EP4393020A2 - Zn-air rechargeable battery - Google Patents
Zn-air rechargeable batteryInfo
- Publication number
- EP4393020A2 EP4393020A2 EP22818103.8A EP22818103A EP4393020A2 EP 4393020 A2 EP4393020 A2 EP 4393020A2 EP 22818103 A EP22818103 A EP 22818103A EP 4393020 A2 EP4393020 A2 EP 4393020A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- air
- rechargeable
- cmc
- battery
- zinc
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 239000011701 zinc Substances 0.000 claims abstract description 99
- 239000004744 fabric Substances 0.000 claims abstract description 58
- 239000000654 additive Substances 0.000 claims abstract description 56
- 229920000742 Cotton Polymers 0.000 claims abstract description 50
- 229920002134 Carboxymethyl cellulose Polymers 0.000 claims abstract description 49
- 239000001768 carboxy methyl cellulose Substances 0.000 claims abstract description 44
- 235000010948 carboxy methyl cellulose Nutrition 0.000 claims abstract description 44
- 239000008112 carboxymethyl-cellulose Substances 0.000 claims abstract description 44
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims abstract description 41
- 230000000996 additive effect Effects 0.000 claims abstract description 37
- 229920002678 cellulose Polymers 0.000 claims abstract description 36
- 239000001913 cellulose Substances 0.000 claims abstract description 36
- 229910052725 zinc Inorganic materials 0.000 claims abstract description 35
- 239000000463 material Substances 0.000 claims abstract description 25
- 239000003792 electrolyte Substances 0.000 claims description 79
- 239000003610 charcoal Substances 0.000 claims description 57
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 35
- 239000012528 membrane Substances 0.000 claims description 35
- 229910002804 graphite Inorganic materials 0.000 claims description 23
- 239000010439 graphite Substances 0.000 claims description 23
- KEAYESYHFKHZAL-UHFFFAOYSA-N Sodium Chemical compound [Na] KEAYESYHFKHZAL-UHFFFAOYSA-N 0.000 claims description 4
- 230000015572 biosynthetic process Effects 0.000 abstract description 27
- 210000001787 dendrite Anatomy 0.000 abstract description 16
- 238000005259 measurement Methods 0.000 abstract description 11
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 92
- 210000004027 cell Anatomy 0.000 description 57
- 241000219146 Gossypium Species 0.000 description 47
- 238000000034 method Methods 0.000 description 40
- 229940105329 carboxymethylcellulose Drugs 0.000 description 39
- 235000011118 potassium hydroxide Nutrition 0.000 description 30
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 29
- 229910052760 oxygen Inorganic materials 0.000 description 29
- 239000001301 oxygen Substances 0.000 description 29
- 230000008569 process Effects 0.000 description 29
- 238000007599 discharging Methods 0.000 description 24
- 238000012360 testing method Methods 0.000 description 22
- 238000006722 reduction reaction Methods 0.000 description 21
- 229920000298 Cellophane Polymers 0.000 description 18
- 239000004743 Polypropylene Substances 0.000 description 18
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 18
- 229920001155 polypropylene Polymers 0.000 description 18
- 150000002500 ions Chemical class 0.000 description 17
- 230000001351 cycling effect Effects 0.000 description 16
- -1 polyethylene Polymers 0.000 description 16
- 230000009467 reduction Effects 0.000 description 16
- 239000000243 solution Substances 0.000 description 16
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 16
- 239000003054 catalyst Substances 0.000 description 15
- 238000006243 chemical reaction Methods 0.000 description 14
- 238000002484 cyclic voltammetry Methods 0.000 description 13
- 230000037361 pathway Effects 0.000 description 13
- 150000003839 salts Chemical class 0.000 description 12
- 239000002356 single layer Substances 0.000 description 12
- 229910052799 carbon Inorganic materials 0.000 description 11
- 230000000694 effects Effects 0.000 description 11
- 229920006395 saturated elastomer Polymers 0.000 description 11
- 238000000926 separation method Methods 0.000 description 11
- 230000008859 change Effects 0.000 description 10
- 239000010411 electrocatalyst Substances 0.000 description 10
- 230000001588 bifunctional effect Effects 0.000 description 9
- 239000011787 zinc oxide Substances 0.000 description 9
- 239000012670 alkaline solution Substances 0.000 description 8
- 238000000151 deposition Methods 0.000 description 8
- 230000008021 deposition Effects 0.000 description 8
- 239000004034 viscosity adjusting agent Substances 0.000 description 8
- 238000011161 development Methods 0.000 description 7
- 238000001704 evaporation Methods 0.000 description 7
- 230000008020 evaporation Effects 0.000 description 7
- 229910001385 heavy metal Inorganic materials 0.000 description 7
- 238000011065 in-situ storage Methods 0.000 description 7
- 230000007774 longterm Effects 0.000 description 7
- 239000011734 sodium Substances 0.000 description 7
- 238000010351 charge transfer process Methods 0.000 description 6
- 125000004122 cyclic group Chemical group 0.000 description 6
- 230000007423 decrease Effects 0.000 description 6
- 238000000724 energy-dispersive X-ray spectrum Methods 0.000 description 6
- 238000002474 experimental method Methods 0.000 description 6
- 239000002657 fibrous material Substances 0.000 description 6
- 230000006870 function Effects 0.000 description 6
- 229910052751 metal Inorganic materials 0.000 description 6
- 239000002184 metal Substances 0.000 description 6
- 238000011056 performance test Methods 0.000 description 6
- 230000002829 reductive effect Effects 0.000 description 6
- 238000011160 research Methods 0.000 description 6
- 238000004626 scanning electron microscopy Methods 0.000 description 6
- 238000001075 voltammogram Methods 0.000 description 6
- 239000004698 Polyethylene Substances 0.000 description 5
- 230000008901 benefit Effects 0.000 description 5
- 125000003178 carboxy group Chemical group [H]OC(*)=O 0.000 description 5
- 238000003487 electrochemical reaction Methods 0.000 description 5
- 239000000835 fiber Substances 0.000 description 5
- 230000037427 ion transport Effects 0.000 description 5
- 239000000203 mixture Substances 0.000 description 5
- 239000004627 regenerated cellulose Substances 0.000 description 5
- 238000001179 sorption measurement Methods 0.000 description 5
- 238000009941 weaving Methods 0.000 description 5
- 238000010146 3D printing Methods 0.000 description 4
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 4
- 239000003513 alkali Substances 0.000 description 4
- 238000010276 construction Methods 0.000 description 4
- 230000003247 decreasing effect Effects 0.000 description 4
- 239000010410 layer Substances 0.000 description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 4
- 239000011148 porous material Substances 0.000 description 4
- 230000008961 swelling Effects 0.000 description 4
- 238000012546 transfer Methods 0.000 description 4
- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical compound [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000011230 binding agent Substances 0.000 description 3
- 230000033228 biological regulation Effects 0.000 description 3
- 230000003197 catalytic effect Effects 0.000 description 3
- 239000002738 chelating agent Substances 0.000 description 3
- 238000004090 dissolution Methods 0.000 description 3
- 239000008151 electrolyte solution Substances 0.000 description 3
- 239000003623 enhancer Substances 0.000 description 3
- 230000007613 environmental effect Effects 0.000 description 3
- 230000002349 favourable effect Effects 0.000 description 3
- 239000000499 gel Substances 0.000 description 3
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 3
- 238000013508 migration Methods 0.000 description 3
- 230000005012 migration Effects 0.000 description 3
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 description 3
- 150000002978 peroxides Chemical class 0.000 description 3
- 229920003023 plastic Polymers 0.000 description 3
- 239000004033 plastic Substances 0.000 description 3
- 229920000573 polyethylene Polymers 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- 230000001105 regulatory effect Effects 0.000 description 3
- 238000001878 scanning electron micrograph Methods 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 230000001629 suppression Effects 0.000 description 3
- 230000002195 synergetic effect Effects 0.000 description 3
- 230000032258 transport Effects 0.000 description 3
- 239000002759 woven fabric Substances 0.000 description 3
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 2
- 239000002000 Electrolyte additive Substances 0.000 description 2
- 239000002202 Polyethylene glycol Substances 0.000 description 2
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- VJHCJDRQFCCTHL-UHFFFAOYSA-N acetic acid 2,3,4,5,6-pentahydroxyhexanal Chemical compound CC(O)=O.OCC(O)C(O)C(O)C(O)C=O VJHCJDRQFCCTHL-UHFFFAOYSA-N 0.000 description 2
- 239000004411 aluminium Substances 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 239000001569 carbon dioxide Substances 0.000 description 2
- 229910002092 carbon dioxide Inorganic materials 0.000 description 2
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 2
- 239000010406 cathode material Substances 0.000 description 2
- 125000002091 cationic group Chemical group 0.000 description 2
- 210000000170 cell membrane Anatomy 0.000 description 2
- 239000012141 concentrate Substances 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 238000003411 electrode reaction Methods 0.000 description 2
- 238000004070 electrodeposition Methods 0.000 description 2
- 238000009950 felting Methods 0.000 description 2
- 229910021389 graphene Inorganic materials 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 2
- 238000010348 incorporation Methods 0.000 description 2
- 238000011835 investigation Methods 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 231100000252 nontoxic Toxicity 0.000 description 2
- 230000003000 nontoxic effect Effects 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 239000012466 permeate Substances 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- 229920000867 polyelectrolyte Polymers 0.000 description 2
- 229920001223 polyethylene glycol Polymers 0.000 description 2
- 239000004810 polytetrafluoroethylene Substances 0.000 description 2
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 2
- 238000009790 rate-determining step (RDS) Methods 0.000 description 2
- 238000012552 review Methods 0.000 description 2
- 238000002791 soaking Methods 0.000 description 2
- JRMUNVKIHCOMHV-UHFFFAOYSA-M tetrabutylammonium bromide Chemical compound [Br-].CCCC[N+](CCCC)(CCCC)CCCC JRMUNVKIHCOMHV-UHFFFAOYSA-M 0.000 description 2
- 239000010936 titanium Substances 0.000 description 2
- 229910052719 titanium Inorganic materials 0.000 description 2
- VNDYJBBGRKZCSX-UHFFFAOYSA-L zinc bromide Chemical compound Br[Zn]Br VNDYJBBGRKZCSX-UHFFFAOYSA-L 0.000 description 2
- 229910021511 zinc hydroxide Inorganic materials 0.000 description 2
- WKBOTKDWSSQWDR-UHFFFAOYSA-N Bromine atom Chemical compound [Br] WKBOTKDWSSQWDR-UHFFFAOYSA-N 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- 229920003043 Cellulose fiber Polymers 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- XDTMQSROBMDMFD-UHFFFAOYSA-N Cyclohexane Chemical compound C1CCCCC1 XDTMQSROBMDMFD-UHFFFAOYSA-N 0.000 description 1
- 125000002353 D-glucosyl group Chemical group C1([C@H](O)[C@@H](O)[C@H](O)[C@H](O1)CO)* 0.000 description 1
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 1
- 239000005977 Ethylene Substances 0.000 description 1
- 235000009438 Gossypium Nutrition 0.000 description 1
- 235000004341 Gossypium herbaceum Nutrition 0.000 description 1
- 240000002024 Gossypium herbaceum Species 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 1
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 1
- 241000219071 Malvaceae Species 0.000 description 1
- 229910003271 Ni-Fe Inorganic materials 0.000 description 1
- 229920000604 Polyethylene Glycol 200 Polymers 0.000 description 1
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 1
- 239000011865 Pt-based catalyst Substances 0.000 description 1
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 1
- AHJLBPMGFAQMTP-UHFFFAOYSA-N [K].[Cu].[C] Chemical compound [K].[Cu].[C] AHJLBPMGFAQMTP-UHFFFAOYSA-N 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 230000000274 adsorptive effect Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 238000000149 argon plasma sintering Methods 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 229910001451 bismuth ion Inorganic materials 0.000 description 1
- GDTBXPJZTBHREO-UHFFFAOYSA-N bromine Substances BrBr GDTBXPJZTBHREO-UHFFFAOYSA-N 0.000 description 1
- 229910052794 bromium Inorganic materials 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 239000003575 carbonaceous material Substances 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 210000003850 cellular structure Anatomy 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 150000004697 chelate complex Chemical class 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 239000008139 complexing agent Substances 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000006297 dehydration reaction Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000010494 dissociation reaction Methods 0.000 description 1
- 230000005593 dissociations Effects 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 238000000921 elemental analysis Methods 0.000 description 1
- 238000002149 energy-dispersive X-ray emission spectroscopy Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000003925 fat Substances 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 125000000524 functional group Chemical group 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000001879 gelation Methods 0.000 description 1
- 150000004676 glycans Chemical class 0.000 description 1
- XLYOFNOQVPJJNP-ZSJDYOACSA-N heavy water Substances [2H]O[2H] XLYOFNOQVPJJNP-ZSJDYOACSA-N 0.000 description 1
- 229920001903 high density polyethylene Polymers 0.000 description 1
- 238000004128 high performance liquid chromatography Methods 0.000 description 1
- 239000004700 high-density polyethylene Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- DLINORNFHVEIFE-UHFFFAOYSA-N hydrogen peroxide;zinc Chemical compound [Zn].OO DLINORNFHVEIFE-UHFFFAOYSA-N 0.000 description 1
- 230000005764 inhibitory process Effects 0.000 description 1
- 229910052741 iridium Inorganic materials 0.000 description 1
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 description 1
- 230000002427 irreversible effect Effects 0.000 description 1
- 238000009940 knitting Methods 0.000 description 1
- 229910001416 lithium ion Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000004949 mass spectrometry Methods 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 239000002048 multi walled nanotube Substances 0.000 description 1
- 239000002055 nanoplate Substances 0.000 description 1
- 239000002071 nanotube Substances 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 229910052755 nonmetal Inorganic materials 0.000 description 1
- 150000002843 nonmetals Chemical class 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 238000013021 overheating Methods 0.000 description 1
- 230000036284 oxygen consumption Effects 0.000 description 1
- 239000001814 pectin Substances 0.000 description 1
- 229920001277 pectin Polymers 0.000 description 1
- 235000010987 pectin Nutrition 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 229920001282 polysaccharide Polymers 0.000 description 1
- 239000005017 polysaccharide Substances 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 229940093932 potassium hydroxide Drugs 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000007639 printing Methods 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 229910052707 ruthenium Inorganic materials 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- 238000001542 size-exclusion chromatography Methods 0.000 description 1
- 150000003384 small molecules Chemical class 0.000 description 1
- 159000000000 sodium salts Chemical class 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000002336 sorption--desorption measurement Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
- 239000001993 wax Substances 0.000 description 1
- 229940102001 zinc bromide Drugs 0.000 description 1
- 229940007718 zinc hydroxide Drugs 0.000 description 1
- 229940105296 zinc peroxide Drugs 0.000 description 1
- NWONKYPBYAMBJT-UHFFFAOYSA-L zinc sulfate Chemical compound [Zn+2].[O-]S([O-])(=O)=O NWONKYPBYAMBJT-UHFFFAOYSA-L 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/24—Electrodes for alkaline accumulators
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/24—Electrodes for alkaline accumulators
- H01M4/244—Zinc electrodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/661—Metal or alloys, e.g. alloy coatings
-
- 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
Definitions
- the invention relates to an environmentally friendly high performance prototype of rechargeable Zn-air battery using cellulose based biodegradable matters as additive and diaphragm is reported.
