Disclosure of Invention
The invention aims to provide a low-closed-hole high-film-breaking aramid fiber lithium battery diaphragm and a preparation method thereof, which are used for overcoming the defects of the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of a low-closed-pore high-film-breaking aramid fiber lithium battery diaphragm comprises the following steps:
(1) Preparing a polymerization solution of a heat-resistant polymer at a concentration of 1.0wt/% -20wt/%, and a polymerization solution of a low-melting polymer at a concentration of 0.5wt/% -30 wt%;
(2) Polymerizing liquid of low-melting point polymer and polymerizing liquid of heat-resistant polymer according to the proportion of 1:1, obtaining a mixed solution, adding a pore-forming agent into the mixed solution, and uniformly stirring to obtain a membrane casting solution;
(3) Coating the casting solution on a substrate, firstly carrying out steam bath, then immersing in water for film formation by a phase inversion method, drying, cooling and shaping to obtain a heat-resistant high polymer porous layer, wherein the heat-resistant high polymer porous layer is the low-closed-pore high-rupture-membrane aramid fiber lithium battery diaphragm.
Further, the heat-resistant high polymer is any one of meta-aramid, para-aramid and aramid 1314.
Further, when the heat-resistant polymer is meta-aramid, the preparation process of the polymerization solution of the heat-resistant polymer is as follows: adding a cosolvent into an organic solvent A under the protection of nitrogen, dissolving m-phenylenediamine, carrying out a reaction in an ice water bath, adding isophthaloyl dichloride while stirring, adding a neutralizer after the reaction is carried out for a preset time, and neutralizing to obtain a meta-aramid polymerization solution with the concentration of 1wt/% -20 wt/%;
when the heat-resistant high polymer is para-aramid, the preparation process of the polymerization liquid of the heat-resistant high polymer is as follows: adding a cosolvent into an organic solvent A under the protection of nitrogen, dissolving p-phenylenediamine, carrying out a reaction in an ice water bath, adding terephthaloyl chloride while stirring, adding a neutralizer after the reaction is carried out for a preset time, and neutralizing to obtain a p-aramid polymer solution with the concentration of 1wt/% -20 wt/%;
when the heat-resistant high polymer is aramid 1314, the preparation process of the polymerization liquid of the heat-resistant high polymer is as follows: adding a cosolvent into an organic solvent A under the protection of nitrogen to dissolve a mixture of p-phenylenediamine and m-phenylenediamine, wherein the mass ratio of the p-phenylenediamine to the m-phenylenediamine is (1-9): (9-1), carrying out the reaction in an ice-water bath, adding a mixture of terephthaloyl chloride and isophthaloyl chloride while stirring, wherein the mass ratio of the terephthaloyl chloride to the isophthaloyl chloride is (1-9): (9-1), adding a neutralizing agent for neutralization after the reaction is carried out for preset time to obtain an aramid 1314 polymerization solution with the concentration of 1 wt/percent-20 wt/percent.
Further, the organic solvent A is any one of N, N-dimethylacetamide, N-dimethylformamide and N-methylpyrrolidone; the cosolvent is lithium chloride or calcium chloride; the neutralizer is any one of sodium hydroxide, calcium hydroxide and potassium hydroxide.
Further, the low-melting-point high polymer is any one or combination of a plurality of materials selected from polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trifluoroethylene, ethylene-octene copolymer, ethylene-propylene copolymer, nylon 6/66/12 terpolymer, nylon 6/66/1010 terpolymer, nylon 6/66/610 terpolymer and polyethylene glycol succinate.
Further, the preparation process of the polymerization solution of the low-melting-point polymer comprises the following steps: dissolving the low-melting-point polymer in an organic solvent B to obtain a polymerization solution of the low-melting-point polymer;
the organic solvent B is any one or combination of more of tetrahydrofuran, acetone, dimethyl sulfoxide and tetramethylurea.
Further, the melting point of the low-melting-point polymer is 100-130 ℃.
