Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device. The secondary battery comprises an electrode assembly, the thickness direction of the electrode assembly is a first direction, the length direction of the electrode assembly is a second direction, and the width direction of the electrode assembly is a third direction. The electrode assembly includes a plurality of pole pieces and a plurality of diaphragms. The multiple pole pieces are arranged in a stacked mode in the first direction. The multiple pole pieces comprise two outermost pole pieces located on the two sides in the first direction, secondary outer pole pieces adjacent to the outermost pole pieces, and a middle pole piece located between the two secondary outer pole pieces. The plurality of diaphragms comprise two first diaphragms positioned on two sides along the first direction and a second diaphragm positioned between the two first diaphragms, and the first diaphragms are positioned between the outermost-layer pole piece and the secondary-layer pole piece. In the second direction, the size of at least one first diaphragm is larger than that of the second diaphragm; and / or in the third direction, the size of at least one first diaphragm is larger than that of the second diaphragm. The secondary battery is favorable for improving the safety performance.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to a secondary battery and an electronic device. Background Art

[0002] Laminated cells have been widely used in the field of lithium-ion batteries due to their high energy density, low internal resistance and long life. When the battery is dropped, the electrode assembly will move relative to the shell. In the thickness direction of the electrode assembly, the electrolyte concentrated on both sides of the electrode assembly will produce a wave-like surge phenomenon, which makes the diaphragms on both sides of the electrode assembly easily shrink under the flushing of the electrolyte, resulting in a short circuit of the pole pieces on both sides of the diaphragm, affecting the safety of the battery. Summary of the invention

[0003] In view of the above situation, the present application provides a secondary battery, which is beneficial to improving safety performance.

[0004] An embodiment of the present application provides a secondary battery, the secondary battery comprising an electrode assembly, the thickness direction of the electrode assembly is a first direction, the length direction of the electrode assembly is a second direction, the width direction of the electrode assembly is a third direction, and the first direction, the second direction and the third direction are perpendicular to each other. The electrode assembly comprises a plurality of pole pieces and a plurality of diaphragms. The plurality of pole pieces are stacked along the first direction. The plurality of pole pieces comprise two outermost pole pieces located on both sides along the first direction, a sub-outermost pole piece adjacent to the outermost pole piece, and an intermediate pole piece located between the two sub-outermost pole pieces. The plurality of diaphragms comprise two first diaphragms located on both sides along the first direction, and a second diaphragm located between the two first diaphragms, the first diaphragm being located between the outermost pole piece and the sub-outermost pole piece. Along the second direction, the size of at least one first diaphragm is larger than the size of the second diaphragm; and / or, along the third direction, the size of at least one first diaphragm is larger than the size of the second diaphragm.

[0005] In the above-mentioned secondary battery, the first diaphragm is located between the adjacent outermost electrode piece and the second outermost electrode piece, and the second diaphragm is located between the two first diaphragms. When the secondary battery falls, the first diaphragm is subjected to a greater impact force of the electrolyte than the second diaphragm, and is more likely to shrink. Along the second direction, the size of at least one first diaphragm is larger than the size of the second diaphragm; and / or, along the third direction, the size of at least one first diaphragm is larger than the size of the second diaphragm, so as to increase the shrinkage margin reserved for the first diaphragm, thereby reducing the risk of short circuit caused by contact between the two electrode pieces on both sides of the first diaphragm, and improving the safety performance of the secondary battery.

[0006] In some embodiments of the present application, the electrode sheet includes a first side and a second side that are relatively arranged along the second direction. The secondary battery includes a plurality of pole ears, which are respectively connected to the corresponding pole sheets and extend from the first side. The first diaphragm includes a first edge and a third edge that are relatively arranged along the second direction, and the second diaphragm includes a second edge and a fourth edge that are relatively arranged along the second direction. The first edge, the second edge and the first side are located on the same side of the electrode assembly in the second direction. Along the second direction, the second edge is located on the outside of the first side, and the first edge is located on the outside of the second edge, so that the size of the first diaphragm is larger than the size of the second diaphragm in the second direction. In addition, the position where the pole ear extends is usually called the head of the secondary battery. The above-mentioned arrangement is also conducive to reducing the risk of short circuit at the head of the secondary battery and improving the safety performance of the secondary battery. The third edge and the fourth edge are located on the same side of the electrode assembly.

[0007] In some embodiments of the present application, along the second direction, the distance between the first edge and the first side is W1, the distance between the second edge and the first side is W2, 1mm≤W1≤4mm, and 1.5≤W1 / W2≤2, so as to improve the safety performance of the secondary battery and help to improve the energy density of the secondary battery.

[0008] In some embodiments of the present application, the electrode sheet includes a third side and a fourth side that are arranged opposite to each other in the third direction. The first diaphragm includes a fifth edge and a seventh edge that are arranged opposite to each other along the third direction, and the second diaphragm includes a sixth edge and an eighth edge that are arranged opposite to each other along the third direction. The fifth edge, the sixth edge, and the third side are located on the same side of the electrode assembly in the third direction. Along the third direction, the sixth edge is located on the outside of the third side, and the fifth edge is located on the outside of the sixth edge, so that the size of the first diaphragm is larger than the size of the second diaphragm in the third direction. And / or, the seventh edge, the eighth edge, and the fourth side are located on the same side of the electrode assembly in the third direction, and along the third direction, the eighth edge is located on the outside of the fourth side, and the seventh edge is located on the outside of the eighth edge, so that the size of the first diaphragm is larger than the size of the second diaphragm in the third direction.

[0009] In some embodiments of the present application, along the third direction, the distance between the fifth edge and the third side is W3, the distance between the sixth edge and the third side is W4, 0.5mm≤W3≤2mm, and 1.5≤W3 / W4≤2, so as to improve the safety performance of the secondary battery and help improve the energy density of the secondary battery. Or, along the third direction, the distance between the seventh edge and the fourth side is W5, the distance between the eighth edge and the fourth side is W6, 0.5mm≤W5≤2mm, and 1.5≤W5 / W6≤2, so as to improve the safety performance of the secondary battery and help improve the energy density of the secondary battery.

[0010] In some embodiments of the present application, multiple diaphragms are sticky, and the surfaces of the diaphragms in the first direction are bonded to the pole pieces. The parts of two adjacent diaphragms located outside the pole pieces are bonded to each other to restrain the diaphragms and limit their shrinkage, thereby improving the safety performance of the secondary battery.

[0011] In some embodiments of the present application, the peel strength between the diaphragm and the corresponding pole piece is greater than or equal to 2N / m, so as to reduce the risk of displacement between the diaphragm and the corresponding pole piece, thereby improving the safety performance of the secondary battery.

[0012] In some embodiments of the present application, the secondary battery includes a first adhesive, and portions of two adjacent diaphragms located outside the pole pieces are bonded by the first adhesive to restrain the diaphragms and limit their shrinkage, thereby improving the safety performance of the secondary battery.

[0013] In some embodiments of the present application, the second diaphragm includes multiple connecting segments and multiple main segments, the multiple main segments are arranged along a first direction, two adjacent pole pieces are separated by the main segments, and the connecting segments connect the two adjacent main segments, so that the second diaphragm has a continuous structure, which is convenient for assembly and molding of the electrode assembly, and is also beneficial for the second diaphragm to have a better isolation effect between the pole pieces.

[0014] In some embodiments of the present application, the secondary battery further includes a shell and a second adhesive member, and the electrode assembly and the second adhesive member are contained in the shell. The second adhesive member includes a first adhesive surface and a second adhesive surface arranged opposite to each other along a first direction, the first adhesive surface is bonded to the electrode assembly, and the second adhesive surface is bonded to the shell, so as to cushion the electrode assembly when the secondary battery falls and reduce the risk of the electrode assembly moving and being damaged in the shell. The shell is a packaging bag.

[0015] An embodiment of the present application provides a secondary battery, the secondary battery includes an electrode assembly, the thickness direction of the electrode assembly is a first direction, the length direction of the electrode assembly is a second direction, the width direction of the electrode assembly is a third direction, and the first direction, the second direction and the third direction are perpendicular to each other. The electrode assembly includes a plurality of pole pieces and a plurality of diaphragms. The plurality of pole pieces are stacked along the first direction. The plurality of pole pieces include two outermost pole pieces located on both sides along the first direction, a sub-outermost pole piece adjacent to the outermost pole piece, and an intermediate pole piece located between the two sub-outermost pole pieces. The plurality of diaphragms include two first diaphragms located on both sides along the first direction, two third diaphragms, and a second diaphragm located between the two third diaphragms. The first diaphragm is located between the outermost pole piece and the sub-outermost pole piece. The third diaphragm is located between the sub-outermost pole piece and the intermediate pole piece. Along the second direction, the size of at least one first diaphragm is larger than the size of the second diaphragm; and / or, along the third direction, the size of at least one first diaphragm is larger than the size of the second diaphragm. Along the second direction, a size of at least one third diaphragm is larger than a size of the second diaphragm; and / or, along the third direction, a size of at least one third diaphragm is larger than a size of the second diaphragm.

