CN112038553B - Modified polyolefin lithium-sulfur battery diaphragm and preparation method thereof - Google Patents
Modified polyolefin lithium-sulfur battery diaphragm and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a modified polyolefin lithium-sulfur battery diaphragm and a preparation method thereof, wherein the diaphragm is obtained by coating a ceramic layer on one side or two sides of a base film layer with an interlayer structure, and the base film layer with the interlayer structure is prepared by culturing sulfate reducing bacteria on an interlayer of the polyolefin diaphragm; the ceramic layer is a boric acid modified silicon dioxide layer; the diaphragm has high liquid absorption and air permeability, good flame retardance and heat resistance and shrinkage resistance, and can effectively inhibit the shuttle effect of polysulfide in the circulating process of the lithium-sulfur battery; the lithium-sulfur battery electrolyte is applied to the lithium-sulfur battery, and effectively improves the charge and discharge rate cycle performance, the service life and the safety performance of the battery.
Description
Technical Field
The invention belongs to the field of lithium-sulfur battery materials, and particularly relates to a modified polyolefin lithium-sulfur battery diaphragm and a preparation method thereof.
Background
The lithium-sulfur battery has higher theoretical specific capacity (1672 mAh/g) and energy density (2600 Wh/kg), and the active substance sulfur has the advantages of rich resources, low price, environmental friendliness and the like, so the lithium-sulfur battery is widely concerned in the field of new energy as a battery system with good application prospect.
The diaphragm is an important component of the lithium-sulfur battery and is used for separating the positive electrode and the negative electrode and preventing the two electrodes from being in direct contact with each other to cause short circuit. The diaphragm allows lithium ions to pass through and prevents electrons from flowing through, so that the lithium ions are transmitted between the positive electrode and the negative electrode in the charging and discharging process; the diaphragm plays an important role in maintaining normal energy exchange of the battery and preventing short circuit of the battery; the diaphragm determines the interface structure, internal resistance, battery capacity and the like of the lithium ion battery, and the performance of the diaphragm can influence the charge-discharge cycle performance, the service life, the safety performance and the like of the battery.
At present, a common diaphragm in the market is a polyolefin diaphragm, and the wettability of the diaphragm to electrolyte is poor due to the lyophobic surface and low surface energy of a polyolefin material, so that the cycle life of a battery is influenced; the thermal deformation temperature of the polyolefin diaphragm is lower, and the diaphragm can be seriously thermally shrunk when the temperature is too high, so that the short circuit of the battery is caused; in addition, when the polyolefin diaphragm is applied to the lithium-sulfur battery, the corrosion phenomenon of the negative electrode of the battery often occurs, so that the cycle decay speed of the battery is accelerated, and the cycle performance of the battery is poor; the conventional polyolefin separator cannot meet the use requirements of the lithium-sulfur battery.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a modified polyolefin lithium-sulfur battery diaphragm, which is prepared by coating boric acid modified silicon dioxide on one side or two sides of a polyolefin base film with a sandwich structure; the diaphragm has high liquid absorption and air permeability, good flame retardance and heat resistance and shrinkage resistance, and can effectively inhibit the shuttle effect of polysulfide in the circulating process of the lithium-sulfur battery; the lithium-sulfur battery electrolyte is applied to the lithium-sulfur battery, and effectively improves the charge-discharge rate cycle performance, the service life and the safety performance of the battery.