- a preferred battery comprises a heavy metal free cell containing non-toxic, commercially available biodegradable feedstock.
- CMC-Na, Mn carboxymethyl cellulose sodium salt
- the applied catalysts can be monofunctional by catalyzing the OER [Park, J.E. et al. Optimization of cell components and operating conditions in primary and rechargeable zinc-air battery, J. Ind. Eng. Chem. 69 (2019) 161—170.] or the ORR [Stephens, I.E.L. et al. Understanding the electrocatalysis of oxygen reduction on platinum and its alloys, Energy Environ. Sci.
- the metal-free catalysts that can be alternatives for constructing environmental friendly cells, are usually modified carbon nanotubes and graphene [Yang, H.B. et al. Identification of catalytic sites for oxygen reduction and oxygen evolution in N-doped graphene materials: Development of highly efficient metal-free bifunctional electrocatalyst, Sci. Adv. 2 (2016) el501122.], and these carbon-based materials are widely used as a mechanically robust skeleton of both types of catalysts (metal-free and metal-based) [21'Wang, YJ. et al.
- the other big challenge is how to control the morphology of the zinc deposition upon charging.
- the morphology of the deposition depends on the operation conditions (such as current density) but it is also influenced by the composition of the electrolyte and quality of the membrane and presence of additives. For instance, it was found that the tetrabutylammonium bromide [Wang J.M. et al. Effects of bismuth ion and tetra- butylammonium bromide on the dendritic growth of zinc in alkaline zincate solutions, J.
- the concentration of the KOH is 2 to 10 M, preferably about 6 M, and the concentration of the [Zn(OH)4] 2 ' is 0.1 to 0.5 M, preferably 0.25 M at the initial stage of the battery.
- the additives are preferably chelating the Zn(ll) ions.
- the rechargeable Zn-air alkaline battery is made of polyethylene and cotton cloth is the diaphragm of the electrode.
- the anode comprises a Zn plate
- the air cathode comprises or consists of graphite and charcoal
- the separator is a semi-permeable membrane made of regenerated cellulose (cellophane)
- the electrolyte comprises KOH and [Zn(OH)4] 2 ' and CMC, preferably CMC-Na as an additive.
- the concentration of the KOH is 2 to 10 M, preferably about 6 M, and the concentration of the [Zn(OH)4] 2 ' is 0.1 to 0.5 M, preferably 0.25 M at the initial stage of the battery.
- the battery has an initial cell potential of 1.1 V to 1.5 V, preferably 1.2 V to 1.4 V.
- the battery during normal operation of the battery no H2 gas is developed.
- the anode comprises a Zn plate
- the air cathode comprises or consists of graphite and charcoal
- the separator is a semi-permeable membrane made of regenerated cellulose (cellophane)
- the electrolyte comprises KOH and [Zn(OH)4] 2 ' and CMC-Na as additive.
- Cotton is a fiber that is made of fibers growing in a protective case around the seeds of the cotton plants of the genus Gossypium in the mallow family Malvaceae.
- the fiber is almost pure cellulose, and can contain minor percentages of waxes, fats, pectins, and water.
- Cotton fabric is a type of fabric made from soft cotton fibres. Cloth is fabric which is made by weaving or knitting, preferably weaving a substance such as cotton.
- Friting means herein combining fibrous material and pressing it into a layer wherein said fibrous material is preferably cellulose fibers herein.
- “Cycle” refers to the process of charging a rechargeable battery and discharging it as required into a load.
- the term is typically used to specify a battery's expected life, as the number of charge cycles affects life more than the mere passage of time.
- Figure 9 shows a chart with features of a preferred embodiment of the rechargeable battery.
- Figure 12 The gross electrochemical processes of the cell in case of 4 electron pathway and 2 electron pathway (or peroxide pathway)
- Figure 13a The energy efficiency versus cycle number of 3D-printed Zn-air battery filled with KOH saturated with K2[Zn(OH)4] electrolyte without additive.
- Figure 13b The energy efficiency versus cycle number of 3D-printed Zn-air battery filled with KOH saturated with K2[Zn(OH)4] electrolyte containing 2 m/v % CMC-Na (90 kDa, f: 0.7).
- Figure 13c The energy efficiency versus cycle number of 3D-printed Zn-air battery filled with KOH saturated with K2[Zn(OH)4] electrolyte containing 2 m/v % CMC-Na (250 kDa, f: 1.2).
- Figure 13d The energy efficiency versus cycle number of 3D-printed Zn-air battery filled with KOH saturated with K2[Zn(OH)4] electrolyte containing 2 m/v % CMC-Na (250 kDa, f: 0.7).
- Figure 14 The long-term charging of the prototype cell.
- Figure 15 The EDS spectrum of the Zn electrode before use.
- Figure 16 The EDS spectrum of the Zn electrode without additive.
- Figure 17 The EDS spectrum of the Zn electrode with CMC-Na (90 kDa f:0.7).
- Figure 18 The EDS spectrum of the Zn electrode with CMC-Na (250 kDa f : 1.2).
- the charge transfer process should be the rate-determining step in the overall recharging process.
- Zn-air rechargeable battery with heavy metal-free, charcoal-based air cathode comprising carboxymethyl-cellulose in the electrolyte is a useful to solve problems of the art.
- Zn-air rechargeable battery with heavy metal-free, charcoal-based air cathode comprising cellulose-based, preferably woven, diaphragm or separator, preferably cotton fabric, in particular woven cotton fabric, as a single layer as diaphragm or separator is also particularly useful.
- the present inventors have also surprisingly found that the construction of a Zn-air rechargeable battery with heavy metal-free, charcoal-based air cathode comprising carboxymethyl-cellulose in the electrolyte wherein a cellulose-based diaphragm or separator, preferably cotton fabric, in particular as a single layer diaphragm or separator is applied, have preferred features.
- the invention relates to Zn-air rechargeable batteries with these features.
- the invention relates to a novel rechargeable Zn-air alkaline battery developed with charcoal/graphite cathode and zinc anode. Using of charcoal/graphite cathode, continuous oxygen supply has been achieved and it has been demonstrated by long-term performance tests that it is an appropriate electrode in the rechargeable Zn-air alkaline battery.
- the overall anode reaction is wherein d is discharging and c is charging.
- a charcoal/graphite air electrode is applied.
- Charcoal is necessary to maintain stable, stationary state of the air electrode by adsorption/desorption of oxygen (scheme 2). Advisably a suitable amount of charcoal is to be applied.
- the cathode process is a two electron process in the present setting (e.g. CMC additive) contrary to the expectable four electron process usual in prior art batteries.
- a cellulose based, preferably woven, preferably single layer separator in particular woven cotton separator has been found particularly useful.
- carboxymethyl cellulose additive was applied in the lye and a single layer cellulose based diaphragm, preferably a cellulose based diaphragm was applied.
- anode (and cathode) processes have been accelerated.
- the present inventors have worked in the opposite direction and found that it is advantageous if the rate-limiting step is the charge transfer.
- Carboxymethyl cellulose-based polyelectrolyte as cationic exchange membrane for zinciodine batteries, Heliyon, 6 (2020) e05391.].
- the charcoal owing to its adsorptive nature serves as a reservoir for the “in situ” evolved oxygen in the cathode during the OER reaction.
- the higher viscosity of the electrolyte by addition of CMC-Na can also aid keeping oxygen in the charcoal.
- the separator also has a role in the cell providing the appropriate ion conductivity and separation of the electrodes [Abbasi, A. et al. Poly(2,6-Dimethyl-1,4-Phenylene Oxide)-Based Hydroxide Exchange Separator Membranes for Zinc-Air Battery, Int. J. Mol. Sci. 20 (2019) 3678-3695. https://doi.org/10.339G/ijms20153678 Tsehaye M.T. et al, Modified Porous Membranes for Zinc Slurry-Air Flow Battery, Molecules 26 (2021) 4062- 4082.].
- the present inventors have used cellulose based, single layer separator for the zinc-air cell.
- a single layer cellulose-based diaphragm or separator, preferably cotton fabric, and carboxymethyl-cellulose additive to the electrolyte were applied.
- the swollen cotton cloth proved to be a particularly suitable cell membrane.
- Woven cotton has a regular (well regulated) pore size which in turn regulates ion migration, whereas is fully permeable for water and hydroxide ions.
- a first problem is the capturing of CO2from the air, resulting in the formation of undesirable precipitate giving rise to uncontrolled change in the composition of the electrolyte solution, whereas a second major problem is the evaporation of water from the electrolyte.
- the present inventors have used an open charcoal based cathode in which the "in situ" forming C is captured by adsorption during the charging process. In this way the small amount of supplementary oxygen is freely entering to the cathode giving rise to limited air transport.
