CN101891179A - Preparation method of LiFePO material, lithium ion battery and positive plate thereof - Google Patents
Preparation method of LiFePO material, lithium ion battery and positive plate thereof Download PDFInfo
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- CN101891179A CN101891179A CN2010102075165A CN201010207516A CN101891179A CN 101891179 A CN101891179 A CN 101891179A CN 2010102075165 A CN2010102075165 A CN 2010102075165A CN 201010207516 A CN201010207516 A CN 201010207516A CN 101891179 A CN101891179 A CN 101891179A
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Abstract
The invention discloses a preparation method of a LiFePO material, a lithium ion battery using the material and a positive plate thereof. The preparation method comprises the following steps: sintering to prepare LiFePO powder; cladding aluminum on the surface of the LiFePO powder particle to form a LiFePO-Al composite material. Compared with the prior art, the LiFePO material prepared by the invention and the cladding aluminum can carry out homodisperse and surface cladding at the molecule level; the conductivity of the electrode plate prepared by the invention is improved by 101-10001 times; and the internal resistance of the LiFePO lithium ion battery is reduced greatly, and the large-current charge-discharge property is obviously improved, thus the material is particularly suitable for a high power lithium ion battery. Compared with the other cladding elementary metal, Al metal is cheaper, has lighter mass, lower melting point, more stable electrochemistry property and the like; and in additional, the aluminum in the composite material and a positive pole current collector are made of the same material, so that primary battery corrosion effect can not be formed.
Description
Technical field
The positive plate and the lithium ion battery that the present invention relates to a kind of preparation method of superpower power lithium-ion battery positive electrode material and adopt described positive electrode material, in particular, positive plate and the lithium ion battery that the present invention relates to the preparation method of the lithium iron phosphate positive material in a kind of superpower power lithium-ion battery and adopt described positive electrode material.
Background technology
In lithium ion battery, the selection of positive electrode material and quality play decisive influence to the performance and the price of lithium ion battery.Positive electrode material master commonly used at present has cobalt-lithium oxide (LiCoO
2), manganese oxide lithium (LiMn
2O
4), nickel oxide lithium (LiNiO
2), cobalt nickel oxide manganses lithium multicomponent material and iron lithium phosphate (LiFePO
4), LiFePO wherein
4Characteristics are applied to fields such as electromobile, space flight, energy storage gradually because of it has cheap, environmental protection, cycle performance is good, stability of material is good etc.
LiFePO
4Be a kind of six sides of little distortion, the closest packing structure belongs to the Pmna spacer.Crystal is by FeO
6Octahedron and PO
4Tetrahedron is alternately arranged and is constituted spatial skeleton, owing to there is not successive FeO
6The octahedra network in limit can not form effective electronic conduction, so LiFePO altogether
4Conductivity very poor; While PO
4Tetrahedron has limited FeO
6Octahedral volume change causes the lithium ion migration in charge and discharge process also to be affected.On the other hand, when discharging and recharging, single-phase LiFePO
4Change two-phase LiFePO into
4/ FePO
4, sharp-pointed interface can appear between the two-phase, and the interface is parallel to the a-c face.High strength internal stress along the b axle causes fissured appearance.The crack makes and polarization of electrode also makes active material or conductive additive die down with contacting of collector, causes the impedance of battery plate to increase, thereby further makes battery undesirable on high-rate performance.
At LiFePO
4Can strengthen the electroconductibility between particle and the particle middle the dispersion or coated with conductive carbon on the one hand, reduces the polarization of battery, and it can also be LiFePO on the other hand
4Provide electron tunnel, with compensation Li
+The charge balance in the process is taken off in embedding, so this has become the LiFePO of investigator's first-selection
4Method of modifying.Yet because the adding of carbon has reduced the actual density of material, be unfavorable for the raising of battery volume and capacity ratio on the other hand.
Yet the another kind of method of current raising LiFePO 4 material conductivity is the metal ion that mixes in the material building-up process about 1%.The doping of this metal ion species influences LiFePO hardly
4Actual density, lay a good foundation for this class material moves towards practicality.In the world ion doping is improved LiFePO at present
4The mechanism of conductivity still do not have final conclusion, relatively the view of main flow is that the introducing of high volence metal ion changes LiFePO
4Crystalline structure and brilliant bag parameter, thus the electronic conduction hole provided by metal ion mixing, improve LiFePO
4The conductivity of material itself.
