| With a theoretical cathode capacity of 1675 m Ah g-1 and battery energy density of2600 Wh kg-1,Li-S battery（LSB）is considered one of the most promising secondary batteries.However,its commercialization is still hampered by the low sulfur utilization,slow reaction kinetics,fast capacity fading and safety concerns.These issues are intrinsically rooted in the insulating S and Li2S,the 70%volume change between S and Li2S,the shuttle effect of dissolved lithium polysulfides（Li2Sx,2<x≤8,Li PSs）intermediates and the unstable lithium metal anode.Moreover,attainment of the DMEanded actual energy density requires a high-sulfur-loading cathode(about 3-5 mg cm-2 of sulfur)and low electrolyte usage(electrolyte contain/sulfur loading ratio≤10μL mg-1).However,high sulfur loading and lean electrolyte leads to higher Li PSs concentration and more severe shuttle effect,lower sulfur utilization and higher cathode resistivity and volume change.Moreover,at such high sulfur loading,a very high areal capacity is also applied on the lithium anode,which aggravates dendrite formation.To overcome these obstacles,in this paper,the commercial functional polymer materials were applied to construct long-cycle-life and high-energy-density lithium-sulfur batteries with scalable manufacturing process.The details as follows:（1）A composite of hyperbranched poly（amidoamine）with terminal carboxyl groups modified multi-walled carbon nanotubes（PAMAM-CNT）was successfully prepared by chemical grafting,and employed as an interlayer material in LSB.The CNTs function as a scaffold and current collector that reduce the internal polarization.The high content and highly dispersed polar functional groups of PAMAM can efficiently adsorb and enhance the redox reaction of Li PSs.The assembled LSB displays a high energy efficiency of 86%and a low capacity-fading rate of 0.037%per cycle over 1200 cycles at 2C.The cell also shows excellent cycle performance,high sulfur utilization and improved stability at high areal capacity of 9 m Ah cm-2(achieved at a sulfur loading of 8.7 mg cm-2)and low E/S ratio of 6.1 m L g-1.This thin（12μm）and lightweight(0.34 mg cm-2)interlayer has negligible impact on the overall cell energy density.（2）To overcome the deficiencies that PAMAM-CNT function is spatially limited to the thin interlayer rather than the bulk cathode in work 1.In this work,a H-bonding cross-linked polymer binder was prepared by physical mixing cationic polyacrylamide（CPAM）with hyper-branched polyester（HBPE）.The co-existence of negative and positively charge moieties endow this binder an amphoteric feature,which shows co-regulation of both lithium cations and polysulfide anions through various intermolecular interactions.These interactions coupled with the physical attributes of the binder,lead to simultaneously improved Li+transport,polysulfide adsorption and cathode robustness.As a result,this multifunctional binder allows Li-S batteries to achieve discharge capacity of 670 m Ah g-1 at high current of 5C.Even at a high sulfur loading of 5.5 mg cm-2 and E/S of 10μL mg-1,the cell still delivers high areal capacity of 3.9 m Ah cm-2 with a capacity retain ratio of 90%after 200 cycles.（3）To reduce the porosity of cathode constructed by CPAM&HBPE binder in work 2,a compact sulfur cathode with high mechanical strength and high sulfur loading was constructed by the high strength and"water reduction"effect of sodium lignosulfonate（SL）to further improve the performance of LSB under lean-electrolyte condition.The strong dispersion effect of SL can reduce the addition of solvents during the preparation of the cathode and then reduce the electrode porosity.The high polarity of SL can improve the infiltration of electrolyte to the electrode.The oxygen contained groups in SL show strong binding effect on the lithium polysulfides that effectively suppress the shuttle effect.The sulfonic acid groups in SL increase the Li+migration rate,thereby improving battery rate performance.The sulfur electrode constructed by SL with sulfur loading of 11.9 mg cm-2 and E/S of 4μL mg-1 achieves a discharge areal capacity of 12 m Ah cm-2 at current density of 0.8 m A cm-2.（4）To suppress the rapid growth of lithium dendrite under high-sulfur-loading condition,a"cation-anion regulation"synergistic separator was successfully prepared by chemical grafting hyperbranched poly（amidoamine）with terminal amino groups on the surface of polyethylene separator（PE-PAMAM）.The large number of terminal amino groups can effectively anchor anions,and therefor maintain a high anion concentration on the surface of the lithium metal anode and also increase the Li+transference number.The internal amide groups can bind Li+through coordination effect,and reduce the Li+concentration gradient on the surface of the lithium metal anode.The coordination also promotes Li+migration and reduces device polarization.As a result,this dual-ion control strategy endows a highly stable lithium metal anode without dendrite growth.Even under ultra-high current density of 20 m A cm-2,the PE-PAMAM assembled Li/Li device achieves a stable cycle performance over 1400 hours. |
