A leaf-vein-like MnO2@PVDF nanofiber gel polymer electrolyte matrix for Li-ion capacitor with excellent thermal stability and improved cyclability

Abstract

Many anode materials are fabricated and their behaviors in Li-ion capacitors (LIC) are investigated to reduce the imbalance of the power capability between the electrodes, which greatly affects the cycle performance of LIC. Yet, the separator of LIC was left out of this contribution. In this work, the in-situ growth of manganese dioxide@polyvinylidene fluoride/tetrabutylammonium chloride (MnO2@PVDF/TBAC) leaf-vein-like nanofiber membrane (LVNM) with enhanced mechanical properties and excellent porosity was developed to effectively improve the ionic conductivity of the matrix and to improve the cycle performance of the LIC. Multi-walled carbon nanotubes (MWCNTs) was employed as reducing agent to produce in-situ growth of MnO2 nanosheets as the shell of the nanofibers, which not only further enhanced the LIC cyclability by providing additional capacity for LIC, but also avoided short circuit problem. The leaf-vein-like structure could greatly enhance the porosity and electrolyte retention of the matrix to accelerate ion transport between the two electrodes. Meanwhile, the in-situ growth of MnO2 nanosheets could promote the thermal stability of the gel polymer electrolyte (GPE) matrix and improve the LIC cycle stability. The MnO2@PVDF/TBAC matrix possessed excellent thermal stability (rose to 170 °C), high porosity (73%) and good ionic conductivity (2.95 * 10−3 S/cm). The LIC assembled with MnO2@PVDF/TBAC LVNM showed enhanced specific capacitance (19.5 F g−1), good rate capability, superior cycling stability (67.20% capacity retention after 10,000 cycles at 0.5 C), and high coulombic efficiency (~100%). Thus, our work provides an effective strategy for enhancing the thermal stability and cyclability of LIC.