Anode-free solid-state sodium batteries: navigating the challenges toward high energy density

Anode-free solid-state sodium batteries (AFSSBs) represent a transformative paradigm, positioning themselves as the ultimate avenue to unlock the high-energy-density potential of sodium-based electrochemistry. However, their practical implementation is hindered by fundamental challenges, including inadequate solid electrolyte properties, unstable interfacial contacts, and uncontrolled sodium deposition morphology. This review provides a timely and systematic analysis of this evolving frontier. Following a clear presentation of the existing challenges, we organize and discuss emerging strategies spanning three key areas: the development of novel electrolytes, the construction of stable interfaces, and the optimization of current collector substrates. The pivotal role of advanced characterization in elucidating underlying mechanisms is also underscored. In the final section, we outline a forward-looking roadmap, identifying critical research pathways to accelerate the translation of AFSSB technology from promising prototypes toward practical, next-generation energy storage solutions.