Enhanced High-Rate Performance of Nanosized Single Crystal ε-VOPO4 with Niobium Substitution for Lithium-Ion Batteries

Abstract

ε-VOPO4 has the potential to be the next high energy density cathode material for lithium-ion batteries due to its high thermal stability and its ability to reversibly intercalate two full Li+, giving a high discharge capacity of 305 mAh g−1. However, vanadyl phosphate materials typically experience poor Li+ kinetics that impedes the high-rate capability at the high voltage plateau. In this work, we applied niobium substitution to improve the high-rate performance of the 4.0 V plateau of ε-VOPO4. Elemental analysis and lattice parameter refinements determined that up to 10% Nb can be substituted into ε-VOPO4 without any impurities. TEM and Synchrotron-based EXAFS confirmed that all the substituted samples have Nb in the ε-VOPO4 structure. Electrochemical tests revealed that 1% Nb substitution can deliver a high discharge capacity of ∼300 mAh g−1 without any degradation in cycling behavior by maintaining its nanosized morphology.