Ultra-stable dendrite-free Na and Li metal anodes enabled by tin selenide host material.

Lithium/sodium metal anodes are considered promising candidates to realize high-energy-density batteries because of their high theoretical specific capacity and low potential. However, their cycling stability are hindered by uncontrolled dendrites growth. Herein, SnSe nanoparticles are tightly anchored on the fiber of carbon cloth (CC) to construct SnSe@CC host material in order to control Li/Na nucleation behavior and restrain dendrites growth. It is demonstrated that the alloying product of Li15Sn4/Na15Sn4 with strong metal affinity can provide abundant active nucleation sites, and three-dimensional structure of CC host can significantly decrease the local electric current, thereby guiding homogeneous metal deposition without Li and Na dendrites. Meanwhile, the conversion product of Li2Se/Na2Se will uniformly cover on the surface of metal to serve as ultra-stable solid state interface film. As a result, high-capacity Li metal anode (20 mAh·cm-2) and Na metal anode (10 mAh·cm-2) can work steadily with ultra-long lifespans over 5000 and 6000 h with low overpotentials of 7 mV and 141 mV, respectively. Moreover, the assembled Li and Na metal full batteries exhibit superior electrochemical performances, confirming the practicability of metal anode confined in composite host. Such a strategy of conversion-alloying-type materials as hosts opens up a new path for dendrite-free metal anode electrode.

Boosting Manganese Selenide Anode for Superior Sodium-Ion Storage via Triggering α → ß Phase Transition.

Sodium-ion batteries (SIBs) have been extensively studied owing to the abundance and low-price of Na resources. However, the infeasibility of graphite and silicon electrodes in sodium-ion storage makes it urgent to develop high-performance anode materials. Herein, α-MnSe nanorods derived from δ-MnO2 (δ-α-MnSe) are constructed as anodes for SIBs. It is verified that α-MnSe will be transferred into ß-MnSe after the initial Na-ion insertion/extraction, and δ-α-MnSe undergoes typical conversion mechanism using a Mn-ion for charge compensation in the subsequent charge-discharge process. First-principles calculations support that Na-ion migration in defect-free α-MnSe can drive the lattice distortion to phase transition (alpha → beta) in thermodynamics and dynamics. The formed ß-MnSe with robust lattice structure and small Na-ion diffusion barrier boosts great structure stability and electrochemical kinetics. Hence, the δ-α-MnSe electrode contributes excellent rate capability and superior cyclic stability with long lifespan over 1000 cycles and low decay rate of 0.0267% per cycle. Na-ion full batteries with a high energy density of 281.2 Wh·kg-1 and outstanding cyclability demonstrate the applicability of δ-α-MnSe anode.

Bismuth Telluride Nanoplates Hierarchically Confined by Graphene and N-Doped C as Conversion-Alloying Anode Materials for Potassium-Ion Batteries.

Potassium-ion batteries (PIBs) have broad application prospects in the field of electric energy storage systems because of its abundant K reserves, and similar "rocking chair" operating principle as lithium-ion batteries (LIBs). Aiming to the large volume expansion and sluggish dynamic behavior of anode materials for storing large sized K-ion, bismuth telluride (Bi2 Te3 ) nanoplates hierarchically encapsulated by reduced graphene oxide (rGO), and nitrogen-doped carbon (NC) are constructed as anodes for PIBs. The resultant Bi2 Te3 @rGO@NC architecture features robust chemical bond of Bi─O─C, tightly physicochemical confinement effect, typical conductor property, and enhanced K-ion adsorption ability, thereby producing superior electrochemical kinetics and outstanding morphological and structural stability. It is visually elucidated via high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) that conversion-alloying dual-mechanism plays a significant role in K-ion storage, allowing 12 K-ion transport per formular unit employing Bi as redox site. Thus, the high first reversible specific capacity of 322.70 mAh g-1 at 50 mA g-1 , great rate capability and cyclic stability can be achieved for Bi2 Te3 @rGO@NC. This work lays the foundation for an in-depth understanding of conversion-alloying mechanism in potassium-ion storage.

Advanced Anode Materials for Rechargeable Sodium-Ion Batteries.

Rechargeable sodium-ion batteries (SIBs) have been considered as promising energy storage devices owing to the similar "rocking chair" working mechanism as lithium-ion batteries and abundant and low-cost sodium resource. However, the large ionic radius of the Na-ion (1.07 Å) brings a key scientific challenge, restricting the development of electrode materials for SIBs, and the infeasibility of graphite and silicon in reversible Na-ion storage further promotes the investigation of advanced anode materials. Currently, the key issues facing anode materials include sluggish electrochemical kinetics and a large volume expansion. Despite these challenges, substantial conceptual and experimental progress has been made in the past. Herein, we present a brief review of the recent development of intercalation, conversion, alloying, conversion-alloying, and organic anode materials for SIBs. Starting from the historical research progress of anode electrodes, the detailed Na-ion storage mechanism is analyzed. Various optimization strategies to improve the electrochemical properties of anodes are summarized, including phase state adjustment, defect introduction, molecular engineering, nanostructure design, composite construction, heterostructure synthesis, and heteroatom doping. Furthermore, the associated merits and drawbacks of each class of material are outlined, and the challenges and possible future directions for high-performance anode materials are discussed.

Boosting cobalt ditelluride quantum-rods anode materials for excellent potassium-ion storage via hierarchical physicochemical encapsulation.

