Pole piece additive, pole piece, preparation method of pole piece and secondary battery

Abstract

The invention relates to the technical field of secondary batteries, and discloses a pole piece additive, a pole piece, a preparation method of the pole piece and a secondary battery. The pole piece additive contains a flame retardant and a stabilizer; the flame retardant is a halogen-containing flame retardant and / or a polyphosphoric acid flame retardant; the stabilizer is any one of a fluorine compound, a boron compound or a fluorine-boron-containing compound. The pole piece additive can avoid continuous decomposition of the flame retardant, and the electrochemical performance and the safety performance of the battery are improved.

Description

Electrode additives, electrodes and their preparation methods, secondary batteries Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to an electrode additive, an electrode and its preparation method, and a secondary battery. Background Technology

[0002] Lithium-ion batteries contain a large amount of flammable electrolyte, which can easily ignite and trigger a chain reaction under extreme conditions, leading to battery explosion and posing a safety hazard.

[0003] Introducing flame retardants can reduce the risk of combustion and improve battery safety. For example, triethyl phosphate (TEP), trimethyl phosphate (TMP), or phosphononitrile additives are often introduced into the electrolyte to improve its non-flammability. Flame retardants achieve their flame-retardant purpose by decomposing to generate free radicals during heating, thus quenching free radicals produced by the combustion of organic matter. Therefore, the stability of flame retardants is generally relatively low, and there is a risk of continuous decomposition on the surfaces of the high-voltage positive electrode and low-voltage negative electrode inside the battery, leading to poor electrical performance. To address this issue, CN117996082A uses a microcapsule structure to avoid the impact of poor flame retardant stability on battery performance. However, this method requires additional production steps, significantly increasing battery costs. Furthermore, the non-combustion exothermic reaction between the solvent and the electrode generates a large amount of heat inside the battery, and even with the presence of flame retardants, there is still a risk of thermal runaway.

[0004] In addition to the heat released by the combustion of the electrolyte during thermal runaway, a large number of redox reactions of the electrolyte and electrodes also occur during the process. Flame retardants cannot inhibit these reactions, so the battery still has the risk of thermal runaway. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems in the prior art, such as the flame retardant material in the electrolyte easily undergoing redox reaction with the electrode material and continuously decomposing and degrading the battery performance during cycling. This invention provides an electrode additive, an electrode and its preparation method, and a secondary battery. The electrode additive can prevent the continuous decomposition of the flame retardant and improve the electrochemical performance and safety performance of the battery.

[0006] To achieve the above objectives, the present invention provides an electrode additive containing a flame retardant and a stabilizer; the flame retardant is a halogen-containing flame retardant and / or a polyphosphoric acid flame retardant; the stabilizer is any one of a fluorine compound, a boron compound, or a fluorine-boron-containing compound.

[0007] A second aspect of the present invention provides an electrode sheet comprising an active material and the electrode sheet additives described in the first aspect of the present invention.

[0008] A third aspect of the present invention provides a method for preparing the electrode sheet described in the second aspect, comprising: mixing the active material, electrode sheet additive, conductive agent, binder and solvent, and then sequentially homogenizing, coating and drying; wherein the electrode sheet additive is the electrode sheet additive described in the first aspect of the present invention.

[0009] A fourth aspect of the present invention provides a secondary battery, wherein the secondary battery contains the electrode provided in the second aspect of the present invention.

[0010] In the electrode additive provided by this invention, during cycling, the stabilizer in direct contact with the electrode decomposes and reacts with the battery material, passivating the electrode and preventing the flame retardant from continuously decomposing due to high-pressure oxidation or low-pressure reduction reactions with the electrode, thus improving the cycle stability of the battery. Furthermore, adding this additive to the electrode avoids the traditional method of adding it to the electrolyte, where the stabilizer not only continuously reacts with the negative electrode and is consumed to generate SEI, leading to a decline in electrochemical performance due to excessive SEI reactions, but also renders the consumed stabilizer ineffective during subsequent battery thermal abuse. Under battery thermal abuse conditions, the flame retardant of this invention can expose the internal stabilizer during decomposition, allowing it to react with the electrode and passivate it, reducing subsequent exothermic reactions between the electrolyte solvent and the electrode, thus improving battery safety. The electrode additive provided by this invention can also address the impact of flame retardants on battery cycle stability and the risk of non-combustible exothermic reactions through the synergistic effect of the flame retardant and stabilizer, further improving battery safety. The electrode preparation method provided by this invention is simple, efficient, cost-controllable, and easy to scale up for production. Attached Figure Description

[0011] Figure 1 is a schematic diagram of the role of the electrode additive in Example 1.

