Yeqian Ge

Carbon-Confined SnO2-Electrodeposited Porous Carbon Nanofiber Composite as High-Capacity Sodium-Ion Battery Anode Material.

Sodium resources are inexpensive and abundant, and hence, sodium-ion batteries are promising alternative to lithium-ion batteries. However, lower energy density and poor cycling stability of current sodium-ion batteries prevent their practical implementation for future smart power grid and stationary storage applications. Tin oxides (SnO2) can be potentially used as a high-capacity anode material for future sodium-ion batteries, and they have the advantages of high sodium storage capacity, high abundance, and low toxicity. However, SnO2-based anodes still cannot be used in practical sodium-ion batteries because they experience large volume changes during repetitive charge and discharge cycles. Such large volume changes lead to severe pulverization of the active material and loss of electrical contact between the SnO2 and carbon conductor, which in turn result in rapid capacity loss during cycling. Here, we introduce a new amorphous carbon-coated SnO2-electrodeposited porous carbon nanofiber (PCNF@SnO2@C) composite that not only has high sodium storage capability, but also maintains its structural integrity while ongoing repetitive cycles. Electrochemical results revealed that this SnO2-containing nanofiber composite anode had excellent electrochemical performance including high-capacity (374 mAh g(-1)), good capacity retention (82.7%), and large Coulombic efficiency (98.9% after 100th cycle).

Poly(vinyl Alcohol) Borate Gel Polymer Electrolytes Prepared by Electrodeposition and Their Application in Electrochemical Supercapacitors

Gel polymer electrolytes (GPEs) have been studied for preparing flexible and compact electrochemical energy storage devices. However, the preparation and use of GPEs are complex, and most GPEs prepared through traditional methods do not have good wettability with the electrodes, which retard them from achieving their performance potential. In this study, these problems are addressed by conceiving and implementing a simple, but effective, method of electrodepositing poly(vinyl alcohol) potassium borate (PVAPB) GPEs directly onto the surfaces of active carbon electrodes for electrochemical supercapacitors. PVAPB GPEs serve as both the electrolyte and the separator in the assembled supercapacitors, and their scale and shape are determined solely by the geometry of the electrodes. PVAPB GPEs have good bonding to the active electrode materials, leading to excellent and stable electrochemical performance of the supercapacitors. The electrochemical performance of PVAPB GPEs and supercapacitors can be manipulated simply by adjusting the concentration of KCl salt used during the electrodeposition process. With a 0.9 M KCl concentration, the as-prepared supercapacitors deliver a specific capacitance of 65.9 F g(-1) at a current density of 0.1 A g(-1) and retain more than 95% capacitance after 2000 charge/discharge cycles at a current density of 1 A g(-1). These supercapacitors also exhibit intelligent high voltage self-protection function due to the electrolysis-induced cross-linking effect of PVAPB GPEs.

Nanoscale Porous Lithium Titanate Anode for Superior High Temperature Performance

In this work, nanoscale porous lithium titanate (LTO) anode material was synthesized by using aqueous spray drying method after ball milling. The size of the LTO nanoparticles was optimized to 200 nm because of its considerable moisture absorption levels for stable performance and its cooperation to make good quality electrodes found with testing. The electrochemical performance of the synthesized LTO nanoparticles was found to be very stable at high operating temperature (50 °C) and high current rate (5 C) which was worth noticing than its usual unfavorable behaviors (gas generation and surface phase transitions) at higher temperatures. In the postanalysis on the aged LTO cells, high-resolution-transmission electron microscope (HRTEM) and fast Fourier transform (FFT) measurements reveal that the LTO phase transitions are maintained to very thin surface level (3-5 nm) even after 500 cycles at 50 °C. Moreover, the synthesized LTO material showed stable cycling with a high capacity of 138.74 mA h g(-1) at 1 C rate and 111.53 mA h g(-1) at 5 C rate. Furthermore, high columbic efficiency and excellent capacity retention over 500 cycles at 50 °C was achieved. The enhanced electrochemical properties can be attributed to the increase in surface area and shortened Li(+) diffusion lengths because of the nanoscale primary particles and porous structure of the synthesized LTO particles.

High-strength, thermally stable nylon 6,6 composite nanofiber separators for lithium-ion batteries

Abstract Electrospun nylon 6,6 composite nanofiber membranes containing TiO2 or SiO2 nanoparticles were fabricated, and their physical and electrochemical properties were assessed for use as high-strength, thermally stable separators for lithium-ion batteries. Experimental results demonstrated that TiO2/nylon 6,6 and SiO2/nylon 6,6 nanofiber membranes not only displayed good mechanical strength and excellent thermal stability, but also showed improved electrochemical properties compared to commercial polypropylene membrane separator. Larger liquid electrolyte uptake, higher ionic conductivity, higher electrochemical oxidation limit, and lower interfacial resistance with lithium were obtained for TiO2/nylon 6,6 and SiO2/nylon 6,6 nanofiber membranes. Among all membranes studied, SiO2/nylon 6,6 nanofiber membranes showed the highest ionic conductivity and lowest interfacial resistance with lithium owing to their highest porosity and well-dispersed nanoparticles. In addition, Li/LiCoO2 and Li/LiFePO4 cells containing these composite nanofiber membranes demonstrated high cell capacities, good cycling performance, and superior C-rate performance at room temperature.