红磷/碳复合材料的制备及电化学性能研究

对比研究了不同制备方法、电解液组成和碳结构对红磷/碳复合材料电化学性能的影响。利用球磨法制备了红磷/活性炭(AC)复合材料, 其较差的首次库伦效率和循环容量表明活性物质红磷没有得到有效利用。对多种电解液进行了优选, 得到最优电解液为1 mol/L LiPF₆的EC/EMC/DMC (1: 1: 1 V/V)酯类电解液。通过气相沉积法制备了红磷/导电碳黑(BP2000)和红磷/活性炭两种复合材料。利用热重分析(TGA)、X射线衍射分析(XRD)、扫描电子显微镜(SEM)、BET比表面分析和循环伏安法(CV)对上述复合材料的形貌、结构和电化学性能进行了研究。结果表明: 含磷量为45%的红磷/活性炭复合材料充放电平台分别为1.0 V和0.75 V, 具有良好的可逆性。首次放电比容量和充电比容量分别为1500和1200 mAh/g, 库伦效率为82.5%。随后循环中库伦效率超过了97.5%。其1200 mAh/g的循环容量对应于2.8个电子的可逆反应。以第二次的稳定放电容量计算, 50次循环后容量保持率为75.0%。该复合材料较高的循环容量和良好的循环稳定性受益于无定形的活性物质红磷在活性炭导电基底孔结构中, 特别是微孔中的均匀分布。

Synthesis and Electrochemical Performance of Red Phosphorus/Carbon Composites

Effect of different fabrication methods, composition of electrolytes and various carbon substrates on the electrochemical performance of red phosphorus/carbon composites were studied. The red phosphorus (red P)/active carbon (AC) composites synthesized via ball milling method exhibited a low coulombic efficiency and cyclic capacity in the initial cycle, meaning poor utilization ratio of red P. It was found that the optimal electrolyte was 1 mol/L LiPF₆ in an ethyl carbonate (EC)/ethyl methyl carbonate (EMC)/dimethyl carbonate (DMC) mixed solvent. Red P/conductive carbon black (BP2000) and red P/AC composites were synthesized by a vapor deposition method. The morphology, structure and electrochemical performance of the as-prepared composites were characterized by thermal gravity analysis (TGA), X-ray diffraction (XRD), scanning electron microscope (SEM), BET surface analysis and cyclic voltammetry (CV). Electrochemical results reveal that the red P/AC composite (45%P) has a good reversibility with charge/discharge potential plateau at 1.0 V and 0.75 V. The initial discharge/charge special capacity is 1500 and 1200 mAh/g (calculated based on the weight of composites), respectively, showing initial coulombic efficiency of 82.5%. In the subsequent cycles the coulombic efficiency is over 97.5%. The stable cyclic capacity is related to 2.8-electron reaction. Relying on the stable discharge capacity in the second cycle, the capacity retention is calculated to be 75.0% after 50 cycles. The as-prepared red P/AC composites exhibit high cyclic capacity and good cyclic stability, which can be attributed to the uniform dispersion of amorphous red P in the porous structure of AC substrate, especially in the micropores.