- the oxygen consumption of the rechargeable batter of the invention is low therefore a very limited amount of air and therefore carbon-dioxide enters only into the battery which if favorable to avoid carbonate formation. Even at high additive chain length and concentration (as well as viscosity) the heat development and water evaporation are of low lever which are important advantages.
- the evaporation of water can be regulated by the viscosity of the electrolyte.
- the higher viscosity decreases the ion transport but usually decreases the efficiency of the secondary batteries [Tsehaye, M. T et al. Membranes for zinc-air batteries: Recent progress, challenges and perspectives. J. Power Sources 2020, 475, 228689,].
- the selection of a proper viscosity modifier is important.
- CMC-Na carboxymethyl cellulose sodium salts
- the CMC-Na salts were found to have double functions: (i) increase the viscosity of the electrolyte thus decreasing the rates of evaporation of water and (ii) control the electrochemical reactions to form stable complex with the Zn 2+ ions minimizing the zinc deposit formation. Based on these results, the relatively lower viscosity of electrolyte and higher functionality are of CMC-Na salts may be more preferable for a higher-performance battery.
- polypropylene cell parts were prepared preferably by 3D-printing.
- 3D printing the geometry can be easily adjusted.
- the wall of the cell can be made by any other way which is suitable for forming it, e.g. by molding or carving.
- the electrode has a flat arrangement.
- the graphite/charcoal air 20 cathode is present in a flat 50 frame to provide mechanical strength
- the 30 separator to separate the cathode space from the anode space is cellulose and the anode comprises a flat 11 Zn plate surrounded by a 70 reservoir.
- the 11 Zn plate is fixed by a 53 PP arm.
- the 50 PP frame may have 54 PP leg for fixing or engagement of the 11 Zn plate (Zn electrode).
- the wall of the 70 reservoir is made of a flexible material withstanding high alkali solutions and also may be made of or covered by dermatologically tolerable material on the outer side and/or may be covered by a material withstanding high alkali solutions in the inner side.
- cotton is a skin-friendly material while is capable of withstanding alkali solution.
- Cotton cloth was a woven fabric cotton having a thickness of about 0.2 mm (300 g/m 2 density and 1.5 g/cm 3 ).
- the Coulomb efficiency has been found to be 100% during the whole experiment. This finding shows an excellent balance between the charging and discharging cycles in the operating battery. No change in the mass of the Zn- electrode was found. Based on these results, the swollen cotton cloth membrane properly stabilized the ion transport hence, highly regulates the reactions on the surface of the Zn electrode. Such regulation is necessary to avoid the formation of an undesired metallic Zn dendrite formation (deposites) on the surfaces the electrode. With the applied parameters (2 mAcm' 2 charging current and 10 min time frame) the capacity was found to be 2.63 mAh. While similar current densities were applied in several Zn-Air battery studies, the high coulombic and energy efficiency of the present electrode is surprisingly high [Yang, H.B.
- Figure 3 shows the cycling test (a, b) and the Coulomb efficiency (c) of the 3D-printed rectangular Zn-air rechargeable battery, equipped with cotton cloth membrane.
- the current density was kept to be constant, i.e., 2 mAcm" 2 , while the time limit if charging and discharging was set to 10 min.
- the cycling test and the coulomb efficiency of the 3D-printed rectangular Zn-air rechargeable battery, equipped with cotton cloth membrane is shown in Fig. 3.
- the current density was kept constant at 2 mAcm" 2 , while the time limit of charging and discharging was set to 10 min (1000 cycle).
- the most common electrolyte for the Zn-air batteries is KOH solution of different concentrations.
- the first problem is the capturing of COz from the air, resulting in the formation of undesirable precipitate giving rise to uncontrolled change in the composition of the electrolyte solution.
- the second major problem is the evaporation of water from the electrolyte
- the evaporation of water can be regulated by the viscosity of the electrolyte.
- the higher viscosity decreases the ion transport but usually decreases the efficiency of the secondary batteries.
- the selection of a proper viscosity modifier is important.
- CMC-Na carboxy methyl cellulose Na salts
- first CMC-Na salt was tested with lower molecular weight (90 kDa, 0.7 functionality).
- the cyclic performance test was carried out up to 400 cycles, as seen in Fig 4.
- Figure 4 shows a cycling test and coulomb efficiency of 3D-printed Zn-air battery filled with KOH saturated with K2[Zn(OH>4] electrolyte containing 2 m/v % CMC-Na (90 kDa with 0.7 functionality).
- CMC electrolyte
- lye electrolyte
- CMC-Na CMC-Na
- the additive is essential to reduce rate of electrode processes in particular Zn incorporation which would otherwise result in dendrite formation - a problem solved by the present invention. Also long term reliable functioning, which an unexpected favorable feature of the battery of the invention, cannot be achieved without the additive.
- the additive is important and - taking into account the effect of the presence of the additive - even the 80% value, or even the 60 and 64%, taking into account the size (length) of CMC, are well beyond expectations.
- the stretched exponential function is suitable for the mathematical modeling of different disordered systems such as electrochemical reactions with a broad activation energy distribution [D.C. Johnston, Stretched exponential relaxation arising from a continuous sum of exponential decays, Phys. Rev. B 74 (2006)].
- Equation 1 The following equation was fitted (equation 1) to the 200 th cycle of all the cycling performance tests.
- Z1E/ and ZIEs are the potential change
- kf and k s are the rate coefficients of the fast and slow decay, respectively.
- the ft is the stretching exponent, while the is the terminal potential.
- the stretching exponent increases with the molecular weight of the CMC-Na.
- the black solid lines represent the fitted curves by Eq. (1) while the fitting parameters are shown in the tables.
- Figure 7 shows voltammograms obtained in the absence and in the presence of CMC-Na additives.
- both anodic and cathodic peak positions are around 0.061 V and -0.128 V, with peak separations approximately 0.2 V.
- the cathodic shifts are higher than the anodic ones but their values are very similar. By applying the shifts, the peak separation can be calculated. Low separation is preferable since usually, it means low over potential.
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Abstract
The invention relates to a rechargeable Zn-air alkaline battery with air cathode and zinc anode, said alkaline battery comprising cellulose-based material as diaphragm. Said cellulose-based fabric is preferably woven or felted, preferably woven cotton diaphragm. The invention also relates to a rechargeable Zn-air alkaline battery with air cathode and zinc anode, said alkaline battery comprising carboxymethyl cellulose additive. Using cotton cloth as diaphragm 100 % Coulomb efficiency was detected during the entire measurement (more than 1000 cycles), while the weight of zinc electrode was constant and its surface remained smooth to solve the problem of dendrite formation.
Description
Zn-Air Rechargeable Battery
FIELD OF THE INVENTION
The invention relates to an environmentally friendly high performance prototype of rechargeable Zn-air battery using cellulose based biodegradable matters as additive and diaphragm is reported. A preferred battery comprises a heavy metal free cell containing non-toxic, commercially available biodegradable feedstock. The fix cell geometry preferably is granted by 3D-printing. Charging/discharging cycle tests were performed using cotton lattice or cellophane diaphragms separately. In a particular embodiment the presence of carboxymethyl cellulose sodium salt (CMC-Na, Mn: 90 kDa and 250 kDa with f=0.7 or f=1.2 average functionality) additives in the electrolyte was also tested. Significant difference was found between the cells operated with and without additives. Two main benefits of the application of CMC-Na salts were observed: (i) by increasing the viscosity of the electrolyte the rate of evaporization of the water was decreased; (ii) owing to the higher viscosity of the lye and the good chelating agent properties of the carboxyl functional groups more stable cell operation was obtained. Using cotton lattice as diaphragm 100 % Coulomb efficiency was detected during the entire measurement (more than 1000 cycles), while the weight of zinc electrode was constant and its surface remained smooth. Additional cyclic voltammetry tests were also carried out to investigate the electrode processes. The change of the electrode surface was monitored by scanning electron microscopy. Preferably dendrite formation is reduced or no dendrite formation was observed on the zinc anode.
BACKGROUND ART
In the last decades the use of green, renewable energy and thus the storage and utilization of the energy have become one of the most important and developing research area in the energy sector. Owing to their high energy density (more than 1080 Wh/kg) nature and safely operation zinc-air batteries have attracted much attention as possible alternative solutions [Armand, M. and Tarascon, J.M., Building better batteries, Nature 451 (2008) 652- 657]. However, the morphology control of zinc deposition upon charging and ensuring appropriate catalyst(s) for the oxygen evolution/reduction reactions (OER/ORR) are the two main challenges concerning zinc-air cells ’[Lee J.-S. et al. Metal-Air Batteries with High Energy Density: Li-Air versus Zn-Air, Adv. Energ. Mat. 1 (2010) 34-50.].
The inhibition of dendritic deposition promoted by modification of electrolyte [Kim, M. et al. Effect of a bromine complex agent on electrochemical performances of zinc electrodeposition and electrodissolution in Zinc- Bromide flow battery, Journal of Power Sources 438 (2019) 227020] can be the cheapest and easiest way from the various available methods such as anode engineering, ion transfer control, electric field regulation, etc. Nevertheless, from the cathode point of view, construction of an environmental friendly zinc-air cell is a serious challenge. The reversibility of oxygen evolution/reduction reactions is essential for improving the performance of a zinc-air batteries. Furthermore, the adsorption of the oxygen on the different electro catalysts affects the type of the ORR reaction (direct four- and two-electron pathways) [ Fang, W. et al., Recent progress and future perspectives of flexible Zn-Air batteries, Journal of Alloys and Compounds 869 (2021) 158918.]. The applied catalysts can be monofunctional by catalyzing the OER [Park, J.E. et al. Optimization of cell components and operating conditions in primary and rechargeable zinc-air battery, J. Ind. Eng. Chem. 69 (2019) 161—170.] or the ORR [Stephens, I.E.L. et al. Understanding the electrocatalysis of oxygen reduction on platinum and its alloys,
Energy Environ. Sci. 5 (2012) 6744-6762.] reactions, while the bifunctional catalyst can promote both reactions [Clark, S. et al. Rational Development of Neutral Aqueous Electrolytes for Zinc-Air Batteries, ChemSusChem 10 (2017) 4735-4747.]. Among the catalysts developed so far, metal-based and metal-free can be distinguished. The metal-based ones usually contain heavy metal ions such as platinum, ruthenium, iridium, cobalt etc. [Huang Z.F. et al. Design of Efficient Bifunctional Oxygen Reduction/Evolution Electrocatalyst: Recent Advances and Perspectives, Adv. Energy Mater. 7 (2017) 1700544.]. The metal-free catalysts that can be alternatives for constructing environmental friendly cells, are usually modified carbon nanotubes and graphene [Yang, H.B. et al. Identification of catalytic sites for oxygen reduction and oxygen evolution in N-doped graphene materials: Development of highly efficient metal-free bifunctional electrocatalyst, Sci. Adv. 2 (2016) el501122.], and these carbon-based materials are widely used as a mechanically robust skeleton of both types of catalysts (metal-free and metal-based) [21'Wang, YJ. et al. Compositing doped-carbon with metals, non-metals, metal oxides, metal nitrides and other materials to form bifunctional electrocatalysts to enhance metal-air battery oxygen reduction and evolution reactions, Chem. Eng. J. 348 (2018) 416-437.]. Application of binders are necessary for the preparation of these type catalysts. However, degradation of the binder can take place during the operation of the cell, decreasing the lifetime of zinc-air battery [Fan, Y. et al. Ni-Fe Nitride Nanoplates on Nitrogen-Doped Graphene as a Synergistic Catalyst for Reversible Oxygen Evolution Reaction and Rechargeable Zn-Air Battery, Small 13 (2017) 1700099.], Therefore, to handle this problem, binder-free, self-supported catalysts were also developed [Xu, N. Flexible self-supported bi-metal electrode as a highly stable carbon- and binder-free cathode for large-scale solid-state zinc-air batteries, Appl. Catal. B Environ. 272 (2020) 118953. Radenahmad, N. et al. A durable rechargeable zinc-air battery via self-supported MnOx-S air electrode, S. J. Alloys Comp. 883 (2021) 160935.].
