Separator, electrode assembly, secondary battery, and electric device

Abstract

The invention provides an isolating membrane, an electrode assembly, a secondary battery and an electric device, the resilience coefficient k of the isolating membrane is 10%-90%, k = (H0-H1) / H0 * 100%, H0 represents the initial thickness of the isolating membrane at 25 DEG C, H0 represents the initial thickness of the isolating membrane at 25 DEG C, and H0 represents the initial thickness of the isolating membrane at 25 DEG C; and H1 represents the thickness of the separator after the separator having the initial thickness H0 is compressed for 60 seconds at a temperature of 25 DEG C under a load of 0.8 MPa and then relaxed for 60 seconds after the load is removed. The isolating membrane provided by the invention has excellent rebound resilience.

Description

Separator, electrode assembly, secondary battery and power-consuming device Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an isolation membrane, an electrode assembly, a secondary battery, and an electrical device. Background Art

[0002] Secondary batteries, also known as rechargeable batteries, are batteries that can be repeatedly discharged and recharged for multiple uses. In recent years, with the increasing use of secondary batteries, such as lithium-ion and sodium-ion batteries, higher demands have been placed on their performance, particularly their cycle life.

[0003] Therefore, further improving the cycle performance of secondary batteries is still a technical problem that needs to be solved urgently.

[0004] Summary of the Invention

[0005] This application is made in view of the above-mentioned problems and provides a polymer and its preparation method, electrode, secondary battery, battery module, battery pack and electrical device to solve the problem of low energy density of lithium-ion batteries.

[0006] The purpose of the present application is to provide an isolation membrane that can improve the cycle performance of a secondary battery containing the isolation membrane; the purpose of the present application is also to provide an electrode assembly, a secondary battery and an electrical device containing the above isolation membrane, so as to obtain improved secondary battery cycle performance.

[0007] Therefore, in the first aspect, an embodiment of the present application provides an isolation membrane, the rebound coefficient k of the isolation membrane is 10% to 90%, wherein k = (H0-H1) / H0×100%, H0 represents the initial thickness of the isolation membrane at a temperature of 25°C, and H1 represents the thickness of the isolation membrane after the isolation membrane with the initial thickness H0 is compressed at a temperature of 25°C with a load of 0.8 MPa for 60 seconds and then the load is removed and relaxed for 60S.

[0008] According to the technical solution of the embodiment of the present application, the isolation membrane has excellent rebound performance. In the process of charging the secondary battery containing the isolation membrane, the active ions combine with the negative electrode material (for example, adsorption or combination) to expand its volume. The squeezed isolation membrane can also absorb the volume expansion of the negative electrode material through its own elastic deformation, thereby reducing the stress generated in the electrode due to the volume expansion of the negative electrode material, thereby reducing or avoiding the shell deformation and / or damage to the internal material of the electrode electrode due to internal stress, and reducing or avoiding the deterioration of the cycle performance of the secondary battery; when the secondary battery containing the diaphragm reduces the volume of the expanded negative electrode active material due to discharge, the isolation membrane can rebound, thereby maintaining good adhesion with the electrode. In this way, the isolation membrane according to the embodiment of the present application can improve the cycle performance of the secondary battery containing the isolation membrane.

[0009] In any embodiment of the present application, 20% < k ≤ 85%. A separator with a coefficient of resilience k within an appropriate range can further mitigate or avoid deformation of the housing and / or damage to the internal materials of the electrode plate caused by internal stress, thereby mitigating or avoiding deterioration in the cycle performance of the secondary battery. When the volume of the negative electrode active material in a secondary battery containing the separator decreases due to discharge, the separator can rebound, further maintaining good adhesion to the electrode plate.

[0010] In any embodiment of the present application, the separator includes an elastic deformation reserved space. During the charging process of a secondary battery containing the separator, active ions combine with the negative electrode material (e.g., adsorption or combination) to expand its volume, the separator is squeezed, and its elastic deformation reserved space can be elastically compressed to absorb the volume expansion of the negative electrode material, thereby reducing the stress in the electrode sheet due to the volume expansion of the negative electrode material, further reducing or avoiding shell deformation and / or damage to the internal materials of the electrode sheet caused by internal stress, and reducing or avoiding the deterioration of the cycle performance of the secondary battery; when the secondary battery containing the separator reduces the volume of the expanded negative electrode active material due to discharge, the elastic deformation reserved space can rebound, so that the separator maintains good adhesion with the electrode sheet.

[0011] In any embodiment of the present application, the separator includes a base film having a plurality of first hollow cavities distributed therein, which serve as elastic deformation reserve spaces. The base film in the separator has a first hollow cavity, which serves as elastic deformation reserve spaces and can absorb the volume expansion of the negative electrode material. The expanded volume can be accommodated in the space vacated after compression, thereby reducing the stress generated in the electrode sheet due to the volume expansion of the negative electrode material, further reducing or avoiding shell deformation and / or damage to the internal materials of the electrode sheet caused by internal stress, and reducing or avoiding deterioration of the cycle performance of the secondary battery; when the volume of the expanded negative electrode active material decreases due to discharge, the first hollow cavity can rebound, so that the separator including the base film having the first hollow cavity maintains good adhesion with the electrode sheet.

[0012] In any embodiment of the present application, the separator includes a base film, which is a corrugated film. The corrugated film has a certain degree of resilience along its thickness direction and includes a plurality of protrusions. The plurality of protrusions can be elastically compressed to absorb the volume expansion of the negative electrode material. The expanded volume can be accommodated in the space vacated after the compression, thereby reducing the stress generated in the electrode sheet due to the volume expansion of the negative electrode material, further reducing or avoiding shell deformation and / or damage to the internal material of the electrode sheet caused by internal stress, and reducing or avoiding deterioration of the cycle performance of the secondary battery.

[0013] In any embodiment of the present application, the separator includes a base membrane, and the base membrane has a compressive elastic modulus of 7 MPa to 1000 MPa, optionally 8 MPa to 300 MPa. The compressive elastic modulus of the base membrane is within the above range, that is, during the elastic deformation stage, the ratio of the normal stress to the corresponding normal strain is within the above range. During the charging process of a secondary battery including the separator, active ions combine with (e.g., adsorb or combine with) the negative electrode material, causing its volume to expand and the separator to be squeezed. Since the compressive elastic modulus of the base membrane is within the above range, it is beneficial to maintain the performance of the separator.

[0014] In any embodiment of the present application, the isolation membrane includes a base membrane, and the base membrane is selected from one or more of a polyethylene film, a polyethylene terephthalate film, a polyethylene oxide film, a styrene-butadiene-styrene film, a poly(styrene-ethylene / butylene-styrene) film, a hydrogenated styrene / isoprene block copolymer film, and a thermoplastic polyester elastomer film. The base membrane can also be other polyester films, polyether films, etc. with excellent rebound properties. The base membrane of the above-mentioned material itself has a certain rebound property, which can further improve the rebound property of the isolation membrane, thereby improving the cycle performance of the secondary battery containing the isolation membrane. The base membrane of the above-mentioned material can also have good strength and toughness, which can effectively ensure the safety of the secondary battery containing the isolation membrane.

[0015] In any embodiment of the present application, the separator includes a coating, and the coating is provided on at least one side of the base film. The separator including the coating has excellent resilience. On the one hand, the coating is not prone to brittle fracture or shedding during winding and bending, and has good mechanical processing performance. On the other hand, during the charging process of the secondary battery including the separator, the active ions combine with the negative electrode material (e.g., adsorption or chemical combination) to expand the volume of the negative electrode material. The separator is squeezed and the coating has good compressibility. When the volume of the negative electrode active material is reduced during discharge, the separator with the coating can enhance the adhesion effect with the electrode, thereby avoiding deterioration of the cycle performance of the secondary battery including the separator.

