Jili Li

LiNi1/3Co1/3Mn1/3O2 Nanoplates with {010} Active Planes Exposing Prepared in Polyol Medium as a High-Performance Cathode for Li-Ion Battery

As we know, Li(+)-ion transport in layered LiNi1/3Co1/3Mn1/3O2 (NCM) is through two-dimensional channels parallel to the Li(+)-ion layers that are indexed as {010} active planes. In this paper, NCM nanoplates with exposed {010} active facets are synthesized in a polyol medium (ethylene glycol) and characterized by XRD, XPS, SEM, and HR-TEM. In addition, the effects of reaction conditions on the morphologies, structures and electrochemical performances are also evaluated. The results show that more {010} facets can be exposed with the thickness of NCM nanoplates increasing which can lead to more channels for Li(+)-ion migration. However, when the annealing temperatures exceed 900 °C, many new crystal planes grow along the thickness direction covering the {010} facets. In all of the NCM nanoplates obtained at different conditions, the NCM nanoplates calcined at 850 °C for 12 h (NCM-850-12H) display a high initial discharge capacity of 207.6 mAh g(-1) at 0.1 C (1 C = 200 mA g(-1)) between 2.5 and 4.5 V higher than most of NCM materials as cathodes for lithium ion batteries. The discharge capacities of NCM-850-12H are 169.8, 160.5, and 149.3 mAh g(-1) at 2, 5, and 7 C, respectively, illustrating the excellent rate capability. The superior electrochemical performance of NCM-850-12H cathode can be attributed to more {010} active planes exposure.

LiNi1/3Co1/3Mn1/3O2 hollow nano-micro hierarchical microspheres with enhanced performances as cathodes for lithium-ion batteries

LiNi1/3Co1/3Mn1/3O2 hollow nano-micro hierarchical microspheres (NCM-HS) are synthesized using MnCO3 both as a self-template and Mn source. The hollow microspheres with diameters of about 1 μm have walls about 250 nm thick, which are composed of approximately 100 nm primary nanoparticles. NCM-HS cathodes have an initial discharge capacity of 212 mA h g−1 at 0.1 C between 2.5 and 4.5 V. After 40 charge–discharge cycles, the capacity retention at 0.1 C is 85.1%. At higher rates, the reversible capacities of the NCM-HS cathodes are 208.9 (0.5 C), 204.8 (1 C), 180.7 (2 C), 155.7 (5 C) and 135.9 mA h g−1 (10 C). The high performances can be attributed to the distinctive hollow microspherical structures with the 100 nm building blocks, which could effectively reduce the path of Li ion diffusion, increase the contact area between electrodes and electrolyte and buffer the volume changes during the Li ion intercalation/deintercalation processes.

Cube-shaped hierarchical LiNi1/3Co1/3Mn1/3O2 with enhanced growth of nanocrystal planes as high-performance cathode materials for lithium-ion batteries

Hierarchical cubed LiNi1/3Co1/3Mn1/3O2 (CH-NCM) with enhanced growth of electrochemically active planes is synthesized using cube structured MnCO3 as a self-template, which is synthesized by a fast, simple, and surfactant-free co-precipitation method. The CH-NCM cathode has a reversible discharge capacity as high as 220.9, 216.2, 211.4, 189.6, 171.7 and 144.5 mA h g−1 at 0.1, 0.5, 1, 2, 5, and 10 C, respectively. After 100 cycles, the capacity retention is 83.34% at 0.1 C. The superior electrochemical performance can be ascribed to the special cube-shaped hierarchical structure and enhanced growth of electrochemically active surface planes of CH-NCM. The primary nanoparticles with enhanced growth of electrochemically active surface planes guarantee ultrafast Li+ intercalation/deintercalation, while the submicroassemblies promise good structural stability.

Lithium Titanate Epitaxial Coating on Spinel Lithium Manganese Oxide Surface for Improving the Performance of Lithium Storage Capability

Spinel lithium titanate (Li4Ti5O12, LTO) is applied as an epitaxial coating layer on LiMn2O4 hollow microspheres (LMO) through solvothermal-assisted processing. The epitaxial interface between LTO and LMO can be clearly observed by high resolution transmission electron microscopy (HR-TEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with atomic resolution images. The epitaxial coating cathode (EC-LMO@LTO) exhibits an excellent cyclability, thermal and rate capability for LIBs cathode due to the complete, thin LTO coating layer with strong adhesion to the host material. In addition, the small structure mismatch and high Li(+)-ion mobility of LTO can be beneficial to forming an efficient tunnel for Li(+)-ion transfer at the interface. It is suggested that EC-LMO@LTO can be recognized as a promising cathode material in electric vehicles (EVs) and plug-in hybrid electric vehicles (HEVs).

The superelastic mechanism of Si3N4 microsprings using micro-Raman spectroscopy

Silicon nitride microsprings with superelasticity are characterized using SEM, XRD, TEM and micro-Raman methods. The internal structure and the superelastic mechanism of silicon nitride microsprings are proposed through analyzing the variation of Raman peaks upon stretching gradually. During the stretching process, since all the vibrations are internal vibrations within the primitive unit cell, the basic structure has no changes and the residual stress never concentrates. The special structure of the fine grains and no sharp grain boundaries make the silicon nitride microsprings possess such good superelastic properties.