CN102386405A

CN102386405A - Strontium and barium activated lithium iron phosphate anode material

Info

Publication number: CN102386405A
Application number: CN2011103379444A
Authority: CN
Inventors: 张健; 张新球; 吴润秀; 王晶; 张雅静; 李�杰; 李安平; 李先兰; 张爱萍
Original assignee: 张爱萍
Priority date: 2011-10-26
Filing date: 2011-10-26
Publication date: 2012-03-21

Abstract

The invention discloses a strontium and barium activated lithium iron phosphate anode material. The chemical general formula of the material can be expressed as: LiSrxBay FePo4, wherein x=0.00002-0.00005, y=0.0003-0.003, the mol ratio of the Li to Sr to Ba to Fe to P is 1 mol of Li: 0.00002-0.00005 mol of Mg: 0.0003-0.003 mol of Ba: 1 mol of Fe: 1 mol of P; because a little amount of strontium and barium are doped, the control of the appearance and the grain size of a product is facilitated; a stable lithium iron phosphate compound is obtained; the crystal lattice of the obtained compound is activated; the diffusion efficient of lithium ions is improved; the first discharging capacity of the lithium ions reaches 160.52 mAh/g; the relative lithium electrode potential of a charging and discharging platform of the compound is about 3.5 V; the initial discharging capacity is over 168mAh/g; and the capacity is attenuated by about 1.2% after 100 times of charging and discharging circulations. Compared with a reference embodiment of non-doped LiFePO4, the specific capacity and the circulation stability are greatly improved.

Description

Strontium, barium activation lithium iron phosphate positive material

Technical field

Strontium of the present invention, barium activation lithium iron phosphate positive material belong to a kind of anode material of lithium battery, particularly a kind of ferric phosphate lithium cell positive electrode.

Background technology

At present; The research present situation of LiFePO4 doping vario-property: LiFePO4 LiFePO4 is because of it is nontoxic, environmentally friendly, safe, abundant, high, the stable cycle performance, cheap of specific capacity in raw material source; Steady discharge platform with theoretical capacity 3.5V of 170mAh/g; LiFePO 4 material has high energy density, cheap price, excellent security, is specially adapted to electrokinetic cell.But its resistivity is bigger.Because LiFePO4; Under the normal temperature, the dynamics of LiFePO4 is bad, the high rate performance extreme difference; Domestic and international research persons have used such as methods such as coating, doping, nanometerizations and have improved high rate performance, and basic idea improves conductivity exactly and shortens ion, electric transmission path.Doping is one type of important material modification method.2002, reported first lithium position doping vario-properties such as Massachusetts science and engineering Chiang professor Yet-Ming can improve the LiFePO4 electronic conductivity greatly.They carry out the doping of high volence metal ion (Mg2+, Al3+, Ti4+, Zr4+, Nb5+ and W6+) solid solution in the lithium position, electronic conductivity has improved 8 one magnitude.Sample through above-mentioned doping has better electrochemical performance, and particularly high-rate performance discharges under the electric current of 21.5C (3225mA/g), still can obtain the capacity of 60mAh/g.Doping carbon: carbon has good electric conductivity and lower mass density, adds a spot of carbon of people, can improve the electric conductivity of material on the one hand, can reduce the particle diameter yardstick of material on the other hand.Xxx has studied different phase and has mixed the influence of people's carbon to material electrochemical performance.Shi Zhicong etc. " adopt solid phase reaction to combine the high speed ball-milling method, synthetic positive electrode LiFePO4, experiment shows: LiFePO4 has the discharge voltage plateau of 3.4V, and discharge capacity only decays 9.5% after reaching 147mAh/g charge and discharge cycles 100 times first.LiFePO4/C composite material behind the carbon dope, the granule-morphology rule, spherical for class, particle is little, and particle size distribution is all colluded.Carbon is scattered between the crystal grain, has strengthened the electrical conductance between the particle.LiFePO4 specific discharge capacity and cycle performance behind the carbon dope all significantly improve.Mix in the lithium position: the LiFePO4 crushed grain is assorted to be a kind of important method of improving chemical property.Mix and can improve the conductivity of LiFePO4 in the lithium position.Tan Xianyan etc. " " adopt the calcination method synthesizing lithium ionic cell positive pole material lithium iron phosphate, mix a spot of Mg2+ and have significantly improved conductivity of electrolyte materials, have improved the chemical property of LiFePO4.After the doping, LiFePO4 discharge capacity first reaches 135.52mAh/g; Unadulterated LiFePO4 discharge capacity first has only 116.25mAh/g.Conductivity after the doping has obtained certain raising.This is because doping little metal ion replaces the Li+ position, constitutes the p N-type semiconductor N, has increased the conductivity of material.The identical ^ of Liu adopts that improved solid phase method has prepared that particle is fine, the uniform LiFePO4 of particle size distribution and Li0,98Mn, and the o.o2LiFePO4 compound, mixing helps controlling the pattern and the particle diameter of product on a small quantity, obtains stable LiFePO4 compound.Because Mn2+ octahedral coordination radius, can think that magnesium ion occupies the replacement lithium ion less than Fe2+.The result shows: the relative lithium electrode current potential of the charge and discharge platform of lithium ion is about 3.5V in the material, and initial discharge capacity surpasses 160mAh/g, and capacity only decays 5.5% after 50 charge and discharge cycles, shows that this method has improved specific energy and cyclical stability.The iron position is assorted disastrously: can improve conductivity of electrolyte materials though mix in the lithium position, because foreign atom can hinder the diffusion of lithium ion in the one dimension passage, thereby be unfavorable for improving the high-rate charge-discharge capability of material.And the rate charge-discharge performance of iron position doping can improvement LiFePO4 improves cycle performance.^ such as Liu Fangling adopt parcel carbon to improve its surface electronic conductivity, and doped metal ion is to improve its body electronic conductivity.Chosen ionic radius near and 4 different metal ion species Ca3+ of valence state; Ti5+, Ta5+, mix in the Fe position of MO6+; Sample unit cell volume after the doping all has minimizing; Electronic conductivity has improved the 4-6 one magnitude than the electronic conductivity of LiFePO4, and its impedance in electrolyte solution is significantly reduced, and chemical property also obviously improves.^ such as Hu Huanyu adopt the synthetic particle tiny and uniform nanoscale positive electrode LiFePO4 of high-temperature solid phase reaction method, have good capacity cycle performance, but its high rate capability are poor.Mix a spot of manganese and can reduce the polarization of material, improve the high rate capability of material.This mainly is because the doping of manganese has increased the unit cell volume of LiFePO4; More help deviating from of lithium; The doping of manganese has caused sintering process to produce crystal structure defects in addition, has improved the electron conduction of material, thereby has made the high-rate charge-discharge capability of material make moderate progress.The phosphate potential crushed grain is assorted: P site doped is feasible in theory, but the doping of carrying out phosphate potential is separately seldom arranged.^ such as Zhang Yurong have studied olivine structural Li2+2xTi2-xCu2x (NbO) 2, and having obtained conductivity through Ti and Cu replacement P is that 1.26 * 10-6S/cm-adds, and initial discharge capacity is the positive electrode of 805.8mAh/g.Said material has higher conductivity, but owing to Fe is all replaced by Ti and Cu, ' guiding discharge voltage is lower, and cycle performance is poor.Though phosphate potential is feasible in theory, study less relatively.