In order to achieve the purpose, the invention adopts the following technical scheme:
a modified polyolefin lithium-sulfur battery diaphragm is obtained by coating a ceramic layer on one side or two sides of a base film layer with an interlayer structure, wherein the base film layer with the interlayer structure is prepared by culturing sulfate reducing bacteria in an interlayer of the polyolefin diaphragm;
preferably, the preparation method of the base film layer with the sandwich structure comprises the following steps: taking a polyolefin diaphragm with a concave-convex structure on the surface as a substrate, casting a sulfate reducing bacteria enrichment culture solution on the surface of the polyolefin diaphragm, placing the polyolefin diaphragm inoculated with a strain in a closed environment for fermentation culture, compounding and laminating the polyolefin diaphragm with persulfate reducing bacteria on the surface, and then drying and sterilizing to obtain a polyolefin film with a sandwich structure; the pressing is to fit and press one side of the polyolefin diaphragm containing the sulfate reducing bacteria;
preferably, the sulfate reducing bacteria enrichment culture solution comprises 1L of deionized water containing 10-12g of ammonium ferrous sulfate, 6-8g of ferric citrate, 20-30g of guar gum, 15-20g of polyethylene glycol and 10-12g of cysteine; the mass of the sulfate reducing bacteria accounts for 8-10% of the mass of the culture solution;
preferably, the culture temperature of the sulfate reducing bacteria is 30-35 ℃; the culture time is 5-6 days;
preferably, the ceramic layer is boric acid modified silicon dioxide;
preferably, the preparation method of the boric acid modified silica comprises the following steps: dispersing silicon dioxide powder in an ethanol solution, adjusting the pH value of the solution to 8-9, dropwise adding an aminosilane coupling agent, reacting at 40-70 ℃ for 2-4h, adding an ethanol solution of boric acid, stirring at constant temperature for reacting for 4-5h, filtering, separating, washing and drying to obtain boric acid modified silicon dioxide;
preferably, the weight ratio of the silicon dioxide to the amino silane coupling agent to the boric acid is 10: 2-4: 4-5;
further, the preparation method of the diaphragm comprises the following steps:
1) Preparing a base film with a sandwich structure:
taking a polyolefin membrane with a concave-convex structure on the surface as a substrate, casting a sulfate reducing bacteria enrichment culture solution on the surface of the polyolefin membrane, placing the polyolefin membrane inoculated with strains in a closed environment for fermentation culture, and compounding and pressing the polyolefin membrane with persulfate reducing bacteria on the surface to obtain a polyolefin base membrane with an interlayer structure;
2) Preparation of boric acid modified silica slurry:
dispersing boric acid modified silicon dioxide in a mixed solution of hydroxycucurbituril and polyethylene glycol, and uniformly stirring to obtain slurry;
3) Coating the modified silicon dioxide slurry on the surface of one side or two sides of a base film with an interlayer structure by adopting a coating mode, immersing the diaphragm into a guar gum solution for crosslinking, and drying to obtain a modified polyolefin lithium-sulfur battery diaphragm;
preferably, the weight ratio of the boric acid modified silicon dioxide to the hydroxycucurbituril to the polyethylene glycol is 10: 0.4-0.6: 0.2;
preferably, the polyolefin-based film is a polyethylene-based film or a polypropylene-based film;
the modified polyolefin lithium-sulfur battery diaphragm disclosed by the invention takes a polyolefin membrane with a sulfate reducing bacteria fermentation product as an interlayer as a base membrane, a boric acid modified silicon dioxide layer is coated on the surface of the polyolefin membrane, guar gum is taken as a cross-linking agent to obtain the composite lithium-sulfur battery diaphragm, the diaphragm has good air permeability, wettability and flame retardance, is used for assembling the lithium-sulfur battery diaphragm, also effectively inhibits the shuttle effect of polysulfide generated in the lithium-sulfur battery, and improves the rate discharge performance and the cycle stability of the battery;
