Gel precursor for battery diaphragm, functional gel diaphragm as well as preparation method and application of functional gel diaphragm

Abstract

The invention discloses a gel precursor for a battery diaphragm, a functional gel diaphragm as well as a preparation method and application of the functional gel diaphragm, and the preparation method comprises the following steps: firstly, preparing the gel precursor with an epoxy group, then uniformly mixing the gel precursor with a functional monomer with a nitrogen heterocyclic ring structure to obtain diaphragm coating slurry, the preparation method comprises the following steps: preparing a gel precursor, coating two surfaces of a base membrane with a slurry roller, carrying out hot drying, carrying out a self-crosslinking reaction on an epoxy group in the gel precursor under the induction of a primary amine / secondary amine group in a functional monomer in the process, forming a layer of a net-shaped crosslinking high polymer material on the surface of the base membrane, and finally carrying out vacuum drying on the membrane to obtain the functional gel membrane. By introducing the functional gel diaphragm, on the premise of not influencing the initial performance of the battery, the key failure mechanism of manganese ion dissolution is specifically inhibited, the breakthrough improvement of the cycle performance is realized, and compared with the prior art, the functional gel diaphragm has remarkable advantages in the aspects of inhibiting manganese ion migration and maintaining the interface stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a gel precursor for a battery separator, a functional gel separator, and a preparation method and application thereof. Background Art

[0002] With the rapid development of the new energy vehicle industry, high energy density, long cycle life, and high safety have become key areas for technological breakthroughs in power battery cathode materials. Lithium iron phosphate (LiFePO4, LFP) cathode materials once dominated the market due to their excellent thermal stability, cycle performance, and low cost. However, their low theoretical energy density (approximately 170 mAh / g) makes them difficult to meet the growing range demands of electric vehicles. While nanomaterialization and carbon coating have nearly reached their performance limits, further improvement is limited.

[0003] In this context, lithium manganese iron phosphate (LiMn 1-x Fe x PO4, LMFP) is an important upgrade direction of the phosphate system because it combines the high safety of LFP and the high voltage platform of lithium manganese phosphate (LiMnPO4) (about 4.1V vs.Li + / Li), the energy density is significantly improved (theoretically up to 210mAh / g), and it is considered to be a promising alternative to medium- and high-nickel ternary materials. However, the practical application of LMFP still faces severe challenges: the inherent Jahn-Teller effect in the LiMnPO4 component leads to the 3+ During the charge and discharge process, the ions undergo lattice distortion, which causes the dissolution of manganese ions. 2+ They migrate to the negative electrode surface, disrupting the dynamic equilibrium of the solid electrolyte interface (SEI film), leading to continuous consumption of active lithium and intensified side reactions, which in turn cause battery capacity decay and shortened cycle life (especially in high-temperature environments). In addition, manganese ions deposited on the negative electrode surface may catalyze the decomposition of the electrolyte, forming unstable interfacial compounds, increasing the battery's internal resistance and the risk of thermal runaway, seriously hindering the industrialization of LMFP.

[0004] To address the issue of manganese dissolution, existing technologies mainly focus on modifying the cathode material itself or optimizing the electrolyte. For example, by surface coating (such as carbon, metal oxide, phosphate and other coating layers), ion doping (such as Mg 2+ 、Al 3+etc.) or structural regulation to inhibit manganese dissolution. However, these methods have significant defects: (1) Process complexity and cost issues: The uniformity of the coating layer and the doping efficiency are highly dependent on harsh synthesis conditions (such as high-temperature calcination and atmosphere control), and the equipment precision and process stability are extremely high, resulting in rising production costs. (2) Performance degradation: The coating layer may hinder the diffusion of lithium ions and reduce the rate performance of the material; excessive doping may destroy the crystal structure of the material and sacrifice the specific capacity. (3) Insufficient long-term effectiveness: Existing modification methods are difficult to continuously inhibit manganese dissolution in long cycles (especially high-temperature conditions), and the vicious cycle of repeated rupture and repair of the SEI film will still lead to a capacity drop.

[0005] In addition, traditional liquid electrolyte systems have safety hazards such as electrolyte leakage and uncontrollable interfacial side reactions, while existing gel electrolyte membranes face bottlenecks such as poor process adaptability and difficulty in mass production, which are difficult to match the LMFP system's dual requirements for high stability and large-scale manufacturing.

[0006] Therefore, there is an urgent need for an innovative solution that can solve the migration of manganese ions from the battery system level while taking into account high safety and long-term cycle performance, rather than being limited to the local optimization of the positive electrode material. Summary of the Invention

[0007] In response to the shortcomings of the existing technology, the present invention provides a gel precursor for battery separators, a functional gel separator, and a preparation method and application thereof, breaking through the traditional technical route. By introducing a functional gel separator, the key failure mechanism of manganese ion dissolution is specifically suppressed without affecting the initial performance of the battery, thereby achieving a breakthrough improvement in cycle performance and being suitable for popularization and application.

