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

Abstract

LiNi0.8Co0.1Mn0.1O2 (NCM) can achieve a high capacity of 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 Oα– to oxygen vacancies, transplant the pumped charges from the oxidized Oα–, 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 °C and 100 cycles at 60 °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.