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

epsilon-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 epsilon-VOPO4. Elemental analysis and lattice parameter refinements determined that up to 10% Nb can be substituted into epsilon-VOPO4 without any impurities. TEM and Synchrotron-based EXAFS confirmed that all the substituted samples have Nb in the epsilon-VOPO4 structure. Electrochemical tests revealed that 1% Nb substitution can deliver a high discharge capacity of similar to 300 mAh g(-1) without any degradation in cycling behavior by maintaining its nanosized morphology.

Automated summary

In this study, niobium substitution was applied to enhance the high-rate performance of epsilon-VOPO4 at the 4.0 V plateau, allowing for up to 10% substitution without impurities. Electrochemical tests showed that 1% niobium substitution can deliver a high discharge capacity of 300 mAh g(-1) while maintaining nanosized morphology without degradation in cycling behavior.