[0016] In the above-mentioned secondary battery, when the secondary battery falls, the first diaphragm and the third diaphragm are subjected to a greater impact force of the electrolyte than the second diaphragm, and are more likely to shrink. Along the second direction, the size of at least one first diaphragm is larger than the size of the second diaphragm; and / or, along the third direction, the size of at least one first diaphragm is larger than the size of the second diaphragm, so as to increase the shrinkage margin reserved for the first diaphragm, thereby reducing the risk of short circuit caused by contact between the two pole pieces on both sides of the first diaphragm, and improving the safety performance of the secondary battery. Along the second direction, the size of at least one third diaphragm is larger than the size of the second diaphragm; and / or, along the third direction, the size of at least one third diaphragm is larger than the size of the second diaphragm, so as to increase the shrinkage margin reserved for the third diaphragm, thereby reducing the risk of short circuit caused by contact between the two pole pieces on both sides of the third diaphragm, and improving the safety performance of the secondary battery.

[0017] An embodiment of the present application provides a secondary battery, the secondary battery includes an electrode assembly, the thickness direction of the electrode assembly is a first direction, the length direction of the electrode assembly is a second direction, the width direction of the electrode assembly is a third direction, and the first direction, the second direction and the third direction are perpendicular to each other. The electrode assembly includes a plurality of pole pieces and a plurality of diaphragms. The plurality of pole pieces are stacked along the first direction. The plurality of pole pieces include two outermost pole pieces located on both sides along the first direction, a sub-outermost pole piece adjacent to the outermost pole piece, a third pole piece adjacent to the sub-outermost pole piece, and an intermediate pole piece located between the two third pole pieces. The plurality of diaphragms include two first diaphragms located on both sides along the first direction, two third diaphragms, two fourth diaphragms, and a second diaphragm located between the two fourth diaphragms. The first diaphragm is located between the outermost pole piece and the sub-outermost pole piece. The third diaphragm is located between the sub-outermost pole piece and the third pole piece. The fourth diaphragm is located between the third pole piece and the intermediate pole piece. In the second direction, the size of at least one first diaphragm is larger than the size of the second diaphragm; and / or, in the third direction, the size of at least one first diaphragm is larger than the size of the second diaphragm. In the second direction, the size of at least one third diaphragm is larger than the size of the second diaphragm; and / or, in the third direction, the size of at least one third diaphragm is larger than the size of the second diaphragm. In the second direction, the size of at least one fourth diaphragm is larger than the size of the second diaphragm; and / or, in the third direction, the size of at least one fourth diaphragm is larger than the size of the second diaphragm.

[0018] In the above-mentioned secondary battery, when the secondary battery falls, the first diaphragm, the third diaphragm and the fourth diaphragm are subjected to a greater impact force of the electrolyte than the second diaphragm, and are more likely to shrink. Along the second direction, the size of at least one first diaphragm is larger than the size of the second diaphragm; and / or, along the third direction, the size of at least one first diaphragm is larger than the size of the second diaphragm, so as to increase the shrinkage margin reserved for the first diaphragm, thereby reducing the risk of short circuit caused by contact between the two pole pieces on both sides of the first diaphragm, and improving the safety performance of the secondary battery. Along the second direction, the size of at least one third diaphragm is larger than the size of the second diaphragm; and / or, along the third direction, the size of at least one third diaphragm is larger than the size of the second diaphragm, so as to increase the shrinkage margin reserved for the third diaphragm, thereby reducing the risk of short circuit caused by contact between the two pole pieces on both sides of the third diaphragm, and improving the safety performance of the secondary battery. Along the second direction, the size of at least one fourth diaphragm is larger than that of the second diaphragm; and / or, along the third direction, the size of at least one fourth diaphragm is larger than that of the second diaphragm, so as to increase the shrinkage margin reserved for the fourth diaphragm, thereby reducing the risk of short circuit caused by contact between the two pole pieces located on both sides of the fourth diaphragm, thereby improving the safety performance of the secondary battery.

[0019] An embodiment of the present application further provides an electronic device, which includes any one of the secondary batteries in the above embodiments.

[0020] In the above electronic device, the first diaphragm is located between the adjacent outermost electrode piece and the second outermost electrode piece, and the second diaphragm is located between the two first diaphragms. When the secondary battery falls, the first diaphragm is subjected to a greater impact force of the electrolyte than the second diaphragm, and is more likely to shrink. Along the second direction, the size of at least one first diaphragm is larger than the size of the second diaphragm; and / or, along the third direction, the size of at least one first diaphragm is larger than the size of the second diaphragm, so as to increase the shrinkage margin reserved for the first diaphragm, thereby reducing the risk of short circuit caused by contact between the two electrode pieces on both sides of the first diaphragm, improving the safety performance of the secondary battery, and thus improving the safety performance of the electronic device.

[0021] In some embodiments of the present application, the electronic device includes a battery compartment and a third adhesive, the secondary battery is arranged in the battery compartment, and the third adhesive is bonded between the battery compartment and the secondary battery in the first direction. Along the second direction, the size of the first diaphragm adjacent to the third adhesive is larger than the size of the second diaphragm; and / or, along the third direction, the size of the first diaphragm adjacent to the third adhesive is larger than the size of the second diaphragm. When the electronic device falls, the side of the secondary battery connected to the third adhesive is subjected to a greater impact than the side not connected to the third adhesive, and the first diaphragm adjacent to the third adhesive is subjected to a greater impact force of the electrolyte than the second diaphragm, thereby being more likely to shrink. Along the second direction, the size of the first diaphragm adjacent to the third adhesive is larger than the size of the second diaphragm; and / or, along the third direction, the size of the first diaphragm adjacent to the third adhesive is larger than the size of the second diaphragm, so as to increase the shrinkage margin reserved for the first diaphragm, thereby reducing the risk of short circuit caused by contact between the two pole pieces on both sides of the first diaphragm adjacent to the third adhesive, improving the safety performance of the secondary battery, and thereby improving the safety performance of the electronic device. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic structural diagram of a secondary battery observed along the second direction in an embodiment of the present application.

[0023] Figure 2 It is a schematic structural diagram of a secondary battery observed along a first direction in an embodiment of the present application.

[0024] Figure 3 It is a schematic structural diagram of a sticky separator of a secondary battery in one embodiment of the present application.

[0025] Figure 4 It is a schematic structural diagram of a secondary battery separator bonded by a first adhesive member in an embodiment of the present application.

[0026] Figure 5 It is a schematic diagram of the continuous structure of the second diaphragm of a secondary battery in one embodiment of the present application.

[0027] Figure 6 It is a schematic structural diagram of a second adhesive component of a secondary battery in one embodiment of the present application.

[0028] Figure 7 It is a schematic structural diagram of a secondary battery observed along the second direction in another embodiment of the present application.

[0029] Figure 8 It is a schematic structural diagram of a secondary battery observed along the second direction in another embodiment of the present application.

[0030] Fig. 9 It is a schematic diagram of the structure of an electronic device in one embodiment of the present application.

[0031] Main component symbols

[0032] Secondary batteries 100A, 100B, 100C

[0033] Electronic device 200

[0034] Electrode assembly 10

[0035] Pole piece 20

[0036] Current collector 201

[0037] Active material layer 202

[0038] Outermost pole piece 20A

[0039] Second outer pole piece 20B

[0040] Intermediate layer pole piece 20C

[0041] The third layer of pole piece 20D

[0042] First side 21

[0043] Second side 22

[0044] The third side 23

[0045] Fourth side 24

[0046] Diaphragm 30

[0047] First diaphragm 30A

[0048] First edge 30A 1

[0049] Third edge 30A2

[0050] Fifth Edge 30A3

[0051] Seventh Edge 30A4

[0052] Second diaphragm 30B

[0053] Second edge 30B 1

[0054] Fourth Edge 30B2

[0055] Sixth Edge 30B3

[0056] Eighth Edge 30B4

[0057] Connection section 301

[0058] Main body section 302

[0059] The third diaphragm 30C

[0060] Fourth diaphragm 30D

[0061] Tab 40

[0062] First tab 41

[0063] Second pole ear 42

[0064] First adhesive member 50

[0065] Housing 60

[0066] Second adhesive member 70

[0067] First bonding surface 71

[0068] Second bonding surface 72

[0069] Battery compartment 80

[0070] The third adhesive member 90

[0071] First direction Z

[0072] Second direction Y

[0073] The third direction X

[0074] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0075] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0076] It should be noted that when an element is considered to be "connected" to another element, it may be directly connected to the other element or there may be a centrally disposed element at the same time. When an element is considered to be "disposed" on another element, it may be directly disposed on the other element or there may be a centrally disposed element at the same time.

