Battery cell and method of manufacturing the same, electrode assembly, separator and method of manufacturing the same, battery device, and electric device

Abstract

The application discloses a battery monomer, a preparation method thereof, an electrode assembly, a separator, a preparation method thereof, a battery device and a power utilization device. The battery monomer comprises a winding electrode assembly, the electrode assembly comprises a bending area and a flat area; the electrode assembly comprises a separator, the separator comprises a porous base film and a coating layer arranged on at least part of the surface of the porous base film; the coating layer comprises an expansion area and a first area; the expansion area is arranged on the surface of the porous base film in the bending area; the expansion area comprises expansion particles, the expansion particles comprise: a core comprising one or more of a silicate composite material and an azo compound; and a shell comprising a thermoplastic polymer. The performance of the battery monomer reduces the active ion precipitation phenomenon, and improves the cycle capacity retention rate and reliability of the battery monomer.

Description

Technical Field

[0001] This application belongs to the field of battery cell technology, specifically relating to a battery cell and its preparation method, an electrode assembly separator and its preparation method, a battery device, and an electrical device. Background Technology

[0002] As a clean energy source, battery cells have been widely used in various fields such as energy storage systems in hydropower, thermal power, wind power, and solar power plants, power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Battery cells rely on the repeated insertion and extraction of active ions between the positive and negative electrodes for charging and discharging, and they have outstanding characteristics such as high energy density and long cycle capacity retention.

[0003] As the market position of battery cells improves, the application scenarios of wound batteries are becoming more and more widespread. People's demand for the comprehensive performance of wound batteries is constantly increasing. The performance of traditional wound batteries is becoming increasingly difficult to meet people's needs, such as the lithium plating problem in wound cells. Therefore, further improvements are needed. Summary of the Invention

[0004] This application provides a battery cell and its preparation method, an electrode assembly separator and its preparation method, a battery device, and an electrical device, aiming to enable the battery cell to have high energy density, high reliability, and good long-term cycle performance.

[0005] In a first aspect, embodiments of this application provide a battery cell including a wound electrode assembly, the electrode assembly including a bending region and a straight region; the electrode assembly includes a separator, the separator including a porous base film and a coating disposed on at least a portion of the surface of one side of the porous base film; the coating includes an expansion region and a first region; the expansion region is in the bending region and disposed on the surface of the porous base film; the expansion region includes expansion particles, the expansion particles including: a core, including one or more of silicate composite materials and azo compounds; and a shell, including a thermoplastic polymer.

[0006] In the battery cell of this application embodiment, the expansion region of the separator contains expansion particles located on the porous base film surface of the bending region. This can reduce the spacing / distance at the bending points of the positive electrode and / or negative electrode, especially the spacing of the innermost electrode at the corner, and make the electrode in the bending region appear smooth. By reducing the spacing between the electrodes, the impact on the stability of the coating structure is reduced, and the further compression of the electrode during the charging and discharging process of the battery cell is reduced. Therefore, while taking into account the performance of the battery cell, the phenomenon of active ion precipitation is reduced, and the cycle capacity retention rate and reliability of the battery cell are improved.

[0007] Using the aforementioned materials for the core-shell structure of the expanding particles is beneficial for ensuring good structural stability of the separator while taking into account the expansion effect of the expansion region of the separator.

[0008] In some alternative embodiments, the thermoplastic polymer includes one or more of polystyrene, polyethylene, and polypropylene. Therefore, the aforementioned thermoplastic polymers possess good elasticity, ductility, and insulation, which facilitates the expansion of particles to increase the volume of the expansion region, reducing the spacing between electrodes at the bending region and minimizing lithium plating in the battery cells.

[0009] In some optional embodiments, the glass transition temperature of the thermoplastic polymer is from -100°C to 100°C, optionally from 25°C to 100°C. A glass transition temperature within this range is beneficial for the expanded particles to remain stable during charge-discharge chemical cycling of the battery cell.

[0010] In some optional embodiments, the weight-average molecular weight of the thermoplastic polymer is 5,000 to 20,000, optionally 10,000 to 18,000. A weight-average molecular weight within this range is advantageous because it provides good ductility and elasticity, which is beneficial for the expansion of the expanded particles; it also provides good insulation, which is beneficial for the performance of the separator.

[0011] In some optional embodiments, the azo compound includes one or more of azodicarbonamide and azobisisobutyronitrile. When these types of azo compounds expand, they form cross-linked structures between molecules. After expansion, the degree of cross-linking and hardness of the azo compound or its core are stronger, resulting in better structural strength and more stable shape of the expanded particles, which is beneficial for the stable operation of the battery cell.

[0012] In some optional embodiments, the silicate composite material includes one or more of MgO / SiO2 composite materials and Al2O3 / SiO2 composite materials. The above-mentioned silicate composite materials can expand, and their structure and performance remain stable after expansion, which is beneficial to the stable operation of the battery cell.

[0013] In some optional embodiments, the expanded region comprises, by mass percentage, 95%–98% expanded particles and 2%–5% binder, optionally 95.5%–97.5% expanded particles and 2.5%–4.5% binder. Thus, the expanded particles and binder in the expanded region, within the aforementioned mass range, can enhance the effectiveness of the expanded region, further reduce the spacing at the bends of the positive and / or negative electrode sheets, and further reduce lithium plating in the battery cells.

[0014] In some optional embodiments, the area of ​​any one of the expansion regions accounts for 30% to 100% of the area of ​​the bending region of the separator; optionally, it is 40% to 80%. Having the area of ​​the expansion region within the above range of the bending region area facilitates more uniform compression of the bending points of the positive and / or negative electrode sheets, shortens the spacing of the electrodes at the corners, makes the electrodes in the bending region appear smooth, and reduces lithium plating in the battery cells.

[0015] In some optional embodiments, the ratio of the arc length l1 of any expansion region within the bending region to the arc length l2 of the separator within the bending region is (0.3 to 1):1; optionally, it is (0.4 to 0.8):1. Since the ratio of l1 to l2 is within the above range, the bending regions of the corresponding positive and / or negative electrode sheets can be compressed more uniformly, resulting in a smooth electrode surface in the bending region and reducing lithium plating in the battery cells.

[0016] In some optional embodiments, the average thickness of the expansion region is 1 μm to 8 μm; optionally, it is 3 μm to 6 μm. An average thickness within this range, without affecting the structure of the separator itself, can reduce the distance between the positive and negative electrode plates, which is beneficial for electrolyte distribution and effective transport of active ions, reducing lithium plating. It also helps to control the pressure exerted during expansion or contraction of the battery cell during charging and discharging, affecting the structural stability of the battery cell, reducing the risk of short circuits between electrodes, and improving the reliability of the battery cell.

[0017] In some optional embodiments, the arc length of any expansion region in the bending region is 1 mm to 10 mm, optionally 2 mm to 4 mm. An arc length of the expansion region in the bending region within the above range allows for more uniform compression of the bending regions of the corresponding positive and / or negative electrode sheets, resulting in a smooth electrode sheet in the bending region.

[0018] In some optional embodiments, the volume change rate of the expanded region in the electrolyte-filled state and the dried state is less than or equal to 5%, optionally less than or equal to 3%. A small volume change rate of the expanded region indicates good stability, allowing for stable reduction of the gap between electrodes during the charging and discharging process of the battery cell, thus reducing lithium plating in the battery cell.

[0019] In some optional embodiments, the electrode assembly includes an inner ring region and an outer ring region along its radial direction from the inside to the outside; the expansion region is located in the inner ring region. The expansion region being located in the inner ring region helps to reduce the spacing of the inner ring electrodes at the corners, reducing lithium plating caused by the large spacing in the inner ring and the uneven distribution of active ions, which helps to improve the cycle capacity retention rate of the battery cell.

[0020] In some optional embodiments, the expansion region is located on the surface of the innermost separator layer in the inner ring region. This location reduces the distance between the negative and positive electrode plates near the innermost separator layer at the corners, mitigating lithium plating caused by the larger distance and uneven distribution of active ions within the inner ring, thus improving the cycle capacity retention of the battery cell.

[0021] In some optional embodiments, the electrode assembly includes a positive electrode and a negative electrode, with the expanded region positioned opposite to the concave surface of either the negative or positive electrode. Therefore, positioning the expanded region opposite to the concave surface of either the negative or positive electrode can reduce the distance between the negative and positive electrodes at the corners, further reducing lithium plating caused by larger distances and uneven distribution of active ions, which is beneficial for improving the cycle capacity retention of the battery cell.

[0022] In some optional embodiments, in the bending region, along the direction away from the porous base film in the expansion region, the maximum spacing between the negative and positive electrode sheets near the expansion region is ≤150 μm. A maximum spacing within this range is beneficial for moderate expansion of the expansion region, reducing the spacing between the negative and positive electrode sheets.