Wu Jingkun et al. have reviewed carbon based cathode materials for rechargeable zinc-air batteries and suggest that carbon based nanotubes (CNT) are with hierarchical structures are favorable due to the high conductivity and surface area. Another effective strategy proposed is providing metallic characteristics to carbon and it is also found that metal-nitrogen-carbon composite catalyst has been found as one of the most promising candidates. However, the authors do not advise using charcoal without additional catalyzators. [Wu Jingkun et al. Carbonbased cathode materials for rechargeable zinc-air batteries: From current collectors to bifunctional integrated air electrodes Carbon Energy. 2020;2:370-386.]
As it is mentioned above, in addition to promotion of OER/ORR reactions the other big challenge is how to control the morphology of the zinc deposition upon charging. The morphology of the deposition depends on the operation conditions (such as current density) but it is also influenced by the composition of the electrolyte and quality of the membrane and presence of additives. For instance, it was found that the tetrabutylammonium bromide [Wang J.M. et al. Effects of bismuth ion and tetra- butylammonium bromide on the dendritic growth of zinc in alkaline zincate solutions, J. Power Sources 102 (2001) 139-143, https://doi.org/10.1016/ S0378- 7753(01)00789-3] or low molecular weight poly(ethylene glycol-diol) (PEG200) [SJ. Banik, R. Akolkar, Suppressing dendrite growth during zinc electrodeposition by PEG-200 additive, J. Electrochem. Soc. 160 (2013) D519-D523] dissolved in the electrolyte could reduce dendrite formation.
As it turns out from the background literature on zinc-air battery, the cells investigated consisted of one or more special components (heavy metals, e.g. Pt based catalysts) to ensure the sufficient performance. However, these
components are very expensive and/or inaccessible on the market and are not compatible with the aspirations of green development. Recently, the research group of the present inventors have reported a rechargeable zinc- air cell [Nagy, T. et al. Environmentally friendly Zn-air rechargeable battery with heavy metal free charcoal based air cathode, Electrochim. Acta 368 (2021) 137592] using binder and heavy metal-free pure charcoal cathode obtaining good charging/discharging performance. The dendritic deposition on the surface of Zn anode was also reduced by applying dicarboxyl polyethylene glycol) additive in the electrolyte. Thus, it was demonstrated that using strong chelating agents, e.g., dicarboxyl polyethylene glycol) (PEG-(COOH)2) the rate of the charge transfer process could be reduced and the deposit formation could be eliminated even at long-term cyclic performance. The problem of complexity of such electrode may provide difficulties in certain applications.
As additives in the electrolyte, Yang, C. et al. have examined the effects of carboxymethyl cellulose on the electrochemical characteristics and dendrite growth of zinc in alkaline solution [Yang, C. et al. Effects of Carboxymethyl Cellulose on the Electrochemical Characteristics and Dendrite Growth of Zinc in Alkaline Solution, Journal of The Electrochemical Society, 163 (9) A(2016) 1836-A1840]. While the authors have found that CMC had a positive effect on dendrite formation, in general they conclude that "considering the high content of CMC used in the current work, the ability of CMC to suppress zinc dentrite growth is obviously not very strong".
The most common electrolyte for the Zn-air batteries is KOH solution of different concentrations. However, there are two major problems associated with the presence of strong alkaline solutions. The first problem is the capturing of COz from the air, resulting in the formation of undesirable precipitate giving rise to uncontrolled change in the composition of the electrolyte solution. The second major problem is the evaporation of water from the electrolyte.
Rechargeable Zn-air batteries often suffer from side reactions, like H2 production and overheating which decrease energy efficiency. Zhang et al. after a review of the literature have found in their review of Zn-air batteries published in 2019 that "due to large ORR and OER overpotentials, even rechargeable Zn-air batteries using state-of-the-art cathode electrocatalysts have a low round-trip energy efficiency of <65% under real working conditions", contrary to conventional lithium-ion batteries (typically having an energy efficiency of 80- 90%) [Zhang J et al. Zinc-air batteries: are they ready for prime time? Chem Sci. 2019 Sep 24;10(39):8924-8929.]. Also the authors suggest that achieving a high coulombic efficiency of larger than 80% would be a goal of the future.
Thus, there is still a need in the art to provide a reliable, heavy metal free, thus non-toxic and environmentfriendly, commercially available, low-cost Zn-air secondary battery.
The object of the present invention is to provide a Zn-air rechargeable battery which solves problem arising with such batteries of the prior art.
The present inventors have found that in an environmental friendly rechargeable Zn-air alkaline battery comprising charcoal-based air cathode have surprisingly high coulombic efficiency and reduced dendritic formation on the Zn electrode surface.
BRIEF DESCRIPTION OF THE INVENTION
The invention relates to a rechargeable Zn-air alkaline battery comprising charcoal-based air cathode essentially consisting of a graphite body or member surrounded by charcoal, as well as a Zn-anode said alkaline battery
comprising a single layer cellulose-based material, preferably fabric, as diaphragm said Zn-air alkaline battery having alkaline electrolyte comprising, as additive, a gel forming viscosity enhancer, preferably a cellulose based carboxyl-group comprising additive, in particular carboxymethyl cellulose in the electrolyte, e.g. in both sides of the diaphragm or at least on the anode side of the diaphragm. Preferably the electrolyte comprises an alkaline solution, preferably KOH as disclosed herein.
Preferably the diaphragm is a single layer separator.
In particular the invention relates to a rechargeable Zn-air alkaline battery with air cathode and zinc anode, said alkaline battery comprising cellulose-based fabric material as diaphragm. Preferably the diaphragm comprises a single layer of the cellulose based fabric material. Said cellulose-based fabric is preferably woven or felted, preferably woven. Said cellulose-based fabric is preferably a cloth.
In a preferred embodiment the invention relates to a rechargeable Zn-air alkaline battery with charcoal-based air cathode and zinc anode, said alkaline battery comprising woven cellulose-based fabric material, preferably cotton cloth membrane material as diaphragm (separator), wherein the electrolyte comprises KOH and [Zn(OH>4]2- and carboxymethyl cellulose (CMC), preferably carboxymethyl cellulose natrium (CMC-Na), as an additive.
In a preferred embodiment the battery has an initial cell potential or working potential of 1.2 V to 1.6 V, e.g 1.2 V to 1.6 V, preferably 1.2 to 1.4 V. CMC is preferably CMC-Na.
Preferably the electrolyte comprises 0.5 to 5 m/v%, more preferably 1 to 4 or 1 to 3 m/v % CMC.
Preferably the concentration of the KOH is 2 to 10 M, preferably about 6 M, and the concentration of the [Zn(OH)4]2- is 0.1 to 0.5 M, preferably 0.25 M at the initial stage of the battery.
The invention also relates to a rechargeable Zn-air alkaline battery with air cathode and zinc anode, said alkaline battery comprising cotton cloth membrane material as diaphragm. A cotton cloth membrane is highly preferred. Said cellulose based fabric is preferably different from a sheet or film of regenerated cellulose like cellophane. A sheet or film of regenerated cellulose is neither woven nor felted, preferably not woven and cannot be considered as a fabric.
In a preferred embodiment the air cathode is a charcoal-based air cathode. Preferably in the charcoal-based air cathode the "in situ" forming O2 is captured by adsorption during the charging process.
Preferably in the air cathode a graphite member is surrounded by charcoal, wherein the surface of the charcoal catalyzes the cathode reaction. Preferably the air cathode is heavy-metal free air cathode.
In a particular embodiment the rechargeable Zn-air alkaline battery of the invention comprises charcoal-based air cathode essentially consisting of a graphite body or member surrounded by charcoal, preferably having a mass of at least of the graphite body, as well as a Zn-anode arranged in a cell wherein the anode space and the cathode space are separated by a single layer separator (diaphragm) of a cellulosed based membrane preferably a cellulosed based fabric, in particular cotton fabric, said Zn-air alkaline battery having alkaline electrolyte comprising, as additive, a gel forming viscosity enhancer, preferably a cellulose based carboxyl-group comprising additive, in particular carboxymethyl cellulose. The gel forming viscosity enhancer, preferably a cellulose based carboxyl-group comprising additive is present in the electrolyte, e.g. in both sides of the diaphragm or at least on the anode side of the diaphragm. The electrolyte comprises an alkaline solution, preferably KOH as disclosed herein.
The electrode comprises electrolyte ions for which the separator is permeable.
Preferably the battery has a frame e.g.a plastic frame or a flexible frame like PE frame or PP frame.
In a preferred embodiment the cell has a rectangular arrangement.
In an embodiment the electrode has a flat arrangement.
In an embodiment the electrode has a longitudial arrangement.
In an embodiment the electrode has a flexible arrangement.
The invention also relates to a rechargeable Zn-air alkaline battery with charcoal-based air cathode and zinc anode, said alkaline battery comprising cellulose-based fabric material, preferably cotton cloth membrane material as diaphragm. Said cellulose-based fabric is preferably woven or felted, preferably woven.
Preferably the electrolyte comprises carboxymethyl cellulose (CMC) as additive. Preferably the CMC is carboxymethyl cellulose natrium (CMC-Na). Preferably the electrolyte comprises 0.5 to 5 m/v%, more preferably 1 to 4 or 1 to 3 m/v % CMC, preferably CMC-Na.
Preferably the average molecular weight (MW) of the CMC is 10 to 500 kDa, more preferably 50 to 400 or 60 to 300 kDa. In an embodiment the MW of the CMC is 50 to 150 kDa, preferably 80 to 100 kDa. In a further embodiment the MW of the CMC is 150 to 300 kDa, preferably 200 to 300 kDa, preferably 220 to 280 kDa.
In an embodiment the functionality of the CMC, preferably CMC-Na, is 0.2 to 2 or 0.5 to 2 or 0.2 to 1.5 or, preferably 0.5 to 1.5 or 0.6 to 1.3. In an embodiment the functionality is 1.0 to 2.0, preferably 1.0 to 1.5.
Highly preferably the CMC is 50 to 150 kDa with a functionality of 0.5 to 2, preferably 0.5 to 1.5, preferably 1.0 to 2.0, preferably 1.0 to 1.5.
Preferably the cell of the rechargeable Zn-air alkaline battery comprises KOH solution as electrolyte.
In a preferred embodiment the electrolyte of the battery contains KOH and [Zn(OH)4]2'.
In a preferred embodiment the battery has an initial cell potential of 1.1 V to 1.5 V, preferably 1.2 V to 1.4 V. i) In a preferred embodiment in the rechargeable Zn-air alkaline battery the anode comprises a Zn plate, the air cathode comprises or consists of graphite and charcoal, the separator is a semi-permeable membrane made of cellulose based woven fabric, preferably a cotton cloth membrane, and the electrolyte comprises KOH and [Zn(OH)4]2' and carboxymethyl cellulose (CMC), preferably carboxymethyl cellulose natrium (CMC-Na), more preferably with a MW of 50 to 300 kDa (or a range as defined above) with a functionality of 0.2 to 2, preferably 0.5 to 1.5 (or a range as defined above) as an additive.
Preferably the concentration of the KOH is 2 to 10 M, preferably about 6 M, and the concentration of the [Zn(OH)4]2' is 0.1 to 0.5 M, preferably 0.25 M at the initial stage of the battery.
In a preferred embodiment the electrolyte of the battery contains KOH and [Zn(OH)4]2'.
In a preferred embodiment the battery has an initial cell potential or working potential of 1.2 V to 1.6 V, preferably 1.2 to 1.4 V.
The additives are preferably chelating the Zn(ll) ions.
In a particularly preferred embodiment in the rechargeable Zn-air alkaline battery cellulose-based woven fabric, preferably cotton cloth membrane serves as the semi-permeable membrane, i.e., the separator (or diaphragm).
Said fabric is different from regenerated cellulose.
In a preferred embodiment the electrolyte of the battery contains alkaline hydroxide solution, preferably potassium-hydroxide solution and the CMC according to the invention as additive.
Preferably in the rechargeable Zn-air alkaline battery is made of polyethylene and cotton cloth is the diaphragm of the electrode. i) In a preferred embodiment in the rechargeable Zn-air alkaline battery the anode comprises a Zn plate, the air cathode comprises or consists of graphite and charcoal, the separator is a semi-permeable membrane made of regenerated cellulose (cellophane), and the electrolyte comprises KOH and [Zn(OH)4]2' and CMC, preferably CMC-Na as an additive.