[0008] The present invention is achieved through the following technical solutions:

[0009] A method for preparing a gel precursor for a battery separator comprises the following steps:

[0010] Step 1) Weighing monomers and additives in proportion and stirring them evenly in a container to prepare a monomer mixture; taking another clean container, adding deionized water and an emulsifier, mechanically stirring at 200-1500 rpm, then quickly pouring the monomer mixture into it and stirring for 30-120 minutes to obtain a pre-emulsion;

[0011] The monomer is one or more of 1,3-hexadiene, methyl methacrylate, ethylene glycol dimethacrylate, 1,3-diisopropenylbenzene, N-succinimidyl acrylate, N,N-diethylacrylamide, isononyl acrylate, ethylene glycol methyl ether acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol diacrylate, N,N-dimethylacrylamide, and hexafluorobutyl acrylate;

[0012] Step 2) Weighing the initiator and deionized water in proportion to prepare an initiator solution;

[0013] Step 3) Deionized water and a buffer were added to the reactor, nitrogen was introduced, and after 30 minutes, the heating device was turned on and mechanical stirring was performed at 200-800 rpm. The temperature was set to 50-100° C. to allow the buffer to fully dissolve at high temperature;

[0014] Step 4) slowly raising the temperature to 50-100° C., and slowly adding the pre-emulsion prepared in step 1-1) and the initiator solution prepared in step 1-2) dropwise into the reaction kettle prepared in step 1-3) via a peristaltic pump;

[0015] Step 5) After the pre-emulsion is added, the container containing the pre-emulsion is rinsed with deionized water, and the rinse solution is slowly added dropwise to the reactor via a peristaltic pump;

[0016] Step 6) After the rinse solution is added, keep warm for 1 to 5 hours;

[0017] Step 7) After the heat preservation is completed, the speed of the reactor is reduced to 60-300 rpm, and after the emulsion is cooled to 20-45° C., the material is discharged to obtain the gel precursor.

[0018] Preferably, the additive in step 1) is one or more of allyl glycidyl ether, 3,4-epoxy-1-butene, neopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycidyl ether, and triglycidyl isocyanurate.

[0019] Preferably, the amount of deionized water used in step 1) is 5wt% to 80wt% of the total mass of the monomers and additives; the amount of the emulsifier used is 0.3wt% to 9wt% of the total mass of the monomers and additives; and the emulsifier is one or more of cetyltrimethylammonium chloride, sodium dodecylbenzenesulfonate, sodium dodecylsulfonate, sodium dodecyl sulfate, NP-10, OP-10, and OP-50.

[0020] Preferably, in step 2), the amount of the initiator used is 0.3 wt% to 10 wt% of the total mass of the monomers and additives; the concentration of the initiator solution is 0.7% to 1.8%; and the initiator is one or more of potassium persulfate, ammonium persulfate, and sodium sulfite.

[0021] Preferably, the amount of deionized water in step 3) is 100wt% to 400wt% of the content of the pre-emulsion; the amount of the buffer is 30% to 300% of the amount of the initiator; the buffer is one or more of sodium hydrogen phosphate, dimethyl sodium carbonate, ammonium bicarbonate, potassium bicarbonate, sodium bicarbonate, sodium dihydrogen phosphate / potassium dihydrogen phosphate buffer solution, sodium chloride / boric acid buffer solution, and ammonia / ammonium chloride buffer solution.

[0022] Preferably, in step 4), the pre-emulsion is added dropwise for 1 to 6 hours; and the initiator solution is added dropwise for 1 to 6 hours.

[0023] Preferably, the amount of deionized water used in step 5) is 50 to 300 g, and the dripping time of the rinse solution is 10 to 30 min.

[0024] A method for preparing a functional gel diaphragm comprises the following steps:

[0025] Step A) Preparation of a diaphragm coating slurry: dissolving the gel precursor prepared by the above preparation method and the functional monomer having a nitrogen-containing heterocyclic structure in water at a mass ratio of (6-8):(2-4), stirring and mixing to obtain a diaphragm coating slurry;

[0026] Step B) Double-sided diaphragm coating: The diaphragm coating slurry prepared in step A) is roll-coated on one side of the base film, and the diaphragm is heated and dried; then, the diaphragm coating slurry is roll-coated on the other side of the base film according to the same steps;

[0027] Step C) vacuum drying: placing the double-sided coated diaphragm in step B) into a vacuum oven to dry out moisture and residual monomers, thereby obtaining the functional gel diaphragm.

[0028] Preferably, the functional monomer in step A) is one or more of aza-12-crown-4, 4'-aminodibenzo-18-crown-6, 4'-aminobenzo-15-crown-5-ether, aza-18-crown-6, 4,10-diaza-15-crown-5-ether, 4,13-diaza-18-crown-6-ether, and 1-aza-15-crown-5-ether.

[0029] The functional gel diaphragm is prepared by the above preparation method.

[0030] Application of the above functional gel separator in the preparation of lithium-ion batteries.

[0031] A lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the positive electrode sheet is an aluminum sheet loaded with lithium manganese iron phosphate material; the negative electrode sheet is a copper sheet loaded with graphite material; the separator is the functional gel separator mentioned above; the electrolyte is

[0032] EC / EMC / DEC / LiPF6 / FEC / DTD / LiPO2F2.

[0033] The beneficial effects of the present invention are as follows:

[0034] (1) The network-like cross-linked polymer material finally formed on the surface of the gel diaphragm of the present invention is grafted with nitrogen-containing heterocyclic functional groups, which have a strong chelating effect on manganese ions, thereby adsorbing manganese ions dissolved from the positive electrode side, acting as a protective barrier to prevent manganese ions from migrating to the negative electrode side and causing capacity decay.

[0035] (2) The network-like cross-linked polymer material finally formed on the surface of the gel diaphragm of the present invention has a strong liquid absorption and liquid locking ability, which can reduce the side reaction between the solvent and the electrode interface, thereby improving the long-cycle performance; there is no free electrolyte inside the battery cell, which is in a gel state, and can eliminate the hidden danger of leakage, improve the impact resistance of the battery, and thus enhance the safety performance.

