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 high-pressure and high-temperature (HPHT) techniques and 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 at 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.