Unleashing the Kinetic Limitation of Co-Free Li-Rich Mn-Based Cathodes via Ionic/Electronic Dual-Regulation.

Abstract

Li-rich Mn-based oxide (LRMO) are promising cathode candidates for next-generation Li-ion batteries with combined cost-effectiveness and high specific capacity. Designing Co-free LRMO can further leverage the low cost of this class of cathodes given the capacity can be maintained. However, implementing cobalt-free LRMO cathode materials are hampered by their sluggish kinetics, resulting in low capacity and poor rate performance that underperform compared with their Co-containing counterparts. Here, it is confirmed that the slow kinetics of Co-free LRMO originates from the structural disorder caused by transition metals (TMs) migration at high voltages (above 4.5 V Vs. Li⁺/Li) and consequent irreversible oxygen redox process. Aware of this, Na⁺/F^- is introduced in surficial lattice to alleviate these issues, ultimately achieving improved discharge voltage (≈0.2 V above 1 C, 1 C = 0.25 A g^-1), exceptional cycle stability in pouch-type cell (95.1% capacity retention in 1 C after 400 cycles at 25 °C, and 80.9% capacity retention after 300 cycles in 0.5 C at 45 °C) and excellent C-rate performance (≈150 mA h g^-1 at 5 C). The newly developed Na⁺/F^- gradient design unleashes the surficial charge transfer kinetics limitation and greatly improves the lattice structure stability, consequently providing valuable guidelines for future high-capacity LRMO cathode design.