CN113363463B - Sludge/biomass co-pyrolysis coke-coated lithium iron phosphate cathode material and preparation method and application thereof - Google Patents
Sludge/biomass co-pyrolysis coke-coated lithium iron phosphate cathode material and preparation method and application thereof Download PDFInfo
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- 239000002028 Biomass Substances 0.000 title claims abstract description 111
- 238000000197 pyrolysis Methods 0.000 title claims abstract description 111
- 239000010802 sludge Substances 0.000 title claims abstract description 99
- 239000000571 coke Substances 0.000 title claims abstract description 96
- 238000002360 preparation method Methods 0.000 title claims abstract description 21
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 title claims abstract description 15
- 239000010406 cathode material Substances 0.000 title claims abstract description 10
- 238000000034 method Methods 0.000 claims abstract description 61
- 239000002243 precursor Substances 0.000 claims abstract description 32
- 238000001035 drying Methods 0.000 claims abstract description 31
- 229910010710 LiFePO Inorganic materials 0.000 claims abstract description 25
- 238000003763 carbonization Methods 0.000 claims abstract description 25
- 238000005406 washing Methods 0.000 claims abstract description 23
- 238000002156 mixing Methods 0.000 claims abstract description 22
- 239000002253 acid Substances 0.000 claims abstract description 20
- 238000001354 calcination Methods 0.000 claims abstract description 19
- 239000010405 anode material Substances 0.000 claims abstract description 13
- 230000001681 protective effect Effects 0.000 claims abstract description 7
- 239000000243 solution Substances 0.000 claims description 63
- 229910052493 LiFePO4 Inorganic materials 0.000 claims description 28
- 238000010438 heat treatment Methods 0.000 claims description 25
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 22
- 238000000498 ball milling Methods 0.000 claims description 22
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 20
- 239000000843 powder Substances 0.000 claims description 20
- 239000011148 porous material Substances 0.000 claims description 18
- 229910001416 lithium ion Inorganic materials 0.000 claims description 17
- 239000011248 coating agent Substances 0.000 claims description 16
- 238000000576 coating method Methods 0.000 claims description 16
- 239000007774 positive electrode material Substances 0.000 claims description 16
- 239000002994 raw material Substances 0.000 claims description 15
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 14
- 229910019142 PO4 Inorganic materials 0.000 claims description 14
- 229910052744 lithium Inorganic materials 0.000 claims description 14
- 239000000463 material Substances 0.000 claims description 13
- 239000000047 product Substances 0.000 claims description 12
- 238000003756 stirring Methods 0.000 claims description 12
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 11
- 239000000203 mixture Substances 0.000 claims description 11
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims description 10
- 239000006258 conductive agent Substances 0.000 claims description 10
- 239000007789 gas Substances 0.000 claims description 10
- 229910021393 carbon nanotube Inorganic materials 0.000 claims description 9
- 239000002041 carbon nanotube Substances 0.000 claims description 9
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 9
- 238000007873 sieving Methods 0.000 claims description 7
- 238000009210 therapy by ultrasound Methods 0.000 claims description 7
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 6
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 6
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 6
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 6
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 6
- 229910052742 iron Inorganic materials 0.000 claims description 6
- 239000011259 mixed solution Substances 0.000 claims description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 6
- 238000000354 decomposition reaction Methods 0.000 claims description 5
- 239000012467 final product Substances 0.000 claims description 5
- IIPYXGDZVMZOAP-UHFFFAOYSA-N lithium nitrate Inorganic materials [Li+].[O-][N+]([O-])=O IIPYXGDZVMZOAP-UHFFFAOYSA-N 0.000 claims description 5
- 235000017060 Arachis glabrata Nutrition 0.000 claims description 4
- 241001553178 Arachis glabrata Species 0.000 claims description 4
- 235000010777 Arachis hypogaea Nutrition 0.000 claims description 4
- 235000018262 Arachis monticola Nutrition 0.000 claims description 4
- 239000011261 inert gas Substances 0.000 claims description 4
- 235000020232 peanut Nutrition 0.000 claims description 4
- 239000010902 straw Substances 0.000 claims description 4
- 239000002023 wood Substances 0.000 claims description 4
- 230000001476 alcoholic effect Effects 0.000 claims description 3
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 3
- 229910052786 argon Inorganic materials 0.000 claims description 3
- 239000011230 binding agent Substances 0.000 claims description 3
- 239000011267 electrode slurry Substances 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
- 229910052754 neon Inorganic materials 0.000 claims description 3
- GKAOGPIIYCISHV-UHFFFAOYSA-N neon atom Chemical compound [Ne] GKAOGPIIYCISHV-UHFFFAOYSA-N 0.000 claims description 3
- 229910052757 nitrogen Inorganic materials 0.000 claims description 3
- 241001474374 Blennius Species 0.000 claims description 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 2
- 229910017604 nitric acid Inorganic materials 0.000 claims description 2
- 238000002604 ultrasonography Methods 0.000 claims description 2
- 150000007513 acids Chemical class 0.000 claims 1
- 235000019441 ethanol Nutrition 0.000 claims 1
- 238000009792 diffusion process Methods 0.000 abstract description 10
- 150000002500 ions Chemical class 0.000 abstract description 10
- 230000010287 polarization Effects 0.000 abstract description 4
- 229910052799 carbon Inorganic materials 0.000 description 6
- 230000008569 process Effects 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- 239000000853 adhesive Substances 0.000 description 4
- 230000001070 adhesive effect Effects 0.000 description 4
- 239000003575 carbonaceous material Substances 0.000 description 4
- 238000003980 solgel method Methods 0.000 description 4
- 238000010532 solid phase synthesis reaction Methods 0.000 description 4
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 3
- 229910021389 graphene Inorganic materials 0.000 description 3
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- -1 polypropylene Polymers 0.000 description 2
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- 239000002910 solid waste Substances 0.000 description 2
- 238000006224 stepwise pyrolysis Methods 0.000 description 2
- 230000002195 synergetic effect Effects 0.000 description 2
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- 239000002033 PVDF binder Substances 0.000 description 1
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- 238000005054 agglomeration Methods 0.000 description 1
