Guoqiang Ma

Flexible self-supporting graphene–sulfur paper for lithium sulfur batteries

A flexible self-supporting graphene–sulfur paper with 67 wt% sulfur was fabricated for lithium sulfur batteries. This binder and current collector-free electrode demonstrated a reversible capacity of 600 mA h g−1 with 83% capacity retention based on the sulfur element after 100 cycles.

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%.

Hollow polyaniline sphere@sulfur composites for prolonged cycling stability of lithium–sulfur batteries

A sulfur cathode with excellent electrochemical performance has been designed based on hollow PANI spheres, which can suppress the shuttle effect and buffer the volume expansion effectively. The discharge capacity is as high as 602 mA h g−1 even after 1000 cycles at 0.5 C.

Enhancement of long stability of Li–S battery by thin wall hollow spherical structured polypyrrole based sulfur cathode

To enhance the long stability of sulfur cathode for a high-energy lithium–sulfur cell, a thin wall hollow spherical structured polypyrrole (T-HSSP) composed of a mono layer of PPy nano-particles is employed as a host to encapsulate the sulfur component. T-HSSP can buffer the volume expansion of sulfur during the discharge and charge processes; therefore can maintain the integrity of the sulfur electrode after long cycling. The distribution of sulfur component is maintained even after 100 charge/discharge cycles in T-HSSP, indicating the efficiency of the design in inhibiting the shuttle effect of the sulfur electrode. The composite with a sulfur content of 58.4 wt% exhibits a reversible capacity of 1563.3 mA h g−1 and a discharge capacity retention over 89% during 40–200 cycles, corresponding to a sulfur utilization rate of 89.2% at 0.2 C. The excellent rate capability of the composite is demonstrated by its cycling performances at 1 C, 2 C, and 5 C for 300 cycles. Moreover, a further heating treatment is carried out to inhibit the severe capacity fade in the initial tens of cycles, and an enhanced cycling stability of the Li–S battery is achieved.

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.

A selenium@polypyrrole hollow sphere cathode for rechargeable lithium batteries

A selenium@polypyrrole hollow sphere composite cathode delivers a reversible specific discharge capacity of 400 mA h g−1 after 80 cycles and a 60% reduction in impedance of the cycled cells is obtained. The soluble polyselenide species are demonstrated to be confined by PPy hollow spheres, thus inhibiting the shuttle effect to a large extent.