Battery separator, electrode assembly, secondary battery and electric apparatus

Abstract

A battery separator (100), an electrode assembly (1000), a secondary battery and an electric apparatus. The battery separator (100) comprises N separator layers and N-1 elastic connection layers (130), wherein the N separator layers are stacked in a first direction (X); and any elastic connection layer (130) is sandwiched between two adjacent separator layers, and is elastically connected to the separator layers, with N being a positive integer greater than 1. By means of providing the elastic connection layers (130) in the battery separator (100), the adverse effects of expansion and compression brought about by battery charging and discharging can be mitigated, thereby improving the stability of a battery structure and prolonging the service life thereof.

Description

Battery separator, electrode assembly, secondary battery, and electric device

[0001] Cross-reference to related applications

[0002] The present disclosure claims priority to Chinese Patent Application No. 202411036924.7 entitled "Battery separator, electrode assembly, secondary battery, and electric device" filed on July 31, 2024, which is incorporated by reference in its entirety into the present disclosure. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of batteries, and in particular to a battery separator, an electrode assembly, a secondary battery, and an electric device. BACKGROUND

[0004] Energy saving and emission reduction is the key to the sustainable development of the automobile industry. Electric vehicles have become an important part of the sustainable development of the automobile industry due to their energy-saving and environmentally friendly advantages. For electric vehicles, battery technology is an important factor for their development.

[0005] During the use of charging and discharging, the battery core will swell. This swelling not only affects the use at the user end, but if the swelling is not inhibited, the performance of the battery in the charging and discharging cycle will deteriorate rapidly, resulting in reduced service life.

[0006] SUMMARY

[0007] The present disclosure aims to at least solve one of the technical problems existing in the background art. To this end, one object of the present disclosure is to provide a battery separator, an electrode assembly, a secondary battery, and an electric device to alleviate the adverse effects of swelling and shrinking of the battery during charging and discharging.

[0008] Embodiments of the first aspect of the present disclosure provide a battery separator, comprising: N separator layers stacked along a first direction; and N-1 elastic connection layers, any elastic connection layer being sandwiched between two adjacent separator layers and elastically connecting the separator layers; wherein N is a positive integer greater than 1.

[0009] In some embodiments, at least one elastic connection layer has at least one void region, the at least one void region being located between two adjacent separator layers.

[0010] In some embodiments, the elastic connection layer comprises a first surface and a second surface oppositely arranged along a thickness direction; at least one of the first surface and the second surface is provided with a recess, the recess defining the at least one void region.

[0011] In some embodiments, the elastic connection layer comprises a plurality of elastic supports, the plurality of elastic supports defining the at least one void region therebetween.

[0012] In some embodiments, the projection of the elastic connecting layer on the adjacent separator layer is one or more of discrete dots, discrete lines, and cross patterns.

[0013] In some embodiments, the elastic support is cylindrical, and the diameter of the elastic support is greater than or equal to 20 μm and less than or equal to 100 mm.

[0014] In some embodiments, the elastic support is a line, and the width of the elastic support is greater than or equal to 20 μm and less than or equal to 100 mm.

[0015] In some embodiments, the maximum thickness of the elastic connecting layer is greater than or equal to 2 μm and less than or equal to 100 μm.

[0016] In some embodiments, the contact area of the elastic connecting layer with the separator layer is less than the area of the separator layer.

[0017] In some embodiments, the ratio of the contact area of the elastic connecting layer with the separator layer to the area of the separator layer is greater than or equal to 2% and less than or equal to 60%.

[0018] In some embodiments, the battery separator includes a first separator layer and a second separator layer located at the two outermost ends along a first direction, respectively; wherein at least one of the first separator layer and the second separator layer is provided with a functional coating on the surface perpendicular to the first direction, and the functional coating includes one or more of a heat-resistant coating, a protective coating, a conductive coating, and an adhesive layer.

[0019] In some embodiments, the two surfaces perpendicular to the first direction in at least one of the first separator layer and the second separator layer are respectively provided with the same type of functional coating.

[0020] In some embodiments, the two surfaces perpendicular to the first direction in at least one of the first separator layer and the second separator layer are respectively provided with different types of functional coatings.

[0021] In some embodiments, the battery separator includes a first separator layer and a second separator layer located at the two outermost ends along a first direction, respectively; wherein the material of the first separator layer is different from that of the second separator layer.

[0022] In some embodiments, at least one of the first separator layer and the second separator layer includes a plurality of polymer layers of different materials.

[0023] Embodiments of the second aspect of the present disclosure provide an electrode assembly, which includes a positive electrode sheet, a negative electrode sheet, and a battery separator according to the above embodiments, the negative electrode sheet and the positive electrode sheet are arranged in a stack opposite to each other, and the battery separator is arranged between the positive electrode sheet and the negative electrode sheet.

[0024] In some embodiments, the negative electrode sheet includes a lithium metal layer or a lithium alloy layer.

[0025] Embodiments of the third aspect of the present disclosure provide a secondary battery comprising the battery separator in the above embodiments or the electrode assembly in the above embodiments.

[0026] Embodiments of the fourth aspect of the present disclosure provide an electric device comprising the secondary battery in the above embodiments, which is used to provide electric energy.

[0027] The above description is only a summary of the technical solutions of the present disclosure. In order to enable one of ordinary skill in the art to better understand the technical means of the present disclosure and implement the same according to the contents of the description, and in order to make the above and other purposes, characteristics and advantages of the present disclosure more apparent and easy to understand, the specific embodiments of the present disclosure are described below. BRIEF DESCRIPTION OF DRAWINGS

[0028] In the drawings, like reference numerals refer to same or similar components throughout the several views. These drawings are not necessarily drawn to scale. It should be understood that these drawings only depict some embodiments in accordance with the present disclosure and should not be considered as limiting the scope of the present disclosure.

