Graft electrolyte additive and secondary battery comprising same

Abstract

The invention discloses a grafted electrolyte additive and a secondary battery containing the same. Wherein the grafted electrolyte additive comprises a high-molecular polymer and an electrolyte functional additive chemically bonded with the high-molecular polymer. Accurate distribution of additive molecules in the battery can be realized, so that the cycle life, the rate capability, the safety and the wide temperature range performance of the secondary battery are improved.

Description

Technical Field

[0001] This application belongs to the field of electrochemistry technology, and particularly relates to a grafted electrolyte additive and a secondary battery containing the same. Background Art

[0002] Lithium secondary batteries are widely used in fields such as consumer electronics, electric vehicles, large-scale energy storage, and low-altitude economy, and are the main body of current power sources and advanced energy storage technologies. Sodium secondary batteries are expected to be applied in scenarios such as large-scale energy storage, low-temperature energy storage, and electric two-wheelers due to the advantages of high abundance, low cost, and fast sodium ion transport of sodium elements. The above-mentioned secondary battery application scenarios put forward higher requirements for the cycle life, energy density, power density, safety, and wide-temperature performance of the battery. Developing advanced electrolytes by designing additives is an effective means to improve the actual electrochemical performance of secondary batteries.

[0003] To meet the important requirements for improving the actual electrochemical performance of secondary batteries, many additive molecules have been developed, including conductive additives, film-forming additives, overcharge prevention additives, and additives for improving high and low temperature and fast charging performance. This type of electrolyte additive molecule mainly plays a role in the battery by being added to the bulk electrolyte. However, after adding the additive molecule to the bulk electrolyte, the additive molecule will be evenly distributed in the entire electrolyte region, making it difficult to maximize its function. Therefore, achieving the precise distribution of additive molecules in the battery is an effective means to further improve the actual electrochemical performance of secondary batteries. Summary of the Invention

[0004] To solve the above problems, this application provides a grafted electrolyte additive, a lithium secondary battery and a sodium secondary battery containing the same, aiming to achieve the precise distribution of additive molecules in the battery, thereby improving the cycle life, rate performance, safety, and wide-temperature performance of secondary batteries.

[0005] In the first aspect of this application, a grafted electrolyte additive is provided, including: a polymer, and an electrolyte functional additive chemically bonded to the polymer.

[0006] The grafted electrolyte additive of the present application includes a polymer and an electrolyte functional additive chemically bonded to the polymer. Thus, the grafted electrolyte additive can be applied to the binder, conductive agent, and separator of a secondary battery as part of the electrode layer or separator. In this way, the grafted electrolyte additive can be accurately and stably distributed in the electrode layer or separator according to the user's design, rather than being dispersed in the electrolyte. This is conducive to maximizing the function of the electrolyte additive, realizing functions such as constructing a stable electrolyte-electrode interface, building fast lithium-ion and electron channels, and enhancing the effective contact between electrode particles, thereby allowing the secondary battery to have good cycle life, rate performance, safety, and wide temperature range performance.

[0007] In any embodiment of the present application, the electrolyte functional additive includes one or more of a conductive additive, a film-forming additive, an overcharge prevention additive, an additive for improving high and low temperature performance, and an additive for improving fast charging performance.

[0008] In any embodiment of the present application, the electrolyte functional additive includes one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, methyl fluoroethyl carbonate, ethylene sulfite, dimethyl carbonate, ethylene sulfate, maleic anhydride, biphenyl, cyclohexylbenzene, acrylonitrile, succinonitrile, adiponitrile, 1,3-propane sultone, dimethyl sulfate, trimethyl phosphate, ethyl hexafluorophosphate, hexamethylphosphoric triamide, propyl pentafluorophosphate, ethylene sulfate, terephthalonitrile, p-dimethylbenzoic acid, trifluoroacetate, tris(trimethylsilyl) phosphate.

[0009] In any embodiment of the present application, the number average molecular weight of the polymer is 1×10 3 to 1×10 7 .

[0010] In any embodiment of the present application, the polymer includes one or more of a binder and a separator material.

