Low Temperature Processing of Sulfide and Oxide Lithium Solid Electrolytes to Bridge Ionically Resistive Boundaries

Open Access
Author:
Berbano, Seth S
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
August 05, 2016
Committee Members:
  • Michael T Lanagan, Dissertation Advisor
  • Clive A Randall, Committee Chair
  • Donghai Wang, Committee Member
  • Susan E Trolier-Mckinstry, Committee Member
  • Dinesh Kumar Agrawal, Outside Member
  • Michael T Lanagan, Committee Chair
  • Clive A Randall, Dissertation Advisor
  • Carlo G Pantano, Committee Member
Keywords:
  • Ionic conductivity
  • Impedance spectroscopy
  • Lithium solid electrolyte
  • Grain boundary
  • Ceramic-polymer composites
Abstract:
Solid electrolytes are enabling materials for solid-state batteries. The theme of the contributions in this thesis center around low temperature processing of solid electrolytes and their resulting microstructures and ionic conductivities. Solid electrolytes are of interest for safer and more reliable replacements to liquid electrolytes at a wide range of operating temperatures. Using pressure-temperature-assisted densification (200 oC and 190 MPa), ionically resistive pores were minimized and ionic conductivity was maximized in x Li2S + (1-x) P2S5 (x = 0.70, 0.75, 0.80) solid electrolytes. For 0.70 Li2S + 0.30 P2S5, the powder-in-a-tube method was demonstrated as a method to fabricate 120 μm thin electrolytes with 10-3 S/cm ionic conductivities at 25 oC for large area format batteries. Using cold sintering, the solid electrolyte Li1+xAlxGe2-x(PO4)3 (x = 0.50) was densified to around 80% theoretical density in minutes at 120 oC and 400 MPa. In order to bridge ionically resistive grain boundaries, a 5 minute post-processing at 650 oC was required. High volume fractions of ceramic electrolyte could be co-sintered with polymer. Up to 95 vol. % Li1.5Al0.5Ge1.5(PO4)3 + 5 vol. % Poly(vinylidene fluoride hexafluoropropylene) composite electrolytes were cold sintered at 120 oC to densities exceeding 85 %. After soaking in 1 M LiPF6 ethylene carbonate-dimethyl carbonate (50:50 vol. %), composite electrolyte ionic conductivities at 25 oC reached 10-4 S/cm. Using cold sintering, processing and integration of solid electrolytes and other important technical ceramics may now be possible at polymer processing temperatures.