Prelithium And Doping Modification Technology Application In Lithium/sodium Ion Batteries

In order to achieve"double carbon"strategic goal,it is essential to effectively utilize renewable clean energy（wind,light,heat etc.）.However,due to the intermittent and uncertain characteristics,renewable energy needs to be supported by large-scale energy storage technology in practical application.Lithium/sodium-ion secondary batteries have become an indispensable part of energy storage system due to flexibility,high energy conversion efficiency and simple maintenance,and have great application prospects for large-scale energy storage.Nevertheless,the defects of electrode materials further limit its electrochemical performance.Therefore,based on the key problems existed in electrode materials,the prelithium and doping technologies were used to improve the charge/discharge capacity and cycle performance in lithium/sodium-ion batteries,and the reaction mechanisms of batteries were analyzed combined with advanced microstructure characterization technology.The specific research contents are as follows:Prelithium technology is one of important strategies to improve the first-cycle Coulombic efficiency and energy density of lithium ion batteries（LIBs）.Therefore,it is particularly important to exploit a new prelithium reagent by a simple method.Based on the mechanism of stress-induced creep,a novel prelithium reagent of submicron air stable lithium spheres（ASLSs）with lithium metal as core and the Li F/Li₂O as shell was prepared by a simple electrochemical deposition technology.ASLSs with uniform sizes have good prelithiation performance for graphite and Si O@C anodes,which can significantly improve the first-cycle Coulombic efficiency of LIBs.The energy density and cycle performance can also be greatly improved by applying ASLSs to anodes in full cells.Due to deficient lithium resources,sodium ion batteries（SIBs）have attracted much attention in the large-scale energy storages.Layered transition metal oxides are main cathodes for SIBs.However,the Na⁺/vacancy order and phase transformation limit its development in practical application.Doping modification technology can effectively inhibit the phase transition of cathodes and improve the electrochemical performance of SIBs.In this paper,P2-type Na_0.7Ni_0.3Mn_0.6Co_0.1O₂（NMC）was synthesised by a simple oxide solid phase method.In order to inhibit phase transition at high voltage,which affects the cycle stability of the battery,NMC was doped by Mg to improve the electrochemical performance.The Na_0.7Ni_0.25Mn_0.6Co_0.1Mg_0.05O₂(NMCMg_0.05)with optimum ratio of Mg doping was chosen to explore the reaction temperature.The optimum synthesis temperature is 900℃by comparing the structure and electrochemical properties of NMCMg_0.05 at different reaction temperatures（800℃,900℃,1000℃）.NMCMg_0.05 has excellent electrochemical performance,and the capacity retention rate is 83.7%after 1000cycles at 5 C.The NMCMg_0.05 full cell matched with hard carbon has excellent electrochemical performance.The specific capacity is 108.2 m Ah g^-1 at 0.1 C,and the capacity retention is 75%after 300 cycles at 1 C.Multiphase composite is also an important strategy to improve the electrochemical performance of layered transition metal oxides.In this paper,a multiphase composite layer oxide material Na_0.7Li_0.2Ni_0.2Mn_0.5Co_0.1O₂（NLNMC）was synthesised by an acetate solid phase method with Li doping to P2-type Na_0.7Ni_0.3Mn_0.6Co_0.1O₂（NNMC）.The atomic structures of NLNMC were characterized by scanning transmission electron microscope,and the atomic arrangement of every phase and phase interfaces can be clearly observed.The O3 phase can improve the capacity,and the P2 phase can stabilize the structure of NLNMC.In addition,Li doping can reduce the numbers of Na⁺vacancies,improve the first-cycle Coulombic efficiency,inhibit the phase transition and reduce the valence reaction of the transition metal.NLNMC has excellent electrochemical properties,and the discharge specific capacity is 181.1 m Ah g^-1 at 0.1 C,the capacity retention rate is 85.2%after 300 cycles at 5 C.The specific capacity of NLNMC full cell matched with hard carbon is 118.9 m Ah g^-1 at 0.1 C,the first-cycle Coulombic efficiency is up to 99.7%,and the capacity retention is 79.5%after 200 cycles at 0.5 C.NLNMC has great practical application prospect.