[0023] In some optional embodiments, the negative electrode sheet includes a negative electrode active material film layer; along the direction opposite to the porous base film of the expanded region, the thickness h of the negative electrode active material film layer of the negative electrode sheet adjacent to the expanded region is 60 μm to 120 μm. When the thickness h of the negative electrode active material film layer is within the above range, the degree of compression of the negative electrode sheet by the expanded region can be controlled within a suitable range, reducing the probability of cracks forming in the negative electrode active material film layer.

[0024] Secondly, embodiments of this application provide a method for preparing a single battery cell, comprising:

[0025] A positive electrode, a separator, and a negative electrode are assembled and wound to obtain a wound electrode assembly. The electrode assembly includes a bending region and a straight region. The electrode assembly includes a separator, which comprises a porous base film and a first coating disposed on at least a portion of one side surface of the porous base film. The first coating includes an expansion region and a first region. The expansion region is located on the surface of the porous base film in the bending region. The expansion region includes expanded particles, and the coefficient of thermal expansion α of the expanded particles is 3.0 × 10⁻⁶. -6 / ℃ to 2.0×10 -5 / ℃;

[0026] The electrode assembly is placed in the housing and dried to cause the expansion region in the first coating to expand, thus obtaining a battery cell. The expansion region is located on the surface of the porous base film in the bending region. During drying and other processes, the expansion particles in the expansion region expand. Since the expansion region is located on the surface of the porous base film in the bending region, it can reduce the spacing between the electrodes. Because the thermal expansion coefficient α of the expansion particles is within a suitable range, the impact on the stability of the coating structure is reduced while reducing the spacing between the electrodes. Therefore, while taking into account the performance of the battery cell, the phenomenon of active ion precipitation is reduced, and the cycle capacity retention rate and reliability of the battery cell are improved.

[0027] In some alternative embodiments, before placing the electrode assembly in the housing and drying it to allow the expansion region to expand to obtain the battery cell, the method further includes:

[0028] Hot-pressing electrode assemblies allows the expandable particles to expand. The hot-pressing process enables the expandable particles to fully expand, further improving the structural stability of the expansion region and reducing the spacing between the electrodes.

[0029] In some optional embodiments, the negative electrode sheet includes a negative electrode active material film layer; along the direction away from the porous base film in the expansion region, the thickness h of the negative electrode active material film layer of the negative electrode sheet adjacent to the expansion region is related to the expansion particles α in the expansion region by the following condition: h = k × α, where k is a coefficient, and the value of k ranges from 4.5 × 10⁻⁶. 6 Up to 3×10 7 The thickness h ranges from 60 μm to 120 μm. Maintaining the relationship between thickness h and the expanded particle α within this range can reduce the excessive expansion volume of the expanded particles, control the degree of compression on the negative electrode sheet within a suitable range, and reduce the probability of cracks forming in the negative electrode active material film.

[0030] In some optional embodiments, the Dv50 of the expanded particles is 0.5 μm to 2 μm, optionally 0.8 μm to 1.8 μm. The expanded region prepared by expanded particles with the above particle size is beneficial for the expanded region to expand more uniformly during the heating or hot pressing process of the battery cell, thereby reducing the spacing between the electrodes in the electrode assembly.

[0031] In some optional embodiments, the drying temperature is ≥100°C, optionally between 105°C and 120°C. This drying temperature range, in addition to drying the battery cell, also allows the expansion particles to expand.

[0032] In some optional embodiments, the drying time is 1 hour to 1.5 hours. A drying time within this range, in addition to drying the battery cell, can also cause the expanding particles to expand.

[0033] In some optional embodiments, the ratio 'a' of the expanded region to the thickness of the first coating satisfies: (1:1) < a ≤ (5:1). Controlling the ratio 'a' within the above range, while ensuring the stability of the coating structure, can reduce the spacing between the electrodes, reduce the phenomenon of active ion precipitation, and improve the cycle capacity retention rate and reliability of the battery cells.

[0034] Thirdly, embodiments of this application provide an electrode assembly, including a positive electrode sheet, a separator, and a negative electrode sheet wound together; the electrode assembly includes a bending region and a straight region; the electrode assembly includes a separator, which includes a porous base film and a coating disposed on at least a portion of the surface of one side of the porous base film; the coating includes an expansion region and a first region; the expansion region is located on the surface of the porous base film in the bending region; the expansion region includes expansion particles, and the coefficient of thermal expansion α of the expansion particles is 3.0 × 10⁻⁶. -6 / ℃ to 2.0×10 -5 / ℃. The separator in the electrode assembly of this application has an expansion region that can reduce the distance between the positive and negative electrode plates, reduce the phenomenon of active ion deposition, and improve the cycle capacity retention and reliability of the battery cell.

[0035] Fourthly, embodiments of this application provide a separating membrane, comprising: a porous base membrane; a coating disposed on at least a portion of the surface of one side of the porous base membrane; the coating comprising an expansion region and a first region; wherein the coefficient of thermal expansion α of the expansion particles is 3.0 × 10⁻⁶. -6 / ℃ to 2.0×10 -5 / ℃. This separator, when placed in the electrode assembly, can reduce the distance between the positive and negative electrode plates, reduce the deposition of active ions, and improve the cycle capacity retention and reliability of the battery cell.

[0036] Fifthly, embodiments of this application provide a method for preparing a separating membrane, comprising: providing a coating slurry containing expanded particles, wherein the coefficient of thermal expansion α of the expanded particles is 3.0 × 10⁻⁶. -6 / ℃ to 2.0×10 -5 / ℃; The coating slurry is applied to one side of the porous base film and dried to obtain a separator membrane including the expanded region. The preparation method of this application uses expanded particles as raw materials, which allows the expanded region of the obtained separator membrane to expand, thereby reducing the distance between the positive and negative electrode plates, reducing the phenomenon of active ion precipitation, and improving the cycle capacity retention rate and reliability of the battery cell.

[0037] Sixthly, embodiments of this application provide a battery device comprising a battery cell of the first aspect or a battery cell prepared by the method of the second aspect. The battery device of this application includes the aforementioned battery cell, and therefore possesses at least the beneficial effects of a battery cell.

[0038] In a seventh aspect, embodiments of this application provide an electrical device including the battery device of the sixth aspect, the battery device being used to provide electrical energy. The electrical device of this application includes the aforementioned battery device, and therefore possesses at least the beneficial effects of a single battery cell. Attached Figure Description

[0039] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some implementation methods of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0040] Figure 1 This is a schematic diagram of one embodiment of the battery cell of this application.

[0041] Figure 2 This is a schematic diagram of one embodiment of the battery module of this application.

[0042] Figure 3 This is a schematic diagram of one embodiment of the battery pack of this application.

[0043] Figure 4 yes Figure 3 The diagram shown is an exploded view of an embodiment of the battery pack of this application.

[0044] Figure 5 This is a schematic diagram of one embodiment of the electrode assembly of this application.

[0045] Figure 6 This is a schematic diagram of one embodiment of the separator membrane of this application.

[0046] Figure 7 This is a schematic diagram of another embodiment of the separator membrane of this application.

[0047] Figure 8 This is a schematic diagram of another embodiment of the electrode assembly of this application.

[0048] Figure 9 This is a schematic diagram of an embodiment of the battery cell of this application used as a power source in an electrical device.

[0049] Explanation of reference numerals in the attached figures:

[0050] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 20 Electrode assembly; 30 Separator; 31 Porous base film; 32 Coating; 311 First region; 32 Expansion region; 40 First electrode; 50 Second electrode; 210 Straight region; 220 Bending region; 230 Inner ring region; 240 Outer ring region. Detailed Implementation

[0051] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell and its preparation method, electrode assembly, separator and its preparation method, battery device, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0052] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0053] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0054] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0055] Unless otherwise specified, in this application, the term "active ion" refers to lithium ions that can be inserted and extracted back and forth between the positive and negative electrodes of a battery cell.

[0056] In this application, "multiple" refers to two or more items (including two). Similarly, "multiple types" or "several kinds" refers to two or more items (including two).

[0057] In this description, it should be noted that, unless otherwise stated, "above" and "below" include the stated number.

[0058] Unless otherwise stated, the test temperature for all parameters mentioned in this disclosure is 25°C.

[0059] The battery device mentioned in the embodiments of this disclosure may include one or more battery modules for providing voltage and capacity. The battery module may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0060] In some alternative embodiments, a battery cell assembly is typically formed by arranging multiple battery cells; as an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells into a single module. As an example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0061] In some alternative embodiments, the battery device can be a battery pack, comprising a housing and one or more battery cell assemblies housed within the housing. As an example, the battery cell assembly can be a battery module, which can be housed within the housing by securing the battery module to the housing. Alternatively, the battery cell assembly can be housed within the housing by directly securing multiple battery cells to the housing.

[0062] A single battery cell is the smallest unit that makes up a battery device, and it can independently perform the functions of charging and discharging. A single battery cell can be cylindrical, cuboid, or other shapes, and the embodiments disclosed herein are not limited to this. Figure 1 The example shown is a rectangular battery cell 5.

