CN115810725A - Core-shell three-layer composite structure cathode material and preparation method and application thereof - Google Patents
Core-shell three-layer composite structure cathode material and preparation method and application thereof Download PDFInfo
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Abstract
The invention provides a core-shell three-layer composite structure positive electrode material and a preparation method and application thereof, wherein the positive electrode material comprises a lithium-rich material core, and a lithium iron phosphate layer and a carbon layer are sequentially laminated and wrapped on the outer surface of the lithium-rich material core; the preparation method comprises the following steps: and mixing the lithium-rich material and the lithium iron phosphate material, sintering to obtain an intermediate material, mixing the intermediate material and a carbon source, and calcining to obtain the anode material with the core-shell three-layer composite structure. The positive electrode material with the core-shell three-layer composite structure provided by the invention can completely avoid the risk of contact reaction of the lithium-rich material with air or a reaction solvent, reduce the material storage environment control cost and the material processing and using process cost, also can give consideration to the lithium supplement effect, overcomes the defect of insufficient conductivity, and improves the material capacity.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a core-shell three-layer composite structure anode material, and a preparation method and application thereof.
Background
In the first charging process of the lithium ion battery, after an organic solvent (ethylene carbonate and the like) in the electrolyte abstracts lithium ions from a positive electrode, the organic solvent is reduced and decomposed on the surface of a negative electrode to generate a passivation film, namely a Solid Electrolyte Interface (SEI) film, and a part of Li from the positive electrode is permanently consumed + And the first charge-discharge coulomb efficiency is reduced. The irreversible capacity loss caused by the currently used negative electrode material is about 10 percent widely, and the energy density of the lithium ion battery is greatly reduced. The lithium iron phosphate material has high safety and good cost performance, and is widely applied to the anode material of the lithium ion battery, but because the gram capacity of the lithium iron phosphate anode material has been developed to the limit, the gram capacity of the material is difficult to be continuously improved in a conventional mode, so that the energy density of the lithium iron phosphate battery is improved.
At present, a new lithium source is added into an electrode material mainly in a lithium supplementing mode to compensate the loss of active lithium caused by the formation of an SEI film in the first charge-discharge process. The lithium supplement method comprises a positive electrode lithium supplement method and a negative electrode lithium supplement method, and compared with the negative electrode lithium supplement method, the positive electrode lithium supplement method has the advantages of simple process, low price, high safety and the like, and has attracted wide attention in recent years. The method for supplementing lithium to the positive electrode can also be divided into two methods, one method is to separate a lithium supplementing additive from a lithium iron phosphate material, and the two methods are used for supplementing lithium through physical mixing of particles; another technical route is to construct lithium supplementation from the material microstructure level.
CN112635770A discloses a lithium ion battery prelithiation positive pole piece and a preparation method of the lithium ion battery, which takes lithium nitride as a prelithiation additive, adds the lithium nitride in the preparation process of slurry, physically mixes the mixture through mechanical stirring, coats the mixture on an aluminum foil, and prepares a high-capacity positive pole piece through drying and rolling. However, in the electrode manufacturing process, the compatibility of lithium nitride with aprotic polar solvents is poor, and the lithium nitride has high reaction activity with common solvents such as N-methylpyrrolidone (NMP) and the like, so that the technical popularization and application of using lithium nitride as a pre-lithium additive are limited. In addition, lithium nitride is easy to hydrolyze to generate lithium hydroxide and ammonia gas, and the environmental control requirement is extremely high.
CN106410120A discloses a method for supplementing lithium to a lithium ion battery pole piece, which comprises the steps of firstly preparing lithium colloidal particles in an inert atmosphere, then coating the lithium colloidal particles and anode powder after pulping together or coating the lithium colloidal particles and the anode powder layer by layer after independent pulping, and then drying and rolling the lithium colloidal particles and the anode powder layer by layer to prepare the anode piece. Although this method involves the risk of lithium to air contact due to lithium gel ion fracturing during roller compaction.
CN109950514A discloses a preparation method of lithium ferrite coated lithium iron phosphate, which comprises the steps of preparing doped lithium iron phosphate by a hydrothermal method, preparing a precursor by liquid phase coating on the surface layer of the lithium iron phosphate, and finally obtaining a lithium iron phosphate material coated with the lithium iron phosphate by high-temperature calcination. In the method, lithium ferrate is used as a coating layer, and all lithium-rich materials are easy to react with H in humid air 2 O and CO 2 The reaction produces LiOH and the like, resulting in reduced performance and high manufacturing and storage costs. CN111769288A discloses a method for in-situ lithium supplement of a lithium ion battery anode material, although carbon and lithium ferrite are used as a coating layer, the lithium ferrite is easy to be similar to H 2 O and CO 2 LiOH and the like are generated by the reaction, resulting in a decrease in performance.
Therefore, a lithium-rich lithium iron material is urgently needed, so that the lithium-rich lithium iron material can be ensured not to be contacted with air or a reaction solvent, the control cost of the material storage environment and the process cost of material processing and use are reduced, the lithium supplement effect is also considered, and the material capacity is improved.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a core-shell three-layer composite structure anode 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 core-shell three-layer composite structure cathode material, which comprises a lithium-rich material core, wherein a lithium iron phosphate layer and a carbon layer are sequentially laminated and wrapped on the outer surface of the lithium-rich material core.
The positive electrode material is of a core-shell three-layer composite structure, wherein the lithium-rich material is used as the core of the positive electrode material, and the lithium iron phosphate material supplemented with lithium and the carbon layer are sequentially laminated and coated on the surface of the core of the lithium-rich material, so that the lithium-rich material is not contacted with air or a reaction solvent, and the material storage environment control cost and the material processing and using process cost are reduced; the lithium-rich material can also give consideration to the lithium supplement effect, lithium ions are separated in the charging process, the irreversible capacity loss caused by the SEI film formed on the surface of the negative electrode is compensated, and the capacity of the positive electrode material is improved; in addition, the carbon layer can effectively overcome the defect of insufficient conductivity of the anode material.
As a preferable technical solution of the present invention, the lithium-rich material has an inverse fluorite structure.
Preferably, the lithium rich material comprises Li 5 FeO 4 。
In the present invention, the lithium-rich material may be Li 5 FeO 4 、Li 6 CoO 4 Or Li 6 MnO 4 Any one or a combination of at least two of them. Due to Li 5 FeO 4 The lithium ion battery has better compatibility with a battery system, low production cost, no toxicity and high gram volume; meanwhile, li 5 FeO 4 At first charge, appears at around 3.5VAnd a voltage platform corresponding to a capacity of 347mAh/g. Thus, li 5 FeO 4 Is a lithium-rich material with extremely high cost performance.
