Auxiliary agent for secondary battery, positive electrode slurry, positive electrode plate and secondary battery

Abstract

The invention provides an auxiliary agent for a secondary battery, positive electrode slurry, a positive plate and the secondary battery. The auxiliary agent for the secondary battery is a copolymer comprising a lubricating unit and an acrylate structural unit, the lubricating unit contains a long-chain hydrocarbon group, and the number of carbon atoms of the long-chain hydrocarbon group is more than 8. The auxiliary agent for the secondary battery provided by the invention can effectively improve the dispersibility of the electrode slurry, and can make the prepared positive plate compact and flexible, the compaction density of the positive plate is improved, and the prepared lithium battery has higher energy density and cycle performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and in particular relates to an auxiliary agent for a secondary battery, a positive electrode slurry, a positive electrode sheet and a secondary battery thereof. Background Art

[0002] Secondary batteries have the advantages of high voltage, high specific energy, stable discharge voltage, good cycle performance, good safety performance and long service life. They are widely used in power vehicles, energy storage and other fields.

[0003] As the requirements for batteries become higher and higher, thinness and high energy density are important trends in the development of batteries. In order to improve the energy density of lithium-ion batteries, the existing technology increases the compaction density of the positive electrode by adjusting the morphology, particle size, and the combination of large and small particles of the active main material, thereby increasing the energy density of the battery. However, if the compaction density is too high, the flexibility of the electrode will be worse, the degree of squeezing between the active material particles will be greater, the porosity will be smaller, and the difficulty of electrolyte infiltration into the electrode will increase, which is not conducive to the embedding and extraction of lithium ions. In order to solve the above problems, the hardness and brittleness of the positive electrode are usually improved by increasing the NMP content in the electrode, but the residual NMP can easily lead to problems such as flatulence, poor cycle performance, and poor high-temperature storage.

[0004] Therefore, there is an urgent need for a new type of additive that can improve the dispersibility of the slurry and increase the compaction density and flexibility of the positive electrode sheet, thereby increasing the cycle life and energy density of the battery. Summary of the invention

[0005] In view of the technical problem in the prior art that a positive electrode sheet cannot have both high compaction and flexibility, the present invention provides an auxiliary agent for a secondary battery, a positive electrode slurry, a positive electrode sheet and a secondary battery thereof.

[0006] In a first aspect, the present invention provides an auxiliary agent for a secondary battery, wherein the auxiliary agent for a secondary battery is a copolymer including a lubricating unit and an acrylate structural unit, wherein the lubricating unit contains a long-chain hydrocarbon group, and the number of carbon atoms of the long-chain hydrocarbon group is 8 or more.

[0007] Preferably, the weight ratio of the lubricating unit to the acrylic ester structural unit is (10-30): (40-60).

[0008] Preferably, the number of straight-chain carbon atoms in the long-chain hydrocarbon group is 8 or more, and more preferably, the number of straight-chain carbon atoms in the long-chain hydrocarbon group is 8-20.

[0009] Preferably, the lubricating unit is obtained by reacting a hydroxy lubricant containing a long-chain hydrocarbon group and a hydroxyl group with a vinyl monomer containing an anhydride group; The hydroxy lubricant includes one or more of 12-hydroxystearic acid, 2-hydroxystearic acid, 14-hydroxystearic acid, 16-hydroxystearic acid, 18-hydroxystearic acid, 12-hydroxystearic acid, and 17-hydroxystearic acid; The vinyl monomer containing anhydride groups includes one or more of maleic anhydride, dimethylmaleic anhydride, aconitic anhydride, and itaconic anhydride.

[0010] Preferably, the auxiliary agent for secondary batteries further comprises an organic acid lithium salt structural unit, and the weight ratio of the organic acid lithium salt structural unit to the lubricating unit is (10-30): (10-30).