[0029] FIG. 1 is a structural schematic diagram of an electrode assembly according to some embodiments of the present disclosure;

[0030] FIG. 2 is a structural schematic diagram of a battery separator according to some embodiments of the present disclosure;

[0031] FIG. 3 is a structural schematic diagram of a battery separator with a void region in the elastic connecting layer according to some embodiments of the present disclosure;

[0032] FIG. 4 is a structural schematic diagram of a battery separator with a void region in the elastic connecting layer according to some other embodiments of the present disclosure;

[0033] FIG. 5 is a structural schematic diagram of a battery separator with a void region in the elastic connecting layer according to some other embodiments of the present disclosure;

[0034] FIG. 6 is a structural schematic diagram of a battery separator with an elastic connecting layer having different structural forms according to some embodiments of the present disclosure;

[0035] FIG. 7 is a structural schematic diagram of a battery separator with a functional coating according to some embodiments of the present disclosure;

[0036] FIG. 8 is a structural schematic diagram of a battery separator with a functional coating according to some other embodiments of the present disclosure;

[0037] FIG. 9 is a structural schematic diagram of a battery separator according to some other embodiments of the present disclosure;

[0038] FIG. 10 is a structural schematic diagram of an electrode assembly according to some other embodiments of the present disclosure.

[0039] Explanation of reference signs: electrode assembly 1000; battery separator 100; first separator layer 110, second separator layer 120, elastic connection layer 130, third separator layer 140, void region 131, elastic support 132, first functional layer 150, second functional layer 160, third functional layer 170, fourth functional layer 180, first polymer layer 1101, second polymer layer 1102; negative electrode sheet 200, negative electrode current collector 210, negative electrode active material layer 220; positive electrode sheet 300, positive electrode current collector 310, positive electrode active material layer 320. DETAILED DESCRIPTION

[0040] The embodiments of the technical solutions of the present disclosure will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present disclosure, and therefore only serve as examples, and cannot limit the protection scope of the present disclosure.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present disclosure; the terms "include" and "have" and any variations thereof in the specification and claims of the present disclosure and the above description of drawings are intended to cover non-exclusive inclusion.

[0042] In the description of the embodiments of the present disclosure, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present disclosure, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0043] In this paper, the reference to "embodiments" means that the specific features, structures or properties described in conjunction with the embodiments can be included in at least one embodiment of the present disclosure. The appearance of this phrase in various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment to other embodiments. The skilled person in the art explicitly and implicitly understands that the embodiments described herein can be combined with other embodiments.

[0044] In the description of the embodiments of the present disclosure, the term "and / or" is only a description of the association relationship between the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents a "or" relationship between the front and rear associated objects.

[0045] In the description of the embodiments of the present disclosure, the term "a plurality of" refers to two or more (including two), and similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces).

[0046] In the description of the embodiments of the present disclosure, the technical terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the embodiments of the present disclosure and simplifying the description, and does not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the embodiments of the present disclosure.

[0047] In the description of the embodiments of the present disclosure, unless otherwise explicitly specified and limited, the technical terms "mounting", "connection", "connection", "fixing" and the like should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present disclosure can be understood according to the specific circumstances.

[0048] Secondary batteries, also commonly referred to as rechargeable batteries or accumulators, are those that can be used for multiple charge-discharge cycles. The charge-discharge process of a secondary battery is reversible, it can store electrical energy and release it when needed. Secondary batteries are widely used in personal computers, smartphones, electric vehicles, energy storage, etc. A secondary battery can be a single battery cell or a battery pack of multiple battery cells connected in series or parallel.

[0049] The electrode assembly is the component in which the electrochemical reaction occurs in the battery cell. The housing of the battery cell can contain one or more electrode assemblies. The electrode assembly is mainly formed by winding or stacking the positive electrode sheet and the negative electrode sheet, and a battery separator is also provided between the positive electrode sheet and the negative electrode sheet.

[0050] The electrode assembly will swell and shrink during the charge and discharge of the secondary battery. Taking a lithium-ion battery as an example, during the charging process, lithium ions are released from the positive electrode material, migrate to the negative electrode material through the electrolyte and are embedded therein. The negative electrode material will swell when lithium ions are embedded, because the embedding of lithium ions will change its crystal structure, resulting in an increase in volume; during the discharging process, lithium ions are released from the negative electrode material, migrate to the positive electrode material through the electrolyte and are embedded therein.

[0051] Lithium ion batteries generally use graphite, or silicon composites and the like as negative active materials. To further improve the energy density of lithium ion batteries, lithium metal secondary batteries using lithium metal as the negative electrode are highly anticipated. In lithium metal secondary batteries, lithium metal is deposited on the negative electrode during charging and dissolved in the non-aqueous electrolyte during discharging, so that the lithium metal secondary battery expands during charging and shrinks during discharging.

[0052] Referring to FIG. 1 and FIG. 2, FIG. 1 is a structural schematic diagram of an electrode assembly according to some embodiments of the present disclosure, and FIG. 2 is a structural schematic diagram of a battery separator according to some embodiments of the present disclosure.

[0053] As shown in FIG. 1, the electrode assembly 1000 includes a negative electrode sheet 200, a positive electrode sheet 300, a battery separator 100, and an electrolyte. The negative electrode sheet 200 can include a negative electrode current collector 210 and a negative electrode active material layer 220, and the positive electrode sheet 300 includes a positive electrode current collector 310 and a positive electrode active material layer 320.