[0063] In some embodiments, individual battery cells can be assembled into a battery module, and the number of individual battery cells contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module. Figure 2 This is a schematic diagram of battery module 4 as an example. Figure 2As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0064] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0065] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0066] Figure 3 and Figure 4 This is a schematic diagram of battery pack 1 as an example. Figure 3 and Figure 4 As shown, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0067] In some embodiments, the battery device may be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0068] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0069] The battery cells provided in the embodiments of this disclosure may include, but are not limited to, lithium battery cells and sodium battery cells. Lithium battery cells may be lithium-ion battery cells, lithium metal battery cells, etc. Sodium battery cells may be sodium-ion battery cells, sodium metal battery cells, etc.

[0070] The battery cell can also be a sodium lithium-ion battery cell, a lithium sulfur battery cell, a magnesium ion battery cell, a nickel-metal hydride battery cell, a nickel-cadmium battery cell, a lead-acid battery cell, etc., but the embodiments of this application are not limited to this.

[0071] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode assembly. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0072] A single battery cell includes an electrode assembly. In some embodiments, the electrode assembly is a wound structure. The positive electrode and the negative electrode are wound into a wound structure.

[0073] As an example, multiple positive and negative electrode sheets can be set, with multiple positive and multiple negative electrode sheets stacked alternately. As an example, multiple positive electrode sheets can be set, and negative electrode sheets are folded to form multiple stacked folded segments, with a positive electrode sheet sandwiched between adjacent folded segments.

[0074] As an example, both the positive and negative electrode sheets are folded to form multiple stacked folded segments.

[0075] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0076] As an example, the separator can be continuously arranged between any adjacent positive or negative electrode plates by folding or rolling.

[0077] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0078] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0079] The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator located between the positive and negative electrode.

[0080] The separator is positioned between the positive and negative electrodes, primarily serving to prevent short circuits between them. This application does not impose any particular restriction on the type of separator; any known porous separator with good chemical and mechanical stability can be selected. The separator is a crucial component supporting the charge-discharge electrochemical process of a single battery cell. To improve its heat resistance, a coating is typically applied to the separator.

[0081] As mentioned in the background technology, improving the overall performance of battery cells is an important direction for the development of battery cells.

[0082] In related technologies, the cycle capacity of battery cells containing wound cells is prone to sharp decline. Analysis of the reasons revealed that wound cells are prone to lithium plating in their corner or bending areas, resulting in poor performance.

[0083] Further research revealed that the electrode assembly formed by the wound positive electrode, separator, and negative electrode, due to the small radius of curvature and stress concentration at the bending points, is prone to the shedding of the active material layer at the bending points, exposing the current collector and leading to lithium plating. Lithium plating occupies space in the active material, reducing the effective surface area available for storing and releasing lithium ions, resulting in a decrease in battery capacity. The lithium plating layer continuously forms and peels off during battery charge-discharge cycles, causing instability in the internal battery structure, increasing battery wear, and accelerating the rate of capacity retention decay. Furthermore, the stress concentration at the bending points can cause tearing or damage to the separator, leading to direct contact between the positive and negative electrode sheets.

[0084] Further research revealed that one possible reason is the kinetic difference between the positive and negative electrode plates. This difference prevents lithium ions extracted from the positive electrode from quickly embedding into the negative electrode. When the rate of lithium ion extraction from the positive electrode exceeds the rate of lithium ion embedding from the negative electrode, or when the total amount of lithium ions extracted from the positive electrode exceeds the total amount of lithium ions that the negative electrode can hold, the lithium ions that cannot embed into the negative electrode in time can only gain electrons on the surface of the negative electrode and be reduced to form lithium metal – this is the lithium plating phenomenon. Lithium plating on the negative electrode plate causes capacity decay in the battery cell, and in severe cases, can lead to internal short circuits, reducing the reliability of the individual battery cells.

[0085] Based on this, this application provides a battery cell that can solve the above-mentioned technical problems.

[0086] This application provides a battery cell including a wound electrode assembly 20, which includes a bending region 220 and a straight region 210. The electrode assembly 20 includes a separator 30, which includes a porous base film 31 and a coating 32 disposed on at least a portion of the surface of one side of the porous base film 31. The coating 32 includes an expansion region 322 and a first region 311. The expansion region 322 is located in the bending region 220 and is disposed on the surface of the porous base film 31. The expansion region 322 includes expansion particles, which include: a core, including one or more of silicate composite materials and azo compounds; and a shell, including a thermoplastic polymer.

[0087] The expansion region 322 of this embodiment includes expanded particles of the above-described structure and material, and the expansion region 322 is located on the surface of the porous base film 31 of the bending region 220. It can reduce the spacing at the bending points of the positive electrode and / or negative electrode, especially the spacing of the innermost electrode at the corner, and make the electrode in the bending region 220 appear smooth. On the basis of reducing the spacing between the electrodes, it reduces the impact on the structural stability of the coating 32 and reduces the further compression of the electrode during the charging and discharging of the battery cell. Therefore, while taking into account the performance of the battery cell, it reduces the phenomenon of active ion precipitation and improves the cycle capacity retention rate and reliability of the battery cell.

[0088] In addition, the expansion region and the first region in the separator help to reduce or solve the problems of small electrode curvature radius and stress concentration in the bending region 220, and also reduce the phenomenon of active ion deposition, such as lithium deposition.

[0089] It is understandable that the expanded particles have a core-shell structure. This core-shell structure prevents the core from directly contacting other active components within the battery cell, reducing the risk of side reactions from contact between different material systems and improving the overall performance of the battery cell.

[0090] The core of the expanding particles can expand in volume at a certain temperature. After expansion, the volume of the core remains relatively fixed or unchanged. The shell of the expanding particles is a thermoplastic polymer, which has good insulation properties and good elasticity and ductility at suitable temperatures, which is beneficial to the expansion of the core. Using the above-mentioned materials for the core-shell structure of the expanding particles helps to improve the structural stability of the separator 30 while taking into account the expansion effect of its expansion region.

[0091] The thermal expansion of expanding particles is irreversible, and the coefficient of thermal expansion of expanding particles can only be detected before expansion.

[0092] In some alternative embodiments, the thermoplastic polymer includes one or more of polystyrene, polyethylene, and polypropylene. Therefore, the aforementioned thermoplastic polymers possess good elasticity, ductility, and insulation, which facilitates the expansion of particles to increase the volume of the expansion region 322, reducing the spacing between the electrodes at the bending region 220, and minimizing lithium plating in the battery cells.

[0093] In some optional embodiments, the glass transition temperature of the thermoplastic polymer is from -100°C to 100°C, optionally from 25°C to 100°C. The glass transition temperature of the thermoplastic polymer can also be -10°C, 0°C, 50°C, etc. A glass transition temperature within the above range is beneficial for the expanded particles to remain stable during charge-discharge chemical cycles of the battery cell.

[0094] During the preparation of battery cells, the cells are heated. The heating temperature is closely related to the glass transition temperature of the thermoplastic polymer. Heating the cells to a temperature higher than the glass transition temperature of the thermoplastic polymer improves its plasticity at high temperatures, making it easier to process, mold, and extrude. At this temperature, the molecular chains are more active, allowing the material to flow and rearrange its shape more easily. It exhibits rubber-like elasticity, enabling the expansion of the particles and allowing for significant displacement under external forces, tightly encapsulating the core.

[0095] Glass transition temperature T of thermoplastic polymers gThe test can be performed as follows: Take an appropriate amount of sample (e.g., 5mg-15mg) and place it in the crucible of the differential scanning calorimeter (DSC), level it, and cover the crucible with the lid; Parameter settings: nitrogen atmosphere, purge gas 60mL / min, protective gas 20mL / min; Program settings: heat from 25℃ to 200℃ at a heating rate of 10℃ / min, hold for 5min to eliminate thermal history, then cool from 200℃ to -40℃ at a cooling rate of 10℃ / min, and then heat to 300℃ at a heating rate of 10℃ / min. The glass transition temperature T of the thermoplastic polymer is obtained from the DSC curve. g Or determine whether a thermoplastic polymer has a glass transition temperature T. g .

[0096] In some optional embodiments, the weight-average molecular weight of the thermoplastic polymer is from 5,000 to 20,000, optionally from 10,000 to 18,000. Exemplarily, the weight-average molecular weight of the thermoplastic polymer can be 11,000, 12,000, 13,000, 14,000, 15,000, 16,000, 17,000, etc. A weight-average molecular weight within the above range is beneficial because the thermoplastic polymer has good ductility and elasticity, which is conducive to the expansion of the expanding particles; it also has good insulation properties, which is beneficial to the performance of the separator 30.

[0097] The weight-average molecular weight of thermoplastic polymers has a meaning known in the art and can be determined using instruments and methods known in the art, such as high-temperature gel permeation chromatography. The test can be performed using a gel permeation chromatography (GPC) instrument, such as the Polymer CharGPC-IR high-temperature gel permeation chromatograph. The test can be referenced to the international standard ISO 16014-1-2019.