[0011] In any embodiment of the present application, the binder includes one or more of polyvinylidene fluoride, carboxymethyl cellulose, polytetrafluoroethylene, styrene-butadiene rubber, polyacrylic acid, polyaniline, and polyethylene oxide.

[0012] In any embodiment of the present application, the separator material includes one or more of polyethylene, polypropylene, polyethylene terephthalate, cellulose, polyimide, polyamide, spandex, and aramid.

[0013] In any embodiment of the present application, the grafted electrolyte additive is obtained by chemically bonding the compound shown in Formula 1 to the polymer, or is polymerized using the compound shown in Formula 1 as a monomer;

[0014]

[0015] Among them, R1, R2, and R3 each independently represent a hydrogen atom, a halogen atom, an oxygen atom, an alkyl group having 1 to 8 carbon atoms, or an alkyl group having 1 to 8 carbon atoms substituted by a halogen atom; n is an integer selected from 1 to 8; R is a derived group obtained by removing a hydrogen atom on one of a methyl group, a methylene group, or a methine group from the molecule of the electrolyte functional additive.

[0016] In any embodiment of the present application, the grafted electrolyte additive is obtained by polymerizing the compound represented by Formula 1 with a monomer of a polymer.

[0017] Optionally, the polymerization method of the compound represented by Formula 1 and the monomer of the polymer includes one or more of photoinitiated polymerization, thermally initiated polymerization, radiation-initiated polymerization, solution polymerization, suspension polymerization, emulsion polymerization, melt polycondensation, interfacial polycondensation, and solution polycondensation.

[0018] The second aspect of the present application provides a secondary battery, including the grafted electrolyte additive according to any embodiment of the first aspect.

[0019] In any embodiment of the present application, the secondary battery includes at least one of a lithium secondary battery and a sodium secondary battery. Description of the Drawings

[0020] Figure 1 It is a schematic structural diagram of the grafted electrolyte additive provided by an embodiment of the present application. Detailed Embodiments

[0021] In order to make the application purpose, technical solutions, and beneficial technical effects of the present application clearer, the following further describes the present application in detail with reference to embodiments. It should be understood that the embodiments described in this specification are only for explaining the present application and are not intended to limit the present application.

[0022] For simplicity, the present application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly recorded; and any lower limit can be combined with other lower limits to form a range not explicitly recorded. Similarly, any upper limit can be combined with any other upper limit to form a range not explicitly recorded. In addition, although not explicitly recorded, each point or single value between the range endpoints is included in this range. Thus, each point or single value can be used as its own lower limit or upper limit and combined with any other point or single value or combined with other lower limits or upper limits to form a range not explicitly recorded.

[0023] In the description of the present application, it should be noted that unless otherwise specified, "above" and "below" include this number, and "multiple" in "one or more" means two or more.

[0024] The above application content of the present application does not intend to describe every disclosed embodiment or every implementation mode in the present application. The following description more specifically exemplifies exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments, which can be used in various combinations. In each instance, the listing is only as a representative group and should not be construed as exhaustive.

[0025] As used herein, the term "alkyl" refers to a saturated hydrocarbon group, including both straight-chain and branched-chain structures. Examples of alkyl include, but are not limited to, methyl, ethyl, propyl (such as n-propyl, isopropyl), butyl (such as n-butyl, isobutyl, sec-butyl, tert-butyl), pentyl (such as n-pentyl, isopentyl, neopentyl). In various embodiments, C1-C6 alkyl, i.e., alkyl, may contain 1-6 carbon atoms.

[0026] Throughout this specification, substituents of compounds are disclosed in groups or ranges, and it is expressly contemplated that such descriptions include every individual sub-combination of the members of these combined ranges. For example, it is expressly contemplated that the term "C1-C6 alkyl" individually discloses C1, C2, C3, C4, C5, C6, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C6, C2-C5, C2-C4, C2-C3, C3-C6, C3-C5, C3-C4, C4-C6, C4-C5, and C5-C6 alkyl.

[0027] As described in the background art, achieving precise distribution of additive molecules in a battery is an effective means to further improve the actual electrochemical performance of secondary batteries.