[0054] Embodiments of the first aspect of the present disclosure provide a battery separator 100, the battery separator 100 comprising: N separator layers and N-1 elastic connection layers 130, the N separator layers being stacked along a first direction X; any elastic connection layer 130 being arranged between two adjacent separator layers and elastically connecting the separator layers; wherein N is a positive integer greater than 1.

[0055] As shown in FIG. 1, the battery separator 100 includes two separator layers, which are a first separator layer 110 and a second separator layer 120, and an elastic connection layer 130 between the two separator layers. As shown in FIG. 2, the battery separator 100 includes three separator layers, which are a first separator layer 110, a second separator layer 120, and a third separator layer 140, and an elastic connection layer 130 between any two adjacent separator layers.

[0056] The first direction X is the thickness direction of the battery separator 100.

[0057] The separator layer can be a porous polymer film having ion permeability and electronic insulation. The material of the porous polymer film can be polyolefin resin, polyamide resin, cellulose, etc., and the polyolefin resin can be polyethylene, polypropylene, and a copolymer of ethylene and propylene, etc.

[0058] The elastic connection layer 130 is made of an elastic material to achieve elastic connection between two adjacent diaphragm layers. The elastic connection layer 130 can be compressed when subjected to pressure due to its own elasticity, and can rebound after the pressure is relieved, so that the battery diaphragm 100 can be compressed during the charging process of the electrode assembly 1000 and rebound during the discharging process, so that the two sides of the battery diaphragm 100 are tightly attached to the positive plate 300 and the negative plate 200, which is beneficial to improve the uniformity of lithium ion precipitation and embedding. The material of the elastic connection layer 130 can be an elastic polymer, such as ordinary rubber, special rubber, thermoplastic elastomer, thermosetting elastomer, resin mixed with inorganic filler, high molecular material with ion conductivity, etc. Rubber-based elastomers can include NR (natural rubber), SBR (styrene-butadiene rubber), BR (butadiene rubber), EPDM (ethylene-propylene rubber), IIR (butyl rubber), NBR (nitrile rubber), CR (chloroprene rubber), SIR (silicone rubber), ACM (acrylate rubber), FKM (fluorine rubber), etc. Thermoplastic elastomers can include styrene-based (SBS, SIS, SEBS, SEPS), olefin-based (TPO, TPV) diene-based (TPB, TPI), chlorovinyl-based (TPVC, TCPE), urethane-based (TPU), ester-based (TPEE), amide-based (TPAE), organic fluorine-based (TPF), etc.

[0059] The elastic connection layer 130 can be a complete sheet-shaped elastic material layer sandwiched between two layers of diaphragm layers, or a film layer with a patterned structure in some positions.

[0060] The elastic connection layer 130 can be connected to the diaphragm layer by adhesion, or a curable elastic material can be coated on the diaphragm layer and then compounded with another diaphragm layer to achieve connection.

[0061] By setting the battery diaphragm 100 as a composite film layer structure with an elastic connection layer 130 contained in the middle of the multiple diaphragm layers, the elasticity of the elastic connection layer 130 can be utilized to compress the elastic connection layer 130 during charging, thereby relieving the degree of expansion of the battery, and the rebound of the elastic connection layer 130 during discharging can relieve the degree of contraction of the battery to a certain extent, which is beneficial to maintain the structural stability of the secondary battery and improve the battery life.

[0062] In addition, the elastic connecting layer 130 is arranged between the two diaphragm layers, which can be arranged at a distance from each other. Even if the lithium dendrite penetrates the diaphragm layer on one side of the elastic connecting layer 130, the elastic connecting layer 130 can still play a barrier role, so as to maintain the integrity of the diaphragm layer on the other side of the elastic connecting layer 130, thereby maintaining the reliable insulation between the positive electrode sheet 300 and the negative electrode sheet 200, and reducing the risk of short circuit. Moreover, the material of the elastic connecting layer 130 is different from that of the diaphragm layer, and the thermal expansion coefficients are also different. If the elastic connecting layer 130 directly contacts the electrode sheet, it may cause local stress concentration of the battery diaphragm and increase the risk of thermal deformation. However, the elastic connecting layer 130 is arranged in the middle of the diaphragm layer, which can avoid direct contact between the elastic connecting layer 130 and the battery electrode sheet, thereby reducing local stress concentration. In addition, the battery diaphragm in the embodiment is generally symmetrical, which can make the expansion or contraction behavior of the entire diaphragm more uniform when the temperature changes, thereby reducing the internal stress and deformation caused by uneven thermal expansion.

[0063] Referring to FIGS. 3 and 6, in some embodiments, the at least one elastic connecting layer 130 has at least one void region 131 located between two adjacent diaphragm layers.

[0064] The void region 131 can be located at any position of the elastic connecting layer 130, such as the surface of the diaphragm layer or the middle of the diaphragm layer. The gas in the void region 131 can be in communication with the outside of the battery diaphragm 100. When there are multiple elastic connecting layers 130, the void region 131 can be arranged in one of the elastic connecting layers 130, or in each of the elastic connecting layers 130.

[0065] The number of void regions 131 can be one or multiple. The void region 131 is located between two adjacent diaphragm layers, which can further improve the deformability of the elastic connecting layer 130, so that the electrode assembly 1000 can realize more effective compression and rebound in the charge and discharge cycle, thereby compensating for the deformation caused by the expansion and contraction of the electrode sheet and maintaining the relative stability of the battery structure.