[0012] Figure 2 is a cross-sectional SEM image of the electrode sheet of Example 4.

[0013] Figure 3 is a cross-sectional SEM image of the electrode sheet of Example 5.

[0014] Figure 4 shows a comparison of the DSC exothermic response in Example 4 and Comparative Example 1. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] The first aspect of the present invention provides an electrode additive, wherein the electrode additive contains a flame retardant and a stabilizer; the flame retardant is a halogen-containing flame retardant and / or a polyphosphate flame retardant; and the stabilizer is any one of a fluorine compound, a boron compound, or a fluorine-boron-containing compound.

[0017] In this invention, the flame retardant can be a high molecular weight polymer or a small molecule compound. In the electrode additive provided by this invention, the structural relationship between the flame retardant and the stabilizer is as follows: the stabilizer is uniformly dispersed within the flame retardant, and the composite material formed by the flame retardant and the stabilizer coats the surface of the positive electrode material. In this invention, the flame retardant and the stabilizer are physically mixed, and there are no chemical bonds between them.

[0018] In this invention, the flame retardant is a halogen-containing flame retardant and / or a polyphosphate flame retardant. According to some preferred embodiments of the invention, the flame retardant is selected from at least one of brominated polystyrene, brominated polybutadiene, brominated epoxy resin, pentabromobenzyl polyacrylate, pentabromobenzyl acrylate-acrylate copolymer, brominated styrene-butadiene copolymer, polydibromostyrene, melamine polyphosphate, polyN-methylmaleimide, hexabromocyclododecane, decabromodiphenyl ethane, tetrabromobisphenol A, tetrabromophthalic acid, methyl octabromoether, ammonium polyphosphate, and polyphosphate esters. More preferably, it is brominated epoxy resin, pentabromobenzyl acrylate polymer, pentabromobenzyl acrylate-acrylate copolymer, brominated styrene-butadiene copolymer, polyN-methylmaleimide, polyphosphate ester, and hexabromocyclododecane.

[0019] In this invention, the pentabromobenzyl acrylate copolymer is prepared by pentabromobenzyl acrylate and acrylate monomers. According to some preferred embodiments of this invention, the mass ratio of pentabromobenzyl acrylate to acrylate monomers is 100:(0-20).

[0020] In this invention, the flame retardant can be a polymeric flame retardant and / or a small molecule flame retardant. This invention does not have a particular limitation on the weight-average molecular weight of the polymeric flame retardant, as long as it can achieve the technical objective of this invention.

[0021] In this invention, the use of the above-mentioned preferred flame retardant is beneficial to generate a composite material of flame retardant and stabilizer inside the electrode during the homogenization process, which is then wrapped around the surface of the positive electrode.

[0022] According to the present invention, preferably, the liquid absorption rate of the flame retardant is ≤10%; more preferably, it is ≤5%, for example, it can be 0%, 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8%, 4%, 4.5%, 4.8%, 5%, and any value in between. In this invention, the method for testing the liquid absorption rate of the flame retardant includes: (1) the flame retardant is a high molecular polymer: 10g of the polymer test material is placed in 100g of electrolyte, placed at 25°C for 1h, then the polymer test material is filtered out and weighed to obtain mass m, liquid absorption rate = (m-10) / 10×100%; (2) the flame retardant is a small molecule compound: 10g of the small molecule test material is placed in 100g of electrolyte, placed at 25°C for 1h, then the small molecule test material is filtered out and weighed to obtain mass m, liquid absorption rate = (10-m) / 10×100%; wherein, the electrolyte used above is EC / EMC / DMC=1 / 1 / 1 (v / v / v), 1mol / L LiPF6.

[0023] According to some preferred embodiments of the present invention, the liquid absorption rate of the flame retardant is 0.1-5%.

[0024] In this invention, if the liquid absorption rate of the flame retardant is too high, it will absorb too many solvent molecules, causing gelation and swelling, and releasing the stabilizer encapsulated inside, causing the stabilizer to be released into the electrolyte and lose its protective function.

[0025] Preferably, the content of the stabilizer is 1-90% based on the mass of the flame retardant, more preferably 30-80%, for example, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 72%, 75%, 80%.

[0026] In this invention, the stabilizer, within the above-mentioned preferred range, is beneficial for passivating the electrode and providing protection, while also being less likely to dissolve from the flame retardant into the electrolyte and affect the battery's electrical performance.

