CN115498358B - Preparation method of cellulose diaphragm for lithium battery - Google Patents
Preparation method of cellulose diaphragm for lithium battery Download PDFInfo
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- CN115498358B CN115498358B CN202211046856.3A CN202211046856A CN115498358B CN 115498358 B CN115498358 B CN 115498358B CN 202211046856 A CN202211046856 A CN 202211046856A CN 115498358 B CN115498358 B CN 115498358B
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- 229920002678 cellulose Polymers 0.000 title claims abstract description 186
- 239000001913 cellulose Substances 0.000 title claims abstract description 186
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 83
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 83
- 238000002360 preparation method Methods 0.000 title claims abstract description 28
- 239000007864 aqueous solution Substances 0.000 claims abstract description 82
- 239000004114 Ammonium polyphosphate Substances 0.000 claims abstract description 43
- 235000019826 ammonium polyphosphate Nutrition 0.000 claims abstract description 43
- 229920001276 ammonium polyphosphate Polymers 0.000 claims abstract description 43
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims abstract description 42
- YDEXUEFDPVHGHE-GGMCWBHBSA-L disodium;(2r)-3-(2-hydroxy-3-methoxyphenyl)-2-[2-methoxy-4-(3-sulfonatopropyl)phenoxy]propane-1-sulfonate Chemical compound [Na+].[Na+].COC1=CC=CC(C[C@H](CS([O-])(=O)=O)OC=2C(=CC(CCCS([O-])(=O)=O)=CC=2)OC)=C1O YDEXUEFDPVHGHE-GGMCWBHBSA-L 0.000 claims abstract description 42
- 229920002749 Bacterial cellulose Polymers 0.000 claims abstract description 41
- 239000005016 bacterial cellulose Substances 0.000 claims abstract description 41
- BRLQWZUYTZBJKN-UHFFFAOYSA-N Epichlorohydrin Chemical compound ClCC1CO1 BRLQWZUYTZBJKN-UHFFFAOYSA-N 0.000 claims abstract description 39
- 239000004952 Polyamide Substances 0.000 claims abstract description 39
- 229920002647 polyamide Polymers 0.000 claims abstract description 39
- 239000007788 liquid Substances 0.000 claims abstract description 36
- 239000006185 dispersion Substances 0.000 claims abstract description 35
- 239000011259 mixed solution Substances 0.000 claims abstract description 34
- 238000006116 polymerization reaction Methods 0.000 claims abstract description 19
- 238000003756 stirring Methods 0.000 claims abstract description 15
- 239000003431 cross linking reagent Substances 0.000 claims abstract description 14
- 238000010438 heat treatment Methods 0.000 claims abstract description 13
- 238000002156 mixing Methods 0.000 claims abstract description 13
- 238000004108 freeze drying Methods 0.000 claims abstract description 12
- 238000005096 rolling process Methods 0.000 claims abstract description 7
- 239000012528 membrane Substances 0.000 claims description 51
- 238000000034 method Methods 0.000 claims description 32
- 238000010521 absorption reaction Methods 0.000 claims description 23
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 18
- 239000001301 oxygen Substances 0.000 claims description 18
- 229910052760 oxygen Inorganic materials 0.000 claims description 18
- 230000004580 weight loss Effects 0.000 claims description 18
- 238000000354 decomposition reaction Methods 0.000 claims description 17
- 150000002500 ions Chemical class 0.000 claims description 17
- 238000012360 testing method Methods 0.000 claims description 12
- 230000008569 process Effects 0.000 claims description 6
- 238000002791 soaking Methods 0.000 claims description 5
- 238000004519 manufacturing process Methods 0.000 claims description 3
- 239000013049 sediment Substances 0.000 claims description 2
- RNFJDJUURJAICM-UHFFFAOYSA-N 2,2,4,4,6,6-hexaphenoxy-1,3,5-triaza-2$l^{5},4$l^{5},6$l^{5}-triphosphacyclohexa-1,3,5-triene Chemical compound N=1P(OC=2C=CC=CC=2)(OC=2C=CC=CC=2)=NP(OC=2C=CC=CC=2)(OC=2C=CC=CC=2)=NP=1(OC=1C=CC=CC=1)OC1=CC=CC=C1 RNFJDJUURJAICM-UHFFFAOYSA-N 0.000 abstract description 17
- 239000003063 flame retardant Substances 0.000 abstract description 14
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 9
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 9
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 29
- 229910019142 PO4 Inorganic materials 0.000 description 23
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 23
- 239000010452 phosphate Substances 0.000 description 23
- 230000000052 comparative effect Effects 0.000 description 22
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 16
- 239000000243 solution Substances 0.000 description 10
- 239000000126 substance Substances 0.000 description 10
- 239000001257 hydrogen Substances 0.000 description 9
- 229910052739 hydrogen Inorganic materials 0.000 description 9
- 230000003993 interaction Effects 0.000 description 8
- 239000002244 precipitate Substances 0.000 description 8
- 239000011148 porous material Substances 0.000 description 7
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 6
- 239000003792 electrolyte Substances 0.000 description 5
- 238000000407 epitaxy Methods 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 4
- 239000004743 Polypropylene Substances 0.000 description 4
- 239000002131 composite material Substances 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 229920005610 lignin Polymers 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 238000001556 precipitation Methods 0.000 description 4
- 239000011734 sodium Substances 0.000 description 4
- 229910052708 sodium Inorganic materials 0.000 description 4
- 235000012431 wafers Nutrition 0.000 description 4
- 230000009286 beneficial effect Effects 0.000 description 3
- 230000005540 biological transmission Effects 0.000 description 3
- 238000004132 cross linking Methods 0.000 description 3
- 238000005520 cutting process Methods 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 125000002924 primary amino group Chemical group [H]N([H])* 0.000 description 3
- 229910001220 stainless steel Inorganic materials 0.000 description 3
- 239000010935 stainless steel Substances 0.000 description 3
- 230000009471 action Effects 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
- 238000013329 compounding Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 239000000835 fiber Substances 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 239000010954 inorganic particle Substances 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 229920002842 oligophosphate Polymers 0.000 description 2
- 230000002195 synergetic effect Effects 0.000 description 2
- UNXRWKVEANCORM-UHFFFAOYSA-N triphosphoric acid Polymers OP(O)(=O)OP(O)(=O)OP(O)(O)=O UNXRWKVEANCORM-UHFFFAOYSA-N 0.000 description 2
- 241000218378 Magnolia Species 0.000 description 1
- 229920001410 Microfiber Polymers 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 230000001476 alcoholic effect Effects 0.000 description 1
- 125000003178 carboxy group Chemical group [H]OC(*)=O 0.000 description 1
- 238000000280 densification Methods 0.000 description 1
- 239000003517 fume Substances 0.000 description 1
- 125000000524 functional group Chemical group 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 230000008595 infiltration Effects 0.000 description 1
- 238000001764 infiltration Methods 0.000 description 1
- 239000012796 inorganic flame retardant Substances 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- GDOPTJXRTPNYNR-UHFFFAOYSA-N methyl-cyclopentane Natural products CC1CCCC1 GDOPTJXRTPNYNR-UHFFFAOYSA-N 0.000 description 1