[0066] In some embodiments, the elastic connecting layer 130 includes a first surface and a second surface arranged opposite along the thickness direction; at least one of the first surface and the second surface is provided with a recess, and the recess defines at least one void region 131.

[0067] The recess is an inner recess structure formed on the surface of the elastic connecting layer 130, and the maximum depth of the recess is less than the thickness of the position of the elastic connecting layer 130 where the recess is located, that is, the recess does not penetrate the elastic connecting layer 130 in the gap region 131 defined by the recess. The number of recesses can be one or more. The plurality of recesses can be arranged at intervals in at least one of the first surface and the second surface. As shown in FIG. 3, in some embodiments, the first surface and the second surface are respectively provided with a plurality of recesses, and the recesses on the two surfaces are arranged one by one in correspondence. In other embodiments, the recesses of the first surface and the second surface can be arranged staggered with each other. It can be understood that the arrangement of the recesses in different elastic connecting layers 130 can be the same or different.

[0068] As shown in FIG. 4, in some embodiments, the elastic connecting layer 130 includes a plurality of elastic supports 132, and at least one gap region 131 is defined between the plurality of elastic supports 132.

[0069] The plurality of elastic supports 132 can be arranged at intervals or connected with each other. The region arranged at intervals or defined between the plurality of elastic supports 132 is the gap region 131, and the gap region 131 in the embodiment is a hollow region, that is, the gap region 131 penetrates the elastic connecting layer 130 in the thickness direction of the elastic connecting layer 130.

[0070] As shown in FIG. 5, when a plurality of elastic connecting layers 130 are provided, the plurality of elastic connecting layers 130 can have the same structure, that is, the arrangement of the plurality of elastic supports 132 is the same. In some embodiments, the gap regions 131 in adjacent elastic connecting layers 130 can be arranged in register, so that the structure size of the elastic connecting layer 130 is completely the same, which can facilitate processing and improve the preparation efficiency. In other embodiments, the gap regions 131 in adjacent elastic connecting layers 130 can be arranged staggered, so that the distribution of the gap regions 131 in the entire battery separator 100 is more uniform, and the elastic deformation capacity of the battery separator 100 is also more uniform, which is more conducive to maintaining uniform contact with the battery pole piece.

[0071] In some embodiments, the projection of the elastic connecting layer 130 on the adjacent separator layer is in one or more of discrete point shape, discrete line shape, and cross pattern shape.

[0072] As shown in FIG. 6, where (a) shows that the elastic connecting layer 130 is composed of a plurality of uniformly spaced cylindrical elastic supports 132, and the spacing areas between the plurality of cylindrical elastic supports 132 form the gap area 131. (b), (c) and (d) show that the elastic connecting layer 130 is composed of a plurality of parallel linear elastic supports 132, and the gap area 131 is formed between two adjacent elastic supports 132. (e) and (f) show that the elastic connecting layer 130 is composed of a cross pattern of a plurality of elastic connecting members 132 intersecting with each other, such as a grid pattern, a honeycomb pattern. The hollowed-out areas in the pattern form the gap area 131. The pattern type of the elastic connecting layer 130 can be adjusted according to the requirement of the elastic deformation amount of the battery separator 100 in actual application, so as to meet the needs of different application scenarios.

[0073] In some embodiments, the elastic support 132 is cylindrical, and the diameter D of the elastic support 132 is greater than or equal to 20 pm and less than or equal to 100 mm. In some embodiments, the diameter D of the elastic support 132 is greater than or equal to 1 mm and less than or equal to 50 mm. In some embodiments, the diameter D of the elastic support 132 is greater than or equal to 2 mm and less than or equal to 20 mm.

[0074] In some embodiments, the elastic support 132 is linear, and the width B of the elastic support 132 is greater than or equal to 20 pm and less than or equal to 100 mm. In some embodiments, the width B of the elastic support 132 is greater than or equal to 1 mm and less than or equal to 50 mm. In some embodiments, the width B of the elastic support 132 is greater than or equal to 2 mm and less than or equal to 20 mm.

[0075] In some embodiments, the maximum thickness of the elastic connecting layer 130 is greater than or equal to 2 pm and less than or equal to 100 pm. The maximum thickness of the elastic connecting layer 130 is the height of the elastic support 132,

[0076] In some embodiments, the contact area of the elastic connecting layer 130 with the separator layer is less than the area of the separator layer.

[0077] The contact area of the elastic connecting layer 130 with the separator layer refers to the area of the connecting region of the elastic connecting layer 130 with the separator layer, and the area of the separator layer refers to the area of the surface of the separator layer perpendicular to the first direction X. The contact area of the elastic connecting layer 130 with the separator layer being less than the area of the separator layer means that there is a gap area 131 at the connecting interface of the elastic connecting layer 130 with the separator layer.

[0078] In some embodiments, the ratio of the contact area of the elastic connecting layer 130 with the separator layer to the area of the separator layer is greater than or equal to 2% and less than or equal to 60%.

[0079] The greater the ratio of the contact area of the elastic connecting layer 130 with the separator layer to the area of the separator layer, the stronger the overall support effect on the battery separator and the battery pole piece, but too large will inhibit the deformation ability of the elastic connecting layer 130; and the smaller the ratio, the smaller the contact area of the elastic connecting layer 130 with the separator layer, and the larger the gap between the two, so although it can provide greater deformation ability, the overall structural support is slightly insufficient. Therefore, the ratio is limited to between 2% and 60% in this embodiment, which can well balance the support strength and deformation ability. In some embodiments, the ratio can also be limited to between 5% and 50%. In other embodiments, the ratio can also be limited to between 10% and 40%.

