Tetragonal Phase Germanium Nanocrystals in Lithium Ion Batteries
Tetragonal Phase Germanium Nanocrystals in Lithium Ion Batteries
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DOI：
10.1021/nn403674z
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发表时间：
2013-10-01
期刊：
影响因子：
17.1
通讯作者：
Kang, Hong Seok
中科院分区：
文献类型：
--
作者：
Cho, Yong Jae;Im, Hyung Soon;Kang, Hong Seok
近年来，各种锗基纳米结构表现出优异的锂离子存储能力，被认为是最有希望取代目前锂离子电池碳质阳极的候选材料。然而，在放电/充电循环期间，对其结构和相演变的理解有限。此外，锂嵌入的理论模型仍然是一个具有挑战性的问题。在此，我们进行了比较研究的周期依赖的锂化/脱锂过程的锗（Ge），硫化锗（GeS），和氧化锗（GeO 2）纳米晶体（NC）。我们使用方便的气相激光光解反应合成了NCs，并在100次循环后获得了优异的可逆容量：1100-1220 mAh/g。值得注意的是，亚稳的四相（ST 12）Ge NC在锂化后不断产生，并且在几个循环后成为主导相，完全取代原始相。结晶ST 12相持续100个循环。对多晶型嵌锂结构的第一性原理计算表明，当x >= 4时，ST_（12）相Ge_（12）Lix结构比具有相同化学计量比的立方相Ge_（8）Lix结构更稳定。ST 12相的产生和持久性可以归因于与立方相相比锂原子的更强的结合相互作用，这增强了循环性能。
Various germanium-based nanostructures have recently demonstrated outstanding lithium ion storage ability and are being considered as the most promising candidates to substitute current carbonaceous anodes of lithium ion batteries. However, there is limited understanding of their structure and phase evolution during discharge/charge cycles. Furthermore, the theoretical model of lithium insertion still remains a challenging issue. Herein, we performed comparative studies on the cycle-dependent lithiation/delithiation processes of germanium (Ge), germanium sulfide (GeS), and germanium oxide (GeO2) nanocrystals (NCs). We synthesized the NCs using a convenient gas phase laser photolysis reaction and attained an excellent reversible capacity: 1100-1220 mAh/g after 100 cycles. Remarkably, metastable tetragonal (ST12) phase Ge NCs were constantly produced upon lithiation and became the dominant phase after a few cycles, completely replacing the original phase. The crystalline ST12 phase persisted through 100 cycles. First-principles calculations on polymorphic lithium-intercalated structures proposed that the ST12 phase Ge12Lix structures at x >= 4 become more thermodynamically stable than the cubic phase Ge8Lix structures with the same stoichiometry. The production and persistence of the ST12 phase can be attributed to a stronger binding interaction of the lithium atoms compared to the cubic phase, which enhanced the cycling performance.