CN115498358A - Preparation method of cellulose diaphragm for lithium battery - Google Patents
Preparation method of cellulose diaphragm for lithium battery Download PDFInfo
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- CN115498358A CN115498358A CN202211046856.3A CN202211046856A CN115498358A CN 115498358 A CN115498358 A CN 115498358A CN 202211046856 A CN202211046856 A CN 202211046856A CN 115498358 A CN115498358 A CN 115498358A
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- cellulose
- lithium battery
- diaphragm
- aqueous solution
- ammonium polyphosphate
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- 229920002678 cellulose Polymers 0.000 title claims abstract description 172
- 239000001913 cellulose Substances 0.000 title claims abstract description 172
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 81
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 81
- 238000002360 preparation method Methods 0.000 title claims abstract description 26
- 239000004114 Ammonium polyphosphate Substances 0.000 claims abstract description 42
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims abstract description 42
- 229920001276 ammonium polyphosphate Polymers 0.000 claims abstract description 42
- 235000019826 ammonium polyphosphate Nutrition 0.000 claims abstract description 42
- 229920002749 Bacterial cellulose Polymers 0.000 claims abstract description 40
- 239000005016 bacterial cellulose Substances 0.000 claims abstract description 40
- 229920005552 sodium lignosulfonate Polymers 0.000 claims abstract description 38
- 239000006185 dispersion Substances 0.000 claims abstract description 34
- 239000011259 mixed solution Substances 0.000 claims abstract description 34
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 34
- 239000004952 Polyamide Substances 0.000 claims abstract description 33
- 229920002647 polyamide Polymers 0.000 claims abstract description 33
- BRLQWZUYTZBJKN-UHFFFAOYSA-N Epichlorohydrin Chemical compound ClCC1CO1 BRLQWZUYTZBJKN-UHFFFAOYSA-N 0.000 claims abstract description 21
- 239000000243 solution Substances 0.000 claims abstract description 20
- 238000006116 polymerization reaction Methods 0.000 claims abstract description 19
- 238000004108 freeze drying Methods 0.000 claims abstract description 16
- 238000010438 heat treatment Methods 0.000 claims abstract description 16
- 239000003431 cross linking reagent Substances 0.000 claims abstract description 14
- 238000003756 stirring Methods 0.000 claims abstract description 14
- 238000002156 mixing Methods 0.000 claims abstract description 12
- 238000005096 rolling process Methods 0.000 claims abstract description 11
- 239000007864 aqueous solution Substances 0.000 claims description 69
- 238000000034 method Methods 0.000 claims description 26
- 239000007788 liquid Substances 0.000 claims description 24
- 238000010521 absorption reaction Methods 0.000 claims description 23
- 230000004580 weight loss Effects 0.000 claims description 19
- 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
- 238000000354 decomposition reaction Methods 0.000 claims description 17
- 239000002244 precipitate Substances 0.000 claims description 14
- 238000012360 testing method Methods 0.000 claims description 10
- 230000008569 process Effects 0.000 claims description 7
- 238000002791 soaking Methods 0.000 claims description 6
- 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
- 239000012528 membrane Substances 0.000 description 25
- 230000000052 comparative effect Effects 0.000 description 22
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 21
- 229910019142 PO4 Inorganic materials 0.000 description 19
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 19
- 239000010452 phosphate Substances 0.000 description 19
- LRWZZZWJMFNZIK-UHFFFAOYSA-N 2-chloro-3-methyloxirane Chemical compound CC1OC1Cl LRWZZZWJMFNZIK-UHFFFAOYSA-N 0.000 description 12
- 239000011148 porous material Substances 0.000 description 11
- 239000004254 Ammonium phosphate Substances 0.000 description 9
- 229910000148 ammonium phosphate Inorganic materials 0.000 description 9
- 235000019289 ammonium phosphates Nutrition 0.000 description 9
- MNNHAPBLZZVQHP-UHFFFAOYSA-N diammonium hydrogen phosphate Chemical compound [NH4+].[NH4+].OP([O-])([O-])=O MNNHAPBLZZVQHP-UHFFFAOYSA-N 0.000 description 9
- 239000001257 hydrogen Substances 0.000 description 9
- 229910052739 hydrogen Inorganic materials 0.000 description 9
- 239000000126 substance Substances 0.000 description 9
- 230000003993 interaction Effects 0.000 description 8
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 6
- 238000000407 epitaxy Methods 0.000 description 6
- 229910001416 lithium ion Inorganic materials 0.000 description 6
- 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 5
- 239000002131 composite material Substances 0.000 description 5
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 5
- 150000002500 ions Chemical class 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 239000011734 sodium Substances 0.000 description 5
- 229910052708 sodium Inorganic materials 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 239000004743 Polypropylene Substances 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 238000004132 cross linking Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 239000003792 electrolyte Substances 0.000 description 4
- 230000005540 biological transmission Effects 0.000 description 3
- 238000005520 cutting process Methods 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 230000002349 favourable effect Effects 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 229920005610 lignin Polymers 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
- 125000003277 amino group Chemical group 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 239000000835 fiber Substances 0.000 description 2
- 239000010954 inorganic particle Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000002105 nanoparticle Substances 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 239000012466 permeate Substances 0.000 description 2
- 229920000137 polyphosphoric acid Polymers 0.000 description 2
- 230000002195 synergetic effect Effects 0.000 description 2
- 235000012431 wafers Nutrition 0.000 description 2
- 229920001410 Microfiber Polymers 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
- ZRIUUUJAJJNDSS-UHFFFAOYSA-N ammonium phosphates Chemical compound [NH4+].[NH4+].[NH4+].[O-]P([O-])([O-])=O ZRIUUUJAJJNDSS-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 125000003178 carboxy group Chemical group [H]OC(*)=O 0.000 description 1
- 238000001035 drying 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
- 230000014759 maintenance of location Effects 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
- 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
- 125000004433 nitrogen atom Chemical group N* 0.000 description 1
- 229920002842 oligophosphate Polymers 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- -1 polypropylene Polymers 0.000 description 1
- 229920001155 polypropylene Polymers 0.000 description 1
- 125000002924 primary amino group Chemical group [H]N([H])* 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
- 125000000542 sulfonic acid group Chemical group 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000012876 topography Methods 0.000 description 1
- UNXRWKVEANCORM-UHFFFAOYSA-N triphosphoric acid Polymers OP(O)(=O)OP(O)(=O)OP(O)(O)=O UNXRWKVEANCORM-UHFFFAOYSA-N 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
Images
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 invention relates to a preparation method of a cellulose diaphragm for a lithium battery, which comprises the steps of mixing and stirring cellulose water dispersion, sodium lignosulfonate water solution, cross-linking agent water solution and ammonium polyphosphate water 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 cross-linking agent is polyamide epichlorohydrin; the cellulose is bacterial cellulose soaked by 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 battery is greatly improved.