Except that the conductivity of LiFePO 4 material own is improved, can also be by in the pole piece manufacturing processed, adding the conductivity that a certain proportion of conventional conductive agent (as carbon black, graphite, acetylene black etc.) improves lithium iron phosphate battery pole piece.Just in anode pole piece, added carbonaceous conductive agent as masschusetts, u.s.a science and engineering CEDER research group at the high-power battery of the 100C rapid discharge that obtains, yet this is prerequisite with the sacrifice energy density up to 40%.Conductive agent commonly used comprises carbon or carbon black, carbon nanotube, VGCF, nano level copper, silver or bronze in the current industrial production.Although adopt after these conductive agents, improved LiFePO to a certain extent
4Conductivity in actual application, but still can not satisfy application on the superpower power lithium-ion battery.
Summary of the invention
At above shortcomings in the prior art, the invention provides a kind of preparation method of LiFePO 4 material, it can improve LiFePO
4The electronic conductivity of material.
At purpose of the present invention, aspect first, the invention provides a kind of preparation method of LiFePO 4 material of the present invention, comprise step: step 1, sintering prepares iron phosphate powder; With step 2, metallized aluminum simple substance forms iron lithium phosphate-aluminum composite on iron phosphate powder particulate surface.
According among the preparation method of LiFePO 4 material of the present invention, preferably, in described step 1, sintering temperature is that 600～750 ℃, soaking time are 0.5～8h, and the yardstick of iron phosphate powder is preferably 200～500nm.
In the foundation preparation method of LiFePO 4 material of the present invention, preferably, described step 2 comprises: substep one, preparation scale are the Al powder of 50～1000nm; Substep two carries out high speed ball milling, dispersion with the iron phosphate powder behind nanometer Al powder and the sintering under inert atmosphere protection, wherein ratio of grinding media to material is 1.5: 1～6: 1, and the speed of high speed ball milling is 500～2000r/min, and described inert atmosphere is N
2Or Ar; Substep three feeds NH in tube furnace
3Or H
2Rare gas element or N
2Or the Ar reducing gas, the mixture of Al powder and iron phosphate powder is carried out sintering and insulation under 650～750 ℃ of temperature, make the Al fusion, thereby aluminium simple substance is coated on the iron phosphate powder particle, forms iron lithium phosphate/aluminum composite; And substep four, described matrix material is cooled off under the protection of described inert atmosphere stream.
In the foundation preparation method of LiFePO 4 material of the present invention; preferably; in described substep two; the mechanical ball milling of iron phosphate powder behind nanometer Al powder and the sintering under inert atmosphere protection carries out in organic solvent, and described organic solvent is a kind of and composition thereof in acetone, Virahol, the propyl carbinol trimethyl carbinol, the hexylene glycol.
In the foundation preparation method of LiFePO 4 material of the present invention, alternately, described step 2 comprises: substep one, preparation aluminum metal melting salt electroplate liquid, described aluminum metal melting salt electroplate liquid comprise aluminum metal room temperature fused salt, organic reducing agent and not with the organic solvent of aluminum metal molten salt reaction, described aluminum metal fused salt comprises the mixture of inorganic metal aluminium halide salt and organic halogenation salt, is liquid under the described aluminum metal fused salt room temperature; Described organic reducing agent comprises any in lithium aluminum hydride, lithium hydride, diisobutyl aluminium hydride, the aluminum isopropylate, and described organic solvent is the mixing of any or they in the benzene,toluene,xylene; Substep two will contain reactive metal Pd, Rh or Ru ionic chlorate solution and add ethanol, propyl alcohol or ethylene glycol, be mixed with the activation solution of alcohol-water mixture; Substep three is at N
2Or under the Ar inert atmosphere, LiFePO 4 material is immersed in the described activation solution, reflux under the protection of inert gas, reactive metal is deposited on the activation matrix LiFePO 4 material, with LiFePO 4 material washing and filtering and the vacuum-drying after the activation; Substep four under inert atmosphere, places described aluminum metal melting salt electroplate liquid with the LiFePO 4 material after the activation, and at iron lithium phosphate particle surface metal refining aluminium simple substance, described redox reaction temperature is 30～50 ℃ by the control reductive condition; Substep five filters described aluminum metal melting salt electroplate liquid, the iron lithium phosphate particle that the surface deposits metallic aluminium simple substance is repeatedly cleaned the iron lithium phosphate/aluminum composite that is obtained to isolate with dehydrated alcohol or acetone; And substep six, with isolated iron lithium phosphate/aluminum composite vacuum-drying.
