Molecular-Level Anion and Li+ Co-Regulation by Amphoteric Polymer Separator for High-Rate Stable Lithium Metal Anode.

Regulating ion transport is a prevailing strategy to suppress lithium dendrite growth, in which the distribution of ion regulatory sites plays an important role. Here a hyperbranched polyamidoamine (HBPA) grafted polyethylene (PE) composite separator (HBPA-g-PE) is reported. The densely and uniformly distributed positive -NH2 and negative -CHNO- groups efficiently restrict the anion migration and promote Li+ transport at the surface of the lithium metal anode. The obtained Li foil symmetric cell delivers a stable cycle performance with a low-voltage hysteresis of 130 mV for over 1500 h (3000 cycles) at an ultrahigh current density of 20 mA cm-2 and a practical areal capacity of 5 mAh cm-2. Moreover, HBPA-g-PE separator enables a practical lithium-sulfur battery to achieve over 200-cycle stable performance with initial and retained capacity of 700 and 455 mAh g-1, at a high sulfur loading of 4 mg cm-2 and a low electrolyte content/sulfur loading ratio of 8 µL mg-1.

The Multi-Functional Effects of CuS as Modifier to Fabricate Efficient Interlayer for Li-S Batteries.

The shuttle effect of lithium polysulfides in lithium-sulfur batteries (LSBs) has a detrimental impact on their electrochemical performance. To effectively mitigate the shuttle effect, in this study, the coral-like CuS is introduced to modify the carbon nanotube (CNTs), which is coated on commercial separator and served as the S cathode interlayer (PE@CuS/CNTs). The CuS/CNTs interlayer possesses efficient physical impediment and chemisorption to polysulfide anions. When achieving maximum adsorption to polysulfide anions, a "polysulfide-phobic" surface would be formed as a shield to restrain the polysulfide anions in the cathode region. Simultaneously, the CuS/CNTs interlayer can improve the lithium ion diffusion and guarantee desirable electrochemical reaction kinetics. Consequently, the LSBs with PE@CuS/CNTs show an initial discharge capacity of 1242.4 mAh g-1 at 0.5 C (1 C = 1675 mA g-1 ) and retain a long-term cycling stability (568.5 mAh g-1 after 1000 cycles, 2 C), corresponding to an ultra-low capacity fading rate of only 0.05% per cycle. Also, the LSBs with PE@CuS/CNTs exhibit high resistance to self-discharge and favorable performance under high S loading (4.5 mg cm-2 ) and lean electrolyte (9.4 mLElectrolyte  g S -1 ).