Department of Chemical & Materials Engineering, University of Alberta , 9107 116th Street, T6G 2 V4, Edmonton, Alberta, Canada.
ACS Nano. 2014 Jul 22;8(7):7115-29. doi: 10.1021/nn502045y. Epub 2014 Jun 6.
Banana peel pseudographite (BPPG) offers superb dual functionality for sodium ion battery (NIB) and lithium ion battery (LIB) anodes. The materials possess low surface areas (19-217 m(2) g(-1)) and a relatively high electrode packing density (0.75 g cm(-3) vs ∼1 g cm(-3) for graphite). Tested against Na, BPPG delivers a gravimetric (and volumetric) capacity of 355 mAh g(-1) (by active material ∼700 mAh cm(-3), by electrode volume ∼270 mAh cm(-3)) after 10 cycles at 50 mA g(-1). A nearly flat ∼200 mAh g(-1) plateau that is below 0.1 V and a minimal charge/discharge voltage hysteresis make BPPG a direct electrochemical analogue to graphite but with Na. A charge capacity of 221 mAh g(-1) at 500 mA g(-1) is degraded by 7% after 600 cycles, while a capacity of 336 mAh g(-1) at 100 mAg(-1) is degraded by 11% after 300 cycles, in both cases with ∼100% cycling Coulombic efficiency. For LIB applications BPPG offers a gravimetric (volumetric) capacity of 1090 mAh g(-1) (by material ∼2200 mAh cm(-3), by electrode ∼900 mAh cm(-3)) at 50 mA g(-1). The reason that BPPG works so well for both NIBs and LIBs is that it uniquely contains three essential features: (a) dilated intergraphene spacing for Na intercalation at low voltages; (b) highly accessible near-surface nanopores for Li metal filling at low voltages; and (c) substantial defect content in the graphene planes for Li adsorption at higher voltages. The <0.1 V charge storage mechanism is fundamentally different for Na versus for Li. A combination of XRD and XPS demonstrates highly reversible Na intercalation rather than metal underpotential deposition. By contrast, the same analysis proves the presence of metallic Li in the pores, with intercalation being much less pronounced.
香蕉皮石墨(graphite)为钠离子电池 (NIB) 和锂离子电池 (LIB) 提供了出色的双重功能。这种材料的比表面积较低 (19-217 m(2) g(-1))，电极堆积密度较高 (0.75 g cm(-3) 对比石墨的 1 g cm(-3))。经过 50 mA g(-1) 10 次循环后，以活性材料计，BPPG 的重量 (和体积) 比容量为 355 mAh g(-1) (355 mAh cm(-3)，以电极体积计为 270 mAh cm(-3))。在低于 0.1 V 的电位下，BPPG 表现出几乎平坦的 200 mAh g(-1) 平台和最小的充放电电压滞后，使其成为钠离子电池的直接电化学模拟物。以 500 mA g(-1) 电流进行测试，BPPG 的充电容量为 221 mAh g(-1)，600 次循环后容量衰减 7%，以 100 mAg(-1) 电流进行测试，300 次循环后容量衰减 11%，在这两种情况下，循环库仑效率均接近 100%。对于 LIB 应用，BPPG 的重量 (体积) 比容量为 1090 mAh g(-1) (以材料计 2200 mAh cm(-3)，以电极计 900 mAh cm(-3))，电流为 50 mA g(-1)。BPPG 之所以能同时适用于 NIB 和 LIB，是因为它具有三个独特的特点：(a) 低电压下插层需要的层间距离扩张；(b) 低电压下易于接近的表面纳米孔，有利于 Li 金属的填充；(c) 石墨烯层中大量的缺陷，有利于高电压下 Li 的吸附。0.1 V 以下的电荷存储机制对于 Na 和 Li 是完全不同的。XRD 和 XPS 的综合分析证明，Na 的嵌入是高度可逆的，而不是金属的欠电位沉积。相比之下，同样的分析证明了多孔中存在金属 Li，而嵌入则不那么明显。