[0077] When a value is considered to be "equal" to another value, it means that the two are equal within a set deviation, and the set deviation range is within 5%. In other words, when at least one of the two values ​​fluctuates within the set deviation range, even if their values ​​are not equal, they are still judged to be approximately equal. When a value is considered to be in a ratio of "1:1" to another value, it means that the two are equal within a set deviation, and the set deviation range is within 5%. In other words, when at least one of the two values ​​fluctuates within the set deviation range, even if their values ​​are not equal, they are still judged to be equal in ratio.

[0078] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more related listed items. The term "overlap" used herein refers to the overlap of the projections of two parts or the overlap of the projections of two parts.

[0079] An embodiment of the present application provides a secondary battery, the secondary battery comprising an electrode assembly, the thickness direction of the electrode assembly is a first direction, the length direction of the electrode assembly is a second direction, the width direction of the electrode assembly is a third direction, and the first direction, the second direction and the third direction are perpendicular to each other. The electrode assembly comprises a plurality of pole pieces and a plurality of diaphragms. The plurality of pole pieces are stacked along the first direction. The plurality of pole pieces comprise two outermost pole pieces located on both sides along the first direction, a sub-outermost pole piece adjacent to the outermost pole piece, and an intermediate pole piece located between the two sub-outermost pole pieces. The plurality of diaphragms comprise two first diaphragms located on both sides along the first direction, and a second diaphragm located between the two first diaphragms, the first diaphragm being located between the outermost pole piece and the sub-outermost pole piece. Along the second direction, the size of at least one first diaphragm is larger than the size of the second diaphragm; and / or, along the third direction, the size of at least one first diaphragm is larger than the size of the second diaphragm.

[0080] In the above-mentioned secondary battery, the first diaphragm is located between the adjacent outermost electrode piece and the second outermost electrode piece, and the second diaphragm is located between the two first diaphragms. When the secondary battery falls, the first diaphragm is subjected to a greater impact force of the electrolyte than the second diaphragm, and is more likely to shrink. Along the second direction, the size of at least one first diaphragm is larger than the size of the second diaphragm; and / or, along the third direction, the size of at least one first diaphragm is larger than the size of the second diaphragm, so as to increase the shrinkage margin reserved for the first diaphragm, thereby reducing the risk of short circuit caused by contact between the two electrode pieces on both sides of the first diaphragm, and improving the safety performance of the secondary battery.

[0081] The embodiments of the present application are further described below in conjunction with the accompanying drawings.

[0082] Please also read Figure 1 and Figure 2 One embodiment of the present application provides a secondary battery 100A. The secondary battery 100A refers to a battery that can be continuously used by activating active materials by charging after the battery is discharged.

[0083] The secondary battery 100A includes an electrode assembly 10, which is used to convert chemical energy into electrical energy. The thickness direction of the electrode assembly 10 is a first direction Z. The electrode assembly 10 includes four side surfaces connected in sequence, and when viewed along the first direction Z, the four side surfaces are arranged to form an approximately rectangular shape. The length direction of the electrode assembly 10 is a second direction Y, and the width direction of the electrode assembly 10 is a third direction X. The first direction Z, the second direction Y, and the third direction X are perpendicular to each other.

[0084] The electrode assembly 10 includes a plurality of pole pieces 20 and a plurality of separators 30. The plurality of pole pieces 20 are stacked along a first direction Z. Each pole piece 20 includes a current collector 201 and an active material layer 202. The active material layer 202 is disposed on at least one surface of the current collector 201 in the first direction Z.

[0085] The plurality of pole pieces 20 include two outermost pole pieces 20A located on both sides along the first direction Z, a sub-outermost pole piece 20B adjacent to the outermost pole piece 20A, and an intermediate pole piece 20C located between the two sub-outermost pole pieces 20B. Along the first direction Z, the polarities of two adjacent pole pieces 20 are opposite.

[0086] The plurality of diaphragms 30 include two first diaphragms 30A located on both sides along the first direction Z, and a second diaphragm 30B located between the two first diaphragms 30A. The first diaphragm 30A is located between the outermost electrode piece 20A and the second outer electrode piece 20B. Part of the second diaphragm 30B is located between the second outer electrode piece 20B and the middle electrode piece 20C, and part of the second diaphragm 30B is located between two adjacent middle electrode pieces 20C. When the secondary battery 100A falls, the first diaphragm 30A is subjected to a greater impact force of the electrolyte than the second diaphragm 30B, and is more likely to shrink.

[0087] Please continue reading Figure 2 In some embodiments, along the second direction Y, the size of at least one first diaphragm 30A is larger than the size of the second diaphragm 30B, so as to increase the shrinkage margin reserved for the first diaphragm 30A in the second direction Y, thereby reducing the risk of short circuit caused by contact between the two pole pieces 20 located on both sides of the first diaphragm 30A, thereby improving the safety performance of the secondary battery 100A.

[0088] Optionally, when there are multiple second diaphragms 30B, along the second direction Y, the sizes of the multiple second diaphragms 30B are the same or different, and the size of at least one first diaphragm 30A is larger than the maximum size of the second diaphragm 30B.

[0089] Furthermore, along the second direction Y, the sizes of the two first separators 30A are larger than the size of the second separator 30B, so as to further increase the shrinkage margin reserved for the first separator 30A in the second direction Y, thereby improving the safety performance of the secondary battery 100A.

[0090] In some embodiments, along the third direction X, the size of at least one first diaphragm 30A is larger than the size of the second diaphragm 30B, so as to increase the shrinkage margin reserved for the first diaphragm 30A in the third direction X, thereby reducing the risk of short circuit caused by contact between the two pole pieces 20 located on both sides of the first diaphragm 30A, thereby improving the safety performance of the secondary battery 100A.

[0091] Optionally, when there are multiple second diaphragms 30B, along the third direction X, the sizes of the multiple second diaphragms 30B are the same or different, and the size of at least one first diaphragm 30A is larger than the maximum size of the second diaphragm 30B.

[0092] Furthermore, along the third direction X, the sizes of the two first separators 30A are larger than the size of the second separator 30B, so as to further increase the shrinkage margin reserved for the first separator 30A in the second direction Y, thereby improving the safety performance of the secondary battery 100A.

[0093] Optionally, the thickness direction of the portion of the diaphragm 30 located outside the pole piece 20 is the same as the first direction Z, or the portion of the diaphragm 30 located outside the pole piece 20 is bent.

[0094] It should be noted that the size of the first diaphragm 30A is the size of the first diaphragm 30A in the expanded state (i.e., the thickness direction of the first diaphragm 30A is the same as the first direction Z), and the size of the second diaphragm 30B is the size of the second diaphragm 30B in the expanded state (i.e., the thickness direction of the second diaphragm 30B is the same as the first direction Z).

[0095] In the above-mentioned secondary battery 100A, the first diaphragm 30A is located between the adjacent outermost electrode sheet 20A and the second outermost electrode sheet 20B, and the second diaphragm 30B is located between the two first diaphragms 30A. When the secondary battery 100A falls, the first diaphragm 30A is subjected to a greater impact force of the electrolyte than the second diaphragm 30B, and is more likely to shrink. Along the second direction Y, the size of at least one first diaphragm 30A is larger than the size of the second diaphragm 30B; and / or, along the third direction X, the size of at least one first diaphragm 30A is larger than the size of the second diaphragm 30B, so as to increase the shrinkage margin reserved for the first diaphragm 30A, thereby reducing the risk of short circuit caused by contact between the two electrode sheets 20 located on both sides of the first diaphragm 30A, and improving the safety performance of the secondary battery 100A.

[0096] Please continue reading Figure 2 In some embodiments, the electrode sheet 20 includes a first side 21 and a second side 22 that are arranged opposite to each other along the second direction Y. The secondary battery 100A further includes a plurality of tabs 40, which are respectively connected to the corresponding electrode sheets 20 and extend from the first side 21. One end of the tab 40 away from the electrode sheet 20 is used for external circuit or electrode terminal connection.

[0097] Specifically, the plurality of pole tabs 40 include a first pole tab 41 and a second pole tab 42, wherein the first pole tab 41 is connected to the pole piece 20 with positive polarity, and the second pole tab 42 is connected to the pole piece 20 with negative polarity. Along the first direction Z, the projection of the pole piece 20 with positive polarity is located within the projection of the pole piece 20 with negative polarity, so as to reduce the risk of lithium deposition at the edge of the pole piece 20.

[0098] In some embodiments, the pole tab 40 and the pole piece 20 are integrally provided to improve the connection stability between the pole tab 40 and the pole piece 20 , facilitate reducing the internal resistance, and have the advantages of simple manufacturing process.

