Battery cell and lithium ion battery

Abstract

The embodiment of the utility model provides a battery cell and a lithium ion battery, and relates to the technical field of batteries. The battery cell comprises a plurality of pole piece units and second diaphragms, each pole piece unit comprises at least one first pole piece, at least one first diaphragm and at least one second pole piece in the third direction of the battery cell, the polarities of the first pole pieces and the second pole pieces are opposite, and the first pole pieces, the first diaphragms and the second pole pieces are sequentially stacked; along the third direction of the battery cell, the second diaphragm is wound from inside to outside to form a plurality of accommodating spaces, and the plurality of pole piece units are sequentially stacked and are arranged in the plurality of accommodating spaces one by one. The ending section of the second diaphragm is located on the flat and straight surface of the outermost side of the battery cell, in the third direction of the battery cell, the length of the projection of the ending section is S2, the width of the projection of the second pole piece is Wa, and S2 and Wa meet the condition that S2 / Wa is larger than or equal to 0.1 and smaller than or equal to 0.3, so that the situation that the battery cell is loose due to the fact that the ending section is too short can be avoided, the situation that the ending section is too long can also be avoided, and the thickness consistency of the battery cell is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of batteries, in particular to a battery core and a lithium-ion battery. Background Art

[0002] Lithium-ion batteries have been widely used in various industries due to their high energy density, lack of memory effect, and long cycle life. With the large-scale application of lithium-ion batteries, the performance and manufacturing processes of lithium-ion batteries have been continuously explored and improved, especially the cycle life and safety performance of lithium-ion batteries.

[0003] In related art, a lithium-ion battery cell includes multiple electrode units and a second separator. The electrode unit includes a first electrode, a first separator, and a second electrode that are stacked. The second separator and the multiple electrode units are wound to form a battery cell.

[0004] However, the battery cells have problems with looseness and poor thickness consistency. Utility Model Content

[0005] The embodiments of the present invention provide a battery cell and a lithium-ion battery to solve the problems of looseness and poor thickness consistency of the battery cells.

[0006] In one aspect, an embodiment of the present invention provides a battery cell, comprising:

[0007] A plurality of electrode pieces, along a third direction of the battery cell, the electrode pieces comprising at least one first electrode piece, at least one first diaphragm, and at least one second electrode piece, wherein the first electrode piece and the second electrode piece have opposite polarities, and the first electrode piece, the first diaphragm, and the second electrode piece are sequentially stacked;

[0008] A second diaphragm is wound from inside to outside along the third direction of the battery core to form a plurality of accommodating spaces, and the plurality of electrode units are stacked in sequence and arranged one by one in the plurality of accommodating spaces;

[0009] The battery cell includes a flat surface and a side surface. The tail section of the second diaphragm is located on the outermost flat surface of the battery cell. In the third direction of the battery cell, the length of the projection of the tail section is S2, and the width of the projection of the second pole piece is Wa, wherein S2 and Wa satisfy: 0.1≤S2 / Wa≤0.3.

[0010] In a possible embodiment, the head portion of the second diaphragm located at the winding center has a folded segment, and in the third direction, a projection of the folded segment and a projection of the tail segment do not overlap with each other.

[0011] In a possible implementation manner, in the third direction, the length of the projection of the folded segment is S1, wherein S1 and Wa satisfy: 0.07≤S1 / Wa≤0.3.

[0012] In one possible embodiment, the adhesion between the first diaphragm and the second pole piece is σa; the thickness of the second pole piece in the thickness direction of the first diaphragm is Ha; the surface density of the first pole piece on one side in the thickness direction of the first diaphragm is CWc; the surface density of the second pole piece on one side in the thickness direction of the first diaphragm is CWa;

[0013] Among them, S1 satisfies: Ha*Wa*(4CWa+2CWc)*9.8 / σa≤S1≤10*Wa.

[0014] In one possible implementation, both the first diaphragm and the second diaphragm include a base film;

[0015] The thickness of the base film is greater than or equal to 3 μm and less than or equal to 20 μm; and / or,

[0016] The porosity of the base film is greater than or equal to 20% and less than or equal to 80%; and / or,

[0017] The air permeability of the first diaphragm and the second diaphragm is greater than or equal to 40 sec / 100 cc and less than or equal to 160 sec / 100 cc.

[0018] In a possible embodiment, the top corners of the first pole piece and the second pole piece each have at least one avoidance portion, and the height of the avoidance portion in the second direction of the battery cell is S6, where S6 satisfies: 1mm≤S6≤5mm;

[0019] The avoidance portion includes a first straight cut edge, an arc cut edge and a second straight cut edge connected in sequence; the arc angle of the arc cut edge is greater than or equal to 110° and less than or equal to 160°; the radius of the arc cut edge is greater than or equal to 0.1 mm and less than or equal to 1 mm; the second straight cut edge extends along the first direction of the battery cell, and the size of the second straight cut edge in the first direction of the battery cell is greater than or equal to 0.1 mm and less than or equal to 5 mm.

[0020] In a possible implementation, along the second direction, a first pole tab is formed on an edge of the first pole piece, and a second pole tab is formed on an edge of the second pole piece;

[0021] The battery cell further includes a protective glue, the protective glue being coated on the outer sides of the plurality of stacked first tabs; and / or the protective glue being coated on the outer sides of the plurality of stacked second tabs;

[0022] The melting point of the protective glue is greater than or equal to 300°C.

[0023] In a possible implementation, in the third direction of the battery cell, the distance between the projection of the folded segment and the projection of the adjacent protective adhesive is L1, where L1 satisfies: L1>0; and / or,

[0024] In the third direction of the battery cell, a distance between a projection of the finishing segment and a projection of the adjacent protective adhesive is L2, where L2 satisfies: L1>0.

[0025] In a possible embodiment, the plurality of pole piece units include a plurality of first pole piece units, the first pole piece unit includes one first pole piece, two second pole pieces and two first diaphragms, the two second pole pieces of the first pole piece unit are located at the outermost sides of the first pole piece unit in the thickness direction of the first diaphragm, and the first pole piece of the first pole piece unit is located between the two first diaphragms in the thickness direction of the first diaphragm; and / or,

[0026] The plurality of electrode piece units further include a plurality of second electrode piece units, the second electrode piece unit including two first electrode pieces, one second electrode piece and two first diaphragms, the two first electrode pieces of the second electrode piece unit are located at the outermost sides of the second electrode piece unit in the thickness direction of the first diaphragm, the second electrode piece of the second electrode piece unit is located between the two first diaphragms in the thickness direction of the first diaphragm, and the outermost sides of the battery cell in the thickness direction of the first diaphragm include two second electrode piece units; and / or,

[0027] The multiple pole piece units also include at least one third pole piece unit, and the third pole piece unit includes a first pole piece, a second pole piece and a first diaphragm. The first diaphragm is arranged between the first pole piece and the second pole piece of the third pole piece unit in the thickness direction of the first diaphragm. The first pole piece unit is arranged on one side of the thickness of the first diaphragm, and the second pole piece unit or the third pole piece unit is arranged on the other side of the thickness of the first diaphragm.

[0028] On the other hand, an embodiment of the present invention provides a lithium-ion battery, comprising a battery cell and a membrane shell as described above, wherein a receiving cavity is provided inside the membrane shell, and the battery cell is located in the receiving cavity.