[0028] In view of this, through in-depth research and a large number of experiments, the inventors provide a grafted electrolyte additive and a secondary battery containing the same.

[0029] In a first aspect of the present application, a grafted electrolyte additive is provided, including: a polymer, and an electrolyte functional additive chemically bonded to the polymer.

[0030] Figure 1 is a schematic diagram of the molecular structure of the grafted electrolyte additive provided by an embodiment of the present application. As Figure 1 shown, the grafted electrolyte additive molecule may include a polymer molecular chain, and at least one R group grafted on the polymer molecular chain. The R group may be a derivative group obtained by removing a hydrogen atom from one methyl, methylene or methine group of the molecule of the electrolyte functional additive.

[0031] The present application does not limit the type of the polymer, which can be any polymer, as long as it is used in a secondary battery as part of the grafted electrolyte additive molecule and does not cause significant negative impacts on the performance of the secondary battery.

[0032] The present application does not limit the electrolyte functional additive, which can include one or more electrolyte functional additives known in the art. For example, it can include one or more of a conductive additive, a film-forming additive, an overcharge prevention additive, an additive for improving high and low temperature performance, and an additive for improving fast charging performance. Those skilled in the art can select appropriate electrolyte functional additives according to the needs of battery performance.

[0033] The present application does not limit the implementation manner of chemically bonding the electrolyte functional additive to the polymer. As an example, those skilled in the art can modify the electrolyte functional additive and / or the polymer, or select appropriate electrolyte functional additives and polymers, so that the electrolyte functional additive can react with the polymer and thus be grafted onto the polymer. As another example, those skilled in the art can also modify the electrolyte functional additive to introduce polymerizable groups into the electrolyte functional additive molecule to obtain a modified electrolyte functional additive molecule. Subsequently, a grafted electrolyte additive molecule can be obtained through the polymerization reaction of multiple modified electrolyte functional additive molecules; or a grafted electrolyte additive molecule can be obtained by the polymerization reaction of the modified electrolyte functional additive molecule and the monomer of the polymer.

[0034] The grafted electrolyte additive of the present application includes a polymer and an electrolyte functional additive chemically bonded to the polymer. Thus, the grafted electrolyte additive can be applied to the binder, conductive agent, and separator of a secondary battery as part of the electrode layer or separator. In this way, the grafted electrolyte additive can be accurately and stably distributed in the electrode layer or separator according to the user's design, rather than being dispersed in the electrolyte. In this way, it is beneficial to maximize the function of the electrolyte additive and achieve functions such as constructing a stable electrolyte-electrode interface, building fast lithium-ion and electron channels, and enhancing the effective contact between electrode particles, thereby allowing the secondary battery to have good cycle life, rate performance, safety, and wide temperature range performance.

[0035] In some embodiments, the electrolyte functional additive can include one or several of a conductive additive, a film-forming additive, an overcharge prevention additive, an additive for improving high and low temperature performance, and an additive for improving fast charging performance.

[0036] In some embodiments, the electrolyte functional additive may include one or more of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), fluoromethyl ethyl carbonate (FEMC), vinylene carbonate (VC), dimethyl carbonate (DMC), divinyl sulfate (DTD), maleic anhydride (MA), biphenyl (BP), cyclohexylbenzene (CHB), acrylonitrile (AN), succinonitrile (SN), adiponitrile (ADN), 1,3 - propanesultone (PS), dimethyl sulfate (DMS), trimethyl phosphate (TMP), ethyl hexafluorophosphate (FEP), hexamethylphosphoramide (HMPA), propyl pentafluorophosphate (FPP), vinyl ethyl sulfate (VEC), p - terephthalonitrile (PTMN), p - dimethylbenzoic acid (DMTB), trifluoroacetate (TFAE), tris(trimethylsilyl) phosphate (TMSP).

[0037] In some embodiments, the number - average molecular weight of the polymer may be 1×10 3 to 1×10 7 .

[0038] In some embodiments, the polymer includes one or more of a binder and a separator material.