[0099] In some embodiments, the first diaphragm 30A includes a first edge 30A1 and a third edge 30A2 disposed opposite to each other along the second direction Y, and the second diaphragm 30B includes a second edge 30B1 and a fourth edge 30B2 disposed opposite to each other along the second direction Y.

[0100] The first edge 30A1, the second edge 30B1, and the first side 21 are located at the same side of the electrode assembly 10 in the second direction Y. The third edge 30A2 and the fourth edge 30B2 are located at the same side of the electrode assembly 10 in the second direction Y.

[0101] Along the second direction Y, the second edge 30B1 is located outside the first side 21, and the first edge 30A1 is located outside the second edge 30B1, so that the size of the first diaphragm 30A is larger than the size of the second diaphragm 30B in the second direction Y. In addition, the position where the tab 40 extends is usually called the head of the secondary battery 100A. The above arrangement is also conducive to reducing the risk of short circuit at the head of the secondary battery 100 and improving the safety performance of the secondary battery 100A.

[0102] It should be noted that when the sizes of the plurality of pole pieces 20 are different, the first side 21 of the pole piece 20 with the larger size is compared with the second edge 30B1. For example, the size of the pole piece 20 with the negative polarity is larger than the size of the pole piece 20 with the positive polarity, and the first side 21 of the pole piece 20 with the negative polarity is compared with the second edge 30B1.

[0103] In some embodiments, along the second direction Y, the distance between the first edge 30A1 and the first side 21 is W1, 1mm≤W1≤4mm. When W1<1mm, the first diaphragm 30A will have a small shrinkage margin in the second direction Y, which may cause the two pole pieces 20 on both sides of the first diaphragm 30A to contact and cause a short circuit. When W1>4mm, the first diaphragm 30A will occupy a large space in the second direction Y, resulting in space waste. By limiting 1mm≤W1≤4mm, the safety performance of the secondary battery 100A is improved, and the energy density of the secondary battery 100A is improved.

[0104] Optionally, W1 may be 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, and any other value within the range of 1 mm ≤ W1 ≤ 4 mm.

[0105] In some embodiments, along the second direction Y, the distance between the second edge 30B1 and the first side 21 is W2, 1.5≤W1 / W2≤2. When W1 / W2<1.5, the first diaphragm 30A will have a smaller shrinkage margin in the second direction Y, which may easily cause the two pole pieces 20 on both sides of the first diaphragm 30A to contact and cause a short circuit. When W1 / W2>2, the first diaphragm 30A will occupy a larger space in the second direction Y, resulting in space waste. By limiting 1.5≤W1 / W2≤2, the safety performance of the secondary battery 100A is improved, and the energy density of the secondary battery 100A is improved.

[0106] Optionally, W1 / W2 may be one of 1.5, 1.6, 1.7, 1.8, 1.9, 2, and any other value in the range of 1.5≤W1 / W2≤2.

[0107] It should be noted that W1 and W2 are measured in the following manner: the first diaphragm 30A and the second diaphragm 30B are unfolded so that the thickness direction of the first diaphragm 30A, the thickness direction of the second diaphragm 30B and the thickness direction of the pole piece 20 are the same as the first direction Z. Along the second direction Y, the distance between the first edge 30A1 and the first side 21 is measured to obtain W1, and the distance between the second edge 30B1 and the first side 21 is measured to obtain W2.

[0108] Please continue reading Figure 2 In some embodiments, along the second direction Y, the fourth edge 30B2 is located outside the second side 22, and the third edge 30A2 is located outside the fourth edge 30B2, so that the size of the first diaphragm 30A is larger than the size of the second diaphragm 30B in the second direction Y.

[0109] It should be noted that when the sizes of the plurality of pole pieces 20 are different, the second side edge 22 of the pole piece 20 with a larger size is compared with the fourth edge 30B2 .

[0110] It is understandable that in other embodiments, along the second direction Y, the distance between the third edge 30A1 and the second side 21 is equal to the distance between the fourth edge 30B2 and the second side 21, so as to facilitate connection by adhesive, thereby improving the structural stability of the rear of the secondary battery 100.

[0111] In some embodiments, the secondary battery 100A also includes an adhesive, the two ends of which are respectively bonded to the two sides of the electrode assembly 10 along the first direction Z, and the adhesive bypasses the side of the electrode assembly 10 provided with a second side 22, a third edge 30A2 and a fourth edge 30B2. The adhesive also bonds the second side 22, the third edge 30A2 and the fourth edge 30B2 to restrain the diaphragm 30 and limit the shrinkage of the diaphragm 30.

[0112] Please continue reading Figure 1 and Figure 2 In some embodiments, the pole piece 20 includes a third side 23 and a fourth side 24 that are arranged opposite to each other in the third direction X.

[0113] The first separator 30A includes a fifth edge 30A3 and a seventh edge 30A4 that are oppositely disposed along the third direction X. The second separator 30B includes a sixth edge 30B3 and an eighth edge 30B4 that are oppositely disposed along the third direction X. The fifth edge 30A3, the sixth edge 30B3, and the third side 23 are located on one side of the electrode assembly 10 in the third direction X. The seventh edge 30A4, the eighth edge 30B4, and the fourth side 24 are located on one side of the electrode assembly 10 in the third direction X.

[0114] In some embodiments, along the third direction X, the sixth edge 30B3 is located outside the third side 23 , and the fifth edge 30A3 is located outside the sixth edge 30B3 , so that the size of the first diaphragm 30A in the third direction X is larger than that of the second diaphragm 30B.

[0115] It should be noted that when the sizes of the plurality of pole pieces 20 are different, the third side 23 of the pole piece 20 with a larger size is compared with the sixth edge 30B3 .

[0116] In some embodiments, along the third direction X, the distance between the fifth edge 30A3 and the third side 23 is W3, 0.5mm≤W3≤2mm. When W3<0.5mm, the first diaphragm 30A will have a smaller shrinkage margin in the third direction X, which may easily cause the two pole pieces 20 on both sides of the first diaphragm 30A to contact and cause a short circuit. When W3>2mm, the first diaphragm 30A will occupy a larger space in the third direction X, resulting in space waste. By limiting 0.5mm≤W3≤2mm, the safety performance of the secondary battery 100A can be improved, and the energy density of the secondary battery 100A can be improved.

[0117] Optionally, W3 can be 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2mm and any other value in the range of 0.5mm≤W3≤2mm.

[0118] In some embodiments, along the third direction X, the distance between the sixth edge 30B3 and the third side 23 is W4, 1.5≤W3 / W4≤2. When W3 / W4<1.5, the first diaphragm 30A will have a smaller shrinkage margin in the third direction X, which may easily cause the two pole pieces 20 on both sides of the first diaphragm 30A to contact and cause a short circuit. When W3 / W4>2, the first diaphragm 30A will occupy a larger space in the third direction X, resulting in space waste. By limiting 1.5≤W3 / W4≤2, the safety performance of the secondary battery 100A can be improved, and the energy density of the secondary battery 100A can be improved.

[0119] Optionally, W3 / W4 may be one of 1.5, 1.6, 1.7, 1.8, 1.9, 2, and any other value in the range of 1.5≤W3 / W4≤2.

[0120] It should be noted that W3 and W4 are measured in the following manner: the first diaphragm 30A and the second diaphragm 30B are unfolded so that the thickness direction of the first diaphragm 30A, the thickness direction of the second diaphragm 30B and the thickness direction of the pole piece 20 are the same as the first direction Z. Along the third direction X, the distance between the fifth edge 30A3 and the third side 23 is measured to obtain W3, and the distance between the sixth edge 30B3 and the third side 23 is measured to obtain W4.

[0121] Please continue reading Figure 1 and Figure 2In some embodiments, along the third direction X, the eighth edge 30B4 is located outside the fourth side 24, and the seventh edge 30A4 is located outside the eighth edge 30B4, so that the size of the first diaphragm 30A is larger than the size of the second diaphragm 30B in the third direction X.

[0122] It should be noted that when the sizes of the plurality of pole pieces 20 are different, the fourth side 24 of the pole piece 20 with a larger size is compared with the eighth edge 30B4 .

[0123] In some embodiments, along the third direction X, the distance between the seventh edge 30A4 and the fourth side 24 is W5, and the following relationship is satisfied: 0.5mm≤W5≤2mm. When W5<0.5mm, the first diaphragm 30A will have a smaller shrinkage margin reserved in the third direction X, which may easily cause the two pole pieces 20 on both sides of the first diaphragm 30A to contact and cause a short circuit. When W5>2mm, the first diaphragm 30A will occupy a larger space in the third direction X, resulting in space waste. By limiting 0.5mm≤W5≤2mm, the safety performance of the secondary battery 100A can be improved, and it is beneficial to improve the energy density of the secondary battery 100A.