[0027] According to some preferred embodiments of the present invention, the stabilizer is a fluorinated compound, and the fluorine content, based on the total mass of the stabilizer, is ≥20%; more preferably ≥30%. According to some preferred embodiments of the present invention, the fluorine content, based on the total mass of the stabilizer, is 30-90%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%.

[0028] According to some preferred embodiments of the present invention, the stabilizer is a boron compound, and the boron content is ≥4% based on the total mass of the stabilizer; more preferably ≥6%. According to some preferred embodiments of the present invention, the boron content is 6-30% based on the total mass of the stabilizer, for example, it can be 6%, 8%, 10%, 12%, 15%, 18%, 20%, 23%, 25%, 28%, or 30%.

[0029] According to some preferred embodiments of the present invention, the stabilizer is a fluorine-boron-containing compound, wherein the sum of the masses of fluorine and boron is ≥20% based on the total mass of the stabilizer. According to some preferred embodiments of the present invention, the sum of the masses of fluorine and boron is 20-90% based on the total mass of the stabilizer, for example, it can be 20%, 23%, 25%, 28%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 99%.

[0030] In this invention, if the fluorine or boron content in the stabilizer is too low, it will cause insufficient stability of the passivation layer formed during the passivation process of the electrode.

[0031] According to the present invention, the stabilizer is a fluorine-containing and / or boron-containing compound. According to some preferred embodiments of the present invention, the stabilizer is selected from at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium tetrafluoroborate, lithium difluorophosphate, lithium difluoro(trifluoromethylsulfonyl)(fluorosulfonyl)imide, tris(pentafluorophenyl)borane, lithium perfluorobutylsulfonate, perfluorobutylsulfonic acid, perfluorobutylsulfonamide, perfluorobutylsulfonyl fluoride, lithium bis(perfluorobutylsulfonyl)imide, 2,2,2-trifluoroacetamide, pentafluorophenol, trifluoroethyl perfluorobutylsulfonate, methyl fluorosulfonyl difluoroacetate, tris(2,2,2-trifluoroethyl)borate, tris(2,2,2-trifluoroethyl) phosphate, triallyl borate, trimethylcyclotriboroxane, trimethoxyboroxane, and 3-thiophene boric acid. More preferably, it is selected from at least one of lithium tetrafluoroborate, lithium bis(perfluorobutylsulfonyl)imide, and lithium difluorooxalate borate.

[0032] In this invention, the use of the aforementioned preferred stabilizer is beneficial because, during cycling, after the flame retardant undergoes high-pressure oxidation or low-pressure reduction, the stabilizer decomposes and reacts with the battery active material to passivate the electrode, preventing continuous decomposition of the flame retardant upon contact with the electrode and improving the battery's cycle stability. In cases of battery thermal abuse, the high-temperature decomposition of the flame retardant can expose the internal stabilizer, allowing it to react with the electrode and passivate it, reducing subsequent exothermic reactions between the electrolyte solvent and the electrode oxidation-reduction reaction, thus improving battery safety.

[0033] A second aspect of the present invention provides an electrode sheet comprising an active material and the electrode sheet additives described in the first aspect of the present invention.

[0034] According to some preferred embodiments of the present invention, the electrode is a positive electrode and the active material is a positive active material.

[0035] This invention does not impose any particular limitation on the type of positive electrode active material, as long as it achieves the technical objective of this invention. According to some preferred embodiments of this invention, the positive electrode active material is selected from at least one of lithium cobalt oxide, lithium nickel cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, ternary lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium manganese iron phosphate, lithium iron phosphate, sulfur, and lithium sulfide.

[0036] According to the present invention, preferably, the content of the flame retardant in the positive electrode sheet is 0.1%-10% based on the total mass of the positive electrode active material; more preferably, it is 0.2-6%, for example, it can be 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 3%, 3.5%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.3%, 5.5%, 5.8%, or 6%.

[0037] In this invention, if the content of electrode additives in the positive electrode is too high, it will lead to an excessive amount of non-hydrophilic agglomerates inside the electrode, which will affect the electrolyte wetting of the electrode material and hinder lithium-ion transport during charging and discharging. If the content is too low, it will lead to a decrease in the effect and be insufficient to improve battery safety.

[0038] According to some preferred embodiments of the present invention, the electrode is a negative electrode and the active material is a negative electrode active material.

[0039] This invention does not impose any particular limitation on the type of negative electrode active material, as long as it achieves the technical objective of this invention. According to some preferred embodiments of this invention, the negative electrode material is selected from at least one of graphite, hard carbon, molybdenum disulfide, lithium titanate, graphene, silicon, silicon-carbon, silicon-oxygen, and silicon-oxygen-carbon negative electrodes.