In a preferred embodiment of the present invention, the mass fraction of the lithium-rich material in the positive electrode material is 5wt% to 10wt%, and may be, for example, 5wt%, 5.2wt%, 5.5wt%, 5.8wt%, 6wt%, 6.2wt%, 6.5wt%, 7wt%, 7.3wt%, 7.5wt%, 7.8wt%, 8wt%, 8.2wt%, 8.5wt%, 8.8wt%, 9wt%, 9.3wt%, 9.5wt%, 9.8wt%, or 10 wt%.
Preferably, the mass fraction of the lithium iron phosphate material in the positive electrode material is 88.5wt% to 94wt%, and may be, for example, 88.5wt%, 88.8wt%, 89wt%, 89.2wt%, 89.5wt%, 89.7wt%, 90wt%, 91.3wt%, 91.5wt%, 91.7wt%, 92wt%, 92.3wt%, 92.5wt%, 92.8wt%, 93wt%, 93.3wt%, 93.5wt%, 93.7wt%, or 94wt%, but is not limited to the enumerated values, and other non-enumerated values within the range of values are also applicable.
The mass fraction of the lithium-rich material in the anode material is limited to 5-10 wt%, the mass fraction of the lithium iron phosphate material is limited to 88.5-94 wt%, and when the mass fraction of the lithium-rich material is too high or too low, the multiplying power charging capability of the material is reduced, because the proportion of the precursor material affects the shape and stability of a crystal interface of the sintered material.
Preferably, the mass fraction of carbon in the positive electrode material is 1wt% to 1.5wt%, and may be, for example, 1wt%, 1.12wt%, 1.15wt%, 1.23wt%, 1.25wt%, 1.28wt%, 1.3wt%, 1.32wt%, 1.35wt%, 1.4wt%, 1.42wt%, 1.45wt%, 1.48wt%, or 1.5wt%, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.
The invention limits the mass fraction of the carbon source in the anode material to be 1-1.5 wt%, and the rate capability of the anode material is reduced when the mass fraction of the lithium-rich material is too high or too low (0.5C) 1 /0.1C 1 ) Can be used forThe rate capability of the cathode material is improved to a certain extent by excessively increasing the mass fraction of the carbon layer, but when the mass fraction of the carbon source is excessively high, the gram capacity of the material is reduced, because the carbon material is not an active substance containing lithium; when the mass fraction of the carbon source is too low, the rate capability of the material is reduced, because the integrity of the coated carbon is deteriorated and the conductivity of the material is reduced.
In a second aspect, the present invention provides a method for preparing the cathode material of the first aspect, the method comprising:
and mixing the lithium-rich material and the lithium iron phosphate material, sintering to obtain an intermediate material, mixing the intermediate material and a carbon source, and calcining to obtain the anode material with the core-shell three-layer composite structure.
As a preferred technical scheme of the invention, the lithium-rich material is prepared by adopting the following method: and mixing an iron source and a lithium source, and roasting to obtain the lithium-rich material.
Preferably, the iron source comprises any one of ferric oxide, ferroferric oxide, ferric oxyhydroxide, ferric nitrate and ferric citrate or a combination of at least two of the foregoing, and further preferably ferric oxide.
Preferably, the lithium source is any one or a combination of at least two of lithium carbonate, lithium hydroxide monohydrate, and lithium hydroxide anhydrous, and more preferably lithium hydroxide monohydrate.
Preferably, the iron source and the lithium source are mixed in a ratio of iron to lithium in an atomic molar ratio of 1 (4 to 8), for example, 4:1, 4.2.
Preferably, the mixing of the iron source and the lithium source is dry ball milling.
Preferably, the dry milling time of the iron source and the lithium source is 3 to 8 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours or 8 hours, but the dry milling time is not limited to the enumerated values, and other non-enumerated values in the numerical range are also applicable.
Preferably, the dry milling speed of the iron source and the lithium source is 300-500 rpm/min, such as 300rpm/min, 320rpm/min, 350rpm/min, 380rpm/min, 400rpm/min, 420rpm/min, 450rpm/min, 480rpm/min or 500rpm/min, but is not limited to the recited values, and other values not recited in the range of values are also applicable.
Preferably, the atmosphere for calcination is an inert atmosphere, such as argon, helium, neon, krypton or xenon.
Preferably, the heating rate of the calcination is 1 to 3 ℃/min, and may be, for example, 1 ℃/min, 1.2 ℃/min, 1.5 ℃/min, 1.8 ℃/min, 2 ℃/min, 2.2 ℃/min, 2.5 ℃/min, 2.7 ℃/min, or 3 ℃/min, but is not limited to the values listed, and other values not listed within the range of values are also applicable.
Preferably, the final temperature of the calcination is 850 to 950 ℃, and may be, for example, 850 ℃, 860 ℃, 870 ℃, 880 ℃, 890 ℃, 900 ℃, 910 ℃, 920 ℃, 930 ℃, 940 ℃ or 950 ℃, but is not limited to the recited values, and other values not recited in the range of values are also applicable.
Preferably, the holding time of the calcination at the final temperature is 25 to 35 hours, for example, 25 hours, 26 hours, 27 hours, 28 hours, 29 hours, 30 hours, 31 hours, 32 hours, 33 hours, 34 hours or 35 hours, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the baking and sintering cycle is furnace-cooled.
Preferably, after the lithium-rich material is cooled along with the furnace, airflow crushing and sieving are sequentially carried out to obtain the lithium-rich material.
Preferably, the mesh size of the screen used for said sieving is 300 to 500 mesh, such as 300 mesh, 350 mesh, 400 mesh, 450 mesh or 500 mesh, but not limited to the recited values, and other values not recited within the range of values are equally applicable.
As a preferred embodiment of the present invention, the mass ratio of the lithium-rich material to the lithium iron phosphate material is (5 to 10) (88.5 to 94), and may be, for example, 5.
Preferably, the mixing of the lithium-rich material and the lithium iron phosphate material is dry ball milling.
Preferably, the dry milling time of the lithium-rich material and the lithium iron phosphate material is 3 to 8 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours or 8 hours, but the dry milling time is not limited to the recited values, and other values not recited in the numerical range are also applicable.
Preferably, the dry milling speed of the lithium-rich material and the lithium iron phosphate material is 300-500 rpm/min, such as 300rpm/min, 320rpm/min, 350rpm/min, 380rpm/min, 400rpm/min, 420rpm/min, 450rpm/min, 480rpm/min or 500rpm/min, but is not limited to the enumerated values, and other non-enumerated values in the numerical range are also applicable.
Preferably, the mixture of the lithium-rich material and the lithium iron phosphate material is subjected to a tabletting process before the sintering.