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- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 239000006256 anode slurry Substances 0.000 description 1
- 239000001110 calcium chloride Substances 0.000 description 1
- 229910001628 calcium chloride Inorganic materials 0.000 description 1
- 238000005253 cladding Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000001351 cycling effect Effects 0.000 description 1
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- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 239000012982 microporous membrane Substances 0.000 description 1
- 150000007522 mineralic acids Chemical class 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 229910021392 nanocarbon Inorganic materials 0.000 description 1
- 239000007773 negative electrode material Substances 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 239000010450 olivine Substances 0.000 description 1
- 229910052609 olivine Inorganic materials 0.000 description 1
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—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
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
- C01B25/45—Phosphates containing plural metal, or metal and ammonium
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
- C10B53/00—Destructive distillation, specially adapted for particular solid raw materials or solid raw materials in special form
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
- C10B53/00—Destructive distillation, specially adapted for particular solid raw materials or solid raw materials in special form
- C10B53/02—Destructive distillation, specially adapted for particular solid raw materials or solid raw materials in special form of cellulose-containing material
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
- C10B57/00—Other carbonising or coking processes; Features of destructive distillation processes in general
- C10B57/005—After-treatment of coke, e.g. calcination desulfurization
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
- C10B57/00—Other carbonising or coking processes; Features of destructive distillation processes in general
- C10B57/08—Non-mechanical pretreatment of the charge, e.g. desulfurization
- C10B57/10—Drying
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E50/00—Technologies for the production of fuel of non-fossil origin
- Y02E50/10—Biofuels, e.g. bio-diesel
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E50/00—Technologies for the production of fuel of non-fossil origin
- Y02E50/30—Fuel from waste, e.g. synthetic alcohol or diesel
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention discloses a sludge/biomass co-pyrolysis coke-coated lithium iron phosphate cathode material and a preparation method and application thereof. The method comprises the following steps: 1) drying and mixing the sludge and the biomass, and carrying out pyrolysis carbonization and acid washing under the condition of introducing protective gas to obtain sludge/biomass co-pyrolysis coke; 2) the sludge/biomass co-pyrolysis coke and LiFePO are adopted4Preparing the precursor solution into sol, drying and calcining to obtain the sludge/biomass co-pyrolysis coke-coated anode material. The method can coat LiFePO on the sludge/biomass co-pyrolysis coke4The conductivity and the ion diffusion rate of the anode material are greatly improved, rapid charge and discharge can be realized, the polarization phenomenon is improved, and the obtained battery has excellent rate performance and cycle performance.
Description
Technical Field
The invention relates to the field of new energy, and relates to a sludge/biomass co-pyrolysis coke-coated lithium iron phosphate cathode material, and a preparation method and application thereof.
Background
The lithium ion battery with the advantages of higher working voltage, low self-discharge efficiency, no memory effect and the like is the most popular environmentally-friendly green chemical energy storage device at present. The positive electrode material is an important composition for determining the performance of the lithium battery, and the excellent positive electrode material of the lithium battery has the following characteristics: (1) does not electrochemically react with the electrolyte; (2) the theoretical specific capacity is high; (3) the operating voltage is high. Lithium iron phosphate (LiFePO)4) The lithium battery anode material has an olivine structure, so the lithium battery anode material has the advantages of good thermal stability and excellent cycle performance while having the characteristics, and has wide raw material sources and low cost, thereby becoming one of the most promising lithium battery anode materials.
But LiFePO4The conductivity is poor, and quick charge and discharge are difficult to realize; and the diffusion rate of lithium ions is low, the polarization phenomenon is serious, and the rate capability of the battery is directly influenced. For increasing LiFePO4The utilization range of the conductive agent is currently researched, and the intrinsic conductivity of the conductive agent is improved by coating or doping metal ions with the conductive agent; by preparing nano-scale LiFePO4Shortening the diffusion path of lithium ions and improving the intrinsic ionsThe ability to diffuse.
The existing conductive agent coating means can effectively improve the LiFePO4But not high in ion diffusion ability. In recent years, graphene materials have been found to have a high specific surface area due to their lamellar structure, and thus can provide sufficient channels for ion diffusion. But the preparation process is complex and the production cost is high.
China has rich biomass and solid waste resources, most of the biomass and solid waste resources are used as fuels except a small amount of resources applied to agriculture and aquatic products, the direct combustion energy supply efficiency is low, and NO generated by combustion isX、SOXAnd the gas seriously pollutes the environment.
CN108033447A discloses porous biomass carbon, a preparation method thereof and application thereof to a lithium ion battery cathode, wherein the preparation method comprises the following steps: mixing straws with a calcium chloride solution, and standing for 12-24 hours to obtain a mixture, wherein the mass ratio of the straws to the calcium chloride in the calcium chloride solution is 1: 1.5-1: 3; drying the mixture, and then carbonizing the mixture at the low temperature of 300-350 ℃ for 2-3 hours to obtain low-temperature carbide; heating the low-temperature carbide to 500-700 ℃ to carry out high-temperature activation treatment for 1-3 hours to obtain a pre-product; and soaking the pre-product in strong inorganic acid for 12-24 hours, and washing the pre-product with water at 70-80 ℃ to be neutral to obtain the porous biomass carbon. The porous biomass carbon prepared by the preparation method of the porous biomass carbon can improve the charge-discharge specific capacity and the cycling stability of the lithium ion battery when being used for the negative electrode.