[0036] (3) The network-like cross-linked polymer material finally formed on the surface of the gel diaphragm of the present invention has a certain viscosity, which can enhance the interface contact ability with the positive and negative electrodes. The sticky diaphragm is tightly attached to the electrode surface, which can reduce the interface gap, shorten the lithium ion transmission path, reduce the interface impedance, and thus improve the ionic conductivity.

[0037] (4) The present invention only requires mixing the independently synthesized gel precursor A with the functional monomer B to form an aqueous slurry, which is then roller-coated on the surface of the diaphragm. A polymerization reaction can then occur spontaneously when the diaphragm is subsequently dried in an oven, without the need for additional initiators. Furthermore, residual monomers can be completely removed after drying, thus avoiding the impact of residual monomers on the battery. The present invention has a simple preparation process, and the diaphragm coating process uses water as a solvent, avoiding the use of organic solvents, making it environmentally friendly and safe. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below with reference to specific embodiments.

[0039] Unless otherwise specified, the technical means used in the following examples are all conventional means well known to those skilled in the art, and experimental methods without specific conditions are all conventional methods in the art.

[0040] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0041] A method for preparing a functional gel diaphragm, comprising the following steps:

[0042] (1) Preparation of gel precursor

[0043] ① Weigh the monomers and additives in proportion and stir them evenly in a container to prepare a monomer mixture; take another clean container, add deionized water (the amount is 5wt% to 80wt% of the total mass of the monomers and additives) and emulsifier (the amount is 0.3wt% to 9wt% of the total mass of the monomers and additives), stir mechanically at 200-1500rpm, then quickly pour the monomer mixture into it and stir for 30-120min to obtain a pre-emulsion.

[0044] The monomer is one or more of 1,3-hexadiene, methyl methacrylate, ethylene glycol dimethacrylate, 1,3-diisopropenylbenzene, N-succinimide acrylate, N,N-diethylacrylamide, isononyl acrylate, ethylene glycol methyl ether acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol diacrylate, N,N-dimethylacrylamide, and hexafluorobutyl acrylate.

[0045] The additive is one or more of allyl glycidyl ether, 3,4-epoxy-1-butene, neopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycidyl ether, and triglycidyl isocyanurate.

[0046] The emulsifier is one or more of cetyltrimethylammonium chloride, sodium dodecylbenzenesulfonate, sodium dodecylsulfonate, sodium dodecyl sulfate, NP-10, OP-10, and OP-50.

[0047] ② Weigh the initiator (the amount used is 0.3wt% to 10wt% of the total mass of the monomers and additives) and deionized water in proportion to prepare an initiator solution with a concentration of 0.7% to 1.8%.

[0048] The initiator is one or more of potassium persulfate, ammonium persulfate, and sodium sulfite.

[0049] ③ Add deionized water (100wt% to 400wt% of the pre-emulsion content) and a buffer (30% to 300% of the initiator amount) to a reactor equipped with a reflux condenser, check the airtightness of the four-necked flask, ensure that it is airtight, and then introduce nitrogen. After 30 minutes, turn on the heating device, stir mechanically at 200 to 800 rpm, and set the temperature to 50 to 100°C to allow the buffer to fully dissolve at high temperature.

[0050] The buffer is one or more of sodium hydrogen phosphate, dimethyl sodium carbonate, ammonium bicarbonate, potassium bicarbonate, sodium bicarbonate, sodium dihydrogen phosphate / potassium dihydrogen phosphate buffer solution, sodium chloride / boric acid buffer solution, and ammonia / ammonium chloride buffer solution.

[0051] ④ Slowly raise the temperature to 50-100°C, and slowly add the pre-emulsion and initiator solution prepared above into the above reactor through peristaltic pumps, respectively, and control the addition time to be 1-6 hours.

[0052] ⑤ After the pre-emulsion is added, rinse the container containing the pre-emulsion with 50-300g of deionized water, and slowly add the rinse solution into the reactor through a peristaltic pump, controlling the addition time to be 10-30min.

[0053] ⑥After the addition of the rinse solution is completed, keep warm for 1 to 5 hours.

[0054] ⑦ After the insulation is completed, the speed of the reactor is reduced to 60-300 rpm, and after the emulsion is cooled to 20-45° C., the material is discharged to obtain the gel precursor.

[0055] (2) Preparation of functional gel membrane

[0056] ① Preparation of membrane coating slurry: The gel precursor and functional monomer prepared above are dissolved in water in a mass ratio of (6-8): (2-4), and stirred and mixed to obtain a membrane coating slurry.

[0057] The functional monomer is a monomer having a nitrogen-containing heterocyclic structure, selected from one or more of aza-12-crown-4, 4'-aminodibenzo-18-crown-6, 4'-aminobenzo-15-crown-5-ether, aza-18-crown-6, 4,10-diaza-15-crown-5-ether, 4,13-diaza-18-crown-6-ether, and 1-aza-15-crown-5-ether.

[0058] ② Single-sided diaphragm coating: The diaphragm coating slurry prepared above was roll-coated on one side of the PE base film, and then the diaphragm was heat-dried at 60°C for 5 hours, and then the diaphragm was heat-dried at 80°C for 5 hours.

[0059] ③Double-sided diaphragm coating: Follow the same steps as ② to roll the diaphragm coating slurry onto the other side of the base film.

[0060] ④ Vacuum drying: Place the double-sided coated diaphragm in a vacuum oven, evacuate to -0.1 MPa, and dry the moisture and residual monomers at 100° C. to obtain the functional gel diaphragm.