[0016] In any embodiment of the present application, the coating layer includes a plurality of second hollow cavities distributed therein. The coating layer in the separator has a second hollow cavity, which serves as a reserved space for elastic deformation and can absorb the volume expansion of the negative electrode material during the charging process of the secondary battery. The expanded volume can be accommodated in the space vacated after being compressed, thereby reducing the stress generated in the electrode sheet due to the volume expansion of the negative electrode material, further reducing or avoiding the deformation of the shell and / or the damage to the internal material of the electrode sheet caused by internal stress, and reducing or avoiding the deterioration of the cycle performance of the secondary battery; when the volume of the expanded negative electrode active material decreases due to discharge, the first hollow cavity can rebound, so that the separator containing the base film having the first hollow cavity maintains good adhesion with the electrode sheet.

[0017] In any embodiment of the present application, the coating is a corrugated coating. The corrugated coating has a certain degree of resilience along its thickness direction, and the corrugated coating itself includes a plurality of protrusions. The plurality of protrusions can be elastically compressed to absorb the volume expansion of the negative electrode material. The expanded volume can be accommodated in the space vacated after the compression, thereby reducing the stress generated in the electrode sheet due to the volume expansion of the negative electrode material, further reducing or avoiding deformation of the shell and / or damage to the internal materials of the electrode sheet caused by internal stress, and reducing or avoiding deterioration of the cycle performance of the secondary battery.

[0018] In any embodiment of the present application, an elastic deformation space exists between the coating layer and the coated surface of the base film. The elastic deformation space between the coating layer and the coated surface of the base film can be elastically compressed to absorb the volume expansion of the negative electrode material. The expanded volume can be accommodated in the space vacated after the compression, thereby reducing the stress generated in the electrode sheet due to the volume expansion of the negative electrode material, further reducing or avoiding deformation of the shell and / or damage to the internal materials of the electrode sheet caused by internal stress, and reducing or avoiding deterioration of the cycle performance of the secondary battery.

[0019] In any embodiment of the present application, the coating comprises a polymer and a filler.

[0020] In any embodiment of the present application, the polymer includes one or more of polyethylene oxide, styrene-butadiene-styrene, poly(styrene-ethylene / butylene-styrene), hydrogenated styrene / isoprene block copolymer, and thermoplastic polyester elastomer. The polymer may also be other polyester films or polyether films with excellent rebound properties. The coating composed of the above polymer materials itself has a certain rebound property, thereby improving the cycle performance of the secondary battery. The coating composed of the above polymer materials may also have good strength and toughness.

[0021] In a second aspect, an embodiment of the present application provides an electrode assembly, comprising a positive electrode sheet, a negative electrode sheet, and a separator separated between the positive electrode sheet and the negative electrode sheet, wherein the separator is the separator of the first aspect.

[0022] In any embodiment of the present application, the rebound amount k×H0 of the separator has a linear relationship with the thickness Q of the positive electrode sheet.

[0023] The thickness Q of the positive electrode sheet has a linear relationship with the amount of active ions such as lithium ions and sodium ions contained in the positive electrode sheet that can be deposited on the negative electrode sheet. The rebound amount of the isolation membrane is marked as k×H0, which can be understood as an isolation membrane with a certain rebound amount having a rebound coefficient k, which can allow the thickness Q of the positive electrode sheet to release a corresponding amount of active ions during the charging process. The active ions combine with the negative electrode material (for example, adsorption or combination) to expand its volume. The squeezed isolation membrane can also absorb the volume expansion of the negative electrode material through its own elastic deformation, thereby reducing the stress generated in the electrode sheet due to the volume expansion of the negative electrode material, thereby reducing or avoiding the deformation of the shell and / or damage to the internal material of the electrode sheet caused by internal stress, and reducing or avoiding the deterioration of the cycle performance of the secondary battery; when the secondary battery containing the diaphragm reduces the volume of the expanded negative electrode active material due to discharge, the isolation membrane can rebound, thereby maintaining good fit with the electrode sheet.

[0024] In any embodiment of the present application, Q=α×k×H0, where α is 20 to 50.

[0025] Optionally, k×H0 is 1.5 to 4 μm; optionally, Q is 30 to 200 μm.

[0026] When the rebound amount of the isolation membrane is marked as k×H0 and the thickness Q of the positive electrode sheet satisfies the above relationship, the thickness Q of the positive electrode sheet is allowed to release a corresponding amount of active ions, and the active ions combine with the negative electrode material (for example, adsorption or combination) to cause its volume to expand. The squeezed isolation membrane can also absorb the volume expansion of the negative electrode material through its own elastic deformation. The rebound amount k×H0 of the isolation membrane and the thickness Q of the positive electrode sheet work together to reduce or avoid the deterioration of the cycle performance of the secondary battery; when the secondary battery containing the separator reduces the volume of the expanded negative electrode active material due to discharge, the isolation membrane can rebound, thereby maintaining good fit with the sheet.

[0027] In any embodiment of the present application, the maximum gap between the negative electrode plate and the separator is ≤ 200 μm. During formation or charge / discharge, the electrode assembly comprising the negative electrode plate and the separator maintains a gap within the aforementioned range to maintain good adhesion to the plate.

[0028] In a third aspect, an embodiment of the present application provides a secondary battery comprising the electrode assembly of the second aspect.

[0029] In a fourth aspect, embodiments of the present application provide an electrical device comprising the secondary battery of the third aspect. The secondary battery or electrical device of the present application comprises the separator of the first aspect of the present application, and thus has at least the advantages of using the separator. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0031] FIG1 is a schematic diagram of a base film according to one embodiment of the present application.

[0032] FIG. 2 is a schematic diagram of a corrugated base film according to an embodiment of the present application.

[0033] FIG3 is a schematic diagram of an isolation film including a coating layer according to an embodiment of the present application.

[0034] FIG4 is a schematic diagram of a corrugated coating according to an embodiment of the present application.

[0035] FIG. 5 is a schematic diagram of an isolation membrane including a corrugated coating according to another embodiment of the present application.

[0036] FIG6 is a schematic diagram of an embodiment of a secondary battery of the present application.

[0037] FIG. 7 is an exploded schematic diagram of the secondary battery shown in FIG. 4 .

[0038] FIG8 is a schematic diagram of an embodiment of an electric device including the secondary battery of the present application as a power source.

[0039] In the accompanying drawings, the drawings are not necessarily drawn to scale. DETAILED DESCRIPTION

[0040] Below, the embodiments of the polymer and its preparation method, pole piece, secondary battery, battery module, battery pack and electric device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0041] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0042] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0043] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0044] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0045] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0046] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0047] Unless otherwise specified, in this application, the term "active ions" refers to ions that can be intercalated and extracted between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions, sodium ions, etc.

[0048] The term "several" used in this application refers to two or more (including two).

[0049] The long diameter appearing in this application can be understood as the maximum long diameter measured in the elastic deformation space.

[0050] The secondary batteries mentioned in the embodiments of the present application may be lithium-ion batteries, sodium-ion batteries, lithium metal batteries, sodium metal batteries, etc., and the embodiments of the present application are not limited thereto.

[0051] A secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet. The electrode sheet will undergo volume expansion during the static and formation processes after the electrolyte injection, which will increase the overall thickness of the battery, thereby affecting the battery performance. Therefore, this factor needs to be considered when designing the battery thickness. The electrode sheet expansion caused by electrolyte injection includes swelling of the binder and stress relaxation expansion between particles. The electrode sheet expansion during the formation process includes volume expansion and stress relaxation expansion caused by the combination of active ions with electrode material particles (such as adsorption, embedding, or combination). In addition, research has found that during the subsequent charging process after the battery is formed, the negative electrode sheet will also undergo volume expansion. The main reason is that the active ions migrate from the positive electrode sheet to the negative electrode sheet and combine with the negative electrode active material (such as adsorption, embedding, or combination) or deposit, causing the volume of the negative electrode sheet to expand.

