Fund Project:Project supported by the National Natural Science Foundation of China (Grant Nos. 11664012, 11564016), the Excellent Youth Foundation of Jiangxi Province, China (Grant No. 20171BCB23035), the Technology Project of Department of Education of Jiangxi Province, China (Grant No. GJJ170186), and the Science Foundation for Ph.D.s of Jiangxi Normal University, China (Grant No. 7957).
Received Date:08 April 2019
Accepted Date:24 April 2019
Available Online:01 July 2019
Published Online:05 July 2019
Abstract:Although Li-ion batteries (LIBs) have had great success in portable electronic devices and electrical vehicles, the improvement of the performances has received intensive attention. Generally, doping is an effective method to modify the battery performance, such as cycling performance. Appropriate doping can effectively reduce the structural deformation of electrode materials during charging and discharging, thus improving the cycling performace of LIBs. Because of the large radius, large charge and strong self-polarization ability of rare earth ions, rare earth element is a promising candidate for doping modification. Motivated by this, we study the structural, electronic and ionic diffusion properties of rare-earth-doped cathode material Li2MnO3 by using first-principles calculations based on density functional theory as implemented in Vienna ab initio simulation package. After the doping of rare earth elements (La, Ce, Pr, Sm), the lattice constants and cell volumes increase with respect to the undoped one. The cell volume of La-doped Li2MnO3 has the biggest change, while the cell volume of Sm-doped one has the smallest change. Due to the different ionic valence states, the electronic structures of the doped Li2MnO3 are various. La-doped Li2MnO3 exhibits metallic characteristic, whereas Ce-, Pr-, and Sm-doped structures are semiconducting with smaller band gap than that of the undoped case. The Li diffusion energy barrier in Li2MnO3 shows complicated variation when the La and Ce are doped. At the sites far away from the rare earth ions, the Li diffusion barriers are lower than that of undoped one. The reason is that the diffusion channels, which are determined by the distance between neighboring O-layers, are enlarged due to the implantment of rare earth ions. However, the situations are various at the sites close to the rare earth ions. The Li diffusion barriers increase essentially when Li ions diffuse from the nearest sites to rare earth ions. Such a result is closely related to the huge changes of local structures around the rare earth ions. In addition, the effect of La doping on the Li diffusion barrier is more obvious than that of Ce doping, which is due to the local structure change around rare earth ions. Keywords:frist-principle calculation/ rare-earth doped/ Li-ion battery/ cathode materials
表1未掺杂与稀土掺杂的Li2MnO3的晶格常数、超胞体积与稀土元素的磁矩 Table1.Lattice constants, volume of supercell, magnetic moment of rare-earth atom of Li2MnO3 without and with rare-earth doping
图 1 Li2MnO3中稀土掺杂位置与Li离子的9种不同等价位示意图 Figure1. Crystal structure of Li2MnO3 with rare-earth doping sites and nine Li sites
表2未掺杂Li2MnO3中的Mn离子与最近邻O离子之间的键长和稀土掺杂结构中稀土离子与最近邻O离子之间的键长 Table2.Distance between Mn and the nearest neighboring O in undoped Li2MnO3 and distance between rare-earth ion and the nearest neighboring O in rare-earth-doped Li2MnO3