CN117525549A - Carbon-coated mixed phosphate positive electrode material, and preparation method and application thereof - Google Patents
Carbon-coated mixed phosphate positive electrode material, and preparation method and application thereof Download PDFInfo
- Publication number
- CN117525549A CN117525549A CN202311697031.2A CN202311697031A CN117525549A CN 117525549 A CN117525549 A CN 117525549A CN 202311697031 A CN202311697031 A CN 202311697031A CN 117525549 A CN117525549 A CN 117525549A
- Authority
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- China
- Prior art keywords
- carbon
- positive electrode
- electrode material
- acid
- source
- Prior art date
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- Pending
Links
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 130
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 127
- 229910019142 PO4 Inorganic materials 0.000 title claims abstract description 98
- 239000010452 phosphate Substances 0.000 title claims abstract description 98
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 title claims abstract description 98
- 239000007774 positive electrode material Substances 0.000 title claims abstract description 97
- 238000002360 preparation method Methods 0.000 title claims abstract description 41
- 239000000243 solution Substances 0.000 claims abstract description 110
- 239000011734 sodium Substances 0.000 claims abstract description 75
- 238000010438 heat treatment Methods 0.000 claims abstract description 63
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 49
- 229910052751 metal Inorganic materials 0.000 claims abstract description 43
- 239000002253 acid Substances 0.000 claims abstract description 37
- 239000002184 metal Substances 0.000 claims abstract description 37
- 239000002243 precursor Substances 0.000 claims abstract description 25
- 238000001035 drying Methods 0.000 claims abstract description 17
- 229910052708 sodium Inorganic materials 0.000 claims abstract description 17
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 claims abstract description 16
- 239000011259 mixed solution Substances 0.000 claims abstract description 16
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 15
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims abstract description 14
- 239000011574 phosphorus Substances 0.000 claims abstract description 14
- 229910052742 iron Inorganic materials 0.000 claims abstract description 11
- 239000010405 anode material Substances 0.000 claims abstract description 10
- 229910052725 zinc Inorganic materials 0.000 claims abstract description 7
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 5
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 5
- YASYEJJMZJALEJ-UHFFFAOYSA-N Citric acid monohydrate Chemical compound O.OC(=O)CC(O)(C(O)=O)CC(O)=O YASYEJJMZJALEJ-UHFFFAOYSA-N 0.000 claims description 36
- 229960002303 citric acid monohydrate Drugs 0.000 claims description 36
- FKNQFGJONOIPTF-UHFFFAOYSA-N Sodium cation Chemical compound [Na+] FKNQFGJONOIPTF-UHFFFAOYSA-N 0.000 claims description 21
- 229910001415 sodium ion Inorganic materials 0.000 claims description 21
- 229960001031 glucose Drugs 0.000 claims description 20
- WQZGKKKJIJFFOK-GASJEMHNSA-N Glucose Natural products OC[C@H]1OC(O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-GASJEMHNSA-N 0.000 claims description 19
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 19
- WQZGKKKJIJFFOK-VFUOTHLCSA-N beta-D-glucose Chemical compound OC[C@H]1O[C@@H](O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-VFUOTHLCSA-N 0.000 claims description 19
- 239000008103 glucose Substances 0.000 claims description 19
- 238000000034 method Methods 0.000 claims description 19
- 229910017604 nitric acid Inorganic materials 0.000 claims description 19
- 238000001694 spray drying Methods 0.000 claims description 12
- 239000002245 particle Substances 0.000 claims description 11
- 238000004321 preservation Methods 0.000 claims description 10
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims description 9
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 claims description 9
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 9
- 239000007787 solid Substances 0.000 claims description 9
- 150000007522 mineralic acids Chemical class 0.000 claims description 8
- 229910000403 monosodium phosphate Inorganic materials 0.000 claims description 8
- 235000019799 monosodium phosphate Nutrition 0.000 claims description 8
- 150000007524 organic acids Chemical class 0.000 claims description 8
- AJPJDKMHJJGVTQ-UHFFFAOYSA-M sodium dihydrogen phosphate Chemical compound [Na+].OP(O)([O-])=O AJPJDKMHJJGVTQ-UHFFFAOYSA-M 0.000 claims description 8
- 238000004090 dissolution Methods 0.000 claims description 7
- 238000004519 manufacturing process Methods 0.000 claims description 7
- -1 polypropylene Polymers 0.000 claims description 7
- CIWBSHSKHKDKBQ-JLAZNSOCSA-N Ascorbic acid Chemical compound OC[C@H](O)[C@H]1OC(=O)C(O)=C1O CIWBSHSKHKDKBQ-JLAZNSOCSA-N 0.000 claims description 6
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 6
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 6
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 6
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims description 6
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 6
- BDAGIHXWWSANSR-UHFFFAOYSA-N methanoic acid Natural products OC=O BDAGIHXWWSANSR-UHFFFAOYSA-N 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 6
- FQENQNTWSFEDLI-UHFFFAOYSA-J sodium diphosphate Chemical compound [Na+].[Na+].[Na+].[Na+].[O-]P([O-])(=O)OP([O-])([O-])=O FQENQNTWSFEDLI-UHFFFAOYSA-J 0.000 claims description 6
- VWDWKYIASSYTQR-UHFFFAOYSA-N sodium nitrate Chemical compound [Na+].[O-][N+]([O-])=O VWDWKYIASSYTQR-UHFFFAOYSA-N 0.000 claims description 6
- 239000001488 sodium phosphate Substances 0.000 claims description 6
- 229940048086 sodium pyrophosphate Drugs 0.000 claims description 6
- 235000019818 tetrasodium diphosphate Nutrition 0.000 claims description 6
- 239000001577 tetrasodium phosphonato phosphate Substances 0.000 claims description 6
- RYFMWSXOAZQYPI-UHFFFAOYSA-K trisodium phosphate Chemical compound [Na+].[Na+].[Na+].[O-]P([O-])([O-])=O RYFMWSXOAZQYPI-UHFFFAOYSA-K 0.000 claims description 6
- 229910000406 trisodium phosphate Inorganic materials 0.000 claims description 6
- 235000019801 trisodium phosphate Nutrition 0.000 claims description 6
- 229910052749 magnesium Inorganic materials 0.000 claims description 5
- 239000012298 atmosphere Substances 0.000 claims description 4
- MNNHAPBLZZVQHP-UHFFFAOYSA-N diammonium hydrogen phosphate Chemical compound [NH4+].[NH4+].OP([O-])([O-])=O MNNHAPBLZZVQHP-UHFFFAOYSA-N 0.000 claims description 4
- LNAZSHAWQACDHT-XIYTZBAFSA-N (2r,3r,4s,5r,6s)-4,5-dimethoxy-2-(methoxymethyl)-3-[(2s,3r,4s,5r,6r)-3,4,5-trimethoxy-6-(methoxymethyl)oxan-2-yl]oxy-6-[(2r,3r,4s,5r,6r)-4,5,6-trimethoxy-2-(methoxymethyl)oxan-3-yl]oxyoxane Chemical compound CO[C@@H]1[C@@H](OC)[C@H](OC)[C@@H](COC)O[C@H]1O[C@H]1[C@H](OC)[C@@H](OC)[C@H](O[C@H]2[C@@H]([C@@H](OC)[C@H](OC)O[C@@H]2COC)OC)O[C@@H]1COC LNAZSHAWQACDHT-XIYTZBAFSA-N 0.000 claims description 3
- BJEPYKJPYRNKOW-REOHCLBHSA-N (S)-malic acid Chemical compound OC(=O)[C@@H](O)CC(O)=O BJEPYKJPYRNKOW-REOHCLBHSA-N 0.000 claims description 3
- KXGFMDJXCMQABM-UHFFFAOYSA-N 2-methoxy-6-methylphenol Chemical compound [CH]OC1=CC=CC([CH])=C1O KXGFMDJXCMQABM-UHFFFAOYSA-N 0.000 claims description 3
- OSWFIVFLDKOXQC-UHFFFAOYSA-N 4-(3-methoxyphenyl)aniline Chemical compound COC1=CC=CC(C=2C=CC(N)=CC=2)=C1 OSWFIVFLDKOXQC-UHFFFAOYSA-N 0.000 claims description 3
- QTBSBXVTEAMEQO-UHFFFAOYSA-M Acetate Chemical compound CC([O-])=O QTBSBXVTEAMEQO-UHFFFAOYSA-M 0.000 claims description 3
- 239000004254 Ammonium phosphate Substances 0.000 claims description 3
- 229920001661 Chitosan Polymers 0.000 claims description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims description 3
- FEWJPZIEWOKRBE-JCYAYHJZSA-N Dextrotartaric acid Chemical compound OC(=O)[C@H](O)[C@@H](O)C(O)=O FEWJPZIEWOKRBE-JCYAYHJZSA-N 0.000 claims description 3
- 229910002651 NO3 Inorganic materials 0.000 claims description 3
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims description 3
- 239000004698 Polyethylene Substances 0.000 claims description 3
- 239000004743 Polypropylene Substances 0.000 claims description 3
- 239000004372 Polyvinyl alcohol Substances 0.000 claims description 3
