A kind of preparation method of pyrolytic carbon-coated lithium iron phosphate compositeTechnical field
The present invention relates to the lithium ion secondary battery anode material field, specially refer to the preparation method of lithium ion secondary battery anode material carbon-coated LiFePO 4 for lithium ion batteries.
Technical background
Lithium rechargeable battery is with its energy density height, the voltage height, specific capacity is big, and self discharge is little, environmentally friendly, memory-less effect, fail safe is good, and cycle-index is many, advantages such as the life-span is long, be widely used in mobile digital product, portable power tool, weaponry etc., the application on electric automobile is also gradually ripe, has become the emphasis that various countries competitively research and develop at present.Positive electrode is as the main storage lithium part in the lithium rechargeable battery, in lithium rechargeable battery, not only to be provided at the lithium ion that takes off embedding in the both positive and negative polarity lithium intercalation compound repeatedly, but also will bear the required lithium of SEI film that the negative material surface forms, thereby research and develop the emphasis that high performance positive electrode has become the lithium ion battery development.
The olivine-type LiFePO 4 of anode material is cheap with its raw material, low toxicity, theoretical specific capacity height, with respect to advantages such as the operating voltage of other lithium ion secondary battery anode material are moderate, become the focus of people's research in recent years.But there are two significant disadvantages in LiFePO4: the one, and conductivity is low, causes high-rate discharge ability poor, and actual specific capacity is low, and under the bigger situation of electric current, electrode polarization is serious, causes discharging and recharging irreversible degree and strengthens, and the electrochemistry capacitance loss is serious; The 2nd, bulk density is low, causes volume and capacity ratio low, and this brings certain difficulty for the practicality of LiFePO4.
For improving the electronic conductivity of LiFePO4, main element doping/coating, the method that reduces the product particle diameter and add conductive agent of adopting of a lot of researchs.Wherein remarkable to add the conductive agent effect, and be easy to industrialization, yet the multi-conducting agent is different material with carbon elements and carbon source, can reduce its tap density owing to the adding of conductive agent material with carbon element when the LiFePO4 conductivity improves, and two kinds of shortcomings can not overcome simultaneously.In addition, synthetic method also has certain influence to the performance of LiFePO4.Common synthetic granting has high temperature solid-state method, microwave method, hydrothermal synthesis method etc.
The method for preparing at present LiFePO4 has:
(1) high temperature solid-state method.This method technology is simple, is easy to realize industrialization, and preparation condition is controlled easily.Catabolite is easy to remove, and reduces the production of impurity.Weak point is that thing is mutually inhomogeneous, and crystalline size is bigger, and particle size distribution is wide, and sintering time is long, uses protective gas, the cost height.At present to be used in research the most extensive for this synthetic method, and the composite ferric lithium phosphate material conductivity that wherein goes out to prepare carbon coated is apparently higher than the pure phase LiFePO4, but this carbon coating layer coats inhomogeneous at particle surface.
(2) hydro thermal method.This method is controlled crystal formation and particle diameter easily, thing phase homogeneous, and diameter of particle is little, and process is simple.Weak point need to be high-temperature high-pressure apparatus, the cost height.As people such as Slivera Scaccia with Fe2+Oxidation obtains FePO42H2O, FePO42H2After O sloughs the crystallization water, in organic solvent such as acetonitrile, add LiI again and carry out lithiumation.Filtration washing then, be deposited in air drying after, at Ar+H2High temperature sintering obtains LiFePO4 under the atmosphere.
(3) microwave method.This method equipment is simple, and heating-up temperature is even, is easy to control, and the reaction time is short.But the industrialized difficulty of this method is bigger.The preparation be mixed with the composite material of carbon the time, carbon-coating is at the particle surface skewness.
All there is certain defective in the above on the performance of the technical and material of the LiFePO4 of existing preparation, and it is imperfect that the carbon-coated LiFePO 4 for lithium ion batteries of preparing coats carbon-coating.
Summary of the invention
Content of the present invention is to provide a kind of preparation method of pyrolytic carbon-coated lithium iron phosphate composite, and this method technology is simple, and the product granularity is moderate, and particle surface evenly coats carbon-coating, stable electrochemical property.
Technical scheme of the present invention:
A kind of preparation method of pyrolytic carbon-coated lithium iron phosphate composite may further comprise the steps:
(1) taking preliminary synthetic monophosphate monophosphate iron lithium is selected from as follows: the LiFePO4 of one or more in pure phase LiFePO4, carbon dope and the metal ion;
(2) LiFePO4 that will tentatively synthesize mixes with the solution that is dissolved with organic carbon source, place the pyrolysis stirred autoclave, be the anoxybiotic environment in the reactor in the course of reaction, temperature-rise period slowly rises to the solvent boiling point temperature by room temperature, make the solvent-stable evaporation, then continue to be warming up to 100～1000 ℃, preferred range is 350～550 ℃, constant temperature 0.5～24h;
(3) powder sample that (2) step is obtained places the inert atmosphere reacting furnace, and in 200～1000 ℃ of sintering temperature 1～10h, carbon-coated lithium iron phosphate composite is prepared in cooling, screening, the synthetic carbon-coated lithium iron phosphate composite of preferred two step method.
