Battery cell, battery and electric apparatus

Abstract

A battery cell (5), a battery and an electric apparatus. The battery cell (5) comprises a negative electrode sheet and a separator, wherein the separator comprises a porous substrate and a coating arranged on at least one surface of the porous substrate, the coating comprising nanocellulose and a granular filler; and the width of the separator is denote as A, the width of the negative electrode sheet is denoted as B, both are in units of mm, and 0<A-B≤5mm. The battery cell (5) incorporates a high energy density, a high reliability and a good processing property.

Description

Battery cells, batteries and electrical devices

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present disclosure claims priority to Chinese patent application 202311685498.5, filed on December 8, 2023, entitled “Battery Cell, Battery and Electrical Device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to a battery cell, a battery, and an electric device. Background Art

[0004] With the growing demand for high-energy-density batteries, ultra-thin separators are being widely used. However, existing ultra-thin separators cannot achieve both low thickness and high heat resistance. Existing ultra-thin separators tend to shrink when heated. Therefore, in order to fully separate the positive and negative electrodes and prevent the positive and negative electrodes from shorting due to separator shrinkage under heated conditions, the separator width needs to be greater than the width of the negative electrode. Generally speaking, the difference in width between the separator and the negative electrode needs to be greater than 6mm. As a result, during the battery production process, the separator is prone to local redundancy, folding, or breakage, which in turn affects the processing performance of the battery. In order to obtain a high-energy-density battery, the width of the negative electrode is increased to reduce the difference in width between the separator and the negative electrode. In a high-temperature environment or thermal abuse environment, the separator shrinks easily, causing shorting. Therefore, existing batteries find it difficult to achieve high energy density, high reliability, and good processing performance.

[0005] Summary of the Invention

[0006] The present disclosure provides a battery cell, a battery, and an electrical device, which can have high energy density, high reliability, and good processing performance.

[0007] In a first aspect, the present disclosure provides a battery cell comprising a negative electrode sheet and a separator, wherein the separator comprises a porous substrate and a coating disposed on at least one surface of the porous substrate, wherein the coating comprises nanocellulose and a granular filler; the width of the separator is denoted as A, and the width of the negative electrode sheet is denoted as B, both in units of mm, and 0<AB≤5mm.

[0008] The battery cells provided by the embodiments of the present disclosure have a width difference between the separator and the negative electrode sheet of less than or equal to 5 mm. This reduced width difference reduces the probability of local redundancy, folding, or breakage of the separator during battery cell assembly, thereby enabling the battery cells to have good processing performance. Furthermore, given the same internal space and separator width within the battery cells, the reduced width difference between the separator and the negative electrode sheet allows for increased coating widths for the negative and positive electrode sheets, thereby enabling the battery cells to have a high volumetric energy density.

[0009] The coating of the isolation membrane used in the battery cell provided by the embodiment of the present disclosure includes nanocellulose and granular fillers. Nanocellulose has good high temperature resistance and its volume changes little after being heated, thereby improving the heat resistance of the isolation membrane; nanocellulose has a low density, thereby reducing the mass of the battery cell and improving the mass energy density of the battery cell; in addition, nanocellulose itself contains a large number of hydroxyl groups, thereby forming a three-dimensional skeleton structure, and further by matching with granular fillers, the mechanical strength and puncture resistance of the isolation membrane can be improved. Nanocellulose itself contains a large number of hydroxyl groups, which can be connected with granular fillers, porous substrates, etc. through hydrogen bonds, van der Waals forces, etc., thereby enhancing the bonding strength between the granular fillers in the coating and between the coating and the porous substrate, reducing the problem of powder loss, and improving the processing performance of the isolation membrane and the battery cell. Therefore, the battery cell provided by the embodiment of the present disclosure can also have high reliability.

[0010] In some embodiments, 2 mm ≤ AB ≤ 4 mm, and optionally, 2.5 mm ≤ AB ≤ 3.5 mm, thereby further improving the volume energy density and processing performance of the battery cell.

[0011] In some embodiments, the average length of the nanocellulose is 100 nm-1200 nm, optionally 200 nm-1000 nm.

[0012] By adjusting the average length of the nanocellulose within the above range, it is beneficial for the nanocellulose to overlap to form a three-dimensional skeleton structure, and it is also beneficial for the three-dimensional skeleton structure to overlap with the granular filler to form an integrated coating, thereby improving the heat resistance of the separator, thereby helping to reduce the risk of short-circuit failure during the use of the battery cell, and also helping to improve the cycle performance of the battery cell. By adjusting the average length of the nanocellulose within the above range, it is also beneficial for the coating slurry to have an appropriate viscosity, thereby facilitating coating and improving the uniformity and consistency of the coating.

[0013] In some embodiments, the average diameter of the nanocellulose is 11 nm-40 nm, optionally 15 nm-32 nm.

[0014] By adjusting the average diameter of the nanocellulose within the above range, it is beneficial for the nanocellulose to overlap to form a three-dimensional skeleton structure, and it is also beneficial for the three-dimensional skeleton structure to overlap with the granular filler to form an integrated coating, which is beneficial to improve the heat resistance of the isolation membrane, and further beneficial to reduce the risk of short-circuit failure during the use of the battery cell, and also beneficial to improve the cycle performance of the battery cell.

[0015] In some embodiments, the aspect ratio of the nanocellulose is 5-60, and can be optionally 12-35.

[0016] Adjusting the aspect ratio of nanocellulose within the above range facilitates the overlapping of the nanocellulose to form a three-dimensional skeleton structure. This also facilitates the overlapping of the formed three-dimensional skeleton structure with the granular filler to form an integrated coating, thereby improving the heat resistance of the separator, thereby reducing the risk of short-circuit failure during battery cell use and improving the cycle performance of the battery cell. Adjusting the aspect ratio of nanocellulose within the above range also helps improve the electrolyte wettability of the separator, thereby facilitating ion transport and reducing dendrites.

[0017] In some embodiments, the nanocellulose includes a modification group, and the modification group includes at least one of an amino group, a carboxyl group, an aldehyde group, a sulfonic acid group, or a phosphoric acid group, and optionally includes at least one of a sulfonic acid group or a phosphoric acid group.

[0018] When nanocellulose has the aforementioned specific modified groups, it can, on the one hand, effectively improve the heat resistance of the separator, enhance the thermal stability of the battery cell, and reduce the risk of short-circuit failure during battery cell use; on the other hand, it can also enhance the bonding strength between the coating and the porous substrate. When nanocellulose has the aforementioned specific modified groups, it is also beneficial for the nanocellulose to overlap with the granular filler to form an integrated coating, thereby giving the coating a stable spatial network structure, thereby improving the electrolyte wettability and liquid retention of the separator, enhancing the separator's ion transport properties and voltage breakdown resistance; it is also beneficial for matching high-voltage positive electrode active materials and further increasing the energy density of the battery cell.

[0019] In some embodiments, the nanocellulose comprises hydroxyl groups and modified groups, and a molar ratio of the modified groups to the hydroxyl groups is 1:4 to 4:1, and optionally 2:3 to 7:3.

[0020] When the molar ratio of the modified group to the hydroxyl group is within the above range, the heat resistance, ion transport properties, electrolyte wettability and liquid retention of the isolation membrane can be further improved, thereby helping to reduce the risk of short-circuit failure during the use of the battery cell and improving the cycle performance of the battery cell.

[0021] In some embodiments, the mass content of the nanocellulose in the coating is 5 wt%-60 wt%, optionally 7 wt%-45 wt%.

[0022] In some embodiments, the mass content of the granular filler in the coating is greater than 38 wt %, and may be 53 wt % to 91 wt %.

[0023] The mass content of nanocellulose and granular filler within the above range can make the isolation membrane have high heat resistance and good ion transport properties, thereby making the battery cell have good cycle performance; it is also beneficial for the coating slurry to have a suitable viscosity, which is beneficial for coating; it is also beneficial for maintaining high bonding strength between the coating and the porous substrate, thereby improving the structural stability of the isolation membrane; it is also beneficial for the nanocellulose and granular filler to overlap to form an integrated coating, so that the coating has a more stable spatial network structure.

[0024] In some embodiments, the thickness of the porous substrate is less than or equal to 5 μm, and can be optionally 3 μm-4.5 μm.

[0025] In some embodiments, the average pore size of the porous substrate is 10 nm to 60 nm, optionally 20 nm to 40 nm.

[0026] In some embodiments, the porosity of the porous substrate is 20%-60%, and optionally 30%-50%.

[0027] In some embodiments, the porous substrate is made of polyolefin, and may optionally be made of polyethylene.

[0028] In some embodiments, the puncture strength of the porous substrate is greater than or equal to 390 gf, and can be optionally 400 gf-480 gf.

[0029] The higher the puncture strength of the porous substrate, the better its puncture resistance, effectively preventing positive and negative electrode particles, as well as metallic foreign particles, from piercing the separator and causing a short circuit between the positive and negative electrodes. Therefore, a porous substrate with a puncture strength within the above range can increase the pass rate of battery cell short-circuit testing and enhance battery cell reliability.

[0030] In some embodiments, the longitudinal thermal shrinkage of the porous substrate at 105° C. for 1 hour is less than 3%, and may be 1%-2.5%.

[0031] In some embodiments, the transverse thermal shrinkage of the porous substrate at 105° C. for 1 hour is less than 2%, and may be 1%-1.8%.

[0032] The reduced thermal shrinkage of the porous substrate indicates that the porous substrate has good heat resistance, which can also increase the passing rate of the battery cell short-circuit test and improve the reliability of the battery cell.

[0033] In some embodiments, the longitudinal tensile strength of the porous substrate is greater than or equal to 2700 kgf / cm 2 , optional 2800kgf / cm 2 -3500kgf / cm 2 .

[0034] In some embodiments, the transverse tensile strength of the porous substrate is greater than or equal to 2500 kgf / cm 2 , optional 2600kgf / cm 2 -3200kgf / cm 2 .

[0035] In some embodiments, the particulate filler includes one or more of organic particles, inorganic particles, and organic-inorganic composite materials.

[0036] In some embodiments, the particulate filler comprises a first component having a secondary particle morphology and a second component having a primary particle morphology.

[0037] The first component of the secondary particle morphology can better integrate with the three-dimensional skeleton structure formed by nanocellulose, thereby giving the coating a more stable spatial network structure, further improving the heat resistance of the separator and the thermal stability of the battery cell. The second component of the primary particle morphology helps reduce the moisture content of the coating and improve the ion transport properties of the coating, thereby contributing to the improved cycling performance of the battery cell.

[0038] In some embodiments, the average particle size of the first component of the secondary particle morphology is smaller than the average particle size of the second component of the primary particle morphology.

[0039] This helps to better play the role of the first component of the secondary particle morphology and the second component of the primary particle morphology. The first component of the secondary particle morphology has a smaller particle size and better affinity with nanocellulose. At the same time, nanocellulose can also overlap in the gaps between the primary particles in the first component that constitutes the secondary particle morphology, which helps to overlap the nanocellulose and the first component of the secondary particle morphology to form an integrated coating, so that the coating has a more stable spatial network structure, which can further improve the heat resistance of the isolation membrane. The second component of the primary particle morphology has a larger particle size and higher strength, which can better play the role of skeleton support in the coating, reduce the thermal shrinkage of the isolation membrane and improve the heat resistance of the isolation membrane; and also help the coating have more pore structure and less moisture content, which can further improve the ion transport properties of the isolation membrane.

[0040] In some embodiments, the average particle size of the first component of the secondary particle morphology is less than 200 nm, and can be optionally 80 nm-180 nm.

[0041] The average particle size of the first component of the secondary particle morphology is within the above range, which can make it have a higher specific surface area, and can better match and overlap with the three-dimensional skeleton structure formed by nanocellulose to form an integrated effect, thereby increasing the heat resistance of the isolation membrane and the isolation membrane's infiltration and retention properties of the electrolyte, thereby helping to improve the thermal stability and cycle performance of the battery cell.

[0042] In some embodiments, the average particle size of the second component of the primary particle morphology is 200 nm-600 nm, optionally 300 nm-500 nm.

[0043] The average particle size of the second component of the primary particle morphology is within the above range, which can better play the supporting role of the second component of the primary particle morphology, so that the coating can maintain a stable pore structure during long-term charging and discharging, thereby helping to reduce the moisture content of the isolation membrane and promote ion transmission, while also improving the heat resistance of the isolation membrane.

[0044] In some embodiments, the particle size of the primary particles in the first component constituting the secondary particle morphology is 15 nm-45 nm, and can be optionally 20 nm-35 nm.

[0045] The particle size of the primary particles in the first component constituting the secondary particle morphology is within the above range, which can make the first component have a good secondary particle morphology, and is conducive to better overlapping and integrating the three-dimensional skeleton structure formed by the first component and nanocellulose.

[0046] In some embodiments, the specific surface area of ​​the first component of the secondary particle morphology is greater than the specific surface area of ​​the second component of the primary particle morphology.

[0047] This is conducive to better play the role of the first component of the secondary particle morphology and the second component of the primary particle morphology.

[0048] In some embodiments, the specific surface area of ​​the first component of the secondary particle morphology is greater than 20m 2 / g, optional 30m 2 / g-80m 2 / g.

[0049] The specific surface area of ​​the first component of the secondary particle morphology is within the above range, and has better affinity with nanocellulose. It can better match and overlap with the three-dimensional skeleton structure formed by nanocellulose to form an integrated effect, thereby increasing the heat resistance of the isolation membrane and the isolation membrane's infiltration and retention properties of the electrolyte, thereby helping to improve the thermal stability and cycle performance of the battery cell.

[0050] In some embodiments, the specific surface area of ​​the second component of the primary particle morphology is less than or equal to 20m 2 / g, optional 5m 2 / g-15m 2 / g.