CN110835107A discloses a biomass porous carbon material which is prepared by the steps of drying, crushing, carbonizing, activating, acid washing, deep cooling and the like. The prepared biomass porous material has stable structure and excellent performance, effectively overcomes the defects of low capacity, complex production process, high cost and the like of the existing carbon material, and can be used for synthesizing the cathode of a lithium ion battery.
However, the biomass carbon material is mostly used as a battery negative electrode material, and how to develop a lithium battery positive electrode material which is environment-friendly, has good rate performance and cycle performance by using biomass has important significance for the development of the battery field.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a sludge/biomass co-pyrolysis coke-coated lithium iron phosphate cathode material, and a preparation method and application thereof.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a method for coating a lithium iron phosphate positive electrode material with sludge/biomass co-pyrolysis coke, which comprises the following steps:
(1) drying and mixing the sludge and the biomass, and carrying out pyrolysis carbonization and acid washing under the condition of introducing protective gas to obtain sludge/biomass co-pyrolysis coke;
(2) the sludge/biomass co-pyrolysis coke and LiFePO are adopted4Preparing the precursor solution into sol, drying and calcining to obtain the sludge/biomass co-pyrolysis coke-coated anode material.
The method adopts the co-pyrolysis of the sludge and the biomass, and the sludge and the biomass have a synergistic effect in the co-pyrolysis process, so that the pyrolysis reaction is more thorough, and the desulfurization and denitrification can be effectively carried out; meanwhile, the coke obtained by the high-temperature pyrolysis of the carbon and the carbon has a graphite-like microcrystalline structure and is excellent in conductivity; moreover, light components are separated out in the pyrolysis process, so that the public pyrolysis coke has an extremely abundant three-dimensional pore structure and a large specific surface area, and compared with graphene with a two-dimensional structure, the public pyrolysis coke has more abundant ion diffusion channels and has better ion transfer capacity. The combined action of the above factors ensures that the LiFePO is coated4The conductivity and the ion diffusion rate of the anode material can be greatly improved, rapid charge and discharge can be realized, the polarization phenomenon is improved, and the obtained battery has excellent rate performance and cycle performance.
The method of the invention is LiFePO synthesized by co-pyrolyzing sludge/biomass into coke and by a sol-gel method4The precursor solution is mixed, so that a three-dimensional pore structure can be better reserved and the LiFePO can be well treated4The coating is uniform, and the adhesive force between the coating and the coating is enhanced. While pure-phase lithium iron phosphate and sludge are adoptedThe effect of the mud/biomass co-pyrolysis coke is not ideal by combining a high-temperature solid phase method.
The method utilizes waste sludge and biomass resources with abundant yield and low utilization rate in China, can realize effective utilization of resources by applying the waste sludge and biomass resources to the anode material of the lithium ion battery, and accords with the environment-friendly concept. Byproducts (pyrolysis gas and pyrolysis oil) in the pyrolysis process can be used as industrial raw materials, so that the resource is cleanly utilized in a gradient manner.
As a preferable technical scheme of the method, the biomass in the step (1) comprises any one or a combination of at least two of straw, corncob, seaweed, peanut shell or sawdust.
Preferably, the mass ratio of the sludge and the biomass after drying in the step (1) is (2-4: 1), such as 2:1, 2.2:1, 2.4:1, 2.5:1, 2.7:1, 3:1, 3.2:1, 3.5:1, 3.7:1 or 4: 1.
Preferably, step (1) further comprises the steps of crushing and sieving the dried sludge and biomass.
Preferably, the protective gas in step (1) comprises any one of nitrogen, helium, argon and neon or a mixed gas of at least two of nitrogen, helium, argon and neon.
Preferably, the protective gas is introduced in step (1) at a flow rate of 400ml/min to 600ml/min, such as 400ml/min, 425ml/min, 450ml/min, 470ml/min, 500ml/min, 530ml/min, 550ml/min or 600 ml/min.
Preferably, the pyrolytic carbonization in the step (1) is stepwise pyrolytic carbonization, which is performed by firstly heating to 400-500 ℃ (for example, 400 ℃, 420 ℃, 430 ℃, 440 ℃, 450 ℃, 465 ℃, 480 ℃ or 500 ℃ and the like) and preserving the temperature for a period of time t1Then continuously heating to 800-950 deg.C (such as 800 deg.C, 820 deg.C, 840 deg.C, 850 deg.C, 860 deg.C, 880 deg.C, 900 deg.C, 915 deg.C, 930 deg.C or 950 deg.C), and holding for a period of time t2。
Preferably, the temperature rise rate of the temperature rise to 400-500 ℃ is 3-10 ℃/min, such as 3, 4, 5, 6, 7, 8, or 10 ℃/min.
Preferably, t is1Is 30min &90min, such as 30min, 40min, 50min, 60min, 70min, 80min or 90min, preferably 50 min-70 min;
preferably, the heating rate of the temperature to 800-950 ℃ is 15-25 ℃/min, such as 15, 16, 18, 20, 22 or 25 ℃/min.
Preferably, t is2Is 10min to 45min, such as 10min, 20min, 30min, 40min or 45min, preferably 20min to 40 min.
The fractional pyrolysis carbonization is beneficial to the complete separation of organic micromolecules to form a rich pore structure, thereby obtaining the pyrolysis coke with a graphite-like microcrystalline structure, rich three-dimensional pores and large specific surface area.
Preferably, the acid used for acid washing in step (1) includes any one of hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid or a combination of at least two of them. The heteroatoms in the co-pyrolysis coke can be removed by acid washing, and a carbon skeleton is reserved.
