Owing to their low electronegativity, excellent electrical conductivity, high specific capacitance, and rich electrochemical redox sites, various transition metal sulfides have attracted significant attention as promising pseudocapacitive electrode materials for supercapacitors. However, their relatively poor electrical conductivity and large volume changes seriously hinder their commercial applications. Herein, ternary Co_0.33Fe_0.67S₂ nanoparticles are in situ embedded between graphene nanosheets through a facile one-step hydrothermal approach to form a sandwich-like composite. Because of its unique and robust structure, the graphene nanosheet/Co_0.33Fe_0.67S₂ composite (GCFS-0.33) exhibits a high specific capacitance (310.2 C g^–1 at 2 mV s^–1) and superb rate capability (61.8% at 200 mV s^–1) in 3 M KOH aqueous electrolyte. Using transition metal sulfides simultaneously as both positive and negative electrodes, for the first time, an aqueous asymmetric supercapacitor (ASC) was fabricated with the GCFS-0.33 composite as the negative electrode and sulfidized graphene/CoNiAl-layered double hydroxides as the positive electrode with well-separated potential windows. Our fabricated ASC delivered an excellent energy density of 66.8 Wh kg^–1 at a power density of 300.5 W kg^–1 and still retained 13.1 Wh kg^–1 even at a high power density of 29.4 kW kg^–1, which is highly comparable with that of previously reported transition-metal-sulfide-based ASC devices. Moreover, the as-fabricated ASC cell displays impressive long-term cycling stability with a capacitance retention of 102.2% relative to the initial capacitance after 10 000 cycles. This versatile synthetic strategy can be readily extended to synthesize other transition-metal-sulfide-based composites with excellent electrochemical performances.

中文翻译：

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嵌入石墨烯纳米片中的三元过渡金属硫化物，作为高性能不对称超级电容器的阳极和阴极

由于其低电负性，优异的导电性，高比电容和丰富的电化学氧化还原位点，各种过渡金属硫化物作为有前途的超级电容器伪电容电极材料备受关注。然而，它们相对较差的电导率和大的体积变化严重阻碍了它们的商业应用。在此，通过简便的一步水热法将三元Co _0.33 Fe _0.67 S ₂纳米颗粒原位嵌入石墨烯纳米片之间，以形成夹心状复合材料。由于其独特而坚固的结构，石墨烯纳米片/ Co _0.33 Fe _0.67 S ₂复合材料（GCFS-0.33）表现出高的比电容（310.2 C g还^-1在2毫伏小号^-1）和高超的速率能力（在200mV小号61.8％^-1中的3M KOH水溶液电解质）。首次同时使用过渡金属硫化物作为正电极和负电极，以GCFS-0.33复合材料为负电极，硫化石墨烯/ CoNiAl层状双氢氧化物为正电极，制备了不对称水超级电容器（ASC）。潜在窗口的分隔良好。我们制造的ASC在300.5 W kg ^–1的功率密度下可提供66.8 Wh kg ^–1的出色能量密度，并仍保持13.1 Wh kg ^–1的功率密度即使在29.4 kW kg ^–1的高功率密度下，也可以与以前报道的基于过渡金属硫化物的ASC设备进行高度比较。此外，所制造的ASC电池具有令人印象深刻的长期循环稳定性，相对于10000次循环后的初始电容，其电容保持率为102.2％。这种通用的合成策略可以轻松扩展，以合成具有出色电化学性能的其他基于过渡金属硫化物的复合材料。