Transforming stainless steel into multifunctional anode/current collector, less than 1.3 μm thick, thin-film Li-ion μ-battery is developed for microelectronics applications. Using time-of-flight secondary ion mass spectrometry, Li-ion plating/stripping on amorphous steel is demonstrated. This highly reduced structure battery is achieved via low-temperature sputtering.

This work presents a less than 1.3 μm thick, low-cost, and ambient-condition-processable Li-ion μ-battery by transforming stainless steel (SS) which is the structural battery component into a multifunctional current collector and the anode. Radio frequency (rf) sputtering of SS under room temperature (RT) and moderate vacuum forms amorphous mix of metal, carbon, and metal oxide providing both electrical conductivity and the ability to host lithium ions. This novel approach breaks the predominant use of SS as a structural component. The full-cell anode-free-all-solid-state μ-battery is fabricated using an RT, layer-by-layer rf-sputtering process, depositing SS, lithium iron phosphate (LiFePO₄), and lithium phosphate (Li₃PO₄) on a silicon wafer. Probing into the μ-battery using time-of-flight secondary ion mass spectrometry confirms successful plating and stripping of lithium on the amorphous SS during cycling and the formation of solid electrolyte interface. A real-time test demonstrates that a single cell μ-battery powers a red-light emitting diode for μ-seconds. This work demonstrates the feasibility of designing a functional μ-battery on a silicon wafer using only two common battery materials and one structural material, eliminating the need for complex procedures. The battery can seamlessly integrate into circuits of micro-power sources for low-power devices.