Physics Division, School of Science and Technology, University of Camerino , 62032 Camerino (MC), Italy.
Department of Solid State Physics, Gdańsk University of Technology , 80-309, Gdansk, Poland.
ACS Appl Mater Interfaces. 2017 Feb 8;9(5):4570-4576. doi: 10.1021/acsami.6b12408. Epub 2017 Jan 26.
Advanced metal oxide electrodes in Li-ion batteries usually show reversible capacities exceeding the theoretically expected ones. Despite many studies and tentative interpretations, the origin of this extra-capacity is not assessed yet. Lithium storage can be increased through different chemical processes developing in the electrodes during charging cycles. The solid electrolyte interface (SEI), formed already during the first lithium uptake, is usually considered to be a passivation layer preventing the oxidation of the electrodes while not participating in the lithium storage process. In this work, we combine high resolution soft X-ray absorption spectroscopy with tunable probing depth and photoemission spectroscopy to obtain profiles of the surface evolution of a well-known prototype conversion-alloying type mixed metal oxide (carbon coated ZnFeO) electrode. We show that a partially reversible layer of alkyl lithium carbonates is formed (∼5-7 nm) at the SEI surface when reaching higher Li storage levels. This layer acts as a Li reservoir and seems to give a significant contribution to the extra-capacity of the electrodes. This result further extends the role of the SEI layer in the functionality of Li-ion batteries.
锂离子电池中的先进金属氧化物电极通常表现出超过理论预期的可逆容量。尽管进行了许多研究和初步解释，但这种额外容量的起源尚未得到评估。通过在充电循环过程中在电极中发展的不同化学过程可以增加锂的存储。在第一次锂吸收过程中形成的固体电解质界面（SEI）通常被认为是一种钝化层，可防止电极氧化，同时不参与锂存储过程。在这项工作中，我们结合高分辨率软 X 射线吸收光谱和可调谐探测深度以及光电子能谱，获得了一种众所周知的原型转换-合金型混合金属氧化物（碳涂层 ZnFeO）电极的表面演化轮廓。我们表明，当达到更高的锂存储水平时，在 SEI 表面形成了一层部分可逆的烷基碳酸锂层（约 5-7nm）。该层充当锂储存库，似乎对电极的额外容量有重大贡献。这一结果进一步扩展了 SEI 层在锂离子电池功能中的作用。