according to the invention, the base membrane takes the sulfate reducing bacteria fermentation product as the interlayer, the sulfate reducing bacteria fermentation product exists in the interlayer of the base membrane, the stability is good, the overflow is not easy, on one hand, the air permeability and the wettability of the base membrane are obviously improved, and the liquid absorption rate of the membrane is improved; on the other hand, the sulfide in the fermentation product has good function of absorbing and converting polysulfide, thereby improving the actual specific capacity and the cycling stability of the lithium-sulfur battery system;
the boric acid modified silicon dioxide ceramic layer is formed by coating slurry formed by dispersing boric acid modified silicon dioxide in hydroxycucurbituril and polyethylene glycol and then crosslinking by using guar gum as a crosslinking agent; the addition of the hydroxyl cucurbituril effectively improves the problem of ceramic layer falling off; the hydroxyl cucurbituril has a cavity structure, so that the conductivity of lithium ions is obviously improved, and the electrical impedance of the battery is reduced; meanwhile, the guar gum is taken as a cross-linking agent, so that the bonding stability of the silicon dioxide ceramic layer is obviously improved, and the falling risk is reduced; meanwhile, the wettability of the diaphragm is improved, and the liquid absorption rate is improved; in addition, the introduction of borate in the boric acid modified silicon dioxide obviously improves the flame retardant property of the diaphragm, reduces the risk of combustion and explosion caused by overhigh temperature in the use process of the battery and improves the safety performance of the battery;
drawings
FIG. 1 is a schematic cross-sectional structural view of a composite separator of the present invention;
wherein the 1-boric acid modified silica ceramic layer; 2-a polyethylene layer; 3-sulfate reducing bacteria fermentation product interlayer;
Detailed Description
The technical solution of the present invention is further described with reference to the accompanying drawings and the detailed description.
Example 1
Preparation of boric acid modified silica
Dispersing 100g of silicon dioxide powder into 500mL of industrial ethanol solution, adjusting the pH value of the solution to 8-9 by using industrial ammonia water, dropwise adding 20g of 3-aminopropyltrimethoxysilane, reacting at 40 ℃ for 4 hours, adding 80g of boric acid ethanol solution (mixing boric acid and industrial ethanol in equal mass), stirring at constant temperature for reacting for 5 hours, filtering, separating, washing and drying to obtain boric acid modified silicon dioxide No. 1;
dispersing 100g of silicon dioxide powder into 500mL of industrial ethanol solution, adjusting the pH value of the solution to 8-9 by using industrial ammonia water, dropwise adding 30g of 3-aminopropyltrimethoxysilane, reacting at 55 ℃ for 3 hours, adding 90g of boric acid ethanol solution (boric acid ethanol and the like for mass mixing), stirring at constant temperature for reacting for 4.5 hours, filtering, separating, washing and drying to obtain boric acid modified silicon dioxide No. 2;
dispersing 100g of silicon dioxide powder into 500mL of industrial ethanol solution, adjusting the pH value of the solution to 8-9 by using industrial ammonia water, dropwise adding 40g of 3-aminopropyltrimethoxysilane, reacting at 70 ℃ for 2 hours, adding 100g of boric acid ethanol solution (mixing boric acid and industrial ethanol in equal mass), stirring at constant temperature for reacting for 4 hours, filtering, separating, washing and drying to obtain boric acid modified silicon dioxide No. 3;
example 2
A modified polyolefin lithium-sulfur battery diaphragm is obtained by coating a ceramic layer on one side or two sides of a base film layer with an interlayer structure, wherein the base film layer with the interlayer structure is prepared by culturing sulfate reducing bacteria in an interlayer of a polyolefin base film; the preparation method comprises the following steps:
(1) Preparing a base film layer with a sandwich structure:
taking a polyethylene film with a concave-convex structure on the surface as a matrix, casting a sulfate reducing bacteria enrichment culture solution on the surface of the polyolefin film, placing the polyolefin film inoculated with strains in a closed constant temperature incubator for fermentation culture at 30 ℃ for 6 days to obtain a polyethylene film with sulfate reducing bacteria loaded on the surface, contacting one side of coating strain solutions of two polyethylene films loaded with sulfate reducing bacteria, pressing the two polyethylene films by a mold, placing the polyethylene films in a drying oven, drying and sterilizing to obtain a polyethylene base film with an interlayer structure;
wherein the sulfate reducing bacteria enrichment culture solution comprises 1L of deionized water containing 10g of ammonium ferrous sulfate, 8g of ferric citrate, 20g of guar gum, 15g of polyethylene glycol and 10g of cysteine; the mass of the sulfate reducing bacteria accounts for 8 percent of the mass of the culture solution;
(2) Preparation of boric acid modified silica slurry:
dispersing boric acid modified silicon dioxide No. 1 (prepared in example 1) in a mixed solution of hydroxycucurbituril and polyethylene glycol, and uniformly stirring to obtain slurry; wherein the weight ratio of the boric acid modified silicon dioxide to the hydroxycucurbituril to the polyethylene glycol is 10: 0.4: 0.2;
(3) Coating the modified silicon dioxide slurry on one side surface of a base film with a sandwich structure by adopting a gravure roll coating mode, immersing the coated base film into a guar gum solution for crosslinking, and drying to obtain a modified polyolefin lithium-sulfur battery diaphragm; ( The schematic cross-sectional structure of the separator is shown in fig. 1, wherein the outermost layer 1 is a boric acid-modified silica ceramic layer; the middle layer 2 is a polyethylene layer; the inner layer 3 is a sandwich layer of sulfate reducing bacteria fermentation products. )
Example 3
A modified polyolefin lithium-sulfur battery diaphragm is obtained by coating a ceramic layer on one side or two sides of a base film layer with an interlayer structure, wherein the base film layer with the interlayer structure is prepared by culturing sulfate reducing bacteria in an interlayer of the polyolefin diaphragm; the preparation method comprises the following steps:
(1) Preparing a base film layer with a sandwich structure:
taking a polyethylene film with a concave-convex structure on the surface as a substrate, casting a sulfate reducing bacteria enrichment culture solution on the surface of the polyolefin film, placing a polyolefin diaphragm inoculated with a strain in a closed constant temperature incubator, fermenting and culturing for 5 days at 35 ℃ to obtain a polyethylene film with sulfate reducing bacteria loaded on the surface, contacting one side of coating strain solutions of two polyethylene films loaded with sulfate reducing bacteria, pressing by a mold, placing in a drying oven, drying and sterilizing to obtain a polyethylene base film with an interlayer structure;
wherein the sulfate reducing bacteria enrichment culture solution comprises 1L of deionized water containing 11g of ammonium ferrous sulfate, 7g of ferric citrate, 25g of guar gum, 17g of polyethylene glycol and 11g of cysteine; the mass of the sulfate reducing bacteria accounts for 9 percent of the mass of the culture solution;
(2) Preparation of boric acid modified silica slurry:
dispersing boric acid modified silicon dioxide No. 1 (prepared in example 1) in a mixed solution of hydroxycucurbituril and polyethylene glycol, and uniformly stirring to obtain slurry; wherein the weight ratio of the boric acid modified silicon dioxide to the hydroxycucurbituril to the polyethylene glycol is 10: 0.5: 0.2;
(3) Coating the modified silicon dioxide slurry on one side surface of a base film with a sandwich structure by adopting a gravure roll coating mode, immersing the coated base film into a guar gum solution for crosslinking, and drying to obtain a modified polyolefin lithium-sulfur battery diaphragm;
example 4
A modified polyolefin lithium sulfur battery diaphragm is obtained by coating a ceramic layer on one side or two sides of a base film layer with a sandwich structure, wherein the base film layer with the sandwich structure is prepared by culturing sulfate reducing bacteria in a sandwich layer of the polyolefin diaphragm; the preparation method comprises the following steps:
(1) Preparing a base film layer with a sandwich structure:
taking a polyethylene film with a concave-convex structure on the surface as a matrix, casting a sulfate reducing bacteria enrichment culture solution on the surface of the polyolefin film, placing the polyolefin film inoculated with strains in a closed constant temperature incubator for fermentation culture at 30 ℃ for 6 days to obtain a polyethylene film with sulfate reducing bacteria loaded on the surface, contacting one side of coating strain solutions of two polyethylene films loaded with sulfate reducing bacteria, pressing the two polyethylene films by a mold, placing the polyethylene films in a drying oven, drying and sterilizing to obtain a polyethylene base film with an interlayer structure;
the sulfate reducing bacteria enrichment culture solution comprises 1L of deionized water containing 12g of ferrous ammonium sulfate, 6g of ferric citrate, 30g of guar gum, 20g of polyethylene glycol and 12g of cysteine; the mass of the sulfate reducing bacteria accounts for 10% of the mass of the culture solution;
(2) Preparation of boric acid modified silica slurry:
dispersing boric acid modified silicon dioxide No. 1 (prepared in example 1) in a mixed solution of hydroxycucurbituril and polyethylene glycol, and uniformly stirring to obtain slurry; wherein the weight ratio of the boric acid modified silicon dioxide to the hydroxycucurbituril to the polyethylene glycol is 10: 0.6: 0.2;
(3) Coating the modified silicon dioxide slurry on one side surface of a base film with a sandwich structure by adopting a gravure roll coating mode, immersing the coated base film into a guar gum solution for crosslinking, and drying to obtain a modified polyolefin lithium-sulfur battery diaphragm;
example 5
Example 5 the same procedure as in example 4 was used to prepare the modified polyolefin lithium sulfur battery separator except that boric acid-modified silica No. 1 was replaced with boric acid-modified silica No. 2 (prepared in example 1) in step (2);
example 6
Example 6 a modified polyolefin lithium sulfur battery separator obtained in example 4 was prepared in substantially the same manner except that boric acid-modified silica No. 1 was replaced with boric acid-modified silica No. 3 (prepared in example 1) in step (2); comparative example 1
Comparative example 1 is substantially the same as the method for preparing the modified polyolefin lithium-sulfur battery separator obtained in example 4, except that sulfate-reducing bacteria are not added to the sulfate-reducing bacteria-enriched culture solution in step (1); namely, the interlayer of the basement membrane is not fermented by sulfate reducing bacteria;
comparative example 2
Comparative example 2 is substantially the same as the method of preparing the modified polyolefin lithium sulfur battery separator obtained in example 4, except that boric acid-modified silica is replaced with an equal amount of unmodified silica;
comparative example 3
Comparative example 3 the modified polyolefin lithium sulfur battery separator obtained in example 4 was prepared by substantially the same method except that hydroxycucurbituril was not added during the preparation of the slurry in step (2);
comparative example 4
Comparative example 4 the modified polyolefin lithium sulfur battery separator obtained in example 4 was prepared in substantially the same manner except that the coated separator in step (3) was directly dried without being dipped in a guar gum solution to be cross-linked to obtain a modified polyolefin lithium sulfur battery separator;
comparative example 5
Comparative example 5 is substantially the same as the method of preparing the modified polyolefin lithium sulfur battery separator obtained in example 4, except for the preparation of silica slurry in step (2), specifically: dispersing unmodified silicon dioxide in a mixed solution of boric acid, hydroxycucurbituril and polyethylene glycol, and uniformly stirring to obtain slurry; wherein the weight ratio of the unmodified silicon dioxide to the boric acid to the hydroxycucurbituril to the polyethylene glycol is 10: 8: 0.6: 0.2;
and (3) performance testing:
the modified polyolefin lithium-sulfur battery separators prepared in examples 2 to 6 of the invention and comparative examples 1 to 5 were tested for mechanical properties, air permeability, liquid absorption rate, heat shrinkage, ionic conductivity, and internal resistance, and the specific test methods were as follows, and the test results are shown in table 1.
Mechanical Property test
The mechanical properties such as tensile strength of the diaphragm were measured using a universal tester.