[0029] An embodiment of the present invention provides a battery cell and a lithium-ion battery, wherein the tail section of the second diaphragm is located on the outermost flat surface of the battery cell. In the third direction of the battery cell, the length of the projection of the tail section is S2, and the width of the projection of the second electrode is Wa, wherein S2 and Wa satisfy: 0.1≤S2 / Wa≤0.3. This can prevent the battery cell from being loose due to the tail section 122 being too short, and can also prevent the tail section 122 from being too long, thereby improving the thickness consistency of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0031] Figure 1 A schematic structural diagram of a battery cell provided in an embodiment of the present utility model;

[0032] Figure 2 for Figure 1 Schematic diagram of the unfolded structure of the battery cell;

[0033] Figure 3 A schematic structural diagram of a first pole piece unit provided in an embodiment of the present utility model;

[0034] Figure 4 A schematic structural diagram of a second pole piece unit provided in an embodiment of the present utility model;

[0035] Figure 5 A schematic structural diagram of a third pole piece unit provided in an embodiment of the present utility model;

[0036] Figure 6 A schematic diagram of the winding process of the second diaphragm and multiple pole piece units provided in an embodiment of the present invention;

[0037] Figure 7 for Figure 2 A schematic diagram of the connection between the second diaphragm, the second pole piece unit and the first pole piece unit;

[0038] Figure 8 A schematic cross-sectional view of a first diaphragm provided in an embodiment of the present utility model;

[0039] Figure 9 A schematic top view of a first pole piece provided in an embodiment of the present utility model;

[0040] Figure 10 for Figure 9 An enlarged schematic diagram of point A in FIG.

[0041] Figure 11 A bottom view schematically shows a battery cell provided in an embodiment of the present utility model.

[0042] Description of reference numerals:

[0043] 10-first pole piece; 101-avoidance portion; 1011-first straight cutting edge; 1012-second straight cutting edge; 1013-arc cutting edge;

[0044] 11-first diaphragm; 111-base film; 112-ceramic layer; 113-adhesive layer;

[0045] 12-second diaphragm; 121-folded section; 122-end section; 1201-accommodation space;

[0046] 20-second pole piece; 21-first pole tab; 22-second pole tab; 23-protective adhesive;

[0047] 100 - first pole piece unit; 200 - second pole piece unit; 300 - third pole piece unit. DETAILED DESCRIPTION

[0048] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions 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 embodiments described are only 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 ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0049] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of this utility model, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0050] In this utility model, unless otherwise specified or limited, the terms "installed," "connected," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection, or communication; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. For those skilled in the art, the specific meanings of the above terms in this utility model can be understood according to the specific circumstances.

[0051] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0052] In the above description, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0053] The battery cell of a lithium-ion battery includes multiple electrode units and a second diaphragm. The electrode units include a first electrode, a first diaphragm, and a second electrode, which are stacked. The second diaphragm and multiple electrode units are wound to form the battery cell. However, the battery cell suffers from looseness and poor thickness consistency. The inventors found that the length of the tail section of the second diaphragm on the outermost flat surface of the battery cell is too short, resulting in looseness of the battery cell; the length of the tail section of the second diaphragm on the outermost flat surface of the battery cell is too long, causing the tail section to overlap with the protective glue on the edge of the electrode tab, increasing the local thickness of the battery cell and making the thickness consistency of the battery cell poor.

[0054] In order to solve the above problems, an embodiment of the present invention provides a battery cell and a lithium-ion battery, in which, in the third direction of the battery cell, the length of the projection of the tail section is S2, and the width of the projection of the second pole piece is Wa, wherein S2 and Wa satisfy: 0.1≤S2 / Wa≤0.3, which can avoid the battery cell from being loose due to the tail section 122 being too short, and can also avoid the tail section 122 being too long, thereby improving the thickness consistency of the battery cell.

[0055] The battery cell and lithium-ion battery provided by the embodiments of the present invention are described in detail below with reference to specific embodiments.

[0056] See also Figure 1As shown, the embodiment of the present invention provides a battery cell, and a direct coordinate system is established for the battery cell. The X-axis direction is the first direction of the battery cell; the Y-axis direction is the second direction of the battery cell (see Figure 9 The Z-axis is the third direction of the battery cell (the height direction of the battery cell); the X-axis, Y-axis and Z-axis are perpendicular to each other.

[0057] The battery cell includes a plurality of electrode units and a second diaphragm 12 .

[0058] Along the third direction of the battery cell, the electrode unit includes at least one first electrode 10, at least one first separator 11 and at least one second electrode 20. Along the third direction of the battery cell, the first electrode 10, the first separator 11 and the second electrode 20 are stacked in sequence.

[0059] Along the third direction of the battery cell, the second separator 12 is wound from the inside to the outside to form a plurality of accommodating spaces 1201. It can be understood that along the third direction of the battery cell, the plurality of accommodating spaces 1201 are arranged in sequence.

[0060] Along the third direction of the battery cell, multiple electrode units are stacked in sequence and arranged one by one in multiple accommodating spaces 1201, that is, along the third direction of the battery cell, each accommodating space 1201 accommodates one electrode unit.

[0061] The battery cell is formed as follows: a second separator 12 and multiple electrode units are wound to form the battery cell. Multiple electrode units are stacked in sequence along the third direction of the battery cell, with the second separator 12 positioned between adjacent electrode units. This means that adjacent electrode units are separated by the second separator 12. The first electrode 10 and second electrode 20 are positioned on either side of the second separator 12, respectively.

[0062] The first electrode 10 and the second electrode 20 have opposite polarities. The first electrode 10 can be a positive electrode or a negative electrode. It is understood that when the first electrode 10 is a positive electrode, the second electrode 20 is a negative electrode, and when the first electrode 10 is a negative electrode, the second electrode 20 is a positive electrode. In this embodiment, the first electrode 10 is a positive electrode and the second electrode 20 is a negative electrode.

[0063] The thickness directions of the first pole piece 10 , the first diaphragm 11 and the second pole piece 20 are all in the Z-axis direction.

[0064] The two outermost pole pieces of the battery cell in the Z-axis direction are two first pole pieces 10, and the two first pole pieces 10 are provided with active material layers on only one side in the thickness direction, while the remaining first pole pieces 10 of the battery cell are provided with active material layers on both sides in the thickness direction.

[0065] Each second electrode sheet 20 of the battery cell is provided with an active material layer on both sides thereof in the thickness direction.

[0066] The first diaphragm 11 of the pole piece unit is disposed between the first pole piece 10 and the second pole piece 20 and can serve to isolate electrons.

[0067] In the thickness direction of the first diaphragm 11, in two adjacent electrode units, the polarities of the two electrode pieces in contact with the second diaphragm 12 are opposite, one of the electrode pieces is the first electrode piece 10, and the other electrode piece is the second electrode piece 20. The second diaphragm 12 is arranged between the first electrode piece 10 and the second electrode piece 20, which can play the role of isolating electrons.

[0068] Figure 2 The middle is a schematic diagram of the second diaphragm 12 and multiple pole piece units after being rolled up and unfolded. Figure 2 In the embodiment, a plurality of electrode units are located on the same side of the second diaphragm 12, and the plurality of electrode units are spaced apart in the length direction of the second diaphragm 12. The length direction of the second diaphragm 12 is the K-axis direction. Each electrode unit is formed by stacking the first electrode, the first diaphragm and the second electrode in sequence by a lamination process, and the second diaphragm 12 and the plurality of electrode units are wound to form a battery cell by a winding process, and the plurality of electrode units are stacked in sequence along the third direction of the battery cell, so that not only the winding process can be used to achieve high production efficiency of the battery cell, but also the advantages of the laminated battery cell with low internal resistance and high space utilization can be utilized, and the lamination process can be used to achieve low internal resistance and high space utilization of the battery cell, thereby making the lithium-ion battery have high production efficiency, low internal resistance and high space utilization.

