Qingsong Wang

Enhanced cycle performance of a Li–S battery based on a protected lithium anode

A conductive polymer layer is prepared on the surface of a lithium anode as the protective layer for a Li–S battery. With the protective layer, a stable and less resistive SEI is formed between the ether-based electrolyte and the Li anode, it can not only inhibit the corrosion reaction between the lithium anode and lithium polysulfides effectively, but also suppress the growth of Li dendrites. Particularly, with approximately 2.5–3 mg cm−2 sulfur loading on the electrode and commercial electrolyte, the discharge capacity remains at 815 mA h g−1 after 300 cycles at 0.5 C with an average coulombic efficiency of 91.3%.

Enhanced performance of lithium sulfur batteries with conductive polymer modified separators

The separators of Li–S batteries are modified with polypyrrole (PPy) nanotubes, PPy nanowires and reduced graphene oxide (rGO), respectively. All the conductive materials for the separator surface decoration can inhibit the migration of lithium polysulfides in the electrolyte and decrease the polarization of the sulfur cathode. Thus, the shuttle effect and redistribution of the active material can be suppressed during the charge/discharge process, resulting in enhanced performance. Moreover, the adsorption effect of PPy to lithium polysulfides is stronger compared to that of rGO, and the wettability of the PPy modified separators towards the electrolyte is much better, resulting in further enhanced electrochemical performance of Li–S batteries. Particularly, with approximately 2.5–3 mg cm−2 sulfur loading, the Li–S battery using the PPy nanotube modified separator displays an initial discharge capacity of 1110.4 mA h g−1, and a retained capacity of 801.6 mA h g−1 after 300 cycles at 0.5C, demonstrating an average coulombic efficiency up to 90.6% in the LiNO3-free electrolyte.

A conductive selenized polyacrylonitrile cathode material for re-chargeable lithium batteries with long cycle life

A conductive heterocyclic selenized polyacrylonitrile compound is designed and successfully synthesized by the dehydrogenation/selenation method at high temperature. The selenized polymer materials are examined as cathodes for lithium batteries whose electrochemical behavior resembles but is not totally the same as that of small selenium molecules with no shuttle effect. The periodic variation of the nitrogen response is observed in the XPS spectra of cathode samples with cycling. A new electrochemical reaction mechanism suggesting that nitrogen groups in the selenized polymer structure may also participate in the reversible discharge/charge reactions is proposed and demonstrated for the first time. The selenized polymer cathode delivers a reversible specific capacity of about 350 mA h g−1 after 1000 cycles at a current density of 0.5 mA cm−2 with a total capacity decay of 0.57% (based on the capacity of the 2nd cycle) and a coulombic efficiency of nearly 100%. A specific capacity of 300 mA h g−1 is obtained even when cycled at an ultrahigh current density of 5 mA cm−2, showing the excellent fast discharge/charge capability of the cathodes. Along with a high energy density of 756 W h kg−1, the selenized polyacrylonitrile cathode possesses great application potential in lithium batteries.

Suppressing the dissolution of polysulfides with cosolvent fluorinated diether towards high-performance lithium sulfur batteries.

The dissolution and shuttle of polysulfides in electrolytes cause severe anode corrosion, low coulombic efficiency, and a rapid fading of the capacity of lithium-sulfur batteries. Fluorinated diether (FDE) was selected as a cosolvent in traditional ether electrolytes to suppress the dissolution of polysulfides. The modified electrolytes lead to a negligible solubility of polysulfides, as well as decreased corrosion of the lithium anode. In an optimal system, the cells show improved cycling performance with an average coulombic efficiency of above 99% and a highly stable reversible discharge capacity of 701 mA h g-1 after 200 cycles at a 0.5C rate. A combination of electrochemical studies and X-ray photoelectron spectroscopy demonstrates the sulfur reduction mechanism with three voltage plateaus.

Carbon Disulfide Cosolvent Electrolytes for High-Performance Lithium Sulfur Batteries

Development of lithium sulfur (Li-S) batteries with high Coulombic efficiency and long cycle stability remains challenging due to the dissolution and shuttle of polysulfides in electrolyte. Here, a novel additive, carbon disulfide (CS2), to the organic electrolyte is reported to improve the cycling performance of Li-S batteries. The cells with the CS2-additive electrolyte exhibit high Coulombic efficiency and long cycle stability, showing average Coulombic efficiency >99% and a capacity retention of 88% over the entire 300 cycles. The function of the CS2 additive is 2-fold: (1) it inhibits the migration of long-chain polysulfides to the anode by forming complexes with polysulfides and (2) it passivates electrode surfaces by inducing the protective coatings on both the anode and the cathode.

A hybrid electrolyte for long-life semi-solid-state lithium sulfur batteries

A novel hybrid electrolyte prepared using NASICON-type oxide ceramics and fluorinated electrolytes has been employed in semi-solid-state Li–S batteries. A high stability of over 1200 cycles and superior tolerance to low temperature were attained. Meanwhile, the hybrid electrolyte configurations have been demonstrated to be applicable to other oxide electrolytes, like garnet-type ceramics.

An in situ element permeation constructed high endurance Li–LLZO interface at high current densities

The construction of a solid/solid SEI is proposed to improve the endurance of LLZO solid electrolytes. Al will spontaneously permeate into LLZO and construct a robust Al enriched SEI by the reaction between Al4Li9 and LLZO, realizing a low interfacial impedance of <1 Ω cm2, high endurance for 3000 h and a high critical current density of more than 0.9 and 2.3 mA cm−2 at 25 °C and 60 °C, respectively.