The Mechanism And Preparation Of SnO₂-based Composite Anodes With Enhanced Initial Coulombic Efficiency

Owing to high theoretical specific capacity,moderate working potential,natural abundance and low price,SnO₂-based materials are promising anodes for next generation of lithium-ion batteries.However,the coarsening of nano-sized Sn is responsible for the low initial Coulombic efficiency,which limited the development and application of SnO₂-base anodes.In order to overcome these issues,two different SnO₂-Co-C and SnO₂-Li₂CO₃-C materials are prepared via mechanical ball milling.Then the microstructure and electrochemical performance of the as-prepared SnO₂-based materials are studied,and the mechanisms of enhancedinitial Coulombic efficiency are revealed.Furthermore,SnO₂-Co-C full cells have been assembled with commercial cathodes to obtain the good cycling performance.The main conclusions are as followed:First,a tenary SnO₂-Co-C composite is produced using planetary and roller ball milling methods,which has a microstructure that refined SnO₂-Co hybrids are embedded in graphite matrix.The SnO₂-Co-C electrodes exhibit high ICEs with an average of 80.8%.A reversible780mAh/g at 0.2A/g after 400 cycles when the composite was manufactured via small planetary ball milling,and they achieve 875mAh/g after 250 cycles when the material is prepared on a large-scale with a roller milling.Even at a high rate of 2A/g,the composite has a long lifetime and delivers 610mAh/g after 1000 cycles.And the XRD measurements of different milled samples prove that the Co additives dramatically inhibit Sn coarsening in the lithiated SnO₂,which enable highly reversible conversion reactions in the SnO₂-Co-C composite during cycling.Second,SnO₂-Li₂CO₃-C material is prepared via a two-step planetary ball milling to obtain a high initial Coulombic efficiency by the method of prelithiation.The influence of milling time on the electrochemical behavior of SnO₂-Li₂CO₃-C anodes has been studied.The SnO₂+5%Li₂CO₃-20h+C-10h composite,with an average ICE of 79.6%,are successfully prepared.And the SnO₂-Li₂CO₃-C composite has a microstructure that ultrafine SnO₂particles are embedded in layered graphite.SnO₂-Li₂CO₃-C composite exhibits excellent cyclic stability and rate performace,andthe electrode deliver a high reversible capacity of 890mAh/g after350 cycles at a current rate of 0.2A/g.Then the additive Li₂CO₃ can suppress the decomposition of electrolyte EC components,and such the prelithiation method can improve the initial Coulombic efficiency of SnO₂-based material.At last,full cells are assembled and electrochemically tested with SnO₂-Co-C as the anode and commercial materials?LiFePO₄ and LiCoO₂?as the cathode.As a result,the SnO₂-Co-C//LiFePO₄ full cell delivers a reversible capacity of 840mAh/g after 50 cycles at2.0C in the potential range of 0.01-3.4V.And the full cell exhibits good rate performance within the potential range.When the potential range is adjusted to 2.3-3.4V,SnO₂-Co-C anode undergoes the reversible alloy reactions and the full cell obtains a capacity of 410mAh/g after50 cycles.Futhermore,another attempt of SnO₂-Co-C//LiCoO₂ full cells is operated.To avoid Li deposition on the surface of anode,the charge cut-off potential is guaranteed as 3.75V by a capacity-limited method.The SnO₂-Co-C//LiCoO₂ full cells deliver discharge specific capacities of 605mAh/g and 410mAh/g in the potential ranges of 1.5-3.75V and 2.6-3.75V,respectively,which demonstrate that the SnO₂-base full cells exhibit good cycling stability.