Secondary battery, electrical device, and liquid-retaining material

Abstract

The present disclosure provides a secondary battery, an electrical device, and a liquid-retaining material. The secondary battery comprises a liquid-retaining material and an electrolyte. The liquid-retaining material comprises a crosslinked polymer. The swelling ratio of the crosslinked polymer is 4-13, and the centrifugal electrolyte amount of the crosslinked polymer is 0.37-0.63 g / Ah. The electrolyte comprises an electrolyte in a gel and a liquid electrolyte. The secondary battery has improved liquid retention capacity, thereby reducing the likelihood of lithium plating in the battery and improving the cycling performance of the battery.

Description

Secondary batteries, electrical devices and liquid retention materials

[0001] Cross-references to related applications

[0002] This disclosure is based on and claims priority to Chinese Patent Application No. 202411029139.9, filed on July 29, 2024, entitled “Secondary Battery, Electrical Device and Liquid Retention Material”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of battery technology, and in particular to a secondary battery, an electrical device, and a liquid-retaining material. Background Technology

[0004] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, and many other fields. During use, batteries experience electrolyte consumption and localized drying, leading to shortened cycle life. Therefore, improving electrolyte retention is crucial for enhancing battery cycle performance. Summary of the Invention

[0005] This disclosure was made in view of the aforementioned problems, and its object is to provide a secondary battery, an electrical device, and a liquid-retaining material. This secondary battery has improved liquid-retaining capacity, thereby reducing the possibility of lithium plating and improving the battery's cycle performance.

[0006] To achieve the above objectives, the first aspect of this disclosure provides a secondary battery. The secondary battery includes a liquid-retaining material and an electrolyte. The liquid-retaining material includes a cross-linked polymer with a swelling ratio of 4 to 13 and a centrifugation electrolyte volume of 0.37 to 0.63 g / Ah. The electrolyte includes an electrolyte in a gel and a liquid electrolyte.

[0007] Because the cross-linked polymers in electrolyte-retaining materials have improved adsorption and retention capabilities for electrolyte, they can swell to form a jelly-like gel, binding the electrolyte within the gel. Furthermore, the electrolyte adsorbed within the gel can resist the compressive effects of gravity and expansion forces. Therefore, electrolyte-retaining materials possess improved electrolyte adsorption and retention capabilities, thereby enhancing the cycle performance of secondary batteries and reducing the risk of lithium plating.

[0008] In some embodiments, the group margin in the thickness direction of the secondary battery is 88% to 94%. This increases the proportion of energy storage material in the battery, which is beneficial for improving the battery's energy density.

[0009] In some embodiments, the secondary battery includes cells with tabs distributed on opposite sides. This allows for optimization of the system and structure, which is beneficial for improving the battery's energy density.

[0010] In some embodiments, the positive electrode active material of the secondary battery includes lithium transition metal oxide, and the ratio of the total electrolyte mass to the battery capacity is 2.0–3.0 g / Ah. This increases the proportion of energy storage material in the battery, which is beneficial for improving the battery's energy density.

[0011] In some embodiments, the lithium transition metal oxide includes nickel, wherein the molar content of nickel in the lithium transition metal oxide is more than 80% relative to all metal elements other than lithium; the negative electrode active material of the secondary battery includes graphite and / or silicon-based negative electrode materials. This improves the specific capacity of both the positive and negative electrode active materials, which is beneficial for increasing the energy density of the battery.

[0012] In some embodiments, the positive electrode active material of the secondary battery includes lithium phosphate, and the ratio of the total electrolyte mass to the battery capacity is 3.0–5.0 g / Ah. This increases the proportion of energy storage material in the battery, which is beneficial for improving the battery's energy density.

[0013] In some embodiments, the degree of crosslinking of the crosslinked polymer is 60% to 90%. This is beneficial for balancing the crosslinked polymer's ability to adsorb electrolyte and resist the squeezing effects of gravity and expansion forces.

[0014] In some embodiments, the crosslinked polymer includes structural units represented by formula (I), structural units represented by formula (II), and structural units derived from the crosslinking agent.

[0015] R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted 6- to 10-membered aryl, substituted or unsubstituted 5- to 10-membered heteroaryl, substituted or unsubstituted 3- to 8-membered cycloalkyl or heterocycloalkyl; when C1- to C10 alkyl, C1- to C10 alkoxy, C2- to C10 alkenyl, 6- to 10-membered aryl, 5- to 10-membered heteroaryl, 3- to 8-membered cycloalkyl or heterocycloalkyl has... When substituents are present, each substituent independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1-C10 alkyl, and 6- to 10-aryl groups; R8 is selected from substituted or unsubstituted C1- to C10 alkyl, substituted or unsubstituted 6- to 10-aryl, and substituted or unsubstituted C2- to C10 alkenyl groups; when C1- to C10 alkyl, 6- to 10-aryl, and C2- to C10 alkenyl groups have substituents, each substituent independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1- to C10 alkyl, and 6- to 10-aryl groups; and R9 is a linking bond or a C1- to C6 alkylene group. The crosslinked polymers with the above structures have improved affinity for electrolytes, which is more beneficial for balancing the electrolyte adsorption and retention capabilities of electrolyte-retaining materials.

[0016] In some embodiments, in formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester, unsubstituted C1-C10 alkyl, and unsubstituted C1-C10 alkoxy groups. This further improves the affinity for the electrolyte.

[0017] In some embodiments, in formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, carboxyl, ester, or unsubstituted C1-C6 alkyl groups; R8 is selected from unsubstituted C1-C6 alkyl groups; and R9 is a linking bond or a methylene group. This further improves the affinity for the electrolyte.

[0018] In some embodiments, in formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen and unsubstituted C1-C4 alkyl groups; R8 is selected from unsubstituted C1-C4 alkyl groups; and R9 is a linking bond. This further improves the affinity for the electrolyte.

[0019] In some embodiments, the mass percentage of the structural unit shown in formula (II) is 75% to 92% relative to the total mass of the structural units shown in formula (I) and formula (II) in the crosslinked polymer. This further improves the affinity for the electrolyte.

[0020] In some embodiments, the crosslinking agent includes one or more compounds containing at least two unsaturated double bonds or organic peroxides. The crosslinking agent can enhance the strength of the crosslinked polymer, further improving its resistance to compression forces such as gravity and expansion, and the crosslinked polymer chains form a network structure, further enhancing its adsorption capacity for electrolytes.

[0021] In some embodiments, the crosslinking agent includes one or more of divinylbenzene, diallyl phthalate, diethylene glycol diacrylate, tetraethylene glycol dimethacrylate, dicumyl peroxide, benzoyl peroxide, and di-tert-butyl peroxide. The crosslinking agent is more conducive to forming a suitable crosslinking structure to achieve a balance between the ability to adsorb electrolyte and the ability to retain electrolyte.

[0022] In some embodiments, the mass percentage of the structural units derived from the crosslinking agent is 2% to 10% relative to the total mass of the structural units shown in formula (I) and formula (II) in the crosslinked polymer. This is more conducive to forming a crosslinked structure with a suitable degree of crosslinking.

[0023] In some embodiments, the crosslinked polymer includes a divinylbenzene-crosslinked ethylene-vinyl acetate copolymer. Ethylene-vinyl acetate copolymers have strong film-forming properties and, after being crosslinked with divinylbenzene, can effectively resist compressive forces such as gravity and expansion.

[0024] In some embodiments, the secondary battery includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. A liquid-retaining material is included in the negative electrode film layer. After adding the liquid-retaining material to the negative electrode slurry and dispersing it sufficiently, a liquid-retaining system can be formed on the graphite surface and in the stacking gaps through a drying process, which can fully adsorb and retain the electrolyte.

[0025] In some embodiments, the liquid-retaining material in the negative electrode film layer has a mass percentage of 0.5% to 3% based on solid content.

[0026] A second aspect of this disclosure provides an electrical device including a secondary battery as described in the first aspect of this disclosure.

[0027] The electrical device disclosed herein includes the secondary battery provided herein, and therefore has at least the same advantages as a secondary battery.

[0028] A third aspect of this disclosure provides a liquid-retaining material. The liquid-retaining material comprises a cross-linked polymer, the cross-linked polymer having a swelling ratio of 4 to 13, and the cross-linked polymer having a centrifugal electrolyte volume of 0.37 to 0.63 g / Ah.

[0029] Because the cross-linked polymers in the electrolyte-retaining material have improved electrolyte adsorption capacity, they can swell to form a jelly-like gel, binding the electrolyte within the gel. Furthermore, the electrolyte adsorbed in the gel can resist the squeezing effects of gravity and expansion forces. Therefore, the electrolyte-retaining material has an improved ability to retain electrolyte, thereby improving the cycle performance of the secondary battery.