[0011] Preferably, the organic acid lithium salt structural unit is selected from one or more of acrylic acid lithium salt structural unit, methacrylic acid lithium salt structural unit, vinyl acrylic acid lithium salt structural unit, β-acryloxypropionic acid lithium salt structural unit, hydroxy acrylic acid lithium salt structural unit, maleic acid lithium salt structural unit, itaconic acid lithium salt structural unit, itaconic acid monobutyl ester lithium salt structural unit, crotonic acid lithium salt structural unit, methacryloyloxyethyl succinic acid monoester lithium salt structural unit, methacryloyloxyethyl maleic acid monoester lithium salt structural unit, methacryloyloxyethyl phosphate lithium salt structural unit, ethylene glycol methacrylate phosphate lithium salt structural unit, alkyl acrylate phosphate lithium salt structural unit, p-styrene sulfonic acid lithium salt structural unit, and 2-acrylamido-2-methylpropane sulfonic acid lithium salt structural unit.

[0012] Preferably, the acrylic acid ester structural unit includes one or more of n-butyl acrylate structural unit, isobutyl acrylate structural unit, tert-butyl acrylate structural unit, n-pentyl acrylate structural unit, n-hexyl acrylate structural unit, isooctyl acrylate structural unit, isobornyl acrylate structural unit, n-butyl methacrylate structural unit, isobutyl methacrylate structural unit, tert-butyl methacrylate structural unit, n-pentyl methacrylate structural unit, n-hexyl methacrylate structural unit, n-octyl methacrylate structural unit, isooctyl methacrylate structural unit, lauryl methacrylate structural unit, cyclohexyl methacrylate structural unit, isobornyl methacrylate structural unit, polyethylene glycol monomethacrylate structural unit, phenyl glycidyl ether acrylate structural unit, ethylene glycol diacrylate structural unit, ethylene glycol methacrylate structural unit, and allyl methacrylate structural unit.

[0013] In a second aspect, the present application provides a positive electrode slurry, comprising a positive electrode active material, a binder, a conductive agent and an auxiliary agent for a secondary battery as described in any one of the above.

[0014] Preferably, the positive electrode slurry comprises the following components by weight: 90-95 parts of positive electrode active material, 0.5-3 parts of binder, 2-5 parts of conductive agent and 0.1-0.5 parts of auxiliary agent for secondary battery.

[0015] In a third aspect, the present application provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode material layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode material layer is formed by coating the positive electrode slurry described above.

[0016] In a fourth aspect, the present application provides a secondary battery, comprising a negative electrode sheet, an electrolyte, and the positive electrode sheet as described above.

[0017] The auxiliary agent for secondary batteries provided in the present application includes a lubricating unit of a specific structure and an acrylate structural unit, which plays a role of lubrication and softening between the positive electrode active material and the conductive agent, and can effectively improve the dispersion state between the positive electrode active material and the conductive agent particles, prevent the positive electrode active material and the conductive agent from agglomerating, and make the positive electrode active material and the conductive agent evenly dispersed and in close contact, so that the positive electrode sheet is dense and flexible, with a higher compaction density, thereby improving the energy density and cycle life of the battery. DETAILED DESCRIPTION

[0018] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0019] An embodiment of the present application provides an auxiliary agent for a secondary battery. The auxiliary agent for a secondary battery is a copolymer including a lubricating unit and an acrylate structural unit. The lubricating unit contains a long-chain hydrocarbon group, and the number of carbon atoms of the long-chain hydrocarbon group is 8 or more.

[0020] The auxiliary agent for secondary batteries provided in the present application includes a lubricating unit of a specific structure and an acrylate structural unit, which plays a role of lubrication and softening between the positive electrode active material and the conductive agent, and can effectively improve the dispersion state between the positive electrode active material and the conductive agent particles, prevent the positive electrode active material and the conductive agent from agglomerating, and make the positive electrode active material and the conductive agent evenly dispersed and in close contact, so that the positive electrode sheet is dense and flexible, with a higher compaction density, thereby improving the energy density and cycle life of the battery.

[0021] In some embodiments, the weight ratio of the lubricating unit to the acrylic ester structural unit is (10-30): (40-60).

[0022] Specifically, the weight ratio of the lubricating unit and the acrylic acid ester structural unit includes but is not limited to 10:40, 10:60, 20:40, 20:50, 20:60, 30:40, 30:50 or 30:60.

[0023] In some embodiments, the long-chain hydrocarbon group has 8 or more carbon atoms, and more preferably, the long-chain hydrocarbon group has 8-20 carbon atoms.

