Design of a stable and voidless surface region by intensive subsurface zirconium doping for a high performance nickel-rich cathode in sodium-ion batteries

O3-type sodium-ion cathodes have emerged as promising candidates for next-generation energy storage systems, owing to their notable specific capacity and cost-effectiveness. Among them, nickel-rich materials have garnered particular interest due to their high specific capacity in high voltage operating environments facilitated by the redox reactions of nickel. However, their commercialization is impeded by several challenges that include side reactions between Ni4+ and the electrolyte under high voltage conditions, oxygen evolution during high-voltage electrochemical tests and degradation upon exposure to CO2 and H2O in humid air. Herein, we present an innovative approach to mitigate these issues by pre-coating the precursor surface with a zirconium (Zr) source using polyacrylic acid (PAA), followed by calcination to achieve controlled surface doping through diffusion near the surface of the nickel-rich material. This study offers a novel solution to the critical issues hindering the commercialization of nickel-rich sodium-ion cathodes, paving the way for their potential application in advanced energy storage technologies. The subsurface Zr doping induced by diffusion in NaNi0.8Mn0.2O2 is used for the Na-ion battery cathode. A uniform subsurface Zr-rich region aided by polyacrylic acid facilitates the primary particle growth of the cathode.