Regulation Of Lithium Storage Performance And The Mechanism For SnO₂ Based Anode Materials In Full/Half Cell

Tin dioxide?SnO₂?anode has been regarded as one of the next generation of potential anode materials because of its abundant sources,low price,environmental friendly and high specific capacity?1494 m A h/g?.However,the commercial application of SnO₂anode is limited by the problems of poor cycling stability and unstable solid electrolyte interface?SEI?.In this paper,SnO₂-Li₂CO₃/G and SnO₂-Co-P-C anode materials were prepared by ball milling in view of the shortages of SnO₂-based anode materials,such as instability of SEI,poor cycling stability and high conversion reaction voltage platform.Firstly,aiming at the instability of SEI,SnO₂-Li₂CO₃/G anode material was prepared by planetary ball milling.The prepared SnO₂-Li₂CO₃/G anode material has a unique structure of amorphous Li₂CO₃particles and crystal SnO₂grains compounded and loaded on graphite layers.The SnO₂-Li₂CO₃/G electrode possess a high initial coulombic efficiency of 79.6%,and a reversible charge specific capacity of 927.5 m A h/g with the capacity retention of 96%was obtained after 350 cycles at the current rate of 0.2 A/g.Increasing the current rate to 1A/g,the SnO₂-Li₂CO₃/G electrode also delivered a stable charge specific capacity of over1200 m A h/g after 900 cycles,exhibited excellent long term cycling performance.The mechanism of Li₂CO₃is to promote the formation of dense and firm SEI for SnO₂-Li₂CO₃/G composite,which could inhibit the agglomeration of nano SnO₂particles,block the long-range diffusion path of agglomeration and coarsening of Sn particles,maintain the stability of nano structure for the composite,effectively inhibit the volume expansion effect and the continuous growth of SEI,thus improve the reversibility of SnO₂conversion reaction,and realize the high initial coloumbic efficiency and stable cyclic performance of first time of SnO₂-Li₂CO₃/G anode.The anode materials that manufactured by compounding Li₂CO₃with different reaction type anode materials and compounding SnO₂anode with other stable inorganic components in SEI shows excellent electrochemical performance,which proves the wide universality of the method developed in this paper.Subsequently,the SnO₂-Li₂CO₃/G anode material was used to pair with Li Fe PO₄cathodeshow a high initial coloumbic efficiency of 80.1%and 77.8%in 0.01-3.45 V,respectively.Moreover,the SnO₂-Li₂CO₃/G anode delivered a high initial specific charge capacity of 944.6m A h/g with a capacity retention of 92.7%after 30 cycles,showing good cycling stability and high reversible specific capacity.According to the electrochemical reaction range of SnO₂-Li₂CO₃/G anode,the cut-off voltage of LFP||SnO₂-Li₂CO₃/G full cell was adjusted to2.5-3.45 V,and the full cell in this voltage range could maintain a capacity retention of95.5%after 100 cycles,with a high output voltage of about 2.8 V,which lays a good foundation for the application of SnO₂-based anode materials in the full cell.Finally,to solve the problem that the capacity related to conversion reaction of SnO₂-based anode is difficult to be used in practice due to the high voltage platform,the de-lithiated voltage of SnO₂anode was regulated by compounding SnO₂anode with P.The SnO₂-P material prepared by planetary milling for 30 hours shows a about 0.5 V decrease on charging voltage platform than that of pure SnO₂material.On the basis of SnO₂-P material,SnO₂-Co-P material was obtained by further milling with Co,which improved the reversibility of conversion reaction for SnO₂in the composite.The capacity decay of SnO₂-Co-P composite caused by P component settled by prepared the SnO₂-Co-P composite using shaking ball milling method.To further improve the cycling performance,SnO₂-Co-P-EG and SnO₂-Co-P-NG:CG=1:1 electrodes were obtained through compounding SnO₂-Co-P with different carbon materials and the exploration of slurrying process.After 200cycles,the reversible specific capacity of about 700 m A h/g could be maintained for SnO₂-Co-P-EG electrode,and a capacity retention of 86%was delivered by the SnO₂-Co-P-NG:CG=1:1 electrode.The LFP||SnO₂-Co-P-EG:CG full cell maintained about95%capacity after 40 cycles in the voltage range of 2.0-3.5 V,showed excellent cycle stability performance.The mechanism of SnO₂-Co-P material was determined by in-situ XRD analysis,the addition of Co improves the reversibility of conversion reaction for SnO₂,thus improving the initial coulombic efficiency and cyclic performance.The Sn P alloy formed by P additive combines with the Sn generated by conversion reaction for SnO₂,which changes the reaction path of the lithiation/delithiation process of SnO₂,thus reducing the charging voltage platform of SnO₂and improving the initial coulombic efficiency of the SnO₂-Co-P anode.