High-Quality 2D SnP₃ Nanosheets: Novel Flexible Electrode for Energy Storage Device Application with Wide Temperature Adaptivity

Tin triphosphide (SnP 3 ), featured with a 2D layered structure similar to rhombohedral black phosphorus (BP), has garnered significant attention for its potential application in high-performance energy storage devices due to the high electrical conductivity and fast ionic mobility superior to BP. Searching for a feasible strategy to produce high-quality SnP 3 materials is a vital prerequisite for industrial device applications; however, thus far it remains a technical challenge. In this work, we report the successful synthesis of large-size crystalline SnP 3 (8 mm in diameter and maximal grain size up to 42.6 μm) with a uniform elemental distribution by a high-pressure and high-temperature method, which exhibits good metallic behavior with electrical conductivity of 1.23 × 10 6 S m –1 at 300 K, above 3000 times higher than that of BP. High-quality 2D SnP 3 nanosheets (NSs) with a mean thickness of 6.2 nm and a largest lateral size of 9.5 μm are achieved by a liquid-phase exfoliation method. Our results show that the fabricated SnP 3 NSs composited by carbon nanotubes (CNTs) exhibit high electrochemical performance as flexible supercapacitor electrode materials with excellent cycle stability (88% retained capacitance after 20,000 cycles) and outstanding mechanical flexibility (72% capacitance remaining at a bending angle of 180°). The assembled supercapacitor with SnP 3 /CNT electrodes shows good temperature tolerance over a wide range from −50 to 60 °C, which displays 82.3% capacitance retention after 6,000 cooling–heating cycles. This study reveals that the produced SnP 3 NSs enable the development of reliable electrodes for flexible energy storage devices under extremely harsh conditions, including strong folding and low-temperature environments.