Hitherto Unknown Solvent and Anion Pairs in Solvation Structures Reveal New Insights into High-Performance Lithium-Ion Batteries

Solvent-solvent and solvent-anion pairings in battery electrolytes have been identified for the first time by nuclear magnetic resonance spectroscopy. These hitherto unknown interactions are enabled by the hydrogen bonding induced by the strong Lewis acid Li⁺ , and exist between the electron-deficient hydrogen (δ⁺ H) present in the solvent molecules and either other solvent molecules or negatively-charged anions. Complementary with the well-established strong but short-ranged Coulombic interactions between cation and solvent molecules, such weaker but longer-ranged hydrogen-bonding casts the formation of an extended liquid structure in electrolytes that is influenced by their components (solvents, additives, salts, and concentration), which in turn dictates the ion transport within bulk electrolytes and across the electrolyte-electrode interfaces. The discovery of this new inter-component force completes the picture of how electrolyte components interact and arrange themselves, sets the foundation to design better electrolytes on the fundamental level, and probes battery performances.

Unusual Activity of Rationally Designed Cobalt Phosphide/Oxide Heterostructure Composite for Hydrogen Production in Alkaline Medium

Design and development of an efficient, nonprecious catalyst with structural features and functionality necessary for driving the hydrogen evolution reaction (HER) in an alkaline medium remain a formidable challenge. At the root of the functional limitation is the inability to tune the active catalytic sites while overcoming the poor reaction kinetics observed under basic conditions. Herein, we report a facile approach to enable the selective design of an electrochemically efficient cobalt phosphide oxide composite catalyst on carbon cloth (CoP-Co_xO_y/CC), with good activity and durability toward HER in alkaline medium (η₁₀ = -43 mV). Theoretical studies revealed that the redistribution of electrons at laterally dispersed Co phosphide/oxide interfaces gives rise to a synergistic effect in the heterostructured composite, by which various Co oxide phases initiate the dissociation of the alkaline water molecule. Meanwhile, the highly active CoP further facilitates the adsorption-desorption process of water electrolysis, leading to extremely high HER activity.

Bismuth-based mixed-anion compounds for anode materials in rechargeable batteries

A facile solvothermal synthesis approach for chemical composition control in ternary Bi-S-I systems is reported by simply controlling the sulfide concentration. We demonstrate the application of these bismuth-based ternary mixed-anion compounds as high capacity anode materials in rechargeable batteries. Cells utilising Bi₁₃S₁₈I₂ achieved an initial capacity value of 807 mA h g^-1, while those with BiSI/Bi₁₃S₁₈I₂ a value of 1087 mA h g^-1 in lithium-ion battery systems.

Interfacial Model Deciphering High-Voltage Electrolytes for High Energy Density, High Safety, and Fast-Charging Lithium-Ion Batteries

High-voltage lithium-ion batteries (LIBs) enabled by high-voltage electrolytes can effectively boost energy density and power density, which are critical requirements to achieve long travel distances, fast-charging, and reliable safety performance for electric vehicles. However, operating these batteries beyond the typical conditions of LIBs (4.3 V vs Li/Li⁺ ) leads to severe electrolyte decomposition, while interfacial side reactions remain elusive. These critical issues have become a bottleneck for developing electrolytes for applications in extreme conditions. Herein, an additive-free electrolyte is presented that affords high stability at high voltage (4.5 V vs Li/Li⁺ ), lithium-dendrite-free features upon fast-charging operations (e.g., 162 mAh g^-1 at 3 C), and superior long-term battery performance at low temperature. More importantly, a new solvation structure-related interfacial model is presented, incorporating molecular-scale interactions between the lithium-ion, anion, and solvents at the electrolyte-electrode interfaces to help interpret battery performance. This report is a pioneering study that explores the dynamic mutual-interaction interfacial behaviors on the lithium layered oxide cathode and graphite anode simultaneously in the battery. This interfacial model enables new insights into electrode performances that differ from the known solid electrolyte interphase approach to be revealed, and sets new guidelines for the design of versatile electrolytes for metal-ion batteries.

Electropolymerized Conjugated Microporous Nanoskin Regulating Polysulfide and Electrolyte for High-Energy Li-S Batteries

A popular practice in Li-S battery research is to utilize highly nanostructured hosts and excessive electrolytes to enhance sulfur-specific capacities. However, from the perspective of commercialization, this is a less meaningful approach in the pursuit of high-energy Li-S batteries. Herein, we report the fabrication of a nanoskin composed of a conjugated microporous polymer by electropolymerization to create a closed system for a sulfur cathode. The nanoskin is ultrathin, conductive, continuous, and contains uniform micropores of approximately 0.8 nm. The nanoskin sealing prevents the shuttling of polysulfide species without using the absorption effect, enhances the utilization of electrolytes, and allows a fast transport of lithium ions. As a result, the Li-S batteries comprising the cathode with nanoskin exhibit superior stability (∼86% capacity retention) under lean electrolyte conditions and a prolonged lifetime (1000 cycles). At a low electrolyte/sulfur ratio of 4 μL mg^-1, the designed cathode delivered a practical energy density of over 300 Wh kg^-1 without using any sophisticated hosts.

