Unlocking the potential of P3 structure for practical Sodium-ion batteries by fabricating zero strain framework for Na+ intercalation

Layered sodium transition metal oxides (NaTMO 2 ) have garned considerate attention as candidates for cathode materials in practical Na-ion batteries because of their potentially high energy density and operating voltage. Among the several categories (P2, P3, O3) of layered NaTMO 2 materials, P3 type cathodes are least studied due to the fast capacity/voltage fading induced by P3-O3 phase transition, as shown by the very few compositions visited in previous reports. It is highly desirable to stabilize the P3 phase throughout the sodium extraction/insertion process as P polytype allows facile migration of Na + -ions between two adjacent prismatic sites. In this work, we synthesized a phase pure P3-Na 0.75 Mg 0.08 Co 0.10 Ni 0.2 Mn 0.60 O 2 (P3-MNCM) via the incorporation of Mg, while successfully maintains the P3 structure during the charging/discharging process. This together with good ionic conductivity , endows good structural reversibility, and consequently leads to superior cycling performance and rate performance than undoped composition. In situ X-ray diffraction (XRD) further verifies that P3-MNCM cathode demonstrates a near zero strain feature. Of special importance is that the P3-O3 phase transition is effectively suppressed with the incoporation of Mg into the transition metal layer. These findings demonstrate the potential of P3 structure as a promising choice for Na ion cathode materials, which open a feritile avenue and will hopefully inspire more endeavors in the exploration of high performance sodium ion batteries.