Preferably, the tabletting treatment is carried out for a period of 2 to 5min, for example, 2min, 2.5min, 3min, 3.5min, 4min, 4.5min or 5min, but not limited to the recited values, and other values not recited in the range of the recited values are also applicable.
Preferably, the compression treatment is carried out at a pressure of 10 to 60MPa, for example 10, 20, 30, 40, 50 or 60MPa, but this is not intended to limit the values listed, and other values not listed in this range are equally applicable.
Preferably, the atmosphere of the sintering is an inert atmosphere.
Preferably, the heating rate of the sintering is 4 to 6 ℃/min, for example, 4 ℃/min, 4.2 ℃/min, 4.5 ℃/min, 4.8 ℃/min, 5 ℃/min, 5.2 ℃/min, 5.5 ℃/min, 5.7 ℃/min or 6 ℃/min, but is not limited to the recited values, and other values not recited within the range of values are also applicable.
Preferably, the final temperature of the sintering is 650 to 750 ℃, for example 650 ℃, 660 ℃, 670 ℃, 680 ℃, 690 ℃, 700 ℃, 710 ℃, 720 ℃, 730 ℃, 740 ℃ or 750 ℃, but is not limited to the recited values, and other values not recited in the range of values are also applicable.
Preferably, the holding time of the sintering at the final temperature is 6 to 10 hours, for example, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours or 10 hours, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the furnace is cooled after the sintering is finished.
Preferably, after cooling with the furnace, sequentially carrying out jet milling and sieving to obtain the intermediate material;
preferably, the mesh size of the screen used for screening is 300 to 500 mesh, and may be, for example, 300 mesh, 320 mesh, 350 mesh, 380 mesh, 400 mesh, 420 mesh, 450 mesh, 480 mesh or 500 mesh, but is not limited to the values listed, and other values not listed in the numerical range are also applicable.
As a preferred technical solution of the present invention, the calcining after mixing the intermediate material with a carbon source specifically comprises:
carrying out primary ball milling on the intermediate material and a carbon source, adding a solvent, adjusting to a thick substance, and then carrying out wet ball milling, drying, primary tabletting and primary calcining in sequence to obtain a precursor material; then, carrying out secondary ball milling, secondary tabletting and secondary calcining on the precursor material in sequence to obtain the anode material with the core-shell three-layer composite structure;
preferably, the mass ratio of the intermediate material to the carbon source is (98.5 to 99): (1.4 to 2.1), and may be, for example, 99.
Preferably, the carbon source includes any one or a combination of at least two of glucose, conductive carbon black, carbon nanotubes, citric acid, sucrose, acetylene black, vapor grown carbon fibers, graphene, and biomass carbon, and is further preferably glucose.
Preferably, the primary ball milling is dry ball milling.
Preferably, the time for the primary ball milling is 3 to 8 hours, and may be, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours or 8 hours, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the rotation speed of the primary ball mill is 300-500 rpm/min, such as 300rpm/min, 320rpm/min, 350rpm/min, 380rpm/min, 400rpm/min, 420rpm/min, 450rpm/min, 480rpm/min or 500rpm/min, but not limited to the enumerated values, and other non-enumerated values within the range are also applicable.
Preferably, the solvent is added in an amount of 10wt% to 20wt%, for example 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%, based on the total mass of the intermediate material and the carbon source, but is not limited to the recited values, and other unrecited values within this range are equally applicable.
Preferably, the solvent comprises ethanol.
Preferably, the wet ball milling time is 2 to 4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the wet ball milling is performed at a speed of 250 to 350rpm/min, such as 250rpm/min, 270rpm/min, 280rpm/min, 290rpm/min, 300rpm/min, 320rpm/min or 350rpm/min, but is not limited to the recited values, and other values not recited in the range of values are also applicable.
Preferably, the temperature of the drying is 70 to 90 ℃, for example, 70 ℃, 72 ℃, 75 ℃, 78 ℃, 80 ℃, 83 ℃, 85 ℃ or 90 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the time for one tabletting is 2-5min, 2min, 2.5min, 3min, 3.5min, 4min, 4.5min or 5min, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the pressure of the primary tabletting is 10 to 60MPa, for example 10MPa, 20MPa, 30MPa, 40MPa, 50MPa or 60MPa, but is not limited to the values listed, and other values not listed in the range are also applicable.
Preferably, the atmosphere of the primary calcination is an inert atmosphere.
Preferably, the temperature increase rate of the primary calcination is 1 to 3 ℃/min, and may be, for example, 1 ℃/min, 1.2 ℃/min, 1.5 ℃/min, 1.8 ℃/min, 2 ℃/min, 2.2 ℃/min, 2.5 ℃/min, 2.7 ℃/min or 3 ℃/min, but is not limited to the values listed, and other values not listed in the numerical range are also applicable.
Preferably, the final temperature of the primary calcination is 300 to 400 ℃, for example, 300 ℃, 310 ℃, 320 ℃, 330 ℃, 340 ℃, 350 ℃, 360 ℃, 370 ℃, 380 ℃, 390 ℃ or 400 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the time for which the primary calcination is maintained at the final temperature is 6 to 10 hours, for example, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, or 10 hours, but is not limited to the recited values, and other values not recited in the range of values are also applicable.
Preferably, the precursor material is obtained by furnace cooling after the primary calcination.
In a preferred embodiment of the present invention, the time of the secondary ball milling is 2 to 4 hours, for example, 2 hours, 2.2 hours, 2.5 hours, 2.8 hours, 3 hours, 3.2 hours, 3.5 hours, 3.7 hours or 4 hours, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable.
Preferably, the rotation speed of the secondary ball milling is 300 to 500rpm/min, for example, 300rpm/min, 320rpm/min, 350rpm/min, 380rpm/min, 400rpm/min, 420rpm/min, 450rpm/min, 480rpm/min or 500rpm/min, but is not limited to the enumerated values, and other non-enumerated values within the range are also applicable.
Preferably, the time for the second tabletting is 2-5 min, for example, 2min, 2.5min, 3min, 3.5min, 4min, 4.5min or 5min, but is not limited to the recited values, and other values not recited in the range of the recited values are also applicable.
Preferably, the pressure of the secondary tabletting is 10 to 60MPa, for example 10MPa, 20MPa, 30MPa, 40MPa, 50MPa or 60MPa, but is not limited to the values listed, and other values not listed in the range are also applicable.
Preferably, the atmosphere of the secondary calcination is an inert atmosphere.
Preferably, the temperature increase rate of the secondary calcination is 1 to 3 ℃/min, and may be, for example, 1 ℃/min, 1.2 ℃/min, 1.5 ℃/min, 1.8 ℃/min, 2 ℃/min, 2.2 ℃/min, 2.5 ℃/min, 2.7 ℃/min or 3 ℃/min, but is not limited to the enumerated values, and other values not enumerated within the numerical range are also applicable.