[0080] In some embodiments, the battery separator 100 includes a first separator layer 110 and a second separator layer 120 located at the two outermost ends along the first direction X, respectively; wherein at least one of the first separator layer 110 and the second separator layer 120 is provided with a functional coating on the surface perpendicular to the first direction X, and the functional coating includes one or more of a heat-resistant coating, a protective coating, a conductive coating, and an adhesive layer.

[0081] The heat-resistant coating can improve the thermal stability of the battery separator 100. Polyolefin-based organic separators are prone to shrinkage or melting at higher temperatures, leading to short circuits in the battery. The heat-resistant coating can reduce the thermal shrinkage rate of the separator, thereby delaying the time of thermal runaway of the battery and reducing the maximum temperature after thermal runaway of the battery. The heat-resistant coating can be a ceramic coating (such as aluminum oxide), hydroxyapatite super-long nanowires, etc.

[0082] The protective coating can enhance the mechanical strength and puncture resistance of the separator layer, reducing the risk of short circuits caused by separator rupture during production or use of the battery. The protective coating can include some reinforcing materials or composite materials, such as glass fibers, carbon fibers, etc., which can improve the overall strength and toughness of the separator.

[0083] The conductive coating can improve the electrical conductivity of the separator layer, reduce the internal resistance of the battery, and improve the charge and discharge efficiency of the battery. The conductive coating can contain conductive materials such as carbon nanotubes, graphene, etc., which have excellent electrical conductivity and thermal conductivity, helping to quickly conduct and disperse heat within the battery.

[0084] The adhesive layer can enhance the adhesion between the separator layer and the electrode material, maintain the close contact between the electrode and the separator during the charging and discharging process, reduce the risk of electrode material falling off or displacement, and also enable uniform stress and synchronous deformation of the battery separator 100 when the electrode expands and contracts, thereby maintaining the stability of the overall structure of the battery; it can also be provided on the side surface of the separator layer connected with the elastic connection layer 130 to improve the adhesion between the separator layer and the elastic connection layer 130 and improve the overall strength of the battery separator 100. The adhesive layer is usually composed of some materials with good adhesion, such as polyimide, epoxy resin, etc. These materials can form a firm chemical or physical bond with the electrode material and the separator.

[0085] One of the first separator layer 110 and the second separator layer 120 faces the positive electrode sheet 300, and the other faces the negative electrode sheet 200. The functional coating layer provided on the first separator layer 110 and the second separator layer 120 can further improve the performance of the battery separator 100, thereby improving the charging and discharging performance and structural stability of the battery.

[0086] In some embodiments, as shown in FIG. 7, the first functional layer 150 is provided on the side surface of the first separator layer 110 facing the battery electrode sheet, and the second functional layer 160 is provided on the side surface of the second separator layer 120 facing the battery electrode sheet. The first functional layer 150 and the second functional layer 160 are respectively provided on the two surfaces of the battery separator 100 perpendicular to the first direction X.

[0087] In some embodiments, as shown in FIG. 8, the third functional layer 170 is provided on the side surface of the first separator layer 110 facing away from the battery electrode sheet, and the fourth functional layer 180 is provided on the side surface of the second separator layer 120 facing away from the battery electrode sheet.

[0088] In some examples, one or more of the first functional layer 150, the second functional layer 160, the third functional layer 170, and the fourth functional layer 180 can also be a composite functional film layer, i.e., a functional coating layer composed of multiple film layers with different functions.

[0089] In some embodiments, at least one of the first separator layer 110 and the second separator layer 120 is provided with the same type of functional coating layer on the two surfaces perpendicular to the first direction X.

[0090] As shown in FIG. 8, the first functional layer 150, the second functional layer 160, the third functional layer 170, and the fourth functional layer 180 can all be heat-resistant coating layers.

[0091] In some embodiments, at least one of the first separator layer 110 and the second separator layer 120 is provided with different types of functional coating layers on the two surfaces perpendicular to the first direction.

[0092] As shown in FIG. 8, the first functional layer 150 and the second functional layer 160 can be heat-resistant coating layers, and the third functional layer 170 and the fourth functional layer 180 can be adhesive layers.

[0093] In some embodiments, the battery separator 100 includes a first separator layer 110 and a second separator layer 120 located at two outermost ends along the first direction X, respectively; wherein the first separator layer 110 and the second separator layer 120 are made of different materials.

[0094] The first separator layer 110 and the second separator layer 120 can be porous membranes made of different polymers. For example, the first separator layer 110 is made of polyethylene, and the second separator layer 120 is made of polyimide.

[0095] In other embodiments, the first separator layer 110 and the second separator layer 120 can be made of the same material. Further, the materials of the plurality of separator layers in the battery separator 100 can be completely the same or at least partially different.

[0096] In some embodiments, at least one of the first separator layer 110 and the second separator layer 120 includes a plurality of polymer layers made of different materials.

[0097] As shown in FIG. 9, the first separator layer 110 can include a composite membrane layer composed of two polymers, for example, the first separator layer 110 includes a first polymer layer 1101 and two second polymer layers 1102 formed on the two surfaces of the first polymer layer 1101, respectively, wherein the first polymer layer 1101 is made of PP (polypropylene), and the second polymer layer 1102 is made of PE (polyethylene). It can be understood that the second separator layer 120 can also be a composite membrane layer including a plurality of polymer layers made of different materials.

[0098] As shown in FIG. 10, the second aspect of the embodiments of the present disclosure provides an electrode assembly 1000 including a positive electrode sheet 300, a negative electrode sheet 200, and the battery separator 100 in the above embodiments, wherein the negative electrode sheet 200 and the positive electrode sheet 300 are arranged in a stack opposite to each other, and the battery separator 100 is arranged between the positive electrode sheet 300 and the negative electrode sheet 200.