[0024] In some embodiments, the lubricating unit is obtained by reacting a hydroxyl lubricant containing a long-chain hydrocarbon group and a hydroxyl group with a vinyl monomer containing an anhydride group.

[0025] The hydroxy lubricant includes one or more of 12-hydroxystearic acid, 2-hydroxystearic acid, 14-hydroxystearic acid, 16-hydroxystearic acid, 18-hydroxystearic acid, 12-hydroxystearic acid, and 17-hydroxystearic acid.

[0026] The vinyl monomer containing anhydride groups includes one or more of maleic anhydride, dimethylmaleic anhydride, aconitic anhydride, and itaconic anhydride.

[0027] Introducing the above-mentioned hydroxyl-containing lubricant into the auxiliary agent for secondary batteries helps to improve the flexibility of the electrode, and the introduction of the hydroxyl-containing long-chain hydrocarbon group in the auxiliary agent for secondary batteries can reduce the sliding resistance between the positive electrode active material and the conductive agent, thereby increasing the flexibility of the electrode and improving the flexibility of the electrode.

[0028] Furthermore, the molar ratio of the hydroxy lubricant to the vinyl monomer containing anhydride groups is 1:(1-1.2).

[0029] In some embodiments, the secondary battery auxiliary agent further includes an organic acid lithium salt structural unit, and the weight ratio of the organic acid lithium salt structural unit to the lubricating unit is (10-30): (10-30).

[0030] By introducing the above organic acid lithium salt structural unit into the auxiliary agent for secondary batteries, on the one hand, it can provide additional lithium source for the battery, improve the problem of reduced initial coulomb efficiency of the negative electrode, and thus improve the capacity, cycle life and energy density of the lithium battery; on the other hand, it can also be very beneficial to further improve the dispersion effect of the slurry. Specifically, the weight ratio of the organic acid lithium salt structural unit to the lubricating unit includes but is not limited to 10:10, 10:20, 10:30, 20:10, 20:30, 30:10, 30:20 or 30:30.

[0031] In some embodiments, the organic acid lithium salt structural unit is a structural unit obtained by polymerization of an acidic monomer with lithium ions; and / or, the organic acid lithium salt structural unit is a structural unit obtained by neutralization reaction of an acidic monomer with a lithium-containing alkaline substance after polymerization, and the acidic monomer includes one or more of acrylic acid, methacrylic acid, vinyl acrylic acid, β-acryloxy propionic acid, hydroxy acrylic acid, maleic acid, itaconic acid, itaconic acid monobutyl ester, crotonic acid, methacryloyloxyethyl succinic acid monoester, methacryloyloxyethyl maleic acid monoester, methacryloyloxyethyl phosphate, ethylene glycol methacrylate phosphate, alkyl acrylate phosphate, p-styrene sulfonic acid, and 2-acrylamido-2-methylpropane sulfonic acid. By selecting the acidic unit formed by the above acidic monomers to be neutralized with lithium hydroxide, the chemical stability of the secondary battery additive is improved, and at the same time, the lithium supplement unit contains a higher content of lithium ions.

[0032] Correspondingly, the obtained organic acid lithium salt structural unit is selected from one or more of acrylic acid lithium salt structural unit, methacrylic acid lithium salt structural unit, vinyl acrylic acid lithium salt structural unit, β-acryloxypropionic acid lithium salt structural unit, hydroxy acrylic acid lithium salt structural unit, maleic acid lithium salt structural unit, itaconic acid lithium salt structural unit, itaconic acid monobutyl ester lithium salt structural unit, crotonic acid lithium salt structural unit, methacryloyloxyethyl succinic acid monoester lithium salt structural unit, methacryloyloxyethyl maleic acid monoester lithium salt structural unit, methacryloyloxyethyl phosphate lithium salt structural unit, ethylene glycol methacrylate phosphate lithium salt structural unit, alkyl acrylate phosphate lithium salt structural unit, p-styrene sulfonic acid lithium salt structural unit, and 2-acrylamido-2-methylpropanesulfonic acid lithium salt structural unit.

[0033] Specifically, after the acidic monomer, the acrylate monomer and the lubricating unit are polymerized to obtain a polymer, the polymer is subjected to a neutralization reaction with lithium hydroxide to obtain an auxiliary agent for a secondary battery having a lithium supplementing unit.