- 239000003658 microfiber Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- DOTMOQHOJINYBL-UHFFFAOYSA-N molecular nitrogen;molecular oxygen Chemical compound N#N.O=O DOTMOQHOJINYBL-UHFFFAOYSA-N 0.000 description 1
- 239000002121 nanofiber Substances 0.000 description 1
- 239000002105 nanoparticle Substances 0.000 description 1
- 125000004433 nitrogen atom Chemical group N* 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- ISWSIDIOOBJBQZ-UHFFFAOYSA-N phenol group Chemical group C1(=CC=CC=C1)O ISWSIDIOOBJBQZ-UHFFFAOYSA-N 0.000 description 1
- 229920000137 polyphosphoric acid Polymers 0.000 description 1
- -1 polypropylene Polymers 0.000 description 1
- 229920001155 polypropylene Polymers 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 230000003014 reinforcing effect Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 238000000967 suction filtration Methods 0.000 description 1
- 230000002459 sustained effect Effects 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000001291 vacuum drying Methods 0.000 description 1
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M50/491—Porosity
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M50/497—Ionic conductivity
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The application relates to a preparation method of a cellulose diaphragm for a lithium battery, which comprises the steps of firstly mixing and stirring cellulose aqueous dispersion liquid, sodium lignin sulfonate aqueous solution, cross-linking agent aqueous solution and ammonium polyphosphate aqueous solution to form a mixed solution, then freeze-drying the mixed solution to form a film, heating and rolling the film to a certain thickness to prepare the cellulose diaphragm for the lithium battery; the thickness of the cellulose diaphragm for the lithium battery is 60-110 mu m; the cross-linking agent is polyamide epichlorohydrin; the cellulose is bacterial cellulose soaked in ethanol; the polymerization degree of the ammonium polyphosphate is less than 20. According to the preparation method of the cellulose diaphragm for the lithium battery, the porosity and the ionic conductivity of the diaphragm are improved, the prepared cellulose diaphragm for the lithium battery is good in mechanical property, the flame retardant property is greatly enhanced, and the safety performance of the lithium ion battery is greatly improved.
Description
Technical Field
The application belongs to the technical field of lithium battery diaphragms, and relates to a preparation method of a cellulose diaphragm for a lithium battery.
Background
Bacterial cellulose-based separators have gained increased attention in lithium batteries because of their excellent thermal stability and being a widely available, environmentally friendly material. Studies based on bacterial cellulose membranes have focused mainly on the following three aspects: (1) Inorganic particles are added to balance the hydrogen bonding action, so that the porosity of the diaphragm is improved. On the one hand, a large number of hydroxyl polar groups on cellulose molecules are beneficial to the affinity of electrolyte. On the other hand, a large number of hydrogen bonds easily form a dense network on the cellulose membrane, and the porosity of the membrane is low, so that the membrane electrolyte is not beneficial to the maintenance and ion transportation of the membrane electrolyte. (2) In order to improve the mechanical strength of cellulose, the prior art has studied a multi-purpose nano-particle, nano-fiber and micro-fiber compounding method, and pretreated cellulose by a TEMPO method to improve the mechanical strength of cellulose membrane. In addition, it is also common to use lignin and its derivatives to simulate the composition of trees to increase strength, but electrostatic repulsion exists between lignin and cellulose, which is unfavorable for the solution compounding of both. In order to solve the problem of electrostatic repulsion, there is a study to introduce PEI as a cross-linking agent which can form electrostatic attraction with cellulose and lignin, so that the problem of dispersion of mixed solution can be well solved, and the mechanical strength of a cellulose film can be improved. (3) In order to improve the flame retardant property of cellulose films, organic and inorganic flame retardants are added. In addition to the above separate studies, inorganic particles are often mixed with a flame retardant to achieve improvements in the porosity, mechanical and flame retardant properties of the cellulose separator at the same time. Meanwhile, most of the added water-insoluble flame retardant is water dispersion, and most of the cellulose is water dispersion, so that the flame retardant and the cellulose are mixed to have the problem of uneven dispersion.
Therefore, there is an urgent need to develop a method of improving the porosity, mechanical and flame retardant properties of a cellulose membrane while well mixing components added during the preparation process with a bacterial cellulose solution.
Disclosure of Invention
The application aims to solve the problems in the prior art and provides a preparation method of a cellulose diaphragm for a lithium battery.
In order to achieve the above purpose, the application adopts the following technical scheme:
the preparation method of the cellulose diaphragm for the lithium battery comprises the steps of firstly mixing and stirring cellulose aqueous dispersion liquid, sodium lignin sulfonate aqueous solution, cross-linking agent aqueous solution and ammonium polyphosphate aqueous solution to form a mixed solution, then freeze-drying the mixed solution to form a film, then heating (covalent cross-linking can occur between sodium lignin sulfonate and cellulose and polyamide epichlorohydrin in the heating process), and rolling to a certain thickness to obtain the cellulose diaphragm for the lithium battery;
the thickness of the cellulose diaphragm for the lithium battery is 60-110 mu m;
the Zeta potential of the mixed solution is less than-30, no sediment is generated, which indicates that the components in the mixed solution are uniformly mixed;
the cross-linking agent is polyamide epichlorohydrin; the cellulose is bacterial cellulose which is soaked in ethanol, and the Bacterial Cellulose (BC) has high aspect ratio, rich hydroxyl and good heat stability, and is suitable for lithium ion battery diaphragms; the polymerization degree of ammonium polyphosphate is less than 20; ammonium polyphosphate with a degree of polymerization of < 20 is very soluble in water, the solubility in 100ml of water is > 90g, ammonium polyphosphate with a degree of polymerization of 30-50 is < 4g in 100ml of water, and ammonium polyphosphate with a higher degree of polymerization is insoluble in water. The cellulose is usually an aqueous dispersion, and the ammonium oligomeric phosphate with good water solubility is selected to better realize the mixing with the cellulose, in addition, the ammonium oligomeric phosphate can be quickly melted at a lower temperature and infiltrate into the surface of the cellulose material to prevent the contact between the fiber and the air, so that the flame retardant sensitivity of the ammonium oligomeric phosphate is higher. Although the high ammonium polyphosphate is insoluble in water, the heat stability is better, so when only the flame retardant function is realized, the high ammonium polyphosphate is more selected as a flame retardant additive, and most of the prior flame retardant technologies use ammonium polyphosphate with the polymerization degree of more than 1000.
