Secondary battery, electric device, and electrode-retaining polymer for battery

Abstract

The present disclosure provides a secondary battery, an electric device, and an electrode-retaining polymer for a battery. The secondary battery comprises a gel composed of an electrode-retaining polymer and at least a part of an electrolyte. The electrode-retaining polymer comprises a structural unit represented by formula (I), a structural unit represented by formula (II), and a structural unit derived from a monomer (III). The structural unit derived from the monomer (III) is selected from one or more of a structural unit derived from a monomer having a nitrile group, a structural unit derived from a monomer having an amide group, a structural unit derived from a monomer having a sulfonate group, and a structural unit represented by formula (IV), wherein in formula (IV), R10 is hydrogen or C1-C6 alkyl, R11 is C1-C6 alkyl or (meth)acryloyl, and p is 3-50.

Description

Secondary battery, power consuming device, and liquid retaining polymer for battery

[0001] Cross Reference to Related Applications

[0002] The present disclosure is based on and claims priority to Chinese Patent Application No. 202411109714.6, filed on August 13, 2024, entitled “Secondary battery, power consuming device, and liquid retaining polymer for battery”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of batteries, and in particular to a secondary battery, a power consuming device, and a liquid retaining polymer for battery. BACKGROUND

[0004] Batteries, as a green energy system, are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, etc. due to their high energy density, long cycle life, high safety and environmental friendliness, etc.

[0005] However, there are problems such as electrolyte consumption and local dryness in the use of batteries, which leads to a shortened cycle life of the battery, etc. Therefore, improving the liquid retention performance of the electrolyte is crucial for improving the cycle performance of the battery. SUMMARY

[0006] The present disclosure is made in view of the above-mentioned problems, and aims to provide a secondary battery, a power consuming device, and a liquid retaining polymer for battery. The secondary battery has excellent cycle performance and kinetic performance.

[0007] To achieve the above-mentioned purpose, the present disclosure provides a secondary battery in a first aspect. The secondary battery includes a gel composed of a liquid retaining polymer and at least a portion of an electrolyte, the liquid retaining polymer including a structural unit represented by Formula (I), a structural unit represented by Formula (II), and a structural unit derived from monomer (III),

[0008] In formula (I) and formula (II), R1, R2, R3, R4, R5, R6, R7are 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-C10 alkyl, C1-C10 alkoxy, C2-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-C10 alkyl, 6- to 10-membered aryl;

[0009] R8is selected from substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted 6- to 10-membered aryl, substituted or unsubstituted C2-C10 alkenyl; when C1-C10 alkyl, 6- to 10-membered aryl, C2-C10 alkenyl has a substituent, the substituent each independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1-C10 alkyl, 6- to 10-membered aryl;

[0010] R9is a connecting bond or C1-C6 alkylene;

[0011] The structural unit derived from monomer (III) is selected from one or more of a structural unit derived from a monomer having a nitrile group, a structural unit derived from a monomer having an amide group, a structural unit derived from a monomer having a sulfonate group, and a structural unit represented by formula (IV),

[0012] In formula (IV), R 10 is hydrogen or C1-C6 alkyl, R 11 is C1-C6 alkyl or (meth)acryloyl, and p is 3-50.

[0013] The above liquid-retaining polymer has strong electrolyte absorption capacity and high lithium ion transmission efficiency, and by including the liquid-retaining polymer, the secondary battery has excellent cycle performance and kinetic performance.

[0014] In some embodiments, in formula (I) and formula (II), R1, R2, R3, R4, R5, R6, R7are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester, unsubstituted C1-C10 alkyl, unsubstituted C1-C10 alkoxy. Thereby, it is more conducive to improving the cycle performance and kinetic performance of the secondary battery.

[0015] In some embodiments, in formula (I) and formula (II), R1, R2, R3, R4, R5, R6, R7are each independently selected from hydrogen, carboxyl, ester group, unsubstituted C1-C6 alkyl; R8is selected from unsubstituted C1-C6 alkyl; R9is a connecting bond or methylene; R 10 is hydrogen or methyl, R 11 is methyl, ethyl or (meth)acryl. Thus, the cycle performance and kinetic performance of the secondary battery are further improved.

[0016] In some embodiments, in formula (I) and formula (II), R1, R2, R3, R4, R5, R6, R7are each independently selected from hydrogen, unsubstituted C1-C4 alkyl; R8is selected from unsubstituted C1-C4 alkyl; R9is a connecting bond; R 10 and R 11 are each methyl. Thus, the cycle performance and kinetic performance of the secondary battery are further improved.

[0017] In some embodiments, in the liquid-retaining polymer, the molar content of the structural unit derived from monomer (III) is 8%-22%. In some embodiments, the molar content of the structural unit derived from monomer (III) is 8%-15%. Thus, the cycle performance and kinetic performance of the secondary battery are further improved.

[0018] In some embodiments, in the liquid-retaining polymer, the molar ratio of the structural unit represented by formula (I) to the structural unit represented by formula (II) is 1:(0.8-6). In some embodiments, the molar ratio of the structural unit represented by formula (I) to the structural unit represented by formula (II) is 1:(3-6). Thus, the cycle performance of the secondary battery is further improved.

[0019] In some embodiments, the liquid-retaining polymer comprises a crosslinking structure. By comprising a crosslinking structure, the strength of the liquid-retaining polymer can be improved, and the network structure formed by the polymer chains after crosslinking can further improve the liquid-retaining capacity.

[0020] In some embodiments, the liquid-retaining polymer has a swelling ratio of 4-8 with respect to the electrolyte.

[0021] In some embodiments, the liquid-retaining polymer has an electrical conductivity of 0.7 mS / cm-1.5 mS / cm.

[0022] In some embodiments, the secondary battery comprises a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material and a liquid-retaining polymer. By causing the negative electrode film layer to comprise the above-mentioned liquid-retaining polymer, the risk of local electrolyte dry-out of the negative electrode sheet and lithium metal precipitation on the negative electrode film sheet leading to cycle diving can be reduced.

[0023] In some embodiments, in the negative electrode film layer, the mass content of the liquid-retaining polymer is 0.5%-2% relative to the mass of the negative electrode film layer. In some embodiments, in the negative electrode film layer, the mass content of the liquid-retaining polymer is 0.5%-1% relative to the mass of the negative electrode film layer. In this way, it is more conducive to reducing the impedance of the secondary battery while ensuring the improvement of the cycle performance.

[0024] In some embodiments, the group margin in the thickness direction of the secondary battery is 88%-94%. In this way, the proportion of the energy storage substance in the battery can be increased, which is conducive to improving the energy density of the battery.

[0025] In some embodiments, the secondary battery comprises a battery with tab distribution on the opposite side. In this way, the system and structure can be optimized, and it is more conducive to improving the energy density of the battery.

[0026] In some embodiments, the positive electrode active material of the secondary battery comprises a lithium transition metal oxide, the lithium transition metal oxide comprises a nickel element, and in the lithium transition metal oxide, the molar content of the nickel element relative to all metal elements other than lithium is 80% or more; the negative electrode active material of the secondary battery comprises graphite and / or a silicon-based negative electrode material. In this way, the gravimetric capacity of the positive electrode active material and the negative electrode active material can be improved, which is further conducive to improving the energy density of the battery.

[0027] In some embodiments, the secondary battery is a winding type battery.

[0028] The second aspect of the present disclosure provides a power utilization device comprising the secondary battery of the first aspect of the present disclosure.

[0029] The power utilization device of the present disclosure comprises the secondary battery provided by the present disclosure, and thus has at least the same advantages as the secondary battery.