Description
Technical Field
The invention 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 increasing attention in lithium batteries because of their excellent thermal stability and being a widely available, environmentally friendly material. The studies based on bacterial cellulose membranes focus mainly on the following three aspects: (1) Inorganic particles are added to balance the action of hydrogen bonds, so that the porosity of the diaphragm is improved. On one hand, a large number of hydroxyl polar groups on cellulose molecules are favorable for the affinity to electrolyte. On the other hand, a large number of hydrogen bonds easily enable the cellulose membrane to form a compact network, and the porosity of the diaphragm is low, so that the diaphragm electrolyte is not favorably maintained and ion transportation is not facilitated. (2) In order to improve the mechanical strength of cellulose, the existing research is mainly used for a composite method of nano particles, nano fibers and micro fibers, and the mechanical strength of a cellulose membrane is improved by pretreating the cellulose by a TEMPO method. In addition, it is also a common method to improve the strength by using lignin and its derivatives to imitate the composition of trees, but electrostatic repulsion exists between lignin and cellulose, which is not favorable for the solution combination of the two. In order to solve the electrostatic repulsion problem, PEI capable of forming electrostatic attraction with cellulose and lignin is introduced as a cross-linking agent, so that the dispersion problem of a mixed solution can be well solved, and the mechanical strength of a cellulose membrane is improved. (3) In order to improve the flame retardant property of cellulose films, organic and inorganic flame retardants are mostly added. In addition to the above-mentioned separate studies, inorganic particles are often mixed with a flame retardant to simultaneously improve the porosity, mechanical properties, and flame retardancy of the cellulose separator. Meanwhile, most of the flame retardant is added as a water-insoluble flame retardant, and most of the cellulose is an aqueous dispersion, so that the problem of dispersion unevenness also exists when the flame retardant is mixed with the cellulose.
Therefore, it is urgently needed to develop a method which can well mix the components added in the preparation process with the bacterial cellulose solution and can simultaneously improve the porosity, mechanical property and flame retardant property of the cellulose membrane.
Disclosure of Invention
The invention 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 purpose, the technical scheme adopted by the invention is as follows:
firstly, mixing and stirring cellulose water dispersion, sodium lignosulfonate water solution, cross-linking agent water solution and ammonium polyphosphate water solution to form mixed solution, then carrying out freeze drying on the mixed solution to form a film, carrying out heating treatment (covalent cross-linking can be generated between the sodium lignosulfonate and the cellulose and polyamide epoxy chloropropane in the heating treatment 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, and no precipitate is generated, which indicates that all components in the mixed solution are uniformly mixed;
the cross-linking agent is polyamide epichlorohydrin; the cellulose is bacterial cellulose soaked by ethanol, and the Bacterial Cellulose (BC) has high aspect ratio, rich hydroxyl and good thermal stability, and is suitable for a lithium ion battery diaphragm; the polymerization degree of the ammonium polyphosphate is less than 20; the ammonium polyphosphate with the polymerization degree of less than 20 is very easy to dissolve in water, the solubility of the ammonium polyphosphate in 100ml of water is more than 90g, the solubility of the ammonium polyphosphate with the polymerization degree of 30-50 in 100ml of water is less than 4g, and the ammonium polyphosphate with the larger polymerization degree is insoluble in water. The cellulose is usually water dispersion, the oligomeric ammonium phosphate with good water solubility can be better mixed with the cellulose, in addition, the oligomeric ammonium phosphate can be quickly melted at a lower temperature and permeates into the surface of a cellulose material to block the contact of fibers and air, so the flame retardant sensitivity of the oligomeric ammonium phosphate is higher. Although the high ammonium polyphosphate is insoluble in water, the thermal stability is better, so the high ammonium polyphosphate is more selected as a flame retardant additive only for realizing the flame retardant function, and most of the ammonium polyphosphate with the polymerization degree of more than 1000 is used in the prior flame retardant technology.
