Sr-Based Sub/Surface Integrated Layer and Bulk Doping to Enhance High-Voltage Cycling of a Ni-Rich Cathode Material

LiNi0.8Co0.1Mn0.1O2 (NCM) can achieve a high capacity of g - more than 200 mAh g(-1) at charging voltages above 4.5 V, but it suffers from severe capacity fading at a high voltage during cycling associated with the lattice oxygen evolution-induced phase and surface structure modifications. Therefore, the big challenge for improving electrochemical performance is suppressing the lattice oxygen loss at a high voltage. Here, a facile strategy to inhibit the lattice oxygen loss of a Ni-rich material at a high charging voltage by a simple Sr treatment method is reported. The Sr treatment leads to the formation of a Sr-based sub/surface integrated layer and induces the atomic rearrangement on the subsurface to form Sr-based perovskite-like LixSr1-xTMO3 (TM = Ni, Co and Mn) during the heat treatment process. The perovskite-like structure can adsorb the oxidized O alpha- to oxygen vacancies, transplant the pumped charges from the oxidized O alpha-, and reduce them back to O2- to inhibit the movement of oxidized oxygen anions at the charged NCM surface. Furthermore, the formed Sr1-xHPO4 outer layer can prevent NCM from corroding by HF in organic electrolytes. Meanwhile, bulk doping stabilizes the metal-oxygen bond by suppressing the Ni migration at a high charging voltage. The modified NCM thus exhibited a significantly enhanced high-voltage cycle stability with 82.3 and 80.1% of capacity retentions at 1C achieved after 250 cycles at 25 degrees C and 100 cycles at 60 degrees C, respectively. This work opened a new avenue to suppress the lattice oxygen loss via surface structure regulations in high-energy-density rechargeable batteries during high-voltage cycling.