A negative electrode additive, a negative electrode material, a negative electrode sheet, and a lithium ion secondary battery

Abstract

The application discloses a negative electrode additive, a negative electrode material, a negative electrode sheet and a lithium ion secondary battery, and belongs to the technical field of lithium ion batteries. The negative electrode additive comprises a structural unit derived from 1,1-difluoroethylene, is a telechelic oligomer containing carboxyl or carboxylate at both ends, the 1,1-difluoroethylene unit in the middle has good electrochemical stability and lithium ion conductivity, the introduction of a hexafluoropropylene structure can improve the flexibility of the chain segment, further improve the lithium ion conductivity, and the carboxyl or carboxylate at both ends can provide hydrophilicity, so that the oligomer can be dispersed into an aqueous slurry and mixed, in addition, the carboxyl or carboxylate at both ends, carboxyl sodium or carboxyl potassium can be replaced into lithium carboxylate in an electrolyte, the lithium ion interface migration rate is improved, the internal resistance is reduced, and the cycle performance and high-temperature performance are improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a negative electrode additive, a negative electrode material, a negative electrode sheet, and a lithium-ion secondary battery. Background Technology

[0002] Lithium-ion rechargeable batteries, as highly efficient energy storage devices, are widely used in mobile phones, computers, headphones, and electric vehicles. However, the development of the new energy industry is placing increasingly higher demands on the performance of lithium-ion rechargeable batteries. During the operation of a lithium-ion battery, the negative electrode undergoes volume changes during lithium insertion and extraction, leading to continuous damage and rebuilding of the solid electrolyte interphase (SEI) membrane, consuming electrolyte and active lithium, thus causing battery capacity decay. Furthermore, under high-temperature conditions, the reactivity of the negative electrode material and electrolyte interface increases, side reactions increase, and problems such as SEI membrane dissolution can all cause battery capacity loss and even continuous gas production leading to battery expansion and safety issues. Adding additives to the negative electrode to improve the interfacial stability of the battery negative electrode material is an important means to improve battery cycle performance and high-temperature performance.

[0003] Existing technologies primarily use electrolyte additives to improve the stability of the negative electrode interface. However, electrolyte additives often consume active lithium components during film formation, reducing the battery's initial efficiency and capacity. One existing negative electrode additive is a fluorinated oligomer containing tetrafluoroethyl and ethylene glycol structural units, added at 0.01-5% of the total mass of the negative electrode material. This additive makes the negative electrode slurry more uniformly mixed, which is beneficial for improving battery cycle performance and capacity. However, this negative electrode additive does not improve the high-temperature performance of lithium battery negative electrode materials.

[0004] Therefore, there is a need in this field to develop a negative electrode additive and negative electrode material that can improve the interfacial stability of battery negative electrode materials, thereby improving both battery cycle performance and high-temperature performance. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of existing lithium-ion battery negative electrode additives that cannot synergistically improve battery cycle performance and high-temperature performance, and to provide a negative electrode additive.

[0006] The purpose of this invention is to provide a negative electrode material.

[0007] Another object of the present invention is to provide a negative electrode sheet.

[0008] Another object of the present invention is to provide a lithium-ion secondary battery.

[0009] The above-mentioned objective of this invention is achieved through the following technical solution: A negative electrode additive comprising structural units derived from 1,1-difluoroethylene, having the compound structural formula as shown in Formula 1:

[0010] Formula 1 Among them, 0%≤n / (m+n)≤50%, the weight-average molecular weight range is 500~15000, and M is one or more of H, Li, Na, and K.

