Low Temperature Epitaxial LiMn₂O₄ Cathodes Enabled by NiCo₂O₄ Current Collector for High-Performance Microbatteries

Epitaxial cathodes in lithium-ion microbatteries are ideal model systems to understand mass and charge transfer across interfaces, plus interphase degradation processes during cycling. Importantly, if grown at <450 °C, they also offer potential for complementary metal-oxide-semiconductor (CMOS) compatible microbatteries for the Internet of Things, flexible electronics, and MedTech devices. Currently, prominent epitaxial cathodes are grown at high temperatures (>600 °C), which imposes both manufacturing and scale-up challenges. Herein, we report structural and electrochemical studies of epitaxial LiMn₂O₄ (LMO) thin films grown on a new current collector material, NiCo₂O₄ (NCO). We achieve this at the low temperature of 360 °C, ∼200 °C lower than existing current collectors SrRuO₃ and LaNiO₃. Our films achieve a discharge capacity of >100 mAh g^-1 for ∼6000 cycles with distinct LMO redox signatures, demonstrating long-term electrochemical stability of our NCO current collector. Hence, we show a route toward high-performance microbatteries for a range of miniaturized electronic devices.