- VMHLLURERBWHNL-UHFFFAOYSA-M Sodium acetate Chemical compound [Na+].CC([O-])=O VMHLLURERBWHNL-UHFFFAOYSA-M 0.000 claims description 3
- 229920002472 Starch Polymers 0.000 claims description 3
- CZMRCDWAGMRECN-UGDNZRGBSA-N Sucrose Chemical compound O[C@H]1[C@H](O)[C@@H](CO)O[C@@]1(CO)O[C@@H]1[C@H](O)[C@@H](O)[C@H](O)[C@@H](CO)O1 CZMRCDWAGMRECN-UGDNZRGBSA-N 0.000 claims description 3
- 229930006000 Sucrose Natural products 0.000 claims description 3
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims description 3
- FEWJPZIEWOKRBE-UHFFFAOYSA-N Tartaric acid Natural products [H+].[H+].[O-]C(=O)C(O)C(O)C([O-])=O FEWJPZIEWOKRBE-UHFFFAOYSA-N 0.000 claims description 3
- 235000011054 acetic acid Nutrition 0.000 claims description 3
- 229960000583 acetic acid Drugs 0.000 claims description 3
- 238000007605 air drying Methods 0.000 claims description 3
- BJEPYKJPYRNKOW-UHFFFAOYSA-N alpha-hydroxysuccinic acid Natural products OC(=O)C(O)CC(O)=O BJEPYKJPYRNKOW-UHFFFAOYSA-N 0.000 claims description 3
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 3
- 229910000148 ammonium phosphate Inorganic materials 0.000 claims description 3
- 235000019289 ammonium phosphates Nutrition 0.000 claims description 3
- 235000010323 ascorbic acid Nutrition 0.000 claims description 3
- 239000011668 ascorbic acid Substances 0.000 claims description 3
- 229960005070 ascorbic acid Drugs 0.000 claims description 3
- 239000006229 carbon black Substances 0.000 claims description 3
- 229910021393 carbon nanotube Inorganic materials 0.000 claims description 3
- 239000002041 carbon nanotube Substances 0.000 claims description 3
- 229940045110 chitosan Drugs 0.000 claims description 3
- FYGDTMLNYKFZSV-MRCIVHHJSA-N dextrin Chemical compound O[C@@H]1[C@@H](O)[C@H](O)[C@@H](CO)OC1O[C@@H]1[C@@H](CO)OC(O[C@@H]2[C@H](O[C@H](O)[C@H](O)[C@H]2O)CO)[C@H](O)[C@H]1O FYGDTMLNYKFZSV-MRCIVHHJSA-N 0.000 claims description 3
- 229940013688 formic acid Drugs 0.000 claims description 3
- 235000019253 formic acid Nutrition 0.000 claims description 3
- 229910021389 graphene Inorganic materials 0.000 claims description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 claims description 3
- 239000001630 malic acid Substances 0.000 claims description 3
- 235000011090 malic acid Nutrition 0.000 claims description 3
- 229940099690 malic acid Drugs 0.000 claims description 3
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 3
- 229920000609 methyl cellulose Polymers 0.000 claims description 3
- 239000001923 methylcellulose Substances 0.000 claims description 3
- 229940116315 oxalic acid Drugs 0.000 claims description 3
- 235000006408 oxalic acid Nutrition 0.000 claims description 3
- 229920001568 phenolic resin Polymers 0.000 claims description 3
- 239000005011 phenolic resin Substances 0.000 claims description 3
- 235000011007 phosphoric acid Nutrition 0.000 claims description 3
- 229920002239 polyacrylonitrile Polymers 0.000 claims description 3
- 229920000573 polyethylene Polymers 0.000 claims description 3
- 229920001155 polypropylene Polymers 0.000 claims description 3
- 229920002451 polyvinyl alcohol Polymers 0.000 claims description 3
- 239000001632 sodium acetate Substances 0.000 claims description 3
- 235000017281 sodium acetate Nutrition 0.000 claims description 3
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 3
- 239000011780 sodium chloride Substances 0.000 claims description 3
- 239000001509 sodium citrate Substances 0.000 claims description 3
- NLJMYIDDQXHKNR-UHFFFAOYSA-K sodium citrate Chemical compound O.O.[Na+].[Na+].[Na+].[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O NLJMYIDDQXHKNR-UHFFFAOYSA-K 0.000 claims description 3
- 239000004317 sodium nitrate Substances 0.000 claims description 3
- 235000010344 sodium nitrate Nutrition 0.000 claims description 3
- ZNCPFRVNHGOPAG-UHFFFAOYSA-L sodium oxalate Chemical compound [Na+].[Na+].[O-]C(=O)C([O-])=O ZNCPFRVNHGOPAG-UHFFFAOYSA-L 0.000 claims description 3
- 229940039790 sodium oxalate Drugs 0.000 claims description 3
- 239000008107 starch Substances 0.000 claims description 3
- 235000019698 starch Nutrition 0.000 claims description 3
- 239000005720 sucrose Substances 0.000 claims description 3
- 229960004793 sucrose Drugs 0.000 claims description 3
- 239000011975 tartaric acid Substances 0.000 claims description 3
- 229960001367 tartaric acid Drugs 0.000 claims description 3
- 235000002906 tartaric acid Nutrition 0.000 claims description 3
- 239000012535 impurity Substances 0.000 abstract description 12
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 51
- 239000011572 manganese Substances 0.000 description 44
- 239000008367 deionised water Substances 0.000 description 32
- 229910021641 deionized water Inorganic materials 0.000 description 32
- 239000012071 phase Substances 0.000 description 28
- 239000011777 magnesium Substances 0.000 description 19
- 239000000463 material Substances 0.000 description 17
- 230000008569 process Effects 0.000 description 12
- 230000000694 effects Effects 0.000 description 9
- 238000002441 X-ray diffraction Methods 0.000 description 8
- 239000012299 nitrogen atmosphere Substances 0.000 description 7
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- 238000001816 cooling Methods 0.000 description 5
- 229910052748 manganese Inorganic materials 0.000 description 5
- 239000000047 product Substances 0.000 description 5
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 4
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 4
- 238000003763 carbonization Methods 0.000 description 4
- 239000011247 coating layer Substances 0.000 description 4
- 238000004146 energy storage Methods 0.000 description 4
- 229910001416 lithium ion Inorganic materials 0.000 description 4
- 229910021645 metal ion Inorganic materials 0.000 description 4
- 238000001000 micrograph Methods 0.000 description 4
- 239000002994 raw material Substances 0.000 description 4
- 230000000630 rising effect Effects 0.000 description 4
- 230000009286 beneficial effect Effects 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- 230000001351 cycling effect Effects 0.000 description 3
- 238000009792 diffusion process Methods 0.000 description 3
- 239000003792 electrolyte Substances 0.000 description 3
- 238000002474 experimental method Methods 0.000 description 3
- 150000002739 metals Chemical class 0.000 description 3
- 238000002156 mixing Methods 0.000 description 3
- 238000011056 performance test Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 2
- KEAYESYHFKHZAL-UHFFFAOYSA-N Sodium Chemical compound [Na] KEAYESYHFKHZAL-UHFFFAOYSA-N 0.000 description 2
- 229960004106 citric acid Drugs 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- BNIILDVGGAEEIG-UHFFFAOYSA-L disodium hydrogen phosphate Chemical compound [Na+].[Na+].OP([O-])([O-])=O BNIILDVGGAEEIG-UHFFFAOYSA-L 0.000 description 2
- 238000007323 disproportionation reaction Methods 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 229910001463 metal phosphate Inorganic materials 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 230000002441 reversible effect Effects 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
- 239000000725 suspension Substances 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- 229910002554 Fe(NO3)3·9H2O Inorganic materials 0.000 description 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 229910020691 Na4M3(PO4)2P2O7 Inorganic materials 0.000 description 1
- 229910020509 Na4Mn3 (PO4)2P2O7 Inorganic materials 0.000 description 1
- 239000002033 PVDF binder Substances 0.000 description 1
- 239000006230 acetylene black Substances 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- LFVGISIMTYGQHF-UHFFFAOYSA-N ammonium dihydrogen phosphate Chemical compound [NH4+].OP(O)([O-])=O LFVGISIMTYGQHF-UHFFFAOYSA-N 0.000 description 1
- 229910000387 ammonium dihydrogen phosphate Inorganic materials 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 238000000498 ball milling Methods 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 239000010406 cathode material Substances 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000013329 compounding Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 229910000388 diammonium phosphate Inorganic materials 0.000 description 1
- 235000019838 diammonium phosphate Nutrition 0.000 description 1
- XPPKVPWEQAFLFU-UHFFFAOYSA-J diphosphate(4-) Chemical compound [O-]P([O-])(=O)OP([O-])([O-])=O XPPKVPWEQAFLFU-UHFFFAOYSA-J 0.000 description 1
