CN117012933A - Lignin nitrogen-rich carbon/silicon oxide composite material with core-shell structure and preparation and application thereof - Google Patents
Lignin nitrogen-rich carbon/silicon oxide composite material with core-shell structure and preparation and application thereof Download PDFInfo
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- CN117012933A CN117012933A CN202311063048.2A CN202311063048A CN117012933A CN 117012933 A CN117012933 A CN 117012933A CN 202311063048 A CN202311063048 A CN 202311063048A CN 117012933 A CN117012933 A CN 117012933A
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- Prior art keywords
- lignin
- silicon oxide
- nitrogen
- carbon
- composite material
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- 229920005610 lignin Polymers 0.000 title claims abstract description 348
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 title claims abstract description 308
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 title claims abstract description 244
- 229910052814 silicon oxide Inorganic materials 0.000 title claims abstract description 239
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 201
- 239000002131 composite material Substances 0.000 title claims abstract description 172
- 229910052757 nitrogen Inorganic materials 0.000 title claims abstract description 156
- 229910002090 carbon oxide Inorganic materials 0.000 title claims abstract description 143
- 239000011258 core-shell material Substances 0.000 title claims abstract description 28
- 238000002360 preparation method Methods 0.000 title claims abstract description 17
- 239000000463 material Substances 0.000 claims abstract description 63
- 238000000034 method Methods 0.000 claims abstract description 48
- 229920000877 Melamine resin Polymers 0.000 claims abstract description 41
- JDSHMPZPIAZGSV-UHFFFAOYSA-N melamine Chemical compound NC1=NC(N)=NC(N)=N1 JDSHMPZPIAZGSV-UHFFFAOYSA-N 0.000 claims abstract description 41
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims abstract description 40
- 229910001416 lithium ion Inorganic materials 0.000 claims abstract description 40
- 238000010000 carbonizing Methods 0.000 claims abstract description 19
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 claims abstract description 17
- 229920001732 Lignosulfonate Polymers 0.000 claims abstract description 14
- 239000000243 solution Substances 0.000 claims description 113
- 238000010438 heat treatment Methods 0.000 claims description 107
- -1 glycidyl ether compound Chemical class 0.000 claims description 64
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 58
- 238000001035 drying Methods 0.000 claims description 57
- 238000003763 carbonization Methods 0.000 claims description 47
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 42
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 39
- 238000005406 washing Methods 0.000 claims description 38
- 238000006243 chemical reaction Methods 0.000 claims description 36
- 239000003513 alkali Substances 0.000 claims description 35
- 239000002253 acid Substances 0.000 claims description 24
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonia chloride Chemical compound [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 claims description 22
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 16
- 239000011259 mixed solution Substances 0.000 claims description 16
- 230000032683 aging Effects 0.000 claims description 15
- 150000003863 ammonium salts Chemical class 0.000 claims description 15
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 claims description 14
- 239000004115 Sodium Silicate Substances 0.000 claims description 14
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 claims description 14
- 229910052911 sodium silicate Inorganic materials 0.000 claims description 14
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims description 12
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 12
- 235000019270 ammonium chloride Nutrition 0.000 claims description 11
- UWFRVQVNYNPBEF-UHFFFAOYSA-N 1-(2,4-dimethylphenyl)propan-1-one Chemical compound CCC(=O)C1=CC=C(C)C=C1C UWFRVQVNYNPBEF-UHFFFAOYSA-N 0.000 claims description 9
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 9
- 150000001450 anions Chemical class 0.000 claims description 9
- 238000001027 hydrothermal synthesis Methods 0.000 claims description 9
- ZPEJZWGMHAKWNL-UHFFFAOYSA-L zinc;oxalate Chemical compound [Zn+2].[O-]C(=O)C([O-])=O ZPEJZWGMHAKWNL-UHFFFAOYSA-L 0.000 claims description 9
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 8
- 239000011261 inert gas Substances 0.000 claims description 8
- 229910017604 nitric acid Inorganic materials 0.000 claims description 8
- 229910052786 argon Inorganic materials 0.000 claims description 6
- 238000004537 pulping Methods 0.000 claims description 6
- 239000004111 Potassium silicate Substances 0.000 claims description 5
- 239000012298 atmosphere Substances 0.000 claims description 5
- 150000001768 cations Chemical class 0.000 claims description 5
- GYZLOYUZLJXAJU-UHFFFAOYSA-N diglycidyl ether Chemical compound C1OC1COCC1CO1 GYZLOYUZLJXAJU-UHFFFAOYSA-N 0.000 claims description 5
- 238000002156 mixing Methods 0.000 claims description 5
- 239000003960 organic solvent Substances 0.000 claims description 5
- NNHHDJVEYQHLHG-UHFFFAOYSA-N potassium silicate Chemical compound [K+].[K+].[O-][Si]([O-])=O NNHHDJVEYQHLHG-UHFFFAOYSA-N 0.000 claims description 5
- 229910052913 potassium silicate Inorganic materials 0.000 claims description 5
- 235000019353 potassium silicate Nutrition 0.000 claims description 5
- 239000002904 solvent Substances 0.000 claims description 5
- PAWQVTBBRAZDMG-UHFFFAOYSA-N 2-(3-bromo-2-fluorophenyl)acetic acid Chemical compound OC(=O)CC1=CC=CC(Br)=C1F PAWQVTBBRAZDMG-UHFFFAOYSA-N 0.000 claims description 4
- 230000002378 acidificating effect Effects 0.000 claims description 4
- 239000001099 ammonium carbonate Substances 0.000 claims description 4
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 claims description 4
- 229910052921 ammonium sulfate Inorganic materials 0.000 claims description 4
- 235000011130 ammonium sulphate Nutrition 0.000 claims description 4
- QXDMQSPYEZFLGF-UHFFFAOYSA-L calcium oxalate Chemical compound [Ca+2].[O-]C(=O)C([O-])=O QXDMQSPYEZFLGF-UHFFFAOYSA-L 0.000 claims description 4
- UHNWOJJPXCYKCG-UHFFFAOYSA-L magnesium oxalate Chemical compound [Mg+2].[O-]C(=O)C([O-])=O UHNWOJJPXCYKCG-UHFFFAOYSA-L 0.000 claims description 4
- 238000000197 pyrolysis Methods 0.000 claims description 4
- YXFVVABEGXRONW-UHFFFAOYSA-N toluene Substances CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 claims description 4
- ATRRKUHOCOJYRX-UHFFFAOYSA-N Ammonium bicarbonate Chemical compound [NH4+].OC([O-])=O ATRRKUHOCOJYRX-UHFFFAOYSA-N 0.000 claims description 3
- 239000007864 aqueous solution Substances 0.000 claims description 3
- 230000002255 enzymatic effect Effects 0.000 claims description 3
- 239000001307 helium Substances 0.000 claims description 3
- 229910052734 helium Inorganic materials 0.000 claims description 3
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 claims description 3
- 229910000013 Ammonium bicarbonate Inorganic materials 0.000 claims description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 2
- 235000012538 ammonium bicarbonate Nutrition 0.000 claims description 2
- 235000012501 ammonium carbonate Nutrition 0.000 claims description 2
- 235000011114 ammonium hydroxide Nutrition 0.000 claims description 2
- 229910052799 carbon Inorganic materials 0.000 abstract description 52
- 230000008569 process Effects 0.000 abstract description 24
- 239000011248 coating agent Substances 0.000 abstract description 13
- 238000000576 coating method Methods 0.000 abstract description 13
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 abstract description 9
- 238000006266 etherification reaction Methods 0.000 abstract description 9
- 230000004048 modification Effects 0.000 abstract description 9
- 238000012986 modification Methods 0.000 abstract description 9
- 229910052710 silicon Inorganic materials 0.000 abstract description 9
- 239000010703 silicon Substances 0.000 abstract description 9
- 239000011148 porous material Substances 0.000 abstract description 8
- 239000002243 precursor Substances 0.000 abstract description 6
- 230000001105 regulatory effect Effects 0.000 abstract description 5
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- 239000007784 solid electrolyte Substances 0.000 abstract description 2
- 238000001816 cooling Methods 0.000 description 51
- 239000000047 product Substances 0.000 description 45
- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Chemical compound [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 description 29
- 238000000227 grinding Methods 0.000 description 25
- 238000005303 weighing Methods 0.000 description 25
- 230000000052 comparative effect Effects 0.000 description 22
- 239000012299 nitrogen atmosphere Substances 0.000 description 19
- 239000000377 silicon dioxide Substances 0.000 description 18
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 17
- 229910052744 lithium Inorganic materials 0.000 description 17
- 239000002244 precipitate Substances 0.000 description 15
- 230000000694 effects Effects 0.000 description 14
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- 238000002791 soaking Methods 0.000 description 13
- 229910004298 SiO 2 Inorganic materials 0.000 description 12
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 description 12
- 239000000843 powder Substances 0.000 description 12
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- YDEXUEFDPVHGHE-GGMCWBHBSA-L disodium;(2r)-3-(2-hydroxy-3-methoxyphenyl)-2-[2-methoxy-4-(3-sulfonatopropyl)phenoxy]propane-1-sulfonate Chemical compound [Na+].[Na+].COC1=CC=CC(C[C@H](CS([O-])(=O)=O)OC=2C(=CC(CCCS([O-])(=O)=O)=CC=2)OC)=C1O YDEXUEFDPVHGHE-GGMCWBHBSA-L 0.000 description 11
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- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 4
- BOTDANWDWHJENH-UHFFFAOYSA-N Tetraethyl orthosilicate Chemical compound CCO[Si](OCC)(OCC)OCC BOTDANWDWHJENH-UHFFFAOYSA-N 0.000 description 4
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
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- OFXSXYCSPVKZPF-UHFFFAOYSA-N methoxyperoxymethane Chemical group COOOC OFXSXYCSPVKZPF-UHFFFAOYSA-N 0.000 description 1
- 239000012229 microporous material Substances 0.000 description 1
- 238000002715 modification method Methods 0.000 description 1
- 239000000178 monomer Substances 0.000 description 1
- 229910021392 nanocarbon Inorganic materials 0.000 description 1
- 239000002064 nanoplatelet Substances 0.000 description 1
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229920001568 phenolic resin Polymers 0.000 description 1
- 239000005011 phenolic resin Substances 0.000 description 1
- 230000026731 phosphorylation Effects 0.000 description 1
- 238000006366 phosphorylation reaction Methods 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 229920000371 poly(diallyldimethylammonium chloride) polymer Polymers 0.000 description 1
- 229920003229 poly(methyl methacrylate) Polymers 0.000 description 1
- 229920000647 polyepoxide Polymers 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000004926 polymethyl methacrylate Substances 0.000 description 1
- 229920002635 polyurethane Polymers 0.000 description 1
- 239000004814 polyurethane Substances 0.000 description 1
- 239000007774 positive electrode material Substances 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 239000012744 reinforcing agent Substances 0.000 description 1
- 230000003014 reinforcing effect Effects 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 229910000077 silane Inorganic materials 0.000 description 1
- 229940080264 sodium dodecylbenzenesulfonate Drugs 0.000 description 1
- 229910001415 sodium ion Inorganic materials 0.000 description 1
- 238000003980 solgel method Methods 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 229920003048 styrene butadiene rubber Polymers 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
- 239000011787 zinc oxide Substances 0.000 description 1
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/366—Composites as layered products
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
- H01G11/22—Electrodes
- H01G11/30—Electrodes characterised by their material
- H01G11/50—Electrodes characterised by their material specially adapted for lithium-ion capacitors, e.g. for lithium-doping or for intercalation
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- H—ELECTRICITY
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- 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
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
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- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
- H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
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Abstract
The invention discloses a lignin nitrogen-rich carbon/silicon oxide composite material with a core-shell structure, and preparation and application thereof. And (3) carrying out etherification modification on lignin serving as a carbon source, adding a silicon source under an alkaline condition to obtain an etherification modified lignin/silicon oxide composite precursor, carbonizing to obtain a lignin carbon/silicon oxide composite material, carrying out hydrothermal treatment on the lignin carbon/silicon oxide composite material, melamine, oxalate and lignin sulfonate to obtain a supermolecular structure, and finally carbonizing again to obtain the lignin nitrogen-rich carbon/silicon oxide composite material. According to the method, on one hand, the uniform and stable coating of the lignin nitrogen-rich carbon on the silicon oxide is realized, the volume expansion of the silicon oxide in the process of removing/embedding lithium ions is inhibited, and the conductivity of the silicon oxide is enhanced; on the other hand, the pore canal structure of the material is regulated, the consumption of lithium ions in the process of forming the solid electrolyte interface film is reduced, and the first coulomb efficiency and the cycling stability of the lithium ion battery are obviously improved.