[0052] When the volume of the negative electrode plate expands, the plate is squeezed and generates a large internal stress. Such internal stress may cause damage to the internal materials of the plate (such as damage to the active material particles) and deformation of the battery shell. In addition, during the subsequent discharge process of the battery, active ions are released from the negative electrode active material, causing the volume of the negative electrode active material to decrease and the volume of the negative electrode plate to shrink. Such volume shrinkage will deteriorate the fit between the positive electrode plate, the negative electrode plate and the separator, affecting battery performance. In addition, the repeated volume expansion / contraction of the negative electrode plate during the charge and discharge process may also lead to repeated destruction and formation of the SEI film, which is not conducive to the stability of the SEI film and further affects the cycle performance of the battery. In short, the repeated volume expansion / contraction of the electrode plate, especially the negative electrode plate, during the charge and discharge process of the battery has an adverse effect on the cycle performance of the battery, which is a challenge faced in improving the cycle performance of the battery. This is especially true for sodium-ion secondary batteries with a significant volume expansion effect of the negative electrode plate.

[0053] To reduce the impact of pole piece volume expansion on battery cycle performance, current measures primarily focus on improving the structure of the active material itself to mitigate its volume expansion and contraction during the battery's charge and discharge processes. However, research has found that improvements to the active material structure itself for this purpose are subject to numerous limitations, such as the range of active material options and capacity requirements, and cannot address pole piece volume expansion caused by other factors (such as the deposition of active ions outside the active material).

[0054] In view of this, the technical solution of the embodiment of the present application provides an isolation membrane, which can at least reduce the adverse effects of repeated volume expansion / contraction of the negative electrode plate during the battery charging and discharging process on the cycle performance of the battery, thereby improving the cycle performance of the secondary battery containing it.

[0055] Isolation film

[0056] In the first aspect, an embodiment of the present application provides an isolation membrane, the rebound coefficient k of the isolation membrane is 10% to 90%, wherein k = (H0-H1) / H0×100%, H0 represents the initial thickness of the isolation membrane at a temperature of 25°C, and H1 represents the thickness of the isolation membrane after the isolation membrane with the initial thickness H0 is compressed at a temperature of 25°C with a load of 0.8 MPa for 60 seconds and then the load is removed and relaxed for 60S.

[0057] In this embodiment, "initial thickness" can be understood as the thickness of the separator measured at 25°C. This can be achieved by measuring multiple points on the separator surface and taking the average value. Alternatively, the prepared separator can be cut into 500 samples and a constant pressure applied to each sample to measure the "initial thickness." "H1" represents the average thickness of the separator after compressing the separator at 25°C with a constant load of 0.8 MPa for 60 seconds, followed by a 60-second relaxation period after the load is removed. As an example, a constant force can be applied to the surface of a separator with an "initial thickness": initially, the separator is subjected to a pressure of 0.1 MPa. The separator is then compressed at a speed of 5 μm / min at 25°C with a load of 0.8 MPa for 60 seconds. After the force is removed (i.e., the pressure is reduced to zero), the separator thickness is measured approximately 40 seconds to 5 minutes later.

[0058] As an example, when pressing down on the isolation membrane, a speed of 5 μm / min can be used. All of the above tests were conducted at 25°C and atmospheric pressure. This test can be performed using an engineering plastic elastic modulus tester, such as the HY-1080, available from Shanghai Hengyi Precision Instrument Co., Ltd. The test can refer to the national standard GBT 14694-1993, Determination of the Compressive Elastic Modulus of Plastics.

[0059] The isolation film is set between the positive electrode and the negative electrode, and its main function is to prevent the positive and negative electrodes from short-circuiting.

[0060] The isolation membrane according to the embodiment of the present application has excellent rebound performance. During the charging process of the secondary battery containing the isolation membrane, even if the active ions combine with the negative electrode material (for example, adsorption or combination) to expand its volume, the squeezed isolation membrane can absorb the volume expansion of the negative electrode material through its own elastic deformation, thereby reducing the stress generated in the electrode due to the volume expansion of the negative electrode material, thereby reducing or avoiding the shell deformation and / or damage to the internal material of the electrode electrode due to internal stress, and reducing or avoiding the deterioration of the cycle performance of the secondary battery; when the secondary battery containing the isolation membrane reduces the volume of the negative electrode active material due to discharge, the isolation membrane can rebound, thereby maintaining good adhesion with the electrode. In addition, since the isolation membrane can provide a buffer for the volume expansion / contraction of the negative electrode electrode, it can reduce the impact of the SEI film during the volume expansion / contraction of the negative electrode electrode, thereby improving the stability of the SEI film. In this way, the isolation membrane according to the embodiment of the present application can improve the cycle performance of the secondary battery containing the isolation membrane.

[0061] In addition, the isolation film has excellent rebound performance and is not prone to breakage or damage during winding or processing. It also has uniform thickness, which improves the safety performance of the battery.

[0062] In some optional embodiments, k may be any one or more of 15%-95%, 15%-90%, 20%-95%, and 20%-90%.

[0063] In some optional embodiments, 20%<k≤85%. Optionally, k can be 25%-50%, 25%-55%, 25%-60%, 25%-65%, 25%-70%, 25%-75%, 25%-80%, 25%-85%, 30%-50%, 30%-55%, 30%-60%, 30%-65%, 30%-70%, 30%-75%, 30%-80%, 30%-85%, 35%-50%, 35%-55%, 35%-60%, 35%-65%, 35%-70%, 35%-75%, 35%-80%, 35%-85%, 40%-50%, 40%-55%, 40%-60%, 40%-65%, 40%-70%, 40%-75%, 40%-80%, 40%-85%, 45%-50%, 45%-55%, 45%~60%, 45%~65%, 45%~70%, 45%~75%, 45%~80%, 45%~85%, 50%~55%, 50%~60%, 50%~65%, 50%~70%, 50%~75%, 50%~80%, 50%~85%, 55%~60%, 55%~65%, 55%~70%, 55%~75%, 55%~80%, 55%~85%, 60%~65%, 60%~70%, 60%~75%, 60%~80%, 60%~85%, 65%~70%, 65%~75%, 65%~80%, 65%~85%, 70%~75%, 70%~80%, 70%~85%, 75%~80%, 75%~85%, 80%~85%, any one or more. The rebound coefficient k of the isolation membrane is within an appropriate range, which can further reduce or avoid shell deformation and / or damage to the internal materials of the electrode plate caused by internal stress, and reduce or avoid the deterioration of the cycle performance of the secondary battery; when the secondary battery containing the isolation membrane causes the volume of the negative electrode active material to decrease due to discharge, the isolation membrane can rebound and further maintain good adhesion with the electrode plate.

[0064] In some optional embodiments, the separator includes an elastic deformation reserved space. During the charging process of a secondary battery containing the separator, active ions combine with the negative electrode material (e.g., adsorption or combination) to cause its volume expansion, the separator is squeezed, and its elastic deformation reserved space can be elastically compressed to absorb the volume expansion of the negative electrode material, thereby reducing the stress in the electrode sheet caused by the volume expansion of the negative electrode material, further reducing or avoiding shell deformation and / or damage to the internal materials of the electrode sheet caused by internal stress, and reducing or avoiding deterioration of the cycle performance of the secondary battery; when the volume of the expanded negative electrode active material decreases due to discharge of the secondary battery containing the separator, the elastic deformation reserved space can rebound, so that the separator maintains good adhesion to the electrode sheet.