[0030] In some embodiments, the degree of crosslinking of the crosslinked polymer is 60% to 90%. This is beneficial for balancing the crosslinked polymer's ability to adsorb electrolyte and resist the squeezing effects of gravity and expansion forces.

[0031] In some embodiments, the crosslinked polymer includes structural units represented by formula (I), structural units represented by formula (II), and structural units derived from the crosslinking agent.

[0032] R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted 6- to 10-membered aryl, substituted or unsubstituted 5- to 10-membered heteroaryl, substituted or unsubstituted 3- to 8-membered cycloalkyl or heterocycloalkyl; when C1- to C10 alkyl, C1- to C10 alkoxy, C2- to C10 alkenyl, 6- to 10-membered aryl, 5- to 10-membered heteroaryl, 3- to 8-membered cycloalkyl or heterocycloalkyl has... When substituents are present, each substituent independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1-C10 alkyl, and 6- to 10-aryl groups; R8 is selected from substituted or unsubstituted C1- to C10 alkyl, substituted or unsubstituted 6- to 10-aryl, and substituted or unsubstituted C2- to C10 alkenyl groups; when C1- to C10 alkyl, 6- to 10-aryl, and C2- to C10 alkenyl groups have substituents, each substituent independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1- to C10 alkyl, and 6- to 10-aryl groups; and R9 is a linking bond or a C1- to C6 alkylene group. The crosslinked polymers with the above structures have improved affinity for electrolytes, which is more beneficial for balancing the electrolyte adsorption and retention capabilities of electrolyte-retaining materials.

[0033] In some embodiments, in formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester, unsubstituted C1-C10 alkyl, and unsubstituted C1-C10 alkoxy groups. This further improves the affinity for the electrolyte.

[0034] In some embodiments, in formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, carboxyl, ester, or unsubstituted C1-C6 alkyl groups; R8 is selected from unsubstituted C1-C6 alkyl groups; and R9 is a linking bond or a methylene group. This further improves the affinity for the electrolyte.

[0035] In some embodiments, in formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen and unsubstituted C1-C4 alkyl groups; R8 is selected from unsubstituted C1-C4 alkyl groups; and R9 is a linking bond. This further improves the affinity for the electrolyte.

[0036] In some embodiments, the mass percentage of the structural unit shown in formula (II) is 75% to 92% relative to the total mass of the structural units shown in formula (I) and formula (II) in the crosslinked polymer. This further improves the affinity for the electrolyte.

[0037] In some embodiments, the crosslinking agent includes one or more compounds containing at least two unsaturated double bonds or organic peroxides. The crosslinking agent can enhance the strength of the crosslinked polymer, further improving its resistance to compression forces such as gravity and expansion, and the crosslinked polymer chains form a network structure, further enhancing its adsorption capacity for electrolytes.

[0038] In some embodiments, the crosslinking agent includes one or more of divinylbenzene, diallyl phthalate, diethylene glycol diacrylate, tetraethylene glycol dimethacrylate, dicumyl peroxide, benzoyl peroxide, and di-tert-butyl peroxide. The crosslinking agent is more conducive to forming a suitable crosslinking structure to achieve a balance between the ability to adsorb electrolyte and the ability to retain electrolyte.

[0039] In some embodiments, the mass percentage of the structural units derived from the crosslinking agent is 2% to 10% relative to the total mass of the structural units shown in formula (I) and formula (II) in the crosslinked polymer. This is more conducive to forming a crosslinked structure with a suitable degree of crosslinking.

[0040] In some embodiments, the crosslinked polymer includes a divinylbenzene-crosslinked ethylene-vinyl acetate copolymer. Ethylene-vinyl acetate copolymers have strong film-forming properties and, after being crosslinked with divinylbenzene, can effectively resist compressive forces such as gravity and expansion.

[0041] This invention provides a secondary battery that uses a liquid-retaining material in the secondary battery. The cross-linked polymer in the liquid-retaining material has an improved ability to adsorb and retain electrolyte. The cross-linked polymer can swell to form a jelly-like gel, so that the total electrolyte includes not only the liquid electrolyte but also the electrolyte in the gel. This results in improved cycle performance and reduced lithium plating risk of the secondary battery. Attached Figure Description

[0042] Figure 1 illustrates an exemplary battery structure with tabs distributed on opposite sides.

[0043] Figure 2 is a schematic diagram of a battery cell according to one embodiment of the present disclosure.

[0044] Figure 3 is an exploded view of a battery cell according to an embodiment of the present disclosure shown in Figure 2.

[0045] Figure 4 is a schematic diagram of a battery module according to one embodiment of the present disclosure.

[0046] Figure 5 is a schematic diagram of a battery pack according to one embodiment of the present disclosure.

[0047] Figure 6 is an exploded view of a battery pack according to an embodiment of the present disclosure, as shown in Figure 5.

[0048] Figure 7 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present disclosure.

[0049] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly; 54 Tab; 55 Terminal post; 56 Upper corner area. Detailed Implementation

[0050] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the secondary battery, power-consuming device, and liquid-retaining material of this disclosure. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this disclosure and are not intended to limit the subject matter of the claims.

[0051] The "range" disclosed in this disclosure is defined by a lower limit and an upper limit, whereby a given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way, unless otherwise stated, include endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is also expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this disclosure, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0053] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions.

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

[0055] Unless otherwise specified, the terminology used in this disclosure has the common meaning as commonly understood by those skilled in the art.

[0056] Unless otherwise specified, the values ​​of the parameters mentioned in this disclosure can be determined using various test methods commonly used in the art, for example, according to the test methods given in this disclosure.

[0057] Unless otherwise specified, in this disclosure, the term "active ion" refers to ions that can be inserted and extracted back and forth between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions.

[0058] The term "alkyl" includes both branched and straight-chain saturated aliphatic hydrocarbon groups and has a specified number of carbon atoms, for example, 1 to 12 carbon atoms. As used herein, the term "C1-C10 alkyl" refers to an alkyl group having 1 to 10 carbon atoms, such as C1-C8, C1-C6, or C1-C4 alkyl. Examples of alkyl groups include, but are not limited to: methyl, ethyl, n-propyl, isopropyl, n-butyl, 3-methylbutyl, tert-butyl, n-pentyl, sec-pentyl, hexyl, heptyl, octyl, isooctyl, nonyl, and decyl.

[0059] The term "alkylene" refers to a divalent alkyl group having two bonding points. Preferably, it contains 1-6 carbon atoms.

[0060] The term "alkoxy" refers to an alkyl group as defined above having a specified number of carbon atoms connected by oxygen bridges. As used herein, the term "C1–C10 alkoxy" refers to an alkyl group having 1 to 10 carbon atoms connected by oxygen bridges, such as C1–C8, C1–C6, or C1–C4 alkoxy groups. Examples of alkoxy groups include, but are not limited to, methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy, octoxy, nonoxy, decoxy, 3-hexoxy, and 3-methylpentoxy.

[0061] The term "alkenyl" refers to a straight-chain or branched hydrocarbon chain comprising one or more unsaturated carbon-carbon double bonds, which can occur at any stable point along the chain. For example, "C2–C10 alkenyl" as used herein has 2 to 10 carbon atoms. Optionally, alkenyl is a lower alkenyl group having 2 to 8 carbon atoms, such as C2–C8, C2–C6, and C2–C4 alkenyl groups. Examples of alkenyl groups include, but are not limited to, vinyl, propenyl, and butenyl groups.

[0062] The term "aryl" refers to an aromatic group that has one or more rings formed by a skeletal structure, for example, containing 5 to 14 carbon atoms. "6- to 10-membered aryl" as used herein contains 6 to 10 carbon atoms, such as phenyl and naphthyl.

[0063] The term "heteroaryl" refers to an aryl group in which one or more (preferably 1, 2 or 3) carbon atoms are replaced by oxygen, nitrogen, phosphorus or sulfur atoms, such as 4-pyridyl, 2-imidazolyl, 3-pyrazolyl and isoquinolinyl.

[0064] The term "cycloalkyl" refers to a saturated or partially unsaturated cyclic group containing one or more rings as the main structure, for example, containing 3 to 14 carbon atoms. "3- to 8-membered cycloalkyl" as used herein contains 3 to 8 carbon atoms, such as cyclopropyl, cyclohexyl, tetrahydronaphthalene, or cyclohex-2-enyl.