[0098] In some optional embodiments, the azo compound includes one or more of azodicarbonamide and azobisisobutyronitrile. When these types of azo compounds expand, they form cross-linked structures between molecules. After expansion, the degree of cross-linking and hardness of the azo compound or its core are stronger, resulting in better structural strength and more stable shape of the expanded particles, which is beneficial for the stable operation of the battery cell.

[0099] In some optional embodiments, the silicate composite material includes one or more of MgO / SiO2 composite materials and Al2O3 / SiO2 composite materials. The above-mentioned silicate composite materials can expand, and their structure and performance remain stable after expansion, which is beneficial to the stable operation of the battery cell.

[0100] Figure 5 This is a schematic diagram of the structure of the electrode assembly 20 provided in some embodiments of this application.

[0101] Please refer to the following: Figure 5This application provides an electrode assembly 20, which includes a first electrode 40, a second electrode 50 and a separator 30. The electrode assembly 20 includes a bending region 220 and a straight region 210.

[0102] Figure 6 This is a schematic diagram of the structure of the isolation membrane 30 provided in some embodiments of this application. Figure 7 This is a schematic diagram of the structure of the isolation membrane 30 provided in some embodiments of this application.

[0103] Please refer to the following: Figure 6 and 7 This application provides a separating membrane 30, which includes a porous base membrane 31 and a coating 32. The coating 32 may include a first region 311 and an expanded region 322. The expanded region 322 may be disposed on the surface of the first region 311 in a direction opposite to the porous base membrane 31. A recess is provided on the side of the first region 311 opposite to the porous base membrane 31, and the expanded region 322 is disposed in the recess in the first region 311. There may be overlapping portions or no overlapping portions. The expanded region 322 may also be disposed inside the first region 311.

[0104] The shape of the expansion region 322 can be arbitrary, such as a rectangle, a square, or an irregular ellipse.

[0105] In some optional embodiments, the expansion region 322 comprises, by mass percentage, 95%–98% expanded particles and 2%–5% binder, optionally 95.5%–97.5% expanded particles and 2.5%–4.5% binder. Thus, the expanded particles and binder in the expansion region 322, within the aforementioned mass range, can enhance the effectiveness of the expansion region 322, further reduce the spacing at the bends of the positive and / or negative electrode sheets, and further reduce lithium plating in the battery cells.

[0106] Exemplarily, the expanded region 322 comprises, by mass percentage, any value or range thereof of expanded particles, consisting of 95.0%, 95.5%, 96.0%, 96.5%, 97.0%, 97.5%, and 98.0%. Exemplarily, the expanded region 322 comprises, by mass percentage, any value or range thereof of adhesive, consisting of 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, and 5.0%.

[0107] In preparing the expanded region, the slurry used to prepare the expanded region comprises, by mass percentage: 85%–90% expanded particles, 2%–5% binder, and 5%–13% solvent; optionally, the expanded region 322 comprises, by mass percentage: 86%–89% expanded particles, 2%–4% binder, and 7%–12% solvent. In some optional embodiments, the solvent includes one or more of N-methylpyrrolidone, water, and ethanol.

[0108] In some alternative embodiments, coating 32 comprises 2% to 9% polymer, 4% to 7% binder, and 87% to 91% inorganic particles. The polymers include styrene-based polymers, and may also be polyvinylidene fluoride, polyacrylonitrile, etc.

[0109] In some optional embodiments, the binder in coating 32 may include, but is not limited to, polyacrylate binders and nitrile rubber binders. The binder in coating 32 may be one or more of polyacrylate, carboxymethyl cellulose, polyacrylic acid, polymethacrylic acid, sodium polyacrylate, polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). The above-mentioned binders are also suitable for the expanded region 322.

[0110] In some optional embodiments, coating 32 may also include a dispersant, such as one or more of the following: alkylphenol polyoxyethylene ethers, polyacrylic acid dispersants, and cellulose dispersants. As an example, the dispersant may include, but is not limited to, sodium carboxymethyl cellulose, sodium polyacrylate, and ammonium polyacrylate.

[0111] In some optional embodiments, the mass content of the dispersant in coating 32 may be 0.5%-3% based on the total mass of coating 32. The type and content of the dispersant described above also apply to the expansion region 322.

[0112] In some alternative embodiments, coating 32 may also comprise 88% to 90% inorganic particles.

[0113] In some optional embodiments, the inorganic particles may include one or more of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon oxides, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, zirconium titanate, barium titanate, magnesium fluoride, aluminum hydroxide, barium oxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, calcium fluoride, barium fluoride, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, and hydratedite. The types of inorganic particles described above are also applicable to expansion region 322.

[0114] In some optional embodiments, the area of ​​any one of the expansion regions 322 accounts for 30% to 100% of the area of ​​the bending region 220 of the separator 30; optionally, it is 40% to 80%. Having the area of ​​the expansion region 322 within the above range of the bending region 220 area facilitates more uniform compression of the bending points of the positive and / or negative electrode sheets, shortens the spacing between the electrodes, and makes the electrodes in the bending region 220 appear smooth, reducing lithium plating in the battery cells.

[0115] For example, the area of ​​the expansion region 322 is any value or combination of 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100% of the area of ​​the bending region 220 of the separator membrane 30.

[0116] The areas of the expansion region 322 and the bending region 220 of the separator 30 are calculated based on curved surfaces parallel to the winding direction of the electrode assembly 20. Alternatively, the areas of the expansion region 322 and the bending region 220 of the separator 30 can be calculated by removing the battery cell from the individual battery cell, marking the areas of the expansion region 322 and the bending region 220 of the separator 30, extending and flattening the separator 30, and then calculating the areas of the expansion region 322 and the bending region 220 of the separator 30.

[0117] In some optional embodiments, the ratio of the arc length l1 of any expansion region 322 within the bending region 220 to the arc length l2 of the separator 30 within the bending region 220 is (0.3 to 1):1; optionally, it is (0.4 to 0.8):1. Since the ratio of l1 to l2 is within the above range, the bending regions 220 of the corresponding positive and / or negative electrode sheets can be compressed more uniformly, resulting in a smooth electrode surface in the bending region 220 and reducing lithium plating in the battery cells.

[0118] Optionally, the ratio of l1 to l2 can be any value or a range thereof from 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1.

[0119] The arc length of the expansion region 322 within the bending region 220 can be understood as the length of an arc parallel to the bending direction or bending tendency. When measuring the length of the expansion region 322, the expansion region 322 of the separator 30 can be marked, and its length calculated; alternatively, the expansion region 322 can be straightened and its length directly measured.

[0120] The arc length of the separator 30 within the bending zone 220 can be understood as the length of the portion of the separator 30 located within the bending zone 220. Since the separator 30 in the bending zone 220 is curved, its length is represented by the arc length. When measuring the length of the separator 30 at this location, the bending zone 220 of the separator 30 can be marked, and the length of the bending zone 220 can be calculated. Alternatively, the bending zone 220 can be straightened and its length directly measured.

[0121] In some optional embodiments, the average thickness of the expansion region 322 is 1 μm to 10 μm; optionally, it is 3 μm to 6 μm. Exemplarily, the average thickness of the expansion region 322 can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, etc. With the average thickness of the expansion region 322 within the above range, without affecting the structure of the separator 30 itself, the distance between the positive and negative electrode plates can be reduced, which is beneficial for the distribution of electrolyte and the effective transport of active ions, reducing lithium plating; it is also beneficial for the magnitude of pressure experienced during expansion or contraction of the battery cell during charging and discharging, affecting the structural stability of the battery cell, reducing the risk of short circuits between electrodes, and improving the reliability of the battery cell.

[0122] The thickness of the expansion region 322 and the thickness of the first region 311 can be understood as the direction in which the electrode and the separator 30 are stacked. Multiple points can be taken in the expansion region 322 to measure its thickness, and the average value can be taken.

[0123] In some optional embodiments, the negative electrode sheet includes a negative electrode active material film layer; along the direction away from the porous base film of the expansion region, the thickness h of the negative electrode active material film layer of the negative electrode sheet adjacent to the expansion region is 60 μm to 120 μm.

[0124] Optionally, the thickness h of the negative electrode active material film can be any value or a range thereof from 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 105μm, 110μm, 115μm, and 120μm. When the thickness h of the negative electrode active material film is within the above range, the degree of compression of the negative electrode sheet by the expansion region can be controlled within a suitable range, reducing the probability of cracks forming in the negative electrode active material film.

[0125] In some optional embodiments, the arc length of any expansion region 322 in the bending region 220 is between 1 mm and 10 mm. Exemplarily, the arc length of the expansion region 322 in the bending region 220 can be any value or a range thereof from 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, and 10 mm. An arc length of the expansion region 322 in the bending region 220 within the above range allows for more uniform compression of the bending region 220 of the corresponding positive and / or negative electrode sheets, resulting in a smooth electrode surface in the bending region 220.

[0126] In some optional embodiments, the volume change rate of the expansion region 322 in the state of being filled with electrolyte and in the state of being dried is less than or equal to 5%, and can be optionally less than or equal to 3%. The small volume change rate of the expansion region 322 indicates that it has good stability, and can stably achieve the reduction of the spacing between the electrodes during the charging and discharging process of the battery cell, thereby reducing the lithium plating phenomenon of the battery cell.