According to the invention, the oligomeric ammonium phosphate is added into the three substances of cellulose, sodium lignosulfonate and polyamide epichlorohydrin, so that the cellulose membrane has a flame retardant function, the mechanical strength of the original three-substance composite membrane can be greatly improved, namely, the original three substances have electrostatic attraction, covalent bond crosslinking, hydrogen bond interaction and the like, after the oligomeric ammonium phosphate is added, the original interaction cannot be destroyed, the mixed dispersion liquid is more stable (the zeta potential value is larger), and the oligomeric ammonium phosphate and the three substances also have electrostatic attraction and hydrogen bond, so that the mechanical strength is further remarkably improved. According to the invention, the cellulose water dispersion, the sodium lignosulfonate aqueous solution, the polyamide epoxy chloropropane cross-linking agent aqueous solution and the ammonium polyphosphate aqueous solution are mixed and stirred to form the mixed solution, on one hand, the process is simple, the time can be saved, more importantly, if the sodium lignosulfonate and the polyamide epoxy chloropropane are mixed firstly, the mixed solution system formed by the two is electropositive, which shows that the electrostatic binding force between the sodium lignosulfonate and the polyamide epoxy chloropropane can be fully exerted by mixing the sodium lignosulfonate and the polyamide epoxy chloropropane firstly, namely the possibility that the polyamide epoxy chloropropane coats the sodium lignosulfonate exists, and further the exertion of the reinforcing effect of the sodium lignosulfonate is influenced to a certain extent; the sodium lignosulfonate, the polyamide epoxy chloropropane, the bacterial cellulose and the ammonium polyphosphate are mixed together, only the polyamide epoxy chloropropane is electropositive, the rest are electronegative, the polyamide epoxy chloropropane and other three substances can simultaneously generate electrostatic binding force, the interaction among the substances is more sufficient, the influence of a part of freeze drying process on the mechanical property of the diaphragm can be counteracted, and the method is more suitable for the lithium ion battery.
As a preferred technical scheme:
according to the preparation method of the cellulose diaphragm for the lithium battery, the mass fraction of the cellulose aqueous dispersion is 0.8-1.3%, the mass fraction of the sodium lignosulfonate 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 diaphragm for the lithium battery, the volume ratio of the sodium lignosulfonate aqueous solution to the cross-linking agent aqueous solution to the cellulose aqueous dispersion and the ammonium polyphosphate aqueous solution is (8-20).
According to the preparation method of the cellulose diaphragm for the lithium battery, the freeze drying process parameters are as follows: the vacuum degree is 0.1-1 Pa, the temperature is-50 to-30 ℃, and the time is 36-48 h.
In the method for preparing the cellulose diaphragm for the lithium battery, the heating treatment is to heat the cellulose diaphragm for 20 to 45min at the temperature of between 130 and 150 ℃.
According to the preparation method of the cellulose diaphragm for the lithium battery, the cellulose is soaked in the ethanol for 36-48 h (at room temperature).
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%.
According to the preparation method of the cellulose diaphragm for the lithium battery, the liquid absorption rate of the cellulose diaphragm for the lithium battery is 417-472%, and the ionic 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 freeze drying is relatively weaker than that of the diaphragm prepared by suction filtration while a plurality of pores are formed, but the tensile strength of 10-14 MPa can bear the normal operation of the diaphragm when the 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 micro calorimetric test is 63-69 KW/m 2 (ii) a The limit oxygen index of the cellulose diaphragm for the lithium battery is 32-38%, and the cellulose diaphragm can not be burnt after being continuously ignited.
The principle of the invention is as follows:
the cellulose has a large number of polar groups such as hydroxyl, carboxyl and the like, and the aqueous solution is electronegative; the sodium lignosulfonate contains a plurality of electronegative groups (phenolic hydroxyl, alcoholic hydroxyl, sulfonic acid groups and the like), and the aqueous solution is electronegative; the crosslinking agent polyamide epichlorohydrin has amino group, the N atom of the amino group has a pair of lone pair electrons, and can combine H ionized by water + Forming positive charge, and the aqueous solution is electropositive; the water solution of the water-soluble ammonium phosphate oligomer is electronegative.
The cellulose aqueous dispersion, the sodium lignosulfonate aqueous solution, the cross-linking agent aqueous solution and the ammonium polyphosphate aqueous solution are mixed and stirred to form a mixed solution, the whole solution is in a dispersion stable state (so that the whole solution can be in a high dispersion stable state, firstly, all components are aqueous solutions and are convenient to mix, secondly, all the components in the solution have electrostatic attraction effect and non-repulsion force, and the components can be stably dispersed in the solution, and the dispersion stability is a stable dispersion system according to the condition that no precipitate exists and no layering phenomenon exists in observation, and secondly, according to the condition that the Zeta potential absolute value is greater than 30).
Besides the interaction of electrostatic attraction between the sodium lignosulfonate-polyamide epoxy chloropropane and the cellulose and between the sodium lignosulfonate-polyamide epoxy chloropropane and the ammonium polyphosphate, the interaction of covalent bond (ester bond) crosslinking and hydrogen bond also exists between the sodium lignosulfonate-polyamide epoxy chloropropane and the cellulose; hydrogen bond action also exists between the sodium lignosulfonate-polyamide epichlorohydrin and the ammonium polyphosphate; the cellulose and ammonium polyphosphate have hydrogen bond (electrostatic attraction or electrostatic repulsion is obtained according to positive and negative charges tested by Zeta potential, covalent bond is obtained by infrared test, and the hydrogen bond is obtained according to that each substance contains polar functional groups such as hydroxyl, amino and the like). The sodium lignosulfonate-polyamide epichlorohydrin, the cellulose and the ammonium polyphosphate form a three-dimensional cross-linked structure, interact with each other, realize synergistic enhancement and have a flame-retardant function.
