Luca Magagnin, Elena Lopez Pazos, Luca Nobili, Politecnico di Milano, Milano, Italy
Energy supply remains one of the main limitations to the development and autonomy of modern microelectronic devices. As systems continue to miniaturize while integrating increasing functionality, conventional power sources struggle to satisfy the stringent requirements in terms of footprint, energy density, power capability, and long-term stability. In this context, micro lithium-ion batteries (μLIBs) represent a promising solution, offering a favorable balance between energy and power densities. In particular, anode-free configurations enable simplified architectures, improved safety, and enhanced volumetric efficiency, making them highly attractive for on-chip integration.
This work focuses on the development and investigation of an anode-free, thin-film μLIB designed for on-chip applications. All functional layers were deposited by sputtering, a technique widely adopted in microbattery fabrication due to its compatibility with microelectronic processing. LiFePO₄ was selected as cathode material because of its good theoretical capacity, chemical stability, material abundance, and environmental compatibility, combined with a moderate operating potential. LiPON was employed as solid-state electrolyte due to its excellent electrochemical stability and its ability to suppress lithium dendrite growth, which is critical in anode-free systems. Experiments were devoted to optimizing LiFePO₄ thin-film deposition, achieving stable plasma conditions and uniform coatings. As-deposited films were amorphous, requiring post-deposition annealing to promote crystallization and electrochemical activity. Further optimization was pursued through carbon co-sputtering to enhance electronic conductivity and overall cathodic performance. Subsequently, full cell stacks incorporating LiPON were fabricated, enabling compatibility assessment and electrochemical characterization of the complete microbattery. The results demonstrate the feasibility of integrating optimized LiFePO₄ thin films into anode-free solid-state μLIB architectures, highlighting key processing parameters influencing cathode performance and interfacial stability.