Description
Technical Field
The invention belongs to the technical field of lithium ion battery cathode materials, and particularly relates to a lignin nitrogen-rich carbon/silicon oxide composite material with a core-shell structure, and preparation and application thereof.
Background
Lithium Ion Batteries (LIB) have the advantages of high energy density, low self-discharge, long cycle life, environmental friendliness and the like, and are widely applied to various fields such as electric automobiles, aerospace and the like in recent years. The negative electrode material is one of the most important components of the lithium ion battery, and plays a key role in the performance of the lithium ion battery. Graphite is the most popular choice due to its high conductivity and good cycling stability. However, the low theoretical capacity (372 mAh/g) makes it difficult for commercial graphite to meet the demands of the energy storage field for high energy and power densities. Therefore, development of a high-performance anode material for next-generation lithium ion batteries having higher energy and power density is urgently required.
Alloy-based negative electrode materials have received attention in recent years as negative electrode materials for lithium ion batteries because of their much higher theoretical capacity of Yu Tanji materials. Silicon oxide (SiO) x ) Due to its high theoretical specific capacity (SiO 2 The material has the advantages of 1965mAh/g, 2680mAh/g SiO, high mechanical strength, low cost, wide source and the like, and gradually becomes one of the most potential lithium ion battery anode materials. However, siO x There are two problems to be solved as lithium ion battery anode materials: (1) There is a severe volume expansion effect (volume change of about 200%) during lithiation/delithiation, resulting in a large decay of capacity; (2) SiO (SiO) x Is unfavorable for long cycle performance and rate capabilityCan be used.
In response to the above problems, researchers have proposed some improvements in SiO x Strategy for lithium storage performance is first to mix SiO x Combined with carbon to produce SiO x And the carbon fibers with high conductivity are connected together to form a continuous conductive network, so that the overall conductivity of the composite material is improved. The carbon skeleton can also effectively adapt to the internal SiO x The repeated change in volume, thereby ensuring the structural integrity of the electrode material. And the continuous carbonaceous network can prevent SiO x Direct contact with the electrolyte facilitates the formation of a stable SEI film during cycling, which facilitates enhancement of lithium ion intercalation/deintercalation reversibility. The specific surface area of the silicon oxide is 208m by taking tetraethoxysilane as a silicon source and sucrose as a carbon source, and regulating and controlling the size and shape of the silicon oxide through hydrofluoric acid, wherein the tetraethoxysilane is taken as a silicon source by Yang et al (adv. Mater. Interfaces (2019) 6 (6): 1801809.) 2 SiO/g x the/C composite material is used as a negative electrode material of a lithium ion battery, and has a capacity of 820mAh/g after being cycled for 200 times under the current density of 100 mA/g. However, a larger specific surface area results in a larger irreversible capacity, which in turn results in a lower initial coulombic efficiency of the lithium ion battery. Luo et al (ACS appl. Energy Mater. (2022) 5:8982-8989) prepared SiO first using vinyltriethoxysilane as the starting material x The surface of the composite material is modified by polydiallyl dimethyl ammonium chloride and is coated by polymethyl methacrylate, and SiO with a core-shell structure is prepared by two-step carbonization x C composite material having a thickness of 22.2m 2 The low specific surface area per gram, the charge-discharge cycle test is carried out at a current density of 0.5A/g, the initial coulombic efficiency reaches 68.5%, and the discharge specific capacity reaches 770mAh/g after 500 times of cycle. Therefore, the SiO with proper specific surface area and pore canal structure can be prepared by regulating and controlling the composite material structure through two-step carbonization x And the C composite material further solves the problems of poor conductivity and low initial coulombic efficiency. However, the carbon sources of the carbon/silicon oxide composite materials are usually saccharides such as sucrose and glucose, high molecular materials such as phenolic resin and epoxy resin, and nanocarbon materials such as carbon nanotubes and graphene, and these carbon sources have high costThe preparation is complex, and low cost and large-scale industrial production are difficult to realize.
Lignin is the most abundant aromatic polymer with a three-dimensional network structure in nature, and is also the natural biomass resource with the second largest reserve. The lignin content in the plant is up to 30%, the carbon content is up to 50%, the cost is low, the plant is renewable, the content of functional groups such as hydroxyl, benzyl, methoxy, ether and carboxyl is rich, and the plant lignin has good structural design, and is an ideal precursor for preparing carbon-based materials in the carbon/silicon oxide composite material.
At present, many related work reports are about lignin/silicon oxide materials and lignin carbon/silicon oxide composite materials, but few work reports about nitrogen doped lignin carbon/silicon oxide composite materials are provided, specifically as follows:
in the research of lignin/silicon oxide materials, zhong Ruisheng and the like (chemical engineering report (2015) 66 (8): 3255-3261.) take alkali lignin as a raw material, obtain phosphorylated alkali lignin through phosphorylation modification, and then prepare lignin/SiO by an acid precipitation coprecipitation method 2 The composite nano particles are added into high-density polyethylene plastic, and the tensile strength and the breaking elongation are respectively improved by 48.68 percent and 73.57 percent. Liu et al (Industrial Crops and Products (2022) 189:115842.) modified lignin by sol gel method, wherein tetraethyl orthosilicate precursor hydrolyzes/condenses SiO 2 Depositing on the surface of lignin, ball milling to obtain lignin/SiO with uniform particle size 2 The composite, the high-density polyethylene material added with 3.0wt.% of the composite has good tensile strength and thermal stability. However, these studies have been mainly directed to SiO 2 The problems of strong polarity and hydrophilicity, easy agglomeration and poor dispersibility of the particle surface are solved, and the SiO of lignin cannot be realized 2 If these materials are carbonized directly, the lignin carbon network will collapse and agglomerate, which is detrimental to lithium ion intercalation and deintercalation. Brovko et al (Materials Chemistry and Physics (2021) 269:124768.) starting from sodium lignin sulfonate, a novel porous aerogel material was obtained using sol-gel technology and supercritical fluid technology, but the material wasThe material has a large number of micropores, has high ion transmission resistance, and is used as a negative electrode material of a lithium ion battery, and the multiplying power performance is poor. He et al (Waste Management (2021) 135:381-388.) used a two-step acid precipitation process to prepare hybrid nanoparticles of different particle sizes and different lignin coating amounts. By varying the pH during silicate polycondensation, the SiO obtained can be controlled 2 The optimized product shows excellent reinforcing performance, and the application of lignin in the field of rubber reinforcing agents is promoted. Xiong et al (Chemical Engineering Journal (2017) 326:803-810.) prepared lignin/SiO by co-precipitation based on sodium metasilicate and quaternized modified alkali lignin 2 Composite for further improving lignin and SiO 2 The dispersion stability of the material is improved, and after the material is blended with polyurethane, the ultraviolet transmittance of 315nm and below 400nm is respectively reduced by 99.3 percent and 87.0 percent. However, as the silicon dioxide content in the materials is too high (more than 50%), lignin only disperses silicon oxide, and does not coat the silicon oxide, if the silicon oxide is directly carbonized, a large volume expansion effect is still caused, and the reversible capacity of the material serving as a lithium battery cathode material is low, and the circulation stability and the rate capability are poor.
In the research of lignin carbon/silicon oxide composite materials, jiang et al (Composites Science and Technology (2022) 230:109775.) takes lignin as a raw material, formaldehyde is added to react for 3 hours at 90 ℃ to obtain hydroxymethyl modified lignin, silane coupling modification is carried out on the hydroxymethyl modified lignin after the reaction is carried out for half an hour at 60 ℃, and the lignin and SiO are improved 2 Affinity of the sol, lignin carbon/SiO was prepared by carbonization at 800 ℃ 2 The compound is added into styrene butadiene rubber, the tensile strength and the elongation at break of the compound rubber are obviously improved, and the prepared lignin carbon/SiO 2 In the composite material, lignin carbon is not coated with silicon oxide, and lithium ions cannot be stored. Zhong et al (International Journal of Biological Macromolecules (2022) 217:66-76.) used silicon and lignin as raw materials, supplemented with additional tetraethyl silicate to crosslink with lignin, and carbonized at 900 ℃ to prepare lignin carbon/SiO 2 Composite material with high specific surface area and mainly applied to superA stage capacitor. The material has rich pore canal structure, mainly about 1nm micropores, and has the problems of low ion transmission rate, low first coulombic efficiency and low reversible capacity when being used as a lithium ion battery anode material.
In the research aspect of using lignin carbon/silicon oxide composite material as lithium ion battery anode material, chinese patent application CN108878813A uses industrial lignin and nano SiO 2 Compounding, and carbonizing to obtain lignin carbon/SiO 2 The composite material is subjected to treatments such as hydrofluoric acid etching and the like to obtain lignin porous carbon/SiO 2 The composite material has certain performance when applied to a lithium battery cathode, and the process has lignin and SiO 2 The composition is uneven, and has the problems of higher specific surface area, lower initial coulombic efficiency and the like. Huang et al (Microporous and Mesoporous Materials (2021) 307:111004-111012.) nano SiO using quaternized alkali lignin as carbon, sodium dodecylbenzenesulfonate as soft template and structure directing agent 2 As a hard template agent, a double-template assisted self-assembly method is adopted to synthesize honeycomb lignin mesoporous carbon/SiO 2 A composite material. The silicon dioxide content of the material is 21wt.%, the reversible capacity of the material reaches 1109mAh/g after the material is circulated for 100 times at 0.1A/g, and the material has excellent electrochemical performance. However, this process requires surface modification thereof in advance, the synthetic route is complicated and the cost is high, and the process etches part of SiO by sodium hydroxide solution 2 The volume expansion effect is relieved, the pore structure is too rich, the specific surface area is relatively high, the initial coulombic efficiency is further reduced remarkably, and meanwhile, the material has poor rate capability, and the capacity is only 372mAh/g at 1A/g. Huang Sai (Huang Sai. Microstructure modification of lignin mesoporous carbon and study of lithium/sodium storage Property [ D ] ]Guangzhou: 2022) preparation of open hollow spherical lignin mesoporous carbon/SiO based on electrostatic action and double hydrolysis by using sodium metasilicate as silicon source and quaternized alkali lignin as carbon source x Composite material, siO obtained after optimization x The composite material with the content of 9.0wt.% has excellent electrochemical performance as a negative electrode of a lithium ion battery, and provides a high specific capacity of 989mAh/g after 400 cycles at a current density of 0.1A/g. However, most of the materialThe silicon dioxide is used as a hard template, and part of the silicon dioxide which is not completely coated is needed to be removed by alkali etching, so that the problem of low initial coulomb efficiency of the lignin carbon material is not solved, and the specific surface area is still up to 902m 2 And/g, the initial coulomb efficiency is only 47.6%, and meanwhile, the structural stability of the material is poor due to weak electrostatic effect, and partial collapse occurs after etching, so that the electrode is broken in the circulation process. In summary, the lignin carbon/silicon oxide composite material prepared by the prior art or process still has the problems of poor rate capability, low initial coulombic efficiency and the like when being applied to the lithium ion battery anode material.
