Qiong Tang

A conductive carbon interlayer modified by magnetron sputtering for improved-performance lithium–sulfur batteries

Cathode materials (S–AC) for lithium–sulfur (Li–S) batteries were synthesised with elemental sulfur (S) and activated carbon (AC). Conductive carbon films (CF1) were prepared with filter paper and aluminum (Al) thin films were plated onto the surface of the filter paper by the method of magnetron sputtering to fabricate modified carbon films (CF2). The as-prepared carbon films were applied as conductive interlayers inserted between the cathode and the separator for Li–S batteries S/AC/CF1 and S/AC/CF2. The properties of the cathode materials and the carbon interlayers were characterized by XRD and FESEM. Electrochemical performances of three Li–S batteries with and without interlayers (S/AC/CF1, S/AC/CF2 and S/AC) were determined by alternating-current impedance, cyclic voltammetry and constant-current charge and discharge. The assessment results show that S/AC/CF2 is superior to the others with an initial discharge specific capacity of 1273 mA h g−1 at a current rate of 1C. It delivered a reversible capacity of 924 mA h g−1 after 100 cycles and the coulombic efficiency after 200 cycles is still over 95%.

Improved-performance lithium–sulfur batteries modified by magnetron sputtering

The cathode material S/AC for lithium–sulfur batteries was synthesized with elemental sulfur as the active material and activated carbon (AC) as the conductive matrix. Al and Ti were respectively deposited onto the surface of S/AC electrodes by the method of radio-frequency magnetron sputtering to modify the electrodes and improve the battery performance. The properties of S/AC and the sputtered cathode materials, labeled S/AC/Ti and S/AC/Al, were characterized by XRD and FESEM. Electrochemical performances of the Li/S batteries with the three cathode materials were determined by alternating-current impedance, cyclic voltammetry (CV) and constant-current charge and discharge. Experiments showed that S/AC, S/AC/Ti and S/AC/Al delivered initial specific capacity of 1197 mA h g−1, 1255 mA h g−1 and 1257 mA h g−1 respectively under the current rate of 0.5C. And the modified batteries operated reversibly over 100 cycles and maintained a discharge specific capacity of 722 mA h g−1 and 977 mA h g−1 after 100 cycles, superior to 634 mA h g−1 of S/AC. Besides, the coulombic efficiencies of the sputtered electrodes were over 0.97 after 100 cycles.

Optimized Assembly of Micro-/Meso-/Macroporous Carbon for Li-S Batteries

In order to explore the effect of hierarchical porous carbon on the performances of Li–S batteries, we synthesized three kinds of micro-/meso-/macroporous carbon materials with different pore properties by facile hard-template method. Different from the majority of reports on porous carbon ensuing large specific surface area (SSA) and total pore volume, it was found that in the case of identically high sulfur content, the pore size distribution substantially influences the performances of Li–S batteries rather than the SSA and total pore volume. Furthermore, in the assembly of micro-/meso-/macropores, the micropore volume ratio to the total pore volume is dominant to the capabilities of batteries. Among the samples, the porous carbon carbonized with the precursor of sucrose at 950∘C presents the highest initial discharge specific capacity of 1327mAh/g and retention of 630mAh/g over 100 cycles at 0.2C rate along with the best rate capability. This sample possesses the largest micropore volume ratio of 47.54% but a medium SSA of 1217m2/g and inferior total pore volume of 0.54cm3/g. The abundant micropores effectively improve the conductivity of dispersed sulfur particles, inhibit the loss of sulfur series and enable the cathode to exhibit superior electrochemical performances.

A dual-faced interlayer prepared by electron beam evaporation for enhanced-performance lithium–sulfur batteries

In this work, a dual-faced carbon paper was prepared by depositing Al2O3 on one side of carbonized filter paper via the technique of electron beam evaporation. Assembled into Li–S batteries, the Al2O3-deposited carbon paper served as a multifunctional interlayer. The cathode of 70% sulfur content with this interlayer presented notable enhancements in electrochemical performance in contrast to that with a single carbon interlayer. At a current rate of 0.5C, the battery with the Al2O3-deposited carbon interlayer delivered a high initial capacity of 1253 mA h g−1 and retention of 700 mA h g−1 over 120 cycles, while the battery with the carbon interlayer delivered an approximate initial capacity of 1117 mA h g−1 but much poorer retention of 441 mA h g−1 over 87 cycles. The carbon side of the interlayer was placed toward the cathode as the upper current collector, which ensured the conductivity of the contact interface with the active material and promoted activation of sulfur. At the same, Al2O3 as a polar material facing toward the separator impeded the leakage of soluble polysulfides and mitigated the shuttle effect by chemical adsorption of soluble polysulfides. Combined with the interstitial structure of the interlayer acting as a physical container, Li–S batteries with this novel interlayer demonstrate superiorities in capacity, variable discharge/charge rate, Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) characteristics.