Department of NanoEngineering, University of California, San Diego , 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093, United States.
ACS Appl Mater Interfaces. 2016 Mar;8(12):7843-53. doi: 10.1021/acsami.6b00833. Epub 2016 Mar 17.
The Li7P3S11 glass-ceramic is a promising superionic conductor electrolyte (SCE) with an extremely high Li(+) conductivity that exceeds that of even traditional organic electrolytes. In this work, we present a combined computational and experimental investigation of the material performance limitations in terms of its phase and electrochemical stability, and Li(+) conductivity. We find that Li7P3S11 is metastable at 0 K but becomes stable at above 630 K (∼360 °C) when vibrational entropy contributions are accounted for, in agreement with differential scanning calorimetry measurements. Both scanning electron microscopy and the calculated Wulff shape show that Li7P3S11 tends to form relatively isotropic crystals. In terms of electrochemical stability, first-principles calculations predict that, unlike the LiCoO2 cathode, the olivine LiFePO4 and spinel LiMn2O4 cathodes are likely to form stable passivation interfaces with the Li7P3S11 SCE. This finding underscores the importance of considering multicomponent integration in developing an all-solid-state architecture. To probe the fundamental limit of its bulk Li(+) conductivity, a comparison of conventional cold-press sintered versus spark-plasma sintering (SPS) Li7P3S11 was done in conjunction with ab initio molecular dynamics (AIMD) simulations. Though the measured diffusion activation barriers are in excellent agreement, the AIMD-predicted room-temperature Li(+) conductivity of 57 mS cm(-1) is much higher than the experimental values. The optimized SPS sample exhibits a room-temperature Li(+) conductivity of 11.6 mS cm(-1), significantly higher than that of the cold-pressed sample (1.3 mS cm(-1)) due to the reduction of grain boundary resistance by densification. We conclude that grain boundary conductivity is limiting the overall Li(+) conductivity in Li7P3S11, and further optimization of overall conductivities should be possible. Finally, we show that Li(+) motions in this material are highly collective, and the flexing of the P2S7 ditetrahedra facilitates fast Li(+) diffusion.
Li7P3S11 玻璃陶瓷是一种很有前途的超离子导体电解质 (SCE)，具有极高的锂离子电导率，甚至超过了传统的有机电解质。在这项工作中，我们结合计算和实验研究了该材料在相和电化学稳定性以及锂离子电导率方面的性能限制。我们发现，考虑到振动熵的贡献，Li7P3S11 在 0 K 时是亚稳的，但在高于 630 K（约 360°C）时是稳定的，这与差示扫描量热法测量结果一致。扫描电子显微镜和计算出的魏尔夫形状都表明 Li7P3S11 倾向于形成相对各向同性的晶体。在电化学稳定性方面，第一性原理计算预测，与 LiCoO2 正极不同，橄榄石 LiFePO4 和尖晶石 LiMn2O4 正极与 Li7P3S11 SCE 可能形成稳定的钝化界面。这一发现强调了在开发全固态架构时考虑多组分集成的重要性。为了探究其体锂离子电导率的基本限制，我们对传统冷压烧结与火花等离子体烧结（SPS）的 Li7P3S11 进行了比较，并结合了第一性原理分子动力学（AIMD）模拟。虽然测量的扩散激活势垒非常吻合，但 AIMD 预测的室温锂离子电导率为 57 mS cm-1，远高于实验值。经过优化的 SPS 样品的室温锂离子电导率为 11.6 mS cm-1，明显高于冷压样品（1.3 mS cm-1），这是由于致密化降低了晶界电阻。我们得出结论，晶界电导率限制了 Li7P3S11 中的整体锂离子电导率，进一步优化整体电导率是可能的。最后，我们表明该材料中的 Li+ 运动高度集体化，P2S7 四面体的弯曲有利于 Li+ 的快速扩散。