[0065] The term "heterocyclic alkyl" refers to a cycloalkyl group as defined above in which one or more (preferably 1, 2 or 3) carbon atoms are replaced by oxygen, nitrogen, phosphorus or sulfur atoms, such as piperidinyl, morpholinyl or piperazine.

[0066] Secondary batteries suffer from electrolyte consumption and localized drying during use, leading to shortened cycle life. On the other hand, the increasing demand for energy density often necessitates increasing the electrolyte margin and reducing the electrolyte injection coefficient to raise the proportion of energy storage materials in the battery, thereby improving its energy density. In particular, batteries with tabs 54 distributed on opposite sides, as shown in Figure 1, offer optimized system and structure design in engineering. However, these batteries feature wound cells and are placed horizontally during use. The electrolyte at the upper corner region 56 is prone to drying out, hindering lithium-ion transport and increasing polarization at the upper corner, potentially exceeding the lithium deposition potential (0V vs Li / Li). + During charging, Li is released from the positive electrode. + Instead of being embedded in the negative electrode active material, lithium is deposited in the upper corner region, which poses a risk of lithium plating in that area, resulting in irreversible Li loss, accelerated battery capacity decay, poor cycle performance, and affecting the use of secondary batteries.

[0067] Therefore, improving the liquid retention capacity of batteries to reduce the possibility of lithium plating and improve the cycle performance of batteries has become an urgent problem to be solved in this field.

[0068] Based on this, the present disclosure provides a secondary battery, an electrical device, and a liquid-retaining material. The present disclosure and preferred embodiments are described in more detail below.

[0069] Secondary batteries

[0070] The first aspect of this disclosure provides a secondary battery. The secondary battery includes a liquid-retaining material and an electrolyte. The liquid-retaining material includes a cross-linked polymer with a swelling ratio of 4 to 13. The cross-linked polymer has a centrifugation electrolyte volume of 0.37 to 0.63 g / Ah. The electrolyte includes an electrolyte in a gel and a liquid electrolyte.

[0071] For example, the swelling ratio of the crosslinked polymer can be 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or any value within the range of any two values. Optionally, the swelling ratio of the crosslinked polymer is 4.7 to 9.8.

[0072] For example, the amount of crosslinked polymer in the centrifugal electrolyte is 0.37 g / Ah, 0.43 g / Ah, 0.50 g / Ah, 0.55 g / Ah, 0.63 g / Ah, or any value within the range of any two values. Optionally, the amount of crosslinked polymer in the centrifugal electrolyte is 0.37 to 0.48 g / Ah.

[0073] The cross-linked polymer in the electrolyte-retaining material improves the adsorption and retention capacity of the electrolyte. Specifically, after adsorbing the electrolyte, the cross-linked polymer swells to form a jelly-like gel, binding the adsorbed electrolyte within the gel. The electrolyte adsorbed in the gel can resist the squeezing effects of gravity and expansion forces, effectively remaining within the gel. This reduces the likelihood of lithium plating due to electrolyte drying and improves the battery's cycle performance. The "electrolyte in the gel" mentioned in this invention refers to the electrolyte bound within the gel.

[0074] The "swelling ratio" of the cross-linked polymer mentioned in this disclosure reflects the ability of the cross-linked polymer to adsorb electrolyte, and can be determined by the following steps: The cross-linked polymer is dried at 100°C for 24 hours to obtain a cross-linked polymer film. Then, the cross-linked polymer film is cut into small pieces, and 0.5 g is weighed and recorded as the initial mass. The weighed film is added to a centrifuge tube, 40 g of electrolyte is added, and the mixture is kept at 60°C for 96 hours. After incubation, the film is removed, the surface free electrolyte is wiped dry, and the mass of the film after 96 hours is recorded as the mass at 96 hours. The swelling ratio is calculated according to the following formula: Swelling ratio = (Mass at 96 hours - Initial mass) ÷ Initial mass. The electrolyte is prepared by dissolving LiPF6 in a mixed solvent of ethylene carbonate, diethyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1, with a LiPF6 concentration of 1 mol / L.

[0075] The “centrifugal electrolyte volume” of the cross-linked polymer mentioned in this disclosure reflects the performance of the cross-linked polymer in resisting the squeezing effects of gravity and expansion forces after adsorbing electrolyte, and can be determined by the following method.

[0076] First, a 4Ah soft-pack battery for testing the amount of electrolyte in centrifugation was prepared according to an electrolyte injection coefficient of 3g / Ah: ternary cathode active material (LiNi) was added at a mass ratio of 90:5:5. 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed, and then 0.43 times their mass of N-methylpyrrolidone (N-methylpyrrolidone) was added. After thorough mixing, a positive electrode slurry (70% solid content) was prepared. The positive electrode slurry was then coated onto both sides of an aluminum foil, with a dry weight of 15.4 mg / cm³ on each side.2 After drying, cold pressing, and cutting, a positive electrode sheet with dimensions of 87mm × 953mm was obtained. Artificial graphite, conductive carbon black, sodium carboxymethyl cellulose binder, and liquid-retaining material (based on their solid content) were added to one equal mass of deionized water at a mass ratio of 94:2:2:2. After thorough mixing, a negative electrode slurry (50% solid content) was prepared. The negative electrode slurry was then coated on both sides of a copper foil, with a dry weight of 9.3 mg / cm³ on each side. 2 After drying, cold pressing, and cutting, a negative electrode sheet with dimensions of 93mm × 1086mm is obtained. LiPF6 is dissolved in a mixed solvent of ethylene carbonate, diethyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1 to form an electrolyte, where the concentration of LiPF6 is 1 mol / L. A 13μm thick polyethylene film is used as the separator. The electrodes are arranged in the order of "separator-negative electrode sheet-separator-positive electrode sheet," with one end of the positive electrode sheet, negative electrode sheet, and two separators fixed to the discharge roller, and the other ends stacked together and fixed to the winding shaft. A motor is used to rotate the winding shaft, winding the positive electrode sheet, negative electrode sheet, and two separators to obtain a wound electrode assembly. This wound electrode assembly has a structure with tabs distributed on opposite sides. The wound electrode assembly is placed in an aluminum-plastic film shell, 12g of electrolyte is injected, and it is sealed using a sealing machine. A pouch battery with dimensions of 130mm × 60mm × 4mm (length × width × thickness) was thus prepared. The total mass M1 of the pouch battery after discharge was weighed; the seal was cut off, and the mass M2 of the cut-off portion was weighed. Some air was injected, and the pouch battery was then sealed using a sealing machine. The pouch battery was placed between the steel clamps of a centrifuge, with one pouch battery in each of the two centrifuge arms. The pouch battery was placed horizontally with the air bag facing outwards to facilitate the discharge of electrolyte from the centrifuged pouch battery. The centrifuge was run at 2000 rpm for 30 minutes. Afterwards, the pouch battery cell was removed from the steel clamps, the seal was cut off again, the electrolyte was poured out, and the mass M3 of the cell after centrifugation was weighed. The cut-off portion was soaked in anhydrous ethanol for 15 minutes, dried in a 60℃ oven for 30 minutes, and then weighed again. The mass M4 of this portion was then measured. The amount of electrolyte was calculated using the following formula: Electrolyte volume = (M1 - M2 - M3 - M4) ÷ 4Ah.

[0077] In some embodiments, the degree of crosslinking of the crosslinked polymer is 60% to 90%, optionally 63% to 89%. Exemplarily, the degree of crosslinking can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any value within the range of any two of these values. This facilitates a balance between the crosslinked polymer's ability to adsorb electrolyte and its ability to retain electrolyte.

[0078] The degree of crosslinking of the crosslinked polymer mentioned in this disclosure reflects the extent of crosslinking in the crosslinked polymer, and is defined as the ratio between the mass of the insoluble matter and the initial mass of the crosslinked polymer after dissolution in a specific solvent. This specific solvent is a mixture of ethylene carbonate and methyl ethyl carbonate in a mass ratio of 3:7. The degree of crosslinking can be determined by the following steps: The crosslinked polymer is dried at 100°C for 24 hours to obtain a crosslinked polymer film. Then, the crosslinked polymer film is cut into small pieces, 0.50 g is weighed, wrapped in a 200-mesh filter cloth, and the total mass is recorded as total mass M1. The filter cloth-wrapped film is placed in a centrifuge tube, 40 g of the ethylene carbonate and methyl ethyl carbonate mixture in a mass ratio of 3:7 is added, and the mixture is kept at 60°C for 72 hours. After rinsing with the same mixed solvent as described above, the filter cloth-wrapped film is dried at 100°C for 24 hours, and its mass is then recorded as mass M2. The degree of crosslinking is calculated using the following formula, where 0.50 - (M1 - M2) represents the mass of insoluble matter:

[0079] In some embodiments, the crosslinked polymer includes structural units represented by formula (I), structural units represented by formula (II), and structural units derived from the crosslinking agent.

