Prospects for high-valent nickel oxides as next-generation cathodes in primary alkaline batteries

The present review casts a spotlight on the primary alkaline battery, which has humbly powered many portable electronic devices in millions of homes for more than half a century despite its non-rechargeable nature. It has remained relevant to date because of its low cost, high-energy density and environmentally safe aqueous chemistry. High-valent nickel-based oxides have emerged as a promising alternative to the conventional MnO₂ cathode owing to their higher voltage, electronic conductivity and multi-electron redox capability. Despite their considerable merits, high-valent nickel oxides suffer from rapid self-discharge and limited chemical stability in concentrated alkaline electrolytes, hindering their practical application in primary alkaline batteries. In this review, we examine high-valent nickel oxide cathodes designed for primary alkaline batteries through a nanoscale lens to unravel the critical influence of the crystalline structure of nickel oxides, cathode-electrolyte interface design and diffusion kinetics of charge carriers on electrochemical performance. A comprehensive discussion of key cathode design strategies, namely, crystal lattice engineering, bulk nanosizing, surface coating, and multiphase cathode composites, serves to illustrate how the nanoscale phenomena within the cathode can be regulated to balance discharge capacity, rate capability, and storage stability. Through systematic integration and comparison of representative high-valent nickel-based cathodes reported to date, this review bridges structural features, chemical compositions and electrochemical performance to guide the rational development of next-generation Ni-Zn primary alkaline batteries, which can fulfil the demand for high power applications.