsulation area. The first encapsulation area is disposed on one side of the first groove along the second direction close to the tab, and the second encapsulation area and the third encapsulation area are respectively disposed on both sides of the first groove along the first direction;

[0033] The distance between the edge of the first groove and the first encapsulation area is W3 mm, and W3 satisfies L < W3 ≤ 4;

[0034] And / or, the distance between the edge of the first groove and the second encapsulation area is W4 mm, and W4 satisfies 0.2 ≤ W4 ≤ 10;

[0035] And / or, the distance between the edge of the first groove and the third encapsulation area is W5 mm, and W5 satisfies 0.2 ≤ W5 ≤ 10.

[0036] Beneficial effects: By adopting the above design, the reliability of the battery cell packaging is ensured, enabling the battery cell to pass the drop test and preventing water vapor from entering the battery body during the battery cycle, which may cause abnormal swelling of the recycled battery. At the same time, sufficient frictional force between the heat-sealing layer 23 in the first groove 201 and the battery cell 10 is ensured, avoiding the existence of an air gap between the battery cell and the packaging film, reducing the contact thermal resistance, improving the thermal uniformity of the battery, and increasing the passing rate of the furnace temperature of the battery. In addition, it is ensured that the outermost first electrode tab of the battery cell can be completely accommodated in the first groove, improving the volumetric energy density of the battery.

[0037] In an alternative embodiment, the first wall body and the second wall body form a first mold shell; the packaging film further includes a second mold shell, which is disposed opposite to the first mold shell and covers the first receiving groove.

[0038] A second groove is formed on the side of the heat-sealing layer of the second mold shell facing the battery cell; along the third direction, at least a part of the battery cell overlaps with the second groove.

[0039] Beneficial effects: By adopting the above design, not only can the thickness of the heat-sealing layer in the first groove and the second groove be reduced, but also the dynamic friction coefficient between the heat-sealing layer in the first groove and the second groove and the battery cell can be increased.

[0040] In an alternative embodiment, along the third direction, the orthographic projection area of the second groove is located within the orthographic projection area of the first groove; the area of the orthographic projection area of the second groove is S3 mm², and the area of the orthographic projection area of the first groove is S4 mm², and S3 and S4 satisfy S3 ≥ 90% × S4.

[0041] And / or, the distance between the edge of the orthographic projection area of the second groove and the edge of the orthographic projection area of the first groove is W2 mm, and W2 satisfies 0 ≤ W2 ≤ 2.

[0042] And / or, within the range of the orthographic projection area of the first groove, the thickness variation of the packaging film does not exceed 10%.

[0043] And / or, within the range of the orthographic projection area of the second groove, the thickness variation of the packaging film does not exceed 10%.

[0044] Beneficial effects: The orthographic projection area of the second groove is located within the orthographic projection area of the first groove. S3 and S4 ensure the consistency of the battery thickness by satisfying S3 ≥ 90% × S4; and / or, W2 ensures that the orthographic projection area of the second groove is completely located within the orthographic projection area of the first groove by satisfying 0 ≤ W2 ≤ 2, thereby ensuring the consistency of the battery thickness; and / or, within the range of the orthographic projection area of the first groove, the thickness variation of the encapsulation film does not exceed 10%, thereby ensuring the consistency of the battery thickness; and / or, within the range of the orthographic projection area of the second groove, the thickness variation of the encapsulation film does not exceed 10%, thereby ensuring the consistency of the battery thickness, and further ensuring the stability of the battery's electrochemical performance.

[0045] In an alternative embodiment, the encapsulation film further includes a third mold shell, which is disposed opposite to the first mold shell; the third mold shell includes a third wall body, and a fourth wall body that is circumferentially disposed on the outer edge of the third wall body and extends along the third direction from the third wall body; the third wall body and the fourth wall body together enclose a second accommodation groove;

[0046] A third groove is formed on the side of the heat-sealing layer of the third wall body facing the battery cell; at least a part of the battery cell overlaps with the third groove.

[0047] Beneficial effects: By adopting the above design, not only can the thickness of the heat-sealing layer in the first groove and the third groove be reduced, but also the dynamic friction coefficient between the heat-sealing layer in the first groove and the third groove and the battery cell can be increased.

[0048] In an alternative embodiment, the first pole piece includes a first active layer; in the cross-section of the battery cell along the third direction, the number of layers of the first pole piece with the first active layer is N, and N ≤ 15;

[0049] and / or, the second pole piece includes a second active layer, and the second active layer includes a silicon-based material; the mass percentage content of silicon element in the second active layer is 1.5% - 50%.

[0050] Beneficial effects: The number of layers of the first pole piece with the first active layer does not exceed 15 layers, which can make the ED improvement effect more significant when this solution is applied to thin battery products. By laser cleaning the heat-sealing layer of the encapsulation film (or other cleaning processes, such as blade cleaning, etc., the specific cleaning method is not limited in this application), the grooves in the above embodiments are formed, and the dynamic friction coefficient between the battery cell and the heat-sealing layer in the grooves is increased. The existence of the grooves can not only provide space for the expansion of the battery cell, but also increase the dynamic friction coefficient between the battery cell and the heat-sealing layer in the grooves when the grooves are formed, which can inhibit the expansion deformation of the battery (especially the silicon anode battery) during the charge and discharge process. Description of the Drawings

[0051] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0052] Figure 1 Cross-sectional schematic view of the first encapsulation film of the secondary battery according to an embodiment of the present invention;

[0053] Figure 2 Cross-sectional schematic view of the second encapsulation film of the secondary battery according to an embodiment of the present invention;

[0054] Figure 3 Cross-sectional schematic view of the first secondary battery according to an embodiment of the present invention;

[0055] Figure 4 Longitudinal-sectional schematic view of the first secondary battery according to an embodiment of the present invention;

[0056] Figure 5 Assembly schematic view of the encapsulation film and the battery cell of the secondary battery according to an embodiment of the present invention;

[0057] Figure 6 Cross-sectional schematic view of the second secondary battery according to an embodiment of the present invention;

[0058] Figure 7 For Figure 6 Cross-sectional schematic view after hiding the battery cell in

[0059] Figure 8 For Figure 6 Top view of the encapsulation film before encapsulation in

[0060] Figure 9 Three-dimensional view of the first mold shell of the encapsulation film of the secondary battery according to an embodiment of the present invention;

[0061] Figure 10 Top view of the first mold shell of the encapsulation film of the secondary battery according to an embodiment of the present invention;

