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单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,XXXX,2,1,Recent developments in cathode materials for lithium ion batteries,Review,Cathode materials,Composite cathodes,Effect of doping,Introduction,Cathode performance,Effect of microstructure and morphology,Conclusions,1,1. Introduction,battery,performance,electrode material,Lithium-ion batteries,：,w,idely utilized,Future,：,light weight,small volume, high energy density,safety,cathode materials,2. Cathode materials,LiCoO,2,：,-NaFeO,2,structure,，,commonly used,，,more costly，less stable，rapid decrease；,LiNiO,2,：,-NaFeO,2,structure,，,lower in cost, higher energy density,less stable，less ordered;,LiMnO,2,：,monoclinic,structure，less ordered;,Li(Ni,1/3,Mn,1/3,Co,1/3,)O,2,:,commonly used, high capacity, good rate capability,higher charging voltage,rapid loss of capacity;,LiMn,2,O,4,:,spinel structure,lower cost and safer than LiCoO,2,lower capacity,easy phase changes;,V,2,O,5,、LiV,3,O,8,:,low voltages,LiFePO,4,:,olivine structure,two-phase(FePO,4,and LiFePO,4,), relatively constant voltage,low electronic conduction;,LiMnPO,4,、LiCoPO,4,:,higher open circuit voltages(4.1v,4.8v),lower capacities;,Li(Mn,Fe,Co)PO4、Li3V2(PO4)3,:,high operating voltage，good performance at high discharge currents,;,3. Cathode performance,Fig. 2. Plateau voltage and capacity (see Fig. 1) for LiFePO4 123,153162 and,LiCoO2 163167 with a charging voltage of 4.2V and discharge current of 1C.,Fig. 3. Plateau voltage and capacity for LiFePO4,123,150,153,156,158161,168174 with a charging voltage of 4.2V and,discharge current of 0.1C.,The,operating voltage,for LiCoO2 is,higher,than that for LiFePO4,，,LiFePO4 has a,narrower,voltage range,.,A,reduction,in the discharge current increases,the capacity of LiFePO4.,Fig. 4. Plateau voltage and capacity for,Li(Ni,1/3,Mn,1/3,Co,1/3,)O,2,LiCoO,2, LiFePO,4,and LiMn,2,O,4,with a charging,voltage of 4.3V and discharge current of,1C.,Fig. 5. Plateau voltage and capacity (see Fig. 1) for,Li(Ni,1/3,Mn,1/3,Co,1/3,)O,2,LiMn2O4 and LiCoO2 with a charging voltage of 4.3V and discharge,current of,0.1C.,T,he capacity of,Li(Ni,1/3,Mn,1/3,Co,1/3,)O,2,increases more,than that of,LiCoO,2, suggesting,that the,kinetics of charge transfer,and/or,mass transport,are,slowe,r in Li(Ni,1/3,Mn,1/3,Co,1/3,)O,2,than in LiCoO,2,.,Fig. 6. Discharge capacity of,LiCoO,2,as a function of discharge rate.,Fig. 7. Discharge capacity of,Li(Ni,Mn,Co)O,2,and LiMn2O4 as,a function of discharge rate.,T,he decrease in capacity,with,increasing discharge current,is generally,smaller,for LiCoO,2,than for,Li(Ni,Mn,Co)O,2,.,Fig. 8. Discharge capacity of LiFePO4 as a function of discharge rate.,Fig. 9. Discharge capacity of LiFePO4 at high discharge currents .,R,apid decrease,in capacity,is for a cell,with a,polymer electrolyte, rather than a liquid,LiPF,6,-based electrolyte,so the,high current performance,may be,limited,by