Co-modification of NCM-622 via Mg2+in situ doping and LiBO2/B2O3 surface coating: a pathway to design high-voltage cathodes for lithium-ion batteries†

NCM-622 cathodes have been promising cathodes for lithium-ion batteries due to their high reversible specific capacity and low cost. However, the NCM-622 cathode suffers from structural instability, especially at high voltage. Moreover, at elevated voltages and temperatures the cathode suffers from surface side reactions and particle cracks due to the presence of grain boundaries. The in situ doping of Mg²⁺ is achieved by doping Mg ions during the synthesis procedure using a CSTR and the LiBO₂/B₂O₃ surface coating is achieved by a simple wet-chemistry method; this dual-modification not only protects the surface of the cathode but the Mg²⁺ ions in the structure also enhance the cycling stability even at high voltage (4.5 V) and temperature (55 °C). As a result, animproved electrochemical behaviour was observed and the cathode could retain 82.5% of its initial capacity after 100 cycles at 4.5 V. Furthermore, the presence of the hybrid coating on the surface protects the cathode from HF attack and reduces the voltage polarisation during high temperature and voltage cycling. Such a dual-modification strategy can be commercially viable and useful for modification of high-energy-density NCM-622 cathodes.