Room-temperature Synthesis And Electrochemical Properties Of Sulfur,Iodine,and Oxocarbon Salts Cathodes For Rechargeable Metal Batteries

Li-ion batteries have been widely applied in many kinds of portable electronic devices,and now have also extended to the fields of electric vehicles and smart grids.Currently,the energy density of Li-ion batteries based on the anode of graphite and cathode of transistion metal oxide has almost reached the upper limited value,which makes it difficult to be further improved.In addition,the distribution of transition metal element of Co,Mn and Ni resource is inhomogeneous.Moreover,the preparation of cathode also involves the mass energy consumption and carbon oxide emission,which deviates the demand of sustainable development and large scale application.Considering these points,rechargeable metal batteries with high capacity metal?Li,Na,K?as anode and oxygen,sulfur,iodine and organic materials as cathodes have been regarded as promising battery systems due to their high capacities,wide abundance and low price.Furthermore,rechargeable metal batteries based on sulfur,iodine and organic cathodes materials share similar battery configurations and packing technologies with current Li-ion batteries,which seem more facile for commercialization.However,all these three cathode materials face similar troubles in battery application.First,the poor conductivity limits the electronic and ion transport.Second,the raw materials or intermediate products among discharge/change are easily dissolved in electrolyte,leading to the capacity fading with cycling.In this dissertation,we design three approaches of preparing sulfur,iodine,and oxocarbon salts cathodes under room-temperature in view of the troubles of poor conductivity and easy dissolution existed in rechargeable metal batteries.All these three approaches are facile,low energy consumption,few by-products and low emission,which is facle for large scale application.When applied as cathode materials in Li-S,Li-iodine and metal-organic batteries,they all demonstrate high rate and long cycling life.The main research results are listed as below:1.Sulfur nanodots with average diameters of 2 nm supported on Ni foam have been fabricated through the electrodeposition method and acted as cathodes in Li-S batteries.Through tuning the loading mass of sulfur on Ni foam,the capacity remained 895 mAh·g^–1 after 300 cycles at 0.5 C,and 521 mA h·g^–1 after 1400 cycles at 5 C.Compared with previous studies,this work initially achieved the goals of fabricating sulfur cathode with ultrasmall size under room temperature.Moreover,the high electrochemical activities of nano sulfur enable the superior cycling life and high rate performance.In addition,in situ Raman and ex situ TEM methods have been carried out to prove the reversibility of S and Li₂S nanodots.2.Iodine/carbon cloth flexible cathodes have been prepared by a room temperature“solution-adsorption”method.The free-standing cathode material was fabricated through adsorbing iodine into the microporous pores of carbon cloth in aqueous solution.The self-discharge phenomenon has been resolved with optimizatied electrolyte.The optimized cathode applied in Li-I batteries exhibits a capacity of 195 mAh·g^–1?300 cycles,0.5 C?.At a high rate of 5 C,the discharge capacity still reached 169 mAh·g^–1.In addition,the soft-packaged Li-I battery shows total energy density of 136 Wh·kg^–1 and 107 Wh·kg^–1 after 60 cycles.Four,five and six membered ring oxocarbon salts of M?CO?_n?M=Li,Na,K;n=4,5,6?have been prepared with room-temperature proton exchanged method and applied as cathodes in rechargeable metal batteries to investigate the Li,Na and K-ion storage performance.The results demonstrate that oxocarbon salts with four membered ring are hard to uptake cation in selected voltage regeion,while the five and six membered ring salts are able to uptake some cations.In addition,we found that the oxocarbon salts of K₂C₆O₆ and K₂C₅O₅ can be applied as fast K-ion insertion/de-insertion materials.The calculation result shows that K₂C₆O₆ is a semiconductor with a narrow band-gap of 0.9 eV.In addition,the K-based oxocarbon salts also reveal higher conductivities than Na-based and Li-based oxocarbon salts.Meanwhile,the diffusion rate of K-ion is also faster than both Li-ion and Na-ion.Moreover,with K₄C₆O₆ as anode and K₂C₆O₆ as cathode,a first example of inorganic-organic rocking-chair K-ion batteriy has been reported.