In addition, can also be made of SiO x The doping of nitrogen atoms is carried out on the basis of the/C composite material, and the doping of nitrogen has been proved to provide additional abundant defect sites for effectively adsorbing lithium ions, so that the cycle performance and the rate performance of the lithium ion battery under the high current density are improved, and the electrochemical performance is better as the nitrogen doping amount is higher under the condition of a certain pore volume and graphitization degree. Wherein melamine is low in cost, high in nitrogen content, and graphite carbon nitride (g-C) produced by decomposition at high temperature 3 N 4 ) Still has rich nitrogen atom content and is commonly used as a nitrogen source of nitrogen doped materials. Kensy et al (Carbon (2020) 161:190-197.) prepared nitrogen-doped Carbon materials with melamine as the nitrogen source, at 700℃with a nitrogen incorporation of 1.14wt.%. Zhang et al (Carbon (2021) 178:202-210.) prepared nitrogen doped Carbon nanoplatelet/silica composite materials from melamine by simple ball milling and carbonization, as lithium ion battery anode materials, after 50 cycles at a current density of 0.5A/g, had a high specific capacity of 1129mAh/g, whereas materials without nitrogen doping had a specific capacity of 688mAh/g under the same conditions. However, g-C from melamine decomposition 3 N 4 Poor thermal stability, beginning to decompose and run off at around 550 ℃, resulting in low nitrogen incorporation (typically less than 5.0 at.%) of the carbon material at high temperatures.
In order to solve the problems of low nitrogen doping amount and uncontrollable nitrogen doping site, researchers explore and find that the metal cyanamide compound can delay g-C generated by high-temperature decomposition of nitrogen sources such as melamine and the like 3 N 4 To be decomposed toThe preparation of the carbon material with high nitrogen doping amount is realized. Zhang et al (Nano Energy (2021) 87:106184) blended melamine and zinc oxide and then carbonized directly to produce a nitrogen doped carbon material having a nitrogen doping level of 21.2at.% and an edge nitrogen content of up to 18.9at.% even at a carbonization temperature of 800 ℃. Further studies have found that the blend pyrolysis of calcium oxide and melamine also enables the preparation of high nitrogen doped carbon materials because of the metal oxide and g-C 3 N 4 The reaction generates high-heat-stability cyanamide salt (ZnNCN and CaNCN), and the cyanamide salt is used as a catalyst to delay the complete decomposition of nitrogen species. The material is used for storing potassium and sodium, and has excellent electrochemical performance. However, the material cannot be used for coating silicon oxide, so that the material is directly used as a negative electrode material of a lithium ion battery, and the lithium storage capacity is low.
In the study of nitrogen doped lignin carbon materials, fan et al (Journal of Energy Storage (2023) 63:106974.) synthesized sodium lignin sulfonate/ZnC by solvent-induced self-assembly with sodium lignin sulfonate as the carbon source 2 O 4 The compound precursor is blended with melamine and carbonized at 800 ℃ to obtain the nitrogen-doped lignin carbon material, and the material has lower specific surface area and higher nitrogen content, and has excellent volume specific capacitance when being used for super capacitors. If the lignin carbon/silicon oxide composite material rich in nitrogen prepared by the process is used for a lithium ion battery, the problem is that a nitrogen-rich carbon layer generated by a one-step method cannot realize further coating of silicon oxide, lignin used by the process is not modified, interaction force with the silicon oxide is weak, expansion of the silicon oxide cannot be inhibited, and the first coulomb efficiency is low and the cycle stability is poor. Huang et al (adv. Funct. Mater. (2020) 32:2203279.) crosslinked phenolic hydroxyl groups in lignin with formaldehyde and urea to form lignin amine urea-formaldehyde resin by in-situ polycondensation, and then electrostatically acted to achieve SiO thereof 2 Is coated uniformly and is finally prepared into SiO 2 And (3) carbonizing the lignin amine urea resin precursor at 600 ℃, and performing alkali etching to obtain the edge nitrogen doped lignin mesoporous carbon. The material is used as a negative electrode material of a sodium ion battery, has high reversible capacity, but SiO in the process 2 Is only used asThe specific surface area of the material is up to 690m as a hard template 2 And/g, increasing the irreversible reaction of the electrode, which is unfavorable for improving the first coulombic efficiency and reversible specific capacity of the material.
In summary, the nitrogen-doped lignin carbon and lignin carbon/silicon oxide composite material prepared by the prior art or process still has the problems of poor rate capability, low initial coulombic efficiency and the like when applied to the lithium ion battery anode material. And because the materials do not find a proper modification method for lignin, only SiO can be realized x Is not capable of dispersing SiO x And (5) uniform and stable coating. Meanwhile, most of the silicon oxide in the materials only plays a role of a hard template, needs to be removed through etching, and can cause overlarge specific surface area and lower initial coulombic efficiency. In addition, in order to obtain more lithium ion adsorption active sites, lignin is directly mixed with a nitrogen source to dope nitrogen atoms, and the problems of low nitrogen doping efficiency, uncontrollable nitrogen doping sites and the like exist. Therefore, the nitrogen-doped lignin carbon/silicon oxide composite material with good lithium storage performance cannot be obtained.
Disclosure of Invention
In order to solve the defects and the shortcomings of the prior art, the primary aim of the invention is to provide a preparation method of a lignin nitrogen-rich carbon/silicon oxide composite material with a core-shell structure.
According to the method, lignin is used as a carbon source, etherification modification is carried out on the lignin, the hydroxyl and molecular weight of the lignin are increased, then a silicon source is added under an alkaline condition to obtain an etherification modified lignin/silicon oxide composite precursor, and then carbonization is carried out to obtain a lignin carbon/silicon oxide composite material, wherein the etherification modified lignin can be efficiently dispersed and uniformly coated with silicon oxide generated by hydrolysis based on hydrogen bond action; further carrying out hydrothermal treatment on the lignin and melamine, oxalate and lignosulfonate to obtain a supermolecular structure, thereby being beneficial to the subsequent improvement of the structural stability of the composite material and the efficient coating of silicon oxide, finally obtaining the lignin nitrogen-rich carbon/silicon oxide composite material through secondary carbonization, and realizing the efficient nitrogen doping of the lignin carbon/silicon oxide composite material through the cyanamide salt generated by the melamine and metal oxide in the secondary carbonization process.
According to the method, on one hand, the uniform and stable coating of the lignin nitrogen-rich carbon on the silicon oxide is realized, the volume expansion of the silicon oxide in the process of removing/embedding lithium ions is inhibited, and the conductivity of the silicon oxide is enhanced; on the other hand, the pore canal structure of the material is further regulated and controlled by carrying out secondary carbonization on the composite material, so that the structural stability of the carbon layer is maintained, the specific surface area is reduced, the consumption of lithium ions in the process of forming the solid electrolyte interface film is further reduced, and the first coulomb efficiency and the cycling stability of the lithium ion battery are obviously improved.
The invention further aims to provide the lignin nitrogen-rich carbon/silicon oxide composite material with the core-shell structure prepared by the method.
The lignin carbon is uniformly doped with nitrogen elements, and the problems of low nitrogen doping efficiency and uncontrollable nitrogen doping sites of the nitrogen-doped lignin carbon material are solved through the high-efficiency nitrogen-preserving effect of the melamine salt intermediate. In addition, due to the core-shell structure with stable materials after secondary carbonization, the nitrogen-rich carbon layer in the shell layer can further coat the silicon oxide, so that the expansion of the silicon oxide can be effectively inhibited, the volume expansion effect is relieved without etching the silicon oxide, and more silicon oxide is used as an active substance. The lignin nitrogen-rich carbon/silicon oxide composite material has higher nitrogen doping amount and higher silicon oxide content, and further increases lithium storage active sites, thereby improving the specific capacity, the first coulombic efficiency and the rate capability of the lithium ion battery.
In the invention, the specific surface area of the lignin nitrogen-rich carbon/silicon oxide composite material is less than 100m 2 And/g, the mass content of the silicon oxide is not less than 20%, and the surface content of nitrogen element in the composite material is not less than 20%.
The invention also aims to provide the application of the lignin nitrogen-rich carbon/silicon oxide composite material with the core-shell structure as a negative electrode material in the fields of lithium ion batteries, supercapacitors and photoelectrocatalysis.
The invention aims at realizing the following technical scheme:
the preparation method of the lignin nitrogen-rich carbon/silicon oxide composite material with the core-shell structure comprises the following steps:
(1) Adding a glycidyl ether compound into the lignin solution with the pH value of 11-13, and reacting for 3-6 hours at the temperature of 70-90 ℃ to obtain an etherified lignin solution;
(2) Adding soluble silicate into the etherified lignin solution in the step (1), uniformly mixing, adding soluble ammonium salt to maintain the pH of the solution at 10-11, reacting for 3-4 hours, adding an acidic regulator to adjust the pH value of a reaction system to 7-9, standing and ageing for 1-3 hours at 50-80 ℃, centrifuging, separating, and drying to obtain etherified lignin/silicon oxide compound;
(3) Carbonizing, washing and drying the etherified lignin/silicon oxide compound of the step (2) to obtain a lignin carbon/silicon oxide compound;
(4) Mixing the lignin carbon/silicon oxide compound, oxalate, melamine and lignin sulfonate of the step (3) with water, performing hydrothermal reaction for 6-12 h at 120-160 ℃, and drying to obtain the lignin carbon/silicon oxide/nitrogen-containing compound;
(5) Carbonizing, washing and drying the lignin carbon/silicon oxide/nitrogen-containing compound in the step (4) to obtain the lignin nitrogen-rich carbon/silicon oxide compound material.
Preferably, the mass ratio of lignin and glycidyl ether compounds in the step (1) to the soluble silicate and soluble ammonium salt in the step (2) is 10:1 to 10: 5-15: 5 to 15; more preferably 10:1 to 4: 5-10: 5 to 10.
Preferably, the lignin solution with the pH value of 11-13 in the step (1) is obtained by the following method: preparing lignin into aqueous solution with the mass concentration of 10-30%, and then adding alkali solution to adjust the pH value to 11-13.
Further preferably, the alkali in the alkali solution is at least one of sodium hydroxide, potassium hydroxide and ammonia water; the mass concentration of the alkali solution is 10-20%.
Preferably, the lignin in the step (1) is at least one of enzymatic lignin extracted from biorefinery residues, organic solvent lignin obtained by pulping by a solvent method and alkali lignin extracted from alkaline pulping black liquor.
Further preferably, the lignin is obtained by purifying at least one of enzymatic lignin extracted from the biorefinery residues, organic solvent lignin obtained by pulping by a solvent method and alkali lignin extracted from alkaline pulping black liquor, and the purification is achieved by a conventional purification method in the field, and can be achieved by the following steps: dissolving lignin in alkali liquor, heating, stirring, dissolving, filtering, adding acid into filtrate to fully aggregate lignin, separating, washing, and drying to obtain purified lignin.
Preferably, the glycidyl ether compound in the step (1) is at least one of o-toluene glycidyl ether, polyoxyethylene glycidyl ether and ethylene glycol diglycidyl ether.