The exploration of anode materials that can store large-sized K-ion to solve the poor kinetics and large volume expansion issues has become the key scientific bottlenecks hindering the development of potassium-ion batteries (PIBs). Herein, ultrafine CoTe2 quantum rods physiochemically encapsulated by graphene and nitrogen-doped carbon (CoTe2@rGO@NC) are regarded as anode electrodes for PIBs. Dual physicochemical confinement and quantum size effect not only enhance electrochemical kinetics but also restrain large lattice stress during repeated K-ion insertion/extraction process. Superior electronic conductivity, K-ion adsorption, and diffusion ability can be acquired for CoTe2@rGO@NC, confirmed through first-principles calculations and kinetics study. K-ion insertion/extraction proceeds via a typical conversion mechanism relying on Co as the redox site, where the robust chemical bond of COCo plays an important role in maintaining the electrode stability. Accordingly, CoTe2@rGO@NC contributes a high initial capacity of 237.6 mAh·g-1 at 200 mA·g-1, a long lifetime over 500 cycles with low-capacity decay of 0.10% per cycle. This research will lay the materials science foundation for the construction of quantum-rod electrodes.

Cr(OH)3nanosheets@ZIF67 electrocatalysts prepared by electrodeposition method for efficient oxygen evolution reaction.

In this paper, a Cr(OH)3NSs@ZIF67 (NSs = nanosheets) electrocatalyst is prepared on foam Ni via a simple and rapid electrochemical deposition method. Excellent electrocatalytic activity of Cr(OH)3NSs@ZIF67 is demonstrated. It can use the overpotential of 281 mV and 390 mV respectively to drive 10 mA cm-2and 50 mA cm-2. It is observed that the Cr(OH)3NSs@ZIF67 electrode has the highest initial current density at 1.57 V compared with the other two monomer electrodes and shows excellent stability at the end of 60 000 s. It has the largest electrochemical activity specific surface and lowest charge-transfer resistance, and M-O bonds (M = Co, Cr) and shifting of binding energy peaks at the interface lead to more active sites and more efficient electron transfer for oxygen evolution reaction. This work highlights the construction of highly efficient composite electrocatalysts composted of low-dimensional non-precious transition metal compounds and metalorganic frameworks, promoting the development of low-cost non-noble metal composites in energy chemistry.

Nitrogen and Oxygen Co-Doped Porous Hard Carbon Nanospheres with Core-Shell Architecture as Anode Materials for Superior Potassium-Ion Storage.

The investigation of carbonaceous-based anode materials will promote the fast application of low-cost potassium-ion batteries (PIBs). Here a nitrogen and oxygen co-doped yolk-shell carbon sphere (NO-YS-CS) is constructed as anode material for K-ion storage. The novel architecture, featuring with developed porous structure and high surface specific area, is beneficial to achieving excellent electrochemical kinetics behavior and great electrode stability from buffering the large volume expansion. Furthermore, the N/O heteroatoms co-doping can not only boost the adsorption and intercalation ability of K-ion but also increase the electron transfer capability. It is also demonstrated by experimental results and DFT calculations that K-ion insertion/extraction proceeds through both intercalation and surface capacitive adsorption mechanisms. As expected, the NO-YS-CS electrodes show high initial charge capacity of 473.7 mAh g-1 at 20 mA g-1 , ultralong cycling life over 2500 cycles with the retention of 85.8% at 500 mA g-1 , and superior rate performance (183.3 mAh g-1 at 1.0 A g-1 ). The K-ion full cell, with a high energy density of 271.4 Wh kg-1 and an excellent cyclic stability over 500 cycles, is successfully fabricated with K2 Fe[Fe(CN)6 ] cathode. This work will provide new insight on the synthesis and mechanism understanding of high-performance hard carbon anode for PIBs.

Sb2S3-based conversion-alloying dual mechanism anode for potassium-ion batteries.

The large volume expansion and sluggish dynamic behavior are the key bottleneck to suppress the development of conversion-alloying dual mechanism anode for potassium-ion batteries (PIBs). Herein, Sb2S3 nanorods encapsulated by reduced graphene oxide and nitrogen-doped carbon (Sb2S3@rGO@NC) are constructed as anodes for PIBs. The synergistic effect of dual physical protection and robust C-Sb chemical bonding boosts superior electrochemical kinetics and great electrode stability. Thus, Sb2S3@rGO@NC exhibits a high initial charge capacity of 505.6 mAh·g-1 at 50 mA·g-1 and a great cycle stability with the lifetime over 200 cycles at 200 mA·g-1. Ex situ XRD, XPS, and TEM characterizations confirm that the electrode undergoes a multielectron transfer process (Sb2S3↔ Sb + K2S ↔ KSb + K3Sb), where K-ion insert into/extract from the material via dual mechanisms of conversion and alloying. This work sheds a light on the construction of high-performance anode materials and the understanding of K-ion storage mechanism.

Three-phase composites of NiFe2O4/Ni@C nanoparticles derived from metal-organic frameworks as electrocatalysts for the oxygen evolution reaction.

Composite electrocatalysts of carbon and metals or metal compounds with homogeneous active sites can be obtained through the carbonization of metal organic framework (MOF) materials under inert atmosphere. In this work, a three-phase composite electrocatalysts NiFe2O4/Ni@C were prepared via pyrolysis from self-assembled MOF nanosheets aggregates. The excellent electrocatalytic activity of the obtained electrocatalysts with various Ni:Fe ratios is demonstrated. Especially, the NiFe2O4/Ni@C sample with the mole ratio of Ni:Fe = 1:1 can use the overpotential (η) of 330 and 423 mV to drive 10 and 50 mA cm-2 respectively. After 80 000 s/22 h, the current density could retained 90% of the initial current density. The excellent activity and stability of the electrocatalysts are attributed to nickel and iron ions with uniform dispersion at atomic level in the NiFe2O4 phase and the synergistic effect of nickel and NiFe2O4 nanoparticles with amorphous carbon atoms or nanoparticles around.