Composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries electrode material and preparation method thereof
Technical field
The present invention relates to a kind of positive electrode of secondary lithium battery, specifically relate to a kind of a kind of composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries electrode material for secondary lithium battery and preparation method thereof.
Background technology
LiFePO4 has that cost is low, aboundresources and structural stability and thermal stability advantages of higher, but under normal temperature, the dynamics of LiFePO4 is bad, and high rate performance extreme difference, has greatly limited the application in practice of this material.In order to improve the transmission path of conductivity and shortening ion, electronics, improve high rate performance, people have adopted methods such as coated, doping, nanometer to carry out modification to it.Armand proposes to improve electronic conductivity at the coated one deck conductive layer of material surface, and in polymer battery, under 80 ℃ and 1C multiplying power, reversible capacity reaches 160mAh/g.Chiang Yet-Ming research group substitutes to improve the electronic conductivity of material to the Li in LiFePO4 by different valency element (Mg, Al, Zr, Ti, Nb, W).Result shows that the material electric conductivity after doping can improve 8 orders of magnitude, when charge-discharge magnification is C/10, capacity can reach 150mAh/g, still keeps the capacity of 60mAh/g when multiplying power is 40C, and through almost not decay of circulation volume in 60 weeks, show good chemical property.1997, M.Armand etc. were at US Patent No. A6, disclosed LiFePO in 514,640
4carry out the doping of iron position and the alternative material of phosphate potential.Yet reduce the granularity of phosphate material and improve the electrical contact performance between particle at its coated with carbon by nanometer, but increased considerably the specific area of material, while causing material coating pole piece, need to add more binding agent, affect the conductivity of pole piece, also make the density of pole piece and the activity substance content of unit volume significantly reduce.So just be unfavorable for producing the battery of high-energy-density.Therefore how at the LiFePO of hundreds of nanometer particle sizes
4particle surface is coated uniformly fine and close thin carbon layer and forms conductive network by carbochain, is to realize high power LiFePO
4the key technology that electrode is manufactured.
Summary of the invention
The object of the invention is when overcoming existing LiFePO 4 material as the positive electrode of serondary lithium battery multiplying power property poor, and make the low density shortcoming of pole piece, thereby a kind of composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries electrode material is provided, and is the nanometer LiFePO by all standing carbon-coating
4layer and form again the network carbon-coating structure that a part covers on this carbon-coating, to improve high rate performance and the energy density of phosphate material battery.
The object of the invention is to realize by following technical scheme: a kind of composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries electrode material, comprises the nanometer LiFePO of all standing carbon-coating
4with network carbon-coating, it is characterized in that: this described material is for forming 1-10 nanometer LiFePO by primary particle surface
4all standing carbon-coating, on this carbon-coating, form again the network carbon-coating structure that part that 10-100nm is thick covers.
Preparation method of the present invention realizes by following steps: 1) prepare nanometer pure phase LiFePO
4; 2) prepare the nanometer LiFePO of all standing carbon-coating
4; 3) prepare composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries; 1), preparation nanometer pure phase LiFePO it is characterized in that:
4:
(1), extra-fine grinding: 0.5:0.5:1:0.3 takes Li according to mol ratio
2cO
3, Fe
2o
3f, NH
4h
2pO
4p and C
6h
8o
7put in deionized water solvent, adopt super grinder nanometer to process, dry also hand lapping and pulverize as mixture;
(2), low temperature presintering: mixture is carried out under high-purity 5% protection of reducing atmosphere to low temperature presintering, be warming up to 350 ℃ with 1 hour from room temperature, at 350 ℃ of constant temperature after 4 hours, drop to room temperature with ten hours, after hand lapping is pulverized;
(3), high temperature sintering: mixture is at high-purity 5% Ar+H
2high temperature sintering under protection of reducing atmosphere: be warming up to 650 ℃ with 4 hours from room temperature, at 650 ℃ of constant temperature after 10 hours, with dropping to room temperature for 18 hours, then obtain the nanometer pure phase LiFePO that particle average grain diameter is 100-2000nm after will solid hand lapping pulverizing
4;
2), the nanometer LiFePO of preparation all standing carbon-coating
4: the organic polymer and the 1.0g nanometer pure phase LiFePO that take 0.1g
4be put in respectively in aluminium oxide magnetic boat A and B; in the boiler tube of the tube furnace that B magnetic boat and A magnetic boat are put into successively by ventilation air-flow order; start to pass into inert protective gas Ar; regulating Ar throughput is 80sccm; service routine heats up and from room temperature, was warming up to 800 ℃ with 1 hour; at 800 ℃ of constant temperature after 12 hours, drop to room temperature with two hours, obtain the nanometer LiFePO of all standing carbon-coating
4;
Described organic polymer is PAN or PVC.
