RESUMO
Lithium-ion batteries (LIBs) are very popular electrochemical energy-storage devices. However, their applications in extreme environments are hindered because their low- and high-temperature electrochemical performance is currently unsatisfactory. In order to build all-climate LIBs, it is highly desirable to fully understand the underlying temperature effects on electrode materials. Here, based on a novel porous-microspherical yttrium niobate (Y0.5 Nb24.5 O62 ) model material, this work demonstrates that the operation temperature plays vital roles in electrolyte decomposition on electrode-material surfaces, electrochemical kinetics, and crystal-structure evolution. When the operation temperature increases, the reaction between the electrolyte and the electrode material become more intensive, causing the formation of thicker solid electrolyte interface (SEI) films, which decreases the initial Coulombic efficiency. Meanwhile, the electrochemical kinetics becomes faster, leading to the larger reversible capacity, higher rate capability, and more suitable working potential (i.e., lower working potential for anodes and higher working potential for cathodes). Additionally, the maximum unit-cell-volume change becomes larger, resulting in poorer cyclic stability. The insight gains here can provide a universal guide for the exploration of all-climate electrode materials and their modification methods.
RESUMO
Niobate Li+ -storage anode materials with shear ReO3 crystal structures have attracted intensive attention due to their inherent safety and large capacities. However, they generally suffer from limited rate performance, cyclic stability, and temperature adaptability, which are rooted in their insufficient interlayer spacings. Here, sodium niobate (NaNb13 O33 ) micron-sized particles are developed as a new anode material owning the largest interlayer spacing among the known shear ReO3 -type niobates. The large interlayer spacing of NaNb13 O33 enables very fast Li+ diffusivity, remarkably contributing to its superior rate performance with a 2500 to 125 mA g-1 capacity percentage of 63.2%. Moreover, its large interlayer spacing increases the volume-accommodation capability during lithiation, allowing small unit-cell-volume variations (maximum 6.02%), which leads to its outstanding cyclic stability with 87.9% capacity retention after as long as 5000 cycles at 2500 mA g-1 . Its cyclic stability is the best in the research field of niobate micron-sized particles, and comparable to that of "zero-strain" Li4 Ti5 O12 . At a low temperature of -10 °C, it also exhibits high rate performance with a 1250 to 125 mA g-1 capacity percentage of 65.6%, and even better cyclic stability with 105.4% capacity retention after 5000 cycles at 1250 mA g-1 . These comprehensively good electrochemical results pave the way for the practical application of NaNb13 O33 in high-performance Li+ storage.
RESUMO
Niobates are very promising anode materials for Li+-storage rooted in their good safety and high capacities. However, the exploration of niobate anode materials is still insufficient. In this work, we explore ~1 wt% carbon-coated CuNb13O33 microparticles (C-CuNb13O33) with a stable shear ReO3 structure as a new anode material to store Li+. C-CuNb13O33 delivers a safe operation potential (~1.54 V), high reversible capacity of 244 mAh g-1, and high initial-cycle Coulombic efficiency of 90.4% at 0.1C. Its fast Li+ transport is systematically confirmed through galvanostatic intermittent titration technique and cyclic voltammetry, which reveal an ultra-high average Li+ diffusion coefficient (~5 × 10-11 cm2 s-1), significantly contributing to its excellent rate capability with capacity retention of 69.4%/59.9% at 10C/20C relative to 0.5C. An in-situ XRD test is performed to analyze crystal-structural evolutions of C-CuNb13O33 during lithiation/delithiation, demonstrating its intercalation-type Li+-storage mechanism with small unit-cell-volume variations, which results in its capacity retention of 86.2%/92.3% at 10C/20C after 3000 cycles. These comprehensively good electrochemical properties indicate that C-CuNb13O33 is a practical anode material for high-performance energy-storage applications.
RESUMO
Ferric gallate (Fe-GA), an ancient metal-organic framework (MOF) material, has been recently employed as an eco-friendly and cost-effective precursor sample to synthesize a porous carbon confined nano-iron composite (Fe/RPC), and the Fe element in the Fe/RPC sample could be further oxidized to Fe3O4 nanocrystals in a 180 °C hydrothermal condition. On this foundation, this work reports an optimized approach to engineering a hierarchical one-dimensional porous carbon and two-dimensional reduced graphene oxide (RGO) supporting framework with Fe3O4 nanoparticles well dispersed. Under mild hydrothermal condition, the redox reaction between metal iron atoms from Fe/RPC and surface functional radicals from few-layered graphene oxide sheets (GO) is triggered. As a result, reinforced microstructure and improved atomic efficiency have been achieved for the Fe3O4@RPC/RGO sample. The homogeneously dispersed Fe3O4 nanoparticles with controlled size are anchored on the surface of the larger sized RGO coating layers while the smaller sized RPC domains are embedded between the RGO sheets as spacer. Challenges including spontaneous aggregation of RPC, over exposure of Fe3O4 nanoparticles and excessive restacking of RGO have been significantly inhibited. Furthermore, micro-sized carbon fiber (CF) is chosen as a structural reinforcement additive during electrode fabrication, and the Fe3O4@RPC/RGO sample delivers a good specific capacity of 1170.5 mAh·g-1 under a current rate of 1000 mA·g-1 for 500 cycles in the half cell form. The reasons for superior electrochemical behaviors have been revealed and the lithium-ion storage performances of the Fe3O4@RPC/RGO sample in the full cell form have been preliminarily investigated.