[0061] Example 1

[0062] A method for preparing a functional gel diaphragm, comprising the following steps:

[0063] (1) Preparation of gel precursor

[0064] ① In a 500mL beaker, weigh 76g of ethylene glycol dimethacrylate and 30g of 3,4-epoxy-1-butene and stir to prepare a monomer mixture. In another clean 500mL beaker, add 21g of deionized water and 0.6g of sodium dodecylsulfonate. Start mechanical stirring at 600rpm and quickly pour the monomer mixture into the beaker. Stir for 40min to obtain a pre-emulsion.

[0065] ② Weigh 0.4g potassium persulfate and 48.6g deionized water to prepare the initiator solution.

[0066] ③ Add 154.1g of deionized water and 0.5g of sodium bicarbonate to a 1L reactor equipped with a reflux condenser. Check the airtightness of the four-necked flask to ensure that it is airtight. Then, introduce nitrogen. After 30 minutes, turn on the heating device and mechanical stirring. Set the stirring speed to 800rpm and the temperature to 50℃ to allow the sodium bicarbonate to fully dissolve at high temperature.

[0067] ④ Slowly raise the temperature to 75°C, and slowly add the pre-emulsion and initiator solution into the above-mentioned reactor through peristaltic pumps, respectively, and control the addition time to be 1 hour.

[0068] ⑤ After the pre-emulsion is added, rinse the pre-emulsification beaker with 65g of deionized water, and slowly add the rinse liquid into the reactor through a peristaltic pump, controlling the addition time to 10min.

[0069] ⑥After the addition of the rinse solution is completed, keep warm for 2 hours.

[0070] ⑦ After the insulation is completed, the speed of the reactor is reduced to 200 rpm. After the emulsion is cooled to 35°C, the material is discharged to obtain a gel precursor.

[0071] (2) Preparation of functional gel membrane

[0072] ① Preparation of diaphragm coating slurry: The above-mentioned gel precursor and functional monomer (4,10-diaza-15-crown 5-ether is used in this embodiment) are dissolved in deionized water in a mass ratio of 7:3, the solid content is set to 10% (mass ratio), and the diaphragm coating slurry is obtained after stirring and mixing.

[0073] ② Single-sided diaphragm coating: Roll the above diaphragm coating slurry onto one side of the PE base film with a coating surface density of 1.2g / cm 2 The membrane was then heat-dried at 60°C for 5 h, and then heat-dried at 80°C for 5 h to complete the reaction.

[0074] ③Double-sided diaphragm coating: Follow the same steps as ② to roll the diaphragm coating slurry onto the other side of the base film. The coating surface density is 1.2g / cm 2 .

[0075] ④ Vacuum drying: Place the double-sided coated diaphragm in a vacuum oven, evacuate to -0.1Mpa, and keep at 100°C for 12 hours to dry out moisture and residual monomers to obtain a functional gel diaphragm.

[0076] (3) Preparation of lithium-ion batteries

[0077] ① Preparation of the positive electrode sheet: The positive electrode slurry ratio is lithium manganese iron phosphate: conductive carbon black (Super P): carbon nanotubes (CNT): binder (PVDF-5130) = 95:2:1.6:1.4 (all percentages by weight). The positive electrode slurry is coated onto aluminum foil and rolled to form a sheet.

[0078] ② Preparation of the negative electrode sheet: The negative electrode slurry ratio is graphite: conductive agent SP: carboxymethyl cellulose (CMC): polyacrylic acid (PAA): styrene-butadiene rubber (SBR) = 97.2:0.5:0.3:1.5:0.5 (all percentages by weight). The negative electrode slurry is coated onto copper foil and rolled to form the negative electrode sheet.

[0079] ③ Assemble the functional gel diaphragm prepared above and the pre-prepared positive and negative electrodes into the shell to prepare a dry cell. After baking for 18 hours, inject the electrolyte. The electrolyte composition is

[0080] EC / EMC / DEC / LiPF6 / FEC / DTD / LiPO2F2 (mass ratio is 19.5:40:22.5:15:5:2:0.5), after being immersed at room temperature for 48 hours, the battery was formed at 25℃, aged at 45℃ for 24 hours, and degassed by double sealing. The battery was divided into different capacities at a rate of 0.33C to obtain the battery for subsequent testing.

[0081] Example 2

[0082] A method for preparing a functional gel diaphragm, comprising the following steps:

[0083] (1) Preparation of gel precursor

[0084] ① In a 500mL beaker, weigh 65g of methyl methacrylate and 41g of allyl glycidyl ether and stir to prepare a monomer mixture. In another clean 500mL beaker, add 16g of deionized water and 0.8g of sodium dodecylsulfonate. Start mechanical stirring at 800rpm and quickly pour the monomer mixture into the beaker. Stir for 40min to obtain a pre-emulsion.

[0085] ② Weigh 0.8g potassium persulfate and 48.2g deionized water to prepare the initiator solution.

[0086] ③ Add 160g of deionized water and 1g of sodium dihydrogen phosphate to a 1L reactor equipped with a reflux condenser. Check the airtightness of the four-necked flask to ensure good airtightness, then introduce nitrogen. After 30 minutes, turn on the heating device and mechanical stirring. Set the stirring speed to 1000rpm and the temperature to 50℃ to allow the sodium dihydrogen phosphate to fully dissolve at high temperature.

[0087] ④ Slowly raise the temperature to 85°C, and slowly add the pre-emulsion and initiator solution into the above-mentioned reactor through peristaltic pumps, respectively, and control the dropping time to be 2 hours.

[0088] ⑤ After the pre-emulsion is added, rinse the pre-emulsification beaker with 67.2g of deionized water, and slowly add the rinse liquid into the reactor through a peristaltic pump, controlling the addition time to 15min.

[0089] ⑥After the addition of the rinse solution is completed, keep warm for 2 hours.