[0127] The expansion region 322 can be determined by detecting whether the coating contains substances with expanding particles. The volume change rate of the expansion region 322 can be tested as follows: the separator 30 is disassembled from the cycled battery cell, a suitable sample of the expansion region 322 (e.g., about 1g) is taken, and its volume is measured as V1; the sample is dried at 30-65℃ for 1h, and the volume of the sample is measured as V2. The volume change rate is calculated as (V1-V2) / V1×100%.

[0128] Figure 8 This is another structural schematic diagram of the electrode assembly 20 provided in some embodiments of this application.

[0129] Please refer to the following: Figure 8 This application provides an electrode assembly 20, which includes an inner ring region 230 and an outer ring region 240 from the inside to the outside along its radial direction; an expansion region 322 is located in the inner ring region 230. The expansion region 322 being located in the inner ring region 230 helps to reduce the spacing of the inner ring electrode sheets at the corners, reduce lithium plating caused by the large spacing in the inner ring, and reduce the uneven distribution of active ions, which helps to improve the cycle capacity retention rate of the battery cell.

[0130] Please refer to the following: Figure 8 The expansion region 322 is located on the surface of the innermost separator 30 in the inner ring region 230. The expansion region 322, located on the surface of the innermost separator 30 in the inner ring region 230, can reduce the distance between the negative electrode and the positive electrode near the innermost separator 30 at the corner, reduce the lithium plating phenomenon caused by the large distance in the inner ring and the uneven distribution of active ions, which is beneficial to improving the cycle capacity retention rate of the battery cell.

[0131] See Figure 8 The electrode assembly 20 includes a positive electrode and a negative electrode, with the expansion region 322 positioned opposite to the concave surface of either the negative or positive electrode. Therefore, the opposing arrangement of the expansion region 322 with the concave surface of either the negative or positive electrode reduces the distance between the negative and positive electrodes at the corners, further reducing lithium plating caused by larger distances and uneven distribution of active ions, thus improving the cycle capacity retention rate of the battery cell.

[0132] In some alternative embodiments, in the bending region 220, along the direction of the expansion region 322 away from the porous base film 31, the maximum spacing between the negative electrode and the positive electrode near the expansion region 322 is ≤150μm.

[0133] The maximum spacing between the negative and positive electrode sheets can be any value or a range thereof from 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 105μm, 110μm, 115μm, and 120μm. A maximum spacing within this range indicates that the expansion region 322 has undergone moderate expansion. Reducing the spacing between the negative and positive electrode sheets can lower the risk of localized overheating or current concentration during battery charging and discharging. A smaller gap can also reduce the risk of potential thermal runaway, thereby improving safety and reliability. Reducing the gap at the corners helps increase the contact area of ​​the active materials on the electrodes, thus improving the battery's capacity utilization.

[0134] In some optional embodiments, the separator includes a first separator located in the innermost region of the inner ring. The first separator includes a first porous base film and a first coating located on at least one side of the first porous base film, with the expansion region located on the surface of the first coating. In this configuration, the expansion region can be considered as an independent coating, which essentially does not affect the structural stability of the first coating. Simultaneously, it can improve the spacing between the negative and positive electrode plates adjacent to the innermost separator at the corners, reducing lithium plating and uneven distribution of active ions caused by the large spacing in the inner ring, thus improving the cycle capacity retention rate of the battery cell.

[0135] This application provides a method for preparing a single battery cell, including:

[0136] A positive electrode, a separator, and a negative electrode are assembled and wound to obtain a wound electrode assembly. The electrode assembly includes a bending region and a straight region. The electrode assembly includes a separator, which comprises a porous base film and a first coating disposed on at least a portion of one side surface of the porous base film. The first coating includes an expansion region and a first region. The expansion region is located on the surface of the porous base film in the bending region. The expansion region includes expanded particles, and the coefficient of thermal expansion α of the expanded particles is 3.0 × 10⁻⁶. -6 / ℃ to 2.0×10 -5 / ℃;

[0137] The electrode assembly is placed in the housing and dried to allow the expansion region in the first coating to expand, thus obtaining a battery cell.

[0138] The wound electrode assembly includes a bending region. Before the bending region, the spacing between the electrodes at the corners is relatively large, leading to lithium deposition in the solution. The expansion region is located on the porous base film surface of the bending region. During drying and other processes, the expansion particles in the expansion region expand. Since the expansion region is located on the porous base film surface of the bending region, it can reduce the spacing between the electrodes. Because the thermal expansion coefficient α of the expansion particles is within a suitable range, the impact on the stability of the coating structure is reduced while reducing the spacing between the electrodes. Therefore, while taking into account the performance of the battery cell, the phenomenon of active ion deposition is reduced, and the cycle capacity retention rate and reliability of the battery cell are improved.

[0139] After expansion, the structure and volume of the expanded region remain relatively stable, making it impossible to measure the original coefficient of thermal expansion of the material. The thermal expansion coefficient α of the expanded particles is within a suitable range, causing the expanded region to expand in volume during drying. This reduces the impact on the stability of the coating structure while minimizing the spacing between electrode plates. Therefore, while maintaining the performance of the battery cells, it reduces the phenomenon of active ion precipitation and improves the cycle capacity retention and reliability of the battery cells.

[0140] In some optional embodiments, the Dv50 of the expanded particles is 0.5 μm to 2 μm, optionally 0.8 μm to 1.8 μm. When the expanded particles are not subjected to heat treatment / drying treatment or hot pressing treatment, the expanded region prepared from the above-mentioned particle size is beneficial for the expanded region to expand more uniformly during the heating or hot pressing process of the battery cell, reducing the spacing between the electrodes in the electrode assembly.

[0141] The Dv50 of expanded particles can be determined during the preparation of the separator membrane by measuring the volumetric particle size (Dv50) of the raw material. The Dv50 of expanded particles can be tested using methods known in the art. For example, it can be determined using a laser particle size analyzer (such as a Malvern Mastersize 3000). The test can be performed according to GB / T 19077.1-2016. Here, Dv50 represents the particle size corresponding to a cumulative volume distribution percentage of 50% for the positive electrode active material.

[0142] The Dv50 of expanded particles can also be understood as the average particle size of the granular biphase compound observed in the separator. The average particle size can also be tested as follows: Using a scanning electron microscope (SEM) according to JY / T010-1996, acquire an SEM image of the separator. Randomly select a test sample with dimensions of 50mm x 100mm on the separator. Randomly select multiple test areas (e.g., 5) within the test sample, and read the particle size of each particle in each test area at a certain magnification (e.g., 500x or higher). Count the number and particle size values ​​of particles in each test area, and take the arithmetic mean of the particle sizes in all test areas as the average particle size. To ensure the accuracy of the test results, multiple test samples (e.g., 10) can be used for the above test, and the average value of each test sample can be taken as the final test result. The testing instrument can be a ZEISS Sigma300. It should be noted that when the particles are irregularly shaped, the distance between the two farthest points on the particle is taken as the particle size of the expanded particle; multiple measurements can be taken and the average value taken. The separator can be a fresh separator that has not undergone drying at 100°C or hot pressing.

[0143] In some optional embodiments, the coefficient of thermal expansion α of the expanding particles is 3.0 × 10⁻⁶. -6 / ℃ to 2.0×10 -5 / ℃, can be selected as 8.0×10 -6 / ℃ to 1.0×10 -5 / ℃.

[0144] Optionally, the coefficient of thermal expansion α of the expanding particles can be 3.0 × 10⁻⁶. -6 / ℃, 4.0×10 -6 / ℃, 5.0×10 -6 / ℃, 6.0×10 -6 / ℃, 7.0×10 -6 / ℃, 8.0×10 -6 / ℃, 8.5×10 -6 / ℃, 9.0×10 -6 / ℃, 9.5×10 -6 / ℃, 1.0×10 -5 / ℃, 1.5×10 -5 / ℃, 2.0×10 -5 Any value or range of its composition in / ℃. Because the thermal expansion coefficient α of the expanding particles is within a suitable range, the expansion region is transformed from its original volume to its current size. This reduces the impact on the stability of the coating structure while decreasing the spacing between the electrodes. Therefore, while taking into account the performance of the battery cells, it reduces the phenomenon of active ion precipitation and improves the cycle capacity retention and reliability of the battery cells.

[0145] The coefficient of thermal expansion α of expanding particles can be measured using methods commonly used in the field, such as dilatometer method and thermomechanical analysis. As an example, the coefficient of thermal expansion α of expanding particles can be measured using differential scanning calorimetry (DSC). The specific steps are as follows: 1. Sample preparation: Select a sample, ensuring it is uniform in size and free of defects, and measure its initial length L0. 2. Sample installation: Install the sample in the fixture of the testing instrument, ensuring that the sample can expand freely without external constraints during heating. Set a suitable temperature range (25℃~105℃) and heating rate (1℃ / s); 3. Temperature control: Start the heating system and heat the sample according to the preset program. Monitor the sample temperature in real time using a sensor and simultaneously record the sample length change data with temperature; 4. Data processing: Calculate the length change ΔL of the sample at different temperatures using the collected data, and calculate the linear coefficient of thermal expansion according to the formula CTE=(ΔL / L0) / ΔT, where ΔT is the temperature change.