According to the application, the ammonium oligomer is added into three substances, namely cellulose, sodium lignin sulfonate and polyamide epichlorohydrin, so that the addition of the ammonium oligomer not only enables the cellulose film to have a flame-retardant function, but also can greatly improve the mechanical strength of the original three-substance composite film, namely the original three substances have interaction such as electrostatic attraction, covalent bond crosslinking and hydrogen bonding, when the ammonium oligomer is added, the original interaction cannot be destroyed, the mixed dispersion liquid is more stable (zeta potential value is larger), and the ammonium oligomer can have electrostatic attraction and hydrogen bonding with the three substances, so that the mechanical strength is further remarkably improved. According to the application, the cellulose aqueous dispersion, the sodium lignin sulfonate aqueous solution, the polyamide epichlorohydrin cross-linking agent aqueous solution and the ammonium polyphosphate aqueous solution are mixed and stirred to form a mixed solution, so that on one hand, the process is simple, the time can be saved, and more importantly, if the sodium lignin sulfonate and the polyamide epichlorohydrin are mixed first, the mixed solution system formed by the sodium lignin sulfonate and the polyamide epichlorohydrin is electropositive, which means that the sodium lignin sulfonate and the polyamide epichlorohydrin are mixed first to fully exert electrostatic binding force between the sodium lignin sulfonate and the polyamide epichlorohydrin, namely the possibility that the polyamide epichlorohydrin coats the sodium lignin sulfonate exists, and further the play of the reinforcing effect of the sodium lignin sulfonate is influenced to a certain extent; and sodium lignin sulfonate, polyamide epichlorohydrin, bacterial cellulose and ammonium polyphosphate are mixed together, only the polyamide epichlorohydrin is electropositive, and the rest are electronegative, so that the polyamide epichlorohydrin can generate electrostatic binding force with other three substances at the same time, the interaction among the substances is more sufficient, the influence of a part of freeze-drying process on the mechanical property of the diaphragm is favorably counteracted, and the lithium ion battery is more suitable for lithium ion batteries.
As a preferable technical scheme:
according to the preparation method of the cellulose diaphragm for the lithium battery, the mass fraction of the cellulose aqueous dispersion liquid is 0.8-1.3%, the mass fraction of the sodium lignin sulfonate aqueous solution is 0.9-1.2%, the mass fraction of the cross-linking agent aqueous solution is 1-1.3%, and the mass fraction of the ammonium polyphosphate aqueous solution is 1-5%.
According to the preparation method of the cellulose membrane for the lithium battery, the volume ratio of the sodium lignin sulfonate aqueous solution to the cross-linking agent aqueous solution to the cellulose aqueous dispersion to the ammonium polyphosphate aqueous solution is 8-20:9-20:40-75:8-20.
The preparation method of the cellulose diaphragm for the lithium battery comprises the following freeze-drying process parameters: vacuum degree is 0.1-1 Pa, temperature is-50 to-30 ℃ and time is 36-48 h.
The preparation method of the cellulose membrane for the lithium battery comprises the step of heating at 130-150 ℃ for 20-45 min.
According to the preparation method of the cellulose diaphragm for the lithium battery, the cellulose is soaked in ethanol for 36-48 hours (soaked under the room temperature condition).
According to the preparation method of the cellulose diaphragm for the lithium battery, the porosity of the cellulose diaphragm for the lithium battery is 70-80%.
The preparation method of the cellulose membrane for the lithium battery has the advantages that the liquid absorption rate of the cellulose membrane for the lithium battery is 417-472%, and the ion conductivity is 2.1-3 mS cm -1 。
According to the preparation method of the cellulose diaphragm for the lithium battery, the tensile breaking strength of the cellulose diaphragm for the lithium battery is 10-14 MPa (the strength of the diaphragm prepared by the suction filtration method is relatively weak when the freeze drying is used for forming a plurality of holes, but the tensile strength of 10-14 MPa can be used for bearing the normal operation of the diaphragm when the cellulose diaphragm is applied to the field of lithium ion batteries); the initial decomposition temperature of the cellulose diaphragm for the lithium battery obtained by TG test is 155-165 ℃, the epitaxial termination temperature is 280-290 ℃, and the weight loss at 500 ℃ is 55-65%; the heat release rate of the cellulose diaphragm for the lithium battery measured by the micro calorimetric test is 63KW/m to 69KW/m 2 The method comprises the steps of carrying out a first treatment on the surface of the The limiting oxygen index of the cellulose diaphragm for the lithium battery is 32-38%, and the cellulose diaphragm can not burn after continuous ignition.
The principle of the application is as follows:
cellulose has a large number of polar groups such as hydroxyl, carboxyl and the like, and the aqueous solution is electronegative; sodium lignin sulfonate contains a plurality of negative groups (phenolic hydroxyl groups, alcoholic hydroxyl groups, sulfonic groups and the like), and the aqueous solution is electronegative; the cross-linking agent polyamide epichlorohydrin has amino, the N atom of the amino has a pair of lone pair electrons, and can combine with H ionized by water + Forming a positively charged aqueous solution which is electropositive; the aqueous solution of water-soluble ammonium oligophosphate is electronegative.
The application mixes and stirs cellulose water dispersion, sodium lignin sulfonate aqueous solution, cross-linking agent aqueous solution and ammonium polyphosphate aqueous solution to form mixed solution, the whole solution presents dispersion stable state (so the whole solution presents high dispersion stable state, firstly, each component is aqueous solution and is convenient to mix, secondly, each component in the solution has electrostatic attraction effect, but not repulsive force, can lead the component to be dispersed stably in the solution, firstly, no precipitation exists according to observation, no layering phenomenon exists, secondly, the dispersion stable is a stable dispersion system according to the size of Zeta potential absolute value, which is larger than 30.