[0065] In some optional embodiments, the elastic deformation reserved space can be multiple hollow cavities distributed in the isolation membrane itself, or can be multiple protrusions of the isolation membrane itself, such as the elastic deformation reserved space brought about by the wavy shape in the thickness direction.

[0066] In some optional embodiments, the long diameter D of the elastic deformation reserved space in the thickness direction of the separator is 20-60 μm. The long diameter can be any one of 25, 30, 35, 40, 45, 50, 55, and 60 μm, or a range thereof. When the long diameter is within the above range, the volume expansion of the negative electrode material is absorbed, thereby reducing the stress generated in the electrode sheet due to the volume expansion of the negative electrode material, thereby reducing or avoiding shell deformation and / or damage to the internal materials of the electrode sheet caused by internal stress, and reducing or avoiding the deterioration of the cycle performance of the secondary battery; when the volume of the expanded negative electrode active material of the secondary battery containing the separator decreases due to discharge, the separator can rebound, thereby maintaining good adhesion with the electrode sheet.

[0067] In some optional embodiments, referring to FIG1 , the separator includes a base film 10 having a plurality of first hollow cavities 11 distributed therein, as an example of a reserved space for elastic deformation. The base film in the separator has a first hollow cavity, which serves as a reserved space for elastic deformation and can absorb the volume expansion of the negative electrode material. The expanded volume can be accommodated in the space vacated after being compressed, thereby reducing the stress generated in the electrode due to the volume expansion of the negative electrode material, further reducing or avoiding the deformation of the shell and / or the damage to the internal material of the electrode plate caused by internal stress, and reducing or avoiding the deterioration of the cycle performance of the secondary battery; when the volume of the expanded negative electrode active material decreases due to discharge, the first hollow cavity can rebound, so that the separator containing the base film having the first hollow cavity maintains good adhesion with the electrode plate.

[0068] In some optional embodiments, the major diameter D of the first hollow cavity 11 in the thickness direction is 20-60 μm. The major diameter can be any one of 25, 30, 35, 40, 45, 50, 55, and 60 μm, or a range thereof. When the major diameter D of the first hollow cavity in the thickness direction is within the above range, the separator can have a certain amount of elastic deformation space, allowing the negative electrode plate to expand to a certain extent.

[0069] In some optional embodiments, referring to FIG2 , the separator includes a base film, and the base film 10 is a corrugated film. A view of the corrugated film in its thickness direction is shown in FIG2 . The base film may include a plurality of convex portions spaced apart in the longitudinal (machine direction, abbreviated as MD) direction and / or the transverse (transverse direction, abbreviated as TD) direction. The plurality of convex portions spaced apart make the base film itself corrugated. The compression film formed by the corrugated film and the dotted line in FIG2 has an elastic reserved space. The elastic reserved space has a long diameter in the thickness direction. The corrugated film has a certain resilience along its thickness direction and itself includes a plurality of convex portions. The plurality of convex portions can be elastically compressed to absorb the volume expansion of the negative electrode material. The expanded volume can be accommodated in the space vacated after being compressed, thereby reducing the stress generated in the electrode sheet due to the volume expansion of the negative electrode material, further reducing or avoiding the deformation of the shell and / or the damage to the internal material of the electrode sheet caused by internal stress, and reducing or avoiding the deterioration of the cycle performance of the secondary battery.

[0070] In some optional embodiments, the long diameter D of the corrugated membrane in the thickness direction is 20-60 μm. The long diameter can be any one of 25, 30, 35, 40, 45, 50, 55, and 60 μm, or a range thereof. When the long diameter D of the corrugated membrane in the thickness direction is within the above range, the separator has a certain amount of elastic deformation reserve, allowing the negative electrode plate to expand to a certain extent.

[0071] In some optional embodiments, the separator includes a base membrane, and the base membrane has a compressive elastic modulus of 7 MPa to 1000 MPa, optionally 8 MPa to 300 MPa. The compressive elastic modulus of the base membrane is within the above range, that is, during the elastic deformation stage, the ratio of the normal stress to the corresponding normal strain is within the above range. During the charging process of a secondary battery including the separator, active ions combine with (e.g., adsorb or combine with) the negative electrode material, causing its volume to expand and the separator to be squeezed. Since the compressive elastic modulus of the base membrane is within the above range, the performance of the separator is maintained.

[0072] The compressive modulus can be measured using testing methods commonly used in the art. As an example, the compressive modulus can be measured at room temperature and normal pressure. The test can be performed using an engineering plastics elastic modulus tester, such as the HY-1080, available from Shanghai Hengyi Precision Instrument Co., Ltd. The test can refer to the national standard GBT 14694-1993, Determination of the Compressive Modulus of Plastics.

[0073] In some optional embodiments, the isolation membrane includes a base film, and the base film is selected from one or more of a polyethylene film, a polyethylene terephthalate film, a polyethylene oxide film, a styrene-butadiene-styrene film, a poly(styrene-ethylene-block / butylene-styrene-block) film, a hydrogenated styrene / isoprene block copolymer film, and a thermoplastic polyester elastomer film. The base film can also be other polyester films, polyether films, etc. with excellent rebound properties. The base film of the above materials itself has a certain rebound property, which can further improve the rebound property of the isolation membrane, thereby improving the cycle performance of the secondary battery containing the isolation membrane. The base film of the above materials can also have good strength and toughness, which can effectively ensure the safety of the secondary battery containing the isolation membrane.

[0074] In some embodiments, the material of the isolation membrane may include one or more of polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different.

[0075] As an example, the polyethylene film includes one or more of polyethylene (PE) and copolymers of ethylene and α-olefins. The α-olefin can be selected from α-olefins with a carbon number of 3 to 10. Optionally, the α-olefin is selected from one or more of propylene, 1-butene, and 1-octene. Specific examples of copolymers of ethylene and α-olefins may include one or more of polyethylene-propylene copolymers, polyethylene-butene copolymers, polyethylene-propylene-butene copolymers, and polyethylene-octene copolymers. The base film obtained with polyethylene polymers as the main polymer composition can have good strength and toughness, can make the isolation membrane have a higher rebound coefficient, and thus improve the cycle performance of the secondary battery.

[0076] In some embodiments, the polyethylene film comprises two or more polyethylene polymers, where the following condition is satisfied: 5 < M1 / M2 ≤ 20. M1 represents the weight-average molecular weight of the polyethylene polymer with the highest weight-average molecular weight among the base film ingredients, and M2 represents the weight-average molecular weight of the polyethylene polymer with the lowest weight-average molecular weight among the base film ingredients. The use of two or more polyethylene polymers in the base film, with the molecular weights of the two or more polyethylene polymers satisfying a suitable relationship, can ensure good uniformity and consistency across the separator, enhancing its strength, toughness, and coefficient of rebound.

[0077] 3 , the isolation film includes a coating 20 disposed on at least one side of the base film 10. As an example, the base film has two surfaces facing each other in its thickness direction, and the coating may be located on either or both of the two surfaces.

[0078] According to the embodiments of the present application, the isolation membrane including the coating has excellent resilience. On the one hand, the coating is not prone to brittle fracture or falling off during winding and bending, and has good mechanical processing performance. On the other hand, during the charging process of the secondary battery including the isolation membrane, the active ions combine with the negative electrode material (for example, adsorption or combination) to expand its volume. The isolation membrane is squeezed and the coating has good compressibility. When the volume of the expanded negative electrode active material decreases due to discharge, the isolation membrane with the coating can enhance the bonding effect with the electrode, thereby avoiding the deterioration of the cycle performance of the secondary battery including the isolation membrane.