Preferably the concentration of the KOH is 2 to 10 M, preferably about 6 M, and the concentration of the [Zn(OH)4]2' is 0.1 to 0.5 M, preferably 0.25 M at the initial stage of the battery.
In the air cathode preferably the graphite is surrounded by charcoal to provide a sufficient charcoal surface. Preferably the graphite is embedded into the charcoal. Preferably the high specific surface area of the charcoal provides the catalyzing effect.
In a preferred embodiment the battery has an initial cell potential of 1.1 V to 1.5 V, preferably 1.2 V to 1.4 V. The battery during normal operation of the battery no H2 gas is developed. ii) In a preferred embodiment in the rechargeable Zn-air alkaline battery the anode comprises a Zn plate, the air cathode comprises or consists of graphite and charcoal, the separator is a semi-permeable membrane made of regenerated cellulose (cellophane), and the electrolyte comprises KOH and [Zn(OH)4]2' and CMC-Na as additive.
Preferably in the electrolyte the concentration of the KOH and [Zn(OH)4]2' is as defined in paragraph i).
In a preferred embodiment the battery has rectangular cells.
In a preferred embodiment the rechargeable Zn-air alkaline battery the charcoal-based air cathode comprises a graphite body.
DEFINITIONS
"Cellulose-based" means that the material comprises structure forming fibers which are essentially or are made of or derived from (e.g. derivatized from) "cellulose" fiber, wherein cellulose is a polysaccharide having the formula (CsHioOsJn, and consisting of a linear chain of a plurality of, e.g. several hundred to many thousands of P(l->4) linked D-glucose units.
Cotton is a fiber that is made of fibers growing in a protective case around the seeds of the cotton plants of the genus Gossypium in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor percentages of waxes, fats, pectins, and water. Cotton fabric is a type of fabric made from soft cotton fibres. Cloth is fabric which is made by weaving or knitting, preferably weaving a substance such as cotton.
A "fabric" is a material made by combining, e.g. weaving or felting, fibrous material, e.g. threads, or yarns herein preferably made of cellulose.
"Woven" means made by weaving wherein weaving means interlacing threads, yarns or other fibrous material,
herein preferably made of cellulose (or making fabric by interlacing), preferably repeatedly crossing fibrous material, e.g. a thread through other fibrous material, e.g. thread(s), preferably two sets of long threads. In particular a woven cotton separator is used to obtain an appropriate pore size. In particular the cellophane or cotton is soaked in the lye for appropriate swelling.
"Felting" means herein combining fibrous material and pressing it into a layer wherein said fibrous material is preferably cellulose fibers herein.
"Molecular weight" as used herein refers to the average molecular mass (or "molecular weight") of a polymer, typically determined by any appropriate method, e.g. size exclusion chromatography or light scattering techniques or can be measured by mass spectrometry or any other appropriate means. The size distribution can be characterized statistically by weight average molecular weight (Mw) or by number average molecular weight (Mn), the ratio of which is called the polydispersity index.
"Electrolyte" as used herein refers to a substance that is capable of conducting electric current as a result of comprising positively and negatively charged ions, which are able to migrate in the electrolyte, wherein preferably the electrolyte is a solution wherein migration of ions takes place negative and positive terminals (cathode and anode) of an electric circuit, respectively.
A "separator" or "diaphragm" is used herein as a permeable membrane placed between a battery's anode and cathode. The separator allows small molecules and ions like water and hydroxyl ions to permeate while does not allow to permeate more complex ions of zink, like zinc-hydroxide ions.
"Cycle" refers to the process of charging a rechargeable battery and discharging it as required into a load. The term is typically used to specify a battery's expected life, as the number of charge cycles affects life more than the mere passage of time.
As used in this specification, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus the meaning of "a" or "an" if the context allows includes the meaning "one or more".
The terms "comprises" or "comprising" (replaceable by the alternative "including") are to be construed here as having a non-exhaustive meaning and allow the addition or involvement of further features or method steps or components to anything which comprises the listed features or method steps or components. The term "consisting of" relates herein a list of features or method steps or components which is exhaustive and does not allow further members to be included. However, the skilled person may understand in a technical description that a device ore method may comprise further features which may be necessary for operation under certain conditions, however, do not belong to the very merit of the inventive idea and therefore, as a teaching, "consisting of" can be amended to "consisting essentially of" without addition of new matter herein. The expression "consisting essentially of" " is to be understood as consisting of mandatory features or method steps or components listed in a list e.g. in a claim whereas allowing to contain additionally other features or method steps or components which do not materially affect the essential characteristics of the use, method, composition or other subject matter.
BRIEF DESCIPTION OF THE FIGURES
Figure 1. Arrangements of the Zn-air rechargeable battery with horizontal orientation (dimensions w=65 mm, s=30 mm, h=42 mm, 1=129 mm)
Figure 2. Arrangements of the Zn-air rechargeable battery with vertical orientation (dimensions w=60 mm, s=30 mm, h=110 mm, d=1.5 mm, 1=50 mm, f=100 mm)
Figure 3. The cycling test (Figure 3a, 3b) and the Coulomb efficiency (Figure 3c) of the 3D-printed rectangular Zn- air rechargeable battery, equipped with cotton cloth membrane. The current density was kept to be constant, i.e., 2 mAcm"2, while the time limit of charging and discharging was set to 10 min.
Figure 4. Cycling test (Figure 4a, 4b) and coulomb efficiency (Figure 4b) of 3D-printed Zn-air battery filled with KOH saturated with K2[Zn(OH)4] electrolyte containing 2 m/v % CMC-Na (90 kDa with 0.7 functionality).
Figure 5. Cycling test (Figure 5a) and the coulomb efficiency (Figure 5b) of 3D-printed Zn air battery filled with KOH saturated with K2[Zn(OH)4] electrolyte containing 2 m/v % CMC-Na (Mn=250 kDa, f=1.2).
Figure 6. Discharging (200th cycle) of the Zn-Air rechargeable battery in the absence (a) and presence of CMC-Na viscosity modifiers, Mn=90 kDa, f=0.7 (b), Mn=250 kDa, f=1.2 (c), Mn=250 kDa, f=0.7 (d) The black solid lines represent the fitted curves by Eq. (1) while the fitting parameters are shown in the tables.
Figure 7. (a-d) Voltammograms obtained in the absence and in the presence of CMC-Na additives. Figure 7.e shows an additional CV measurement which was carried out applying the charcoal-based cathode in the presence of additives.
Figure 8. The SEM images of the zinc electrode, obtained with the battery equipped by cotton cloth diaphragm in the absence and presence of CMC-Na additives (the electrodes were obtained from cyclic performance tests presented in Fig.7. a-d).
Figure 9 shows a chart with features of a preferred embodiment of the rechargeable battery.
Figure 10. (a) The cycling test of the 3D printed rectangular Zn-air rechargeable battery equipped with cellophane cloth membrane. The current density was kept to be constant, i.e., 2 mAcm"2, while the time limit if charging and discharging was setto 5 min. (b) The Coulomb-efficiency during the cycling test was 100% during the 600 cycles carried out.
Figure 11. Cycling test of 3D printed Zn air battery filled with KOH saturated with K2[Zn(OH>4] electrolyte containing 2m/v % CMC (250 kDa f=0.7).
Figure 12 The gross electrochemical processes of the cell in case of 4 electron pathway and 2 electron pathway (or peroxide pathway)
Figure 13 The energy efficiency of the rechargeable battery of the invention
Figure 13a The energy efficiency versus cycle number of 3D-printed Zn-air battery filled with KOH saturated with K2[Zn(OH)4] electrolyte without additive.
Figure 13b The energy efficiency versus cycle number of 3D-printed Zn-air battery filled with KOH saturated with K2[Zn(OH)4] electrolyte containing 2 m/v % CMC-Na (90 kDa, f: 0.7).
Figure 13c The energy efficiency versus cycle number of 3D-printed Zn-air battery filled with KOH saturated with K2[Zn(OH)4] electrolyte containing 2 m/v % CMC-Na (250 kDa, f: 1.2).
Figure 13d The energy efficiency versus cycle number of 3D-printed Zn-air battery filled with KOH saturated with K2[Zn(OH)4] electrolyte containing 2 m/v % CMC-Na (250 kDa, f: 0.7).
Figure 14 The long-term charging of the prototype cell.
Figure 15 The EDS spectrum of the Zn electrode before use.
Figure 16 The EDS spectrum of the Zn electrode without additive.
Figure 17 The EDS spectrum of the Zn electrode with CMC-Na (90 kDa f:0.7).
Figure 18 The EDS spectrum of the Zn electrode with CMC-Na (250 kDa f : 1.2).
Figure 19 The EDS spectrum of the Zn electrode with CMC-Na (250 kDa f:0.7).
DETAILED DESCRIPTION OF THE INVENTION
In the electric double-layer of the Zn-electrode during recharging the following fundamental processes occur: (i) dissociation of Zn-complexes to yield Zn 2+ ions, (ii) charge transfer process to neutralize Zn2+ ions to form metallic Zn, (iii) incorporation of metallic zinc in the crystalline lattice of the Zn-electrode.
If deposit formation is to be avoided one should fundamentally define conditions to slow down the charge transfer process, i.e., the charge transfer process should be the rate-determining step in the overall recharging process.
The development of Zn-air rechargeable batteries is a widely investigated field of research nowadays. However, most of the research concentrate on the general challenges of the Zn anode and the application of bifunctional catalyst systems [Stock, D et al. Benchmarking Anode Concepts: The Future of Electrically Rechargeable Zinc-Air Batteries, ACS Energy Lett. 4 (2019) 1287-1300]. Additionally, many studies are applying only half cells, thus the importance of membranes is not properly investigated yet, as well as the role of cathodes may have been neglected.
The present inventors have surprisingly found that the construction of a Zn-air rechargeable battery with heavy metal-free, charcoal-based air cathode comprising carboxymethyl-cellulose in the electrolyte is a useful to solve problems of the art. Also Zn-air rechargeable battery with heavy metal-free, charcoal-based air cathode comprising cellulose-based, preferably woven, diaphragm or separator, preferably cotton fabric, in particular woven cotton fabric, as a single layer as diaphragm or separator is also particularly useful.
The present inventors have also surprisingly found that the construction of a Zn-air rechargeable battery with heavy metal-free, charcoal-based air cathode comprising carboxymethyl-cellulose in the electrolyte wherein a cellulose-based diaphragm or separator, preferably cotton fabric, in particular as a single layer diaphragm or separator is applied, have preferred features. Thus, the invention relates to Zn-air rechargeable batteries with these features.
The invention relates to a novel rechargeable Zn-air alkaline battery developed with charcoal/graphite cathode and zinc anode. Using of charcoal/graphite cathode, continuous oxygen supply has been achieved and it has been demonstrated by long-term performance tests that it is an appropriate electrode in the rechargeable Zn-air alkaline battery.
Based on the generally accepted electrochemical processes of such systems we take into account the following reactions taking place on the Zn electrode (Scheme 1):
Zn(OH)2 — ►ZnO + H2O R3
Scheme 1. Reactions taking place on the zinc electrode
Thus, the overall anode reaction is
wherein d is discharging and c is charging.
It was known in the art that if Zn(OH>2 is present in the electrolyte in the boundary of the Zn electrode, an irreversible dehydration reaction may occur resulting in the formation of a solid ZnO layer on the surface of the electrode. The formed ZnO layer decreases the active surface area and thus highly reduces the capacity and Coulomb efficiency of the battery, which, ultimately led to the corrosion of the zinc electrode. In order to avoid the formation of deposits, the rate of the charge transfer process should be reduced.
In the present invention a charcoal/graphite air electrode is applied.
Charcoal is necessary to maintain stable, stationary state of the air electrode by adsorption/desorption of oxygen (scheme 2). Advisably a suitable amount of charcoal is to be applied.