[0069] In one possible embodiment, see 2 and Figure 3 As shown, the multiple pole piece units include multiple first pole piece units 100, the first pole piece unit 100 includes a first pole piece 10, two second pole pieces 20 and two first diaphragms 11, the two second pole pieces 20 of the first pole piece unit 100 are located at the outermost sides of the first pole piece unit 100 in the thickness direction of the first diaphragm 11, and the first pole piece 10 of the first pole piece unit 100 is located between the two first diaphragms 11 in the thickness direction of the first diaphragm 11.

[0070] In one possible implementation, see Figure 2 and Figure 4 As shown, the plurality of pole piece units further include a plurality of second pole piece units 200. The second pole piece unit 200 includes two first pole pieces 10, one second pole piece 20, and two first diaphragms 11. The two first pole pieces 10 of the second pole piece unit 200 are located at the outermost sides of the second pole piece unit in the thickness direction of the first diaphragm 11, and the second pole piece 20 of the second pole piece unit 200 is located between the two first diaphragms 11 in the thickness direction of the first diaphragm 11.

[0071] The battery cell includes two second pole piece units 200 on the outermost side in the thickness direction of the first diaphragm 11 .

[0072] In one possible implementation, see Figure 2 and Figure 5 As shown, the multiple pole piece units also include at least one third pole piece unit 300, the third pole piece unit 300 includes a first pole piece 10, a second pole piece 20 and a first diaphragm 11, and the first diaphragm 11 is arranged between the first pole piece 10 and the second pole piece 20 of the third pole piece unit 300 in the thickness direction of the first diaphragm 11.

[0073] The first pole piece unit 100 is provided with a second pole piece unit 200 on one side of the thickness of the first diaphragm 11, and the first pole piece unit 100 is provided with a second pole piece unit 200 or a third pole piece unit 300 on the other side of the thickness of the first diaphragm 11. It can be understood that the first pole piece unit 100 can be provided with the second pole piece unit 200 on both sides of the thickness of the first diaphragm 11, or the second pole piece unit 200 and the third pole piece unit 300 can be provided on both sides of the thickness of the first diaphragm 11.

[0074] Exemplarily, the battery cell includes four first pole piece units 100, five second pole piece units 200, and one third pole piece unit 300. One end of the second diaphragm 12 in the -K-axis direction is the starting end of the second diaphragm 12, and one end of the second diaphragm 12 in the +K-axis direction is the ending end of the second diaphragm 12. Before the second diaphragm 12 is wound, the 10 pole piece units on the second diaphragm 12 along the +K-axis direction are: first pole piece unit 100, second pole piece unit 200, second pole piece unit 200, first pole piece unit 100, third pole piece unit 300, second pole piece unit 200, first pole piece unit 100, first pole piece unit 100, second pole piece unit 200, and second pole piece unit 200.

[0075] The second diaphragm 12 and the ten pole piece units are wound from the starting end of the second diaphragm 12 to the ending end of the second diaphragm 12. Figure 2 and Figure 6 In the +K axis direction, the first pole piece unit is wound along the W1 direction, and the first pole piece unit and the second pole piece unit are stacked in sequence in the thickness direction of the first diaphragm 11, and then the first pole piece unit and the second pole piece unit continue to be wound along the W1 direction, and the first pole piece unit, the second pole piece unit and the third pole piece unit are stacked in sequence in the thickness direction of the first diaphragm 11, and continue to wind. When the second diaphragm 12 and the 10 pole piece units are wound, the 10 pole piece units are stacked in sequence in the thickness direction of the first diaphragm 11.

[0076] It should be noted that in Figure 2 In the +K axis direction, the size of the second diaphragm 12 between two adjacent pole piece units can be set according to actual needs.

[0077] In the battery cell, the extending direction of the second separator 12 from the starting end of the second separator 12 toward the ending end of the second separator 12 is the winding direction of the battery cell.

[0078] In one possible embodiment, the battery cell includes a flat surface and side surfaces. The surface of the battery cell in the plane defined by the Y-axis and the X-axis is a flat surface. The surfaces of the battery cell on both sides in the X-axis direction and the surfaces on both sides in the Y-axis direction are side surfaces.

[0079] See also Figure 1 As shown, the end section 122 of the second diaphragm 12 is located on the outermost flat surface of the battery cell.

[0080] The tail section 122 of the second separator 12 extends beyond the last pole piece unit in the winding direction of the battery cell among the plurality of pole piece units.

[0081] The last pole piece unit in the winding direction of the battery cell among the multiple pole piece units is the second pole piece unit 200. Figure 2 Along the +K axis direction, a section of the second diaphragm 12 that exceeds the last pole piece unit is the end section 122 of the second diaphragm 12. It should be noted that, Figure 2 The size of the tail section 122 of the second diaphragm 12 in the +K axis direction is set according to actual needs.

[0082] In the third direction of the battery cell, the length of the projection of the tail section 122 is S2. Specifically, the projection of the tail section 122 of the second diaphragm 12 in the height direction of the battery cell is the second projection. The size of the second projection in the first direction of the battery cell is S2 (see Figure 1 shown).

[0083] In the third direction of the battery cell, the width of the projection of the second electrode piece 20 is Wa. Specifically, in the third direction of the battery cell, the projection of the second electrode piece 20 is the third projection. The width of the third projection in the first direction of the battery cell is Wa, that is, the width of the second electrode piece 20 in the first direction of the battery cell is Wa (see Figure 7 shown).

[0084] Wherein, S2 and Wa satisfy: 0.1≤S2 / Wa≤0.3. For example, S2 / Wa can be 0.1, 0.2 or 0.3, etc., and no specific limitation is made here. When S2 / Wa is less than 0.1, the tail section 122 is too short, and the bonding effect of the tail section 122 is poor, resulting in loose battery cells. When S2 / Wa is greater than 0.3, the tail section 122 is too long, resulting in the tail section 122 overlapping with the protective glue on the second pole ear 22 at the edge of the second pole piece 20, increasing the local thickness of the battery cell, and making the thickness consistency of the battery cell poor. Setting S2 / Wa to be greater than or equal to 0.1 and less than or equal to 0.3 can avoid the looseness of the battery cell due to the tail section 122 being too short, and can avoid the tail section 122 being too long, thereby improving the thickness consistency of the battery cell.

[0085] In one possible implementation, see Figure 1 and Figure 7 As shown, the head portion of the second diaphragm 12 located at the winding center has a folded section 121 .

[0086] The folded section 121 of the second diaphragm 12 is adhesively connected to the first pole piece unit in the winding direction of the battery cell among the plurality of pole piece units.

[0087] The size of the folded section 121 of the second diaphragm 12 in the first direction of the battery cell is smaller than the size of the electrode unit in the first direction of the battery cell. Because there are two layers of diaphragms between the first electrode unit and the second electrode unit in the winding direction of the battery cell, the size of the folded section 121 of the second diaphragm 12 in the first direction of the battery cell is smaller than the size of the electrode unit in the first direction of the battery cell. This can reduce the volume occupied by the second diaphragm 12 in the battery cell, thereby improving the volumetric energy density of the battery cell.

[0088] The projection of the folded section 121 of the second diaphragm 12 in the height direction of the battery cell is the first projection.

