An additive for a secondary battery, a positive electrode slurry, a positive electrode sheet, and a secondary battery

Abstract

This invention provides an additive for secondary batteries, a positive electrode slurry, a positive electrode sheet, and a secondary battery thereof. The additive for secondary batteries is a copolymer comprising a lubricating unit and an acrylate structural unit, wherein the lubricating unit contains a long-chain hydrocarbon group with eight or more carbon atoms. The additive for secondary batteries provided in this application can effectively improve the dispersibility of the electrode slurry, and can make the prepared positive electrode sheet dense and flexible, increasing the compaction density of the positive electrode sheet, resulting in a lithium battery with higher energy density and cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, specifically relating to an additive for secondary batteries, a positive electrode slurry, a positive electrode sheet, and a secondary battery thereof. Background Technology

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

[0003] With increasingly stringent requirements for batteries, thinness and high energy density are key trends in battery development. To improve the energy density of lithium-ion batteries, existing technologies increase the compaction density of the positive electrode by adjusting the morphology, particle size, and the combination of particles of different sizes of the active material. However, excessive compaction density leads to decreased electrode flexibility, greater compression between active material particles, lower porosity, and increased difficulty in electrolyte wetting, hindering lithium-ion intercalation and extraction. While increasing the NMP content in the electrode can mitigate the brittleness of the positive electrode, residual NMP can cause problems such as gas expansion, poor cycle life, and deterioration during 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 improving the cycle life and energy density of the battery. Summary of the Invention

[0005] To address the technical problem that existing cathode sheets cannot simultaneously possess both high compaction and flexibility, this invention provides an additive for secondary batteries, a cathode slurry, a cathode sheet, and a secondary battery thereof.

[0006] In a first aspect, the present invention provides an additive for secondary batteries, wherein the additive for secondary batteries is a copolymer comprising a lubricating unit and an acrylate structural unit, wherein the lubricating unit contains a long-chain hydrocarbon group, and the long-chain hydrocarbon group has eight or more carbon atoms.

[0007] Preferably, the weight ratio of the lubrication unit to the acrylate structural unit is (10~30):(40~60).

[0008] Preferably, the long-chain hydrocarbon group has 8 or more straight-chain carbon atoms; more preferably, the long-chain hydrocarbon group has 8-20 straight-chain carbon atoms.

[0009] Preferably, the lubrication unit is obtained by reacting a hydroxyl lubricant containing long-chain hydrocarbon groups and hydroxyl groups with a vinyl monomer containing an anhydride group;

[0010] The hydroxyl lubricant includes one or more of the following: dodecyl alcohol-1, dodecyl alcohol-2, tetradecyl alcohol-1, hexadecyl alcohol-1, octadecyl alcohol-1, eicosyl alcohol-1, 12-hydroxystearic acid, methyl 2-hydroxystearate, methyl 12-hydroxystearate, and methyl 17-hydroxystearate.

[0011] The vinyl monomer containing anhydride groups includes one or more of maleic anhydride, dimethylmaleic anhydride, aconitic anhydride, and itaconic anhydride.

[0012] Preferably, the secondary battery additive further includes an organic lithium acid salt structural unit, and the weight ratio of the organic lithium acid salt structural unit to the lubrication unit is (10~30):(10~30).

[0013] Preferably, the organic acid lithium salt structural unit is selected from one or more of the following: lithium acrylate structural unit, lithium methacrylate structural unit, lithium vinyl acrylate structural unit, lithium β-acryloyloxypropionate structural unit, lithium hydroxyacrylate structural unit, lithium maleate structural unit, lithium itaconic acid structural unit, lithium itaconic acid monobutyl ester structural unit, lithium crotonate structural unit, lithium methacryloyloxyethyl succinate structural unit, lithium methacryloyloxyethyl maleate structural unit, lithium methacryloyloxyethyl phosphate structural unit, lithium glycol methacrylate phosphate structural unit, lithium alkyl acrylate phosphate structural unit, lithium p-styrene sulfonate structural unit, and lithium 2-acrylamido-2-methylpropanesulfonate structural unit.

