Development of Solid Electrolytes for Structural Supercapacitors

Abstract

Structural supercapacitors are multifunctional energy storage devices that can store electrical energy and bear the mechanical loading simultaneously. The utilization of composite materials in supercapacitor offers the opportunity to improve the electrochemical properties and stability of electricity supply system. In the present work, NASCION-type lithium conducting solid electrolyte Li1.4Al0.4Ti1.6(PO4)3 which was prepared by the sol-gel method was used to provide high ionic conductivity at room temperature and physical support. The influence of milling process of LATP electrolyte and the influence of the sintering temperature in the atmosphere of air/nitrogen on electrochemical properties of 1-layer pellets were investigated. Results show that BM4h (planetary ball milling with ethanol for 4h) is considered as the optimal milling process for LATP materials; The highest ionic conductivity of 1-layer pellet was obtained by sintering in air at 950°C (4.23 × 10−4 S/cm) and in nitrogen at 700°C (4.07×10−5 S/cm) respectively. Additionally, LATP/CNT composite electrode materials are combined with pure LATP electrolyte to be pressed into 2-layers pellets and 3-layer pellets respectively to form a functioning structural electrochemical double layer capacitor composite. Sintering at 700°C in nitrogen was chosen to be the optimal condition for 2-layers pellets and 3-layers pellets. As a results, dramatic improvements in capacitance has been achieved after introducing CNT into devices. For 2-layers pellets, by varying the parameters of CNT-loading, mixing method and weight ratio of layers in LATP/CNT composite, the highest CNT normalized capacitance with 0.72 F/gCNT and also high ionic conductivity with 9.88 × 10−5 S/cm were obtained (by devices with 1 wt% CNT-loading; mixed by planetary ball mill; m(LATP/CNT composite layer) : m(pure LATP layer) = 0.080 g/0.1810 g (y1)). Based on the optimized parameters of 2-layers pellets, a maximum CNT normalized capacitance of 5.12 F/gCNT is achieved in 3-layers pellet. The importance of microstructures for both electrolyte and electrode materials was highlighted. CV and EIS tests, laser diffraction spectrometer, XRD, SEM were used to characterize the products.