Hwang Taesoon, Cho Maenghyo, Cho Kyeongjae
Department of Mechanical and Aerospace Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea.
Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080, United States.
ACS Omega. 2021 Mar 31;6(14):9492-9499. doi: 10.1021/acsomega.0c06199. eCollection 2021 Apr 13.
Graphite is currently utilized as anode materials for Li-ion batteries, but it is well-known that graphite does not show good electrochemical performances as the anode material for sodium-ion batteries (SIBs). It was also reported that the low electrochemical performances of graphite originated from the larger ionic radius of the sodium ion due to the required higher strain energy for sodium-ion intercalation into graphite leading to an unstable sodium-ion intercalated graphite intercalation compound (GIC). In this work, using first-principles calculations, we introduce pillaring effects of Na X ( = 3 and 4; X = F, Cl, or Br) halide clusters in GICs, which become electrochemically active for Na redox reactions. Specifically, to enable sodium-ion intercalation into graphite, the interlayer spacing of graphite is required to increase over 3.9 Å, and Na X halide cluster GICs maintain an expanded interlayer spacing of >3.9 Å. This enlarged interlayer spacing of Na X halide cluster GICs facilitates stable intercalation of sodium ions. NaF, NaCl, and NaBr halide clusters are identified as suitable pillar candidates for anode materials because they not only expand the interlayer spacing but also provide reasonable binding energy for intercalated sodium ions for reversible deintercalation. Based on the model analysis, theoretical capacities of NaF, NaCl, and NaBr halide cluster GICs are estimated respectively to be 186, 155, and 155 mA h g. These predictions would provide a rational strategy guiding the search for promising anode materials for SIBs.
目前，石墨被用作锂离子电池的负极材料，但众所周知，石墨作为钠离子电池（SIB）的负极材料时，其电化学性能并不理想。也有报道称，石墨的低电化学性能源于钠离子的离子半径较大，因为钠离子嵌入石墨需要更高的应变能，从而导致形成不稳定的钠离子嵌入石墨层间化合物（GIC）。在这项工作中，我们使用第一性原理计算，引入了GIC中NaX（X = 3和4；X = F、Cl或Br）卤化物簇的支撑效应，这些卤化物簇对Na氧化还原反应具有电化学活性。具体而言，为了使钠离子能够嵌入石墨，需要将石墨的层间距增加到3.9 Å以上，而NaX卤化物簇GICs保持大于3.9 Å的扩大层间距。NaX卤化物簇GICs的这种扩大的层间距有利于钠离子的稳定嵌入。NaF、NaCl和NaBr卤化物簇被确定为负极材料的合适支撑候选物，因为它们不仅扩大了层间距，还为嵌入的钠离子提供了合理的结合能，以便进行可逆脱嵌。基于模型分析，NaF、NaCl和NaBr卤化物簇GICs的理论容量分别估计为186、155和155 mA h g。这些预测将为寻找有前景的SIB负极材料提供合理的策略指导。
