Insight into the intrinsic mechanism of improving electrochemical performance via constructing the preferred crystal orientation in lithium cobalt dioxide
Insight into the intrinsic mechanism of improving electrochemical performance via constructing the preferred crystal orientation in lithium cobalt dioxide
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DOI：
10.1016/j.cej.2020.125708
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发表时间：
2020-11
影响因子：
15.1
通讯作者：
Yue Chen;Y. Niu;Chun Lin;Jiaxin Li;Yingbin Lin;Guigui Xu;R. Palmer;Zhigao Huang
中科院分区：
文献类型：
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作者：
Yue Chen;Y. Niu;Chun Lin;Jiaxin Li;Yingbin Lin;Guigui Xu;R. Palmer;Zhigao Huang
正极材料的表面性能对于锂离子/电子的传输和表面钝化层的形成起着重要作用。优化正极材料的暴露晶面可以促进锂离子的扩散并增强正极表面稳定性，这可能最终决定锂离子电池正极的性能和稳定性。这里，制备具有(0003)和{10 1-1}择优取向的多晶LiCoO 2 (LCO)薄膜作为明确的模型电极。采用原位电流感应原子力显微镜（CSAFM）研究纳米尺度有机电解质中（0003）和{10 1-1}事实的锂脱嵌和电子电导率演化。研究发现，LCO晶粒中的锂脱嵌遵循“富锂核模型”，并且具有(0003)晶面的LCO晶粒表现出比具有{10 1-1}晶面的LCO晶粒更低的电导率。此外，带电电极表面的X射线光电子能谱表征表明，{10 1-1}上形成了比(0003)晶面上更致密的表面钝化层。密度泛函理论（DFT）和开尔文探针力显微镜（KPFM）结果证实，这是由于{10 1-1}晶面分解分子的吸附能较低和{10 1-1}晶面较高的功函数（由于表面原子结构）造成的。此外，电化学测量证实，与(0003)择优取向相比，具有{10 1-1}择优取向的薄膜电极不仅表现出更小的电极极化，而且更容易形成稳定的表面钝化层。这项工作强调了阴极电导率的重要性，并表明LCO {10 1-1}面原子结构可能在热力学上促进电解质的物理/化学吸附和分解。
Surface properties of cathode materials play important roles in the transport of lithium-ions/electrons and the formation of surface passivation layer. Optimizing the exposed crystal facets of cathode materials can promote the diffusion of lithium-ions and enhance cathode surface stability, which may ultimately dominate cathode’s performance and stability in lithium-ion batteries. Here, polycrystalline LiCoO 2 (LCO) thin films with (0003) and {10 1-1} preferred orientations were prepared as the well-defined model electrodes. In situ Current-Sensing Atomic Force Microscopy (CSAFM) was employed to investigate the lithium de-intercalation and electronic conductivity evolution of the (0003) and {10 1-1} facts in organic electrolyte at the nanoscale. It was found that the lithium deintercalation following a “Li-rich core model” in the LCO grains, and the LCO grains with (0003) crystal face show less conductivity than those with {10 1-1} faces. Moreover, X-ray Photoelectron Spectroscopy characterization of the charged electrode surface indicates that a denser surface passivation layer is formed on {10 1-1} than that on (0003) crystal faces. This is caused by the lower adsorption energy of decomposition molecule on {10 1-1} crystal faces and higher work function (due to the surface atomic structure) for {10 1-1} crystal faces, as confirmed by Density Functional Theory (DFT) and Kelvin probe force microscopy (KPFM) results. In addition, electrochemical measurements confirm that the thin film electrodes with {10 1-1} preferred orientation not only show smaller electrode polarization, but also more readily form a stable surface passivation layer compared with the (0003) preferred orientation. This work highlights the importance of cathode conductivity, and suggests that the LCO {10 1-1} facet atomic structure may thermodynamically promote the physical/chemical adsorption and decomposition of electrolyte.