Engineering Sodium-Ion Solvation Structure to Stabilize Sodium Anodes: Universal Strategy for Fast-Charging and Safer Sodium-Ion Batteries

Sodium-ion batteries are promising alternatives for lithium-ion batteries due to their lower cost caused by global sodium availability. However, the low Coulombic efficiency (CE) of the sodium metal plating/stripping process represents a serious issue for the Na anode, which hinders achieving a higher energy density. Herein, we report that the Na⁺ solvation structure, particularly the type and location of the anions, plays a critical role in determining the Na anode performance. We show that the low CE results from anion-mediated corrosion, which can be tackled readily through tuning the anion interaction at the electrolyte/anode interface. Our strategy thus enables fast-charging Na-ion and Na-S batteries with a remarkable cycle life. The presented insights differ from the prevailing interpretation that the failure mechanism mostly results from sodium dendrite growth and/or solid electrolyte interphase formation. Our anionic model introduces a new guideline for improving the electrolytes for metal-ion batteries with a greater energy density.

Performance and Stability Improvement of Layered NCM Lithium-Ion Batteries at High Voltage by a Microporous Al2O3 Sol-Gel Coating

A simple and low-cost polymer-aided sol-gel method was developed to prepare γ-Al₂O₃ protective layers for LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cathode materials. The selected polyvinyl alcohol polymer additive not only facilitates the formation of a uniform and thin γ-Al₂O₃ layer on the irregular and rough cathode particle surface to protect it from corrosion but also serves as a pore-forming agent to generate micropores in the film after sintering to allow fast transport of lithium ions, which guaranteed the excellent and stable battery performance at high working voltage. Detailed studies in the full battery mode showed that the leached corrosion species from the cathode had a more profound harmful effect to the graphite anode, which seemed to be the dominating factor that caused the battery performance decay.

Design and Mechanistic Study of Highly Durable Carbon-Coated Cobalt Diphosphide Core-Shell Nanostructure Electrocatalysts for the Efficient and Stable Oxygen Evolution Reaction

The facile synthesis of hierarchically functional, catalytically active, and electrochemically stable nanostructures holds a tremendous promise for catalyzing the efficient and durable oxygen evolution reaction (OER) and yet remains a formidable challenge. Herein, we report the scalable production of core-shell nanostructures composed of carbon-coated cobalt diphosphide nanosheets, C@CoP₂, via three simple steps: (i) electrochemical deposition of Co species, (ii) gas-phase phosphidation, and (iii) carbonization of CoP₂ for catalytic durability enhancement. Electrochemical characterizations showed that C@CoP₂ delivers an overpotential of 234 mV, retains its initial activity for over 80 h of continuous operation, and exhibits a fast OER rate of 63.8 mV dec^-1 in base.

Lithium dendrite-free plating/stripping: a new synergistic lithium ion solvation structure effect for reliable lithium–sulfur full batteries

A new synergistic Li⁺ solvation structure effect is introduced to mitigate the growth of lithium-dendrites and applied for safer Li–S full batteries.

Scalable Approach To Construct Free-Standing and Flexible Carbon Networks for Lithium-Sulfur Battery

Reconstructing carbon nanomaterials (e.g., fullerene, carbon nanotubes (CNTs), and graphene) to multidimensional networks with hierarchical structure is a critical step in exploring their applications. Herein, a sacrificial template method by casting strategy is developed to prepare highly flexible and free-standing carbon film consisting of CNTs, graphene, or both. The scalable size, ultralight and binder-free characteristics, as well as the tunable process/property are promising for their large-scale applications, such as utilizing as interlayers in lithium-sulfur battery. The capability of holding polysulfides (i.e., suppressing the sulfur diffusion) for the networks made from CNTs, graphene, or their mixture is pronounced, among which CNTs are the best. The diffusion process of polysulfides can be visualized in a specially designed glass tube battery. X-ray photoelectron spectroscopy analysis of discharged electrodes was performed to characterize the species in electrodes. A detailed analysis of lithium diffusion constant, electrochemical impedance, and elementary distribution of sulfur in electrodes has been performed to further illustrate the differences of different carbon interlayers for Li-S batteries. The proposed simple and enlargeable production of carbon-based networks may facilitate their applications in battery industry even as a flexible cathode directly. The versatile and reconstructive strategy is extendable to prepare other flexible films and/or membranes for wider applications.