In the foundation preparation method of LiFePO 4 material of the present invention, preferably, described inorganic metal aluminium salt comprises aluminum halide, and the content of described aluminum halide accounts for 10～60% of melting salt total amount; Described organic halogenation salt comprises imidazolium halide salt, pyridinium salt, quaternary amine, and the content of described organic halogenation salt accounts for 30～80% of melting salt total amount; The concentration range of described organic reducing agent in described electroplate liquid is 0.005～0.5mol/L, and the mol ratio of aluminium salt is 0.5～5 in described organic reducing agent and the described aluminum metal fused salt.
In the foundation preparation method of LiFePO 4 material of the present invention, preferably, described activation solution comprises that also concentration is not more than the polymer stabilizer of 0.01mol/L, and described polymer stabilizer comprises polyvinyl alcohol or polyoxyethylene glycol.
According among the preparation method of LiFePO 4 material of the present invention, preferably, cover the aluminium amount and account for 0.1～5% of iron lithium phosphate/aluminum composite total amount.
At purpose of the present invention, aspect second of the present invention, the invention provides a kind of positive plate of ferric phosphate lithium ion battery, described positive plate contains iron lithium phosphate/aluminum composite prepared in the above-mentioned first aspect.
At purpose of the present invention, aspect the 3rd of the present invention, the invention provides a kind of ferric phosphate lithium ion battery, the positive plate of described ferric phosphate lithium ion battery contains the prepared iron lithium phosphate/aluminum composite of above-mentioned first aspect.
Beneficial effect of the present invention is as follows:
(1) collector owing to metal simple-substance that is coated on the iron lithium phosphate surface and the anodal employing of power lithium-ion battery is a same material, therefore the aluminium simple substance that is coated on material surface can not only form effective conductive network between material granule, can also effectively improve simultaneously contact and contact resistance between powder body material and the collector, especially carry out in the charge and discharge process repeatedly at battery, repeatedly the take off embedding meeting of lithium ion in positive electrode material makes battery anode slice form the crack, also make active material or conductive additive die down with contacting of collector, cause the impedance of battery plate to increase, polarization of electrode increases, yet carry out after aluminium is coated with on the pole piece surface, because the intermetallic contact resistance is extremely low, the metal simple-substance that therefore is distributed in particle surface has reduced the contact resistance and the polarization resistance of battery plate greatly.Than prior art, can implement homodisperse and surface coating in the molecule rank according to the LiFePO 4 material of the present invention's preparation and the aluminium simple substance of coating, specific conductivity according to the electrode slice of the present invention preparation can improve 10～1000 times, internal resistance according to the ferric phosphate lithium ion battery of the present invention preparation reduces significantly, high rate during charging-discharging obviously promotes, and this is particularly suitable for using in the superpower power lithium-ion battery.
(2) compare with adopt coating other metal simple-substances, that the Al metal has is more cheap, quality is lighter, fusing point lower (easier thawing), the more stable numerous advantages such as (Al itself are exactly a plus plate current-collecting body) of chemical property.When battery completely filled, electropotential was higher on the other hand, generally was higher than 3.6V, exceeded big polymetallic stripping current potential, if metal selects material improper, can make the metal ion stripping enter electrolytic solution, had a strong impact on the charge-discharge characteristic and the cycle characteristics of secondary cell.The same utmost point that does not also exist in battery simultaneously forms between different metals and metal ion because of existing that to discharge and recharge electricity right, thereby forms corrosion galvanic cell, causes the formation of the self-discharge of inside battery to influence battery performance.
