Congjie Lv,Yi Peng,Jing Yang,Xiaochuan Duan,Jianmin Ma,Taihong Wang
Nb-Doped LiNi0.4Co0.2Mn0.4O2 (Nb-NCM) nanobelts have been successfully fabricated for the first time through a facile electrospinning method by the delicate control of PAN pyrolysis and Nb-NCM formation (including nucleation and subsequent growth processes). According to the experimental evidence from temperature-dependent characterization and isolation of the intermediates, the formation of nanobelts undergoes a morphology evolution from nanofibres to nanotubes, and finally to the nanobelts composed of subunit nanoparticles. When used as a cathode for lithium-ion batteries, the as-electrospun Nb-NCM nanobelts exhibit superior electrochemical performances, which could be attributed to their unique features, such as their 1D nanostructure, well-crystallized nature and Nb-doping. These features can improve the ionic conductivity of Nb-NCM nanobelts and stabilize the electrode/electrolyte interface. Therefore, the 1D Nb-NCM nanobelts developed in this study not only provide an excellent model to investigate the fabrication of multi-element oxides using the electrospinning method, but also open up a facile route for designing 1D layered cathodes with a complex component for high performance lithium-ion batteries.
An ultrathin Y2O3 layer is applied to improve the unsatisfactory cyclability and rate performance of LiNi0.4Co0.2Mn0.4O2 (NCM) cathodes for the first time. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were implemented to characterize the physical performance of synthetical materials. In addition, charge-discharge cycling, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were executed to investigate the electrochemical actions. In particular, the 0.5 wt% Y2O3-coated NCM manifests a significantly upgraded initial specific capacity of 185.4 mAh g−1 at 1 C and a capacity retention as high as 93.7% after 100 cycles. Nevertheless, bare NCM manifests a capacity retention of 59.4%. Even at 5 C, modified NCM samples still have high capacity. The remarkably ameliorative electrochemical performance of Y2O3-coated NCM materials during cycling is because of the Y2O3 coating that may hinder the deleterious reactions between the electrolyte and the cathodes and decrease the charge-transfer resistance.
Graphical What′s on tap today ? Li 4 Ti 5 O 12 (LTO) and 0.5 Li 2 MnO 3 ⋅0.5 LiNi 0.4 Co 0.2 Mn 0.4 O 2 (NCM) microspheres show a good electrochemical performance and high tap density. The Li 4 Ti 5 O 12 / x Li 2 MnO 3 ⋅(1- x ) LiMO 2 lithium-ion battery system can offer a higher energy density than Li 4 Ti 5 O 12 /LiCoO 2 cells. In this work, we propose an effective way to prepare nanosized Li 4 Ti 5 O 12 (LTO) microspheres and 0.5 Li 2 MnO 3 ⋅0.5 LiNi 0.4 Co 0.2 Mn 0.4 O 2 (NCM) microspheres by similar spray-drying methods. Both obtained materials are accumulated by primary nanoparticles and show a spherical morphology with particle distribution of 10–20 μm. The LTO microspheres deliver a tap density of 1.04 g cm −3 , while the tap density of NCM microspheres is 2.07 g cm −3 , which means an enhanced volumetric energy density. The as-prepared LTO microspheres have a reversible capacity of 170 mA h g −1 at 0.1 C and a capacity retention of 97 % after 250 cycles at 1 C. The NCM microspheres have an initial discharge capacity of 270 mA h g −1 with a corresponding Coulombic efficiency of 88 % at 0.03 C. Both materials show a relatively good rate capability. The Li 4 Ti 5 O 12 /0.5 Li 2 MnO 3 ⋅0.5 LiNi 0.4 Co 0.2 Mn 0.4 O 2 cells deliver a high cathode specific capacity of 273 mA h g −1 and good initial Coulombic efficiency of 88 % at 0.03 C, and can be developed for powering hybrid and plug-in hybrid vehicles.
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