Preparation And Li/Na Storage Properties Of Flexible SPAN Cathode Materials

Energy plays a vital role in the development of human society.With the continuous development of renewable energy such as nuclear energy and solar energy,energy storage technology is indispensable for the effective use of these renewable energy sources.Sulfur cathode materials have a very high theoretical specific capacity,extremely low cathode cost and environmental inertness,which can be matched with metallic lithium or sodium anodes to form a high energy density power system.However,the practical application of lithium-sulfur batteries or Room-Temperature sodium-sulfur batteries still faces many problems,including the insulation of elemental sulfur,the dissolution of polysulfides and the shuttling effect.The sulfur element in sulfurized polyacrylonitrile composite was existed as short-chain sulfur grafted in the conductive carbon matrix.Therefore,the“shuttle effect”of polysulfide can be avoided,which makes it have a good application prospect in high specific energy secondary metal-sulfur batteries.In this article,we construct a high-performance sulfurized polyacrylonitrile cathode material through structural design and explore the effects of different binders on the electrochemical performance of sulfurized polyacrylonitrile in Room Temperature sodium-sulfur batteries.The research contents are as follows:?1?We have prepared a flexible sulfurized polyacrylonitrile film with hollow tubular nanofibers?H-SPAN?by coaxial electrospinning and simple heat treatment,which can be directly used as the cathode for lithium-sulfur batteries.Benefiting from its unique hollow tubular nanofiber structure,there is a greater contact area between the electrolyte and the electrode,and the utilization of the electrode is improved.At the same time,the energy density of the battery is increased by eliminating the metal current collector,conductive carbon black,and binder.The superior Li/Na storage performance of H-SPAN were proved by a series electrochemical characterization.The working mechanism and stability of H-SPAN is well elucidated by ex situ Raman spectroscopy and ex situ X-ray Photoelectron Spectroscopy?XPS?.Finally,the flexible pouch cell was fabricated by using a H-SPAN film as cathode to demonstrate the potential applications in flexible electronic devices.?2?Sodium carboxymethyl cellulose?Na CMC?was used instead of polyvinylidene fluoride?PVDF?as a binder for the SPAN powder electrode.The electrochemical performance was further characterized in a RT-Na/S batteries.It can be expected that the Na CMC binder will have the following advantages:1)Na CMC is often used as a negative electrode binder due to its good mechanical strength,which helps to alleviate the large volume expansion effect?175%?during the conversion between S and Na₂S.2)The abundant oxygen functional groups endow Na CMC with great polysulfide capturing ability,which can enhance the reversible specific capacity of SPAN in RT-Na/S batteries.3)Na CMC itself contains sodium ions,which facilitates the transport of sodium ions between the electrode material particles.Comprehensive electrochemical analysis indicates the facilitated kinetics of Na CMC electrode.The Na CMC binder also gives rise to a high reversible capacity of 756 m Ahg^-1 at a current density of 2C and a capacity retention rate of50%after 200 cycles.This work shows the greatly improved rate performance of sulfurized polyacrylonitrile cathode with Na CMC binder.