[0062] Figure 11 For Figure 10 Top view of the first first region on the bottom wall of the first groove in

[0063] Figure 12 For Figure 10 Top view of the second first region on the bottom wall of the first groove in

[0064] Figure 13 For Figure 10Top view of the third first region on the bottom wall of the first groove;

[0065] Figure 14 For Figure 10 Top view of the fourth first region on the bottom wall of the first groove;

[0066] Figure 15 Schematic projection diagram of the first groove and the second groove of the secondary battery according to the embodiment of the present invention in the third direction;

[0067] Figure 16 Schematic projection diagram of the first groove and the seal edge of the secondary battery according to the embodiment of the present invention in the third direction;

[0068] Figure 17 Cross-sectional schematic diagram of the third secondary battery according to the embodiment of the present invention;

[0069] Figure 18 For Figure 17 Cross-sectional schematic diagram after hiding the battery cell;

[0070] Figure 19 For Figure 17 Top view of the encapsulation film before encapsulation;

[0071] Figure 20 Schematic diagram of the accumulated glue in the groove.

[0072] Explanation of reference numerals:

[0073] 10, battery cell; 101, first encapsulation area; 102, second encapsulation area; 103, third encapsulation area; 11, first electrode tab; 12, second electrode tab; 13, separator;

[0074] 20, encapsulation film; 201, first groove; 202, second groove; 203, third groove; 204, deposition area;

[0075] 21, protective layer;

[0076] 22, metal layer; 23, heat-sealing layer;

[0077] 24, first region;

[0078] 25, first mold shell; 251, first wall body; 252, second wall body; 253, transition area; 254, first receiving groove; 26, second mold shell;

[0079] 27, third mold shell; 271, third wall body; 272, fourth wall body; 273, second receiving groove;

[0080] X - first direction; Y - second direction; Z - third direction. Detailed implementation manners

[0081] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0082] Combine the following Figures 1 to 20 , describing an embodiment of the present invention.

[0083] According to an embodiment of the present invention, there is provided a secondary battery, comprising:

[0084] Battery cell 10;

[0085] Encapsulation film 20, see Figure 7 As shown, the packaging film 20 is formed with a first receiving groove 254 for receiving the battery cell 10; see Figure 1 and Figure 2 As shown, the packaging film 20 includes a protective layer 21, a metal layer 22 and a heat sealing layer 23 which are stacked in sequence, the heat sealing layer 23 is arranged on the side of the metal layer 22 facing the first receiving groove 254, and the protective layer 21 is arranged on the side of the metal layer 22 away from the first receiving groove 254;

[0086] The first receiving groove 254 includes a first wall 251 and a second wall 252 surrounding the first wall 251. The heat sealing layer 23 of the first wall 251 is disposed facing the battery cell 10. The first wall 251 includes a first region, and the thickness of the heat sealing layer 23 in the first region is less than the thickness of the heat sealing layer 23 in other regions of the packaging film 20 except the first region.

[0087] See also Figure 5 As shown, the battery cell 10 includes a first pole piece 11. At the outermost circle of the battery cell 10, the surface of the first pole piece 11 facing the first receiving groove 254 has a second area without a coating layer, and the dynamic friction coefficient between the second area and the heat sealing layer 23 of the first area is greater than the dynamic friction coefficient between the second area and the heat sealing layer 23 of other areas of the packaging film 20 except the first area.

[0088] It should be noted that the "first direction X" herein refers to the width direction of the battery cell 10 and / or the secondary battery; the "second direction Y" herein refers to the height direction of the battery cell 10 and / or the secondary battery; the "third direction Z" herein refers to the thickness direction of the battery cell 10 and / or the secondary battery; the first direction X, the second direction Y and the third direction Z are mutually perpendicular. The "outermost circle" of the battery cell 10 herein refers to a layer located closest to the winding end of the core in the winding core structure and / or a layer of the core closest to the packaging film 20.

[0089] The secondary battery provided by the present invention forms a first accommodation groove 254 in the encapsulation film 20, controls the thickness of the heat-sealing layer 23 in the first region to be less than the thickness of the heat-sealing layer 23 in other regions of the encapsulation film 20 except the first region, and at the same time makes the dynamic friction coefficient between the second region of the outermost first electrode tab of the battery cell 10 and the heat-sealing layer 23 in other regions of the encapsulation film 20 except the first region larger, so as to increase the friction force between the second region of the outermost first electrode tab of the battery cell 10 and the first region. On the one hand, it can make the battery cell 10 fit more closely with the encapsulation film 20, thereby reducing the air gap between the battery cell 10 and the encapsulation film 20, lowering the contact thermal resistance, improving the overall heat dissipation efficiency of the battery, improving the thermal uniformity, and increasing the furnace temperature passing rate. On the second hand, the battery will expand during the charge and discharge process (especially high-nickel ternary or silicon-based system high-energy density batteries expand more violently). When there is a certain friction force between the battery cell 10 and the encapsulation film 20, the existence of the friction force can make the encapsulation film 20 more flexibly absorb stress through small deformations. At the same time, the increase in the friction force can limit the deformation amplitude, avoid excessive stretching and rupture of the encapsulation film 20, help reduce the internal stress during the charge and discharge process of the battery, improve the cyclic expansion of the battery cell, improve the performance stability of the battery, and reduce the decline in battery performance caused by internal expansion. On the third hand, the increase in the friction force between the second region of the battery cell 10 and the heat-sealing layer 23 in the first region of the encapsulation film 20 can prevent the battery cell 10 from having a small displacement in the first accommodation groove 254 during vibration, impact or long-term cycling, and reduce the risk of internal short circuits such as electrode tab scratching and diaphragm 13 damage caused by mechanical friction. On the fourth hand, the reduction in the thickness of the heat-sealing layer 23 in the first accommodation groove 254 can shorten the heat conduction path between the encapsulation film 20 and the battery cell 10, accelerate the transfer of heat from the inside of the battery cell 10 to the outer layer of the encapsulation film 20, improve the overall heat dissipation efficiency of the battery, increase the furnace temperature passing rate, and reduce the risk of battery failure caused by local overheating of the battery cell in high-temperature or fast-charging scenarios. In addition, the reduction in the thickness of the heat-sealing layer 23 in the first accommodation groove 254 leaves more accommodation space for the battery cell 10, which is beneficial to reducing the overall thickness of the battery and increasing the volumetric energy density of the battery cell.