[0014] Preferably, the acrylate structural units include one or more of the following: n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, isooctyl acrylate, isoborneol acrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, isooctyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, isoborneol methacrylate, polyethylene glycol monomethacrylate, phenyl glycidyl ether acrylate, ethylene glycol diacrylate, ethylene glycol methacrylate, and allyl methacrylate.

[0015] Secondly, this application provides a positive electrode slurry, comprising a positive electrode active material, a binder, a conductive agent, and an additive for secondary batteries as described in any one of the above.

[0016] 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 secondary battery additive.

[0017] Thirdly, this application provides a positive electrode sheet, including a positive current collector and a positive electrode material layer disposed on at least one side surface of the positive current collector, wherein the positive electrode material layer is formed by coating the positive electrode slurry described above.

[0018] Fourthly, this application provides a secondary battery, including a negative electrode, an electrolyte, and a positive electrode as described above.

[0019] The additives for secondary batteries provided in this application include lubrication units with specific structures and acrylate structural units, which play a role in lubrication and flexibility between the positive electrode active material and the conductive agent. They can also 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 uniformly dispersed and in close contact. This makes the positive electrode sheet dense and flexible, with a high compaction density, thereby improving the energy density and cycle life of the battery. Detailed Implementation

[0020] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] One embodiment of this application provides an additive for secondary batteries. The additive for secondary batteries is a copolymer comprising a lubricating unit and an acrylate structural unit. The lubricating unit contains a long-chain hydrocarbon group, and the long-chain hydrocarbon group has 8 or more carbon atoms.

[0022] The additives for secondary batteries provided in this application include lubrication units with specific structures and acrylate structural units, which play a role in lubrication and flexibility between the positive electrode active material and the conductive agent. They can also 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 uniformly dispersed and in close contact. This makes the positive electrode sheet dense and flexible, with a high compaction density, thereby improving the energy density and cycle life of the battery.

[0023] In some embodiments, the weight ratio of the lubrication unit to the acrylate structural unit is (10~30):(40~60).

[0024] Specifically, the weight ratio of the lubrication unit and the acrylate 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.

[0025] 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.

[0026] In some embodiments, the lubrication unit is obtained by reacting a hydroxyl lubricant containing long-chain hydrocarbon groups and hydroxyl groups with a vinyl monomer containing an anhydride group.

[0027] The hydroxyl lubricant includes one or more of dodecane alcohol-1, dodecane alcohol-2, tetradecane alcohol-1, hexadecane alcohol-1, octadecane alcohol-1, eicosyl alcohol-1, 12-hydroxystearic acid, methyl 2-hydroxystearate, methyl 12-hydroxystearate, and methyl 17-hydroxystearate.

[0028] The vinyl monomer containing anhydride groups includes one or more of maleic anhydride, dimethylmaleic anhydride, aconitic anhydride, and itaconic anhydride.

[0029] Introducing the aforementioned hydroxyl-containing lubricant into the additives for secondary batteries helps improve the flexibility of the electrode. Furthermore, the introduction of hydroxyl-containing long-chain hydrocarbon groups into the additives for secondary batteries can reduce the slip resistance between the positive electrode active material and the conductive agent, thereby increasing the flexibility of the electrode and improving its overall flexibility.

[0030] Furthermore, the molar ratio of the hydroxyl lubricant to the vinyl monomer containing anhydride groups is 1:(1~1.2).

[0031] In some embodiments, the secondary battery additive further includes an organic lithium acid salt structural unit, wherein the weight ratio of the organic lithium acid salt structural unit to the lubrication unit is (10~30):(10~30).

[0032] By introducing the aforementioned organic lithium acid salt structural units into additives for secondary batteries, on the one hand, an additional lithium source can be provided for the battery, improving the problem of reduced initial coulombic efficiency of the negative electrode, thereby increasing the capacity, cycle life, and energy density of the lithium battery; on the other hand, it is also highly beneficial for further improving the dispersion effect of the slurry.

[0033] Specifically, the weight ratio of the organic acid lithium salt structural unit to the lubrication unit includes, but is not limited to, 10:10, 10:20, 10:30, 20:10, 20:30, 30:10, 30:20 or 30:30.

