The Discharge Mechanism for Solid-State Lithium-Sulfur Batteries

Bridging the gap between academic research and industrial development in advanced all-solid-state lithium-sulfur batteries

The energy storage and vehicle industries are heavily investing in advancing all-solid-state batteries to overcome critical limitations in existing liquid electrolyte-based lithium-ion batteries, specifically focusing on mitigating fire hazards and improving energy density. All-solid-state lithium-sulfur batteries (ASSLSBs), featuring earth-abundant sulfur cathodes, high-capacity metallic lithium anodes, and non-flammable solid electrolytes, hold significant promise. Despite these appealing advantages, persistent challenges like sluggish sulfur redox kinetics, lithium metal failure, solid electrolyte degradation, and manufacturing complexities hinder their practical use. To facilitate the transition of these technologies to an industrial scale, bridging the gap between fundamental scientific research and applied R&D activities is crucial. Our review will address the inherent challenges in cell chemistries within ASSLSBs, explore advanced characterization techniques, and delve into innovative cell structure designs. Furthermore, we will provide an overview of the recent trends in R&D and investment activities from both academia and industry. Building on the fundamental understandings and significant progress that has been made thus far, our objective is to motivate the battery community to advance ASSLSBs in a practical direction and propel the industrialized process.

Order-Disorder Phase Transition and Ionic Conductivity in a Li2B12H12 Solid Electrolyte

Temperature-induced phase transitions and ionic conductivities of Li2B12H12 and LiCB11H12 were simulated with the use of machine learning interatomic potentials based on van der Waals-corrected density functional theory (rev-vdW-DF2 functional). The simulated temperature of order-disorder phase transition, lattice parameters, diffusion, ionic conductivity, and activation energies are in good agreement with experimental data. Our simulations of Li2B12H12 uncover the importance of the reorientational motion of the [B12H12]2- anion. In the ordered α-phase (T < 625 K), these anions have well-defined orientations, while in the disordered β-phase (T > 625 K), their orientations are random. In vacancy-rich systems, its complete rotation was observed, while in the ideal crystal, the anions display limited vabrational motion, indicating the static nature of the phase transition without dynamic disordering. The use of machine learning interatomic potentials has allowed us to study large systems (>2000 atoms) in long (nanosecond-scale) molecular dynamics runs with ab initio quality.

Promoting favorable interfacial properties in lithium-based batteries using chlorine-rich sulfide inorganic solid-state electrolytes

The use of inorganic solid-state electrolytes is considered a viable strategy for developing high-energy Li-based metal batteries. However, suppression of parasitic interfacial reactions and growth of unfavorable Li metal depositions upon cycling are challenging aspects and not yet fully addressed. Here, to better understand these phenomena, we investigate various sulfide inorganic solid electrolytes (SEs), i.e., Li_7-xPS_6-xCl_x (x = 0.6, 1.0, 1.3, 1.45, and 1.6), via ex situ and in situ physicochemical and electrochemical measurements. We found that the Cl distribution and the cooling process applied during the SE synthesis strongly influence the evolution of the Li|SE interface in terms of microstructure, interphase composition, and morphology. Indeed, for a SE with a moderate chlorine content (i.e., x = 1.3) and obtained via a slow cooling process after sintering, the Cl atoms are located on the surface of the SE grains as interconnected LiCl nanoparticles that form an extended LiCl-based framework. This peculiar microstructure facilitates the migration of the Cl ions to the Li|SE interface during electrochemical cycling, thus, favouring the formation of a LiCl-rich interphase layer capable of improving the battery cycling performances.

A mechanistic investigation of the Li10GeP2S12|LiNi1-x-yCoxMnyO2 interface stability in all-solid-state lithium batteries

All-solid-state batteries are intensively investigated, although their performance is not yet satisfactory for large-scale applications. In this context, the combination of Li₁₀GeP₂S₁₂ solid electrolyte and LiNi_1-x-yCo_xMn_yO₂ positive electrode active materials is considered promising despite the yet unsatisfactory battery performance induced by the thermodynamically unstable electrode|electrolyte interface. Here, we report electrochemical and spectrometric studies to monitor the interface evolution during cycling and understand the reactivity and degradation kinetics. We found that the Wagner-type model for diffusion-controlled reactions describes the degradation kinetics very well, suggesting that electronic transport limits the growth of the degradation layer formed at the electrode|electrolyte interface. Furthermore, we demonstrate that the rate of interfacial degradation increases with the state of charge and the presence of two oxidation mechanisms at medium (3.7 V vs. Li⁺/Li < E < 4.2 V vs. Li⁺/Li) and high (E ≥ 4.2 V vs. Li⁺/Li) potentials. A high state of charge (>80%) triggers the structural instability and oxygen release at the positive electrode and leads to more severe degradation.

Fundamental investigations at the electrode/electrolyte interface are essential for developing high-energy batteries. Here, the authors investigate the degradation mechanisms at the LGPS/NCM622 interface providing a quantitative model to interpret the interfacial resistance growth.