[0051] The specific surface area of ​​the second component of the primary particle morphology is within the above range, which is beneficial to reducing the moisture content of the isolation membrane and improving the heat resistance of the isolation membrane.

[0052] In some embodiments, the mass content of the first component of the secondary particle morphology in the coating is greater than the mass content of the second component of the primary particle morphology in the coating.

[0053] This is conducive to better play the role of the first component of the secondary particle morphology and the second component of the primary particle morphology.

[0054] In some embodiments, the mass content of the first component of the secondary particle morphology in the coating is 10 wt%-85 wt%, optionally 20 wt%-75 wt%.

[0055] The mass content of the first component of the secondary particle morphology is within the above range, which is conducive to the coating slurry having a suitable viscosity and is more conducive to coating; in addition, it is also conducive to overlapping with the three-dimensional skeleton structure formed by nanocellulose to form an integrated effect, thereby enabling the coating to have a more stable spatial network structure and improving the heat resistance and ion transmission properties of the isolation membrane.

[0056] In some embodiments, the mass content of the second component in the primary particle morphology in the coating is 5 wt % to 70 wt %, optionally 7 wt % to 60 wt %.

[0057] The mass content of the second component of the primary particle morphology within the above range can better leverage its supporting role, enabling the coating to maintain a stable pore structure during long-term charge and discharge processes, thereby reducing the moisture content of the separator and promoting ion transport. The mass content of the second component of the primary particle morphology within the above range can also increase the overall packing density of the granular filler, thereby improving the heat resistance and puncture resistance of the separator.

[0058] In some embodiments, the coating further comprises a non-granular binder. Optionally, the content of the non-granular binder in the coating is less than or equal to 3 wt %, based on the total weight of the coating.

[0059] In some embodiments, the isolation film further comprises an adhesive layer disposed on at least a portion of the surface of the coating. Optionally, the adhesive layer comprises a granular binder. Optionally, the binder comprises at least one of an acrylate monomer homopolymer or copolymer, an acrylic acid monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer.

[0060] In some embodiments, the coating has a thickness of 0.2 μm-2 μm, optionally 0.4 μm-1 μm. A coating thickness within the above range can provide both high energy density for the battery cell and low thermal shrinkage for the separator, resulting in high reliability for the battery cell.

[0061] In some embodiments, the total thickness of the separator is 4 μm-10 μm, optionally 4.5 μm-8.5 μm. When the separator thickness is within the above range, the battery cell can have a high energy density and low thermal shrinkage, resulting in high reliability of the battery cell.

[0062] In some embodiments, the longitudinal thermal shrinkage rate of the isolation film at 150° C. for 1 hour is less than or equal to 3%.

[0063] In some embodiments, the isolation film has a transverse thermal shrinkage rate of less than or equal to 2% at 150° C. for 1 hour.

[0064] The separator has a low thermal shrinkage rate at high temperatures, thereby enabling the battery cell to have high reliability.

[0065] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a carbon material. Optionally, the carbon material includes one or more of artificial graphite and natural graphite.

[0066] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material. Optionally, the silicon-based material also includes one or more alkali metal elements and alkaline earth metal elements, optionally including one or more of Li and Mg. Optionally, the mass proportion of the silicon-based material in the negative electrode active material is greater than or equal to 5wt%, and optionally 8wt%-20wt%. This allows the battery cell to have both high energy density and long cycle life.

[0067] In some embodiments, the upper charging cutoff voltage of the battery cell is greater than or equal to 4.25V, and can be optionally 4.30V-4.45V.

[0068] In some embodiments, the battery cell also includes a positive electrode plate, the positive electrode plate includes a positive electrode collector and a positive electrode film layer arranged on at least one surface of the positive electrode collector, the positive electrode film layer includes a positive electrode active material, the positive electrode active material includes a layered lithium-containing transition metal oxide, and the volume distribution particle size Dv50 of the positive electrode active material is less than or equal to 6μm, and can be optionally 2μm-5μm.

[0069] The positive electrode plates provided by the disclosed embodiments utilize positive electrode active materials with a small volume distribution particle size (Dv50). This shortens the diffusion path of lithium ions within the positive electrode active material, thereby rapidly consuming lithium ions transferred from the negative electrode to the positive electrode through the separator. This increases the difference in lithium ion concentration between the negative and positive sides of the separator, increasing the driving force for lithium ion transfer from the negative electrode to the positive electrode, thereby improving the low-temperature performance and cycle performance of the battery cells.

[0070] In some embodiments, the volume distribution particle size Dv90 of the positive electrode active material is less than or equal to 14 μm, and can be optionally 4.5 μm-13.5 μm.

[0071] By further adjusting the volume distribution particle size Dv90 of the positive electrode active material, the diffusion path of lithium ions in the positive electrode active material can be further shortened, thereby further increasing the lithium ion concentration difference between the negative and positive sides of the separator, increasing the driving force for lithium ion transfer from the negative electrode to the positive electrode, and further improving the low-temperature performance of the battery cell. By further adjusting the volume distribution particle size Dv90 of the positive electrode active material, battery side reactions can be reduced and the battery capacity decay rate can be lowered, thereby improving the cycle performance of the battery cell. By further adjusting the volume distribution particle size Dv90 of the positive electrode active material, the positive electrode sheet can also have a higher compaction density, which is also beneficial to improving the energy density of the battery cell.

[0072] In some embodiments, the volume distribution particle size Dv10 of the positive electrode active material is less than or equal to 3 μm, and can be optionally 1 μm-2 μm.

[0073] By further adjusting the volume distribution particle size Dv10 of the positive electrode active material, the battery side reactions can be reduced and the battery capacity decay rate can be lowered, which is beneficial to improving the cycle performance of the battery cell. It can also make the positive electrode sheet have a higher compaction density, which is also beneficial to improving the energy density of the battery cell.

[0074] In some embodiments, the particle size distribution of the positive electrode active material (Dv90-Dv10) / Dv50 is 0.8-2.5, and can be optionally 1.3-2.3.

[0075] By further adjusting the particle size distribution (Dv90-Dv10) / Dv50 of the positive electrode active material within the above range, the compaction density of the positive electrode sheet can be increased, the space utilization rate of the positive electrode active material can be improved, and thus the energy density of the battery cell can be increased. By further adjusting the particle size distribution (Dv90-Dv10) / Dv50 of the positive electrode active material within the above range, the contact resistance between the positive electrode active material particles can be reduced, the impedance of the battery cell can be reduced, and thus the low-temperature performance of the battery cell can be improved.

[0076] In some embodiments, the positive electrode active material includes a layered lithium-containing transition metal oxide with a single crystal morphology, or includes both a layered lithium-containing transition metal oxide with a single crystal morphology and a layered lithium-containing transition metal oxide with a polycrystalline morphology.

[0077] In some embodiments, the volume distribution particle size Dv50 of the single-crystal layered lithium-containing transition metal oxide is less than or equal to 5 μm, and can be optionally 2 μm-4 μm.

[0078] In some embodiments, the volume distribution particle size Dv90 of the single-crystal layered lithium-containing transition metal oxide is less than or equal to 10 μm, and can be optionally 4.5 μm-8 μm.

[0079] In some embodiments, the volume distribution particle size Dv10 of the single-crystal layered lithium-containing transition metal oxide is less than or equal to 3 μm, and can be optionally 1 μm-2 μm.

[0080] The particle size of the layered lithium-containing transition metal oxide with a single crystal morphology is reduced, which can further shorten the diffusion path of lithium ions in the positive electrode active material, so that the positive electrode active material quickly consumes the lithium ions in the electrolyte, thereby further increasing the lithium ion concentration difference between the negative electrode side and the positive electrode side of the separator, increasing the driving force for the transfer of lithium ions from the negative electrode to the positive electrode, and further improving the low-temperature performance of the battery cell; however, the cycle performance of the battery cell will decline to a certain extent.

[0081] By adjusting the volume distribution particle size Dv50, Dv90 and / or Dv10 of the layered lithium-containing transition metal oxide with a single crystal morphology within the above range, it is beneficial for the battery cell to have both good low-temperature performance and good cycle performance.

[0082] In some embodiments, the particle size distribution of the single-crystalline layered lithium-containing transition metal oxide is (Dv90-Dv10) / Dv50, which is 0.8-2.5, and can be 1.3-1.5.

[0083] By adjusting the particle size distribution (Dv90-Dv10) / Dv50 of the layered lithium-containing transition metal oxide with a single crystal morphology within the above range, the compaction density of the positive electrode plate can be improved, the space utilization rate of the positive electrode active material can be improved, and thus the energy density of the battery cell can be improved; the contact resistance between the particles of the positive electrode active material can be reduced, the impedance of the battery cell can be reduced, and thus the low-temperature performance of the battery cell can be improved.

[0084] In some embodiments, the volume distribution particle size Dv50 of the polycrystalline layered lithium-containing transition metal oxide is 7 μm-12 μm, and optionally 8 μm-10 μm.

[0085] In some embodiments, the volume distribution particle size Dv90 of the polycrystalline layered lithium-containing transition metal oxide is 12 μm-20 μm, and optionally 13 μm-18 μm.

[0086] In some embodiments, the volume distribution particle size Dv10 of the polycrystalline layered lithium-containing transition metal oxide is 2 μm-6 μm, and can be optionally 3 μm-5 μm.

[0087] By adjusting the volume distribution particle size Dv50, Dv90 and / or Dv10 of the polycrystalline layered lithium-containing transition metal oxide within the above range, the battery cell is advantageously provided with high energy density, good low temperature performance, good cycle performance and low manufacturing cost.

[0088] In some embodiments, the particle size distribution of the polycrystalline layered lithium-containing transition metal oxide is (Dv90-Dv10) / Dv50 of 1.1-1.5, and optionally 1.2-1.4.

[0089] By adjusting the particle size distribution (Dv90-Dv10) / Dv50 of the polycrystalline layered lithium-containing transition metal oxide within the above range, the compaction density of the positive electrode plate can be improved, the space utilization rate of the positive electrode active material can be improved, and thus the energy density of the battery cell can be improved; the contact resistance between the particles of the positive electrode active material can be reduced, the impedance of the battery cell can be reduced, and thus the low-temperature performance of the battery cell can be improved.

[0090] A second aspect of the present disclosure provides a battery comprising the battery cell according to the first aspect of the present disclosure.

[0091] A third aspect of the present disclosure provides an electrical device comprising the battery according to the second aspect of the present disclosure.

[0092] The electric device of the present disclosure includes the battery provided by the present disclosure, and thus has at least the same advantages as the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] To more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments of the present disclosure. Obviously, the drawings described below are only some embodiments of the present disclosure, and those skilled in the art can derive other drawings based on the drawings without inventive effort.

[0094] FIG1 is a schematic diagram of a battery cell provided by some embodiments of the present disclosure.

[0095] FIG2 is a schematic diagram of an electrical device provided in some embodiments of the present disclosure.

[0096] In the accompanying drawings, which are not necessarily drawn to scale, the reference numerals are as follows: 5. Battery cell. DETAILED DESCRIPTION

[0097] Below, the embodiments of the battery cell, battery, and electrical device disclosed herein are described in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0098] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0099] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present disclosure.

[0100] Unless otherwise specified, all technical features and optional technical features of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present disclosure.

[0101] Unless otherwise specified, all steps of the present disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which 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 may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0102] If not otherwise specified, in the present disclosure, the terms "first", "second", etc. are used to distinguish different objects rather than to describe a specific order or a primary-secondary relationship.

[0103] In the present disclosure, the terms "plurality" and "multiplicity" refer to two or more.

[0104] In the description of the embodiments of the present disclosure, unless otherwise specified, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, a first feature being "above," "above," and "above" a second feature may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. A first feature being "below," "below," and "below" a second feature may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0105] Unless otherwise specified, terms used in the present disclosure have common meanings that are commonly understood by those skilled in the art.

[0106] Unless otherwise stated, the numerical values ​​of the various parameters mentioned in this disclosure can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this disclosure. Unless otherwise stated, the test temperature of each parameter is 25°C.

[0107] In the present disclosure, the terms "layered lithium-containing transition metal oxide with a single crystal morphology" and "layered lithium-containing transition metal oxide with a polycrystalline morphology" have the same meanings as those well known in the art.

[0108] "Single-crystal layered lithium-containing transition metal oxide" also includes quasi-single-crystal (also known as single-crystal-like) layered lithium-containing transition metal oxide. Quasi-single-crystal (single-crystal-like) is a well-known term in the art and generally refers to particles formed by the agglomeration of a small number (e.g., 2-5) of primary particles. Polycrystalline layered lithium-containing transition metal oxide refers to layered lithium-containing transition metal oxide in the form of secondary particles formed by the agglomeration of multiple primary particles.

[0109] The “layered lithium-containing transition metal oxide with a single crystal morphology” and the “layered lithium-containing transition metal oxide with a polycrystalline morphology” can be distinguished by scanning electron microscopy.

[0110] The Dv10, Dv50, and Dv90 of a material are all well-known in the art and can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer (such as the Malvern Mastersizer 3000) with reference to GB / T 19077-2016. The physical definition of Dv90 is the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 90%; the physical definition of Dv50 is the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%; the physical definition of Dv10 is the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 10%. During the test, take an appropriate amount of the sample to be tested (ensuring 8%-12% shading), add 20 ml of deionized water, and simultaneously operate under an external superconductor for 5 minutes (for example, 53KHz / 120W) to completely disperse the sample to be tested.

[0111] The specific surface area of ​​a material is well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis test method in accordance with GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. Alternatively, the nitrogen adsorption specific surface area analysis test can be performed using a Micromeritics Tri-Star 3020 specific surface area pore size analyzer.