[0090] ⑦ After the insulation is completed, the speed of the reactor is reduced to 200 rpm. After the emulsion is cooled to 35°C, the material is discharged to obtain a gel precursor.

[0091] (2) Preparation of functional gel membrane

[0092] ① Preparation of diaphragm coating slurry: The above-mentioned gel precursor and functional monomer (in this embodiment, aza-18-crown ether-6) are dissolved in deionized water at a mass ratio of 8:2, the solid content is set to 10% (mass ratio), and the diaphragm coating slurry is obtained after stirring and mixing evenly.

[0093] ② Single-sided diaphragm coating: Roll the above diaphragm coating slurry onto one side of the PE base film with a coating surface density of 1.2g / cm 2 The membrane was then heat-dried at 60°C for 5 h, and then heat-dried at 80°C for 5 h to complete the reaction.

[0094] ③Double-sided diaphragm coating: Follow the same steps as ② to roll the diaphragm coating slurry onto the other side of the base film. The coating surface density is 1.2g / cm 2 .

[0095] ④ Vacuum drying: Place the double-sided coated diaphragm in a vacuum oven, evacuate to -0.1Mpa, and keep at 100°C for 12 hours to dry out moisture and residual monomers to obtain a functional gel diaphragm.

[0096] (3) Preparation of lithium-ion batteries

[0097] ① Preparation of the positive electrode sheet: The positive electrode slurry ratio is lithium manganese iron phosphate: conductive carbon black (Super P): carbon nanotubes (CNT): binder (PVDF-5130) = 95:2:1.6:1.4 (all percentages by weight). The positive electrode slurry is coated onto aluminum foil and rolled to form a sheet.

[0098] ② Preparation of the negative electrode sheet: The negative electrode slurry ratio is graphite: conductive agent SP: carboxymethyl cellulose (CMC): polyacrylic acid (PAA): styrene-butadiene rubber (SBR) = 97.2:0.5:0.3:1.5:0.5 (all percentages by weight). The negative electrode slurry is coated onto copper foil and rolled to form the negative electrode sheet.

[0099] ③ Assemble the functional gel diaphragm prepared above and the pre-prepared positive and negative electrodes into the shell to prepare a dry cell. After baking for 18 hours, inject the electrolyte. The electrolyte composition is

[0100] EC / EMC / DEC / LiPF6 / FEC / DTD / LiPO2F2 (mass ratio is 19.5:40:22.5:15:5:2:0.5), after being immersed at room temperature for 48 hours, the battery was formed at 25℃, aged at 45℃ for 24 hours, and degassed by double sealing. The battery was divided into different capacities at a rate of 0.33C to obtain the battery for subsequent testing.

[0101] Example 3

[0102] A method for preparing a functional gel diaphragm, comprising the following steps:

[0103] (1) Preparation of gel precursor

[0104] ① In a 500mL beaker, weigh and add 50g of hexafluorobutyl acrylate, 30g of 3,4-epoxy-1-butene, and 26g of neopentyl glycol diglycidyl ether, respectively, and stir to prepare a monomer mixture. In another clean 500mL beaker, add 16g of deionized water and 0.8g of sodium dodecylsulfonate. Start mechanical stirring at 800rpm, then quickly pour the monomer mixture into the beaker and stir for 40min to obtain a pre-emulsion.

[0105] ② Weigh 0.8g potassium persulfate and 48.2g deionized water to prepare the initiator solution.

[0106] ③ Add 160g of deionized water and 1g of sodium hydrogen phosphate to a 1L reactor equipped with a reflux condenser. Check the airtightness of the four-necked flask to ensure good airtightness, then introduce nitrogen. After 30 minutes, turn on the heating device and mechanical stirring. Set the stirring speed to 1000rpm and the temperature to 50℃ to allow the sodium hydrogen phosphate to fully dissolve at high temperature.

[0107] ④ Slowly raise the temperature to 85°C, and slowly add the pre-emulsion and initiator solution into the above-mentioned reactor through peristaltic pumps, respectively, and control the dropping time to be 2 hours.

[0108] ⑤ After the pre-emulsion is added, rinse the pre-emulsification beaker with 67.2g of deionized water, and slowly add the rinse liquid into the reactor through a peristaltic pump, controlling the addition time to 15min.

[0109] ⑥After the addition of the rinse solution is completed, keep warm for 2 hours.

[0110] ⑦ After the insulation is completed, the speed of the reactor is reduced to 200 rpm. After the emulsion is cooled to 35°C, the material is discharged to obtain a gel precursor.

[0111] (2) Preparation of functional gel membrane

[0112] ① Preparation of diaphragm coating slurry: The above-mentioned gel precursor and functional monomer (in this embodiment, aza-18-crown ether-6) are dissolved in deionized water at a mass ratio of 8:2, the solid content is set to 10% (mass ratio), and the diaphragm coating slurry is obtained after stirring and mixing evenly.

[0113] ② Single-sided diaphragm coating: Roll the above diaphragm coating slurry onto one side of the PE base film with a coating surface density of 1.2g / cm 2 The membrane was then heat-dried at 60°C for 5 h, and then heat-dried at 80°C for 5 h to complete the reaction.

[0114] ③Double-sided diaphragm coating: Follow the same steps as ② to roll the diaphragm coating slurry onto the other side of the base film. The coating surface density is 1.2g / cm 2 .

[0115] ④ Vacuum drying: Place the double-sided coated diaphragm in a vacuum oven, evacuate to -0.1Mpa, and keep at 100°C for 12 hours to dry out moisture and residual monomers to obtain a functional gel diaphragm.