- 235000011180 diphosphates Nutrition 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000001804 emulsifying effect Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 description 1
- 229910052808 lithium carbonate Inorganic materials 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 235000019837 monoammonium phosphate Nutrition 0.000 description 1
- 238000007709 nanocrystallization Methods 0.000 description 1
- 239000002086 nanomaterial Substances 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000033116 oxidation-reduction process Effects 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- DPTATFGPDCLUTF-UHFFFAOYSA-N phosphanylidyneiron Chemical compound [Fe]#P DPTATFGPDCLUTF-UHFFFAOYSA-N 0.000 description 1
- 229920000447 polyanionic polymer Polymers 0.000 description 1
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000004080 punching Methods 0.000 description 1
- 229940048084 pyrophosphate Drugs 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 238000004626 scanning electron microscopy Methods 0.000 description 1
- 238000010008 shearing Methods 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 238000003746 solid phase reaction Methods 0.000 description 1
- 241000894007 species Species 0.000 description 1
- 239000012798 spherical particle Substances 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
- 230000002195 synergetic effect Effects 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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
- C01B25/45—Phosphates containing plural metal, or metal and ammonium
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
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Abstract
The invention provides a carbon-coated mixed phosphate positive electrode material, a preparation method and application thereof. The preparation method comprises the steps of preparing an acid solution, dissolving a sodium source, a phosphorus source, a carbon source and a metal source in water, and adding the water into the acid solution to obtain a mixed solution; wherein the metal elements in the metal source comprise Fe, mn and M elements, and the M element is one or more of Ni, al, ti, V, mg or Zn; drying the mixed solution to obtain a precursor; the precursor is subjected to inert atmosphereThe segmented heat treatment of the carbon-coated mixed phosphate anode material is obtained; and wherein the mixed phosphate has the formula Na 4 Fe x Mn y M z (PO 4 ) 2 P 2 O 7 Where x+y+z=3, and x, y, and z are not 0. The obtained carbon-coated mixed phosphate positive electrode material has higher crystallinity and no NaMPO 4 、Na 2 MP 2 O 7 The phase purity and the electrochemical performance of the impurity phases are obviously improved.
Description
Technical Field
The invention relates to the field of sodium ion batteries, in particular to a carbon-coated mixed phosphate positive electrode material, a preparation method and application thereof.
Background
In recent years, renewable clean energy sources such as solar energy, wind energy, tidal energy, geothermal energy and the like are rapidly developed, but these clean energy sources belong to intermittent energy sources and cannot be continuously supplied, so in order to fully utilize these renewable energy sources, energy storage systems matched with these renewable energy sources need to be developed. Lithium ion batteries are dominant in the energy storage market due to high energy density and mature technology, but the shortage and uneven distribution of lithium ore resources lead to a great increase in lithium carbonate price, and the application of the lithium ion batteries in large-scale energy storage systems is limited by the excessive cost. Sodium ion batteries have a similar working mechanism to lithium ion batteries, and sodium metal is widely distributed worldwide and low in price, so that the sodium ion batteries are regarded as the most potential substitutes of the lithium ion batteries in the energy storage field.
Mixed phosphate Na 4 M 3 (PO 4 ) 2 P 2 O 7 (m= Fe, mn, ni, co) is a positive electrode material of a sodium ion battery with a polyanion structure, has the advantages of phosphate and pyrophosphate, and has higher oxidation-reduction potential and excellent cycling stability in application. Wherein the phosphate Na is mixed 4 Fe 3 (PO 4 ) 2 P 2 O 7 The theoretical reversible specific capacity of the positive electrode material is 129mAh g -1 The average operating voltage was 3.1V (vs.Na + Na), has excellent electrochemical sodium storage performance and low raw material cost, and is a sodium ion battery anode material with great development potential.
However, mixed phosphate Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 The cathode material has the following three problems that firstly, the electron conductivity of the material is low; at present, researchers often use Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 Compounding with carbon materialsTo improve the electron conductivity and obtain obvious effect. Secondly, the sodium ion diffusion coefficient is low, and in order to shorten the ion diffusion path, the material needs to be nanocrystallized; at present, the nano material is mainly obtained by controlling the particle size of raw materials and a heat treatment process. Thirdly, naFePO4 and Na are very easy to generate in the preparation process 2 FeP 2 O 7 The problem of the reversible specific capacity and the cycle stability of the material is seriously influenced by waiting for mixed phases, and Cao Yuliang teaches that the subject group prepares the anode material Na with good electrochemical performance by designing the thought of the iron-phosphorus ratio and introducing an iron defect regulation strategy 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 . However, the currently reported Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 The preparation method mainly adopts Fe (NO) 3 ) 3 ·9H 2 O and FePO 4 Na produced from such raw materials as an iron source 4 Fe 3 (PO 4 ) 2 P 2 O 7 The products inevitably contain NaFePO 4 、Na 2 FeP 2 O 7 And an impurity phase. The reason for this is mainly that Fe (NO) 3 ) 3 ·9H 2 O is easily decomposed into FeO at low temperature, and FeO is easily decomposed with NaH 2 PO 4 Production of NaFePO 4 An impurity phase; fePO 4 Then is easy to be matched with NaH 2 PO 4 Formation of NaFePO 4 、Na 2 FeP 2 O 7 An impurity phase; meanwhile, the crystallization water introduced by the raw materials in the sintering process is insufficiently controlled and optimized in the high-temperature low-temperature heat treatment process.
Based on this, there is a need in the art to provide a preparation method with simple and efficient process flow, so as to solve the problems that the phase purity of the mixed phosphate positive electrode material obtained by the existing preparation method is low and the application of the sodium ion battery cannot be satisfied.
Disclosure of Invention
The invention mainly aims to provide a carbon-coated mixed phosphate positive electrode material, a preparation method and application thereof, and aims to solve the problems that the mixed phosphate positive electrode material obtained by the existing preparation method is low in phase purity and cannot meet the application requirement of a sodium ion battery.
In order to achieve the above object, according to one aspect of the present invention, there is provided a method for preparing a carbon-coated mixed phosphate positive electrode material, comprising: step S1, preparing an acid solution, dissolving a sodium source, a phosphorus source, a carbon source and a metal source in water, and then adding the water into the acid solution to obtain a mixed solution; wherein the metal elements in the metal source comprise Fe, mn and M elements, and the M element is one or more of Ni, al, ti, V, mg or Zn; step S2, drying the mixed solution to obtain a precursor; step S3, carrying out sectional heat treatment on the precursor in inert atmosphere to obtain carbon-coated mixed phosphate, namely a carbon-coated mixed phosphate anode material; and the molecular formula of the mixed phosphate in the carbon-coated mixed phosphate positive electrode material is Na 4 Fe x Mn y M z (PO 4 ) 2 P 2 O 7 Where x+y+z=3, and x, y, and z are not 0.