Surprisingly, the inventors have also found that the cathode process is a two electron process in the present setting (e.g. CMC additive) contrary to the expectable four electron process usual in prior art batteries.
Furthermore, the use of a cellulose based, preferably woven, preferably single layer separator (diaphragm), in particular woven cotton separator has been found particularly useful.
To design a high-performance Zn -air rechargeable battery the present inventors have elaborated and used the following approaches:
To reduce the rate of charge transfer process carboxymethyl cellulose additive was applied in the lye and a single layer cellulose based diaphragm, preferably a cellulose based diaphragm was applied. In the prior art quite often anode (and cathode) processes have been accelerated. However, the present inventors have worked in the opposite direction and found that it is advantageous if the rate-limiting step is the charge transfer.
In an experiment to arrive at a preferred embodiment of the invention in the rechargeable Zn-air battery the graphite/charcoal cathode was immersed into a 6 M KOH solution saturated with K2[(Zn(OH>4)] electrolyte containing high molecular weight carboxymethyl cellulose sodium salts (CMC-Na), as a commercially available chelating additive [Liu J. et al. Synergistic effects of carboxymethyl cellulose and ZnO as alkaline electrolyte additives for aluminium anodes with a view towards Al-air batteries J. Power Sources 335 (2016) 1-11.; Tangthuam P. et al. Carboxymethyl cellulose-based polyelectrolyte as cationic exchange membrane for zinciodine batteries, Heliyon, 6 (2020) e05391.]. The charcoal owing to its adsorptive nature serves as a reservoir for the “in situ" evolved oxygen in the cathode during the OER reaction. The higher viscosity of the electrolyte by addition of CMC-Na can also aid keeping oxygen in the charcoal.
In addition, the separator also has a role in the cell providing the appropriate ion conductivity and separation of the electrodes [Abbasi, A. et al. Poly(2,6-Dimethyl-1,4-Phenylene Oxide)-Based Hydroxide Exchange Separator Membranes for Zinc-Air Battery, Int. J. Mol. Sci. 20 (2019) 3678-3695. https://doi.org/10.339G/ijms20153678
Tsehaye M.T. et al, Modified Porous Membranes for Zinc Slurry-Air Flow Battery, Molecules 26 (2021) 4062- 4082.]. To develop and to simplify the cell, the present inventors have used cellulose based, single layer separator for the zinc-air cell.
The development of Zn-air rechargeable batteries is a widely investigated area of research nowadays. However, most of the research concentrate on the general challenges of the Zn anode and the application of bifunctional catalyst systems [Stock, D. et al. Benchmarking Anode Concepts: The Future of Electrically Rechargeable Zinc-Air Batteries. ACS Energy Letters 2019, 4 (6), 1287-1300]. Additionally, many studies apply currently half cells only, thus the importance of membranes is not properly investigated yet. However, Lee et al have suggested that the membrane may have a role in the performance of Zn-air batteries, since it can regulate the ion transport [Lee, B.-S. et al. Dendrite Suppression Membranes for Rechargeable Zinc Batteries, ACS Appl. Mater. Interfaces 10 (2018) 38928-38935] between the anode and the cathode. In early work, a combination of cellophane and cotton cloth as a membrane was used. The present inventors have surprisingly found that cellulose based, single layer diaphragm provides a simple cell type with good performance. In particular, cellulose based fabric material, preferably swollen cotton cloth proved to be a suitable cell membrane.
In a particularly preferred embodiment a single layer cellulose-based diaphragm or separator, preferably cotton fabric, and carboxymethyl-cellulose additive to the electrolyte were applied. The swollen cotton cloth proved to be a particularly suitable cell membrane. Woven cotton has a regular (well regulated) pore size which in turn regulates ion migration, whereas is fully permeable for water and hydroxide ions.
High regulation on the ion transfer resulting in the lack or significant suppression of dendrite and mossy formation and stable long-term battery performance were attained over 1000 charging-discharging cycles. In preferred embodiments the Coulomb efficiency was determined to be 100%, and no change in the mass of the Zn anode before and after use was found. It is to be noted that H2 evolution was not observed during the cyclic performance tests.
In the literature a 1.65 V equilibrium cell potential is typically accepted. However, in the present invention the pure charcoal acts as a catalyst for oxygen evolution/reduction reactions (ORR/OER) by adsorbing the "in situ" formed O2. Low redox potentials for O2 reduction, even near zero under alkaline conditions have been reported for different types of carbon-based electro catalysts.
However, it could not be foreseen that in the present rechargeable battery of the invention the cathode process will follow a 2 electron (or peroxide) pathway with an electrode potential of Eo=-0,065V.
The gross electrochemical processes are as follows (Scheme 2):
As it can be seen in Scheme 2, if the reduction of the oxygen takes place according to the 4 electron pathway, the well-known ~1.65 V equilibrium potential can be obtained for a zinc-air battery. However, in the electrode of the invention, the cell potential of the zinc-air battery was significantly lower (~1.3 V) than 1.65 V. Based on this experimental finding we came to the conclusion that the two electron pathway as dominant process takes place in the cathode compartment.
With commonly used KOH electrolyte in Zn-air cells a first problem is the capturing of CO2from the air, resulting in the formation of undesirable precipitate giving rise to uncontrolled change in the composition of the electrolyte solution, whereas a second major problem is the evaporation of water from the electrolyte. In a preferred embodiment the present inventors have used an open charcoal based cathode in which the "in situ"
forming C is captured by adsorption during the charging process. In this way the small amount of supplementary oxygen is freely entering to the cathode giving rise to limited air transport.
Many studies [Al-Saleh, M. A. et al Effect of carbon dioxide on the performance of Ni/PTFE and Ag/PTFE electrodes in an alkaline fuel cell. J. Appl. Electrochem. 1994, 24 (6), 575-580, doi.10.1007/BF00249861] worked with the use of pure oxygen, however, these results cannot be adopted to air electrode systems. The open charcoal based cathode in which the "in situ" forming Ch is captured by adsorption during the charging process. Thus, small amount of supplementary oxygen freely enters the cathode giving rise to limited air transport and, hence, the formation of carbonates highly reduces.
The oxygen consumption of the rechargeable batter of the invention is low therefore a very limited amount of air and therefore carbon-dioxide enters only into the battery which if favorable to avoid carbonate formation. Even at high additive chain length and concentration (as well as viscosity) the heat development and water evaporation are of low lever which are important advantages.
The evaporation of water can be regulated by the viscosity of the electrolyte. The higher viscosity decreases the ion transport but usually decreases the efficiency of the secondary batteries [Tsehaye, M. T et al. Membranes for zinc-air batteries: Recent progress, challenges and perspectives. J. Power Sources 2020, 475, 228689,]. Thus the selection of a proper viscosity modifier is important.
In particular embodiments a complexing agent like carboxymethyl cellulose, in particular its sodium salts (CMC- Na) has been used as additive. CMC-Na-s are biodegradable and, commercially available chelating agents with various carboxyl functionality [Liu J. et al. Synergistic effects of carboxymethyl cellulose and ZnO as alkaline electrolyte additives for aluminium anodes with a view towards Al-air batteries J. Power Sources 335 (2016) 1- 11.; Tangthuam P. et al. Carboxymethyl cellulose-based polyelectrolyte as cationic exchange membrane for zinciodine batteries, Heliyon, 6 (2020) e05391.].
Thus, the present inventors have successfully applied carboxymethyl cellulose sodium salts (CMC-Na) with different molecular weights and functionality to solve the general problem of water loss and to control the ion mobility in the electrolyte. The CMC-Na salts were found to have double functions: (i) increase the viscosity of the electrolyte thus decreasing the rates of evaporation of water and (ii) control the electrochemical reactions to form stable complex with the Zn2+ ions minimizing the zinc deposit formation. Based on these results, the relatively lower viscosity of electrolyte and higher functionality are of CMC-Na salts may be more preferable for a higher-performance battery.
To investigate the Zn electrode reactions cyclic voltammetry measurements were carried out. Higher peak separation was observed for the CMC-Na containing electrolytes than for the additive-free one as it was expected based on their higher viscosities.
The discharging steps of the 200th cycle of all electrolyte systems were modeled mathematically by a stretched exponential function. Excellent agreement was found between the measured and calculated values. Applying the CMC-Na (90 kDa, f=0.7) complex discharge process was identified since a fast decay component was necessary to implement into the model. The obtained stretching exponent was found to increase with the increasing molecular weight of CMC-Na additive, while a lower functionality resulted in a further increase. All our findings have been supported by scanning electron microscopy measurements showing that smooth electrode surface was obtained after long-term performance tests.
Among the CMC additives tested the 250 kDa f = 1,2 functionality CMC-Na has marked advantages. The higher molecular weight resulted in ha higher viscosity in the electrolyte and thereby particularly facilitated the oxygen formed in the OER reaction to be maintained in adsorbed form on the active carbon, i.e. charcoal cathode and thereby reducing the leakage of oxygen into the environment. Moreover, a higher viscosity of the electrolyte reduced diffusion in the electrolyte on the anode side as well thereby contributed the reduction of dendrite formation.
It may also be noted that a higher viscosity reduces ion migration which in turn increases cell resistance which is however, is lower if CMC functionality is higher. Increase in resistance may reduce energy efficiency. The effect of the CMC additive is complex and these complex features do not question the advantageous character of the battery.
In further particular embodiments, to ensure the fix cell geometry polypropylene cell parts were prepared preferably by 3D-printing. With 3D printing the geometry can be easily adjusted. The possibility of 3D printing is an advantage, however, the wall of the cell can be made by any other way which is suitable for forming it, e.g. by molding or carving.
The wall of the cell is not particularly important, the main requirement is that it has to withstand the affect of the electrolyte which is a strong alkali solution, preferably a KOH solution.
Another appropriate material is polyethylene based plastic e.g. high density polyethylene.
In a particular embodiment the rechargeable Zn-air alkaline battery of the invention comprises charcoal-based air cathode comprising a graphite body or member, e.g. a 21 graphite rod and a Zn-anode preferably a 11 Zn- plate anode arranged in a cell wherein the anode space and the cathode space are separated by a separator (diaphragm). In a particular arrangement the 20 cathode, comprising a 21 graphite rod and 22 charcoal is fixed within the cell, e.g. is placed in a frame, e.g. in a plastic frame, like an 50 frame, like PE (polyethylene) or PP (polypropylene) frame (or 51 PP skeleton). The electrode comprises electrolyte ions for which the separator is permeable.
In an embodiment the electrode has a flat arrangement. In this arrangement the graphite/charcoal air 20 cathode is present in a flat 50 frame to provide mechanical strength, the 30 separator to separate the cathode space from the anode space is cellulose and the anode comprises a flat 11 Zn plate surrounded by a 70 reservoir. Optionally the 11 Zn plate is fixed by a 53 PP arm. The 50 PP frame may have 54 PP leg for fixing or engagement of the 11 Zn plate (Zn electrode).
Furthermore, to ensure the fix cell geometry, in an embodiment 3D-printer was used for printing polypropylene parts of the cell out. In a preferred embodiment the cell has a rectangular arrangement.
In a further preferred embodiment the rechargeable Zn-air alkaline battery is a flexible rechargeable Zn-air alkaline battery, wherein the rechargeable Zn-air alkaline battery has significantly improved mechanical flexibility under repeated bending deformation compared to the conventional Zn-air battery technologies. In a preferred embodiment the cell of the flexible rechargeable Zn-air alkaline battery has a planar arrangement with a bendable structure characteristics, e.g. the cells are placed in a frame or separated by a separator or cross-linked each other within the planar arrangement. Preferably the flexible rechargeable Zn-air alkaline battery may be used for wearable electronics applications. In a highly preferred embodiment the wall of the 70 reservoir is made of a flexible material withstanding high alkali solutions and also may be made of or covered by dermatologically
tolerable material on the outer side and/or may be covered by a material withstanding high alkali solutions in the inner side. To be noted cotton is a skin-friendly material while is capable of withstanding alkali solution.
Upon operations of the cell 60 electric wires are connected to the electrodes while electrode reactions take place as explained herein and potential difference is generated between the electrodes which is measureable through e.g. the electric wires and may result in electric current if the electric circuit is closed between the electrodes preferably e.g. 60 electric wires are connected.