Preferably, the acid washing in step (1) is followed by a step of ball milling until material D50 is 100nm to 200nm, such as 100nm, 120nm, 150nm, 160nm, 180nm, or 200 nm.
As a preferred technical scheme of the method, the sludge/biomass co-pyrolysis coke and LiFePO are adopted in the step (2)4The method for preparing the sol from the precursor solution comprises the following steps:
(a) mixing the solution of iron source and the solution of lithium source, and then adding H3PO4Obtaining a mixed solution;
(b) adding sludge/biomass co-pyrolysis coke into the mixed solution obtained in the step (a), performing ultrasonic treatment, and heating under the stirring condition to obtain sol.
Preferably, the solution of the iron source in step (a) is an alcoholic solution of a trivalent iron source, and the concentration is 0.5mol/L to 1.5mol/L, such as 0.5mol/L, 0.6mol/L, 0.8mol/L, 0.9mol/L, 1mol/L, 1.2mol/L, 1.3mol/L or 1.5mol/L, and the like.
Preferably, the lithium source solution in step (a) is an alcoholic lithium source solution with a concentration of 0.5mol/L to 1.5mol/L, such as 0.5mol/L, 0.6mol/L, 0.8mol/L, 0.9mol/L, 1mol/L, 1.2mol/L, 1.3mol/L or 1.5mol/L, etc.
Preferably, in the mixed solution of step (a), the molar ratio of each element satisfies Li+：Fe3+：PO4 -＝1:1:1。
Preferably, the amount of the sludge/biomass co-pyrolysis coke added in the step (b) satisfies the following conditions: the sludge/biomass co-pyrolysis coke accounts for the LiFePO finally prepared45 wt.% to 10 wt.%, e.g., 5 wt.%, 5.5 wt.%, 6 wt.%, 6.5 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, or 10 wt.% of the mass, etc.
Preferably, the time of the ultrasound in step (b) is 0.5h to 2h, such as 0.5h, 0.6h, 0.8h, 1h, 1.2h, 1.5h or 2h, etc.
Preferably, the heating in step (b) is at a temperature of 75 ℃ to 90 ℃, such as 75 ℃, 80 ℃, 85 ℃ or 90 ℃ and the like.
Preferably, the heating time in step (b) is 4h to 7h, such as 4h, 5h, 5.5h, 6h, 6.5h or 7h, etc.
Preferably, the method further comprises the step of ball milling after the sol is dried in the step (2), wherein the ball milling is carried out until the material D50 is 1-5 μm.
Preferably, the calcination in step (2) is a stepwise calcination, in which the temperature is raised to 350-450 ℃ (such as 350 ℃, 375 ℃, 400 ℃, 425 ℃ or 450 ℃ and the like) and is maintained for a period of time t3Then, the temperature is increased to 850 to 950 ℃ (for example 850 ℃, 860 ℃, 875 ℃, 880 ℃, 900 ℃, 910 ℃, 920 ℃, 930 ℃ or 950 ℃, preferably 900 ℃) and the temperature is preserved for a period of time t4。
Preferably, t is3Is 1h to 6h, for example 1h, 2h, 3h, 4h, 5h or 6h, preferably 4h to 5 h.
Preferably, t is4Is 8 to 13 hours, for example, 8, 9, 9.5, 10, 11, 12 or 13 hours, preferably 10 to 12 hours.
Preferably, the method further comprises the step of performing ball milling after calcining until the material D50 is 0.5-2 μm.
As a further preferred technical solution of the method of the present invention, the method comprises the steps of:
preparation of sludge/biomass co-pyrolysis coke:
s1, respectively placing the raw material sludge and the biomass in a drying oven, drying for 6-12 h at 65-90 ℃, crushing by using a crusher, sieving by 50 meshes for later use, uniformly mixing the obtained sludge powder and biomass powder according to the mass ratio of 9: 1-1: 9, placing in a tubular furnace, introducing inert gas with the flow rate of 400-600 ml/min, starting a heating device, and carrying out pyrolysis and carbonization to obtain coke; wherein, pyrolysis and carbonization comprises a low-temperature section and a high-temperature section: the low temperature section is heated to 400-500 ℃ at the speed of 3-10 ℃/min and stays for 50-70 min; the high temperature section is heated to the final temperature of 800-950 ℃ at the speed of 15-25 ℃/min and stays for 20-40 min;
s2, carrying out acid washing, washing and drying on the coke obtained by pyrolysis and carbonization in the step S1, and carrying out ball milling for 1h to obtain sludge/biomass co-pyrolysis coke;
LiFePO4preparing a precursor solution:
s3, mixing Fe (NO)3)3·9H2Dissolving O in absolute ethyl alcohol to prepare 0.5-1.5 mol/L solution, and adding LiNO3Dissolving the mixture in absolute ethyl alcohol to prepare 0.5-1.5 mol/L solution, mixing the solution and the solution, and finally adding H with the mass fraction of 85 percent3PO4Obtaining LiFePO4Precursor solution of molar ratio Li+：Fe3 +：PO4 -＝1:1:1；
LiFePO coated by sludge/biomass co-pyrolysis coke4The preparation of the positive electrode material of (2):
s4, adding the sludge/biomass co-pyrolysis coke obtained in the step S2 into the LiFePO prepared in the step S34Performing ultrasonic treatment for 0.5 to 2 hours in the precursor solution, heating the precursor solution to 75 to 90 ℃ in a water bath under the stirring condition of a magnetic stirrer, and continuously stirring the precursor solution for 4 to 7 hours to obtain wet sol;
s5, drying the wet sol, calcining for 4-5 h at 350-450 ℃ after ball milling for 1h for primary decomposition, calcining for 10-12 h at 850-950 ℃, putting the calcined product into a ball mill for ball milling for 1h to obtain the productLiFePO coated by final product sludge/biomass co-pyrolysis coke4The positive electrode material of (1).