[0034] In some embodiments, the organic lithium acid salt structural unit is a structural unit obtained by polymerization of an acidic monomer containing lithium ions; and / or, the organic lithium acid salt structural unit is a structural unit obtained by neutralization reaction of an acidic monomer after polymerization with a lithium-containing alkaline substance, wherein the acidic monomer includes one or more of acrylic acid, methacrylic acid, vinylacrylic acid, β-acryloyloxypropionic acid, hydroxyacrylic acid, maleic acid, itaconic acid, itaconic acid monobutyl ester, crotonic acid, methacryloyloxyethyl succinate monoester, methacryloyloxyethyl maleic acid monoester, methacryloyloxyethyl phosphate, ethylene glycol methacrylate phosphate, alkyl acrylate phosphate, p-styrene sulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid. By using the acidic unit formed by the above-mentioned acidic monomers to neutralize lithium hydroxide, the chemical stability of the additive for secondary batteries is improved, while the lithium replenishment unit contains a higher content of lithium ions.

[0035] Correspondingly, the obtained organic acid lithium salt structural units are selected from one or more of the following: lithium acrylate structural units, lithium methacrylate structural units, lithium vinyl acrylate structural units, lithium β-acryloyloxypropionate structural units, lithium hydroxyacrylate structural units, lithium maleate structural units, lithium itaconic acid structural units, lithium itaconic acid monobutyl ester structural units, lithium crotonate structural units, lithium methacryloyloxyethyl succinate structural units, lithium methacryloyloxyethyl maleate structural units, lithium methacryloyloxyethyl phosphate structural units, lithium glycol methacrylate phosphate structural units, lithium alkyl acrylate phosphate structural units, lithium p-styrene sulfonate structural units, and lithium 2-acrylamido-2-methylpropanesulfonate structural units.

[0036] Specifically, a polymer is obtained by polymerizing an acidic monomer, an acrylate monomer, and a lubricating unit. The polymer is then neutralized with lithium hydroxide to obtain an additive for secondary batteries with a lithium replenishment unit.

[0037] In a preferred embodiment, the acidic monomer is selected from at least one of acrylic acid, alkyl acrylate phosphate, and 2-acrylamido-2-methylpropanesulfonic acid.

[0038] In some embodiments, the acrylate structural units include one or more of the following: n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, isooctyl acrylate, isoborneol acrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, isooctyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, isoborneol methacrylate, polyethylene glycol monomethacrylate, phenyl glycidyl ether acrylate, ethylene glycol diacrylate, ethylene glycol methacrylate, and allyl methacrylate.

[0039] The acrylate structural units are obtained by polymerization of acrylate monomers. Correspondingly, the acrylate monomers include one or more of the following: 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. By using the acrylate units formed from the above-mentioned acrylate monomers in synergy with the lubrication units and organic lithium acid salt structural units, the additives for secondary batteries can exhibit better dispersibility.

[0040] In a preferred embodiment, the acrylate monomer is selected from at least one of butyl acrylate and isooctyl acrylate.

[0041] Specifically, the preparation method of additives for secondary batteries includes the following steps:

[0042] (1) A hydroxyl lubricant containing hydroxyl and long-chain hydrocarbon groups is reacted with a vinyl monomer containing an anhydride group and a solvent to obtain a lubrication unit;

[0043] (2) The lubricating unit obtained in step (1) is reacted with acrylate monomer, acid monomer, initiator and solvent, neutralized and the solvent is removed by vacuum distillation to obtain the auxiliary agent for secondary batteries.

[0044] One embodiment of this application provides a positive electrode slurry, comprising a positive electrode active material, a binder, a conductive agent, and an additive for secondary batteries as described in any one of the above.

[0045] In some embodiments, 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 secondary battery additives.

[0046] One embodiment of this application provides a positive electrode sheet, including a positive current collector and a positive electrode material layer disposed on at least one side surface of the positive current collector, wherein the positive electrode material layer is formed by coating the positive electrode slurry described above.

[0047] One embodiment of this application provides a secondary battery, including a negative electrode, an electrolyte, and a positive electrode as described in the above embodiment.

[0048] The present invention will be further illustrated by the following examples.

[0049] Specifically, this invention discloses the additives for secondary batteries, the positive electrode sheet, and the secondary battery thereof.