[0090] Furthermore, the heat-sealing layer 23 can be made of PP material; the metal layer 22 can be made of aluminum material; the protective layer 21 can be made of nylon material.

[0091] In some embodiments, the dynamic friction coefficient between the second region and the heat-sealing layer 23 in the first region is μ1, and the dynamic friction coefficient between the second region and the heat-sealing layer 23 in other regions of the encapsulation film 20 except the first region is μ2, and μ1 and μ2 satisfy 1.1 ≤ μ1 / μ2 ≤ 5.

[0092] By satisfying μ1 / μ2≥1.1, μ1 and μ2 can not only effectively increase the friction between the battery cell 10 and the heat-sealing layer 23 in the first receiving groove 254, making the battery cell 10 fit more closely with the packaging film 20, reducing the air gap between the battery cell 10 and the packaging film 20, lowering the contact thermal resistance, thereby improving the overall heat dissipation efficiency of the battery, enhancing the thermal uniformity, and increasing the furnace temperature passing rate; but also ensure that the packaging film 20 can more flexibly absorb stress through minute deformation, while the increase in friction can limit the deformation amplitude, avoiding excessive stretching and rupture of the packaging film 20, contributing to reducing the internal stress of the battery during charge and discharge, improving the cyclic swelling of the battery, enhancing the performance stability of the battery, and reducing the degradation of battery performance caused by internal stress; at the same time, during vibration, impact or long-term cycling, it can effectively prevent the battery cell 10 from undergoing minute displacement in the first receiving groove 254, reducing the risk of internal short circuits such as pole piece scratching and diaphragm 13 damage caused by mechanical friction.

[0093] If the value of μ1 / μ2 is too large, not only are the material requirements and process requirements too high, increasing the preparation difficulty and production cost, but also when cleaning the heat-sealing layer 23 in the first receiving groove 254 to increase the value of μ1 / μ2, it is easy to over-clean the heat-sealing layer 23 in the first receiving groove 254, and it is easy to clean to the metal layer 22 under the heat-sealing layer 23, resulting in a reduction in the mechanical properties of the packaging film 20 and the inability to pass the drop test. Therefore, by satisfying μ1 / μ2≤5, μ1 and μ2 can reduce the material requirements and process requirements, lower the preparation difficulty and production cost, while avoiding cleaning to the metal layer 22 under the heat-sealing layer 23, ensuring the mechanical properties of the packaging film 20, and guaranteeing that the battery cell can pass the drop test.

[0094] In some embodiments, please refer to Figure 2 and Figure 7 As shown, on the surface of at least a part of the first wall body 251 of the packaging film 20 facing the battery cell 10 in the first receiving groove 254, a first groove 201 is provided, and the first groove 201 is provided on at least a part of the heat-sealing layer 23; at least a part of the battery cell 10 is placed in the first groove 201;

[0095] The depth of the first groove 201 is less than or equal to the thickness of the heat-sealing layer 23;

[0096] And / or, please refer to Figure 2 As shown, the depth of the first groove 201 is H1 mm, and the thickness of the heat-sealing layer 23 in the first groove 201 is H2 mm, and H1 and H2 satisfy 30%≤H1 / (H1 + H2)≤100%;

[0097] And / or, the area of the first wall body 251 is S1 mm², and the area of the positive projection of the first groove 201 along the third direction Z is S2 mm², and S1 and S2 satisfy 0.7≤S2 / S1≤0.98.

[0098] By providing a first groove 201 on one surface of the encapsulation film 20 facing the battery cell 10, and the first groove 201 is provided on at least part of the heat-sealing layer 23, not only can at least part of the battery cell 10 be accommodated by the first groove 201, thereby improving the battery energy density; but also the heat conduction path between the metal layer 22 of the encapsulation film 20 and the battery cell 10 can be shortened, accelerating the transfer of heat from the inside of the battery cell 10 to the outer layer of the encapsulation film 20. Especially in high-temperature or fast-charging scenarios, it helps to reduce the risk of local overheating; by forming the first groove 201 on the heat-sealing layer 23, the dynamic friction coefficient between the battery cell 10 and the heat-sealing layer 23 corresponding to the first groove 201 is increased, thereby effectively increasing the frictional force between the battery cell 10 and the heat-sealing layer 23 in the first receiving groove 254.

[0099] It should be noted that the first groove 201 can be formed by laser cleaning the heat-sealing layer 23. The bottom wall of the first groove 201 forms a first region 24, and the first region 24 contacts the second region of the outermost first pole piece 11 of the battery cell 10. The dynamic friction coefficient between the second region and the first region 24 is μ1. Please refer to Figures 11 - 14 As shown, during the process of machining to form the first region 24, laser cleaning can adopt Figure 11 the loop path in Figure 12 or the bow path in Figure 13 or the reciprocating path in Figure 14 or the one-way path in

[0100] The depth of the first groove 201 is less than or equal to the thickness of the heat-sealing layer 23 to avoid damaging the metal layer 22 during cleaning and ensure the encapsulation effect of the encapsulation film 20 on the battery cell 10.

[0101] It should be noted that if the value of H1 / (H1 + H2) is too small, that is, the depth of the first groove 201 is too shallow, on the one hand, it cannot effectively shorten the heat conduction path between the metal layer 22 of the encapsulation film 20 and the battery cell 10, and there is a risk of local overheating; on the other hand, during the cleaning process of the heat-sealing layer 23, it is difficult to effectively increase the dynamic friction coefficient μ1 of the heat-sealing layer 23 in the first groove 201, so it is difficult to effectively increase the value of μ1 / μ2 and difficult to ensure the tightness of the fit between the battery cell and the encapsulation film.

[0102] When H1 and H2 satisfy H1 / (H1 + H2) ≥ 30%, not only can the heat conduction path between the metal layer 22 of the encapsulation film 20 and the battery cell 10 be effectively shortened, accelerating the transfer of heat from the inside of the battery cell 10 to the outer layer of the encapsulation film 20, especially in high-temperature or fast-charging scenarios, which helps reduce the risk of local overheating and improve the furnace temperature passing rate of the battery cell; at the same time, it can effectively increase the dynamic friction coefficient μ1 of the heat-sealing layer 23 in the first groove 201, ensuring μ1 / μ2 ≥ 1.1, making the battery cell fit more tightly with the encapsulation film, reducing the air gap between the battery cell and the encapsulation film, lowering the contact thermal resistance, thereby enhancing the overall heat dissipation efficiency of the battery, improving thermal uniformity, and increasing the furnace temperature passing rate of the battery cell; moreover, it can leave more accommodation space for the battery cell 10, which is beneficial to reducing the overall thickness of the battery and increasing the volume energy density. When H1 and H2 satisfy H1 / (H1 + H2) ≤ 100%, it can effectively avoid damaging the metal layer 22 during cleaning, ensure the encapsulation effect of the encapsulation film 20 on the battery cell 10, ensure the mechanical properties of the encapsulation film 20, and ensure that the battery cell can pass the drop test.

