Abstract:

Phosphorus-doped hard carbon/MnO _x composites were synthesized by hydrothermal treatment and one-step pyrolysis using coconut shell as a biomass carbon source, phosphoric acid as a phosphorus source and a pore-forming agent, and manganese sulphate as a manganese source, and were used in the field of supercapacitors. The effects of the additions of phosphoric acid and manganese sulfate on the structural and electrochemical properties of the composites were analyzed, and the mechanism of the enhancement of the electrochemical properties of phosphorus-doped hard carbon/MnO _x composites was investigated. The etching of phosphoric acid contributed to the formation of a multistage pore structure of microporous-mesoporous composite, which provided not only the composites with bilayer capacitance, but also space for the growth of MnO _x and reduced its agglomeration, thus exposing more pseudocapacitive active sites. Phosphorus doping not only increased the layer spacing of the hard carbon and improved the defects in its structure, but also introduced phosphorus-containing functional groups such as C—P\stackrel{}{̿}O, C—P—O and C/P—O—P, which synergistically interacted with MnO _x to further enhance its electrochemical performance. The specific capacitance of the composite was as high as 302F/g, and the capacitance retention was still 70.5% after 10000 cycles at 10A/g. When assembled into a symmetric supercapacitor, the power density was up to 400W/kg at the energy density of 156Wh/kg, which indicated that it had a great potential for application in the field of supercapacitors.

Key words: coconut shell, phosphorus doping, MnO _x, hard carbon, pseudocapacitance

摘要：

以椰壳为生物质碳源，磷酸为磷源和造孔剂，硫酸锰为锰源，通过水热处理和一步热解法合成磷掺杂硬碳/MnO _x 复合材料，并将其用于超级电容器中。分析了磷酸和硫酸锰的添加对复合材料结构和电化学性能的影响，并对复合材料电化学性能提升的机制进行了研究。磷酸的刻蚀作用有助于形成微孔-介孔复合的多级孔结构，这不仅可为复合材料提供双电层电容，也可为MnO _x 的生长提供空间，减少其团聚，从而暴露出更多的赝电容活性位点。磷掺杂不仅可以增加硬碳的层间距，增加其结构中的缺陷，也会引入C—P\stackrel{}{̿}O、C—P—O和C/P—O—P等含磷官能团，与MnO _x 发生协同作用，进一步提升其电化学性能。复合材料的比电容高达302F/g，在10A/g条件下循环10000次后，电容保持率为70.5%；组装成对称超级电容器，在能量密度为156Wh/kg时，功率密度可达400W/kg，表明其在超级电容器领域具有巨大的应用潜力。

关键词: 椰壳, 磷掺杂, MnO _x, 硬碳, 赝电容