Further, the M element is Mg, al or Zn; preferably, 0 < x < 3,0 < y < 3,0 < z.ltoreq.0.2.
Further, in step S1, the acid solution is a mixed solution of an organic acid and an inorganic acid, wherein the organic acid is one or more selected from citric acid monohydrate, oxalic acid, formic acid, acetic acid, ascorbic acid, tartaric acid and malic acid, and the inorganic acid is one or more selected from concentrated nitric acid, hydrochloric acid and sulfuric acid; preferably, the acid solution is a mixed solution of citric acid monohydrate and concentrated nitric acid; more preferably, citric acid monohydrate in acid solution and HNO in concentrated nitric acid 3 The molar ratio of (2.19-2.40) is 1.
Further, in step S1, the carbon source is one or more selected from glucose, sucrose, chitosan, citric acid monohydrate, carbon nanotubes, graphene, carbon black, mesoporous carbon, soluble starch, corn dextrin, methylcellulose, phenolic resin, polypropylene, polyacrylonitrile, polyethylene, and polyvinyl alcohol; preferably, the carbon source is a mixture of glucose and citric acid monohydrate; more preferably, the molar ratio of glucose to citric acid monohydrate in the carbon source is 1 (1.8-2.2).
Further, in the step S1, the total acid mass concentration of the acid solution is 13-17%; the volume ratio of the acid solution to the water is (0.2-0.35) 1, and the weight ratio of the total mass of the sodium source, the phosphorus source, the carbon source and the metal source to the water is (0.2-0.3) 1; preferably, the molar ratio of the carbon source to the metal source is (1.1 to 1.2): 1.
Further, in step S3, the sectional heat treatment includes: the first stage of heat treatment, the temperature is 250-350 ℃, the heating rate is 1-2 ℃/min, and the heat preservation time is 5-10 h; and the second stage of heat treatment, the temperature is 500-700 ℃, the heating rate is 5-10 ℃/min, and the heat preservation time is 10-20 h.
Further, in step S1, the dissolution standard of the metal source is solid particle size d50=0.2 to 0.5 μm.
Further, the metal source is added in the form of one or more of nitrate, phosphate, sulfate, acetate, chloride, oxide and hydroxide; and/or sodium source is selected from one or more of sodium carbonate, sodium hydroxide, sodium nitrate, sodium chloride, sodium citrate, sodium oxalate, sodium acetate, sodium pyrophosphate, trisodium phosphate, sodium dihydrogen phosphate and sodium dihydrogen phosphate; and/or the phosphorus source is selected from one or more of sodium pyrophosphate, trisodium phosphate, sodium dihydrogen phosphate, ammonium phosphate and phosphoric acid.
Further, the implementation of the drying in step S2 is selected from the group consisting of forced air drying, flash drying, or spray drying; preferably, the drying is achieved by spray drying; more preferably, the air inlet temperature of spray drying is 140-250 ℃ and the air outlet temperature is 80-120 ℃.
The invention also provides a carbon-coated mixed phosphate positive electrode material, which is prepared by the preparation method.
In yet another aspect, the invention provides a sodium ion battery comprising a positive electrode sheet of the carbon-coated mixed phosphate positive electrode material described above.
Compared with other preparation methods, the carbon-coated mixed phosphate anode material prepared by the technical scheme of the invention has higher crystallinity and no NaMPO 4 、Na 2 MP 2 O 7 And the impurity phases are equal, so that the phase purity of the crystal can be obviously improved. The carbon-coated mixed phosphate positive electrode material prepared by the invention is applied to sodium ion batteries, and the battery cycle performance can be obviously improved.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention. In the drawings:
FIG. 1 is a carbon-coated Na 4 Mn 1.5 Fe 1.4 Al 0.1 (PO 4 ) 2 P 2 O 7 X-ray diffraction pattern of the positive electrode material;
FIG. 2 is a carbon-coated Na 4 Mn 1.5 Fe 1.4 Al 0.1 (PO 4 ) 2 P 2 O 7 Scanning electron microscope pictures of the positive electrode material;
FIG. 3 is a carbon-coated Na 4 Mn 1.5 Fe 1.4 Mg 0.1 (PO 4 ) 2 P 2 O 7 X-ray diffraction pattern of the positive electrode material;
FIG. 4 is a carbon-coated Na 4 Mn 1.5 Fe 1.4 Mg 0.1 (PO 4 ) 2 P 2 O 7 Scanning electron microscope pictures of the positive electrode material;
FIG. 5 is a carbon-coated Na 4 Mn 1.5 Fe 1.4 Zn 0.1 (PO 4 ) 2 P 2 O 7 X-ray diffraction pattern of the positive electrode material;
FIG. 6 is a carbon-coated Na 4 Mn 1.5 Fe 1.4 Zn 0.1 (PO 4 ) 2 P 2 O 7 Scanning electron microscope pictures of the positive electrode material;
FIG. 7 is a carbon-coated Na 4 Mn 1.5 Fe 1.4 Mg 0.05 Zn 0.05 (PO 4 ) 2 P 2 O 7 X-ray diffraction pattern of the positive electrode material;
FIG. 8 is a carbon-coated Na 4 Mn 1.5 Fe 1.4 Mg 0.05 Zn 0.05 (PO 4 ) 2 P 2 O 7 Scanning electron microscopy of the positive electrode material.
Detailed Description
It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other. The present invention will be described in detail with reference to examples.
As described in the background art, the mixed phosphate positive electrode material obtained by the existing preparation method has the problems of low phase purity and incapability of meeting the application of sodium ion batteries. In order to solve the technical problems, the application provides a preparation method of a carbon-coated mixed phosphate positive electrode material, which comprises the following steps: step S1, preparing an acid solution, dissolving a sodium source, a phosphorus source, a carbon source and a metal source in water, and then adding the water into the acid solution to obtain a mixed solution; wherein the metal elements in the metal source comprise Fe, mn and M elements, and the M element is one or more of Ni, al, ti, V, mg or Zn; step S2, drying the mixed solution to obtain a precursor; step S3, carrying out sectional heat treatment on the precursor in inert atmosphere to obtain carbon-coated mixed phosphate, namely a carbon-coated mixed phosphate anode material; and the molecular formula of the mixed phosphate in the carbon-coated mixed phosphate positive electrode material is Na 4 Fe x Mn y M z (PO 4 ) 2 P 2 O 7 Where x+y+z=3, and x, y, and z are not 0.
The carbon-coated mixed phosphate anode material prepared by the preparation method provided by the invention has higher crystallinity and no NaMPO 4 、Na 2 MP 2 O 7 The purity of the impurity phases is obviously improved, and the electrochemical performance is also improved to a certain extent. Specifically, the precursor is prepared in the acid solution, so that the formation of metal phosphate precipitate can be prevented, the mixing uniformity of Na, P, fe, mn, M and other elements is improved, the phase purity of the mixed phosphate in the carbon-coated mixed phosphate positive electrode material is improved, and NaMPO is avoided 4 、Na 2 MP 2 O 7 Formation of an isopipe phase and carbon-coated Na prepared under such acidic conditions 4 Fe x Mn y M z (PO 4 ) 2 P 2 O 7 The applicability of the mixed phosphate material is wider. Meanwhile, the metal elements introduced into the mixed solution for preparing the precursor comprise Fe, mn and M elements, and the elements, the sodium source and the phosphorus source are matched with Na 4 Fe x Mn y M z (PO 4 ) 2 P 2 O 7 Where x+y+z=3, and x, y, and z are not all quantitative requirements of 0. Firstly, the quantitative doping of one or more of Fe and Mn elements and Ni, al, ti, V, mg or Zn into the carbon-coated mixed phosphate positive electrode material can better improve the electronic conductivity of the positive electrode material compared with the doping of only Fe and Mn elements, and particularly, the doping amount of M element is controlled within the range, so that the electrochemical performance of the positive electrode material is further improved. In addition, the doping elements can be more uniformly doped into the mixed phosphate positive electrode material by means of dissolution of an acid solution, drying and sectional heat treatment, and the carbon coating is more uniform, so that the method has a better promoting effect on ensuring the electrochemical performance of the material, and can provide higher cycle stability when being applied to the positive electrode of a sodium ion battery.