[0103] If S2 / S1 is too small, not only can the first groove 201 not fully accommodate the battery cell 10, but also the battery cell 10 and the heat-sealing layer 23 in the first groove 201 cannot be effectively contacted. Therefore, when S1 and S2 satisfy S2 / S1 ≥ 0.7, it can not only make the first groove 201 provide a larger accommodation space for the battery cell 10, thereby increasing the energy density of the battery, but also ensure sufficient contact area between the battery cell 10 and the heat-sealing layer 23 in the first groove 201, thus ensuring sufficient frictional force between the battery cell 10 and the heat-sealing layer 23 in the first groove 201. Since the encapsulation film 20 needs to be processed to form the first accommodation groove 254, if S2 / S1 is too large, it is easy to cause insufficient mechanical strength in the transition area 253 of the accommodation cavity of the encapsulation film 20, which not only easily affects the encapsulation performance of the encapsulation film 20, but also easily causes corner breakage due to subsequent cyclic expansion of the battery cell 10. Therefore, when S1 and S2 satisfy S2 / S1 ≤ 0.98, it can ensure the mechanical strength of the transition area 253 of the accommodation cavity of the encapsulation film 20, guarantee the encapsulation performance of the encapsulation film 20, and avoid corner breakage caused by subsequent cyclic expansion of the battery cell 10.

[0104] Furthermore, please refer to Figure 20 As shown, during the cleaning process, after cleaning is completed, some vaporized heat-sealing particles will be deposited in the first groove 201, forming a deposition area 204 as shown in Figure 20 , resulting in a small amount of heat-sealing residue in the first groove 201; the area of the deposition area 204 is less than or equal to 50% of the positive projection area of the first groove 201 along the third direction Z, thereby ensuring a certain adhesiveness between the encapsulation film 20 and the battery cell 10 after cleaning while preventing too much heat-sealing residue from affecting the overall flatness of the battery.

[0105] In some embodiments, please refer to Figure 1 As shown, within the range of the orthographic projection area of the first groove 201, the thickness of the metal layer 22 is H3 mm;

[0106] Outside the range of the orthographic projection area of the first groove 201, the thickness of the metal layer 22 is H4 mm;

[0107] H3 and H4 satisfy 0.9 ≤ H3 / H4 ≤ 1.1.

[0108] By satisfying 0.9 ≤ H3 / H4 ≤ 1.1 for H3 and H4, it is ensured that the metal layer 22 exposed in the first groove 201 will not be damaged, thereby improving the battery energy density while ensuring the encapsulation effect of the encapsulation film 20 on the battery cell 10.

[0109] In some embodiments, please refer to Figure 9 As shown, the encapsulation film 20 forms a first mold shell 25. The first mold shell 25 includes a first wall body 251 and a second wall body 252 that is circumferentially provided on the outer edge of the first wall body 251 and extends along the third direction Z by the first wall body 251. The first wall body 251 and the second wall body 252 enclose a first accommodation groove 254; a transition area 253 is formed at the junction of the first wall body 251 and the second wall body 252;

[0110] Please also refer to Figure 10 As shown, the distance between the edge of the first groove 201 and the transition area 253 is W1 mm, and W1 satisfies 0 ≤ W1 ≤ 10.

[0111] It should be noted that if at least part of the first groove 201 is located within the transition area 253, the subsequent cyclic expansion of the battery cell 10 is likely to cause corner breakage. Therefore, W1 needs to satisfy W1 ≥ 0; if the area of the first groove 201 is too small, it will not only easily reduce the contact area between the heat-sealing layer 23 in the first groove 201 and the battery cell 10, reduce the friction force between the heat-sealing layer 23 in the first groove 201 and the battery cell 10, easily cause an air gap between the battery cell and the encapsulation film, increase the contact thermal resistance, reduce the battery thermal uniformity, and affect the furnace temperature passing rate of the battery, but also easily cause the outermost first pole piece 11 of the battery cell 10 not to be fully accommodated in the first groove 201, easily reducing the volume energy density of the battery. Therefore, W1 also needs to satisfy W1 ≤ 10.

[0112] By satisfying 0 ≤ W1 ≤ 10, W1 can not only ensure the mechanical strength of the transition region 253 of the encapsulation film 20, guarantee the encapsulation performance of the encapsulation film 20, avoid corner breakage caused by subsequent cyclic expansion of the battery cell 10, and ensure that the battery cell passes the drop test; but also ensure the contact area between the heat-sealing layer 23 in the first groove 201 and the battery cell 10, guarantee sufficient frictional force between the heat-sealing layer 23 in the first groove 201 and the battery cell 10, make the battery cell fit more closely with the encapsulation film, reduce the air gap between the battery cell and the encapsulation film, lower the contact thermal resistance, thereby improving the overall heat dissipation efficiency of the battery, improving the thermal uniformity, increasing the furnace temperature passing rate of the battery cell, and improving the cyclic expansion of the battery cell. At the same time, it ensures that more battery cells can be accommodated in the first groove 201, and improves the volumetric energy density of the battery.

[0113] In some embodiments, referring to Figure 5 as shown, the battery cell 10 further includes a second pole piece 12, the second pole piece 12 has a polarity opposite to that of the first pole piece 11, and the second pole piece 12 is a negative pole piece; along the second direction Y, the edge of the first groove 201 is disposed between the first pole piece 11 and the second pole piece 12;

[0114] and / or, along the second direction Y, the distance between the edge of the first groove 201 and the edge of the second pole piece 12 is L mm, and L satisfies L ≥ 0.2.

[0115] It should be noted that the first pole piece 11 is a positive pole piece and the second pole piece 12 is a negative pole piece. After the first groove 201 is formed on the heat-sealing layer 23 of the encapsulation film 20, the thickness of the heat-sealing layer 23 becomes thinner. When a drop occurs, the edge of the second pole piece 12 inside the battery is likely to pierce the heat-sealing layer 23, and the second pole piece 12 is likely to directly contact the metal layer 22 of the encapsulation film 20, increasing the risk of electrochemical corrosion or short circuit of the battery.

