Hangjun Ying

Ultrasmall Sn nanodots embedded inside N-doped carbon microcages as high-performance lithium and sodium ion battery anodes

Sn based materials are promising anodes both in Li-ion batteries and Na-ion batteries due to their high theoretical capacities (994 mA h g−1 for LIBs and 847 mA h g−1 for SIBs, respectively). In order to improve the cycle performance, Sn/N-doped carbon microcage composites (Sn/NMCs) with Sn nanodots uniformly embedded inside the N-doped carbon microcages are synthesized through a simple spray drying process, followed by thermal treatment. When used as electrodes, Sn/NMCs exhibit an initial reversible capacity of 780 mA h g−1 at 200 mA g−1, and maintain 472 mA h g−1 after 500 cycles in LIBs. For Na-ion batteries, Sn/NMCs deliver an initial reversible capacity of 439 mA h g−1 at 50 mA g−1 and maintain 332 mA h g−1 after 300 cycles. The remarkable electrochemical performance is mainly owing to the advanced structure of Sn/NMCs, which could be attributed to the pore-formation using NaCl, and the grain size inhibition of Sn using N-doped carbon. Moreover, this preparation method is accessible to scale up and can be extended to fabricate other electrode materials.

Facial Synthesis of Three-Dimensional Cross-Linked Cage for High-Performance Lithium Storage.

Silicon/C composite is a promising anode material for high-energy Li-ion batteries. However, synthesizing high-performance Si-based materials at large scale and low cost remains a huge challenge. Here, we for the first time report the preparation of an interconnected three-dimensional (3D) porous Si-hybrid architecture by using a spray drying method. In this unique structure, the highly robust C-CNT-RGO cages not only can improve the conductivity of the electrode and buffer the volume expansion but also suppress the Si nanoparticles aggregation. As a result, the 3D Si@po-C/CNT/RGO electrode achieves long-life cycling stability at high rates (a reversible capacity of 854.9 mA h g(-1) at 2 A g(-1) after 500 cycles and capacity decay less than 0.013% per cycle) and good rate capability (1454.7, 1198.8, 949.2, 597.8, and 150 mA h g(-1) at current densities of 1, 2, 4, 10, and 20 A g(-1), respectively). Moreover, this novel electrode could deliver high reversible capacities and long-life stabilities even with high mass loading density (764.9 mA h g(-1) at 1.0 mg cm(-2) after 500 cycles and 472.2 mA h g(-1) at 1.5 mg cm(-2) after 400 cycles, respectively). This cheap and scalable strategy can be extended to fabricate other materials with large volume expansion (Sn, Ge, transition-metal oxides) and 3D porous carbon for other potential applications.

Polyiodide-Shuttle Restricting Polymer Cathode for Rechargeable Lithium/Iodine Battery with Ultralong Cycle Life

Rechargeable lithium/iodine (Li/I2) batteries have attracted much attention because of their high gravimetric/volumetric energy densities, natural abundance and low cost. However, problems of the system, such as highly unstable iodine species under high temperature, their subsequent dissolution in electrolyte and continually reacting with lithium anode prevent the practical use of rechargeable Li/I2 cells. A polymer-iodine composite (polyvinylpyrrolidone-iodine) with high thermostability is employed as cathode material in rechargeable Li/I2 battery with an organic electrolyte. Because of the chemical interaction between polyvinylpyrrolidone (PVP) and polyiodide, most of the polyiodide in the cathode could be effectively trapped during charging/discharging. In-situ Raman observation revealed the evolution of iodine species in this system could be controlled during the process of I5- ↔ I3- ↔ I-. Herein, the Li/I2 battery delivered a high discharge capacity of 278 mAh g-1 at 0.2 C and exhibited a very low capacity decay rate of 0.019% per cycle for prolonged 1100 charge/discharge cycles at 2 C. More importantly, a high areal capacity of 4.1 mAh cm-2 was achieved for the electrode with high iodine loading of 21.2 mg cm-2. This work may inspire new approach to design the Li/I2 (or Li/polyiodide) system with long cycle life.