Liquid Madelung energy accounts for the huge potential shift in electrochemical systems

Practical issues toward high-voltage aqueous rechargeable batteries

This review offers a critical and exhaustive examination of the current state and innovative advances in high-voltage Li, Na, K, and Zn aqueous rechargeable batteries, an area poised for significant technological breakthroughs in energy storage systems. The practical issues that have traditionally hampered the development of aqueous batteries, such as limited operating potential windows, challenges in stable solid-electrolyte interphase (SEI) formation, the need for active materials optimized for aqueous environments, the misunderstood intercalation chemistry, the unreliable assessment techniques, and the overestimated performance and underestimated physicochemical and electrochemical drawbacks, are highlighted. We believe that this review not only brings together existing knowledge but also pushes the boundaries by providing a roadmap for future research and development efforts aimed at overcoming the longstanding challenges faced by the promising aqueous rechargeable batteries.

Electronic Localization Enables Long-Cycling Sulfides-Based All-Solid-State Lithium Batteries

Argyrodite-based sulfide electrolytes have received considerable attention in all-solid-state lithium metal batteries owing to their high ionic conductivity and good mechanical property. However, the reactivity between sulfide electrolytes and lithium anode leads to continuous interfacial reactions and dendrites growth, which severely hinders their practical applications. We propose an electron localization strategy by modulating the d-p orbital hybridization within the PS4 tetrahedral structure of Li6PS5Cl through homogeneous incorporation of yttrium (Y) and oxygen (O). The introduction of Y strengthens the Madelung energy with sulfur (S) atom and induces the electronic localization of S atom, which suppresses the interaction between lithium metal and S atom of the tetrahedron. The air-stability is also enhanced due to oxygen introduction. Furthermore, the in situ formation of Li2O interphase acts as a protective barrier, synergistically mitigating the interfacial reactions between lithium metal and Li6PS5Cl. The Li symmetric cell with the modulated Li6PS5Cl electrolyte achieves stable lithium plating/stripping for over 4800 h. The all-solid-state batteries with LiCoO2/Li-In electrode display a remarkable long cycle performance with 100% retention after 1300 cycles at 0.5 C. This study presents a distinct strategy that employs the electron localization driven by modulating orbital hybridization to achieve ultrastable interface in sulfide-based all-solid-state lithium batteries.

Efficient prediction of the local electronic structure of ionic liquids from low-cost calculations

Understanding and predicting ionic liquid (IL) electronic structure is crucial for their development, as local, atomic-scale electrostatic interactions control both the ion-ion and ion-dipole interactions that underpin all applications of ILs. Core-level binding energies, EB(core), from X-ray photoelectron spectroscopy (XPS) experiments capture the electrostatic potentials at nuclei, thus offering significant insight into IL local electronic structure. However, our ability to measure XPS for the many thousands of possible ILs is limited. Here we use an extensive experimental XPS dataset comprised of 44 ILs to comprehensively validate the ability of a very low-cost and technically accessible calculation method, lone-ion-SMD (solvation model based on density) density functional theory (DFT), to produce high quality EB(core) for 14 cations and 30 anions. Our method removes the need for expensive and technically challenging calculation methods to obtain EB(core), thus giving the possibility to efficiently predict local electronic structure and understand electrostatic interactions at the atomic scale. We demonstrate the ability of the lone-ion SMD method to predict the speciation of halometallate anions in ILs.

From Ab Initio to Instrumentation: A Field Guide to Characterizing Multivalent Liquid Electrolytes

In this field guide, we outline empirical and theory-based approaches to characterize the fundamental properties of liquid multivalent-ion battery electrolytes, including (i) structure and chemistry, (ii) transport, and (iii) electrochemical properties. When detailed molecular-scale understanding of the multivalent electrolyte behavior is insufficient we use examples from well-studied lithium-ion electrolytes. In recognition that coupling empirical and theory-based techniques is highly effective, but often nontrivial, we also highlight recent electrolyte characterization efforts that uncover a more comprehensive and nuanced understanding of the underlying structures, processes, and reactions that drive performance and system-level behavior. We hope the insights from these discussions will guide the design of future electrolyte studies, accelerate development of next-generation multivalent-ion batteries through coupling of modeling with experiments, and help to avoid pitfalls and ensure reproducibility of modeling results.