Through retrieval, put down in writing 1043 of relevant lithium battery applications for a patent for invention, 2181 of lithium ion battery applications for a patent for invention at present, wherein having a great deal of is relevant method of mixing.

Confirm it is the lithium position in theory, or the iron position, or phosphate potential obtains mixing and role, and relevant authoritative experts still have different separately brilliant idea, also constantly studying, exploring.

Present more consistent viewpoint is, LiFePO4 has that fail safe is good, pollution-free, stable cycle performance, specific capacity is high and advantage such as cheap, but also has poorly conductive and the lower shortcoming of tap density.Poorly conductive is to influence the biggest factor that LiFePO4 is used, and can conductivity be improved through mixing, and high-rate charge-discharge capability also improves, and has suppressed the effect of capacity attenuation to a certain extent.The doping approach can improve, improve the lithium ion anode material performance, has been a kind of feasible mode of generally acknowledging.

Summary of the invention

The objective of the invention is to: based on the structural limitations of the lithium iron phosphate positive material (LiFePO4) of prior art; There are its poorly conductive and the low deficiency of lithium ion diffusion coefficient, propose strontium, barium activation lithium iron phosphate positive material that a kind of strontium, barium activation improve its performance at present.

The present invention can improve, improve the lithium ion anode material performance in view of the doping approach, has been a kind of feasible mode of generally acknowledging.According to the chemical property of barium/lithium, electric property, crystal structure characteristic is the characteristics of akin element:

Barium is element the most active in the alkaline-earth metal, because it is very active, and oxidized easily, should be kept in kerosene and the atoleine.

5.212 electron-volts of ionization energy, the first ionization energy 502.9kJ/mol;

Crystal structure: structure cell is a body centred cubic cell, and each structure cell contains 2 metallic atoms;

Cell parameter: a=502.8pm; B=502.8pm; C=502.8pm; α=90 °; β=90 °; γ=90 °.

Lithium, metallic element can react with a large amount of inorganic reagents and organic reagent.With equal ability such as oxygen, nitrogen, sulphur chemical combination, the deepening owing to be prone to oxidated, and density is littler than kerosene, so should deposit in the atoleine.