[0040] Preferably, the flame retardant content in the negative electrode sheet is 0.1%-10% based on the total mass of the negative electrode active material; more preferably, it is 0.2-6%, for example, it can be 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 3%, 3.5%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.3%, 5.5%, 5.8%, or 6%.

[0041] In this invention, if the content of the electrode additive in the negative electrode is too high, it will lead to an excessive amount of non-hydrophilic agglomerates inside the electrode, which will affect the electrolyte wetting of the electrode material and hinder lithium-ion transport during charging and discharging. If it is too low, it will lead to a decrease in the effect and be insufficient to improve battery safety.

[0042] A third aspect of the present invention provides a method for preparing the electrode sheet described in the second aspect, comprising: mixing the active material, electrode sheet additive, conductive agent, binder and solvent, and then sequentially homogenizing, coating and drying; wherein the electrode sheet additive is the electrode sheet additive described in the first aspect of the present invention.

[0043] The electrode preparation method provided by this invention is simple, efficient, cost-controllable, and easy to scale up for production.

[0044] In this invention, there is no particular limitation on the type of conductive agent, as long as it can achieve the technical objective of this invention. According to some preferred embodiments of this invention, the conductive agent is selected from at least one of conductive carbon black, conductive graphite, graphene, carbon nanotubes, and conductive fibers.

[0045] In this invention, there is no particular limitation on the type of solvent, as long as it can achieve the technical objective of this invention. According to some preferred embodiments of this invention, the solvent is N-methylpyrrolidone (NMP).

[0046] In this invention, there are no particular limitations on the type and molecular weight of the adhesive, as long as it achieves the technical objective of this invention. According to some preferred embodiments of this invention, the adhesive is selected from at least one of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0047] In this invention, there is no particular limitation on the order of adding materials in the mixing process, as long as the technical objective of this invention can be achieved.

[0048] A fourth aspect of the present invention provides a secondary battery, wherein the secondary battery contains the electrode provided in the second aspect of the present invention.

[0049] According to some preferred embodiments of the present invention, the secondary battery provided by the present invention uses the positive electrode sheet provided in the second aspect of the present invention as the positive electrode. The present invention does not have any particular limitation on the type of negative electrode and electrolyte in the secondary battery, as long as the technical objective of the present invention can be achieved.

[0050] According to some preferred embodiments of the present invention, the secondary battery provided by the present invention uses the negative electrode sheet provided in the second aspect of the present invention as the negative electrode. The present invention does not have any particular limitation on the type of positive electrode and electrolyte in the secondary battery, as long as the technical objective of the present invention can be achieved.

[0051] According to some preferred embodiments of the present invention, the secondary battery provided by the present invention uses the positive electrode sheet provided in the second aspect of the present invention as the positive electrode and the negative electrode sheet provided in the second aspect of the present invention as the negative electrode. The present invention does not have any particular limitation on the type of electrolyte in the secondary battery, as long as it can achieve the technical purpose of the present invention.

[0052] The secondary battery provided by this invention has advantages such as long lifespan and high safety.

[0053] The present invention will be described in detail below through embodiments. Unless otherwise specified, all raw materials in the following embodiments are commercially available.

[0054] Test method: Ionic conductivity test: Dissolve flame retardant and stabilizer in NMP according to the design ratio to prepare a 10% film-forming solution. Pour the film-forming solution into a polytetrafluoroethylene mold, dry it at 80℃ for 24 hours, and then vacuum dry it at 80℃ for 24 hours to obtain the sample to be tested. Cut the sample into round pieces and assemble it into stainless steel / sample / stainless steel. During the assembly process, EIS test is performed to obtain the sample impedance. Ionic conductivity is calculated as film thickness / (impedance × area).

[0055] DSC test: Disassemble the fully charged battery, scrape off the electrode material with a ceramic knife, clean it with DMC and vacuum dry it. Add it to the DSC device at a powder / electrolyte mass ratio of 1:1 for testing, and the scan rate is 5℃ / min.

[0056] Needle penetration test: The battery is fully charged and a 5mm steel needle is used to perform a needle penetration test at a speed of 25mm / s; Hot chamber test: The battery is fully charged and the temperature is increased to 130℃ at a rate of 5℃ / min, and then held at 10℃ for 1 hour until the battery thermal runaway or the temperature reaches 200℃.