[0011] It should be noted that: The negative electrode additive of this invention comprises a structural unit derived from 1,1-difluoroethylene, which is a 1,1-difluoroethylene oligomer. It is a telechelic oligomer containing carboxyl groups or carboxylates at both ends. The central 1,1-difluoroethylene unit exhibits good electrochemical stability and lithium-ion conductivity. The introduction of the hexafluoropropylene structure enhances the flexibility of the chain segments, further improving lithium-ion conductivity. The carboxyl groups or carboxylates at both ends provide hydrophilicity, allowing the oligomer to be dispersed in aqueous slurries. Furthermore, the carboxyl groups at both ends, or sodium or potassium carboxylate, can be replaced by lithium carboxylate in the electrolyte, improving lithium-ion interfacial mobility, reducing internal resistance, and enhancing cycle performance. In addition, the additive is a polymer, capable of forming a strong film on the negative electrode surface, similar to an artificial solid electrolyte film, improving interfacial stability and suppressing side reactions at the negative electrode interface at high temperatures, thereby improving the high-temperature performance of the battery.

[0012] The weight-average molecular weight of the additives in this invention was determined using the following method: The weight-average molecular weight of the copolymer was obtained by gel permeation chromatography (GPC) and converted to polymethyl methacrylate as the standard. The mobile phase was N,N-dimethylacetamide (DMAc).

[0013] In a specific embodiment, the negative electrode additive of the present invention may be, for example: HOOC-(CH2CF2)m-COOH, n / (m+n)=0, weight-average molecular weight is 5220, PDI is 1.79. LiOOC-(CH2CF2)m-COOLi, n / (m+n)=0, weight-average molecular weight is 5310, PDI is 1.78. NaOOC-(CH2CF2)m-COONa, n / (m+n)=0, weight-average molecular weight is 5340, PDI is 1.82. KOOC-(CH2CF2)m-COOK, n / (m+n)=0, weight-average molecular weight is 5460, PDI is 1.81. LiOOC-(CH2CF2)m-(CF2CF(CF3))n-COOLi, n / (m+n)=45%, weight-average molecular weight is 650, PDI is 2.42. LiOOC-(CH2CF2)m-(CF2CF(CF3))n-COOLi, n / (m+n)=22%, weight-average molecular weight is 10300, PDI is 2.25. LiOOC-(CH2CF2)m-(CF2CF(CF3))n-COOLi, n / (m+n)=9%, weight-average molecular weight is 14600, PDI is 2.04.

[0014] The present invention also specifically protects a negative electrode material, which includes a negative electrode active substance, a conductive agent, a dispersant, a binder, and an additive, wherein the additive is the aforementioned negative electrode additive.

[0015] It should be noted that: The negative electrode material of the present invention contains the negative electrode additive of the present invention. The negative electrode additive is distributed on the surface of the negative electrode material and can form a protective film. After being prepared into a lithium-ion battery, the negative electrode additive is located at the interface between the negative electrode and the electrolyte, which improves the interface stability and reduces side reactions, thereby improving the first efficiency, cycle performance and high temperature performance of the lithium-ion battery.

[0016] The negative electrode active material in the negative electrode material of the present invention can be a conventional negative electrode active material in the art, such as one or more of graphitized carbon materials, amorphous carbon materials, and silicon-based materials.

[0017] The conductive agent in the negative electrode material of the present invention can be a conventional conductive agent in the art, such as one or more of carbon black, natural graphite, artificial graphite, carbon fiber, carbon nanotubes, and graphene.

[0018] The dispersant in the negative electrode material of the present invention can be a conventional dispersant in the art, such as sodium carboxymethyl cellulose, polyacrylic acid and its derivatives, sodium alginate or several thereof.

[0019] The binder in the negative electrode material of the present invention can be a conventional binder in the art, such as one or more of polyacrylic acid and its derivatives, styrene-butadiene emulsion, and acrylate emulsion.

[0020] In a specific embodiment, the mass content of the negative electrode additive is preferably 0.1-5% of the mass of the negative electrode material.

[0021] More preferably, the content of the negative electrode additive is 1% of the mass of the negative electrode material.

[0022] By controlling the mass content of negative electrode additives in the negative electrode material, not only can the cycle performance and high-temperature performance of lithium-ion batteries be improved, but the peeling force of the negative electrode sheet can also be further guaranteed without affecting the adhesion of the electrode sheet.

