Coordination-Assisted Coating for Improved Cycling Performance of High-Voltage Spinel Cathode Materials

LiNi0.5Mn1.5O4 (LNMO) is a promising cathode material for lithium-ion batteries with advantages in high energy density and low cost. However, its stable working is challenged by aggravated interfacial instability during its operation at voltages up to 5 V. Here, a coordination-assisted process was developed to build conformal Nb2O5 nanoshells around LNMO particles for their surface protection. Using hydroxypropyl cellulose (HPC) as a stabilization agent, whose multi-hydroxyl groups are capable of forming strong coordination with the highly active Nb5+ in solution, we succeeded in suppressing the fast hydrolysis of Nb5+ so that a well-tamed Nb5+ precipitation could be achieved to ensure its heterogeneous growth around the LNMO seeds instead of fast precipitating into independent particles. We found this solution-based protocol shows high flexibility in controlling the thickness of the conformal nanoshells without eroding the LNMO particles, making it efficient to build core-shell-type LNMO cathodes with improved interfacial stability. Typically, we identified that the LNMO with a Nb2O5 coating of around 4 nm shows much improved structural and electrochemical stability with substantially suppressed parasitic reactions. Accordingly, this surface-modified LNMO demonstrated extraordinary capacity retention of 87.2% after 500 cycles at 0.5 C for its working at 5 V compared to only 27.3% for the untreated one. This work highlights the potential of solution-based synthetic processes in constructing nanoshells with high precision and provides useful control protocols to enable high energy cathode materials with high stability.