Structural regulation enabled stable hollow molybdenum diselenide nanosheet anode for ultrahigh energy density sodium ion pouch cell

P2-Na0.67Mn0.7Ni0.2Co0.1O2 stabilized by optimal active facets for sodium-ion batteries

Considering factors such as crustal reserves, atomic mass, redox potential and energy density, sodium-ion batteries (SIBs) are regarded as the most promising alternative to lithium-ion batteries (LIBs). Transition metal-based layered oxides, especially typical NaxMnO2, stand out among cathode materials due to their low cost and high energy density. However, NaxMnO2 cathodes face several challenges, including Jahn-Teller distortion, manganese dissolution, structural collapse, irreversible phase transition and significant capacity loss. In addition, the significant changes in lattice parameters can lead to the formation of cracks and nanovoids. It has been reported that optimizing the assembly of surface facets can be beneficial to electrochemical properties. In this work, Na0.67MnO2 (NMO) with a multilayered structure featuring (distinct {010} active facets and Na0.67Mn0.7Ni0.2Co0.1O2 (NMNCO) with a homogeneous polyhedra structure featuring distinct {001} active facets were synthesized. The initial charge capacity of NMNCO reached 110.1 mA h g-1 at a current density of 10 mA g-1. After 100 cycles at 100 mA g-1, it displayed a good cycling retention rate of 82.1 %. The distribution of relaxation times (DRT) reveals the facile transfer of Na+ ions in the NMNCO cathode. In addition, the effects of Ni and Co are revealed, and the mechanism underlying the relationship between distinct surface facet and crack formation is studied.

Enhancing the sodium storage performance of hard carbon by constructing thin carbon coatings via esterification reactions

Hard carbons derived from pitch are considered a competitive low-cost anode for sodium-ion batteries. However, the preparation of pitch-based hard carbon (PHC) requires the aid of a pre-oxidation strategy, which introduces unnecessary defects and oxygen elements, which leads to low initial Coulombic efficiency (ICE) and poor cycling stability. Herein, we demonstrate a new surface engineering strategy by grafting chemically active glucose molecules on the PHC surface via esterification reactions, which can achieve low-cost nano-scaled carbon coating. Thin glucose coating can be carbonized at a lower temperature, which results in a more closed pore structure and fewer functional groups. The as prepared PHC exhibits a high reversible capacity of 328.5 mAh/g with a high ICE of 92.08 % at 0.02 A/g. It is noteworthy that the PHC can be adapted to a variety of cathode materials for full-cell assembling without pre-sodiation, which maintains the characteristics of high capacity and excellent cycling stability. The performance of resin-based hard carbon coated with a similar method was also improved, demonstrating the universality of the technique.

Transition Metal Selenide-Based Anodes for Advanced Sodium-Ion Batteries: Electronic Structure Manipulation and Heterojunction Construction Aspect

In recent years, sodium-ion batteries (SIBs) have gained a foothold in specific applications related to lithium-ion batteries, thanks to continuous breakthroughs and innovations in materials by researchers. Commercial graphite anodes suffer from small interlayer spacing (0.334 nm), limited specific capacity (200 mAh g-1), and low discharge voltage (<0.1 V), making them inefficient for high-performance operation in SIBs. Hence, the current research focus is on seeking negative electrode materials that are compatible with the operation of SIBs. Many studies have been reported on the modification of transition metal selenides as anodes in SIBs, mainly targeting the issue of poor cycling life attributed to the volume expansion of the material during sodium-ion extraction and insertion processes. However, the intrinsic electronic structure of transition metal selenides also influences electron transport and sodium-ion diffusion. Therefore, modulating their electronic structure can fundamentally improve the electron affinity of transition metal selenides, thereby enhancing their rate performance in SIBs. This work provides a comprehensive review of recent strategies focusing on the modulation of electronic structures and the construction of heterogeneous structures for transition metal selenides. These strategies effectively enhance their performance metrics as electrodes in SIBs, including fast charging, stability, and first-cycle coulombic efficiency, thereby facilitating the development of high-performance SIBs.

Morphology design and electronic configuration of MoSe2 anchored on TiO2 nanospheres for high energy density sodium-ion half/full batteries

Molybdenum selenide (MoSe2) has shown potential sodium storage properties due to its large layer spacing (0.646 nm) and high theoretical capacity and narrow band gap. However, as the anode material of sodium ion batteries (SIBs), the MoSe2's performance is not ideal, especially due to the layer agglomeration and stacking caused by volume expansion and low intrinsic conductivity. Hence, morphology design and electronic configuration of MoSe2 is proposed via building MoSe2 nanosheets and auxiliary sulfur doping on the surface of the TiO2 hollow nanosphere (S-MoSe2@TiO2). The hierarchical shaped S-MoSe2@TiO2 effectively overcomes the shortcomings of high surface energy and weak interlayer van der Waals force of MoSe2. As anode for SIBs, S-MoSe2@TiO2 delivers enhanced cycling life and rate capability (308 mAh/g at 10 A/g after 1000 cycles) with the comparison of MoSe2@TiO2 or pure MoSe2 and TiO2. Such excellent sodium storage performance is due to the fast diffusion kinetics of Na+. When it is applied in sodium ion full batteries, the S-MoSe2@TiO2 anode based cell can reach a high energy density of 187.8 W h kg-1 at 148.3 W kg-1. The design of the new MoSe2-based hybrid provides a novel scheme for the preparation of advanced anode in SIBs.

Metal-injection and interface density engineering induced nickel diselenide with rapid kinetics for high-energy sodium storage

The key to the innovation of sodium-ion batteries (SIBs) is to find efficient sodium-storage electrode. Here, metal Mo doping of NiSe2 is proposed by modified electrospinning strategy followed by in situ conversion process. The Mo-NiSe2 anchoring on hollow carbon nanofibers (HCNFs) would make full use of the multi-channel HCNFs in the inner layer and the active sites of Mo-NiSe2 in the outer layer, which plays an important role in buffering the volume stress of Na+ (de)insertion and reducing the adsorption energy barrier of Na+. Innovatively, it is proposed to jointly regulate the SIBs performance of NiSe2 by both metal atom doping and interface effects, thereby adjusting the sodium ion adsorption barrier of NiSe2. The Mo-NiSe2@HCNFs exhibits remarkable performance in SIBs, demonstrating a high specific capacity of 396 mAh/g after 100 cycles at 1 A/g. Moreover, it maintains outstanding cycling stability, retaining 77.6 % of its capacity (211 mAh/g) even after 1000 cycles at 10 A/g. This comprehensive electrochemical performances are due to the structural stability and outstanding electronic conductance of the Mo-NiSe2@HCNFs, as evidenced by the diffusion analysis and ex situ charge-discharge process characterization. Furthermore, coupled with the Na3V2(PO4)2O2F cathodes, the full cell also achieves a high energy density of 123 Wh kg-1. The theoretical calculation of the hypervalent Mo doing further proves the benefit of its Na+ adsorption and denser conduction band distribution. This study provides a reference for the construction of transition metal selenide via doping and interface engineering in sodium storage.