Xiangming Feng

Synergistic effect induced ultrafine SnO2/graphene nanocomposite as an advanced lithium/sodium-ion batteries anode

SnO2/graphene materials have received extensive attention in broad applications owning to their excellent performances. However, multi-step and harsh synthetic methods with high temperatures and high pressures are major obstacles that need to be overcome. Herein a simple, low-cost, and scalable approach is proposed to construct ultrafine SnO2/graphene nanomaterials effectively under constant pressure and at the low temperature of 80 °C for 4 h, in which ultrafine SnO2 nanoparticles grow on graphene sheets uniformly and firmly via Sn–O–C bonding. This result depends on the synergetic effect of two reactions, the reduction of graphene oxide and formation of SnO2 nanoparticles, which are achieved successfully. More importantly, the constructed SnO2/graphene material exhibits excellent electrochemical properties in both lithium-ion batteries and sodium-ion batteries. As an anode material for lithium-ion batteries, it displays a high reversible capacity (1420 mA h g−1 at 0.1 A g−1 after 90 cycles) and good cycling life (97% at 1 A g−1 after 230 cycles), whereas in sodium-ion batteries, it maintains a capacity of 1280 mA h g−1 at 0.05 A g−1 and 650 mA h g−1 at 0.2 A g−1 after 90 cycles. The proposed synthetic methodology paves the way for the effective and large scale preparation of graphene-based composites for broad applications such as energy storage, optoelectronic devices, and catalysis.

From α-NaMnO2 to crystal water containing Na-birnessite: enhanced cycling stability for sodium-ion batteries

In this work, α-NaMnO2 has been synthesized first. And then, after reacting with water, α-NaMnO2 translates into crystal water containing Na-birnessite with a large interlayer distance of 7.15 A. The synthesized α-NaMnO2 exhibits a discharge capacity (126.4 mA h g−1) higher than that of the crystal water containing Na-birnessite (100.9 mA h g−1). However, the crystal water containing Na-birnessite exhibits a cycling stability higher than α-NaMnO2 owing to the larger interlayer distance of Na-birnessite with the crystal water in the interlayer. Therefore, an effective way to improve the cycling stability of this kind of material is by changing the interlayer distance.

Synthesis of Li2FeSiO4/C and its excellent performance in aqueous lithium-ion batteries

A carbon-coated Li2FeSiO4 (Li2FeSiO4/C) material was synthesized through a liquid-phase-assisted method. The obtained sample can be used as an anode material for aqueous lithium-ion batteries. The aqueous electrolyte cell system used in this study delivers a capacity of approximately 90 mA h g−1 based on the total weight of the anode material Li2FeSiO4/C and an export voltage of 1.2 V. The aqueous electrolyte cell system also exhibits excellent cycling stability with a capacity loss of less than 10% after 30 cycles and a high coulombic efficiency of almost 100% in the preliminary 30 cycles. This study provides the most promising anode material for aqueous lithium-ion batteries because of its environmental inertness and low cost and since Fe and Si are among the most abundant and inexpensive elements.

Hierarchical porous onion-shaped LiMn2O4 as ultrahigh-rate cathode material for lithium ion batteries

Spinel LiMn2O4 is a widely utilized cathode material for Li-ion batteries. However, its applications are limited by its poor energy density and power density. Herein, a novel hierarchical porous onion-like LiMn2O4(LMO) was prepared to shorten the Li+ diffusion pathway with the presence of uniform pores and nanosized primary particles. The growth mechanism of the porous onion-like LiMn2O4 was analyzed to control the morphology and the crystal structure so that it forms a polyhedral crystal structure with reduced Mn dissolution. In addition, graphene was added to the cathode (LiMn2O4/graphene) to enhance the electronic conductivity. The synthesized LiMn2O4/graphene exhibited an ultrahigh-rate performance of 110.4 mAh·g–1 at 50 C and an outstanding energy density at a high power density, maintaining 379.4 Wh·kg–1 at 25,293 W·kg–1. Besides, it shows durable stability, with only 0.02% decrease in the capacity per cycle at 10 C. Furthermore, the (LiMn2O4/graphene)/graphite full-cell exhibited a high discharge capacity. This work provides a promising method for the preparation of outstanding, integrated cathodes for potential applications in lithium ion batteries.

Electrospun Flexible Cellulose Acetate-Based Separators for Sodium-Ion Batteries with Ultralong Cycle Stability and Excellent Wettability: The Role of Interface Chemical Groups

Na-ion batteries are one of the best technologies for large-scale applications depending on almost infinite and widespread sodium resources. However, the state-of-the-art separators cannot meet the engineering needs of large-scale sodium-ion batteries to match the intensively investigated electrode materials. Here, a kind of flexible modified cellulose acetate separator (MCA) for sodium-ion batteries was synthesized via the electrospinning process and subsequently optimizing the interface chemical groups by changing acetyl to hydroxyl partly. Upon the rational design, the flexible MCA separator exhibits high chemical stability and excellent wettability (contact angles nearly 0°) in electrolytes (EC/PC, EC/DMC, diglyme, and triglyme). Moreover, the flexible MCA separator shows high onset temperature of degradation (over 250 °C) and excellent thermal stability (no shrinkage at 220 °C). Electrochemical measurements, importantly, show that the Na-ion batteries with flexible MCA separator exhibit ultralong cycle life (93.78%, 10 000 cycles) and high rate capacity (100.1 mAh g-1 at 10 C) in the Na/Na3V2(PO4)3 (NVP) half cell (2.5-4.0 V) and good cycle performance (98.59%, 100 cycles) in the Na/SnS2 half cell (0.01-3 V), respectively. Moreover, the full cell (SnS2/NVP) with flexible MCA separator displays the capacity of 98 mAh g-1 and almost no reduction after 40 cycles at 0.118 A g-1. Thus, this work provides a kind of flexible modified cellulose acetate separator for Na-ion batteries with great potential for practical large-scale applications.