[0079] In some embodiments, referring to FIG3 , the coating layer includes a plurality of second hollow cavities 21 distributed therein. The coating layer in the separator has a second hollow cavity, which serves as a reserved space for elastic deformation and can absorb the volume expansion of the negative electrode material during the charging process of the secondary battery. The expanded volume can be accommodated in the space vacated after compression, thereby reducing the stress generated in the electrode sheet due to the volume expansion of the negative electrode material, further reducing or avoiding shell deformation and / or damage to the internal materials of the electrode sheet caused by internal stress, and reducing or avoiding the deterioration of the cycle performance of the secondary battery; when the volume of the expanded negative electrode active material decreases due to discharge, the first hollow cavity can rebound, so that the separator containing the base film having the first hollow cavity maintains good adhesion with the electrode sheet.

[0080] In some embodiments, the second hollow cavity 21 has a major diameter in the thickness direction of 20-60 μm. The major diameter may be the inner diameter. The inner diameter may be any one of 25, 30, 35, 40, 45, 50, 55, and 60 μm, or a range thereof. When the major diameter in the thickness direction of the second hollow cavity is within the above range, the separator can have a certain amount of elastic deformation reserve space, allowing the negative electrode plate to expand to a certain extent.

[0081] In some embodiments, as shown in FIG4 , the coating is a corrugated coating. The corrugated coating has a certain degree of resilience along its thickness and includes a plurality of protrusions. The protrusions can be elastically compressed to absorb the volume expansion of the negative electrode material. The expanded volume can be accommodated in the space vacated by the compression, thereby reducing the stress in the electrode sheet caused by the volume expansion of the negative electrode material, further alleviating or avoiding deformation of the housing and / or damage to the internal materials of the electrode sheet caused by internal stress, and reducing or avoiding deterioration of the cycle performance of the secondary battery.

[0082] In some embodiments, as shown in FIG5 , there is an elastic deformation space 30 between the coating layer and the coated surface of the base film. The elastic deformation space between the coating layer and the coated surface of the base film can be elastically compressed to absorb the volume expansion of the negative electrode material. The expanded volume can be accommodated in the space vacated after the compression, thereby reducing the stress generated in the electrode sheet due to the volume expansion of the negative electrode material, further reducing or avoiding shell deformation and / or damage to the internal material of the electrode sheet caused by internal stress, and reducing or avoiding deterioration of the cycle performance of the secondary battery.

[0083] In some embodiments, the major diameter of the elastic deformation space 30 in the thickness direction is 20-60 μm. The major diameter can be any one of 25, 30, 35, 40, 45, 50, 55, and 60 μm, or a range thereof. When the major diameter of the elastic deformation space in the thickness direction is within the above range, the separator has a certain amount of space reserved for elastic deformation, allowing the negative electrode plate to expand to a certain extent.

[0084] In some alternative embodiments, the coating comprises a polymer and a filler.

[0085] In some optional embodiments, the polymer includes one or more of polyethylene oxide, styrene-butadiene-styrene, poly(styrene-ethylene / butylene-styrene), hydrogenated styrene / isoprene block copolymer, and thermoplastic polyester elastomer. The polymer may also be other polyester films or polyether films with excellent rebound properties. Coatings composed of these polymer materials inherently possess certain rebound properties, thereby improving the cycling performance of the secondary battery. Coatings composed of these polymer materials may also have good strength and toughness.

[0086] In some embodiments, the coating layer comprises polymer particles. The polymer particles can be one or more of the aforementioned polymers. Pores can be formed between the particles for ion transport.

[0087] In some embodiments, the filler may be inorganic particles. For example, the inorganic particles include one or more of aluminum oxide, silicon oxide, titanium oxide, calcium carbonate, magnesium oxide, magnesium hydroxide, boehmite, barium titanate, and barium sulfate. These particles can effectively suppress the short-circuit area caused by the separator melting due to heat generated by a short circuit, thereby further reducing the risk of thermal runaway or short-circuit failure in the secondary battery.

[0088] In some embodiments, the polymer accounts for 40% to 95% by weight of the coating, optionally 40% to 99%, 60% to 99%, 80% to 99%, 80% to 97%, 80% to 95%, 80% to 90%, 90% to 97%, or 85% to 95%. The inclusion of an appropriate amount of polymer in the coating can further enhance the resilience of the separator, thereby further improving the cycling performance of the secondary battery.

[0089] In some embodiments, the coating has a thickness of 0.01 mm to 0.2 mm. Alternatively, the coating has a thickness of 0.01 mm to 0.2 mm, 0.05 mm to 0.2 mm, 0.1 mm to 0.2 mm, or 0.05 mm to 0.1 mm. A coating thickness that meets the above conditions can effectively improve the resilience of the isolation membrane.

[0090] The thickness of the base film, isolation film, coating, and elastic deformation reserved space in the thickness direction of the isolation film, the major diameter D, are all well known in the art and can be tested using instruments and methods known in the art. An exemplary test method for the thickness of the isolation film is as follows: take a sample of 500 mm long and 100 mm wide; take 5 points evenly on the sample (for example, take a point every 100 mm along the length of the sample), use a 10,000-point thickness gauge to test the thickness of the isolation film at these 5 different positions, and take the average value as the thickness of the isolation film. The length direction of the sample is parallel to the TD direction of the isolation film. The thickness of the base film can be tested with reference to the above method. If a coating is provided on one side of the isolation film, the thickness of the isolation film is subtracted from the thickness of the base film to obtain the thickness of the coating. If the opposite sides of the isolation film are provided with a coating to be tested and a coating on the opposite side of the coating to be tested, the thickness of the isolation film is subtracted from the sum of the thickness of the base film and the coating on the opposite side to obtain the thickness of the coating to be tested.

[0091] The porosity of the base film is well known in the art and can be measured using instruments and methods known in the art. An exemplary test method is as follows: Take five 100 mm x 100 mm base film samples, weigh them separately, and take the average value as the base film weight M (mg). The porosity X of the base film is calculated using the formula X = [1-M / (T x S x ρ)] x 100%, where T is the thickness of the base film, S is the area of ​​the base film, and ρ is the density of the polymer in the base film formulation.

[0092] The isolation films shown in Figures 1 to 5 are merely exemplary. In other examples, the isolation film may include a base film 10 and a coating layer 20 laminated on two opposite surfaces of the base film 10 in a thickness direction.

[0093] In some embodiments, the present application also provides a method for preparing an isolation film, comprising:

[0094] providing a molten base film formulation comprising a polymer and a pore-forming agent;

[0095] Extruding and cooling the base film furnish to form a sheet;

[0096] Stretching the sheet in the MD direction and / or stretching the sheet in the TD direction;

[0097] Removing the pore-forming agent from the sheet to form a microporous sheet;

[0098] The porous sheet is heat-set to obtain a base film.

[0099] The pore-forming agent in the sheet can be removed by methods known in the art to form a porous sheet. For example, the pore-forming agent can be removed by extraction using an extractant. Examples of extractants include dichloromethane. The extraction can be carried out in an apparatus known in the art. As a specific example, the sheet can be pulled to an extraction section having an internal circulation extraction apparatus, and an internal circulation extraction method is used. The film is backwashed in the extractant, and the extractant is used to completely remove the pore-forming agent in the sheet. The extracted sheet is dried to obtain a porous sheet. Drying can be carried out in an apparatus known in the art, such as a drying furnace. The porous sheet can also be heat-set using methods and apparatus known in the art. For example, a horizontal stretching machine. As an example, the porous sheet can be pulled to a second horizontal stretching machine for heat setting. The second horizontal stretching machine can include three areas: preheating, stretching, and setting. The base film obtained after the heat setting treatment can be rolled up for use. The base film can be used as an isolation film.