[0034] In a preferred embodiment, the acidic monomer is selected from at least one of acrylic acid, alkyl acrylate phosphate, and 2-acrylamido-2-methylpropane sulfonic acid.

[0035] In some embodiments, the acrylic acid ester structural unit includes one or more of n-butyl acrylate structural unit, isobutyl acrylate structural unit, tert-butyl acrylate structural unit, n-pentyl acrylate structural unit, n-hexyl acrylate structural unit, isooctyl acrylate structural unit, isobornyl acrylate structural unit, n-butyl methacrylate structural unit, isobutyl methacrylate structural unit, tert-butyl methacrylate structural unit, n-pentyl methacrylate structural unit, n-hexyl methacrylate structural unit, n-octyl methacrylate structural unit, isooctyl methacrylate structural unit, lauryl methacrylate structural unit, cyclohexyl methacrylate structural unit, isobornyl methacrylate structural unit, polyethylene glycol monomethacrylate structural unit, phenyl glycidyl ether acrylate structural unit, ethylene glycol diacrylate structural unit, ethylene glycol methacrylate structural unit, and allyl methacrylate structural unit.

[0036] The acrylic acid ester structural unit is obtained by polymerization of acrylic acid ester monomers. Correspondingly, the acrylic acid ester monomers include one or more of n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, isooctyl acrylate, isobornyl acrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, isooctyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, polyethylene glycol monomethacrylate, phenyl glycidyl ether acrylate, ethylene glycol diacrylate, ethylene glycol methacrylate, and allyl methacrylate. The acrylic acid ester unit formed by selecting the above acrylic acid ester monomers to cooperate with the lubricating unit and the organic acid lithium salt structural unit can make the auxiliary agent for secondary batteries have better dispersibility.

[0037] In a preferred embodiment, the acrylic acid ester monomer is selected from at least one of butyl acrylate and isooctyl acrylate.

[0038] Specifically, the preparation method of the auxiliary agent for secondary batteries comprises the following steps: (1) reacting a hydroxy lubricant containing a hydroxyl group and a long-chain hydrocarbon group with a vinyl monomer containing an anhydride group and a solvent to obtain a lubricating unit; (2) The lubricating unit obtained in step (1) is reacted with an acrylate monomer, an acidic monomer, an initiator, and a solvent, and then neutralized and the solvent is removed by reduced pressure distillation to obtain an auxiliary agent for a secondary battery.

[0039] An embodiment of the present application provides a positive electrode slurry, comprising a positive electrode active material, a binder, a conductive agent, and any one of the auxiliary agents for secondary batteries described above.

[0040] In some embodiments, the positive electrode slurry includes the following components by weight: 90-95 parts of positive electrode active material, 0.5-3 parts of binder, 2-5 parts of conductive agent and 0.1-0.5 parts of auxiliary agent for secondary battery.

[0041] An embodiment of the present application provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode material layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode material layer is formed by coating the positive electrode slurry described above.

[0042] An embodiment of the present application provides a secondary battery, comprising a negative electrode sheet, an electrolyte, and the positive electrode sheet as described in the above embodiment.

[0043] The present invention is further described below by way of examples.

[0044] The auxiliary agent for secondary batteries, the positive electrode sheet and the secondary batteries disclosed in the present invention are specifically described.

[0045] Example 1 Secondary battery additives Add 70 parts of 1-octadecanol (hydroxy lubricant), 30 parts of maleic anhydride monomer (vinyl monomer containing anhydride group) and NMP into a reactor and stir until the maleic anhydride is completely dissolved. Heat and control the reaction temperature to 100°C for heat preservation esterification reaction. After the reaction is completed, cool, filter and evaporate to remove residual water to obtain a solution containing lubricating units.

[0046] Add NMP to the reactor, control the temperature to 80°C, add 0.5 parts of initiator solution, then drop 20 parts of lubricating unit, 50 parts of isooctyl acrylate (acrylate monomer), and 30 parts of NMP solution of alkyl acrylate phosphate (acidic monomer), and keep the temperature to allow polymerization to occur. After the reaction is completed, cool the reactor, neutralize with lithium hydroxide aqueous solution, filter, and distill under reduced pressure to obtain an additive for secondary batteries.