The cellulose is soaked by the ethanol, ethanol molecules replace partial water molecules to enter the cellulose molecules, the ethanol molecules are more easily volatilized in the soaking process, and the retention time between the cellulose molecules is shorter compared with that of water molecules. Because ethanol volatilizes faster than water molecules, the collapse of the bacterial cellulose with the pores occupied by ethanol molecules is reduced relative to that occupied by water, thereby forming voids and pores in the micro-topography. The treatment by using the ethanol soaking and freeze drying method is favorable for increasing the porosity of the diaphragm, and the formed pore size structure is micron-sized and nano-sized, so that the liquid absorption rate and the ionic conductivity are improved, and the performance of the battery is promoted.
Has the advantages 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, disclosed by the invention, the mechanical property is 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 invention, the environment-friendly flame retardant is added, the flame retardant performance is also greatly enhanced, and the safety performance of the lithium battery is enhanced.
Drawings
FIG. 1 is a porosity map (where PP is a commercial polypropylene separator, BC is a pure bacterial cellulose membrane, BL is a cellulose separator prepared in comparative example 1 without added ammonium polyphosphate, and BLA is a cellulose separator for a lithium battery prepared in example 1);
FIG. 2 is a mechanical tensile diagram (wherein BC is a pure bacterial cellulose membrane, BL is a cellulose membrane prepared in comparative example 1 without ammonium polyphosphate added, and BLA is a cellulose membrane for a lithium battery prepared in example 1);
fig. 3 is a thermogravimetric plot (where BC is a pure bacterial cellulose membrane, BL is a cellulose separator prepared in comparative example 1 without addition of ammonium polyphosphate, and BLA is a cellulose separator for a lithium battery prepared in example 1).
Detailed Description
The invention will be further illustrated with reference to specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention can be made by those skilled in the art after reading the teaching of the present invention, and these equivalents also fall within the scope of the claims appended to the present application.
The material sources adopted by the invention are as follows:
(1) Sodium lignosulfonate: from Shanghai Michelin Biochemical technology, inc., CAS number 8061-51-6;
(2) Aqueous polyamide epichlorohydrin solution: is from Jinhua paper industry Co Ltd, has a pH value of 3.0-6.0 and a viscosity of 30-120 mPa & s;
(3) Bacterial cellulose: is from Guilingqi Hongkie technology Co., ltd, and the cellulose content is 0.8%;
(4) Ammonium polyphosphate: from Shanghai Michelin Biochemical technology, inc., CAS number 68333-79-9.
The invention adopts the following test method:
(1) Zeta potential: the Zeta potential of the solution was tested using a Zeta potential analyzer from Marvern Panalytical Corp;
(2) Liquid absorption rate: cutting the prepared diaphragm into small wafers with the diameter of 19mm by a slicer, drying the wafers in vacuum, and measuring the mass W of the diaphragm 0 Soaking the diaphragm in electrolyte for 2h in a fume hood, taking out, measuring the mass W of the diaphragm after soaking, calculating the liquid absorption rate of the diaphragm through a formula according to the difference of the mass of the diaphragm before and after liquid absorption, and calculating the liquid absorption rate (%) = (W-W) 0 )/W 0 ×100％；
(3) Ionic conductivity: cutting the diaphragm into a circular sheet with the diameter of 19mm by using a slicing machine, assembling the circular sheet according to the sequence of the positive electrode shell → the stainless steel sheet → the diaphragm → the stainless steel sheet → the negative electrode shell, standing the circular sheet for 12 hours after packaging, then placing the circular sheet in a button cell clamp, testing the circular sheet by using an electrochemical workstation of EIS, and converting the ionic conductivity (d) of the diaphragm by using a formula: d = L/(Rb × a); where Rb denotes a bulk resistance derived from a nyquist diagram, L denotes a thickness of the separator, and a denotes a contact area between the separator and the stainless steel electrode;
(4) Tensile breaking strength: cutting the diaphragm into a rectangular sample strip of 4cm multiplied by 1cm, clamping two ends of the sample strip 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: adopting a TG Q600 thermogravimetric analyzer (TG) of the American TA company to carry out weight loss test on the diaphragm sample, wherein the mass of the sample is 5-10mg, the temperature of the sample is increased in a nitrogen environment, the temperature increase rate is 20 ℃/min, and the test range is 30-600 ℃;
(6) Rate of heat release: adopting an FTT0001 micro calorimeter of an FTT company in England, weighing 5-10mg of a sample in a crucible, measuring by using the micro calorimeter, heating in a mixed atmosphere (80% of nitrogen and 20% of oxygen), and testing the heat release rate of the diaphragm at the heating rate of 1 ℃/s;
(7) Limiting oxygen index: the diaphragm is cut into a 100mm x 10mm sample, the sample is vertically fixed in a glass combustion cylinder, the base of the sample is connected with a device capable of generating nitrogen-oxygen mixed gas flow, the top end of the sample is ignited, and the oxygen concentration in the mixed gas flow is continuously reduced until the flame is extinguished.