[0099] The negative electrode sheet 200 can include a negative electrode current collector 210, which is a member that conducts a negative electrode current, and a negative electrode active material layer 220. The negative electrode current collector 210 can be made of a conductive material other than lithium metal and lithium alloy. The conductive material can be a metal, a metal material such as an alloy, or a composite material of a metal and another material. The conductive material is preferably a material that does not react with lithium, such as a material that does not form an alloy and an intermetallic compound with lithium. Such a conductive material can include, for example, copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metal elements, such as copper alloys and stainless steel (SUS). Among these, copper and / or a copper alloy having high electrical conductivity is preferred.

[0100] The negative electrode current collector 210 can be a foil, a tape, a flat plate, or a metal foam.

[0101] The thickness of the negative electrode current collector 210 is not particularly limited and can be, for example, 3 μm or more and 300 μm or less.

[0102] In some embodiments, a functional coating can be provided on the surface of the negative electrode current collector 210, for example, by applying a slurry containing a negative electrode active material such as graphite or a carbon nanotube or a conductive material to at least a portion of the surface of the negative electrode current collector 210.

[0103] The positive electrode sheet 300 includes a positive electrode current collector 310 and a positive electrode active material layer 320. The positive electrode active material layer 320 contains a positive electrode active material, a conductive material, a binder material, and a functional additive. The positive electrode active material layer 320 can be formed on only one surface of the positive electrode current collector 310 or on both surfaces.

[0104] The positive electrode sheet 300 can be formed, for example, by applying a positive electrode slurry containing a positive electrode active material, a conductive material, a binder material, and a functional additive to both surfaces of the positive electrode current collector 310, drying the coated film, calendering, and punching to a specified size.

[0105] The positive electrode active material is a material that can intercalate and deintercalate lithium ions. Examples include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, transition metal sulfides, and the like. Among these, a lithium-containing transition metal oxide is preferred.

[0106] Examples of the transition metal element contained in the lithium-containing transition metal oxide include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, W, and the like. The lithium-containing transition metal oxide can contain one or two or more kinds of transition metal elements. The transition metal element can be Co, Ni, and / or Mn. The lithium-containing transition metal oxide can contain one or more kinds of doping elements such as Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, Bi, and the like, as needed.

[0107] The conductive material can be a carbon material such as carbon black, acetylene black, ketjen black, carbon nanotubes, and graphene, etc.

[0108] The binder material can be a fluororesin, a polyacrylonitrile, a polyimide resin, an acrylic resin, a polyolefin resin, a rubber-like polymer, etc. The fluororesin can include polytetrafluoroethylene, polyvinylidene fluoride, etc.

[0109] The positive current collector 310 can be coated with a conductive material or other functional coating on the surface of the positive current collector 310 as long as it is a conductive material. The material of the positive current collector 310 can be a metal material including Al, Ti, Fe, etc. such as Al, Al alloy, Ti, Ti alloy, stainless steel (SUS), etc.

[0110] The thickness of the positive current collector 310 is not particularly limited and can be, for example, 5 μm or more and 30 μm or less.

[0111] In some embodiments, the negative tab 200 includes a lithium metal layer or a lithium alloy layer.

[0112] For a lithium metal secondary battery, the negative tab 200 in the electrode assembly 1000 included therein is a lithium metal layer or a lithium alloy layer as a negative active material. The lithium metal layer or the lithium alloy layer can be partially or entirely disposed on the surface of the negative current collector 210 as the negative active material layer 220. The lithium metal or lithium alloy layer can be pre-formed on the surface of the negative current collector 210 or can be formed during the first charging of the lithium metal secondary battery.

[0113] The expansion of the lithium metal secondary battery during charging and discharging is related to the deposition and dissolution of lithium metal, and this can be accompanied by the growth of lithium dendrites and the unstable rupture of the SEI film, and the growth of lithium dendrites can pierce the separator, causing a short circuit, thereby affecting the structural integrity and reliability of the battery. The battery separator 100 in the embodiments of the present disclosure can maintain the close combination of the two sides of the battery separator 100 with the positive and negative electrode surfaces, which is beneficial to ensuring the uniformity of the deposition of lithium metal on the negative electrode surface; and the multiple layers of the separator layer arranged at intervals can achieve multi-layer insulation, and the elastic connection layer 130 in the battery separator 100 can effectively block the lithium dendrites, reduce the risk of the battery separator being completely pierced, and maintain the structural integrity and reliability.

[0114] Embodiments of the third aspect of the present disclosure provide a secondary battery including the battery separator 100 in the above embodiments or the electrode assembly 1000 in the above embodiments.

[0115] The secondary battery further includes a non-aqueous electrolyte, wherein the non-aqueous electrolyte having lithium ion conductivity can be an organic solvent, a lithium salt dissolved in the organic solvent, and a functional additive. The non-aqueous electrolyte can be liquid, gel-like, a polymer electrolyte, or a solid electrolyte. The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in an organic solvent. The lithium salt is dissolved in the organic solvent to generate lithium ions and anions. The gel-like non-aqueous electrolyte includes a lithium salt and a polymer, or a lithium salt, an organic solvent, and a polymer. The polymer can be a fluororesin, an acrylic resin, a polyether resin, or the like.

