Unveil the Chemistry of Olivine FePO4 as Magnesium Battery Cathode

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• 作者：Ruigang Zhang ; Chen Ling
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2016
• 出版时间：July 20, 2016
• 年：2016
• 卷：8
• 期：28
• 页码：18018-18026
• 全文大小：498K
• 年卷期：0
• ISSN：1944-8252

文摘

Despite growing interest in magnesium batteries, it is still a challenge to find a cathode that fulfills requirements such as high capacity and good cyclability. Because of their positions in the periodic table and the similar ionic sizes of lithium and magnesium, it was naturally postulated that a classical intercalation-type Li-ion battery cathode may also accommodate the intercalation of Mg. On the contrary, many Li-ion battery cathodes performed very poorly in Mg cells, although the mechanism behind such phenomena is still unclear. Here we provide first-hand evidence about the chemistry of olivine FePO₄ as Mg battery cathode using a combined theoretical and experimental approach. Although LiFePO₄ is a commercial cathode with extraordinary good performance in Li-ion batteries, the measured capacity of FePO₄ in nonaqueous Mg cell was only ∼13 mAh/g. Density functional theory calculations predicted sufficient mobility of Mg²⁺ in FePO₄ lattice to support the insertion of Mg at a reasonable rate, suggesting the poor performance cannot be simply attributed to the limitation of Mg²⁺ diffusion. Instead, the recorded low capacity was the result of surface amorphorization that prohibited the electrochemical reaction from penetrating deeply into the bulk phase. The amorphorization had a thermodynamic origin from the instability of intercalated product, which was predicted from DFT calculations and supported by the failure to synthesize magnesiated FePO₄ in the solid state reaction route. These results highlighted the importance of a thermodynamically preferred intercalation in order to achieve successful Mg battery cathode.