[0089] In the third direction, the projection of the folded section 121 does not overlap with the projection of the tail section 122, that is, the first projection and the second projection do not overlap. This arrangement reduces the volume occupied by the second separator 12 in the battery cell, thereby increasing the volume energy density of the battery cell.

[0090] Specifically, the size of the first projection in the first direction of the battery cell is S1, and the size of the folded section 121 of the second diaphragm 12 in the first direction of the battery cell is equal to the size of the first projection in the first direction of the battery cell.

[0091] S1 and Wa satisfy: 0.07≤S1 / Wa≤0.3. When S1 / Wa is less than 0.07, the bonding effect between the folded section 121 and the pole piece unit is poor, and the possibility of the folded section 121 and the pole piece unit falling off increases. When S1 / Wa is greater than 0.3, the lithium ion transmission path between the first pole piece 10 and the second pole piece 20 of the innermost layer of the battery cell becomes longer. Setting S1 / Wa to be greater than or equal to 0.07 and less than or equal to 0.3 can avoid poor bonding effect between the folded section 121 and the pole piece unit, reduce the possibility of the folded section 121 and the pole piece unit falling off, and reduce the lithium ion transmission path between the first pole piece 10 and the second pole piece 20 of the innermost layer of the battery cell.

[0092] The first pole piece unit in the winding direction of the battery cell is the first pole piece unit 100 . The size of the first pole piece unit 100 in the first direction of the battery cell is S3 , where S1 < S3 .

[0093] Furthermore, the first diaphragm 11 is bonded to the second pole piece 20 , and the bonding force between the first diaphragm 11 and the second pole piece 20 is σa.

[0094] The thickness of the second pole piece 20 in the thickness direction of the first diaphragm 11 is Ha (see Figure 7 shown).

[0095] The surface density of the first pole piece 10 on one side in the thickness direction of the first diaphragm 11 is CWc.

[0096] The surface density of the second pole piece 20 on one side in the thickness direction of the first diaphragm 11 is CWa.

[0097] The width of the second electrode 20 in the first direction of the battery cell is Wa (see Figure 7 shown).

[0098] Among the multiple pole piece units, there are two layers of diaphragms adhesively connected between the first pole piece unit and the second pole piece unit in the winding direction of the battery core.

[0099] S1 satisfies Ha*Wa*(4CWa+2CWc)*9.8 / σa≤S1≤10*Wa. This configuration can prevent the return section 121 of the second diaphragm 12 from being too large in the first direction of the battery cell, which would result in a longer lithium ion transmission path. It can also prevent the return section 121 of the second diaphragm 12 from being too small in the first direction of the battery cell, which would result in the return section 121 of the second diaphragm 12 and the first electrode unit in the winding direction of the battery cell falling off, thus preventing the battery cell from being formed.

[0100] S1+S2≤Wa. This configuration can ensure that the first projection and the second projection do not overlap.

[0101] In one possible embodiment, the material of the first diaphragm 11 is described below. The material of the second diaphragm 12 is not specifically limited and can be the same as or different from the material of the first diaphragm 11. In this embodiment, the material of the second diaphragm 12 can be the same as the material of the first diaphragm 11.

[0102] The air permeability of the first diaphragm 11 and the second diaphragm 12 is 40 to 160 sec / 100cc, that is, the air permeability is greater than or equal to 40 sec / 100cc and less than or equal to 160 sec / 100cc. In some examples, the air permeability of the first diaphragm 11 and the second diaphragm 12 is 40 to 120 sec / 100cc. For example, the air permeability of the first diaphragm 11 and the second diaphragm 12 is 40 sec / 100cc, 50 sec / 100cc, 6 sec / 100cc, 70 sec / 100cc, 80 sec / 100cc, 90 sec / 100cc, 100 sec / 100cc, 110 sec / 100cc, or 120 sec / 100cc, etc., without specific limitation herein. When the air permeability of the first separator 11 and the second separator 12 is less than 40 sec / 100 cc, the tensile strength and puncture strength of the base membrane of the first separator 11 deteriorate, and the tensile strength and puncture strength of the base membrane of the second separator 12 deteriorate. When the air permeability of the first separator 11 and the second separator 12 is greater than 160 sec / 100 cc, the porosity of the base membrane of the first separator 11 and the second separator 12 is low, the speed at which lithium ions pass through the separators is slow, and the charge and discharge performance is reduced. When the air permeability of the first separator 11 and the second separator 12 is 40 to 160 sec / 100 cc, the tensile strength and puncture strength of the base membrane of the first separator 11 can be improved, and the tensile strength and puncture strength of the base membrane of the second separator 12 can be improved. By increasing the porosity of the base membrane of the first separator 11 and the second separator 12, the speed at which lithium ions pass through the separators is fast, and the charge and discharge performance is improved.

[0103] See also Figure 8 As shown, the first diaphragm 11 includes a base film 111, and the thickness of the base film 111 in the thickness direction of the first diaphragm 11 is 3 to 20 um, that is, the thickness is greater than or equal to 3 um and less than or equal to 20 um. Exemplarily, the thickness of the base film 111 is 3 um, 5 um, 8 um, 10 um, 15 um or 20 um, etc., which is not specifically limited here. When the thickness of the base film 111 is less than 3 um, the diaphragm has poor puncture resistance and the risk of self-discharge of the battery cell increases. When the thickness of the base film 111 is greater than 20 um, the volume occupied by the diaphragm in the battery cell is large and the volume energy density of the battery cell is low. When the thickness of the base film 111 is 3 to 20 um, the diaphragm's puncture resistance is improved, the risk of self-discharge of the battery cell is reduced, the volume occupied by the diaphragm in the battery cell is reduced, and the volume energy density of the battery cell is increased.

[0104] In the present application, the porosity of the base film 111 is greater than or equal to 20% and less than or equal to 80%, that is, the porosity is 20% to 80%.

[0105] It is defined herein that a porosity greater than or equal to 35% is considered high porosity, and a porosity less than 35% is considered low porosity. In some examples, the porosity of the base film 111 is 35% to 80%. Exemplarily, the porosity of the base film 111 is 35%, 40%, 50%, 60%, 70% or 80%, and no specific limitation is given here. Such a setting makes the base film 111 a base film with high porosity, which can provide a good migration channel for lithium ions, increase the electrolyte retention, and improve the high-rate charge and discharge performance.

[0106] The base film 111 includes one of polyethylene, polypropylene, polyamide, polyester, polyether, polyvinyl chloride, polymethyl methacrylate, polytetrafluoroethylene, polyethersulfone, polyimide, polyetheretherketone, polystyrene, polyurethane, fluorinated polymer, silicone rubber, glass fiber, aramid, and ceramic composite material.

[0107] The thickness direction of the base film 111 is the same as the thickness direction of the first diaphragm 11 .

[0108] The first diaphragm 11 further includes two adhesive layers 113 , which are respectively disposed on both sides of the base film 111 in the thickness direction.

[0109] Adhesive layer 113 includes an adhesive and other materials, the other materials of which are not specifically described here. The adhesive includes at least one of polyacrylate, polyvinyl alcohol, polyimide, polyether ketone, polyether sulfide, polytetrafluoroethylene, polymethyl methacrylate, polystyrene, polyurethane, and polyethylene terephthalate. In some examples, the adhesive comprises greater than 50% of adhesive layer 113. This arrangement can enhance the adhesion between the diaphragm and the electrode, reducing the risk of cell deformation during cycling.