[0039] The above - mentioned binder may include a positive - electrode binder and / or a negative - electrode binder.

[0040] According to the above - mentioned embodiments, the polymer includes one or more of a binder and a separator material. Thus, the grafted electrolyte additive can be used as a binder or a separator material and applied to a secondary battery, which is conducive to achieving the precise distribution of the grafted electrolyte additive in the battery.

[0041] In some embodiments, the binder may include one or more of polyvinylidene fluoride, carboxymethyl cellulose, polytetrafluoroethylene, styrene - butadiene rubber, polyacrylic acid, polyaniline, and polyethylene oxide.

[0042] In some embodiments, the separator material may include one or more of polyethylene, polypropylene, polyethylene terephthalate, cellulose, polyimide, polyamide, spandex, and aramid.

[0043] In some embodiments, the grafted electrolyte additive can be obtained by chemically bonding the compound shown in Formula 1 with the polymer, or polymerized with the compound shown in Formula 1 as a monomer.

[0044]

[0045] In Formula 1, R1, R2, and R3 each independently represent a hydrogen atom, a halogen atom, an oxygen atom, an alkyl group having 1 to 8 carbon atoms, or an alkyl group having 1 to 8 carbon atoms substituted with a halogen atom; n is an integer selected from 1 to 8; R is a derivative group obtained by removing a hydrogen atom from one methylene, methylene, or methine group of the molecule of the electrolyte functional additive.

[0046] In the above embodiment, the compound shown in Formula 1 is chemically bonded to the polymer, which may include the reaction of the compound shown in Formula 1 with some groups on the molecular chain of the polymer, thereby chemically bonding to the polymer; it may also include the polymerization reaction of the compound shown in Formula 1 with the monomer of the polymer, thereby chemically bonding to the polymer.

[0047] It can be understood that the grafted electrolyte additive can be obtained by chemically bonding one or several compounds shown in Formula 1 to the polymer, or polymerized with one or several compounds shown in Formula 1 as monomers, so as to introduce one or more electrolyte functional additives into the grafted electrolyte additive.

[0048] In some embodiments, the grafted electrolyte additive is obtained by polymerizing the compound shown in Formula 1 with the monomer of the polymer.

[0049] Optionally, in some embodiments, the polymerization method of the compound shown in Formula 1 and the monomer of the polymer includes one or several of photoinitiated polymerization, thermally initiated polymerization, radiation-initiated polymerization, solution polymerization, suspension polymerization, emulsion polymerization, melt polycondensation, interfacial polycondensation, and solution polycondensation.

[0050] In some embodiments, the grafted electrolyte additive can be polymerized with the compound shown in Formula 1 as a monomer.

[0051] Optionally, in some embodiments, the polymerization method using the compound shown in Formula 1 as a monomer includes one or several of photoinitiated polymerization, thermally initiated polymerization, radiation-initiated polymerization, solution polymerization, suspension polymerization, emulsion polymerization, melt polycondensation, interfacial polycondensation, and solution polycondensation.

[0052] According to the above embodiment, depending on the difference of the compound shown in Formula 1, it can be directly polymerized into a polymer to be used as a battery conductive agent, binder, separator, or a part thereof.

[0053] The present application also provides a preparation method of a grafted electrolyte additive, including the following steps S10 to S20.

[0054] S10, providing a precursor of an electrolyte functional additive, the molecule of which includes a carbon-carbon double bond and an R group. The R group is a derivative group obtained by removing a hydrogen atom from one methylene, methylene, or methine group of the molecule of the electrolyte functional additive.

[0055] S20. Polymerize the precursor of the electrolyte functional additive to obtain a grafted electrolyte additive.

[0056] In step S20, the polymerization method may include one or more of photoinitiated polymerization, thermally initiated polymerization, radiation-initiated polymerization, solution polymerization, suspension polymerization, emulsion polymerization, melt polycondensation, interfacial polycondensation, and solution polycondensation. Those skilled in the art can select a suitable polymerization method according to the physical and chemical properties of the electrolyte functional additive precursor, which is not limited herein.