[0030] The third aspect of the present disclosure provides a liquid-retaining polymer for a battery. The liquid-retaining polymer comprises a structural unit represented by formula (I), a structural unit represented by formula (II), and a structural unit derived from monomer (III),

[0031] In formula (I) and formula (II), R1, R2, R3, R4, R5, R6, R7are 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-C10 alkyl, C1-C10 alkoxy, C2-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-C10 alkyl, 6- to 10-membered aryl;

[0032] R8is selected from substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted 6- to 10-membered aryl, substituted or unsubstituted C2-C10 alkenyl; when C1-C10 alkyl, 6- to 10-membered aryl, C2-C10 alkenyl has a substituent, the substituent each independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1-C10 alkyl, 6- to 10-membered aryl;

[0033] R2is a connecting bond or C1-C6 alkylene;

[0034] The structural unit derived from monomer (III) is selected from one or more of a structural unit derived from a monomer having a nitrile group, a structural unit derived from a monomer having an amide group, a structural unit derived from a monomer having a sulfonate group, and a structural unit represented by formula (IV),

[0035] In formula (IV), R 10 is hydrogen or C1-C6 alkyl, R 11 is C1-C6 alkyl or (meth)acryloyl, and p is 3-50.

[0036] The above liquid-retaining polymer has strong electrolyte absorption capacity and high lithium ion transmission efficiency, and by including the liquid-retaining polymer, the secondary battery has excellent cycle performance and kinetic performance.

[0037] In some embodiments, in formula (I) and formula (II), R1, R2, R3, R4, R5, R6, R7are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester, unsubstituted C1-C10 alkyl, unsubstituted C1-C10 alkoxy. Thereby, it is more conducive to improving the cycle performance and kinetic performance of the secondary battery.

[0038] In some embodiments, in formula (I) and formula (II), R1, R2, R3, R4, R5, R6, R7are each independently selected from hydrogen, carboxyl, ester group, unsubstituted C1-C6 alkyl; R8is selected from unsubstituted C1-C6 alkyl; R9is a connecting bond or methylene; R 10 is hydrogen or methyl, R 11 is methyl, ethyl or (meth)acryl. Thus, the cycle performance and kinetic performance of the secondary battery are further improved.

[0039] In some embodiments, in formula (I) and formula (II), R1, R2, R3, R4, R5, R6, R7are each independently selected from hydrogen, unsubstituted C1-C4 alkyl; R8is selected from unsubstituted C1-C4 alkyl; R9is a connecting bond; R 10 and R 11 are each methyl. Thus, the cycle performance and kinetic performance of the secondary battery are further improved.

[0040] In some embodiments, in the liquid-retaining polymer, the molar content of the structural unit derived from monomer (III) is 8%-22%. In some embodiments, the molar content of the structural unit derived from monomer (III) is 8%-15%. Thus, the cycle performance and kinetic performance of the secondary battery are further improved.

[0041] In some embodiments, in the liquid-retaining polymer, the molar ratio of the structural unit represented by formula (I) to the structural unit represented by formula (II) is 1:(0.8-6). In some embodiments, the molar ratio of the structural unit represented by formula (I) to the structural unit represented by formula (II) is 1:(3-6). Thus, the cycle performance of the secondary battery is further improved.

[0042] In some embodiments, the liquid-retaining polymer comprises a crosslinking structure. By comprising a crosslinking structure, the strength of the liquid-retaining polymer can be improved, and the network structure formed by the polymer chains after crosslinking can further improve the liquid-retaining capacity.

[0043] In some embodiments, the liquid-retaining polymer has a swelling ratio of 4-8 with respect to the electrolyte.

[0044] In some embodiments, the liquid-retaining polymer has an electrical conductivity of 0.7 mS / cm-1.5 mS / cm. BRIEF DESCRIPTION OF DRAWINGS

[0045] FIG. 1 schematically shows a battery structure with tab hetero-distribution.

[0046] FIG. 2 is a schematic view of a battery cell according to an embodiment of the present disclosure.

[0047] FIG. 3 is an exploded view of the battery cell shown in FIG. 2 according to an embodiment of the present disclosure.

[0048] Figure 4 is a schematic diagram of a battery module according to one embodiment of the present disclosure.

[0049] Figure 5 is a schematic diagram of a battery pack according to one embodiment of the present disclosure.

[0050] Figure 6 is an exploded view of a battery pack according to an embodiment of the present disclosure, as shown in Figure 5.

[0051] 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.

[0052] 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

[0053] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the secondary battery, power-consuming device, and battery-retaining polymer 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.

[0054] 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.

[0055] If not particularly specified, all the embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0056] If not particularly specified, all the technical features and optional technical features of the present disclosure can be combined with each other to form new technical solutions.

[0057] If not particularly specified, all the steps of the present disclosure can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, it is mentioned that the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0058] If not particularly specified, the terms used in the present disclosure have the commonly understood meanings understood by those skilled in the art.

[0059] If not particularly specified, the values of the parameters mentioned in the present disclosure can be measured by various test methods commonly used in the art, for example, the test methods given in the present disclosure can be used.

[0060] If not particularly specified, in the present disclosure, the term "active ion" refers to an ion that can be reversibly inserted and extracted between the positive and negative electrodes of a secondary battery, including but not limited to lithium ion.

[0061] In use, the electrolyte of the secondary battery is consumed, partially dried, etc., which leads to problems such as shortening of the cycle life of the battery. In addition, the requirement for energy density is increasing, and it is often necessary to increase the margin and reduce the liquid injection coefficient to increase the proportion of energy storage materials in the battery, thereby increasing the energy density of the battery. In particular, as shown in FIG. 1, the soft pack battery in which the tabs 54 are distributed on the opposite sides in the shell 51 can optimize the system and structure in terms of engineering design. However, the electrode assembly of the battery of this structure has a wound cell, which is placed horizontally in use, and the electrolyte in the upper corner area 56 is easily discharged under the influence of gravity, cyclic expansion force, etc., causing electrolyte deficiency, which leads to blocked lithium ion transport, increased polarization on the upper corner side, and the lithium deposition potential (0V vs Li / Li + ), Li + not inserted into the negative active material but deposited on the upper corner side, which increases the risk of lithium precipitation in this part, resulting in irreversible Li loss and accelerated battery capacity decay and poor cycle performance.

[0062] To improve the above problems, there are reports that propose a method of providing a liquid retaining layer at the outermost side of the battery, but this method has insufficient adsorption capacity for electrolyte, and on the other hand, causes a decrease in ion transport efficiency, resulting in an increase in the impedance of the battery and a decrease in the kinetic performance.

[0063] Based on this, the present disclosure proposes a secondary battery, a power using device, and a liquid retaining polymer. The following is described in detail.

[0064] Secondary battery

[0065] A first aspect of the present disclosure provides a secondary battery. The secondary battery includes a liquid retaining polymer containing at least a portion of an electrolyte in a gel composed of the liquid retaining polymer, the liquid retaining polymer including a structural unit represented by Formula (I), a structural unit represented by Formula (II), and a structural unit derived from monomer (III),

[0066] In Formula (I) and Formula (II), R1, R2, R3, R4, R5, R6, R7 are each independently selected from hydrogen, a hydroxyl group, a nitro group, a cyano group, a carboxyl group, an ester group, a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C1-C10 alkoxy group, a substituted or unsubstituted C2-C10 alkenyl group, a substituted or unsubstituted 6- to 10-membered aryl group, a substituted or unsubstituted 5- to 10-membered heteroaryl group, a substituted or unsubstituted 3- to 8-membered cycloalkyl or heterocycloalkyl group; when the C1-C10 alkyl group, the C1-C10 alkoxy group, the C2-C10 alkenyl group, the 6- to 10-membered aryl group, the 5- to 10-membered heteroaryl group, the 3- to 8-membered cycloalkyl or heterocycloalkyl group has a substituent, the substituent each independently includes one or more of a hydroxyl group, a nitro group, a cyano group, a carboxyl group, an ester group, a C1-C10 alkyl group, a 6- to 10-membered aryl group;

[0067] R8 is selected from a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted 6- to 10-membered aryl group, a substituted or unsubstituted C2-C10 alkenyl group; when the C1-C10 alkyl group, the 6- to 10-membered aryl group, the C2-C10 alkenyl group are substituted, their substituents each independently include one or more of a hydroxyl group, a nitro group, a cyano group, a carboxyl group, an ester group, a C1-C10 alkyl group, a 6- to 10-membered aryl group;

[0068] R9 is a bond or a C1-C6 alkylene group;

[0069] The structural unit derived from monomer (III) is selected from one or more of a structural unit derived from a monomer having a nitrile group, a structural unit derived from a monomer having an amide group, a structural unit derived from a monomer having a sulfonate group, and a structural unit represented by Formula (IV),

[0070] In Formula (IV), R 10R is hydrogen or C1-C6alkyl, R 11 R is C1-C6alkyl or (meth)acryloyl, p is 3-50, and the electrolyte includes electrolyte in a gel and free electrolyte.

