Anti-freezing, high-voltage, and ultra-stable micro-supercapacitors enabled by phase engineering of 2D SiP2 in LiCl-DMSO electrolyte

Abstract

To meet the growing demand for advanced energy storage in flexible wearable electronics and microelectronics, this work focuses on the design of high-performance micro-supercapacitors (MSCs) with significantly improved cryogenic tolerance, wide voltage window, and long-term cycling stability through a synergistic optimization strategy coordinating electrode materials and electrolyte formulation. Here, cubic-phase and orthorhombic-phase SiP2 electrode materials were successfully prepared by the high-pressure and high-temperature (HPHT) techniques and the flux growth methods. Meanwhile, a LiCl-DMSO binary gel electrolyte was developed through the incorporation of dimethyl sulfoxide (DMSO) as an organic solvent modifier into a LiCl-based electrolyte matrix. The modified electrolyte endows the MSCs with remarkable freeze resistance (-30 °C) and a high operating voltage (2 V), while the phase-engineering strategy enables the orthorhombic SiP2 to exhibit superior electrochemical performance compared to black phosphorus. The MSC based on orthorhombic-phase SiP2 achieves a specific capacitance of 12.39 mF cm-2 (10.25 F g-1) at a voltage of 2 V, which is significantly higher than that of the MSC based on cubic-phase SiP2 (8.42 mF cm-2). Additionally, the orthorhombic-phase SiP2-based MSC demonstrates exceptional long-term cycling stability: no obvious capacitance degradation is observed after 20,000 cycles, and the capacitance retention rate remains 82.37% even after 30,000 cycles. It can also operate stably at a low temperature of -30 °C with a capacitance retention rate of 74.81%. Through the synergistic effect of phase structure engineering and electrolyte optimization, this work establishes a new paradigm for the development of micro-energy storage devices with high reliability and wide temperature range applicability.