[0057] In some embodiments, after step S20, the physical and chemical properties of the grafted electrolyte additive can also be detected. Specifically, the conductivity, adhesiveness, ion permeability, chemical resistance, mechanical properties, thermal stability, etc. of the grafted electrolyte additive can be detected to determine whether the grafted electrolyte additive can be used as a material for battery conductive agents, binders, and separators.

[0058] The present application also provides another method for preparing a grafted electrolyte additive, including the following steps S30 to S40.

[0059] S30. Provide a precursor of an electrolyte functional additive, the molecule of which includes a carbon-carbon double bond and an R group. The R group is a derivative group obtained by removing a hydrogen atom from one of the methyl, methylene, or methine groups of the molecule of the electrolyte functional additive.

[0060] S40. Polymerize the precursor of the electrolyte functional additive with a monomer of a polymer to obtain a grafted electrolyte additive. Optionally, the polymer includes one or more of a binder and a separator material.

[0061] The second aspect of the present application provides a secondary battery, including the grafted electrolyte additive according to any one of the embodiments of the first aspect.

[0062] The secondary battery may include a positive electrode plate, a separator, a negative electrode plate, and an electrolyte. The above-mentioned grafted electrolyte additive can be used as a material for the positive electrode film layer in the positive electrode plate, a separator material, and a material for the negative electrode film layer in the negative electrode plate, and is distributed in the positive electrode plate, the separator, and the negative electrode plate. The dosage of the grafted electrolyte additive can be determined according to factors such as the function of the grafted electrolyte additive, the use position of the grafted electrolyte additive, and the interaction between the grafted electrolyte additive and the other materials in the battery. Those skilled in the art can select a suitable dosage of the grafted electrolyte additive according to actual needs, which is not limited herein.

[0063] In some embodiments, the secondary battery may include at least one of a lithium secondary battery and a sodium secondary battery. For example, it may include one or more of a lithium-ion battery, a lithium metal battery, a lithium-sulfur battery, a sodium-ion battery, a sodium metal battery, and a solid-state battery. Optionally, the secondary battery may be a button battery, a cylindrical battery, a square battery, or a soft-pack battery.

[0064] In the secondary battery, the positive electrode plate may include a positive electrode active material, which may include positive electrode active materials known in the art and applicable to lithium secondary batteries or sodium secondary batteries. For example, it may include, but is not limited to, one or more of lithium cobaltate, lithium nickel cobalt aluminate, lithium nickel cobalt manganate, lithium manganate, elemental sulfur, sodium cobaltate, sodium nickel iron manganate, sodium iron phosphate, sodium iron sulfate, sodium fluorophosphate, and Prussian blue.

[0065] In the secondary battery, the negative electrode plate may include a negative electrode active material, which may include negative electrode active materials known in the art and applicable to lithium secondary batteries or sodium secondary batteries. For example, it may include, but is not limited to, one or more of graphite, hard carbon, soft carbon, lithium titanate, metallic lithium, and metallic sodium.

[0066] Embodiment

[0067] The following embodiments more specifically describe the content disclosed in the present invention. These embodiments are for illustrative purposes only, as various modifications and variations within the scope of the present invention are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the embodiments are all commercially available.

[0068] Embodiment 1

[0069] Fluoroethylene carbonate (FEC) is a commonly used film-forming additive for lithium battery electrolytes. On the one hand, FEC molecules can undergo a film reaction; on the other hand, FEC molecules can decompose to form LiF with lithium ions, thereby improving the electrolyte-electrode interface properties. Although the interface film-forming performance of FEC is optimized, the intermolecular force of FEC molecules is relatively strong, and an excessive proportion of it will significantly increase the viscosity of the electrolyte and reduce the bulk conductivity. Therefore, the proportion of it added to the bulk electrolyte is limited.

[0070] The molecular structure of FEC is Based on this molecular structure, three grafted additive molecules are designed as follows:

[0071] Molecule 1-1: Molecule 1-2: Molecule 1-3

[0072] For the above three molecules, an initiator (azobisisobutyronitrile) was added respectively and heated to 80 °C to polymerize and synthesize their corresponding high molecular polymers, namely, the high molecular polymer with molecule 1-1 as the monomer, the high molecular polymer with molecule 1-2 as the monomer, and the high molecular polymer with molecule 1-3 as the monomer, to obtain three grafted electrolyte additives.

