Constructing Hollow Ni 0.2 Co 0.8 S@rGO Composites at Low Temperature Conditions as Anode Material for Lithium‐Ion batteries

Enhanced High-Rate Capability and Long Cycle Stability of FeS@NCG Nanofibers for Sodium-Ion Battery Anodes

The development of advanced hierarchical anode materials has recently become essential to achieving high-performance sodium-ion batteries. Herein, we developed a facile and cost-effective scheme for synthesizing graphene-wrapped, nitrogen-rich carbon-coated iron sulfide nanofibers (FeS@NCG) as an anode for SIBs. The designed FeS@NCG can provide a significant reversible capacity of 748.5 mAh g^-1 at 0.3 A g^-1 for 50 cycles and approximately 3.9-fold higher electrochemical performance than its oxide analog (Fe₂O₃@NCG, 192.7 mAh g^-1 at 0.3 A g^-1 for 50 cycles). The sulfur- and nitrogen-rich multilayer package structure facilitates efficient suppression of the porous FeS volume expansion during the sodiation process, enabling a long cycle life. The intimate contact between graphene and porous carbon-coated FeS nanofibers offers strong structural barriers associated with charge-transfer pathways during sodium insertion/extraction. It also reduces the dissolution of polysulfides, enabling efficient sodium storage with superior stable kinetics. Furthermore, outstanding capacity retention of 535 mAh g^-1 at 5 A g^-1 is achieved over 1010 cycles. The FeS@NCG also exhibited a specific capacity of 640 mAh g^-1 with a Coulombic efficiency of above 99.8% at 5 A g^-1 at 80 °C, indicating its development prospects in high-performance SIB applications.

In-situ self-assembled hollow urchins F-Co-MOF on rGO as advanced anodes for lithium-ion and sodium-ion batteries

To obtain MOFs materials with good electrochemical performance in both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), a kind of hollow urchins Co-MOF with doping fluorine (F) was in-situ assembled on reduced graphene oxide (rGO) using a simple solvothermal reaction. According to XRD, XPS and EDS mapping analysis, the molecular structure should be Co₂[F_x(OH)_1-x]₂(C₈O₄H₄) (denoted as F-Co-MOF). When the composite material is used as active material to assemble LIBs, it not only presents the outstanding reversible capacity (1202.0 mA h g^-1 at 0.1 A g^-1), but also gives the excellent rate performance and cycle performance (771.5 mA h g^-1 at 2 A g^-1 after 550 repeated cycles). The remarkable lithium storage capacity of F-Co-MOF/rGO is also reflected in the full cell, where it can still maintain a high capacity of 165.2 mA h g^-1 after 300 cycles at 0.2 A g^-1. It benefits from the synergistic effect of F-Co-MOF and high conductive rGO networks, so that the reversibility of lithium and sodium storage can be improved. This kind of F doped solvothermal synthesis of MOFs is of great significance for the exploration of high performance materials.

Understanding the High-Performance Anode Material of CoC2 O4 ⋅2 H2 O Microrods Wrapped by Reduced Graphene Oxide for Lithium-Ion and Sodium-Ion Batteries

Metal oxalate has become a most promising candidate as an anode material for lithium-ion and sodium-ion batteries. However, capacity decrease owing to the volume expansion of the active material during cycling is a problem. Herein, a rod-like CoC₂ O₄ ⋅2 H₂ O/rGO hybrid is fabricated through a novel multistep solvo/hydrothermal strategy. The structural characteristics of the CoC₂ O₄ ⋅2 H₂ O microrod wrapped using rGO sheets not only inhibit the volume variation of the hybrid electrode during cycling, but also accelerate the transfer of electrons and ions in the 3 D graphene network, thereby improving the electrochemical properties of CoC₂ O₄ ⋅2 H₂ O. The CoC₂ O₄ ⋅2 H₂ O/rGO electrode delivers a specific capacity of 1011.5 mA h g^-1 at 0.2 A g^-1 after 200 cycles for lithium storage, and a high capacity of 221.1 mA h g^-1 at 0.2 A g^-1 after 100 cycles for sodium storage. Moreover, the full cell CoC₂ O₄ ⋅2 H₂ O/rGO//LiCoO₂ consisting of the CoC₂ O₄ ⋅2 H₂ O/rGO anode and LiCoO₂ cathode maintains 138.1 mA h g^-1 after 200 cycles at 0.2 A g^-1 and has superior long-cycle stability. In addition, in situ Raman spectroscopy and in situ and ex situ X-ray diffraction techniques provide a unique opportunity to understand fully the reaction mechanism of CoC₂ O₄ ⋅2 H₂ O/rGO. This work also gives a new perspective and solid research basis for the application of metal oxalate materials in high-performance lithium-ion and sodium-ion batteries.