A Multi‐Wall Sn/SnO 2 @Carbon Hollow Nanofiber Anode Material for High‐Rate and Long‐Life Lithium‐Ion Batteries

Accurately Localizing Multiple Nanoparticles in a Multishelled Matrix Through Shell-to-Core Evolution for Maximizing Energy-Storage Capability

Robust and fast lithium energy storage with a high energy density is highly desired to accelerate the market adoption of electric vehicles. To realize such a goal requires the development of electrode materials with a high capacity, however, such electrode materials suffer from huge volume expansion and induced short cycling life. Here, using tin (Sn) as an example, an ideal structure is designed to effectively solve these problems by separately localizing multiple Sn nanoparticles in a nitrogen-doped carbon hollow multishelled structure with duplicated layers for carbon shell (Sn NPs@N_x C HoMS-DL). The fabricated composite can promote ion and electron diffusion owing to the conductive network formed by connected multiple shells and cores, effectively buffer the volume expansion, and maintain a stable electrode-electrolyte interface. Despite the challenging fabrication, such a structure is realized through an innovative and facile synthesis strategy of "in situ evolution of shell to core", which is applicable for diverse low-melting-point materials. As expected, such a structure enables the high-capacity electrode material to realize nearly its theoretical lithium-storage capability: the developed Sn NPs@N_x C HoMS-DL electrode maintains 96% of its theoretical capacity after 2000 cycles at 2C.

Construction of MoS2/Mxene heterostructure on stress-modulated kapok fiber for high-rate sodium-ion batteries

Molybdenum disulfide (MoS₂) has possession of a layered structure and high theoretical capacity, which is a candidate anode material for sodium ion batteries. However, unmodified MoS₂ are inflicted with a poor cycling stability and an inferior rate capability upon charge/discharge processes. Considering that the shape and size of anode materials play a key role in the performance of anode materials, this paper proposes a multi-level composite structure formed by the micro-nano materials based on self-assembled molybdenum disulfide (MoS₂) nanoflowers, Mxene and hollow carbonized kapok fiber (CKF). The micro-nano materials can be connected to form heterojunction and agglomeration can be avoided. The load bearing of heterostructure and stress release of CKF are coordinated to form a double protection mechanism, which improves the conductivity and structural stability of hybrid materials. Based on the above advantages, it has higher specific capacity than pure MoS₂, and has better rate performance (639.3, 409.5, 386.2, 372, 338, 422.8 and 434.7 mAh g^-1 at the current density of 0.05, 0.1, 0.2, 0.5, 1 ,0.1 and 0.05 A·g^-1, respectively). The stress-modulated strategies can provide new insights for the design and construction of transition metal sulfides heterostructures to achieve high performance sodium ion batteries.

Enhanced Diffusion Kinetics of Li Ions in Double-Shell Hollow Carbon Fibers

The rational design and preparation of hierarchical hollow structures have promising potential in electrochemical energy storage systems. In this paper, double-shell hollow carbon fibers (DSHCFs) with tunable thickness and shell spacing are prepared using hollow electrospun polystyrene fibers as the hard template and in situ coated polypyrrole as the carbon source. The as-prepared DSHCFs with an optimized structure exhibit a submicrometer shell spacing and a nanoscaled shell thickness, which guarantees sufficient contact area with the electrolyte and provides abundant electrochemical active sites for Li⁺ storage. Owing to the unique structural advantages, a DSHCF-based anode shows favorable transport kinetics for both Li⁺ ions and electrons during the lithiation/delithiation process, and a high reversible capacity of 348 mAh g^-1 at 5.0 A g^-1 is well maintained even after 500 cycles with no obvious capacity attenuation. Particular emphasis is given to kinetic Li⁺ storage mechanisms in DSHCFs that are discussed in detail, providing a new avenue for developing high-performance carbon materials for the practical application of energy storage devices.

Iron Nitride@C Nanocubes Inside Core-Shell Fibers to Realize High Air-Stability, Ultralong Life, and Superior Lithium/Sodium Storages

Poor air stability and severe structure pulverization are crucial issues for metal nitrides in metal-ion batteries. Herein, core-shell hybrid fibers (CSHN fiber) filled with metal nitride@C hollow nanocubes are introduced to be a new self-supporting anode for sodium-ion and lithium-ion batteries. The hierarchical carbon network provides fast electronic pathways and gives high protection for iron nitrides. Meanwhile, the self-supporting electrode avoids the complicated electrode fabrication process and decreases the opportunity to air exposure. Moreover, its porous nature ensures high buffer to volumetric expansion and improves the cycling stability. Therefore, it is a good platform to realize fast kinetics and high durability. For the first time, Fe₂N@N-doped carbon CSHN hybrid fibers are constructed. Their influences on air stability and electrochemical behaviors are studied. Impressively, they achieve high stabilities in both lithium-ion (92.8%, at 5 A g^-1, 1000 cycles) and sodium-ion (95.6%, at 2 A g^-1, 2000 cycles) batteries. Therefore, this work introduces a new method to construct superior performance nitride anodes. Moreover, it also provides a new insight on the fabrication of highly efficient structures for diverse functional materials.