[0023] In specific embodiments, the mass content of the negative electrode active material of the present invention can refer to the conventional content in the art, and is preferably 90% to 98% of the negative electrode material.

[0024] In specific embodiments, the mass content of the adhesive of the present invention can refer to the conventional content in the art, and is preferably 0.5 to 5.0% of the mass of the negative electrode material.

[0025] In specific embodiments, the mass content of the conductive agent of the present invention can refer to the conventional content in the art, and is preferably 0.1 to 2% of the mass of the negative electrode material.

[0026] In specific embodiments, the mass content of the dispersant of the present invention can refer to the conventional content in the art, and is preferably 0.5 to 2.5% of the mass of the negative electrode material.

[0027] The present invention also specifically protects a negative electrode sheet, the negative electrode sheet including a negative electrode, a current collector, and a negative electrode material layer coated on the current collector, wherein the negative electrode material is the aforementioned negative electrode material.

[0028] The present invention also specifically protects a lithium-ion battery, wherein the lithium-ion battery comprises the above-mentioned negative electrode sheet.

[0029] Compared with the prior art, the beneficial effects of the present invention are: The negative electrode additive of the present invention comprises a structural unit derived from 1,1-difluoroethylene, which is a telechelic oligomer containing carboxyl groups or carboxylates at both ends. The 1,1-difluoroethylene unit in the middle has good electrochemical stability and lithium-ion conductivity. The introduction of the hexafluoropropylene structure can improve the flexibility of the chain segment and further improve the lithium-ion conductivity. Moreover, the carboxyl groups or carboxylates at both ends can provide hydrophilicity, which can disperse the oligomer into the aqueous slurry. In addition, the carboxyl groups at both ends or sodium carboxylate and potassium carboxylate can be replaced by lithium carboxylate in the electrolyte, which can improve the lithium-ion interface mobility, reduce internal resistance, and improve cycle performance and high temperature performance.

[0030] The negative electrode additive of this invention, when applied to the preparation of negative electrode sheets for lithium-ion batteries, can maintain the initial efficiency of lithium-ion batteries above 90.9%, and has good capacity retention at room temperature and high temperature. Moreover, the capacity recovery rate after 7 days of storage at 60°C is above 96%, demonstrating good high-temperature performance. Furthermore, it does not affect the adhesion of the electrode sheet, and the peeling force is above 8.5 N / m. Therefore, it can be widely used in the preparation of lithium-ion batteries. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0032] Example 1 A negative electrode additive comprising structural units derived from 1,1-difluoroethylene, with the compound structural formula: HOOC-(CH2CF2)m-COOH, n / (m+n)=0, a weight-average molecular weight of 5220, and a PDI of 1.79.

[0033] Additive weight-average molecular weight determination The weight-average molecular weight of the copolymer was obtained by gel permeation chromatography (GPC) and converted to polymethyl methacrylate as the standard. The mobile phase was N,N-dimethylacetamide (DMAc).

[0034] The above-mentioned negative electrode additive was applied to the preparation of lithium-ion batteries, and the specific preparation method is as follows: Preparation of additive dispersion Add 500g of deionized water to a 2L enamel-lined reactor, heat to 70℃, and start a high-speed mechanical stirrer at 1000 rpm. Slowly add 125g of deionized water into the reactor through the filling port. After the dicarboxyl oligomer HOOC-(CH2CF2)m-COOH (n / (m+n)=0, molecular weight MW = 5200, molecular weight distribution PDI=1.79) was added over 1 hour, the mixture was stirred at high speed for 6 hours, and then the temperature was lowered to room temperature to obtain an aqueous dispersion of the additive.

[0035] Battery negative electrode preparation Take 1% of the above-mentioned additives, 1.3% of sodium carboxymethyl cellulose (CMC), 1.8% of styrene-butadiene latex (SBR), 0.8% of conductive carbon black and 95.1% of artificial graphite by mass, add them to deionized water, stir and mix thoroughly to obtain a negative electrode slurry with a solid content of 50%, coat the negative electrode slurry onto a copper foil current collector, and dry it to obtain a negative electrode sheet.