[0050] Example 1

[0051] Additives for secondary batteries

[0052] 70 parts of octadecyl alcohol-1 (hydroxy lubricant), 30 parts of maleic anhydride monomer (vinyl monomer containing anhydride group), and NMP were added to a reactor and stirred until the maleic anhydride was completely dissolved. The reaction temperature was heated to 100°C and the reaction was carried out under heat preservation esterification. After the reaction was completed, the mixture was cooled, filtered, and the residual water was removed by rotary evaporation to obtain a solution containing lubricating unit.

[0053] NMP was added to the reactor, and the temperature was controlled at 80°C. 0.5 parts of initiator solution were added, followed by the addition of 20 parts of lubrication unit, 50 parts of isooctyl acrylate (acrylate monomer), and 30 parts of alkyl acrylate phosphate (acid monomer) NMP solution. The polymerization reaction was carried out under heat. After the reaction was completed, the mixture was cooled and neutralized with lithium hydroxide aqueous solution. After filtration and vacuum distillation, the additive for secondary batteries was obtained.

[0054] Preparation of positive electrode

[0055] Lithium cobalt oxide (positive electrode active material), conductive carbon black, secondary battery additives, and positive electrode binder were mixed in a mass ratio of 94:3:0.3:2.7, and NMP was added to prepare a positive electrode slurry. The positive electrode slurry was coated onto aluminum foil and dried to obtain a positive electrode sheet.

[0056] Preparation of negative electrode

[0057] 96% graphite (negative electrode active material), 1% conductive carbon black (negative electrode conductive agent), and 3% binder are mixed and then mixed with deionized water to form a negative electrode sheet. The negative electrode sheet is then coated onto both surfaces of a copper foil current collector, and after drying, cold pressing, and slitting, the negative electrode sheet is obtained.

[0058] Secondary battery preparation

[0059] The negative electrode, separator (PE film), and positive electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, thus forming an electrode assembly. The electrode assembly is then placed in an outer package, injected with commercially available electrolyte, and sealed. After processes such as electrolyte injection, formation, and venting, a secondary battery is obtained.

[0060] Example 2

[0061] Most of the steps in Example 2 are the same as those in Example 1, except that the lubrication unit is 30 units.

[0062] Example 3

[0063] Most of the steps in Example 3 are the same as those in Example 1, except that there are 10 lubrication units.

[0064] Example 4

[0065] Most of the steps in Example 4 are the same as those in Example 1, except that there are 5 lubrication units.

[0066] Example 5

[0067] Most of the steps in Example 5 are the same as those in Example 1, except that there are 40 lubrication units.

[0068] Example 6

[0069] Most of the steps in Example 6 are the same as those in Example 1, except that the amount of acrylate monomer is 40 parts.

[0070] Example 7

[0071] Most of the steps in Example 7 are the same as those in Example 1, except that the amount of acrylate monomer is 60 parts.

[0072] Example 8

[0073] Most of the steps in Example 8 are the same as those in Example 1, except that the amount of acrylate monomer is 30 parts.

[0074] Example 9

[0075] Most of the steps in Example 9 are the same as those in Example 1, except that the amount of acrylate monomer is 70 parts.

[0076] Example 10

[0077] Most of the steps in Example 10 are the same as those in Example 1, except that the acidic monomer is 10 parts.

[0078] Example 11

[0079] Most of the steps in Example 11 are the same as those in Example 1, except that the acid monomer is in parts of 5.

[0080] Example 12

[0081] Example 12 is similar to Example 1 in most steps, except that the hydroxyl lubricant is 12-hydroxystearic acid, the acrylate monomer is polyethylene glycol monomethacrylate, and the acidic monomer is 2-acrylamido-2-methylpropanesulfonic acid.

[0082] Example 13

[0083] Example 13 is similar to Example 1 in most steps, except that the hydroxyl lubricant is methyl 2-hydroxystearate, the acrylate monomer is phenyl glycidyl ether acrylate, and the acidic monomer is methacryloyloxyethyl maleic acid monoester.

[0084] Example 14

[0085] Example 14 is similar to Example 1 in most steps, except that the hydroxyl lubricant is dodecyl alcohol-1, the acrylate monomer is ethylene glycol diacrylate, and the acid monomer is vinyl acrylate.