[0112] It should be noted that the various parameter tests of the separator, positive electrode sheet, negative electrode sheet, etc. in the embodiments of the present disclosure can be performed during the preparation of the battery cell, or after the various components are disassembled from the prepared battery cell.

[0113] The battery mentioned in the embodiments of the present disclosure may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present disclosure may include a battery cell, a battery module or a battery pack, etc. A battery cell is the smallest unit that makes up a battery, which can realize the function of charging and discharging on its own. When there are multiple battery cells, the multiple battery cells are connected in series, in parallel or in mixed connection through a busbar. In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, which includes a case and battery cells, and the battery cells or battery modules are housed in the case. In some embodiments, the case may serve as part of the chassis structure of a vehicle. For example, part of the case may become at least a part of the floor of the vehicle, or part of the case may become at least a part of the crossbeam and longitudinal beam of the vehicle.

[0114] In some embodiments, the battery may be an energy storage device, including an energy storage container, an energy storage cabinet, and the like.

[0115] The battery cells mentioned in the embodiments of the present disclosure may include lithium-ion battery cells.

[0116] The battery cell can be a rectangular parallelepiped structure or a soft-pack structure, which is not limited in the present disclosure. FIG1 shows a battery cell 5 with a rectangular parallelepiped structure as an example.

[0117] A battery cell consists of an electrode assembly and outer packaging. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is placed between the positive and negative electrode sheets, primarily preventing short circuits between the positive and negative electrodes while allowing ions to flow freely through the circuit.

[0118] In some embodiments, the electrode assembly may be a wound structure or a laminated structure.

[0119] The outer packaging is used to encapsulate the electrode assembly. In some embodiments, the outer packaging can be made of a soft packaging material or a hard shell material. The soft packaging material can be plastic, such as one or more of aluminum-plastic film, polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS). The hard shell material can include, but is not limited to, a hard plastic shell, an aluminum shell, or a steel shell.

[0120] In some embodiments, the outer packaging may be made of a hard shell material.

[0121] The outer package may include a shell and an end cap assembly. The shell may be a hollow structure with one side open, and the end cap assembly covers the opening of the shell and forms a sealed connection to form a receiving cavity for accommodating the electrode assembly.

[0122] The outer packaging may also include a shell and two end cover assemblies. The shell is a hollow structure with openings on opposite sides. One end cover assembly covers one opening of the shell and forms a sealed connection to form a housing cavity for accommodating the electrode assembly.

[0123] The end cap assembly may include an end cap that covers the opening of the housing. The end cap may have various structures, such as a plate-like structure, a hollow structure with one end open, etc. The end cap may be made of an insulating material (such as plastic) or a conductive material (such as metal). When the end cap is made of a conductive material, the end cap assembly may further include an insulating member located on the side of the end cap facing the electrode assembly to insulate the end cap from the electrode assembly.

[0124] The end cap assembly may also include electrode terminals, which are mounted on the end cap. There may be two electrode terminals, defined as a positive electrode terminal and a negative electrode terminal, respectively. Both the positive electrode terminal and the negative electrode terminal are used to electrically connect to the electrode assembly to output the electrical energy generated by the electrode assembly. The positive and negative electrode terminals may be located at the same end of the battery cell or at opposite ends of the battery cell.

[0125] The electrode assembly includes a main body and a pole ear portion extending from the main body. In some embodiments, the number of the pole ear portions may be two. The two pole ear portions are defined as a positive pole ear portion and a negative pole ear portion, respectively. The two pole ear portions may extend from the same end of the main body portion of the electrode assembly, for example, the two pole ear portions extend from one end of the main body portion of the electrode assembly close to the end cap assembly. The two pole ear portions may also extend from opposite ends of the main body portion of the electrode assembly, for example, from opposite ends of the main body portion of the electrode assembly along the length direction of the battery cell. This can make the positive pole ear portion and the negative pole ear portion wider (i.e., larger in the non-extended direction of the main body portion), which is beneficial to improving the electronic conductivity of the electrode sheet. When the two pole ear portions extend from opposite ends of the main body portion of the electrode assembly, the electrode terminals may be located at the same end of the battery cell or at opposite ends of the battery cell.

[0126] The main body is the core component of the electrode assembly, enabling charge and discharge functions. The tabs are used to conduct the current generated by the main body. The main body includes the positive current collector (positive electrode current collector), the positive electrode film layer, the negative current collector (negative electrode current collector), the negative electrode film layer, and the separator. The positive tabs can include multiple positive tabs, and the negative tabs can include multiple negative tabs.

[0127] The tab portion is electrically connected to the electrode terminal. The tab portion can be directly connected to the electrode terminal by welding or other means, or indirectly connected to the electrode terminal through other components. For example, the electrode assembly also includes a current collecting component, which is used to electrically connect the electrode terminal and the tab portion. There can be two current collecting components, which are defined as a positive current collecting component and a negative current collecting component, respectively. The positive current collecting component is used to electrically connect the positive electrode terminal and the positive tab portion, and the negative current collecting component is used to electrically connect the negative electrode terminal and the negative tab portion. When a battery cell is provided with multiple electrode assemblies, the positive current collecting components of the multiple electrode assemblies can be provided as a whole, and the negative current collecting components of the multiple electrode assemblies can be provided as a whole.

[0128] The separator includes a porous substrate and a coating layer disposed on at least one surface of the porous substrate, wherein the coating layer includes nanocellulose and a granular filler.

[0129] The width of the separator is recorded as A, and the width of the negative electrode is recorded as B, both in units of mm, 0<AB≤5mm.

[0130] The difference in width between the separator and the negative electrode sheet of the battery cell provided by the embodiment of the present disclosure is less than or equal to 5mm. As the difference in width between the separator and the negative electrode sheet is reduced, the probability of local redundancy, folding or breakage of the separator during the assembly of the battery cell is reduced, thereby enabling the battery cell to have good processing performance; at the same time, when the internal space of the battery cell is the same and the width of the separator is the same, the difference in width between the separator and the negative electrode sheet is reduced, and the coating width of the negative electrode sheet and the positive electrode sheet is increased, thereby enabling the battery cell to have a high volume energy density. In addition, after the volume energy density of the battery cell is improved, the design space of the battery module and battery pack can be further increased, thereby further improving the overall life and reliability of the battery. For example, some components that improve the overall reliability of the battery can be set within the limited space of the battery module and battery pack.

[0131] The coating of the isolation membrane used in the battery cell provided by the embodiment of the present disclosure includes nanocellulose and granular fillers. Nanocellulose has good high temperature resistance and its volume changes little after being heated, thereby improving the heat resistance of the isolation membrane; nanocellulose has a low density, thereby reducing the mass of the battery cell and improving the mass energy density of the battery cell; in addition, nanocellulose itself contains a large number of hydroxyl groups, thereby forming a three-dimensional skeleton structure, and further by matching with granular fillers, the mechanical strength and puncture resistance of the isolation membrane can be improved. Nanocellulose itself contains a large number of hydroxyl groups, which can be connected with granular fillers, porous substrates, etc. through hydrogen bonds, van der Waals forces, etc., thereby enhancing the bonding strength between the granular fillers in the coating and between the coating and the porous substrate, reducing the problem of powder loss, and improving the processing performance of the isolation membrane and the battery cell. Therefore, the battery cell provided by the embodiment of the present disclosure can also have high reliability.

[0132] 0<AB≤5mm. For example, AB can be 2mm, 2.5mm, 2.7mm, 3.1mm, 3.5mm, 3.8mm, 4mm, 4.5mm, 5mm, or a range consisting of any of the above values.

[0133] Optionally, 2 mm ≤ AB ≤ 4 mm, and more preferably, 2.5 mm ≤ AB ≤ 3.5 mm, which is beneficial for further improving the volume energy density and processing performance of the battery cell.

[0134] [Isolation film]

[0135] In some embodiments, the porous substrate is made of polyolefin, and may optionally be made of polyethylene.

[0136] Currently used ultra-thin separators are primarily made from polyolefin resins, which have a low melting point and therefore offer good processing properties. However, separators made from these materials typically experience significant thermal shrinkage, requiring them to be designed with a relatively large width when used in battery cells, increasing the difficulty of assembling the cells. The porous substrate provided by the disclosed embodiments can achieve both high strength and heat resistance while maintaining a relatively low thickness. This helps separators achieve both low thickness and high heat resistance, and also helps battery cells achieve high energy density, good processing properties, and high reliability.

[0137] In some embodiments, the thickness of the porous substrate may be less than or equal to 5 μm, and may be 3 μm to 4.5 μm.

[0138] In some embodiments, the puncture strength of the porous substrate may be greater than or equal to 390 gf, and may be 400 gf-480 gf.

[0139] The higher the puncture strength of the porous substrate, the better its puncture resistance, effectively preventing positive and negative electrode particles, as well as metallic foreign particles, from piercing the separator and causing a short circuit between the positive and negative electrodes. Therefore, a porous substrate with a puncture strength within the above range can increase the pass rate of battery cell short-circuit testing and enhance battery cell reliability.

[0140] In some embodiments, the thermal shrinkage of the porous substrate in the machine direction (MD) at 105° C. for 1 hour may be less than 3%, and may be optionally 1%-2.5%.

[0141] In some embodiments, the thermal shrinkage rate of the porous substrate in the transverse direction (TD) at 105° C. for 1 h may be less than 2%, and may be optionally 1%-1.8%.

[0142] The reduced thermal shrinkage of the porous substrate indicates that the porous substrate has good heat resistance, which can also increase the passing rate of the battery cell short-circuit test and improve the reliability of the battery cell.

[0143] The thermal shrinkage of a porous substrate has a well-known meaning in the art and can be measured using methods known in the art. For example, it can be tested with reference to GB / T 36363-2018.

[0144] In some embodiments, the longitudinal tensile strength of the porous substrate may be greater than or equal to 2700 kgf / cm 2 , optional 2800kgf / cm 2 -3500kgf / cm 2 .

[0145] In some embodiments, the transverse tensile strength of the porous substrate may be greater than or equal to 2500 kgf / cm 2 , optional 2600kgf / cm 2 -3200kgf / cm 2 .

[0146] The increased tensile strength of the porous substrate is conducive to the effective coating of the positive and negative electrode particles, which can effectively reduce the short circuit between the positive and negative electrodes and improve the reliability of the battery cells.

[0147] The tensile strength of a porous substrate has a well-known meaning in the art and can be measured using methods known in the art. For example, it can be tested in accordance with GB / T 36363-2018.

[0148] In some embodiments, the average pore size of the porous substrate may be 10 nm to 60 nm, optionally 20 nm to 40 nm.

[0149] The average pore size of a porous substrate has a well-known meaning in the art and can be measured using methods known in the art, for example, using a capillary flow pore size analyzer, such as a PMIPorometer.

[0150] In some embodiments, the porous substrate may have a porosity of 20% to 60%, optionally 30% to 50%.

[0151] The porosity of a porous substrate has a well-known meaning in the art and can be measured using methods known in the art. For example, the porosity can be measured in accordance with GB / T 36363-2018.

[0152] The coating includes nanocellulose and a granular filler. In some embodiments, the nanocellulose content in the coating can be 5wt%-60wt%, optionally 7wt%-45wt%. In some embodiments, the granular filler content in the coating can be greater than or equal to 38wt%, optionally 53wt%-91wt%.

[0153] The mass content of nanocellulose and granular filler within the above range can make the isolation membrane have high heat resistance and good ion transport properties, thereby making the battery cell have good cycle performance; it is also beneficial for the coating slurry to have a suitable viscosity, which is beneficial for coating; it is also beneficial for maintaining high bonding strength between the coating and the porous substrate, thereby improving the structural stability of the isolation membrane; it is also beneficial for the nanocellulose and granular filler to overlap to form an integrated coating, so that the coating has a more stable spatial network structure.

[0154] In some embodiments, the average length of the nanocellulose may be 100 nm-1200 nm, optionally 200 nm-1000 nm, 200 nm-800 nm, 200 nm-600 nm, or 300 nm-600 nm.

[0155] By adjusting the average length of the nanocellulose within the above range, it is beneficial for the nanocellulose to overlap to form a three-dimensional skeleton structure, and it is also beneficial for the three-dimensional skeleton structure to overlap with the granular filler to form an integrated coating, thereby improving the heat resistance of the separator, thereby helping to reduce the risk of short-circuit failure during the use of the battery cell, and also helping to improve the cycle performance of the battery cell. By adjusting the average length of the nanocellulose within the above range, it is also beneficial for the coating slurry to have an appropriate viscosity, thereby facilitating coating and improving the uniformity and consistency of the coating.

[0156] In some embodiments, the average diameter of the nanocellulose may be 11 nm-40 nm, optionally 15 nm-32 nm.

[0157] By adjusting the average diameter of the nanocellulose within the above range, it is beneficial for the nanocellulose to overlap to form a three-dimensional skeleton structure, and it is also beneficial for the three-dimensional skeleton structure to overlap with the granular filler to form an integrated coating, which is beneficial to improve the heat resistance of the isolation membrane, and further beneficial to reduce the risk of short-circuit failure during the use of the battery cell, and also beneficial to improve the cycle performance of the battery cell.

[0158] In some embodiments, the aspect ratio of the nanocellulose may be 5-60, optionally 12-35.

[0159] Adjusting the aspect ratio of nanocellulose within the above range facilitates the overlapping of the nanocellulose to form a three-dimensional skeleton structure. This also facilitates the overlapping of the formed three-dimensional skeleton structure with the granular filler to form an integrated coating, thereby improving the heat resistance of the separator, thereby reducing the risk of short-circuit failure during battery cell use and improving the cycle performance of the battery cell. Adjusting the aspect ratio of nanocellulose within the above range also helps improve the electrolyte wettability of the separator, thereby facilitating ion transport and reducing dendrites.