[0100] In some embodiments, the base film can also be used as an isolation film after post-treatment. For example, a coating is formed on the base film. In these embodiments, the method for preparing the isolation film may further include forming a coating on at least one surface of the base film. As an example, a coating can be formed on any one surface or both surfaces in the thickness direction of the base film itself. The particles in the coating can be selected from those described herein. The solvent of the slurry forming the coating can be one or more of an aqueous solvent (such as deionized water, etc.) and an organic solvent (such as N-methylpyrrolidone NMP, dimethylacetamide DMAC, acetone, etc.). The slurry may also contain a binder. The binder can be a binder commonly used in the art. The coating method of the slurry can be any one or more of gravure coating (such as micro-gravure coating), dip coating, blade coating, wire rod coating, spray coating, and electrostatic spinning.

[0101] Electrode assembly

[0102] In a second aspect, an embodiment of the present application provides an electrode assembly, comprising a positive electrode sheet, a negative electrode sheet, and a separator separated between the positive electrode sheet and the negative electrode sheet, wherein the separator is the separator of the first aspect.

[0103] In some embodiments, the rebound amount k×H0 of the separator has a linear relationship with the thickness Q of the positive electrode sheet.

[0104] The thickness Q of the positive electrode sheet has a linear relationship with the amount of active ions such as lithium ions and sodium ions contained in the positive electrode sheet that can be deposited on the negative electrode sheet. The rebound amount of the isolation membrane is marked as k×H0, which can be understood as an isolation membrane with a certain rebound amount having a rebound coefficient k, which can allow the thickness Q of the positive electrode sheet to release a corresponding amount of active ions during the charging process. The active ions combine with the negative electrode material (for example, adsorption or combination) to expand its volume. The squeezed isolation membrane can also absorb the volume expansion of the negative electrode material through its own elastic deformation, thereby reducing the stress generated in the electrode sheet due to the volume expansion of the negative electrode material, thereby reducing or avoiding the deformation of the shell and / or damage to the internal material of the electrode sheet caused by internal stress, and reducing or avoiding the deterioration of the cycle performance of the secondary battery; when the secondary battery containing the diaphragm reduces the volume of the expanded negative electrode active material due to discharge, the isolation membrane can rebound, thereby maintaining good fit with the electrode sheet.

[0105] In some embodiments, Q=α×k×H0, where α is 20 to 50.

[0106] Optionally, k×H0 is 1.5 to 4 μm; optionally, Q is 30 to 200 μm.

[0107] When the rebound amount of the separator is marked as k×H0 and the thickness Q of the positive electrode sheet satisfies the above relationship, the thickness Q of the positive electrode sheet is allowed to release a corresponding amount of active ions. The active ions combine with the negative electrode material (for example, adsorption or combination) to cause its volume to expand. The squeezed separator can also absorb the volume expansion of the negative electrode material through its own elastic deformation. The rebound amount k×H0 of the separator and the thickness Q of the positive electrode sheet work together to reduce or avoid the deterioration of the cycle performance of the secondary battery. When the volume of the expanded negative electrode active material decreases due to discharge of the secondary battery containing the separator, the separator can rebound, thereby maintaining good adhesion to the electrode sheet. In some embodiments, the maximum gap between the negative electrode sheet and the separator is ≤200μm. When the electrode assembly containing the negative electrode sheet and the separator is formed or charged and discharged, the gap between the negative electrode sheet and the separator is within the above range, which can maintain good adhesion to the electrode sheet.

[0108] [Negative electrode]

[0109] The specific composition and structure of the negative electrode plate can be selected according to the type of battery cell, and the embodiments of the present application are not limited thereto.

[0110] For example, when the battery cell is a lithium-ion battery cell or a sodium-ion battery cell, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces that are opposed in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0111] The negative electrode active material is a material that can extract and embed active ions (such as lithium ions, sodium ions, etc.), and the negative electrode active material can adopt materials well known in the art. As an example, the negative electrode active material includes but is not limited to one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate. Silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite and silicon alloy materials. Tin-based materials may include one or more of elemental tin, tin oxide and tin alloy materials. The present application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials may also be used.

[0112] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present application does not particularly limit the type of the negative electrode conductive agent. For example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0113] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. The present application does not particularly limit the type of the negative electrode binder. As examples, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0114] In some embodiments, the negative electrode film layer may optionally include other additives. For example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC-Na), a PTC thermistor material, and the like.

[0115] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0116] The negative electrode film layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying it, and cold pressing it. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0117] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate of the present application may further include a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode plate of the present application may further include a protective layer covering the surface of the negative electrode film layer.

[0118] When the battery cell is a lithium metal battery cell, the negative electrode plate may not include a negative electrode active material capable of extracting and inserting active ions. For example, in some embodiments, the negative electrode plate may include a lithium plate or a lithium alloy plate; in other embodiments, the negative electrode plate includes a mesh or foam-like three-dimensional skeleton layer, such as copper foam (or copper alloy), nickel foam (or nickel alloy), copper (or copper alloy) mesh, nickel (or nickel alloy) mesh, etc.

[0119] When the battery cell is a sodium metal battery cell, the negative electrode plate may not include a negative electrode active material capable of extracting and inserting active ions. For example, in some embodiments, the negative electrode plate may include a sodium plate or a sodium alloy plate; in other embodiments, the negative electrode plate includes a mesh or foam three-dimensional skeleton layer, such as copper foam (or copper alloy), nickel foam (or nickel alloy), aluminum foam (or aluminum alloy), copper (or copper alloy) mesh, nickel (or nickel alloy) mesh, aluminum (or aluminum alloy) mesh, etc.

[0120] [Positive electrode]

[0121] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in the thickness direction of the positive electrode current collector, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0122] The positive electrode film layer includes a positive electrode active material, and the positive electrode active material can be a positive electrode active material for battery cells known in the art.

[0123] For example, when the battery cell is a lithium-ion battery cell or a lithium metal battery cell, the positive electrode active material may include one or more of a lithium transition metal oxide, an olivine-structured lithium-containing phosphate, and their respective modified compounds. Examples of lithium transition metal oxides may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of lithium phosphates containing an olivine structure may include one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds. The present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials may also be used.

[0124] In some embodiments, in order to further improve the energy density of the battery cell, the positive electrode active material may include a general formula of Li a Ni b Co c M d O e A f One or more lithium transition metal oxides and modified compounds thereof. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes one or more selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes one or more selected from N, F, S and Cl.

[0125] As an example, the positive electrode active material may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523),LiNi 0.6 Co 0.2 Mn 0.2O2(NCM622),LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 One or more of O2, LiFePO4 and LiMnPO4.

[0126] When the secondary battery is a sodium ion battery cell or a sodium metal battery cell, the positive electrode active material may include but is not limited to one or more of sodium-containing transition metal oxides, polyanion materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.

[0127] As an example, the positive electrode active material may include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, NaNi 1 / 2 Ti 1 / 2 O2、NaNi 1 / 2 Mn 1 / 2 O2、Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2、NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue materials and general formula X p M' q (PO4) r O x Y 3-x One or more materials. p M' q (PO4) r O x Y 3-x , 0<p≤4, 0<q≤2, 1≤r≤3, 0≤x≤2, X includes H + 、Li + 、Na + , K + and NH4 + One or more of, M' is a transition metal cation, which can be selected from one or more of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halogen anion, which can be selected from one or more of F, Cl and Br.

[0128] The modified compounds of the above-mentioned positive electrode active materials may be used to perform doping modification and / or surface coating modification on the positive electrode active materials.

