Advancements and Challenges in Potassium Ion Batteries: A Comprehensive Review

2D MXene-based nanomaterials have attracted tremendous attention because of their unique physical/chemical properties and wide range of applications in energy storage, catalysis, electronics, optoelectronics, and photonics. However, MXenes and their derivatives have many inherent limitations in terms of energy storage applications. In order to further improve their performance for practical application, the nanoengineering of these 2D materials is extensively investigated. In this Review, the latest research and progress on 2D MXene-based nanostructures is introduced and discussed, focusing on their preparation methods, properties, and applications for energy storage such as lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, and supercapacitors. Finally, the critical challenges and perspectives required to be addressed for the future development of these 2D MXene-based materials for energy storage applications are presented.

Nanoengineering of 2D MXene-Based Materials for Energy Storage Applications

The development of sodium-ion batteries for large-scale applications requires the synthesis of electrode materials with high capacity, high initial Coulombic efficiency (ICE), high rate performance, long cycle life, and low cost. A rational design of freestanding anode materials is reported for sodium-ion batteries, consisting of molybdenum disulfide (MoS2) nanosheets aligned vertically on carbon paper derived from paper towel. The hierarchical structure enables sufficient electrode/electrolyte interaction and fast electron transportation. Meanwhile, the unique architecture can minimize the excessive interface between carbon and electrolyte, enabling high ICE. The as-prepared MoS2@carbon paper composites as freestanding electrodes for sodium-ion batteries can liberate the traditional electrode manufacturing procedure, thereby reducing the cost of sodium-ion batteries. The freestanding MoS2@carbon paper electrode exhibits a high reversible capacity, high ICE, good cycling performance, and excellent rate capability. By exploiting in situ Raman spectroscopy, the reversibility of the phase transition from 2H-MoS2 to 1T-MoS2 is observed during the sodium-ion intercalation/deintercalation process. This work is expected to inspire the development of advanced electrode materials for high-performance sodium-ion batteries.

MoS2 Nanosheets Vertically Aligned on Carbon Paper: A Freestanding Electrode for Highly Reversible Sodium Ion Batteries

Carbon quantum dot micelles tailored hollow carbon anode for fast potassium and sodium storage

Hard carbon (HC) is recognized as a promising anode material with outstanding electrochemical performance for alkali metal-ion batteries including lithium-ion batteries (LIBs), as well as their analogs sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). Herein, a comprehensive review of the recent research is presented to interpret the challenges and opportunities for the applications of HC anodes. The ion storage mechanisms, materials design, and electrolyte optimizations for alkali metal-ion batteries are illustrated in-depth. HC is particularly promising as an anode material for SIBs. The solid-electrolyte interphase, initial Coulombic efficiency, safety concerns, and all-climate performances, which are vital for practical applications, are comprehensively discussed. Furthermore, commercial prototypes of SIBs based on HC anodes are extensively elaborated. The remaining challenges and research perspectives are provided, aiming to shed light on future research and early commercialization of HC-based SIBs.

Hard carbon anodes: fundamental understanding and commercial perspectives for Na-ion batteries beyond Li-ion and K-ion counterparts

Unlike zero-dimensional quantum dots, one-dimensional nanowires/nanorods, and three-dimensional networks or even their bulk counterparts, the charge carriers in two-dimensional (2D) materials are confined along the thickness while being allowed to move along the plane. They have distinct characteristics like strong quantum confinement, tunable thickness, and high specific surface area, which makes them a promising candidate in a wide range of applications such as electronics, topological spintronic devices, energy storage, energy conversion, sensors, biomedicine, catalysis, and so on. After the discovery of the extraordinary properties of graphene, other graphene-like 2D materials have attracted a great deal of attention. Like graphene, to realize their potential applications, high efficiency and low cost industrial scale methods should be developed to produce high-quality 2D materials. The electrochemical methods usually performed under mild conditions are convenient, controllable, and suitable for mass production. In this review, we introduce the latest and most representative investigations on the fabrication of 2D monoelemental Xenes, 2D transition-metal dichalcogenides, and other important emerging 2D materials such as organic framework (MOF) nanosheets and MXenes through electrochemical exfoliation. The electrochemical exfoliation conditions of the bulk layered materials are discussed. The numerous factors which will affect the quality of the exfoliated 2D materials, the possible exfoliating mechanism and potential applications are summarized and discussed in detail. A summary of the discussion together with perspectives and challenges for the future of this emerging field is also provided in the last section.

Electrochemical exfoliation of graphene-like two-dimensional nanomaterials

Garnet Solid Electrolyte for Advanced All-Solid-State Li Batteries

The practical application of Li‐rich Mn‐based oxide cathode is predominately retarded by the capacity decline and voltage fading, associated with the structure distortion and anionic redox reactions. Here, a linkage‐functionalized modification approach to tackle these challenges via a synchronous lithium oxidation strategy is reported. The doping of Ce in the bulk phase activates the pseudo‐bonding effect, effectively stabilizing the lattice oxygen evolution and suppressing the structure distortion. Interestingly, it also induces the formation of spinel phase Li4Mn5O12 in the subsurface, which in turn constructs the phase boundaries, thereby arousing the interior self‐built‐in electric field to prevent the outward migration of bulk oxygen anions and boost the charge transfer. Moreover, the formed coating layer Li2CeO3 with oxygen vacancies accelerates Li+ diffusion and mitigates electrolyte cauterization. The corresponding cathode exhibits superior long‐cycle stability after 300 cycles with only a 0.013% capacity drop and 1.76 mV voltage decay per cycle. This work sheds new light on the development of Li‐rich Mn‐based oxide cathodes toward high energy density applications.

Pseudo-Bonding and Electric-Field Harmony for Li-Rich Mn-Based Oxide Cathode

Prelithiation/Presodiation Techniques for Advanced Electrochemical Energy Storage Systems: Concepts, Applications, and Perspectives

Sodium-ion capacitors (SICs), as new-generation electrochemical energy-storage systems, have combined the advantages of high energy and power densities, meeting the urgent demand for versatile electronic equipment and grid energy-storage stations. Nevertheless, the electrochemical performance of SICs is seriously restricted by the kinetic mismatch between the battery-type anode and capacitor-type cathode. In this work, N-doped 3D carbon (NHPC) delivered a high reversible specific capacity of 197 mA h g−1 at 2 A g−1, and the mechanism of its electrochemistry mainly involved strong pseudocapacitive storage that promoted quick physical adsorption/desorption. Moreover, further activation of NHPC yielded nitrogen-doped hierarchical porous activated carbon (NHPAC), which displayed a large specific surface area of 1478 m2 g−1 with abundant meso/macropores, and brought about fast adsorption/desorption of anions on its surface. The full-carbon SIC device benefitted from the similar material systems used for its anode and cathode, and hence achieved a high energy density of 115 W h kg−1 at 200 W kg−1 as well as long-term cyclability in the potential range of 0–4.0 V. This rational strategy of kinetic matching might open up a potential avenue for the development of additional advanced SICs.

Jiayang Li

Papers

Electrochemical exfoliation of graphene-like two-dimensional nanomaterials

Garnet Solid Electrolyte for Advanced All-Solid-State Li Batteries

Pseudo-Bonding and Electric-Field Harmony for Li-Rich Mn-Based Oxide Cathode

Prelithiation/Presodiation Techniques for Advanced Electrochemical Energy Storage Systems: Concepts, Applications, and Perspectives

A kinetically well-matched full-carbon sodium-ion capacitor