Preferably, the soluble silicate in step (2) is at least one of potassium silicate and sodium silicate, and the cation thereof is the same as the cation of the alkali in the lignin solution in step (1).
Preferably, at least one of the soluble ammonium salts ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium sulfate and ammonium nitrate of step (2).
Preferably, the acid regulator in the step (2) is an acid solution with the mass concentration of 10-20%; the acid in the acid solution is at least one of hydrochloric acid, acetic acid, nitric acid and sulfuric acid, and anions of the acid solution are required to be the same as anions in the soluble ammonium salt in the step (2).
Preferably, the rotational speed of the centrifugal separation in the step (2) is 5000-20000 rpm; the centrifugal separation time is 10-30 min.
Preferably, the drying in step (2) is at least one of air drying, vacuum drying and infrared drying; more preferably at 40 to 60 ℃.
Preferably, the carbonization in step (3) is performed under an inert gas atmosphere, and the inert gas is at least one of nitrogen, argon and helium.
Preferably, the carbonization conditions of step (3) are: carbonizing at 150-350 deg.c for 10-60 min and 500-700 deg.c for 1-5 hr; more preferably, the carbonization is carried out for 1 to 3 hours at 200 to 300 ℃ for 30 to 60 minutes and then 500 to 600 ℃.
Preferably, the carbonization procedure of step (3) is: raising the temperature to 150-350 ℃ at 5-15 ℃/min, and keeping for 10-60 min; heating to 500-700 ℃ at 5-15 ℃/min, maintaining for 1-5 h, and cooling to room temperature; more preferably: heating to 200-300 ℃ at 10 ℃/min, and keeping for 30-60 min; heating to 500-600 ℃ at 10 ℃/min, maintaining for 1-3 h, and cooling to room temperature.
Preferably, the washing in the step (3) means immersing the carbonized product in water, and washing to remove residual pyrolysis products; the drying is carried out at 60-100 ℃.
Preferably, the carbonization process of step (3) is performed in a tube furnace.
Preferably, the mass ratio of the lignin carbon/silicon oxide compound, the oxalate, the melamine and the lignin sulfonate in the step (4) is 1:1-10:1-10; more preferably: 1:1-4:1-4.
Preferably, the oxalate in the step (4) is at least one of zinc oxalate, calcium oxalate and magnesium oxalate.
Preferably, the lignosulfonate in the step (4) is one of calcium lignosulfonate, ammonium lignosulfonate and sodium lignosulfonate.
Preferably, the lignin carbon/silicon oxide compound, oxalate, melamine and lignin sulfonate in the step (4) are mixed with water to prepare a mixed solution with the mass concentration of 5-20%.
Preferably, the temperature of the hydrothermal reaction in the step (4) is 140-160 ℃ and the time is 8-12 h.
Preferably, the drying in the step (4) is at least one of forced air drying, vacuum drying and infrared drying; more preferably at 40 to 60 ℃.
Preferably, the carbonization in step (5) is performed under an inert gas atmosphere, and the inert gas is at least one of nitrogen, argon and helium.
Preferably, the carbonization conditions of step (5) are: carbonizing at 150-350 deg.c for 10-60 min and then carbonizing at 800-1000 deg.c for 1-5 hr; more preferably, the carbonization is carried out for 1 to 3 hours at the temperature of between 800 and 900 ℃ after 30 to 60 minutes at the temperature of between 200 and 300 ℃.
Preferably, the carbonization procedure of step (5) is: raising the temperature to 150-350 ℃ at 5-15 ℃/min, and keeping for 10-60 min; heating to 800-1000 ℃ at 5-15 ℃/min, maintaining for 1-5 h, and cooling to room temperature; more preferably: heating to 200-300 ℃ at 10 ℃/min, and keeping for 30-60 min; heating to 800-900 ℃ at 10 ℃/min, maintaining for 1-3 h, and cooling to room temperature.
Preferably, the washing in the step (5) means immersing the carbonized product in a dilute acid solution, and washing to remove residual pyrolysis products; the mass concentration of the dilute acid solution is 5-20%; the acid in the dilute acid solution is at least one of hydrochloric acid, acetic acid, nitric acid and sulfuric acid, and anions of the dilute acid solution are required to be the same as anions in the soluble ammonium salt in the step (2).
Preferably, the carbonization process of step (5) is performed in a tube furnace.
Preferably, the drying in step (5) is at least one of air drying, vacuum drying and infrared drying; more preferably at 40 to 60 ℃.
The lignin nitrogen-rich carbon/silicon oxide composite material with the core-shell structure is prepared by the method.
The lignin nitrogen-rich carbon/silicon oxide composite material with the core-shell structure is applied to the fields of lithium ion batteries, supercapacitors and photoelectrocatalysis.
Preferably, the lignin nitrogen-rich carbon/silicon oxide composite material with the core-shell structure is used as a cathode material in a lithium ion battery.
The present invention will be described in more detail below.
(1) Preparing lignin into a solution with the mass concentration of 10-30%, and adding an alkali solution to adjust the pH value to 11-13; adding a glycidyl ether compound into the lignin solution, and reacting for 3-6 hours at 70-90 ℃ to obtain an etherified lignin solution;
The step is to carry out etherification modification on lignin, increase the molecular weight, obtain more oxygen-containing functional groups such as hydroxyl, not only can strengthen the hydrogen bond action between lignin and silicon oxide and improve the stability of the lignin for coating the silicon oxide, but also the high molecular weight improves the thermal stability of the lignin, thereby being beneficial to improving the structural stability of the carbonized composite material.
In the step, the glycidyl ether compound is grafted to active hydrogen atoms of phenolic hydroxyl groups in lignin through etherification reaction, so that etherified lignin with good solubility is obtained, the problem of serious aggregation of lignin in aqueous solution is solved, and uniform dispersion of lignin and silicon oxide is facilitated.
The alkali solution is added in this step and the pH is controlled to 11 to 13 or more in order to sufficiently dissolve lignin in the solution, and the alkali added in step (1) and the cation of silicate added in step (2) must be the same in order not to introduce other impurities.
In the step, the reaction temperature is controlled to be 70-90 ℃, and the reaction temperature is too low, so that the generation of etherified lignin is not facilitated, the reaction rate is low, the efficiency is low, and the reaction is insufficient; too high a temperature will result in more severe etherification reactions, and also by-products, and will increase energy consumption and costs.
(2) Adding soluble silicate into the etherified lignin solution in the step (1), adding soluble ammonium salt to maintain the pH of the solution at 10-11, reacting for 3-4 hours, adding an acidic regulator to adjust the pH value of a reaction system to 7-9, standing and ageing for 1-3 hours at 50-80 ℃, and then centrifugally separating to obtain precipitate, and drying the precipitate to obtain etherified lignin/silicon oxide compound;
the step is to form strong hydrogen bond action between etherified lignin and silicon oxide generated by hydrolysis, so that the lignin is favorable for uniformly dispersing and stably coating the silicon oxide.
In the step, soluble ammonium salt is added to maintain the pH value of the solution to be 10-11, and weak acid ammonium salt and SiO in silicate are added 3 2- Hydrolysis occurs between the two, and silicon oxide is gradually generated. Meanwhile, based on the hydrogen bond action between the silicon oxide and etherified lignin, the silicon oxide and etherified lignin grow into a loose structure compound in situ. The pH value must be controlled in the step, if the pH value is too low, lignin can be aggregated and separated out in advance, which is not beneficial to the full coating of the lignin on the silicon oxide; if the pH is too high, the silicate is insufficiently hydrolyzed, and the produced silica is small, and the effect is not preferable.
In the step, an acid regulator is added to regulate the pH value of a reaction system to 7-9, which is favorable for pi-pi and hydrophobic effect among etherified lignin molecules to gradually shrink a loose compound, so that a compact lignin/silicon oxide compound is formed.
In the step, the dosage of the soluble ammonium salt and the acid regulator needs to be controlled, and too small dosage can lead to slow reaction rate and is unfavorable for the adjustment of the pH value; too large amount can lead to direct aggregation and precipitation of lignin, which is unfavorable for uniform coating of lignin on silicon oxide. In order to avoid introducing other impurities, the anions of the ammonium salt and the acid solution in step (2) should be the same.
(3) Carbonizing, washing and drying the etherified lignin/silicon oxide compound of the step (2) to obtain a lignin carbon/silicon oxide compound;
the atmosphere of the carbonization gas in this step is not necessarily nitrogen, and may be replaced with other inert gases such as argon. The carbonization temperature is required to be within the range of 500-600 ℃ and the time is 1-5 hours, if the temperature is too low and the time is too short, incomplete carbonization can be caused, and the conductivity of the material is poor; if the temperature is too high and the time is too long, the material structure is unstable, partial collapse occurs, the energy consumption is increased, and the production cost is increased.
(4) Adding oxalate, melamine and lignosulfonate into the lignin carbon/silicon oxide compound in the step (3), adding a certain amount of water to prepare a mixed solution with the mass concentration of 5-20%, performing hydrothermal reaction for 6-12 h at 120-160 ℃, and drying to obtain the lignin carbon/silicon oxide/nitrogen-containing compound;
The step is to further coat the silicon oxide, so as to relieve the volume expansion effect of the silicon oxide; simultaneously, the pore canal structure of the lignin carbon/silicon oxide composite material is regulated and controlled, and the specific surface area of the material is reduced; in addition, the lignin carbon/silicon oxide composite material is doped with nitrogen, so that a nitrogen-rich carbon layer is formed in the subsequent secondary carbonization process.
According to the method, the melamine and the lignosulfonate can be subjected to condensation reaction through hydrothermal reaction, the synthesized continuous nitrogen-rich lignin molecular network is further coated on the surface of the lignin carbon/silicon oxide composite material, a nitrogen-rich carbon layer formed after carbonization can play a role of supporting materials, the structural stability of the composite material is enhanced, collapse of the material in the secondary carbonization process is avoided, in addition, the nitrogen content in the composite material is improved by the nitrogen-rich carbon layer, and the lithium storage performance of the material is further improved. The time and the temperature of the hydrothermal reaction need to be controlled, if the time and the temperature of the hydrothermal reaction are too long, the aggregation of melamine monomers is easy to be caused, and melamine cannot be grafted in lignin, so that the subsequent nitrogen doping effect is not ideal; if the hydrothermal reaction time is too short and the temperature is too low, insufficient reaction can be caused, so that the formation of a subsequent nitrogen-rich carbon layer is affected, and the structure regulation and the doping of nitrogen atoms of the composite material are not facilitated.
In the step, oxalate must be added to nitrogen doped in the composite material, and lignin carbon/silicon oxide composite and melamine cannot be directly carbonized after being mixed, because the melamine has poor thermal stability, and is easy to decompose first in the carbonization process, so that the nitrogen doped amount of the material is extremely low, and the nitrogen doped effect is not ideal. The metal oxide generated by oxalate decomposition can react with melamine to generate melamine salt, high Wen Baodan is realized, the loss of nitrogen species is reduced, the nitrogen doping efficiency is further improved, an additional lithium storage site is provided, and meanwhile, the carbon skeleton can be more stable due to metal ions. It should be noted that the temperature of the metal oxide generated by the decomposition of the oxalate is higher than the carbonization temperature (about 350 ℃) of lignin, otherwise, the metal ions can react with sulfur element in lignin to generate metal sulfide, but not to generate melamine salt, and the effect of high-efficiency nitrogen protection can not be achieved.