[0160] The average length and average diameter of the nanocellulose can be measured by the following method: a 3.6 mm × 3.6 mm sample is cut out from any area of ​​the isolation membrane, and the microscopic morphology of the coating in the sample is mapped using a scanning electron microscope (e.g., ZEISS Sigma 300), the high vacuum mode is selected, the operating voltage is 3 kV, the magnification is 30,000 times, and a SEM image is obtained; based on the obtained SEM image, multiple (e.g., more than 5) test areas are selected for length statistics, the size of each test area is 0.5 μm × 0.5 μm, and then the average value of the length of the nanocellulose obtained in each test area is taken as the average length of the nanocellulose; based on the obtained SEM image, multiple (e.g., more than 5) test areas are selected for diameter statistics using Nano Measurer particle size distribution statistical software, the size of each test area is 0.5 μm × 0.5 μm, and then the average value of the diameter of the nanocellulose obtained in each test area is taken as the average diameter of the nanocellulose.

[0161] In some embodiments, the nanocellulose may include a modification group, which may include at least one of an amine group, a carboxyl group, an aldehyde group, a sulfonic acid group, or a phosphoric acid group, and may optionally include at least one of a sulfonic acid group or a phosphoric acid group.

[0162] When nanocellulose has the above-mentioned specific modified groups, on the one hand, it can effectively improve the heat resistance of the isolation membrane, enhance the thermal stability of the battery cell, and reduce the risk of short-circuit failure during the use of the battery cell; on the other hand, it can also improve the bonding strength between the coating and the porous substrate.

[0163] When nanocellulose has the above-mentioned specific modified groups, it is also beneficial for the nanocellulose to overlap with the granular filler to form an integrated coating, thereby enabling the coating to have a stable spatial network structure, which is beneficial to improving the electrolyte wettability and liquid retention of the isolation membrane, and improving the ion transmission characteristics and voltage breakdown resistance of the isolation membrane; it is also beneficial to match high-voltage positive electrode active materials and further improve the energy density of the battery cell.

[0164] In addition, the presence of the modified group can also reduce the proportion of hydroxyl groups, thereby helping the coating slurry to have a suitable viscosity and being more conducive to coating, thereby also improving the production efficiency of the isolation film and improving the uniformity and consistency of the coating.

[0165] In some embodiments, the nanocellulose comprises hydroxyl groups and modified groups, and the molar ratio of modified groups to hydroxyl groups can be 1:4 to 4:1, optionally 2:3 to 7:3.

[0166] When the molar ratio of the modified group to the hydroxyl group is within the above range, the heat resistance, ion transport properties, electrolyte wettability and liquid retention of the isolation membrane can be further improved, thereby helping to reduce the risk of short-circuit failure during the use of the battery cell and improving the cycle performance of the battery cell.

[0167] The type of modified group in nanocellulose can be determined by infrared spectroscopy. For example, the infrared spectrum of the material can be tested to determine the characteristic peaks contained therein, thereby determining the type of modified group. Specifically, the material can be subjected to infrared spectroscopy analysis using instruments and methods well known in the art, for example, using an infrared spectrometer (such as the IS10 Fourier transform infrared spectrometer from Nicolet, USA), and tested in accordance with GB / T 6040-2019 General Rules for Infrared Spectroscopy Analysis Methods.

[0168] The molar ratio of modified groups to surface hydroxyl groups in nanocellulose can be measured by the following method: The hydroxyl value (mg of potassium hydroxide equivalent to the hydroxyl content per gram of sample) of the raw cellulose and nanocellulose is measured according to the phthalic anhydride method specified in GB / T 12008.3-2009. The resulting value, expressed in mg KOH / g, is converted to mmol / g to represent the hydroxyl content. The modified group content (i.e., the amount of modified hydroxyl groups) is then subtracted from the hydroxyl content of the nanocellulose to obtain the molar ratio of modified groups to hydroxyl groups.

[0169] In some embodiments, the nanocellulose includes sulfonic acid groups, and the content of sulfur element can be ≥0.1 wt %, optionally 0.2 wt %-0.5 wt %, based on the total mass of the nanocellulose.

[0170] The sulfur content in nanocellulose can be determined as follows: After drying, grind the nanocellulose in a mortar (e.g., an agate mortar) for 30 minutes. Then, analyze the nanocellulose using an X-ray diffractometer (e.g., a Miniflex 600-C) to determine the sulfur content. The test uses a Cu target, a Ni filter, a tube voltage of 40 kV, a tube current of 15 mA, and a continuous scan range of 5°-80°.

[0171] In some embodiments, the weight average molecular weight of the nanocellulose may be from 10,000 to 60,000, optionally from 30,000 to 50,000.

[0172] The weight average molecular weight of nanocellulose is within the above range, which can make the coating slurry have a suitable viscosity, and the coating slurry has good fluidity and wettability during coating, which is beneficial to improving the quality of the coating, and further beneficial to improving the heat resistance and ion transmission properties of the isolation membrane.

[0173] In some embodiments, nanocellulose can be obtained by the following method: providing cellulose powder with a whiteness ≥ 80%; mixing and reacting the obtained cellulose powder with a modified solution, washing and removing impurities, adjusting the pH to neutral, and grinding and cutting to obtain nanocellulose.

[0174] Alternatively, the cellulose powder having a whiteness of 80% or greater can be commercially available, or obtained by chemical methods (e.g., acid hydrolysis, alkali treatment, Tempo catalytic oxidation), biological methods (e.g., enzyme treatment), mechanical methods (e.g., ultrafine grinding, ultrasonic crushing, high-pressure homogenization), etc. The fiber raw material used to prepare the cellulose powder having a whiteness of 80% or greater can include plant fibers, such as at least one of cotton fibers (e.g., cotton fibers, kapok fibers), hemp fibers (e.g., sisal fibers, ramie fibers, jute fibers, flax fibers, hemp fibers, abaca fibers, etc.), palm fibers, wood fibers, bamboo fibers, and grass fibers.

[0175] In some embodiments, the cellulose powder with a whiteness of ≥80% can also be prepared by the following method: after the fiber raw material is loosened and deslagging, it is cooked with an alkali solution (for example, a NaOH aqueous solution, the concentration of which can be 4wt% to 20wt%, optionally 5wt% to 15wt%), and then sequentially subjected to water washing to remove impurities (for example, 3 to 6 times of water washing), bleaching (for example, sodium hypochlorite and / or hydrogen peroxide can be used), acid washing to remove impurities, water washing to remove impurities, water removal, and air drying to obtain cellulose powder.

[0176] In some embodiments, the modification solution may be an acid solution (eg, aqueous sulfuric acid solution, aqueous phosphoric acid solution, aqueous acetic acid solution) or an alkaline solution (eg, urea organic solvent solution). Optionally, the modification solution is an acid solution.

[0177] Alternatively, the concentration of the acid solution may be 5 wt% to 80 wt%. When a sulfuric acid aqueous solution is used as the modification solution, the concentration of the acid solution may be 40 wt% to 80 wt%, thereby obtaining a cellulose powder having sulfonic acid groups. When a phosphoric acid aqueous solution is used as the modification solution, the concentration of the acid solution may be 45 wt% to 75 wt%, thereby obtaining a cellulose powder having phosphoric acid groups. When an acetic acid aqueous solution is used as the modification solution, the concentration of the acid solution may be 40 wt% to 80 wt%, thereby obtaining a cellulose powder having carboxylic acid groups.

[0178] Alternatively, the urea organic solvent solution may be a urea xylene solution, thereby obtaining cellulose powder having amino groups.

[0179] In some embodiments, optionally, the mass ratio of cellulose powder to modifying solution may be 1:2.5 to 1:50, optionally 1:5 to 1:30.

[0180] When the modification solution is a sulfuric acid aqueous solution, the mass ratio of cellulose powder to the acid solution can be 1:5 to 1:30. When the modification solution is a phosphoric acid aqueous solution, the mass ratio of cellulose powder to the acid solution can be 1:5 to 1:30. When the modification solution is an acetic acid aqueous solution, the mass ratio of cellulose powder to the acid solution can be 1:5 to 1:30. When the modification solution is a urea organic solvent solution, the mass ratio of cellulose powder to the urea organic solvent solution can be 1:4 to 1:40.

[0181] In some embodiments, when the modified solution is an acid solution, the reaction can be carried out at a temperature not higher than 80°C, optionally at 30°C to 60°C, and the reaction time of the cellulose powder and the modified solution can be 0.25h to 4h, optionally 0.5h to 3h.

[0182] In some embodiments, when the modifying solution is an alkaline solution, the reaction can be carried out at 100° C. to 145° C., and the reaction time of the cellulose powder and the modifying solution can be 0.5 h to 5 h.

[0183] In some embodiments, grinding can be performed using a grinder, and cutting can be performed using a high-pressure homogenizer. Nanocellulose with different average diameters and / or different average lengths can be obtained by adjusting the grinding parameters of the grinder (e.g., number of grindings, grinding time, etc.) and the cutting parameters of the high-pressure homogenizer.

[0184] In some embodiments, the particulate filler may include one or more of organic particles, inorganic particles, and organic-inorganic composite materials.

[0185] In some embodiments, the particulate filler may include a first component in the form of a secondary particle and a second component in the form of a primary particle.

[0186] The first component of the secondary particle morphology can better overlap with the three-dimensional skeleton structure formed by nanocellulose to form an integrated effect, thereby enabling the coating to have a more stable spatial network structure, thereby further improving the heat resistance of the isolation membrane and the thermal stability of the battery cell.

[0187] The second component of the primary particle morphology is beneficial to reducing the moisture content of the coating and improving the ion transport properties of the coating, thereby helping to improve the cycle performance of the battery cell.

[0188] In some embodiments, the average particle size of the first component of the secondary particle morphology is smaller than the average particle size of the second component of the primary particle morphology.

[0189] This is conducive to better play the role of the first component of the secondary particle morphology and the second component of the primary particle morphology.

[0190] The first component of the secondary particle morphology has a smaller particle size and better affinity with nanocellulose. At the same time, the nanocellulose can also be overlapped in the gaps between the primary particles in the first component that constitutes the secondary particle morphology, thereby helping to overlap the nanocellulose and the first component of the secondary particle morphology to form an integrated coating, so that the coating has a more stable spatial network structure, thereby further improving the heat resistance of the isolation membrane.

[0191] The second component of the primary particle morphology has a larger particle size and higher strength, which can better play a skeleton support role in the coating, reduce the thermal shrinkage of the isolation membrane and improve the heat resistance of the isolation membrane; and also help the coating have more pore structure and less moisture content, which can further improve the ion transmission properties of the isolation membrane.

[0192] In some embodiments, the average particle size of the first component of the secondary particle morphology is less than 200 nm, and can be selected from 80 nm to 180 nm. The average particle size of the first component of the secondary particle morphology within the above range can provide a higher specific surface area and better match and overlap the three-dimensional skeleton structure formed by the nanocellulose to form an integrated effect. This can increase the heat resistance of the separator and the separator's ability to wet and retain the electrolyte, thereby helping to improve the thermal stability and cycling performance of the battery cell.

[0193] In some embodiments, the primary particles in the first component constituting the secondary particle morphology may have a particle size of 15 nm to 45 nm, and optionally 20 nm to 35 nm. The particle size of the primary particles in the first component constituting the secondary particle morphology within the above range can provide the first component with a good secondary particle morphology, which facilitates better integration of the three-dimensional framework formed by the first component and the nanocellulose.

[0194] In some embodiments, the average particle size of the second component of the primary particle morphology can be 200 nm to 600 nm, optionally 300 nm to 500 nm. When the average particle size of the second component of the primary particle morphology is within this range, the second component of the primary particle morphology can better play its supporting role, allowing the coating to maintain a stable pore structure during long-term charge and discharge processes, thereby reducing the moisture content of the separator and promoting ion transport, while also improving the heat resistance of the separator.

[0195] The average particle size of the first component of the secondary particle morphology and the second component of the primary particle morphology can be measured using equipment and methods known in the art. For example, a scanning electron microscope (e.g., a ZEISS Sigma 300) can be used to map the microscopic morphology of the coating in the sample. Referring to JY / T 0584-2020, a scanning electron microscope (SEM) image of the separator coating can be obtained. The longest diagonal length of the particles in the SEM image can be measured and then averaged to obtain the average value. The number of selected particles can be greater than 100.

[0196] In some embodiments, the specific surface area of ​​the first component of the secondary particle morphology may be greater than the specific surface area of ​​the second component of the primary particle morphology, thereby facilitating better performance of the first component of the secondary particle morphology and the second component of the primary particle morphology.

[0197] In some embodiments, the specific surface area of ​​the first component of the secondary particle morphology can be greater than 20 m 2 / g, optional 30m 2 / g-80m 2 / g. The specific surface area of ​​the first component of the secondary particle morphology is within the above range, which has a better affinity with nanocellulose and can better match and overlap with the three-dimensional skeleton structure formed by nanocellulose to form an integrated effect. This can increase the heat resistance of the separator and the separator's ability to infiltrate and retain the electrolyte, thereby helping to improve the thermal stability and cycle performance of the battery cell.

[0198] In some embodiments, the specific surface area of ​​the second component of the primary particle morphology can be less than or equal to 20m 2 / g, optional 5m 2 / g-15m 2 The specific surface area of ​​the second component of the primary particle morphology is within the above range, which is beneficial to reducing the moisture content of the separator and improving the heat resistance of the separator.

[0199] In some embodiments, the mass content of the first component of the secondary particle morphology in the coating layer may be greater than the mass content of the second component of the primary particle morphology in the coating layer, thereby facilitating better performance of the first component of the secondary particle morphology and the second component of the primary particle morphology.