[0110] The thickness of the adhesive layer 113 in the thickness direction of the base film 111 may be greater than or equal to 0.5um and less than or equal to 4um, that is, the thickness is 0.5 to 4um. In some examples, the thickness of the adhesive layer 113 in the thickness direction of the base film 111 may be 0.5 to 2um. For example, the thickness of the adhesive layer in the thickness direction of the base film 111 is 0.5um, 0.6um, 0.8um, 1um, 1.2um, 1.5um or 2um, etc., and no specific limitation is made here. When the thickness of the adhesive layer 113 is less than 0.5um, the adhesion between the diaphragm and the electrode is small, and the risk of deformation of the battery cell during the cycle is high. When the thickness of the adhesive layer 113 is greater than 4um, the volume occupied by the diaphragm in the battery cell is large, and the volume energy density of the battery cell is low. When the thickness of the adhesive layer 113 is 0.5-4 μm, the adhesion between the diaphragm and the electrode is increased, the risk of deformation of the battery cell during the cycle is reduced, the volume occupied by the diaphragm in the battery cell is reduced, and the volume energy density of the battery cell is improved.

[0111] In the thickness direction of the base film 111 , the ceramic layer 112 may or may not be provided between the adhesive layer 113 and the base film 111 .

[0112] Ceramic layer 112 includes ceramic materials and other materials, which are not specifically described here. The ceramic material includes at least one of aluminum oxide, silicon oxide, zirconium oxide, titanium oxide, magnesium oxide, yttrium oxide, antimony oxide, iron oxide, zinc oxide, and potassium aluminum oxide. In some examples, the proportion of ceramic material in ceramic layer 112 is greater than 50%. This configuration can improve the puncture resistance of the separator, thereby enhancing the safety of the battery cell.

[0113] The thickness of the ceramic layer 112 along the thickness direction of the base film 111 can be greater than or equal to 0.5 μm and less than or equal to 10 μm, i.e., the thickness is between 0.5 and 10 μm. For example, the thickness of the ceramic layer 112 along the thickness direction of the base film 111 can be between 1 and 3 μm. In some examples, the thickness of the ceramic layer 112 along the thickness direction of the base film 111 is 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm, etc., without specific limitation. When the thickness of the ceramic layer 112 is greater than 10 μm, the volume occupied by the separator in the battery cell is large, and the volumetric energy density of the battery cell is low. When the thickness of the ceramic layer 112 is less than 0.5 μm, the separator's puncture resistance is poor, increasing the risk of self-discharge and short circuits in the battery cell. When the thickness of the ceramic layer 112 is between 0.5 and 10 μm, the volume occupied by the separator in the battery cell is reduced, the volumetric energy density of the battery cell is increased, the separator's puncture resistance is improved, and the risk of self-discharge and short circuits in the battery cell is reduced.

[0114] The first separator 11 has a thickness D1 along its thickness direction, where D1 is greater than or equal to 4 μm and less than or equal to 25 μm. In some examples, the first separator 11 has a thickness D1 along its thickness direction, where D1 is between 6 and 15 μm. For example, the thickness of the first separator 11 along its thickness direction is 6 mm, 8 mm, 10 mm, 12 mm, or 15 mm, etc., without specific limitation. When the thickness of the first separator 11 is greater than 25 μm, the volume occupied by the separator in the battery cell is large, and the volumetric energy density of the battery cell is low. When the thickness of the first separator 11 is less than 4 μm, the separator's puncture resistance is poor, increasing the risk of self-discharge, short circuit, and furnace failure of the battery cell. When the thickness of the first separator 11 is between 4 and 25 μm, the volume occupied by the separator in the battery cell is reduced, the volumetric energy density of the battery cell is increased, the separator's puncture resistance is improved, and the risk of self-discharge, short circuit, and furnace failure of the battery cell is reduced.

[0115] In one possible embodiment, a ceramic layer 112 and an adhesive layer 113 are provided on both sides of the base film 111 in the thickness direction of the base film 111, and the adhesive layer 113 is provided on the side of the ceramic layer 112 facing away from the base film 111. It should be noted that the ceramic layer 112 is provided on the side of the base film 111 of the first diaphragm 11 facing the first pole piece 10, and the ceramic layer 112 is provided on the side of the base film of the second diaphragm 12 facing the first pole piece 10.

[0116] In one possible implementation, see Figure 9 and Figure 10 As shown, the top corners of the first pole piece 10 and the second pole piece 20 each have at least one avoidance portion 101. For example, the first pole piece 10 has four top corners in the plane where the X-axis and the Y-axis are located, and each top corner is provided with a avoidance portion 101; the second pole piece 20 has four top corners in the plane where the X-axis and the Y-axis are located, and each top corner is provided with a avoidance portion 101. With this arrangement, during the transportation of lithium-ion batteries, the avoidance portions 101 are less likely to cause battery short circuits due to knocking and powder loss, and the top corners of the first pole piece 10 and the second pole piece 20 are less likely to puncture the aluminum-plastic film, causing the risk of corner damage and leakage.

[0117] It should be noted that the specific structure of the avoidance portion 101 of the second pole piece 20 can be referred to Figure 10 The avoidance portion 101 of the first pole piece 10 in the embodiment.

[0118] The avoidance portion 101 is formed by cutting the top corners of the first pole piece 10 and the second pole piece 20 .

[0119] The height S6 of the avoidance portion 101 in the second direction of the battery cell satisfies: 1mm≤S6≤5mm. In some examples, S6 is 1.3-1.6mm. Exemplarily, S6 is 1.3mm, 1.4mm, 1.5mm or 1.6mm, etc., and no specific limitation is given here. When S6 is less than 1mm, the distance between the pole piece and the aluminum-plastic film is close, and the risk of the pole piece puncturing the aluminum-plastic film increases when the battery cell cyclically expands. When S6 is greater than 5mm, the pole piece space utilization is low, which reduces the volume energy density of the battery cell. When S6 satisfies: 1mm≤S6≤5mm, the distance between the pole piece and the aluminum-plastic film can be increased, reducing the risk of the pole piece puncturing the aluminum-plastic film when the battery cell cyclically expands, and the pole piece space utilization is high, thereby improving the volume energy density of the battery cell.

[0120] The avoidance portion 101 includes a first straight cutting edge 1011 , a circular cutting edge 1013 and a second straight cutting edge 1012 connected in sequence. The first straight cutting edge 1011 is tangent to the circular cutting edge 1013 , and the second straight cutting edge 1012 is tangent to the circular cutting edge 1013 .

[0121] The second straight cut edge 1012 extends along the first direction of the battery cell. The dimension S7 of the second straight cut edge 1012 in the first direction of the battery cell satisfies the following conditions: 0.1 mm ≤ S7 ≤ 5 mm. In some examples, S7 is between 0.7 and 1.2 mm. Exemplarily, S7 is 0.7 mm, 0.9 mm, 1.1 mm, or 1.2 mm, among others, without specific limitations. When S7 is less than 0.1 mm, the distance between the electrode and the aluminum-plastic film is close, increasing the risk of the electrode puncturing the film during cell cyclic expansion. When S7 is greater than 5 mm, the electrode space utilization is low, reducing the volumetric energy density of the battery cell. When S7 satisfies the following conditions: 0.1 mm ≤ S7 ≤ 5 mm, the distance between the electrode and the aluminum-plastic film can be increased, reducing the risk of the electrode puncturing the film during cell cyclic expansion. Furthermore, the electrode space utilization is improved, thereby increasing the volumetric energy density of the battery cell.