the,electrolyte rather than the electrode,.,LiFePO,4,can,be used at,high discharge currents,.,Fig,s,.,10,12. Capacity after 1st/50th cycle and percent change in capacity after 50 cycles,for LiFePO4 LiCoO2,Li(Ni,Mn,Co)O2 cathodes,.,The decrease in capacity of LiFePO,4,(,1020%,),after cycling is much smaller than that for LiCoO,2,or Li(Ni,Mn,Co)O,2,(,3040%,).,4. Composite cathodes,C,ombination of two electrode materials,To,improve,capacity retention,during cycling and,performance,at high discharge currents,add,ing,LiFePO,4,to,LiCoO,2,Li(Li,0.17,Mn,0.58,Ni,0.25,)O,2,Li(Ni,0.5,Mn,0.3,Co,0.2,)O,2,.,To,improve performance,C,oating particles of,one cathode material with another active material,W,ith a,Co,3,O,4,coating,the,cycling and rate capability,of,LiMn,2,O,4,has been improved,.,1+1,2,5. Effect of doping,D,opant additions,Fe,Ru,LiNiO,2,、Li2MnO,3,、LiNi,0.125,Mn,0.75,Co,0.125,O,2,LiMn,2,O,4,、LiFePO,4,、LiMn,1.5,Ni,0.5,O,4,、Li,3,V,2,(PO4),3,Cr,LiMn,2,O,4,、LiMn,1.5,Ni,0.5,O,4,、Li(Mn,0.5,Ni,0.5,)O,2,、V,2,O,5,、Li(Ni,1/3,Mn,1/3,Co,1/3,)O,2,、 Li,3,V,2,(PO,4,),3,Zn、Al、Ti、Mg、La,C,apacity,、cycling、electrical conductivity,H,igh,voltages,high discharge current,good capacities,are,require,d,.,6.Conclusions,Progress has been made by,engineering the,electrode composition,microstructure,and,morphology,but,additional improvements,are needed.,Niobium doped lithium titanate as a high rate anode material for Li-ion batteries,2,1,Introduction,2 Experimental,3,Results and discussion,4,Conclusions,1. Introduction,Lithium-ion batteries,：,w,idely utilized,Future,：,light weight,small volume, high energy density,safety,As a anode material,Li,4,Ti,5,O,12,is,promising,compared to the currently used graphite：,zero strain,material,safe, stable.,advantages,obstacles,L,ow,electronic conductivity,which leads to its,low,rate capacity,.,Solution,(1),improving the,synthesis route,to get nano-sized particles,；,(2),adding,a second conductive phase,into the Li,4,Ti,5,O,12, such as metal powder,and carbon ;,(3),substituting Li or Ti,by other metal cations,such as Cr,3+, V,5+, Mn,4+, Fe,3+, Al,3+, Co,3+, Ta,5+, Cu,2+,;,N,o investigation,was reported,on the electrochemical characteristics of,Nb-doped Li,4,Ti,5,O,12,as an,anode material.,Nb,2. Experimental,Cathode(+):,Li,4,Ti,4.95,Nb,0.05,O,12,(solgel method),CH,3,COOL,i+,Ti(OC,4,H,9,),4,+,Nb(OH),5,A,node,(-),:,Lithium metal,E,lectrolyte,:,ethylene carbonate,(,EC,),+,dimethyl,carbonate,(,DMC,),(1:1 in,volume),+,LiPF,6,(,1.0 mol,/,dm,3,),Separator:,porous membrane of polypropylene,For comparison,，,Li,4,Ti,5,O,12,were also prepared using,similar method,.,3. Results and discussion,Fig. 1.,(a) XRD patterns and (b) magnified (1 1 1) peaks of the Li,4,Ti,5,O,12,and the,Li,4,Ti,4.95,Nb,0.05,O,12,with Si power as the internal standard.,Without obvious impurity phase.,The lattice parameters of the,Li,4,Ti,4.95,Nb,0.05,O,12,and the,Li,4,Ti,5,O,12,are,8.363,and,8.355,respectively.,(1),Nb,5+,(0.69 ) is larger than,Ti,4+,(0.68 ),(,2,),Ti,3+,(0.76 ) is larger than,Ti,4+,(0.68 ).,Nb,5+,has successfully entered the lattice of the spinel.,Fig. 2.,SEM pictures of (a) Li,4,Ti,5,O,12,and (b) Li,4,Ti,4.95,Nb,0.05,O,12,.,It is obvious that both powders,exhibit a,uniform,particle size,distribution,.,Fig. 3.,EDS element mapping of the Li,4,Ti,4.95,Nb,0.05,O,12,.,It,can be seen that,most,Nb and Ti are,uniformly distributed,in,Li,4,Ti,4.95,Nb,0.05,O,12,.,Fig. 4.,Initial dischargecharge curves of (a) Li,4,Ti,5,O,12,and (b) Li,4,Ti,4.95,Nb,0.05,O,12,at,different rates (0.5 C, 1 C, 2 C, 10 C, 20 C, 40 C).,Compared with,the Li,4,Ti,5,O,12, the Li,4,Ti,4.95,Nb,0.05,O,12,electrode exhibits,an excellent,rate capability,caused by a certain,amount of,Ti ions transferred from Ti,4+,to Ti,3+,.,178.8,82.4,167.9,52.2,Fig. 5.,Cyclic performance of the Li,4,Ti,5,O,12,and the Li,4,Ti,4.95,Nb,0.05,O,12,at (a) 1 C and(b) 10 C.,The,improvement in capacity could be attributed to,the enlarged lattice,volume,of the Li,4,Ti,4.95,Nb,0.05,O,12,as the result of,Nb,5+,doping, which,is helpful for,the insertion and extraction,of Li,+,.,Fig. 6.,Dischargecharge capacity performance and coulombic efficiency of theLi,4,Ti,4.95,Nb,0.05,O,12,electrode.,Discharge current:,0.5 C,.,Charge current,: (A) 0.5 C, (B)1 C, (C) 2 C, (D) 5 C, (E) 10 C, (F) 20 C and (G) 0.2 C.,As the charge current increases,the Li,4,Ti,4.95,Nb,0.05,O,12,shows,excellent,ability of capacity retention,.,Li,4,Ti,4.95,Nb,0.05,O,12,is a,promising,anode material with,high rate capability,and,good cycling reversibility,.,Fig. 7.,Cyclic voltammograms of the Li,4,Ti,5,O,12,and the Li,4,Ti,4.95,Nb,0.05,O,12, with scan,rate of 0.5mV,s,1,.,(1),T,he,Li,4,Ti,4.95,Nb,0.05,O,12,possesses a,lower electrode polarization,and,a,higher lithium-ion diffusivity,in the bulk than the Li,4,Ti,5,O,12,.,(2),Nb,doping,greatly improves the,electrode kinetics characteristics,of,the Li,4,Ti,5,O,12,electrode,.,T,he dopingof,Nb,is,beneficial,to the reversible intercalation and deintercalation,of lithium-ion,.,Fig. 8.,(a) Electrochemical impedance spectra of the Li,4,Ti,5,O,12,and the,Li,4,Ti,4.95,Nb,0.05,O,12,discharged to the depth of 50% followed by two cycles; (b)equivalent circuit for Fig. 8 (a) R,s,: electrolyte resistance; R,ct,: charge-transfer resistance;CPE: double-layer capacitance and passivation film capacitance; Z,w,:Warburg,impedance.,T,he Li,4,Ti,4.95,Nb,0.05,O,12,electrode exhibits much,higher,conductivity,than the Li,4,Ti,5,O,12,electrode.,4. Conclusions,good crystallinity,and,high phase purity,.,higher specific capacity,and,better cycling performance,.,higher,electronic conductivity,and,lithium-ion,diffusivity,implying that,Nb-doping,is beneficial to the reversible,intercalation,and,extraction,of Li,+,.,Li,4,Ti,4.95,Nb,0.05,O,12,electrode is,a,promising,anode material,for lithium-ion batteries.,thanks,
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