(5) Carbonizing, washing and drying the lignin carbon/silicon oxide/nitrogen-containing compound in the step (4) to obtain a lignin nitrogen-rich carbon/silicon oxide compound material;
the preparation method comprises the steps of preparing a lignin nitrogen-rich carbon/silicon oxide composite material with a core-shell structure, reducing specific surface area, relieving volume expansion of silicon oxide, adding additional lithium storage active sites and further improving lithium storage performance of the composite material.
The atmosphere of the carbonization gas in this step is not necessarily nitrogen, and may be replaced with other inert gases such as argon. The carbonization temperature is required to be within the range of 800-900 ℃ and the time is 1-5 hours, if the temperature is too low and the time is too short, incomplete carbonization can be caused, and the conductivity of the material is poor; if the temperature is too high and the time is too long, the material structure is unstable, partial collapse occurs, nitrogen loss is caused, the nitrogen doping amount of the material is low, in addition, the energy consumption is increased, and the production cost is increased.
In the invention, the specific surface area of the lignin nitrogen-rich carbon/silicon oxide composite material with the core-shell structure is less than 100m 2 And/g, the mass content of the silicon oxide is not less than 20%, and the surface element content of nitrogen is not less than 20%. Can be applied to the fields of lithium ion battery cathode materials, supercapacitors and photoelectrocatalysis (serving as a photoelectrocatalyst).
Compared with the prior art, the invention has the following advantages:
(1) The lignin nitrogen-rich carbon/silicon oxide composite material prepared by the method has low specific surface area and high nitrogen doping amount, silicon oxide serving as a main active substance is uniformly distributed in the lignin nitrogen-rich carbon-based material, and a continuous lignin nitrogen-rich carbon layer can not only improve the overall conductivity of the composite material and reduce the specific surface area of the material, but also effectively relieve the volume expansion of the silicon oxide, so that higher first coulomb efficiency and better multiplying power performance and cycle performance are obtained. In addition, due to the high-efficiency nitrogen protection of the cyanamide salt, the composite material has high nitrogen content, and further improvement of lithium storage performance of the material is brought. As a lithium ion battery cathode material, compared with pure silicon oxide, the material has higher first coulombic efficiency, cycle performance and multiplying power performance and good application prospect.
(2) According to the preparation method of the lignin nitrogen-rich carbon/silicon oxide composite material, lignin is used as a carbon source, melamine is used as a nitrogen source, and silicate is used as a silicon source, so that the lignin nitrogen-rich carbon uniformly disperses and stably coats silicon oxide. The raw materials of the invention are renewable resources with abundant reserves and low cost, the preparation process is safe and environment-friendly, and the invention can realize the high-value utilization of papermaking black liquor or biorefinery waste, thereby saving resources and protecting environment.
Drawings
FIG. 1 is a constant current charge-discharge spectrum of the lignin nitrogen-rich carbon/silicon oxide composite material prepared in example 1 of the present invention at a current density of 100 mA/g.
FIG. 2 is a constant current charge-discharge spectrum of the lignin nitrogen-rich carbon/silicon oxide composite material prepared in example 1 of the present invention at a current density of 200 mA/g.
FIG. 3 is a graph showing the rate performance of the lignin nitrogen-rich carbon/silica composite material prepared in example 1 of the present invention.
FIG. 4 is an SEM image of a lignin nitrogen-rich carbon/silica composite material prepared according to example 1 of the present invention.
Fig. 5 is a TEM and its elemental mapping map of the lignin nitrogen-enriched carbon/silica composite material prepared in example 1 of the present invention.
FIG. 6 is a nitrogen adsorption/desorption chart of the lignin nitrogen-rich carbon/silicon oxide composite material prepared in example 1 of the present invention.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but embodiments of the present invention are not limited thereto.
The specific conditions are not noted in the examples of the present invention, and are carried out according to conventional conditions or conditions suggested by the manufacturer. The raw materials, reagents, etc. used, which are not noted to the manufacturer, are conventional products commercially available.
Example 1
Adding 10g of alkali lignin powder into 50ml of water to prepare a solution with the mass concentration of 20%, adding a sodium hydroxide solution with the mass concentration of 20% to adjust the pH value to 12, adding 4g of ethylene glycol diglycidyl ether, reacting for 5 hours at 80 ℃, and cooling the reaction system to room temperature to obtain an etherified lignin solution;
weighing 10g of sodium silicate, adding 10g of ammonium chloride into the etherified lignin solution, maintaining and adjusting the pH value to 10, reacting for 3 hours, adding a hydrochloric acid solution with the mass concentration of 20% to adjust the pH value of a reaction system to 7, standing and ageing for 1 hour at 60 ℃, centrifuging for 10 minutes at the rotating speed of 10000rpm, and transferring the centrifugal precipitate into an infrared oven at 60 ℃ to dry for 24 hours to prepare etherified lignin/silicon oxide compound;
grinding the etherified lignin/silicon oxide composite to the micron level, transferring to a nitrogen atmosphere, heating to 250 ℃ at the heating rate of 10 ℃/min, keeping for 30min, heating to 600 ℃ at the heating rate of 10 ℃/min, keeping for 2h, cooling to room temperature, washing carbonized products with water, and drying to obtain the lignin carbon/silicon oxide composite;
Weighing 1g of lignin carbon/silicon oxide composite, adding 4g of sodium lignin sulfonate, 4g of zinc oxalate and 4g of melamine, adding 130ml of water to prepare a mixed solution with the mass concentration of 10%, heating at 140 ℃ in a hydrothermal kettle for 8 hours, cooling to room temperature, and drying to obtain lignin carbon/silicon oxide/nitrogen-containing composite;
grinding the prepared lignin carbon/silicon oxide/nitrogen-containing compound to the micron level, transferring to a nitrogen atmosphere, heating to 250 ℃ at the heating rate of 10 ℃/min, keeping for 30min, heating to 900 ℃ at the heating rate of 10 ℃/min, keeping for 2h, cooling to room temperature, soaking a carbonized product in a hydrochloric acid solution with the mass concentration of 10%, washing with water, and transferring the washed product to an infrared oven with the temperature of 80 ℃ for drying for 24h to obtain the lignin nitrogen-rich carbon/silicon oxide composite material.
Example 2
Adding 10g of alkali lignin powder into 100ml of water to prepare a solution with the mass concentration of 10%, adding a potassium hydroxide solution with the mass concentration of 20% to adjust the pH value to 11, adding 1g of ethylene glycol diglycidyl ether, reacting for 3 hours at 70 ℃, and cooling the reaction system to room temperature to obtain an etherified lignin solution;
weighing 5g of potassium silicate, adding 5g of ammonium sulfate into the etherified lignin solution, maintaining and adjusting the pH value to 10, reacting for 3 hours, adding a sulfuric acid solution with the mass concentration of 20% to adjust the pH value of a reaction system to 7, standing and ageing for 1 hour at 50 ℃, centrifuging for 10 minutes at a rotating speed of 5000rpm, and transferring the centrifugal precipitate into an infrared oven at 40 ℃ to dry for 24 hours to prepare etherified lignin/silicon oxide composite;
Grinding the etherified lignin/silicon oxide composite to the micron level, transferring to argon atmosphere, raising the temperature to 150 ℃ at the heating rate of 5 ℃/min, keeping for 10min, raising the temperature to 500 ℃ at the heating rate of 5 ℃/min, keeping for 1h, cooling to room temperature, washing carbonized products with water, and drying to obtain lignin carbon/silicon oxide composite;
weighing 1g of lignin carbon/silicon oxide composite, adding 1g of calcium lignosulfonate, 1g of calcium oxalate and 1g of melamine, adding 80ml of water to prepare a mixed solution with the mass concentration of 5%, heating at 120 ℃ in a hydrothermal kettle for 6 hours, cooling to room temperature, and drying to obtain lignin carbon/silicon oxide/nitrogen-containing composite;
grinding the prepared lignin carbon/silicon oxide/nitrogen-containing compound to the micron level, transferring to argon atmosphere, heating to 150 ℃ at the heating rate of 5 ℃/min, keeping for 10min, heating to 800 ℃ at the heating rate of 5 ℃/min, keeping for 1h, cooling to room temperature, soaking carbonized products in sulfuric acid solution with the mass concentration of 10%, washing with water, transferring the washed products to an infrared oven with the temperature of 60 ℃ and drying for 24h to obtain the lignin nitrogen-rich carbon/silicon oxide composite material.
Example 3
Adding 10g of enzymolysis lignin powder into 67ml of water to prepare a solution with the mass concentration of 15%, adding a sodium hydroxide solution with the mass concentration of 20% to adjust the pH value to 12, adding 2g of o-toluene glycidyl ether, reacting for 4 hours at 75 ℃, and cooling the reaction system to room temperature to obtain an etherified lignin solution;
Weighing 7g of sodium silicate, adding 7g of ammonium nitrate into the etherified lignin solution, maintaining and adjusting the pH value to 11, reacting for 4 hours, adding a nitric acid solution with the mass concentration of 20% to adjust the pH value of a reaction system to 8, standing and ageing for 2 hours at 55 ℃, centrifuging for 20 minutes at the rotating speed of 10000rpm, and moving the centrifugal precipitate into a blast oven at 50 ℃ to dry for 24 hours to prepare etherified lignin/silicon oxide composite;
grinding the etherified lignin/silicon oxide composite to the micron level, transferring to a nitrogen atmosphere, heating to 200 ℃ at the heating rate of 10 ℃/min, keeping for 20min, heating to 550 ℃ at the heating rate of 10 ℃/min, keeping for 2h, cooling to room temperature, washing carbonized products with water, and drying to obtain the lignin carbon/silicon oxide composite;
weighing 1g of lignin carbon/silicon oxide composite, adding 2g of ammonium lignin sulfonate, 2g of magnesium oxalate and 2g of melamine, adding 88ml of water to prepare a mixed solution with the mass concentration of 8%, heating at 130 ℃ in a hydrothermal kettle for 7 hours, cooling to room temperature, and drying to obtain lignin carbon/silicon oxide/nitrogen-containing composite;
grinding the prepared lignin carbon/silicon oxide/nitrogen-containing compound to the micron level, transferring to a nitrogen atmosphere, heating to 200 ℃ at the heating rate of 10 ℃/min, keeping for 20min, heating to 850 ℃ at the heating rate of 10 ℃/min, keeping for 2h, cooling to room temperature, soaking a carbonized product in a nitric acid solution with the mass concentration of 10%, washing with water, and transferring the washed product to a blast oven with the temperature of 50 ℃ for drying for 24h to obtain the lignin nitrogen-rich carbon/silicon oxide composite material.
