Li+ substitution induced O3/O′3 biphasic tailoring strategies enhancing anion/cation synergetic redox of Na-rich manganese-based cathode for sodium-ion batteries

Abstract

Na-rich manganese-based layered oxide cathodes have presented potential applications in high energy–density sodium-ion batteries due to their cost-effectiveness and large theoretical specific capacity. However, the low kinetics of anionic redox reaction and lattice distortion caused by the Mn³⁺ Jahn-teller effect greatly hindered the actual capacity, rate, and cycling performances of these cathodes. Herein, a Li⁺ substitution induced O3/O′3 biphasic tailoring strategy has been proposed for constructing the Na-rich NaLi_0.2Mn_0.8O₂ (NLMO) cathode. Compared with conventional O′3-Na_1.2Mn_0.8O₂ (NMO) cathode, the O3/O′3-NLMO cathode enabled to provide an ultrahigh capacity of 233 mAh/g, superior capacity retention of 86 % after 50 cycles, and outstanding rate performance with the recorded-up capacity of 165 mAh/g at a high current density of 200 mA g⁻¹. In addition, NLMO also displayed rapid Na⁺-diffusion and more structural reversibility of O3/O′3-P3-O1-P3-O3/O′3 during the entire charging and discharging processes. The above excellent performances of NLMO cathode could be attributed to the well-designed O3/O′3 biphasic structure that provides the synergistic function of drastically enhancing reaction kinetics of anionic (O⁻/O^2–) couple and efficiently alleviating multiphase transitions caused by Mn⁴⁺/Mn³⁺ cationic couple. This unique finding of Li⁺ substitution induced biphasic structure provides an insight for developing economical and high-performance Na-rich oxide cathodes.