Preferably, the final temperature of the second calcination is 650 to 750 ℃, and may be 650 ℃, 660 ℃, 670 ℃, 680 ℃, 690 ℃, 700 ℃, 710 ℃, 720 ℃, 730 ℃, 740 ℃ or 750 ℃, for example, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the holding time of the secondary calcination at the final temperature is 13 to 17 hours, for example, 13 hours, 13.5 hours, 14 hours, 14.5 hours, 15 hours, 15.5 hours, 16 hours, 16.5 hours or 17 hours, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the secondary calcined cake is cooled along with the furnace.
Preferably, after the core-shell three-layer composite structure is cooled along with the furnace, airflow crushing, sieving and demagnetizing are sequentially carried out, so that the core-shell three-layer composite structure cathode material is obtained.
Preferably, the mesh size of the screen used for screening is 300 to 500 mesh, and may be, for example, 300 mesh, 320 mesh, 350 mesh, 380 mesh, 400 mesh, 420 mesh, 450 mesh, 480 mesh or 500 mesh, but is not limited to the values listed, and other values not listed in the numerical range are also applicable.
As a preferable technical scheme of the invention, the preparation method comprises the following steps:
(1) Carrying out dry ball milling on an iron source and a lithium source for 3-8 h at the rotating speed of 300-500 rpm/min according to the proportion of iron to lithium in the atomic molar ratio of 1 (4-8), then heating to 850-950 ℃ at the heating rate of 1-3 ℃/min in an inert atmosphere, then keeping the temperature for 25-35 h for roasting, then cooling along with a furnace, and then sequentially carrying out air flow crushing and sieving through a 300-500-mesh sieve to obtain a lithium-rich material;
(2) Carrying out dry ball milling on a lithium-rich material and a lithium iron phosphate material according to the mass ratio of (5-10) to (88.5-94) at the rotating speed of 300-500 rpm/min for 3-8 h, then carrying out tabletting treatment at the pressure of 10-60 Mpa for 2-5 min, then heating to 650-750 ℃ at the heating rate of 4-6 ℃/min in an inert atmosphere, then carrying out heat preservation for 6-10 h for sintering, then cooling along with a furnace, and then sequentially carrying out air flow crushing and sieving through a 300-500 mesh sieve to obtain an intermediate material;
(3) Carrying out primary dry ball milling on an intermediate material and a carbon source for 3-8 h at the rotating speed of 300-500 rpm/min according to the mass ratio of (98.5-99) to (1.4-2.1), then adding 10-20 wt% of a solvent to adjust to a thick substance on the basis of the total mass of the intermediate material and the carbon source, carrying out wet ball milling on the thick substance at the rotating speed of 250-350 rpm/min for 2-4 h, drying at 70-90 ℃, then carrying out primary tabletting treatment at the pressure of 10-60 Mpa for 2-5 min, then heating to 300-400 ℃ at the heating rate of 1-3 ℃/min in an inert atmosphere, carrying out primary calcination at the temperature of 6-10 h, and then carrying out furnace cooling to obtain a precursor material;
(4) Performing secondary ball milling on the precursor material at the rotating speed of 300-500 rpm/min for 2-4 h, performing secondary tabletting treatment at the pressure of 10-60 Mpa for 2-5 min, heating to 650-750 ℃ at the heating rate of 1-3 ℃/min in an inert atmosphere, preserving heat for 13-17 h for secondary calcination, cooling along with a furnace, sequentially performing air flow crushing and sieving with a 300-500 mesh sieve, and demagnetizing to obtain the cathode material with the core-shell three-layer composite structure.
In a third aspect, the invention provides a lithium ion battery, which comprises a positive electrode, a diaphragm and a negative electrode which are sequentially stacked, wherein the positive electrode adopts the positive electrode material of the first aspect.
Compared with the prior art, the invention has the beneficial effects that:
according to the positive electrode material with the core-shell three-layer composite structure and the preparation method thereof, the lithium-rich material is used as the core of the positive electrode material, and the lithium iron phosphate material and the carbon layer which are supplemented with lithium are sequentially laminated and coated on the surface of the lithium-rich material core, so that the risk of contact reaction of the lithium-rich material and air or a reaction solvent can be completely avoided, the material storage environment control cost and the material processing and using process cost can be reduced, the lithium supplementing effect can be considered, the defect of insufficient conductivity can be overcome, and the material capacity can be improved.
Drawings
Fig. 1 is a schematic diagram of a core-shell three-layer composite structure of the positive electrode material provided by the invention.
FIG. 2 is a scanning electron microscope photograph of the positive electrode material in example 4 of the present invention.
Wherein, 1-lithium-rich material core; 2-a lithium iron phosphate layer; 3-carbon layer.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
According to the positive electrode material with the core-shell three-layer composite structure, as shown in fig. 1, the positive electrode material comprises a lithium-rich material core 1, and a lithium iron phosphate layer 2 and a carbon layer 3 are sequentially laminated and wrapped on the outer surface of the lithium-rich material core 1.
Example 1
The embodiment provides a core-shell three-layer composite structure cathode material, which comprises the following components: li 5 FeO 4 Is 7wt%, and lithium iron phosphate (LiFePO) 4 ) The mass fraction of (2) is 91.7wt%, the mass fraction of C is 1.3wt%;
the preparation method of the cathode material specifically comprises the following steps:
(1) Dry ball milling and mixing ferroferric oxide and anhydrous lithium hydroxide for 5h at the rotating speed of 400rpm/min according to the atomic molar ratio of iron to lithium of 1:6, heating to 900 ℃ at the heating rate of 2 ℃/min in the argon atmosphere, keeping the temperature for 30h for roasting, cooling along with a furnace, sequentially carrying out air flow crushing and sieving through a 400-mesh sieve to obtain Li 5 FeO 4 ；
(2) Mixing Li 5 FeO 4 With LiFePO 4 According to the mass ratio of 7:91.7, carrying out dry ball milling and mixing at the rotating speed of 400rpm/min for 5h, then carrying out tabletting treatment at the pressure of 40Mpa for 3min, then heating to 700 ℃ at the heating rate of 5 ℃/min under the argon atmosphere, then preserving heat for 8h for sintering, then cooling along with a furnace, sequentially carrying out jet milling and sieving with a 400-mesh sieve to obtain an intermediate material;
(3) Performing primary dry ball milling and mixing on an intermediate material and biomass carbon at a rotating speed of 400rpm/min for 5h according to a mass ratio of 98.7 to 1.8, then adding 15wt% of ethanol to adjust the mixture to a thick substance on the basis of the total mass of the intermediate material and the biomass carbon, performing wet ball milling on the thick substance at a rotating speed of 300rpm/min for 3h, drying at 80 ℃, performing primary tabletting treatment at a pressure of 40MPa for 3min, heating to 350 ℃ at a heating rate of 2 ℃/min in an argon atmosphere, then preserving heat for 8h for primary calcination, and then cooling along with a furnace to obtain a precursor material;
(4) Performing secondary dry ball milling on the precursor material at the rotating speed of 400rpm/min for 3h, performing secondary tabletting treatment at the pressure of 40Mpa for 3min, heating to 700 ℃ at the heating rate of 2 ℃/min under the argon atmosphere, performing heat preservation for 15h for secondary calcination, cooling along with a furnace, sequentially performing jet milling and sieving with a 400-mesh sieve, and finally demagnetizing to obtain the Li with the core-shell three-layer composite structure 5 FeO 4 @LiFePO 4 @ C positive electrode material.
