Yansong Bai

Suppressed capacity/voltage fading of high-capacity lithium-rich layered materials via the design of heterogeneous distribution in the composition

Lithium-rich layered materials, Li1+xM1−xO2 (M = Mn, Ni, Co), have been under intense investigation as high-performance cathode materials for lithium ion batteries due to their high discharge capacity, low cost and environmental benignity. Unfortunately, the practical uses of these oxides have so far been hindered by their severe capacity and voltage fading during high voltage cycling (>4.5 V vs. Li/Li+). In an attempt to overcome these problems, herein, a novel lithium-rich Li1.14[Mn0.60Ni0.25Co0.15]0.86O2 microsphere with heterogeneous distribution in the composition has been reasonably designed and successfully synthesized via a co-precipitation method. The chemical composition in the spherical particle is gradually altered by increasing the Mn concentration while reducing the Co content from the particle center to the outer layer. At the same time, the Ni content remains almost constant throughout the particle. The coin cell with the heterogeneous cathode material delivers a high discharge capacity of over 230 mA h g−1 between 2.0 V and 4.6 V, and shows excellent cyclic stability due to the continuous increase of the stable tetravalent Mn towards the outer surface of the spherical particles, corresponding to 93.8% capacity retention after 200 cycles at 0.5 C. More importantly, the as-prepared material exhibits a significantly lower discharge voltage decay compared with conventional materials, which may mainly be ascribed to the suppression of the layered-to-spinel transformation in the Co-rich/Mn-depleted regions of the spherical particle. The capacity and voltage fading of the lithium-rich layered material are simultaneously suppressed by the special architecturual design, and the results here will shed light on developing cathode materials with special structures and superior electrochemical properties for high-performance lithium ion batteries.

Facile synthesis and performances of nanosized Li2TiO3-based shell encapsulated LiMn1/3Ni1/3Co1/3O2 microspheres

LiMn1/3Ni1/3Co1/3O2 microspheres covered by a nanosized Li2TiO3-based shell are prepared by a facile synthesis method. First, a controllable TiO2 nano-layer is grown on the surface of a spherical Mn1/3Ni1/3Co1/3CO3 precursor, and then the resultant TiO2@LiMn1/3Ni1/3Co1/3O2 hybrid is synchronously transformed in situ into a hierarchical Li2TiO3@LiMn1/3Ni1/3Co1/3O2 microsphere through a solid-phase reaction. It has been found that the hierarchical Li2TiO3@LiMn1/3Ni1/3Co1/3O2 microspheres exhibit a good rate capability with a discharge capacity of 92.3 mA h g−1 even at higher rates of 20 C between 3.0 and 4.3 V. Besides, they possess excellent cyclic stability especially at high rates, with a capacity retention of 90.3% after 500 cycles at a 20 C rate. The enhanced electrochemical performance of the hierarchical Li2TiO3@LiMn1/3Ni1/3Co1/3O2 at high rates is attributed to the stable and fast Li+-conductor characteristic of the nanosized Li2TiO3-based shell. Thus, the Li2TiO3@LiMn1/3Ni1/3Co1/3O2 microspheres will be a promising cathode material for lithium-ion batteries with high power density and excellent cycling performance.

Sheet-like structure FeF3/graphene composite as novel cathode material for Na ion batteries

A sheet-like structure FeF3/graphene composite is successfully synthesized by a novel and facile sol–gel method. The structure and electrochemical performance of the as-synthesized FeF3/graphene composite are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and electrochemical measurement. The results indicate that the FeF3 nanosheets are loaded on the surface of the graphene sheets to form the sheet-like structure hybrid. Fourier transform infrared (FTIR) spectrum confirms that C–F bonds exist in FeF3/graphene composite, and it further indicates that a chemical bond between FeF3 and graphene has been formed and FeF3 can preferably stick to the surface of the graphene. The FeF3/graphene composite as cathode material of rechargeable Na ion batteries (NIB) exhibits a fairly high initial discharge capacity of 550 mA h g−1 at 0.1 C, and it still keeps a capacity of 115 mA h g−1 after 50 cycles at 0.3 C at a range of 1.0–4.0 V for NIB.

Preparation and performance of hierarchically porous carbons as oxygen electrodes for lithium oxygen batteries

Abstract The hierarchically porous carbons (HPCs) were prepared by sol–gel selassembly technology in different surfactant concentrations and were used as the potential electrode for lithium oxygen batteries. The physical and electrochemical properties of the as-prepared HPCs were investigated by filed emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), nitrogen adsorption–desorption isotherm and galvanostatic charge/discharge. The results indicate that all of the HPCs mainly possess mesoporous structure with nearly similar pore size distribution. Using the HPCs as the electrode, a high discharge capacity for lithium oxygen battery can be achieved, and the discharge capacity increases with the specific surface area. Especially, the HPCs-3 oxygen electrode with CTAB concentration of 0.27 mol/L exhibits good capacity retention through controlling discharge depth to 800 mA·h/g and the highest discharge capacity of 2050 mA·h/g at a rate of 0.1 mA/cm2.

Effects of preparation temperature on electrochemical performance of nitrogen-enriched carbons

Abstract The activated nitrogen-enriched novel carbons (NENCs) were prepared by direct carbonization using polyaniline coating activated mesocarbon microbead composites as the precursor. Herein the influences of the carbonization temperature on the structure and morphology of the NENCs samples were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N 2 adsorption/desorption isotherm at 77 K. The electrochemical properties of the supercapacitors were characterized by cyclic voltammetry, galvanostatic charge/discharge, electrochemical impedance spectroscopy (EIS), cycle life, leakage current and self-discharge measurements in 6 mol/L KOH solution. The results demonstrate that the NENC samples carbonized at 600 °C show the highest specific capacitance of 385 F/g at the current density of 1 A/g and the lowest ESR value (only 0.93 Ω). Furthermore, the capacity retention ratio of the NENCs-600 supercapacitor is 92.8 % over 2500 cycles.