The preparation method of the pyrolytic carbon-coated lithium iron phosphate composite of the present invention's preparation is characterised in that:
The metallic element that mixes in described (1) is selected from one or more in magnesium, manganese, titanium, aluminium, calcium, vanadium, chromium, cobalt, nickel, copper, zinc, group of the lanthanides or the actinium series;
Pyrolysis stirred autoclave in described (2) adopts and scrapes the stirring of wall slurry.The solution composition that wherein is dissolved with organic carbon source is, organic carbon source is selected from: one or more in polyvinyl alcohol, polyvinyl butyral resin, petroleum asphalt, coal tar pitch, building asphalt, sucrose, starch, glucose, phenolic resins, the epoxy resin, consumption is 2～50% of a first synthesizing iron lithium phosphate quality, is dissolved in following solvent: one or more in acetone, kerosene, ethanol, carbon tetrachloride, carbolineum, benzene, dimethylbenzene, light oil, the washing oil:
The inert atmosphere source of the gas is selected from one or more in hydrogen, argon gas, nitrogen, carbon monoxide, the carbon dioxide in described (3).
Compared with prior art, the invention has the advantages that and adopt independently that the RESEARCH OF PYROCARBON cladding process prepares carbon-coated lithium iron phosphate composite, preparation material granule rounding, particle diameter is moderate, the particle surface carbon coating layer is complete, and the carbon coated amount is easy to control, and the coating process makes preliminary synthetic LiFePO4 particle constitute offspring, improve the packing density of material, material electrochemical performance is good.
Embodiment
Embodiment one:
Selecting preliminary synthetic pure phase LiFePO4 for use is raw material, mix with the acetone soln that is dissolved with polyvinyl butyral resin (PVB), the addition of PVB is 10% of a last reaction acquisition LiFePO4 quality, in the pyrolysis stirred autoclave, above suspension-turbid liquid slowly is warming up to 150 ℃ of insulation 1h by room temperature, then be warming up to 400 ℃ of insulation 2h, atmosphere keeps nonoxidizing atmosphere in the reactor, the cooling sample, sample is placed the inert atmosphere reacting furnace, in 700 ℃ of insulation 2h, cooling, screening obtain carbon-coated lithium iron phosphate composite.
Embodiment two:
The LiFePO4 of selecting carbon containing 5% (mass ratio) for use is a raw material, the petroleum asphalt that takes by weighing mass ratio 5% is dissolved in the kerosene, cross the elimination insoluble matter, the LiFePO4 that filtrate and microwave reaction is synthetic mixes, in the pyrolytic reaction still, above material slowly is warming up to 270 ℃ of insulation 1h by room temperature, then be warming up to 450 ℃ of insulation 2h, atmosphere keeps nonoxidizing atmosphere in the reactor, the cooling powder sample, sample is placed the inert atmosphere reacting furnace, in 700 ℃ of insulation 2h, cooling, screening obtain carbon-coated lithium iron phosphate composite.
Embodiment three:
The LiFePO4 of selecting carbon containing 6% (mass ratio) for use and being doped with manganese ion is a raw material, mix with the ethanolic solution that is dissolved with phenolic resins, the addition of phenolic resins is 10% of a last reaction acquisition LiFePO4 quality, place the pyrolysis stirred autoclave, slowly rise to 80 ℃ by room temperature, insulation 1.5h, then be warming up to 500 ℃, insulation 2h, atmosphere keeps nonoxidizing atmosphere in the reactor, the cooling powder sample, sample is placed the inert atmosphere reacting furnace, in 700 ℃ of insulation 2h, cooling, screening obtain carbon-coated lithium iron phosphate composite.
Embodiment four:
The LiFePO4 of selecting for use carbon containing 6% (mass ratio) also to be doped with manganese and magnesium ion simultaneously is a raw material, the petroleum asphalt that takes by weighing mass ratio 5% is dissolved in the kerosene, cross the elimination insoluble matter, the LiFePO4 of filtrate with the doped with manganese ion of preceding step solid phase synthesis mixed, in the pyrolytic reaction still, above material slowly is warming up to 270 ℃ of insulation 1h by room temperature, then be warming up to 450 ℃ of insulation 2h, atmosphere keeps nonoxidizing atmosphere in the reactor, the cooling powder sample, sample is placed the inert atmosphere reacting furnace, in 700 ℃ of insulation 2h, cooling, screening obtains carbon-coated lithium iron phosphate composite.
Embodiment five:
Select carbon containing for use and be doped with manganese ion and the LiFePO4 of titanium ion is a raw material, the building asphalt that takes by weighing mass ratio 5% is dissolved in the kerosene, cross the elimination insoluble matter, the LiFePO4 of filtrate with preceding step solid phase synthesis mixed, in the pyrolytic reaction still, above material slowly is warming up to 270 ℃ of insulation 1h by room temperature, then be warming up to 450 ℃ of insulation 2h, atmosphere keeps nonoxidizing atmosphere in the reactor, the cooling powder sample, sample is placed the inert atmosphere reacting furnace, in 700 ℃ of insulation 1.5h, cooling, screening obtain carbon-coated lithium iron phosphate composite.