In addition to the interaction of electrostatic attraction between sodium lignosulfonate-polyamide epichlorohydrin and cellulose and between sodium lignosulfonate-polyamide epichlorohydrin and ammonium polyphosphate, covalent bond (ester bond) crosslinking and hydrogen bond interaction also exist between sodium lignosulfonate-polyamide epichlorohydrin and cellulose; hydrogen bonding also exists between sodium lignin sulfonate-polyamide epichlorohydrin and ammonium polyphosphate; the cellulose and the ammonium polyphosphate also have hydrogen bond action (electrostatic attraction or electrostatic repulsion is obtained by testing positive and negative charges according to Zeta potential, covalent bonds are obtained by infrared testing, and the hydrogen bond is obtained according to polar functional groups such as hydroxyl, amino and the like on each substance). The sodium lignin sulfonate, the polyamide epichlorohydrin, the cellulose and the ammonium polyphosphate form a three-dimensional cross-linked structure, and the three components interact to realize synergistic enhancement and have a flame-retardant function.
The cellulose is soaked in the ethanol, ethanol molecules replace partial water molecules to enter cellulose molecules, and in the soaking process, the ethanol molecules are more volatile, and compared with the water molecules, the cellulose has shorter residence time among the cellulose molecules. Because ethanol volatilizes faster than water molecules, bacterial cellulose occupied by ethanol molecules will collapse less than bacterial cellulose occupied by water, thereby forming microscopic voids and holes. The porosity of the diaphragm is increased by ethanol soaking and freeze drying, and the aperture structure of micron and nanometer level is formed, which is favorable for improving the liquid absorption rate and the ion conductivity and promoting the battery performance.
The beneficial effects are that:
(1) According to the preparation method of the cellulose diaphragm for the lithium battery, the porosity of the diaphragm is improved, and the ionic conductivity is also greatly improved;
(2) According to the preparation method of the cellulose diaphragm for the lithium battery, the mechanical properties are greatly improved due to the interaction among the selected materials;
(3) According to the preparation method of the cellulose diaphragm for the lithium battery, disclosed by the application, the environment-friendly flame retardant is added, so that the flame retardant property is greatly enhanced, and the safety performance of the lithium ion battery is enhanced.
Drawings
FIG. 1 is a graph of porosity (where PP is a commercial polypropylene separator, BC is a pure bacterial cellulose membrane, BL is a cellulose separator without ammonium polyphosphate added prepared in comparative example 1, and BLA is a cellulose separator for lithium batteries prepared in example 1);
FIG. 2 is a mechanical stretching chart (wherein BC is a pure bacterial cellulose membrane, BL is a cellulose membrane without ammonium polyphosphate added prepared in comparative example 1, and BLA is a cellulose membrane for lithium battery prepared in example 1);
FIG. 3 is a thermogravimetric graph (wherein BC is a pure bacterial cellulose membrane, BL is a cellulose membrane without ammonium polyphosphate added prepared in comparative example 1, and BLA is a cellulose membrane for lithium batteries prepared in example 1).
Detailed Description
The application is further described below in conjunction with the detailed description. It is to be understood that these examples are illustrative of the present application and are not intended to limit the scope of the present application. Furthermore, it should be understood that various changes and modifications can be made by one skilled in the art after reading the teachings of the present application, and such equivalents are intended to fall within the scope of the application as defined in the appended claims.
The sources of the substances adopted by the application are as follows:
(1) Sodium lignin sulfonate: from Shanghai Michelia Biochemical technology Co., ltd., CAS number 8061-51-6;
(2) Aqueous polyamide epichlorohydrin solution: from Jin Huacheng paper company, pH value is 3.0-6.0, viscosity is 30-120 mPa.s;
(3) Bacterial cellulose: from Gui Linji macro technologies, inc., cellulose content was 0.8%;
(4) Ammonium polyphosphate: is from Shanghai Michlin Biochemical technologies Co., ltd., CAS No. 68333-79-9.
The application adopts the following test method:
(1) Zeta potential: testing the Zeta potential of the solution by using a Zeta potential analyzer of Marvern Panalytical company;
(2) Liquid absorption rate: cutting the prepared diaphragm into small discs with the diameter of 19mm by a slicer, vacuum drying, and measuring the diaphragm mass W 0 In a fume hood, a diaphragm is placed in electrolyte and soaked for 2 hours, after the diaphragm is taken out, the mass W of the diaphragm after soaking is measured, the liquid absorption rate of the diaphragm is calculated through a formula by the difference of the mass of the diaphragm before and after liquid absorption, and the liquid absorption rate (%) = (W-W) 0 )/W 0 ×100％；
(3) Ion conductivity: cutting the diaphragm into wafers with the diameter of 19mm by using a slicer, assembling the wafers in the sequence of a positive electrode shell, a stainless steel sheet, the diaphragm, the stainless steel sheet and a negative electrode shell, standing for 12 hours after packaging, placing the wafers in a button cell clamp, testing the wafers by using an electrochemical workstation of an EIS, and converting the ion conductivity (d) of the diaphragm by using a formula: d=l/(rb×a); wherein Rb represents the bulk resistance obtained from the Nyquist plot, L represents the thickness of the diaphragm, and A represents the contact area between the diaphragm and the stainless steel electrode;
(4) Tensile breaking strength: cutting the diaphragm into rectangular bars with the length of 4cm multiplied by 1cm, clamping two ends of the rectangular bars on an Instron universal tensile testing machine, and testing the tensile breaking strength of the diaphragm at the speed of 20 mm/min;
(5) Weight loss: carrying out weight loss test on a diaphragm sample by adopting a TG Q600 type thermogravimetric analyzer (TG) of the American TA company, wherein the mass of the sample is 5-10mg, the temperature is raised in a nitrogen environment of the sample, the temperature raising rate is 20 ℃/min, and the test range is 30-600 ℃;
(6) Heat release rate: measuring 5-10mg of sample in a crucible by adopting an FTT0001 micro calorimeter of the UK FTT company, heating in a mixed atmosphere (80% of nitrogen and 20% of oxygen) at a heating rate of 1 ℃/s, and testing the heat release rate of a diaphragm;
(7) Limiting oxygen index: the membrane is cut into a sample with the diameter of 100mm multiplied by 10mm, the sample is vertically fixed in a glass combustion cylinder, the base of the sample is connected with a device capable of generating a nitrogen-oxygen mixed gas flow, the top end of the sample is ignited, and the oxygen concentration in the mixed gas flow continuously drops until flame is extinguished.
