Recent progress in electrochemical performance of binder-free anodes for potassium-ion batteries

Bimetallic Cobalt-Nickel Selenide Nanocubes Embedded in a Nitrogen-Doped Carbon Matrix as an Excellent Li-Ion Battery Anode

Lithium-ion batteries (LIBs) have been widely used for portable electronics and electric vehicles; however, the low capacity in the graphite anode limits the improvement of energy density. Transition-metal selenides are promising anode material candidates due to their high theoretical capacity and controllable structure. In this study, we successfully synthesize a bimetallic transition-metal selenide nanocube composite, which is well embedded in a nitrogen-doped carbon matrix (denoted as CoNiSe₂/NC). This material shows a high capacity and excellent cycling for Li-ion storage. Specifically, the reversible capacity approaches ∼1245 mA h g^-1 at 0.1 A g^-1. When cycled at 1 A g^-1, the capacity still remains at 642.9 mA h g^-1 even after 1000 cycles. In-operando XRD tests have been carried out to investigate the lithium storage mechanism. We discover that the outstanding performance is due to the unique CoNiSe₂/NC nanocomposite characteristics, such as the synergistic effect of bimetallic selenide on lithium storage, the small particle size, and the stable and conductive carbon structure. Therefore, this morphology structure not only reduces the volume change of metal selenides but also produces more lithium storage active sites and shortens lithium diffusion paths, which results in high capacity, good rate, and long cycling.

Organic Cathode Materials for Rechargeable Aluminum-Ion Batteries

Organic electrode materials (OEMs) have shown enormous potential in ion batteries because of their varied structural components and adaptable construction. As a brand-new energy-storage device, rechargeable aluminum-ion batteries (RAIBs) have also received a lot of attention due to their high safety and low cost. OEMs are expected to stand out among many traditional RAIB cathode materials. However, how to improve the electrochemical performance of OEMs in RAIBs on a laboratory scale is still challenging. This work reviews and discusses the uses of conductive polymers, carbonyl compounds, imine polymers, polycyclic aromatic hydrocarbons, organic frameworks, and other organic materials as the cathodes of RAIBs, as well as energy-storage mechanisms and research progress. It is hoped that this Review can provide the design guidelines for organic cathode materials with high capacity and great stability used in aluminum-organic batteries and develop more efficient organic energy storage cathodes.

Self-Supporting Co/CeO2 Heterostructures for Ampere-Level Current Density Alkaline Water Electrolysis

Remodeling the active surface through fabricating heterostructures can substantially enhance alkaline water electrolysis driven by renewable electrical energy. However, there are still great challenges in the synthesis of highly reactive and robust heterostructures to achieve both ampere-level current density hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we report a new Co/CeO₂ heterojunction self-supported electrode for sustainable overall water splitting. The self-supporting Co/CeO₂ heterostructures required only low overpotentials of 31.9 ± 2.2, 253.3 ± 2.7, and 316.7 ± 3 mV for HER and 214.1 ± 1.4, 362.3 ± 1.9, and 400.3 ± 3.7 mV for OER at 0.01, 0.5, and 1.0 A·cm^-2, respectively, being one of the best Co-based bifunctional electrodes. Electrolyzer constructed from this electrode acting as an anode and cathode merely required cell voltages of 1.92 ± 0.02 V at 1.0 A·cm^-2 for overall water splitting. Multiple characterization techniques combined with density functional theory calculations disclosed the different active sites on the anode and cathode, and the charge redistributions on the heterointerfaces that can optimize the adsorption of H and oxygen-containing intermediates, respectively. This study presents the tremendous prospective of self-supporting heterostructures for effective and economical overall water splitting.

Emerging carbon-based flexible anodes for potassium-ion batteries: Progress and opportunities