[0080] R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted 6- to 10-membered aryl, substituted or unsubstituted 5- to 10-membered heteroaryl, substituted or unsubstituted 3- to 8-membered cycloalkyl or heterocycloalkyl; when the C1- to C10 alkyl, C1- to C10 alkoxy, C2- to C10 alkenyl, 6- to 10-membered aryl, 5- to 10-membered heteroaryl, 3- to 8-membered cycloalkyl or heterocycloalkyl has a substituent, the substituent independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1- to C10 alkyl, and 6- to 10-membered aryl. R8 is selected from substituted or unsubstituted C1-C10 alkyl groups, substituted or unsubstituted 6- to 10-membered aryl groups, and substituted or unsubstituted C2- to C10 alkenyl groups; when the C1- to C10 alkyl groups, 6- to 10-membered aryl groups, and C2- to C10 alkenyl groups have substituents, each substituent independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1- to C10 alkyl, and 6- to 10-membered aryl groups; and R9 is a linking bond or a C1- to C6 alkylene group. The crosslinked polymer with the above structure has improved affinity for the electrolyte, which is more beneficial for balancing the electrolyte adsorption and retention capabilities of the electrolyte-retaining material.

[0081] In some embodiments, in formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester, unsubstituted C1-C10 alkyl, and unsubstituted C1-C10 alkoxy groups. This further improves the affinity for the electrolyte.

[0082] In some embodiments, in formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, carboxyl, ester, or unsubstituted C1-C6 alkyl groups; R8 is selected from unsubstituted C1-C6 alkyl groups; and R9 is a linking bond or a methylene group. This further improves the affinity for the electrolyte.

[0083] In some embodiments, in formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen and unsubstituted C1-C4 alkyl groups; R8 is selected from unsubstituted C1-C4 alkyl groups; and R9 is a linking bond. This further improves the affinity for the electrolyte.

[0084] In some embodiments, the mass percentage of the structural unit represented by formula (II) is 75% to 92%, optionally 78% to 88%, relative to the total mass of the structural units represented by formula (I) and formula (II) in the crosslinked polymer. Exemplarily, the mass percentage of the structural unit represented by formula (II) can be any value within the range of 75%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, or any two of these values. This further improves the affinity for the electrolyte.

[0085] In some embodiments, the crosslinking agent includes one or more compounds containing at least two unsaturated double bonds or organic peroxides. After crosslinking with the above-mentioned crosslinking agent, the polymer chains form a network structure, further enhancing the adsorption capacity for electrolyte. The crosslinking agent can increase the strength of the crosslinked polymer, further improving its resistance to extrusion forces such as gravity and expansion.

[0086] In some embodiments, the crosslinking agent includes one or more of divinylbenzene, diallyl phthalate, diethylene glycol diacrylate, tetraethylene glycol dimethacrylate, dicumyl peroxide, benzoyl peroxide, and di-tert-butyl peroxide. The crosslinking agent is more conducive to forming a suitable crosslinking structure to achieve a balance between the ability to adsorb electrolyte and the ability to retain electrolyte.

[0087] In some embodiments, the mass percentage of structural units derived from the crosslinking agent is 2% to 10% relative to the total mass of the structural units shown in formula (I) and formula (II) in the crosslinked polymer. Exemplarily, the mass percentage of structural units derived from the crosslinking agent can be 2%, 4%, 6%, 8%, 10%, or any value within the range of any two of these values. This is more advantageous for the crosslinked polymer to have a suitable degree of crosslinking, and more advantageous for forming a crosslinked structure with a suitable degree of crosslinking.

[0088] In some embodiments, the crosslinking agent is a compound containing at least two unsaturated double bonds, and the mass percentage of the structural units derived from the compound containing at least two unsaturated double bonds is 2% to 10%. This is more conducive to forming a crosslinked structure with a suitable degree of crosslinking.

[0089] In some embodiments, the crosslinked polymer includes a divinylbenzene-crosslinked ethylene-vinyl acetate copolymer. Ethylene-vinyl acetate copolymers have strong film-forming properties and, after being crosslinked with divinylbenzene, can effectively resist compressive forces such as gravity and expansion.

[0090] The term "secondary battery" used in this article refers to a single battery cell, a battery module, or a battery pack. These will be explained separately below.

[0091] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0092] In some embodiments, at least one of the positive electrode, negative electrode, electrolyte, and separator includes the liquid-retaining material described above.

[0093] Negative electrode sheet

[0094] The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

[0095] In some embodiments, the electrolyte-retaining material mentioned above is included in the negative electrode film layer. After the electrolyte-retaining material is added to the negative electrode slurry and fully dispersed, a electrolyte-retaining system can be formed on the surface of the negative electrode active material and in the stacking gaps through a drying process, which can fully adsorb and retain the electrolyte.

[0096] In some embodiments, the mass percentage of the electrolyte-retaining material in the negative electrode film layer, based on solid content, is 0.5% to 3%. Exemplarily, the mass percentage of the electrolyte-retaining material is 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3%, or any two of the above values. Controlling the mass percentage of the electrolyte-retaining material within the above range allows it to appropriately exert its ability to adsorb and retain electrolyte without excessively affecting the addition ratio of the negative electrode active material.

[0097] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0098] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0099] In some embodiments, the negative electrode film layer includes a negative electrode active material. The negative electrode active material may be any negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this disclosure is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0100] In some embodiments, the negative electrode active material includes graphite with a specific capacity ≥355 mAh / g, or silicon-doped graphite, wherein, by weight, silicon:graphite = (5-25):(95-75). This increases the specific capacity of the negative electrode active material, further contributing to improved battery energy density.

[0101] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), sodium carboxymethyl cellulose, and carboxymethyl chitosan (CMCS).

[0102] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0103] In some embodiments, the negative electrode film layer may optionally include other additives, such as thickeners.

[0104] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder, liquid retaining material and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0105] Positive electrode sheet

[0106] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive active material and an optional liquid-retaining material as described above.

[0107] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0108] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0109] In some embodiments, the battery cell is a lithium-ion battery. In this case, the positive electrode active material can be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this disclosure is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNiO2). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.1 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0110] In some embodiments, the lithium transition metal oxide includes nickel, wherein the molar content of nickel in the lithium transition metal oxide is more than 80% relative to all metal elements other than lithium. This increases the specific capacity of the positive electrode active material, further contributing to improved battery energy density.

[0111] During the charging and discharging process, active ions are intercalated and deintercalated, resulting in varying molar contents of active ions at different discharge states. In the examples of positive electrode active materials in this disclosure, the molar content of Li refers to the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar content of Li changes after charge-discharge cycles.

[0112] In the examples of positive electrode active materials in this disclosure, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0113] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0114] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0115] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder, optional liquid retaining material and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0116] electrolytes

[0117] The electrolyte acts as a conductor of ions between the positive and negative electrodes. The electrolyte disclosed herein is an electrolyte solution. The electrolyte solution comprises an electrolyte salt and a solvent.

[0118] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0119] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0120] In some embodiments, the electrolyte is a solution of LiPF6 in a carbonate solvent.

[0121] In some embodiments, the electrolyte is a solution of LiPF6 in a mixed solvent of ethylene carbonate, diethyl carbonate, and dimethyl carbonate.

[0122] In some embodiments, the electrolyte is a solution of LiPF6 in a mixed solvent of ethylene carbonate, diethyl carbonate and dimethyl carbonate, wherein the concentration of LiPF6 is 1 mol / L.

[0123] In some embodiments, the electrolyte is a solution of LiPF6 in a mixed solvent of ethylene carbonate, diethyl carbonate and dimethyl carbonate mixed in a volume ratio of 1:1:1, wherein the concentration of LiPF6 is 1 mol / L.

[0124] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and at least one of the above-mentioned liquid-retaining materials, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0125] Separating membrane

[0126] In some embodiments, the battery cell also includes a separator. This disclosure does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0127] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0128] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0129] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0130] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include aluminum-plastic film, polypropylene, polyethylene, polybutylene terephthalate, and polybutylene succinate.

[0131] This disclosure does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 shows a square battery cell 5 as an example.

