Xiaobin Hong

Surface-oriented and nanoflake-stacked LiNi0.5Mn1.5O4 spinel for high-rate and long-cycle-life lithium ion batteries

Spinel LiNi0.5Mn1.5O4 has attracted extensive interest as an appealing cathode material of next generation lithium-ion batteries to meet the cost/performance requirements for electric vehicle applications and renewable electric energy storage. In this paper, we report, for the first time, a nanoflake-stacked LiNi0.5Mn1.5O4 spinel with oriented growth of the (001) planes synthesized via an in situ template route. The resultant LiNi0.5Mn1.5O4 cathode delivers an initial discharge capacity of 133.5 mA h g−1 at 1 C with capacity retention of 86% after 500 cycles. X-ray diffraction and transmission electron microscopy results suggest that the growth of (111) facets on the surfaces of the nanoflake-stacked LiNi0.5Mn1.5O4 spinel is significantly restricted, which helps to inhibit the dissolution of manganese from the lattice and ensure an excellent cycling stability. Moreover, the very thin nanoflakes and large interspaces between the nanoflakes are favorable for Li ion transportation, leading to a fast kinetics of the LiNi0.5Mn1.5O4 spinel. As a result, the material demonstrates a reversible capacity of 96 mA h g−1 even at 50 C rate, showing a feasible application for high-power lithium ion batteries. In particular, this study provides a synthetic strategy to fabricate insertion materials with a surface-oriented morphology and nanoflake-stacked structure for energy storage, fast-ion conductors and other applications.

A 3D nanostructure of graphene interconnected with hollow carbon spheres for high performance lithium–sulfur batteries

To better suppress the capacity decay over cycling and improve the electrical insulation of the sulfur cathode for lithium–sulfur (Li–S) batteries, we designed a novel three-dimensional nanostructure of graphene interconnected with hollow carbon spheres (3D rGO–HCS) as the sulfur host. The 3D rGO–HCS nanostructure was first prepared via a hydrothermal self-assembly method followed by carbonization and etching of the SiO2 core, then sulfur was impregnated into the nanostructure by an in situ solution deposition method to obtain the S@rGO–HCS cathode. The as-prepared cathode material delivers a high discharge capacity of ∼770 mA h g−1 at 4 C rate. More importantly, it has a high capacity retention of 93.9% after 100 cycles and demonstrates a low capacity-decay rate of 0.052% per cycle after 400 cycles at 0.5 C rate. The superior comprehensive electrochemical performance of the S@rGO–HCS cathode is ascribed to the synergic effects from the 3D graphene-network design, including fast electron and ion transportation, efficient confinement of polysulfide dissolution and shuttling and successful maintenance of structural integrity.

Electrochemical performance of lithium/sulfur batteries using perfluorinated ionomer electrolyte with lithium sulfonyl dicyanomethide functional groups as functional separator

Lithium/sulfur (Li/S) batteries using the novel perfluorinated ionomer electrolyte with lithium sulfonyl dicyanomethide functional groups as both separator and electrolyte are demonstrated. Comparison was made with the Li/S batteries with the conventional liquid electrolyte, poly(vinylidenefluoride-hexafluoropropylene) [P(VDF-HFP)] gel polymer electrolyte, the lithiated Nafion ionomer electrolyte, and the novel perfluorinated ionomer electrolyte. The battery with novel perfluorinated ionomer electrolyte shows stable capacity retention compared with the batteries with the conventional liquid electrolyte and the gel electrolyte, and good rate performance compared with the battery with the lithiated Nafion ionomer electrolyte.

Graphene oxide wrapped hierarchical porous carbon–sulfur composite cathode with enhanced cycling and rate performance for lithium sulfur batteries

A graphene oxide sheet wrapped hierarchical porous carbon–sulfur (HPC–S@GO) composite was designed by a two-step method to improve the lithium sulfur battery performance. With this nanostructure design, the hierarchical porous carbon supplies an electronic transport pathway and provides a large pore volume to load the sulfur while the encapsulated graphene oxide sheet is effective in trapping sulfur and polysulfides during cycling. The obtained HPC–S@GO composite delivers prolonged cycling stability and an enhanced rate performance: the capacity fading is 0.12% per cycle over 400 cycles at 1 C (1672 mA g−1) rate, and the capacities at 0.2, 0.5, 1, 2 and 5 C rate are 1333.3, 896.9, 763.0, 669.5 and 505.6 mA h g−1, respectively.

Synthesis and electrochemical properties of a perfluorinated ionomer with lithium sulfonyl dicyanomethide functional groups

A novel type of perfluorinated ionomer with lithium sulfonyl dicyanomethide functional groups was prepared for Li-ion batteries with high rate performance. The immobile sulfonyl dicyanomethide anion on the backbone of the polymer chain results in the unity transference number of Li+ and high ionic conductivity of the ionomer electrolyte, which could prevent problems caused by a concentration gradient in the electrolyte. 19F NMR and FT-IR confirmed that the polymer was synthesized successfully. With the appropriate solvent, the ionomer electrolytes ionic conductivities were observed to be as high as 10−4 S cm−1 at room temperature. The ionomer electrolyte was electrochemically stable up to 4.5 V, and it still had a stable interface with the Li electrode after a long storage time. The ionomer electrolyte has a promising future in practical application for lithium-ion batteries.

Encapsulating sulfur into highly graphitized hollow carbon spheres as high performance cathode for lithium–sulfur batteries

Encapsulating sulfur into a highly graphitized hollow carbon sphere (GHCS) is proposed as sulfur cathode for the first time. After annealing the amorphous hollow carbon sphere (HCS) at a high temperature of 2600 °C, the obtained GHCS shows polyhedral morphology and few layers graphene characteristic with extremely low oxygen content. When used as sulfur cathode, the S@GHCS composite delivers a high discharge capacity of ∼800 mA h g−1 at 4C rate and high capacity retention of 93.7% after 240 cycles at 1C rate, demonstrating much better rate capability and cycling performance compared to those of S@HCS composite.

Safer lithium metal battery based on advanced ionic liquid gel polymer nonflammable electrolytes

Uncontrolled parasitic side-reactions with metallic lithium and their hazardous behaviour hinders the development of advanced energy storage technologies based on organic solvents. Ionic Liquids (ILs) have very interesting and safer properties for the aim of realizing safer devices without hindering their electrochemical performance. Ionic liquid gel polymer electrolytes (ILGPEs) based on a micro-porous polymer membrane were designed to both improve the battery safety and maintain rapid migration channels for Li+, which possess a high ionic conductivity of 1.11 mS cm−1 at 25 °C with an electrochemical stability window up to 5 V versus Li/Li+ at room temperature. Moreover the ILGPEs increased compatibility with the lithium anode which suppressed the growth of lithium dendrites and lowered the SEI resistance. Furthermore, they also demonstrate excellent cycling stability with 91.1% capacity retention up to 100 cycles and a high columbic efficiency of 99% at 25 °C. With the addition of good thermal stability and non-volatile and non-flammable properties, all these features allow this novel gel polymer electrolyte to function as a high performance and highly safe lithium ionic conductor as well as a separator for lithium metal batteries.