In actual production, the inert atmosphere used in the present invention may be of a type commonly used in the art, such as nitrogen, etc. According to the molecular formula of Na of the mixed phosphate 4 Fe x Mn y M z (PO 4 ) 2 P 2 O 7 The skilled person can determine the relation of the addition amounts of the sodium source, the phosphorus source, the carbon source, the metal source and the like in the preparation process, and the description is omitted herein.
More specifically, in the preparation method provided by the invention, the specific experimental steps for obtaining the mixed solution in the step S1 are preferably as follows: (1) Adding a metal source into deionized water to form a solution A; (2) Dissolving acid in deionized water to form a solution B (acid solution); (3) Dissolving a sodium source, a phosphorus source and a carbon source in deionized water to form a solution C; (4) adding solution C to solution B to form solution D; (5) The solution A is added to the solution D to obtain the desired solution E, i.e., a mixed solution. The materials are added and prepared in the sequence, on one hand, the generation probability of insoluble metal phosphate is reduced, and the phase purity of the obtained mixed phosphate is improved; on the other hand, the inventor discovers through a large number of experiments that the solution in which the sodium source, the phosphorus source and the carbon source are dissolved is mixed with the acid solution before the solution in which the metal source is dissolved, so that the mixing uniformity of each element in the system can be further improved, the generation of impurity phases is avoided to a greater extent, and the cycle stability of the obtained material is improved.
In a preferred embodiment, the M element is Mg, al or Zn, and the three metal elements can have better synergistic action with Fe and Mn metals due to the specificity of the electronic structure, so that the electrochemical performance of the obtained mixed phosphate is more remarkably optimized; on the basis, preferably, 0 < x < 3,0 < y < 3, and 0 < z < 0.2, and the metal components except Na in the mixed phosphate are limited in the proportion, so that the advantages of the metals can be exerted to a greater extent, and the mixed phosphate component with more excellent microstructure and electrochemical performance is obtained.
It is worth mentioning that the inventors creatively obtained the mixed phosphate Na in which M is both metals through a large number of experiments 4 Fe x Mn y M1 0.05 M2 .0.05 (PO 4 ) 2 P 2 O 7 Wherein M1 is Al, M2 is Mg, and the molecular formula of the obtained mixed phosphate is Na 4 Fe x Mn y Al 0.05 Mg .0.05 (PO 4 ) 2 P 2 O 7 . The compound, due to Al therein 3+ And Mg (magnesium) 2+ Can inhibit Mn by the presence of 3+ The ginger-Taylor effect is generated to prevent the disproportionation reaction of manganese element and slow down the Mn of manganese 2+ The form is dissolved in electrolyte, so that the crystal structure stability of the material in the charge and discharge process is improved, more outstanding electrochemical cycling stability is shown, and the capacity and cycling stability of the sodium ion battery can be greatly improved when the material is applied to the positive electrode material of the sodium ion battery.
In a typical embodiment, the acid solution in step S1 is a mixed solution of an organic acid and an inorganic acid,the organic acid and the inorganic acid are mixed, the defect of insufficient acidity of the organic acid can be overcome through the inorganic acid with stronger acidity, and the pH value of the system can be in a lower state, so that the experimental effect can be improved, the solid components in the system can be dissolved and etched to a certain extent, the particle size of the solid components can be reduced, the nanocrystallization of the material is facilitated, and the more excellent structural performance is realized. The organic acid can be selected from one or more of citric acid monohydrate, oxalic acid, formic acid, acetic acid, ascorbic acid, tartaric acid and malic acid, and the inorganic acid can also be selected from one or more of concentrated nitric acid, hydrochloric acid and sulfuric acid. Since concentrated nitric acid is an oxidizing acid, it is capable of providing a large amount of H + Thus, in a preferred embodiment, the acid solution is a mixture of citric acid monohydrate and concentrated nitric acid, where concentrated nitric acid is a 65% strength by mass nitric acid solution; and, in order to set the pH in a range more favorable for the dissolution of the solid components, achieving a better acid dissolution effect while reducing the risk of the valence state of each metal element being changed by oxidation, obtaining a mixed phosphate having a more uniform structural composition, more preferably, citric acid monohydrate in an acid solution and HNO in concentrated nitric acid 3 The molar ratio of the mixed acid solution is 1 (2.19-2.40), and the mixed acid solution prepared by the molar ratio can maintain a clear state for a longer time, so that the stability and uniformity of the system are improved, the mixed phosphate with a more excellent structure is favorably obtained, and the long-cycle stability of the subsequent obtained material in the application process of the battery is improved.
Further, the carbon source in step S1 may be selected from any of the commonly used types in the art, including, but not limited to, glucose, sucrose, chitosan, citric acid monohydrate, carbon nanotubes, graphene, carbon black, mesoporous carbon, soluble starch, corn dextrin, methylcellulose, phenolic resin, polypropylene, polyacrylonitrile, polyethylene, and polyvinyl alcohol. The inventor has found through a lot of experiments that in a preferred embodiment, the carbon source is selected as a mixture of glucose and citric acid monohydrate, and the obtained carbon-coated mixed phosphate positive electrode material has more uniform morphology of a carbon coating layer and more proper thickness, so that the sodium ion battery has larger specific capacity and more excellent long-cycle stability when being used as the positive electrode material of the sodium ion battery; on the basis, the molar ratio of glucose to citric acid monohydrate in the carbon source is more preferably 1 (1.8-2.2), and the molar ratio of the glucose to the citric acid monohydrate is selected within the range, so that the coordination effect of the glucose and the citric acid monohydrate and the carbonization temperature in the subsequent heat treatment can be more fully exerted, and the anode material with more uniform coating layer can be obtained.
In a preferred embodiment, in step S1, the total acid mass concentration of the acid solution is 13-17%, and the acid solution at the mass concentration can provide the pH value for the system which is more beneficial to the uniformity of the system and the reaction, and can also protect Mn ions from forming MnPO to a greater extent 4 Is a precipitate of (a) and (b). In order to improve the dispersing effect of the system, the volume ratio of the acid solution to the water is (0.2-0.35): 1, and in order that the sodium source, the phosphorus source, the carbon source and the metal source can be better dissolved, the total mass of the solid components before dissolution and the weight ratio of the water are (0.2-0.3): 1. In order to improve the effect of carbon coating, a positive electrode material with a more complete and uniform coating layer is obtained, the molar ratio of the carbon source to the metal source is preferably 1.1-1.2:1, and the molar ratio of the carbon source to the metal source is selected within the range, which is also beneficial to the citric acid monohydrate in the carbon source to protect the metal in the mixed phosphate therein from being oxidized in the subsequent heat treatment process, thereby obtaining the carbon-coated Na with more stable structure, high phase purity and high microscopic uniformity 4 Fe x Mn y M z (PO 4 ) 2 P 2 O 7 Material (where x+y+z=3, and x, y, and z are not all 0).
Further, in order to enhance the effect of the heat treatment as a whole, in step S3, the sectional heat treatment includes: the first stage of heat treatment, the temperature is 250-350 ℃, the heating rate is 1-2 ℃/min, and the heat preservation time is 5-10 h; the second stage of heat treatment, the temperature is 500-700 ℃, the heating rate is 5-10 ℃/min, and the heat preservation time is 10-20 h; the adoption of the sectional heat treatment process with the above parameter settings can obtain the carbon package with more excellent crystallinity and phase purityCoating the mixed phosphate material. In the first heat treatment, the carbonization temperature of the mixture carbon source selected according to the invention is selected to be 250-350 ℃, and meanwhile, the slow heating rate of 1-2 ℃/min is selected, so that carbonization can be more completely carried out compared with the heating rate of more than 2 ℃/min, and meanwhile, metal ions in the precursor are more effectively prevented from being oxidized, a better structure is more favorably obtained, and the complete carbonization is also facilitated when the heat preservation time is selected to be longer for 5-10 hours, so that the anode material with a complete coating layer is obtained; the second stage heat treatment selects a faster heating rate of 5-10 ℃/min, compared with a heating rate below 5 ℃/min, the heating rate can reduce heat diffusion, and can reach the set heat treatment temperature more quickly, thereby improving the phase purity and structural uniformity, and simultaneously, the higher temperature of 500-700 ℃ is used as the heat treatment temperature, so that each metal ion, especially Al, selected in the invention 3+ Can better react with PO in the solid phase reaction process 4 3- The combination is carried out, and the longer heat preservation time of 10-20 h can be combined with the higher heat treatment time of 500-700 ℃, so that the crystallinity of the obtained carbon-coated phosphate positive electrode material is improved, and the long-cycle stability of the finally obtained sodium ion battery is improved.