[0071] The above liquid-retaining polymer has a strong adsorption capacity for electrolyte, can swell to form a jelly-like gel, has a certain strength, and can bind electrolyte. The electrolyte bound by the gel can resist the extrusion of gravity and swelling force, so as to always bind electrolyte in the upper corner area of the wound battery. In addition, the liquid-retaining polymer contains a group with strong affinity for lithium ions, thereby reducing the lithium ion transmission impedance and improving the kinetic characteristics. Therefore, by including the above liquid-retaining polymer in the secondary battery, the secondary battery can have excellent cycle performance and kinetic performance.

[0072] Herein, the term "alkyl" includes both branched and straight chain saturated aliphatic hydrocarbon groups and has the indicated number of carbon atoms, e.g., 1 to 12 carbon atoms. The term "C1-C10 alkyl" as used herein denotes an alkyl group having 1 to 10 carbon atoms, e.g., C1-C8, C1-C6, or C1-C4 alkyl. Examples of alkyl groups include, but are not limited to: methyl, ethyl, n-propyl, i-propyl, n-butyl, 3-methylbutyl, t-butyl, n-pentyl, sec-pentyl, hexyl, heptyl, octyl, iso-octyl, nonyl, decyl.

[0073] Herein, the term "alkylene" refers to a divalent alkyl group having two points of attachment in the compounds of the application. Preferably, it contains 1 to 6 carbon atoms.

[0074] Herein, the term "alkoxy" refers to an alkyl group as defined above having the indicated number of carbon atoms attached via an oxygen bridge. The term "C1-C10 alkoxy" as used herein denotes an alkyl group having 1 to 10 carbon atoms attached via an oxygen bridge, e.g., C1-C8, C1-C6, or C1-C4 alkoxy. Examples of alkoxy groups include, but are not limited to: methoxy, ethoxy, propoxy, butoxy, pentoxy, hexyloxy, heptyloxy, octyloxy, nonyloxy, decyloxy, 3-hexyloxy, and 3-methylpentoxy.

[0075] Herein, the term "alkenyl" refers to straight and branched chain hydrocarbon chains including one or more sites of unsaturation in the form of carbon-carbon double bonds. "C2-C10 alkenyl" herein has 2 to 10 carbon atoms. Alternatively, the alkenyl is lower alkenyl having 2 to 8 carbon atoms, such as C2-C8, C2-C6, and C2-C4 alkenyl. Examples of alkenyl groups include, but are not limited to: ethenyl, propenyl, and butenyl.

[0076] In the present specification, the term "aryl" means an aromatic group having one or more rings formed by a skeleton structure. The "6- to 10-membered aryl group" herein contains 6 to 10 carbon atoms, for example, phenyl, naphthyl. The term "heteroaryl" means an aryl group in which one or more (preferably 1, 2 or 3) carbon atoms are replaced by an oxygen atom, a nitrogen atom, a phosphorus atom or a sulfur atom, for example, 4-pyridyl, 2-imidazolyl, 3-pyrazolyl and isoquinolyl.

[0077] In the present specification, the term "cycloalkyl" means a saturated or partially unsaturated cyclic group having one or more rings as a skeleton structure, for example, containing 3 to 14 carbon atoms. The "3- to 8-membered cycloalkyl group" herein contains 3 to 8 carbon atoms, for example, cyclopropyl, cyclohexyl, tetrahydronaphthalene or cyclohex-2-enyl. The term "heterocycloalkyl" means a cycloalkyl group as defined above in which one or more (preferably 1, 2 or 3) carbon atoms are replaced by an oxygen atom, a nitrogen atom, a phosphorus atom or a sulfur atom, for example, piperidyl, morpholinyl, piperazinyl.

[0078] In the present specification, the structural unit represented by formula (I) is derived from monomer (I) represented by formula (V),

[0079] wherein R1, R2, R3, R4are the same as defined above. As monomer (I), for example, ethylene, propylene, butylene, pentene, hexene, heptene and the like can be mentioned.

[0080] In the present specification, the structural unit represented by formula (II) is derived from monomer (II) represented by formula (VI),

[0081] wherein R5, R6, R7, R8, R9are the same as defined above. As monomer (II), for example, vinyl acetate, allyl acetate and the like can be mentioned.

[0082] As monomer having an acrylonitrile group, for example, acrylonitrile, methacrylonitrile and the like can be mentioned.

[0083] As monomer having an amide group, for example, acrylamide, methacrylamide and the like can be mentioned.

[0084] As monomer having a sulfonate group, for example, 3-sulfopropyl methacrylate lithium salt (represented by formula (VII)) and the like can be mentioned,

[0085] The structural unit shown in formula (IV) is derived from monomer (IIIa), as monomer (IIIa) can be exemplified by polyethylene glycol methyl ether methacrylate (PEGMEMA), polyethylene glycol ethyl ether methacrylate (PEGEEMA), polyethylene glycol methyl ether acrylate (PEGMEA), polyethylene glycol ethyl ether acrylate (PEGEEA), polyethylene glycol dimethacrylate (PEGDMA), and the like.

[0086] The structural units in the liquid-retaining polymer of the present application can be determined by instruments and methods known in the art. For example, by employing Fourier infrared test, the stretching vibration of carbonyl group derived from vinyl acetate and carbonyl group derived from monomer (IIIa) corresponds to absorption peak at 1740-1730 cm -1 , the asymmetric stretching vibration of ester group ether bond derived from vinyl acetate and PEGMEMA (-(O=)C-O-C-) corresponds to absorption peak at 1240-1110 cm -1 .

[0087] In some embodiments, in formula (I) and formula (II), R1, R2, R3, R4, R5, R6, R7are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester group, unsubstituted C1-C10 alkyl, unsubstituted C1-C10 alkoxy. The liquid-retaining polymer with the above structure has stronger adsorption of electrolyte capacity and higher lithium ion transmission effect. Alternatively, in formula (I) and formula (II), R1, R2, R3, R4, R5, R6, R7are each independently selected from hydrogen, carboxyl, ester group, unsubstituted C1-C6 alkyl; R8is selected from unsubstituted C1-C6 alkyl; R9is a connecting bond or methylene; R 10 is hydrogen or methyl, and R 11 is methyl, ethyl or (meth)acryl. Further alternatively, in formula (I) and formula (II), R1, R2, R3, R4, R5, R6, R7are each independently selected from hydrogen, unsubstituted C1-C4 alkyl; R8is selected from unsubstituted C1-C4 alkyl; R9is a connecting bond; R 10 and R 11 are each methyl.

[0088] In some embodiments, the molar content of the structural unit derived from monomer (III) in the liquid-retaining polymer is 8%-22%. By having the content within the above range, it is further beneficial to improve the migration and transmission rate of lithium ion and to enhance the kinetic performance of the secondary battery. Exemplarily, the molar content of the structural unit derived from monomer (III) in the liquid-retaining polymer is 8%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, 22% or any value within the range composed of any two of the values. Alternatively, the molar content of the structural unit derived from monomer (III) is 8%-15%.

[0089] In some embodiments, the molar ratio of the structural unit represented by formula (I) to the structural unit represented by formula (II) in the liquid-retaining polymer is 1:(0.8-6). In this way, the affinity for the electrolyte is further improved, and the adsorption capacity of the electrolyte is increased. For example, the molar ratio of the structural unit represented by formula (I) to the structural unit represented by formula (II) in the liquid-retaining polymer is 1:0.8, 1:1, 1:2, 1:3, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, or any value within the range defined by any two of the above values. Alternatively, the molar ratio of the structural unit represented by formula (I) to the structural unit represented by formula (II) is 1:(3-6).