3), prepare composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries: take respectively the pitch of 0.05g, the nanometer LiFePO of the conductive agent of 0.02g and 1.0g all standing carbon-coating
4be put in zirconia ball grinding jar, add appropriate absolute ethyl alcohol, ball milling 10 minutes; Slurry spraying after ball milling is dry, and gained powder is put into porcelain boat, porcelain boat is put into the boiler tube of tube furnace, starts to pass into inert protective gas Ar, and regulating Ar throughput is 80sccm; Service routine heats up and from room temperature, to be warming up to 600 ℃ with 1 hour, at 600 ℃ of constant temperature after 2 hours, drops to room temperature with two hours, obtains composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries material, wherein LiFePO
4primary particle average grain diameter is 100-2000nm, on this carbon-coating, form again the network carbon-coating structure that a thick part of 10-100nm covers, network carbon-coating is to connect continuously or partial continuous perforation, the content of its carbon accounts for 2~3wt% of iron phosphate lithium-based body weight, the geometric shape of the second particle of network carbon-coating is spherical or elliposoidal, and average grain diameter is 2um-20um.
Described conductive agent is carbon fiber, carbon nano-tube or Graphene.
Composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries material provided by the invention can improve high rate performance and the energy density of existing phosphate material battery.With such material, doing anodal secondary lithium battery, to have power density large, and cryogenic property is good, the high remarkable advantage that waits of specific capacity.Be specially adapted to high power electrokinetic cell, as be used in electric tool, electric automobile, hybrid electric vehicle, electric topedo, the fields such as accumulation power supply.
Accompanying drawing explanation
Fig. 1 is LiFePO of the present invention
4sEM figure.
Fig. 2 is electromicroscopic photograph of the present invention.
Embodiment
There is composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries electrode material, comprise the nanometer LiFePO of all standing carbon-coating
4with network carbon-coating, this material is to form 1-10 nanometer LiFePO by primary particle surface
4all standing carbon-coating, on this carbon-coating, form again the network carbon-coating structure that part that 10-100nm is thick covers.
Embodiment 1:
Preparation has the method for composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries electrode material, by following steps:
1, preparation nanometer pure phase LiFePO
4: first, according to mol ratio, 0.5:0.5:1:0.3 takes Li
2cO
3, Fe
2o
3, NH
4h
2pO
4, C
6h
8o
7(citric acid) also puts into deionized water solvent, adopts super grinder nanometer processing rear (rotating speed is 3000 revs/min, and 6 hours, it was the zirconia ball of diameter 0.3mm that mill is situated between), dries after also hand lapping pulverizing.By this mixture at high-purity Ar+H
2(5%) the lower heat treatment of gas protection (heat treated step is: be warming up to 350 ℃ with 1 hour from room temperature, at 350 ℃ of constant temperature after 4 hours, with dropping to room temperature for ten hours), after hand lapping pulverizing, mixture is at high-purity Ar+H
2(5%) under gas protection again sintering (sintering step is: with 4 hours, from room temperature, be warming up to 650 ℃, at 650 ℃ of constant temperature after 10 hours, with within 18 hours, dropping to room temperature.After being pulverized, solid hand lapping just can obtain nanometer pure phase LiFePO
4.As shown in Figure 1, the electromicroscopic photograph of gained sample is as Fig. 2 for gained sample SEM picture.