Figure 9 explains the most important features of the electrode of a highly preferred embodiment of the invention. The electrode arrangement of the invention results in a stable operation and a lack of dendrite formation .
EXAMPLES
EXAMPLE 1
Materials and Methods
The graphite rod electrode with spectroscopic purity was purchased from Ceramics Praha (Czech Republic, Prague). Zinc foil (thickness 0.65 mm, Rheinzink, EN/DIN 988) was used. The zinc electrodes were rinsed with n- hexane then allowed to dry before use. n-Hexane (HPLC grade), Potassium hydroxide (analytical grade), Charcoal (analytical grade), Zinc oxide (analytical grade), were purchased from VWR (Debrecen, Hungary). The carboxymethyl cellulose Na salts (CMC-Na, Mn = 90 kDa and 250 kDa with different (f=0.7 or f=1.2) functionalities, respectively) and zinc wire (diameter: 0.5 mm, 99.99%) were obtained from Sigma-Aldrich. All chemicals were used as received.
Diaphragm
Cellophane used was a commercial household cellophane. Such cellophane can be purchased from any provider (e.g. Kelly, Hewa or Mazzini). The thickness of the cellophane used was 60-75 pm depending on the manufactured.
Cotton cloth was a woven fabric cotton having a thickness of about 0.2 mm (300 g/m2 density and 1.5 g/cm3).
Both cellophane and cotton cloth was soaked into the electrolyte for swelling for 1 h. A sufficient swelling is also essential to reduce pore size.
Potentiostat
The cyclic charging discharging test of 3D-printed zinc-air rechargeable battery and the cyclic voltammetry (CV) measurements were performed by BioLogic SP-150 potentiostat (Seyssinet-Pariset, France) equipped with EC- Lab software package. The working potential range was chosen from 0.7 V to 1.9 V for the charging/discharging cycle tests with current density 2 mAcm'2, while the voltammograms were recorded in the range of -0.5-0.55 V vs. Zn/Zn2+ with 20 mV/s scan rate.
Scanning electron microscopy (SEM)
The morphology of the surface of Zn electrode was visualized by Scanning Electron Microscopy (SEM) (Hitachi S- 4300 scanning electron microscope (Tokyo, Japan)).
Viscosimetry
The viscosimetric measurements were carried out by a Master Smart viscometer produced by Fungilab S.A. (Barcelona, Spain), at the temperature of 25°C.
Construction ofZn-air rechargeable batteries
The skeleton of Zn-air battery cells were designed by Tinkercad (Autodesk, Inc, online cloud platform) then all parts of the cell were printed out by Prusa i3 MK3S 3D printer using polypropylene (PP) filament (Fiberlogy). The applicability of the PP was tested by soaking it in lye (6M KOH solution containing 0.25 M ZnO) for 24 hours. Based on three parallel measurements no significant changes in the weight of the PP container were observed. Then two different orientations (horizontal and vertical) of the cells were planned and used for the measurements. The arrangements of the Zn-air rechargeable batteries are shown in Fig 1 and Fig 2. Cellophane or cotton were soaked in the lye for 1 hour before use. Soaking is essential for appropriate swelling. In particular in case of cotton separator, in particular in case of woven cotton separator it is essential to obtain an appropriate pore size. A single layer cellophane or cotton was used as diaphragm for the cell. The shape of the diaphragm was constructed for fitting into the inner space of the polypropylene (PP) skeleton. The zinc anode plate (cut from the zinc foil, length 10 cm, width 10 mm, thickness 0.65 mm) was fixed to the PP skeleton keeping constant distance (1.5 mm) between the zinc anode and the diaphragm. Then a mud was made from charcoal and 6 M aqueous potassium hydroxide solution containing ZnO and CMC-Na at a concentrations of 0.25 M and 2 m/v % (2 g CMC-Na was dissolved in 100 mL lye), respectively. The mud obtained was loaded into the PP skeleton interior space containing approximately 22 g charcoal. The filled PP skeleton was placed into the PP container in which the level of the lye was kept constant.
Figure 1 shows arrangements of the Zn-air rechargeable battery with horizontal orientation (dimensions w=65 mm, s=30 mm, h=42 mm, 1=129 mm)
Figure 2. shows arrangements of the Zn-air rechargeable battery with vertical orientation (dimensions w=60 mm, s=30 mm, h=110 mm, d=1.5 mm, 1=50 mm, f=100 mm)
Air cathode
The air cathode was constructed from the charcoal and the graphite rod. The charcoal was soaked for 8 hours in the electrolyte to obtain the mud before the use. No further additive and/or catalyst were used.
It is essential to apply an abundant amount of charcoal, e.g. an amount of charcoal higher than the graphite (in particular having a larger weight) so as to obtain a sufficient surface area thereof to arrive at a catalytic effect.
EXAMPLE 2
The applicability of swollen cotton cloth in the Zn-air rechargeable battery
The membrane has an important role in the performance of Zn-air batteries, since the membrane can effectively regulate the ion transport between the anode and the cathode [Lee, B.-S. Dendrite Suppression Membranes for Rechargeable Zinc Batteries, ACS Appl. Mater. Interfaces 10 (2018) 38928-38935]. In our previous work, we have used a combination of cellophane and cotton cloth as a membrane and charcoal based air cathode in our novel Zn-air rechargeable battery. Herein, we investigated the applicability of both membranes separately.
First, the applicability of swollen cotton cloth in the Zn-air rechargeable battery was checked by chargingdischarging tests and we found an excellent battery performance.
Fig 3 shows 1000 cycles of charging-discharging events. The working potential range is surprisingly small, it is around 0.2 V (1.2V-1.4V), and stable performance was observed during the whole 1000 cycles. At the beginning of the cycling test higher potential range was recorded, however, stable working potential range was achieved
after some cycles.
The working potential seems to be low, compared to those reported in the literature, where 1.65 V equilibrium cell potential is typically accepted. However, in our prototype, the pure charcoal acts as a catalyst for oxygen evolution/reduction reactions (ORR/OER) by adsorbing the "in situ" formed C . Low redox potentials for Ch reduction, even near zero under alkaline conditions have been reported for different types of carbon-based electro catalysts. The low potential value was explained by the higher activity of edges serving as active sites for reduction of oxygen, whereas a peroxide ion pathway can explain a lower potential [Shen, A. et al. Oxygen Reduction Reaction in a Droplet on Graphite: Direct Evidence that the Edge Is More Active than the Basal Plane, Angew. Chem. Int. 53 (2014) 10804-10808, Qu, D. Investigation of oxygen reduction on activated carbon electrodes in alkaline solution, Carbon 45 (2007) 1296-1301., Yeager, E. Electrocatalysts for 02 reduction, Electrochim. Acta 29 (1984) 1527-1537.].
The gross electrochemical processes are as follows (Scheme 2):
Cathode process in case of 4 electron pathway: d _
O2 + 2H2O + 4e- c 40H’ Eo=+0,401 V
Cathode process in case of 2 electron (or peroxide) pathway: d _
O2 + H2O + 2e’ c HO2- + OH’ Eo=-0,065V d _
Zn + 2OH’ c ZnO + H2O + 2e’ EO=-1.26V d: discharging c: charging
The gross electrochemical processes are also shown in Figure 12 (Scheme 2).
As it can be seen in Scheme 2, if the reduction of the oxygen takes place according to the 4 electron pathway, the well-known ~1.65 V equilibrium potential can be obtained for a zinc-air battery. In our particular case, the cell potential of our zinc-air battery was lower (~1.3 V) than 1.65 V. Based on this experimental finding we came to the conclusion that the two electron pathway as dominant process takes place in the cathode compartment. In this case, the equilibrium cell potential calculated from the standard electrode potentials is 1.195 V. As an explanation without being bound to theory, it has been reported that the HOz’ adsorbed on carbon may be stable under alkaline conditions [Yeager, infra]. The stability and the negligible decomposition of HOz’ was supported by the high reproducibility of cycling test (Fig. 3).
In order to investigate the electrochemical reactions, long-term charging of the battery was performed.
A charging process is shown in Figure 14. The 1.65 V charging potential was achieved only after 61,1 hours. We suggest that the surprisingly low working potential (<1.4 V) is the result of the combination of different possible oxygen reduction pathways as explained above regarding electrode processes.
To suppress the undesirable dissolution of Zn anode yielding H2 evolution via [Zn(OH)4]2’, we used concentrated KOH solution saturated with K2[Zn(OH>4]. It must be noted, that preliminary experiments were carried out to identify the cell potential where the formation of hydrogen is relevant. It was found that significant evolution of H2 occurs only at charging potential higher than 2V.
The Coulomb efficiency has been found to be 100% during the whole experiment. This finding shows an excellent balance between the charging and discharging cycles in the operating battery. No change in the mass of the Zn- electrode was found. Based on these results, the swollen cotton cloth membrane properly stabilized the ion transport hence, highly regulates the reactions on the surface of the Zn electrode. Such regulation is necessary
to avoid the formation of an undesired metallic Zn dendrite formation (deposites) on the surfaces the electrode. With the applied parameters (2 mAcm'2 charging current and 10 min time frame) the capacity was found to be 2.63 mAh. While similar current densities were applied in several Zn-Air battery studies, the high coulombic and energy efficiency of the present electrode is surprisingly high [Yang, H.B. et al. Identification of catalytic sites for oxygen reduction and oxygen evolution in N-doped graphene materials: Development of highly efficient metal- free bifunctional electrocatalyst, Sci. Adv. 2 (2016) el501122, Qi, Y. et al. (Fe,Co)/N-Doped Multi-Walled Carbon Nanotubes as Efficient Bifunctional Electrocatalysts for Rechargeable Zinc-Air Batteries, ChemCatChem 13 (2021) 1023-1033.].
Figure 3. shows the cycling test (a, b) and the Coulomb efficiency (c) of the 3D-printed rectangular Zn-air rechargeable battery, equipped with cotton cloth membrane. The current density was kept to be constant, i.e., 2 mAcm"2, while the time limit if charging and discharging was set to 10 min.
The cycling test and the coulomb efficiency of the 3D-printed rectangular Zn-air rechargeable battery, equipped with cotton cloth membrane is shown in Fig. 3. The current density was kept constant at 2 mAcm"2, while the time limit of charging and discharging was set to 10 min (1000 cycle).
On the other hand, in the case of cellophane ( Fig 10a and 10b) the cell potential was within a low range and stable performance was obtained up to 500 charging-discharging cycle. Similarly to the swollen cotton cloth, at the beginning of the test higher potential range was observed. Since the cell with cotton cloth has higher physical resistance than that of the cellophane only the cell prepared with cotton cloth was used for further experiments. Moreover, cotton cloth has resulted in a narrower working potential range which is also a definite advantage vis- a-vis cellophane.
EXAMPLE 3
Gelation with carboxy methyl cellulose (CMC)-Na salts
The most common electrolyte for the Zn-air batteries is KOH solution of different concentrations. However, there are two major problems associated with the presence of strong alkaline solutions. The first problem is the capturing of COz from the air, resulting in the formation of undesirable precipitate giving rise to uncontrolled change in the composition of the electrolyte solution. The second major problem is the evaporation of water from the electrolyte
Many studies [Sun et al. A rechargeable zinc-air battery based on zinc peroxide chemistry, Science 371 (2021) 46- 51] used pure oxygen, however, these results cannot be adopted to air electrode systems. The present inventors have created an open charcoal based cathode in which the "in situ" forming O2 is captured by adsorption during the charging process. Thus, small amount of supplementary oxygen is freely entering the cathode giving rise to limited air transport and, hence, the formation of carbonates highly reduces.
The evaporation of water can be regulated by the viscosity of the electrolyte. The higher viscosity decreases the ion transport but usually decreases the efficiency of the secondary batteries. Thus the selection of a proper viscosity modifier is important.
In our rechargeable Zn-air battery, carboxy methyl cellulose Na salts (CMC-Na) with different molecular weights and functionality have been applied.