In a second aspect, the invention provides a sludge/biomass co-pyrolysis coke-coated lithium iron phosphate cathode material prepared by the method of the first aspect, wherein the cathode material comprises LiFePO4And coating the LiFePO4The three-dimensional pore structure of (a) pyrolyzes coke;
the pyrolysis coke with the three-dimensional pore structure is obtained by co-pyrolysis of sludge and biomass and has a graphite-like microcrystalline structure.
In a third aspect, the present invention provides a positive electrode slurry comprising the positive electrode material according to the second aspect, a conductive agent, and a binder.
Preferably, the conductive agent is a combination of carbon nanotubes and conductive carbon black, the mass of the carbon nanotubes accounts for 20% to 40% (e.g., 20%, 23%, 25%, 28%, 30%, 33%, 36%, 38%, 40%, etc.) of the three-dimensional pore structure pyrolytic coke, and the mass of the conductive carbon black accounts for 5% to 10% (e.g., 5%, 6%, 7%, 8%, 9%, 10%, etc.) of the three-dimensional pore structure pyrolytic coke.
The anode material is mixed with the carbon nano tube, the conductive carbon black and the binder to be used as the anode slurry of the battery, and the sludge/biomass co-pyrolysis coke with the three-dimensional structure, the carbon nano tube and the conductive carbon black are in a heterogeneous structure formed by mutually staggering the carbon nano tube and the conductive carbon black, so that the ion diffusion capacity can be improved, the agglomeration phenomenon of a single nano carbon material can be effectively avoided, and the lithium storage performance of the composite material is finally improved.
In a fourth aspect, the present invention provides a lithium ion battery comprising the positive electrode material according to the second aspect.
Compared with the prior art, the invention has the following beneficial effects:
(1) the method adopts the co-pyrolysis of the sludge and the biomass, and the sludge and the biomass have a synergistic effect in the co-pyrolysis process, so that the pyrolysis reaction is more thorough, and the desulfurization and denitrification can be effectively carried out; at the same time, the coke obtained by pyrolysis of the two hasThe graphite microcrystalline structure has excellent conductivity; moreover, light components are separated out in the pyrolysis process, so that the public pyrolysis coke has an extremely abundant three-dimensional pore structure and a large specific surface area, and compared with graphene with a two-dimensional structure, the public pyrolysis coke has more abundant ion diffusion channels and has better ion transfer capacity. The combined action of the above factors ensures that the LiFePO is coated4The conductivity and the ion diffusion rate of the anode material can be greatly improved, rapid charge and discharge can be realized, the polarization phenomenon is improved, and the obtained battery has excellent rate performance and cycle performance.
(2) The method of the invention is LiFePO synthesized by co-pyrolyzing sludge/biomass into coke and by a sol-gel method4The precursor solution is mixed, so that a three-dimensional pore structure can be better reserved and the LiFePO can be well treated4The coating is uniform, and the adhesive force between the coating and the coating is enhanced. The effect is not ideal when pure-phase lithium iron phosphate and sludge/biomass co-pyrolysis coke are combined by a high-temperature solid-phase method.
(3) The method is simple and easy to realize large-scale production. Waste sludge and biomass resources with abundant yield and low utilization rate in China are utilized and applied to the lithium ion battery anode material, so that the resources can be effectively utilized, and the environment-friendly concept is met. Byproducts (pyrolysis gas and pyrolysis oil) in the pyrolysis process can be used as industrial raw materials, so that the resource is cleanly utilized in a gradient manner.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments.
Example 1
This embodiment provides a mud/living beings pyrolysis coke cladding LiFePO4The method of (3), said method comprising the steps of:
preparation of sludge/biomass co-pyrolysis coke:
s1, respectively drying the raw material sludge and the biomass (wood chips) in a drying box at 80 ℃ for 10h, crushing the dried raw material sludge and the biomass (wood chips) by using a crusher, sieving the crushed raw material sludge and the crushed biomass (wood chips) by using a 50-mesh sieve for later use, uniformly mixing the obtained sludge powder and the biomass powder according to the mass ratio of 7:3, and placing the mixture in the drying boxIn a tube furnace, the flux is N of 500ml/min2Starting a heating device to carry out pyrolysis and carbonization to obtain coke;
wherein, pyrolysis and carbonization comprises a low-temperature section and a high-temperature section: raising the temperature of the low-temperature section to 450 ℃ at the speed of 5 ℃/min, and staying for 60 min; the high temperature section is heated to the final temperature of 900 ℃ at the speed of 20 ℃/min and stays for 30 min;
s2, acid washing the coke obtained by pyrolysis and carbonization in the step S1, washing and drying the coke by adopting hydrochloric acid as acid washing liquid, and performing ball milling for 1h to obtain sludge/biomass co-pyrolysis coke with the particle size D50 of 150 nm;
LiFePO4preparing a precursor solution:
s3, mixing Fe (NO)3)3·9H2Dissolving O in absolute ethyl alcohol to prepare 1mol/L solution, and adding LiNO3Dissolving in anhydrous ethanol to obtain 1mol/L solution, mixing the two solutions, and adding 85% H3PO4Obtaining LiFePO4Precursor solution of molar ratio Li+：Fe3 +：PO4 -＝1:1:1；
LiFePO coated by sludge/biomass co-pyrolysis coke4The preparation of the positive electrode material of (2):
s4, adding the sludge/biomass co-pyrolysis coke obtained in the step S2 into the LiFePO prepared in the step S34Performing ultrasonic treatment on the precursor solution for 1h, heating the precursor solution to 80 ℃ in a water bath under the stirring condition of a magnetic stirrer, and continuously stirring the precursor solution for 5h to obtain wet sol;
s5, drying the wet sol, ball-milling for 1h until the material D50 is 3 microns, calcining for 5h at 400 ℃ for primary decomposition, calcining for 12h at 900 ℃, placing the calcined product in a ball mill, ball-milling for 1h until the material D50 is 1 micron, and obtaining the final product, namely the sludge/biomass co-pyrolysis coke coated LiFePO4The co-pyrolysis coke accounts for LiFePO48 wt.% of mass.
