Research On Cathode Carrier/Polysulfide Electrolyte Additive Electrode System

Compared with the current commercial lithium ion battery,the lithium sulfur secondary battery has been considered as one of the most promising cathode materials because of its high specific capacity(1675 m Ah/g),low production cost and friendly environment.However,there are still some disadvantages which restrict the development of li-sulfur batteries such as poor electrical conductivity,serious shuttle effect and volume expansion.This paper builds a type of a new battery system.The system was disigned using Li Fe PO4 or activated carbon as cathodes and polysulfide as the active material dissolved in the electrolyte.And the polysulfied can be adsorped in the cathodes because the Li Fe PO4 or activated carbon have strong adsorption to polysulfide.In this paper,the adsorption,interfacial properties and electrochemical activities of LFP with polysulfide were investigated.The electrochemical properties of two activated carbon/polysulfide battery systems were studied.The active electrolyte additive containing Li2S6,Li2S4 was prepared by reaction of Li2 S and S in commercial lithium sulfur electrolyte.UV test,XPS test and theoretical calculation show that the Li Fe PO4 has strong adsorption to polysulfide.They have the interaction on the interface(The XPS characteristic peak offset of polysulfide on the LFP electrode was 0.3 e V).The binding energy of Li Fe PO4 with Li2 S is-4.67 e V,and electroncloud enrichment will be gathered at the interface.The Li Fe PO4/polysulfide electrolyte additive electrode system has been built.And it has three discharge platform(3.4 V?2.3 V?2.1 V).The specific capacity of the active material is 335.4 m Ah/g at 0.2C and 244.8 m Ah/g at 2C.And the capacity retention rate is 82.0% after 200 cycles at 0.2C.The electrochemical performance is better than that of Li Fe PO4 coating S cathode system because the Li Fe PO4/polysulfide electrode system suppressed the shuttle effect effectively.Two kinds of activated carbon were studied in adsorptionto polysulfide and electrode performance.The results of experiments show that activated carbon 2(AC2)with high specific surface area has stronger adsorption effect to polysulfide.And AC2/polysulfide electrolyte additive electrode system has better cycling stability.The the capacity retention rates of AC1 cathodes and AC2 cathodes are 65.1% and 72.1% after 200 cycles.In addition,the passivation treatment of the anode metal lithium can make the SEI film on the surface of metal lithium in advance and prevent the contact between the polysulfide and the athode,which can improve the cycle performance of the battery.By optimizing the content of sulfide,the eletode system with 0.35 mg AC2 and 40 μL 0.15 mol/L polysulfide electrolyte additive has the best electrochemical performance.The initial discharge capacity of the electrode is 528.5 m Ah/g at 0.3 A/g,375.89 m Ah/g at 3 A/g and the capacity retention rate is 81.9% after 300 cycles at 0.3 A/g.Compared with the performance of elemental sulfur and AC1/polysulfide electrolyte additive electrode system.The specific capacity of sulfur cathode is 177.0 m Ah/g at 0.3 A/g after 200 cycles,and the capacity retention rate is just 16.0%.The performance AC2/polysulfide is much better than that of elemental sulfur electrode.The results showed that the adsorption to polysulfide on the surface of activated carbon limited the dissolution of polysulfide and inhibited the shuttle effect.In this paper,cathode carrier/polysulfide electrode systems were built by using the cathode materials of adsorption to polysulfide and polysulfide as the active material dissolved in the electrolyte.The system inhibit the transport of polysulfide and greatly improves the electrochemical performance of lithium-sulfur battery.This type of electrode system has the advantages of easy preparation process and strong matching,which provides a new idea for the development of lithium sulfur battery.