High-Energy Symmetric Li-Ion Battery Enabled by Binder-Free FeOF-MXene Heterostructure with Doubly Matched Capacity and Kinetics.

Fluorides are viewed as promising conversion-type Li-ion battery cathodes to meet the desired high energy density. FeOF is a typical member of conversion-type fluorides, but its major drawback is sluggish kinetics upon deep discharge. Herein, a heterostructured FeOF-MXene composite (FeOF-MX) is demonstrated to overcome this limitation. The rationally designed FeOF-MX electrode features a microsphere morphology consisting of closely packed FeOF nanoparticles, providing fast transport pathways for lithium ions while a continuous wrapping network of MXene nanosheets ensures unobstructed electron transport, thus enabling high-rate lithium storage with enhanced pseudocapacitive contribution. In/ex situ characterization techniques and theoretical calculations, both reveal that the lithium storage mechanism in FeOF arises from a hybrid intercalation-conversion process, and strong interfacial interactions between FeOF and MXene promote Li-ion adsorption and migration. Remarkably, through demarcating the conversion-type reaction with a controlled potential window, a symmetric full battery with prelithiated FeOF-MX as both cathode and anode is fabricated, achieving a high energy density of 185.5 Wh kg-1 and impressive capacity retention of 88.9% after 3000 cycles at 1 A g-1. This work showcases an effective route toward high-performance MXene engineered fluoride-based electrodes and provides new insights into constructing symmetric batteries yet with high-energy/power densities.

Design of heterostructured hydrangea-like FeS2/MoS2 encapsulated in nitrogen-doped carbon as high-performance anode for potassium-ion capacitors.

The means of structural hybridization such as heterojunction construction and carbon-coating engineering for facilitating charge transfer and electron transport are considered viable strategies to address the challenges associated with the low rate capability and poor cycling stability of sulfide-based anodes in potassium-ion batteries (PIBs). Motivated by these concepts, we have successfully prepared a hydrangea-like bimetallic sulfide heterostructure encapsulated in nitrogen-doped carbon (FMS@NC) using a simple solvothermal method, followed by poly-dopamine wrapping and a one-step sulfidation/carbonization process. When served as an anode for PIBs, this FMS@NC demonstrates a high specific capacity (585 mAh g-1 at 0.05 A/g) and long cycling stability. Synergetic effects of mitigated volume expansions and enhanced conductivity that are responsbile for such high performance have been verified to originate from the heterostructured sulfides and the N-doped carbon matrix. Meanwhile, comprehensive characterization reveals existence of an intercalation-conversion hybrid K-ion storage mechanism in this material. Impressively, a K-ion capacitor with the FMS@NC anode and a commercial activated carbon cathode exhibits a superior energy density of up to 192 Wh kg-1, a high power density, and outstanding cycling stability. This study provides constructive guidance for designing high-performance and durable potassium-ion storage anodes for next-generation energy storage devices.

Heterostructured CoS2/SnS2 encapsulated in sulfur-doped carbon exhibiting high potassium ion storage capacity.

Metallic sulfides are currently considered as ideal anode materials for potassium-ion batteries by virtue of their high specific capacities. However, their low intrinsic electronic conductivity, large volume variation and dissolution of polysulfides in electrochemical reactions hinder their further development toward practical applications. Here, we propose an effective structural design strategy by encapsulating CoS2/SnS2 in sulfur-doped carbon layers, in which internal voids are created to relieve the strain in the CoS2/SnS2 core, while the sulfur-doped carbon layer serves to improve the electron transport and inhibit the dissolution of polysulfides. These features enable the as-designed anode to deliver a high specific capacity (520 mAh/g at 0.1 A/g), a high rate capability (185 mA h g-1 at 10 A/g) and lifespan (0.016 % capacity loss per cycle up to 1500 cycles). Our comprehensive electrochemical characterization reveals that the heterostructure of CoS2/SnS2 not only promotes charge transfer at its interfaces, but also enhances the rate of K+ diffusion. Additionally, potassium-ion capacitors based on this novel anode are able to attain an energy density up to 162 Wh kg-1 and âˆ¼ 96 % capacity retention after 3000 cycles at 10 A/g.The demonstrated design rule combining morphological and structural engineering strategies sheds light on the development of advanced electrodes for high performance potassium-based energy storage devices.

Fe2(MoO4)3 assembled by cross-stacking of porous nanosheets enables a high-performance aluminum-ion battery.

Rechargeable aluminum-ion batteries have attracted increasing attention owing to the advantageous multivalent ion storage mechanism thus high theoretical capacity as well as inherent safety and low cost of using aluminum. However, their development has been largely impeded by the lack of suitable positive electrodes to provide both sufficient energy density and satisfactory rate capability. Here we report a candidate positive electrode based on ternary metal oxides, Fe2(MoO4)3, which was assembled by cross-stacking of porous nanosheets, featuring superior rate performance and cycle stability, and most importantly a well-defined discharge voltage plateau near 1.9 V. Specifically, the positive electrode is able to deliver reversible capacities of 239.3 mA h g-1 at 0.2 A g-1 and 73.4 mA h g-1 at 8.0 A g-1, and retains 126.5 mA h g-1 at 1.0 A g-1 impressively, after 2000 cycles. Furthermore, the aluminum-storage mechanism operating on Al3+ intercalation in this positive electrode is demonstrated for the first time via combined in situ and ex situ characterization studies and density functional theory calculations. This work not only explores potential positive electrodes for aluminum-based batteries but also sheds light on the fundamental charge storage mechanism within the electrode.

Nanosized MoSe2@Carbon Matrix: A Stable Host Material for the Highly Reversible Storage of Potassium and Aluminum Ions.

Owing to their low cost and abundant reserves relative to conventional lithium-ion batteries (LIBs), potassium-ion batteries (PIBs), and aluminum-ion batteries (AIBs) have shown appealing potential for electrochemical energy storage, but progress so far has been limited by the lack of suitable electrode materials. In this work, we demonstrated a facile strategy to achieve highly reversible potassium and aluminum ions storage in strongly coupled nanosized MoSe2@carbon matrix, induced through an ion complexation strategy. We present a broad range of electrochemical characterization of the synthesized product that exhibits high specific capacities, good rate capability, and excellent cycling stability toward PIBs and AIBs. Through a series of systematic ex situ X-ray photoelectron spectroscopy (XPS) characterizations and density functional theory (DFT) calculations, the Al3+ intercalation mechanism of MoSe2-based AIBs are elucidated. Moreover, both the assembled PIBs and AIBs worked well when exposed to low and high temperatures within the range of -10 to 50 °C, showing promise for energy storage devices in harsh environment. The present study provides new insights into the exploration of MoSe2 as high-performance electrode materials for PIBs and AIBs.