Modarres Mohammad H, Lim Jonathan Hua-Wei, George Chandramohan, De Volder Michael
Department of Engineering, Institute for Manufacturing, 17 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom.
Cavendish Laboratory, Department of Physics, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
J Phys Chem C Nanomater Interfaces. 2017 Jun 22;121(24):13018-13024. doi: 10.1021/acs.jpcc.7b02878. Epub 2017 May 30.
Hybrid nanomaterials where active battery nanoparticles are synthesized directly onto conductive additives such as graphene hold the promise of improving the cyclability and energy density of conversion and alloying type Li-ion battery electrodes. Here we investigate the evolution of hybrid reduced graphene oxide-tin sulfide (rGO-SnS) electrodes during battery cycling. These hybrid nanoparticles are synthesized by a one-step solvothermal microwave reaction which allows for simultaneous synthesis of the SnS nanocrystals and reduction of GO. Despite the hybrid architecture of these electrodes, electrochemical impedance spectroscopy shows that the impedance doubles in about 25 cycles and subsequently gradually increases, which may be caused by an irreversible surface passivation of rGO by sulfur enriched conversion products. This surface passivation is further confirmed by post-mortem Raman spectroscopy of the electrodes, which no longer detects rGO peaks after 100 cycles. Moreover, galvanostatic intermittent titration analysis during the 1st and 100th cycles shows a drop in Li-ion diffusion coefficient of over an order of magnitude. Despite reports of excellent cycling performance of hybrid nanomaterials, our work indicates that in certain electrode systems, it is still critical to further address passivation and charge transport issues between the active phase and the conductive additive in order to retain high energy density and cycling performance.
将活性电池纳米颗粒直接合成在诸如石墨烯等导电添加剂上的混合纳米材料，有望提高转换型和合金型锂离子电池电极的循环性能和能量密度。在此，我们研究了混合还原氧化石墨烯-硫化锡（rGO-SnS）电极在电池循环过程中的演变。这些混合纳米颗粒通过一步溶剂热微波反应合成，该反应可同时合成SnS纳米晶体并还原氧化石墨烯。尽管这些电极具有混合结构，但电化学阻抗谱表明，阻抗在约25个循环中翻倍，随后逐渐增加，这可能是由于富含硫的转换产物对rGO进行不可逆的表面钝化所致。电极的事后拉曼光谱进一步证实了这种表面钝化，在100个循环后不再检测到rGO峰。此外，第1次和第100次循环期间的恒电流间歇滴定分析表明，锂离子扩散系数下降了一个多数量级。尽管有报道称混合纳米材料具有优异的循环性能，但我们的工作表明，在某些电极系统中，进一步解决活性相和导电添加剂之间的钝化和电荷传输问题对于保持高能量密度和循环性能仍然至关重要。