Electrostatic Aspect of the Proton Reactivity in Concentrated Electrolyte Solutions

Water-in-salt electrolytes with a surprisingly large electrochemical stability window of ≤3 V have revived interest in aqueous electrolytes for rechargeable lithium-ion batteries. However, recent reports of acidic pH measured in concentrated electrolyte solutions appear to be in contradiction with the suppressed activity of the hydrogen evolution reaction (HER). Therefore, the fundamental thermodynamics of proton reactivity in concentrated electrolyte solutions remains elusive. In this work, we have used density functional theory-based molecular dynamics (MD) simulations and the proton insertion method to investigate how the HER potential shifts in concentrated LiCl solutions under both acidic and alkaline conditions. Our results show that the intrinsic HER activity increases significantly with the salt concentration under acidic conditions but remains relatively constant under alkaline conditions. Moreover, by leverage over finite-field MD simulations, it is found that a determining factor for the HER activity is the Poisson potential of the liquid phase, which increases in concentrated electrolyte solutions with comparable values from both density functional theory and point-charge models.

Ether-Modified Nonflammable Phosphate Enabling Anion-Rich Electrolyte for High-Voltage Lithium Metal Batteries

Phosphate-based localized high-concentration electrolytes (LHCE) feature high flame retardant and satisfactory cathodic stability for lithium metal batteries. However, stable cycling of those electrolytes at ultra-high upper cut-off voltages for long-term stability remains challenging. Herein, an ether-modified phosphate, diethyl (2-methoxy ethoxy) methylphosphonate (DMEP), is designed for high-voltage applications. The ether modification enhances the stability of the Li+-DMEP-FSI- coordination structure, promoting the formation of cation-anion aggregates (AGG) dominated solvation structure, which favors the generation of LiF-rich cathode electrolyte interphase layers compared to triethyl phosphate (TEP)-based LHCE. Consequently, cathode degradation, including transition-metal dissolution and electrode cracking, is well-suppressed. The LiNi0.8Co0.1Mn0.1O2 (NCM811)||Li full cells using DMEP-based LHCEs show more than 90.7% capacity retention at an ultrahigh upper cut-off voltage of 4.7 V after 100 cycles. Notably, DMEP-LHCE exhibits enhanced safety than that of TEP-LHCE, suggesting its versatility and potential for next-generation lithium metal batteries.

Mastering Proton Activities in Aqueous Batteries

Advanced aqueous batteries are promising solutions for grid energy storage. Compared with their organic counterparts, water-based electrolytes enable fast transport kinetics, high safety, low cost, and enhanced environmental sustainability. However, the presence of protons in the electrolyte, generated by the spontaneous ionization of water, may compete with the main charge-storage mechanism, trigger unwanted side reactions, and accelerate the deterioration of the cell performance. Therefore, it is of pivotal importance to understand and master the proton activities in aqueous batteries. This Perspective comments on the following scientific questions: Why are proton activities relevant? What are proton activities? What do we know about proton activities in aqueous batteries? How do we better understand, control, and utilize proton activities?

Hidden Negative Issues and Possible Solutions for Advancing the Development of High-Energy-Density in Lithium Batteries: A Review

This review article discusses the hidden or often overlooked negative issues of large-capacity cathodes, high-voltage systems, concentrated electrolytes, and reversible lithium metal electrodes in high-energy-density lithium batteries and provides some feasible solutions that can realize the construction of realistic rechargeable batteries with higher energy densities. Similar objective discussion of the negative aspects of lithium-air batteries, multi-valent shuttles, anion shuttles, sulfur cathode systems, and all-solid ceramic batteries can help fabricate more realistic batteries.