Example 2
Preparation of sludge/biomass co-pyrolysis coke:
s1, respectively placing the raw material sludge and the biomass (peanut shells) in a drying oven to be dried for 12h at 70 ℃, crushing the raw material sludge and the biomass with a crusher, sieving the dried raw material sludge and the biomass with a 50-mesh sieve for later use, uniformly mixing the obtained sludge powder and the biomass powder according to the mass ratio of 3.5:1, placing the mixture in a tubular furnace, introducing inert gas with the flow rate of 450ml/min, starting a heating device, and carrying out pyrolysis and carbonization to obtain coke; wherein, pyrolysis and carbonization comprises a low-temperature section and a high-temperature section: the low temperature section is increased to 500 ℃ at the speed of 5 ℃/min and stays for 50 min; the high temperature section is heated to the final temperature of 850 ℃ at the speed of 15 ℃/min and stays for 40 min;
s2, acid washing the coke obtained by pyrolysis and carbonization in the step S1, washing and drying the acid washing solution by using sulfuric acid, and performing ball milling for 1h to obtain sludge/biomass co-pyrolysis coke with the particle size D50 of 160 nm;
LiFePO4preparing a precursor solution:
s3, mixing Fe (NO)3)3·9H2Dissolving O in absolute ethyl alcohol to obtain 1.5mol/L solution, and adding LiNO3Dissolving in anhydrous ethanol to obtain 1.5mol/L solution, mixing the two solutions, and adding 85% H3PO4Obtaining LiFePO4Precursor solution of molar ratio Li+：Fe3 +：PO4 -＝1:1:1；
LiFePO coated by sludge/biomass co-pyrolysis coke4The preparation of the positive electrode material of (2):
s4, adding the sludge/biomass co-pyrolysis coke obtained in the step S2 into the LiFePO prepared in the step S34Performing ultrasonic treatment for 2h in the precursor solution, heating the precursor solution to 90 ℃ in a water bath under the stirring condition of a magnetic stirrer, and continuously stirring the precursor solution for 4.5h to obtain wet sol;
s5, drying the wet sol, ball-milling for 1h until the material D50 is 3.3 microns, calcining for 4.5h at 450 ℃ for primary decomposition, calcining for 11h at 850 ℃, placing the calcined product in a ball mill, ball-milling for 1h until the material D50 is 1.2 microns, and obtaining the final product, namely the sludge/biomass co-pyrolysis coke coated LiFePO4The co-pyrolysis coke accounts for LiFePO410 wt.% of mass.
Example 3
Preparation of sludge/biomass co-pyrolysis coke:
s1, respectively placing the raw material sludge and the biomass (peanut shells) in a drying oven to be dried for 8 hours at 90 ℃, crushing the raw material sludge and the biomass with a crusher, sieving the dried raw material sludge and the biomass with a 50-mesh sieve for later use, uniformly mixing the obtained sludge powder and the biomass powder according to the mass ratio of 2.5:1, placing the mixture in a tubular furnace, introducing inert gas with the flow rate of 600ml/min, starting a heating device, and carrying out pyrolysis and carbonization to obtain coke; wherein, pyrolysis and carbonization comprises a low-temperature section and a high-temperature section: the low temperature section is increased to 480 ℃ at the speed of 6 ℃/min and stays for 55 min; the high temperature section is heated to the final temperature of 800 ℃ at the speed of 18 ℃/min and stays for 40 min;
s2, acid washing the coke obtained by pyrolysis and carbonization in the step S1, wherein the acid washing solution is phosphoric acid, washing, drying and ball-milling for 1h to obtain sludge/biomass co-pyrolysis coke, and the particle size D50 is 140 nm;
LiFePO4preparing a precursor solution:
s3, mixing Fe (NO)3)3·9H2Dissolving O in absolute ethyl alcohol to obtain 0.5mol/L solution, and adding LiNO3Dissolving in anhydrous ethanol to obtain 1mol/L solution, mixing the two solutions, and adding 85% H3PO4Obtaining LiFePO4Precursor solution of molar ratio Li+：Fe3 +：PO4 -＝1:1:1；
LiFePO coated by sludge/biomass co-pyrolysis coke4The preparation of the positive electrode material of (2):
s4, adding the sludge/biomass co-pyrolysis coke obtained in the step S2 into the LiFePO prepared in the step S34Performing ultrasonic treatment on the precursor solution for 1.5h, heating the precursor solution to 85 ℃ in a water bath under the stirring condition of a magnetic stirrer, and continuously stirring the precursor solution for 6h to obtain wet sol;
s5, drying the wet sol, ball-milling for 1h until the material D50 is 3 microns, calcining for 5h at 420 ℃ for primary decomposition, calcining for 10h at 875 ℃, ball-milling the calcined product in a ball mill for 1h until the material D50 is 1.1 microns, and obtaining the final product, namely the sludge/biomass co-pyrolysis coke coated LiFePO4The co-pyrolysis coke accounts for LiFePO46 wt.% of mass.