[0132] In some embodiments, referring to FIG3, the outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can cover the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0133] In some embodiments, the group margin in the thickness direction of the secondary battery is 88% to 94%. Exemplarily, the group margin in the thickness direction is 88%, 89%, 90%, 91%, 92%, 93%, 94%, or any value within the range of any two of these values. This increases the proportion of energy storage material in the battery, which is beneficial for improving the battery's energy density.

[0134] Typically, group margin reflects the space filling degree of a battery cell. The "group margin in the thickness direction" mentioned in this disclosure refers to the ratio of the size of the electrode assembly 52 of the battery to the size of the battery casing 51 in the thickness direction X of the battery cell 5.

[0135] In some embodiments, the secondary battery includes a battery with tabs distributed on opposite sides. This opposite-side tab distribution prevents short circuits between the positive and negative tabs, thereby improving battery safety. Furthermore, it helps reduce internal resistance, facilitating high-rate charge and discharge. Additionally, it allows for the design of structures with higher group margins in the thickness direction. Thus, the system and structure can be optimized, further improving the battery's energy density.

[0136] Compared to batteries with lower group margin and / or higher electrolyte filling coefficient, batteries with higher group margin and / or lower electrolyte filling coefficient require less electrolyte, thus increasing the risk of localized electrolyte drying. In particular, batteries with tabs 54 distributed on opposite sides as shown in Figure 1, i.e., batteries with tabs on opposite sides of the battery, have higher group margin and a more extreme electrolyte filling design. As the battery cycles, the electrolyte in the upper corner area is discharged under the influence of gravity and cyclic expansion forces, easily leading to insufficient electrolyte in the upper corner area 56, causing drying and increasing the risk of lithium plating in this area, resulting in accelerated battery capacity decay and poor cycle performance. By including the electrolyte-retaining material of this disclosure in a battery with this structure, the electrolyte in the upper corner can be effectively locked within the electrode, overcoming the influence of gravity and expansion forces on electrolyte distribution, reducing the possibility of electrolyte drying in the upper corner electrode, thereby reducing the risk of lithium plating and improving battery cycle performance.

[0137] In some embodiments, the positive electrode active material of the secondary battery includes a lithium transition metal oxide, and the ratio of the total electrolyte mass to the battery capacity in the secondary battery is 2.0 to 3.0 g / Ah. Exemplarily, when the positive electrode active material of the secondary battery includes a lithium transition metal oxide, the ratio of the total electrolyte mass to the battery capacity in the secondary battery can be 2.0 g / Ah, 2.2 g / Ah, 2.4 g / Ah, 2.6 g / Ah, 2.8 g / Ah, 3.0 g / Ah, or any value within the range of any two of these values. This further increases the proportion of energy storage material in the battery, further contributing to an increase in the battery's energy density.

[0138] The "ratio of total electrolyte mass to battery capacity" mentioned in this disclosure can also be called the "electrolyte injection coefficient." It refers to the mass of electrolyte per Ah of battery capacity, calculated based on the battery's design capacity through a combination of actual testing and theoretical calculations. The unit is g / Ah; the smaller the value, the less electrolyte is added to the battery. Total electrolyte includes the electrolyte in the gel and the liquid electrolyte. The liquid electrolyte can also be called free electrolyte.

[0139] In some embodiments, the lithium transition metal oxide includes nickel, and the molar content of nickel in the lithium transition metal oxide is more than 80% relative to all metal elements other than lithium; the negative electrode active material of the secondary battery includes graphite and / or silicon-based negative electrode materials. In these embodiments, these positive electrode active materials have a high specific capacity, which is beneficial for improving the battery capacity. However, at the same time, the nickel content in these positive electrode active materials is also high, with its molar content accounting for more than 80% of the total molar content of all metal elements other than lithium. Batteries formed by combining such positive electrode active materials with negative electrode active materials with a large specific capacity, such as graphite and / or silicon-based negative electrode materials, are prone to lithium plating. For these batteries, it is especially necessary for the electrolyte to be uniformly bound within the electrode sheets, ensuring that the electrode sheets are always immersed in the electrolyte, reducing the possibility of localized drying and subsequent lithium plating. By incorporating the electrolyte-retaining material disclosed herein into such a battery, the electrolyte can be effectively locked within the electrode, overcoming the influence of forces such as gravity and expansion on the electrolyte distribution, reducing the possibility of localized electrolyte drying, thereby reducing the risk of lithium plating and improving the battery's cycle performance.

[0140] In some embodiments, the positive electrode active material of the secondary battery includes lithium phosphate, and the ratio of the total electrolyte mass to the battery capacity in the secondary battery is 3.0 to 5.0 g / Ah. Exemplarily, when the positive electrode active material of the secondary battery includes lithium phosphate, the ratio of the total electrolyte mass to the battery capacity can be 3.0 g / Ah, 3.2 g / Ah, 3.4 g / Ah, 3.6 g / Ah, 3.8 g / Ah, 4.0 g / Ah, 4.2 g / Ah, 4.4 g / Ah, 4.6 g / Ah, 4.8 g / Ah, 5.0 g / Ah, or any value within the range of any two of these values. This increases the proportion of energy storage material in the battery, which is beneficial for improving the battery's energy density.

[0141] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0142] Figure 4 shows a battery module 4 as an example. Referring to Figure 4, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0143] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0144] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0145] Figures 5 and 6 show a battery pack 1 as an example. Referring to Figures 5 and 6, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0146] Electrical appliances

[0147] A second aspect of this disclosure also provides an electrical device, which will be described below with appropriate reference to the accompanying drawings.

[0148] The electrical device disclosed herein includes the secondary battery provided in this disclosure. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0149] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0150] Figure 7 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0151] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0152] Liquid retention material

[0153] A third aspect of this disclosure also provides a liquid-retaining material. The liquid-retaining material comprises a cross-linked polymer, the cross-linked polymer having a swelling ratio of 4 to 13, and the cross-linked polymer having a centrifugal electrolyte volume of 0.37 to 0.63 g / Ah.

[0154] Because the cross-linked polymers in the electrolyte-retaining material have improved electrolyte adsorption capacity, they can swell to form a jelly-like gel, binding the liquid electrolyte within the gel. Furthermore, the electrolyte adsorbed in the gel can resist the squeezing effects of gravity and expansion forces. Therefore, the electrolyte-retaining material has an improved ability to retain electrolyte, thereby improving the cycle performance of the secondary battery.

[0155] In some embodiments, the degree of crosslinking of the crosslinked polymer is 60% to 90%, optionally 63% to 89%. This is more conducive to balancing the crosslinked polymer's ability to adsorb electrolyte and resist the squeezing effects of gravity and expansion forces.

[0156] In some embodiments, the crosslinked polymer includes structural units represented by formula (I), structural units represented by formula (II), and structural units derived from the crosslinking agent.

[0157] R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted 6- to 10-membered aryl, substituted or unsubstituted 5- to 10-membered heteroaryl, substituted or unsubstituted 3- to 8-membered cycloalkyl or heterocycloalkyl; when the C1- to C10 alkyl, C1- to C10 alkoxy, C2- to C10 alkenyl, 6- to 10-membered aryl, 5- to 10-membered heteroaryl, 3- to 8-membered cycloalkyl or heterocycloalkyl has a substituent, the substituent independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1- to C10 alkyl, and 6- to 10-membered aryl. R8 is selected from substituted or unsubstituted C1-C10 alkyl groups, substituted or unsubstituted 6- to 10-membered aryl groups, and substituted or unsubstituted C2- to C10 alkenyl groups; when the C1- to C10 alkyl groups, 6- to 10-membered aryl groups, and C2- to C10 alkenyl groups have substituents, each substituent independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1- to C10 alkyl, and 6- to 10-membered aryl groups; and R9 is a linking bond or a C1- to C6 alkylene group. The crosslinked polymer with the above structure has improved affinity for the electrolyte, which is more beneficial for balancing the electrolyte adsorption and retention capabilities of the electrolyte-retaining material.

[0158] In some embodiments, in formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester, unsubstituted C1-C10 alkyl, and unsubstituted C1-C10 alkoxy groups. This further improves the affinity for the electrolyte.

[0159] In some embodiments, in formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, carboxyl, ester, or unsubstituted C1-C6 alkyl groups; R8 is selected from unsubstituted C1-C6 alkyl groups; and R9 is a linking bond or a methylene group. This further improves the affinity for the electrolyte.

[0160] In some embodiments, in formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen and unsubstituted C1-C4 alkyl groups; R8 is selected from unsubstituted C1-C4 alkyl groups; and R9 is a linking bond. This further improves the affinity for the electrolyte.

