Application Of One-Dimensional Chain Keggin Structural Polyoxometallate And Polyaniline Composite Materials In Lithium-Sulfur Battery

Due to the irregular deposition of discharge product Li₂S and the shuttle effect of lithium polysulfide,the poor cycle performance and coulombic efficiency is limiting lithium-sulfur batteries.Aiming at these problems,in this paper,taking advantage of the protonation process of conductive polyaniline?PANI?,the polyaniline chain would be doped by positive charge,and anion as a charge-balance ion intercalated in the polyaniline interlayer.A 1D Keggin chain structure polyoxometallate would be a suitable one that is intercalated as a charge-balancing ion between the polyaniline layers to obtain a 1D composite structural material PANI/POM.The one-dimensional chain composite structure would chosen for host material of S and the modification material for the lithium-sulfur battery separator to solve the above two main problems.This method is relied on the one-dimensional chain composite structure and the heterogeneous dopant atoms on the POM which is aimed on improvement of the charge-discharge specific capacity and cycle performance.The main results of these materials are as follows:?1?The polyaniline and K₃[H₃Ag^IPW₁₁^IVO₃₉]·xH₂O with double-layered chain structure were molecularly self-assembled by solution method,and the composite material with one-dimensional chain structure PANI-POM-PANI was successfully prepared as S Host material.Through galvanostatic charge-discharge,cyclic voltammetry,electrochemical impedance spectroscopy and other tests,it could be concluded that the composite structure has an in situ adsorption on lithium polysulfide and Li₂S,and Li₂S would also be catalyzed during charging process and overpotential was disappeared.At 0.1 C,the first discharge specific capacity was1375 mAh g^-1.After 0.1 C 50 cycles,the capacity retention was 96.9%base on the first dicharging process,the coulombic efficiency was maintained at 95%,and the specific discharge capacity at 1 C was 795 mAh g^-1.?2?According to the above method,a single-layer chain structure of[?CH₄?₃N]_3.5H_1.5[PW₁₁O₃₉Ca?H₂O?₂]·xH₂O and[?CH₄?₃N]_3.5H_1.5[PW₁₁O₃₉Sr?H₂O?₂]·xH₂O and PANI were molecularly self-assembled,and a composite material of PANI-POM-PANI with one-dimensional chain structure was successfully prepared as the host material of S.Through galvanostatic charge-discharge,cyclic voltammetry,electrochemical impedance spectroscopy and other tests,it could be concluded that the composite structure has an in situ adsorption on lithium polysulfide and Li₂S,and Li₂S would also be catalyzed during charging process and overpotential was disappeared.At 0.1 C,the first discharge specific capacities of the two as host materials for S were 1501.51 mAh g^-1 and 1438.17 mAh g^-1,respectively.After 0.1 C50 cycles,the capacity retention were 90.41%and 90.38%,respectively?the main loss was due to small amount of free S?,the coulombic efficiency was maintained at97%and 96%,respectively,and the specific discharge capacity at 1 C current was1024.24 mAh g^-1 and 935.85 mAh g^-1.?3?The composite material of PANI-POM-PANI of one-dimensional chain structure synthesized by?1?and?2?was used for separator modification for lithium-sulfur battery.Through galvanostatic charge-discharge,cyclic voltammetry,electrochemical impedance spectroscopy and other tests,it could be concluded that the composite structure has the adsorption of lithium polysulfide and also ensures rapid conduction of Li⁺.Under this condition,a complete discharging process for S could be completed.With the sacrifice of cycle performance to achieve the higher S loading,this modification has an improved meaning.