Description of drawings
Fig. 1 is 18650 battery 5C multiplying power discharging graphic representations of different pole piece assemblings.
Embodiment
The following describes according to first embodiment of the present invention, promptly adopt the mechanical ball milling hybrid system to prepare the process of iron lithium phosphate/aluminum composite.
Comprise step in the method for preparing iron lithium phosphate/aluminum composite according to employing mechanical ball milling hybrid system of the present invention: step 1, sintering prepares iron phosphate powder; Step 2, preparation nanometer Al powder; Step 3 is carried out high speed ball milling, dispersion with the iron phosphate powder behind nanometer Al powder and the sintering under inert atmosphere protection; Step 4 feeds rare gas element or reducing gas in tube furnace, the mixture of Al powder and iron phosphate powder is advanced sintering and insulation, make the Al fusion, thereby aluminium simple substance is coated on the iron phosphate powder particle, forms iron lithium phosphate/aluminum composite; Step 5 is cooled off described matrix material under the protection of inert atmosphere stream.
In step 1, adopt the sintering temperature of the once sintered preparation iron phosphate powder of tubular type atmosphere furnace to be preferably 750 ℃, the yardstick of iron phosphate powder is preferably 200～500nm.
In step 2, adopt CO
2The nanometer aluminium powder that needs among the present invention of laser apparatus laser powdering systems produce.Nanometer Al powder yardstick is 50～1000nm, and wherein the yardstick of preferred nanometer aluminium powder is 100～200nm.Even the yardstick of the nanometer Al powder that adopts is during greater than the yardstick (greater than 500nm) of iron phosphate powder, because in step 3, the abrading-ball of high speed ball milling can carry out secondary to particle to be pulverized, thereby makes further tinyization of big aluminum particle; Simultaneously, because aluminium powder will be in step 4, aluminium powder will be sintered and form molten state, and therefore, the yardstick of nanometer Al powder can suitably amplify.Preferred yardstick is less, mainly less in the coating per-cent total amount of material surface based on aluminium powder, and the material of reduced size is stronger in nanometer aluminium powder more uniform dispersion and covering in iron phosphate powder.
In step 3, ratio of grinding media to material is: 1.5: 1～6: 1, preferred ratio of grinding media to material was 3: 1.The speed of high speed ball milling is 500～2000r/min, and favor speed is 1500r/min, so that the iron phosphate powder behind nanometer Al powder and the sintering is disperseed well and uniform mixing, and nanometer Al powder is not reunited; Described inert atmosphere is N
2, Ar etc., to prevent the Al oxidation.
In step 3, the mechanical ball milling of the iron phosphate powder behind nanometer Al powder and the sintering under inert atmosphere protection can carry out in organic solvent, and described organic solvent can be acetone, Virahol, the propyl carbinol trimethyl carbinol, hexylene glycol etc.Owing to adopted organic solvent, form solid-liquid two-phase mixed solution, can more help the dispersion of iron phosphate powder and Al powder, but because ball milling speed is big, ball material inside is given birth to heat easily under high-speed friction, organic solvent is volatile, therefore controls the temperature rise of ball material in mechanical milling process by the cooling water recirculation system of ball mill, selects the higher relatively solvent of boiling point simultaneously as far as possible.In step 4 subsequently, mixing powder adopts high sintering temperature to help thoroughly removing organic solvent, thereby make not have organic solvent residual between aluminium simple substance and the quilt iron lithium phosphate particle that coats, thereby guaranteed the bonding force of aluminium simple substance on the iron lithium phosphate particle.
In step 4, the sintering temperature of the mixture of iron lithium phosphate and aluminium powder is 650～750 ℃ in tube furnace, insulation 0.5～8h.In order to obtain good crystal habit and uniform size and pattern, sintering temperature after nanometer Al powder and the iron phosphate powder mixing and ball milling is preferably 700 ℃, under this temperature, favourable when being coated on degree of uniformity on the LiFePO 4 powder with raising for the diffusion of fusion aluminium powder.Slightly increase with the size of LiFePO 4 powder behind the aluminium powder mixing double sintering, show that the LiFePO 4 powder material surface has coated layer of aluminum simple substance, but material does not cause agglomeration in the double sintering process; Described reducing gas can be NH
3, H
2, described inert atmosphere is N
2, Ar etc.
