Impurity-vibrational entropy enables quasi-zero-strain layered oxide cathodes for high-voltage sodium-ion batteries

Layered transition metal oxides based on cationic/anionic redox have gained much attention for high-energy-density sodium ion batteries (SIBs). However, irreversible oxygen activity and unstable crystal structure lead to fast capacity fading and undesired rate performance, limiting its large-scale commercial application. Based on the solid-state physics theory, here we demonstrate that the electrochemical capability in P2-type Na2/3Ni1/3Mn2/3O2 cathode can be significantly improved when impurity-vibrational entropy is increased by simultaneously constructing surface ZrO2 coating and Zr4+ doping ([email protected]). In-situ and ex-situ X-ray diffraction (XRD) verifies that quasi-zero-strain [email protected] cathode maintains P2 phase structure during the charging/discharging process, achieving an ultra-low volume change (1.18%) upon Na+ entire extraction at a high cut-off voltage of 4.5 V. Besides, according to First-principles calculations, we first investigate that the oxygen vacancy formation energy of [email protected] (−2.11 eV) is higher than that of sample P2-NaNM (−2.61 eV), strongly indicating stable and reversible anionic redox reaction. As a result, [email protected] material reveals highly Na storage performance, retaining 86% capacity retention after 1000 cycles at the rate of 5 C within the voltage range of 2.5 − 4.0 V, delivering reversible capacity of 132 mA h g−1 after 50 cycles within 2.0 − 4.5 V.