[0200] In some embodiments, the mass content of the first component in the secondary particle morphology in the coating can be 10wt%-85wt%, optionally 20wt%-75wt%. A mass content of the first component in the secondary particle morphology within this range helps the coating slurry have a suitable viscosity, which is more conducive to coating. Furthermore, it facilitates integration with the three-dimensional skeleton structure formed by the nanocellulose, thereby providing the coating with a more stable spatial network structure and improving the heat resistance and ion transport properties of the separator.

[0201] In some embodiments, the mass content of the second component of the primary particle morphology in the coating can be 5wt%-70wt%, optionally 7wt%-60wt%. When the mass content of the second component of the primary particle morphology is within the above range, the supporting role of the second component of the primary particle morphology can be better exerted, so that the coating maintains a stable pore structure during long-term charge and discharge, thereby helping to reduce the moisture content of the isolation membrane and promote ion transport. When the mass content of the second component of the primary particle morphology is within the above range, it can also increase the overall packing density of the granular filler, thereby also improving the heat resistance and puncture resistance of the isolation membrane.

[0202] In addition, by adjusting the content of nanocellulose, the first component of secondary particle morphology and the second component of primary particle morphology within the above range, the coating can have a thinner thickness and highly developed pores, thereby further improving the electrolyte wettability of the isolation membrane.

[0203] In some embodiments, the first component of the secondary particle morphology may include one or more of inorganic particles and organic particles.

[0204] Optionally, the inorganic particles include boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon oxide SiO x (0<x≤2), tin dioxide (SnO2), titanium oxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), hafnium dioxide (HfO2), cerium oxide (CeO2), zirconium titanate (ZrTiO3), barium titanate (BaTiO3) and magnesium fluoride (MgF2) One or more. More optionally, the inorganic particles include boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), silicon oxide SiO x(0<x≤2), one or more of titanium oxide (TiO2), zinc oxide (ZnO), cerium oxide (CeO2) and barium titanate (BaTiO3).

[0205] Optionally, the organic particles include one or more of polystyrene and polyacrylic wax.

[0206] In some embodiments, the first component of the secondary particle morphology may include inorganic particles in the secondary particle morphology, and the crystal form of the inorganic particles in the secondary particle morphology includes at least two of α-crystalline form, θ-crystalline form, γ-crystalline form, and η-crystalline form. Alternatively, the crystal form of the inorganic particles in the secondary particle morphology includes at least two of α-crystalline form, θ-crystalline form, and γ-crystalline form.

[0207] In some embodiments, the mass content of inorganic particles with α-crystal secondary particle morphology in inorganic particles with secondary particle morphology may be ≥1.2wt%, optionally 1.2wt% to 10wt%, and more optionally 1.2wt% to 5wt%, based on the total mass of inorganic particles with secondary particle morphology.

[0208] In some embodiments, the mass content of inorganic particles with secondary particle morphology of θ crystal form in the inorganic particles with secondary particle morphology may be ≥50wt%, optionally 60wt% to 85wt%, and more optionally 60wt% to 82.5wt%, based on the total mass of the inorganic particles with secondary particle morphology.

[0209] In some embodiments, the mass content of inorganic particles with γ-crystal secondary particle morphology in the inorganic particles with secondary particle morphology may be ≥10wt%, optionally 15wt% to 60wt%, and more optionally 15wt% to 35wt%, based on the total mass of the inorganic particles with secondary particle morphology.

[0210] In some embodiments, the mass content of inorganic particles with η crystal secondary particle morphology in inorganic particles with secondary particle morphology may be ≤5wt%, optionally ≤2wt%, and more optionally ≤1wt%, based on the total mass of inorganic particles with secondary particle morphology.

[0211] Inorganic particles with an α-crystal secondary particle morphology offer advantages such as high hardness, excellent heat resistance, a low dielectric constant, high safety, and a high true density. Inorganic particles with a θ-crystal secondary particle morphology have a moderate specific surface area and hardness, thereby simultaneously improving the heat resistance and ion transport properties of the separator. Inorganic particles with γ-crystal and η-crystal secondary particle morphologies have the advantage of a large specific surface area. Therefore, selecting inorganic particles with different crystal morphologies can help improve at least one of the separator's heat resistance, ion transport properties, bonding strength, and electrolyte wettability.

[0212] In some embodiments, the first component of the secondary particle morphology may include inorganic particles with secondary particle morphology, and the crystal forms of the inorganic particles with secondary particle morphology include α crystal form, θ crystal form, γ crystal form and η crystal form, and the mass content of the inorganic particles with secondary particle morphology of α crystal form in the inorganic particles with secondary particle morphology may be 1.2wt% to 5wt%, the mass content of the inorganic particles with secondary particle morphology of θ crystal form in the inorganic particles with secondary particle morphology may be 60wt% to 82.5wt%, the mass content of the inorganic particles with secondary particle morphology of γ crystal form in the inorganic particles with secondary particle morphology may be 15wt% to 35wt%, and the mass content of the inorganic particles with secondary particle morphology of η crystal form in the inorganic particles with secondary particle morphology may be ≤1wt%, all based on the total mass of the inorganic particles with secondary particle morphology.

[0213] The X-ray diffraction pattern of inorganic particles with secondary particle morphology can be obtained by the following method: After drying, grind the inorganic particles with secondary particle morphology in a mortar (such as an agate mortar) for 30 minutes. Then, use an X-ray diffractometer (such as the Miniflex 600-C) to obtain the X-ray diffraction pattern. The test can use a Cu target, a Ni filter, a tube voltage of 40 kV, a tube current of 15 mA, and a continuous scanning range of 5°-80°.

[0214] In some embodiments, the first component of the secondary particle morphology may include inorganic particles with a secondary particle morphology. The inorganic particles with a secondary particle morphology may be prepared as follows: a precursor solution of the inorganic particles is subjected to an oxidation reaction by high-pressure sputtering, followed by heating at 600° C. to 900° C. (e.g., 1 to 3 hours) to form small particles, and then drying and shaping at 150° C. to 250° C. (e.g., 30 to 60 minutes) to obtain inorganic particles with a secondary particle morphology. The average particle size of the inorganic particles with a secondary particle morphology can be adjusted by adjusting sputtering parameters, such as temperature and time.

[0215] In some embodiments, the shape of the first component of the secondary particle morphology may include one or more of string-like, chain-like, amorphous, spherical, spheroidal, and pyramidal.

[0216] In some embodiments, the second component of the primary particle morphology may include inorganic particles in the primary particle morphology.

[0217] Alternatively, the inorganic particles in the primary particle morphology may include one or more of inorganic particles having a dielectric constant of 5 or greater, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of undergoing electrochemical reactions.

[0218] Optionally, the inorganic particles having a dielectric constant of 5 or more include one or more of the following: boehmite, aluminum oxide, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hectorite, zirconium titanate, barium titanate, Pb(Zr,Ti)O3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti n O3 (abbreviated as PLZT, 0<m<1, 0<n<1), Pb(Mg3Nb 2 / 3 )O3-PbTiO3 (abbreviated as PMN-PT), and their respective modified inorganic particles. Optionally, the modification method of each inorganic particle may be chemical modification and / or physical modification. Chemical modification methods include coupling agent modification (for example, using silane coupling agent, titanate coupling agent, etc.), surfactant modification, polymer grafting modification, etc. Physical modification methods may be mechanical force dispersion, ultrasonic dispersion, high energy treatment, etc. The modification treatment can reduce the agglomeration of inorganic particles, thereby enabling the coating to have a more stable and more uniform spatial network structure; in addition, by selecting a coupling agent, surfactant or polymer with a specific functional group to modify the inorganic particles, it is also helpful to improve the coating's wetting and retention properties for the electrolyte and improve the coating's adhesion to the porous substrate.

[0219] Optionally, the inorganic particles having ion conductivity but not storing ions include one or more of the following: Li3PO4, lithium titanium phosphate Li x1 Ti y1 (PO4)3, lithium aluminum titanium phosphate Li x2 Al y2 Ti z1 (PO4)3, (LiAlTiP) x3 O y3 Type glass, lanthanum lithium titanate Li x4 La y4 TiO3, lithium germanium thiophosphate Li x5 Ge y5 P z2 S w , lithium nitride Li x6 N y6 、SiS2 type glass Li x7 Si y7 S z3 and P2S5 glass Li x8 P y8 S z4, 0<x1<2, 0<y1<3, 0<x2<2, 0<y2<1, 0<z1<3, 0<x3<4, 0<y3<13, 0<x4<2, 0<y4<3, 0<x5<4, 0<y5<1, 0<z2<1, 0<w<5, 0<x6<4, 0<y6<2, 0<x7<3, 0<y7<2, 0<z3<4, 0<x8<3, 0<y8<3, 0<z4<7. This can further improve the ion transport characteristics of the isolation membrane.

[0220] Optionally, the inorganic particles capable of undergoing electrochemical reaction include one or more of the following: lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials, and lithium-titanium compounds.

[0221] In some embodiments, the second component of the primary particle morphology may include inorganic particles in the form of primary particles. The crystal form of the inorganic particles in the form of primary particles may include one or more of an α-crystalline form and a γ-crystalline form, and may optionally include an α-crystalline form. Inorganic particles in the form of primary particles in the form of α-crystalline form have the advantages of high hardness, good heat resistance, low dielectric constant, high safety, and high true density, thereby further improving the heat resistance of the coating.

[0222] In some embodiments, the crystal form of the inorganic particles with primary particle morphology includes α crystal form, and the mass content of the inorganic particles with primary particle morphology with α crystal form in the inorganic particles with primary particle morphology may be ≥90wt%, optionally 95wt% to 100wt%, based on the total mass of the inorganic particles with primary particle morphology.

[0223] In some embodiments, the shape of the second component of the primary particle morphology may include at least one of a spherical shape, a dumbbell shape, and a polygonal shape.

[0224] The inorganic particles of the α-crystal form have diffraction peaks at 57.48°±0.2° and 43.34°±0.2° in 2θ in an X-ray diffraction spectrum measured using an X-ray diffractometer.

[0225] The inorganic particles of the θ crystal form have diffraction peaks at 36.68°±0.2° and 31.21°±0.2° in 2θ in an X-ray diffraction spectrum measured using an X-ray diffractometer.

[0226] The inorganic particles of the γ crystal form have diffraction peaks at 66.95°±0.2° and 45.91°±0.2° in 2θ in an X-ray diffraction spectrum measured using an X-ray diffractometer.

[0227] The inorganic particles of the η crystal form have diffraction peaks at 31.89°±0.2° and 19.37°±0.2° in 2θ in an X-ray diffraction spectrum measured using an X-ray diffractometer.

[0228] X-ray diffraction patterns of inorganic particles can be obtained as follows: After drying, grind the particles in a mortar (e.g., an agate mortar) for 30 minutes. Then, use an X-ray diffractometer (e.g., a Miniflex 600-C) to obtain the X-ray diffraction pattern. The test uses a Cu target, a Ni filter, a tube voltage of 40 kV, a tube current of 15 mA, and a continuous scan range of 5°-80°.

[0229] In some embodiments, the coating further comprises a non-granular binder. The present disclosure does not particularly limit the type of the non-granular binder, and any known material with good adhesive properties may be selected, such as a linear binder, an emulsion binder, and a mixed linear and emulsion binder.

[0230] Optionally, the non-granular binder may have at least one polar group selected from the group consisting of a hydroxyl group (-OH), a carboxyl group (-COOH), an ester group (-COO-), a cyano group (-CN), an imide group (-CO-NH-CO-), a maleic anhydride group (-COOOC-), a sulfonate group (-SO3H) and a pyrrolidone group (-NCO-).

[0231] Alternatively, the non-particulate binder may include a homopolymer or copolymer selected from the group consisting of allyl polyether sulfate, acrylic acid, methacrylic acid, acrylamide, methyl acrylate, butyl acrylate, ethyl acrylate, glycidyl methacrylate, vinyl alcohol, acrylonitrile, hydroxyethyl acrylate, styrene, acetoxyethyl methacrylate, vinyltrimethoxysilane, lithium acrylate, sodium acrylate, lithium methacrylate, isobutylene, and maleic anhydride.

[0232] Optionally, the non-granular binder may include at least one of: polymethyl methacrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polystyrene-co-methyl methacrylate, polystyrene-co-butyl acrylate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, acrylonitrile-styrene-butadiene copolymer, polyimide.

[0233] Optionally, the non-granular binder content in the coating can be less than or equal to 3 wt%, and optionally 0.3 wt% to 1.5 wt%, based on the total weight of the coating. The nanocellulose and granular fillers in the coating can form a stable spatial network structure, thereby enabling the separator to maintain high bonding strength, good ion transport properties, and high heat resistance while reducing the amount of binder used.

[0234] In some embodiments, the coating may not contain a wetting agent, such as common acrylates or polyoxyethylene-polyoxypropylene block copolymers. Wetting agents are typically low-surface-tension, high-fluidity compounds, which can easily lead to pore clogging in the porous substrate during the coating slurry application and drying process. The isolation membrane provided by the present disclosure does not contain a wetting agent, thereby avoiding pore clogging in the porous substrate caused by the wetting agent during the coating slurry application and drying process.

[0235] In some embodiments, the separator may further include an adhesive layer disposed on at least a portion of the coating surface. The adhesive layer not only prevents the coating from peeling, thereby improving the reliability of the battery cell, but also improves the interface between the separator and the electrodes (e.g., the positive electrode and the negative electrode), thereby improving the cycle performance of the battery cell.

[0236] In some embodiments, the adhesive layer may include an adhesive. Alternatively, the adhesive layer may include a granular adhesive.

[0237] In some embodiments, the binder in the adhesive layer may include at least one of an acrylate monomer homopolymer or copolymer, an acrylic acid monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer.

[0238] The comonomer may include, but is not limited to, at least one of the following: an acrylate monomer, an acrylic acid monomer, an olefin monomer, a halogen-containing olefin monomer, a fluoroether monomer, and the like.