[0090] In some embodiments, the liquid-retaining polymer comprises a crosslinked structure. The method for forming the crosslinked structure is not particularly limited, and crosslinking can be performed using a crosslinking agent, such as an organic peroxide, for example, dicumyl peroxide, benzoyl peroxide, di-t-butyl peroxide, or the like. By comprising a crosslinked structure, the strength of the liquid-retaining polymer can be improved, and the extrusion resistance against the force of gravity and the swelling force is further improved. In addition, the network structure formed by the polymer chains after crosslinking can further improve the liquid-retaining capacity.

[0091] In some embodiments, the liquid-retaining polymer has a swelling ratio of 4-8 with respect to the electrolyte. For example, the liquid-retaining polymer has a swelling ratio of 4, 5, 6, 7, 8, or any value within the range defined by any two of the above values.

[0092] The "swelling ratio" of the liquid-retaining polymer mentioned in the present disclosure reflects the liquid-retaining capacity of the liquid-retaining polymer, and can be determined by the following steps: after drying the liquid-retaining polymer at 100°C for 24h, cut it into small pieces, take about 0.5g, measure the initial mass, immerse it in 40g of electrolyte (dissolve LiPF6 in a mixed solvent of ethylene carbonate, diethyl carbonate and dimethyl carbonate in a volume ratio of 1:1:1, and the concentration of LiPF6 is 1mol / L), take it out after incubation at 60°C for 96h, wipe off the surface free electrolyte, and measure the mass at 96h. Swelling ratio = (mass at 96h-initial mass) ÷ initial mass.

[0093] In some embodiments, the liquid-retaining polymer has an electrical conductivity of 0.7mS / cm-1.5mS / cm. For example, the liquid-retaining polymer has an electrical conductivity of 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5mS / cm, or any value within the range defined by any two of the above values.

[0094] The "conductivity" of the liquid-retaining polymer mentioned in the present disclosure reflects the ability of the liquid-retaining polymer to transport ions, and can be determined by the following steps: 200 μL of a liquid-retaining polymer emulsion (solid content 53 wt%) is dropped onto a stainless steel sheet with a diameter of 20 mm and a thickness of 0.4 mm, and a film is obtained by spin coating at a speed of 2000 rpm (acceleration 500 rpm / s) for 2 min; the total thickness d1 of the steel sheet and the film is measured with a micrometer, and the thickness d2 of the steel sheet is subtracted, and the thickness value d of the film is d1-d2; the film-attached stainless steel sheet is loaded into a positive shell of a button cell in a glove box (center alignment), 100 μL of an electrolyte is added, and after the film is soaked for 2 min, a stainless steel sheet with a diameter of 14 mm and a thickness of 0.4 mm is stacked on the soaked film (center alignment); on the stainless steel sheet with a diameter of 14 mm and a thickness of 0.4 mm, a hollow circular truncated cone type stainless steel buffer spring with a large base diameter of 20 mm is further stacked (center alignment, large circular base upward), and then the negative shell of the button cell is buckled; the assembled button cell is placed on the sample stage of an automatic packaging machine, and the sealing is completed under a pressure of 75 kg / cm 2 The conductivity of the liquid-retaining polymer mentioned in the present disclosure reflects the ability of the liquid-retaining polymer to transport ions, and can be determined by the following steps: 200 μL of a liquid-retaining polymer emulsion (solid content 53 wt%) is dropped onto a stainless steel sheet with a diameter of 20 mm and a thickness of 0.4 mm, and a film is obtained by spin coating at a speed of 2000 rpm (acceleration 500 rpm / s) for 2 min; the total thickness d1 of the steel sheet and the film is measured with a micrometer, and the thickness d2 of the steel sheet is subtracted, and the thickness value d of the film is d1-d2; the film-attached stainless steel sheet is loaded into a positive shell of a button cell in a glove box (center alignment), 100 μL of an electrolyte is added, and after the film is soaked for 2 min, a stainless steel sheet with a diameter of 14 mm and a thickness of 0.4 mm is stacked on the soaked film (center alignment); on the stainless steel sheet with a diameter of 14 mm and a thickness of 0.4 mm, a hollow circular truncated cone type stainless steel buffer spring with a large base diameter of 20 mm is further stacked (center alignment, large circular base upward), and then the negative shell of the button cell is buckled; the assembled button cell is placed on the sample stage of an automatic packaging machine, and the sealing is completed under a pressure of 75 kg / cm

[0095] The conductivity of the liquid-retaining polymer mentioned in the present disclosure reflects the ability of the liquid-retaining polymer to transport ions, and can be determined by the following steps: 200 μL of a liquid-retaining polymer emulsion (solid content 53 wt%) is dropped onto a stainless steel sheet with a diameter of 20 mm and a thickness of 0.4 mm, and a film is obtained by spin coating at a speed of 2000 rpm (acceleration 500 rpm / s) for 2 min; the total thickness d1 of the steel sheet and the film is measured with a micrometer, and the thickness d2 of the steel sheet is subtracted, and the thickness value d of the film is d1-d2; the film-attached stainless steel sheet is loaded into a positive shell of a button cell in a glove box (center alignment), 100 μL of an electrolyte is added, and after the film is soaked for 2 min, a stainless steel sheet with a diameter of 14 mm and a thickness of 0.4 mm is stacked on the soaked film (center alignment); on the stainless steel sheet with a diameter of 14 mm and a thickness of 0.4 mm, a hollow circular truncated cone type stainless steel buffer spring with a large base diameter of 20 mm is further stacked (center alignment, large circular base upward), and then the negative shell of the button cell is buckled; the assembled button cell is placed on the sample stage of an automatic packaging machine, and the sealing is completed under a pressure of 75 kg / cm

[0096] The preparation method of the liquid-retaining polymer in the present disclosure is not particularly limited, for example, a mixture of monomer (I) comprising a structural unit represented by formula (I), monomer (II) comprising a structural unit represented by formula (II), and monomer (III) can be polymerized by an emulsion polymerization method.

[0097] The term "secondary battery" mentioned herein refers to a battery cell, a battery module, or a battery pack. The following are described separately.

[0098] Generally, a battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During charging and discharging of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and mainly serves to prevent short circuiting of the positive and negative electrodes, while allowing ions to pass through.

[0099] Negative electrode sheet

[0100] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.

[0101] In some embodiments, the negative electrode film layer includes a negative electrode active material and the liquid-retention polymer described above. After the liquid-retention polymer is added to the negative electrode slurry and dispersed sufficiently, the liquid-retention system can be formed on the surface of the graphite and in the stacking gap through a drying process, can sufficiently adsorb the electrolyte, form a gel, and can lock the electrolyte at the upper corner of the sheet at all times, reducing the influence of gravity and expansion force on the distribution of the electrolyte.

[0102] In some embodiments, in the negative electrode film layer, the mass content of the liquid-retention polymer is 0.5%-2% relative to the mass of the negative electrode film layer, illustratively, can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.2%, 1.4%, 1.5%, 1.8%, 2%, or any value within the range between any two values. By including the liquid-retention polymer in the negative electrode sheet in the above content, the adsorption capacity of the negative electrode sheet for the electrolyte can be improved, and the lithium ion transmission efficiency can be improved, so that the secondary battery has excellent cycle performance and kinetic performance. Alternatively, in the negative electrode film layer, the mass content of the liquid-retention polymer is 0.5%-1% relative to the mass of the negative electrode film layer.