Air permeability test
The prepared modified polyolefin lithium-sulfur battery separator was tested for air permeation time using a Gurley tester, which is expressed in terms of Gurley values.
Liquid uptake test
Weighing a certain mass of a diaphragm (M) 1 ) Soaking in electrolyte, taking out after absorbing electrolyte sufficiently, absorbing the redundant electrolyte on the surface of the diaphragm with filter paper, and weighing (M) 2 ) (ii) a The imbibition rate was calculated as follows:
L＝(M 2 -M 1 )/M 1 *100％
heat shrinkage test
The modified polyolefin lithium sulfur battery separator was cut into a sample of a certain size, and the longitudinal length (MD) thereof was measured separately 1 ) And transverse length (TD) 1 ) Baking at 110 deg.C for 2 hr, taking out the membrane, cooling to room temperature, and measuring the longitudinal length (MD) 2 ) And transverse length (TD) 2 ) (ii) a The heat shrinkage was calculated as follows:
S MD ＝(MD 1 -MD 2 )/MD 1 *100％
S TD ＝(TD 1 -TD 2 )/TD 1 *100％
internal resistance test
Cutting the prepared diaphragm into a wafer with the diameter of 3cm, putting the wafer into a clamp, and dripping sufficient electrolyte; and (4) carrying out internal resistance test by using an electrochemical workstation and adopting an alternating current impedance method.
And (3) ion conductivity test: the ionic conductivity of the electrolyte-infiltrated membrane was measured by an ac impedance method.
TABLE 1 results of performance test of separators for modified polyolefin lithium sulfur batteries of examples 2 to 6 and comparative examples 1 to 5
As can be seen from table 1, the separators prepared in examples 2 to 6 of the present invention have excellent mechanical strength and good air permeability, have a high liquid absorption rate for the lithium-sulfur battery electrolyte, are heated at 110 ℃ for 2 hours, have a transverse and longitudinal thermal shrinkage rate of 0, exhibit good shrinkage resistance, and can effectively improve the safety performance of the battery;
the modified polyolefin lithium sulfur battery diaphragm obtained by the preparation of the embodiment 2-4 has small increase in tensile strength and liquid absorption rate along with the increase of the concentration of the fermentation liquid;
examples 4 to 6 are modified polyolefin lithium sulfur battery separators obtained by coating the boric acid-modified silica No. 1, boric acid-modified silica No. 2, and boric acid-modified silica No. 3 prepared in example 1, and the tensile strength and the liquid absorption rate of the modified polyolefin lithium sulfur battery separator are gradually increased, which may be due to the fact that the content of the reactive group on the surface of the modified silica is increased with the increase of the modification amount of the boric acid, so that the formed network structure is more compact, and the mechanical strength of the modified polyolefin lithium sulfur battery separator is further improved; meanwhile, the content of the cross-linked guar gum is increased, so that the liquid absorption rate of the modified polyolefin lithium-sulfur battery diaphragm is increased;
compared with the example 4, the tensile strength, the air permeability value, the liquid absorption rate and the ionic conductivity of the modified polyolefin lithium-sulfur battery diaphragm are obviously reduced, and the thermal shrinkage rate is increased, so that the sandwich structure of the sulfate reducing bacteria fermentation product layer in the modified polyolefin lithium-sulfur battery diaphragm has obvious influence on the mechanical strength, the air permeability, the liquid absorption rate, the ionic conductivity and the thermal shrinkage resistance;
compared with the embodiment 4, the modified polyolefin lithium sulfur battery diaphragm obtained by adopting pure silicon dioxide to replace boric acid modified silicon dioxide has the advantages of reduced tensile strength and liquid absorption rate, remarkably increased heat shrinkage rate, reduced ionic conductivity and increased resistance, and shows that the boric acid modified silicon dioxide has remarkable influence on the performance of the modified polyolefin lithium sulfur battery diaphragm;