[0057] Synthesis method of pentabromobenzyl acrylate copolymer: 20g pentabromobenzyl acrylate and acrylate monomer (the mass ratio of the two depends on the specific embodiment) and 100g dimethyl carbonate are added to a three-necked flask and stirred for 30min. Then, 1%wt of azobisisobutyronitrile (AIBN) is added and the mixture is heated to 45℃ in a water bath and stirred for 24h. After that, the polymerization product is poured into a glass evaporating dish and dried in a forced-air dryer at 80℃ for 24h to obtain the polymer.

[0058] Example 11) 10g of PVDF was added to 190g of NMP, stirred until homogeneous, and then pentabromobenzyl acrylate copolymer (synthesized according to the method for pentabromobenzyl acrylate copolymer, wherein the amount of acrylate monomer added was 0), lithium tetrafluoroborate, conductive agent SP, and LiNi were added sequentially. 0.9 Co 0.05 Mn 0.05O2 ternary cathode material was used to obtain a cathode slurry; the mass ratio of PVDF: pentabromobenzyl acrylate copolymer: lithium tetrafluoroborate: conductive agent: cathode material was 1:5:2.5:0.05:100. The slurry was then coated, dried, and rolled to obtain a safety cathode sheet; the sheet was then subjected to surface resistivity testing and cross-sectional SEM scanning.

[0059] 2) The negative electrode sheet was prepared according to the general process flow, wherein the binder (CMC+SBR, CMC and SBR mass ratio of 1:2): conductive agent SP: graphite: silicon suboxide mass ratio of 1.5:1:85:15 in the negative electrode sheet of step 1) and PE+Al2O3 coated separator were used to assemble a 10Ah cell, and electrolyte (EC / EMC / FEC in volume ratio of 1 / 8 / 1, 1M LiPF6) was injected. After being left at room temperature for 48h, formation and capacity testing were performed to obtain the soft pack battery to be tested; 4) After charging to 100% SOC with a 0.1C current, DSC test, hot box test and nail penetration test were performed respectively. The liquid absorption rate of flame retardant, electrode surface resistance and safety performance test results are shown in Table 1, and the ionic conductivity test results are shown in Table 2. The schematic diagram of the role of electrode additives is shown in Figure 1. It can be seen that after the completion of homogenization, dispersion and coating, the composite material formed by flame retardant and stabilizer is wrapped on the surface of electrode material.

[0060] Example 2 follows the same method as Example 1, except that the mass ratio of pentabromobenzyl acrylate to acrylate is 100:2 during the synthesis of pentabromobenzyl acrylate-acrylate copolymer. The performance test results are shown in Table 1.

[0061] Example 3 follows the method of Example 1, except that the mass ratio of pentabromobenzyl acrylate to acrylate is 100:4 during the synthesis of pentabromobenzyl acrylate-acrylate copolymer. The performance test results are shown in Table 1.

[0062] Example 4 follows the method of Example 1, except that the mass ratio of pentabromobenzyl acrylate to acrylate in the synthesis of the pentabromobenzyl acrylate-acrylate copolymer is 100:8. The performance test results are shown in Table 1. The cross-sectional SEM of the electrode is shown in Figure 2. As can be seen from Figure 2, a small amount of safety material is covered between the electrode particles inside the electrode.

[0063] Example 5 follows the same method as Example 1, except that the mass ratio of pentabromobenzyl acrylate to acrylate in the synthesis of the pentabromobenzyl acrylate-acrylate copolymer is 100:12. The test results are shown in Table 1, and the ionic conductivity test results are shown in Table 2. The cross-sectional SEM of the electrode is shown in Figure 3. As can be seen from Figure 3, a large amount of safety material is filled between the electrode particles inside the electrode.

[0064] Example 6 follows the method of Example 1, except that the amount of lithium tetrafluoroborate is changed so that the mass ratio of PVDF:pentabromobenzyl acrylate copolymer:lithium tetrafluoroborate:conductive agent:positive electrode material is 1:5:0.5:0.05:100. The liquid absorption rate of the flame retardant and the performance test results are shown in Table 1.

[0065] Example 7 follows the method of Example 1, except that the amount of lithium tetrafluoroborate is changed so that the mass ratio of PVDF:pentabromobenzyl acrylate copolymer:lithium tetrafluoroborate:conductive agent:positive electrode material is 1:5:1.5:0.05:100. The performance test results are shown in Table 1.

[0066] Example 8 follows the method of Example 1, except that the amount of lithium tetrafluoroborate is changed so that the mass ratio of PVDF:pentabromobenzyl acrylate copolymer:lithium tetrafluoroborate:conductive agent:positive electrode material is 1:5:4:0.05:100. The performance test results are shown in Table 1.

