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

Tin triphosphide (SnP3), 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 SnP3 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 SnP3 (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 × 106 S m–1 at 300 K, above 3000 times higher than that of BP. High-quality 2D SnP3 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 SnP3 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 SnP3/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 SnP3 NSs enable the development of reliable electrodes for flexible energy storage devices under extremely harsh conditions, including strong folding and low-temperature environments.