Example 1
The preparation method of the cellulose diaphragm for the lithium battery comprises the following specific steps:
(1) Firstly, mixing aqueous cellulose dispersion liquid with the mass fraction of 0.8%, sodium lignin sulfonate aqueous solution with the mass fraction of 1.2%, polyamide epichlorohydrin aqueous solution with the mass fraction of 1.3% and ammonium oligomeric phosphate (the polymerization degree is less than 20) aqueous solution with the mass fraction of 5%, stirring to form a mixed solution with the Zeta potential of-50, and generating no precipitate;
wherein the cellulose is bacterial cellulose which is soaked in ethanol for 40 hours at room temperature; the volume ratio of the sodium lignin sulfonate aqueous solution, the polyamide epichlorohydrin aqueous solution, the cellulose aqueous dispersion and the ammonium oligomeric phosphate aqueous solution is 8:9:75:8;
(2) Then the mixed solution obtained in the step (1) is freeze-dried for 48 hours to form a film under the conditions of 0.1Pa of vacuum degree and-47 ℃, and after the film is formed, the film is heated for 20 minutes at 150 ℃ and rolled to the thickness of 110 mu m, so as to prepare the cellulose diaphragm for the lithium battery;
the prepared cellulose membrane for lithium battery has the porosity of 80 percent (shown in figure 1), the liquid absorption rate of 472 percent and the ion conductivity of 3mS cm -1 The tensile breaking strength is 14MPa (as shown in FIG. 2), the initial decomposition temperature is 156.9 ℃, the epitaxial termination temperature is 282.2 ℃, the weight loss at 500 ℃ is 60% (as shown in FIG. 3), and the heat release rate is 67KW/m 2 The method comprises the steps of carrying out a first treatment on the surface of the The limiting oxygen index of the prepared cellulose diaphragm for the lithium battery is 36%, and the cellulose diaphragm can not burn after being continuously ignited.
Comparative example 1
A method for preparing a cellulose membrane, substantially as in example 1, except that in step (1), an aqueous solution of ammonium oligomeric phosphate is not added; the Zeta potential of the mixed solution obtained after full stirring in the step (1) is-27, and no precipitation is generated;
the porosity of the prepared cellulose membrane is 66% (shown in figure 1), the liquid absorption rate is 220%, and the ionic conductivity is 2.1mS cm -1 The tensile breaking strength was 6MPa (as shown in FIG. 2), the initial decomposition temperature was 249.7℃and the epitaxial termination temperature was 339℃atThe weight loss at 500℃was 88% (as shown in FIG. 3), and the heat release rate was 140KW/m 2 The method comprises the steps of carrying out a first treatment on the surface of the The limiting oxygen index of the cellulose membrane is 16.6%, and the cellulose membrane can burn after being continuously ignited.
Comparing comparative example 1 with example 1, it can be found that the porosity, the liquid absorption rate and the ionic conductivity of the cellulose membrane prepared in comparative example 1 are lower than those of example 1, because the absolute value of the zeta potential of comparative example 1 is smaller than that of example 1 without adding the aqueous solution of ammonium polyphosphate, the solution stability is slightly poor, and new chemical bonds are formed by adding the solution of ammonium polyphosphate, which is favorable for the infiltration of electrolyte and the transmission of ions; the tensile break strength of comparative example 1 was also lower than that of example 1 because no ammonium oligomeric phosphate was added, only sodium lignin sulfonate itself and intermolecular covalent crosslinks in the film enhanced the strength of the film, and no flame retardant was added, the film heat release rate was increased, and the flame retardant effect was not exhibited.
Comparative example 2
A method for producing a cellulose separator, substantially the same as in example 1, except that the ammonium oligophosphate in step (1) was replaced with a medium ammonium polyphosphate (polymerization degree: 30< n < 50); the Zeta potential of the mixed solution obtained after full stirring in the step (1) is-22, and no precipitation is generated;
the porosity of the prepared cellulose membrane is 31%, the liquid absorption rate is 120%, and the ionic conductivity is 0.9mS cm -1 The tensile breaking strength is 1.4MPa, the initial decomposition temperature is 164.3 ℃, the epitaxial termination temperature is 277.4 ℃, the weight loss at 500 ℃ is 55%, and the heat release rate is 61KW/m 2 The method comprises the steps of carrying out a first treatment on the surface of the The limiting oxygen index of the cellulose membrane is 40.1%, and the cellulose membrane can not burn after continuous ignition.
Comparing comparative example 2 with example 1, it can be found that the porosity, the liquid absorption and the ionic conductivity of the cellulose membrane prepared in comparative example 2 are all significantly lower than those of example 1, because the middle ammonium polyphosphate prepared in comparative example 2 has smaller pore diameter and 30< n <50 can block a part of pores; the tensile breaking strength of comparative example 2 is also significantly lower than that of example 1 because the middle ammonium polyphosphate of 30< n <50 is poorly soluble in water, the mixed solution is unstable, and when the film is formed, the middle ammonium polyphosphate cannot be well fused with cellulose to produce an effective effect, but rather, the effective interaction between other components is blocked, so that the strength of the manufactured composite separator is reduced.
Comparative example 3
A method for preparing a cellulose membrane, the specific steps being substantially the same as in example 1, except that the ammonium oligomeric phosphate in step (1) is replaced with high ammonium polymeric phosphate (polymerization degree > 1500); the Zeta potential of the mixed solution obtained after full stirring in the step (1) is-19, and no precipitation is generated;
the porosity of the prepared cellulose membrane is 27%, the liquid absorption rate is 113%, and the ionic conductivity is 0.74mS cm -1 The tensile breaking strength is 1.2MPa, the initial decomposition temperature is 163.1 ℃, the epitaxy termination temperature is 274.7 ℃, the weight loss at 500 ℃ is 52%, and the heat release rate is 59KW/m 2 The method comprises the steps of carrying out a first treatment on the surface of the The limiting oxygen index of the cellulose membrane is 43.3%, and the cellulose membrane can not burn after continuous ignition.