[0073] For the above three grafted electrolyte additives, LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) was used as the positive electrode active material of the battery and mixed with the three grafted electrolyte additives, PVDF, and conductive agent carbon black in a mass ratio of 94:2:2:2. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred evenly to obtain the positive electrode paste; the positive electrode paste was coated on aluminum foil, and then dried, cold-pressed, and slit to obtain the positive electrode plates corresponding to the three grafted electrolyte additives respectively.

[0074] The positive electrode plates corresponding to the above three grafted electrolyte additives were respectively assembled with a lithium metal negative electrode into button cells, denoted as molecule 1-1 battery, molecule 1-2 battery, and molecule 1-3 battery. The button cells used a PE separator and an electrolyte of 1.0 M LiPF6 + 0.1 M LiFSI in EC / EMC (volume ratio 1:1).

[0075] In addition, a button cell control sample was prepared. The preparation process of the control sample was basically the same as that of the molecule 1-1 battery to the molecule 1-3 battery, except that the positive electrode without any grafted electrolyte additive was used for the control sample.

[0076] The electrochemical performance of each button cell was evaluated. The experimental results are as follows.

[0077]

[0078] Example 2

[0079] In Example 1, the three additive molecule precursors polymerized through self-polymerization reactions to form their corresponding high molecular polymers. In addition, it is also possible to consider grafting FEC additive molecules onto the chain segments of PVDF. Here, molecule 1-3 is selected for illustration.

[0080] Molecule 1-3 and the PVDF precursor vinylidene fluoride (VDF) were mixed according to three mixing mass ratios respectively to obtain three binder precursors. The three mixing mass ratios were 0:10 (control group), 1:10, and 2:10. The three binder precursors were respectively placed in a dimethylformamide solution for polymerization reaction, and the reaction temperature was controlled at 60 °C to obtain three PVDF-based binders.

[0081] For the above three PVDF-based binders, the anode active material graphite, PVDF-based binder, and conductive agent carbon black were respectively mixed according to a mass ratio of 94:4:2, and then dispersed in NMP. After stirring evenly, the anode slurry was obtained; the anode slurry was evenly coated on the surface of the anode current collector copper foil, dried, and then dried, cold-pressed, and slit to obtain the anode electrode sheet.

[0082] Lithium iron phosphate (LFP), binder PVDF, and conductive agent carbon black were mixed according to a mass ratio of 94:3:3, and then dispersed in NMP. After stirring evenly, the cathode slurry was obtained; the cathode slurry was evenly coated on the surface of the cathode current collector aluminum foil, dried, and then dried, cold-pressed, and slit to obtain the cathode electrode sheet.

[0083] PE separator and 1.0 M LiPF6 in EC / DMC (volume ratio 1:1) electrolyte were selected, and the anode electrode sheets corresponding to the above three PVDF-based binders were assembled with the cathode electrode sheets into cylindrical batteries respectively. The cycling performance of the batteries was evaluated in the voltage range of 2.5 - 3.8 V. The experimental results are as follows.

[0084] Mass ratio of molecules 1-3 to VDF 0:10 1:10 2:10 Capacity retention rate at the 500th cycle 88％ 91％ 89％

[0085] Example 3

[0086] Trimethyl phosphate (TMP) is a battery flame retardant additive. It can decompose to generate phosphorus-containing free radicals at high temperatures, which further combine with other free radicals, thereby inhibiting combustion and effectively improving the thermal safety performance of the battery. However, phosphate esters are incompatible with graphite anodes. If TMP is directly introduced into the bulk electrolyte, on the one hand, it is difficult for TMP to form a stable SEI on the anode surface, and on the other hand, it may undergo a co-insertion reaction with lithium ions, damaging the layered structure of graphite. This problem can be solved by the design strategy of grafted electrolyte additives.