Example 1
A preparation method of a cellulose diaphragm for a lithium battery comprises the following specific steps:
(1) Mixing 0.8% by mass of cellulose water dispersion, 1.2% by mass of sodium lignosulfonate aqueous solution, 1.3% by mass of polyamide-epichlorohydrin aqueous solution and 5% by mass of ammonium oligomeric phosphate (the degree of polymerization is less than 20) aqueous solution, and stirring to form a mixed solution with the Zeta potential of-50 without generating precipitates;
wherein the cellulose is bacterial cellulose which is soaked by ethanol for 40 hours at room temperature; the volume ratio of the sodium lignosulfonate aqueous solution to the polyamide epichlorohydrin aqueous solution to the cellulose aqueous dispersion to the ammonium oligomeric phosphate aqueous solution is 8;
(2) Freeze-drying the mixed solution obtained in the step (1) for 48 hours under the conditions that the vacuum degree is 0.1Pa and the temperature is-47 ℃ to form a film, heating the film at 150 ℃ for 20min and rolling the film to the thickness of 110 mu m to obtain the cellulose diaphragm for the lithium battery;
the prepared cellulose diaphragm for the lithium battery has the porosity of 80 percent (shown in figure 1), the liquid absorption rate of 472 percent and the ionic conductivity of 3mS cm -1 Tensile break strength of 14MPa (as shown in FIG. 2), initial decomposition temperature of 156.9 deg.C, epitaxy termination temperature of 282.2 deg.C, weight loss of 60% at 500 deg.C (as shown in FIG. 3), and heat release rate of 67KW/m 2 (ii) a The prepared cellulose diaphragm for the lithium battery has the limiting oxygen index of 36 percent, and cannot be combusted after continuous ignition.
Comparative example 1
A method for preparing a cellulose diaphragm, which is substantially the same as that in example 1, except that no ammonium oligomeric phosphate aqueous solution is added in the step (1); the Zeta potential of the mixed solution obtained after fully stirring in the step (1) is-27, and no precipitate is generated;
the porosity of the cellulose membrane was 66% (as shown in FIG. 1), the liquid absorption was 220%, and the ion concentration was 220%The conductivity was 2.1mS · cm -1 Tensile break strength of 6MPa (as shown in FIG. 2), initial decomposition temperature of 249.7 ℃ and epitaxy termination temperature of 339 ℃ and weight loss of 88% at 500 ℃ (as shown in FIG. 3), and heat release rate of 140KW/m 2 (ii) a The limiting oxygen index of the cellulose membrane was 16.6% and continued ignition was allowed to burn.
Comparing comparative example 1 with example 1, it can be seen that the porosity, liquid absorption rate and ionic conductivity of the cellulose diaphragm prepared in comparative example 1 are all lower than those of example 1, because no oligomeric ammonium phosphate aqueous solution is added in comparative example 1, the zeta potential absolute value is smaller than that of example 1, the solution stability is slightly poor, and new chemical bonds are formed by adding the oligomeric ammonium phosphate solution, which is beneficial to 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 the strength of the film was enhanced only by sodium lignosulfonate itself and intermolecular covalent crosslinking without adding ammonium oligophosphate, and the rate of heat release from combustion of the film was increased without adding a flame retardant, and there was no flame retardant effect.
Comparative example 2
A method of producing a cellulose membrane, substantially as in example 1, except that ammonium oligomeric phosphate in step (1) is replaced with ammonium mesopolyphosphate (having a degree of polymerization of 30-n-50); the Zeta potential of the mixed solution obtained after fully stirring in the step (1) is-22, and no precipitate is generated;
the prepared cellulose diaphragm has the porosity of 31 percent, the liquid absorption rate of 120 percent and the ionic conductivity of 0.9 mS-cm -1 Tensile break strength of 1.4MPa, initial decomposition temperature of 164.3 ℃, epitaxial termination temperature of 277.4 ℃, weight loss of 55% at 500 ℃ and heat release rate of 61KW/m 2 (ii) a The limiting oxygen index of the cellulose membrane was 40.1%, and it did not burn after continuous ignition.
Comparing comparative example 2 with example 1, it can be seen that the porosity, liquid absorption rate and ionic conductivity of the cellulose diaphragm prepared in comparative example 2 are all obviously lower than those of example 1, because the cellulose diaphragm prepared in comparative example 2 has smaller pore diameter and ammonium polyphosphate in which 30< n <50 blocks part of pores; the tensile break strength of comparative example 2 is also significantly lower than that of example 1, because the ammonium polyphosphate 30< n <50 is poorly soluble in water, the mixed solution is unstable, and when a film is formed, the ammonium polyphosphate cannot be well fused with cellulose to produce an effective effect, but can block effective interaction between other components, so that the strength of the prepared composite diaphragm is reduced.
Comparative example 3
A method for preparing a cellulose diaphragm, which comprises the steps basically same as example 1, but is different from the steps in that ammonium oligomeric phosphate in the step (1) is replaced by high ammonium polyphosphate (the degree of polymerization is more than 1500); the Zeta potential of the mixed solution obtained after fully stirring in the step (1) is-19, and no precipitate is generated;
the obtained cellulose membrane has porosity of 27%, liquid absorption rate of 113%, and ionic conductivity of 0.74mS cm -1 Tensile break strength of 1.2MPa, initial decomposition temperature of 163.1 ℃, epitaxial termination temperature of 274.7 ℃, weight loss of 52% at 500 ℃ and heat release rate of 59KW/m 2 (ii) a The limiting oxygen index of the cellulose membrane was 43.3% and continued ignition failed to burn.
Comparing comparative example 3 with example 1, it can be seen that the porosity, liquid absorption rate and ionic conductivity of the cellulose diaphragm prepared in comparative example 3 are all obviously lower than those of example 1, because the cellulose diaphragm prepared in comparative example 3 has smaller pore diameter and a part of pores can be blocked by high ammonium polyphosphate with n being more than 1500; the tensile breaking strength of comparative example 3 is also significantly lower than that of example 1, because the high ammonium polyphosphate with n >1500 is insoluble in water, the mixed solution is unstable, and when a film is formed, the high ammonium polyphosphate cannot be well fused with cellulose to generate an effective effect, but can block the effective interaction between other components, so that the strength of the prepared composite membrane is reduced.
