High-entropy layer assisting quasi-zero-strain cathodes for P2-Na2/3Ni1/3Mn2/3O2

Abstract

Layered transition metal oxides have attracted much attention for high-energy density sodium ion batteries. However, most P2-type layered oxides undergo a large volume change when they are charged at a deep desodiated state, accompanied by inevitable anisotropic stress, leading to poor structural stability and terrible ion transfer. In this work, a high entropy (HE) material with a robust structure and fast ion transportation was decorated on P2-Na2/3Ni1/3Mn2/3O2 (NM) layered oxides. The unique characteristics of HE shells with similar lattice constants could effectively depress particle crack and exfoliation through buffering severe lattice strains, thus leading to enhanced cycling stability and kinetic properties of the HE-NM electrode. In situ x-ray diffraction analysis confirms that the volume expansion of NM could be prominently restrained both under thermal treatments and electrochemical after HE decoration. The modified cathode exhibits a volume change as low as 0.5%. The findings highlight the significance and superiority of the HE coating layer and provide insight for the rational design of high-performance sodium-ion batteries.