[0103] As an example, the negative electrode current collector has two opposite surfaces in the thickness direction of itself, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0104] In some embodiments, the negative electrode current collector can adopt a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be adopted. The composite current collector can include a high polymer material base layer and a metal layer formed on at least one surface of the high polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a high polymer material base layer (such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0105] In some embodiments, the negative electrode film layer includes a negative electrode active material. The negative electrode active material can employ a negative electrode active material known in the art for use in a battery. As an example, the negative electrode active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy. However, the present disclosure is not limited to these materials, and other conventional materials that can be used as a negative electrode active material for a battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0106] In some embodiments, the negative electrode active material includes graphite with a gravimetric capacity of ≥ 355 mAh / g, or silicon-doped graphite in which silicon:graphite = (5-25):(95-75) by weight. In this way, the gravimetric capacity of the negative electrode active material can be increased, further facilitating an increase in the energy density of the battery.

[0107] In some embodiments, the negative electrode film layer can also optionally include a binder. The binder can 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 (CMC-Na), and carboxymethyl chitosan (CMCS).

[0108] In some embodiments, the negative electrode film layer can also optionally include a conductive agent. The conductive agent can be selected from at least one of super-conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0109] In some embodiments, the negative electrode film layer can also optionally include other auxiliary agents, such as thickening agents, etc.

[0110] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, the liquid-retaining polymer, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying, cold pressing, etc., the negative electrode sheet can be obtained.

[0111] Positive electrode sheet

[0112] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material and optionally the above-mentioned liquid-retaining polymer.

[0113] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is provided on either one or both of the two opposite surfaces of the positive electrode current collector.

[0114] In some embodiments, the positive electrode current collector can employ a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0115] In some embodiments, when the battery cell is a lithium ion battery, the positive electrode active material can employ a positive electrode active material for a lithium ion battery known in the art. As an example, the positive electrode active material can include at least one of a lithium-containing phosphate having an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present disclosure is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material can also be used. These positive electrode active materials can be used alone only one or in combination of two or more. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2(also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.1Al 0.05 O2) and modified compounds thereof, etc. Examples of the lithium-containing phosphate of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (which can also be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon.

[0116] In some embodiments, the positive electrode active material of the secondary battery includes a lithium transition metal oxide including a nickel element, and the molar content of the nickel element is 80% or more with respect to all metal elements other than lithium in the lithium transition metal oxide. In this way, the positive electrode active material capacity can be increased, and the energy density of the battery can be further improved.

[0117] In some embodiments, the battery is accompanied by Li deintercalation and consumption during charging and discharging, and the molar content of Li is different when the battery is discharged to different states. In the enumeration of the positive electrode active material in the present disclosure, the molar content of Li is the initial state of the material, i.e., the state before feeding, and the positive electrode active material is applied to the battery system. After charging and discharging cycles, the molar content of Li changes.

[0118] In the enumeration of the positive electrode active material in the present disclosure, the molar content of O is only the theoretical state value, and the release of oxygen from the lattice causes the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0119] In some embodiments, the positive electrode film layer can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0120] In some embodiments, the positive electrode film layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0121] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, the optional above-mentioned liquid-retaining polymer, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet can be obtained.

[0122] Electrolyte

[0123] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The electrolyte of the present disclosure uses an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent. In some embodiments, the electrolyte solution includes the aforementioned liquid-retaining polymer.

[0124] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0125] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0126] In some embodiments, the electrolyte solution can optionally further include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0127] Separator film

[0128] In some embodiments, the battery cell further includes a separator film. The type of the separator film is not particularly limited in the present disclosure, and any publicly known porous structure separator film having good chemical stability and mechanical stability can be used.

[0129] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0130] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator film can be used to manufacture an electrode assembly through a winding process or a stacking process.

[0131] In some embodiments, the battery cell can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0132] 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 polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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 height of the electrode assembly 52 of the battery to the height of the battery casing 51 in the thickness direction X of the battery cell 5.

[0137] 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. Additionally, the opposite-side tab distribution helps reduce the battery's internal resistance, facilitating high-rate charge and discharge. Furthermore, the opposite-side tab distribution also allows for the design of structures with higher group margins in the thickness direction. This enables system and structure optimization and further improves the battery's energy density.

[0138] Compared with the battery with a small group margin, the battery with a large group margin has a small amount of electrolyte added, thereby increasing the risk of local dryness of the electrolyte. In particular, as shown in FIG. 1, the battery with the tab 54 distributed on the opposite sides of the battery, i.e., the battery with the tab 54 distributed on the opposite sides of the battery, has a high group margin, and the injection amount is designed to be limited. With the effect of gravity and cyclic expansion force, the electrolyte in the upper corner area 56 is discharged, which is prone to cause electrolyte deficiency in the upper corner area, dryness, increase the risk of lithium precipitation in this area, and accelerate the capacity attenuation of the battery and the deterioration of the cycle performance. By including the liquid-retaining polymer of the present disclosure in the battery with such a structure, the gel formed by the liquid-retaining polymer and at least part of the electrolyte can effectively lock the electrolyte in the pole piece, overcome the influence of forces such as gravity and expansion force on the distribution of the electrolyte, reduce the possibility of dryness of the electrolyte in the upper corner area, and further reduce the risk of lithium precipitation and improve the cycle performance of the battery.

[0139] In some embodiments, the positive electrode material of the secondary battery includes a lithium transition metal oxide including a nickel element, and in the lithium transition metal oxide, the molar content of the nickel element is 80% or more with respect to the total molar content of all metal elements other than lithium. The negative electrode material of the secondary battery includes graphite and / or a silicon-based negative electrode material. In these embodiments, the gram capacity of the positive electrode material is high, which is beneficial to improve the capacity of the battery. However, at the same time, the nickel content in the positive electrode material is also high, and the molar content of the nickel element is 80% or more with respect to the total molar content of all metal elements other than lithium. Such a positive electrode material combined with a negative electrode material with a large gram capacity, such as graphite and / or a silicon-based negative electrode material, is prone to lithium precipitation. For these batteries, it is particularly necessary to uniformly bind the electrolyte in the pole piece, so that the pole piece is always soaked in the electrolyte, and the possibility of local dryness and lithium precipitation is reduced. By including the liquid-retaining polymer of the present disclosure in such a battery, the gel formed by the liquid-retaining polymer and at least part of the electrolyte can effectively lock the electrolyte in the pole piece, overcome the influence of forces such as gravity and expansion force on the distribution of the electrolyte, reduce the possibility of dryness of the electrolyte in the local area, and further reduce the risk of lithium precipitation and improve the cycle performance of the battery.

[0140] In some embodiments, the secondary battery is a wound battery.

[0141] In some embodiments, the battery monomer can be assembled into a battery module, and the number of battery monomers contained in the battery module can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0142] FIG. 4 is a battery module 4 as an example. Referring to FIG. 4, in the battery module 4, a plurality of battery cells 5 can be arranged in series along a length direction of the battery module 4. Of course, the plurality of battery cells 5 can be arranged in any other manner. The plurality of battery cells 5 can be fixed by fasteners.

[0143] Optionally, the battery module 4 can further include a housing having an accommodation space in which the plurality of battery cells 5 are accommodated.

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

[0145] FIGS. 5 and 6 are a battery pack 1 as an example. Referring to FIGS. 5 and 6, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0146] Electric device

[0147] A second aspect of the present disclosure also provides an electric device, and the secondary battery of the present disclosure is described below with appropriate reference to the accompanying drawings.

[0148] The electric device mentioned in the embodiments of the present disclosure includes the secondary battery provided by the present disclosure. The secondary battery can be used as a power source of the electric device or as an energy storage unit of the electric device. The electric device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0149] As the electric device, the battery cell, the battery module, or the battery pack can be selected according to the usage requirements thereof.

[0150] FIG. 7 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the electric device, a battery pack or a battery module can be used.

[0151] As another example of the device, it can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinness, and a battery cell can be used as a power source.

[0152] Embodiments

[0153] Hereinafter, the embodiments of the present disclosure will be described. The embodiments described below are exemplary and are for the purpose of explaining the present disclosure and should not be understood as limiting the present disclosure. In the embodiments, specific techniques or conditions not mentioned are performed in accordance with the techniques or conditions described in the literature in the field or in accordance with the product manual. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained commercially.