[0239] Alternatively, the binder in the adhesive layer may include a vinylidene fluoride-based polymer, such as a homopolymer of vinylidene fluoride monomer (VDF) and / or a copolymer of vinylidene fluoride monomer and a comonomer. The comonomer may be at least one of an olefin monomer, a fluorine-containing olefin monomer, a chlorine-containing olefin monomer, an acrylate monomer, an acrylic acid monomer, and a fluoroether monomer.

[0240] Alternatively, the comonomer may include at least one of trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ether (e.g., perfluoro(methyl vinyl) ether PMVE, perfluoro(ethyl vinyl) ether PEVE, perfluoro(propyl vinyl) ether PPVE), perfluoro(1,3-dioxole) and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD).

[0241] In some embodiments, the binder in the bonding layer may include at least one of the following: polyperfluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polystyrene-co-methyl methacrylate, polystyrene-co-butyl acrylate, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, polyethylene-co-vinyl acetate, polyimide, and polyethylene oxide.

[0242] In some embodiments, the total thickness of the separator can be 4 μm-10 μm, optionally 4.5 μm-8.5 μm. When the total thickness of the separator is within the above range, the battery cell can have a high energy density while also having low thermal shrinkage, resulting in high reliability of the battery cell.

[0243] Providing a common ceramic coating on a porous substrate can reduce the overall thermal shrinkage of the isolation membrane. However, this method often requires a larger ceramic coating thickness, which will sacrifice the energy density of the battery cell; in addition, it will also sacrifice the processing performance of the isolation membrane, for example, the probability of powder loss during winding of the isolation membrane is high. In some embodiments, the thickness of the coating of the isolation membrane provided by the embodiment of the present disclosure can be 0.2μm-2μm, optionally 0.4μm-1μm. The coating includes nanocellulose and granular fillers, so that the coating can have both low thickness and high heat resistance, and can also make the battery cell have good processing performance. The thickness of the coating is within the above range, which can not only make the battery cell have high energy density, but also make the isolation membrane have low thermal shrinkage, and make the battery cell have high reliability. The thickness of the coating refers to the thickness of the coating located on one side of the porous substrate.

[0244] In some embodiments, the thermal shrinkage rate of the separator in the machine direction (MD) at 150° C. for 1 hour may be less than or equal to 3%.

[0245] In some embodiments, the thermal shrinkage rate of the isolation film in the transverse direction (TD) at 150° C. for 1 hour may be less than or equal to 2%.

[0246] The separator has a low thermal shrinkage rate at high temperatures, thereby enabling the battery cell to have high reliability.

[0247] The thermal shrinkage of the separator has a well-known meaning in the art and can be measured using methods known in the art. For example, the test can be performed with reference to GB / T 36363-2018.

[0248] It should be noted that the above-mentioned isolation film coating parameters (such as thickness, etc.) are the coating parameters of a single side of the porous substrate. When the coating is provided on both sides of the porous substrate, the coating parameters on either side meet the requirements of this disclosure and are considered to fall within the scope of protection of this disclosure.

[0249] [Negative electrode]

[0250] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0251] The negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either one or both of the two opposite surfaces of the negative electrode current collector.

[0252] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As examples of metal foils, copper foil, copper alloy foil, aluminum foil, and aluminum alloy foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0253] In some embodiments, the negative electrode active material may include a carbon material. Alternatively, the carbon material may include one or more of artificial graphite and natural graphite.

[0254] In some embodiments, the negative electrode active material may include a silicon-based material, thereby increasing the energy density of the battery cell. The silicon-based material may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy.

[0255] In some embodiments, in addition to silicon, the silicon-based material may further include one or more of an alkali metal element and an alkaline earth metal element, optionally including one or more of Li and Mg. As an example, the silicon-based material may be a silicon-based material pre-embedded with an alkali metal and / or alkaline earth metal, such as a silicon-based material pre-embedded with Li and / or Mg.

[0256] In some embodiments, the mass proportion of the silicon-based material in the negative electrode active material may be greater than or equal to 5 wt %, and may be 8 wt % to 20 wt %.

[0257] In some embodiments, the negative electrode active material may include a carbon material and a silicon-based material. The silicon-based material may account for 8% to 20% by weight of the negative electrode active material, and the carbon material may account for greater than or equal to 80% by weight of the negative electrode active material. This allows the battery cell to have both high energy density and long cycle life.

[0258] In some embodiments, the volume distribution particle size Dv10 of the negative electrode active material may be 4 μm-8 μm, optionally 4.5 μm-6.5 μm.

[0259] In some embodiments, the volume distribution particle size Dv50 of the negative electrode active material may be 6 μm-15 μm, optionally 8 μm-13 μm.

[0260] In some embodiments, the volume distribution particle size Dv90 of the negative electrode active material may be 15 μm-30 μm, optionally 18 μm-25 μm.

[0261] By adjusting the volume distribution particle size Dv10, Dv50 and / or Dv90 of the negative electrode active material within the above range, battery side reactions can be reduced, the battery cell can have a long cycle life, and the battery cell can also have good low-temperature performance.

[0262] In some embodiments, the negative electrode film layer may further include a negative electrode binder, for example, it may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA) and carboxymethyl chitosan (CMCS), and the embodiments of the present disclosure are not limited to this.

[0263] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present disclosure does not particularly limit the type of the negative electrode conductive agent. For example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0264] In some embodiments, the negative electrode film layer may further include other additives, such as thickeners, sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.

[0265] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate may further include a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode plate may further include a protective layer covering the surface of the negative electrode film layer.

[0266] The negative electrode sheet can be prepared by dispersing the negative electrode active material, optional negative electrode binder, optional negative electrode conductive agent, and optional other additives in a solvent and stirring uniformly to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and performing drying, cold pressing, and other steps to form the negative electrode sheet. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0267] [Positive electrode]

[0268] In some embodiments, the upper cutoff voltage of the battery cell may be greater than or equal to 4.25 V, and may be 4.30 V to 4.45 V. This may enable the battery cell to have a higher energy density.

[0269] In some embodiments, the positive electrode sheet may include a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two surfaces that are opposite to each other in the thickness direction of the positive electrode current collector, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0270] The positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a layered lithium-containing transition metal oxide.

[0271] In some embodiments, the layered lithium-containing transition metal oxide may include a Ni element. The molar amount of the Ni element may account for more than 70% of the total molar amount of the transition metal elements in the layered lithium-containing transition metal oxide; alternatively, the molar amount of the Ni element may account for more than 80% of the total molar amount of the transition metal elements in the layered lithium-containing transition metal oxide; more alternatively, the molar amount of the Ni element may account for more than 90% of the total molar amount of the transition metal elements in the layered lithium-containing transition metal oxide.

[0272] In some embodiments, the layered lithium-containing transition metal oxide may include Li a Ni b Co c M d O e A f , where 0 < a ≤ 1.2; 0.8 ≤ b < 1; 0 < c < 1; 0 < d < 1; 1 ≤ e ≤ 2; 0 ≤ f ≤ 1; M includes, but is not limited to, one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B; and A includes, but is not limited to, one or more of N, F, S, and Cl. This can further improve the energy density of the battery cell.

[0273] In some embodiments, as an example, the layered lithium-containing transition metal oxide may include but is not limited to LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.80 Co 0.15 Al 0.05 O2、LiNi 0.9 Co 0.06 Mn 0.04 O2、LiNi 0.92 Co 0.06 Mn 0.02 O2、LiNi0.96 Co 0.02 Mn 0.02 One or more of O2.

[0274] Battery cells experience Li intercalation and deintercalation during the charge and discharge process, resulting in different molar Li contents in different discharge states. The molar Li contents listed in this disclosure for positive electrode active materials refer to the initial state of the material, i.e., the state before addition. The molar Li contents of positive electrode active materials used in battery cells will change after charge and discharge cycles. The molar O contents listed in this disclosure for positive electrode active materials are only theoretical values. Lattice oxygen release can cause changes in the molar O content, and the actual molar O content will also fluctuate.

[0275] The higher the content of Ni element in the layered lithium-containing transition metal oxide, the higher the upper charge cutoff voltage of the battery cell is, and the higher the energy density of the battery cell is.

[0276] In some embodiments, the positive electrode active material may include a layered lithium-containing transition metal oxide with a single crystal morphology, or include both a layered lithium-containing transition metal oxide with a single crystal morphology and a layered lithium-containing transition metal oxide with a polycrystalline morphology.

[0277] When the layered lithium-containing transition metal oxide is of the same type and the battery cell has the same upper charge cutoff voltage, the cycling stability of the layered lithium-containing transition metal oxide with a single crystal morphology is higher than that of the layered lithium-containing transition metal oxide with a polycrystalline morphology. When the volume distribution particle size is the same, the specific surface area of ​​the layered lithium-containing transition metal oxide with a single crystal morphology is smaller than that of the layered lithium-containing transition metal oxide with a polycrystalline morphology, thereby reducing side reactions, capacity loss, and gas production. Therefore, the layered lithium-containing transition metal oxide with a single crystal morphology can enable the battery cell to have a higher upper charge cutoff voltage and can also provide high-voltage battery cells with good cycling stability.

[0278] In some embodiments, the volume distribution particle size Dv50 of the positive electrode active material may be less than or equal to 6 μm, and may be 2 μm-5 μm.

[0279] The separator provided in the embodiments of the present disclosure includes a coating comprising nanocellulose and a granular filler on at least one surface of a porous substrate. When the coatings have the same thickness and contain both nanocellulose and a granular filler, the porosity of the separator decreases, thereby affecting ion diffusion and, in turn, the low-temperature performance of the battery cell.

[0280] At low temperatures, the impedance of the battery cell increases, the discharge voltage platform decreases, and the terminal voltage of the battery cell drops rapidly, resulting in a rapid attenuation of the available capacity and power of the battery cell.

[0281] The positive electrode plates provided by the disclosed embodiments utilize positive electrode active materials with a small volume distribution particle size (Dv50). This shortens the diffusion path of lithium ions within the positive electrode active material, thereby rapidly consuming lithium ions transferred from the negative electrode to the positive electrode through the separator. This increases the difference in lithium ion concentration between the negative and positive sides of the separator, increasing the driving force for lithium ion transfer from the negative electrode to the positive electrode, thereby improving the low-temperature performance and cycle performance of the battery cells.

[0282] In some embodiments, the volume distribution particle size Dv90 of the positive electrode active material may be less than or equal to 14 μm, and may be 4.5 μm-13.5 μm, 4.5 μm-11 μm, or 4.4 μm-9.0 μm.

[0283] By further adjusting the volume distribution particle size Dv90 of the positive electrode active material, the diffusion path of lithium ions in the positive electrode active material can be further shortened, thereby further increasing the lithium ion concentration difference between the negative and positive sides of the separator, increasing the driving force for lithium ion transfer from the negative electrode to the positive electrode, and further improving the low-temperature performance of the battery cell. By further adjusting the volume distribution particle size Dv90 of the positive electrode active material, battery side reactions can be reduced and the battery capacity decay rate can be lowered, thereby improving the cycle performance of the battery cell. By further adjusting the volume distribution particle size Dv90 of the positive electrode active material, the positive electrode sheet can also have a higher compaction density, which is also beneficial to improving the energy density of the battery cell.

[0284] In some embodiments, the volume distribution particle size Dv10 of the positive electrode active material may be less than or equal to 3 μm, and may be 1 μm-2 μm, or 1.4 μm-2 μm.

[0285] By further adjusting the volume distribution particle size Dv10 of the positive electrode active material, the battery side reactions can be reduced and the battery capacity decay rate can be lowered, which is beneficial to improving the cycle performance of the battery cell. It can also make the positive electrode sheet have a higher compaction density, which is also beneficial to improving the energy density of the battery cell.

[0286] In some embodiments, the particle size distribution of the positive electrode active material (Dv90-Dv10) / Dv50 may be 0.8-2.5, optionally 1.3-2.3, or 1.3-2.1.

[0287] By further adjusting the particle size distribution (Dv90-Dv10) / Dv50 of the positive electrode active material within the above range, the compaction density of the positive electrode sheet can be increased, the space utilization rate of the positive electrode active material can be improved, and thus the energy density of the battery cell can be increased. By further adjusting the particle size distribution (Dv90-Dv10) / Dv50 of the positive electrode active material within the above range, the contact resistance between the positive electrode active material particles can be reduced, the impedance of the battery cell can be reduced, and thus the low-temperature performance of the battery cell can be improved.

[0288] In some embodiments, the volume distribution particle size Dv50 of the single-crystal layered lithium-containing transition metal oxide may be less than or equal to 5 μm, optionally 2 μm-4 μm, and more optionally 2.3 μm-3.5 μm.

[0289] In some embodiments, the volume distribution particle size Dv90 of the single-crystal layered lithium-containing transition metal oxide may be less than or equal to 10 μm, and may be optionally 4.5 μm-8 μm, and more optionally 4.5 μm-7 μm.

[0290] In some embodiments, the volume distribution particle size Dv10 of the single-crystal layered lithium-containing transition metal oxide may be less than or equal to 3 μm, optionally 1 μm-2 μm, and more optionally 1.4 μm-2 μm.

[0291] The particle size of the layered lithium-containing transition metal oxide with a single crystal morphology is reduced, which can further shorten the diffusion path of lithium ions in the positive electrode active material, so that the positive electrode active material quickly consumes the lithium ions in the electrolyte, thereby further increasing the lithium ion concentration difference between the negative electrode side and the positive electrode side of the separator, increasing the driving force for the transfer of lithium ions from the negative electrode to the positive electrode, and further improving the low-temperature performance of the battery cell; however, the cycle performance of the battery cell will decline to a certain extent.