[0116] By disposing the edge of the first groove 201 between the first pole piece 11 and the second pole piece 12 along the second direction Y, and / or, along the second direction Y, the distance between the edge of the first groove 201 and the edge of the second pole piece 12 is L mm, and L satisfies L ≥ 0.2, thereby ensuring that the remaining heat-sealing layer 23 of the encapsulation film 20 can effectively block the second pole piece 12 and the metal layer 22, reducing the risk of electrochemical corrosion or short circuit of the battery, and increasing the passing rate of the battery drop test.

[0117] In some embodiments, referring to Figure 16 as shown, a tab (not shown in the figure) is provided on one side of the battery cell 10 along the second direction Y;

[0118] The encapsulation film 20 further includes a first encapsulation area 101, a second encapsulation area 102, and a third encapsulation area 103. The first encapsulation area 101 is disposed on one side of the first groove 201 along the second direction Y close to the tab, and the second encapsulation area 102 and the third encapsulation area 103 are respectively disposed on both sides of the first groove 201 along the first direction X;

[0119] The distance between the edge of the first groove 201 and the first encapsulation area 101 is W3 mm, and W3 satisfies L < W3 ≤ 4;

[0120] And / or, the distance between the edge of the first groove 201 and the second encapsulation area 102 is W4 mm, and W4 satisfies 0.2 ≤ W4 ≤ 10;

[0121] And / or, the distance between the edge of the first groove 201 and the third encapsulation area 103 is W5 mm, and W5 satisfies 0.2 ≤ W5 ≤ 10.

[0122] It should be noted that if the distance between the edge of the first groove 201 and the first encapsulation area 101 is too close, it is easy to reduce the reliability of the cell encapsulation, and the drop test cannot be passed. At the same time, moisture is likely to enter the battery body during the battery cycle, resulting in abnormal expansion of the cycle battery. Therefore, W3 needs to satisfy W3 > L; if the distance between the edge of the first groove 201 and the first encapsulation area 101 is too far, it is not only easy to reduce the contact area between the heat-sealing layer 23 in the first groove 201 and the cell 10, reduce the friction force between the heat-sealing layer 23 in the first groove 201 and the cell 10, easily cause an air gap between the cell and the encapsulation film, increase the contact thermal resistance, reduce the battery thermal uniformity, and affect the furnace temperature passing rate of the battery; moreover, it is easy to cause the outermost first pole piece 11 of the cell 10 not to be completely accommodated in the first groove 201, which is likely to reduce the volume energy density of the battery. Therefore, W3 also needs to satisfy W3 ≤ 4.

[0123] If the distance between the edge of the first groove 201 and the second encapsulation area 102 is too close, it is easy to reduce the reliability of the cell encapsulation, and the drop test cannot be passed. At the same time, moisture is likely to enter the battery body during the battery cycle, resulting in abnormal expansion of the cycle battery. Therefore, W4 needs to satisfy W4 ≥ 0.2; if the distance between the edge of the first groove 201 and the second encapsulation area 102 is too far, it is not only easy to reduce the contact area between the heat-sealing layer 23 in the first groove 201 and the cell 10, reduce the friction force between the heat-sealing layer 23 in the first groove 201 and the cell 10, easily cause an air gap between the cell and the encapsulation film, increase the contact thermal resistance, reduce the battery thermal uniformity, and affect the furnace temperature passing rate of the battery, but also easy to cause the outermost first pole piece 11 of the cell 10 not to be completely accommodated in the first groove 201, which is likely to reduce the volume energy density of the battery. Therefore, W4 also needs to satisfy W4 ≤ 10.

[0124] The distance between the edge of the first groove 201 and the third encapsulation area 103 is the same as that between the edge of the first groove 201 and the second encapsulation area 102, which will not be elaborated here.

[0125] In some embodiments, please refer to Figure 6 and Figure 7 As shown, the first wall body 251 and the second wall body 252 form the first mold shell 25; the encapsulation film 20 further includes a second mold shell 26, and the second mold shell 26 is disposed opposite to the first mold shell 25 along the third direction Z after encapsulation, and the second mold shell 26 covers the first accommodation groove 254;

[0126] On the side of the heat-sealing layer 23 of the second mold shell 26 facing the battery cell 10, a second groove 202 is formed; along the third direction Z, at least a part of the battery cell 10 overlaps with the second groove 202.

[0127] It should be noted that the encapsulation film 20 can form the first mold shell 25 and the second mold shell 26 by die-cutting; the first groove 201 and the second groove 202 can be formed by laser cleaning; for the cleaning of the encapsulation film 20, the encapsulation film 20 can be pre-treated and cleaned before die-cutting, or the encapsulation film 20 can be cleaned after die-cutting, and die-cutting is performed before the battery cell is put into the shell.

[0128] By adopting the above design, not only can the thickness of the heat-sealing layer 23 in the first groove 201 and the second groove 202 be reduced, but also the dynamic friction coefficient between the heat-sealing layer 23 in the first groove 201 and the second groove 202 and the battery cell 10 can be increased. The beneficial effects brought about are the same as the analysis of the first groove 201 above, which will not be elaborated here.

[0129] In some embodiments, please refer to Figure 15 As shown, along the third direction Z, the orthographic projection area of the second groove 202 is located within the orthographic projection area of the first groove 201; the area of the orthographic projection area of the second groove 202 is S3 mm², and the area of the orthographic projection area of the first groove 201 is S4 mm², and S3 and S4 satisfy S3≥90%×S4;

[0130] And / or, still referring to Figure 15 As shown, the distance between the edge of the orthographic projection area of the second groove 202 and the edge of the orthographic projection area of the first groove 201 is W2 mm, and W2 satisfies 0≤W2≤2;

[0131] And / or, within the range of the orthographic projection area of the first groove 201, the thickness variation of the encapsulation film 20 does not exceed 10%;

[0132] And / or, within the range of the orthographic projection area of the second groove 202, the thickness variation of the encapsulation film 20 does not exceed 10%.