[0067] Example 9 follows the method of Example 4, except that the amount of lithium tetrafluoroborate is changed so that the mass ratio of PVDF:pentabromobenzyl acrylate copolymer:lithium tetrafluoroborate:conductive agent:positive electrode material is 1:5:4.5:0.05:100. The performance test results are shown in Table 1.

[0068] Example 10 follows the method of Example 4, except that the stabilizer is changed from lithium tetrafluoroborate to lithium bis(perfluorobutylsulfonyl)imide. The liquid absorption rate, electrode surface resistance, and safety performance test results of the flame retardant are shown in Table 1.

[0069] Example 11 follows the method of Example 4, except that the stabilizer is changed from lithium tetrafluoroborate to lithium difluorooxalate borate. The liquid absorption rate, electrode surface resistance, and safety performance test results of the flame retardant are shown in Table 1.

[0070] Example 12 follows the method of Example 4, except that the flame retardant is changed from pentabromobenzyl acrylate copolymer to brominated polystyrene. The liquid absorption rate, electrode surface resistance, and safety performance test results of the flame retardant are shown in Table 1.

[0071] Example 13 follows the method of Example 4, except that the flame retardant is changed from pentabromobenzyl acrylate copolymer to polybrominated styrene-butadiene copolymer. The liquid absorption rate, electrode surface resistance, and safety performance test results of the flame retardant are shown in Table 1.

[0072] Example 141) 10g of CMC and SBR (CMC to SBR mass ratio of 1:2) binder were added to 190g of water and stirred evenly. Then, ammonium polyphosphate, lithium tetrafluoroborate, conductive agent SP, graphite, and silicon suboxide were added sequentially to obtain a negative electrode slurry. The mass ratio of binder:ammonium polyphosphate:lithium tetrafluoroborate:conductive agent:negative electrode material was 1:5:2.5:0.05:100. The slurry was then coated, dried, and rolled to obtain a safe negative electrode sheet. The sheet was subjected to surface resistivity testing and cross-sectional SEM scanning.

[0073] 2) Prepare the positive electrode sheet according to the general process flow, wherein PVDF: conductive agent SP: LiNi 0.9 Co 0.05 Mn 0.05 The mass ratio of the O2 ternary cathode material is 1:0.05:100; 3) Using the cathode sheet from step 1) and the anode sheet from step 2) along with the PE+Al2O3 coated separator, a 10Ah cell is assembled and an electrolyte (EC / EMC / FEC in a volume ratio of 1 / 8 / 1, 1M LiPF6) is injected. After being left at room temperature for 48 hours, formation and capacity testing are performed to obtain the soft-pack battery to be tested; 4) After charging to 100% SOC with a 0.1C current, DSC test, hot box test, and nail penetration test are performed respectively. The liquid absorption rate of the flame retardant, the surface resistance of the electrode sheet, and the test results of safety performance are shown in Table 1.

[0074] Comparative Example 11) 10g of PVDF was added to 190g of NMP, stirred until homogeneous, and then conductive agents SP and LiNi were added sequentially. 0.9 Co 0.05 Mn 0.05 O2 ternary cathode material was used to obtain a cathode slurry; the ratio of PVDF: conductive agent: cathode material was 1:0.05:100. The slurry was then coated, dried, and rolled to obtain a safety cathode sheet. The sheet was then subjected to surface resistivity testing and cross-sectional SEM scanning.

[0075] 2) The negative electrode sheet was prepared according to the general process flow, wherein the mass ratio of the binder (CMC+SBR, CMC to SBR mass ratio is 1:2): conductive agent: graphite: silicon suboxide mass ratio is 1.5:1:85:15; 3) Using the positive electrode sheet from step 1) and the negative electrode sheet from step 2) and a PE+Al2O3 coated separator, a 10Ah cell was assembled and injected with electrolyte (EC / EMC / FEC=1 / 8 / 1, 1M LiPF6). After being left at room temperature for 48 hours, formation and capacity testing were performed to obtain the soft-pack battery to be tested; 4) After charging to 100% SOC with a 0.1C current, DSC test, hot box test, and nail penetration test were performed. The liquid absorption rate of the flame retardant, the surface resistance of the electrode sheet, and the test results of safety performance are shown in Table 1. Figure 4 shows a comparison of the DSC exothermic reaction between Example 4 and Comparative Example 1. As can be seen from Figure 4, after the addition of the safety additive, the DSC showed that the exothermic peak at 220°C was significantly suppressed, and the temperature of intense exothermic reaction was delayed to about 250°C. This indicates that the safety additive has a significant inhibitory effect on the intense redox reaction between the electrode and the electrolyte.