Example 2
The embodiment provides a core-shell three-layer composite structure cathode material, which comprises the following components: li 6 CoO 4 Is 5wt%, liFePO 4 The mass fraction of C is 94wt%, and the mass fraction of C is 1wt%;
the preparation method of the cathode material specifically comprises the following steps:
(1) Dry ball milling and mixing cobaltosic oxide and lithium hydroxide monohydrate according to the atomic molar ratio of cobalt to lithium of 1:4 for 8h at the rotating speed of 300rpm/min, heating to 950 ℃ at the heating rate of 1 ℃/min in the atmosphere of helium, keeping the temperature for 25h for roasting, cooling along with a furnace, sequentially carrying out air flow crushing and sieving by a 300-mesh sieve to obtain Li 6 CoO 4 ；
(2) Mixing Li 6 CoO 4 With LiFePO 4 According to the mass ratio of 5;
(3) Performing primary dry ball milling and mixing on the intermediate material and the carbon nano tube at the rotating speed of 300rpm/min for 8h according to the mass ratio of 99.4, then adding 10wt% of ethanol to adjust the mixture to a thick substance on the basis of the total mass of the intermediate material and the carbon nano tube, performing wet ball milling on the thick substance at the rotating speed of 250rpm/min for 4h, drying at 70 ℃, performing primary tabletting treatment at the pressure of 10MPa for 5min, heating to 400 ℃ at the heating rate of 1 ℃/min in the helium atmosphere, performing primary calcination for 6h, and cooling along with a furnace to obtain a precursor material;
(4) Performing secondary dry ball milling on the precursor material at the rotating speed of 300rpm/min for 4h, performing secondary tabletting treatment at the pressure of 10Mpa for 5min, heating to 750 ℃ at the heating rate of 1 ℃/min in the helium atmosphere, performing heat preservation for 13h for secondary calcination, cooling along with a furnace, sequentially performing jet milling andli with core-shell three-layer composite structure obtained by sieving with 300-mesh sieve 6 CoO 4 @LiFePO 4 @ C positive electrode material.
Example 3
The embodiment provides a core-shell three-layer composite structure cathode material, which comprises the following components: li 6 MnO 4 Is 10wt%, liFePO 4 The mass fraction of (B) is 88.5wt%, and the mass fraction of C is 1.5wt%;
the preparation method of the cathode material specifically comprises the following steps:
(1) Performing dry ball milling and mixing on manganese monoxide and lithium hydroxide monohydrate at the atomic molar ratio of manganese to lithium of 1:8 for 3h at the rotating speed of 500rpm/min, then heating to 850 ℃ at the heating rate of 3 ℃/min under the argon atmosphere, preserving heat for 35h for roasting, then cooling along with a furnace, sequentially performing jet milling and sieving through a 500-mesh sieve to obtain Li 6 MnO 4 ；
(2) Mixing Li 6 MnO 4 With LiFePO 4 Carrying out dry ball milling and mixing for 3h at the rotating speed of 500rpm/min according to the mass ratio of 10.5, then carrying out tabletting treatment for 2min at the pressure of 60Mpa, then heating to 650 ℃ at the heating rate of 6 ℃/min under the argon atmosphere, then preserving heat for 10h for sintering, then cooling along with a furnace, sequentially carrying out jet milling and sieving with a 500-mesh sieve to obtain an intermediate material;
(3) Performing primary dry ball milling and mixing on an intermediate material and glucose for 3h at the rotating speed of 500rpm/min according to the mass ratio of 98.5 to 2.1, then adding 20wt% of a solvent to adjust the mixture to a thick substance on the basis of the total mass of the intermediate material and a carbon source, performing wet ball milling on the thick substance at the rotating speed of 350rpm/min for 2h, drying at 90 ℃, performing primary tabletting treatment at the pressure of 60MPa for 2min, heating to 300 ℃ at the heating rate of 3 ℃/min in an argon atmosphere, then preserving heat for 10h for primary calcination, and then cooling along with a furnace to obtain a precursor material;
(4) Performing secondary dry ball milling on the precursor material at the rotating speed of 500rpm/min for 2h, performing secondary tabletting treatment at the pressure of 60Mpa for 2min, and then performing inert tabletting treatmentHeating to 650 ℃ at a heating rate of 3 ℃/min under an atmosphere of nature, preserving heat for 17 hours for secondary calcination, cooling along with a furnace, sequentially performing jet milling and sieving with a 500-mesh sieve, and finally demagnetizing to obtain Li with a core-shell three-layer composite structure 6 MnO 4 @LiFePO 4 @ C positive electrode material.
Example 4
The embodiment provides a core-shell three-layer composite structure cathode material, which comprises the following components: li 5 FeO 4 Is 5wt%, liFePO 4 The mass fraction of C is 94wt%, and the mass fraction of C is 1wt%; the scanning electron microscope image of the cathode material is shown in FIG. 2;
the preparation method of the cathode material specifically comprises the following steps:
(1) Carrying out dry ball milling and mixing on ferric oxide and lithium hydroxide monohydrate according to the atomic molar ratio of iron to lithium of 1:6 for 5h at the rotating speed of 400rpm/min, then heating to 900 ℃ at the heating rate of 2 ℃/min under the argon atmosphere, preserving heat for 30h for roasting, then cooling along with a furnace, sequentially carrying out jet milling and sieving through a 400-mesh sieve to obtain Li 5 FeO 4 ；
(2) Mixing Li 5 FeO 4 With LiFePO 4 According to the mass ratio of 5;
(3) Performing primary dry ball milling and mixing on an intermediate material and glucose at a rotating speed of 400rpm/min for 5h according to a mass ratio of 99.4, then adding 15wt% of ethanol to adjust to a thick substance on the basis of the total mass of the intermediate material and the glucose, performing wet ball milling on the thick substance at a rotating speed of 300rpm/min for 3h, drying at 80 ℃, performing primary tabletting treatment at a pressure of 40MPa for 3min, heating to 350 ℃ at a heating rate of 2 ℃/min in an argon atmosphere, performing primary calcination for 8h, and then cooling along with a furnace to obtain a precursor material;
(4) Performing secondary dry ball milling on the precursor material at the rotating speed of 400rpm/min for 3h, performing secondary tabletting treatment at the pressure of 40Mpa for 3min, heating to 700 ℃ at the heating rate of 2 ℃/min under the argon atmosphere, performing heat preservation for 15h for secondary calcination, cooling along with a furnace, sequentially performing jet milling and sieving with a 400-mesh sieve, and finally demagnetizing to obtain the Li with the core-shell three-layer composite structure 5 FeO 4 @LiFePO 4 @ C positive electrode material.