[0133] It should be noted that the orthographic projection area of the second groove 202 is located within the orthographic projection area of the first groove 201. S3 and S4 satisfy S3≥90%×S4 to ensure the consistency of the battery thickness; and / or, W2 satisfies 0≤W2≤2 to ensure that the orthographic projection area of the second groove 202 is completely located within the orthographic projection area of the first groove 201, thereby ensuring the consistency of the battery thickness; and / or, within the range of the orthographic projection area of the first groove 201, the thickness variation of the encapsulation film 20 does not exceed 10%, thereby ensuring the consistency of the battery thickness; and / or, within the range of the orthographic projection area of the second groove 202, the thickness variation of the encapsulation film 20 does not exceed 10%, thereby ensuring the consistency of the battery thickness, and further ensuring the stability of the battery electrochemical performance.

[0134] In some embodiments, please refer to Figure 17 and Figure 18 As shown, the encapsulation film 20 further includes a third mold shell 27. The third mold shell 27 is disposed opposite to the first mold shell 25 along the third direction Z after encapsulation; the third mold shell 27 includes a third wall body 271 and a fourth wall body 272 that is circumferentially disposed on the outer edge of the third wall body 271 and extends from the third wall body 271 along the third direction Z; the third wall body 271 and the fourth wall body 272 together enclose a second receiving groove 273;

[0135] A third groove 203 is formed on the side of the heat-sealing layer 23 of the third wall body 271 facing the battery cell 10; at least a part of the battery cell 10 overlaps with the third groove 203.

[0136] It should be noted that the encapsulation film 20 can be formed into the first mold shell 25 and the third mold shell 27 by die-cutting; the first groove 201 and the third groove 203 can be formed by laser cleaning.

[0137] By adopting the above design, not only can the thickness of the heat-sealing layer 23 in the first groove 201 and the third groove 203 be reduced, but also the dynamic friction coefficient between the heat-sealing layer 23 in the first groove 201 and the third groove 203 and the battery cell 10 can be increased. The beneficial effects brought about are the same as the analysis of the above first groove 201 and will not be elaborated here.

[0138] In some embodiments, the first pole piece 11 includes a first active layer; in the cross-section of the battery cell 10 along the third direction Z, the number of layers of the first pole piece 11 with the first active layer is N, and N≤15;

[0139] and / or, the second pole piece 12 includes a second active layer, and the second active layer includes a silicon-based material; the mass percentage content of silicon element in the second active layer is 1.5% - 50%.

[0140] It should be noted that the first electrode 11 is a positive electrode, and the first active layer is a positive electrode active coating. In the cross-section of the battery cell 10 along the third direction Z, the number of layers of the first electrode 11 with the first active layer does not exceed 15 layers, which can make the ED improvement effect more significant when this solution is applied to thin battery products. For a battery cell with a silicon-carbon negative electrode, the second electrode 12 is a negative electrode, and the second active layer is a negative electrode active coating. The second active layer includes a silicon-based material, and the mass percentage of silicon element in the second active layer is 1.5% - 50%. During the lithium intercalation process of the silicon-carbon negative electrode, there is a large volume expansion, which will cause a large expansion stress on the battery outer packaging material, and there is a safety failure that the corner of the outer packaging material is prone to rupture. By laser cleaning (or other cleaning processes, such as blade cleaning, etc., the specific cleaning method is not limited in this application) the heat-sealing layer 23 of the packaging film 20, the groove structure (the first groove 201, or the first groove 201 and the second groove 202, or the first groove 201 and the third groove 203) in the above embodiment is formed, and the dynamic friction coefficient between the battery cell 10 and the heat-sealing layer 23 in the groove is increased. The existence of the groove can not only provide space for the expansion of the battery cell on the one hand, but also increase the dynamic friction coefficient between the battery cell and the heat-sealing layer 23 in the groove when the groove is formed, which can inhibit the expansion deformation of the battery (especially the silicon negative electrode battery) during the charge and discharge process.

[0141] To verify the influence of the first groove 201 provided on the packaging film 20 on the performance of the secondary battery, the following experiments were carried out:

[0142] 1. Oven temperature test:

[0143] The battery cell is charged at a constant current of 0.7C to the upper limit voltage of 4.4V, and then charged at a constant voltage of 4.4V to 0.025C. After charging is completed, the battery cell is placed in an oven with an initial temperature of 25 ± 3°C, and the temperature is increased at a rate of 5 ± 2°C / min to the set target temperature (130°C, 140°C), and the target temperature is maintained for 60 minutes, and then the test ends. The judgment criterion for passing the oven temperature test is that the battery cell does not catch fire or explode. If the temperature of the battery cell continues to rise to catch fire or explode during the test, the test fails. For each example or comparative example, 10 battery cells are used as parallel samples for testing, and the number of battery cells passing the oven temperature test is recorded.

[0144] 2. Cyclic expansion test:

[0145] Before the test starts, it is charged at a constant current of 1C to the upper limit voltage of 4.4V, and then charged at a constant voltage of 4.4V to 0.02C, and the thickness of the battery cell in the initial fully charged state is recorded as the initial thickness, and then it is discharged at a current of 0.5C to 3V.

[0146] Cyclic swelling test: Charge at a constant current of 1C to the upper limit voltage of 4.4V, then charge at a constant voltage of 4.4V to 0.02C, and let it stand for 10 minutes; after standing, discharge at a current of 0.5C to 3V and let it stand for 10 minutes. This is one charge-discharge cycle. Repeat such charge / discharge cycles 1000 times. After 1000 times, charge the battery cell to 100% SOC and record the thickness of the fully charged battery cell after 1000 times, which is the thickness for the cyclic test.

[0147] Calculate the cyclic thickness swelling rate of the battery. Cyclic thickness swelling rate = (thickness for cyclic test - initial thickness) / initial thickness * 100%. For each example or comparative example, 3 battery cells are used as parallel samples for testing, and record the average value of cyclic swelling after 1000 cycles for the three battery cells.

[0148] 3. Drop test:

[0149] Charge the battery cell at a constant current of 0.7C to the upper limit voltage of 4.4V, then charge at a constant voltage of 4.4V to 0.025C. After charging is completed, place the battery cell in a fixed fixture. Check the appearance of the battery cell and take pictures before and after the test. Drop the battery cell freely onto the ground from a height of 1.5m. Drop the battery cell once on each of the six sides and four corners, which is one round, and a total of 10 rounds of tests are carried out. The passing standard for the drop test: no smoking, no leakage of liquid, and the voltage drop of the battery cell < 30mV. Among them, the battery voltage drop = voltage value before the drop test - voltage value after the drop test. For each example or comparative example, 10 lithium-ion batteries are tested, and record the number of battery cells passing the drop test.

