High energy density Li/Ni/Co-free O3/P2 sodium layered oxide intergrowth for sodium-ion batteries

Abstract

Sodium-ion batteries have attracted widespread interest due to the potential for providing safe and cheap energy storage. However, large scale use of Na-ion batteries is limited by insufficient performance from positive electrode materials, while also avoiding the use of expensive and toxic elements. Here, we present a bi-phasic sodium layered oxide material, O3/P2-Na0.75Mn0.35Fe0.35Ti0.1Al0.1Cu0.1O2, free of Li, Ni, and Co, which delivered high energy densities up to 420 Wh kg-1, discharge potential of 3.03 V, and high capacity retention of 80% over 70 cycles in half cells (292 Wh Kg-1 in full cells). Crucially, the high Na content is sufficient to provide high energy densities in full cell format. The intergrown nature of the material was confirmed by TEM and SAED analysis, while ex-situ XRD studies revealed the two phases undergo complementary c-parameter evolution, reducing overall volume change. These results demonstrate the potential for future commercialisation of bi-phasic materials utilising only Earth abundant elements.