Example 5
This example differs from example 4 in that: the positive electrode material comprises the following components: li 5 FeO 4 Is 5wt%, liFePO 4 The mass fraction of (A) is 93.5wt%, and the mass fraction of C is 1.5wt%;
in step (2), li 5 FeO 4 With LiFePO 4 The mass ratio of (A) to (B) is 5; in the step (3), the mass ratio of the intermediate material to the glucose is 98.5; the remaining process parameters and operating procedures were the same as in example 4.
Example 6
This example differs from example 4 in that: the positive electrode material comprises the following components: li 5 FeO 4 Is 6.5wt%, liFePO 4 The mass fraction of C is 92.5wt%, and the mass fraction of C is 1wt%;
in step (2), li 5 FeO 4 With LiFePO 4 The mass ratio of (A) to (B) is 6.5; the remaining process parameters and operating procedures were the same as in example 4.
Example 7
This example differs from example 4 in that: the positive electrode material comprises the following components: li 5 FeO 4 Is 6.5wt%, liFePO 4 The mass fraction of C is 92wt%, and the mass fraction of C is 1.5wt%;
in step (2), li 5 FeO 4 With LiFePO 4 The mass ratio of (2) is 6.5; in the step (3), the quality of the intermediate material and glucoseThe ratio is 98.5; the remaining process parameters and operating procedures were the same as in example 4.
Example 8
This example differs from example 4 in that: the positive electrode material comprises the following components: li 5 FeO 4 Is 8.5wt%, liFePO 4 The mass fraction of C is 90.5wt%, and the mass fraction of C is 1wt%;
in step (2), li 5 FeO 4 With LiFePO 4 The mass ratio of (A) to (B) is 8.5; the remaining process parameters and operating procedures were the same as in example 4.
Example 9
This example differs from example 4 in that: the positive electrode material comprises the following components: li 5 FeO 4 Is 8.5wt%, liFePO 4 The mass fraction of C is 90wt%, and the mass fraction of C is 1.5wt%;
in step (2), li 5 FeO 4 With LiFePO 4 The mass ratio of (A) to (B) is 8.5; in the step (3), the mass ratio of the intermediate material to the glucose is 98.5; the remaining process parameters and operating procedures were the same as in example 4.
Example 10
This example differs from example 4 in that: the positive electrode material comprises the following components: li 5 FeO 4 Is 10wt%, liFePO 4 The mass fraction of C is 89wt%, and the mass fraction of C is 1wt%;
in step (2), li 5 FeO 4 With LiFePO 4 The mass ratio of (A) to (B) is 10; the remaining process parameters and operating procedures were the same as in example 4.
Example 11
This example differs from example 4 in that: the positive electrode material comprises the following components: li 5 FeO 4 Is 10wt%, liFePO 4 The mass fraction of (B) is 88.5wt%, and the mass fraction of C is 1.5wt%;
in step (2), li 5 FeO 4 With LiFePO 4 The mass ratio of (1) to (2) is 10; in the step (3), the mass ratio of the intermediate material to the glucose is 98.5; the remaining process parameters and operating procedures were the same as in example 4.
Example 12
This example differs from example 4 in that: the positive electrode material comprises the following components: li 5 FeO 4 Is 12wt%, liFePO 4 The mass fraction of C is 87wt%, and the mass fraction of C is 1wt%;
in step (2), li 5 FeO 4 With LiFePO 4 The mass ratio of (1) to (4) is 12; the remaining process parameters and operating procedures were the same as in example 4.
Example 13
This example differs from example 4 in that: the positive electrode material comprises the following components: li 5 FeO 4 Is 3wt%, liFePO 4 The mass fraction of C is 96wt%, and the mass fraction of C is 1wt%;
in step (2), li 5 FeO 4 With LiFePO 4 The mass ratio of (1) to (3); the remaining process parameters and operating procedures were the same as in example 4.
Example 14
This example differs from example 4 in that: the positive electrode material comprises the following components: li 5 FeO 4 Is 5wt%, liFePO 4 The mass fraction of C is 93wt%, and the mass fraction of C is 2wt%;
in step (2), li 5 FeO 4 With LiFePO 4 The mass ratio of (1) is 5; in the step (3), the mass ratio of the intermediate material to the glucose is 98.8; the remaining process parameters and operating procedures were the same as in example 4.
Example 15
This example differs from example 4 in that: the positive electrode material comprises the following components: li 5 FeO 4 Is 5.5wt%, liFePO 4 The mass fraction of C is 94wt%, and the mass fraction of C is 0.5wt%;
in step (2), li 5 FeO 4 With LiFePO 4 The mass ratio of (A) to (B) is 5.5; in the step (3), the mass ratio of the intermediate material to the glucose is 100; the remaining process parameters and operating procedures were the same as in example 4.
Comparative example 1
This comparative example differs from example 4 in that: the positive electrode material comprises the following components: liFePO 4 The mass fraction of C is 99wt%, and the mass fraction of C is 1wt%; omit Li 5 FeO 4 The core is of a core-shell double-layer structure, wherein the core is made of lithium iron phosphate, and the shell is a carbon layer 3; the remaining process parameters and operating procedures were the same as in example 4.
Comparative example 2
This comparative example differs from example 4 in that: the positive electrode material comprises the following components: li 5 FeO 4 The mass fraction of C is 99wt%, and the mass fraction of C is 1wt%; save LiFePO 4 The obtained cathode material is of a core-shell double-layer structure, wherein the core is Li 5 FeO 4 The shell is a carbon layer 3; the remaining process parameters and operating procedures were the same as in example 4.
Comparative example 3
This comparative example differs from example 4 in that: the positive electrode material comprises the following components: li 5 FeO 4 Is 6wt%, liFePO 4 Is 94 wt.%; the carbon layer 3 is omitted, and the obtained anode material is of a core-shell double-layer structure, wherein the core is Li 5 FeO 4 The outer shell is LiFePO 4 (ii) a The remaining process parameters and operating procedures were the same as in example 4.