[0122] The arc angle of the arc cutting edge 1013 is greater than or equal to 110° and less than or equal to 160°. In some examples, the arc angle of the arc cutting edge 1013 is 132° to 138°. Exemplarily, the arc angle of the arc cutting edge 1013 is 132°, 133°, 134°, 135°, 136°, 137°, or 138°, etc., which is not specifically limited here.

[0123] The radius of the arc cutting edge is greater than or equal to 0.1 mm and less than or equal to 1 mm. For example, the radius of the arc cutting edge 1013 is 0.5 mm.

[0124] Figure 11 The second diaphragm 12 is not shown. Figure 11 The position of the folded section 121 and the tail section 122 of the second diaphragm 12 are shown in FIG.

[0125] In one possible implementation, see Figure 11 As shown, along the second direction, a first pole tab 21 is formed on the edge of the first pole piece 10 , and a second pole tab 22 is formed on the edge of the second pole piece 20 .

[0126] The first electrode tabs 21 corresponding to the first electrode sheets 10 are stacked and welded together.

[0127] The second pole tabs 22 corresponding to the second pole sheets 20 are stacked and welded together.

[0128] The battery cell also includes a protective adhesive 23, which is coated on the outside of the multiple stacked second electrode tabs 22. A portion of the protective adhesive 23 is located on the second electrode tab 22, while another portion is located on the electrode sheet. In other embodiments, the protective adhesive is coated on the outside of the multiple stacked first electrode tabs 21; or, the protective adhesive is coated on the outside of the multiple stacked first electrode tabs 21 and the outside of the multiple stacked second electrode tabs 22.

[0129] It should be noted that the welding points of the plurality of stacked second electrode tabs 22 are covered by a protective adhesive 23 .

[0130] The protective adhesive can be polyimide (PI) tape. The melting point of the protective adhesive is greater than or equal to 300°C. This configuration provides high-temperature protection for the tabs, partially insulates the tabs, and provides anti-static properties. It also prevents solder joints on the tabs from piercing the diaphragm and disrupting the cell circuit. It also effectively protects the tabs from vibration and excessive stress, improving the safety and reliability of lithium-ion batteries.

[0131] Furthermore, in the third direction of the battery cell, the distance between the projection of the folded segment 121 and the adjacent protective glue 23 is L1, where L1 satisfies: L1>0. Specifically, in the third direction of the battery cell, the projection of the folded segment 121 is the first projection. In the third direction of the battery cell, the projection of the protective glue 23 is the fourth projection. In the first direction of the battery cell, the distance between the first projection and the fourth projection is L1, L1>0, that is, the first projection and the fourth projection do not overlap with each other. With such a setting, in the third direction of the battery cell, the overlap of the folded segment 121 and the protective glue 23 is avoided, resulting in an increase in the local thickness of the battery cell, thereby improving the thickness consistency of the battery cell. It can also reduce the volume occupied by the diaphragm in the battery cell and improve the volume energy density of the battery cell.

[0132] In the third direction of the battery cell, the distance between the projection of the tail section 122 and the projection of the adjacent protective glue 23 is L2, where L2 satisfies: L1>0. Specifically, in the third direction of the battery cell, the projection of the tail section 122 is the second projection. In the third direction of the battery cell, the projection of the protective glue 23 is the fourth projection. In the first direction of the battery cell, the distance between the first projection and the fourth projection is L2, L2>0, that is, the second projection and the fourth projection do not overlap with each other. With such a setting, in the third direction of the battery cell, the overlap of the tail section 122 and the protective glue 23 is avoided, resulting in an increase in the local thickness of the battery cell, thereby improving the thickness consistency of the battery cell. It can also reduce the volume occupied by the diaphragm in the battery cell and improve the volume energy density of the battery cell.

[0133] An embodiment of the present invention provides a lithium-ion battery, comprising a battery cell and a membrane shell. The membrane shell is provided with an accommodating cavity inside which the battery cell is located.

[0134] Among them, the battery cell in this embodiment has the same structure as the battery cell provided in any of the above embodiments, and can bring the same or similar technical effects, which will not be described one by one here, and the details can be referred to the description of the above embodiments.

[0135] The lithium-ion battery of the present application is described in detail below through specific embodiments, and the specific differences between the following lithium-ion batteries are shown below.

[0136] Example 1-1

[0137] The preparation of the lithium ion battery of this embodiment includes the following steps:

[0138] 1. Preparation of the first pole piece 10.

[0139] Lithium cobalt oxide, polyvinylidene fluoride, carbon black, and carbon tubes are added to N-methylpyrrolidone in a mass ratio of 97.5:1.5:0.5:0.5, and dispersed to obtain a first electrode slurry, which is then coated, rolled, and cut to obtain a first electrode piece 10.

[0140] 2. Preparation of the second pole piece 20.

[0141] Graphite, styrene-butadiene rubber, lithium polyacrylate and carbon black are added into deionized water in a mass ratio of 98:1.0:0.5:0.5, dispersed to obtain a second electrode slurry, and then coated, rolled, cut and the like to obtain a second electrode piece 20.

[0142] 3. Preparation of the first diaphragm 11 and the second diaphragm 12.

[0143] The structure of the first diaphragm 11 includes a ceramic layer 112 , a base film 111 and an adhesive layer 113 . The base film 111 has a thickness of 5 μm, a porosity of 70%, and a thickness of the ceramic layer 112 of 1 μm.

[0144] The air permeability of the first separator 11 is 110 sec / 100 cc.

[0145] The structure of the second diaphragm 12 is the same as that of the first diaphragm 11 .

[0146] 4. Cut the first pole piece 10 and the second pole piece 20 .

[0147] Use a cutter to chop the four corners of the first pole piece 10 and the second pole piece 20 .

[0148] The arc angle of the arc cutting edge 1013 of the avoidance portion 101 of the first pole piece 10 and the second pole piece 20 is 135°, and the radius of the arc cutting edge 1013 of the avoidance portion 101 is 0.5 mm.

[0149] The dimension S6 of the avoidance portion 101 of the first pole piece 10 and the second pole piece 20 in the second direction of the battery cell is 1.4 mm.

[0150] The dimension S7 of the second straight cutting edge 1012 of the first pole piece 10 and the second pole piece 20 in the first direction of the battery cell is 0.9 mm.

[0151] 4. Prepare the first pole piece unit 100 , the second pole piece unit 200 and the third pole piece unit 300 .

[0152] Two first pole pieces 10 , one second pole piece 20 and two first diaphragms 11 are combined to form a first pole piece unit 100 .

[0153] A first electrode sheet 10 , two second electrode sheets 20 and two first diaphragms 11 are combined to form a second electrode sheet unit 200 .

[0154] A first pole piece 10 , a second pole piece 20 and a first diaphragm 11 are combined to form a third pole piece unit 300 .

[0155] The adhesive layer of the first diaphragm 11 is hot pressed onto the first pole piece 10 and the second pole piece 20 at a temperature of 80° C. and a pressure of 1.0 MPa.

[0156] The plurality of first pole piece units 100 are thermally laminated on the second diaphragm 12 at a temperature of 80° C. and a pressure of 1.2 MPa.

[0157] The plurality of second pole piece units 200 are thermally laminated on the second diaphragm 12 at a temperature of 80° C. and a pressure of 1.2 MPa.

[0158] A third pole piece unit 300 is thermally laminated on the second diaphragm 12 at a temperature of 80° C. and a pressure of 1.2 MPa.

[0159] The size of the first projection in the first direction of the battery cell is S1, and S1 is 6 mm.