[0124] Optionally, W5 can be 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2mm and any other value in the range of 0.5mm≤W5≤2mm.

[0125] In some embodiments, the distance between the eighth edge 30B4 and the fourth side 24 is W6, 1.5≤W5 / W6≤2. When W5 / W6<1.5, the first diaphragm 30A will have a smaller shrinkage margin in the third direction X, which may easily cause the two pole pieces 20 on both sides of the first diaphragm 30A to contact and cause a short circuit. When W5 / W6>2, the first diaphragm 30A will occupy a larger space in the third direction X, resulting in space waste. By limiting 1.5≤W5 / W6≤2, the safety performance of the secondary battery 100A is improved, and it is beneficial to improve the energy density of the secondary battery 100A.

[0126] Optionally, W5 / W6 may be one of 1.5, 1.6, 1.7, 1.8, 1.9, 2, and any other value in the range of 1.5≤W5 / W6≤2.

[0127] It should be noted that W5 and W6 are measured in the following manner: the first diaphragm 30A and the second diaphragm 30B are unfolded so that the thickness direction of the first diaphragm 30A, the thickness direction of the second diaphragm 30B and the thickness direction of the pole piece 20 are the same as the first direction Z. Along the third direction X, the distance between the seventh edge 30A4 and the fourth side 24 is measured to obtain W5, and the distance between the eighth edge 30B4 and the fourth side 24 is measured to obtain W6.

[0128] See also Figure 3 In some embodiments, the plurality of separators 30 are adhesive, and the surface of the separator 30 in the first direction Z is bonded to the pole piece 20, and the portions of two adjacent separators 30 located outside the pole piece 20 are bonded to each other, so as to restrain the separator 30 and limit the shrinkage of the separator 30, thereby improving the safety performance of the secondary battery 100A. Specifically, the portion of the first separator 30A located outside the pole piece 20 and the portions of the two adjacent second separators 30B located outside the pole piece 20 at least partially overlap and are bonded to each other.

[0129] In some embodiments, the diaphragm 30 includes a bonding layer, a substrate layer, and a bonding layer stacked in the thickness direction of the diaphragm 30. The bonding layer is formed by an adhesive coated on the surface of the substrate layer, and the ratio of the coating area of ​​the bonding layer to the area of ​​the corresponding side of the substrate layer is greater than or equal to 20% to improve the bonding performance.

[0130] The material of the substrate layer is selected from at least one of polyolefin, polyvinylidene fluoride, polyethylene terephthalate, cellulose, polyimide, polyamide, spandex or polyphenylene phthalide.

[0131] Inorganic particles are also provided in the bonding layer. The inorganic particles are selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The inorganic particles are used to improve the heat resistance and puncture resistance of the diaphragm 30.

[0132] It should be noted that different peel strengths can be achieved by setting the same type of adhesive but different contents, or different peel strengths can be achieved by using different adhesives.

[0133] In some embodiments, the peel strength between the first separator 30A and the corresponding electrode piece 20 is greater than or equal to 2 N / m, so as to reduce the risk of displacement between the first separator 30A and the corresponding electrode piece 20 , thereby improving the safety performance of the secondary battery 100A.

[0134] Optionally, the peel strength between the first diaphragm 30A and the corresponding pole piece 20 can be 2N / m, 3N / m, 4N / m, 5N / m, 6N / m, 7N / m, 8N / m, 9N / m, 10N / m, 11N / m, 12N / m and any other value greater than or equal to 2N / m.

[0135] In some embodiments, the peel strength between the second separator 30B and the corresponding electrode piece 20 is greater than or equal to 2 N / m, so as to reduce the risk of displacement between the second separator 30B and the corresponding electrode piece 20 , thereby improving the safety performance of the secondary battery 100A.

[0136] Optionally, the peel strength between the second diaphragm 30B and the corresponding pole piece 20 can be 2N / m, 3N / m, 4N / m, 5N / m, 6N / m, 7N / m, 8N / m, 9N / m, 10N / m, 11N / m, 12N / m and any other value greater than or equal to 2N / m.

[0137] Furthermore, the peel strength between the separator 30 and the positive electrode sheet 20 is greater than or equal to 3 N / m, so as to further reduce the risk of the separator 30 and the positive electrode sheet 20 being offset, thereby improving the safety performance of the secondary battery 100A.

[0138] Furthermore, the peel strength between the separator 30 and the electrode sheet 20 with negative polarity is greater than or equal to 8 N / m, so as to further reduce the risk of the separator 30 and the electrode sheet 20 with negative polarity being offset, thereby improving the safety performance of the secondary battery 100A.

[0139] It should be noted that this application uses a high-speed rail tensile machine to test the peel strength of the diaphragm 30 and the electrode 20 according to GB / T 2792-2014 "Test method for peel strength of adhesive tape". The test process is as follows: discharge the secondary battery to 3.0V, then disassemble the secondary battery, remove the diaphragm and the electrode bonded to it as a whole, and wipe the electrolyte on the surface with dust-free paper. Then cut into 10mm×30mm strip specimens. Along the length direction of the specimen, the side of the electrode assembly in the specimen is adhered to the steel plate with double-sided tape (Nitto 5000NS), and the adhesion length is not less than 10mm. Fix the steel plate at the corresponding position of the high-speed rail tensile testing machine, pull up the other end of the electrode piece that is not adhered to the diaphragm, and clamp the sample in the chuck, where the angle between the pulled-up sample part and the steel plate in space is 180°. The chuck pulls the sample at a speed of 5±0.2mm / s, and the average tensile force in the stable area is finally measured and recorded as the peel strength between the diaphragm and the electrode piece, recorded as F, in N / m.

[0140] See also Figure 4In some embodiments, the secondary battery 100A further includes a first adhesive 50, and the portions of two adjacent diaphragms 30 located outside the pole piece 20 are bonded by the first adhesive 50 to restrain the diaphragms 30 and limit the shrinkage of the diaphragms 30, thereby improving the safety performance of the secondary battery 100A.

[0141] In some embodiments, the first adhesive member 50 is glue.

[0142] See also Figure 5 In some embodiments, the second diaphragm 30B includes a plurality of connecting segments 301 and a plurality of main segments 302, wherein the plurality of main segments 302 are arranged along a first direction Z, two adjacent pole pieces 20 are separated by the main segments 302, and the connecting segments 303 connect the two adjacent main segments 302, so that the second diaphragm 30B has a continuous structure, which is convenient for assembling and forming the electrode assembly 10, and is also beneficial for the second diaphragm 30B to have a better isolation effect between the pole pieces 20.

[0143] Specifically, during the preparation process, the continuous second diaphragm 30B is folded in multiple layers in a Z-shape to form a plurality of connecting segments 301 and a plurality of main body segments 302 .

[0144] See also Figure 6 In some embodiments, the secondary battery 100A further includes a shell 60 and a second adhesive 70. The electrode assembly 10 and the second adhesive 70 are accommodated in the shell 60, and the tab 40 is connected to the electrode assembly 10 and extends from the shell 60. Along the first direction Z, at least one side of the electrode assembly 10 is provided with a second adhesive 70. The second adhesive 70 includes a first adhesive surface 71 and a second adhesive surface 72 that are arranged opposite to each other along the first direction Z, the first adhesive surface 71 is bonded to the electrode assembly 10, and the second adhesive surface 72 is bonded to the shell 60, so as to cushion the electrode assembly 10 when the secondary battery 100A falls, and reduce the risk of the electrode assembly 10 moving and being damaged in the shell 60.

[0145] Optionally, the shell is a packaging bag or a hard shell, the packaging bag is an aluminum-plastic film or a steel-plastic film, and the hard shell is a stainless steel shell, an aluminum shell, or the like.

[0146] In some embodiments, the outer surface of the current collector 201 of the outermost electrode piece is not provided with an active material layer 202. The first bonding surface 71 is bonded to the outer surface of the outermost electrode piece.

[0147] See also Figure 7 One embodiment of the present application further provides a secondary battery 100B. The difference between the secondary battery 100B and the secondary battery 100A is that a third separator 30C is further defined.

[0148] The plurality of diaphragms 30 include two first diaphragms 30A located on both sides along the first direction Z, two third diaphragms 30C, and a second diaphragm 30B located between the two third diaphragms 30C. The first diaphragm 30A is located between the outermost electrode piece 20A and the second outermost electrode piece 20B. The third diaphragm 30C is located between the second outermost electrode piece 20B and the middle electrode piece 20C. The second diaphragm 30B is located between two adjacent middle electrode pieces 20C. When the secondary battery 100B falls, the first diaphragm 30A and the third diaphragm 30C are subjected to a greater impact force of the electrolyte than the second diaphragm 30B, and are more likely to shrink.

