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Li 3xLa (2/3)–x† (1/3)–2xTiO 3(LLTO)是一类颇具前景的锂离子电池固态电解质. 本文采用第一性原理结合分子动力学方法对贫锂相和富锂相两种类型的LLTO表面进行研究, 分析表面Li含量对其稳定性、电子结构及Li离子输运性质的影响. 结果表明, 具有La/O/Li-原子终端的(001)面为最稳定晶面. 对于LLTO (001)面, 当贫锂相/富锂相终端Li含量为0.17/0.33, 0.29/0.40, 0.38/0.45时, 其表面结构更为稳定. 电子结构分析表明, 随着Li含量的增大, 不论是贫锂相还是富锂相, 其(001)表面均发现金属至半导体的转变. Li离子输运性质的研究结果表明, 贫锂相和富锂相LLTO (001)表面均具有沿 ab平面的二维扩散通道, 且当终端Li含量分别达到0.38和0.40时具有最大的Li离子扩散系数及最低的Li离子扩散能垒, 最低扩散能垒分别为0.42 eV和0.30 eV. 因而, 改变终端Li含量有利于提高LLTO(001)表面稳定性、打开表面带隙、改善Li离子迁移性能, 这有助于抑制LLTO表面锂枝晶的生长.Li 3xLa (2/3)–x† (1/3)–2xTiO 3(LLTO) is a promising solid-state electrolyte for Li-ion batteries. We study the effect of Li content on the stability, electronic and Li-ion diffusion properties of LLTO surface based on first-principles and molecular dynamics simulations. We consider both Li-poor and Li-rich LLTO surfaces. The results show that La/O/Li-terminated LLTO (001) is the most stable crystal surface. Further, LLTO (001) surface gives better stability when Li content is 0.17, 0.29, and 0.38 for Li-poor phase, while 0.33, 0.40, and 0.45 for Li-rich phase . Electronic structure calculations infer that in both Li-poor and Li-rich LLTO(001) surfaces there occurs the transition from conductor to semiconductor with the increase of Li content. Besides, we find that Li-ion always keeps a two-dimensional diffusion path for different Li content. As Li content increases from 0.17 to 0.38 for Li-poor LLTO (001) surface, Li-ion diffusion coefficient increases gradually and Li-ion diffusion barrier decreases from 0.58 eV to 0.42 eV. Differently, when Li content increases from 0.33 to 0.45 for Li-rich LLTO(001) surface, it does not follow a monotonic trend for diffusion coefficient nor for diffusion barrier of Li-ion. In this case, Li-ion diffusion coefficient is the largest and Li-ion diffusion barrier is the lowest (0.30 eV) when Li content is 0.40. Thus, our study suggests that by varying Li content, the stability, band gap, and Li-ion diffusion performance of LLTO (001) can be changed favorably. These advantages can inhibit the formation of lithium dendrites on the LLTO (001) surface.
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Functional a b c Eg GGA+PBE 7.842 7.771 7.843 1.630 GGA+PW91 7.835 7.768 7.838 1.585 LDA 7.705 7.638 7.697 1.624 PBE+U(UTi= 2.3 eV) 7.892 7.822 7.871 1.861 PBE+U(UTi= 2.5 eV) 7.897 7.827 7.834 1.851 PBE+U(UTi= 4.0 eV) 7.935 7.852 7.899 1.853 B3LYP[23] 7.828 7.812 7.902 — PBE+U(ULa= 7.5 eV)[24] 7.828 7.754 7.871 — 
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Facets Termination SFs Esurf/(J·m–2) (001) La/O- Li3La11Ti10O35(Li2La14Ti16O52) 2.89 (1.95) Ti/O- Li3La6Ti15O40(LiLa9Ti16O44) 1.40 (1.33) La/O/Li- Li10La12Ti20O65(Li3La11Ti16O52) 0.69 (0.78) Li/O- Li11La11Ti20O65 0.78 (010) La/O- Li7La13Ti20O64 0.93 Ti/O- Li7La11Ti24O68 0.87 La/O/Li- Li9La13Ti20O64 0.82 (100) La/O- Li7La13Ti20O64 1.05 Ti/O- Li7La11Ti24O68 0.90 La/O/Li- Li9La13Ti20O64 0.83 (110) O- Li7La11Ti20O68 0.98 Ti/La/O- Li7La13Ti24O64 3.40 Ti/O/La/Li- Li9La14Ti24O72 1.21 (111) La/O- Li9La13Ti24O72 2.21 Ti/O- Li7La11Ti20O60 0.85 Ti/O/La/Li- Li7La11Ti20O60 0.93 下载:
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T/K Li-poor phase/(cm2·S–1) Li-rich phase/(cm2·S–1) Dmin Dmax Dmin Dmax 550 1.06×10–7 2.37×10–7 7.02×10–7 1.14×10–6 600 2.02×10–7 8.12×10–7 9.96×10–7 2.53×10–6 650 3.84×10–7 1.46×10–6 2.26×10–6 3.38×10–6 700 1.77×10–6 2.01×10–6 3.34×10–6 4.80×10–6 750 2.22×10–6 3.27×10–6 4.69×10–6 7.08×10–6 800 4.03×10–6 4.28×10–6 6.33×10–6 9.36×10–6 下载:
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