Center for Advanced Photovoltaics, Department of Electrical Engineering and Computer Science, South Dakota State University, Brookings, SD 57007, USA.
Nanoscale. 2018 Aug 30;10(34):15956-15966. doi: 10.1039/c8nr01507d.
It has been a challenge to use transition metal oxides as anode materials in Li-ion batteries due to their low electronic conductivity, poor rate capability and large volume change during charge/discharge processes. Here, we present the first demonstration of a unique self-recovery of capacity in transition metal oxide anodes. This was achieved by reducing tungsten trioxide (WO3) via the incorporation of urea, followed by annealing in a nitrogen environment. The reduced WO3 successfully self-retained the Li-ion cell capacity after undergoing a sharp decrease upon cycling. Significantly, the reduced WO3 also exhibited excellent rate capability. The reduced WO3 exhibited an interesting cycling phenomenon where the capacity was significantly self-recovered after an initial sharp decrease. The quick self-recoveries of 193.21%, 179.19% and 166.38% for the reduced WO3 were observed at the 15th (521.59/457.41 mA h g-1), 36th (538.49/536.61 mA h g-1) and 45th (555.39/555.39 mA h g-1) cycles respectively compared to their respective preceding discharge capacity. This unique self-recovery phenomenon can be attributed to the lithium plating and conversion reaction which might be due to the activation of oxygen vacancies that act as defects which make the WO3 electrode more electrochemically reactive with cycling. The reduced WO3 exhibited a superior electrochemical performance with 959.1/638.9 mA h g-1 (1st cycle) and 558.68/550.23 mA h g-1 (100th cycle) vs. pristine WO3 with 670.16/403.79 mA h g-1 (1st cycle) and 236.53/234.39 mA h g-1 (100th cycle) at a current density of 100 mA g-1.
在锂离子电池中，过渡金属氧化物由于其电子电导率低、倍率性能差以及在充放电过程中体积变化大，因此作为阳极材料一直是一个挑战。在这里，我们首次展示了过渡金属氧化物阳极中独特的容量自恢复能力。这是通过在氮气环境中退火，将尿素掺入三氧化钨 (WO3) 来实现的。还原后的 WO3 在循环过程中急剧下降后成功地自行保留了锂离子电池的容量。重要的是，还原后的 WO3 还表现出优异的倍率性能。还原后的 WO3 表现出有趣的循环现象，在初始急剧下降后，容量得到了显著的自我恢复。在第 15 次（521.59/457.41 mA h g-1）、第 36 次（538.49/536.61 mA h g-1）和第 45 次（555.39/555.39 mA h g-1）循环时，还原 WO3 的快速自恢复分别为 193.21%、179.19%和 166.38%，与各自之前的放电容量相比。这种独特的自恢复现象可以归因于锂电镀和转化反应，这可能是由于氧空位的激活，氧空位作为缺陷使 WO3 电极在循环过程中具有更高的电化学活性。还原后的 WO3 表现出优异的电化学性能，在 100 mA g-1 的电流密度下，其首次循环时的容量为 959.1/638.9 mA h g-1，第 100 次循环时的容量为 558.68/550.23 mA h g-1，而原始 WO3 的首次循环时的容量为 670.16/403.79 mA h g-1，第 100 次循环时的容量为 236.53/234.39 mA h g-1。