[0146] In some alternative embodiments, before placing the electrode assembly in the housing and drying it to allow the expansion region to expand to obtain the battery cell, the method further includes:

[0147] Hot-pressing electrode assemblies allows the expanded particles to expand. The hot-pressing process ensures the expanded particles fully expand, further improving the structural stability of the expanded region and reducing the spacing between the electrodes.

[0148] In some optional embodiments, the pressure of the hot pressing process can be 4000 kgf / 12000 mm. 2 Up to 6000 kgf / 12000 mm 2 Optional 5000kgf / 12000mm 2 .

[0149] In some optional embodiments, the hot-pressing temperature can be 95-130°C, or 110°C. In some optional embodiments, the hot-pressing time can be 60-90 seconds.

[0150] The hot pressing and drying processes can be performed arbitrarily; hot pressing can be performed first, drying can be performed first, or both processes can be performed simultaneously.

[0151] In some optional embodiments, the negative electrode sheet includes a negative electrode active material film layer; along the direction away from the porous base film in the expansion region, the thickness h of the negative electrode active material film layer of the negative electrode sheet adjacent to the expansion region is related to the expansion particles α in the expansion region by the following condition: h = k × α, where k is a coefficient, and the value of k ranges from 4.5 × 10⁻⁶. 6 Up to 3×10 7h ranges from 60 μm to 120 μm. The value of k can be 4.5 × 10⁶, 5.0 × 10⁶, 5.5 × 10⁶, 6.0 × 10⁶, 6.5 × 10⁶, 7.0 × 10⁶, 7.5 × 10⁶, 8.0 × 10⁶, 8.5 × 10⁶, 9.0 × 10⁶, 9.5 × 10⁶, 10 × 10⁶, 10.5 × 10⁶, 11 × 10⁶, 11.5 × 10⁶, 12 × 10⁶, 12.5 × 10⁶, 13 × 10⁶, 13.5 × 10⁶, 14 × 10⁶, 14.5 × 10⁶, 15 × 10⁶, 15.5 × 10⁶, 16 × 10⁶, 16.5 × 10⁶, 17 × 10⁶, 17 Any value or a range thereof from 0.5×10⁶, 18×10⁶, 18.5×10⁶, 19×10⁶, 19.5×10⁶, 20×10⁶, 20.5×10⁶, 21×10⁶, 21.5×10⁶, 22×10⁶, 22.5×10⁶, 23×10⁶, 23.5×10⁶, 24×10⁶, 24.5×10⁶, 25×10⁶, 25.5×10⁶, 26×10⁶, 26.5×10⁶, 27×10⁶, 27.5×10⁶, 28×10⁶, 28.5×10⁶, 29×10⁶, 29.5×10⁶, and 30×10⁶.

[0152] If the relationship between thickness h and expansion particle α is within the above range, the volume of expansion particles can be reduced from being too large, the degree of compression on the negative electrode sheet can be kept within a suitable range, and the probability of cracks in the negative electrode active material film layer can be reduced.

[0153] The thicknesses of the porous base membrane, coating, separator, and expansion region are all well-known in the art and can be tested using instruments and methods known in the art. An exemplary method for testing the thickness of the separator is as follows: Take a sample 500 mm long × 100 mm wide; uniformly select 5 points on the sample (e.g., one point every 100 mm along the length of the sample), and use a ten-thousand-dimension thickness gauge to test the thickness of the separator at these 5 different locations, taking the average value as the thickness of the separator. The length direction of the sample is parallel to the TD direction of the separator. The thickness of the porous base membrane can be tested using the same method. If a coating is provided on one side of the separator, the thickness of the separator is subtracted from the thickness of the porous base membrane to obtain the coating thickness. If the separator has a coating to be tested and a coating on the opposite side of the coating to be tested on opposite sides, the thickness of the separator is subtracted from the sum of the thicknesses of the porous base membrane and the coating on the opposite side to obtain the thickness of the coating to be tested. The thickness of the expansion region can be determined by marking the relative areas of the expansion region under an electron microscope or other instruments, uniformly selecting multiple points on the sample, and detecting the thickness of the expansion region.

[0154] In some optional embodiments, the drying temperature is ≥100°C, optionally between 105°C and 120°C. This drying temperature range, in addition to drying the battery cell, also allows the expansion particles to expand.

[0155] In some optional embodiments, the drying time is 1 to 1.5 hours. A drying time within this range, in addition to drying the battery cell, can also cause the expanding particles to expand.

[0156] In some optional embodiments, the ratio 'a' of the expanded region to the thickness of the first coating satisfies: (1:1) < a ≤ (5:1). Controlling the ratio 'a' within the above range, while ensuring the stability of the coating structure, can reduce the spacing between the electrodes, reduce the phenomenon of active ion precipitation, and improve the cycle capacity retention rate and reliability of the battery cells.

[0157] A method for preparing a separating membrane includes: providing a coating slurry containing expanded particles, wherein the coefficient of thermal expansion α of the expanded particles is 3.0 × 10⁻⁶. -6 / ℃ to 2.0×10 -5 / ℃; The coating slurry is applied to one side of the porous base film and dried to obtain a separator membrane including the expanded region. The preparation method of this application uses expanded particles as raw materials, which allows the expanded region of the obtained separator membrane to expand, thereby reducing the distance between the positive and negative electrode plates, reducing the phenomenon of active ion precipitation, and improving the cycle capacity retention rate and reliability of the battery cell.

[0158] In some optional embodiments, the method for preparing the separator includes: coating a slurry onto one side of a porous base membrane to obtain a base coating layer; coating a coating slurry containing expanded particles onto the surface of the base coating layer, and drying to obtain a separator comprising an expanded region and a base coating layer, wherein the coefficient of thermal expansion α of the expanded particles is 3.0 × 10⁻⁶. -6 / ℃ to 2.0×10 -5 / ℃.

[0159] In some optional embodiments, the method for preparing the separator membrane includes: coating a slurry onto a first region on one side of a porous base membrane; coating a coating slurry containing expanded particles onto an expanded region on one side of the porous base membrane; and drying to obtain a coating containing the expanded region and the first region, thereby preparing the separator membrane, wherein the coefficient of thermal expansion α of the expanded particles is 3.0 × 10⁻⁶. -6 / ℃ to 2.0×10 -5 / ℃.

[0160] The slurry can be a commonly used slurry for preparing the separator membrane, and generally includes one or more of inorganic particles and polymers.

[0161] The separator can be placed between the positive and negative electrode plates, mainly to prevent internal short circuits. This application does not have any particular restrictions on the type of porous base membrane; any known porous membrane with good chemical and mechanical stability can be selected.

[0162] As an example, the main material of the porous base membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be applied to the surface of the porous base membrane.

[0163] [Positive electrode plate]

[0164] In some alternative embodiments, the positive electrode includes a positive current collector and a positive active material film layer disposed on at least one surface of the positive current collector, the positive active material film layer comprising a positive active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive active material film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0165] The type of positive electrode active material can be selected according to the type of battery cell, and this application embodiment does not limit this.

[0166] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material is disposed on either or both of the two opposite surfaces of the positive current collector.

[0167] As an example, the positive current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0168] As an example, the positive electrode active material may include at least one of the following materials: lithium iron phosphate and lithium iron manganese phosphate, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, at least one of LiFePO4 (also referred to as LFP), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites may be used.

[0169] In some optional embodiments, the positive electrode active material includes lithium transition metal oxides. Examples may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Modified compounds refer to substances obtained by modification methods such as doping or coating based on the above-mentioned substances.

[0170] In some optional embodiments, the positive electrode active material includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium iron manganese phosphate, sodium iron phosphate, and sodium iron pyrophosphate.

[0171] When the battery cell is a sodium-ion battery cell, a sodium metal battery cell, etc., the positive electrode active material may include, but is not limited to, one or more of the following: sodium-containing transition metal oxides, polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.

[0172] As an example, positive electrode active materials may include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, and NaNi 1 / 2Ti 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 materials with the general formula X p M' q (PO4) r O x Y 3-x One or more of the materials. In general formula X p M' q (PO4) r O x Y 3-x In the given condition, 0 < p ≤ 4, 0 < q ≤ 2, 1 ≤ r ≤ 3, 0 ≤ x ≤ 2, and X includes elements selected from H. + Li + Na + K + and NH4 + One or more of the following, M' is a transition metal cation, which may be selected from one or more of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halide anion, which may be selected from one or more of F, Cl and Br.

[0173] The modified compounds for the above-mentioned positive electrode active materials can be obtained by doping and / or surface coating of the positive electrode active materials.