[0292] By adjusting the volume distribution particle size Dv50, Dv90 and / or Dv10 of the layered lithium-containing transition metal oxide with a single crystal morphology within the above range, it is beneficial for the battery cell to have both good low-temperature performance and good cycle performance.

[0293] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the single-crystalline layered lithium-containing transition metal oxide may be 0.8-2.5, optionally 1.2-1.6, or 1.3-1.5.

[0294] By adjusting the particle size distribution (Dv90-Dv10) / Dv50 of the layered lithium-containing transition metal oxide with a single crystal morphology within the above range, the compaction density of the positive electrode plate can be improved, the space utilization rate of the positive electrode active material can be improved, and thus the energy density of the battery cell can be improved; the contact resistance between the particles of the positive electrode active material can be reduced, the impedance of the battery cell can be reduced, and thus the low-temperature performance of the battery cell can be improved.

[0295] Polycrystalline layered lithium-containing transition metal oxides have a higher lithium-ion diffusion coefficient, better electrolyte wettability, and shorter lithium-ion diffusion paths. Therefore, when the positive electrode active material includes both single-crystalline layered lithium-containing transition metal oxides and polycrystalline layered lithium-containing transition metal oxides, it helps improve the low-temperature performance of the battery cell.

[0296] In some embodiments, the volume distribution particle size Dv50 of the polycrystalline layered lithium-containing transition metal oxide may be 7 μm-12 μm, and optionally 8 μm-10 μm.

[0297] In some embodiments, the volume distribution particle size Dv90 of the polycrystalline layered lithium-containing transition metal oxide may be 12 μm-20 μm, and optionally 13 μm-18 μm.

[0298] In some embodiments, the volume distribution particle size Dv10 of the polycrystalline layered lithium-containing transition metal oxide may be 2 μm-6 μm, and optionally 3 μm-5 μm.

[0299] The particle size of the polycrystalline layered lithium-containing transition metal oxide is reduced, which is beneficial to improving the low-temperature performance of the battery cell; however, the energy density of the battery cell will also decrease to a certain extent, and at the same time, the manufacturing cost of the battery cell will increase significantly.

[0300] By adjusting the volume distribution particle size Dv50, Dv90 and / or Dv10 of the polycrystalline layered lithium-containing transition metal oxide within the above range, the battery cell is advantageously provided with high energy density, good low temperature performance, good cycle performance and low manufacturing cost.

[0301] In some embodiments, the particle size distribution of the polycrystalline layered lithium-containing transition metal oxide may be (Dv90-Dv10) / Dv50 of 1.1-1.5, and optionally 1.2-1.4.

[0302] By adjusting the particle size distribution (Dv90-Dv10) / Dv50 of the polycrystalline layered lithium-containing transition metal oxide within the above range, the compaction density of the positive electrode plate can be improved, the space utilization rate of the positive electrode active material can be improved, and thus the energy density of the battery cell can be improved; the contact resistance between the particles of the positive electrode active material can be reduced, the impedance of the battery cell can be reduced, and thus the low-temperature performance of the battery cell can be improved.

[0303] In some embodiments, the positive electrode film layer may further 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.

[0304] In some embodiments, the positive electrode film layer may further 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), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0305] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0306] The positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional positive electrode conductive agent, optional positive electrode binder, and any other components in a solvent and stirring them uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0307] [Electrolyte]

[0308] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. In some embodiments, the electrolyte may include an electrolyte salt and a solvent.

[0309] In some embodiments, as an example, the electrolyte salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP).

[0310] In some embodiments, as an example, the solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0311] In some embodiments, the electrolyte may further include additives. For example, the additives may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), and vinylene carbonate (VC).

[0312] Optionally, the total mass of the additives may be 0.5 wt%-12 wt% of the total mass of the electrolyte, and optionally 2 wt%-8 wt%.

[0313] The preparation method of battery cells is well known. In some embodiments, the positive electrode sheet, separator, negative electrode sheet and electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator and negative electrode sheet can be made into an electrode assembly, which is placed in an outer package, dried and injected with the above-mentioned electrolyte. After vacuum packaging, standing, formation and other processes, a battery cell is obtained. Multiple battery cells can also be further connected in series, in parallel or in a mixed connection to form a battery module. Multiple battery modules can also be connected in series, in parallel or in a mixed connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0314] The present disclosure also provides an electrical device, which includes a battery provided by the present disclosure. The battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0315] The electrical device can select the type of battery according to its usage requirements, such as a battery cell, a battery module or a battery pack.

[0316] Figure 2 is a schematic diagram of an exemplary electric device. This device can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module can be used.

[0317] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0318] Example

[0319] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0320] The porous substrate and nanocellulose used in the embodiments of the present disclosure can be purchased commercially.

[0321] Example 1

[0322] Preparation of positive electrode

[0323] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive agent acetylene black, and binder polyvinylidene fluoride are mixed in a mass ratio of 94:3:3, and an appropriate amount of solvent NMP is added and stirred evenly to obtain a positive electrode slurry; the positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil, and after drying, cold pressing, and cutting, a positive electrode sheet is obtained. 0.8 Co 0.1 Mn0.1 O2 has a single crystal morphology and a volume distribution particle size Dv50 of 2.5 μm.

[0324] Preparation of negative electrode sheet

[0325] A mixture of artificial graphite and silicon oxide (mass ratio 90:10) of negative electrode active materials, acetylene black as a conductive agent, and styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) as a binder (mass ratio 95:2:2:1) are mixed evenly in an appropriate amount of deionized water as a solvent to obtain a negative electrode slurry; the negative electrode slurry is coated on both surfaces of the negative electrode current collector copper foil, and after drying, cold pressing, and slitting, a negative electrode sheet is obtained.

[0326] Preparation of isolation membrane

[0327] The porous substrate is a PE porous substrate with a thickness of 4 μm, a puncture strength of 450 gf, a longitudinal heat shrinkage rate of 2.0% at 105° C. / 1 h, and a transverse heat shrinkage rate of 1.5% at 105° C. / 1 h.

[0328] Nanocellulose, a first component with a secondary particle morphology, a second component with a primary particle morphology, and a binder polyacrylic acid are mixed uniformly in an appropriate amount of solvent deionized water in a mass ratio of 20:55:23:2 to obtain a coating slurry. The average length of the nanocellulose is 420nm, the average diameter is 24nm, and the aspect ratio is 17.5. The first component with a secondary particle morphology adopts alumina with a secondary particle morphology, and the volume distribution particle size Dv50 is 150nm. The contents of α crystal form, θ crystal form, γ crystal form and η crystal form in the alumina are 1.1wt%, 68.7wt%, 29.6wt% and 0.6wt%, respectively, based on the total mass of the alumina. The second component with a primary particle morphology adopts alumina with a primary particle morphology, and the volume distribution particle size Dv50 is 350nm. The crystal form of the alumina is mainly α crystal form, and the content is more than 99wt%, based on the total mass of the alumina.

[0329] Vinylidene fluoride monomer (VDF) homopolymer particles, polymethyl methacrylate, dispersant sodium carboxymethyl cellulose (CMC) and surfactant were uniformly mixed in an appropriate amount of solvent deionized water at a mass ratio of 87:8:3:2 to obtain an adhesive layer slurry.

[0330] The prepared coating slurry is coated on both surfaces of the PE porous substrate by micro-gravure method, and after drying, the adhesive layer slurry is coated on the coating, and then the isolation film is obtained through drying and slitting processes.

[0331] Preparation of electrolyte

[0332] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 20:80 to obtain an organic solvent. Fully dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L. Fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) were then added. The mass content of FEC was 3 wt% of the total mass of the electrolyte, and the mass content of PS was 0.5 wt% of the total mass of the electrolyte.

[0333] Battery preparation

[0334] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in sequence to form an electrode assembly. The electrode assembly is then placed in an aluminum casing, dried, and then filled with electrolyte. After vacuum packaging, standing, forming, and shaping, the battery is completed. The battery measures 28.5mm × 148mm × 97.5mm.

[0335] In the prepared battery, the coating thickness on one side of the PE porous substrate was 0.75 μm, with a total coating thickness of 1.5 μm. The adhesive layer on the coating was 0.5 μm thick, and the total adhesive layer thickness in the separator was 1 μm. The separator had a total thickness of 6.5 μm and a width of 91.0 mm. The negative electrode sheet was 88.0 mm wide, and the positive electrode sheet was 84.0 mm wide.

[0336] Example 2

[0337] The battery was prepared using a method similar to that of Example 1, except that the width of the negative electrode sheet was 87.2 mm and the width of the positive electrode sheet was 83.2 mm.

[0338] Example 3

[0339] The battery was prepared using a method similar to that of Example 1, except that the width of the negative electrode sheet was 89.0 mm and the width of the positive electrode sheet was 85.0 mm.

[0340] Example 4

[0341] The battery was prepared using a method similar to that of Example 1, except that the width of the negative electrode sheet was 86.0 mm and the width of the positive electrode sheet was 82.0 mm.

[0342] Example 5

[0343] The preparation method of the battery is similar to that of Example 1 except for the following differences.

[0344] The porous substrate is a PE porous substrate with a thickness of 5 μm, a puncture strength of 420 gf, a longitudinal heat shrinkage rate of 2.5% at 105° C. / 1 h, and a transverse heat shrinkage rate of 1.8% at 105° C. / 1 h.

[0345] In the prepared battery, the coating thickness on one side of the PE porous substrate was 0.75 μm, with a total coating thickness of 1.5 μm. The adhesive layer on the coating was 0.5 μm thick, and the total adhesive layer thickness in the separator was 1 μm. The separator had a total thickness of 7.5 μm and a width of 91.0 mm. The width of the negative electrode sheet was 88.0 mm, and the width of the positive electrode sheet was 84.0 mm.

[0346] Example 6

[0347] The preparation method of the battery is similar to that of Example 1 except for the following differences.

[0348] The porous substrate is a PE porous substrate with a thickness of 5 μm, a puncture strength of 380 gf, a longitudinal heat shrinkage rate of 2.8% at 105° C. / 1 h, and a transverse heat shrinkage rate of 2.1% at 105° C. / 1 h.

[0349] In the prepared battery, the coating thickness on one side of the PE porous substrate was 0.75 μm, with a total coating thickness of 1.5 μm. The adhesive layer on the coating was 0.5 μm thick, and the total adhesive layer thickness in the separator was 1 μm. The separator had a total thickness of 7.5 μm and a width of 91.0 mm. The width of the negative electrode sheet was 88.0 mm, and the width of the positive electrode sheet was 84.0 mm.

[0350] Comparative Example 1

[0351] The battery was prepared using a method similar to that of Example 1, except that the width of the negative electrode sheet was 84.0 mm and the width of the positive electrode sheet was 80.0 mm.

[0352] Comparative Example 2

[0353] The preparation method of the battery is similar to that of Example 1 except for the following differences.

[0354] The porous substrate is a PE porous substrate with a thickness of 5 μm, a puncture strength of 420 gf, a longitudinal heat shrinkage rate of 2.5% at 105° C. / 1 h, and a transverse heat shrinkage rate of 1.8% at 105° C. / 1 h.

[0355] Alumina and a binder, polyacrylic acid, were mixed uniformly in a suitable amount of deionized water in a mass ratio of 94:6 to form a coating slurry. The alumina had a primary particle morphology and a volume distribution particle size (Dv50) of 800 nm. The alumina was primarily α-crystalline, with the α-crystalline accounting for more than 99% by weight based on the total mass of the alumina.

[0356] Vinylidene fluoride monomer (VDF) homopolymer particles, polymethyl methacrylate, dispersant sodium carboxymethyl cellulose (CMC) and surfactant were uniformly mixed in an appropriate amount of solvent deionized water at a mass ratio of 87:8:3:2 to obtain an adhesive layer slurry.

[0357] The prepared coating slurry is coated on both surfaces of the PE porous substrate by a coating machine, and after drying, the adhesive layer slurry is coated on the coating layer, and then the isolation film is obtained through drying and slitting processes.

[0358] In the prepared battery, the coating thickness on one side of the PE porous substrate was 1.5 μm, with a total coating thickness of 3 μm. The adhesive layer on the coating was 0.5 μm thick, and the total adhesive layer thickness in the separator was 1.0 μm. The separator had a total thickness of 9 μm and a width of 91.0 mm. The negative electrode tab was 84.0 mm wide, and the positive electrode tab was 80.0 mm wide.

[0359] Comparative Example 3

[0360] The battery was prepared using a method similar to that of Comparative Example 2, except that the width of the negative electrode sheet was 88.0 mm and the width of the positive electrode sheet was 84.0 mm.

[0361] Test section

[0362] (1) Puncture strength test of porous substrates

[0363] Use a blade to cut the sample. The length and width of the sample must be greater than 64mm. After checking that the high-speed rail tensile testing machine is clean, install the puncture fixture, place the sample in the center of the fixture, and cover it with the upper cover. On the computer operation panel of the high-speed rail tensile testing machine, set the test to "sample compression" and the speed to 50mm / min. Click "Start" and perform the puncture test in sequence, and save the force-displacement curve. Each group should be tested at least three times in parallel. If there are three force-displacement curves with good repeatability, proceed to the next group of tests. For accuracy, the average value of 5 parallel samples can be taken as the test result.

[0364] (2) Thermal shrinkage test of porous substrate and isolation film

[0365] Take a 100mm*50mm die and use a punching machine to punch out the sample into 100mm*50mm samples. Mark the number of the punched 100mm*50mm sample with a marker in the lower right corner and measure it before baking under the second dimension. Set the baking temperature and time. After the oven reaches the set temperature, put the sample together with the steel plate into the oven for baking. Take it out after the specified baking time and let it stand for 10 minutes. Measure the transverse and longitudinal dimensions of the sample with the same number after baking. The transverse dimension is recorded as X2 and the longitudinal dimension is recorded as Y2. The longitudinal heat shrinkage rate = (100-Y2) / 100*100%, and the transverse heat shrinkage rate = (50-X2) / 50*100%. If the shrinkage of the sample edge is uneven, the maximum shrinkage position shall prevail. For accuracy, the average value of 5 parallel samples can be taken as the test result.

