Fengxia Xin

A lithiation/delithiation mechanism of monodispersed MSn5 (M = Fe, Co and FeCo) nanospheres

A designed Sn based alloy host as a higher capacity and longer cycle life next generation lithium-ion battery, consisting of monodisperse nanospheres of intermetallic MSn5 (M = Fe, Co and FeCo) phases was synthesized by a nanocrystal conversion chemistry method using preformed Sn nanospheres as templates. The same crystal structure, identical particle surface morphology and the similar particle size distribution (30-50 nm) of these intermetallic MSn5 (M = Fe, Co and FeCo) phases are ideal for comparison of the electrochemical performance, reaction mechanism, thermodynamics and kinetics during lithiation/delithiation. Importantly, MSn5 (M = Fe, Co and FeCo) phases with defect structures Fe0.74Sn5, Co0.83Sn5 and Fe0.35Co0.35Sn5, exhibit the highest theoretical capacity of >917 mA h g(-1) among the reported M-Sn (M is electro-chemically inactive) based intermetallic anodes. The ex situ XRD and XAFS illustrate the complete reversibility of MSn5 (M = Fe, Co and FeCo) phases during lithium insertion/extraction for the first cycle. The Fe0.35Co0.35Sn5 anode can take advantage of both high capacity of Fe0.74Sn5 and long cycle life of Co0.83Sn5, providing 736 mA h g(-1) and maintaining 92.7% of initial capacity after 100 cycles with an average capacity loss of only 0.07% per cycle. The excellent electrochemical performance of the Fe0.5Co0.5Sn5 system is attributed to higher reversibility, lower reaction resistance. This work provides a novel insight toward designing and exploring an optimal Sn based alloy anode for next generation Li-ion batteries.

Scalable fabrication of micro-sized bulk porous Si from Fe–Si alloy as a high performance anode for lithium-ion batteries

Silicon has been perceived as one of the most promising anodes in the next generation lithium-ion batteries (LIBs) due to its superior theoretical capacity. However, bulk silicon experiences an enormous volume expansion during the lithiation/delithiation process, resulting in rapid capacity fading. And, its high-cost and low coulombic efficiency also present significant challenges for applications. Here, we presented a facile and large-scale approach for preparing micro-sized porous silicon by acid etching the abundant and inexpensive metallurgical Fe–Si alloy as a high-performance anode in LIBs. Profiting from the unique micro-sized structure, it exhibited a fantastic first-cycle coulombic efficiency of 88.1% and an excellent reversible capacity of 1250 mA h g−1 at 500 mA g−1 after 100 cycles. Furthermore, the micro-sized porous silicon without carbon coating could deliver a reversible capacity of 558 mA h g−1 at a high current density of 5 A g−1 due to the unique porous structure. This work provides a promising route for a large-scale production of high-performance micro-sized Si as anode materials in LIBs.

Enhanced Electrochemical Performance of Fe0.74Sn5@Reduced Graphene Oxide Nanocomposite Anodes for Both Li-Ion and Na-Ion Batteries.

The recently found intermetallic FeSn5 phase with defect structure Fe0.74Sn5 has shown promise as a high capacity anode for lithium-ion batteries (LIBs). The theoretical capacity is as high as 929 mAh g(-1) thanks to the high Sn/Fe ratio. However, despite being an alloy, the cycle life remains a great challenge. Here, by combining Fe0.74Sn5 nanospheres with reduced graphene oxide (RGO) nanosheets, the Fe0.74Sn5@RGO nanocomposite can achieve capacity retention 3 times that of the nanospheres alone, after 100 charge/discharge cycles. Moreover, the nanocomposite also displays its versatility as a high-capacity anode in sodium-ion batteries (SIBs). The enhanced cell performance in both battery systems indicates that the Fe0.74Sn5@RGO nanocomposite can be a potential anode candidate for the application of Li-ion and Na-ion battery.

High lithium electroactivity of boron-doped hierarchical rutile submicrosphere TiO2

We have reported a facile method to fabricate hierarchical boron-doped rutile submicrosphere TiO2 (SMT), whose primary particles are ∼20 nm in diameter. The as-synthesized boron-doped SMT shows excellent cycling performance and rate capability in comparison with undoped TiO2 as an anode material in Lithium-Ion Batteries (LIBs). It has a very stable capacity of ∼190 mA h g−1 for 500 cycles at 1C. In addition, the density functional theory (DFT) calculations are carried out to indicate that a low concentration (<1.0 at%) of boron doping could enhance the carrier mobility μ and electrical conductivity σ, and thus reveal the relationship between the electronic structure of boron-doped SMT and the performances of the boron-doped SMT anode in LIBs. Our results also clearly demonstrate the importance and advantage of the hierarchical submicrometer-sized spherical morphology of the TiO2 anode in LIBs.

Three-dimensional interconnected network GeOx/multi-walled CNT composite spheres as high-performance anodes for lithium ion batteries

Germanium (Ge) anode materials are one of the most potential anodes for next generation lithium-ion batteries (LIBs) due to their high theoretical capacity, fast Li-ion diffusivity and high intrinsic electronic conductivity. However, Ge anode materials face significant challenges due to the 260% volume change during the lithiation/delithiation process, which results in pulverization and destabilization of the solid electrolyte interphase (SEI) film and leads to the loss of electrical contact and poor cycle life. Here, we report an industrially established spray-drying process for the synthesis of micro-sized durable three-dimensional (3D) network structure GeOx/multi-walled carbon nanotube (MWCNT) composite spheres consisting of 5–15 nm nanoparticles for LIB anodes. The 3D GeOx/MWCNT composite sphere structure not only provides high ability for Li-ion intercalation, but also enhances the electronic conductivity of the composite spheres for LIBs, increasing the rate capabilities. Meanwhile, the 3D network structure provides adequate space for GeOx expansion resulting in good long-term cycling stability. The interconnected 3D network structure GeOx/MWCNT spheres exhibited a capacity of over 1000 mA h g−1 at 500 mA g−1 after 300 deep charge–discharge cycles and provided a capacity of 550 mA h g−1 at 5 A g−1. Even at a high current density of 10 A g−1, it can deliver a reversible capacity of 365 mA h g−1. The results showed that when the active material loading reached >1.2 mg cm−2, the discharge capacity could also retain 723 mA h g−1 after 150 cycles. This scalable and industrial method provides attractive future prospects for high-performance Ge-based anodes with excellent electrochemical performance with a high active material loading in the next generation LIBs.