[0036] Preparation of electrodes and lithium-ion batteries: Take lithium nickel cobalt manganese oxide (NCM 622) active material with a solid mass percentage of 97%, 0.8% conductive agent (SP) and 1.2% polyvinylidene fluoride (PVDF), and gradually add N-methylpyrrolidone (NMP) and stir thoroughly to obtain a positive electrode slurry. Adjust the solid content of the slurry to 50% with NMP. Coat the positive electrode slurry evenly on both sides of aluminum foil, dry and roll to obtain a positive electrode sheet.

[0037] Take 1.0% of the above-mentioned additives, 1.3% of sodium carboxymethyl cellulose (CMC), 1.8% of styrene-butadiene latex (SBR), 0.8% of conductive carbon black and 95.1% of artificial graphite by solid mass, add them to deionized water, stir and mix thoroughly to obtain a negative electrode slurry with a solid content of 50%. Coat the negative electrode slurry onto a copper foil current collector, dry and roll to obtain a negative electrode sheet.

[0038] The diaphragm is a single-sided ceramic PE membrane (9µm base membrane, 3µm Al2O3 ceramic layer). The electrolyte is prepared by mixing 1.0M LiPF6 with ethylene carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC). The volume ratio of ethylene carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) is EC:EMC:DEC = 30:50:30.

[0039] After the positive and negative electrode sheets and the separator are vacuum dried at 100°C for 24 hours, they are then cut, stacked, placed into the casing, injected with liquid, pre-sealed, formed, re-sealed, and volume-adjusted to obtain a lithium-ion soft-pack battery.

[0040] Example 2 A negative electrode additive comprising structural units derived from 1,1-difluoroethylene, with the compound structural formula: LiOOC-(CH2CF2)m-COOLi, n / (m+n)=0, a weight-average molecular weight of 5310, and a PDI of 1.78.

[0041] The above-mentioned negative electrode additive was used to prepare lithium-ion batteries, and the specific preparation method was the same as in Example 1.

[0042] Example 3 A negative electrode additive comprising structural units derived from 1,1-difluoroethylene, with the compound structural formula: NaOOC-(CH2CF2)m-COONa, n / (m+n)=0, a weight-average molecular weight of 5340, and a PDI of 1.82.

[0043] The above-mentioned negative electrode additive was used to prepare lithium-ion batteries, and the specific preparation method was the same as in Example 1.

[0044] Example 4 A negative electrode additive comprising structural units derived from 1,1-difluoroethylene, with the compound structural formula: KOOC-(CH2CF2)m-COOK, n / (m+n)=0, a weight-average molecular weight of 5460, and a PDI of 1.81.

[0045] The above-mentioned negative electrode additive was used to prepare lithium-ion batteries, and the specific preparation method was the same as in Example 1.

[0046] Example 5 A negative electrode additive comprising structural units derived from 1,1-difluoroethylene, with the compound structure: LiOOC-(CH2CF2)m-(CF2CF(CF3))n-COOLi, n / (m+n)=45%, weight-average molecular weight of 650, and PDI of 2.42.

[0047] The above-mentioned negative electrode additive was used to prepare lithium-ion batteries, and the specific preparation method was the same as in Example 1.

[0048] Example 6 A negative electrode additive comprising structural units derived from 1,1-difluoroethylene, with the compound structure: LiOOC-(CH2CF2)m-(CF2CF(CF3))n-COOLi, n / (m+n)=22%, weight-average molecular weight of 10300, and PDI of 2.25.

[0049] The above-mentioned negative electrode additive was used to prepare lithium-ion batteries, and the specific preparation method was the same as in Example 1.

[0050] Example 7 A negative electrode additive comprising structural units derived from 1,1-difluoroethylene, with the compound structure: LiOOC-(CH2CF2)m-(CF2CF(CF3))n-COOLi, n / (m+n)=9%, weight-average molecular weight of 14600, and PDI of 2.04.