[0047] Preparation of positive electrode The positive electrode active material lithium cobalt oxide, conductive carbon black, secondary battery additives, and positive electrode binder are mixed in a mass ratio of 94:3:0.3:2.7, and NMP is added to prepare positive electrode slurry. The positive electrode slurry is coated on aluminum foil and dried to obtain a positive electrode sheet.

[0048] Preparation of negative electrode 96% of negative electrode active material graphite, 1% of negative electrode conductive agent conductive carbon black, and 3% of binder are mixed, and deionized water is added for stirring to make a negative electrode sheet. Then the negative electrode sheet is coated on both surfaces of the negative electrode current collector copper foil, and after drying, cold pressing, slitting and other processes, the negative electrode sheet is obtained.

[0049] Secondary battery preparation The negative electrode sheet, isolation film (PE film), and positive electrode sheet are stacked in order, with the isolation film placed between the positive and negative electrodes to play an isolating role, to form an electrode assembly, which is placed in an outer package, injected with commercially available electrolyte and packaged, and then subjected to processes such as liquid injection, formation, and exhaust to obtain a secondary battery.

[0050] Example 2 Most of the steps of Example 2 are the same as those of Example 1, except that the lubrication unit is 30 parts.

[0051] Example 3 Most of the steps of Example 3 are the same as those of Example 1, except that the lubrication unit is 10 parts.

[0052] Example 4 Most of the steps of Example 4 are the same as those of Example 1, except that the lubrication unit is 5 portions.

[0053] Example 5 Most of the steps of Example 5 are the same as those of Example 1, except that 40 units are lubricated.

[0054] Example 6 Most of the steps of Example 6 are the same as those of Example 1, except that the amount of the acrylate monomer is 40 parts.

[0055] Example 7 Most of the steps of Example 7 are the same as those of Example 1, except that the amount of the acrylate monomer is 60 parts.

[0056] Example 8 Most of the steps of Example 8 are the same as those of Example 1, except that the amount of the acrylate monomer is 30 parts.

[0057] Example 9 Most of the steps of Example 9 are the same as those of Example 1, except that the amount of the acrylate monomer is 70 parts.

[0058] Example 10 Most of the steps of Example 10 are the same as those of Example 1, except that the amount of the acidic monomer is 10 parts.

[0059] Embodiment 11 Most of the steps of Example 11 are the same as those of Example 1, except that the amount of the acidic monomer is 5 parts.

[0060] Example 12 Most of the steps of Example 12 are the same as those of Example 1, except that the hydroxy lubricant is 12-hydroxystearic acid, the acrylate monomer is polyethylene glycol monomethacrylate, and the acidic monomer is 2-acrylamido-2-methylpropanesulfonic acid.

[0061] Example 13 Most of the steps of Example 13 are the same as those of Example 1, except that the hydroxy lubricant is methyl 2-hydroxystearate, the acrylate monomer is phenyl glycidyl ether acrylate, and the acidic monomer is methacryloyloxyethyl maleate.

[0062] Embodiment 14 Most of the steps of Example 14 are the same as those of Example 1, except that the hydroxy lubricant is 1-dodecanol, the acrylate monomer is ethylene glycol diacrylate, and the acidic monomer is vinyl acrylic acid.

[0063] Embodiment 15 Most of the steps of Example 15 are the same as those of Example 1, except that the mass ratio of the positive electrode active material lithium manganese oxide, the conductive carbon black, the auxiliary agent for secondary batteries, and the positive electrode binder is 94:3:0.5:2.5.

[0064] Example 16 Most of the steps of Example 16 are the same as those of Example 1, except that the mass ratio of the positive electrode active material lithium manganese oxide, conductive carbon black, auxiliary agent for secondary battery, and positive electrode binder is 94:3:0.1:2.9.

[0065] Embodiment 17 Most of the steps of Example 17 are the same as those of Example 1, except that the mass ratio of the positive electrode active material lithium manganese oxide, the conductive carbon black, the auxiliary agent for secondary batteries, and the positive electrode binder is 94:3:1:2.

[0066] Comparative Example 1 Most of the steps of Comparative Example 1 are the same as those of Example 1, except that no auxiliary agent for secondary battery is added to the positive electrode slurry.

