【作者】 张蕾；

【导师】 张会刚；

【作者基本信息】 南京大学 ， 材料学， 2019， 硕士

【摘要】 随着电动汽车和便携电子设备的快速发展,人们对于高能量密度锂离子电池的需求越来越大。选择高容量的电极材料是提高锂离子电池比容量的重要方法之一。在为数众多的锂离子电池负极材料中,二氧化锡由于有很高的理论容量和快速的充放电性能而受到广泛的关注。二氧化锡的容量由两部分反应提供,第一步是二氧化锡的转化反应,第二步是金属锡的合金化反应。其中合金化反应生成Li4.4Sn可以提供994 mAh g-1的容量。而第一步转化反应由于生成的Li2O的可逆性较差,从而限制了转化反应的可逆转化,使得二氧化锡充放电过程中产生不可逆的容量损失。通过在二氧化锡中掺杂过渡族金属可以提高放电过程中生成的Li20的可逆性,但是没有深入探究其提高反应可逆性的机理。为了设计更好的锂离子电池负极,本论文在原子尺度研究了纳米金属和氧化锂反应的界面,并且制备了一种纳米多孔的锰锡二元金属氧化物。通过第一性原理的计算,我们可以发现,Mn/Li2O的界面能要小于Sn/Li20的界面能,所以在氧化锂基体中,锰的成核粒径要小于锡的成核粒径。基于这一理论计算,本文所设计的锰锡基二元金属氧化物在作为锂离子电池负极材料发生电化学反应时,生成的超细锰纳米晶可以限制锡在电池反应过程中的晶粒粗化过程,提高锡和氧化锂的接触界面,从而促进生成Li20的可逆转化。该复合材料通过精心的实验设计而产生的大量锰锡界面可以极大的提高二氧化锡在锂嵌入和脱出反应过程中的可逆性,从而提升其作为锂离子电池负极材料的容量。通过相应的电化学性能测试,本论文中所制备的锰锡基复合材料在0.05Ag-1的电流密度下具有高达1620.6 mAh g-1的初始容量。由于锰的存在抑制了锡负极的团聚,该复合材料从而显示出良好的循环性能。在2 A g-1的电流密度下循环1000圈后仍然保持547.3 mAh g-1的高比容量。总体来说,本文提出了一种通过低界面能调控纳米结构界面反应来提高锡基氧化物可逆反应容量的方法,并且研究了其容量提高的机理,并为研究其他类型的金属氧化物复合材料提供了一种新的思路。更多还原

【Abstract】 The rapid development of electric vehicles and portable electronic devices increases the demand for high-energy density lithium ion batteries.High-capacity electrode materials is one of the important approach to increasing the specific energy of lithium-ion batteries.Among many anode materials,tin dioxides have received extensive attention because of their high theoretical capacity.The capacity of tin dioxide is provided by a two-step reaction.The first step is the conversion reaction of tin dioxides,and the second step is the alloying reaction of tin metal.Among them,the formation of Li4.4Sn by alloying reaction can provide a capacity of 994 mAh g-1.However,the first-stage conversion reaction has poor reversibility of Li2O,which restricts the cycleability of the conversion reaction,resulting in irreversible capacity loss during the charging and discharging of tin dioxides.Previous studies have reported that the reversibility of Li2O generated during discharge can be improved by doping the transition metal in tin dioxides,but the mechanism of improving the reversibility of the reaction is not revealed yet.In order to design a better lithium ion battery anode,the nano-metal and lithium oxide reaction interface was studied at the atomic scale and a nanoporous manganese-tin binary metal oxide was prepared.The first principle calculation leads to the finding that the Mn/Li2O interface energy is smaller than the Sn/Li2O interface energy,so in the lithium oxide matrix,the nucleation particle size of manganese is smaller than that of tin.Based on this theoretical calculation,we infer that when the designed manganese-tin binary metal oxide is electrochemically cycled as a negative electrode material for lithium ion batteries,the ultrafine manganese nanocrystals formed during lithiation can suppress the grain coarsening of tin during the reaction of the battery,improving the contact interface between tin and lithium oxide promotes the reversible conversion of Li2O.The large amount of manganese-tin interface produced by designing this composite can greatly increase the reversible capacity of tin dioxide during the reaction.Through the corresponding electrochemical performance test,we are able to demonstrate the composite having an initial capacity of up to 1620.6 mAh g-1 at a current density of 0.05 A g-1.Because the presence of manganese inhibits the agglomeration of metallic tin particles,the composite exhibits good cycling properties.Even after 1000 cycles,the nanoframe anode could deliver a capacity of 547.3 mAh g-1 at 2 A g-1.In general,we demonstrate a strategy of nanostructuring interfaces with low interface energy to enhance the Li-ion storage capability of binary tin oxides and revealed the mechanism of property enhancement,which might be applied to analyze other tin oxide composites.The results of this work provide a high-performance anode material and help the in-depth understanding of property enhancement,which may be applied to other composite oxide systems.更多还原