Synthesis of SnS2 Ultrathin Nanosheets as Anode Materials for Potassium Ion Batteries

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 ∼ 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.

Structural engineering of SnS quantum dots embedded in N, S Co-Doped carbon fiber network for ultrafast and ultrastable sodium/potassium-ion storage

Tin sulfides have received significant attention as potential candidates for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) due to their abundance, high theoretical capacity, and favorable working potential. However, the inherent drawbacks such as slow kinetics, low intrinsic electronic conductivity, and significant volume change during cycling, have not been adequately addressed. In this study, we propose a rational and effective approach to simultaneously overcome these challenges by embedding stannous sulfide (SnS) quantum dots (QDs) within a crosslinked nitrogen (N) and sulfur (S) co-doped carbon fiber network (SnS-CFN). The well-dispersed and densely packed SnS QDs, measuring approximately 2 nm, not only minimize the diffusion distance of Na+/K+ ions but also buffer the volume expansion effectively. The N, S co-doped carbon fiber network in SnS-CFN serves as a highly conductive and stable support structure that inhibits SnS QDs aggregation, creates ion/electron transport channels, and alleviates volume variations. Density functional theory (DFT) calculations further confirm that the combination of SnS QDs and the N, S co-doped carbon effectively reduces the adsorbed energies in the interlayer of SnS-CFN. These advantages synergistically contribute to the exceptional sodium/potassium storage performance of the SnS-CFN composite. Consequently, SnS-CFN demonstrates exceptional cyclability, retaining a capacity of 251.5 mAh/g over 10,000 cycles, and exhibits excellent rate capability (299.5 mAh/g at 20 A/g) when employed in SIBs. When used in PIBs, a high capacity of 112.3 mAh/g at 2 A/g after 1000 cycles, a remarkable capacity of 51.4 mAh/g at 5 A/g after 10,000 cycles, and a remarkable rate capability with a specific capacity of 55.5 mAh/g at a high current density of 20 A/g have been achieved.

Three-dimensional Ti3C2Tx and MnS composites as anode materials for high performance alkalis (Li, Na, K) ion batteries

Exploring capable and universal electrode materials could promote the development of alkalis (Li, Na, K) ion batteries. 2D MXene material is an ideal host for the alkalis (Li, Na, K) ion storage, but its electrochemical performance is limited by serious re-stacking and aggregation problems. Herein, we cleverly combined electrostatic self-assembly with gas-phase vulcanization method to successfully combine Ti₃C₂T_x-MXene with ultra-long recyclability and high conductivity with MnS, which presents high specific capacity but poor conductivity. The as-prepared 3D hierarchical Ti₃C₂T_x/MnS composites have an unique sandwich-like constituent units. The tiny MnS nanoparticles are restricted between the Ti₃C₂T_x layers and play a key role in expanding the Ti₃C₂T_x interlayer spacing. As a result, the 3D Ti₃C₂T_x/MnS composites as the anode of LIBs exhibits a superior capacities of 826 and 634 mAh/g after 1000 and 3000 cycles at 0.5 and 1.0 A/g, respectively. More importantly, we reveal the reaction mechanism that the specific capacity first increases and then gradually stabilizes with the increase of charge and discharge cycle times when the as-prepared 3D Ti₃C₂T_x/MnS was used as the anode of LIBs. In addition, we have also used this material in SIBs and PIBs and achieved remarkable electrochemical capability, with a specific capacity of 107 mAh/g after 2500 cycles at 0.5 A/g or 127 mAh/g after the 2000th cycle at 0.2 A/g, respectively.

Encapsulation of BiOCl nanoparticles in N-doped carbon nanotubes as a highly efficient anode for potassium ion batteries

With gradually increasing cost and shrinking crustal abundance for lithium ion batteries (LIBs), it is necessary to develop potassium ion batteries (PIBs) and explore suitable electrode materials for advanced PIBs. In this work, nanoscale BiOCl nanoparticles encapsulated in N-doped carbon nanotubes (BiOCl@N-CNTs) are designed and used as the anode material for K ion storage. The BiOCl@N-CNT composite is composed of BiOCl nanoparticles (≈ 5 nm) and N-doped carbon nanotubes. The ultralsmall BiOCl nanoparticles offer excellent electrochemical activity for K ion storage and short ion diffusion path for rapid reaction kinetics, while the outer layer of N-CNTs can effectively improve the conductivity and provide space to accommodate volume expansion. Due to this synergistic effect of small size and a highly conductive skeleton, the BiOCl@N-CNT composite delivers good rate capability and long-term cycling stability when evaluated as an anode for PIBs. The special structure of embedding ultrasmall active materials with high performance in highly conductive N-CNTs represents an effective way of improving the activity of the electrode material, facilitating ion/charge transfer, and alleviating volume change towards excellent energy storage technology.