[0086] Example 15

[0087] Most of the steps in Example 15 are the same as those in Example 1, except that the mass ratio of the positive electrode active material lithium manganese oxide, conductive carbon black, secondary battery additives, and positive electrode binder is 94:3:0.5:2.5.

[0088] Example 16

[0089] Most of the steps in Example 16 are the same as those in Example 1, except that the mass ratio of the positive electrode active material lithium manganese oxide, conductive carbon black, secondary battery additives, and positive electrode binder is 94:3:0.1:2.9.

[0090] Example 17

[0091] Example 17 is similar to Example 1 in most steps, except that the mass ratio of the positive electrode active material lithium manganese oxide, conductive carbon black, secondary battery additives, and positive electrode binder is 94:3:1:2.

[0092] Comparative Example 1

[0093] Most of the steps in Comparative Example 1 and Example 1 are the same, except that no secondary battery additives are added to the positive electrode slurry.

[0094] Comparative Example 2

[0095] Comparative Example 2 and Example 1 follow most of the same steps, except that a lubrication unit was not added in the preparation of the secondary battery additive.

[0096] Comparative Example 3

[0097] Comparative Example 3 is similar to Example 1 in most steps, except that no acidic monomer was added in the preparation of the additive for secondary batteries.

[0098] Comparative Example 4

[0099] Comparative Example 4 is similar to Example 1 in most steps, except that no lubricating unit and acidic monomer were added in the preparation of the secondary battery additive.

[0100] Electrical performance testing:

[0101] The secondary battery additives, positive electrode slurry, positive electrode sheet, and secondary batteries prepared in the above examples and comparative examples were tested as follows.

[0102] 1. Li content: The Li content of the secondary battery additives was tested using an inductively coupled plasma atomic emission spectrometer (ICP).

[0103] 2. Slurry viscosity: The viscosity of the positive electrode slurry was tested using an NJ-1 rotational viscometer.

[0104] 3. Adhesion test: Cut the positive electrode sheet into 30*100mm specifications and test the adhesion strength using an electronic tensile testing machine.

[0105] 4. Flexibility test: The positive electrode sheet is tested for flexibility using the needle winding method.

[0106] 5. Compacted density test: The positive electrode sheet is stamped into 15 small discs using a stamping die, and the compacted density of the positive electrode coating on the discs is calculated by weighing.

[0107] 6. Charge the battery at 0.5C to 4.5V at 25℃, maintain a constant voltage of 4.5V, and cut off the current at 0.05C. Record the charging capacity. Then discharge the battery at a constant current of 0.5C to 3V and record the discharge capacity. Calculate the capacity by dividing the initial discharge capacity by the initial charge capacity.

[0108] 7. Room temperature cycle test: After placing the battery in a constant temperature test chamber at 25℃±2℃ for 1 hour, charge it to 3.65V with 1C constant current and constant voltage, and cut off the current at 0.05C; discharge it to 2.5V with 1C constant current and record the discharge capacity; repeat the above steps 500 times and calculate the capacity retention rate.

[0109] The test results are shown in Table 1 below.

[0110] Table 1

[0111]

[0112] Comparing the test results of Examples 1 and 2-5, it can be seen that when the lubricating unit in the secondary battery additive is within a reasonable range, the prepared positive electrode sheet has higher compaction density and excellent flexibility, and good capacity retention. When the content of the lubricating unit is too high, although the prepared positive electrode sheet has higher compaction density, the excessive lubricity leads to a decrease in the bonding performance of the positive electrode sheet, and powder shedding is likely to occur.

[0113] Comparing the test results of Examples 1 and 6-9, it can be seen that when the proportion of acrylate segments is within the range of this example, as the content increases, the prepared positive electrode slurry has a lower slurry viscosity under the same solid content, which is convenient for coating; when the proportion is too small, the slurry viscosity is too 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.

[0114] Comparing the test results of Examples 1 and 10-12, it can be seen that when the acidic monomer ratio is within the range of this example, it has a high Li content, which can improve the battery energy density and increase the battery cycle life. If the acidic monomer ratio is too low, the Li content is low (<8000ppm), and there is basically no lithium supplementation effect. If the acidic monomer ratio is too high, it will cause the solubility of the additives for secondary batteries to decrease in the solvent, and precipitation is easy to occur during the preparation process, making them difficult to use.