Comparative example 4
A method for preparing a cellulose diaphragm, which is substantially the same as in example 1, except that the bacterial cellulose in the step (1) is not subjected to ethanol soaking treatment, and the finally prepared cellulose diaphragm has a porosity of 50%, a liquid absorption rate of 178%, and an ionic conductivity of 1.6mS · cm -1 Tensile break strength of 15MPa and initial decomposition temperature of 162.8The temperature of the epitaxial termination was 273.1 ℃, the weight loss at 500 ℃ was 54%, and the heat release rate was 57KW/m 2 (ii) a The limiting oxygen index of the cellulose membrane was 43.9% and continued ignition failed to burn.
Comparing comparative example 4 with example 1, it can be seen that the porosity, liquid absorption rate and 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 number of pores formed in the cellulose is smaller than that formed in the cellulose, so that a channel for efficient transmission of ions in the operation process of the lithium ion battery cannot be constructed, and the ionic conductivity is low.
Example 2
A preparation method of a cellulose diaphragm for a lithium battery comprises the following specific steps:
(1) Mixing 0.9 mass percent of cellulose water dispersion, 0.9 mass percent of sodium lignosulfonate aqueous solution, 1 mass percent of polyamide-epichlorohydrin aqueous solution and 1 mass percent of ammonium oligomeric phosphate (the polymerization degree is less than 20) aqueous solution, and stirring to form a mixed solution with the Zeta potential of-39, wherein no precipitate is generated;
wherein the cellulose is bacterial cellulose which is soaked by ethanol for 40 hours at room temperature; the volume ratio of the sodium lignosulfonate aqueous solution to the polyamide epichlorohydrin aqueous solution to the cellulose aqueous dispersion to the ammonium oligomeric phosphate aqueous solution is 10;
(2) Freeze-drying the mixed solution obtained in the step (1) for 46h to form a film under the conditions that the vacuum degree is 0.3Pa and the temperature is-45 ℃, heating for 45min at 130 ℃ after film formation, and rolling to the thickness of 90 mu m to obtain the cellulose diaphragm for the lithium battery;
the prepared cellulose diaphragm for the lithium battery has the porosity of 74 percent, the liquid absorption rate of 448 percent and the ionic conductivity of 2.6 mS-cm -1 Tensile break strength of 12.7MPa, initial decomposition temperature of 157.5 ℃, epitaxial termination temperature of 281.4 ℃, weight loss at 500 ℃ of 62%, and heat release rate of 65KW/m 2 (ii) a The prepared cellulose diaphragm for the lithium battery has the limiting oxygen index of 32 percent and can not be combusted after continuous ignition.
Example 3
A preparation method of a cellulose diaphragm for a lithium battery comprises the following specific steps:
(1) Mixing 1% by mass of cellulose aqueous dispersion, 1.1% by mass of sodium lignosulfonate aqueous solution, 1.1% by mass of polyamide epichlorohydrin aqueous solution and 2% by mass of ammonium oligomeric phosphate (the degree of polymerization is less than 20), and stirring to form a mixed solution with a Zeta potential of-31, wherein no precipitate is generated;
wherein the cellulose is bacterial cellulose which is soaked by ethanol for 48 hours at room temperature; the volume ratio of the sodium lignosulfonate aqueous solution to the polyamide epichlorohydrin aqueous solution to the cellulose aqueous dispersion to the ammonium oligomeric phosphate aqueous solution is 20;
(2) Freeze-drying the mixed solution obtained in the step (1) for 44 hours to form a film under the conditions that the vacuum degree is 0.2Pa and the temperature is-42 ℃, heating for 25min at 145 ℃ after film formation, and rolling to the thickness of 80 mu m to obtain 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 ionic 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 (ii) a The prepared cellulose diaphragm for the lithium battery has the limiting oxygen index of 32.6 percent and can not be combusted after continuous ignition.
Example 4
A preparation method of a cellulose diaphragm for a lithium battery comprises the following specific steps:
(1) Mixing 1% by mass of cellulose aqueous dispersion, 1.1% by mass of sodium lignosulfonate aqueous solution, 1.2% by mass of polyamide epichlorohydrin aqueous solution and 2% by mass of ammonium oligomeric phosphate (the degree of polymerization is less than 20), and stirring to form a mixed solution with a Zeta potential of-39, wherein no precipitate is generated;
wherein the cellulose is bacterial cellulose soaked in ethanol at room temperature for 42 h; the volume ratio of the sodium lignosulfonate aqueous solution to the polyamide epichlorohydrin aqueous solution to the cellulose aqueous dispersion to the ammonium oligomeric phosphate aqueous solution is 8;
(2) Freeze-drying the mixed solution obtained in the step (1) for 40 hours at the vacuum degree of 1Pa and the temperature of-41 ℃ to form a film, heating the film at 135 ℃ for 40 minutes, and rolling the film to the thickness of 85 micrometers to obtain the cellulose diaphragm for the lithium battery;
the prepared cellulose diaphragm for the lithium battery has the porosity of 73 percent, the liquid absorption rate of 451 percent and the ionic conductivity of 2.6mS cm -1 Tensile breaking strength of 12.3MPa, initial decomposition temperature of 155.8 ℃, epitaxial termination temperature of 287.3 ℃, weight loss of 57% at 500 ℃, and heat release rate of 63KW/m 2 (ii) a The prepared cellulose diaphragm for the lithium battery has the limiting oxygen index of 33.9 percent and can not be combusted after continuous ignition.