The positive electrode materials prepared in the examples 1 to 15 and the comparative examples 1 to 3 are assembled into a button cell according to the conventional process, and the electrolyte system is LiPF with 1.12mol/L 6 Medium (EC/PC/EMC =35/5/60,3% VC), 0.1C was used at room temperature, respectively 1 And 0.5C 1 Carrying out a first charging test on the multiplying power current to obtain a first charging capacity; the upper limit charging voltage was 3.7V.
The results of the performance tests of the positive electrode materials prepared in examples 1 to 15 and comparative examples 1 to 3 are shown in table 1.
TABLE 1
As can be seen from the data in table 1:
(1) 0.1C of Positive electrode Material of core-Shell three-layer composite Structure obtained in examples 1 to 3 1 The first charging capacity is higher than 165mAh/g and 0.5C 1 The first charge capacity is higher than 150mAh/g, and the first charge rate efficiency (0.5C) 1 /0.1C 1 ) The content of the core-shell three-layer composite structure is higher than 90%, which shows that the core-shell three-layer composite structure anode material prepared by the preparation method of the anode material provided by the invention has excellent performance.
(2) The performance data of the core-shell three-layer composite structure positive electrode materials obtained in examples 4 to 11 can be obtained as follows: the 0.1C of the positive electrode material is increased along with the increase of the proportion of the lithium-rich material in the positive electrode material 1 And 0.5C 1 The first charge capacity gradually increases. When the lithium-rich material accounts for 6.5wt%, the capacity of the anode material is improved by-10% compared with the conventional lithium iron phosphate material, the irreversible capacity loss (about 10% in wide) caused by the cathode material can be completely compensated, and the energy density of the lithium ion battery is greatly improved. At the same time, too little or too much of the lithium-rich material will reduce the rate capability of the material (0.5C) 1 /0.1C 1 ) However, the ratio of the carbon layer 3 in the positive electrode material can be improved to some extent.
(3) Positive electrode materials 0.1C of examples 12 and 13 1 And 0.5C 1 The first charge capacity is lower than that of the embodiment 4, because the mass fraction of the lithium-rich material is too high and the mass fraction of the lithium iron phosphate is too low in the embodiment 12; example 13 shows that the mass fraction of the lithium-rich material is too low, and the mass fraction of the lithium iron phosphate is too high.When the mass fraction of the lithium-rich material is too high or too low, the rate charging capability of the material is reduced, because the ratio of the lithium-rich material to the lithium iron phosphate material affects the morphology and stability of the crystal interface of the sintered cathode material.
(4) Positive electrode materials 0.1C of examples 14 and 15 1 And 0.5C 1 The first charge capacity was lower than that of example 4 because the mass fraction of the carbon layer 3 was too high in example 14 and too low in example 15. When the mass fraction of the carbon source is too high, the gram volume of the material is reduced because the carbon material is not an active substance containing lithium; when the mass fraction of the carbon source is too low, the integrity of the coated carbon is deteriorated, the conductivity of the material is reduced, and the rate capability of the material is reduced.
(5) Positive electrode Material 0.1C of comparative examples 1 to 3 1 And 0.5C 1 The initial charge capacity is lower than that of the embodiment 4, because the positive electrode material of the comparative example 1 has no lithium-rich material core 1, the lithium supplement process can not be realized; the positive electrode material of comparative example 2 was free of an iron-lithium phosphate interlayer, so that the positive electrode material lacked an active material; comparative example 3 has no carbon layer 3, so that the obtained cathode material has poor conductivity. Therefore, according to the core-shell three-layer composite structure cathode material provided by the invention, the lithium-rich material is used as the core of the cathode material, and the lithium iron phosphate material supplemented with lithium and the carbon layer 3 are sequentially laminated and coated on the surface of the lithium-rich material core 1, so that the risk of contact reaction of the lithium-rich material with air or a reaction solvent can be completely avoided, the lithium supplementing effect can be considered, the defect of insufficient conductivity can be overcome, and the material capacity can be improved.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention disclosed herein fall within the scope and disclosure of the present invention.
Claims (10)
1. The positive electrode material with the core-shell three-layer composite structure is characterized by comprising a lithium-rich material core, wherein a lithium iron phosphate layer and a carbon layer are sequentially laminated and wrapped on the outer surface of the lithium-rich material core.
2. The positive electrode material according to claim 1, wherein the lithium-rich material has an inverted fluorite structure;
preferably, the lithium rich material comprises Li 5 FeO 4 。
3. The positive electrode material according to claim 1 or 2, wherein the mass fraction of the lithium-rich material in the positive electrode material is 5 to 10wt%;
preferably, the mass fraction of the lithium iron phosphate material in the positive electrode material is 88.5wt% -94 wt%;
preferably, the mass fraction of carbon in the cathode material is 1wt% to 1.5wt%.
4. A method for producing the positive electrode material according to any one of claims 1 to 3, characterized by comprising:
and mixing the lithium-rich material and the lithium iron phosphate material, sintering to obtain an intermediate material, mixing the intermediate material and a carbon source, and calcining to obtain the anode material with the core-shell three-layer composite structure.
5. The preparation method according to claim 4, wherein the lithium-rich material is prepared by the following method:
mixing an iron source and a lithium source, and roasting to obtain the lithium-rich material;
preferably, the iron source comprises any one of ferric oxide, ferroferric oxide, ferric oxyhydroxide, ferric nitrate and ferric citrate, and is further preferably ferric oxide;
preferably, the lithium source is any one of lithium carbonate, lithium hydroxide monohydrate and lithium hydroxide anhydrous, and is further preferably lithium hydroxide monohydrate;
preferably, the iron source and the lithium source are mixed in a ratio of iron to lithium atoms in a molar ratio of 1 (4-8);
preferably, the mixing of the iron source and the lithium source is dry ball milling;
preferably, the dry ball milling time of the iron source and the lithium source is 3-8 h;
preferably, the dry ball milling rotating speed of the iron source and the lithium source is 300-500 rpm/min;
preferably, the atmosphere of the calcination is an inert atmosphere;
preferably, the heating rate of the roasting is 1-3 ℃/min;
preferably, the final temperature of the roasting is 850-950 ℃;
preferably, the heat preservation time of the roasting at the final temperature is 25-35 h;
preferably, the baking and sintering beams are cooled along with the furnace;
preferably, after cooling along with the furnace, sequentially carrying out airflow crushing and sieving to obtain the lithium-rich material;
preferably, the mesh number of the screen used for sieving is 300-500 meshes.