Example 4
The difference from example 1 is that the mass ratio of sludge powder to biomass powder is 6: 1.
Example 5
The difference from example 1 is that the mass ratio of sludge powder to biomass powder is 1:1.
Example 6
The difference from example 1 is that the co-pyrolysis coke comprises LiFePO43 wt.% of mass.
Example 7
The difference from example 1 is that the pyrolysis of step S1 is carbonized into: directly heating to the final temperature of 900 ℃ at the speed of 5 ℃/min, and staying for 90 min.
Comparative example 1
The difference from example 1 is that the sludge and biomass are replaced by the entire sludge and the content is guaranteed to be the same as the total mass of the two in example 1.
Comparative example 2
The difference from example 1 is that the sludge and biomass are replaced by the whole biomass and the content is guaranteed to be the same as the total mass of the two in example 1.
Comparative example 3
The difference from the embodiment 1 is that pure-phase lithium iron phosphate and sludge/biomass co-pyrolysis coke are combined by a high-temperature solid phase method, and the mass ratio of the lithium iron phosphate to the co-pyrolysis coke is the same as that in the embodiment 1.
And (3) detection:
uniformly mixing the composite anode material, the adhesive PVDF and the conductive agent in a ratio of 80:10:10, wherein the conductive agent is a mixture of carbon nano tubes and conductive carbon black, the mass of the carbon nano tubes accounts for 30% of that of the co-pyrolytic coke, the mass of the conductive carbon black accounts for 8% of that of the co-pyrolytic coke, preparing a slurry by using NMP, uniformly coating the slurry on an aluminum foil, and drying to obtain the anode. A soft package battery is assembled by using a metal lithium sheet as a negative electrode, a polypropylene microporous membrane as a diaphragm and 1mol/L lithium hexafluorophosphate as electrolyte, and the rate performance and the cycle performance are tested, and the results are shown in Table 1.
Multiplying power performance test parameters: at 25 ℃ based on 0.5C magnification.
Cycle performance test parameters: at 25 deg.C, 1C charged and 1C discharged.
TABLE 1
And (3) analysis:
as can be seen from the comparison between example 1 and examples 4-5, the mass ratio of the sludge powder to the biomass powder is in a preferred range, and the ratio of the sludge powder to the biomass powder is optimized to obtain better rate capability and cycle performance.
It is understood from the comparison between example 1 and example 6 that the content of the co-pyrolysis coke is small, which is not favorable for the improvement of the rate capability and the cycle performance.
It can be seen from the comparison between example 1 and example 7 that the electrochemical performance of the product obtained by the step-wise pyrolysis and carbonization is better, probably because the step-wise pyrolysis and carbonization facilitates the complete precipitation of small organic molecules to form a rich pore structure, thereby obtaining the pyrolysis coke with a graphite-like microcrystalline structure, rich three-dimensional pores and a large specific surface area.
It is understood from the comparison of example 1 with comparative examples 1-2 that the use of sludge powder or biomass powder alone results in a large decrease in rate capability and cycle capability.
As can be seen from the comparison between example 1 and comparative example 3, the preparation of the material by the sol-gel method is more beneficial to improving the electrochemical performance of the product compared with the conventional high-temperature solid phase method. This is probably because the sol-gel process preparation can better preserve the three-dimensional pore structure and make it compatible with LiFePO4The coating is uniform, and the adhesive force between the coating and the coating is enhanced.
The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
Claims (36)
1. A method for coating a lithium iron phosphate positive electrode material by sludge/biomass co-pyrolysis coke is characterized by comprising the following steps:
(1) drying and mixing the sludge and the biomass, and carrying out pyrolysis carbonization and acid washing under the condition of introducing protective gas to obtain sludge/biomass co-pyrolysis coke;
(2) the sludge/biomass co-pyrolysis coke and LiFePO are adopted4Preparing the precursor solution into sol, drying and calcining to obtain the sludge/biomass co-pyrolysis coke-coated anode material.
2. The method of claim 1, wherein the biomass of step (1) comprises any one of straw, corncobs, seaweed, peanut hulls, or wood chips, or a combination of at least two thereof.
3. The method according to claim 1, wherein the mass ratio of the sludge and the biomass after drying in the step (1) is (2-4): 1.
4. The method of claim 1, wherein step (1) further comprises the step of crushing and sieving the dried sludge and biomass.
5. The method of claim 1, wherein the protective gas of step (1) comprises any one of nitrogen, helium, argon, neon, or a mixture of at least two thereof.
6. The method according to claim 1, wherein the protective gas is introduced in the step (1) at a flow rate of 400ml/min to 600 ml/min.
7. The method of claim 1, wherein step (1) is performedThe pyrolytic carbonization is step-by-step pyrolytic carbonization, and the temperature is firstly raised to 400 to 500 ℃ and is kept for a period of time t1Then continuously heating to 800-950 ℃ and preserving the heat for a period of time t2。
8. The method according to claim 7, wherein the heating rate to 400 ℃ to 500 ℃ is 3 ℃/min to 10 ℃/min.
9. The method of claim 7, wherein t is1Is 30-90 min.
10. The method of claim 9, wherein t is1Is 50min to 70 min.
11. The method of claim 7, wherein the rate of heating to 800 ℃ to 950 ℃ is 15 ℃/min to 25 ℃/min.
12. The method of claim 7, wherein t is2Is 10min to 45 min.
13. The method of claim 12, wherein t is2Is 20min to 40 min.
14. The method of claim 1, wherein the acid used in the acid washing in step (1) comprises any one of hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid or a combination of at least two of the acids.
15. The method of claim 1, wherein the acid washing in step (1) is followed by a ball milling step until D50 is 100-200 nm.