Further, the pore-forming agent is any one or combination of more of calcium chloride, lithium chloride, polyvinylpyrrolidone and polyethylene glycol, and the addition amount of the pore-forming agent is 2 wt%/10 wt% of the mass of the mixed solution.
Further, the temperature of the steam bath is 30-60 ℃, and the humidity is 50% -100%.
The low-closed-hole high-rupture-membrane aramid fiber lithium battery diaphragm is 5-30 microns thick and 0.5-3 microns in pore diameter.
Compared with the prior art, the invention has the following beneficial technical effects:
the invention adopts the heat-resistant high polymer as the porous base layer, can remove the limitation of the polyolefin diaphragm on the heat resistance, has no heat shrinkage phenomenon at the temperature of 250 ℃, and can greatly improve the heat resistance of the diaphragm; in addition, by adding the low-melting-point polymer, the diaphragm has low closed pore temperature, and double protection is provided for the safety performance of the lithium battery; meanwhile, the heat-resistant high polymer is used as a porous base layer, so that the porosity of the diaphragm can be improved, the wettability of electrolyte can be improved, the energy density of the battery can be improved, and the endurance mileage of the automobile can be improved.
Furthermore, the invention can improve the thermal stability of the diaphragm, and the high-temperature resistant polymer is used as the porous base layer, so that the heat resistance of the diaphragm can be greatly improved, the shrinkage value of the diaphragm at high temperature is reduced, and the thermal shrinkage value of the diaphragm at 250 ℃ for 1h is 0.
Furthermore, in the first charge and discharge process of the lithium battery, the electrode material and the electrolyte react on a solid-liquid interface to form a passivation layer, namely an SEI (solid electrolyte interface) film for short, covering the surface of the electrode material, so that the interaction between the electrolyte and the graphite cathode can be prevented. However, when the temperature rises above 100 ℃, the SEI film undergoes a decomposition reaction, causing an irreversible reaction between the electrolyte and the surface of the negative electrode, resulting in the formation of irreversible capacity and the generation of heat, which further increases the temperature. When the temperature exceeds 130 ℃, the SEI film can be completely broken down, side reactions occur when the electrode and the electrolyte are contacted, and when enough heat is accumulated, the electrolyte is decomposed and finally thermally runaway. Therefore, the invention selects the aramid fiber 1313, the aramid fiber 1414 and the aramid fiber 1314 as the membrane breaking temperature of the membrane, and improves the safety of the battery from the two aspects of the hole closing temperature and the membrane breaking temperature.
Furthermore, the invention can reduce the thermal closed pore temperature of the diaphragm, the melting point of the selected low-melting-point polymer is 100-130 ℃, and the diaphragm can generate closed pore behavior before the temperature reaches the temperature of the SEI film and is completely decomposed, thereby preventing the temperature from being rapidly increased and improving the safety of the battery.
Furthermore, the invention can improve the uniformity of micropores of the diaphragm, and the steam bath is added for pre-perforating before the casting film liquid enters the water tank for film formation, so that the rapid solidification of the casting film liquid entering the water tank is avoided, the uniformity of holes formed in the diaphragm and the pore size of the surface layer are influenced, and the air permeability of the diaphragm is improved.
Furthermore, the invention can improve the cycle performance of the battery, the heat-resistant high polymer is used as a base layer through phase-transition wet film formation, the aperture of the diaphragm is larger, and the low-melting-point polymer is added into the film casting solution, so that the aperture of the diaphragm can be improved, the self-discharge phenomenon of the battery is reduced, the attenuation phenomenon of the battery in the cycle process is reduced, and the cycle performance of the battery is improved.
Detailed Description
The invention is further described below.
A lithium battery diaphragm with low closed pores and high rupture strength is mainly composed of a heat-resistant high polymer porous layer, wherein the heat-resistant high polymer porous layer is prepared by a phase conversion method from a casting solution composed of a heat-resistant high polymer and a low-melting-point high polymer, the low-melting-point high polymer is uniformly dispersed in the heat-resistant high polymer, the thickness of the heat-resistant high polymer porous layer is 5-30 mu m, and the pore diameter is 0.5-3 mu m.