[0051] The above-mentioned negative electrode additive was used to prepare lithium-ion batteries, and the specific preparation method was the same as in Example 1.

[0052] Example 8 A negative electrode additive, same as in Example 6.

[0053] The above-mentioned negative electrode additive was applied to the preparation of lithium-ion batteries. The specific preparation method was basically the same as in Example 1, with the following difference: Battery negative electrode preparation Take 0.1% of the above-mentioned additives, 1.3% of sodium carboxymethyl cellulose (CMC), 1.8% of styrene-butadiene latex (SBR), 0.8% of conductive carbon black and 96% of artificial graphite by mass, add them to deionized water, stir and mix thoroughly to obtain a negative electrode slurry with a solid content of 50%, coat the negative electrode slurry onto a copper foil current collector, and dry it to obtain a negative electrode sheet.

[0054] Example 9 A negative electrode additive, same as in Example 6.

[0055] The above-mentioned negative electrode additive was applied to the preparation of lithium-ion batteries. The specific preparation method was basically the same as in Example 1, with the following difference: Battery negative electrode preparation Take 5% of the above-mentioned additives, 1.3% of sodium carboxymethyl cellulose (CMC), 1.8% of styrene-butadiene latex (SBR), 0.8% of conductive carbon black and 91.1% of artificial graphite by mass, add them to deionized water, stir and mix thoroughly to obtain a negative electrode slurry with a solid content of 50%, coat the negative electrode slurry onto a copper foil current collector, and dry it to obtain a negative electrode sheet.

[0056] Example 10 A negative electrode additive, same as in Example 6.

[0057] The above-mentioned negative electrode additive was applied to the preparation of lithium-ion batteries. The specific preparation method was basically the same as in Example 1, with the following difference: Battery negative electrode preparation Take 7% of the above-mentioned additives, 1.3% of sodium carboxymethyl cellulose (CMC), 1.8% of styrene-butadiene latex (SBR), 0.8% of conductive carbon black and 89.1% of artificial graphite by mass, add them to deionized water, stir and mix thoroughly to obtain a negative electrode slurry with a solid content of 50%, coat the negative electrode slurry onto a copper foil current collector, and dry it to obtain a negative electrode sheet.

[0058] Comparative Example 1 Battery negative electrode preparation Take 1.3% sodium carboxymethyl cellulose (CMC), 1.8% styrene-butadiene latex (SBR), 0.8% conductive carbon black and 96.1% artificial graphite by mass, add them to deionized water, stir and mix thoroughly to obtain a negative electrode slurry with a solid content of 50%. Coat the negative electrode slurry onto a copper foil current collector and dry it to obtain a negative electrode sheet.

[0059] Preparation of electrodes and lithium-ion batteries: Take lithium nickel cobalt manganese oxide (NCM 622) active material with a solid mass percentage of 97%, 0.8% conductive agent (SP) and 1.2% polyvinylidene fluoride (PVDF), and gradually add N-methylpyrrolidone (NMP) and stir thoroughly to obtain a positive electrode slurry. Adjust the solid content of the slurry to 50% with NMP. Coat the positive electrode slurry evenly on both sides of aluminum foil, dry and roll to obtain a positive electrode sheet.

[0060] Take 1.3% sodium carboxymethyl cellulose (CMC), 1.8% styrene-butadiene latex (SBR), 0.8% conductive carbon black and 96.1% artificial graphite by mass, add them to deionized water, stir and mix thoroughly to obtain a negative electrode slurry with a solid content of 50%. Coat the negative electrode slurry onto a copper foil current collector, dry and roll to obtain a negative electrode sheet.

[0061] The diaphragm is a single-sided ceramic PE membrane (9µm base membrane, 3µm Al2O3 ceramic layer). The electrolyte is prepared by mixing 1.0M LiPF6 with ethylene carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC). The volume ratio of ethylene carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) is EC:EMC:DEC = 30:50:30.