Example 5
A preparation method of a cellulose diaphragm for a lithium battery comprises the following specific steps:
(1) Mixing 1.1% by mass of cellulose aqueous dispersion, 1% by mass of sodium lignosulfonate aqueous solution, 1.1% by mass of polyamide epichlorohydrin aqueous solution and 3% by mass of ammonium oligomeric phosphate (the degree of polymerization is less than 20), and stirring to form a mixed solution with a Zeta potential of-47, wherein no precipitate is generated;
wherein the cellulose is bacterial cellulose which is soaked in ethanol for 36 hours at room temperature; the volume ratio of the sodium lignosulfonate aqueous solution to the polyamide epichlorohydrin aqueous solution to the cellulose aqueous dispersion to the ammonium oligomeric phosphate aqueous solution is 15;
(2) Freeze-drying the mixed solution obtained in the step (1) for 39 hours at the vacuum degree of 0.7Pa and the temperature of-38 ℃ to form a film, heating the film at 140 ℃ for 30min, and rolling the film to the thickness of 70 mu m to obtain the cellulose diaphragm for the lithium battery;
the prepared cellulose diaphragm for the lithium battery has the porosity of 72 percent, the liquid absorption rate of 437 percent and the ionic conductivity of 2.3 mS-cm -1 Tensile break strength of 11.1MPa, initial decomposition temperature of 155 ℃, epitaxy termination temperature of 284.4 ℃, weight loss of 60% at 500 ℃, and heatThe release rate is 64KW/m 2 (ii) a The prepared cellulose diaphragm for the lithium battery has the limiting oxygen index of 33.5 percent and can not be combusted after continuous ignition.
Example 6
A preparation method of a cellulose diaphragm for a lithium battery comprises the following specific steps:
(1) Mixing 1.1% by mass of cellulose water dispersion, 1% by mass of sodium lignosulfonate aqueous solution, 1.2% by mass of polyamide-epichlorohydrin aqueous solution and 3% by mass of ammonium oligomeric phosphate (the polymerization degree is less than 20) aqueous solution, and stirring to form a mixed solution with a Zeta potential of-43, wherein no precipitate is generated;
wherein the cellulose is bacterial cellulose which is soaked in ethanol for 36 hours at room temperature; the volume ratio of the sodium lignosulfonate aqueous solution to the polyamide epichlorohydrin aqueous solution to the cellulose aqueous dispersion to the ammonium oligomeric phosphate aqueous solution is 10;
(2) Freeze-drying the mixed solution obtained in the step (1) for 39 hours to form a film under the conditions that the vacuum degree is 0.5Pa and the temperature is-33 ℃, heating for 35min at 140 ℃ after film formation, 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 percent, the liquid absorption rate of 467 percent and the ionic conductivity of 2.8mS cm -1 Tensile breaking strength of 10.6MPa, initial decomposition temperature of 159.8 ℃, epitaxy termination temperature of 290 ℃, weight loss of 55% at 500 ℃, and heat release rate of 63KW/m 2 (ii) a The prepared cellulose diaphragm for the lithium battery has the limiting oxygen index of 35.8 percent and can not be combusted after continuous ignition.
Example 7
A preparation method of a cellulose diaphragm for a lithium battery comprises the following specific steps:
(1) Mixing 1.2 mass percent of cellulose water dispersion, 1.2 mass percent of sodium lignosulfonate aqueous solution, 1.1 mass percent of polyamide-epichlorohydrin aqueous solution and 4 mass percent of ammonium oligomeric phosphate (the polymerization degree is less than 20) aqueous solution, and stirring to form a mixed solution with a Zeta potential of-44 without generating precipitates;
wherein the cellulose is bacterial cellulose which is soaked in ethanol for 36 hours at room temperature; the volume ratio of the sodium lignosulfonate aqueous solution to the polyamide epichlorohydrin aqueous solution to the cellulose aqueous dispersion to the ammonium oligomeric phosphate aqueous solution is 12;
(2) Freeze-drying the mixed solution obtained in the step (1) for 37h to form a film under the conditions that the vacuum degree is 0.8Pa and the temperature is-31 ℃, heating for 40min at 135 ℃ after the film is formed, and rolling to the 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 ionic conductivity of 2.1mS cm -1 Tensile break strength of 10MPa, initial decomposition temperature of 165 deg.C, epitaxial termination temperature of 289.5 deg.C, weight loss at 500 deg.C of 58%, and heat release rate of 65KW/m 2 (ii) a The prepared cellulose diaphragm for the lithium battery has the limiting oxygen index of 36.5 percent and can not be combusted after continuous ignition.