Wherein the heat-resistant high polymer is any one of meta-aramid, para-aramid and aramid 1314; the low-melting-point high polymer is any one or more than two of polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trifluoroethylene, ethylene-octene copolymer, ethylene-propylene copolymer, nylon 6/66/12 terpolymer, nylon 6/66/1010 terpolymer, nylon 6/66/610 terpolymer and polyethylene glycol succinate; the melting point of the low-melting-point high polymer is 100-130 ℃;
a preparation method of a lithium battery diaphragm with low closed pores and high rupture strength comprises the following steps:
(1) Preparing a polymerization solution of a heat-resistant polymer at a concentration of 1 to 20wt/%, and preparing a polymerization solution of a low-melting polymer at a concentration of 0.5 to 30 wt.%;
(2) Polymerizing liquid of low-melting point polymer and polymerizing liquid of heat-resistant polymer according to the proportion of 1:1 to obtain a mixed solution, adding a pore-forming agent into the mixed solution, wherein the addition amount of the pore-forming agent is 2wt% -10wt% of the mass of the mixed solution, and uniformly stirring to obtain a membrane casting solution;
(3) Coating the casting solution on a release film or a stainless steel strip by coating equipment, wherein the coating mode is any one of micro-gravure coating, scraper coating, slit extrusion and wire rod coating, the casting solution is firstly subjected to steam bath (the temperature of the steam bath is 30-60 ℃ and the humidity is 50-100%), then the casting solution is soaked in a water tank for phase inversion method film formation, and then the casting solution enters a drying box for drying, cooling and shaping, and then the drying box is wound to obtain a heat-resistant high polymer porous layer, and the heat-resistant high polymer porous layer is the low-closed-pore high-rupture-film aramid lithium battery diaphragm.
Wherein, the preparation of the polymerization solution of the heat-resistant polymer specifically comprises the following steps:
when the heat-resistant high polymer is meta-aramid, the preparation process of the polymerization liquid of the heat-resistant high polymer is as follows: adding a cosolvent into an organic solvent A under the protection of nitrogen, dissolving m-phenylenediamine, carrying out a reaction in an ice water bath, adding isophthaloyl dichloride while stirring, adding a neutralizer after the reaction is carried out for a preset time, and neutralizing to obtain a meta-aramid polymerization solution;
when the heat-resistant high polymer is para-aramid, the preparation process of the polymerization liquid of the heat-resistant high polymer is as follows: adding a cosolvent into an organic solvent A under the protection of nitrogen, dissolving p-phenylenediamine, carrying out a reaction in an ice water bath, adding terephthaloyl chloride while stirring, and adding a neutralizer for neutralization after the reaction is carried out for a preset time to obtain a para-aramid polymerization solution;
when the heat-resistant high polymer is aramid 1314, the preparation process of the polymerization liquid of the heat-resistant high polymer is as follows: adding a cosolvent into an organic solvent A under the protection of nitrogen to dissolve a mixture of p-phenylenediamine and m-phenylenediamine, wherein the mass ratio of the p-phenylenediamine to the m-phenylenediamine is (1-9): (9-1), carrying out the reaction in an ice-water bath, adding a mixture of terephthaloyl chloride and isophthaloyl chloride while stirring, wherein the mass ratio of the terephthaloyl chloride to the isophthaloyl chloride is (1-9): (9-1), adding a neutralizer for neutralization after the reaction is carried out for a preset time to obtain an aramid 1314 polymerization solution;
the preparation of the polymerization solution of the low-melting-point polymer comprises the following steps: and dissolving the low-melting-point polymer in an organic solvent B to obtain a polymerization solution of the low-melting-point polymer.