[0087] The molecular structure of TMP is The precursor of the grafted electrolyte additive designed based on this structure is The precursor was placed in a dimethylformamide solution and subjected to a polymerization reaction. The reaction temperature was controlled at 80 °C to obtain the grafted electrolyte additive.

[0088] The anode active material graphite, grafted electrolyte additive, binder carboxymethyl cellulose (CMC), and conductive agent carbon black were mixed according to a mass ratio of 94:2.5:2.5:1, and then dispersed in deionized water. After stirring evenly, the anode slurry was obtained; the anode slurry was evenly coated on the surface of the anode current collector copper foil, dried, and then dried, cold-pressed, and slit to obtain the anode electrode sheet.

[0089] After mixing the cathode active material NCM811, grafted electrolyte additive, CMC binder, and conductive agent carbon black in a mass ratio of 94:2:2:2, it was dispersed in deionized water. After stirring evenly, a cathode slurry was obtained. The cathode slurry was evenly coated on the surface of the cathode current collector aluminum foil, dried, and then dried, cold-pressed, and slit to obtain the cathode plate.

[0090] The above-mentioned anode plate and cathode plate were assembled into a 1 Ah soft-pack battery. Among them, a PE separator was used, and the electrolyte was an EC / DMC (volume ratio 1:1) electrolyte of 1.0 M LiPF6.

[0091] In addition, anode plates and cathode plates without grafted electrolyte additives were prepared and assembled into a 1 Ah soft-pack battery to obtain a control sample. In the control sample battery, the electrolyte was added with TMP having the same mass as the grafted electrolyte additive.

[0092] The cycling performance and thermal safety of the soft-pack battery were tested. The results are as follows. In the following table, the thermal initiation temperature T1 can represent the self-heat starting temperature, marking the beginning of an irreversible exothermic reaction inside the battery and being the initial index for thermal stability evaluation. The higher the T1 temperature, the better the thermal stability of the material under normal use conditions. The thermal initiation temperature T2 can represent the thermal runaway starting temperature, which is the triggering temperature of thermal runaway. At this time, intense chemical reactions occur inside the battery, such as redox reactions between the positive and negative electrodes. The higher the T2 temperature, the greater the possibility of the battery passing the safety test and the lower the risk of thermal runaway. The thermal initiation temperature T3 can represent the maximum thermal runaway temperature, which is a key parameter for evaluating the risk of thermal runaway diffusion in the battery. The lower the T3, the smaller the risk of thermal runaway diffusion.

[0093]

[0094]

[0095] Example 4

[0096] The design strategy of the grafted electrolyte additive is not only applicable to lithium batteries but also to sodium batteries. The anode of a sodium-ion battery generally uses hard carbon, and during the charging process, sodium ions adsorb and deposit in the hard carbon, forming metallic sodium. Therefore, the hard carbon anode reacts violently with the conventional electrolyte, which is also the main reason for the rapid capacity decay of sodium-ion batteries. Ethylene carbonate (VC) is a common film-forming additive. In this example, it is considered to be grafted onto the binder segment of the anode of a sodium-ion battery to solve the problem of the anode interface reaction in sodium-ion batteries.

[0097] The molecular structure of VC is On this basis, the precursor structure of the grafted electrolyte additive is considered

[0098] Mix the precursor with VDF at a mixing ratio of 1:10, add azobisisobutyronitrile initiator, and copolymerize at 80 °C to generate a binder (VC-PVDF) of a new block copolymer type.

[0099] Mix the negative electrode active material hard carbon, VC-PVDF-based binder, and conductive agent in a mass ratio of 94:5:1, disperse them in NMP, and stir evenly to obtain a negative electrode slurry; coat the negative electrode slurry evenly on the surface of the negative electrode current collector copper foil, dry it, and then obtain a negative electrode sheet through drying, cold pressing, and slitting.

[0100] Mix the positive electrode active material Na3V2(PO4)3, VC-PVDF-based binder, and conductive agent in a mass ratio of 94:3:3, disperse them in NMP, and stir evenly to obtain a positive electrode slurry; coat the positive electrode slurry evenly on the surface of the positive electrode current collector aluminum foil, dry it, and then obtain a positive electrode sheet through drying, cold pressing, and slitting.

