Publication Date

2017-12-12

Availability

Embargoed

Embargo Period

2019-12-12

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Mechanical Engineering (Engineering)

Date of Defense

2017-11-16

First Committee Member

Xiangyang Zhou

Second Committee Member

Weiyong Gu

Third Committee Member

Hongtan Liu

Fourth Committee Member

Chunlei Wang

Abstract

The present dissertation focuses on three different topics of supercapacitor (SC) technology: 1) combination of galvanic cell components into SCs to mitigate the problem of self-discharge, 2) development of an all-solid-state SC/battery based on a superionic ceramic electrolyte and 3) mechanical-electrochemical study of a composite structural SC. A new hybrid supercapacitor SC with the galvanic cell materials is proposed to mitigate the self-discharge problem and to increase the storage-life. The galvanic cell components in the hybrid SC can provide a micro-current to compensate the self-discharge current. The hybrid SC was fabricated with active carbon electrodes, a polyvinylidene fluoride (PVDF)/lithium trifluoromethanesulfonate (LiTFS) membrane with 1.5 M zinc sulfate (ZnSO4) aqueous electrolyte. Copper and zinc foils were used as the current collectors and as the galvanic cell cathode and anode. The hybrid SC exhibited a greater maximum specific capacitance and specific energy than a baseline SC with gold foil collectors and a symmetrical design. The capacitance retention of the hybrid SC was 80% after 2000 cycles. In a month, the open circuit voltage of the charged hybrid SC declined slightly from initial 0.90 V to 0.85 V. The steady-state leakage current density was as low as 1.57 μA cm-2 at 0.90 V. The equations derived from the equivalent circuit models fit well to the self-discharge experimental data. In the second part of the dissertation, a high power all-solid-state SC with RbAg4I5 is proposed and fabricated without sealing. RbAg4I5 powders can conduct silver ions between electrodes and provide the energy storage simultaneously. The ionic conductivity of RbAg4I5 powders was 0.21 S cm-1 greater than or comparable to that of a typical liquid electrolyte. The all-solid-state SC can work in oxygen and moisture environment at room temperature and show the hybrid behavior including SC and battery. The maximum specific energy can reach more than 60 Wh kg-1. The charge capacity of the all-solid-state SC dropped to 16% of the maximum capacity after 200 cycles and the capacity can be recovered by an annealing process at 150°C for 12 hours. This SC can achieve both high specific power and energy simultaneously by reducing the thicknesses of the electrodes and the electrolyte. The last part is on mechanical-electrochemical study of a composite structural SC based on an epoxy based adhesive polymer electrolyte. The epoxy based adhesive polymer electrolyte was prepared using PVDF, LiTFS and epoxy. The maximum conductivity of the epoxy based adhesive polymer electrolyte can achieve 10-2 S cm-1. Structural SCs were fabricated using a vacuum bagging method. The specific energy can reach 2.64 Wh kg-1 and the ultimate tensile strength (UTS) can reach 80 MPa. The response of electrochemical performance of the structural SCs to in-plane tensile stress was studied. Before fracture, both the specific power and the specific energy increases slightly.

Keywords

Self-discharge; Galvanic cell; Rubidium silver iodide; Mechanical-electrochemical; Structural supercapacitor

Available for download on Thursday, December 12, 2019

Share

COinS