[0116] The lithium salt is not particularly limited, for example, the lithium salt is selected from one or two of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylborate (LiB(C6H5)4), lithium methylsulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis-trifluoromethanesulfonylimide (LiN(SO2CF3)2), LiC(SO2CF3)3, lithium hexafluorosilicate (LiSiF6), lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate (LiF2OB), lithium trifluoroacetate (LiCF3CO2), lithium difluoro(oxalato)borate LiBF2(C2O4), lithium tetrafluoro(oxalato)phosphate LiPF4(C2O4), lithium difluoro(oxalato)phosphate LiPF2(C2O4)2.

[0117] The organic solvent can use an ester, an ether, a nitrile, an amide, or a halogen-substituted thereof. These organic solvents can be used alone, or a mixture of two or more organic solvents can be used.

[0118] The ester-based solvent can include a carbonate, a carboxylic acid ester, or the like. The cyclic carbonate can include ethylene carbonate, propylene carbonate, fluoroethylene carbonate (FEC), or the like. The chain carbonate can include, for example, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate, or the like. The cyclic carboxylic acid ester can include, for example, γ-butyrolactone, γ-valerolactone, or the like. The chain carboxylic acid ester can include, for example, ethyl acetate, methyl propionate, fluoro methyl propionate, or the like.

[0119] The ether-based solvent can include, for example, a cyclic ether and a chain ether. The cyclic ether can include, for example, 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, or the like. The chain ether can include, for example, 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methyl phenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, diethylene glycol dimethyl ether, or the like.

[0120] The concentration of the lithium salt in the non-aqueous electrolyte can be greater than or equal to 0.5 mol / L and less than or equal to 3.5 mol / L.

[0121] The non-aqueous electrolyte can further include a functional additive such as a film-forming additive for suppressing dendrite growth, vinyl ethylene carbonate (VEC), etc.

[0122] The secondary battery can be a lithium metal secondary battery, and the negative electrode sheet 200 in the electrode assembly 1000 thereof includes a lithium metal layer or a lithium alloy layer. The elastic connection layer 130 in the battery separator 100 can be compressed during charging of the lithium metal secondary battery and can rebound during discharging of the lithium metal secondary battery, thereby suppressing swelling of the lithium metal secondary battery during charging, reducing thickness reduction of the lithium metal secondary battery during discharging, maintaining structural stability of the lithium metal secondary battery, and thus improving the life characteristics of the battery.

[0123] Embodiments of the fourth aspect of the disclosure provide an electric device including the secondary battery in the above-described embodiments, which is used to provide electric energy.

[0124] The electric device can be, but is not limited to, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, an electric car, an electric vehicle, a ship, a spacecraft, etc. The electric toy can include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric aircraft toy, etc. The spacecraft can include an airplane, a rocket, a space shuttle, a spacecraft, etc.

[0125] The disclosure will be described in more detail below with reference to the embodiments.

[0126] Embodiment 1

[0127] (i) Preparation of the positive electrode

[0128] A positive electrode slurry was prepared by mixing a lithium-containing positive electrode active material NCM 622, a conductive agent acetylene black, and a positive electrode binder polyvinylidene fluoride (PVDF) at a mass ratio of 95:2.5:2.5, then adding N-methyl pyrrolidone (NMP) as a solvent and stirring. The positive electrode slurry was uniformly coated on both sides of an aluminum foil with a thickness of 12 μm, then dried, and the coating film of the positive electrode material was calendered using a roller. Finally, the obtained positive electrode current collector and positive electrode material were cut into a prescribed electrode size to prepare the positive electrode.

[0129] (ii) Preparation of the negative electrode

[0130] A rectangular electrolytic copper foil (thickness 12 μm) was prepared as a negative electrode current collector. A lithium foil with a thickness of 40 μm was calendered on both sides of the negative electrode current collector to form the negative electrode.

[0131] (iii) Preparation of the non-aqueous electrolyte

[0132] The organic solvents EC, EMC and DEC are mixed in a mass ratio of 30:50:20 under a dry argon atmosphere, then LiPF6 is added to the organic solvents to dissolve and mix uniformly, to obtain a mixed solvent, and then FEC and LiDFOB are added to the mixed solvent. The molar concentration of LiPF6 in the electrolyte is 1.2 mol / L; the mass percentage of FEC W1 is 1% and the mass percentage of LiDFOB W2 is 0.6% based on the mass of the electrolyte.

[0133] (iv) Preparation of battery separator with elastic support

[0134] A 9-μm-thick polyethylene separator is cut into a specified size, a binder polyvinylidene fluoride (PVDF) is added to an N-methyl pyrrolidone (NMP) solvent to stir to form a binder slurry, and the binder slurry is coated on the polyethylene separator to form a plurality of elastic supports. The width of the linear elastic support is 10 mm, the pitch is 100 mm, and the binder coating is dried and then coated repeatedly until the height of the elastic support reaches 10 μm.

[0135] Two pieces of the polyethylene separator coated with the striped PVDF coating are placed opposite each other, and the PVDF layer is bonded by hot pressing at 100°C for 10 seconds to form a battery separator with an elastic support, with a total thickness of 29 μm.

[0136] (v) Preparation of lithium metal secondary battery

[0137] An Al tab is welded on the positive electrode obtained above, and a Ni tab is welded on the copper foil of the negative electrode unit obtained above. The tab and the separator obtained above are stacked in the order of negative electrode / separator / positive electrode / separator to form an electrode assembly.

[0138] The electrode assembly obtained above is placed in a bag-shaped outer shell made of an aluminum plastic film, non-aqueous electrolyte is injected, the bag-shaped outer shell is sealed, and after immersion and formation, a lithium metal secondary battery A1 is formed.

[0139] Example 2

[0140] In the preparation of the separator elastic body, the coating and drying of the binder slurry are repeated until the height of the elastic support reaches 15 μm. In addition to the above, the same operation as in Example 1 is performed to prepare a lithium metal secondary battery A2.

