Tailoring Interfaces in Solid-State Batteries Using Interfacial Thermochemistry and Band Alignment

Abstract

Solid-state lithium ion batteries have enhanced thermal stability compared to batteries using liquid electrolytes. Although their practical implementation is limited by undesired side reactions between the electrode and electrolyte, different modification strategies have been proposed to stabilize these reactive interfaces. These approaches have been primarily based upon bulk materials properties, however, which may not necessarily be representative of the chemistry at the solid/solid interface. Herein, first-principles calculations and X-ray scattering experiments are used to elucidate molecular-level reactivity and develop design principles for tailored interfaces based on surface and interfacial properties. Because of its well-known instability, the interface between the Li metal anode and the lithium lanthanum titanate (LLTO) solid electrolyte is applied as a model system. Density functional theory calculations are used to describe bulk, surface, and interfacial thermochemistry of the Li/LLTO system, and interfacial reconstruction is probed using ab initio molecular dynamics. These simulations of the Li/LLTO interface demonstrate facile decomposition concomitant with reduction of Ti 4+ ions. Based on further insights from computational analysis of the surface band edge positions, La 2 O 3 is proposed as an interlayer coating and is shown to provide an energetic barrier for interfacial charge transfer and decomposition reactions from X-ray reflectivity measurements and theoretical calculations. The findings in this work suggest that design strategies based on surface and interfacial properties can be used to kinetically stabilize electrode/electrolyte interfaces in solid-state batteries.

Benefits and Limitations of 226 Substitutions into Li-La-Ti-O Perovskites

“…In our previous study, we discovered that unsubstituted LLTO is a metastable phase and secondary phases are needed to stabilize it such phase is TiO 2 . Recently, Warburton et al in their computational study similarly found that LLTO is metastable . In the current study, we conclude that a number of substitutions stabilize the perovskite, enabling single-phase perovskites to form.…”

“…20 Recently, Warburton et al in their computational study similarly found that LLTO is metastable. 22 In the current study, we conclude that a number of substitutions stabilize the perovskite, enabling single-phase perovskites to form.…”

Lithium-Ion Diffusion in Perovskite-Type Solid Electrolyte Lithium Lanthanum Titanate Revealed by Pulsed-Field Gradient Nuclear Magnetic Resonance

“…Figure b compares the reported diffusion coefficient data attained by MD simulations ,,,− , with the present experimental data. With the exception of the earliest data, all the reported results agree with our experimental data within one order of magnitude.…”

“…Comparison of the diffusion coefficients of lithium lanthanum titanates with literature data and the present data. (a) Experimental diffusion coefficients using neutron radiography ( D NR ), PFG-NMR, , and QENS and (b) classical MD simulations ( D MD ), ,,− AIMD simulations ( D AIMD ), and machine learning interatomic potential MD simulations ( D MLMD ) …”

Electrochemical Stability Window and Electrolyte Breakdown Mechanisms of Lithium Lanthanum Titanate

“…15,16 Nonetheless, the thermodynamically stable potential range is limited, and first-principles calculations predict an electrochemical phase stability window of 1.75-3.7 V vs Li metal. [17][18][19] Consequently, application of more than 2 V bias to Li-ion blocking electrodes may result in electrochemical decomposition of the electrolyte. These first-principles calculations predict O 2 evolution and formation of La 2 Ti 2 O 7 and Li 4 Ti 5 O 12 at the anode, whereas Li-rich phases that contain Ti 3+ , like Li 7 Ti 11 O 24 , La 2 Ti 2 O 7 and Li 4 Ti 5 O 12 are the most stable phases at the cathode.…”