16. The method of claim 1, wherein said step (2) of co-pyrolyzing coke and LiFePO with said sludge/biomass4Method for preparing sol from precursor solutionThe method comprises the following steps:
(a) mixing the solution of iron source and the solution of lithium source, and then adding H3PO4Obtaining a mixed solution;
(b) adding sludge/biomass co-pyrolysis coke into the mixed solution obtained in the step (a), performing ultrasonic treatment, and heating under the stirring condition to obtain sol.
17. The method of claim 16, wherein the solution of the iron source in step (a) is an alcoholic solution of a trivalent iron source with a concentration of 0.5mol/L to 1.5 mol/L.
18. The method of claim 16, wherein the lithium source solution of step (a) is an alcohol solution of lithium source with a concentration of 0.5mol/L to 1.5 mol/L.
19. The method according to claim 16, wherein the molar ratio of each element in the mixed solution of step (a) satisfies Li+：Fe3+：PO4 -＝1:1:1。
20. The method of claim 16, wherein the sludge/biomass co-pyrolysis coke of step (b) is added in an amount satisfying: the sludge/biomass co-pyrolysis coke accounts for the LiFePO finally prepared45 wt.% to 10 wt.% of mass.
21. The method of claim 16, wherein the time of the ultrasound in step (b) is 0.5h to 2 h.
22. The method of claim 16, wherein the heating of step (b) is at a temperature of 75 ℃ to 90 ℃.
23. The method of claim 16, wherein the heating of step (b) is for a time period of 4 to 7 hours.
24. The method according to claim 1, further comprising a step of ball milling after drying the sol in step (2) until material D50 is 1-5 μm.
25. The method according to claim 1, wherein the calcination in the step (2) is a stepwise calcination, and the temperature is raised to 350-450 ℃ and is kept for a period of time t3Then continuously heating to 850-950 ℃ and preserving the heat for a period of time t4。
26. The method of claim 25, wherein t is3Is 1-6 h.
27. The method of claim 26, wherein t is3Is 4-5 h.
28. The method of claim 25, wherein t is4Is 8-13 h.
29. The method of claim 28, wherein t is4Is 10 to 12 hours.
30. The method of claim 1, further comprising the step of ball milling after calcining until material D50 is between 0.5 μm and 2 μm.
31. Method according to claim 1, characterized in that it comprises the following steps:
preparation of sludge/biomass co-pyrolysis coke:
s1, respectively placing the raw material sludge and the biomass in a drying oven, drying for 6-12 h at 65-90 ℃, crushing by using a crusher, sieving by 50 meshes for later use, uniformly mixing the obtained sludge powder and biomass powder according to the mass ratio of 9: 1-1: 9, placing in a tubular furnace, introducing inert gas with the flow rate of 400-600 ml/min, starting a heating device, and carrying out pyrolysis and carbonization to obtain coke; wherein, pyrolysis and carbonization comprises a low-temperature section and a high-temperature section: the low temperature section is raised to 400-500 ℃ at the speed of 3-10 ℃/min and stays for 50-70 min; the high temperature section is heated to the final temperature of 800-950 ℃ at the speed of 15-25 ℃/min and stays for 20-40 min;
s2, carrying out acid washing, washing and drying on the coke obtained by pyrolysis and carbonization in the step S1, and carrying out ball milling for 1h to obtain sludge/biomass co-pyrolysis coke;
LiFePO4preparing a precursor solution:
s3, mixing Fe (NO)3)3·9H2Dissolving O in absolute ethyl alcohol to prepare 0.5-1.5 mol/L solution, and adding LiNO3Dissolving the mixture in absolute ethyl alcohol to prepare 0.5-1.5 mol/L solution, mixing the solution and the solution, and finally adding H with the mass fraction of 85 percent3PO4Obtaining LiFePO4Precursor solution of molar ratio Li+：Fe3 +：PO4 -＝1:1:1；
LiFePO coated by sludge/biomass co-pyrolysis coke4The preparation of the positive electrode material of (2):
s4, adding the sludge/biomass co-pyrolysis coke obtained in the step S2 into the LiFePO prepared in the step S34Performing ultrasonic treatment for 0.5 to 2 hours in the precursor solution, heating the precursor solution to 75 to 90 ℃ in a water bath under the stirring condition of a magnetic stirrer, and continuously stirring the precursor solution for 4 to 7 hours to obtain wet sol;
s5, drying the wet sol, calcining for 4-5 h at 350-450 ℃ after ball milling for 1h, performing primary decomposition, calcining for 10-12 h at 850-950 ℃, placing the calcined product in a ball mill, and performing ball milling for 1h to obtain the final product, namely, the sludge/biomass co-pyrolysis coke coated LiFePO4The positive electrode material of (1).
32. The sludge/biomass co-pyrolysis coke-coated lithium iron phosphate cathode material prepared by the method of claim 1, wherein the cathode material comprises LiFePO4And coating the LiFePO4The three-dimensional pore structure of (a) pyrolysis coke.
33. The sludge/biomass co-pyrolysis coke-coated lithium iron phosphate cathode material as claimed in claim 32, wherein the three-dimensional pore structure pyrolysis coke is obtained by co-pyrolysis of sludge and biomass and has a graphite-like microcrystalline structure.
34. A positive electrode slurry, comprising the positive electrode material according to claim 32, a conductive agent, and a binder.
35. The positive electrode slurry according to claim 34, wherein the conductive agent is a combination of carbon nanotubes and conductive carbon black, the mass of the carbon nanotubes is 20 to 40% of the three-dimensional pore structure pyrolytic coke, and the mass of the conductive carbon black is 5 to 10% of the three-dimensional pore structure pyrolytic coke.
36. A lithium ion battery comprising the positive electrode material according to claim 32.
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