Comparing comparative example 3 with example 1, it can be found that the porosity, the liquid absorption and the ionic conductivity of the cellulose membrane prepared in comparative example 3 are all significantly lower than those of example 1, because the cellulose membrane prepared in comparative example 3 has smaller pore size and the ammonium polyphosphate with n >1500 blocks a part of pores; the tensile break strength of comparative example 3 is also significantly lower than that of example 1 because the ammonium polyphosphate having n >1500 is insoluble in water, the mixed solution is unstable, and when formed into a film, the ammonium polyphosphate is not well fused with cellulose to produce an effective effect, but rather, the effective interaction between other components is blocked, so that the strength of the produced composite separator is lowered.
Comparative example 4
A method for preparing a cellulose membrane is substantially the same as in example 1, except that bacterial cellulose in step (1) is not subjected to an ethanol soaking treatment, and the finally prepared cellulose membrane has a porosity of 50%, a liquid absorption of 178%, and an ionic conductivity of 1.6 mS.cm -1 The tensile breaking strength is 15MPa, the initial decomposition temperature is 162.8 ℃, the epitaxial termination temperature is 273.1 ℃, the weight loss at 500 ℃ is 54%, and the heat release rate is 57KW/m 2 The method comprises the steps of carrying out a first treatment on the surface of the Limiting oxygen index of cellulose separator43.9%, and the ignition was continued without combustion.
Comparing comparative example 4 with example 1, it can be seen that the porosity, the liquid absorption rate and the ionic conductivity of the cellulose membrane prepared in comparative example 3 are all significantly lower than those of example 1, because comparative example 1 is not soaked in ethanol, and the pores formed in cellulose are smaller, so that a channel for efficient transmission cannot be constructed for ions in the operation process of the lithium ion battery, and the ionic conductivity is low.
Example 2
The preparation method of the cellulose diaphragm for the lithium battery comprises the following specific steps:
(1) Firstly, mixing aqueous cellulose dispersion liquid with the mass fraction of 0.9%, sodium lignin sulfonate aqueous solution with the mass fraction of 0.9%, polyamide epichlorohydrin aqueous solution with the mass fraction of 1% and ammonium oligomeric phosphate (the polymerization degree is less than 20) aqueous solution with the mass fraction of 1%, stirring to form a mixed solution with the Zeta potential of-39, and generating no precipitate;
wherein the cellulose is bacterial cellulose which is soaked in ethanol for 40 hours at room temperature; the volume ratio of the sodium lignin sulfonate aqueous solution, the polyamide epichlorohydrin aqueous solution, the cellulose aqueous dispersion and the ammonium oligomeric phosphate aqueous solution is 10:10:70:10;
(2) Then the mixed solution obtained in the step (1) is freeze-dried for 46 hours to form a film under the conditions of vacuum degree of 0.3Pa and temperature of-45 ℃, and the film is heated for 45 minutes at 130 ℃ and rolled to the thickness of 90 mu m to prepare the cellulose diaphragm for the lithium battery;
the prepared cellulose membrane for lithium battery has the porosity of 74%, the liquid absorption rate of 448% and the ion conductivity of 2.6mS cm -1 The tensile breaking strength is 12.7MPa, the initial decomposition temperature is 157.5 ℃, the epitaxy termination temperature is 281.4 ℃, the weight loss at 500 ℃ is 62%, and the heat release rate is 65KW/m 2 The method comprises the steps of carrying out a first treatment on the surface of the The limiting oxygen index of the prepared cellulose diaphragm for the lithium battery is 32%, and the cellulose diaphragm can not burn after being continuously ignited.
Example 3
The preparation method of the cellulose diaphragm for the lithium battery comprises the following specific steps:
(1) Firstly, mixing 1% of cellulose aqueous dispersion liquid, 1.1% of sodium lignin sulfonate aqueous solution, 1.1% of polyamide epichlorohydrin aqueous solution and 2% of ammonium oligomeric phosphate (polymerization degree is less than 20) aqueous solution, stirring to form a mixed solution with Zeta potential of-31, and generating no precipitate;
wherein the cellulose is bacterial cellulose which is soaked in ethanol for 48 hours at room temperature; the volume ratio of the sodium lignin sulfonate aqueous solution to the polyamide epichlorohydrin aqueous solution to the cellulose aqueous dispersion to the ammonium oligomeric phosphate aqueous solution is 20:20:50:10;
(2) Then, the mixed solution obtained in the step (1) is freeze-dried for 44 hours to form a film under the conditions of 0.2Pa of vacuum degree and-42 ℃, and after the film is formed, the film is heated for 25 minutes at 145 ℃ and rolled to the thickness of 80 mu m, so as to prepare the cellulose diaphragm for the lithium battery;
the prepared cellulose diaphragm for the lithium battery has the porosity of 75 percent, the liquid absorption rate of 450 percent and the ion conductivity of 2.7mS cm -1 The tensile breaking strength is 13.3MPa, the initial decomposition temperature is 161.2 ℃, the epitaxy termination temperature is 285.3 ℃, the weight loss at 500 ℃ is 65%, and the heat release rate is 68KW/m 2 The method comprises the steps of carrying out a first treatment on the surface of the The limiting oxygen index of the prepared cellulose diaphragm for the lithium battery is 32.6%, and the cellulose diaphragm can not burn after being continuously ignited.
Example 4
The preparation method of the cellulose diaphragm for the lithium battery comprises the following specific steps:
(1) Firstly, mixing 1% of cellulose aqueous dispersion liquid, 1.1% of sodium lignin sulfonate aqueous solution, 1.2% of polyamide epichlorohydrin aqueous solution and 2% of ammonium oligomeric phosphate (polymerization degree is less than 20) aqueous solution, stirring to form a mixed solution with Zeta potential of-39, and generating no precipitate;
wherein the cellulose is bacterial cellulose which is soaked in ethanol for 42 hours at room temperature; the volume ratio of the sodium lignin sulfonate aqueous solution to the polyamide epichlorohydrin aqueous solution to the cellulose aqueous dispersion to the ammonium oligomeric phosphate aqueous solution is 8:12:60:20;
(2) Freeze-drying the mixed solution obtained in the step (1) for 40 hours under the conditions of vacuum degree of 1Pa and temperature of-41 ℃ to form a film, heating the film at 135 ℃ for 40 minutes, and rolling the film to a thickness of 85 mu m to obtain the cellulose diaphragm for the lithium battery;
the prepared cellulose membrane for lithium battery has the porosity of 73%, the liquid absorption rate of 451% and the ion conductivity of 2.6mS cm -1 The tensile breaking strength is 12.3MPa, the initial decomposition temperature is 155.8 ℃, the epitaxy termination temperature is 287.3 ℃, the weight loss at 500 ℃ is 57%, and the heat release rate is 63KW/m 2 The method comprises the steps of carrying out a first treatment on the surface of the The limiting oxygen index of the prepared cellulose diaphragm for the lithium battery is 33.9%, and the cellulose diaphragm can not burn after being continuously ignited.