Example 4
Adding 10g of enzymolysis lignin powder into 42ml of water to prepare a solution with the mass concentration of 24%, adding a potassium hydroxide solution with the mass concentration of 20% to adjust the pH value to 13, adding 6g of o-toluene glycidyl ether, reacting for 6 hours at the temperature of 85 ℃, and cooling the reaction system to room temperature to obtain an etherified lignin solution;
weighing 12g of potassium silicate, adding 12g of ammonium chloride into the etherified lignin solution, maintaining and adjusting the pH value to 11, reacting for 4 hours, adding a hydrochloric acid solution with the mass concentration of 20% to adjust the pH value of a reaction system to 8, standing and aging for 3 hours at 65 ℃, centrifuging for 20 minutes at the rotating speed of 15000rpm, and transferring the centrifugal precipitate into a blast oven at the temperature of 40 ℃ for drying for 24 hours to obtain etherified lignin/silicon oxide compound;
grinding the etherified lignin/silicon oxide composite to the micron level, transferring to argon atmosphere, heating to 300 ℃ at the heating rate of 15 ℃/min, keeping for 40min, heating to 650 ℃ at the heating rate of 15 ℃/min, keeping for 3h, cooling to room temperature, washing carbonized products with water, and drying to obtain lignin carbon/silicon oxide composite;
weighing 1g of lignin carbon/silicon oxide composite, adding 6g of sodium lignin sulfonate, 6g of zinc oxalate and 6g of melamine, adding 146ml of water to prepare a mixed solution with the mass concentration of 13%, heating at 150 ℃ in a hydrothermal kettle for 9 hours, cooling to room temperature, and drying to obtain lignin carbon/silicon oxide/nitrogen-containing composite;
Grinding the prepared lignin carbon/silicon oxide/nitrogen-containing compound to the micron level, transferring to argon atmosphere, raising the temperature to 300 ℃ at the heating rate of 15 ℃/min, keeping for 40min, raising the temperature to 950 ℃ at the heating rate of 15 ℃/min, keeping for 3h, cooling to room temperature, soaking a carbonized product in a hydrochloric acid solution with the mass concentration of 10%, washing with water, and transferring the washed product to a blast oven with the temperature of 90 ℃ for drying for 24h to obtain the lignin nitrogen-rich carbon/silicon oxide composite material.
Example 5
Adding 10g of organic solvent lignin powder into 37ml of water to prepare a solution with the mass concentration of 27%, adding sodium hydroxide solution with the mass concentration of 20% to adjust the pH value to 11, adding 8g of polyoxyethylene glycidyl ether, reacting for 3 hours at 90 ℃, and cooling the reaction system to room temperature to obtain etherified lignin solution;
weighing 14g of sodium silicate, adding 14g of ammonium sulfate into the etherified lignin solution, maintaining and adjusting the pH value to 10, reacting for 3 hours, adding a sulfuric acid solution with the mass concentration of 20% to adjust the pH value of a reaction system to 9, standing and ageing for 2 hours at 70 ℃, centrifuging for 30 minutes at the rotating speed of 20000rpm, and transferring the centrifugal precipitate into a vacuum oven at 50 ℃ for drying for 24 hours to prepare etherified lignin/silicon oxide composite;
Grinding the etherified lignin/silicon oxide composite to the micron level, transferring to a nitrogen atmosphere, raising the temperature to 350 ℃ at the temperature raising rate of 5 ℃/min, keeping for 50min, raising the temperature to 700 ℃ at the temperature raising rate of 5 ℃/min, keeping for 4h, cooling to room temperature, washing carbonized products with water, and drying to obtain the lignin carbon/silicon oxide composite;
weighing 1g of lignin carbon/silicon oxide composite, adding 8g of calcium lignosulfonate, 8g of calcium oxalate and 8g of melamine, adding 139ml of water to prepare a mixed solution with the mass concentration of 18%, heating for 10 hours at 160 ℃ in a hydrothermal kettle, cooling to room temperature, and drying to obtain lignin carbon/silicon oxide/nitrogen-containing composite;
grinding the prepared lignin carbon/silicon oxide/nitrogen-containing compound to the micron level, transferring to a nitrogen atmosphere, raising the temperature to 350 ℃ at the temperature raising rate of 5 ℃/min, keeping for 50min, raising the temperature to 1000 ℃ at the temperature raising rate of 5 ℃/min, keeping for 4h, cooling to room temperature, soaking a carbonized product in a sulfuric acid solution with the mass concentration of 10%, washing with water, and transferring the washed product to a vacuum oven with the temperature of 100 ℃ for drying for 24h to obtain the lignin nitrogen-rich carbon/silicon oxide composite material.
Example 6
Adding 10g of organic solvent lignin powder into 33ml of water to prepare a solution with the mass concentration of 30%, adding a potassium hydroxide solution with the mass concentration of 20% to adjust the pH to 13, adding 10g of polyoxyethylene glycidyl ether, reacting for 5 hours at 80 ℃, and cooling the reaction system to room temperature to obtain etherified lignin solution;
Weighing 15g of potassium silicate, adding 15g of ammonium nitrate into the etherified lignin solution, maintaining and adjusting the pH value to 11, reacting for 4 hours, adding a nitric acid solution with the mass concentration of 20% to adjust the pH value of a reaction system to 9, standing and aging for 3 hours at 80 ℃, centrifuging for 30 minutes at a rotating speed of 5000rpm, and transferring the centrifugal precipitate into a vacuum oven at 60 ℃ for drying for 24 hours to obtain etherified lignin/silicon oxide composite;
grinding the etherified lignin/silicon oxide composite to the micron level, transferring to argon atmosphere, heating to 250 ℃ at the heating rate of 15 ℃/min, keeping for 60min, heating to 600 ℃ at the heating rate of 15 ℃/min, keeping for 5h, cooling to room temperature, washing carbonized products with water, and drying to obtain lignin carbon/silicon oxide composite;
weighing 1g of lignin carbon/silicon oxide composite, adding 10g of ammonium lignin sulfonate, 10g of magnesium oxalate and 10g of melamine, adding 155ml of water to prepare a mixed solution with the mass concentration of 20%, heating at 140 ℃ in a hydrothermal kettle for 12 hours, cooling to room temperature, and drying to obtain the lignin carbon/silicon oxide/nitrogen-containing composite;
grinding the prepared lignin carbon/silicon oxide/nitrogen-containing compound to the micron level, transferring to argon atmosphere, heating to 250 ℃ at the heating rate of 15 ℃/min, maintaining for 60min, heating to 900 ℃ at the heating rate of 15 ℃/min, maintaining for 5h, cooling to room temperature, soaking a carbonized product in a nitric acid solution with the mass concentration of 10%, washing with water, and transferring the washed product to a vacuum oven at 80 ℃ for drying for 24h to obtain the lignin nitrogen-rich carbon/silicon oxide composite material.
Comparative example 1 (pure silica)
Weighing 10g of sodium silicate, adding into 50ml of water, adding sodium hydroxide solution with the mass concentration of 20% to adjust the pH value to 12, adding 10g of ammonium chloride, maintaining and adjusting the pH value to 10, reacting for 3 hours, centrifuging for 10 minutes at the rotating speed of 10000rpm, and transferring the centrifugal precipitate into an infrared oven at the temperature of 60 ℃ to dry for 24 hours to prepare silicon oxide;
grinding the prepared silicon oxide to the micron level, moving to a nitrogen atmosphere, heating to 250 ℃ at the heating rate of 10 ℃/min, keeping for 30min, heating to 600 ℃ at the heating rate of 10 ℃/min, keeping for 2h, cooling to room temperature, washing a carbonized product with water, and drying to obtain the carbonized silicon oxide material;
grinding the carbonized silicon oxide material to the micron level, transferring to a nitrogen atmosphere, heating to 250 ℃ at the heating rate of 10 ℃/min, maintaining for 30min, heating to 900 ℃ at the heating rate of 10 ℃/min, maintaining for 2h, cooling to room temperature, soaking the carbonized product in hydrochloric acid solution with the mass concentration of 10%, washing with water, transferring the washed product to an infrared oven at 80 ℃ and drying for 24h to obtain the twice carbonized silicon oxide material.
Comparative example 2 (direct lignin employed without etherification modification)
Adding 10g of alkali lignin powder into 50ml of water to prepare a solution with the mass concentration of 20%, and adding a sodium hydroxide solution with the mass concentration of 20% to adjust the pH value to 12;
weighing 10g of sodium silicate, adding 10g of ammonium chloride into the alkali lignin solution, maintaining and adjusting the pH value to 10, reacting for 3 hours, adding a hydrochloric acid solution with the mass concentration of 20% to adjust the pH value of a reaction system to 7, standing and aging for 1 hour at 60 ℃, centrifuging for 10 minutes at a rotating speed of 10000rpm, and moving the centrifugal precipitate into an infrared oven at 60 ℃ to dry for 24 hours to prepare an alkali lignin/silicon oxide compound;
grinding the alkali lignin/silicon oxide composite to the micron level, transferring to a nitrogen atmosphere, heating to 250 ℃ at the heating rate of 10 ℃/min, keeping for 30min, heating to 600 ℃ at the heating rate of 10 ℃/min, keeping for 2h, cooling to room temperature, washing carbonized products with water, and drying to obtain the lignin carbon/silicon oxide composite;
weighing 1g of lignin carbon/silicon oxide composite, adding 4g of sodium lignin sulfonate, 4g of zinc oxalate and 4g of melamine, adding 130ml of water to prepare a mixed solution with the mass concentration of 10%, heating at 140 ℃ in a hydrothermal kettle for 8 hours, cooling to room temperature, and drying to obtain lignin carbon/silicon oxide/nitrogen-containing composite;
Grinding the prepared lignin carbon/silicon oxide/nitrogen-containing compound to the micron level, transferring to a nitrogen atmosphere, heating to 250 ℃ at the heating rate of 10 ℃/min, keeping for 30min, heating to 900 ℃ at the heating rate of 10 ℃/min, keeping for 2h, cooling to room temperature, soaking a carbonized product in a hydrochloric acid solution with the mass concentration of 10%, washing with water, and transferring the washed product to an infrared oven with the temperature of 80 ℃ for drying for 24h to obtain the lignin nitrogen-rich carbon/silicon oxide composite material.
Comparative example 3 (one-step carbonization only)
Adding 10g of alkali lignin powder into 50ml of water to prepare a solution with the mass concentration of 20%, adding a sodium hydroxide solution with the mass concentration of 20% to adjust the pH value to 12, adding 4g of ethylene glycol diglycidyl ether, reacting for 5 hours at 80 ℃, and cooling the reaction system to room temperature to obtain an etherified lignin solution;
weighing 10g of sodium silicate, adding 10g of ammonium chloride into the etherified lignin solution, maintaining and adjusting the pH value to 10, reacting for 3 hours, adding a hydrochloric acid solution with the mass concentration of 20% to adjust the pH value of a reaction system to 7, standing and ageing for 1 hour at 60 ℃, centrifuging for 10 minutes at the rotating speed of 10000rpm, and transferring the centrifugal precipitate into an infrared oven at 60 ℃ to dry for 24 hours to prepare etherified lignin/silicon oxide compound;
Weighing 1g of etherified lignin/silicon oxide compound, adding 4g of sodium lignin sulfonate, 4g of zinc oxalate and 4g of melamine, adding 130ml of water to prepare a mixed solution with the mass concentration of 10%, heating at 140 ℃ in a hydrothermal kettle for 8 hours, cooling to room temperature, and drying to obtain lignin carbon/silicon oxide/nitrogen-containing compound;
grinding the prepared lignin carbon/silicon oxide/nitrogen-containing compound to the micron level, transferring to a nitrogen atmosphere, heating to 250 ℃ at the heating rate of 10 ℃/min, keeping for 30min, heating to 900 ℃ at the heating rate of 10 ℃/min, keeping for 2h, cooling to room temperature, soaking a carbonized product in a hydrochloric acid solution with the mass concentration of 10%, washing with water, and transferring the washed product to an infrared oven with the temperature of 80 ℃ for drying for 24h to obtain the lignin nitrogen-rich carbon/silicon oxide composite material.