[0116] (3) Preparation of lithium-ion batteries

[0117] ① Preparation of the positive electrode sheet: The positive electrode slurry ratio is lithium manganese iron phosphate: conductive carbon black (Super P): carbon nanotubes (CNT): binder (PVDF-5130) = 95:2:1.6:1.4 (all percentages by weight). The positive electrode slurry is coated onto aluminum foil and rolled to form a sheet.

[0118] ② Preparation of the negative electrode sheet: The negative electrode slurry ratio is graphite: conductive agent SP: carboxymethyl cellulose (CMC): polyacrylic acid (PAA): styrene-butadiene rubber (SBR) = 97.2:0.5:0.3:1.5:0.5 (all percentages by weight). The negative electrode slurry is coated onto copper foil and rolled to form the negative electrode sheet.

[0119] ③ Assemble the functional gel diaphragm prepared above and the pre-prepared positive and negative electrodes into the shell to prepare a dry cell. After baking for 18 hours, inject the electrolyte. The electrolyte composition is

[0120] EC / EMC / DEC / LiPF6 / FEC / DTD / LiPO2F2 (mass ratio is 19.5:40:22.5:15:5:2:0.5), after being immersed at room temperature for 48 hours, the battery was formed at 25℃, aged at 45℃ for 24 hours, and degassed by double sealing. The battery was divided into different capacities at a rate of 0.33C to obtain the battery for subsequent testing.

[0121] Example 4

[0122] A method for preparing a functional gel diaphragm, comprising the following steps:

[0123] (1) Preparation of gel precursor

[0124] ① In a 500mL beaker, weigh and add 55g of ethylene glycol diacrylate, 15g of N,N-dimethylacrylamide, 20g of allyl glycidyl ether, and 16g of trimethylolpropane triglycidyl ether, respectively, and stir to prepare a monomer mixture. In another clean 500mL beaker, add 16g of deionized water and 0.8g of sodium dodecylsulfonate. Start mechanical stirring at 800rpm, then quickly pour the monomer mixture into the beaker and stir for 40min to obtain a pre-emulsion.

[0125] ② Weigh 0.8g potassium persulfate and 48.2g deionized water to prepare the initiator solution.

[0126] ③ Add 160g of deionized water and 1g of potassium dihydrogen phosphate to a 1L reactor equipped with a reflux condenser. Check the airtightness of the four-necked flask to ensure good airtightness, then introduce nitrogen. After 30 minutes, turn on the heating device and mechanical stirring. Set the stirring speed to 1000rpm and the temperature to 50°C to allow the potassium dihydrogen phosphate to fully dissolve at high temperature.

[0127] ④ Slowly raise the temperature to 85°C, and slowly add the pre-emulsion and initiator solution into the above-mentioned reactor through peristaltic pumps, respectively, and control the dropping time to be 2 hours.

[0128] ⑤ After the pre-emulsion is added, rinse the pre-emulsification beaker with 67.2g of deionized water, and slowly add the rinse liquid into the reactor through a peristaltic pump, controlling the addition time to 30min.

[0129] ⑥After the addition of the rinse solution is completed, keep warm for 2 hours.

[0130] ⑦ After the insulation is completed, the speed of the reactor is reduced to 200 rpm. After the emulsion is cooled to 35°C, the material is discharged to obtain a gel precursor.

[0131] (2) Preparation of functional gel membrane

[0132] ① Preparation of diaphragm coating slurry: The above-mentioned gel precursor and functional monomer (in this embodiment, aza-18-crown ether-6) are dissolved in deionized water at a mass ratio of 8:2, the solid content is set to 10% (mass ratio), and the diaphragm coating slurry is obtained after stirring and mixing evenly.

[0133] ② Single-sided diaphragm coating: Roll the above diaphragm coating slurry onto one side of the PE base film with a coating surface density of 1.2g / cm 2 The membrane was then heat-dried at 60°C for 5 h, and then heat-dried at 80°C for 5 h to complete the reaction.

[0134] ③Double-sided diaphragm coating: Follow the same steps as ② to roll the diaphragm coating slurry onto the other side of the base film. The coating surface density is 1.2g / cm 2 .

[0135] ④ Vacuum drying: Place the double-sided coated diaphragm in a vacuum oven, evacuate to -0.1Mpa, and keep at 100°C for 12 hours to dry out moisture and residual monomers to obtain a functional gel diaphragm.

[0136] (3) Preparation of lithium-ion batteries

[0137] ① Preparation of the positive electrode sheet: The positive electrode slurry ratio is lithium manganese iron phosphate: conductive carbon black (Super P): carbon nanotubes (CNT): binder (PVDF-5130) = 95:2:1.6:1.4 (all percentages by weight). The positive electrode slurry is coated onto aluminum foil and rolled to form a sheet.

[0138] ② Preparation of the negative electrode sheet: The negative electrode slurry ratio is graphite: conductive agent SP: carboxymethyl cellulose (CMC): polyacrylic acid (PAA): styrene-butadiene rubber (SBR) = 97.2:0.5:0.3:1.5:0.5 (all percentages by weight). The negative electrode slurry is coated onto copper foil and rolled to form the negative electrode sheet.

[0139] ③ Assemble the functional gel diaphragm prepared above and the pre-prepared positive and negative electrodes into the shell to prepare a dry cell. After baking for 18 hours, inject the electrolyte. The electrolyte composition is

[0140] EC / EMC / DEC / LiPF6 / FEC / DTD / LiPO2F2 (mass ratio is 19.5:40:22.5:15:5:2:0.5), after being immersed at room temperature for 48 hours, the battery was formed at 25℃, aged at 45℃ for 24 hours, and degassed by double sealing. The battery was divided into different capacities at a rate of 0.33C to obtain the battery for subsequent testing.