In step 5, established matrix material has in the certain limit under the drive of inert atmosphere stream or reducing gas stream and flows, thereby make aluminium simple substance more even in the coating of material surface in process of cooling.
In the mechanical ball milling hybrid system that foundation the present invention adopts, cover the aluminium amount and account for 0.1～5% of iron lithium phosphate/aluminum composite total amount, wherein preferred proportion is 0.5～1%.
The following examples 1～6 have provided the LiFePO according to the present invention's preparation
4/ Al matrix material and test result.
Embodiment 1～6
Adopt Prepared by Ball Milling LiFePO
4The specific embodiment of/Al matrix material is: with Li
2CO
3, FeC
2O
4, NH
4H
2PO
4For starting material pass through the once sintered iron lithium phosphate LiFePO of high temperature solid-state method
4Material, the material behind the sintering is pulverized for the first time.Pressed ratio of grinding media to material 3: 1, and selected abrading-ball Φ 1/ Φ 5 (mm of unit) of two kinds of diameters, amount ratio is Φ 1: Φ 5=7: 3, and in the inert protective atmosphere glove box, with LiFePO
4Material, nanometer aluminium powder, abrading-ball and Virahol, acetone, propyl carbinol, the trimethyl carbinol, hexylene glycol organic solvent mix in the ball grinder of packing into, and the aluminium powder consumption is LiFePO
40.1～5% of material usage, consumption of organic solvent with cover the ball material fully, a little higher than ball feed liquid of liquid level face is as the criterion, ball milling speed is 500～2000r/min, the ball milling time is 4～24h.Behind the ball milling, ball material filtering separation changes powder in the quartz boat over to, places tube furnace, and inert atmosphere protection rises to 700 ℃ with 5 ℃/min, insulation 0.5～8h, and materials for later use is taken out in the cooling cooling.
Table 1
The following describes according to second embodiment of the present invention, promptly adopt electroless plating method to prepare the process of iron lithium phosphate/aluminum composite.
Preparing in the method for iron lithium phosphate/aluminum composite according to employing electroless plating method of the present invention, comprising step: step 1, sintering prepares iron phosphate powder; Step 2, preparation aluminum metal melting salt electroplate liquid, wherein electroplate liquid comprise aluminum metal room temperature fused salt, organic reducing agent and not with the organic solvent of aluminum metal molten salt reaction; Step 3, preparation contains reactive metal Pd, Rh, the isoionic chlorate solution of Ru, and adds ethanol, propyl alcohol, ethylene glycol etc., is prepared into alcohol-water mixture, to obtain activation solution; Step 4 under inert atmosphere, is immersed in LiFePO 4 material in the above-mentioned activation solution, refluxes under the protection of inert gas, makes reactive metal be deposited on the activation matrix LiFePO 4 material washing and filtering, vacuum-drying; Step 5, the LiFePO 4 material after will activating again under the inert atmosphere places aluminum metal melting salt electroplate liquid, by controlling reductive condition at iron lithium phosphate particle surface metal refining aluminium simple substance; Step 6 is filtered electroplate liquid, repeatedly cleans the iron lithium phosphate/aluminum composite that is obtained to isolate with dehydrated alcohol or acetone; Step 7 is with isolated iron lithium phosphate/aluminum composite vacuum-drying.
In step 1, adopt the sintering temperature of the once sintered preparation iron phosphate powder of tubular type atmosphere furnace to be preferably 750 ℃, the yardstick of iron phosphate powder is preferably 200～500nm.
