Study On The Preparation And Electrochemical Performance Of Sulfur-containing Polyphosphazenes As Cathod Materials

It is an effective way to develop new active materials with the high specificcapacity of cathodes for increasing the specific capacity in the lithium secondarybatteries. This study mainly focuses on the preparation, structure characterization andelectrochemical performances of several sulfur-containing polyphosphazenes cathodematerials.The main contents are as follows:1、 Two kinds of sulfur-containing polyphosphazenes were synthesized bynucleophilic substitution from sodium sulfide and polydichlorophosphazene,Thestructures of the resulted materials were characterized by FTIR and XRD spectra.Themechanism of sulfur-containing polyphosphazenes as cathode material for lithiumsecondary battery was studied, the cyclic voltammetry curves and the reason forcapacity fading had been discussed. In1M LiCF3SO3/DME+DGM electrolyte, thefirst discharge capacity of the mono-substituted sulfur-containing polyphosphazenesand mix-substituted sulfur-containing polyphosphazenes was952mAh·g-1and754.5mAh·g-1comparably. the average charge-discharge efficiency was88%and90%.For the30~50thcycles, the discharge capacity stabilized at120~100mAh·g-1. It wasconcluded that sulfur-containing polyphosphazenes could reduce capacity fading andrestrain shuttle-effect.2、Two kinds of sulfur-containing composite materials have been synthesizedwith the methode of heat-treatment. XRD test showed that the structure of materialscould be regarded as amorphous phase. The initial discharge capacity ofMEEP/sulfur composites was very low, and without the distinct charge-dischargeplateau. AC impedance analysis indicated that the composites provided better way forthe electrons and ions to transfer, decreasing the contacted resistance between anodeand electrolyte. The integrity of matrix structure was enhanced and the dischagespecific capacity was improved by heat-treatment.3、The sulfide cyclotriphosphazene was prepared by chemical crosslinking. Thecyclic voltammetry indicated the anodic peak was observed at about2.5V,and thecathodic peaks at1.3V with the larger reduction current.The initial discharge capacity of the inorganic-polymer material was604mAh·g-1,when the charge-dischargecurrent density is20mA/g. For the10~40th cycles, the discharge specific capacitystabilized, It was249.3mAh·g-1at the40th cycles. the average charge-dischargeefficiency was90%. It showed that the electrochemical reaction with high degreereversibility was proceeded and the high utilization efficiency was found inoxidation-reduction process.