锡基量子点-碳纳米管-石墨烯多维复合电极材料的协同构筑、界面增强及电化学性能研究

In order to overcome the problems of the low specific capacity of commercial graphite and the bad cycling performance of tin-based anodes, this proposal aims to develop novel high performance tin-/carbon-based composite electrodes with high specific capacity and superior cycling performance. Three-dimensional porous frameworks facilitating the transportation of lithium ions and electrons will be constructed by using one-dimensional carbon nanotubes and two-dimensional graphenes, which are simultaneously loaded with zero-dimensional tin-based quantum dots to further increase the lithium storage capacities. The project endeavors to synergistically engineer the host-guest materials in order to realize the effective hybridizing of tin-based quantum dots and carbon-based supports with uniform distribution and firm conjunction, namely, through the size, shape and composition control of tin-based quantum dots together with the rational construction of carbon nanotubes and graphenes (through the proper choosing of size, ratio and surface modification). On the aspect of tin-based materials, the project aims to prepare ultrafine particles (such as tin oxide quantum dots) with controlled compositions (ranging from SnO2, SnO and SnOx with desired oxygen vacancies or doping). Besides, in-situ fabrication of metallic tin particles on the carbon supports would be realized by controlling the sintering atmosphere and the assistance of the reduction effect of carbon materials, on order to enhance the interfacial conjunction, which can prevent the pulverization of the tin-based materials during the alloying-dealloying process. And the effects of interface engineering will be in-depth investigated on the improvement and failure of the composite electrodes during the lithium storage.

为了解决商用石墨比容量不高和锡基负极材料循环性能差的问题，本项目拟利用一维碳纳米管和二维石墨烯构筑有利于锂离子和电子传输的三维多孔骨架，同时负载储锂容量高的零维锡基量子点，以开发高比容量、循环性能优异的新型高性能锡基/碳基复合电极材料。通过主客体（锡基量子点、碳纳米管和石墨烯）的协同设计，即锡基量子点材料的尺寸、形貌与成分设计，结合碳纳米管和石墨烯的合理搭建（如尺寸、比例选择及表面改性），来实现三者之间的均匀分散和牢固复合。在锡基材料方面，将着重尺寸超细（如制备氧化锡量子点），成分可控（如二氧化锡，氧化锡及其氧空位缺陷控制和掺杂）方面的设计合成；并借助气氛控制、热处理和碳材料的化学还原作用，实现氧化锡在碳基底上的原位金属化，制备界面增强的复合材料，防止锡基材料在合金化-脱合金化的过程中破碎脱落失效。同时深入开展复合界面工程在该材料储锂性能改善和失效方面的机理研究。

以锂离子电池为代表的电化学储能受到广泛的关注。然而，随着新能源电动汽车、智能电网等领域对能量和功率密度的更高需求，当前商用石墨负极理论容量偏低（仅为372 mA h/g），已难以满足需求。因此，开发能量/功率密度高、循环性能好的负极材料势在必行。基于合金化储锂机制的锡基负极材料（SnO2理论比容量782mAh/g）具有比容量高、电压平台低、资源丰富且环境友好等优势。然而，锡基负极材料在充放电过程中具有巨大的体积效应，从而易于导致电极材料破碎粉化脱落，严重降低了电池的循环寿命，限制了其商业化应用。基于此，本项目通过锡基材料纳米化及其与碳纳米材料复合化等结构设计优化，以抑制该类材料的体积膨胀和破碎失效，进而开发出性能优异的锡/碳基锂离子电池负极材料。主要成果如下：1）开发了两种SnO2量子点的简易制备方法，即辛酸亚锡空气气氛下低温热解法和二氯化锡室温水解法。两种方法都能实现SnO2和各种碳纳米材料的复合以及规模化生产，所制备的SnO2纳米颗粒尺寸范围在2-20nm可控。2）开发了多种新型石墨化结晶纳米碳材料：①通过结合化学气相沉积法和模板法制备技术，以碱式碳酸镁薄片为模板，制备了类蜂窝状、具多孔网络、石墨化结晶的薄片碳纳米材料；以微米碳酸钙块体为模板制备了共形的、由多层石墨烯交联构筑的多孔碳方块。利用这些新型碳纳米材料的多孔性和优异导电性，通过负载超微SnO2纳米颗粒，大幅度提升了材料的比容量和循环性能。②利用静电纺丝技术，制备出了SnO2纳米颗粒负载的多孔碳纤维复合材料。3）深入研究了所制备复合材料的电化学性能。作为锂离子电池负极材料，多次循环可逆容量均能保持在800-1100mAh/g，远高于SnO2理论比容量782mAh/g。通过非原位TEM、XPS分析，发现纳米化促进了SnO2第一步反应由不可逆向可逆转变，即SnO2 + Li+ + 4e- ⇌ Li2O + Sn，进而大幅度提升了SnO2理论比容量达到1400 mAh/g。通过纳米化和碳复合，有效提高了材料的电化学性能，为下一代高性能负极材料的开发奠定了一定基础。