Synthesis and structural stability of Cr-doped Li2MnSiO4/C cathode materials by solid-state method

The crystal structure of the Li 2 MnSiO 4 cathode material would collapse during the charge and discharge process because of that the Mn-O coordination polyhedron changed from [MnO 4 ] into [MnO 6 ] in the process of Mn +2 to Mn +4 , but the Cr element could remain [CrO 4 ] crystal ligand from Cr +2 to Cr +4 , so Cr element substitution was used to improve the structural stability of the Li 2 MnSiO 4 cathode material. In this work, Li 2 Mn 1-x Cr x SiO 4 /C nanocomposites were synthesized by solid-state method. XRD, SEM and TEM observations show that the as-prepared Li 2 Mn 1-x Cr x SiO 4 /C materials presents an orthorhombic crystal structure (S.G. Pmn2 1 ), the particle size of Li 2 Mn 1-x Cr x SiO 4 /C powder ranges from 50 to 100   nm. The XRD and XPS results indicate that Cr +2 is successfully doped into Li 2 MnSiO 4 lattice and has well compatibility with Li 2 MnSiO 4 . The electrochemical results display that Li 2 Mn 92.5% Cr 7.5% SiO 4 /C exhibits significantly enhanced cycle stability and discharge capability. The initial discharge capacity of the Li 2 Mn 92.5% Cr 7.5% SiO 4 /C sample is 255 mAh   g −1 , and the discharge capacity was still about 60   mAh   g −1 after 50 cycles. Furthermore, the XRD patterns, TEM images and Raman analysis reveal that the Cr doping enhances the structural stability of Li 2 Mn 1-x Cr x SiO 4 /C and improves the electrochemical activity of the cathode. Thus, the Li 2 Mn 92.5% Cr 7.5% SiO 4 /C have shown potential applications for lithium ion batteries.