[0161] In some embodiments, the mass percentage of the structural unit shown in formula (II) is 75% to 92%, optionally 78% to 88%, relative to the total mass of the structural units shown in formula (I) and formula (II) in the crosslinked polymer. This further improves the affinity for the electrolyte.

[0162] In some embodiments, the crosslinking agent includes one or more compounds containing at least two unsaturated double bonds or organic peroxides. The crosslinking agent can enhance the strength of the crosslinked polymer, further improving its resistance to compression forces such as gravity and expansion, and the crosslinked polymer chains form a network structure, further enhancing the electrolyte adsorption capacity.

[0163] In some embodiments, the crosslinking agent includes one or more of divinylbenzene, diallyl phthalate, diethylene glycol diacrylate, tetraethylene glycol dimethacrylate, dicumyl peroxide, benzoyl peroxide, and di-tert-butyl peroxide. The crosslinking agent is more conducive to forming a suitable crosslinking structure to achieve a balance between the ability to adsorb electrolyte and the ability to retain electrolyte.

[0164] In some embodiments, the mass percentage of structural units derived from the crosslinking agent is 2% to 10% relative to the total mass of the structural units shown in formula (I) and formula (II) in the crosslinked polymer. Exemplarily, the mass percentage of structural units derived from the crosslinking agent can be 2%, 4%, 6%, 8%, 10%, or any value within the range of any two of these values. This is more advantageous for the crosslinked polymer to have a suitable degree of crosslinking, and more advantageous for forming a crosslinked structure with a suitable degree of crosslinking.

[0165] In some embodiments, the crosslinking agent is a compound containing at least two unsaturated double bonds, and the mass percentage of the structural units derived from the compound containing at least two unsaturated double bonds is 2% to 10%. This is more conducive to forming a crosslinked structure with a suitable degree of crosslinking. For example, the mass percentage of the structural units derived from the compound containing at least two unsaturated double bonds is 2%, 4%, 6%, 8%, 10%, or any value within the range of any two of these values.

[0166] In some embodiments, the crosslinked polymer includes a divinylbenzene-crosslinked ethylene-vinyl acetate copolymer. Ethylene-vinyl acetate copolymers have strong film-forming properties and, after being crosslinked with divinylbenzene, can effectively resist compressive forces such as gravity and expansion.

[0167] Example

[0168] The following describes embodiments of this disclosure. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0169] Example 1

[0170] Preparation of liquid-retaining materials

[0171] 189g of an ethylene-vinyl acetate copolymer (EVA) emulsion (Sinopec Chongqing Chuanwei Chemical Co., Ltd., solid content 53%; vinyl acetate unit content 84% relative to the mass of ethylene-vinyl acetate copolymer), 5g of crosslinking agent divinylbenzene (DVB), and 100g of a 1wt% ammonium persulfate aqueous solution were mixed and stirred for 30 min to ensure uniform dispersion. The mixture was then reacted at 70°C for 12 h to obtain a liquid-retaining material in emulsion form. In this example, the proportion of DVB relative to the solid mass of EVA was 5%.

[0172] Preparation of secondary batteries

[0173] Preparation of the positive electrode: The ternary positive electrode active material (LiNi) was prepared according to a mass ratio of 90:5:5. 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed, and N-methylpyrrolidone (N-Methylpyrrolidone) was added as a solvent. After thorough mixing, a positive electrode slurry was prepared. The positive electrode slurry was then coated on both sides of an aluminum foil, dried, cold-pressed, and cut to obtain a positive electrode sheet with dimensions of 314 mm × 3211 mm.

[0174] Preparation of the negative electrode sheet: Artificial graphite, conductive carbon black, sodium carboxymethyl cellulose binder, and the liquid-retaining material prepared above (based on its solid content) were added to deionized water at a mass ratio of 94:2:2:2. After thorough mixing, a negative electrode slurry was prepared. The negative electrode slurry was then coated onto both sides of a copper foil. After drying, cold pressing, and cutting, a negative electrode sheet with dimensions of 321 mm × 3363 mm was obtained.

[0175] Electrolyte preparation: LiPF6 was dissolved in a mixed solvent of ethylene carbonate, diethyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1 to form an electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0176] Separator: A polyethylene film with a thickness of 13μm is used as the separator.

[0177] Assembly of the secondary battery: The electrodes are arranged in the order of "separator - negative electrode - separator - positive electrode". One end of the positive electrode, negative electrode, and two separators is fixed to the discharge roller, and the other ends are stacked together and fixed to the winding shaft. A motor is used to rotate the winding shaft, winding the positive electrode, negative electrode, and two separators to obtain a wound electrode assembly. This wound electrode assembly has a structure with tabs distributed on opposite sides, called the M6T structure. This structure is shown in Figure 1. The wound electrode assembly is placed in outer packaging and undergoes processes such as electrolyte injection, encapsulation, settling, formation, and aging to produce a secondary battery with a thickness margin of 92% and an electrolyte injection coefficient of 2.4 g / Ah.

[0178] Example 2

[0179] The liquid-retaining material and the secondary battery were prepared according to the method of Example 1, except that in the preparation of the liquid-retaining material, the amount of divinylbenzene (DVB) added was 2g, so that the proportion of crosslinking agent DVB relative to the solid mass of EVA was 2%.

[0180] Example 3

[0181] The liquid-retaining material and the secondary battery were prepared according to the method of Example 1, except that in the preparation of the liquid-retaining material, the amount of divinylbenzene (DVB) added was 10g, so that the proportion of crosslinking agent DVB relative to the solid mass of EVA was 10%.

[0182] Example 4

[0183] The liquid-retaining material and the secondary battery were prepared according to the method of Example 1, except that 5g of benzoyl peroxide was used instead of DVB as the crosslinking agent, and 100g of 1wt% ammonium persulfate aqueous solution was replaced with 100g of deionized water. In this example, the crosslinking agent benzoyl peroxide accounted for 5% of the solid mass of EVA.

[0184] Comparative Example 1

[0185] The liquid-retaining material and the secondary battery were prepared according to the method of Example 1, except that in the preparation of the liquid-retaining material, the amount of divinylbenzene (DVB) added was 0.5g, so that the crosslinking agent DVB accounted for 0.5% of the solid mass of EVA.

[0186] Comparative Example 2

[0187] The liquid-retaining material and the secondary battery were prepared according to the method of Example 1, except that in the preparation of the liquid-retaining material, the amount of divinylbenzene (DVB) added was 15g, so that the crosslinking agent DVB accounted for 15% of the solid mass of EVA.

[0188] Comparative Example 3

[0189] The secondary battery was prepared according to the method of Example 1, except that in the preparation of the negative electrode sheet, a commercially available polybutyl methacrylate emulsion (solid content 24%, manufacturer: Hangzhou Yuhao Chemical, YH67418) was used to replace the liquid-retaining material prepared in Example 1.

[0190] Comparative Example 4

[0191] The secondary battery was prepared according to the method of Example 1, except that no liquid-retaining material was added during the preparation of the negative electrode sheet. Specifically, the negative electrode sheet was prepared according to a mass ratio of artificial graphite, conductive carbon black, and sodium carboxymethyl cellulose binder of 96:2:2.

[0192] Reference example

[0193] In the reference example, a secondary battery with tabs distributed on the same side without any liquid-retaining material was prepared. Specifically, the positive electrode, electrolyte, and separator were prepared according to the method of Example 1, and the negative electrode was prepared with artificial graphite, conductive carbon black, and sodium carboxymethyl cellulose binder in a mass ratio of 96:2:2, without the addition of any liquid-retaining material. In this reference example battery, the thickness group margin was 89%, and the liquid filling coefficient was 2.6 g / Ah.

[0194] Characterization of liquid-retaining materials

[0195] 1. Swelling ratio test

[0196] 10g of the liquid-retaining material from Examples 1 to 4 and Comparative Examples 1 to 3 was added to a polytetrafluoroethylene mold and dried at 100°C for 24 hours to obtain a cross-linked polymer film. Then, the cross-linked polymer film was cut into small pieces, and 0.5g was weighed and recorded as the initial mass. The weighed film was added to a centrifuge tube, 40g of electrolyte was added, and the mixture was kept in a 60°C forced-air drying oven for 96 hours. After removal, the surface free electrolyte was wiped dry, and the mass of the film after 96 hours was recorded as the mass at 96 hours. The swelling ratio was calculated using the following formula: Swelling ratio = (Mass at 96 hours - Initial mass) ÷ Initial mass. The above electrolyte was prepared by dissolving LiPF6 in a mixed solvent of ethylene carbonate, diethyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1, with a LiPF6 concentration of 1 mol / L.