[0149] In some embodiments, along the second direction Y, the size of at least one third diaphragm 30C is larger than the size of the second diaphragm 30B, so as to increase the shrinkage margin reserved for the third diaphragm 30C in the second direction Y, thereby reducing the risk of short circuit caused by contact between the two pole pieces 20 located on both sides of the third diaphragm 30C, thereby improving the safety performance of the secondary battery 100A.

[0150] In some embodiments, along the third direction X, the size of at least one third diaphragm 30C is larger than that of the second diaphragm 30B, so as to increase the shrinkage margin reserved for the third diaphragm 30C in the third direction X, thereby reducing the risk of short circuit caused by contact between the two pole pieces 20 located on both sides of the third diaphragm 30C, thereby improving the safety performance of the secondary battery 100A.

[0151] Optionally, along the second direction Y, the size of the first diaphragm 30A is greater than the size of the third diaphragm 30C. Alternatively, along the second direction Y, the size of the first diaphragm 30A is equal to the size of the third diaphragm 30C.

[0152] Optionally, along the third direction X, the size of the first diaphragm 30A is greater than the size of the third diaphragm 30C. Alternatively, along the third direction X, the size of the first diaphragm 30A is equal to the size of the third diaphragm 30C.

[0153] Except for the above differences, the parameters of the secondary battery 100B are substantially the same as those of the secondary battery 100A, and reference may be made to the description of the secondary battery 100A.

[0154] See also Figure 8 One embodiment of the present application further provides a secondary battery 100C. The difference between the secondary battery 100C and the secondary battery 100B is that a fourth separator 30D is further defined.

[0155] The plurality of pole pieces 20 include two outermost pole pieces 20A located on both sides along the first direction Z, a sub-outermost pole piece 20B adjacent to the outermost pole piece 20A, a third pole piece 20D adjacent to the sub-outermost pole piece 20B, and an intermediate pole piece 20C located between the two third pole pieces 20D.

[0156] The multiple diaphragms 30 include two first diaphragms 30A, two third diaphragms 30C, two fourth diaphragms 30D, and a second diaphragm 30B located between the two fourth diaphragms 30D, which are located on both sides along the first direction Z. The first diaphragm 30A is located between the outermost electrode piece 20A and the second outermost electrode piece 20B. The third diaphragm 30C is located between the second outermost electrode piece 20B and the third electrode piece 20D. The fourth diaphragm 30D is located between the third electrode piece 20D and the middle electrode piece 20C. The second diaphragm 30B is located between two adjacent middle electrode pieces 20C. When the secondary battery 100A falls, the first diaphragm 30A, the third diaphragm 30C, and the fourth diaphragm 30D are subjected to a greater impact force of the electrolyte than the second diaphragm 30B, and are more likely to shrink.

[0157] In some embodiments, along the second direction Y, the size of at least one fourth diaphragm 30D is larger than the size of the second diaphragm 30B, so as to increase the shrinkage margin reserved for the fourth diaphragm 30D in the second direction Y, thereby reducing the risk of short circuit caused by contact between the two pole pieces 20 located on both sides of the fourth diaphragm 30D, thereby improving the safety performance of the secondary battery 100A.

[0158] In some embodiments, along the third direction X, the size of at least one fourth diaphragm 30D is larger than the size of the second diaphragm 30B, so as to increase the shrinkage margin reserved for the fourth diaphragm 30D in the third direction X, thereby reducing the risk of short circuit caused by contact between the two pole pieces 20 located on both sides of the fourth diaphragm 30D, thereby improving the safety performance of the secondary battery 100A.

[0159] Optionally, along the second direction Y, the size of the first diaphragm 30A is greater than the size of the fourth diaphragm 30D. Alternatively, along the second direction Y, the size of the first diaphragm 30A is equal to the size of the fourth diaphragm 30D.

[0160] Optionally, along the third direction X, the size of the first diaphragm 30A is greater than the size of the fourth diaphragm 30D. Alternatively, along the third direction X, the size of the first diaphragm 30A is equal to the size of the fourth diaphragm 30D.

[0161] Except for the above differences, the parameters of the secondary battery 100C and the secondary battery 100B are substantially the same, and reference may be made to the description of the secondary battery 100B.

[0162] See also Fig. 9 In some embodiments, an embodiment of the present application further provides an electronic device 200. The electronic device 200 includes the secondary battery (100A, 100B, 100C) in any of the above embodiments.

[0163] In the above-mentioned secondary battery (100A, 100B, 100C) and electronic device 200, the first diaphragm 30A is located between the adjacent outermost electrode sheet 20A and the second outermost electrode sheet 20B, and the second diaphragm 30B is located between the two first diaphragms 30A. When the secondary battery 100A falls, the first diaphragm 30A is subjected to a greater impact force of the electrolyte than the second diaphragm 30B, and is more likely to shrink. Along the second direction Y, the size of at least one first diaphragm 30A is larger than the size of the second diaphragm 30B; and / or, along the third direction X, the size of at least one first diaphragm 30A is larger than the size of the second diaphragm 30B, so as to increase the shrinkage margin reserved for the first diaphragm 30A, thereby reducing the risk of short circuit caused by contact between the two electrode sheets 20 located on both sides of the first diaphragm 30A, improving the safety performance of the secondary battery 100A, and thereby improving the safety performance of the electronic device 200.

[0164] In some embodiments, the electronic device 200 includes a battery compartment 80 and a third adhesive member 90, the secondary battery (100A, 100B, 100C) is disposed in the battery compartment 80, and the third adhesive member 90 is bonded between the battery compartment 80 and the secondary battery (100A, 100B, 100C) in the first direction Z. When the electronic device 200 falls, the side of the secondary battery (100A, 100B, 100C) connected to the third adhesive member 90 is subjected to a greater impact than the side not connected to the third adhesive member 90, and the first diaphragm 30A adjacent to the third adhesive member 90 is subjected to a greater impact force of the electrolyte than the second diaphragm 30B, and is more likely to shrink.

[0165] In some embodiments, along the second direction Y, the size of the first diaphragm 30A adjacent to the third adhesive 90 is larger than the size of the second diaphragm 30B, so as to increase the shrinkage margin reserved for the first diaphragm 30A in the second direction Y, thereby reducing the risk of short circuit caused by contact between the two pole pieces 20 located on both sides of the first diaphragm 30A, thereby improving the safety performance of the secondary battery 100A.

[0166] In some embodiments, along the third direction X, the size of the first diaphragm 30A adjacent to the third adhesive 90 is larger than the size of the second diaphragm 30B, so as to increase the shrinkage margin reserved for the first diaphragm 30A in the third direction X, thereby reducing the risk of short circuit caused by contact between the two pole pieces 20 located on both sides of the first diaphragm 30A, thereby improving the safety performance of the secondary battery 100A.

[0167] An embodiment of the present application further provides a method for preparing an electrode assembly, the method comprising the following steps:

[0168] The diaphragm 30, the electrode sheet 20 with negative polarity and the diaphragm 30 are stacked and arranged along the first direction Z and hot pressed to form an integral structure;

[0169] The overall structure and the pole pieces 20 with positive polarity are alternately stacked in sequence along the first direction Z, and the plurality of diaphragms 30 include two first diaphragms 30A located on both sides of the first direction Z, and a second diaphragm 30B located between the two first diaphragms 30A;

[0170] The diaphragm 30 is shaped so that along the second direction Y, the size of at least one first diaphragm 30A is larger than the size of the second diaphragm 30B; and / or along the third direction X, the size of at least one first diaphragm 30A is larger than the size of the second diaphragm 30B.

[0171] The specific steps of hot pressing the diaphragm 30, the pole piece 20 with negative polarity and the diaphragm 30 are: hot pressing the overlapping parts of the two diaphragms 30 and the pole piece 20 with negative polarity so that the two diaphragms 30 and the pole piece 20 with negative polarity are bonded to each other, and hot pressing the parts of the two diaphragms 30 located outside the pole piece 20 with negative polarity so that the two diaphragms 30 are bonded to each other.

[0172] In some embodiments, the two outermost electrode sheets are electrode sheets 20A with positive polarity, and the outer surface of the current collector 201 of the outermost electrode sheet is not provided with an active material layer 202 .

[0173] In some embodiments, the two diaphragms 30 are a continuous structure in an integral structure.

[0174] In the above-mentioned preparation method of the electrode assembly, the diaphragm 30, the pole piece 20 and the diaphragm 30 are stacked and arranged along the first direction Z and hot pressed to form an integral structure, so as to improve the structural stability between the pole piece 20 and the diaphragm 30. By shaping the diaphragm 30, the shrinkage margin reserved for the first diaphragm 30A is increased, thereby reducing the risk of short circuit caused by contact between the two pole pieces 20 located on both sides of the first diaphragm 30A, and improving the safety performance of the secondary battery 100A.