[0154] Example 1

[0155] Preparation of the liquid-retaining polymer:

[0156] 50 g of PVA1788, 50 g of PVA0588, 10 g of zinc formaldehyde sulfoxylate, and 2350 g of deionized water were added to a high-pressure reaction kettle, the air in the kettle was replaced with nitrogen, and then stirred at room temperature for 30 min. After being heated to 85°C and stirred for 2 h, it was cooled to room temperature.

[0157] Then, 1000 g of vinyl acetate and 660 g of PEGMEMA (average molecular weight 300 g / mol) were added. After the nitrogen in the kettle was replaced with ethylene twice, the pressure was charged with ethylene to 3 MPa, and the stirring speed was set to 500 rpm for pre-emulsification treatment for 30 min.

[0158] After the pre-emulsification treatment was completed, the temperature in the kettle was slowly increased to 80°C, and the reactor pressure and speed were set to 6.0 MPa and 500 rpm, respectively. Then, 2.0% hydrogen peroxide by mass was continuously added at a rate of 3 g / min, and 450 g of vinyl acetate and 450 g of PEGMEMA monomer were continuously added at a rate of 30 g / min after 5 min. During the process, the opening of the ethylene feeding valve was automatically controlled to maintain the pressure in the reactor at 6.0 MPa, and the temperature of the reactor oil bath was automatically controlled to maintain the reaction temperature at 80°C.

[0159] After the continuous monomer feeding was completed, the hydrogen peroxide feeding rate was kept constant, the reaction temperature was maintained at 80°C, and the dropping was continued for 60 min before the reaction was stopped. After reducing the temperature of the material in the reactor to 30°C, the reactor pressure relief valve was gradually opened, and after complete pressure relief, the polymer emulsion was discharged through the discharge valve, with a solid content of 50%. Through infrared spectrum analysis of the organic functional groups of the polymer, the VA unit, the ethylene unit E, and the unit derived from PEGMEMA had their respective characteristic absorption peaks. After comprehensive analysis and evaluation by the infrared test analysis software based on the characteristic peak position, peak strength, and peak shape of the test spectrum, it was found that the molar ratio of the structural unit derived from ethylene to the structural unit derived from vinyl acetate was 1:4, and the molar content of the structural unit derived from PEGMEMA in the obtained liquid-retaining polymer was 15%.

[0160] Preparation of a secondary battery:

[0161] 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 PVDF are mixed, N-methylpyrrolidone solvent is added, and the mixture is coated on both sides of aluminum foil. After cold pressing and cutting, the positive electrode sheet is obtained.

[0162] Preparation of the negative electrode sheet: Artificial graphite, conductive carbon black, sodium carboxymethyl cellulose binder, and liquid-retaining polymer were mixed evenly in deionized water at a mass ratio of 94:2:2:2 to prepare a negative electrode slurry. Next, this negative electrode slurry was coated onto both sides of a copper foil, and after cold pressing and cutting, the negative electrode sheet was obtained.

[0163] 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.

[0164] Separator: A polyethylene film with a thickness of 13μm is used as the separator.

[0165] 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 tabs distributed on opposite sides. 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 group margin of 92% and an electrolyte injection coefficient of 2.4 g / Ah.

[0166] Example 2-3

[0167] The liquid-retaining polymer and the secondary battery were prepared according to the method of Example 1, except that the molar ratio of ethylene to vinyl acetate structural units in the polymerization product was adjusted.

[0168] Example 4

[0169] The liquid-retaining polymer and the secondary battery were prepared according to the method of Example 1, except that the monomer ethylene was replaced with acrylic acid, and the molar ratio of the structural units derived from acrylic acid to the structural units derived from vinyl acetate was 1:4.

[0170] Example 5

[0171] A liquid-retaining polymer and a secondary battery were prepared according to the method of Example 1, except that the monomer vinyl acetate was changed to propylene acetate, and the molar ratio of the structural unit derived from ethylene and the structural unit derived from propylene acetate was 1:4.

[0172] Examples 6-9

[0173] A liquid-retaining polymer and a secondary battery were prepared according to the method of Example 1, except that the monomer PEGMEMA was changed to polyethylene glycol dimethacrylate (PEGDMA, average molecular weight 250 g / mol), acrylonitrile, methacrylamide, 3-sulfopropyl methacrylate lithium salt, respectively, as shown in Table 1.

[0174] Comparative Example 1

[0175] A secondary battery was prepared according to the method of Example 1, except that no liquid-retaining polymer was added during the preparation of the negative electrode sheet. Specifically, the mass ratio of artificial graphite, conductive carbon black, and binder carboxymethyl cellulose sodium in the negative electrode sheet was 96:2:2.

[0176] Comparative Example 2

[0177] A secondary battery was prepared according to the method of Example 1, except that the liquid-retaining polymer in the negative electrode sheet was replaced with ethylene-vinyl acetate copolymer (EVA) during the preparation of the negative electrode sheet, wherein the molar ratio of the structural unit derived from ethylene and the structural unit derived from vinyl acetate was 1:4.

[0178] Properties of the liquid-retaining polymer

[0179] 1. Swelling ratio test

[0180] The polymer emulsion was added to a polytetrafluoroethylene mold, and a film was obtained after drying at 60°C for 24 h. The film was cut into pieces, about 0.5 g was taken, the initial mass was measured, and it was immersed in 40 g of electrolyte (LiPF6 was dissolved in a mixed solvent of ethylene carbonate, diethyl carbonate, and dimethyl carbonate mixed at a volume ratio of 1:1:1, and the concentration of LiPF6 was 1 mol / L), and after 96 h of incubation at 60°C, the surface free electrolyte was wiped off, and the mass at 96 h was measured. Swelling ratio = (mass at 96 h - initial mass) ÷ initial mass.

[0181] 2. Conductivity test

[0182] 200 μL of the liquid-retaining polymer emulsion (solid content 53 wt%) was dropped onto a stainless steel sheet with a diameter of 20 mm and a thickness of 0.4 mm, and a film was obtained by spin coating at a speed of 2000 rpm (acceleration 500 rpm / s) for 2 min. The total thickness d1 of the steel sheet and the film was measured with a micrometer, and the thickness of the film was calculated as d = d1-d2, where d2 was the thickness of the steel sheet.

[0183] The stainless steel sheet with the attached adhesive film was loaded into the positive shell of the button cell (center alignment) in the glove box, 100 μL of electrolyte was added dropwise, and the adhesive film was soaked for 2 min. A stainless steel sheet with a diameter of 14 mm and a thickness of 0.4 mm was stacked on the soaked adhesive film (center alignment).

[0184] A hollow circular truncated cone type stainless steel buffer spring with a large base diameter of 20 mm was continuously stacked on the stainless steel sheet with a diameter of 14 mm and a thickness of 0.4 mm (center alignment, large circular base upward), and then the negative shell of the button cell was buckled. The assembled button cell was placed on the sample stage of the automatic packaging machine, and the sealing was completed under a pressure of 75 kg / cm 2 The sealed button cell was placed in a thermostat at 25°C for 24 hours

[0185] The button cell was subjected to EIS test, and the test parameters were temperature 25±0.5°C, frequency range 1 k Hz-1M Hz, and AC amplitude 10 mV.

[0186] Conductivity = d / (Re x S), where d is the thickness of the material, S is the surface area of the material (the bottom area of the small steel sheet), and Re is the resistance value obtained by fitting the EIS test data.

[0187] 3. Centrifugal electrolyte volume test

[0188] 3.1 Preparation of soft package battery

[0189] A 4 Ah soft package battery was prepared according to the injection coefficient of 3 g / Ah for testing the centrifugal electrolyte volume. The specific preparation process is as follows.