Example 5
The preparation method of the cellulose diaphragm for the lithium battery comprises the following specific steps:
(1) Firstly, mixing 1.1% of cellulose aqueous dispersion liquid, 1% of sodium lignin sulfonate aqueous solution, 1.1% of polyamide epichlorohydrin aqueous solution and 3% of ammonium oligomeric phosphate (polymerization degree is less than 20) aqueous solution, stirring to form a mixed solution with Zeta potential of-47, and generating no precipitate;
wherein the cellulose is bacterial cellulose which is soaked in ethanol for 36 hours at room temperature; the volume ratio of the sodium lignin sulfonate aqueous solution to the polyamide epichlorohydrin aqueous solution to the cellulose aqueous dispersion to the ammonium oligomeric phosphate aqueous solution is 15:20:45:20;
(2) Freeze-drying the mixed solution obtained in the step (1) for 39 hours to form a film under the conditions of 0.7Pa of vacuum degree and-38 ℃, heating for 30 minutes at 140 ℃ after film forming, and rolling to a thickness of 70 mu m to obtain the cellulose diaphragm for the lithium battery;
the prepared cellulose membrane for lithium battery has the porosity of 72 percent, the liquid absorption rate of 437 percent and the ion conductivity of 2.3mS cm -1 The tensile breaking strength is 11.1MPa, the initial decomposition temperature is 155 ℃, the epitaxial termination temperature is 284.4 ℃, the weight loss at 500 ℃ is 60%, and the heat release rate is 64KW/m 2 The method comprises the steps of carrying out a first treatment on the surface of the The limiting oxygen index of the prepared cellulose diaphragm for the lithium battery is 33.5%, and the cellulose diaphragm can not burn after being continuously ignited.
Example 6
The preparation method of the cellulose diaphragm for the lithium battery comprises the following specific steps:
(1) Firstly, mixing 1.1% of cellulose aqueous dispersion liquid, 1% of sodium lignin sulfonate aqueous solution, 1.2% of polyamide epichlorohydrin aqueous solution and 3% of ammonium oligomeric phosphate (polymerization degree is less than 20) aqueous solution, stirring to form a mixed solution with Zeta potential of-43, and generating no precipitate;
wherein the cellulose is bacterial cellulose which is soaked in ethanol for 36 hours at room temperature; the volume ratio of the sodium lignin sulfonate aqueous solution, the polyamide epichlorohydrin aqueous solution, the cellulose aqueous dispersion and the ammonium oligomeric phosphate aqueous solution is 10:20:50:20;
(2) Freeze-drying the mixed solution obtained in the step (1) for 39 hours to form a film under the conditions of 0.5Pa and-33 ℃ of vacuum degree, heating for 35 minutes at 140 ℃ after film forming, and rolling to the thickness of 95 mu m to obtain the cellulose diaphragm for the lithium battery;
the prepared cellulose diaphragm for the lithium battery has the porosity of 78%, the liquid absorption rate of 467% and the ion conductivity of 2.8mS cm -1 The tensile breaking strength is 10.6MPa, the initial decomposition temperature is 159.8 ℃, the epitaxy termination temperature is 290 ℃, the weight loss at 500 ℃ is 55%, and the heat release rate is 63KW/m 2 The method comprises the steps of carrying out a first treatment on the surface of the The limiting oxygen index of the prepared cellulose diaphragm for the lithium battery is 35.8%, and the cellulose diaphragm can not burn after being continuously ignited.
Example 7
The preparation method of the cellulose diaphragm for the lithium battery comprises the following specific steps:
(1) Firstly, mixing 1.2% of cellulose aqueous dispersion liquid, 1.2% of sodium lignin sulfonate aqueous solution, 1.1% of polyamide epichlorohydrin aqueous solution and 4% of ammonium oligomeric phosphate (polymerization degree is less than 20) aqueous solution, stirring to form a mixed solution with Zeta potential of-44, and generating no precipitate;
wherein the cellulose is bacterial cellulose which is soaked in ethanol for 36 hours at room temperature; the volume ratio of the sodium lignin sulfonate aqueous solution to the polyamide epichlorohydrin aqueous solution to the cellulose aqueous dispersion to the ammonium oligomeric phosphate aqueous solution is 12:16:54:18;
(2) Freeze-drying the mixed solution obtained in the step (1) for 37 hours to form a film under the conditions of 0.8Pa and-31 ℃ of vacuum degree, heating for 40 minutes at 135 ℃ after film forming, and rolling to a thickness of 100 mu m to obtain the cellulose diaphragm for the lithium battery;
the prepared cellulose diaphragm for the lithium battery has the porosity of 70 percent, the liquid absorption rate of 417 percent and the ion conductivity of 2.1mS cm -1 The tensile breaking strength is 10MPa, the initial decomposition temperature is 165 ℃, the epitaxial termination temperature is 289.5 ℃, the weight loss at 500 ℃ is 58%, and the heat release rate is 65KW/m 2 The method comprises the steps of carrying out a first treatment on the surface of the The limiting oxygen index of the prepared cellulose diaphragm for the lithium battery is 36.5%, and the cellulose diaphragm can not burn after being continuously ignited.