[0197] 2. Crosslinking degree test

[0198] 10g of the liquid-retaining material from Examples 1 to 4 and Comparative Examples 1 to 3 was added to a polytetrafluoroethylene mold and dried at 100°C for 24 hours to obtain a cross-linked polymer film. Then, the cross-linked polymer film was cut into small pieces, 0.50g was weighed, wrapped in 200-mesh filter cloth, and the total mass was recorded as total mass M1. The filter cloth-wrapped film was placed in a centrifuge tube, and 40g of a mixed solvent of ethylene carbonate and methyl ethyl carbonate in a mass ratio of 3:7 was added. The mixture was then kept in a 60°C drying oven for 72 hours and removed. After rinsing with the same mixed solvent as above, the filter cloth-wrapped film was dried in a 100°C drying oven for 24 hours, and its mass was recorded as mass M2. The degree of cross-linking was calculated using the following formula, where 0.50 - (M1 - M2) represents the mass of insoluble matter:

[0199] 3. Centrifugal electrolyte volume test

[0200] 3.1 Preparation of pouch cells

[0201] A 4Ah pouch cell was prepared according to an electrolyte injection coefficient of 3 g / Ah for testing the electrolyte volume during centrifugation. The specific preparation process is as follows.

[0202] Preparation of the positive electrode: The ternary positive electrode active material (LiNi) was prepared according to a mass ratio of 90:5:5. 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed, and then 0.43 times their mass of N-methylpyrrolidone (N-methylpyrrolidone) was added. After thorough mixing, a positive electrode slurry (70% solid content) was prepared. The positive electrode slurry was then coated onto both sides of an aluminum foil, with a dry weight of 15.4 mg / cm³ on each side. 2After drying, cold pressing, and cutting, a positive electrode sheet with a size of 87mm×953mm is obtained.

[0203] Preparation of the negative electrode sheet: Artificial graphite, conductive carbon black, sodium carboxymethyl cellulose binder, and liquid-retaining material (based on their solid content) were added to one volume of deionized water at a mass ratio of 94:2:2:2. After thorough mixing, a negative electrode slurry (50% solid content) was prepared. The negative electrode slurry was then coated onto both sides of a copper foil, with a dry weight of 9.3 mg / cm³ on each side. 2 After drying, cold pressing, and cutting, a negative electrode sheet with a size of 93mm×1086mm is obtained.

[0204] Electrolyte preparation: LiPF6 was dissolved in a mixed solvent of ethylene carbonate, diethyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1 to form an electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0205] Separator: A polyethylene film with a thickness of 13μm is used as the separator.

[0206] The electrodes are arranged in the following order: separator - negative electrode - separator - positive electrode. One end of the positive electrode, negative electrode, and two separators is fixed to the discharge roller, and the other ends are stacked together and fixed to the winding shaft. A motor is used to rotate the winding shaft, winding the positive electrode, negative electrode, and two separators to obtain a wound electrode assembly. This wound electrode assembly has tabs distributed on opposite sides. The wound electrode assembly is placed in an aluminum-plastic film shell, 12g of electrolyte is injected, and it is sealed using a sealing machine. This yields a soft-pack battery with dimensions of 130mm × 60mm × 4mm (length × width × thickness).

[0207] 3.2 Test the volume of electrolyte in centrifuged solution

[0208] Weigh the total mass M1 of the discharged pouch cells; cut off the seal, weigh the cut-off portion M2, inject some air, and then seal the pouch cells using a sealing machine; place the pouch cells between the steel clamps of a centrifuge, with one pouch cell in each of the two centrifuge arms. The pouch cells are placed horizontally with the air bag facing outwards to facilitate the drainage of electrolyte from the centrifuged pouch cells. Centrifuge at 2000 rpm for 30 minutes; then remove the pouch cells from the steel clamps, cut off the seal again, pour out the electrolyte, weigh the centrifuged cells M3, and soak the cut-off portion in anhydrous ethanol for 15 minutes, dry it in a 60℃ oven for 30 minutes, and then weigh this portion M4. Calculate the centrifuged electrolyte volume using the following formula: Centrifuged electrolyte volume = (M1 - M2 - M3 - M4) ÷ 4Ah.

[0209] Battery performance characterization

[0210] 1. Cyclic life test

[0211] 1.1 Capacity Calibration Process

[0212] The battery was charged and discharged for the first time under a constant temperature environment of 25℃. It was charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage of 4.25V to a current of 0.05C, and then discharged at a constant current of 0.33C until the final voltage was 2.8V. The actual capacity C0 of the battery was recorded.

[0213] 1.2 Cyclic Test Process

[0214] Under constant temperature conditions of 25℃, the capacitor is charged to 4.25V at a constant current of 0.33C0, then charged to 0.05C0 at a constant voltage of 4.25V, and finally discharged to 2.8V at a constant current of 0.33C0. This discharge capacity (C1) is obtained. This charging and discharging process is repeated until the 1200th cycle, yielding the discharge capacity after 1200 cycles, denoted as C. n .

[0215] Capacity retention rate = discharge capacity after 1200 cycles (C) n ) / First-cycle discharge capacity (C1).

[0216] 2. Lithium plating test

[0217] The battery that has undergone 1200 cycles was disassembled, and the upper corner was inspected for lithium plating.

[0218] The parameters of the liquid-retaining materials and the secondary battery performance test results of the above embodiments, comparative examples and reference examples are shown in Table 1 below.

[0219] Table 1

[0220] In Table 1, " / " indicates that there are no related items.

[0221] As shown in Table 1 above, compared with Comparative Examples 1 and 2, which used an inappropriate amount of crosslinking agent, Examples 1-4, by using an appropriate amount of crosslinking agent to crosslink the ethylene-vinyl acetate copolymer, achieved a swelling ratio of 4.7-9.8 and a centrifugal electrolyte volume of 0.38-0.48 g / Ah. This resulted in improved electrolyte adsorption capacity of the crosslinked polymer, and the electrolyte adsorbed in the colloid could resist the squeezing effects of gravity and expansion forces. Consequently, the secondary battery exhibited improved cycle performance and reduced lithium plating risk. Its cycle performance was comparable to that of the battery with tabs distributed on the same side as the reference example, and significantly improved compared to Comparative Example 3, which used commercially available polybutyl methacrylate as the electrolyte retention material, and Comparative Example 4, which did not use any electrolyte retention material. The electrolyte retention material in Comparative Example 1 had too low a crosslinking ratio, resulting in low electrolyte adsorption and retention capacity, low swelling ratio, large centrifugal electrolyte volume, and insufficient electrolyte retention, leading to poor cycle performance and lithium plating. In Comparative Example 2, the electrolyte-retaining material had excessively high cross-linking, resulting in an overly dense polymer network structure that hindered liquid absorption and led to a low swelling ratio. Consequently, its ability to retain electrolyte was also very low, resulting in poor cycle performance and lithium plating. In Comparative Example 3, the electrolyte-retaining material had poor liquid absorption and a low swelling ratio, and the large volume of electrolyte absorbed during centrifugation made it difficult to retain electrolyte, leading to poor cycle performance and lithium plating. In Comparative Example 4, no electrolyte-retaining material was used, resulting in an excessive volume of electrolyte absorbed during centrifugation, severe capacity loss, and lithium plating.

[0222] Examples 5 and 6 and Comparative Examples 5 and 6

[0223] Except for adjusting the parameters according to Table 2, the steps are the same as in Example 1. The content of vinyl acetate units was adjusted to 76%, 91%, 71%, and 95% relative to the mass of the ethylene-vinyl acetate copolymer, all from Chongqing Chuanwei Chemical Co., Ltd., a subsidiary of China Petrochemical Corporation.

[0224] The parameters of the liquid-retaining materials prepared in Examples 1, 5, and 6, as well as the test results of the secondary battery performance, are shown in Table 2 below.

[0225] Table 2

[0226] As shown in Table 2 above, with the increase of the mass percentage of vinyl acetate units in EVA, the amount of electrolyte in the centrifuged electrolyte exhibits a phenomenon of first decreasing and then increasing, corresponding to a first increase and then decrease in the electrolyte retention capacity. This is because with the increase of the mass percentage of vinyl acetate units, the liquid absorption capacity of the cross-linked EVA increases, but the mechanical strength of the gel decreases. In Comparative Example 5, the mass percentage of vinyl acetate units in the electrolyte retention material is too low, resulting in a reduced ability of the formed gel to retain electrolyte. In contrast, the mass percentage of vinyl acetate units in the electrolyte retention material of Comparative Example 6 is too high, resulting in a reduced mechanical strength of the formed gel. Both cases lead to excessive extrusion of electrolyte, resulting in a significant decrease in cycle capacity retention and the occurrence of lithium plating.

