Enabling High Energy Density All-Solid Batteries

Advances in hybrid and electric vehicle technologies combined with a demand for green initiatives have motivated necessary diversification in energy storage research. To achieve customer expectations for hybrid and electric vehicles, new battery systems with higher energy densities, power densities and cycle life than the current state-of-art Lithium (Li)-ion battery are needed. Post Li-ion battery systems, especially those focused on the utilization of Li metal have recently come to the forefront of research. The ability to directly utilize Li metal anodes in rechargeable batteries presents itself as an ideal situation via the accessibility of a maximum possible theoretical specific capacity (3860 mAh/g) in comparison to commercially used anodes (e.g. graphite – 380 mAh/g). Hence, significant efforts in recent literature have targeted the development of robust Li metal anode systems coupled with a sulfur cathode. Tatsumisago <i>et al</i>.¹ illustrated and impressive initial cycling results using lithium-indium alloy anode, a lithium iodide/lithium sulfide solid-solution cathode, and a solid sulfide electrolyte: over 1000 mAh/g at 2C cycling for over 2000 cycles. Inspired by the results, developing all solid Li-S batteries presents hope for a high-energy density battery.<br/>The potential benefits of solid-state electrolytes, such as polymer electrolytes, gel electrolytes and ion-conducting ceramics electrolytes, are wide-operating windows, active material dissolution prevention and metal dendrite inhibition. However, low ionic conductivity and interfacial stability require continued development to achieve a viable energy storage system. Recently, ionic conductivities rivaling liquid based-systems have been observed for the sulfide-based, glass-ceramic L₁₀GeP₂S₁₂ (LGPS),² encouraging continued research into solid-state batteries using sulfide-based solid-electrolytes. The major road-block to enabling AS-LiS batteries lies is the capability to utilize lithium metal. Researchers have recently observed the decomposition of sulfide electrolytes in contact with lithium metal, as well as the tendency for the active metal to plate within the electrolyte layer and create electrical shorts.^3,4<br/>Here, we present a study into the chemo-mechanical transformations within lithium thiophosphates and at their solid-solid interfaces. Tandem analytical <i>ex-situ</i> and <i>in-situ</i> studies via X-ray tomography and transmission electron microcopy are used to reveal the interfacial interactions and failure modes between Li metal and lithium thiophosphates, the deposition and dissolution properties of Li metal from these electrolytes, and the effects of the deposition and dissolution properties on the bulk electrolyte structure. Additionally, we will present the electrochemical discharge mechanism of solid state Li-S batteries using glass-ceramic, sulfide-based solid-electrolyte and a lithium metal anode. The solid-state reactions of the active materials with the solid-electrolyte are evidenced through X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and thermal analysis.<br/><br/>[1] Tatsumisago, M. <i>et al</i>. Adv. Sustainable Syst. 2017, 1700017, 1-6.<br/>[2] Kanno, R. <i>et al</i>. Nat. Mater. 2011, 10, 682-686.<br/>[3] Sakamoto, J. <i>et al</i>. Electrochimica Acta 2017, 237, 144-151.<br/>[4] Janek <i>et al.</i> Solid-State Ionics 2016, 286, 24-33.