5.392 electron-volts of ionization energy, the first ionization energy 520.2kJ/mol;

Cell parameter: a=351pm; B=351pm; C=351pm; α=90 °; β=90 °; γ=90 °.

Think that barium should be to be easy to the doping effect of lithium position most.The present invention be mix through barium make an experiment, in the situation of mixing with barium, can add 1-2 other element again, constitute 2 yuan or 3 yuan of doping, with obtained performance anode material of lithium battery preferably.

Strontium of the present invention, barium activation lithium iron phosphate positive material, it is characterized in that: its chemical composition or chemical general formula can be expressed as: LiSrxBayFePO ₄, x=0.00002-0.00005, y=0.0003-0.003; Wherein the mol of Li, Sr, Ba, Fe, P ratio is: 1mol Li: 0.00002-0.00005mol Sr: 0.0003-0.003mol Ba: 1mol Fe: 1mol P.

Strontium of the present invention, barium activation lithium iron phosphate positive material can adopt the preparation method of the anode material of lithium battery LiFePO4 of prior art to obtain.

The present invention's beneficial effect compared with prior art: strontium of the present invention, barium activation lithium iron phosphate positive material; Perhaps because a small amount of strontium, barium of replacing that mixes; Help controlling the pattern and the particle diameter of product, obtain stable LiFePO4 compound, strontium, barium ions occupy the replacement lithium ion; Its lattice has obtained activation, has improved the lithium ion diffusion coefficient; Dopant ion though mixing, barium lithium position can improve conductivity of electrolyte materials, owing to can hinder the diffusion of lithium ion in the one dimension passage, thereby be unfavorable for improving the high-rate charge-discharge capability of material.Product unit cell volume behind the strontium doping all has minimizing, and electronic conductivity improves than the electronic conductivity of LiFePO4, and its impedance in electrolyte solution is significantly reduced, and chemical property also obviously improves; Its first discharge capacity reach 160.52mAh/g; The relative lithium electrode current potential of its charge and discharge platform is about 3.5V, and initial discharge capacity surpasses 168mAh/g, and capacity decays about 1.2% approximately after 100 charge and discharge cycles; Specific capacity and cyclical stability and unadulterated LiFePO4 discharge capacity first have only 116.25mAh/g to compare, and are greatly improved.

Embodiment

Below in conjunction with embodiment the present invention is described further, but execution mode of the present invention is not limited thereto.

Below adopt the calcination method synthetic method,, be illustrated strontium of the present invention, barium activation lithium iron phosphate positive material.

Strontium of the present invention, barium activation lithium iron phosphate positive material; Its lithium source can be used: lithium salts such as lithium carbonate, lithium hydroxide or lithium dihydrogen phosphate; Source of iron can be used: ferrous oxalate etc., and the phosphoric acid root can be used: ammonium dihydrogen phosphate or diammonium hydrogen phosphate etc., the strontium source is a Preparation of Metallic Strontium; Strontium hydroxide (Sr (OH) 2), strontium carbonate SrCO3, the barium source can be used: barium salts such as brium carbonate, barium hydroxide, barium chloride, barium nitrate, barium monoxide, barium sulphide.

Select for use: lithium carbonate (Li2CO3) (99.73%), strontium carbonate (AR), brium carbonate (BaCO3) (99.8%), ferrous oxalate (FeC2O4.2H2O) (99.06%), diammonium hydrogen phosphate (NH4H2PO4) (98%) is a raw material; According to 1mol Li: 0.00002-0.00005mol Sr: 0.0003-0.003mol Ba: 1mol Fe: after the 1mol P mixed, in ethanol medium, rotating speed 200-800r/mimn high speed ball milling 15-20h; With 105-120 ℃ of oven dry; Obtain presoma, the presoma that oven dry is obtained places in the high temperature furnace, in blanket of nitrogen; Through 500-750 ℃ of high-temperature calcination 16-24h, promptly get strontium of the present invention, barium activation lithium iron phosphate positive material.

Embodiment 1

Li2CO3 (99.73%); SrCO3 (AR), BaCO3 (99.8%), FeC2O4.2H2O (99.06%); NH4H2PO4 (98%) raw material; According to 1mol Li: 0.00002mol Sr: 0.0003mol Ba: 1mol Fe: after the 1molP mixed, in absolute ethyl alcohol (AR) medium, high speed ball milling 20h (rotating speed 200r/mimn.After the 105-120 ℃ of oven dry, obtain presoma, the presoma that oven dry is obtained places in the high temperature furnace, in common purity nitrogen (＞99.5%) atmosphere, and through 500-750 ℃, high-temperature calcination 24h.Promptly get strontium of the present invention, barium activation lithium iron phosphate positive material.