In step 2, the aluminum metal fused salt comprises the mixture of inorganic metal aluminium halide salt and organic halogenation salt, is liquid under the room temperature.Inorganic metal aluminium salt mainly comprises aluminum halide, adopts aluminum chloride, its content to account for 10～60% of melting salt total amount usually, and preferable range is 20～30%.Organic halogenation salt comprises imidazolium halide salt, pyridinium salt, quaternary amine etc., and its content accounts for 30～80% of melting salt total amount, wherein its preferable range 50～70%.The organic solvent with the aluminum metal molten salt reaction is not one or more solvent such as benzene,toluene,xylene, and the amount of described organic solvent is that 0.01～0.1mol/L is suitable consumption with the concentration of final trivalent aluminium salt in electroplate liquid; Organic reducing agent comprises lithium aluminum hydride, lithium hydride, diisobutyl aluminium hydride, aluminum isopropylate etc., and organic reducing agent concentration range in electroplate liquid is 0.005～0.5mol/L, and the mol ratio of aluminium salt is 0.5～5 in organic reducing agent and the aluminum metal fused salt.In the present invention, adopt organic reducing agent effectively trivalent aluminium to be reduced into aluminium simple substance and be coated on the iron lithium phosphate surface, and organic reducing agent is removed easily, make material in the electroless plating process, be difficult for introducing new impurity.
In step 3, the concentration of chlorate solution is 0.001～0.01mol/L, and the ethanol of adding, propyl alcohol or ethylene glycol are equal-volume, to be mixed with 50% alcohol-water mixture, can stir in preparation process.
In step 3, will carry out can also adding a certain amount of polymer stabilizer in the activatory process to LiFePO 4 material, its concentration is not more than 0.01mol/L.Wherein, described polymer stabilizer comprises polyvinyl alcohol, polyoxyethylene glycol etc.
In step 4, inert atmosphere can be N
2, Ar etc.
In step 5; described control reductive condition is under the inert protective atmosphere; earlier LiFePO 4 material and electroplate liquid are carried out low speed magnetic agitation 0.5～1h; make material and electroplate liquid thorough mixing even; leave standstill 1～5h again; fully reduce, refilter cleaning, whole process is a prerequisite not damage existing iron lithium phosphate grain diameter and surface topography.Because electroless plating method itself carries out in liquid phase, so can guarantee the dispersiveness of aluminum metal melting salt and the dispersiveness of the metallic aluminium simple substance of separating out.In deposition process, carry out certain stirring, the iron phosphate powder sedimentation can be prevented, thereby the deposition uniformity of aluminium simple substance on the iron lithium phosphate particle can be increased.
In step 5, the redox reaction temperature is 30～50 ℃, because electroplate liquid at room temperature itself is exactly a kind of ionic liquid, does not therefore need to heat from the feasibility of reaction, can help accelerating reaction process but carry out certain heating, shorten the reaction times.By the concentration of control reductive agent and the relative mass of material and electroplate liquid, may command is the chemistry amount of aluminizing on LiFePO 4 material finally, and test and Selection covering amount scope is 0.1～5%, is preferably 0.1～1%.
Following table is the embodiment that carries out according to the present embodiment.
Table 2
Following brief description is based on iron lithium phosphate/aluminum composite of the present invention and anode pole piece preparation process and the pole piece of this matrix material assembling and the conductivity and the chemical property of battery.After the surperficial metallized aluminum simple substance of iron lithium phosphate forms iron lithium phosphate/aluminum composite, traditionally materials such as iron lithium phosphate/aluminum composite, binding agent, conductive agent are joined in the organic solution subsequently, mix into the uniform mixing material, thereby obtain being used for the iron phosphate lithium positive pole slurry, then the iron phosphate lithium positive pole slurry is coated on the positive collection liquid surface, makes anode pole piece.Described conductive agent is preferably carbon or carbon black, thereby form the composite conducting network, be the conductive network of carbon or carbon black formation and the conductive network that aluminium simple substance forms, because the electroconductibility of aluminium simple substance itself is stronger than carbon or carbon black, so based on the formation of conductive network, the electroconductibility of LiFePO 4 material is further improved.
In addition, because plus plate current-collecting body adopts aluminium foil, aluminium and plus plate current-collecting body in this moment iron lithium phosphate/aluminum composite are metal of the same race, thus help between positive electrode material and the plus plate current-collecting body combine tightr, contact impedance is littler, thereby has further improved the electroconductibility of LiFePO 4 material.
Embodiment 13
Choose that to cover the aluminium amount among the embodiment 1～12 be 0.1%, 0.5%, 1% LiFePO
4/ Al Composite Preparation slurry and pole piece.By matrix material: the C conductive agent: the binding agent ratio is to mix slurry at 93: 2: 5, again with slurry coating on aluminium foil, oven dry obtains pole piece.Mix guaranteeing in the slurry process that the tangential speed in the slurry whipping process is not less than 15m/s, to guarantee that composite nanoparticle and conductive agent, binding agent fully are uniformly dispersed.