To test the effect of the molecular weight of CMC-Na on battery performance, first CMC-Na salt was tested with
lower molecular weight (90 kDa, 0.7 functionality). The cyclic performance test was carried out up to 400 cycles, as seen in Fig 4.
Figure 4 shows a cycling test and coulomb efficiency of 3D-printed Zn-air battery filled with KOH saturated with K2[Zn(OH>4] electrolyte containing 2 m/v % CMC-Na (90 kDa with 0.7 functionality).
After a short instacionary state, the potential range is decreasing, reaching a range of 0.3 V (1.05-1.35V). This range is close to the one measured with the electrolyte in the absence of a viscosity modifier. In addition to the excellent cyclic performance, high Coulomb efficiency was also observed. Capacity was found to be the same as the case of electrolyte containing CMC-Na (250 kDa, 1.2 functionality). In both experiments, the batteries were charged and discharged with the same current density without reaching the set potential limits. The performance of the cycling tests with the use of CMC-Na (250 kDa, f=1.2) is shown in Fig 5.
Figure 5 shows a cycling test and the coulomb efficiency of 3D-printed Zn air battery filled with KOH saturated with K2[Zn(OH>4] electrolyte containing 2 m/v % CMC-Na (Mn=250 kDa, f=1.2).
As seen in Figure 5, applying CMC-Na (250 kDa, f=1.2), the performance of the secondary battery is appropriate, since none of the cycles reaches the set potential limits (0.7 V and 1.9 V). The Coulomb efficiency during the cycling test was constant (100%). On the contrary, CMC-Na salt with the same molecular weight but with lower functionality (0.7 vs. 1.2) resulted in poorer performance (Fig 11). All the cycles reached the set potential limits within the applied time frame, and changing capacity was observed from cycle to cycle. Despite the lower performance, the Coulomb efficiency was still 100%, which suggests an appropriate charging-discharging balance.
In addition, the energy efficiencies were also calculated. The highest value was obtained in the case of the additive-free cells (91 %). Applying additives CMC-Na 90 kDa, f:0.7, 250 kDa, f : 1.2 and 250 kDa, f:0.7, 80 %, 64 % and 60 % energy efficiencies were obtained, respectively. The energy efficiency versus cycle number plots are shown in the Supporting Information (Figures 13a to 13d).
As an explanation which CMC (here: CMC-Na) additive increases the apolar character of the electrolyte (lye) and thus increases cell resistance, lowering energy efficiency to a certain extent. The effect of the additive is complex, and increasing size and viscosity reduces ion transfer and increases resistance resulting in lower energy efficiency. However, increasing functionality reduces (in a relative manner) resistance, and thus (relatively) increases energy efficiency, compared with additive of the same size but lower functionality. Nevertheless, the additive is essential to reduce rate of electrode processes in particular Zn incorporation which would otherwise result in dendrite formation - a problem solved by the present invention. Also long term reliable functioning, which an unexpected favorable feature of the battery of the invention, cannot be achieved without the additive. Therefore, while the 91% energy efficiency of the cell without additive is extremely high, the additive is important and - taking into account the effect of the presence of the additive - even the 80% value, or even the 60 and 64%, taking into account the size (length) of CMC, are well beyond expectations.
EXAMPLE 4
Mathematical Modeling of Discharging Process
In order to model mathematically the potential change during the discharging process of a battery the 200th cycle was selected in each case. It has been shown that the stretched exponential function, supplemented by a fast
decay component was successfully applicable to model the potential change during the discharging steps [Nagy, T. et al. Environmentally friendly Zn-air rechargeable battery with heavy metal free charcoal based air cathode, Electrochimica Acta, Volume 368, 2021, 137592]. In general, the stretched exponential function is suitable for the mathematical modeling of different disordered systems such as electrochemical reactions with a broad activation energy distribution [D.C. Johnston, Stretched exponential relaxation arising from a continuous sum of exponential decays, Phys. Rev. B 74 (2006)]. The following equation was fitted (equation 1) to the 200th cycle of all the cycling performance tests.
where Z1E/ and ZIEs are the potential change, kf and ks are the rate coefficients of the fast and slow decay, respectively. The ft is the stretching exponent, while the
is the terminal potential.
In the case of additive-free electrolyte the stretched exponential function was applied, without the fast decay component of Equation 1 (Eq. 1). Good agreements were found between the measured and fitted curves in every case, as can be seen in Fig 6. However, complex, two component decay was observed only with CMC-Na (90 kDa, f:0.7), where the AEf and kf were obtained to be 0.013 V and 158000 min’1, respectively. For the other additives, CMC-Na 250 kg/mol, f:1.2 and f:0.7, the fast decay term was not necessary to be involved in the model. Similar stretching exponents were found for the additive-free and CMC-Na (90 kDa, f=0.7) systems (0.32). The stretching exponent increases with the molecular weight of the CMC-Na. The highest value was determined for the CMC-Na (250 kDa, f=0.7). This finding suggests the lower viscosity (see later) and higher functionality make the dissolution of the zinc more uniform, resulting in higher battery performance.
Figure 6 illustrates discharging (200th cycle) of the Zn-air rechargeable battery in the absence (a) and presence of CMC-Na viscosity modifiers, Mn=90 kDa, f=0.7 (b), Mn=250 kDa, f=1.2 (c), Mn=250 kDa, f=0.7 (d) The black solid lines represent the fitted curves by Eq. (1) while the fitting parameters are shown in the tables.
EXAMPLE 5
Cyclic voltammetry
For the investigation of anode reactions, i.e., zinc deposition and dissolution, further cyclic voltammetry measurements were carried out. The reference electrode was a zinc wire, and the voltammograms were recorded in the range of -0.5-0.55 V vs. Zn/Zn2+ The voltammograms obtained in the presence and in the absence of CMC-Na salts are shown in Fig 7.
Figure 7 shows voltammograms obtained in the absence and in the presence of CMC-Na additives.
All the voltammograms show clear oxidation and reduction peaks. Characteristic data obtained from the cyclic voltammetry measurements are summarized in Table 1.
Table 1. The results of cyclic voltammetry including the electrolyte densities, the positions of anodic/cathodic peaks, the current densities and the peaks separations.
Without any viscosity modifier, both anodic and cathodic peak positions are around 0.061 V and -0.128 V, with peak separations approximately 0.2 V. Applying CMC-Na salts higher anodic and cathodic shifts were recognized as compared to the additive-free electrolyte. It was found that the anodic peak shift was the highest for the CMC- Na with Mn=250 kDa and f=0.7 functionality while in the case of other two CMC-Na salts similar anodic shifts were observed. The cathodic shifts are higher than the anodic ones but their values are very similar. By applying the shifts, the peak separation can be calculated. Low separation is preferable since usually, it means low over potential. Low separations were found in the case of additive-free electrolyte (0.189 V). In the presence of CMC- Na additives in the electrolyte higher peak separation were obtained. The CMC-Na additives with Mn=250 kDa (f=1.2) and 90 kDa (f=0.7) have similar values while the CMC-Na with Mn=250 kDa (f=0.7) resulted in higher separation (0.3 V). The peak separations are likely depend on the viscosity of the solution and the functionality of the applied CMC-Na. The dynamic viscosity of the CMC-Na salt-containing electrolytes are 7.5, 48 and 75 Pas for the Mn=90 kDa (f=0.7), Mn=250 kDa (f=0.7) and Mn=250 kDa (f=1.2) additives, respectively. In spite of the fact that there is one order of magnitude difference in the viscosities similar peak separation was found for the CMC- Na additives with Mn=250 kDa (f=1.2) and Mn=90 kDa (f=0.7) This finding reflects the double functions of the additives i.e. altering the rate of the electrochemical reactions on the surface of the Zn electrode through the control of ion mobility by the electrolyte viscosity and formation of the stable chelate complex with the Zn2+ ions. These findings are in line with the cycling tests of the batteries with different viscosity modifiers.
The profiles of the cyclic voltammograms at low voltages i.e., at around -0.5 V vs. Zn/Zn2+ can be ascribed to the electrochemical processes accompanied by the corrosion of Zn electrode.
In order to investigate the low charging potentials, an additional CV measurement was carried out applying the charcoal-based cathode in the presence of additives (CMC-Na, 90 kDa (f=0.7) The parameters all were the same as those used for the other CV measurements. The obtained cyclic voltammogram is shown in Figure 7.e
The cyclic voltammogram is similar to those presented in Fig.7.a-d. Accordingly, clear oxidation and reduction peaks are observed indicating the presence of electrochemical reactions, i.e., the charcoal cathode does not act as a (super)capacitor.
EXAMPLE 6
Scanning electron microscopy
Visually, the formation of deposits was not observed. In order to get deeper knowledge on the morphology change of the Zn electrode, scanning electron microscopy measurements were carried out. After completing the experiments, the electrodes were washed with water and acetone then stored in cyclohexane prior to analysis. The SEM images confirm the results of visual analysis, i.e., the lack of formation of deposits on the electrodes surface. The surfaces are uniform. The morphology of the electrode surface changed differently in the absence and in the presence of CMC-Na additives, mossy-like deposition was formed without additive (after 1000 charging-discharging cycles). Applying the CMC-Na as viscosity modifier, dendrite and mossy depositions were significantly suppressed.
Additionally, the elemental analysis was performed by energy dispersive spectroscopy for all electrodes, where in addition to zinc, titanium, copper potassium carbon and oxygen have been found (see Figures 15 to 19 (S SS)). The titanium and the copper are the alloying elements of the zinc (standard EN/DIN 988) while the potassium originated from the alkaline solution.
Figures 15 to 19 show the SEM images and EDS spectrum of the zinc electrode obtained with the battery equipped by the additive-free electrolyte and cotton cloth diaphragm after 1000 charging-discharging cycles.
EXAMPLE 7 flexible Zn-Air batteries
Fang, W. et al. teaches flexible Zn-Air batteries which are also applicable int eh present invention.
Fang, W. et al., Recent progress and future perspectives of flexible Zn-Air batteries, Journal of Alloys and Compounds 869 (2021
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Claims
1. A rechargeable Zn-air alkaline battery with a charcoal-based air cathode and zinc anode, said alkaline battery comprising cellulose-based fabric material as diaphragm and having electrolyte comprising carboxymethyl cellulose (CMC) as additive.
2. The rechargeable Zn-air alkaline battery of claim 1, said alkaline battery comprising woven or felted, preferably woven cellulose-based fabric material, preferably cotton cloth membrane material as diaphragm (separator), wherein the electrolyte comprises KOH and [Zn(OH)4]2' and carboxymethyl cellulose (CMC), preferably carboxymethyl cellulose natrium (CMC-Na), as an additive.
3. The rechargeable Zn-air alkaline battery of claim 1, or claim 2 said battery having a working potential of
1.2 V to 1.5 V, preferably 1.2 to 1.4 V.
4. The rechargeable Zn-air alkaline battery of any of claims 2 to 3 wherein the electrolyte comprises 0.5 to 5 m/v%, more preferably 1 to 4 or 1 to 3 m/v % CMC, preferably CMC-Na.
5. The rechargeable Zn-air alkaline battery of any of claims 2 to 4 wherein the concentration of the KOH is 2 to 10 M, preferably about 6 M, and the concentration of the [Zn(OH)4]2' is 0.1 to 0.5 M, preferably 0.25 M at the initial stage of the battery
6. The rechargeable Zn-air alkaline battery of any of claims 1 to 5 wherein said cellulose-based fabric is woven, preferably said rechargeable Zn-air alkaline battery comprising a cotton cloth membrane material as diaphragm.
7. The rechargeable Zn-air alkaline battery of any one of claims 1 to 6 wherein said charcoal-based air cathode comprising or essentially consisting of graphite and charcoal.
8. The rechargeable Zn-air alkaline battery of any of claims 1 to 7, in particular claim 4 wherein the average molecular weight (MW) of the CMC is 10 to 500 kDa.
9. The rechargeable Zn-air alkaline battery of any of claims 1 to 8, in particular claim 4 or 8, wherein the functionality of the CMC, preferably CMC-Na, is 0.2 to 2.
10. The rechargeable Zn-air alkaline battery of any of claims 1 to 9 said battery having one or more rectangular cells.
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