The organic solvent A is any one of N, N-dimethylacetamide, N, N-dimethylformamide and N-methylpyrrolidone; the cosolvent is any one of lithium chloride and calcium chloride; the neutralizer is any one of sodium hydroxide, calcium hydroxide and potassium hydroxide; the organic solvent B is one or more than two of tetrahydrofuran, acetone, dimethyl sulfoxide and tetramethylurea; the pore-forming agent is one or more than two of calcium chloride, lithium chloride, polyvinylpyrrolidone and polyethylene glycol, and the addition amount of the pore-forming agent is 2 wt%/10 wt% of the mixed solution.
The present invention will be described in detail with reference to examples. It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.
The following detailed description is illustrative of the embodiments and is intended to provide further details of the invention. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention.
Example 1
Preparing meta-aramid polymerization solution: liCl is added into 250ml of DMAc (N, N-dimethylacetamide) under the protection of nitrogen, 1.0814g of m-phenylenediamine is dissolved, the reaction is carried out in an ice-water bath, 2.0302g of isophthaloyl dichloride is slowly added while stirring, after the reaction is carried out for 30min, 0.074g of calcium hydroxide is added for neutralization, and the m-aramid polymer solution with the concentration of 1.0wt/% is obtained.
Preparing a casting solution: dissolving polyvinylidene fluoride-hexafluoropropylene in a mass fraction of 0.5wt% in 250ml of tetrahydrofuran, mixing with the meta-aramid polymerization solution to obtain a mixed solution, adding a pore-forming agent calcium chloride accounting for 2wt% of the mixed solution, and uniformly stirring to obtain a casting solution;
preparation of a porous layer of a heat-resistant high polymer: the casting solution is coated on a stainless steel strip by coating equipment and is subjected to steam bath at the temperature of 30 ℃ and the humidity of 50 percent. Then soaking the film in a water tank for film formation by a phase inversion method, drying the film in a drying oven, cooling and shaping the film, and rolling the film to the thickness of 5 mu m.
Example 2
Preparing a para-aramid polymerization solution: adding CaCl to 250ml of NMP (N-methylpyrrolidone) under nitrogen protection221.628g of p-phenylenediamine is dissolved, the reaction is carried out in an ice-water bath, 40.604g of terephthaloyl chloride is slowly added while stirring, 1.48g of calcium hydroxide is added for neutralization after the reaction is carried out for 30min, and the p-aramid polymerization solution with the concentration of 20wt/% is obtained.
Preparing a casting solution: dissolving an ethylene-octene copolymer in 250ml of tetrahydrofuran by mass percent of 30%, mixing with the para-aramid polymerization solution to obtain a mixed solution, adding a pore-forming agent lithium chloride by mass percent of 10% of the mixed solution, and uniformly stirring to obtain a casting solution;
preparation of a porous layer of a heat-resistant high polymer: the casting solution is coated on a stainless steel strip by coating equipment, and the stainless steel strip is subjected to steam bath at the temperature of 60 ℃ and the humidity of 100%. Then soaking the film in a water tank for film formation by a phase inversion method, drying the film in a drying oven, cooling and shaping the film, and rolling the film to a thickness of 30 mu m.
Example 3
Preparing an aramid 1314 polymerization solution: adding CaCl to 250ml of NMP (N-methylpyrrolidone) under nitrogen protection210.814g of a mixture of p-phenylenediamine and m-phenylenediamine (mass ratio: 1And m-phthaloyl chloride (mass ratio of 1.
Preparing a casting solution: dissolving polyethylene glycol succinate in 250ml of tetrahydrofuran by weight percent, mixing with the aramid 1314 polymerization solution to obtain a mixed solution, adding a pore-forming agent polyethylene glycol of which the mass is 5wt% of the mixed solution, and uniformly stirring to obtain a casting solution;
preparation of a porous layer of a heat-resistant high polymer: the casting solution is coated on a stainless steel strip by coating equipment, and the stainless steel strip is subjected to steam bath at the temperature of 45 ℃ and the humidity of 75%. Then soaking the film in a water tank for film formation by a phase inversion method, drying the film in a drying oven, cooling and shaping the film, and rolling the film to 15 mu m in thickness.
