The effect of polymeric binders in the sulfur cathode on the cycling performance for lithium-sulfur batteries.

Recently, great advances of the Li-S battery technology have enabled its penetration as the power source of mid- and large-sized devices, which require high energy and power density that cannot be achieved with Li-ion batteries. While the most successful Li-S battery operation is enabled by the tailoring of the sulfur composite cathode composite structure, the binder system has recently been considered as another important factor. We study the structural and electrochemical performance of sulfur cathodes prepared with two different binders. Enhanced battery performance is observed in the SBR/CMC-based electrode and its origin is scrutinized.

Tailoring crystal structure and morphology of LiFePO4/C cathode materials synthesized by heterogeneous growth on nanostructured LiFePO4 seed crystals.

Porous and coarse (5-10 µm) LiFePO4/C composites with excellent electrochemical performance were synthesized by a growth technology using nanostructured (100-200 nm) LiFePO4 as seed crystals for the 2nd crystallization process. The porous and coarse LiFePO4/C presented a high initial discharge capacity (∼155 mA h g⁻¹ at 0.1 C), superior rate-capability (∼100 mA h g⁻¹ at 5 C, ∼65 % of the discharge capacity at 0.1 C), and excellent cycling performance (∼131 mA h g⁻¹, ∼98 % of its initial discharge capacity after 100 cycles at 1 C). The improvement in the rate-capability of the LiFePO4/C was attributed to the high reaction area resulted from the pore tunnels formed inside LiFePO4 particles and short Li-ion diffusion length. The improved cycling performance of the LiFePO4/C resulted from the enhanced structural stability against Li-deficient LiFePO4 phase formation after cycling by the expansion of the 1D Li-ion diffusion channel in the LiFePO4 crystal structure.

Preparation of single-walled carbon nanotube/silicon composites and their lithium storage properties.

Single-walled carbon nanotube (SWCNT)/silicon composites were produced from the purified SWCNTs and Si powder by high-energy ball-milling and then electrochemically inserted with Li using Li/(SWCNT/Si) cells. The highest reversible capacity and lowest irreversible capacity of the SWCNT/Si composites were measured to be 1845 and 474 mAh g(-1) after ball-milling for 60 min, respectively. During the charge/discharge process, most of the Li ions were inserted into the SWCNT/Si composites by alloying with Si particles below 0.2 V and extracted from the SWCNT/Si composites by dealloying with Si particles around 0.5 V. The enhanced capacity and cycle performance of the SWCNT/Si composites produced by high-energy ball-milling were due primarily to the fact that SWCNTs provided a flexible conductive matrix, which compensated for the dimensional changes of Si particles during Li insertion and avoided loosening of the interparticle contacts during the crumbling of Si particles. The ball-milling contributed to a decrease in the particle size of SWCNTs and Si particles and to an increase in the electrical contact between SWCNTs and Si particles in the SWCNT/Si composites.