[0067] Comparative Example 2 Most of the steps of Comparative Example 2 and Example 1 are the same, except that no lubricating unit is added in the preparation of the auxiliary agent for secondary batteries.

[0068] Comparative Example 3 Comparative Example 3 is similar to Example 1 in most steps, except that no acidic monomer is added in the preparation of the auxiliary agent for secondary batteries.

[0069] Comparative Example 4 Comparative Example 4 is similar to Example 1 in most steps, except that no lubricating unit and acidic monomer are added in the preparation of the auxiliary agent for secondary battery.

[0070] Electrical performance test: The secondary battery additives, positive electrode slurries, positive electrode sheets, and secondary batteries prepared in the above examples and comparative examples were subjected to the following tests.

[0071] 1. Li content: The Li content of the secondary battery additives was tested using an ICP (inductively coupled plasma) spectrometer.

[0072] 2. Slurry viscosity: The viscosity of the positive electrode slurry was tested using an NJ-1 rotational viscometer.

[0073] 3. Adhesion test: Cut the positive electrode sheet into 30*100mm specifications and use an electronic tensile testing machine to test the bonding strength.

[0074] 4. Flexibility test: The positive electrode is subjected to flexibility test using the needle rolling method.

[0075] 5. Compaction density test: Use a stamping die to punch out 15 small discs from the positive electrode sheet, and weigh and calculate the compaction density of the positive electrode coating on the discs.

[0076] 6. Charge the battery to 4.5V at 0.5C at 25°C, 4.5V constant voltage, 0.05C cutoff current, and record the charging capacity; then discharge the battery to 3V at 0.5C constant current, record the discharge capacity, and calculate it according to the first discharge capacity / first charge capacity.

[0077] 7. Normal temperature cycle test: After the battery is placed in a constant temperature test room at 25℃±2℃ for 1h, it is charged to 3.65V at 1C constant current and constant voltage, with a cut-off current of 0.05C; it is discharged to 2.5V at 1C constant current, and the discharge capacity is recorded; the above steps are repeated 500 times, and the capacity retention rate is calculated.

[0078] The test results are shown in Table 1 below.

[0079] Table 1

[0080] By comparing the test results of Example 1 and Examples 2 to 5, it can be seen that when the lubricating unit contained in the secondary battery additive is within a reasonable range, the prepared positive electrode sheet has a higher compaction density and excellent flexibility, and has a good capacity retention rate. When the lubricating unit content is too high, the prepared positive electrode sheet has a higher compaction density, but due to the high lubricity, the bonding performance of the positive electrode sheet is reduced, and powder falling is prone to occur.

[0081] By comparing the test results of Example 1 and Examples 6 to 9, it can be seen that when the proportion of the acrylate segment is within the range of this embodiment, as the content increases, the prepared positive electrode slurry has a lower slurry viscosity at the same solid content, which is convenient for coating; when the proportion is too small, the slurry viscosity is high and it is not easy to coat; when the proportion is too large, the compaction density of the prepared positive electrode sheet is not significantly improved.

[0082] By comparing the test results of Example 1 and Examples 10 to 12, it can be seen that when the acidic monomer ratio is within the range of this embodiment, it has a higher Li content, can improve the battery energy density, and increase the cycle life of the battery. When the acidic monomer ratio is too small, the Li content is low (<8000ppm), and there is basically no lithium supplementation effect. When the acidic monomer ratio is too high, the solubility of the secondary battery additive in the solvent decreases, precipitation is easy to occur during the preparation process, and it is not easy to use.

[0083] Comparing Example 1 with Comparative Examples 1 to 4, the auxiliary agent for secondary battery is not used. The viscosity of the positive electrode slurry during processing is high, which is not easy to apply, and has no compaction and lithium supplement effect on the positive electrode sheet. The cycle performance of the prepared battery cell is biased; lacking the lubrication unit, the compaction density of the prepared positive electrode sheet is at a normal level (4.1 g / cm 3 ), the energy density is low and the cycle performance is average; the auxiliary agent prepared lacks organic acid lithium salt structural units and does not contain Li, has no lithium supplementation effect, and cannot improve the battery energy density and cycle life; when the auxiliary agent for secondary batteries only uses acrylate segments, it only has a dispersing effect and a single function.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A secondary battery auxiliary agent, characterized in that: The auxiliary agent for secondary batteries is a copolymer including a lubricating unit and an acrylate structural unit. The lubricating unit contains a long-chain hydrocarbon group, and the carbon number of the long-chain hydrocarbon group is 8 or more.

