Xiaoyuan Yu

Controlled synthesis of SnO2@carbon core-shell nanochains as high-performance anodes for lithium-ion batteries

A new low-flow-rate inert atmosphere strategy has been demonstrated for the synthesis of perfect SnO2@carbon core-shell nanochains (SCNCs) by carbonization of an SnO2@carbonaceous polysaccharide (CPS) precursor at a relatively high temperature. This strategy results in the thorough carbonization of CPS whilst avoiding the carbothermal reduction of SnO2 at 700 °C. It has been investigated that a moderate carbon content contributes to the 1-D growth of SCNCs, and the thickness of the carbon shell can be easily manipulated by varying the hydrothermal treatment time in the precursor process. Such a unique nanochain architecture could afford a very high lithium storage capacity as well as resulting in a desirable cycling performance. SCNCs with about 8 nm carbon shell synthesized by optimized routes were demonstrated for optimal electrochemical performances. More than 760 mAh g¬1 of reversible discharge capacity was achieved at a current density of 300 mA g−1, and above 85% retention can be obtained after 100 charge-discharge cycles. TEM analysis of electrochemically-cycled electrodes indicates that the structural integrity of the SnO2@carbon core-shell nanostructure is retained during electrochemical cycling, contributing to the good cycleability demonstrated by the robust carbon shell.

Tin dioxide@carbon core-shell nanoarchitectures anchored on wrinkled graphene for ultrafast and stable lithium storage.

The SnO2@C@GS composites as a new type of 3D nanoarchitecture have been successfully synthesized by a facile hydrothermal process followed by a sintering strategy. Such a 3D nanoarchitecture is made up of SnO2@C core-shell nanospheres and nanochains anchored on wrinkled graphene sheets (GSs). Transmission electron microscopy shows that these core-shell nanoparticles consist of 3-9 nm diameter secondary SnO2 nanoparticles embedded in about 50 nm diameter primary carbon nanospheres. Large quantities of core-shell nanoparticles are uniformly attached to the surface of wrinkled graphene nanosheets, with a portion of them further connected into nanochains. This new 3D nanoarchitecture consists of two different kinds of carbon-buffering matrixes, i.e., the carbon layer produced by glucose carbonization and the added GS template, leading to enhanced lithium storage properties. The lithium-cycling properties of the SnO2@C@GS composite have been evaluated by galvanostatic discharge-charge cycling and electrochemical impedance spectroscopy. Results show that the SnO2@C@GS composite has discharge capacities of 883.5, 845.7, and 830.5 mA h g(-1) in the 20th, 50th and 100th cycles, respectively, at a current density of 200 mA g(-1) and delivers a desirable discharge capacity of 645.2 mA h g(-1) at a rate of 1680 mA g(-1). This new 3D nanoarchitecture exhibits a high capability and excellent cycling and rate performance, holding great potential as a high-rate and stable anode material for lithium storage.

Electrochemical lithium storage of Li4Ti5O12/NiO nanocomposites for high-performance lithium-ion battery anodes

Li4Ti5O12/NiO (LTO/NiO) composites with various NiO contents were prepared successfully as anode materials for high-performance lithium-ion battery. The preparation procedure consisted of high-energy ball milling, high-temperature calcination, and solution coating in succession. Several techniques such as X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge-discharge, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were applied to fully investigate the micromorphology, composition structure, and electrochemical performances of the LTO/NiO composites. It was found that all the LTO/NiO composites showed higher discharge capacity than the pure LTO anode within the representative 20 cycles. The LTO/5 wt.% NiO, which had the largest specific surface area of 2.1229 m2 g−1 among all the LTO/NiO composites, delivered a capacity of 203 mAh g−1 in a voltage window of 0.5–3.0 V at 1 C rate and retained a capacity of 176 mAh g−1 after 100 cycles. The CV and EIS analysis indicated that the charge/discharge processes of LTO/NiO composites included the Li+ diffusion into or out of LTO phase and the redox reaction of NiO phase. The results demonstrate that the surface modification of LTO with small amounts of NiO nanoparticles can decrease the overall charge transfer resistance by forming in situ the electron-conductive Ni, leading to the improved electrochemical behavior of the composites.

Electrospray synthesis of nano-Si encapsulated in graphite/carbon microplates as robust anodes for high performance lithium-ion batteries

Developing efficient Si-based anode materials for new-generation lithium-ion batteries (LIBs) has drawn extensive attention. Here, an electrosprayed Si/graphite/carbon (Si/G/C) composite is explored as a prominent anode material for LIBs. The designed Si/G/C composite possesses a reasonable structure with nano-Si encapsulated in the conductive graphite flake/amorphous carbon framework. The Si/G/C composite achieves superior reversible Li+ storage capability, showing a considerable discharge capacity of 832 mA h g−1 at 200 mA g−1. Moreover, it realizes an encouraging capacity of ca. 400 mA h g−1 under a high current density of 500 mA g−1 after 200 cycles. The excellent capacity and rate performance can be attributed to the structural benefits of the Si/G/C composite: (i) the highly conductive graphite flakes serve as good dispersive scaffolds and electronic conductors, allowing for fast charge transfer and favorable ion diffusion; (ii) the amorphous carbon layer acts as a protective coating to bind/fix nano-Si onto graphite and reduce the formation of unstable solid electrolyte interphase (SEI) film; and (iii) both the layered graphite and amorphous carbon layer introduce adequate buffer space or voids to alleviate the volume changes of Si during the Li+ insertion/extraction cycles. This high-capacitive and robust Si/graphite-based hybrid is attractive as an alternative anode material for practical rechargeable LIBs.

Hierarchical Fe2O3@CNF fabric decorated with MoS2 nanosheets as a robust anode for flexible lithium-ion batteries exhibiting ultrahigh areal capacity

Flexible lithium ion batteries (LIBs) have been recognized as indispensable energy storage devices compatible with the emerging flexible/stretchable wearable electronics. Herein, we design a three-dimensional (3D) hierarchical Fe2O3@CNFs@MoS2 fabric film as a self-standing and robust anode, in which ultrathin curly MoS2 nanosheets are tightly anchored onto the surface of an interconnected Fe2O3@carbon nanofiber (CNF) substrate. The flexible Fe2O3@CNFs fabric electrode can establish a 3D continuous conducting network and maintain superior structural integrity, while the unique hierarchical MoS2 nanosheets can further shorten the Li+ diffusion path, expand the interfacial contact and offer increased active sites for reversible lithium insertion/extraction reactions. The as-prepared hierarchical Fe2O3@CNFs@MoS2 fabric is directly used as a film anode for LIB half-cells, which exhibits an excellent reversible capacity of 938 mA h g−1 at 0.2 A g−1 after 300 cycles and high rate capabilities of 304 mA h g−1 at 5.0 A g−1. When combined with a LiCoO2 (LCO) cathode and PVDF/PPC gel polymer electrolyte, the Fe2O3@CNFs@MoS2 fabric-based quasi-solid-state flexible full cell realizes outstanding capacity performance and mechanical flexibility. It delivers an ultrahigh areal specific capacity of ≈6.47 mA h cm−2, superior cycling tolerance and a high capacity retention of 90.8% after 300 cycles even in the 90° bending position, which are among those of the so far reported best-performing flexible LIBs. Along with a simple and eco-friendly fabrication process, this 3D nanoarchitectured Fe2O3@CNFs@MoS2 fabric could provide a promising avenue toward high performance flexible LIBs and other rechargeable batteries.