[0129] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. The present application does not particularly limit the type of the positive electrode conductive agent. For example, the positive electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0130] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. This application does not particularly limit the type of positive electrode binder. As an example, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0131] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0132] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0133] [Preparation method]

[0134] The preparation method of the battery of the present application is well known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery cell. As an example, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process, and the electrode assembly is placed in an outer package, and the electrolyte is injected after drying. After packaging, standing, forming, shaping and other processes, a battery cell is obtained. Multiple battery cells can also be further connected in series, in parallel or in a mixed connection to form a battery module. Multiple battery modules can also be connected in series, in parallel or in a mixed connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0135] secondary batteries

[0136] In a third aspect, an embodiment of the present application provides a secondary battery comprising the electrode assembly of the second aspect.

[0137] The present application has no particular limitation on the type of secondary battery. For example, the secondary battery may be a lithium-ion battery, a sodium-ion battery, etc. A sodium-ion battery may be selected.

[0138] In some embodiments, a secondary battery includes an electrolyte. The electrolyte conducts active ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte may be selected based on needs. For example, the electrolyte may be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte solution).

[0139] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0140] The type of electrolyte salt is not specifically limited and can be selected according to actual needs. For example, the electrolyte salt includes one or more selected from lithium salts for lithium ion batteries and sodium salts for sodium ion batteries. As an example, the lithium salt includes one or more selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP), lithium tetrafluorooxalatophosphate (LiTFOP). As an example, the sodium salt includes one or more selected from NaPF6, NaClO4, NaBCl4, NaSO3CF3, Na(CH3)C6H4SO3.

[0141] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0142] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0143] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0144] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0145] The present application has no particular limitation on the shape of the secondary battery, which can be a flat body, a rectangular parallelepiped, or other shapes. FIG6 shows a secondary battery 5 with a rectangular parallelepiped structure as an example.

[0146] In some embodiments, as shown in Figure 7, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate together form a accommodating cavity. The shell 51 has an opening connected to the accommodating cavity, and the cover plate 53 is used to cover the opening to close the accommodating cavity. The electrode assembly 52 of the first aspect of the embodiment of the present application or the electrode assembly 52 prepared by the method according to the second aspect of the embodiment of the present application is encapsulated in the accommodating cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to demand.

[0147] The method for preparing the secondary battery of the present application is well known and includes at least the step of preparing the electrode assembly according to the second aspect of the embodiment of the present application. In some embodiments, the electrode assembly can be placed in an outer package, dried, injected with electrolyte, and subjected to vacuum packaging, static standing, formation, and shaping to obtain a secondary battery.

[0148] In some embodiments of the present application, the secondary batteries according to the present application can be assembled into a battery module. The battery module can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0149] Optionally, the battery module may further include a housing having an accommodation space, and the plurality of secondary batteries are accommodated in the accommodation space.

[0150] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0151] Electrical devices

[0152] In a fourth aspect, embodiments of the present application provide an electrical device comprising the secondary battery of the third aspect. The secondary battery or electrical device of the present application comprises the separator of the first aspect of the present application, and thus has at least the advantages of using the separator.

[0153] Secondary batteries can be used as power sources or energy storage units for electrical devices. These devices include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, and energy storage systems.

[0154] Figure 8 is a schematic diagram of an exemplary electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module may be used.

[0155] As another example, the electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a secondary battery as a power source.

[0156] Example

[0157] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0158] Example 1

[0159] Preparation of isolation membrane

[0160] Preparation of base film: Polyethylene is used as the raw material of the base film. Through the hollow blow molding film stretching process, the base film itself has a first hollow structure as an elastic reserved space. The specific parameters are shown in Table 1.

[0161] The porosity of the base film was 30%, and the thickness d of the base film was 10 μm.

[0162] Preparation of positive electrode

[0163] 94 parts by weight of positive electrode active material sodium vanadium phosphate, 3 parts by weight of conductive carbon, and 3 parts by weight of binder PVDF were added to the solvent NMP, stirred and mixed evenly, and then coated on the surface of Al foil. After drying, cold pressing, and striping, the positive electrode sheet was obtained.

[0164] Preparation of negative electrode sheet

[0165] 97.5 parts by weight of artificial graphite as the negative electrode active material, 1.5 parts by weight of SBR as the binder, and 1 part by weight of CMC-Na as the thickener were added to deionized water, stirred and mixed evenly, and then coated on the surface of Cu foil. After drying, cold pressing, and stripping, the negative electrode sheet was obtained.

[0166] Preparation of electrolyte

[0167] 11.9 parts by weight of NaPF6 were added to a solution of 88.1 parts by weight of PC, EC and DEC (mass ratio of 1:1:1), and the mixture was stirred evenly to fully dissolve to obtain an electrolyte.

[0168] Preparation of sodium ion secondary batteries

[0169] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrode sheets to provide isolation, and then wound to form a bare cell. The bare cell is then placed in an outer packaging, injected with electrolyte, and packaged and formed to produce a sodium-ion secondary battery.

[0170] Examples 2 to 5: The preparation method is similar to that of Example 1, except that the relevant parameters in the preparation steps of the isolation membrane are adjusted, as shown in Table 1 for details.

[0171] Examples 7 to 12: The preparation method is similar to that of Example 1, except that the relevant parameters in the preparation steps of the isolation membrane are adjusted so that the isolation membrane is a corrugated membrane, as shown in Table 1 for details.

[0172]

[0173] Comparative Example 1

[0174] The isolation film used in this application is a commercially available polyethylene film, and its parameters such as the rebound coefficient are shown in Table 1.

[0175] Comparative Examples 2-7

[0176] The preparation method is similar to that of Example 1, except that the relevant parameters in the preparation steps of the isolation membrane are adjusted so that its performance-related structure and parameters are shown in Table 1.

[0177] Examples 13-18: The preparation method is similar to that of Example 1, except that a commercially available polyethylene film is used as the base film. The coating comprises a thermoplastic polyester elastomer and ceramic powder, which includes Al2O3. A stretching process is used to impart secondary hollow cavities to the coating. After oven drying, a barrier film containing the coating is obtained. The coating thickness is 2 μm. See Table 2 for details.

[0178] Examples 19 to 24

[0179] A commercially available polyethylene film is used as the base film. The coating comprises a thermoplastic polyester elastomer and ceramic powder. The ceramic powder comprises Al2O 3， Through the stretching process, the coating itself is made corrugated in the thickness direction. The coating is a corrugated coating with an elastic deformation space between the coating and the base film. The components of the coating of the isolation membrane and the relevant parameters in the preparation steps are adjusted, as shown in Table 2, to obtain an isolation membrane containing the coating.

[0180] Comparative Examples 2 to 4: A commercially available stretched base film made of polyethylene film was used. The coating preparation method was similar to that of Example 13, except that the relevant parameters in the isolation film coating preparation step were adjusted, as shown in Table 2.

[0181] Examples 25 to 31

[0182] The preparation method is similar to that of Example 19, except that the relevant thickness of the positive electrode plate and the thickness of the isolation membrane are adjusted, as shown in Table 3 for details.

[0183] Comparative Examples 5-8

[0184] The preparation method of this comparative example is similar to that of Examples 1 and 25-47, except that the thickness of the positive electrode sheet is adjusted. See Table 3 for details.

[0185] Test section

[0186] 1) Test Method for Coefficient of Resilience k of Isolation Film: At 25°C, cut 500 isolation film samples from the examples or comparative examples and stack them. Measure the initial thickness 500H0 of the 500 isolation film layers under a pressure of 0.1 MPa. 500H1 represents the thickness of the 500 isolation film layers after compressing them at 25°C under a load of 0.8 MPa at a rate of 5 μm / min for 60 seconds, followed by a 60-second relaxation period after the load is removed. Coefficient of Resilience k = (H0 - H1) / H0.