Embodiment 2

Li2CO3 (99.73%); SrCO3 (AR), BaCO3 (99.8%), FeC2O4.2H2O (99.06%); NH4H2PO4 (98%) raw material; According to 1mol Li: 0.00004mol Sr: 0.001mol Ba: 1mol Fe: after the 1molP mixed, in absolute ethyl alcohol (AR) medium, high speed ball milling 20h (rotating speed 200r/mimn.After the 105-120 ℃ of oven dry, obtain presoma, the presoma that oven dry is obtained places in the high temperature furnace, in common purity nitrogen (＞99.5%) atmosphere, and through 500-750 ℃, high-temperature calcination 24h.Promptly get strontium of the present invention, barium activation lithium iron phosphate positive material.

Embodiment 3

Li2CO3 (99.73%); SrCO3 (AR), BaCO3 (99.8%), FeC2O4.2H2O (99.06%); NH4H2PO4 (98%) raw material; According to 1mol Li: 0.00005mol Sr: 0.003mol Ba: 1mol Fe: after the 1molP mixed, in absolute ethyl alcohol (AR) medium, high speed ball milling 20h (rotating speed 200r/mimn.After the 105-120 ℃ of oven dry, obtain presoma, the presoma that oven dry is obtained places in the high temperature furnace, in common purity nitrogen (＞99.5%) atmosphere, and through 500-750 ℃, high-temperature calcination 24h.Promptly get strontium of the present invention, barium activation lithium iron phosphate positive material.

Embodiment 4 (not mixing contrast)

With Li2CO3 (99.73%), FeC2O4.2H2O (99.06%), NH4H2PO4 (98%) raw material, according to 1molLi: 1mol Fe: after the 1mol P mixed, in absolute ethyl alcohol (AR) medium, high speed ball milling 20h (rotating speed 200r/mimn.After the 105-120 ℃ of oven dry, obtain presoma, the presoma that oven dry is obtained places in the high temperature furnace, in common purity nitrogen (＞99.5%) atmosphere, and through 500-750 ℃, high-temperature calcination 24h.Promptly get lithium ion anode material.

Adopt the testing equipment of prior art and the method for testing of prior art,, carry out test result with the control Example of not mixing 4 and be strontium, the barium activation lithium iron phosphate positive material of above embodiment 1-3:

The strontium of embodiment of the invention 1-3, barium activation lithium iron phosphate positive material, discharge capacity reaches more than the 155.52mAh/g first; Unadulterated LiFePO4 discharge capacity first has only in the 116.25mAh/g.

The barium activation lithium iron phosphate positive material of embodiment of the invention 1-3, the relative lithium electrode current potential of its charge and discharge platform is about 3.5V, and initial discharge capacity surpasses 164mAh/g, and capacity decays about 3.0% approximately after 100 charge and discharge cycles.

Barium activation lithium iron phosphate positive material of the present invention, the back of mixing is assorted, the raising of specific capacity and cyclical stability; Perhaps this be because a small amount of strontium, barium of replacing that mixes; Help controlling the pattern and the particle diameter of product, obtain stable LiFePO4 compound, barium ions occupies the replacement lithium ion; Its lattice has obtained activation, has improved the lithium ion diffusion coefficient; Dopant ion though mixing, barium lithium position can improve conductivity of electrolyte materials, owing to can hinder the diffusion of lithium ion in the one dimension passage, thereby be unfavorable for improving the high-rate charge-discharge capability of material.And the rate charge-discharge performance of iron position doping can improvement LiFePO4 improves cycle performance.Product unit cell volume behind the strontium doping all has minimizing, and electronic conductivity improves than the electronic conductivity of LiFePO4, and its impedance in electrolyte solution is significantly reduced, and chemical property also obviously improves; Its first discharge capacity reach 155.52mAh/g; The relative lithium electrode current potential of its charge and discharge platform is about 3.5V, and initial discharge capacity surpasses 164mAh/g, and capacity decays about 3.0% approximately after 100 charge and discharge cycles; Specific capacity and cyclical stability and unadulterated LiFePO4 discharge capacity first have only 116.25mAh/g to compare, and are greatly improved.Be to replace strontium, barium on a small quantity owing to mix, help controlling the pattern and the particle diameter of product, obtain stable LiFePO4 compound, its lattice has obtained activation, has improved the result of lithium ion diffusion coefficient.

Claims

1. a strontium, barium activation lithium iron phosphate positive material, it is characterized in that: its chemical composition is: LiSrxBayFePO ₄, x==0.00002-0.00005, y=0.0003-0.003; The mol ratio of its Li, Sr, Ba, Fe, P is: 1mol Li: 0.00002-0.00005mol Sr: 0.0003-0.003mol Ba: 1mol Fe: 1mol P.