[0150] 4. Volume energy density:

[0151] Charge the battery cell at a constant current of 0.5C to 4.4V, then charge at a constant voltage to 0.02C to complete the charging of the battery cell; next, discharge at a constant current of 0.5C until the voltage of the battery cell drops to 3.0V, record the total capacity C discharged during the discharge process, and calculate the actual volume V of the lithium-ion battery. VED = discharge capacity C * voltage platform / battery cell volume V, with the unit of Wh / L.

[0152] The following details the specific settings in each example and comparative example in the experiment. Among them, the first electrode 11 is the positive electrode, and the second electrode 12 is the negative electrode.

[0153] Examples and comparative examples:

[0154] Example 1

[0155] Battery preparation:

[0156] (1) Preparation of the positive electrode sheet: The positive electrode conductive agent is added to the positive electrode binder solution and stirred evenly, and then the positive electrode active material particles are added and stirred evenly to prepare the positive electrode active layer slurry. Based on the dry weight, the mass content of the positive electrode active material particles is 97.3%, the mass content of the positive electrode binder is 1.3%, and the mass content of the positive electrode conductive agent is 1.4%. The active slurry is coated on the aluminum foil and the positive electrode sheet is obtained after baking and rolling.

[0157] (2) Preparation of the negative electrode sheet: 43.1% of the silicon-carbon composite material, 53.8% of graphite, 0.5% of conductive carbon black, 1.3% of binder and 1.3% of dispersant are mixed evenly, and then an appropriate amount of deionized water is added and dispersed evenly to prepare the negative electrode slurry. The negative electrode slurry is coated on the copper foil with carbon coating and the negative electrode sheet is obtained after baking and rolling.

[0158] (3) The positive and negative electrode sheets are slit, fabricated and wound with the separator to obtain the core.

[0159] (4) The heat-sealing layer at the bottom of the accommodating groove of the laser-formed packaging film is cleaned to form a groove, the core is placed in the accommodating groove of the formed packaging film, and the lithium-ion battery is obtained after packaging, baking, liquid injection, formation, secondary packaging, sorting and OCV.

[0160] The parameters in each example and comparative example are shown in Table 1.

[0161] Table 1

[0162]

[0163] Table 1 (continued)

[0164]

[0165] Note: (1) The value of W1 in Example 11 in Table 1 being -0.5 means that at least part of the first groove 201 is provided in the transition zone 253, that is, at least part of the transition zone 253 is also cleaned;

[0166] (2) The "*" in Comparative Example 2 in Table 1 means that the first groove 201 has actually been cleaned to the metal layer 22, that is, at least part of the corresponding metal layer 22 in the first groove 201 is cleaned.

[0167] The experimental results in each example and comparative example are shown in Table 2.

[0168] Table 2

[0169]

[0170] Table 2 (continued)

[0171]

[0172] Note: In Table 2, "PASS" means passing. For example, "5PASS / 10" means that 5 out of 10 samples pass the experimental test.

[0173] From the above experiments, comparing Examples 1 to 6 with Comparative Example 1, it can be seen that by satisfying μ1 / μ2≥1.1 for μ1 and μ2, the passing rate of the furnace temperature of the battery cell can be improved, and the cyclic swelling of the battery cell can be improved. Moreover, within the range of 1.1≤μ1 / μ2≤5, the greater the value of μ1 / μ2, the better the effect. Comparing Examples 1 to 6 with Comparative Example 2, for μ1 and μ2, by satisfying μ1 / μ2≤5, the mechanical properties of the encapsulation film 20 can be ensured, and it can be guaranteed that the battery cell can pass the drop test.

[0174] Comparing Examples 8 to 10 with Example 7, it can be seen that by satisfying H1 / (H1 + H2)≥30% for H1 and H2, the passing rate of the furnace temperature of the battery cell can be improved, the cyclic swelling of the battery cell can be improved, and at the same time, the volume energy density of the battery cell can be increased. Moreover, within the range of 30%≤H1 / (H1 + H2)≤100%, the greater the value of H1 / (H1 + H2), the better the effect. If H1 / (H1 + H2)≥100%, it is easy to cause damage to the metal layer 22 during cleaning, and the mechanical properties of the encapsulation film 20 cannot be ensured. Therefore, no more examples are set here.

[0175] Comparing Examples 12 to 14 with Example 11, it can be seen that by satisfying W1≥0 for W1, it can be ensured that the battery cell passes the drop test. Comparing Examples 12 to 14 with Example 15, it can be seen that by satisfying W1≤10 for W1, the passing rate of the furnace temperature of the battery cell can be improved, the cyclic swelling of the battery cell can be improved, and the volume energy density of the battery can be increased. Moreover, within the range of 0≤W1≤10, the smaller the value of W1, the better the effect.

[0176] Comparing Examples 17 to 19 with Example 16, it can be seen that by satisfying W3>L for W3, it can be ensured that the battery passes the drop test and the cyclic swelling of the battery can be improved. Comparing Examples 17 to 19 with Example 20, it can be seen that by satisfying W3≤4 for W3, the passing rate of the furnace temperature of the battery can be improved and the volume energy density of the battery can be increased.

[0177] Comparing Examples 22 to 24 with Example 21, it can be seen that by satisfying W4≥0.2 for W4, it can be ensured that the battery passes the drop test and the cyclic swelling of the battery can be improved. Comparing Examples 22 to 24 with Example 25, it can be seen that by satisfying W4≤10 for W4, the passing rate of the furnace temperature of the battery can be improved and the volume energy density of the battery can be increased.

[0178] As can be seen from Examples 27 to 29 compared with Example 26, by satisfying W5≥0.2, W5 can ensure that the battery passes the drop test and improve the cyclic swelling of the battery; as can be seen from Examples 27 to 29 compared with Example 30, by satisfying W5≤10, W5 can improve the passing rate of the furnace temperature of the battery and increase the volume energy density of the battery.

[0179] As can be seen from Example 32 and Example 33 compared with Example 31, by satisfying L≥0.2, L can increase the passing rate of the battery drop test.

[0180] Although embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations fall within the scope defined by the appended claims.