[0174] During the charging and discharging process, battery cells undergo Li or Na insertion / extraction and consumption, resulting in varying molar contents of Li or Na at different discharge states. In the examples of positive electrode active materials in this disclosure, the molar contents of Li or Na represent the initial state of the material, i.e., the state before material addition. After charge-discharge cycles, the molar contents of Li or Na will change when the positive electrode active material is applied to the battery cell. Similarly, the molar contents of oxygen (O) in the examples of positive electrode active materials in this disclosure are only theoretical values. Lattice oxygen release will cause changes in the molar contents of O, and the actual molar contents of O will also fluctuate.

[0175] In some alternative embodiments, the positive electrode sheet can be made of foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. When foamed metal is used as the positive electrode, the surface of the foamed metal may or may not contain a positive electrode active material. As an example, positive electrode active material is filled and / or deposited within the foamed metal.

[0176] In some optional embodiments, the positive electrode active material film layer may also optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0177] In some optional embodiments, the positive electrode active material film layer may also optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0178] In some alternative embodiments, the positive 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 polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0179] The positive electrode active material film layer can be formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0180] [Negative electrode plate]

[0181] In some alternative embodiments, the negative electrode may include a negative current collector.

[0182] As an example, the negative electrode current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material substrate and a metal layer. The composite current collector can be formed by forming a metal material (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0183] In some alternative embodiments, the negative electrode can be a negative electrode sheet, which may include a negative electrode material film layer disposed on at least one side of the negative electrode current collector.

[0184] As an example, the negative electrode sheet may include a negative current collector and a negative active material disposed on at least one surface of the negative current collector.

[0185] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0186] In some alternative embodiments, the negative electrode active material includes one or more of silicon-carbon, silicon-oxygen, natural graphite, artificial graphite, lithium titanate, amorphous carbon, hard carbon, lithium metal, sodium metal, and lithium alloys.

[0187] As an example, the negative electrode active material may be a negative electrode active material known in the art for use in battery cells. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for battery cells may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0188] In some alternative embodiments, the negative electrode can be made of foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. When foamed metal is used as the negative electrode sheet, the surface of the foamed metal may or may not contain a negative electrode active material.

[0189] As an example, negative electrode active materials can be filled or / and deposited within the negative electrode current collector.

[0190] In some alternative embodiments, the negative electrode current collector can be made of copper.

[0191] For example, when the battery cell is a lithium metal battery cell, the negative electrode sheet may include a negative current collector and a first metal layer disposed on at least one surface of the negative current collector. The metal element in the first metal layer may include one or more of alkali metal elements and alkaline earth metal elements.

[0192] For example, when the battery cell is a sodium battery cell, in some alternative embodiments, the negative electrode may include a sodium sheet or a sodium alloy sheet.

[0193] In some alternative embodiments, the metal material in the first metal layer may include one or more of elemental lithium and lithium alloys.

[0194] Lithium alloys can be alloys formed from metallic lithium with other metallic or non-metallic elements. For example, other metallic elements in lithium alloys may include one or more of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, and platinum, while non-metallic elements may include one or more of boron, carbon, and silicon.

[0195] The methods for preparing battery cells are well known. In some optional embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a battery cell is obtained. Multiple battery cells can be further connected in series, parallel, or a combination thereof to form a battery module. Multiple battery modules can also be connected in series, parallel, or a combination thereof to form a battery pack. In some optional embodiments, multiple battery cells can also be directly assembled into a battery pack.

[0196] [Electrolytes]

[0197] In some embodiments, the battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. The electrolyte can be liquid, gel-like, or solid.

[0198] Liquid electrolytes include electrolyte salts and solvents.

[0199] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0200] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent may also be an ether solvent. Ether solvents may include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ethers.

[0201] In some optional embodiments, the electrolyte may also include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the battery cell, such as additives that improve the overcharge / fast charge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature performance of the battery cell.

[0202] The gel electrolyte includes a polymer as a backbone network and can be used in conjunction with an ionic liquid-lithium salt.

[0203] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0204] As an example, the polymers of polymeric solid electrolytes may include polyethers (polyoxyethylene), polysiloxanes, polycarbonates, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, monoionic polymers, polyionic liquids, cellulose, etc.

[0205] As an example, inorganic solid electrolytes can be one or more of the following: oxide solid electrolytes (crystalline perovskite, sodium superconducting ion conductors, garnet, amorphous LiPON thin films), sulfide solid electrolytes (crystalline lithium superconducting ion conductors, such as lithium germanium phosphate and silver sulfide, amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0206] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0207] Electrical appliances

[0208] This application provides an electrical device, including the battery device described above.

[0209] A single battery cell can be used as a power source for an electrical device or as an energy storage unit for that device. Electrical devices can be, but are not limited to, mobile devices (such as mobile phones, tablets, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0210] Electrical devices can be equipped with individual battery cells, battery modules, or battery packs depending on their usage requirements.

[0211] Figure 9 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0212] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0213] Example

[0214] The following examples describe the contents of this disclosure in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0215] Example 1

[0216] Preparation of the separating membrane:

[0217] A raw material separator membrane with a commercially available 7μm thick PE porous base membrane and a 1μm thick alumina coating, purchased from Ningde Zhuogao New Material Technology Co., Ltd., was prepared. Core-shell structured expanded particles and binder polyacrylate were mixed at a mass ratio of 97:3. 12% (by mass) of N-methylpyrrolidone solvent was added to the total mass of the expanded particles and binder polyacrylate to prepare the separator membrane slurry. The core of the expanded particles was azodicarbonamide, the shell was polypropylene, and the Dv50 of the expanded particles was 1μm. The slurry was coated onto the surface of the raw material separator membrane and dried to obtain a separator membrane including the expanded region. The thickness of the expanded region after drying was 6μm, and the coating length of the expanded region was 4mm. The porous base membrane, alumina coating, and expanded region of the separator membrane are shown below. Figure 7 As shown.

[0218] Preparation of battery cells:

[0219] Positive electrode preparation: The positive active material LiFePO4 (LFP), binder polyvinylidene fluoride (PVDF) and conductive carbon black (Super P) are uniformly mixed at a mass ratio of LPF:PVDF:Super P = 95:3:2. The mixed slurry is dispersed in 1-methyl-2-pyrrolidone (NMP) as solvent. The obtained positive electrode slurry is coated on both sides of an aluminum foil with a thickness of 1.5. After drying, rolling, die-cutting and slitting, the positive electrode is obtained.

[0220] Negative electrode preparation: The negative electrode active material graphite, binder (SBR) and conductive carbon black (Super P) are uniformly mixed in a mass ratio of graphite:SBR:Super P = 94:4:2. Deionized water is used as a solvent to disperse the mixed slurry. The negative electrode slurry is coated on both sides of copper foil. After drying, rolling, die cutting and slitting, the negative electrode sheet is obtained.

[0221] Bare cell fabrication: The prepared positive electrode sheet, separator, and negative electrode sheet are wound together, with the separator positioned between the positive and negative electrodes. During winding, ensure that the expansion area corresponds to the bending area of ​​the negative electrode sheet closest to the separator, and that the concave surface of the negative electrode sheet corresponds to the expansion area. Afterward, the cells undergo hot pressing and shaping, with the hot pressing pressure being 5000 kgf / 12000 mm². 2 The hot pressing temperature is 110℃ and the time is 80s.

[0222] After the tabs are welded, a bare cell is obtained. The length of the expansion region corresponds to 100% of the length of the innermost bending region of the separator.

[0223] Electrolyte preparation: Lithium hexafluorophosphate (LFPF6) was added to ethylene carbonate (EC) in successive batches, and the mass fraction of LiPF6 in the electrolyte was controlled to be 12.5% ​​to obtain the electrolyte.

[0224] Assembly: Place the bare cell in the aluminum shell of the outer packaging, weld the positive and negative electrode tabs and the top cover post and dry them; inject the prepared electrolyte into the dried battery, and complete the preparation of the lithium-ion battery by standing, forming and capacity testing.

[0225] Example 2-3

[0226] Except for the following differences, the preparation of the separator is the same as in Example 1.

[0227] The thickness of the expansion region of the separator is different. In the separators of Examples 2-3, the thickness of the expansion region is 6.3 μm and 5.8 μm respectively, as shown in Table 1.

[0228] Examples 4-8

[0229] Except for the following differences, the preparation of the battery cells is the same as in Example 1. The types of expanded particles are different: in Examples 4-5, the types of shells of the expanded particles are different; in Examples 6-8, the types of cores of the expanded particles are different; resulting in different thickness change rates T1 of the expanded region, as shown in Table 2.

[0230] Comparative Example 1

[0231] Except for the following differences, the preparation of the battery cells is the same as in Example 1.

[0232] Different types of separators are used. In the process of preparing bare cells, the separator is a commercially available 7μm PE porous base membrane with a 1μm alumina coating purchased from Ningde Zhuogao New Material Technology Co., Ltd.

[0233] Performance testing

[0234] (1) Thermal expansion test of the isolation film: The isolation films prepared in Examples 1-3 were placed in ovens at 100℃, 110℃ and 120℃ respectively, and left to stand for 1 hour to test the thickness change of the expansion coating position.