Embodiment 14
Choose that to cover the aluminium amount among the embodiment 1～12 be 5% LiFePO4/Al Composite Preparation slurry and pole piece.The material that makes is made slurries by embodiment 13 again, and this moment, the formula of size ratio changed to matrix material: the C conductive agent: the binding agent ratio is to mix slurry at 90: 2: 8, because of content of aluminium powder increases, must strengthen the binding agent consumption, with the assurance pole piece not dry linting that bonds reliably.
Comparative example
Directly with the once sintered iron lithium phosphate that obtains as active substance, by LiFePO 4 material: the C conductive agent: the binding agent ratio is to mix slurry at 89: 5: 6, again with slurry coating on aluminium foil, dry, obtain pole piece.Because it is relatively poor not carry out aluminium compound material electroconductibility, therefore carbon content need be increased to 5%, along with the increase of carbon content, the content of binding agent also must correspondingly increase, and this moment, content of active substance dropped to 89%.
Based on embodiment 13,14 and comparative example, carry out follow-up test.
At first, measure the pole piece specific conductivity: get the above-mentioned pole piece of unit surface, press 2.2g/cm
3Density carry out compressing tablet, accurately measure the thickness (d/cm) and the area (A/cm of pole piece this moment
2).Electrode slice is clipped between two battery lead plates (graphite, stainless steel plate, copper coin etc.), fixes, keep keeping between the two-plate insulation simultaneously with fastening screw.Measure its resistance R with exchanging the internal resistance instrument, then can calculate the conductivity=d/ (RA) of pole piece, the S/cm of unit.Table 3 has provided the test comparing result of different embodiment pole piece specific conductivity.
Table 3
Secondly, the matrix material pole piece is formed the high rate performance test of power cell: the power cell with pole piece and the graphite cathode of table 3 is assembled into 18650 types, with the charging of 1C multiplying power, carry out multiplying power discharging property with 1C, 2C, 5C, 10C respectively then and test.
The 18650 battery 5C high rate performance comparison diagrams that the pole piece that Fig. 1 prepares for the embodiment of employing table 3 and comparative example is assembled into.Fig. 1 has provided 18650 battery 5C multiplying power discharging graphic representations of different pole piece assemblings.
Test-results shows that the specific conductivity of the electrode slice of the unit surface that the material after the coating makes with same process can improve 10～1000 times on original basis.The material that adopts this law to prepare is assembled into cylindrical 18650 batteries of battery such as routine, internal resistance is reduced to 15～30m Ω from 80～100m Ω, heavy-current discharge curve from figure as can be seen, it is anodal to use iron lithium phosphate of the present invention-Al matrix material to do, its heavy-current discharge platform is than the discharge platform height of common LiFePO 4 material, and the capacity of emitting is also more, this be because, the internal resistance of battery plate has obtained bigger improvement behind the use matrix material, thereby reduced the internal resistance of battery greatly, charge-discharge performance is obviously promoted, and therefore, this material is suitable for using in the superpower power lithium-ion battery.
Claims (10)
1. the preparation method of a LiFePO 4 material comprises step:
Step 1, sintering prepare the iron phosphate powder particle;
It is characterized in that described preparation method also comprises step:
Step 2, metallized aluminum simple substance forms iron lithium phosphate-aluminum composite on iron phosphate powder particulate surface.
2. the preparation method of LiFePO 4 material as claimed in claim 1 is characterized in that, in described step 1, sintering temperature is that 600～750 ℃, soaking time are 0.5～8h, and the yardstick of iron phosphate powder is 200～500nm.