2. The auxiliary agent for secondary battery according to claim 1, characterized in that The weight ratio of the lubricating unit to the acrylic ester structural unit is (10-30): (40-60).

3. The auxiliary agent for secondary battery according to claim 1, characterized in that The lubricating unit is obtained by reacting a hydroxy lubricant containing a long-chain hydrocarbon group and a hydroxyl group with a vinyl monomer containing an anhydride group; The hydroxy lubricant includes one or more of 12-hydroxystearic acid, 2-hydroxystearic acid, 14-hydroxystearic acid, 16-hydroxystearic acid, 18-hydroxystearic acid, 12-hydroxystearic acid, and 17-hydroxystearic acid; The vinyl monomer containing anhydride groups includes one or more of maleic anhydride, dimethylmaleic anhydride, aconitic anhydride, and itaconic anhydride.

4. The auxiliary agent for secondary battery according to claim 1, characterized in that The auxiliary agent for secondary batteries further includes an organic acid lithium salt structural unit, and the weight ratio of the organic acid lithium salt structural unit to the lubricating unit is (10-30): (10-30).

5. The auxiliary agent for secondary battery according to claim 4, characterized in that: The organic acid lithium salt structural unit is selected from one or more of acrylic acid lithium salt structural unit, methacrylic acid lithium salt structural unit, vinyl acrylic acid lithium salt structural unit, β-acryloxy propionic acid lithium salt structural unit, hydroxy acrylic acid lithium salt structural unit, maleic acid lithium salt structural unit, itaconic acid lithium salt structural unit, itaconic acid monobutyl ester lithium salt structural unit, crotonic acid lithium salt structural unit, methacryloyloxyethyl succinic acid monoester lithium salt structural unit, methacryloyloxyethyl maleic acid monoester lithium salt structural unit, methacryloyloxyethyl phosphate lithium salt structural unit, ethylene glycol methacrylate phosphate lithium salt structural unit, alkyl acrylate phosphate lithium salt structural unit, p-styrene sulfonic acid lithium salt structural unit, and 2-acrylamido-2-methylpropane sulfonic acid lithium salt structural unit.

6. The auxiliary agent for secondary battery according to claim 1, characterized in that The acrylic acid ester structural unit includes one or more of n-butyl acrylate structural unit, isobutyl acrylate structural unit, tert-butyl acrylate structural unit, n-pentyl acrylate structural unit, n-hexyl acrylate structural unit, isooctyl acrylate structural unit, isobornyl acrylate structural unit, n-butyl methacrylate structural unit, isobutyl methacrylate structural unit, tert-butyl methacrylate structural unit, n-pentyl methacrylate structural unit, n-hexyl methacrylate structural unit, n-octyl methacrylate structural unit, isooctyl methacrylate structural unit, lauryl methacrylate structural unit, cyclohexyl methacrylate structural unit, isobornyl methacrylate structural unit, polyethylene glycol monomethacrylate structural unit, phenyl glycidyl ether acrylate structural unit, ethylene glycol diacrylate structural unit, ethylene glycol methacrylate structural unit, and allyl methacrylate structural unit.

7. A positive electrode slurry, characterized in that: The invention comprises a positive electrode active material, a binder, a conductive agent and an auxiliary agent for a secondary battery as claimed in any one of claims 1 to 6.

8. The positive electrode slurry according to claim 7, characterized in that: The positive electrode slurry comprises the following components by weight: 90-95 parts of positive electrode active material, 0.5-3 parts of binder, 2-5 parts of conductive agent and 0.1-0.5 parts of auxiliary agent for secondary battery.

9. A positive electrode sheet, characterized in that: It comprises a positive electrode current collector and a positive electrode material layer arranged on at least one side surface of the positive electrode current collector, wherein the positive electrode material layer is formed by coating the positive electrode slurry according to claim 7 or 8.

10. A secondary battery, characterized in that: It comprises a negative electrode sheet, an electrolyte and the positive electrode sheet as claimed in claim 9.

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