[0235] Table 1

[0236]

[0237] The results in Table 1 show that the thickness of the expansion region in the isolation film coating changed under the heating conditions in the oven, indicating that the expansion region of the coating can expand under heating.

[0238] (2) Measurement of Gap value at the innermost bend of the cell: The distance (GAP value) at the innermost bend of the cells of the example or comparative example before liquid injection after drying and baking was measured using a computed tomography (CT) scan. The maximum distance between the positive electrode and the negative electrode adjacent to the innermost separator at the innermost bend is expressed as the GAP value. The test results are shown in Table 2.

[0239] (3) Test method for the cycle performance of a single battery cell: Place the battery in the test channel of the Chenhua electrochemical workstation, charge it at a constant current rate of 1C to the charging cutoff voltage of 3.65V, let it stand for 5 minutes, then discharge it at a constant current rate of 1C to the discharge cutoff voltage of 2.25V, record the discharge capacity, and let it stand for another 5 minutes. Repeat this cycle. The cycle capacity retention rate = capacity after 500 cycles / capacity of the first cycle × 100%. Generally, it is the ratio of the capacity after 500 cycles to the capacity of the first cycle.

[0240] Table 2

[0241]

[0242] The test results above show that the separator of the battery cell disclosed in this invention, by setting an expansion region containing different types of expansion particles, can reduce the gap value between the innermost folded electrodes in the battery cell, reduce the probability of lithium plating, and improve the reliability of the battery cell. Furthermore, by setting an expansion region containing expansion particles, the cycle capacity retention rate of the battery cell can be improved to a certain extent.

[0243] It should be noted that this disclosure is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same essential structure and achieving the same effect as the technical concept within the scope of this disclosure are included in the technical scope of this disclosure. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, are also included in the scope of this disclosure without departing from the spirit of this disclosure.

Claims

1. A battery cell, comprising an electrode assembly wound together, the electrode assembly including a bending region and a straight region; the electrode assembly including a separator, the separator including a porous base film and a coating disposed on at least a portion of the surface of one side of the porous base film; The coating includes an expansion region and a first region, wherein the expansion region is located in the bending region and is disposed on the surface of the porous base film; The first region is at least partially located within the flat region; in, The expansion region includes expanded particles, which include: The nucleus includes one or more of silicate composites and azo compounds; Shells, including thermoplastic polymers.

2. The battery cell according to claim 1, characterized in that, The expanded particles satisfy one or more of the following conditions: 1) The thermoplastic polymer includes one or more of polystyrene, polyethylene, and polypropylene; 2) The glass transition temperature of the thermoplastic polymer is -100℃ to 100℃; 3) The weight-average molecular weight of the thermoplastic polymer is 5,000 to 20,000; 4) The azo compound includes one or more of azodicarbonamide and azobisisobutyronitrile; 5) The silicate composite material includes one or more of MgO / SiO2 composite material and AL2O3 / SiO2 composite material.

3. The battery cell according to claim 1 or 2, characterized in that, The expanded particles satisfy one or more of the following conditions: 1) The thermoplastic polymer includes one or more of polystyrene, polyethylene, and polypropylene; 2) The glass transition temperature of the thermoplastic polymer is 25°C to 100°C; 3) The weight-average molecular weight of the thermoplastic polymer is 10,000 to 18,000.

4. The battery cell according to any one of claims 1 to 3, characterized in that, The expansion region satisfies one or more of the following conditions: 1) The expanded region comprises, by mass percentage, 95%–98% expanded particles and 2%–5% binder; 2) The area of ​​any one of the expansion regions accounts for 30% to 100% of the area of ​​the bending region of the isolation membrane; 3) The ratio of the arc length l1 of any one of the expansion regions within the bending zone to the arc length l2 of the isolation membrane within the bending zone is (0.3~1):1; 4) The average thickness of the expansion region is 1 μm to 8 μm; 5) The arc length of any one of the expansion regions in the bending area is 1 mm to 10 mm; 6) The volume change rate of the expansion region in the state of being filled with electrolyte and in the state of being dried is less than or equal to 5%.

5. The battery cell according to any one of claims 1 to 4, characterized in that, The expansion region satisfies one or more of the following conditions: 1) The expanded region comprises, by mass percentage, 95.5% to 97.5% expanded particles and 2.5% to 4.5% binder; 2) The area of ​​any one of the expansion regions accounts for 40% to 80% of the area of ​​the bending region of the separator membrane; 3) The ratio of the arc length l1 of any one of the expansion regions within the bending zone to the arc length l2 of the isolation membrane within the bending zone is (0.4~0.8):1; 4) The average thickness of the expansion region is 3μm to 6μm; 5) The arc length of any one of the expansion regions and the bending region is 2mm to 4mm; 6) The volume change rate of the expansion region under the conditions of being filled with electrolyte and being dried is less than or equal to 3%.

6. The battery cell according to any one of claims 1 to 5, characterized in that, The electrode assembly includes an inner ring region and an outer ring region from the inside to the outside along its radial direction; the expansion region is located in the inner ring region.

7. The battery cell according to claim 6, characterized in that, The expansion region is located on the surface of the innermost layer of the isolation membrane in the inner ring region.

8. The battery cell according to any one of claims 1 to 7, characterized in that, The electrode assembly includes a positive electrode and a negative electrode, and the expansion region is disposed opposite to the concave surface of the negative electrode or the positive electrode.

9. The battery cell according to claim 8, characterized in that, In the bending region, along the direction away from the porous base film in the expansion region, the maximum distance between the negative electrode and the positive electrode near the expansion region is ≤150μm.

10. The preparation method according to claim 8 or 9, characterized in that, The negative electrode sheet includes a negative electrode active material film layer; along the direction away from the porous base film in the expansion region, the thickness h of the negative electrode active material film layer of the negative electrode sheet adjacent to the expansion region is 60 μm to 120 μm.

11. A method for preparing a single battery cell, comprising: A positive electrode, a separator, and a negative electrode are assembled and wound to obtain a wound electrode assembly, wherein the electrode assembly includes a bending region and a straight region; the electrode assembly includes a separator, the separator comprising a porous base film and a first coating disposed on at least a portion of one side surface of the porous base film; the first coating includes an expansion region and a first region; the expansion region is located on the surface of the porous base film in the bending region; the expansion region includes expansion particles; The electrode assembly is placed in the housing and dried to allow the expansion region in the first coating to expand, thus obtaining a battery cell.

12. The preparation method according to claim 11, characterized in that, Before placing the electrode assembly in the housing and drying it to allow the expansion region to expand in order to obtain a single battery cell, the method further includes: The electrode assembly is hot-pressed to cause the expanding particles to expand.

13. The preparation method according to claim 11 or 12, characterized in that, The preparation method satisfies one or more of the following conditions: 1) The coefficient of thermal expansion α of the expanding particles is 3.0 × 10⁻⁶. -6 / ℃ to 2.0×10 -5 / ℃; 2) The drying temperature is ≥100℃; 3) The drying time is 1 hour to 1.5 hours; 4) The ratio 'a' of the expanded region to the thickness of the first coating satisfies: (1:1) < a ≤ (5:1) 5) The Dv50 of the expanded particles is 0.5 μm to 2 μm.

14. The preparation method according to any one of claims 11 to 13, characterized in that, The negative electrode sheet includes a negative electrode active material film layer; along the direction away from the porous base film in the expansion region, the thickness h of the negative electrode active material film layer of the negative electrode sheet adjacent to the expansion region is 60 μm to 120 μm.

15. An electrode assembly comprising a positive electrode, a separator, and a negative electrode wound together; the electrode assembly includes a bending region and a straight region; the electrode assembly includes a separator, the separator comprising a porous base film and a coating disposed on at least a portion of one side surface of the porous base film; the coating includes an expansion region and a first region; The expansion region is located on the surface of the porous base membrane in the bending region; the expansion region includes expanded particles, and the coefficient of thermal expansion α of the expanded particles is 3.0 × 10⁻⁶. -6 / ℃ to 2.0×10 -5 / ℃.

16. A separating membrane, comprising: Porous base membrane; A coating disposed on at least a portion of the surface of one side of the porous base membrane; The coating includes an expansion region and a first region; The expansion region includes expanding particles, and the coefficient of thermal expansion α of the expanding particles is 3.0 × 10⁻⁶. -6 / ℃ to 2.0×10 -5 / ℃.

17. A method for preparing a separating membrane, comprising: A coating slurry comprising expanded particles is provided, wherein the coefficient of thermal expansion α of the expanded particles is 3.0 × 10⁻⁶. -6 / ℃ to 2.0×10 -5 / ℃; The coating slurry is applied to one side of a porous base membrane and dried to obtain the isolation membrane.

18. A battery device comprising a battery cell according to any one of claims 1 to 11 or a battery cell prepared by the preparation method according to claims 12 to 14.

19. An electrical device comprising a battery device according to claim 18, the battery device being used to provide electrical energy.

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