Storage performance of LiFe1 − x Mn x PO4 nanoplates (x = 0, 0.5, and 1)

Abstract

Although LiFePO4 (LFP) is considered to be a potential cathode material for the lithium-ion batteries, its rate performance is significantly restricted by sluggish kinetics of electrons and lithium ions. Several attempts have been made so far to improve the performance of LiFePO4 by reducing the grain size, doping with aliovalent atoms, and coating conductive materials such as carbon or RuO2. We report here synthesis of LFP nanoplates by solvothermal method, tailoring the thickness as well as carbon coverage at surfaces to explore their influence on the storage performance. Due to the fact that Li+ ion diffuses along the b-axis, solvothermal method was aimed to control the thickness of nanoplates across the b-axis. We synthesized several nanoplates with various plate thicknesses along b-axis; among those, nanoplates of LFP with ∼30-nm-thick b-axis having thin (2–5 nm) and uniform layer of carbon coating exhibits high storage capacity as well as high rate performances. Thus, a favorable morphology for LiFePO4 has been achieved via solvothermal method for fast insertion/extraction of Li+ as compared to spherical nanoparticles of carbon-coated LFP. Galvanostatic cycling shows a capacity of 164 ± 5 mAh g−1 at 0.1 C rate, 100 ± 5 mAh g−1 at 10 C rate, and 46 ± 5 mAh g−1 at 30 C rate, with excellent capacity retention of up to 50 cycles. Further attempts have been made to synthesize LiMnPO4 (LMP) as well as Li(Fe1 − x Mn x )PO4/C (x = 0.5) nanoplates using solvothermal method. Although LiMnPO4 does not exhibit high storage behavior comparable with that of LiFePO4, the mixed systems have shown an impressive storage performance.