Claims

1. A secondary battery, characterized in that, include: Battery cell (10); A packaging film (20), the packaging film (20) being formed with a first receiving groove (254) for receiving the battery cell (10); the packaging film (20) comprising a protective layer (21), a metal layer (22) and a heat-sealing layer (23) which are stacked in sequence, the heat-sealing layer (23) being arranged on a side of the metal layer (22) facing the first receiving groove (254), and the protective layer (21) being arranged on a side of the metal layer (22) facing away from the first receiving groove (254); The first containing groove (254) comprises a first wall (251) and a second wall (252) surrounding the first wall (251), the heat sealing layer (23) of the first wall (251) being arranged facing the battery core (10); the first wall (251) comprises a first region, the thickness of the heat sealing layer (23) of the first region is smaller than the thickness of the heat sealing layer (23) of other regions of the packaging film (20) except the first region; The battery cell (10) comprises a first pole piece (11), and at the outermost circle of the battery cell (10), the surface of the first pole piece (11) facing the first receiving groove (254) has a second area without a paste layer, and the dynamic friction coefficient between the second area and the heat sealing layer (23) of the first area is greater than the dynamic friction coefficient between the second area and the heat sealing layer (23) of other areas of the packaging film (20) except the first area.

2. The secondary battery according to claim 1, characterized in that, The dynamic friction coefficient between the second region and the heat sealing layer (23) of the first region is μ1, and the dynamic friction coefficient between the second region and the heat sealing layer (23) of other regions of the packaging film (20) except the first region is μ2, and μ1 and μ2 satisfy 1.1≤μ1 / μ2≤5.

3. The secondary battery according to claim 1, wherein In the first containing groove (254), a first groove (201) is provided on a surface of at least a portion of the packaging film (20) of the first wall (251) facing the battery cell (10), and the first groove (201) is arranged on at least a portion of the heat sealing layer (23); at least a portion of the battery cell (10) is built into the first groove (201); The depth of the first groove (201) is less than or equal to the thickness of the heat sealing layer (23); And / or, the depth of the first groove (201) is H1 mm, the thickness of the heat-sealing layer (23) in the first groove (201) is H2 mm, and H1 and H2 satisfy 30%≤H1 / (H1+H2)≤100%; And / or, the area of ​​the first wall (251) is S1 mm2, the orthographic projection area of ​​the first groove (201) is S2 mm2, and S1 and S2 satisfy 0.7≤S2 / S1≤0.

98.

4. The secondary battery according to claim 3, wherein Within the orthographic projection area of ​​the first groove (201), the thickness of the metal layer (22) is H3 mm; Outside the orthographic projection area of ​​the first groove (201), the thickness of the metal layer (22) is H4 mm; H3 and H4 satisfy 0.9≤H3 / H4≤1.

1.

5. The secondary battery according to claim 3, characterized in that, A transition region (253) is formed at the junction of the first wall body (251) and the second wall body (252); The distance between the edge of the first groove (201) and the transition region (253) is W1 mm, and W1 satisfies 0 ≤ W1 ≤ 10.

6. The secondary battery according to claim 3, characterized in that, The battery cell (10) further includes a second electrode tab (12), the polarity of the second electrode tab (12) is opposite to that of the first electrode tab (11), and the second electrode tab (12) is a negative electrode tab; along the second direction (Y), the edge of the first groove (201) is disposed between the first electrode tab (11) and the second electrode tab (12); And / or, along the second direction (Y), the distance between the edge of the first groove (201) and the edge of the second electrode tab (12) is L mm, and L satisfies L ≥ 0.

2.

7. The secondary battery according to claim 6, characterized in that, A tab is provided on one side of the battery cell (10) along the second direction (Y); The encapsulation film (20) further includes a first encapsulation region (101), a second encapsulation region (102) and a third encapsulation region (103), the first encapsulation region (101) is disposed on the side of the first groove (201) close to the tab along the second direction (Y), and the second encapsulation region (102) and the third encapsulation region (103) are respectively disposed on both sides of the first groove (201) along the first direction (X); The distance between the edge of the first groove (201) and the first encapsulation region (101) is W3 mm, and W3 satisfies L < W3 ≤ 4; And / or, the distance between the edge of the first groove (201) and the second encapsulation region (102) is W4 mm, and W4 satisfies 0.2 ≤ W4 ≤ 10; And / or, the distance between the edge of the first groove (201) and the third encapsulation region (103) is W5 mm, and W5 satisfies 0.2 ≤ W5 ≤ 10.

8. The secondary battery according to claim 5, wherein The first wall body (251) and the second wall body (252) form a first mold shell (25); The encapsulation film (20) further includes a second mold shell (26), the second mold shell (26) is disposed opposite to the first mold shell (25), and the second mold shell (26) covers the first receiving groove (254); A second groove (202) is formed on the side of the heat-sealing layer (23) of the second mold shell (26) facing the battery cell (10); along the third direction (Z), at least a part of the battery cell (10) overlaps with the second groove (202).

9. The secondary battery according to claim 8, characterized in that, Along the third direction (Z), the orthographic projection region of the second groove (202) is located within the orthographic projection region of the first groove (201); the area of the orthographic projection region of the second groove (202) is S3 mm², and the area of the orthographic projection region of the first groove (201) is S4 mm², and S3 and S4 satisfy S3 ≥ 90% × S4; And / or, the distance between the edge of the orthographic projection region of the second groove (202) and the edge of the orthographic projection region of the first groove (201) is W2 mm, and W2 satisfies 0 ≤ W2 ≤ 2; And / or, within the range of the orthographic projection region of the first groove (201), the thickness variation of the encapsulation film (20) does not exceed 10%; And / or, within the range of the orthographic projection area of the second groove (202), the thickness variation of the encapsulation film (20) does not exceed 10%.

10. The secondary battery according to claim 8, characterized in that, The encapsulation film (20) further includes a third mold shell (27), and the third mold shell (27) is disposed opposite to the first mold shell (25); the third mold shell (27) includes a third wall body (271), and a fourth wall body (272) that is circumferentially provided on the outer edge of the third wall body (271) and is formed by the third wall body (271) extending along the third direction (Z); the third wall body (271) and the fourth wall body (272) jointly enclose to form a second accommodation groove (273); A third groove (203) is formed on the side of the heat-sealing layer (23) of the third wall body (271) facing the battery cell (10); at least a part of the battery cell (10) overlaps with the third groove (203).

11. The secondary battery according to claim 7, characterized in that, The first pole piece (11) includes a first active layer; in the cross-section of the battery cell (10) along the third direction (Z), the number of layers of the first pole piece (11) with the first active layer is N, and N ≤ 15; And / or, the second pole piece (12) includes a second active layer, and the second active layer includes a silicon-based material; the mass percentage content of silicon element in the second active layer is 1.5% - 50%.

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