[0366] When testing the thermal shrinkage of the porous substrate, the oven temperature was set to 105°C and the time was 1 hour.

[0367] When testing the thermal shrinkage of the isolation film, the oven temperature was set to 150°C and the time was 1 hour.

[0368] (3) Hot box performance test of batteries

[0369] At 25°C, the batteries were charged at a constant current of 1C to 4.25V. They were then charged at a constant voltage until the current was less than or equal to 0.05C and allowed to rest for 5 minutes. Each battery was then tested in a DHG-9070ADHG series high-temperature oven with a fixture, heating the temperature from 25°C to 60°C ± 2°C at a rate of 5°C / min and holding for 30 minutes. The temperature was then increased at a rate of 5°C / min, with each 5°C increase lasting 30 minutes. The hot-box temperature at failure and the holding time were recorded. A higher hot-box failure temperature indicates better thermal stability. For batteries with the same hot-box failure temperature, a longer holding time indicates better thermal stability. For accuracy, the average of five replicate samples can be used as the test result.

[0370] (4) Battery volume energy density test

[0371] At 25°C, charge the battery at a constant current of 0.33C to 4.25V. Continue charging at a constant voltage until the current is less than or equal to 0.05C. After standing for 5 minutes, discharge the battery at 0.33C to 2.8V to obtain the discharge energy Q. The volumetric energy density of the battery (Wh / L) = discharge energy Q / battery volume V. For accuracy, the average of two parallel samples can be used as the test result.

[0372] (5) Battery process quality test

[0373] 1,000 batteries were produced and subjected to a Hi-pot test. During the test, the wound electrode assembly was hot-pressed at 90°C and 7 MPa for 15 seconds. After hot-pressing, a Hioki resistance meter was used to apply 100V between the positive and negative tabs of the electrode assembly and measure the resistance. If the resistance is <2MΩ, the battery is considered a Hi-pot defective product; otherwise, it passes the Hi-pot test. The number of batteries that passed the Hi-pot test was counted and its percentage of the total number of batteries was calculated.

[0374] Table 1 shows the test results of the porous substrates and separators of Examples 1 to 6 and Comparative Examples 1 to 3.

[0375] Table 2 shows the battery test results of Examples 1 to 6 and Comparative Examples 1 to 3.

[0376] Table 1

[0377] It can be seen from the test results in Table 1 that the isolation film provided by the embodiments of the present disclosure can have both low thickness and low thermal shrinkage.

[0378] Table 2

[0379] It can be seen from the test results of Examples 1 to 6 and Comparative Examples 1 to 3 that by using a specific isolation film coating and making the difference in width between the isolation film and the negative electrode plate less than or equal to 5 mm, the battery can have high thermal stability while having high process efficiency and high volume energy density.

[0380] In Comparative Examples 1 and 2, the difference in width between the isolation membrane and the negative electrode plate is large, and the probability of local redundancy, folding or breakage of the isolation membrane during battery assembly is high, thereby affecting the process efficiency of the battery.

[0381] It can be seen from the test results of Comparative Examples 2 to 3 that ordinary ceramic separators have poor heat resistance. On this basis, reducing the difference in width between the separator and the negative electrode plate will lead to a deterioration in the battery process quality rate and a significant reduction in the Hi-pot test pass rate.

[0382] It can also be seen from the test results of Comparative Examples 2 to 3 that simply by increasing the width difference between the ordinary ceramic isolation membrane and the negative electrode plate, the risk of battery short circuit can be reduced and the battery's hot box failure temperature can be increased to a certain extent, but the degree of improvement is limited, and the battery's process quality rate is also poor.

[0383] From the test results of Example 1, Example 5 and Example 6, it can be seen that, under the premise of thin thickness, a battery using a porous substrate with higher puncture strength and lower thermal shrinkage can have a better process efficiency.

[0384] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A battery cell, comprising a negative electrode plate and a separator, wherein: The isolation membrane comprises a porous substrate and a coating disposed on at least one surface of the porous substrate, wherein the coating comprises nanocellulose and a granular filler; The width of the isolation film is recorded as A, and the width of the negative electrode plate is recorded as B, both in units of mm, 0<AB≤5mm.

2. The battery cell according to claim 1, wherein: 2mm≤AB≤4mm, optionally, 2.5mm≤AB≤3.5mm.

3. The battery cell according to any one of claims 1 to 2, wherein: The nanocellulose satisfies one or more of the following conditions (1) to (5): (1) The average length of the nanocellulose is 100nm-1200nm, and can be optionally 200nm-1000nm; (2) The average diameter of the nanocellulose is 11 nm-40 nm, and can be 15 nm-32 nm; (3) The aspect ratio of the nanocellulose is 5-60, and can be 12-35; (4) the nanocellulose includes a modified group, wherein the modified group includes at least one of an amine group, a carboxyl group, an aldehyde group, a sulfonic acid group or a phosphoric acid group, and optionally includes at least one of a sulfonic acid group or a phosphoric acid group; (5) The nanocellulose includes hydroxyl groups and modified groups, and the molar ratio of the modified groups to the hydroxyl groups is 1:4 to 4:1, and can be optionally 2:3 to 7:

3.

4. The battery cell according to any one of claims 1 to 3, wherein: The mass content of the nanocellulose in the coating is 5wt%-60wt%, optionally 7wt%-45wt%; and / or, The mass content of the granular filler in the coating is greater than 38wt%, and can be optionally 53wt%-91wt%.

5. The battery cell according to any one of claims 1 to 4, wherein: The porous substrate satisfies one or more of the following conditions (1) to (9): (1) The thickness of the porous substrate is less than or equal to 5 μm, and can be 3 μm-4.5 μm; (2) The average pore size of the porous substrate is 10 nm-60 nm, and can be 20 nm-40 nm; (3) The porosity of the porous substrate is 20%-60%, and can be 30%-50%; (4) The material of the porous substrate includes polyolefin, and may optionally include polyethylene; (5) The puncture strength of the porous substrate is greater than or equal to 390 gf, and can be 400 gf-480 gf; (6) The longitudinal heat shrinkage rate of the porous substrate at 105°C for 1 hour is less than 3%, and can be selected from 1% to 2.5%; (7) The transverse heat shrinkage of the porous substrate at 105°C for 1 hour is less than 2%, and can be selected from 1% to 1.8%; (8) The longitudinal tensile strength of the porous substrate is greater than or equal to 2700 kgf / cm 2 , optional 2800kgf / cm 2 -3500kgf / cm 2 ; (9) The transverse tensile strength of the porous substrate is greater than or equal to 2500 kgf / cm 2 , optional 2600kgf / cm 2 -3200kgf / cm 2 .

6. The battery cell according to any one of claims 1 to 5, wherein: The granular filler includes one or more of organic particles, inorganic particles, and organic-inorganic composite materials.

7. The battery cell according to claim 6, wherein: The granular filler includes a first component in the form of secondary particles and a second component in the form of primary particles.

8. The battery cell according to claim 7, wherein: The average particle size of the first component of the secondary particle morphology is smaller than the average particle size of the second component of the primary particle morphology.

9. The battery cell according to any one of claims 7 to 8, wherein: The average particle size of the first component of the secondary particle morphology is less than 200 nm, and can be 80 nm-180 nm; and / or, The average particle size of the second component of the primary particle morphology is 200nm-600nm, and can be optionally 300nm-500nm.

10. The battery cell according to any one of claims 7 to 9, wherein: The particle size of the primary particles in the first component constituting the secondary particle morphology is 15nm-45nm, and can be optionally 20nm-35nm.

11. The battery cell according to any one of claims 7 to 10, wherein: The specific surface area of ​​the first component of the secondary particle morphology is greater than the specific surface area of ​​the second component of the primary particle morphology.

12. The battery cell according to any one of claims 7 to 11, wherein: The specific surface area of ​​the first component of the secondary particle morphology is greater than 20m 2 / g, optional 30m 2 / g-80m 2 / g; and / or, The specific surface area of ​​the second component of the primary particle morphology is less than or equal to 20m 2 / g, optional 5m 2 / g-15m 2 / g.

13. The battery cell according to any one of claims 7 to 12, wherein: The mass content of the first component of the secondary particle morphology in the coating is greater than the mass content of the second component of the primary particle morphology in the coating.

14. The battery cell according to any one of claims 7 to 13, wherein: The mass content of the first component of the secondary particle morphology in the coating is 10wt%-85wt%, and can be optionally 20wt%-75wt%; and / or, The mass content of the second component in the primary particle morphology in the coating is 5wt%-70wt%, and can be optionally 7wt%-60wt%.

15. The battery cell according to any one of claims 1 to 14, wherein: The coating also includes a non-particulate binder; Optionally, the content of the non-granular binder in the coating is less than or equal to 3 wt %, based on the total mass of the coating.

16. The battery cell according to any one of claims 1 to 15, wherein: The isolation film further comprises an adhesive layer, which is disposed on at least a portion of the surface of the coating. Optionally, the bonding layer comprises a granular binder; Optionally, the binder includes at least one of an acrylate monomer homopolymer or copolymer, an acrylic acid monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer.

17. The battery cell according to any one of claims 1 to 16, wherein: The coating has a thickness of 0.2 μm-2 μm, and optionally 0.4 μm-1 μm; and / or, The total thickness of the isolation film is 4 μm-10 μm, and can be 4.5 μm-8.5 μm; and / or, The longitudinal heat shrinkage rate of the isolation film at 150° C. for 1 hour is less than or equal to 3%; and / or, The isolation film has a transverse heat shrinkage rate of less than or equal to 2% at 150° C. for 1 hour.

18. The battery cell according to any one of claims 1 to 17, wherein: The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a carbon material; optionally, the carbon material includes one or more of artificial graphite and natural graphite.

19. The battery cell according to any one of claims 1 to 18, wherein: The negative electrode plate comprises a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, and the negative electrode active material comprises a silicon-based material; Optionally, the silicon-based material further comprises one or more of alkali metal elements and alkaline earth metal elements, and may optionally comprise one or more of Li and Mg; and / or, Optionally, the mass proportion of the silicon-based material in the negative electrode active material is greater than or equal to 5wt%, and can be optionally 8wt%-20wt%.

20. The battery cell according to any one of claims 1 to 19, wherein: The upper cut-off voltage of the battery cell is greater than or equal to 4.25V, and can be selected to be 4.30V-4.45V.

21. The battery cell according to any one of claims 1 to 20, wherein: The battery cell also includes a positive electrode plate, which includes a positive electrode collector and a positive electrode film layer arranged on at least one surface of the positive electrode collector, the positive electrode film layer includes a positive electrode active material, the positive electrode active material includes a layered lithium-containing transition metal oxide, and the volume distribution particle size Dv50 of the positive electrode active material is less than or equal to 6μm, and can be optionally 2μm-5μm.

22. The battery cell according to claim 21, wherein: The positive electrode active material further satisfies one or more of the following conditions (1) to (3): (1) The volume distribution particle size Dv90 of the positive electrode active material is less than or equal to 14 μm, and can be optionally 4.5 μm-13.5 μm; (2) The volume distribution particle size Dv10 of the positive electrode active material is less than or equal to 3 μm, and can be optionally 1 μm-2 μm; (3) The particle size distribution of the positive electrode active material (Dv90-Dv10) / Dv50 is 0.8-2.5, and can be optionally 1.3-2.

3.

23. The battery cell according to any one of claims 21 to 22, wherein: The positive electrode active material includes a layered lithium-containing transition metal oxide in a single crystal morphology, or includes both a layered lithium-containing transition metal oxide in a single crystal morphology and a layered lithium-containing transition metal oxide in a polycrystalline morphology.

24. The battery cell according to claim 23, wherein: The single-crystal layered lithium-containing transition metal oxide satisfies one or more of the following conditions (1) to (4): (1) The volume distribution particle size Dv50 of the single crystal layered lithium-containing transition metal oxide is less than or equal to 5 μm, and can be 2 μm-4 μm; (2) The volume distribution particle size Dv90 of the single crystal layered lithium-containing transition metal oxide is less than or equal to 10 μm, and can be selected to be 4.5 μm-8 μm; (3) The volume distribution particle size Dv10 of the single crystal layered lithium-containing transition metal oxide is less than or equal to 3 μm, and can be 1 μm-2 μm; (4) The particle size distribution (Dv90-Dv10) / Dv50 of the single crystal layered lithium-containing transition metal oxide is 0.8-2.5, and can be optionally 1.3-1.

5.

25. The battery cell according to any one of claims 23 to 24, wherein: The polycrystalline layered lithium-containing transition metal oxide satisfies one or more of the following conditions (1) to (4): (1) The volume distribution particle size Dv50 of the polycrystalline layered lithium-containing transition metal oxide is 7 μm-12 μm, and can be 8 μm-10 μm; (2) The volume distribution particle size Dv90 of the polycrystalline layered lithium-containing transition metal oxide is 12 μm-20 μm, and can be 13 μm-18 μm; (3) The volume distribution particle size Dv10 of the polycrystalline layered lithium-containing transition metal oxide is 2 μm-6 μm, and can be 3 μm-5 μm; (4) The particle size distribution (Dv90-Dv10) / Dv50 of the polycrystalline layered lithium-containing transition metal oxide is 1.1-1.5, and can be optionally 1.2-1.

4.

26. A battery comprising the battery cell according to any one of claims 1 to 25.

27. An electrical device comprising the battery according to claim 26.

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