[0141] Comparative Example 1

[0142] The preparation process of conventional lithium-ion batteries is as follows:

[0143] ① Preparation of the positive electrode sheet: The positive electrode slurry ratio is lithium manganese iron phosphate: conductive carbon black (Super P): carbon nanotubes (CNT): binder (PVDF-5130) = 95:2:1.6:1.4 (all percentages by weight). The positive electrode slurry is coated onto aluminum foil and rolled to form a sheet.

[0144] ② Preparation of the negative electrode sheet: The negative electrode slurry ratio is graphite: conductive agent SP: carboxymethyl cellulose (CMC): polyacrylic acid (PAA): styrene-butadiene rubber (SBR) = 97.2:0.5:0.3:1.5:0.5 (all percentages by weight). The negative electrode slurry is coated onto copper foil and rolled to form the negative electrode sheet.

[0145] ③ Use conventional lithium battery separators and pre-prepared positive and negative electrode sheets to assemble into the shell to prepare dry batteries. After baking for 18 hours, inject electrolyte. The electrolyte composition is EC / EMC / DEC / LiPF6 / FEC / DTD / LiPO2F2 (mass ratio is 19.5:40:22.5:15:5:2:0.5). After soaking at room temperature for 48 hours, the battery is formed at 25°C, aged at 45°C for 24 hours, and degassed. The battery is divided at a rate of 0.33C to obtain a battery for subsequent testing.

[0146] Test Example 1

[0147] The lithium ion batteries prepared in Examples 1-4 and Comparative Example 1 were subjected to cycle performance and thickness tests, as follows:

[0148] The cycle test method is a 25°C oven test, the charge and discharge rate is 0.5C, the charge and discharge system is constant current and constant voltage charging, constant current discharge, and the test voltage range is 2.5~4.35V. The test results are shown in Table 1 below.

[0149] Table 1 Performance test results

[0150]

[0151] As can be seen from the data in Table 1, Examples 1-4 and Comparative Example 1 are basically consistent in terms of initial battery capacity (2.35-2.37Ah) and internal resistance (12.4-12.7mΩ) after capacity separation, indicating that the functional gel separator provided by the present invention does not negatively affect the initial performance of the battery. However, after 500 cycles, the capacity retention rate of Examples 1-4 is significantly better than that of Comparative Example 1 (89.6%-90.5% vs. 85.7%), and the increase in internal resistance after cycling is significantly lower (Examples: 12.8-13.0mΩ; Comparative Example: 14.5mΩ). The specific comparative analysis is as follows:

[0152] (1) Difference in capacity retention rate

[0153] The capacity retention rates of Examples 1-4 were all above 89.6%, while that of Comparative Example 1 was only 85.7%. This difference indicates that the functional gel separator of the present invention significantly slows down the irreversible loss of active materials by effectively inhibiting the dissolution of manganese ions, thereby improving the long-term cycle stability of the battery.

[0154] (2) Comparison of internal resistance changes

[0155] After the cycle, the internal resistance of Comparative Example 1 increased to 14.5mΩ (an increase of about 16%), while the internal resistance of Examples 1-4 only increased slightly to 12.8~13.0mΩ (an increase of ≤3.5%). The significant difference in internal resistance further verifies the inhibitory effect of the diaphragm of the present invention on the dissolution of manganese ions. Traditional diaphragms cannot prevent manganese ions from migrating to the electrolyte and depositing on the negative electrode, resulting in increased interfacial impedance; the present invention effectively blocks the transmembrane migration of manganese ions through the physical and chemical synergistic effect of the gel diaphragm, maintaining the stability of the battery interface.

[0156] During the process of roller-coating the diaphragm coating slurry onto the PE base film, the epoxy groups in the gel precursor undergo a self-crosslinking reaction under the induction of the primary / secondary amine groups in the functional monomer, forming a layer of network-like cross-linked polymer material on the surface of the base film. The material is grafted with nitrogen-containing heterocyclic functional groups, which have a strong chelating effect on manganese ions, thereby adsorbing manganese ions dissolved from the positive electrode side, acting as a protective barrier to prevent manganese ions from migrating to the negative electrode side and causing capacity decay. In addition, the network-like cross-linked polymer material has a strong liquid absorption and liquid locking ability, which can reduce side reactions at the solvent and electrode interface, thereby improving long-cycle performance; there is no free electrolyte inside the battery cell, which is in a gel state, which can eliminate the hidden danger of leakage, improve the battery's impact resistance, and thus enhance safety performance. At the same time, the network-like cross-linked polymer material also has a certain viscosity, which can enhance the interfacial contact ability with the positive and negative electrodes. The sticky diaphragm is tightly attached to the electrode surface, which can reduce interfacial gaps, shorten the lithium ion transmission path, reduce interfacial impedance, and thus improve ionic conductivity.

[0157] In the prior art, the capacity decay and impedance increase caused by manganese ion dissolution in manganese-based positive electrode materials have long been an unresolved problem. The present invention introduces a functional gel separator to specifically inhibit manganese ion dissolution, a key failure mechanism, without affecting the initial performance of the battery, thereby achieving a breakthrough improvement in cycle performance. This invention solves the problem of cycle performance degradation caused by manganese ion dissolution in manganese-based batteries and offers significant advantages over prior art in inhibiting manganese ion migration and maintaining interface stability.