[0175] The specific implementation of the secondary battery in the examples and comparative examples is described below.

[0176] 1. Secondary battery drop test:

[0177] The secondary battery was pre-treated at 25°C, and after standing at room temperature for 60 minutes, the voltage of the secondary battery before the drop test was tested; the secondary battery was placed in a fixture, and the drop device was used to freely drop from a position 1.5m above the ground in the following order: head-tail-right corner of the head-right corner of the tail-left corner of the head-left corner of the tail (angle: 45±15°), and repeated 6 rounds. After the drop, it was left at room temperature for 24 hours, and the voltage of the secondary battery was measured and recorded. The appearance of the secondary battery was checked before and after the test and photographed. The pass criteria for the drop test: no smoke, no leakage, and voltage drop <30mV. 100 cells were tested, and the number of cells that passed the test was X, and the test pass rate was X / 100.

[0178] Embodiment 1:

[0179] A secondary battery with an initial thickness of 5.9 mm, a length of 100 mm, and a width of 50 mm at 50% SOC is assembled as follows:

[0180] (1) Preparation of negative electrode sheet: Mix the negative electrode active materials artificial graphite, conductive carbon black (Super P), and styrene-butadiene rubber (SBR) in a weight ratio of 96:1.5:2.5, add deionized water as a solvent, prepare a slurry with a weight percentage of 50wt%, and stir evenly. The slurry is evenly coated on one surface of the copper foil, and then dried at 110°C to obtain a negative electrode sheet coated with a negative electrode active material layer on one side. When preparing a double-sided coated negative electrode sheet, repeat the above steps on the other surface of the negative electrode sheet to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. Then the coated electrode sheet is cold pressed to a thickness of 105μm, cut and die-cut out the negative electrode tab on the copper foil at the edge of the negative electrode sheet, and the material of the negative electrode tab is copper.

[0181] (2) Preparation of positive electrode sheet: The positive electrode active materials lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%, and stirred evenly. The slurry is evenly coated on one surface of the aluminum foil, and then dried at 90°C to obtain a positive electrode sheet coated with positive electrode active materials on one side. When preparing a double-sided coated positive electrode sheet, repeat the above coating steps on the other surface of the aluminum foil. The coated electrode sheet is then cold pressed to a thickness of 95μm, cut and die-cut out the positive electrode tab on the aluminum foil at the edge of the positive electrode sheet, and the material of the positive electrode tab is aluminum.

[0182] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed in a mass ratio of EC:EMC:DEC=30:50:20 to form a basic organic solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0183] (4) Preparation of diaphragm: A three-layer diaphragm is used, which includes a stacked bonding layer, a substrate layer and a bonding layer. The first substrate layer is made of polyethylene (PE), the bonding agent in the bonding layer is PVDF, and the bonding layer also contains inorganic particles Al2O3 ceramics, and the content of the bonding agent in the bonding layer is 9%.

[0184] (5) Preparation of electrode assembly: The positive electrode sheet, the separator and the negative electrode sheet are stacked and arranged, and the separator is shaped so that only one side of the electrode assembly satisfies the requirement that the size of the first separator located between the outermost electrode sheet and the second outermost electrode sheet is larger than the size of the second separator located between the two first separators.

[0185] (6) Electrode assembly: Place the aluminum-plastic film with holes punched and formed in an assembly fixture, with the holes facing upward, place the electrode assembly in the holes, and apply external force to press it. Then, cover the electrode assembly with another aluminum-plastic film with holes punched and formed, with the holes facing downward, and heat-seal the four sides of the two aluminum-plastic films by hot pressing to obtain an assembled electrode assembly.

[0186] (7) Liquid injection packaging: The electrolyte is injected into the assembled electrode assembly, and after vacuum packaging, static standing, hot pressing, shaping and other processes, a secondary battery is obtained. Along the thickness direction of the secondary battery, the secondary battery includes a top end and a bottom end that are relatively set.

[0187] Comparative Example 1: The size of the first diaphragm and the size of the second diaphragm of the electrode assembly are the same. It should be noted that, except for the size of the first diaphragm, the other parameters of Comparative Example 1 are the same as those of Example 1.

[0188] Comparative Example 2: The size of the first diaphragm of the electrode assembly is smaller than the size of the second diaphragm It should be noted that, in Comparative Example 2, other parameters are the same as those of Example 1 except for the size of the first diaphragm.

[0189] Table 1 (Except for the parameters mentioned in Table 1, all other parameters of Examples 2-30 are the same as those of Example 1.)

[0190]

[0191]

[0192] It can be seen from Comparative Examples 1-2 and Examples 1-4 that the passing rate of the secondary battery drop test can be improved by making the size of at least one first diaphragm 30A larger than the size of the second diaphragm 30B along the second direction Y; and / or making the size of at least one first diaphragm 30A larger than the size of the second diaphragm 30B along the third direction X. Moreover, the more the number of sides of the electrode assembly 10 that satisfy the requirement that the size of the first diaphragm 30A is larger than the size of the second diaphragm 30B is, the higher the passing rate of the drop test is.

[0193] Table 2 (Except for the parameters mentioned in Table 2, all other parameters of Examples 5-16 are the same as those of Example 4)

[0194]

[0195] It can be seen from Examples 4-8 that by limiting 1mm≤W1≤4mm, the pass rate of the secondary battery drop test can be improved. It should be noted that when W1>4mm, the first diaphragm 30A will occupy a larger space in the second direction Y, resulting in space waste, and may also reduce the sealing strength of the first diaphragm 30A when it is sealed in the packaging bag.

[0196] It can be seen from Examples 4, 9-12 that by limiting 0.5 mm ≤ W3 ≤ 2 mm, the pass rate of the secondary battery drop test can be improved. It should be noted that when W3>2 mm, the first diaphragm 30A will occupy a larger space in the third direction X, resulting in space waste, and may also reduce the sealing strength of the first diaphragm 30A when it is sealed in the packaging bag.

[0197] It can be seen from Examples 4 and 13-16 that by limiting 0.5 mm ≤ W5 ≤ 2 mm, the pass rate of the secondary battery drop test can be improved. It should be noted that when W5>2 mm, the first diaphragm 30A will occupy a larger space in the third direction X, resulting in space waste, and may also cause the first diaphragm 30A to be sealed in the packaging bag and reduce the sealing strength.

[0198] Table 3 (Except for the parameters mentioned in Table 3, all other parameters of Examples 22-34 are the same as those of Example 4.)

[0199] Serial number <![CDATA[W1 / W2]]> <![CDATA[W3 / W4]]> <![CDATA[W5 / W6]]> Drop test pass rate Example 4 1.8 1.8 1.8 88 Embodiment 17 1 1.8 1.8 66 Embodiment 18 1.5 1.8 1.8 75 Embodiment 19 2 1.8 1.8 89 Embodiment 20 2.5 1.8 1.8 90 Embodiment 21 1.8 1 1.8 70 Embodiment 22 1.8 1.5 1.8 82 Embodiment 23 1.8 2 1.8 89 Embodiment 24 1.8 2.5 1.8 90 Embodiment 25 1.8 1.8 1 72 Embodiment 26 1.8 1.8 1.5 80 Embodiment 27 1.8 1.8 2 87 Embodiment 28 1.8 1.8 2.5 89

[0200] It can be seen from Examples 4 and 17-20 that the pass rate of the secondary battery drop test can be improved by limiting 1.5≤W1 / W2≤2. It should be noted that when W1 / W2>2, the first diaphragm 30A will occupy a larger space in the third direction X, resulting in space waste, and may also reduce the sealing strength of the first diaphragm 30A when it is sealed in the packaging bag.

[0201] It can be seen from Examples 4 and 21-24 that the pass rate of the secondary battery drop test can be improved by limiting 1.5≤W3 / W4≤2. It should be noted that when W3 / W4>2, the first diaphragm 30A will occupy a larger space in the third direction X, resulting in space waste, and may also reduce the sealing strength of the first diaphragm 30A when it is sealed in the packaging bag.

[0202] It can be seen from Examples 4 and 25-28 that the pass rate of the secondary battery drop test can be improved by limiting 1.5≤W5 / W6≤2. It should be noted that when W5 / W6>2, the first diaphragm 30A will occupy a larger space in the third direction X, resulting in space waste, and may also reduce the sealing strength of the first diaphragm 30A when it is sealed in the packaging bag.

[0203] Table 4 (Except for the parameters mentioned in Table 4, all other parameters of Examples 29-32 are the same as those of Example 4.)

[0204]

[0205] It can be seen from Examples 4, 29-32 that the passing rate of the secondary battery drop test can be improved by making the size of at least one third diaphragm 30C larger than the size of the second diaphragm 30B along the second direction Y; and / or making the size of at least one third diaphragm 30C larger than the size of the second diaphragm 30B along the third direction X. Moreover, the more the number of sides of the electrode assembly 10 that satisfy the condition that the size of the third diaphragm 30C is larger than the size of the second diaphragm 30B is, the higher the passing rate of the drop test is.