[0062] After the positive and negative electrode sheets and the separator are vacuum dried at 100°C for 24 hours, they are then cut, stacked, placed into the casing, injected with liquid, pre-sealed, formed, re-sealed, and volume-adjusted to obtain a lithium-ion soft-pack battery.

[0063] Result detection The specific testing methods are as follows: 1. First-time efficiency test (initial Coulomb efficiency test) The prepared battery underwent formation and capacity testing. Formation involved charging at a constant current of 0.05C to 3.7V, resting for 10 minutes, then charging at a constant current of 0.1C to 4.25V, followed by constant voltage charging at 4.25V until the cutoff current of 0.02C. The total capacity of these three charging stages was Q1. After resting for 10 minutes, the battery was discharged at 0.33C to 2.75V, yielding the discharge capacity Q2. The initial coulombic efficiency was calculated as Q2 / Q1*100%.

[0064] 2. Room temperature charge-discharge cycle test In a constant temperature chamber at 25°C, the pouch cells prepared for the embodiment and brought to capacity were first charged at a constant current of 1C to 4.25V, and then charged at a constant voltage to the cutoff current of 0.02C. After resting for 10 minutes, they were discharged at a constant current of 1C to 2.75V and then rested for 10 minutes. This completes one cycle. After 600 charge / discharge cycles, the discharge capacity of the 600th cycle was calculated. Cycle performance is characterized by capacity retention rate, calculated as follows: Capacity retention rate of the 600th cycle at room temperature (%) = Discharge capacity of the 600th cycle at room temperature / Discharge capacity of the first cycle at room temperature * 100%.

[0065] 3. High-temperature charge-discharge cycle test In a constant temperature chamber at 45°C, the pouch cell, after being prepared and capacitated in the embodiment, was first charged at a constant current of 1C to 4.25V, and then charged at a constant voltage to the cutoff current of 0.02C. After resting for 10 minutes, it was discharged at a constant current of 1C to 2.75V, and then rested for 10 minutes. This completes one cycle. After 600 charge / discharge cycles, the discharge capacity of the 600th cycle is calculated. Cycle performance is characterized by capacity retention rate, calculated as: High-temperature 600th cycle capacity retention rate (%) = High-temperature 600th cycle discharge capacity / High-temperature 1st cycle discharge capacity * 100%.

[0066] 4. High-temperature storage performance test In a 25°C constant temperature chamber, the formed, capacitively sized pouch cells were first charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage to a cutoff current of 0.02C, obtaining the initial charge capacity C1. After standing for 10 minutes, the cells were placed in a 60°C constant temperature chamber and left to stand for 7 days. After storage, the cells were removed and placed back in a 25°C constant temperature chamber for constant current discharge to 2.75V at 0.33C. After standing for 10 minutes, the cells were charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage to a cutoff current of 0.02C, obtaining the restored charge capacity C3.

[0067] Capacity recovery rate after 7 days of storage at 60℃ = C3 / C1 * 100% 5. Electrode peel strength test The rolled negative electrode sheet was cut into 20*200 mm strips. One side of the electrode sample was adhered to 3M double-sided tape, and the other side of the double-sided tape was adhered to the surface of a 25*200 mm stainless steel plate. A 2 kg roller was used to roll the double-sided tape bonding area back and forth three times to ensure complete adhesion of the electrode sheet, double-sided tape, and steel plate. The sample was then bent 180° in the opposite direction. A universal electronic tensile testing machine was used. One end of the stainless steel plate was fixed to the lower clamp of the tensile testing machine, and the bent end of the sample was fixed to the upper clamp. The angle of the sample was adjusted to ensure that the upper and lower ends were in a vertical position. The sample was then stretched at a speed of 50 mm / min until it was completely peeled off from the substrate. The displacement and force during the process were recorded. The force at which the forces are balanced is generally considered to be the adhesive force of the electrode sheet.