In recent years, carbon-based flexible anodes for potassium-ion batteries are increasingly investigated owing to the low reduction potential and abundant reserve of K and the simple preparation process of flexible electrodes. In this review, three main problems on pristine carbon-based flexible anodes are summarized: excessive volume change, repeated SEI growth, and low affinity with K⁺, which thus leads to severe capacity fade, sluggish K⁺ diffusion dynamics, and limited active sites. In this regard, the recent progress on the various modification strategies is introduced in detail, which are categorized as heteroatom-doping, coupling with metal and chalcogenide nanoparticles, and coupling with other carbonaceous materials. It is found that the doping of heteroatoms can bring the five enhancement effects of increasing active sites, improving electrical conductivity, expediting K⁺ diffusion, strengthening structural stability, and enlarging interlayer spacing. The coupling of metal and chalcogenide nanoparticles can largely offset the weakness of the scarcity of K⁺ storage sites and the poor wettability of pristine carbon-based flexible electrodes. The alloy nanoparticles consisting of the electrochemically active and inactive metals can concurrently gain a stable structure and high capacity in comparison to mono-metal nanoparticles. The coupling of the carbonaceous materials with different characteristics can coordinate the advantages of the nanostructure from graphite carbon, the defects and vacancies from amorphous carbon, and the independent structure from support carbon. Finally, the emerging challenges and opportunities for the development of carbon-based flexible anodes are presented.

Fundamental Understanding and Research Progress on the Interfacial Behaviors for Potassium-Ion Battery Anode

Potassium-ion batteries (PIBs) exhibit a considerable application prospect for energy storage systems due to their low cost, high operating voltage, and superior ionic conductivity. As a vital configuration in PIBs, the two-phase interface, which refers to K-ion diffusion from the electrolyte to the electrode surface (solid-liquid interface) and K-ion migration between different particles (solid-solid interface), deeply determines the diffusion/reaction kinetics and structural stability, thus significantly affecting the rate performance and cyclability. However, researches on two-phase interface are still in its infancy and need further attentions. This review first starts from the fundamental understanding of solid-liquid and solid-solid interfaces to in-depth analyzing the effect mechanism of different improvement strategies on them, such as optimization of electrolyte and binders, heterostructure design, modulation of interlayer spacing, etc. Afterward, the research progress of these improvement strategies is summarized comprehensively. Finally, the major challenges are proposed, and the corresponding solving strategies are presented. This review is expected to give an insight into the importance of two-phase interface on diffusion/reaction kinetics, and provides a guidance for developing other advanced anodes in PIBs.

Recent Progress of Carbon-Based Anode Materials for Potassium Ion Batteries

With the increasing demand for clean energy, rechargeable batteries with K⁺ as carriers have attracted wide attention due to their advantages of expandability and low cost. High-performance anode materials are the key to the development of potassium ion batteries (PIBs), improving their competitiveness and feasibility. Carbon materials have become promising anodes for PIBs due to their abundant resources, low cost, non-toxicity and electrochemical diversity. This article reviews the research progress of carbon based anode materials in recent years. Firstly, the unique characteristics of carbon as a competitive anode for advanced PIBs are discussed, which provides guidance for optimal design and exploration. Then, various carbon materials as the anodes towards PIBs are summarized in detail, and the involved problems and corresponding solutions are analyzed. Finally, the future development and perspective of advanced carbons for next-generation PIBs are proposed.

Au(111)@Ti6O11 heterostructure composites with enhanced synergistic effects as efficient electrocatalysts for the hydrogen evolution reaction

Developing cost-effective electrocatalysts for the hydrogen evolution reaction (HER) is of great significance for the renewable energy field. The Magnéli phase Ti_nO_2n-1 (4 ≤ n ≤ 10) has attracted much attention as a promising carbon-free support for electrocatalysts due to its high electrical conductivity and favorable electrochemical stability. Herein, we report the synthesis of a specific crystal-plane coupling heterostructure between Au(111) nanoparticles (NPs) and Ti₆O₁₁ by photoreduction. Benefitting from the modification of the electronic structure and synergistic effects of the heterostructure, the electron density around Au atoms is enhanced, and the Gibbs free energy of hydrogen absorption (ΔG_H*) was dramatically optimized to facilitate the HER process. The best electrocatalyst Au(111)@Ti₆O₁₁-50 exhibits a lower overpotential of 49 mV at a current density of -10 mA cm^-2 and a Tafel slope of 39 mV dec^-1 in 0.5 M H₂SO₄, and shows long-term electrochemical stability over 30 h. Au(111)@Ti₆O₁₁-50 shows a mass activity of 9.25 A mg_Au^-1, which is about 18 times higher than that of commercial Pt/C (0.51 A mg_Pt^-1). Meanwhile, the density functional theory (DFT) calculations suggest that the ΔG_H* of Au(111)@Ti₆O₁₁ is -0.098 eV, which is comparable to that of Pt (-0.09 eV). This work would be a powerful guide for the realization of efficient utilization of noble metals in catalysis.