[0190] Preparation of positive electrode sheet: the ternary positive active material (LiNi 0.8 Co 0.1 Mn 0.1 O2, NCM811), conductive carbon black and polyvinylidene fluoride PVDF were mixed according to the mass ratio of 90:5:5, 0.43 times the mass of solvent N-methyl pyrrolidone was added, and the mixture was fully stirred and mixed uniformly to prepare a positive electrode slurry (solid content 70%). Then the positive electrode slurry was coated on both sides of the aluminum foil, and the dry weight of the positive electrode slurry on each side was 15.4 mg / cm 2 . After drying, cold pressing and cutting, a positive electrode sheet with a size of 87 mm x 953 mm was obtained.

[0191] Preparation of the negative electrode sheet: Add artificial graphite, conductive carbon black, binder carboxymethyl cellulose sodium and liquid-retaining polymer (calculated by solid content) in a mass ratio of 94:2:2:2 into 1 times mass of deionized water, mix well after stirring, and then prepare the negative electrode slurry (solid content 50%). Then coat the negative electrode slurry on both sides of the copper foil, and the dry weight of the negative electrode slurry on each side is 9.3 mg / cm 2 After drying, cold pressing and cutting, a negative electrode sheet with a size of 93 mm x 1086 mm is obtained.

[0192] Preparation of the electrolyte: Dissolve LiPF6 in a mixed solvent of ethylene carbonate, diethyl carbonate and dimethyl carbonate mixed in a volume ratio of 1:1:1 to form an electrolyte. In the electrolyte, the concentration of LiPF6 is 1 mol / L.

[0193] Separator: A polyethylene film with a thickness of 13 μm is used as the separator.

[0194] Place in the order of "separator-negative electrode sheet-separator-positive electrode sheet". Fix one end of the positive electrode sheet, the negative electrode sheet and the two separators to the discharge roller, and fix the other end after stacking together to the winding shaft. Rotate the winding shaft by using the motor to wind the positive electrode sheet, the negative electrode sheet and the two separators to obtain a wound electrode assembly. The wound electrode assembly has a structure with the tabs distributed on different sides. Place the wound electrode assembly in an aluminum plastic film shell, inject 12 g of electrolyte, and use a sealing machine to package. Thus, a soft-pack battery with a size of length x width x thickness = 130 mm x 60 mm x 4 mm is prepared.

[0195] 3.2 Test the centrifugal electrolyte amount

[0196] Weigh the total mass M1 of the soft-pack battery after the discharge; cut off the sealing part, weigh the mass M2 of the cut-off part, fill in the air, and then use the sealing machine to package the soft-pack battery; place the soft-pack battery between the steel clamps of the centrifuge, and place one soft-pack battery in each of the two centrifuge arms. Place the soft-pack battery horizontally with the air bag facing outward to facilitate the discharge of the electrolyte centrifuged out of the soft-pack battery. Centrifuge at a speed of 2000 rpm for 30 min; then take out the soft-pack battery from the steel clamps, cut off the sealing part again, pour out the electrolyte, weigh the mass M3 of the battery after centrifugation, and soak the cut-off part in anhydrous ethanol for 15 min, dry in a 60°C oven for 30 min, and then weigh the mass M4 of the part. Calculate the centrifugal electrolyte amount according to the following formula: centrifugal electrolyte amount = (M1-M2-M3-M4) ÷ 4 Ah.

[0197] Battery performance characterization

[0198] 1. Cycle performance test

[0199] 1.1 Capacity calibration process

[0200] The prepared battery was first charged and discharged at a constant temperature of 25°C, constant current charged to 4.25V at a charge current of 0.33C, then constant voltage charged to a current of 0.05C at a voltage of 4.25V, then constant current discharged at a discharge current of 0.33C until the final voltage was 2.8V, and the actual capacity C0 of the battery was recorded.

[0201] 1.2 Cycle test process

[0202] The prepared battery was first charged and discharged at a constant temperature of 25°C, constant current charged to 4.25V at a charge current of 0.33C, then constant voltage charged to a current of 0.05C at a voltage of 4.25V, then constant current discharged at a discharge current of 0.33C until the final voltage was 2.8V, and the actual capacity C0 of the battery was recorded. n， until the capacity decayed to 80% of C1.

[0203] The cycle number corresponding to the capacity decay to 80% was taken as the test result.

[0204] 2. Lithium precipitation test

[0205] The battery with a capacity of 80% of the initial capacity after the above cycle life test was disassembled, and whether there was lithium precipitation at the upper corner was observed.

[0206] 3. Battery direct current resistance DCR (25°C)

[0207] The lithium ion battery was charged to 3.95V at 0.5C, and then constant voltage charged to a current of 0.05C at 25°C; rested for 30min; discharged at 0.1C for 10s (100ms for each point, and the corresponding voltage value U1 was recorded), and discharged at 1C for 1s (100ms for each point, and the corresponding voltage value U2 was recorded).

[0208] Impedance value = (U2-U1) / 1C. "1C" is the current value of completely discharging the battery capacity within 1 hour.

[0209] The compositions of the liquid-retaining polymers prepared in the above examples and comparative examples are shown in Table 1, and the performance test results of the liquid-retaining polymers and secondary batteries are shown in Table 2.

[0210] Table 1

[0211] Note: The structural unit represented by formula (I) is from monomer (I), and the structural unit represented by formula (II) is from monomer (II).

[0212] Table 2

[0213] Wherein, "-" means no corresponding structure; " / " means no corresponding performance test data.

[0214] From the above Table 1 and Table 2, it can be seen that compared with Comparative Example 1 without using the liquid retention polymer, the centrifugal electrolyte amount in Examples 1-9 containing the above liquid retention polymer is significantly reduced, indicating that the liquid retention polymer adsorbs at least part of the electrolyte to form a gel, which can bind the electrolyte, and the cycle number at which the capacity of the secondary battery decays to 80% is significantly increased, improving the cycle performance of the battery.

[0215] In addition, in Comparative Example 2 using ethylene-vinyl acetate copolymer, the cycle performance is slightly improved compared with Comparative Example 1, but is still poor, and the lithium ion conduction performance is decreased, resulting in an increase in the internal resistance DCR of the battery and a decrease in the kinetic performance. Compared with Comparative Example 2, by containing the liquid retention polymer of the present disclosure in Examples 1-9, the cycle performance of the battery is improved, and at the same time, the kinetic performance of the battery is also improved.

[0216] Examples 10-11

[0217] The liquid retention polymer material and the secondary battery were prepared according to the method of Example 1, with the only difference being that the amount of PEGMEMA added in the preparation of the liquid retention polymer was adjusted to change the molar content of the structural unit derived from PEGMEMA in the liquid retention polymer.

[0218] Examples 12-13

[0219] The liquid retention polymer material and the secondary battery were prepared according to the method of Example 1, with the only difference being that the amount of liquid retention polymer added in the preparation of the negative electrode sheet was adjusted.

[0220] Examples 10-13 were tested according to the same method as Example 1, and the results are shown in Table 3.

[0221] Table 3

[0222] From the above Table 3, it can be seen that as the molar content of the structural unit derived from PEGMEMA increases from 8% to 22%, the ionic conductivity increases from 1.08 to about 1.30 mS / cm, because the ether segment in the structural unit derived from PEGMEMA can form a coordination bond with lithium ions, reducing the transmission impedance of lithium ions and improving the lithium ion conductivity.

[0223] In addition, the amount of liquid retention polymer added in the range of 0.5%-2% can improve the cycle performance of the secondary battery.

[0224] Note that the present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present disclosure are included in the technical scope of the present disclosure. Furthermore, various modifications that can be thought of by those skilled in the art, and other modes of embodiment constructed by combining part of the configurations of the embodiments, are also included in the scope of the present disclosure without departing from the spirit of the present disclosure.