Comparative example 4 (Nitrogen-doped melamine was not added)
Adding 10g of alkali lignin powder into 50ml of water to prepare a solution with the mass concentration of 20%, adding a sodium hydroxide solution with the mass concentration of 20% to adjust the pH value to 12, adding 4g of ethylene glycol diglycidyl ether, reacting for 5 hours at 80 ℃, and cooling the reaction system to room temperature to obtain an etherified lignin solution;
weighing 10g of sodium silicate, adding 10g of ammonium chloride into the etherified lignin solution, maintaining and adjusting the pH value to 10, reacting for 3 hours, adding a hydrochloric acid solution with the mass concentration of 20% to adjust the pH value of a reaction system to 7, standing and ageing for 1 hour at 60 ℃, centrifuging for 10 minutes at the rotating speed of 10000rpm, and transferring the centrifugal precipitate into an infrared oven at 60 ℃ to dry for 24 hours to prepare etherified lignin/silicon oxide compound;
Grinding the etherified lignin/silicon oxide composite to the micron level, transferring to a nitrogen atmosphere, heating to 250 ℃ at the heating rate of 10 ℃/min, keeping for 30min, heating to 600 ℃ at the heating rate of 10 ℃/min, keeping for 2h, cooling to room temperature, washing carbonized products with water, and drying to obtain the lignin carbon/silicon oxide composite;
weighing 1g of lignin carbon/silicon oxide composite, adding 4g of sodium lignin sulfonate and 4g of zinc oxalate, adding 90ml of water to prepare a mixed solution with the mass concentration of 10%, heating at 140 ℃ in a hydrothermal kettle for 8 hours, cooling to room temperature, and drying to obtain lignin carbon/silicon oxide/nitrogen-free composite;
grinding the prepared lignin carbon/silicon oxide/nitrogen-free compound to the micron level, transferring to a nitrogen atmosphere, heating to 250 ℃ at the heating rate of 10 ℃/min, keeping for 30min, heating to 900 ℃ at the heating rate of 10 ℃/min, keeping for 2h, cooling to room temperature, soaking a carbonized product in a hydrochloric acid solution with the mass concentration of 10%, washing with water, transferring the washed product to an infrared oven with the temperature of 80 ℃ and drying for 24h to obtain the twice carbonized lignin carbon/silicon oxide compound material.
Comparative example 5 (no oxalate added before secondary carbonization)
Adding 10g of alkali lignin powder into 50ml of water to prepare a solution with the mass concentration of 20%, adding a sodium hydroxide solution with the mass concentration of 20% to adjust the pH value to 12, adding 4g of ethylene glycol diglycidyl ether, reacting for 5 hours at 80 ℃, and cooling the reaction system to room temperature to obtain an etherified lignin solution;
weighing 10g of sodium silicate, adding 10g of ammonium chloride into the etherified lignin solution, maintaining and adjusting the pH value to 10, reacting for 3 hours, adding a hydrochloric acid solution with the mass concentration of 20% to adjust the pH value of a reaction system to 7, standing and ageing for 1 hour at 60 ℃, centrifuging for 10 minutes at the rotating speed of 10000rpm, and transferring the centrifugal precipitate into an infrared oven at 60 ℃ to dry for 24 hours to prepare etherified lignin/silicon oxide compound;
grinding the etherified lignin/silicon oxide composite to the micron level, transferring to a nitrogen atmosphere, heating to 250 ℃ at the heating rate of 10 ℃/min, keeping for 30min, heating to 600 ℃ at the heating rate of 10 ℃/min, keeping for 2h, cooling to room temperature, washing carbonized products with water, and drying to obtain the lignin carbon/silicon oxide composite;
weighing 1g of lignin carbon/silicon oxide composite, adding 4g of sodium lignin sulfonate and 4g of melamine, adding 90ml of water to prepare a mixed solution with the mass concentration of 10%, heating at 140 ℃ for 8 hours in a hydrothermal kettle, cooling to room temperature, and drying to obtain lignin carbon/silicon oxide/nitrogen-containing composite;
Grinding the prepared lignin carbon/silicon oxide/nitrogen-containing compound to the micron level, transferring to a nitrogen atmosphere, heating to 250 ℃ at the heating rate of 10 ℃/min, keeping for 30min, heating to 900 ℃ at the heating rate of 10 ℃/min, keeping for 2h, cooling to room temperature, soaking a carbonized product in a hydrochloric acid solution with the mass concentration of 10%, washing with water, and transferring the washed product to an infrared oven with the temperature of 80 ℃ for drying for 24h to obtain the lignin nitrogen-rich carbon/silicon oxide composite material.
Comparative example 6 (no sodium Lignosulfonate before Secondary carbonization)
Adding 10g of alkali lignin powder into 50ml of water to prepare a solution with the mass concentration of 20%, adding a sodium hydroxide solution with the mass concentration of 20% to adjust the pH value to 12, adding 4g of ethylene glycol diglycidyl ether, reacting for 5 hours at 80 ℃, and cooling the reaction system to room temperature to obtain an etherified lignin solution;
weighing 10g of sodium silicate, adding 10g of ammonium chloride into the etherified lignin solution, maintaining and adjusting the pH value to 10, reacting for 3 hours, adding a hydrochloric acid solution with the mass concentration of 20% to adjust the pH value of a reaction system to 7, standing and ageing for 1 hour at 60 ℃, centrifuging for 10 minutes at the rotating speed of 10000rpm, and transferring the centrifugal precipitate into an infrared oven at 60 ℃ to dry for 24 hours to prepare etherified lignin/silicon oxide compound;
Grinding the etherified lignin/silicon oxide composite to the micron level, transferring to a nitrogen atmosphere, heating to 250 ℃ at the heating rate of 10 ℃/min, keeping for 30min, heating to 600 ℃ at the heating rate of 10 ℃/min, keeping for 2h, cooling to room temperature, washing carbonized products with water, and drying to obtain the lignin carbon/silicon oxide composite;
weighing 1g of lignin carbon/silicon oxide composite, adding 4g of zinc oxalate and 4g of melamine, adding 90ml of water to prepare a mixed solution with the mass concentration of 10%, heating at 140 ℃ in a hydrothermal kettle for 8 hours, cooling to room temperature, and drying to obtain lignin carbon/silicon oxide/nitrogen-containing composite;
grinding the prepared lignin carbon/silicon oxide/nitrogen-containing compound to the micron level, transferring to a nitrogen atmosphere, heating to 250 ℃ at the heating rate of 10 ℃/min, keeping for 30min, heating to 900 ℃ at the heating rate of 10 ℃/min, keeping for 2h, cooling to room temperature, soaking a carbonized product in a hydrochloric acid solution with the mass concentration of 10%, washing with water, and transferring the washed product to an infrared oven with the temperature of 80 ℃ for drying for 24h to obtain the lignin nitrogen-rich carbon/silicon oxide composite material.
Comparative example 7 (no hydrothermal treatment before secondary carbonization)
Adding 10g of alkali lignin powder into 50ml of water to prepare a solution with the mass concentration of 20%, adding a sodium hydroxide solution with the mass concentration of 20% to adjust the pH value to 12, adding 4g of ethylene glycol diglycidyl ether, reacting for 5 hours at 80 ℃, and cooling the reaction system to room temperature to obtain an etherified lignin solution;
weighing 10g of sodium silicate, adding 10g of ammonium chloride into the etherified lignin solution, maintaining and adjusting the pH value to 10, reacting for 3 hours, adding a hydrochloric acid solution with the mass concentration of 20% to adjust the pH value of a reaction system to 7, standing and ageing for 1 hour at 60 ℃, centrifuging for 10 minutes at the rotating speed of 10000rpm, and transferring the centrifugal precipitate into an infrared oven at 60 ℃ to dry for 24 hours to prepare etherified lignin/silicon oxide compound;
grinding the etherified lignin/silicon oxide composite to the micron level, transferring to a nitrogen atmosphere, heating to 250 ℃ at the heating rate of 10 ℃/min, keeping for 30min, heating to 600 ℃ at the heating rate of 10 ℃/min, keeping for 2h, cooling to room temperature, washing carbonized products with water, and drying to obtain the lignin carbon/silicon oxide composite;
weighing 1g of lignin carbon/silicon oxide composite, adding 4g of sodium lignin sulfonate, 4g of zinc oxalate and 4g of melamine, adding 130ml of water to prepare a mixed solution with the mass concentration of 10%, evaporating water at 140 ℃, and drying to obtain lignin carbon/silicon oxide/nitrogen-containing composite;
Grinding the prepared lignin carbon/silicon oxide/nitrogen-containing compound to the micron level, transferring to a nitrogen atmosphere, heating to 250 ℃ at the heating rate of 10 ℃/min, keeping for 30min, heating to 900 ℃ at the heating rate of 10 ℃/min, keeping for 2h, cooling to room temperature, soaking a carbonized product in a hydrochloric acid solution with the mass concentration of 10%, washing with water, and transferring the washed product to an infrared oven with the temperature of 80 ℃ for drying for 24h to obtain the lignin nitrogen-rich carbon/silicon oxide composite material.
The morphology and size of the inventive samples were determined by field emission scanning electron microscopy (SEM, hitachi S-550).
The nitrogen surface element content of the inventive samples was measured by means of an X-ray photoelectron spectrometer (Thermo Scientific).
The silica mass content of the inventive samples was measured by a comprehensive thermal analyzer (STA 499C).
The specific surface area of the inventive sample was determined by a fully automated specific surface area and pore analyzer (ASAP 2020).
The battery assembly adopts half battery assembly, and the model is CR2032. The positive electrode material comprises 80wt.% of active substance, 10wt.% of carbon black and 10wt.% of polyvinylidene fluoride (PVDF), and is coated by using N-methyl-2-pyrrolidone (NMP) as a solvent, wherein the active substance is the lignin nitrogen-rich carbon/silicon oxide composite material prepared by the method. The lithium sheet is used as a counter electrode, and the electrolyte is prepared from 1mol/L LiPF 6 Is dissolved in a mixed solution of Ethylene Carbonate (EC)/diethyl carbonate (DEC) with the volume ratio of 1:1, and 5wt.% fluoroethylene carbonate (FEC) is added. The whole installation process of the lithium ion half cell is completed in a glove box protected by argon. Constant current charge/discharge performance tests of the battery were performed at a current density of 200mA/g in a voltage range of 0.01V to 3.0V using a Newware battery performance test system, and rate performance tests were completed at current densities of 50mA/g, 100mA/g, 250mA/g, 500mA/g and 1000 mA/g.
The lignin nitrogen-rich carbon/silicon oxide composite material prepared in the example 1 is applied to a lithium ion battery anode material, and subjected to electrochemical tests and material characterization, and the results are shown in tables 1, 2 and figures 1-5.
Table 1 is a comparison of the lignin nitrogen-rich carbon/silica composite prepared in the above example with the samples prepared in the above comparative example in terms of cycle performance.
TABLE 1 cycle performance of lignin nitrogen-rich carbon/silica composites and comparative examples 1-7
Table 1 illustrates:
under the current density of 200mA/g, the initial coulomb efficiency of the lignin nitrogen-rich carbon/silicon oxide composite materials of examples 1-6 is more than 63%, and the specific discharge capacity after 100 cycles is more than 800mAh/g, which is superior to other comparative samples; the first coulomb efficiency of the sample prepared in the embodiment 1 reaches 64.5%, the discharge specific capacity is 822mAh/g after 100 times of circulation, and the cycle stability is better, and the sample is obviously better than that of the similar material, which is mainly beneficial to the fact that the lignin nitrogen-rich carbon/silicon oxide composite material has smaller specific surface area, the core-shell structure with a nitrogen-rich carbon layer and the proper carbon/nitrogen/silicon oxide ratio in the composite material, and can fully play the roles of the three materials in the composite material.