[0101] Assemble the above-mentioned negative electrode sheet and positive electrode sheet into a 1 Ah soft-pack battery. Among them, a PE separator is used, and the electrolyte is an EC / DMC / PC (volume ratio of 1:1:1) electrolyte of 1.0 M NaPF6.

[0102] Test the gas generation situation and cycling performance of the assembled sodium-ion battery above. The obtained results are as follows.

[0103] Sample PVDF VC-PVDF Capacity retention rate at the 100th cycle 85％ 90％ Gas generation situation There is an obvious gas generation site Hardly any gas is generated

[0104] As described above, it is only the specific implementation manner of this application, but the protection scope of this application is not limited thereto. Any person skilled in the art within the technical scope disclosed in this application can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claims.

Claims

1. A grafted electrolyte additive, characterized in that, Comprising: A high molecular polymer, and an electrolyte functional additive chemically bonded to the high molecular polymer.

2. The graft electrolyte additive according to claim 1, wherein The electrolyte functional additive includes one or more of a conductive additive, a film-forming additive, an overcharge prevention additive, an additive for improving high and low temperature performance, and an additive for improving fast charging performance.

3. The grafting electrolyte additive according to claim 1, wherein The electrolyte functional additive includes one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, fluoromethyl ethyl carbonate, ethylene sulfite, dimethyl carbonate, ethylene sulfate, maleic anhydride, biphenyl, cyclohexylbenzene, acrylonitrile, succinonitrile, adiponitrile, 1,3-propane sultone, dimethyl sulfate, trimethyl phosphate, ethyl hexafluorophosphate, hexamethylphosphoric triamide, propyl pentafluorophosphate, ethylene sulfate, terephthalonitrile, p-dimethylbenzoic acid, trifluoroacetate, tris(trimethylsilyl) phosphate.

4. The grafting electrolyte additive according to claim 1, wherein The number-average molecular weight of the polymer is 1×10 3 to 1×10 7 .

5. The graft electrolyte additive according to claim 1, characterized in that, The high molecular polymer includes one or more of a binder and a separator material.

6. The grafted electrolyte additive according to claim 5, wherein The binder includes one or more of polyvinylidene fluoride, carboxymethyl cellulose, polytetrafluoroethylene, styrene-butadiene rubber, polyacrylic acid, polyaniline, and polyethylene oxide; and / or The separator material includes one or more of polyethylene, polypropylene, polyethylene terephthalate, cellulose, polyimide, polyamide, spandex, and aramid.

7. The grafting electrolyte additive according to any one of claims 1-6, characterized in that, The grafted electrolyte additive is obtained by chemically bonding the compound represented by Formula 1 to the high molecular polymer, or is polymerized using the compound represented by Formula 1 as a monomer; Wherein, R1, R2, and R3 each independently represent a hydrogen atom, a halogen atom, an oxygen atom, an alkyl group having 1 to 8 carbon atoms, or an alkyl group having 1 to 8 carbon atoms substituted by a halogen atom; n is an integer selected from 1 to 8; R is a derived group obtained by removing a hydrogen atom from one methyl, methylene, or methine group of the molecule of the electrolyte functional additive.

8. The graft electrolyte additive according to claim 7, wherein, The grafted electrolyte additive is obtained by polymerizing the compound represented by Formula 1 with the monomer of the high molecular polymer; Optionally, the polymerization method of the compound represented by Formula 1 and the monomer of the high molecular polymer includes one or more of photoinitiated polymerization, thermally initiated polymerization, radiation-initiated polymerization, solution polymerization, suspension polymerization, emulsion polymerization, melt polycondensation, interfacial polycondensation, and solution polycondensation.

9. A secondary battery, characterized in that, Comprising the grafted electrolyte additive according to any one of claims 1-8.

10. The secondary battery according to claim 9, characterized in that, The secondary battery includes at least one of a lithium secondary battery and a sodium secondary battery.

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