[0187] 2) Testing method for the rebound amount k×H0 of the isolation film: Test the isolation film of the embodiment or comparative example according to 1) and calculate K×H0.

[0188] 3) Test method for compressive elastic modulus of isolation membrane: refer to national standard GBT 14694-1993, determination standard for compressive elastic modulus of plastics.

[0189] 4) Determination of polymer content in coating: Take an appropriate amount of sample for thermogravimetric analysis. The temperature is raised from room temperature to 600°C. The thermogravimetric curve is obtained. The ratio of weight loss at the corresponding temperature to total weight is the polymer content.

[0190] 5) Positive electrode sheet thickness test method: Remove the electrode from the fully discharged battery, use a thickness gauge to test 12 points and record the average value as the thickness of the positive electrode sheet.

[0191] 6) Test method for the maximum gap between the negative electrode plate and the separator: Fully discharge the cell, use CT scanning, and measure the gap size with a ruler in the figure.

[0192] 7) Test method for the long diameter of the elastic reserved space in the thickness direction: Because the elastic reserved space is related to the hollow design of the material, its long diameter is the maximum compressible space. Therefore, the compression coefficient test method can be used to raise the pressure to 10Mpa, and the measured H1 minus H0 is the long diameter.

[0193] 8) Cycle life performance test: 25°C, charge at 0.33C to 3.8V; rest for 30 minutes; discharge at 0.33C to 3.8V; rest for 30 minutes; repeat this cycle until the battery reaches 80% of the initial capacity C, and record the number of cycles.

[0194] Table 1

[0195]

[0196] Table 2

[0197]

[0198] Table 3

[0199]

[0200] From the test results in Table 1, it can be seen that when the rebound coefficient of the isolation membrane is within the above range, the electrode can be prevented from being squeezed by the deposited ions, thereby preventing the shell from being deformed, and reducing or avoiding the deterioration of the cycle performance of the secondary battery; in the discharge state, the active ions escape from the negative electrode, and the volume of their expansion decreases. The isolation membrane has a certain resilience in its thickness direction, so that the isolation membrane and the electrode have good adhesion, and the cycle performance of the secondary battery containing the isolation membrane is comprehensively improved.

[0201] In Examples 1-12 in Table 1, the springback coefficient of the separator is controlled by controlling the major diameter of the first hollow cavity in the base membrane in the thickness direction or controlling the major diameter range of the corrugated membrane in the thickness direction and the base membrane material. When the springback coefficient of Examples 1-12 is between 10% and 90%, during the charging process of the secondary battery containing the separator, the active ions combine with the negative electrode material (for example, adsorption or combination) to cause its volume expansion. The squeezed separator can also absorb the volume expansion of the negative electrode material through its own elastic deformation, thereby reducing the stress generated in the electrode sheet due to the volume expansion of the negative electrode material, thereby reducing or avoiding shell deformation and / or damage to the internal material of the electrode sheet caused by internal stress, and reducing or avoiding deterioration of the cycle performance of the secondary battery; when the volume of the negative electrode active material in the secondary battery containing the separator decreases due to discharge, the separator can rebound, thereby maintaining good adhesion to the electrode sheet, and the battery cycle life is better. When the springback coefficient of the separator of Comparative Example 1 is less than 10%, the battery cycle life is relatively low.

[0202] In Examples 13-24 in Table 2, the springback coefficient of the separator is controlled by controlling the length of the second hollow cavity in the separator coating in the thickness direction, or controlling the length range of the corrugated membrane and the base membrane in the thickness direction, and the material of the coating. When the springback coefficient of Examples 13-24 is between 10% and 90%, during charging of the secondary battery containing the separator, the active ions combine with the negative electrode material (e.g., adsorption or combination) to cause its volume expansion. The squeezed separator can also absorb the volume expansion of the negative electrode material through its own elastic deformation, thereby reducing the stress generated in the electrode sheet due to the volume expansion of the negative electrode material, thereby reducing or avoiding shell deformation and / or damage to the internal material of the electrode sheet caused by internal stress, and reducing or avoiding deterioration of the cycle performance of the secondary battery. When the volume of the negative electrode active material in the secondary battery containing the separator decreases due to discharge, the separator can rebound, thereby maintaining good adhesion to the electrode sheet, and the battery cycle life is better. When the springback coefficient of the separator of Comparative Examples 2-4 is less than 10%, the battery cycle life is relatively low.

[0203] As shown in Table 3, Examples 1 and 25-31 utilize the resilience of the separator to control the relationship between the separator's rebound and the thickness Q of the positive electrode sheet, mitigating or preventing deterioration in the secondary battery's cycle performance while also maintaining good adhesion to the electrode sheet. However, the positive electrode sheet thickness design and the corresponding parameter a between the separator's rebound and the thickness Q of the positive electrode sheet in Comparative Examples 5-8 are not within the appropriate range, which is detrimental to the battery's cycle life and partially fails to maintain good adhesion to the electrode sheet.

[0204] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

[0205] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. An isolation film, wherein the coefficient of resilience k of the isolation film is 10% to 90%, wherein k =(H0-H1) / H0×100%, H0 represents the initial thickness of the isolation membrane at a temperature of 25°C; H1 represents the thickness of the isolation membrane after the isolation membrane with the initial thickness H0 is compressed at a temperature of 25°C with a load of 0.8 MPa for 60 seconds and then the load is removed and relaxed for 60S.

2. The isolation film according to claim 1, wherein: 20％＜k≤85％。 3. The isolation film according to claim 1 or 2, wherein: The isolation membrane includes a reserved space for elastic deformation.

4. The isolation film according to any one of claims 1 to 3, wherein: The isolation film includes a base film having a plurality of first hollow cavities distributed therein as the elastic deformation reserved space.

5. The isolation film according to any one of claims 1 to 4, wherein: The isolation film includes a base film, and the base film is a corrugated film.

6. The isolation film according to any one of claims 1 to 5, wherein: The isolation film comprises a base film, and the compressive elastic modulus of the base film is 7MPa-1000MPa, and can be 8MPa-300MPa; and / or, The base film is selected from polyethylene film, polyethylene terephthalate film, polyethylene oxide film, poly(styrene-butadiene-styrene) film, poly(styrene-ethylene / butylene-styrene) film, hydrogenated styrene / isoprene block copolymer film, thermoplastic polyester elastomer film or a combination thereof.

7. The isolation film according to any one of claims 1 to 6, wherein: The isolation film includes a coating layer disposed on at least one side of the base film.

8. The isolation film according to claim 7, wherein: The coating comprises a plurality of second hollow cavities distributed therein; and / or, The coating is a corrugated coating; and / or, There is an elastic deformation space between the coating layer and the coating surface of the base film.

9. The isolation film according to claim 7 or 8, wherein: The coating comprises a polymer and a filler; Optionally, the polymer includes one or more of polyethylene oxide, styrene-butadiene-styrene, poly(styrene-ethylene-block / butylene-styrene-block), hydrogenated styrene / isoprene block copolymer, and thermoplastic polyester elastomer.

10. An electrode assembly, comprising a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, wherein: The isolation membrane is the isolation membrane described in any one of claims 1 to 9. 11 . The electrode assembly according to claim 10 , wherein the rebound amount k×H0 of the separator has a linear relationship with the thickness Q of the positive electrode sheet.

12. The electrode assembly according to claim 11, wherein: Q = α × k × H0, α is 20 to 50; Optionally, k×H0 is 1.5 to 10 μm; optionally, Q is 30 to 200 μm.

13. The electrode assembly according to any one of claims 10 to 12, wherein: The maximum gap between the negative electrode plate and the isolation film is ≤200 μm.

14. A secondary battery comprising the electrode assembly according to any one of claims 10 to 13.

15. An electrical device comprising the secondary battery according to claim 14.

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