Flexible yet Robust Framework of Tin(II) Oxide Carbodiimide for Reversible Lithium Storage

Metal-organic frameworks (MOFs) can become promising electrode materials for advanced lithium-ion batteries (LIBs), because their loosely packed porous structures may mitigate volume expansion and metal atom aggregation, which occur at the respective metal oxides. However, they suffer from poor electrical conductivity and irreversible structural degradation upon charge/discharge processes, which impede their practical utilization. Herein, we investigate MOF-like Sn₂ O(CN₂ ) as a new electrode material. The conductive yet flexible [N=C=N] linkers are tilted between [Sn₄ O] nodes and cross-linked into a porous quasi-layered structure. Such structure offers abundant channels for fast Li-ion transport and tolerance of enormous volume expansion. Notably, anisotropic [N=C=N]^2- arrays hardly migrate so that Sn⁰ nanodots are physically separated via robust [N=C=N]^2- framework during discharge, thereby effectively preventing the formation of large Sn islands. Owing to the structural advantage, the Sn₂ O(CN₂ ) electrode exhibits an initial Coulombic efficiency as high as ∼80 %. With the addition of graphite as conductive supporter, the electrode provides 978 mAh g^-1 at 1.0 A g^-1 even after 300 cycles. Such MOF-like carbodiimides hold potential for the advanced electrodes in LIBs and other battery systems.

New rationally designed hybrid polypyrrole@SnCoS4 as an efficient anode for lithium-ion batteries

Three active materials containing binary metal sulfide (SnCoS₄) were obtained via a simple hydrothermal method. Also, the electrochemical performance of the anode materials was investigated in a lithium-ion half-cell.

Dual Immobilization of SnOx Nanoparticles by N-Doped Carbon and TiO2 for High-Performance Lithium-Ion Battery Anodes

The grain aggregation engendered kinetics failure is regarded as the main reason for the electrochemical decay of nanosized anode materials. Herein, we proposed a dual immobilization strategy to suppress the migration and aggregation of SnO_x nanoparticles and corresponding lithiation products through constructing SnO_x/TiO₂@PC composites. The N-doped carbon could anchor the tin oxide particles and inhibit their aggregation during the preparation process, leading to a uniform distribution of ultrafine SnO_x nanoparticles in the matrix. Meanwhile, the incorporated TiO₂ component works as parclose to suppress the migration and coarsening of SnO_x and corresponding lithiation products. In addition, the N-doped carbon and TiO₂/Li_xTiO₂ can significantly improve the electrical and ionic conductivities of the composites, enabling a good diffusion and charge-transfer dynamics. Owing to the dual immobilization from the "synergistic effect" of N-doped carbon and the "parclose effect" of TiO₂, the conversion reaction of SnO_x remains fully reversible throughout the cycling. Thereby, the composites exhibit excellent cycling performance in half cells and can be fully utilized in full cells. This work may provide an inspiration for the rational design of tin-based anodes for high-performance lithium-ion batteries.

Pseudocapacitive Lithium Storage of Cauliflower-Like CoFe2 O4 for Low-Temperature Battery Operation

Binary transition-metal oxides (BTMOs) with hierarchical micro-nano-structures have attracted great interest as potential anode materials for lithium-ion batteries (LIBs). Herein, we report the fabrication of hierarchical cauliflower-like CoFe₂ O₄ (cl-CoFe₂ O₄ ) via a facile room-temperature co-precipitation method followed by post-synthetic annealing. The obtained cauliflower structure is constructed by the assembly of microrods, which themselves are composed of small nanoparticles. Such hierarchical micro-nano-structure can promote fast ion transport and stable electrode-electrolyte interfaces. As a result, the cl-CoFe₂ O₄ can deliver a high specific capacity (1019.9 mAh g^-1 at 0.1 A g^-1 ), excellent rate capability (626.0 mAh g^-1 at 5 A g^-1 ), and good cyclability (675.4 mAh g^-1 at 4 A g^-1 for over 400 cycles) as an anode material for LIBs. Even at low temperatures of 0 °C and -25 °C, the cl-CoFe₂ O₄ anode can deliver high capacities of 907.5 and 664.5 mAh g^-1 at 100 mA g^-1 , respectively, indicating its wide operating temperature. More importantly, the full-cell assembled with a commercial LiFePO₄ cathode exhibits a high rate performance (214.2 mAh g^-1 at 5000 mA g^-1 ) and an impressive cycling performance (612.7 mAh g^-1 over 140 cycles at 300 mA g^-1 ) in the voltage range of 0.5-3.6 V. Kinetic analysis reveals that the electrochemical performance of cl-CoFe₂ O₄ is dominated by pseudocapacitive behavior, leading to fast Li⁺ insertion/extraction and good cycling life.

Recent Developments of Nanomaterials and Nanostructures for High-Rate Lithium Ion Batteries

Lithium ion batteries have been considered as a promising energy-storage solution, the performance of which depends on the electrochemical properties of each component, including cathode, anode, electrolyte and separator. Currently, fast charging is becoming an attractive research field due to the widespread application of batteries in electric vehicles, which are designated to replace conventional diesel automobiles in the future. In these batteries, rate capability, which is closely linked to the topology and morphology of electrode materials, is one of the determining parameters of interest. It has been revealed that nanotechnology is an exceptional tool in designing and preparing cathodes and anodes with outstanding electrochemical kinetics due to the well-known nanosizing effect. Nevertheless, the negative effects of applying nanomaterials in electrodes sometimes outweigh the benefits. To better understand the exact function of nanostructures in solid-state electrodes, herein, a comprehensive review is provided beginning with the fundamental theory of lithium ion transport in solids, which is then followed by a detailed analysis of several major factors affecting the migration of lithium ions in solid-state electrodes. The latest developments in characterisation techniques, based on either electrochemical or radiology methodologies, are covered as well. In addition, state-of-the-art research findings are provided to illustrate the effect of nanomaterials and nanostructures in promoting the rate performance of lithium ion batteries. Finally, several challenges and shortcomings of applying nanotechnology in fabricating high-rate lithium ion batteries are summarised.