Investigation Of Electrode Materials For Lithium Sulfur Cathode And Lithium Ion Anode

Lithium-ion batteries?LIBs?are one of the most successful rechargeable battery systems to date,owing to the high specific energy/energy density,no memory effect,and good cycling lifespan.With the development of green energies,especially the development of electrical veichles,high energy density storage system is desirable.In this paper,enhanded sulfur cathode and lithium iron oxide anode are designed and prepared,which deliver higher capacity and stable cycling performance.Carbon coated sulfur cathode material was prepared via solvent method.Tetrohydrofuran?THF?is selected here for its proper boiling point,which is easy for cycling and energy saving.The composite has remarkable conductivity and ability of accomdating volume expansion due to the unique structure.Meanwhile,the microporous carbon can prevent lithium polysulfides from difussing away,which evidently buffered the“shuttle effect”.As anticipated,a capacity as high as 598.3 mAh g^-1 was obtained after being tested for 200 cycles at 1 C,implying enhanced cycling performance.We developed a novel hybrid nitrogen doped carbon material via an aerosol spray drying technique and subsequent CVD process.The obtained carbon material?MCCNT?possessed a unique porous mesoporous carbon sphere core and CNTs were bonded seamlessly during the growth stage,forming a 3D hierarchical structure.Nitrogen was in-situ doped during the growth of CNTs,which facilitates the chemical adsorption of LPSs.When the as-prepared MCCNT hybrids were used as a matrix to accommodate sulfur,a high initial capacity of 535.6 mAh g^-1 could be achieved at 1 C and after 300cycles,demonstrating highly improved cycling stability.A sulfur cathode modified by functional Nafion/?-Al₂O₃ membrane has been successfully prepared.The cation selective Nafion and adsorbent?-Al₂O₃ worked synergistically to prevent the anions and effectively adsorb the ploysulfides.When 1wt%?-Al₂O₃ was added in the film,the initial capacity can be improved to 1448.0 mAh g^-1 and preserves 788.6 mAh g^-1 after 200 cycles.In-situ graphitical carbon coated lithium iron oxide?LFO?was designed and synthesized via a scalable chemival route.The preset Li in the LFO compensates the irreversible loss of Li during the first cycle,providing a high initial CE of around 90%,much higher than that of ca.70-80%for conventional iron oxides nanoparticles.Meanwhile,it delivered a high reversible capacity of 700 mAh g^-1 after 400 cycles with remarkable cycling performance.Full cells were demonstrated by coupling LiCoO₂ and LiNi_0.5Mn_1.5O₄ cathode and LFO anode.The LFO anode with high initial CE increased the utilization of Li in the cathode,substantially boosting the performance of the whole battery.A core-shell structured LFO/graphite hybrid anode was prepared via a two-step process,which can bear high“C”rate charge-discharge and also has high ICE.The hybrid anode delivered a capacity of 612.4 mAh g^-1 after 1000 cycles at a high current density of 2 A g^-1,which suggests high rate stability and ultralong cycling life.When coupling with LiCoO₂ to farbircate full cell,enhanced electrochemical performance could be achevied.