Research On Sodium/Lithium-based Electrochemical Storage Materials With High Performance

In non-water system,the anode energy storage materials based on alkali metal Na,Li and their corresponding ions(hereinafter referred to as Na/Li based energy storage materials)are the key components of the construction of high specific energy electrochemical energy storage system.In this paper,high performance Na/Li anode energy storage materials are studied,especially the evolution process from ion storage stage to metal storage stage and related electrochemical research.The main contents and results are as follows:1.High capacity Na ion energy storage material based on high temperature calcination and surface coating.Sodium hard carbon anode material was prepared by high temperature calcination with starch as precursor.Firstly,the physical and chemical properties of sodium ions stored in the initial hard carbon calcined at different calcination temperatures were investigated.Different calcination temperatures would affect the capacity of the initial hard carbon in the high voltage(>0.1 V vs.Na/Na+)slope and low voltage(<0.1 V vs.Na/Na+)platform,and 1200℃(HC-1200)was determined as the appropriate temperature for calcination of the hard carbon precursor.Subsequently,the carbon coating of HC-1200 samples was modified by chemical vapor deposition(CVD)technology.With CVD process,the physical and chemical properties of HC-1200 surface changed,so its electrochemical performance of sodium ion storage also improved,and the low voltage(<0.1 V vs.Na/Na+)platform capacity was greatly increased.Specifically,when the CVD carbon coating time is 4 h,at the current density of 25 mA g-1,the initial Coulombic efficiency of CCHC-1200-4 h is 89.6%,the initial reversible capacity is 301 mAh g-1,and the capacity retention rate of 100 cycles is 94%.For CCHC-1200-6 h sample,at the current density of 25 mA g-1,the initial Coulombic efficiency and reversible capacity of are 93.8%and 332 mAh g-1,respectively.2.High power Sodium ion energy storage materials based on multistage structure and O-doping.Using cheap starch as precursor,a carbon-based material(HSIH-CMs)with multistage structure and O-doping was calcined at high temperature by template method,which improved the storage capacity of sodium ion at high voltage(>0.1 V vs.Na/Na+)slope.Hard carbon stores sodium ions at low voltage(<0.1 V vs.Na/Na+),which is a diffusion process of Na ion intercalation/deintercalation,and has a slow kinetic process.The multi-defect porous carbon material can store sodium ion capacity in a high voltage(>0.1 V vs。Na/Na+)slope,which is a surface capacitive process of ion adsorption/desorption.It has a fast kinetic process and meets the demand of releasing a large amount of energy in a short time.When HSIH-CMs was used as the anode of sodium ion battery,it showed high reversible specific capacity,good cycle stability and excellent rate performance.Because HSIH-CMs exhibited excellent electrochemical properties as both anode and cathode,a "dual carbon"HSIH-CMs//HSIH-CMs SICs device was constructed.The superior energy density and power density were 224 Wh kg-1 and 17160 W kg-1,respectively.At the same time,a very stable cycle life(at 2 A g-1 current density,91%capacity retention after10000 cycles)was obtained.3.Extended from sodium ion storage to sodium metal anode.Using starch as precursor and template method,open three-dimensional O-doped "sodiophilic"porous carbon foam(OCF)with porous structure were prepared.OCF not only could effectively guide the nucleation and growth of metal Na,but also had the ability to accommodate metal Na.The integrity and reversibility of the OCF structure guaranteed the excellent cycling stability of the electrode under high current density.The results showed that the overpotential only increases to～15.73 mV at a high current density of 5 mA cm-2.When the current densities were 0.5,1,2 and 10 mA cm-2,the Coulomb efficiency could reach 99.78%,99.89%,99.94%and 99.83%,respectively.When the current density is 5 mA cm-2 and the deposition capacity is 5 mAh cm-2,the cycle life of the electrode can reach 2000 h with 99.90%average Coulombic efficiency.4.A Li anode solid electrolyte interface(SEI)film with dendrite tip suppression function was constructed.For this purpose,a 2-Fluorophenylsulfur Pentafluoride(2FSPF)were employed as an additive in carbonate-based electrolyte that can be decomposed electrochemically during battery operation to form such a polysulfiderich interphase.These polysulfides with certain fluidity can adhere dynamically the budding tip of Li metal,as a so-called tip-inhibitor,when the local current density of the tip rising,thus to hinder Li+diffusion toward the tip,resulting in inhibiting the further growth of Li dendrites and leveling the Li deposition.At the current density of 1 mA cm-2,the average Coulombic efficiency of Li//Cu cells is as high as 98.39%during 600 cycles,and the stable cycling of Li//Li symmetric cell reaches 3500 h.Furthermore,due to the high anodic stability of carbonate-based electrolyte,the highvoltage Li//LiCoO2(LCO)and Li-O2 full cells achieve excellent cycle performance with lean electrolyte.