Claims

1. A secondary battery, the secondary battery comprising a gel composed of a liquid-retaining polymer and at least a portion of an electrolyte, the liquid-retaining polymer comprising structural units of formula (I), structural units of formula (II), and structural units derived from monomer (III). In the formula (I) and the formula (II), R1, R2, R3, R4, R5, R6, 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 6-10 membered aryl, substituted or unsubstituted 5-10 membered heteroaryl, substituted or unsubstituted 3-8 membered cycloalkyl or heterocycloalkyl; when C1-C10 alkyl, C1-C10 alkoxy, C2-C10 alkenyl, 6-10 membered aryl, 5-10 membered heteroaryl, 3-8 membered cycloalkyl or heterocycloalkyl has a substituent, the substituent each independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1-C10 alkyl, 6-10 membered aryl; R8 is selected from substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted 6-10 membered aryl, substituted or unsubstituted C2-C10 alkenyl; when C1-C10 alkyl, 6-10 membered aryl, C2-C10 alkenyl has a substituent, the substituent each independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1-C10 alkyl, 6-10 membered aryl; R9 is a connecting bond or C1-C6 alkylene; said structural units derived from monomers (III) are selected from one or more of structural units derived from monomers having an acrylonitrile group, structural units derived from monomers having an amide group, structural units derived from monomers having a sulfonate group and structural units of formula (IV), In formula (IV), R 10 is hydrogen or C1-C6 alkyl, R 11 is C1-C6 alkyl or (meth)acryloyl, and p is 3-50.

2. The secondary battery according to claim 1, wherein In the formula (I) and the formula (II), R1, R2, R3, R4, R5, R6, R7 are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester, unsubstituted C1-C10 alkyl, unsubstituted C1-C10 alkoxy.

3. The secondary battery according to claim 2, wherein In said formula (I) and (II), R1, R2, R3, R4, R5, R6, R7are each independently selected from the group consisting of hydrogen, carboxyl, ester, unsubstituted C1-C6alkyl; R8is selected from the group consisting of unsubstituted C1-C6alkyl; R9is a bond or methylene; R 10 is hydrogen or methyl, R 11 is methyl, ethyl or (meth)acryloyl.

4. The secondary battery according to claim 3, wherein In said formula (I) and (II), R1, R2, R3, R4, R5, R6, R7are each independently selected from the group consisting of hydrogen, unsubstituted C1-C4alkyl; R8is selected from the group consisting of unsubstituted C1-C4alkyl; R9is a bond; R 10 and R 11 are each methyl.

5. The secondary battery according to any one of claims 1 to 4, wherein In the liquid-retaining polymer, the molar content of the structural unit derived from the monomer (III) is 8%-22%.

6. The secondary battery according to claim 5, wherein In the liquid-retaining polymer, the molar content of the structural unit derived from the monomer (III) is 8%-15%.

7. The secondary battery according to any one of claims 1 to 6, wherein In the liquid-retaining polymer, the molar ratio of the structural unit represented by the formula (I) to the structural unit represented by the formula (II) is 1:(0.8-6).

8. The secondary battery according to claim 7, wherein In the liquid-retaining polymer, the molar ratio of the structural unit represented by the formula (I) to the structural unit represented by the formula (II) is 1:(3-6).

9. The secondary battery according to any one of claims 1 to 8, wherein The liquid-retaining polymer comprises a crosslinking structure.

10. The secondary battery according to any one of claims 1 to 9, wherein The liquid-retaining polymer has a swelling ratio to electrolyte of 4-8.

11. The secondary battery according to any one of claims 1 to 10, wherein The liquid-retaining polymer has an electrical conductivity of 0.7 mS / cm-1.5 mS / cm.

12. The secondary battery according to any one of claims 1 to 11, wherein The secondary battery comprises a negative electrode tab, the negative electrode tab comprising a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material and the liquid-retaining polymer.

13. The secondary battery according to claim 12, wherein In the negative electrode film layer, the mass content of the liquid-retaining polymer relative to the mass of the negative electrode film layer is 0.5%-2%.

14. The secondary battery according to claim 13, wherein In the negative electrode film layer, the mass content of the liquid-retaining polymer relative to the mass of the negative electrode film layer is 0.5%-1%.

15. The secondary battery according to any one of claims 1 to 14, wherein The secondary battery has a group margin in the thickness direction of 88%-94%.

16. The secondary battery according to any one of claims 1 to 15, wherein The secondary battery comprises a battery with tab heterolateral distribution.

17. The secondary battery according to any one of claims 1 to 16, wherein The positive electrode active material of the secondary battery includes a lithium transition metal oxide including a nickel element, in which the molar content of the nickel element is 80% or more with respect to all metal elements other than lithium; and the negative electrode active material of the secondary battery includes graphite and / or a silicon-based negative electrode material.

18. The secondary battery according to any one of claims 1 to 17, wherein The secondary battery is a wound battery.

19. An electric device comprising the secondary battery according to any one of claims 1 to 18.

20. A liquid-retaining polymer for a battery, the liquid-retaining polymer comprising structural units represented by Formula (I), structural units represented by Formula (II), and structural units derived from monomer (III), In the formula (I) and the formula (II), R1, R2, R3, R4, R5, R6, 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-C10 alkyl, C1-C10 alkoxy, C2-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-C10 alkyl, 6- to 10-membered aryl; R8 is selected from substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted 6- to 10-membered aryl, substituted or unsubstituted C2-C10 alkenyl; when the C1-C10 alkyl, 6- to 10-membered aryl, C2-C10 alkenyl has a substituent, the substituent each independently includes one or more of hydroxyl, nitro, cyano, carboxyl, ester, C1-C10 alkyl, 6- to 10-membered aryl; R9 is a connecting bond or C1-C6 alkylene; the structural units derived from monomers (III) are selected from one or more of structural units derived from monomers having an acrylonitrile group, structural units derived from monomers having an amide group, structural units derived from monomers having a sulfonate group, and structural units of the formula (IV), In formula (IV), R 10 is hydrogen or C1-C6 alkyl, R 11 is C1-C6 alkyl or (meth)acryloyl, and p is 3-50.

21. The liquid-retaining polymer of claim 20, wherein, In the formula (I) and the formula (II), R1, R2, R3, R4, R5, R6, R7 are each independently selected from hydrogen, hydroxyl, nitro, cyano, carboxyl, ester, unsubstituted C1-C10 alkyl, unsubstituted C1-C10 alkoxy.

22. The liquid-retaining polymer of claim 21, wherein, In said formula (I) and (II), R1, R2, R3, R4, R5, R6, R7are each independently selected from the group consisting of hydrogen, carboxyl, ester, unsubstituted C1-C6alkyl; R8is selected from the group consisting of unsubstituted C1-C6alkyl; R9is a bond or methylene; R 10 is hydrogen or methyl, R 11 is methyl, ethyl or (meth)acryloyl.

23. The liquid-retaining polymer of claim 22, wherein, In said formula (I) and (II), R1, R2, R3, R4, R5, R6, R7are each independently selected from the group consisting of hydrogen, unsubstituted C1-C4alkyl; R8is selected from the group consisting of unsubstituted C1-C4alkyl; R9is a bond; R 10 and R 11 are each methyl.

24. The liquid-retaining polymer of any one of claims 20-23, wherein, In the liquid-retaining polymer, the molar content of the structural unit derived from the monomer (III) is 8% to 22%.

25. The liquid-retaining polymer of claim 24, wherein, In the liquid-retaining polymer, the molar content of the structural unit derived from the monomer (III) is 8% to 15%.

26. The liquid-retaining polymer of any one of claims 20-25, wherein, In the liquid-retaining polymer, the molar ratio of the structural unit represented by the formula (I) to the structural unit represented by the formula (II) is 1: (0.8 to 6).

27. The liquid-retaining polymer of claim 26, wherein, In the liquid-retaining polymer, the molar ratio of the structural unit represented by the formula (I) to the structural unit represented by the formula (II) is 1: (3 to 6).

28. The liquid-retaining polymer of any one of claims 20-27, wherein, The liquid-retaining polymer includes a crosslinked structure.

29. The liquid-retaining polymer of any one of claims 20-28, wherein, The liquid-retaining polymer has a swelling ratio with respect to an electrolyte of 4 to 8.

30. The liquid-retaining polymer of any one of claims 20-29, wherein, The liquid-retaining polymer has an electrical conductivity of 0.7 mS / cm to 1.5 mS / cm.

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