Electro-chemo-mechanical modeling of solid-state batteries

Engineering Solution-Processed Non-Crystalline Solid Electrolytes for Li Metal Batteries

Non-crystalline Li-ion solid electrolytes (SEs), such as lithium phosphorus oxynitride, can uniquely enable high-rate solid-state battery operation over thousands of cycles in thin film form. However, they are typically produced by expensive and low throughput vacuum deposition, limiting their wide application and study. Here, we report non-crystalline SEs of composition Li-Al-P-O (LAPO) with ionic conductivities > 10^-7 S cm^-1 at room temperature made by spin coating from aqueous solutions and subsequent annealing in air. Homogenous, dense, flat layers can be synthesized with submicrometer thickness at temperatures as low as 230 °C. Control of the composition is shown to significantly affect the ionic conductivity, with increased Li and decreased P content being optimal, while higher annealing temperatures result in decreased ionic conductivity. Activation energy analysis reveals a Li-ion hopping barrier of ≈0.4 eV. Additionally, these SEs exhibit low room temperature electronic conductivity (< 10^-11 S cm^-1) and a moderate Young's modulus of ≈54 GPa, which may be beneficial in preventing Li dendrite formation. In contact with Li metal, LAPO is found to form a stable but high impedance passivation layer comprised of Al metal, Li-P, and Li-O species. These findings should be of value when engineering non-crystalline SEs for Li-metal batteries with high energy and power densities.

Insights into interfacial chemistry of Ni-rich cathodes and sulphide-based electrolytes in all-solid-state lithium batteries

All-solid-state lithium batteries (ASSLBs) have attracted increasing attention recently because they are more safe and have higher energy densities than conventional lithium-ion batteries. In particular, ASSLBs composed of Ni-rich cathodes, sulphide-based solid-state electrolytes (SSEs) and lithium metal anodes have been regarded as the most competitive candidates. Ni-rich cathodes possess high operating potential, high specific energy and low cost, and sulphide-based SSEs have excellent ionic conductivity comparable to that of liquid electrolytes. However, severe parasitic reactions and chemo-mechanical issues hinder their practical application. Herein, the structure, ionic conductivity, chemical or electrochemical stability and mechanical property of sulphide-based SSEs are introduced. Critical interfacial problems between Ni-rich cathodes and sulphide-based SSEs, including chemical or electrochemical parasitic reactions, space charge layer effect, mechanical stress and contact loss, are summarised. The corresponding solutions including coating layer construction and structure design are expounded. Finally, the remaining challenges are discussed, and perspectives are outlined to provide guidelines for the future development of ASSLBs.

Review on Modeling for Chemo-mechanical Behavior at Interfaces of All-Solid-State Lithium-Ion Batteries and Beyond

The all-solid-state lithium-ion battery (ASSLIB) is a promising candidate for next-generation rechargeable batteries due to its high-energy density and potentially low risk of fire hazard compared with that of traditional lithium-ion batteries. However, the widespread application of ASSLIBs is unfortunately hindered by new critical issues arising from the all-solid-state structure, especially mechanical instability. First, employing solid electrolytes (SEs) in ASSLIBs is accompanied by a reduction of cell compliance. The SEs are normally much stiffer than liquid electrolytes, and they are no longer able to effectively accommodate the swelling and shrinkage of active particles during (de)lithiation. This may lead to the interfacial delamination and fragmentation of the active particles and electrolytes. In addition, although SEs are expected to mechanically suppress the growth of lithium dendrites at the lithium metal (Li)/SE interface, lithium dendrites are still observed frequently in battery cells employing SEs even with high stiffness. Hence, comprehending these phenomena and providing solutions to these issues are crucial to promote the application of ASSLIBs. A number of theoretical models have been developed to investigate the chemo-mechanical behavior of ASSLIBs in recent decades. This mini-review aims to comprehensively review them, focusing on the mechanically informed modeling on two main topics: (1) lithium dendrite initiation at the Li/SE interface and propagation through SEs and (2) delamination and fragmentation within a composite electrode due to (de)lithiation of an active particle. With this mini-review, we want to supply a more nuanced understanding for chemo-mechanical behavior at different interfaces in ASSLIBs from a modeling perspective.

Stability, Elastic Properties, and the Li Transport Mechanism of the Protonated and Fluorinated Antiperovskite Lithium Conductors

Lithium-rich antiperovskites (APs) have attracted significant research attention due to their ionic conductivity above 1 mS cm^-1 at room temperature. However, recent experimental reports suggest that proton-free lithium-rich APs, such as Li₃OCl, may not be synthesized using conventional methods. While Li₂OHCl has a lower conductivity of about 0.1 mS cm^-1 at 100 °C, its partially fluorinated counterpart, Li₂(OH)_0.9F_0.1Cl, is a significantly better ionic conductor. In this article, using density functional theory simulations, we show that it is easier to synthesize Li₂OHCl and two of its fluorinated variants, i.e., Li₂(OH)_0.9F_0.1Cl and Li₂OHF_0.1Cl_0.9, than Li₃OCl. The transport properties and electrochemical windows of Li₂OHCl and the fluorinated variants are also studied. The ab initio molecular dynamics simulations suggest that the greater conductivity of Li₂(OH)_0.9F_0.1Cl is due to structural distortion of the lattice and correspondingly faster OH reorientation dynamics. Partially fluorinating the Cl site to obtain Li₂OHF_0.1Cl_0.9 leads to an even greater ionic conductivity without impacting the electrochemical window and synthesizability of the materials. This study motivates further research on the correlation between local structure distortion, OH dynamics, and increased Li mobility. Furthermore, it introduces Li₂OHF_0.1Cl_0.9 as a novel Li conductor.