Vanderbilt Institute of Nanoscale Science and Engineering , Nashville, Tennessee 37235, United States.
ACS Nano. 2015 Nov 24;9(11):11156-65. doi: 10.1021/acsnano.5b04700. Epub 2015 Nov 11.
Nanocrystals with quantum-confined length scales are often considered impractical for metal-ion battery electrodes due to the dominance of solid-electrolyte interphase (SEI) layer effects on the measured storage properties. Here we demonstrate that ultrafine sizes (∼4.5 nm, average) of iron pyrite, or FeS2, nanoparticles are advantageous to sustain reversible conversion reactions in sodium ion and lithium ion batteries. This is attributed to a nanoparticle size comparable to or smaller than the diffusion length of Fe during cation exchange, yielding thermodynamically reversible nanodomains of converted Fe metal and NaxS or LixS conversion products. This is compared to bulk-like electrode materials, where kinetic and thermodynamic limitations of surface-nucleated conversion products inhibit successive conversion cycles. Reversible capacities over 500 and 600 mAh/g for sodium and lithium storage are observed for ultrafine nanoparticles, with improved cycling and rate capability. Unlike alloying or intercalation processes, where SEI effects limit the performance of ultrafine nanoparticles, our work highlights the benefit of quantum dot length-scale nanocrystal electrodes for nanoscale metal sulfide compounds that store energy through chemical conversion reactions.
由于固态电解质界面 (SEI) 层效应对测量存储性能的主导作用，具有量子限制长度尺度的纳米晶体通常被认为不适用于金属离子电池电极。在这里，我们证明了超小尺寸（约 4.5nm，平均）的黄铁矿或 FeS2 纳米颗粒有利于在钠离子和锂离子电池中维持可逆的转化反应。这归因于纳米颗粒的尺寸与阳离子交换过程中 Fe 的扩散长度相当或更小，从而产生了热力学可逆的转化为 Fe 金属和 NaxS 或 LixS 转化产物的纳米域。与块状电极材料相比，表面成核转化产物的动力学和热力学限制抑制了连续的转化循环，在超细纳米颗粒中观察到超过 500 和 600mAh/g 的钠和锂存储可逆容量，并且具有改进的循环和倍率性能。与合金化或插层过程不同，SEI 效应限制了超细纳米颗粒的性能，我们的工作强调了量子点长度尺度纳米晶体电极在通过化学转化反应存储能量的纳米尺度金属硫化物化合物中的益处。