The cycle performance data of the comparative example samples in Table 1 show that the pure silica of comparative example 1 has a specific discharge capacity of only 11mAh/g due to the severe volume expansion effect during charge and discharge after 100 cycles at 200mA/g as well; in the comparative example 2, lignin is not modified, the water solubility is poor, and the acting force between the lignin and the silicon oxide is weak, so that the lignin and the silicon oxide are difficult to uniformly disperse and stably coat, and the silicon oxide which is not coated in part still exists in the carbonized composite material, so that the specific discharge capacity of the composite material is only 478mAh/g; in the comparative example 3, the nitrogen-rich carbon layer cannot further coat the lignin carbon/silicon oxide material due to only one-step carbonization, and a stable core-shell structure cannot be formed, so that the specific discharge capacity is only 605mAh/g; in the comparative example 4, since melamine is not added for nitrogen doping, in the carbonization process, the lignin is self-condensed so that a continuous and stable nitrogen-rich carbon layer network structure cannot be formed on the surface of silicon oxide, the lithium storage active sites are fewer, and the specific discharge capacity is 523mAh/g; in the comparative example 5, melamine is directly added, oxalate is not added, melamine salt cannot be generated in the secondary carbonization process to realize high-efficiency nitrogen protection, the melamine has poor self thermal stability, the lignin carbon/silicon oxide composite material has lower nitrogen doping amount due to easy decomposition and dissipation in the carbonization process, and the specific discharge capacity is 516mAh/g; in comparative example 6, sodium lignin sulfonate is not added, so that a carbon layer cannot be formed in the secondary carbonization process, silicon oxide cannot be further coated, and the effect of relieving the volume expansion of the silicon oxide is limited, so that the discharge specific capacity of the composite is 397mAh/g; in comparative example 7, since the raw materials were not subjected to the hydrothermal treatment, the raw materials were mixed and dispersed, and a nitrogen-rich lignin network could not be formed, and a large amount of bulk lignin carbon was present after carbonization, and the lithium storage performance was poor, so that the specific discharge capacity was 553mAh/g.
FIG. 1 and FIG. 2 are constant current charge and discharge spectra of the lignin nitrogen-rich carbon/silicon oxide composite material prepared in the embodiment 1 of the present invention, wherein the lignin nitrogen-rich carbon/silicon oxide composite material has a specific charge and discharge capacity of 1103mAh/g and 1659mAh/g respectively at a current density of 100mA/g, a first coulomb efficiency of 66.5%, and a reversible capacity of 1286mAh/g after 100 cycles; the first charge-discharge specific capacity is 815mAh/g and 1264mAh/g under the current density of 200mA/g, the first coulomb efficiency reaches 64.5%, and the reversible capacity is 822mAh/g after 100 cycles, which is mainly beneficial to the smaller specific surface area and the higher nitrogen doping amount of the composite material.
FIG. 3 is a graph showing the rate capability of the lignin nitrogen-rich carbon/silicon oxide composite material prepared in the embodiment 1 of the present invention, wherein the specific capacity of the lignin nitrogen-rich carbon/silicon oxide composite material can reach a stable state after several cycles under different current intensities, and the lignin nitrogen-rich carbon/silicon oxide composite material can be quickly stabilized after being converted from 1000mA/g to 50mA/g, which indicates that the lignin nitrogen-rich carbon/silicon oxide composite material has excellent rate capability and cycle stability, and can be normally used under different working environments.
FIG. 4 is an SEM image of a lignin nitrogen-rich carbon/silica composite material prepared according to example 1 of the present invention. From the figure, the particle size of the lignin nitrogen-rich carbon/silicon oxide composite material is about 100-200 nm, and the silicon oxide particles are stably coated by a continuous lignin nitrogen-rich carbon layer.
Fig. 5 is a TEM and its elemental mapping map of the lignin nitrogen-enriched carbon/silica composite material prepared in example 1 of the present invention. The C, N, O, si element is uniformly distributed and has a stable core-shell structure, which means that the silicon oxide is uniformly coated in the lignin nitrogen-rich carbon.
FIG. 6 is a nitrogen adsorption/desorption isotherm plot of the lignin nitrogen-rich carbon/silica composite material prepared in example 1 of the present invention. As can be seen from the graph, the nitrogen adsorption capacity of the composite material is smaller, and the specific surface area is only 76.72m 2 And/g, a hysteresis loop still exists in the high-pressure area of the composite material, which indicates that mesopores exist in the structure.
Table 2 shows the comparison of the surface element content and silica mass content of lignin nitrogen-rich carbon/silica composites prepared in the above examples with the samples prepared in the above comparative examples.
TABLE 2 surface element content and silica mass content of lignin Nitrogen-rich carbon/silica composite and comparative examples 1 to 7
Table 2 illustrates:
as can be seen from table 2, the lignin nitrogen-rich carbon/silicon oxide composite materials prepared in examples 1 to 6 have a nitrogen content higher than 20at.%, and a high nitrogen doping amount can add additional lithium storage active sites through the conductivity of the material, while the low nitrogen content of the samples of comparative examples 4 to 5 indicates the necessity of the nitrogen doping treatment step in this scheme. In the lignin nitrogen-rich carbon/silicon oxide composite materials prepared in the embodiments 1 to 6, the surface element content of silicon is lower than 1at percent, and the mass content of silicon oxide is higher than 20wt.%, which indicates that the scheme realizes uniform and stable coating of silicon oxide, and the silicon oxide is coated in the nitrogen-rich carbon layer, so that the volume expansion effect of the silicon oxide can be effectively relieved, and the lithium storage performance of the material is improved; in addition, the higher surface silicon element content of the comparative example indicates the presence of a large amount of unstabilized coated silica, further demonstrating the necessity of the coating treatment step in this scheme.
The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principle of the present invention should be made in the equivalent manner, and the embodiments are included in the protection scope of the present invention.
Claims (10)
1. The preparation method of the lignin nitrogen-rich carbon/silicon oxide composite material with the core-shell structure is characterized by comprising the following steps of:
(1) Adding a glycidyl ether compound into the lignin solution with the pH value of 11-13, and reacting for 3-6 hours at the temperature of 70-90 ℃ to obtain an etherified lignin solution;
(2) Adding soluble silicate into the etherified lignin solution in the step (1), uniformly mixing, adding soluble ammonium salt to maintain the pH of the solution at 10-11, reacting for 3-4 hours, adding an acidic regulator to adjust the pH value of a reaction system to 7-9, standing and ageing for 1-3 hours at 50-80 ℃, centrifuging, separating, and drying to obtain etherified lignin/silicon oxide compound;
(3) Carbonizing, washing and drying the etherified lignin/silicon oxide compound of the step (2) to obtain a lignin carbon/silicon oxide compound;
(4) Mixing the lignin carbon/silicon oxide compound, oxalate, melamine and lignin sulfonate of the step (3) with water, performing hydrothermal reaction for 6-12 h at 120-160 ℃, and drying to obtain the lignin carbon/silicon oxide/nitrogen-containing compound;
(5) Carbonizing, washing and drying the lignin carbon/silicon oxide/nitrogen-containing compound in the step (4) to obtain the lignin nitrogen-rich carbon/silicon oxide compound material.
2. The preparation method of the lignin nitrogen-rich carbon/silicon oxide composite material with the core-shell structure, which is characterized in that the mass ratio of lignin and glycidyl ether compound in the step (1) to soluble silicate and soluble ammonium salt in the step (2) is 10:1 to 10: 5-15: 5 to 15;
the mass ratio of the lignin carbon/silicon oxide compound, the oxalate, the melamine and the lignin sulfonate in the step (4) is 1:1-10:1-10.
3. The method for preparing a lignin nitrogen-rich carbon/silicon oxide composite material with a core-shell structure according to claim 1, wherein the carbonization condition in the step (3) is as follows: carbonizing at 150-350 deg.c for 10-60 min and 500-700 deg.c for 1-5 hr;
the carbonization conditions in the step (5) are as follows: carbonizing at 150-350 deg.c for 10-60 min and then carbonizing at 800-1000 deg.c for 1-5 hr.
4. The method for preparing the lignin nitrogen-rich carbon/silicon oxide composite material with the core-shell structure according to claim 1, wherein the lignin in the step (1) is at least one of enzymatic lignin extracted from biorefinery residues, organic solvent lignin obtained by pulping with a solvent method and alkali lignin extracted from alkaline pulping black liquor;
The glycidyl ether compound in the step (1) is at least one of o-toluene glycidyl ether, polyoxyethylene glycidyl ether and ethylene glycol diglycidyl ether;
the soluble silicate in the step (2) is at least one of potassium silicate and sodium silicate, and the cation of the soluble silicate is the same as the cation of alkali in the lignin solution in the step (1);
the soluble ammonium salt in the step (2) is at least one of ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium sulfate and ammonium nitrate;
the oxalate in the step (4) is at least one of zinc oxalate, calcium oxalate and magnesium oxalate.
5. The method for preparing the lignin nitrogen-rich carbon/silicon oxide composite material with the core-shell structure according to claim 1, wherein the lignin solution with the pH of 11-13 in the step (1) is obtained by the following method: preparing lignin into an aqueous solution with the mass concentration of 10-30%, and then adding an alkali solution to adjust the pH value to 11-13; the alkali in the alkali solution is at least one of sodium hydroxide, potassium hydroxide and ammonia water; the mass concentration of the alkali solution is 10-20%;
and (3) mixing the lignin carbon/silicon oxide compound, oxalate, melamine and lignin sulfonate in the step (4) with water to prepare a mixed solution with the mass concentration of 5-20%.
6. The method for preparing the lignin nitrogen-rich carbon/silicon oxide composite material with the core-shell structure according to claim 1, wherein the acidic regulator in the step (2) is an acid solution with the mass concentration of 10-20%; the acid in the acid solution is at least one of hydrochloric acid, acetic acid, nitric acid and sulfuric acid, and the anions of the acid solution are the same as the anions in the soluble ammonium salt in the step (2);
the carbonization in the steps (3) and (5) is carried out under the atmosphere of inert gas, wherein the inert gas is at least one of nitrogen, argon and helium;
and (3) and (5) the carbonization heating rates are 5-15 ℃/min.
7. The preparation method of the lignin nitrogen-rich carbon/silicon oxide composite material with the core-shell structure, which is characterized in that the mass ratio of lignin and glycidyl ether compound in the step (1) to soluble silicate and soluble ammonium salt in the step (2) is 10:1 to 4: 5-10: 5 to 10;
the mass ratio of the lignin carbon/silicon oxide compound, the oxalate, the melamine and the lignin sulfonate in the step (4) is 1:1-4:1-4;
the temperature of the hydrothermal reaction in the step (4) is 140-160 ℃ and the time is 8-12 h;
The carbonization conditions in the step (3) are as follows: carbonizing at 200-300 deg.c for 30-60 min and 500-600 deg.c for 1-3 hr;
the carbonization conditions in the step (5) are as follows: carbonizing at 200-300 deg.c for 30-60 min and then carbonizing at 800-900 deg.c for 1-3 hr.
8. The method for preparing a lignin nitrogen-rich carbon/silicon oxide composite material with a core-shell structure according to claim 1, wherein the washing in the step (5) means immersing the carbonized product in a dilute acid solution, and washing to remove residual pyrolysis products; the mass concentration of the dilute acid solution is 5-20%; the acid in the dilute acid solution is at least one of hydrochloric acid, acetic acid, nitric acid and sulfuric acid, and anions of the dilute acid solution are required to be the same as anions in the soluble ammonium salt in the step (2).
9. A lignin nitrogen-rich carbon/silicon oxide composite material with a core-shell structure prepared by the preparation method of any one of claims 1 to 8.
10. The application of the lignin nitrogen-rich carbon/silicon oxide composite material with the core-shell structure in the fields of lithium ion batteries, supercapacitors and photoelectrocatalysis.
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