Effect of doping amount on capacity retention and electrolyte decomposition of LiNi0.5Mn1.5O4-based cathode at high temperature

The long service life of batteries is one of the most desired parameters for the battery industry and end-users. Several doping elements have been proposed to increase discharge capacity, capacity retention, and rate capability of high voltage LiNi0.5Mn1.5O4 (LNMO) cathode. In this study, two different doping elements, i.e., boron (III) and vanadium (IV), are compared to investigate the doping effect on capacity retention of LNMO-electrodes at high temperatures (50 C) and extended cycle performance. Different doping amounts are investigated for comparison, i.e., 1, 3, 5, 7, 10 wt% for boron and 10 wt% for vanadium. The actual benefit of doping is observed over extended cycle tests (> 1000 cycles) at 50 C and 1C. While pristine LNMO electrodes fail after 80 cycles, 10% B-doped LNMO exhibits the highest capacity retention, 80% at 50 C and 1C after 1200 cycles. The operando differential electrochemical mass spectroscopy results reveal that LNMO electrodes show the highest amount of gas emission (H2 and O2) at ~ 4.7 V, where the oxidation of Ni4þ/3þ and Ni3þ/2þ occurs. Since high amount doping strategy increases Mn3þ amount and, consequently, the charge voltage plateau at ~4 V (Mn3þ/Mn4þ), this implicitly prevents electrolyte decomposition at high voltage due to decreasing of nickel voltage plateau and less charging step duration at ~ 4.7 V. This investigation shows that the cathode life remarkably can be extended by reducing the nickel content with high amount of doping.