2, the nanometer LiFePO of preparation all standing carbon-coating
4: the organic polymer PAN and the 1.0g nanometer pure phase LiFePO that take 0.1g
4be put in respectively in aluminium oxide magnetic boat A and B; in the boiler tube of the tube furnace that B magnetic boat and A magnetic boat are put into successively by ventilation air-flow order; start to pass into inert protective gas Ar; regulating Ar throughput is 80sccm; service routine heats up and from room temperature, was warming up to 800 ℃ with 1 hour; at 800 ℃ of constant temperature after 12 hours, drop to room temperature with two hours, obtain the nanometer LiFePO of all standing carbon-coating
4;
3, prepare composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries: take respectively the pitch of 0.05g, the nanometer LiFePO of the electric conduction of carbon fiber agent of 0.02g and 1.0g all standing carbon-coating
4be put in zirconia ball grinding jar, add appropriate absolute ethyl alcohol, ball milling 10 minutes; Slurry spraying after ball milling is dry, and gained powder is put into porcelain boat, porcelain boat is put into the boiler tube of tube furnace, starts to pass into inert protective gas Ar, and regulating Ar throughput is 80sccm; Service routine heats up and from room temperature, to be warming up to 600 ℃ with 1 hour, at 600 ℃ of constant temperature after 2 hours, drops to room temperature with two hours, obtains composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries material, wherein LiFePO
4primary particle average grain diameter is 200nm, on this carbon-coating, form again the network carbon-coating structure that a thick part of 10-100nm covers, network carbon-coating is to connect continuously or partial continuous perforation, the content of its carbon accounts for 2~3wt% of iron phosphate lithium-based body weight, the geometric shape of the second particle of network carbon-coating is spherical or elliposoidal, and average grain diameter is 2um-20um.
The present invention is used for the electrochemical measurement of lithium iron phosphate positive material:
First with C/10, charge to 4.2V, then identical multiplying power current discharge is to 2.2V, and the capacity of emitting is with LiFePO
4mass Calculation reach 167mAh/g, charging and discharging curve is shown in Fig. 4. when discharging current is increased to 5C, the discharge capacity of this material is 97mAh/g, and this result shows that composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries positive electrode has good high-multiplying-power discharge performance.
The advantage of composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries material provided by the invention is:
1) the present invention has prepared the LiFePO 4 material of surperficial coated thin carbon layer first.
2) composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries material provided by the invention, there is larger tap density and less specific area, can significantly reduce the consumption of binding agent in pole coating process, improve pole piece electric conductivity and unit volume pole piece activity substance content, be conducive to improve the energy density of battery.
3) due in this composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries material provided by the invention, on primary particle, there is fine and close continuous thin carbon layer, so just promote the speed of interfacial reaction and improved the stability of material to oxygen and water, the passage that can transport fast for ion is provided and has there is large reaction interface, overcome the poor and slow shortcoming of interfacial reaction of LiFePO 4 material interface transport property, be conducive to improve the high rate performance of battery.
4) due in this composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries material provided by the invention, can on primary particle thin carbon layer coating layer, form again network-like thick carbon-coating, can by this layer of conductive carbon film, whole second particle overlap joint be formed to the conductive network of continuous uniform, therefore can keep good electrically contacting with active material.
5) composite nanostructure carbon-coating coated LiFePO 4 for lithium ion batteries material provided by the invention, can form a good conductive network after coated thick carbon-coating.Using it as conductive additive, mix use with other positive electrode, during for secondary lithium battery, can improve the multiplying power property of existing positive electrode and battery, there is the large remarkable advantage that waits of power density.In addition, due to LiFePO
4the material of class has good fail safe, can also improve the security performance of other positive electrode.