Example 4
Preparing an aramid 1314 polymerization solution: adding CaCl into 250ml of DMF (N, N-dimethylformamide) under the protection of nitrogen2And 10.814g of a mixture of p-phenylenediamine and m-phenylenediamine (mass ratio 1.
Preparing a casting solution: dissolving a nylon 6/66/12 terpolymer in 250ml of tetrahydrofuran by the mass fraction of 10wt%, mixing with the aramid 1314 polymerization solution to obtain a mixed solution, adding a pore-forming agent, namely, polyvinylpyrrolidone, of which the mass is 5wt% of the mixed solution, and uniformly stirring to obtain a casting solution;
preparation of a porous layer of a heat-resistant high polymer: the casting solution is coated on a stainless steel strip by coating equipment and is subjected to steam bath at the temperature of 45 ℃ and the humidity of 75 percent. Then soaking the film in a water tank for film formation by a phase inversion method, drying the film in a drying oven, cooling and shaping the film, and rolling the film to a thickness of 15 mu m.
Example 5
Preparing an aramid fiber 1314 polymerization solution: 250ml of NMP (N-methyl) under nitrogen protectionPyrrolidone) with CaCl2And 10.814g of a mixture of p-phenylenediamine and m-phenylenediamine (mass ratio 9.
Preparing a casting solution: dissolving a nylon 6/66/1010 terpolymer, a nylon 6/66/610 terpolymer and polyvinylidene fluoride-trifluoroethylene (mass ratio is 1;
preparation of a porous layer of a heat-resistant high polymer: the casting solution is coated on a stainless steel strip by coating equipment and is subjected to steam bath at the temperature of 45 ℃ and the humidity of 75 percent. Then soaking the film in a water tank for film formation by a phase inversion method, drying the film in a drying oven, cooling and shaping the film, and rolling the film to a thickness of 15 mu m.
Comparative example 1:
a 7 μm PE-based film is commercially available.
Comparative example 2:
preparing meta-aramid polymerization solution: liCl is added into 250ml of DMAc (N, N-dimethylacetamide) under the protection of nitrogen, 1.0814g of m-phenylenediamine is dissolved, the reaction is carried out in an ice-water bath, 2.0302g of isophthaloyl chloride is slowly added while stirring, after 30min of reaction, 0.074g of calcium hydroxide is added for neutralization, and the m-aramid polymerization solution with the concentration of 1.0wt/% is obtained.
Preparing a casting solution: and adding a pore-forming agent calcium chloride into the meta-aramid polymerized liquid, wherein the pore-forming agent calcium chloride accounts for 0.5wt% of the meta-aramid polymerized liquid by mass, and uniformly stirring to obtain a membrane casting solution.
Preparation of a porous layer of a heat-resistant high polymer: the casting solution is coated on a stainless steel strip by coating equipment, and is firstly subjected to steam bath, wherein the temperature of the steam bath is 30 ℃, and the humidity is 50%. Then soaking the film in a water tank for film formation by a phase inversion method, drying the film in a drying oven, cooling and shaping the film, and rolling the film to a thickness of 5 mu m.
TABLE 1 example and comparative example separator Performance
As can be seen from Table 1, compared with the PE-based film, the thermal hole-closing temperature of the diaphragm prepared in examples 1-5, to which the low-melting polymer was added, was reduced, and the film breaking temperature was increased to 250 ℃ or higher; the PE film becomes transparent at the temperature of 250 ℃ and shrinks; in the comparative example 2, only the heat-resistant high polymer porous layer is adopted, the low-melting-point polymer is not added, the diaphragm has no closed pore temperature, and the diaphragm can directly break after reaching a certain temperature.
It will be appreciated by those skilled in the art that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed above are therefore to be considered in all respects as illustrative and not restrictive. All changes which come within the scope of or equivalence to the invention are intended to be embraced therein.