3. the preparation method of LiFePO 4 material as claimed in claim 1 is characterized in that, described step 2 comprises:
Substep one, preparation scale are the Al powder of 50～1000nm;
Substep two carries out high speed ball milling, dispersion with the iron phosphate powder behind nanometer Al powder and the sintering under inert atmosphere protection, wherein ratio of grinding media to material is 1.5: 1～6: 1, and the speed of high speed ball milling is 500～2000r/min, and described inert atmosphere is N
2Or Ar;
Substep three feeds NH in tube furnace
3Or H
2Rare gas element or N
2Or the Ar reducing gas, the mixture of Al powder and iron phosphate powder is carried out sintering and insulation under 650～750 ℃ of temperature, make the Al fusion, thereby aluminium simple substance is coated on the iron phosphate powder particle, forms iron lithium phosphate/aluminum composite; And
Substep four cools off described matrix material under the protection of described inert atmosphere stream.
4. the preparation method of LiFePO 4 material as claimed in claim 3; it is characterized in that; in described substep two; the mechanical ball milling of iron phosphate powder behind nanometer Al powder and the sintering under inert atmosphere protection carries out in organic solvent, and described organic solvent is a kind of and composition thereof in acetone, Virahol, the propyl carbinol trimethyl carbinol, the hexylene glycol.
5. the preparation method of LiFePO 4 material as claimed in claim 1 is characterized in that, in described step 2, covers the aluminium amount and accounts for 0.1～5% of iron lithium phosphate/aluminum composite total amount.
6. the preparation method of LiFePO 4 material as claimed in claim 1 is characterized in that, described step 2 comprises:
Substep one, preparation aluminum metal melting salt electroplate liquid, described aluminum metal melting salt electroplate liquid comprise aluminum metal room temperature fused salt, organic reducing agent and not with the organic solvent of aluminum metal molten salt reaction, described aluminum metal fused salt comprises the mixture of inorganic metal aluminium halide salt and organic halogenation salt, is liquid under the described aluminum metal fused salt room temperature; Described organic reducing agent comprises any in lithium aluminum hydride, lithium hydride, diisobutyl aluminium hydride, the aluminum isopropylate, and described organic solvent is the mixing of any or they in the benzene,toluene,xylene;
Substep two will contain reactive metal Pd, Rh or Ru ionic chlorate solution and add ethanol, propyl alcohol or ethylene glycol, be mixed with the activation solution of alcohol-water mixture;
Substep three is at N
2Or under the Ar inert atmosphere, LiFePO 4 material is immersed in the described activation solution, reflux under the protection of inert gas, reactive metal is deposited on the activation matrix LiFePO 4 material, with LiFePO 4 material washing and filtering and the vacuum-drying after the activation;
Substep four under inert atmosphere, places described aluminum metal melting salt electroplate liquid with the LiFePO 4 material after the activation, and at iron lithium phosphate particle surface metal refining aluminium simple substance, described redox reaction temperature is 30～50 ℃ by the control reductive condition;
Substep five filters described aluminum metal melting salt electroplate liquid, the iron lithium phosphate particle that the surface deposits metallic aluminium simple substance is repeatedly cleaned the iron lithium phosphate/aluminum composite that is obtained to isolate with dehydrated alcohol or acetone;
Substep six is with isolated iron lithium phosphate/aluminum composite vacuum-drying.
7. the preparation method of LiFePO 4 material as claimed in claim 6 is characterized in that, in described substep one, described inorganic metal aluminium salt comprises aluminum halide, and the content of described aluminum halide accounts for 10～60% of melting salt total amount; Described organic halogenation salt comprises imidazolium halide salt, pyridinium salt, quaternary amine, and the content of described organic halogenation salt accounts for 30～80% of melting salt total amount; The concentration range of described organic reducing agent in described electroplate liquid is 0.005～0.5mol/L, and the mol ratio of aluminium salt is 0.5～5 in described organic reducing agent and the described aluminum metal fused salt.
8. the preparation method of LiFePO 4 material as claimed in claim 6, it is characterized in that, in described substep two, described activation solution comprises that also concentration is not more than the polymer stabilizer of 0.01mol/L, and described polymer stabilizer comprises polyvinyl alcohol or polyoxyethylene glycol.
9. a based lithium-ion battery positive plate is characterized in that, described positive plate contains the iron lithium phosphate/aluminum composite according to each preparation among the claim 1-8.
10. a lithium ion battery comprises positive plate, it is characterized in that, described positive plate contains the iron lithium phosphate/aluminum composite according to each preparation among the claim 1-8.
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