[0076] Comparative Example 2 follows the same method as Example 1, except that the mass ratio of pentabromobenzyl acrylate to trifluoroethyl acrylate is 2:1 during the synthesis of the pentabromobenzyl acrylate copolymer, and lithium tetrafluoroborate is not added. The performance test results are shown in Table 1.

[0077] Comparative Example 3 followed the method of Example 1, except that lithium tetrafluoroborate was removed. The performance test results are shown in Table 1.

[0078] Comparative Example 41) 10g of pentabromobenzyl polyacrylate and 5g of lithium tetrafluoroborate were added to 100g of NMP and stirred to dissolve to prepare a mixture. Then, the mixture was coated onto the surface of the diaphragm with a 20µm height scraper. After coating, the diaphragm was placed in an 80℃ oven and dried for 2 hours to obtain the coated diaphragm.

[0079] 2) Prepare positive and negative electrode sheets according to the general process flow. The negative electrode sheet contains a binder (CMC+SBR, CMC to SBR mass ratio 1:2): conductive agent SP: graphite: silicon suboxide mass ratio of 1.5:1:85:15. The positive electrode sheet contains PVDF: conductive agent SP: LiNi... 0.9 Co 0.05 Mn 0.05 O2 ternary cathode material = 1:0.05:100; 3) Assemble a 10Ah cell using the separator from step 1) and the electrode from step 2), and inject electrolyte (EC / EMC / FEC = 1 / 8 / 1, 1M LiPF6), and after standing at room temperature for 48h, perform formation and capacity testing to obtain the soft-pack battery to be tested; 4) Charge to 100% SOC using 0.1C current and then perform DSC test, hot box test and nail penetration test respectively.

[0080] 5) The assembled battery was charged and discharged using a 0.1C current.

[0081] Table 1

[0082] Table 2

[0083] The results in the table show that the battery prepared using the embodiments of the present invention has better thermal stability and battery cycle stability, and the heat box temperature and battery cycle number are significantly better.

[0084] As can be seen from Figures 2 and 3, the added safety additives form localized agglomerates inside the electrode and come into contact with the positive electrode surface.

[0085] The results from the examples and comparative examples show that when the flame retardant has a low liquid absorption rate, the battery exhibits better electrical and safety performance. However, when the liquid absorption rate is high, battery performance deteriorates. This is because excessive liquid absorption after electrolyte injection causes the flame retardant to swell, rendering the internal stabilizer ineffective. Adding a stabilizer improves cycle life, but excessive addition leads to excessive contact with the electrode, resulting in an overly thick interfacial film that hinders ion transport, reducing capacity and electrical performance. The addition of a stabilizer helps to rapidly passivate the electrode after the flame retardant decomposes, allowing the interfacial film to form a stable layer rich in LiF, significantly reducing DSC exothermics and improving needle penetration and thermal box performance. When the flame retardant is a soluble material, it lacks protection for the internal stabilizer, causing a large amount of stabilizer and flame retardant to dissolve into the electrolyte, deteriorating battery cycle performance. Without a stabilizer, the flame retardant exhibits poor stability under high voltage for extended periods, resulting in deteriorated long-cycle performance. Furthermore, without a flame retardant, a stabilizer alone cannot improve battery safety.

[0086] The results of Example 1 and Comparative Examples 2 and 3 show that while directly modifying flame retardant molecules through monomer copolymerization can help improve capacity and cycle stability, it still cannot achieve the same effect as the example. Furthermore, its safety performance is far inferior to that of the example. This is because the stabilizer and flame retardant in this example are independent components without chemical bonds. Moreover, the stabilizer has good solubility in the electrolyte. When the flame retardant decomposes due to electrochemical and high-temperature processes, the internal stabilizer can be released and dissolved into the electrolyte to undergo a liquid-solid reaction with the electrode. The reaction rate and uniformity are much higher than the solid-solid reaction in Comparative Example 2, which significantly improves the formation rate of the electrode passivation layer.

[0087] As can be seen from Example 1 and Comparative Example 4, the additive in this scheme has a better effect inside the positive electrode than the membrane coating. This is because the membrane surface coating only contacts the surface of the electrode and is difficult to suppress the reaction inside the electrode.