[0206] Table 5 (Except for the parameters mentioned in Table 5, all other parameters of Examples 33-36 are the same as those of Example 32.)

[0207]

[0208] It can be seen from Examples 32-36 that the passing rate of the secondary battery drop test can be improved by making the size of at least one fourth diaphragm 30D larger than the size of the second diaphragm 30B along the second direction Y; and / or making the size of at least one fourth diaphragm 30D larger than the size of the second diaphragm 30B along the third direction X. In addition, the more the number of side surfaces of the electrode assembly 10 that satisfy the condition that the size of the fourth diaphragm 30D is larger than the size of the second diaphragm 30B is, the higher the passing rate of the drop test is.

[0209] In addition, those skilled in the art may also make other changes within the spirit of the present application. Of course, these changes made according to the spirit of the present application should be included in the scope disclosed in the present application.

Claims

1. A secondary battery, characterized in that: The secondary battery comprises an electrode assembly, wherein the thickness direction of the electrode assembly is a first direction, the length direction of the electrode assembly is a second direction, the width direction of the electrode assembly is a third direction, the first direction, the second direction and the third direction are perpendicular to each other, and the electrode assembly comprises: A plurality of pole pieces are stacked along a first direction, the plurality of pole pieces comprising two outermost pole pieces located on both sides along the first direction, a sub-outermost pole piece adjacent to the outermost pole piece, and an intermediate pole piece located between the two sub-outermost pole pieces; A plurality of diaphragms, including two first diaphragms located at both sides along the first direction, and a second diaphragm located between the two first diaphragms, wherein the first diaphragm is located between the outermost pole piece and the second outermost pole piece; Along the second direction, a size of at least one of the first diaphragms is larger than a size of the second diaphragm; and / or, Along the third direction, a size of at least one of the first diaphragms is larger than a size of the second diaphragm.

2. The secondary battery according to claim 1, wherein: The pole piece comprises a first side edge and a second side edge disposed opposite to each other along the second side; The secondary battery comprises a plurality of pole tabs, the plurality of pole tabs are respectively connected to the corresponding pole pieces and extend from the first side; The first diaphragm includes a first edge and a third edge disposed opposite to each other along the second direction, and the second diaphragm includes a second edge and a fourth edge disposed opposite to each other along the second direction; The first edge, the second edge and the first side edge are located on the same side of the electrode assembly in the second direction, and along the second direction, the second edge is located outside the first side edge, and the first edge is located outside the second edge; The third edge and the fourth edge are located on a same side of the electrode assembly.

3. The secondary battery according to claim 2, characterized in that: Along the second direction, a distance between the first edge and the first side is W1, a distance between the second edge and the first side is W2, 1 mm≤W1≤4 mm, and 1.5≤W1 / W2≤2.

4. The secondary battery according to claim 1 or 2, characterized in that: The pole piece comprises a third side and a fourth side which are arranged opposite to each other along the third direction; The first diaphragm includes a fifth edge and a seventh edge disposed oppositely along the third direction, and the second diaphragm includes a sixth edge and an eighth edge disposed oppositely along the third direction; The fifth edge, the sixth edge and the third side are located on the same side of the electrode assembly in the third direction, and along the third direction, the sixth edge is located outside the third side, and the fifth edge is located outside the sixth edge; and / or, The seventh edge, the eighth edge and the fourth side are located on the same side of the electrode assembly in the third direction, and along the third direction, the eighth edge is located outside the fourth side, and the seventh edge is located outside the eighth edge.

5. The secondary battery according to claim 4, characterized in that: Along the third direction, the distance between the fifth edge and the third side is W3, the distance between the sixth edge and the third side is W4, 0.5 mm ≤ W3 ≤ 2 mm, and 1.5 ≤ W3 / W4 ≤ 2; or, Along the third direction, the distance between the seventh edge and the fourth side is W5, the distance between the eighth edge and the fourth side is W6, 0.5 mm ≤ W5 ≤ 2 mm, and 1.5 ≤ W5 / W6 ≤ 2.

6. The secondary battery according to claim 1, wherein: The plurality of diaphragms are adhesive, and surfaces of the diaphragms in the first direction are bonded to the pole piece, and portions of two adjacent diaphragms located outside the pole piece are bonded to each other.

7. The secondary battery according to claim 6, characterized in that: The peel strength between the diaphragm and the corresponding electrode piece is greater than or equal to 2N / m.

8. The secondary battery according to claim 1, wherein: The secondary battery comprises a first adhesive member, and portions of two adjacent separators located outside the pole piece are bonded together by the first adhesive member.

9. The secondary battery according to claim 1, wherein: The second diaphragm includes a plurality of connecting segments and a plurality of main body segments, the plurality of main body segments are arranged along the first direction, two adjacent pole pieces are separated by the main body segments, and the connecting segment connects two adjacent main body segments.

10. The secondary battery according to claim 1, wherein: The secondary battery also includes a shell and a second adhesive member, the electrode assembly and the second adhesive member are accommodated in the shell, the second adhesive member includes a first adhesive surface and a second adhesive surface arranged opposite to each other along the first direction, the first adhesive surface is adhered to the electrode assembly, and the second adhesive surface is adhered to the shell, and the shell is a packaging bag.

11. A secondary battery, characterized in that: The secondary battery comprises an electrode assembly, wherein the thickness direction of the electrode assembly is a first direction, the length direction of the electrode assembly is a second direction, the width direction of the electrode assembly is a third direction, the first direction, the second direction and the third direction are perpendicular to each other, and the electrode assembly comprises: A plurality of pole pieces are stacked along a first direction, the plurality of pole pieces comprising two outermost pole pieces located on both sides along the first direction, a sub-outermost pole piece adjacent to the outermost pole piece, and an intermediate pole piece located between the two sub-outermost pole pieces; A plurality of diaphragms, including two first diaphragms located on both sides along the first direction, two third diaphragms, and a second diaphragm located between the two third diaphragms, wherein the first diaphragm is located between the outermost pole piece and the second outer pole piece, and the third diaphragm is located between the second outer pole piece and the middle pole piece; Along the second direction, the size of at least one of the first diaphragms is larger than the size of the second diaphragm; and / or, along the third direction, the size of at least one of the first diaphragms is larger than the size of the second diaphragm; Along the second direction, a size of at least one of the third diaphragms is larger than a size of the second diaphragm; and / or, along the third direction, a size of at least one of the third diaphragms is larger than a size of the second diaphragm.

12. A secondary battery, characterized in that: The secondary battery comprises an electrode assembly, wherein the thickness direction of the electrode assembly is a first direction, the length direction of the electrode assembly is a second direction, the width direction of the electrode assembly is a third direction, the first direction, the second direction and the third direction are perpendicular to each other, and the electrode assembly comprises: A plurality of pole pieces are stacked along a first direction, the plurality of pole pieces comprising two outermost pole pieces located on both sides along the first direction, a second outermost pole piece adjacent to the outermost pole piece, a third pole piece adjacent to the second outermost pole piece, and an intermediate pole piece located between the two third pole pieces; A plurality of diaphragms, including two first diaphragms, two third diaphragms, two fourth diaphragms, and a second diaphragm located between the two fourth diaphragms along the first direction, wherein the first diaphragm is located between the outermost electrode piece and the second outermost electrode piece, the third diaphragm is located between the second outermost electrode piece and the third electrode piece, and the fourth diaphragm is located between the third electrode piece and the middle electrode piece; Along the second direction, the size of at least one of the first diaphragms is larger than the size of the second diaphragm; and / or, along the third direction, the size of at least one of the first diaphragms is larger than the size of the second diaphragm; Along the second direction, the size of at least one of the third diaphragms is larger than the size of the second diaphragm; and / or, along the third direction, the size of at least one of the third diaphragms is larger than the size of the second diaphragm; Along the second direction, a size of at least one of the fourth diaphragms is larger than a size of the second diaphragm; and / or, along the third direction, a size of at least one of the fourth diaphragms is larger than a size of the second diaphragm.

13. An electronic device, characterized in that: The electronic device includes the secondary battery according to any one of claims 1 to 12.

14. The electronic device according to claim 13, wherein: The electronic device comprises a battery compartment and a third adhesive member, the secondary battery is arranged in the battery compartment, and the third adhesive member is adhered between the battery compartment and the secondary battery in the first direction; Along the second direction, the size of the first diaphragm adjacent to the third adhesive member is larger than the size of the second diaphragm; and / or, Along the third direction, a size of the first diaphragm adjacent to the third adhesive member is larger than a size of the second diaphragm.

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