Chiral Conformation of Subnanometric Materials

Subnanometric materials (SNMs) refer to nanomaterials with sizes comparable to the diameter of common linear polymers or confined at the level of a single unit cell in at least one dimension, usually <1 nm. Conventional inorganic nanoparticles are usually deemed to be rigid, lacking self-adjustable conformation. In contrast, the size at subnanometric scale endows SNMs with flexibility analogous to polymers, resulting in their abundant self-adjustable conformation. It is noteworthy that some highly flexible SNMs can adjust their shape automatically to form chiral conformation, which is rare in conventional inorganic nanoparticles. Herein, we summarize the chiral conformation of SNMs and clarify the driving force behind their formation, in an attempt to establish a better understanding for the origin of flexibility and chirality at subnanometric scale. In addition, the general strategies for controlling the conformation of SNMs are elaborated, which might shed light on the efficient fabrications of chiral inorganic materials. Finally, the challenges facing this area as well as some unexplored topics are discussed.

Reduced Graphene-Oxide-Encapsulated MoS2/Carbon Nanofiber Composite Electrode for High-Performance Na-Ion Batteries

Sodium-ion batteries (SIBs) have been increasingly studied due to sodium (Na) being an inexpensive ionic resource (Na) and their battery chemistry being similar to that of current lithium-ion batteries (LIBs). However, SIBs have faced substantial challenges in developing high-performance anode materials that can reversibly store Na⁺ in the host structure. To address these challenges, molybdenum sulfide (MoS₂)-based active materials have been considered as promising anodes, owing to the two-dimensional layered structure of MoS₂ for stably (de)inserting Na⁺. Nevertheless, intrinsic issues of MoS₂—such as low electronic conductivity and the loss of active S elements after a conversion reaction—have limited the viability of MoS₂ in practical SIBs. Here, we report MoS₂ embedded in carbon nanofibers encapsulated with a reduced graphene oxide (MoS₂@CNFs@rGO) composite for SIB anodes. The MoS₂@CNFs@rGO delivered a high capacity of 345.8 mAh g⁻¹ at a current density of 100 mA g⁻¹ for 90 cycles. The CNFs and rGO were synergistically taken into account for providing rapid pathways for electrons and preventing the dissolution of S sources during repetitive conversion reactions. This work offers a new point of view to realize MoS₂-based anode materials in practical SIBs.

Conjugated Porous Polydiaminophenylsulfone-Triazine Polymer-A High-Performance Anode for Li-Ion Batteries

Organic compounds are promising electrode materials because of their resource sustainability, environmental friendliness, and highly tailorable properties. The porous conjugated polymer shows great potential as an electrode material for its tunable redox nature, conjugated skeleton, and porous structure. Herein, a novel conjugated porous polymer, polydiaminophenylsulfone-triazine, was synthesized by a simple nucleophilic substitution reaction. The conjugated structure and triazine ring can improve the conductivity, charge-transfer efficiency, and physicochemical stability. Also, the porous polymeric framework shows a large specific surface area and high porosity, providing a large contact area with electrolytes and reducing diffusion distance. The polymer demonstrates highly stable cycling performance and good rate capability as an anode for lithium-ion batteries, suggesting a promising strategy to design a competitive electrode material.

Facile self-assembly of carbon-free vanadium sulfide nanosheet for stable and high-rate lithium-ion storage

Metal sulfides are recognized as potential candidates for the anode materials of lithium ion batteries (LIBs) because of their high theoretical capacity. However, the low reaction kinetics of metal sulfides leads to their poor cycle life and rate performance, which limits their practical application in the field of energy storage. In this work, we synthesized a self-assembled carbon-free vanadium sulfide (V₃S₄) nanosheet via a facile and efficient method. The unique mesoporous nanostructure of V₃S₄ can not only accelerate the migration of ions/electrons, but also alleviate the volume expansion during the lithium ion insertion/extraction process. When used as the anode material of LIBs, the carbon-free V₃S₄ electrode exhibits remarkable electrochemical performance with ultra-high charge capacity (1099.3 mAh g^-1 at 0.1 A g^-1), superior rate capability (668.8 mAh g^-1 at 2 A g^-1 and 588.8 mAh g^-1 at 5 A g^-1) and impressive cycling ability (369.6 mAh g^-1 after 200 cycles at 10 A g ^-1), which is very competitive compared with those of most metal sulfides-based anode materials reported so far. The strategy in this work provides inspiration for the rational design of advanced nanostructured electrode materials for energy storage devices.