[0158] The embodiments described above are only some of the embodiments of the present invention, rather than all of the embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but merely represents selected embodiments of the present invention. The scope of protection of the present invention shall be based on the scope required by the claims. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making creative efforts shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing a gel precursor for a battery separator, characterized in that: The following steps are involved: Step 1) Weighing monomers and additives in proportion and stirring them evenly in a container to prepare a monomer mixture; taking another clean container, adding deionized water and an emulsifier, mechanically stirring at 200-1500 rpm, then quickly pouring the monomer mixture into it and stirring for 30-120 minutes to obtain a pre-emulsion; The monomer is one or more of 1,3-hexadiene, methyl methacrylate, ethylene glycol dimethacrylate, 1,3-diisopropenylbenzene, N-succinimidyl acrylate, N,N-diethylacrylamide, isononyl acrylate, ethylene glycol methyl ether acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol diacrylate, N,N-dimethylacrylamide, and hexafluorobutyl acrylate; Step 2) Weighing the initiator and deionized water in proportion to prepare an initiator solution; Step 3) Deionized water and a buffer were added to a reaction kettle, nitrogen was introduced, and after 30 minutes, the heating device was turned on and mechanical stirring was performed at 200-800 rpm. The temperature was set to 50-100° C. to allow the buffer to fully dissolve at high temperature. Step 4) The temperature was slowly raised to 50-100° C., and the pre-emulsion prepared in step 1-1) and the initiator solution prepared in step 1-2) were slowly added dropwise to the reaction kettle described in step 1-3) using a peristaltic pump. Step 5) After the pre-emulsion is added, the container containing the pre-emulsion is rinsed with deionized water, and the rinse solution is slowly added dropwise to the reactor via a peristaltic pump; Step 6) After the rinse solution is added, keep warm for 1 to 5 hours; Step 7) After the heat preservation is completed, the speed of the reactor is reduced to 60-300 rpm, and after the emulsion is cooled to 20-45° C., the material is discharged to obtain the gel precursor.

2. The method for preparing a gel precursor for a battery separator according to claim 1, characterized in that: In step 1), the additive is one or more of allyl glycidyl ether, 3,4-epoxy-1-butene, neopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycidyl ether, and triglycidyl isocyanurate.

3. The method for preparing a gel precursor for a battery separator according to claim 1, characterized in that: In step 1), the amount of deionized water is 5 wt% to 80 wt% of the total mass of the monomers and additives; the amount of the emulsifier is 0.3 wt% to 9 wt% of the total mass of the monomers and additives; and the emulsifier is one or more of cetyltrimethylammonium chloride, sodium dodecylbenzenesulfonate, sodium dodecylsulfonate, sodium dodecyl sulfate, NP-10, OP-10, and OP-50.

4. The method for preparing a gel precursor for a battery separator according to claim 1, wherein: In step 2), the amount of the initiator is 0.3 wt% to 10 wt% of the total mass of the monomers and additives; the concentration of the initiator solution is 0.7% to 1.8%; and the initiator is one or more of potassium persulfate, ammonium persulfate, and sodium sulfite.

5. The method for preparing a gel precursor for a battery separator according to claim 1, characterized in that: In step 3), the amount of deionized water is 100 wt% to 400 wt% of the pre-emulsion content; the amount of the buffer is 30% to 300% of the initiator amount; the buffer is one or more of sodium hydrogen phosphate, dimethyl sodium carbonate, ammonium bicarbonate, potassium bicarbonate, sodium bicarbonate, sodium dihydrogen phosphate / potassium dihydrogen phosphate buffer solution, sodium chloride / boric acid buffer solution, and ammonia / ammonium chloride buffer solution.

6. The method for preparing a gel precursor for a battery separator according to claim 1, characterized in that: Step 4) The pre-emulsion is added dropwise for 1 to 6 hours; the initiator solution is added dropwise for 1 to 6 hours.

7. The method for preparing a gel precursor for a battery separator according to claim 1, characterized in that: In step 5), the amount of deionized water used is 50 to 300 g, and the dripping time of the rinse solution is 10 to 30 minutes.

8. A method for preparing a functional gel membrane, characterized in that: The following steps are involved: Step A) Preparation of a diaphragm coating slurry: dissolving the gel precursor prepared by the preparation method according to any one of claims 1 to 7 and the functional monomer having a nitrogen-containing heterocyclic structure in water at a mass ratio of (6 to 8): (2 to 4), stirring and mixing to obtain a diaphragm coating slurry; Step B) Double-sided diaphragm coating: The diaphragm coating slurry prepared in step A) is roll-coated on one side of the base film, and the diaphragm is heated and dried; then, the diaphragm coating slurry is roll-coated on the other side of the base film according to the same steps; Step C) vacuum drying: placing the double-sided coated diaphragm in step B) into a vacuum oven to dry out moisture and residual monomers, thereby obtaining the functional gel diaphragm.

9. The method for preparing a functional gel membrane according to claim 8, characterized in that: The functional monomer in step A) is one or more of aza-12-crown-4, 4'-aminodibenzo-18-crown-6, 4'-aminobenzo-15-crown-5-ether, aza-18-crown-6, 4,10-diaza-15-crown-5-ether, 4,13-diaza-18-crown-6-ether, and 1-aza-15-crown-5-ether.

10. The functional gel membrane prepared by the preparation method according to claim 8 or 9.

11. Use of the functional gel separator according to claim 10 in preparing lithium-ion batteries.

12. A lithium ion battery, characterized in that: It includes a positive electrode sheet, a negative electrode sheet, a diaphragm and an electrolyte; the positive electrode sheet is an aluminum sheet loaded with lithium manganese iron phosphate material; the negative electrode sheet is a copper sheet loaded with graphite material; the diaphragm is the functional gel diaphragm as described in claim 10; the electrolyte is EC / EMC / DEC / LiPF6 / FEC / DTD / LiPO2F2.

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