compared with the embodiment 4, the preparation method has the advantages that the hydroxyl cucurbituril is not added in the preparation of the boric acid modified silicon dioxide slurry, so that the tensile strength, the air permeability value and the liquid absorption rate of the obtained modified polyolefin lithium-sulfur battery diaphragm are reduced slightly, and the ionic conductivity is obviously reduced; the cavity structure of the hydroxyl cucurbituril has the effect of remarkably improving the ionic conductivity of the modified polyolefin lithium-sulfur battery diaphragm;
compared with the embodiment 4, after the boric acid modified silicon dioxide coating is coated, the modified polyolefin lithium sulfur battery diaphragm is not immersed in guar gum for crosslinking treatment, so that the tensile strength and the liquid absorption rate of the obtained modified polyolefin lithium sulfur battery diaphragm are obviously reduced, and the crosslinking effect of the guar gum is proved to obviously improve the mechanical strength and the liquid absorption rate of the modified polyolefin lithium sulfur battery diaphragm;
compared with the example 4, the tensile strength, the air permeability value and the liquid absorption rate of the membrane of the coating layer obtained by using the mixed slurry of the boric acid, the unmodified silica, the hydroxyl cucurbituril and the polyethylene glycol are reduced, and the heat shrinkage rate is increased compared with the membrane of the coating layer obtained by using the mixed slurry of the boric acid, the unmodified silica, the hydroxyl cucurbituril and the polyethylene glycol; the ionic conductivity is also reduced;
electrochemical performance test
The separator prepared in the examples and comparative examples of the present invention was assembled into a lithium sulfur battery, and the electrochemical performance of the lithium sulfur battery was tested.
And (3) testing the cycle performance: the battery performance tester for the assembled lithium-sulfur battery is used for testing the electrochemical performance of the battery, the charge-discharge current density of the battery is 0.5C, the charge-discharge cycle performance of the battery is tested, and the results are shown in Table 2.
Table 2 results of cycle performance tests of batteries assembled from examples 2 to 6 and comparative examples 1 to 5 composite separators
As can be seen from Table 2, the first discharge capacity of the battery assembled by using the separators prepared in examples 2 to 6 of the present invention reached 950mAh g -1 After the battery is cycled for 100 times, the specific capacity retention rate reaches more than 80%, and the battery assembled by the diaphragm prepared by the invention has higher specific capacity and specific capacity retention rate; the lithium-sulfur battery assembled by the modified polyolefin diaphragm prepared by the invention has good cycling stability;
the specific discharge capacity and specific capacity retention rate of the batteries assembled and formed by the modified polyolefin lithium-sulfur battery diaphragms prepared in comparative examples 1-5 are reduced, wherein the specific capacity and specific capacity retention rate of the batteries assembled and formed by the diaphragms prepared in comparative example 1 are reduced by a larger extent, which indicates that the cycling stability of the lithium-sulfur batteries assembled and formed by the polyolefin diaphragms is obviously affected by the interlayer and coating of the sulfate reducing bacteria fermentation products, and the analysis reason is that the sulfate reducing fermentation product layer has an absorption effect on polysulfide, so that the shuttle effect of polysulfide is effectively inhibited, the lithium cathode corroded by the reaction of polysulfide and the lithium cathode is reduced, and the cycling stability of the lithium-sulfur batteries is further improved;
in conclusion, the modified polyolefin diaphragm provided by the invention has strong mechanical strength, good air permeability and heat-resistant shrinkage performance, meets the requirements of the diaphragm of the lithium-sulfur battery, and the lithium-sulfur battery formed by assembling the diaphragm has good cycling stability and safety performance.
Finally, the above embodiments are only used for illustrating the technical solution of the present invention and not for limiting, and other modifications or equivalent substitutions made by the technical solution of the present invention by those skilled in the art should be covered within the scope of the claims of the present invention without departing from the spirit and scope of the technical solution of the present invention.