[0160] The size of the second projection in the first direction of the battery cell is S2, and S2 is 15 mm.

[0161] The second diaphragm 12 and 10 electrode units are wound to form a battery cell, the structure of which is as follows: Figure 1 shown.

[0162] The adhesive force between the first diaphragm 11 and the second pole piece 20 is σa, and σa is 16 N / m.

[0163] The surface density of the first electrode 10 on one side in the thickness direction of the first diaphragm 11 is CWc, which is 0.0213 g / cm 2 .

[0164] The surface density of the second electrode 20 on one side in the thickness direction of the first diaphragm 11 is CWa, which is 0.0115 g / cm 2 .

[0165] The thickness of the second pole piece 20 in the thickness direction of the first diaphragm 11 is Ha, and Ha is 10.85 cm.

[0166] The battery cells are packaged, injected, formed and sorted to obtain lithium-ion batteries.

[0167] Example 1-2

[0168] The difference between Example 1-2 and Example 1-1 is that the size of the first projection in the first direction of the battery cell is S1, and S1 is 10 mm.

[0169] Examples 1-3

[0170] The difference between Example 1-3 and Example 1-1 is that the size of the first projection in the first direction of the battery cell is S1, and S1 is 15 mm.

[0171] Examples 1-4

[0172] The difference between Example 1-4 and Example 1-1 is that the size of the first projection in the first direction of the battery cell is S1, and S1 is 20 mm.

[0173] Example 2-1

[0174] The difference between Example 2-1 and Example 1-1 is that the porosity of the base films of the first diaphragm 11 and the second diaphragm 12 is both 70%, and the air permeability of the first diaphragm 11 and the second diaphragm 12 is both 140 sec / 100 cc.

[0175] Example 2-2

[0176] The difference between Example 2-2 and Example 2-1 is that the size of the first projection in the first direction of the battery cell is S1, and S1 is 10 mm.

[0177] Example 2-3

[0178] The difference between Example 2-3 and Example 2-1 is that the size of the first projection in the first direction of the battery cell is S1, and S1 is 15 mm.

[0179] Examples 2-4

[0180] The difference between Example 2-4 and Example 2-1 is that the size of the first projection in the first direction of the battery cell is S1, and S1 is 20 mm.

[0181] Example 3-1

[0182] The difference between Example 3-1 and Example 3-2 is that the bonding force between the first diaphragm 11 and the second pole piece 20 is σa, and σa is 12 N / m.

[0183] Example 3-2

[0184] The difference between Example 3-2 and Example 3-1 is that the size of the first projection in the first direction of the battery cell is S1, and S1 is 10 mm.

[0185] Example 3-3

[0186] The difference between Example 3-3 and Example 3-1 is that the size of the first projection in the first direction of the battery cell is S1, and S1 is 15 mm.

[0187] Examples 3-4

[0188] The difference between Example 3-4 and Example 3-1 is that the size of the first projection in the first direction of the battery cell is S1, and S1 is 20 mm.

[0189] Comparative Example 1

[0190] The difference between Comparative Example 1 and Example 1-1 is that the size of the first projection in the first direction of the battery cell is S1, and S1 is 5 mm.

[0191] Comparative Example 2

[0192] The difference between Comparative Example 2 and Example 1-1 is that the size of the first projection in the first direction of the battery cell is S1, which is 50 mm, and the size of the second projection in the first direction of the battery cell is S2, which is 40 mm.

[0193] Comparative Example 3

[0194] The difference between Comparative Example 3 and Example 1-1 is that the porosity of the base films of the first separator 11 and the second separator 12 is both 30%, and the air permeability of the first separator 11 and the second separator 12 is both 190 sec / 100 cc.

[0195] Comparative Example 4

[0196] The difference between Comparative Example 4 and Example 1-1 is that the air permeability of the first separator 11 and the second separator 12 are both 200 sec / 100 cc.

[0197] Table 1:

[0198]

[0199] Table 2:

[0200]

[0201] The air permeabilities of the first diaphragm and the second diaphragm are both the air permeabilities of the diaphragms in Table 1.

[0202] The ratio of the folded section between the electrode unit and the second diaphragm to fall off: In one embodiment, the number of lithium-ion batteries is 50. The ratio of the number of lithium-ion batteries in which the folded section between the electrode unit and the second diaphragm has fallen off to the total number of lithium-ion batteries is the ratio of the folded section between the electrode unit and the second diaphragm to fall off.

[0203] The thickness of the base film of the first diaphragm is the thickness of the diaphragm in Table 2; the thickness of the base film of the second diaphragm is the thickness of the diaphragm in Table 2.

[0204] The thickness of one adhesive layer of the first separator is the thickness of the adhesive layer in Table 2; the thickness of one adhesive layer of the second separator is the thickness of the adhesive layer in Table 2.

[0205] The thickness of one ceramic layer of the first diaphragm is the thickness of the ceramic layer in Table 2. The thickness of one ceramic layer of the second diaphragm is the thickness of the ceramic layer in Table 2.

[0206] The thickness of the first diaphragm is the total thickness of the diaphragms in Table 2; the thickness of the second diaphragm is the total thickness of the diaphragms in Table 2.

[0207] Porosity of the basement membrane: Use a micrometer to measure the thickness of the basement membrane, and use a cutter to cut a sample of a certain area of the basement membrane to obtain the apparent volume of the sample, apparent volume = thickness * area; place the sample in a true density meter for testing to obtain the true volume of the sample; sample porosity = (sample apparent volume - sample true volume) / sample apparent volume * 100%.

[0208] Air permeability of base film: Use a cutter to cut a base film sample with a width of 100 mm and a length of 100 mm, and use an air permeability meter to test it with a test pressure of 0.05 MPa and a test time of 8 seconds to obtain the air permeability of the sample.

[0209] Thickness of the base film, bonding layer, and ceramic layer of the first diaphragm: Under the protection of liquid nitrogen, use an ion mill to cut a cross section of the diaphragm. Using a scanning electron microscope (EDM) with a magnification of 5kx to 10kx, locate the cross-sectional locations of the base film, ceramic layer, and bonding layer. The average thickness of the base film at five different locations is taken as the base film thickness. The average thickness of the ceramic layer at five different locations is taken as the ceramic layer thickness. The average thickness of the bonding layer at five different locations is taken as the bonding layer thickness. The thickness of the base film, bonding layer, and ceramic layer of the second diaphragm is measured in the same manner as the first diaphragm.

[0210] Adhesion strength between the first diaphragm and the second electrode piece: disassemble the battery cell; select the bonded first diaphragm and second electrode piece, and use a tool to cut the size in the X-axis direction to 15m, and the size in the Y-axis direction remains unchanged; use a testing machine, with the upper clamp clamping one end of the first diaphragm and the lower clamp clamping the second electrode piece, and the angle between the upper clamp and the lower clamp is 180°; peel off the first diaphragm and the second electrode piece, set the test distance to 50mm, start the test at a speed of 100mm / min, and record the adhesion strength; test 5 times with an error of no more than 10%, and take the average value.

[0211] The size of the second pole piece in the first direction of the battery cell is tested through a microscope: the thickness of the second pole piece in the thickness direction of the first diaphragm is tested through a microscope; the size of the first projection of the second diaphragm in the first direction of the battery cell is tested through a microscope; the size of the second projection of the second diaphragm in the first direction of the battery cell is tested through a microscope; the cutting angle parameters of the second pole piece are tested through a microscope.

