Chunlong Dai

Selenium Embedded in Metal–Organic Framework Derived Hollow Hierarchical Porous Carbon Spheres for Advanced Lithium–Selenium Batteries

Metal-organic framework derived hollow hierarchical porous carbon spheres (MHPCS) have been fabricated via a facile hydrothermal method combined with a subsequent annealing treatment. Such MHPCS are composed of masses of small hollow carbon bubbles with a size of ∼20 nm and shells of ∼5 nm thickness interconnected to each other. MHPCS/Se composite is developed as a cathode for Li-Se cells and delivers an initial specific capacity up to 588.2 mA h g(-1) at a current density of 0.5 C, exhibiting an outstanding cycling stability over 500 cycles with a decay rate even down to 0.08% per cycle. This material is capable of retaining up to 200 mA h g(-1) even after 1000 cycles at a current density of 1 C. Such good electrochemical performance may be ascribed to the distinct hollow structure of the carbon spheres and a large amount of Se wrapped within small carbon bubbles, thus not only enhancing the electronic/ionic transport but also providing additional buffer space to adjust volume changes of Se during charge/discharge processes.

Exploration of Na7Fe4.5(P2O7)4 as a cathode material for sodium-ion batteries

A novel Na7Fe4.5(P2O7)4 compound was fabricated as a cathode for sodium-ion batteries by a mechanical milling assisted solid state method for the first time. The as-prepared material exhibits superior electrochemical performance based on half-cell testing. After uniform carbon coating, it exhibits lower electrochemical polarization, better conductivity and faster sodium ion diffusion kinetics. Benefiting from these advantages, the Na7Fe4.5(P2O7)4 was endowed with higher charge–discharge capacity, better cycle life and outstanding rate performance. The high rate capability and good cyclability of this material in non-aqueous electrolytes are advantageous for low-cost and safe battery systems.

Sodium-rich ferric pyrophosphate cathode for stationary room-temperature sodium-ion batteries

In this article, carbon-coated Na3.64Fe2.18(P2O7)2 nanoparticles (∼10 nm) were successfully synthesized via a facile sol-gel method and employed as cathode materials for sodium-ion batteries. The results show that the carbon-coated Na3.64Fe2.18(P2O7)2 cathode delivers a high reversible capacity of 99 mAh g-1 at 0.2 C, outstanding cycling life retention of 96%, and high Coulomb efficiency of almost 100% even after 1000 cycles at 10 C. Furthermore, the electrochemical performances of full batteries consisting of carbon-coated Na3.64Fe2.18(P2O7)2 nanoparticles as the cathode and commercialized hard carbon as the anode are tested. The full batteries exhibit a reversible capacity of 86 mAh g-1 at 0.5 C and capacity retention of 80% after 100 cycles. Therefore, the above-mentioned cathode is a potential candidate for developing inexpensive sodium-ion batteries in large-scale energy storage with long life.

Selenium Encapsulated into Metal–Organic Frameworks Derived N-Doped Porous Carbon Polyhedrons as Cathode for Na–Se Batteries

The substitution of Se for S as cathode for rechargeable batteries, which confine selenium in porous carbon, attracts much attention as a potential area of research for energy storage systems. To date, there are no reports about metal-organic frameworks (MOFs) to use for Na-Se batteries. Herein, MOFs-derived nitrogen-doped porous carbon polyhedrons (NPCPs) have been obtained via facile synthesis and annealing treatment. Se is encapsulated into the mesopores of carbon polyhedrons homogeneously by melt-diffusion process to form Se/NPCPs composite, using as cathode for advanced Na-Se batteries. Se/NPCPs cathode exhibits excellent rate capabilities of 351.6 and 307.8 at 0.5C and 2C, respectively, along with good cycling performance with high Coulombic efficiency of 99.7% and slow decay rate of 0.05% per cycle after 1000 cycles at 2C, which result from the NPCPs having a unique porous structure to accommodate volumetric expansion of Se during discharge-charge processes. Nitrogen doping could enhance the electrical conductivity of carbon matrix and facilitate rapid charge transfer.

Improving the Performance of Hard Carbon//Na3V2O2(PO4)2F Sodium-Ion Full Cells by Utilizing the Adsorption Process of Hard Carbon

Hard carbon has been regarded as a promising anode material for Na-ion batteries. Here, we show, for the first time, the effects of two Na+ uptake/release routes, i.e., adsorption and intercalation processes, on the electrochemical performance of half and full sodium batteries. Various Na+-storage processes are isolated in full cells by controlling the capacity ratio of anode/cathode and the sodiation state of hard carbon anode. Full cells utilizing adsorption region of hard carbon anode show better cycling stability and high rate capability compared to those utilizing intercalation region of hard carbon anode. On the other hand, the intercalation region promises a high working voltage full cell because of the low Na+ intercalation potential. We believe this work is enlightening for the further practical application of hard carbon anode.