[0115] Compared with Comparative Examples 1-4, Example 1, which did not use the aforementioned secondary battery additives, had a higher viscosity during the positive electrode slurry processing, making it difficult to coat and providing no compaction or lithium replenishment effect on the positive electrode sheet. This resulted in poor cycle performance of the prepared battery cells. Furthermore, the lack of the aforementioned lubrication unit meant that the compaction density of the prepared positive electrode sheet was at a normal level (4.1 g / cm³). 3 The energy density is low and the cycle performance is average; lacking organic acid lithium salt structural units, the prepared additive does not contain Li and has no lithium replenishment effect, thus failing to improve the battery energy density and cycle life; when the additive for secondary batteries only uses acrylate segments, it only has a dispersing effect and its function is singular.

[0116] 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 within the protection scope of the present invention.

Claims

1. An additive for secondary batteries, characterized in that, The additive for secondary batteries is a copolymer comprising a lubricating unit and an acrylate structural unit, wherein the lubricating unit contains a long-chain hydrocarbon group and the long-chain hydrocarbon group has 8 or more carbon atoms; The weight ratio of the lubrication unit to the acrylate structural unit is (10~30):(40~60). The additive for secondary batteries also includes an organic lithium acid salt structural unit, wherein the weight ratio of the organic lithium acid salt structural unit to the lubrication unit is (10~30):(10~30). The organic acid lithium salt structural unit is selected from one or more of the following: lithium acrylate structural unit, lithium methacrylate structural unit, lithium β-acryloyloxypropionate structural unit, lithium hydroxyacrylate structural unit, lithium maleate structural unit, lithium itaconic acid structural unit, lithium itaconic acid monobutyl ester structural unit, lithium crotonate structural unit, lithium methacryloyloxyethyl succinate structural unit, lithium methacryloyloxyethyl maleate structural unit, lithium methacryloyloxyethyl phosphate structural unit, lithium glycol methacrylate phosphate structural unit, lithium alkyl acrylate phosphate structural unit, lithium p-styrene sulfonate structural unit, and lithium 2-acrylamido-2-methylpropanesulfonate structural unit.

2. The additive for secondary batteries according to claim 1, characterized in that, The lubrication unit is obtained by reacting a hydroxyl lubricant containing long-chain hydrocarbon groups and hydroxyl groups with a vinyl monomer containing anhydride groups; The hydroxyl lubricant includes one or more of the following: dodecyl alcohol-1, dodecyl alcohol-2, tetradecyl alcohol-1, hexadecyl alcohol-1, octadecyl alcohol-1, eicosyl alcohol-1, 12-hydroxystearic acid, methyl 2-hydroxystearate, methyl 12-hydroxystearate, and methyl 17-hydroxystearate. The vinyl monomer containing anhydride groups includes one or more of maleic anhydride, dimethylmaleic anhydride, aconitic anhydride, and itaconic anhydride.

3. The additive for secondary batteries according to claim 1, characterized in that, The acrylate structural units include one or more of the following: n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, isooctyl acrylate, isoborneol acrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, isooctyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, isoborneol methacrylate, polyethylene glycol monomethacrylate, phenyl glycidyl ether acrylate, ethylene glycol diacrylate, ethylene glycol methacrylate, and allyl methacrylate.

4. A positive electrode slurry, characterized in that, It includes positive electrode active material, binder, conductive agent and additives for secondary batteries as described in any one of claims 1 to 3.

5. The positive electrode slurry according to claim 4, characterized in that, The positive electrode slurry comprises the following components by weight: 90-95 parts positive electrode active material, 0.5-3 parts binder, 2-5 parts conductive agent, and 0.1-0.5 parts secondary battery additives.

6. A positive electrode plate, characterized in that, It includes a positive current collector and a positive electrode material layer disposed on at least one side surface of the positive current collector, the positive electrode material layer being formed by coating the positive electrode slurry as described in claim 4 or 5.

7. A secondary battery, characterized in that, It includes a negative electrode, an electrolyte, and a positive electrode as described in claim 6.

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