[0068] The specific test results are shown in Table 1 below: Table 1

[0069] As can be seen from the test data in Table 1 above, the negative electrode additive of the present invention can not only improve the cycle performance of lithium-ion batteries, with an initial efficiency of 90.9% or higher, but also has a high capacity retention rate after 600 cycles at room temperature. Furthermore, it takes into account the high-temperature performance of lithium-ion batteries, with a capacity retention rate of over 78.6% after 600 cycles at high temperature, and a capacity recovery rate of over 96% after 7 days of storage at 60°C.

[0070] In contrast, the lithium-ion battery in Comparative Example 1, which did not contain the negative electrode additive of the present invention, not only failed to meet the requirements of the present invention in terms of battery capacity, but also had lower first-efficiency performance and lower capacity retention rate after 600 cycles at room temperature than the present invention. It also lacked good high-temperature resistance, with lower capacity retention rate after 600 cycles at high temperature and lower capacity recovery rate after 7 days of storage at 60°C than the present invention.

[0071] As can be seen from Examples 1-7 and Examples 8-10, further limiting the amount of the negative electrode additive of the present invention in the preparation of the negative electrode sheet of lithium-ion battery can further improve the peeling force, so that it has good battery capacity, cycle performance and high temperature performance, while having better electrode adhesion.

[0072] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. The application of a negative electrode additive in improving the cycle performance and high-temperature performance of lithium-ion batteries, characterized in that, The negative electrode additive comprises structural units derived from 1,1-difluoroethylene, and the structural formula of the negative electrode additive is as shown in Formula 1: Formula 1 Among them, 0%≤n / (m+n)≤50%, the weight-average molecular weight range is 500~15000, and M is one or more of H, Li, Na, and K.

2. The application as described in claim 1, characterized in that, The negative electrode additive is: HOOC-(CH2CF2)m-COOH, n / (m+n)=0, weight-average molecular weight is 5220. LiOOC-(CH2CF2)m-COOLi, n / (m+n)=0, weight-average molecular weight is 5310. NaOOC-(CH2CF2)m-COONa, n / (m+n)=0, weight-average molecular weight is 5340. KOOC-(CH2CF2)m-COOK, n / (m+n)=0, weight-average molecular weight is 5460. One or more of the following: LiOOC-(CH2CF2)m-(CF2CF(CF3))n-COOLi, n / (m+n)=45%, with a weight-average molecular weight of 650; LiOOC-(CH2CF2)m-(CF2CF(CF3))n-COOLi, n / (m+n)=22%, with a weight-average molecular weight of 10300; and LiOOC-(CH2CF2)m-(CF2CF(CF3))n-COOLi, n / (m+n)=9%, with a weight-average molecular weight of 14600.

3. A negative electrode material, characterized in that, The negative electrode material includes a negative electrode active material, a conductive agent, a dispersant, a negative electrode binder, and a negative electrode additive, wherein the additive is a negative electrode additive, and the negative electrode additive includes structural units derived from 1,1-difluoroethylene, and the structural formula of the negative electrode additive is shown in Formula 1: Formula 1 Among them, 0%≤n / (m+n)≤50%, the weight-average molecular weight range is 500~15000, and M is one or more of H, Li, Na, and K.

4. The negative electrode material as described in claim 3, characterized in that, The mass content of the negative electrode additive is 0.1-5% of the mass of the negative electrode material.

5. The negative electrode material as described in claim 3, characterized in that, The content of the negative electrode binder is 0.5~5.0% of the mass of the negative electrode material.

6. The negative electrode material as described in claim 3, characterized in that, The mass content of the negative electrode active material is 90% to 98% of the mass of the negative electrode material.

7. The negative electrode material as described in claim 3, characterized in that, The conductive agent has a mass content of 0.1-2% of the negative electrode material.

8. The negative electrode material as described in claim 3, characterized in that, The dispersant content is 0.5~2.5% of the mass of the negative electrode material.

9. A negative electrode sheet, characterized in that, The negative electrode sheet includes a current collector and a negative electrode material layer coated on the current collector, wherein the negative electrode material is the negative electrode material according to any one of claims 3 to 8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet described in claim 9.

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