[0227] It should be noted that this disclosure is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same essential structure and achieving the same effect as the technical concept within the scope of this disclosure are included in the technical scope of this disclosure. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, are also included in the scope of this disclosure without departing from the spirit of this disclosure.

Claims

1. A secondary battery, the secondary battery comprising a liquid-retaining material and an electrolyte, the liquid-retaining material comprising a cross-linked polymer, the cross-linked polymer having a swelling ratio of 4 to 13, the cross-linked polymer having a centrifugation electrolyte volume of 0.37 to 0.63 g / Ah, and the electrolyte comprising an electrolyte in a gel and a liquid electrolyte.

2. The secondary battery according to claim 1, wherein, The group margin in the thickness direction of the secondary battery is 88% to 94%.

3. The secondary battery according to claim 1 or 2, wherein, The secondary battery includes batteries with tabs distributed on opposite sides.

4. The secondary battery according to any one of claims 1 to 3, wherein, The positive electrode active material of the secondary battery includes lithium transition metal oxide, and the ratio of the total electrolyte mass to the battery capacity in the secondary battery is 2.0 to 3.0 g / Ah.

5. The secondary battery according to claim 4, wherein, The lithium transition metal oxide includes nickel, and the molar content of nickel in the lithium transition metal oxide is more than 80% relative to all metal elements other than lithium; the negative electrode active material of the secondary battery includes graphite and / or silicon-based negative electrode materials.

6. The secondary battery according to any one of claims 1 to 3, wherein, The positive electrode active material of the secondary battery includes lithium phosphate, and the ratio of the total electrolyte mass to the battery capacity in the secondary battery is 3.0 to 5.0 g / Ah.

7. The secondary battery according to any one of claims 1 to 6, wherein, The degree of crosslinking of the crosslinked polymer is 60% to 90%.

8. The secondary battery according to any one of claims 1 to 7, wherein, The crosslinked polymer includes structural units represented by formula (I), structural units represented by formula (II), and structural units derived from the crosslinking agent. R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted 6- to 10-membered aryl, substituted or unsubstituted 5- to 10-membered heteroaryl, substituted or unsubstituted 3- to 8-membered cycloalkyl or heterocycloalkyl; when the C1- to C10 alkyl, C1- to C10 alkoxy, C2- to C10 alkenyl, 6- to 10-membered aryl, 5- to 10-membered heteroaryl, 3- to 8-membered cycloalkyl or heterocycloalkyl has a substituent, the substituent each independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1- to C10 alkyl, and 6- to 10-membered aryl; R8 is selected from substituted or unsubstituted C1-C10 alkyl groups, substituted or unsubstituted 6- to 10-membered aryl groups, and substituted or unsubstituted C2- to C10 alkenyl groups; when the C1- to C10 alkyl groups, 6- to 10-membered aryl groups, and C2- to C10 alkenyl groups have substituents, each of the substituents independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1- to C10 alkyl groups, and 6- to 10-membered aryl groups; Furthermore, R9 is a linking bond or a C1-C6 alkylene group.

9. The secondary battery according to claim 8, wherein, In formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester, unsubstituted C1-C10 alkyl, and unsubstituted C1-C10 alkoxy.

10. The secondary battery according to claim 9, wherein, In formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, carboxyl, ester, or unsubstituted C1-C6 alkyl groups; R8 is selected from unsubstituted C1-C6 alkyl groups; and R9 is a linking bond or a methylene group.

11. The secondary battery according to claim 10, wherein, In formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen and unsubstituted C1 to C4 alkyl groups; R8 is selected from unsubstituted C1 to C4 alkyl groups; and R9 is a linking bond.

12. The secondary battery according to any one of claims 7 to 11, wherein, The mass percentage of the structural unit shown in formula (II) is 75% to 92% relative to the total mass of the structural units shown in formula (I) and formula (II) in the crosslinked polymer.

13. The secondary battery according to any one of claims 7 to 12, wherein, The crosslinking agent includes one or more compounds containing at least two unsaturated double bonds or organic peroxides.

14. The secondary battery according to claim 13, wherein, The crosslinking agent includes one or more of divinylbenzene, diallyl phthalate, diethylene glycol diacrylate, tetraethylene glycol dimethacrylate, dicumyl peroxide, benzoyl peroxide, and di-tert-butyl peroxide.

15. The secondary battery according to any one of claims 7 to 14, wherein, The mass percentage of the structural units derived from the crosslinking agent is 2% to 10% relative to the total mass of the structural units shown in formula (I) and formula (II) in the crosslinked polymer.

16. The secondary battery according to any one of claims 1 to 15, wherein, The crosslinked polymer includes a divinylbenzene crosslinked ethylene-vinyl acetate copolymer.

17. The secondary battery according to any one of claims 1 to 16, wherein, The secondary battery includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, and the liquid-retaining material is included in the negative electrode film layer.

18. The secondary battery according to claim 17, wherein, In the negative electrode film layer, the liquid-retaining material has a mass percentage of 0.5% to 3% based on solid content.

19. An electrical device comprising a secondary battery according to any one of claims 1 to 18.

20. A liquid-retaining material, the liquid-retaining material comprising a cross-linked polymer, the cross-linked polymer having a swelling ratio of 4 to 13, and the cross-linked polymer having a centrifugal electrolyte volume of 0.37 to 0.63 g / Ah.

21. The liquid-retaining material according to claim 20, wherein, The degree of crosslinking of the crosslinked polymer is 60% to 90%.

22. The liquid-retaining material according to claim 20 or 21, wherein, The crosslinked polymer includes structural units represented by formula (I), structural units represented by formula (II), and structural units derived from the crosslinking agent. R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted 6- to 10-membered aryl, substituted or unsubstituted 5- to 10-membered heteroaryl, substituted or unsubstituted 3- to 8-membered cycloalkyl or heterocycloalkyl; when the C1- to C10 alkyl, C1- to C10 alkoxy, C2- to C10 alkenyl, 6- to 10-membered aryl, 5- to 10-membered heteroaryl, 3- to 8-membered cycloalkyl or heterocycloalkyl has a substituent, the substituent each independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1- to C10 alkyl, and 6- to 10-membered aryl; R8 is selected from substituted or unsubstituted C1-C10 alkyl groups, substituted or unsubstituted 6- to 10-membered aryl groups, and substituted or unsubstituted C2- to C10 alkenyl groups; when the C1- to C10 alkyl groups, 6- to 10-membered aryl groups, and C2- to C10 alkenyl groups have substituents, each of the substituents independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1- to C10 alkyl groups, and 6- to 10-membered aryl groups; Furthermore, R9 is a linking bond or a C1-C6 alkylene group.

23. The liquid-retaining material according to claim 22, wherein, In formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester, unsubstituted C1-C10 alkyl, and unsubstituted C1-C10 alkoxy.

24. The liquid-retaining material according to claim 23, wherein, In formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen, carboxyl, ester, or unsubstituted C1-C6 alkyl groups; R8 is selected from unsubstituted C1-C6 alkyl groups; and R9 is a linking bond or a methylene group.

25. The liquid-retaining material according to claim 24, wherein, In formulas (I) and (II), R1, R2, R3, R4, R5, R6, and R7 are each independently selected from hydrogen and unsubstituted C1 to C4 alkyl groups; R8 is selected from unsubstituted C1 to C4 alkyl groups; and R9 is a linking bond.

26. The liquid-retaining material according to any one of claims 22 to 25, wherein, The mass percentage of the structural unit shown in formula (II) is 75% to 92% relative to the total mass of the structural units shown in formula (I) and formula (II) in the crosslinked polymer.

27. The liquid-retaining material according to any one of claims 22 to 26, wherein, The crosslinking agent includes one or more compounds containing at least two unsaturated double bonds or organic peroxides.

28. The liquid-retaining material according to claim 27, wherein, The crosslinking agent includes one or more of divinylbenzene, diallyl phthalate, diethylene glycol diacrylate, tetraethylene glycol dimethacrylate, dicumyl peroxide, benzoyl peroxide, and di-tert-butyl peroxide.

29. The liquid-retaining material according to any one of claims 22 to 28, wherein, The mass percentage of the structural units derived from the crosslinking agent is 2% to 10% relative to the total mass of the structural units shown in formula (I) and formula (II) in the crosslinked polymer.

30. The liquid-retaining material according to any one of claims 22 to 29, wherein, The crosslinked polymer includes a divinylbenzene crosslinked ethylene-vinyl acetate copolymer.

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