Claims (8)
1. The modified polyolefin lithium-sulfur battery diaphragm is characterized in that the diaphragm is obtained by coating a ceramic layer on one side or two sides of a base film layer with a sandwich structure, and the base film layer with the sandwich structure is prepared by culturing sulfate reducing bacteria in an interlayer of the polyolefin diaphragm;
the preparation method of the base film layer with the sandwich structure comprises the following steps: taking a polyolefin diaphragm with a concave-convex structure on the surface as a substrate, casting a sulfate reducing bacteria enrichment culture solution on the surface of the polyolefin diaphragm, placing the polyolefin diaphragm inoculated with a strain in a closed environment for fermentation culture, compounding and laminating the polyolefin diaphragm with persulfate reducing bacteria on the surface, and then drying and sterilizing to obtain a polyolefin film with a sandwich structure; the pressing is to fit and press one side of the polyolefin diaphragm containing the sulfate reducing bacteria;
the sulfate reducing bacteria enrichment culture solution comprises 1L deionized water containing 10-12g ferrous ammonium sulfate, 6-8g ferric citrate, 20-30g guar gum, 15-20g polyethylene glycol and 10-12g cysteine; the mass of the sulfate reducing bacteria accounts for 8-10% of the mass of the culture solution.
2. The modified polyolefin lithium sulfur battery separator of claim 1, wherein the sulfate-reducing bacteria are cultured at a temperature of 30 to 35 ℃; the culture time is 5-6 days.
3. The modified polyolefin lithium sulfur battery separator of claim 1, wherein said ceramic layer is boric acid modified silica.
4. The modified polyolefin lithium sulfur battery separator of claim 3, wherein said boric acid modified silica
The preparation method comprises the following steps: dispersing silicon dioxide powder in an ethanol solution, adjusting the pH value of the solution to 8-9, dropwise adding an aminosilane coupling agent, reacting at 40-70 ℃ for 2-4h, adding an ethanol solution of boric acid, stirring at constant temperature for reacting for 4-5h, filtering, separating, washing and drying to obtain the boric acid modified silicon dioxide.
5. The modified polyolefin lithium sulfur battery separator of claim 4, wherein said silica, amino groups
The weight ratio of the silane coupling agent to the boric acid is 10: 2-4: 4-5.
6. The preparation method of the modified polyolefin lithium-sulfur battery separator as claimed in claim 1 comprises the following specific steps:
1) Preparing a base film with a sandwich structure:
taking a polyolefin diaphragm with a concave-convex structure on the surface as a substrate, casting a sulfate reducing bacteria enrichment culture solution on the surface of the polyolefin diaphragm, placing the polyolefin diaphragm inoculated with a strain in a closed environment for fermentation culture, and then carrying out surface culture on persulfate
Compounding and pressing the polyolefin diaphragm of the original bacteria to obtain a polyolefin film with a sandwich structure;
2) Preparation of boric acid modified silica slurry:
dispersing boric acid modified silicon dioxide in a mixed solution of hydroxycucurbituril and polyethylene glycol, and uniformly stirring to obtain slurry;
3) Coating the modified silicon dioxide slurry on one side or two side surfaces of a base membrane with a sandwich structure by adopting a coating mode, immersing the diaphragm into a guar gum solution for crosslinking, and drying and sterilizing to obtain the modified polyolefin lithium-sulfur battery diaphragm.
7. The modified polyolefin lithium sulfur battery separator of claim 6, wherein the weight ratio of boric acid modified silica, hydroxycucurbituril and polyethylene glycol is 10: 0.4-0.6: 0.2.
8. The modified polyolefin lithium sulfur battery separator of claim 1, wherein said polyolefin separator is a polyethylene-based film or a polypropylene-based film.
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| CN104752658B (en) * | 2013-12-27 | 2018-04-27 | 中国科学院青岛生物能源与过程研究所 | Lithium battery fire-retardant cellulose membrane prepared by a kind of electrostatic spinning |
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