Example 8
The preparation method of the cellulose diaphragm for the lithium battery comprises the following specific steps:
(1) Firstly, mixing 1.3% of cellulose aqueous dispersion liquid, 0.9% of sodium lignin sulfonate aqueous solution, 1.2% of polyamide epichlorohydrin aqueous solution and 4% of ammonium oligomeric phosphate (polymerization degree is less than 20) aqueous solution, stirring to form a mixed solution with Zeta potential of-49, and generating no precipitate;
wherein the cellulose is bacterial cellulose which is soaked in ethanol for 36 hours at room temperature; the volume ratio of the sodium lignin sulfonate aqueous solution, the polyamide epichlorohydrin aqueous solution, the cellulose aqueous dispersion and the ammonium oligomeric phosphate aqueous solution is 20:20:40:20;
(2) Then the mixed solution obtained in the step (1) is freeze-dried for 36 hours to form a film under the conditions of 0.4Pa of vacuum degree and-30 ℃, and after the film is formed, the film is heated for 35 minutes at 145 ℃ and rolled to the thickness of 60 mu m, so as to prepare the cellulose diaphragm for the lithium battery;
the prepared cellulose diaphragm for the lithium battery has the porosity of 80 percent, the liquid absorption rate of 469 percent and the ion conductivity of 2.7mS cm -1 The tensile breaking strength is 12.8MPa, the initial decomposition temperature is 162.2 ℃, the epitaxial termination temperature is 280 ℃, and the tensile breaking strength is 5Weight loss at 00℃was 61% and heat release rate was 66KW/m 2 The method comprises the steps of carrying out a first treatment on the surface of the The limiting oxygen index of the prepared cellulose diaphragm for the lithium battery is 38%, and the cellulose diaphragm can not burn after being continuously ignited.
In addition, as can be seen from fig. 1, the porosity of PP is the lowest among the four kinds of separators, and the porosity of the cellulose separator for lithium ion batteries is further increased on the basis of maintaining the excellent porosity of BC and BL separators, because new binding force is provided after ammonium polyphosphate is added, the pore canal can be protected from collapsing, the efficient transmission of ions in the separator is effectively ensured, and the superiority of the separator for lithium ion batteries is reflected.
The mechanical tensile properties of the BC, BL, BLA membranes are only compared in fig. 2, because the PP membranes are different in material and have no contrast. Among the three films, the BC film has the worst mechanical tensile property, and the BL film has a certain improvement compared with BC because of the combination of electrostatic force between the two substances, the BC and the polyamide epichlorohydrin are crosslinked after being heated at high temperature, and the added sodium lignin sulfonate can effectively enhance the mechanical property of the BC; the mechanical properties of the BLA membrane are improved more, and the BLA membrane can be improved more due to the synergistic effect of electrostatic force, hydrogen bond and covalent bond among BC, LS (sodium lignin sulfonate), PAE (polyamide epichlorohydrin) and APP (ammonium polyphosphate) besides the factors.
As can be seen from fig. 3, as the temperature increases, the BC and BL films begin to exhibit significant weight loss at about 200 ℃ with a maximum weight loss rate temperature of 310 ℃, indicating excellent thermal stability of the BC and BL films. As APP is added to BL, the BLA composite film shows two main weight loss peaks: one is melting of APP, which can be considered to be low in polymerization degree and water-soluble, in the temperature range of 120 to 200 ℃, which can be melted rapidly at a relatively low temperature compared to APP of high polymerization degree, and then penetrate into the pores of BC film, isolating BC from air fraction; the other is 200 to 360 ℃, the partial decomposition attributable to BC is accompanied by decomposition of APP, which typically decomposes to NH at about 310 °c 3 、H 2 O and densification ofPolyphosphoric acid layer of (2), NH 3 And H 2 The O dilutes the combustible gas and oxygen concentrations to some extent and the polyphosphoric acid layer covers the surface of the BC fiber preventing sustained decomposition of BC.
Claims (9)
1. A preparation method of a cellulose diaphragm for a lithium battery is characterized by comprising the following steps: firstly, mixing and stirring cellulose aqueous dispersion liquid, sodium lignin sulfonate aqueous solution, cross-linking agent aqueous solution and ammonium polyphosphate aqueous solution to form a mixed solution, freeze-drying the mixed solution to form a film, heating and rolling the film to a certain thickness to prepare the cellulose diaphragm for the lithium battery;
the thickness of the cellulose diaphragm for the lithium battery is 60-110 mu m;
the tensile breaking strength of the cellulose diaphragm for the lithium battery is 10-14 MPa; the limiting oxygen index of the cellulose diaphragm for the lithium battery is 32-38%, and the cellulose diaphragm can not burn after continuous ignition;
the Zeta potential of the mixed solution is less than-30, and no sediment is generated;
the cross-linking agent is polyamide epichlorohydrin; the cellulose is bacterial cellulose soaked in ethanol; the polymerization degree of the ammonium polyphosphate is less than 20.
2. The method for preparing a cellulose membrane for a lithium battery according to claim 1, wherein the mass fraction of the cellulose aqueous dispersion is 0.8-1.3%, the mass fraction of the sodium lignin sulfonate aqueous solution is 0.9-1.2%, the mass fraction of the cross-linking agent aqueous solution is 1-1.3%, and the mass fraction of the ammonium polyphosphate aqueous solution is 1-5%.
3. The method for preparing a cellulose membrane for a lithium battery according to claim 2, wherein the volume ratio of the sodium lignin sulfonate aqueous solution, the cross-linking agent aqueous solution, the cellulose aqueous dispersion and the ammonium polyphosphate aqueous solution is 8-20:9-20:40-75:8-20.
4. The method for preparing the cellulose membrane for the lithium battery according to claim 1, wherein the freeze-drying process parameters are as follows: vacuum degree is 0.1-1 Pa, temperature is-50 to-30 ℃ and time is 36-48 h.
5. The method for preparing a cellulose separator for lithium batteries according to claim 1, wherein the heating treatment is heating at 130 to 150 ℃ for 20 to 45 minutes.
6. The method for preparing the cellulose membrane for the lithium battery, which is disclosed in claim 1, is characterized in that the time for soaking the cellulose in ethanol is 36-48 hours.
7. The method for producing a cellulose separator for lithium batteries according to any one of claims 1 to 6, wherein the porosity of the cellulose separator for lithium batteries is 70 to 80%.
8. The method for producing a cellulose separator for lithium batteries according to claim 7, wherein the cellulose separator for lithium batteries has a liquid absorption of 417 to 472% and an ion conductivity of 2.1 to 3mS cm -1 。
9. The method for preparing a cellulose membrane for lithium batteries according to claim 8, wherein the initial decomposition temperature of the cellulose membrane for lithium batteries obtained by TG test is 155-165 ℃, the epitaxial termination temperature is 280-290 ℃, and the weight loss at 500 ℃ is 55-65%; the heat release rate of the cellulose diaphragm for the lithium battery measured by the micro calorimetric test is 63KW/m to 69KW/m 2 。
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