6. The preparation method according to claim 4 or 5, wherein the mass ratio of the lithium-rich material to the lithium iron phosphate material is (5-10) to (88.5-94);
preferably, the mixing of the lithium-rich material and the lithium iron phosphate material is dry ball milling;
preferably, the dry ball milling time of the lithium-rich material and the lithium iron phosphate material is 3-8 h;
preferably, the dry ball milling rotating speed of the lithium-rich material and the lithium iron phosphate material is 300-500 rpm/min;
preferably, before sintering, tabletting a mixture of the lithium-rich material and the lithium iron phosphate material;
preferably, the tabletting treatment time is 2-5 min;
preferably, the pressure of the tabletting treatment is 10-60 Mpa;
preferably, the atmosphere of the sintering is an inert atmosphere;
preferably, the temperature rise rate of the sintering is 4-6 ℃/min;
preferably, the final temperature of the sintering is 650-750 ℃;
preferably, the heat preservation time of the sintering at the final temperature is 6-10 h;
preferably, the furnace is cooled after the sintering is finished;
preferably, after cooling with the furnace, sequentially carrying out jet milling and sieving to obtain the intermediate material;
preferably, the mesh number of the screen used for sieving is 300-500 meshes.
7. The method according to any one of claims 4 to 6, wherein the calcination after mixing the intermediate material with the carbon source specifically comprises:
carrying out primary ball milling on the intermediate material and a carbon source, adding a solvent, adjusting to a thick substance, and then carrying out wet ball milling, drying, primary tabletting and primary calcining in sequence to obtain a precursor material; then, carrying out secondary ball milling, secondary tabletting and secondary calcining on the precursor material in sequence to obtain the anode material with the core-shell three-layer composite structure;
preferably, the mass ratio of the intermediate material to the carbon source is (98.5-99) to (1.4-2.1);
preferably, the carbon source comprises any one or a combination of at least two of glucose, conductive carbon black, citric acid, sucrose, carbon nanotubes, acetylene black, vapor grown carbon fibers, graphene and biomass carbon, and further preferably glucose;
preferably, the primary ball milling is dry ball milling;
preferably, the time of the primary ball milling is 3-8 h;
preferably, the rotation speed of the primary ball milling is 300-500 rpm/min;
preferably, the addition amount of the solvent is 10wt% to 20wt% based on the total mass of the intermediate material and the carbon source;
preferably, the solvent comprises ethanol;
preferably, the time of the wet ball milling is 2-4 h;
preferably, the rotation speed of the wet ball milling is 250-350 rpm/min;
preferably, the drying temperature is 70-90 ℃;
preferably, the time for one-time tabletting is 2-5 min;
preferably, the pressure of the primary tabletting is 10-60 Mpa;
preferably, the atmosphere of the primary calcination is an inert atmosphere;
preferably, the temperature rise rate of the primary calcination is 1-3 ℃/min;
preferably, the final temperature of the primary calcination is 300-400 ℃;
preferably, the heat preservation time of the primary calcination at the final temperature is 6-10 h;
preferably, the precursor material is obtained by furnace cooling after the primary calcination.
8. The preparation method of claim 7, wherein the time of the secondary ball milling is 2 to 4 hours;
preferably, the rotation speed of the secondary ball milling is 300-500 rpm/min;
preferably, the time for secondary tabletting is 2-5 min;
preferably, the pressure of the secondary tabletting is 10-60 Mpa;
preferably, the atmosphere of the secondary calcination is an inert atmosphere;
preferably, the temperature rise rate of the secondary calcination is 1-3 ℃/min;
preferably, the final temperature of the secondary calcination is 650-750 ℃;
preferably, the heat preservation time of the secondary calcination at the final temperature is 13-17 h;
preferably, the secondary calcining is cooled along with the furnace after sintering;
preferably, after the core-shell three-layer composite structure is cooled along with the furnace, sequentially carrying out air flow crushing, sieving and demagnetizing to obtain the core-shell three-layer composite structure anode material;
preferably, the mesh number of the screen used for sieving is 300-500 meshes.
9. The method according to any one of claims 4 to 8, characterized by comprising the steps of:
(1) Carrying out dry ball milling on an iron source and a lithium source at the atomic molar ratio of iron to lithium of 1 (4-8) for 3-8 h at the rotating speed of 300-500 rpm/min, then heating to 850-950 ℃ at the heating rate of 1-3 ℃/min under an inert atmosphere, then keeping the temperature for 25-35 h for roasting, then cooling along with a furnace, sequentially carrying out air flow crushing and sieving through a 300-500-mesh sieve to obtain a lithium-rich material;
(2) Carrying out dry ball milling on a lithium-rich material and a lithium iron phosphate material according to the mass ratio of (5-10) to (88.5-94) at the rotating speed of 300-500 rpm/min for 3-8 h, then carrying out tabletting treatment at the pressure of 10-60 Mpa for 2-5 min, then heating to 650-750 ℃ at the heating rate of 4-6 ℃/min in an inert atmosphere, then carrying out heat preservation for 6-10 h for sintering, then cooling along with a furnace, and then sequentially carrying out air flow crushing and sieving through a 300-500 mesh sieve to obtain an intermediate material;
(3) Carrying out primary dry ball milling on an intermediate material and a carbon source for 3-8 h at the rotating speed of 300-500 rpm/min according to the mass ratio of (98.5-99) to (1.4-2.1), then adding 10-20 wt% of a solvent to adjust the mixture to a thick substance on the basis of the total mass of the intermediate material and the carbon source, carrying out wet ball milling on the thick substance at the rotating speed of 250-350 rpm/min for 2-4 h, drying at 70-90 ℃, then carrying out primary tabletting treatment at the pressure of 10-60 Mpa for 2-5 min, then heating to 300-400 ℃ at the heating rate of 1-3 ℃/min in an inert atmosphere, carrying out primary calcination at the temperature of 6-10 h, and then carrying out furnace cooling to obtain a precursor material;
(4) Performing secondary ball milling on the precursor material at the rotating speed of 300-500 rpm/min for 2-4 h, performing secondary tabletting treatment at the pressure of 10-60 Mpa for 2-5 min, heating to 650-750 ℃ at the heating rate of 1-3 ℃/min in an inert atmosphere, then performing heat preservation for 13-17 h for secondary calcination, performing air flow crushing and 300-500 mesh screen mesh in sequence after furnace cooling, and finally demagnetizing to obtain the core-shell three-layer composite structure anode material.
10. A lithium ion battery, which is characterized by comprising a positive electrode, a diaphragm and a negative electrode which are sequentially stacked, wherein the positive electrode adopts the positive electrode material of any one of claims 1 to 3.
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| CN114242980B (en) * | 2021-12-16 | 2023-10-31 | 蜂巢能源科技股份有限公司 | Lithium iron phosphate composite material, preparation method and application |
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