Example 8
A preparation method of a cellulose diaphragm for a lithium battery comprises the following specific steps:
(1) Mixing 1.3 mass percent of cellulose water dispersion, 0.9 mass percent of sodium lignosulfonate aqueous solution, 1.2 mass percent of polyamide-epichlorohydrin aqueous solution and 4 mass percent of ammonium oligomeric phosphate (the polymerization degree is less than 20) aqueous solution, and stirring to form a mixed solution with the Zeta potential of-49 without generating precipitates;
wherein the cellulose is bacterial cellulose which is soaked in ethanol for 36 hours at room temperature; the volume ratio of the sodium lignosulfonate aqueous solution to the polyamide epichlorohydrin aqueous solution to the cellulose aqueous dispersion to the ammonium oligomeric phosphate aqueous solution is 20;
(2) Freeze-drying the mixed solution obtained in the step (1) for 36 hours to form a film under the conditions that the vacuum degree is 0.4Pa and the temperature is-30 ℃, heating for 35min at 145 ℃ after film formation, and rolling to the thickness of 60 mu m to obtain the cellulose diaphragm for the lithium battery;
the prepared cellulose diaphragm for the lithium battery has the porosity of 80 percent and the liquid absorption rate of 469 percent,the ionic conductivity is 2.7mS cm -1 The tensile breaking strength is 12.8MPa, the initial decomposition temperature is 162.2 ℃, the epitaxy termination temperature is 280 ℃, the weight loss at 500 ℃ is 61%, and the heat release rate is 66KW/m 2 (ii) a The prepared cellulose diaphragm for the lithium battery has the limiting oxygen index of 38 percent and can not be combusted after continuous ignition.
In addition, as can be seen from fig. 1, among the four separators, the porosity of PP is the lowest, and the porosity of the cellulose separator for the lithium ion battery is further increased on the basis of maintaining the excellent porosities of BC and BL separators, because the ammonium polyphosphate is added, a new bonding force is provided, so that the pore channel can be protected from collapsing, the high-efficiency transmission of ions in the separator is effectively ensured, and the superiority of the separator for the lithium ion battery is reflected.
Since the PP films are different in material and have no contrast, fig. 2 only compares the mechanical tensile properties of the three kinds of diaphragms BC, BL, BLA. Among the three films, the mechanical tensile property of the BC film is the worst, and the mechanical property of the BL film is improved to a certain extent compared with that of the BC film, because the two substances are combined by electrostatic force, after being heated at high temperature, the BC and the polyamide epichlorohydrin are crosslinked, and the added sodium lignosulfonate can effectively enhance the mechanical property of the BC; the mechanical property of the BLA membrane is greatly improved due to the synergistic effect of electrostatic force, hydrogen bond and covalent bond among BC, LS (sodium lignosulfonate), PAE (polyamide epichlorohydrin) and APP (ammonium polyphosphate) besides the above factors, so that the mechanical property of the BLA membrane can be greatly improved.
As can be seen from fig. 3, as the temperature increases, the BC and BL films begin to show significant weight loss at around 200 ℃, and the maximum weight loss rate temperature is 310 ℃, indicating that the BC and BL films have excellent thermal stability. With APP added to BL, BLA composite membranes show two major weight loss peaks: one is in the temperature range of 120 to 200 ℃, which can be considered as melting of APP, which as used herein is low polymerization and water soluble, which can melt rapidly at a relatively lower temperature than APP of high polymerization, and then permeate into the pores of the BC membrane, partially isolating the BC from air; the other is 20From 0 to 360 ℃, the partial decomposition attributable to BC is accompanied by decomposition of APP, which can be decomposed to NH at about 310 ℃ in general 3 、H 2 O and a dense polyphosphoric acid layer, NH 3 And H 2 The O will dilute the combustible gas and oxygen concentration to some extent, and the polyphosphoric acid layer will cover the surface of the BC fiber, preventing the continuous decomposition of the BC.
Claims (9)
1. A preparation method of a cellulose diaphragm for a lithium battery is characterized by comprising the following steps: mixing and stirring cellulose water dispersion, sodium lignosulfonate water solution, cross-linking agent water solution and ammonium polyphosphate water solution to form mixed solution, freeze-drying the mixed solution to form a film, heating and rolling the film 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, and no precipitate is generated;
the cross-linking agent is polyamide epichlorohydrin; the cellulose is bacterial cellulose soaked by ethanol; the polymerization degree of the ammonium polyphosphate is less than 20.
2. The method for preparing the cellulose diaphragm for the lithium battery as claimed in claim 1, wherein the mass fraction of the cellulose aqueous dispersion is 0.8-1.3%, the mass fraction of the sodium lignosulfonate aqueous solution is 0.9-1.2%, the mass fraction of the crosslinking 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 the cellulose diaphragm for the lithium battery, according to claim 2, is characterized in that the volume ratio of the sodium lignosulfonate aqueous solution, the cross-linking agent aqueous solution, the cellulose aqueous dispersion and the ammonium polyphosphate aqueous solution is 8-20.
4. The method for preparing the cellulose diaphragm for the lithium battery as claimed in claim 1, wherein the freeze-drying process parameters are as follows: the vacuum degree is 0.1-1 Pa, the temperature is-50 to-30 ℃, and the time is 36-48 h.
5. The method of claim 1, wherein the heat treatment is performed at a temperature of 130 to 150 ℃ for 20 to 45min.
6. The method of claim 1, wherein the soaking time of the cellulose in the ethanol is 36-48 h.
7. The method of preparing a cellulose separator for a lithium battery as claimed in any one of claims 1 to 6, wherein the porosity of the cellulose separator for a lithium battery is 70 to 80%.
8. The method of claim 7, wherein the cellulose separator for a lithium battery has a liquid absorption rate of 417 to 472% and an ionic conductivity of 2.1 to 3 mS-cm -1 。
9. The method for preparing a cellulose separator for a lithium battery as claimed in claim 8, wherein the cellulose separator for a lithium battery has a tensile breaking strength of 10 to 14MPa; 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 a micro calorimetric test is 63-69 KW/m 2 (ii) a The limit oxygen index of the cellulose diaphragm for the lithium battery is 32-38%, and the cellulose diaphragm can not be burnt after being continuously ignited.
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