In order to enable the metal source to be better dissolved and provide a system with more abundant metal ions, in a preferred embodiment, the dissolution standard of the metal source in step S1 is that the solid particle size d50=0.2-0.5 μm, and compared with the larger particle size d50=0.5 μm or more, the particle size range can enable the metal which is not completely dissolved in the deionized water to be dissolved at a higher speed and enter the system in the form of metal ions after entering the acid solution, so that the dispersion uniformity among elements in the whole system is improved, and the structural uniformity of the mixed phosphate component in the finally obtained carbon-coated mixed phosphate positive electrode material is improved.
In several exemplary embodiments, the metal source is added in the form of one or more of nitrate, phosphate, sulfate, acetate, chloride, oxide, and hydroxide; and/or the sodium source is selected from the species commonly used in the art, including, but not limited to, sodium carbonate, sodium hydroxide, sodium nitrate, sodium chloride, sodium citrate, sodium oxalate, sodium acetate, sodium pyrophosphate, trisodium phosphate, sodium dihydrogen phosphate, and sodium monohydrogen phosphate; and/or the phosphorus source is also selected from the classes commonly used in the art including, but not limited to, sodium pyrophosphate, trisodium phosphate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium phosphate, and phosphoric acid.
Further, the drying in step S2 is performed by a method selected from the group consisting of forced air drying, flash drying and spray drying, which are commonly used in the art; in a typical embodiment, the drying is performed by spray drying, and more preferably, the inlet air temperature is 140-250 ℃ and the outlet air temperature is 80-120 ℃, so that the drying of the precursor is realized in a faster time, and the precursor with better drying property is obtained while saving cost, thereby being beneficial to obtaining the carbon-coated mixed phosphate material with better uniformity in the subsequent sectional heat treatment.
The invention also provides a carbon-coated mixed phosphate positive electrode material, which is prepared by the preparation method. The prepared positive electrode material has higher crystallinity and no NaMPO 4 、Na 2 MP 2 O 7 The purity of the impurity phases is higher; meanwhile, the particle size is uniform, the structure is stable, and the cathode can provide a plurality of excellent electrochemical performances including gram capacity, long-cycle stability and the like when being used for the anode of a sodium ion battery.
In yet another aspect, the invention provides a sodium ion battery comprising a positive electrode sheet of the carbon-coated mixed phosphate positive electrode material described above. The obtained sodium ion battery has good sodium storage performance and excellent long-cycle stability, and can be well applied to various electrochemical scenes.
The present application is described in further detail below in conjunction with specific embodiments, which should not be construed as limiting the scope of the claims.
Unless defined otherwise, all technical and scientific terms used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the scope of the present invention.
Example 1
Preparation of a carbon-coated mixed phosphate positive electrode material:
36.7635g Mn (CH) 3 COO) 2 ·4H 2 O、56.56g Fe(NO 3 ) 3 ·9H 2 O and 0.78g Al (OH) 3 Adding into 200mL deionized water to form solution A (each metal salt is ball-milled for 8h to 0.2 μm before adding into deionized water<D50<0.5 μm and washing the ball-milling pot with deionized water 3-5 times, the washing liquid being transferred to the beaker in total as well); 63.042g of citric acid monohydrate and 50mL of concentrated nitric acid (65% by mass) were added to 200mL of deionized water to form a solution B; 62.404g NaH 2 PO 4 ·2H 2 O, 21.6g glucose and 50.4g citric acid monohydrate were added to 200mL deionized water to form solution C; adding the solution C into the solution B to form a solution D; adding the solution A into the solution D, and regulating the solution to 900mL by using deionized water to form a uniform yellowish transparent clear solution E, wherein the solid particle size D50 is 0.3-0.5 mu m. And (3) spray-drying the transparent solution, wherein the air inlet temperature is 220 ℃, and the air outlet temperature is 110 ℃, so as to obtain a powdery dry light yellow precursor. Heating the precursor to 300 ℃ at a heating rate of 1 ℃/min in a nitrogen atmosphere, preserving heat for 5 hours, heating to 650 ℃ at a heating rate of 5 ℃/min, preserving heat for 12 hours, and cooling to room temperature to obtain carbon-coated Na 4 Mn 1.5 Fe 1.4 Al 0.1 (PO 4 ) 2 P 2 O 7 And a positive electrode material.
FIG. 1 shows the obtained carbon-coated Na 4 Mn 1.5 Fe 1.4 Al 0.1 (PO 4 ) 2 P 2 O 7 The X-ray diffraction pattern of the positive electrode material shows that the phase purity and crystallinity of the product are high, and NaFePO is not generated 4 、Na 2 FeP 2 O 7 、NaMnPO 4 、NaMnP 2 O 7 An impurity phase;
FIG. 2 shows the obtained carbon-coated Na 4 Mn 1.5 Fe 1.4 Al 0.1 (PO 4 ) 2 P 2 O 7 The scanning electron microscope image of the positive electrode material shows that the positive electrode material is approximately spherical particles with uneven sizes of 1-5 um, and has smooth surface and no tiny air holes.
Example 2
Preparation of a carbon-coated mixed phosphate positive electrode material:
this embodiment differs from embodiment 1 only in that: 0.78g of Al (OH) was not added to the solution A 3 Instead, 1.4832g of Mg (NO 3 ) 2 。
FIG. 3 shows the obtained carbon-coated Na 4 Mn 1.5 Fe 1.4 Mg 0.1 (PO 4 ) 2 P 2 O 7 The X-ray diffraction pattern of the positive electrode material shows that the phase purity and crystallinity of the product are high, and NaFePO is not generated 4 、Na 2 FeP 2 O 7 、NaMnPO 4 、NaMnP 2 O 7 An impurity phase;
FIG. 4 shows the obtained carbon-coated Na 4 Mn 1.5 Fe 1.4 Mg 0.1 (PO 4 ) 2 P 2 O 7 The scanning electron microscope image of the positive electrode material shows that the positive electrode material is a sheet with irregular shape, and the surface of the positive electrode material is provided with air holes with different sizes.
Example 3
Preparation of a carbon-coated mixed phosphate positive electrode material:
this embodiment differs from embodiment 1 only in that: 0.78g of Al (OH) was not added to the solution A 3 But 1.894g of Zn (NO) 3 ) 2 。
FIG. 5 shows the obtained carbon-coated Na 4 Mn 1.5 Fe 1.4 Zn 0.1 (PO 4 ) 2 P 2 O 7 The X-ray diffraction pattern of the positive electrode material shows that the phase purity and crystallinity of the product are high, and NaFePO is not generated 4 、Na 2 FeP 2 O 7 、NaMnPO 4 、NaMnP 2 O 7 An impurity phase;
FIG. 6 shows the obtained carbon-coated Na 4 Mn 1.5 Fe 1.4 Zn 0.1 (PO 4 ) 2 P 2 O 7 The scanning electron microscope image of the positive electrode material shows that the positive electrode material is an irregularly-shaped sheet, and the surface of the positive electrode material is provided with tiny air holes, and the size of the positive electrode material is 1-5 um.
Example 4
Preparation of a carbon-coated mixed phosphate positive electrode material:
this embodiment differs from embodiment 1 only in that: 0.78g of Al (OH) was not added to the solution A 3 But 0.947g of Zn (NO) 3 ) 2 And 0.7416g of Mg (NO 3 ) 2 。
FIG. 7 shows the obtained carbon-coated Na 4 Mn 1.5 Fe 1.4 Mg 0.05 Zn 0.05 (PO 4 ) 2 P 2 O 7 The X-ray diffraction pattern of the positive electrode material shows that the phase purity and crystallinity of the product are high, and NaFePO is not generated 4 、Na 2 FeP 2 O 7 、NaMnPO 4 、NaMnP 2 O 7 An impurity phase;
FIG. 8 shows the obtained carbon-coated Na 4 Mn 1.5 Fe 1.4 Mg 0.05 Zn 0.05 (PO 4 ) 2 P 2 O 7 The scanning electron microscope image of the positive electrode material shows that the positive electrode material is an irregularly-shaped sheet, the surface of the positive electrode material is provided with pores with different sizes, and the particle size is 1-10 um.