[0088] As can be seen from Table 2, in the preferred embodiment of the present invention, the stabilizer and flame retardant exist as two independent phases. In particular, when the stabilizer is a salt, it does not dissociate in the flame retardant and possesses ion transport capabilities, with an electrical conductivity <1*10⁻⁶. -7 With a flow rate of S / cm, there is almost no ion transport. As can be seen from Comparative Example 4, when this polymer film is coated on the surface of the separator and immersed in the electrolyte to act as the electrolyte, the battery capacity is significantly affected. This further indicates that the lithium ions inside are in an undissociated state and cannot move. Coating the separator surface affects lithium ion transport, and it cannot transport lithium ions like traditional polymer electrolytes. This ensures that some dissociable stabilizers inside, such as salt stabilizers, will not be exchanged and dissolved due to electric field drive during battery charging and discharging.

[0089] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An electrode additive, characterized in that, The electrode additive contains a flame retardant and a stabilizer; the flame retardant is a halogen-containing flame retardant and / or a polyphosphoric acid flame retardant; the stabilizer is any one of a fluorine compound, a boron compound, or a fluorine-boron-containing compound.

2. The electrode additive according to claim 1, wherein, The flame retardant and stabilizer are physically mixed; preferably, the flame retardant is selected from at least one of brominated polystyrene, brominated polybutadiene, brominated epoxy resin, pentabromobenzyl acrylate polymer, pentabromobenzyl acrylate-acrylate copolymer, brominated styrene-butadiene copolymer, polydibromostyrene, melamine polyphosphate, polyN-methylmaleimide, hexabromocyclododecane, decabromodiphenyl ethane, tetrabromobisphenol A, tetrabromophthalic acid, methyl octabromoether, polyphosphate, and ammonium polyphosphate; preferably, the liquid absorption rate of the flame retardant is ≤10%, more preferably ≤5%.

3. The electrode additive according to claim 1 or 2, wherein, The content of the stabilizer is 1-90% based on the mass of the flame retardant, more preferably 30-80%.

4. The electrode additive according to any one of claims 1-3, wherein, The stabilizer is a fluorine compound, and the fluorine content is ≥20% based on the total mass of the stabilizer, preferably ≥30%; or, the stabilizer is a boron compound, and the boron content is ≥4% based on the total mass of the stabilizer, preferably ≥6%; or, the stabilizer is a fluorine-boron compound, and the sum of the masses of fluorine and boron is ≥20% based on the total mass of the stabilizer.

5. The electrode additive according to any one of claims 1-4, wherein, The stabilizer is selected from at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium tetrafluoroborate, lithium difluorophosphate, lithium difluoro(trifluoromethylsulfonyl)(fluorosulfonyl)imide, tris(pentafluorophenyl)borane, lithium perfluorobutyl sulfonate, perfluorobutyl sulfonic acid, perfluorobutyl sulfonamide, perfluorobutyl sulfonyl fluoride, lithium bis(perfluorobutylsulfonyl)imide, 2,2,2-trifluoroacetamide, pentafluorophenol, trifluoroethyl perfluorobutyl sulfonate, methyl fluorosulfonyl difluoroacetate, tris(2,2,2-trifluoroethyl)borate, tris(2,2,2-trifluoroethyl) phosphate, triallyl borate, trimethylcyclotriboroxane, trimethoxyboroxane, and 3-thiophene boric acid.

6. An electrode sheet, characterized in that, The electrode comprises an active material and the electrode additive as described in any one of claims 1-5.

7. The electrode according to claim 6, wherein, The electrode sheet is a positive electrode sheet, and the active material is a positive electrode active material; preferably, the positive electrode active material is selected from at least one of lithium cobalt oxide, lithium nickel cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, ternary lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium manganese iron phosphate, lithium iron phosphate, sulfur, and lithium sulfide; preferably, the content of the flame retardant in the positive electrode sheet, based on the total mass of the positive electrode active material, is 0.1%-10%; more preferably, it is 0.2-6%.

8. The electrode according to claim 6, wherein, The electrode sheet is a negative electrode sheet, and the active material is a negative electrode active material; preferably, the negative electrode material is selected from at least one of graphite, hard carbon, molybdenum disulfide, lithium titanate, graphene, silicon, silicon-carbon, silicon-oxygen, and silicon-oxygen-carbon negative electrodes; preferably, the content of the flame retardant in the negative electrode sheet is 0.1%-10% based on the total mass of the negative electrode active material; more preferably, it is 0.2%-6%.

9. A method for preparing the electrode sheet according to any one of claims 6-8, comprising: The active material, electrode additive, conductive agent, binder and solvent are mixed and then subjected to homogenization, coating and drying in sequence. The electrode additive is the electrode additive described in any one of claims 1-5.

10. A secondary battery, characterized in that, The secondary battery contains the electrode as described in any one of claims 6-8.

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