| In this paper, a series of LiMn1-xMxO2 (0≤x<1, M is one or more of Co, Ni, Al, Ti, Mg, Y) were synthesized by solid-state reaction method. The influences of the preparing conditions, including raw materials, lithium and transition metal atomic ratio, heating temperature and atmosphere, on their microstructure and electrochemical properties were investigated by XRD, SEM, TG, cyclic voltammetry and charge/discharge cycling analysis.The synthesis and light doping of LiMnO2 showed that LiMnO2 with high phase purity can be obtained by strict control of reacting atmosphere, heating temperature, lithium and transition metal atomic ratio etc. But when the materials were used as cathode in lithium ion batteries, both pure and lightly Al/Co- doped LiMnO2 transformed to spinel Li2Mn2O2. As a result, the voltage profile contained step but not a monotonic and smooth discharge plateau.Further studies showed that LiMn1/3Ni1/3Co1/3O2, heavily doped LiMnO2, has significant prospect for application due to its stable layered structure and monotonic voltage plateau. In order to improve electrochemical property of synthesized LiMn1/3Ni1/3Co1/3O2, selection of lithium and transition metal raw materials was carried out. The effect of Li/(Mn+Ni+Co) ratio on structure and property of LiMn1/3Ni1/3Co1/3O2 was also investigated. Results indicated that using Li2CO3 and Mn1/3Ni1/3Co1/3(OH)2 as lithium and transition metal sources respectively, with Li/(Mn+Ni+Co) atomic ratio of 1.0-1.05, was suit for preparation of LiMn1/3Ni1/3Co1/3O2 with suitable particle sizes and better electrochemical property.The reaction process of the mixture of Li2CO3 and Mn1/3Ni1/3Co1/3(OH)2 with Li/(Mn+Ni+Co) atomic ratio of 1.05 was studied by TG and DTG On the basis of TG and DTG analysis, the effect of different pre-heating and sintering temperature on electrochemical property of LiMn1/3Ni1/3Co1/3O2 was investigated. It was shown that LiMn1/3Ni1/3Co1/3O2 prepared by 730°C pre-heating and 900℃ sintering has higher discharge capacity and better cycling stability.Finally, doping LiMn1/3Ni1/3Co1/3O2 was studied using Al, Y, Ti and Mg as doping atom respectively. The lightly Ti-doped LiMn1/3Ni1/3Co1/3O2 exhibited high capacityretention ratio up to 98% after 20 charge-discharge cycles. Furthermore, the charge-discharge tests revealed that the Ti-doped LiMni/3Nii/3Coi/3O2 has markedly higher initial charge/discharge rate and voltage plateau than the undoped one. The initial charge/discharge rate and voltage plateau of the prepared Ti-doped material reached up to 85.6% and 86.7% respectively, while a initial discharge capacity of 135mAh/g over 2.5-4.3V was obtained. |
PDF Full Text Request