Example 5
Preparation of a carbon-coated mixed phosphate positive electrode material:
this embodiment differs from embodiment 1 only in that: to solution B, 50mL of concentrated nitric acid was not added.
Example 6
Preparation of a carbon-coated mixed phosphate positive electrode material:
this embodiment differs from embodiment 1 only in that: 63.042g of citric acid monohydrate and 22.83mL of concentrated nitric acid (65% by mass) were added to 200mL of deionized water to form solution B, i.e., HNO in citric acid and concentrated nitric acid 3 The molar ratio of (2) is 1:1.
Example 7
Preparation of a carbon-coated mixed phosphate positive electrode material:
this embodiment differs from embodiment 1 only in that: 63.042g of citric acid monohydrate and 68.49mL of concentrated nitric acid (65% by mass) were added to 200mL of deionized water to form solution B, i.e., HNO in citric acid and concentrated nitric acid 3 The molar ratio of (2) is 1:3.
Example 8
Preparation of a carbon-coated mixed phosphate positive electrode material:
this embodiment differs from embodiment 1 only in that: glucose was not added to solution C and replaced with equimolar (25.2 g) citric acid monohydrate.
Example 9
Preparation of a carbon-coated mixed phosphate positive electrode material:
this embodiment differs from embodiment 1 only in that: 62.404g NaH 2 PO 4 ·2H 2 O, 31.5g glucose and 36.75g citric acid monohydrate were added to 200mL deionized water to form solution C, i.e., a 1:1 molar ratio of glucose to citric acid monohydrate.
Example 10
Preparation of a carbon-coated mixed phosphate positive electrode material:
this embodiment differs from embodiment 1 only in that: 62.404g NaH 2 PO 4 ·2H 2 O, 15.75g glucose and 55.125g citric acid monohydrate were added to 200mL deionized water to form solution C, i.e., a 1:3 molar ratio of glucose to citric acid monohydrate.
Example 11
Preparation of a carbon-coated mixed phosphate positive electrode material:
this embodiment differs from embodiment 1 only in that: 62.404g NaH 2 PO 4 ·2H 2 O, 18.00g glucose and 42.00g citric acid monohydrate were added to 200mL deionized water to form solution C, i.e., a 1:1 molar ratio of carbon source to metal source.
Example 12
Preparation of a carbon-coated mixed phosphate positive electrode material:
this embodiment differs from embodiment 1 only in that: 62.404g NaH 2 PO 4 ·2H 2 O, 36.00g glucose and 84.00g citric acid monohydrate were added to 200mL deionized water to form solution C, i.e., a 2:1 molar ratio of carbon source to metal source.
Example 13
Preparation of a carbon-coated mixed phosphate positive electrode material:
this embodiment differs from embodiment 1 only in that: the precursor is heated to 300 ℃ at a heating rate of 5 ℃/min in nitrogen atmosphere, is kept for 3 hours, and is heated to 650 ℃ at a heating rate of 5 ℃/min, and is kept for 12 hours. In the sectional heat treatment, the temperature rising rate in the first temperature rising process is improved, and the heat preservation time is shortened.
Example 14
Preparation of a carbon-coated mixed phosphate positive electrode material:
this embodiment differs from embodiment 1 only in that: the precursor is heated to 300 ℃ at a heating rate of 1 ℃/min in nitrogen atmosphere, is kept for 5 hours, and is heated to 650 ℃ at a heating rate of 2 ℃/min, and is kept for 10 hours. In the sectional heat treatment, the temperature rising rate in the first temperature rising process is improved, and the heat preservation time is shortened.
Example 15
Preparation of a carbon-coated mixed phosphate positive electrode material:
this embodiment differs from embodiment 1 only in that: the solid particle diameter D50 contained in the solution E is 0.1-0.2 μm.
Example 16
Preparation of a carbon-coated mixed phosphate positive electrode material:
this embodiment differs from embodiment 1 only in that: adjusting the weight of each metal source so that the molecular formula of the mixed phosphate in the finally obtained carbon-coated mixed phosphate positive electrode material is Na 4 Mn 0.9 Fe 2.0 Al 0.1 (PO 4 ) 2 P 2 O 7 。
Example 17
Preparation of a carbon-coated mixed phosphate positive electrode material:
this embodiment differs from embodiment 1 only in that: adjusting the weight of each metal source so that the molecular formula of the mixed phosphate in the finally obtained carbon-coated mixed phosphate positive electrode material is Na 4 Mn 2.0 Fe 0.9 Al 0.1 (PO 4 ) 2 P 2 O 7 。
Comparative example 1
Preparation of a carbon-coated mixed phosphate positive electrode material:
45.2448g FePO 4 Adding into 100mL of deionized water to obtain solution A; 42.028g of citric acid monohydrate was added to 200mL of deionized water to form solution B; 15.8985g of Na 2 CO 3 、15.601g NaH 2 PO 4 ·2H 2 O and 19.817g of glucose monohydrate are added into 200mL of deionized water in sequence to form a solution C; adding the solution C into the solution B to form a solution D; solution A was added to solution D and the solution was adjusted to 900mL with deionized water to give the desired solution E. Dispersing for 4 hours by adopting a high-speed emulsifying shearing machine to obtain an off-white opaque suspension aqueous solution which is uniformly dispersed. The water of the opaque suspension water solution is instantaneously evaporated by a spray dryer, the air inlet temperature is 200 ℃, and the air outlet temperature is 110 ℃, so as to obtain a powdery dry light white precursor. Heating the precursor to 280 ℃ at a heating rate of 1 ℃/min in a nitrogen atmosphere furnace, preserving heat for 5 hours, then heating to 580 ℃ at a heating rate of 5 ℃/min, preserving heat for 15 hours, and cooling to room temperature to obtain the carbon-coated Na4Fe 3 (PO 4 ) 2 P 2 O 7 And a positive electrode material.
Comparative example 2
Preparation of a carbon-coated mixed phosphate positive electrode material:
73.527g of Mn (CH) 3 COO) 2 ·4H 2 O is added into 200mL of deionized water to form solution A; 50mL of 65% concentrated nitric acid was dissolved in 200mL of deionized water to form solution B; 26.59g of Na 4 P 2 O 7 、23.0056g NH 4 H 2 PO 4 And 63.042g citric acid monohydrate were added sequentially to 200mL deionized water to form solution C; adding solution C into solution B to formForming a solution D; solution A was added to solution D and the solution was adjusted to 900mL with deionized water to give the desired solution E. And (3) spray-drying the transparent solution, wherein the air inlet temperature is 230 ℃, and the air outlet temperature is 120 ℃, so as to obtain a powdery dry light yellow precursor. Heating the precursor to 300 ℃ at a heating rate of 1 ℃/min in a nitrogen atmosphere, preserving heat for 5 hours, heating to 700 ℃ at a heating rate of 5 ℃/min, preserving heat for 20 hours, and cooling to room temperature to obtain carbon-coated Na 4 Mn 3 (PO 4 ) 2 P 2 O 7 And a positive electrode material.
Comparative example 3
Preparation of a carbon-coated mixed phosphate positive electrode material:
22.0581g Mn (CH) 3 COO) 2 ·4H 2 O and 84.84g Fe (NO) 3 ) 3 9H2O was added to 200mL of deionized water to form solution A; 73.549g of citric acid monohydrate was added to 200mL of deionized water to form solution B; 62.404g NaH 2 PO 4 ·2H 2 O is added into 200mL of deionized water to form solution C; adding the solution C into the solution B to form a solution D; solution A was added to solution D and the solution was adjusted to 800mL with deionized water to form a homogeneous pale yellow clear solution E. And (3) spray-drying the transparent solution, wherein the air inlet temperature is 220 ℃, and the air outlet temperature is 110 ℃, so as to obtain a powdery dry light yellow precursor. Heating the precursor to 300 ℃ at a heating rate of 1 ℃/min in a nitrogen atmosphere, preserving heat for 5 hours, heating to 600 ℃ at a heating rate of 5 ℃/min, preserving heat for 10 hours, and cooling to room temperature to obtain carbon-coated Na 4 Mn 0.9 Fe 2.1 (PO 4 ) 2 P 2 O 7 And a positive electrode material.
