Interfaces Comprehension at Electrodes on Sulfide-Based Solid State Batteries
Authors: Orue Ander , Cheddadi Manar , Zamperlin Nico , Tron Artur , Beutl Alexander , Oliver Pedro 
Published: August 2024

The increasing demand for safe, highly efficient, and cost-effective energy storage systems has accelerated the development of solid-state batteries (SSBs) with lithium metal (LiM) anodes. This technology offers remarkable advantages over conventional lithium-ion batteries with liquid electrolytes; from improved safety with non-flammable electrolyte to higher gravimetric and volumetric energy density enabled using LiM anode along with the multilayered bipolar stacking cell fabrication. The combination of solid electrolyte (SE) mechanical strength, flexibility, and safety against self-ignition allows for optimized battery design to meet the specific requirements.1–4

In recent years, soft, flexible, and easily deformable sulfide-based solid electrolytes have received significant attention due to their attractive mechanical properties, high conductivity, and feasibility of processing at ambient temperature, which makes them appealing candidates for upscaling the technology to large format devices.2,4,5 Despite the high ionic conductivity and attractive mechanical properties of sulfide-based SSBs, this chemistry still faces key challenges to encompass fast rate and long cycling performance, mainly arising from the dynamic and complex solid-solid interfaces. Solid-state materials are characterized by a significant impact of interface-related phenomena on their functional characteristics, such as mechanical properties, conductivity mechanisms, or electrochemical performance. For SSBs with ceramic or glass-ceramic electrolytes, the stacking of the composite cathode, the SE and the LiM anode leads to multiple interfaces from voids, cracks, secondary phases from chemical and electrochemical reactions and grain boundaries.6,7 As electrochemical kinetics is governed by the contact area at the interface, ensuring the adhesion between the electrolyte and active electrode materials is the key to obtain high performance devices, especially at fast rates.

The goal of the present work is to provide understanding on the complex solid-solid interfaces regulating sulfide-based battery performance. As shown in Figure 1, cells under different configurations with LPSCl, Li or In metal anodes, and LiNi0.6Mn0.2Co0.2O2 (NMC622)-based composite cathodes have been systematically studied aiming to bring insights on the dynamic interfaces at component level dominating processes during cell operation. From a multi-configurational approach and an advanced deconvolution of electrochemical impedance signals into distribution of relaxation times, we disentangle intricate underlying interfacial processes taking place at the battery components and that play major role on the overall performance. For the Li metal solid-state batteries, the cycling performance is highly sensitive to the chemomechanical properties of the cathode active material, the formation of the SEI, and processes ascribed to Li diffusion in the cathode composite and in the space-charge layer. The outcomes of this work aim to facilitate the design of sulfide solid-state batteries and provide methodological inputs for battery ageing assessment.

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Figure 1