Modification And Performance Of Graphene-based Carbon Anode Materials For Sodium-ion Batteries

Sodium-ion batteries?SIBs?possess similar charge storage principle to lithium-ion batteries and are the most promising choice for large scale energy storage,because of the abundant natural resources and lower cost of sodium.However,the lack of appropriate anode materials severely restricts the development of SIBs.Carbon materials are the most potential candidate.Various kind of carbon materials have been widely investigated,but the sodium storage mechanism is still debatable and the electrochemical performance still need further improving.To address above-mentioned issues,solutions are proposed from the perspective of graphene,which is the basic structural unit of carbon materials.From both surface modification and stacking structure regulation approaches,two different kind of carbon materials,namely sulfur functionalized porous graphene monolith and biomass-derived hard carbon respectively,are designed and prepared as the anodes for SIBs.The main content and conclusion are as follows:Firstly,we functionalized the graphene monolith and introduced electrochemical active sulfur-containing functional groups on the surface of graphene.to obtain sulfur functionalized porous graphene monolith?donated as SPGM?.The prepared SPGM delivered a high capacity of⁴00 mAh/g at the current density of 0.1 A/g.Besides,excellent rate capability were demonstrated as well,namely ahigh reversible capacity of 123 mAh/g can be achieved even at a current density of 5 A/g.It's further unvealed that-C-S_x-C-?x=1-2?sulfur-containing functional groups are the main contribution of high capacity of SPGM.We also investigated the the influences of sulfur contents on the micro-structure and electrochemical performance of SPGM.The as-prepared SPGM with a low sulfur content delivers lower initial reversible capacity while the SPGM with high sulfur content suffers a fast capacity fading.The SPGM with optimized sulfur contents?16.8 wt%?can obtain both high capacity and good cycling stability.In addition to the modification of surface chemistry,the regulation of stacking structure of graphene also influenced the sodium storage behavior and electrochemical performance of carbon materials.Therefore,we aimed to regulate the stacking structure of graphene.The wasted biomass litchi shell was utilized as carbon precursor to prepare the litchi shell-derived hard carbon?denoted as LSC?through a simple high-temperature carbonization process under inert atmosphere for the first time.It's found that carbonization temperature was the key factor for the regulation of stacking structure of graphene and enhancing electrochemical performance.From 900? to 1400?,along with the increase of temperature of carbonization,the obtained LSC witnessed a decrease in specific surface area and increasesin the ordered stacking degree of graphene sheets and interlayer distance.Therefore,the sodium storage capability is increased and the initial coulombic efficiency is on the increasing trend as a whole.The sample prepared at 1400? exhibited a high capacity of 334 mAh/g and a high initial coulombic efficiency of 72% under a current density of 20 mA/gFurthermore,we assembled full sodium-ion batteries with LSC-1400 as the anode and Na[Ni_1/3Fe_1/3Mn_1/3]O₂ as the cathode,which delivered a high capacity of 57mAh/gand energy density of 177 Wh/kg.