Comparative example 4
Preparation of a carbon-coated mixed phosphate positive electrode material:
36.7635g Mn (CH) 3 COO) 2 4H2O and 60.6g Fe (NO) 3 ) 3 ·9H 2 O is added into 200mL of deionized water to form solution A; 73.549g of citric acid monohydrate was added to 200mL of deionized water to form solution B; 62.404g NaH 2 PO 4 ·2H 2 O is added into 200mL of deionized water to form solution C; adding the solution C into the solution B to form a solution D; solution A was added to solution D and the solution was adjusted to 800mL with deionized water to form a homogeneous pale yellow clear solution E. And (3) spray-drying the transparent solution, wherein the air inlet temperature is 220 ℃, and the air outlet temperature is 110 ℃, so as to obtain a powdery dry light yellow precursor. Heating the precursor to 300 ℃ at a heating rate of 1 ℃/min in a nitrogen atmosphere, preserving heat for 5 hours, heating to 650 ℃ at a heating rate of 5 ℃/min, preserving heat for 10 hours, and cooling to room temperature to obtain carbon-coated Na 4 Mn 1.5 Fe 1.5 (PO 4 ) 2 P 2 O 7 And a positive electrode material.
Performance test:
the resulting carbon-coated mixed phosphate material, acetylene black and PVDF were mixed according to 85:10:5, adding a small amount of NMP, mixing into uniform slurry, coating the slurry on aluminum foil, and drying in vacuum at 120 ℃ for 12 hours. Punching the electrode plate into a circular plate with the diameter of 12 mm; sodium metal sheet is used as a counter electrode, cellgard2035 is used as a diaphragm, and 1mol/L NaPF is used 6 Ec+dmc (1:1vol%) +5% FEC was used as the electrolyte, and CR2025 type coin cell was assembled in a glove box. The button cell was subjected to constant current charge-discharge cycle test with current densities of 0.1C and 0.5C (1c=129 mah·g -1 ) The voltage test interval is 1.5-4.0V (vs. Na/Na + )。
The results of the electrochemical performance tests of the obtained examples and comparative examples are shown in table 1, and the performance tests comprise the first-cycle charge-discharge specific capacity at 0.1C rate, the first-cycle discharge specific capacity at 0.5C rate and the capacity retention rate of 100 cycles of charge-discharge cycle.
TABLE 1
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From the aboveIn the description of (2), it can be seen that the above examples of the present invention are free of NaMPO due to the higher crystallinity 4 、Na 2 MP 2 O 7 The phase purity of the isopipe phase is remarkably improved, so that the electrochemical performance is improved to a certain extent, wherein in example 4, carbon-coated Na 4 Fe x Mn y Al 0.05 Mg .0.05 (PO 4 ) 2 P 2 O 7 Because of Al therein 3+ And Mg (magnesium) 2+ Can inhibit Mn by the presence of 3+ The ginger-Taylor effect is generated, the disproportionation reaction of manganese element is prevented, and partial manganese is slowed down to Mn 2+ The form is dissolved in electrolyte, so that the crystal structure stability of the material in the charge and discharge processes is improved, and the material shows more outstanding electrochemical cycle stability.
It should be noted that the terms "first," "second," and the like in the description and in the claims of the present application are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those described herein.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (11)
1. The preparation method of the carbon-coated mixed phosphate positive electrode material is characterized by comprising the following steps of:
step S1, preparing an acid solution, dissolving a sodium source, a phosphorus source, a carbon source and a metal source in water, and adding the water into the acid solution to obtain a mixed solution; wherein the metal elements in the metal source comprise Fe, mn and M elements, and the M element is one or more of Ni, al, ti, V, mg or Zn;
step S2, drying the mixed solution to obtain a precursor;
step S3, carrying out sectional heat treatment on the precursor under inert atmosphere to obtain carbon-coated mixed phosphate, namely the carbon-coated mixed phosphate anode material; and the molecular formula of the mixed phosphate in the carbon-coated mixed phosphate positive electrode material is Na 4 Fe x Mn y M z (PO 4 ) 2 P 2 O 7 Where x+y+z=3, and x, y, and z are not 0.
2. The method for producing a carbon-coated mixed phosphate positive electrode material according to claim 1, wherein the M element is Mg, al, or Zn; preferably, 0 < x < 3,0 < y < 3,0 < z.ltoreq.0.2.
3. The method for preparing a carbon-coated mixed phosphate positive electrode material according to claim 1, wherein in the step S1, the acid solution is a mixed solution of an organic acid and an inorganic acid, wherein the organic acid is one or more selected from citric acid monohydrate, oxalic acid, formic acid, acetic acid, ascorbic acid, tartaric acid and malic acid, and the inorganic acid is one or more selected from concentrated nitric acid, hydrochloric acid and sulfuric acid; preferably, the acid solution is a mixed solution of citric acid monohydrate and concentrated nitric acid; more preferably, the citric acid monohydrate in the acid solution and HNO in the concentrated nitric acid 3 The molar ratio of (2.19-2.40) is 1.
4. The method for preparing a carbon-coated mixed phosphate positive electrode material according to any one of claims 1 to 3, wherein in step S1, the carbon source is one or more selected from glucose, sucrose, chitosan, citric acid monohydrate, carbon nanotubes, graphene, carbon black, mesoporous carbon, soluble starch, corn dextrin, methylcellulose, phenolic resin, polypropylene, polyacrylonitrile, polyethylene, and polyvinyl alcohol; preferably, the carbon source is a mixture of glucose and citric acid monohydrate;
more preferably, the molar ratio of glucose to citric acid monohydrate in the carbon source is 1 (1.8-2.2).
5. The method for producing a carbon-coated mixed phosphate positive electrode material according to claims 1 to 3, wherein in step S1, the total acid mass concentration of the acid solution is 13 to 17%; the volume ratio of the acid solution to water is (0.2-0.35) 1, and the weight ratio of the total mass of the sodium source, the phosphorus source, the carbon source and the metal source to water is (0.2-0.3) 1; preferably, the molar ratio of the carbon source to the metal source is (1.1 to 1.2): 1.
6. A method of preparing a carbon-coated mixed phosphate positive electrode material according to any one of claims 1 to 3, wherein in step S3, the staged heat treatment comprises:
the first stage of heat treatment, the temperature is 250-350 ℃, the heating rate is 1-2 ℃/min, and the heat preservation time is 5-10 h;
and the second stage of heat treatment, the temperature is 500-700 ℃, the heating rate is 5-10 ℃/min, and the heat preservation time is 10-20 h.
7. The method for producing a carbon-coated mixed phosphate positive electrode material according to any one of claims 1 to 3, wherein in step S1, the dissolution standard of the metal source is solid particle diameter d50=0.2 to 0.5 μm.
8. The method for producing a carbon-coated mixed phosphate positive electrode material according to any one of claim 1 to 3, wherein,
the metal source is added in the form of one or more of nitrate, phosphate, sulfate, acetate, chloride, oxide and hydroxide; and/or
The sodium source is selected from one or more of sodium carbonate, sodium hydroxide, sodium nitrate, sodium chloride, sodium citrate, sodium oxalate, sodium acetate, sodium pyrophosphate, trisodium phosphate, sodium dihydrogen phosphate and sodium dihydrogen phosphate; and/or
The phosphorus source is selected from one or more of sodium pyrophosphate, trisodium phosphate, sodium dihydrogen phosphate, ammonium phosphate and phosphoric acid.
9. A method of preparing a carbon coated mixed phosphate positive electrode material according to any one of claims 1 to 3, wherein the drying in step S2 is effected in a manner selected from the group consisting of forced air drying, flash drying or spray drying; preferably, the drying is achieved by spray drying; more preferably, the air inlet temperature of the spray drying is 140-250 ℃, and the air outlet temperature is 80-120 ℃.
10. A carbon-coated mixed phosphate positive electrode material, characterized in that the carbon-coated mixed phosphate positive electrode material is produced by the production method according to any one of claims 1 to 9.
11. A sodium ion battery comprising a positive electrode sheet, wherein the positive electrode sheet comprises the carbon-coated mixed phosphate positive electrode material of claim 10.
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