[0212] Surface density measurement of the first pole piece: Take the first pole piece after rolling and use the automatic punching equipment to punch out an area of 15.4cm 2 Weigh the total weight of the pole piece. Surface density = (total weight - foil weight) / disc area. Foil weight = foil surface density * disc area. The surface density measurement of the second pole piece is the same as that of the first pole piece.

[0213] Volumetric Energy Density: The volumetric energy density of a lithium-ion battery is ED = E / V, where E is the discharge energy of the battery. The test method involves charging the lithium-ion battery at a current of 0.2C to the upper voltage limit, then charging at a constant voltage until the current drops to 0.02C. The battery is then discharged at a current of 0.2C to 3.0V. The discharged energy is E. V is the volume of the lithium-ion battery. The volume of the lithium-ion battery is obtained by measuring the thickness, width, and length of the lithium-ion battery and calculating the product of the three. E / V is the volumetric energy density obtained from the test.

[0214] Capacity retention rate: Charge a lithium-ion battery at 0.5C to the upper voltage limit, then charge it at a constant voltage until the current drops to 0.05C. After standing for 5 minutes, discharge it at 0.2C to 3.0V. The capacity is C0. After standing for 5 minutes, charge the lithium-ion battery at 0.2C to the upper voltage limit, then charge it at a constant voltage until the current drops to 0.02C. After standing for 5 minutes, discharge it at 1C to 3.0V. The capacity is C1. C1 / C0 is the capacity retention rate.

[0215] Comparing the results of Example 1-1 with Comparative Example 1, it can be seen that the membrane shedding ratio of the first electrode unit and the folded section 121 of the second membrane 12 can be reduced by the size of the first projection in the first direction of the battery cell.

[0216] Comparing the results of Examples 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, and 2-4 with Comparative Example 2, it can be seen that adjusting S1 and S2, when S1+S2≤Wa, has no effect on the volume energy density.

[0217] Comparing the results of Example 1-1 with those of Comparative Example 3, it can be seen that the base film has a large porosity, which can improve the air permeability of the diaphragm and provide good rate discharge performance of the battery.

[0218] Comparing the results of Examples 1-1, 1-2, 1-3, and 1-4, it can be seen that the smaller S1 is, the better the battery rate discharge performance is.

[0219] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery cell, characterized in that: include; A plurality of electrode pieces, along a third direction of the battery cell, the electrode pieces comprising at least one first electrode piece, at least one first diaphragm, and at least one second electrode piece, wherein the first electrode piece and the second electrode piece have opposite polarities, and the first electrode piece, the first diaphragm, and the second electrode piece are sequentially stacked; A second diaphragm is wound from inside to outside along the third direction of the battery core to form a plurality of accommodating spaces, and the plurality of electrode units are stacked in sequence and arranged one by one in the plurality of accommodating spaces; The battery cell includes a flat surface and a side surface. The tail section of the second diaphragm is located on the outermost flat surface of the battery cell. In the third direction of the battery cell, the length of the projection of the tail section is S2, and the width of the projection of the second pole piece is Wa, wherein S2 and Wa satisfy: 0.1≤S2 / Wa≤0.

3.

2. The battery cell according to claim 1, characterized in that The head portion of the second diaphragm located at the winding center has a folded section, and in the third direction of the battery core, a projection of the folded section and a projection of the tail section do not overlap with each other.

3. The battery cell according to claim 2, characterized in that In the third direction of the battery cell, the length of the projection of the folded segment is S1, wherein S1 and Wa satisfy: 0.07≤S1 / Wa≤0.

3.

4. The battery cell according to claim 3, characterized in that The adhesion between the first diaphragm and the second pole piece is σa; the thickness of the second pole piece in the thickness direction of the first diaphragm is Ha; the surface density of the first pole piece on one side in the thickness direction of the first diaphragm is CWc; the surface density of the second pole piece on one side in the thickness direction of the first diaphragm is CWa; Among them, S1 satisfies: Ha*Wa*(4CWa+2CWc)*9.8 / σa≤S1≤10*Wa.

5. The battery cell according to claim 1, characterized in that The first diaphragm and the second diaphragm each include a base film; The thickness of the base film is greater than or equal to 3 μm and less than or equal to 20 μm; and / or, The porosity of the base film is greater than or equal to 20% and less than or equal to 80%; and / or, The air permeability of the first diaphragm and the second diaphragm is greater than or equal to 40 sec / 100 cc and less than or equal to 160 sec / 100 cc.

6. The battery cell according to claim 1, characterized in that The top corners of the first pole piece and the second pole piece each have at least one avoidance portion, and the height of the avoidance portion in the second direction of the battery cell is S6, wherein S6 satisfies: 1mm≤S6≤5mm; The avoidance portion includes a first straight cut edge, an arc cut edge and a second straight cut edge connected in sequence; the arc angle of the arc cut edge is greater than or equal to 110° and less than or equal to 160°; the radius of the arc cut edge is greater than or equal to 0.1 mm and less than or equal to 1 mm; the second straight cut edge extends along the first direction of the battery cell, and the size of the second straight cut edge in the first direction of the battery cell is greater than or equal to 0.1 mm and less than or equal to 5 mm.

7. The battery cell according to claim 2, characterized in that Along the second direction of the battery cell, a first pole tab is formed at the edge of the first pole piece, and a second pole tab is formed at the edge of the second pole piece; The battery cell further includes a protective glue, the protective glue being coated on the outer sides of the plurality of stacked first tabs; and / or the protective glue being coated on the outer sides of the plurality of stacked second tabs; The melting point of the protective glue is greater than or equal to 300°C.

8. The battery cell according to claim 7, characterized in that: In the third direction of the battery cell, the distance between the projection of the folded segment and the projection of the adjacent protective adhesive is L1, wherein L1 satisfies: L1>0; and / or, In the third direction of the battery cell, a distance between a projection of the finishing segment and a projection of the adjacent protective adhesive is L2, where L2 satisfies: L1>0.

9. The battery cell according to any one of claims 1 to 8, characterized in that: The plurality of pole piece units include a plurality of first pole piece units, wherein the first pole piece unit includes one first pole piece, two second pole pieces, and two first diaphragms, the two second pole pieces of the first pole piece unit are located at the outermost sides of the first pole piece unit in the thickness direction of the first diaphragm, and the first pole piece of the first pole piece unit is located between the two first diaphragms in the thickness direction of the first diaphragm; and / or, The plurality of electrode piece units further include a plurality of second electrode piece units, the second electrode piece units including two first electrode pieces, one second electrode piece and two first diaphragms, the two first electrode pieces of the second electrode piece unit being located at the outermost sides of the second electrode piece unit in the thickness direction of the first diaphragm, the second electrode piece of the second electrode piece unit being located between the two first diaphragms in the thickness direction of the first diaphragm, and the outermost sides of the battery cell in the thickness direction of the first diaphragm including the two second electrode piece units; and / or, The multiple pole piece units also include at least one third pole piece unit, and the third pole piece unit includes a first pole piece, a second pole piece and a first diaphragm. The first diaphragm is arranged between the first pole piece and the second pole piece of the third pole piece unit in the thickness direction of the first diaphragm. The first pole piece unit is arranged on one side of the thickness of the first diaphragm, and the second pole piece unit or the third pole piece unit is arranged on the other side of the thickness of the first diaphragm.

10. A battery, characterized in that: It comprises the battery cell and membrane shell according to any one of claims 1 to 9, wherein a receiving cavity is provided inside the membrane shell, and the battery cell is located in the receiving cavity.

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