[0141] Example 3

[0142] In the preparation of the separator elastic body, the slurry is a ceramic slurry of Al2O3:PVDF=1:9. In addition to the above, the same operation as in Example 1 is performed to prepare a lithium metal secondary battery A3.

[0143] Example 4

[0144] In the production of the separator elastic body, the slurry SBR slurry was used, and the same operation as in Example 1 was performed except for the above, to produce a lithium metal secondary battery A4.

[0145] Example 5

[0146] In the production of the separator elastic body, the pitch of the linear elastic support was set to 50 mm, and the same operation as in Example 1 was performed except for the above, to produce a lithium metal secondary battery A5.

[0147] Comparative Example

[0148] In the production of the lithium metal secondary battery, a single-layer polyethylene separator was used, and the same operation as in Example 1 was performed except for the above, to produce a lithium metal secondary battery B1.

[0149] For all the batteries obtained above, a charge-discharge test was performed. The charge-discharge test was performed in a constant temperature chamber at 25°C, and the charge-discharge of the battery was performed under the following conditions:

[0150] Constant current charging was performed at a current of 2 mA per unit area (cm2) of the electrode until the voltage reached 4.2 V, and then switched to 4.2 V constant voltage charging until the charging current decreased to 0.5 mA / cm 2 .

[0151] Constant current discharge was performed at a current of 2 mA / cm 2 until the battery voltage reached 3.0 V.

[0152] The thickness of all the batteries at the end of charging was measured using a constant pressure thickness gauge with a weight of 500 g, and the thickness of the battery at the end of discharge was measured using the same constant pressure thickness gauge with the same weight.

[0153] (H2 / H1-1) x 100% was taken as the battery charging expansion rate, and the results are shown in Table 1 below:

[0154] Table 1

[0155] According to the expansion beam of the different batteries in Table 1, the expansion rate of the battery during charging was significantly improved using the battery separator with the elastic support.

[0156] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than limit them; although the present disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some or all of the technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present disclosure, and they should be covered in the scope of the claims and the specification of the present disclosure. In particular, as long as there is no structural conflict, each technical feature mentioned in each embodiment can be combined in any way. The present disclosure is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery separator, comprising: N separator layers stacked along a first direction; and N-1 elastic connection layers, any one of which is sandwiched between two adjacent separator layers and elastically connects the two separator layers; wherein N is a positive integer greater than 1. At least one of the elastic connection layers has at least one void region located between two adjacent separator layers.

2. The battery separator of claim 1, wherein, The elastic connection layer comprises a first surface and a second surface oppositely arranged along a thickness direction; at least one of the first surface and the second surface is provided with a recess, which defines the at least one void region.

3. The battery separator of claim 2, wherein, The elastic connection layer comprises a plurality of elastic supports, between which the at least one void region is defined.

4. The battery separator of claim 2, wherein, A projection of the elastic connection layer on an adjacent separator layer is in one or more of a discrete dot shape, a discrete line shape, and a cross pattern shape.

5. The battery separator of claim 4, wherein, The plurality of elastic supports are in a cylindrical shape, and a diameter of any one of the plurality of elastic supports is greater than or equal to 20 μm and less than or equal to 100 mm.

6. The battery separator of claim 5, wherein, Alternatively The plurality of elastic supports are in a line shape, and a width of any one of the plurality of elastic supports is greater than or equal to 20 μm and less than or equal to 100 mm. A maximum thickness of the elastic connection layer is greater than or equal to 2 μm and less than or equal to 100 μm.

7. The battery separator of any of claims 1-6, wherein, A contact area of the elastic connection layer with the separator layer is less than an area of the separator layer.

8. The battery separator of any of claims 1-7, wherein, A ratio of the contact area of the elastic connection layer with the separator layer to the area of the separator layer is greater than or equal to 2% and less than or equal to 60%.

9. The battery separator of claim 8, wherein, The battery separator comprises a first separator layer and a second separator layer located at two outermost ends along the first direction, respectively; 10. The battery separator of any of claims 1-9, wherein, wherein at least one of the first separator layer and the second separator layer is provided with a functional coating on a surface perpendicular to the first direction, the functional coating comprising one or more of a heat-resistant coating, a protective coating, a conductive coating, and an adhesive layer. At least one of the first separator layer and the second separator layer is provided with the same type of functional coating on two surfaces perpendicular to the first direction, respectively.

11. The battery separator of claim 10, wherein, At least one of the first separator layer and the second separator layer is provided with different types of functional coating on two surfaces perpendicular to the first direction, respectively.

12. The battery separator of claim 10, wherein, The battery separator comprises a first separator layer and a second separator layer located at two outermost ends along the first direction, respectively; 13. The battery separator of any of claims 1-12, wherein, wherein the first separator layer and the second separator layer are made of different materials. At least one of the first separator layer and the second separator layer comprises a plurality of polymer layers made of different materials.

14. The battery separator of claim 13, wherein, 15.An electrode assembly, comprising: a positive electrode sheet; a negative electrode sheet stacked opposite to the positive electrode sheet; and the battery separator of any one of claims 1-14, sandwiched between the positive electrode sheet and the negative electrode sheet. comprising: The negative electrode sheet comprises a lithium metal layer or a lithium alloy layer.

16. The electrode assembly of claim 15, wherein, 17.A secondary battery comprising the battery separator of any one of claims 1-14, or the electrode assembly of claim 15 or 16. ​ ​ 18. An electric device comprising the secondary battery as claimed in claim 17, the secondary battery being used to supply electric power.

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