Li Chunmei, He Linxin, Luo Jianglei, Tang Jianfeng, Cheng Nanpu, Chen Zhiqian
School of Materials and Energy, Southwest University, Chongqing 400715, China.
Nanoscale. 2020 May 28;12(20):11095-11111. doi: 10.1039/d0nr02359k.
The lithium-sulfur battery system has appeared as a new-generation alternative to lithium-ion batteries with 5-7 times higher specific energy density than conventional lithium-ion batteries. But its commercial implementation is still impeded by a series of technical challenges. Modifying separation with the anchoring material is viewed as an effective way to overcome these problems and achieve long-term cycling stability and high-rate performance. In this paper, eight phosphorus allotropes, α-P, β-P, γ-P, δ-P, ε-P, ζ-P, θ-P and η-P, are investigated as anchoring materials for separation in lithium-sulfur batteries based on binding energy and diffusion barrier discussion. The results show that the crystal structures of phosphorus polymorphs are crucial to the suitability of their application as anchoring materials for lithium-sulfur batteries. The binding energy results show that except ε-P, all the other phosphorus allotropes can strike a balance between binding strength and intactness of the Li2Sn species. Among these, ε-P composed of P4 squares is a strong anchoring material and may lead to the decomposition of the Li2S cluster. Furthermore, for Li atoms and lithium sulfides, the most convenient diffusion paths are all along the grooves in the phosphorus monolayers, including the life-boat shaped (α-P, γ-P, δ-P and ε-P), wave shaped (β-P, ζ-P) and back-to-back shaped (θ-P, η-P) grooves. Except ε-P, all the other phosphorus allotropes can be applied to modify the separation for lithium-sulfur batteries. But among these, α-P, β-P, γ-P and δ-P composed of P6 hexagons can act as more suitable substrates for Li atom and lithium sulfide diffusion with lower barriers. As a result, α-P, β-P, γ-P and δ-P composed of P6 hexagons are good choices as separation modification materials in lithium-sulfur batteries among phosphorus allotropes. In addition, the structure correlations among α-P, β-P, γ-P and δ-P, and the likely conversion pathways from α-P to β-P, from β-P to γ-P, and from γ-P to δ-P are discussed.
锂硫电池系统已成为锂离子电池的新一代替代品，其比能量密度比传统锂离子电池高5至7倍。但其商业应用仍受到一系列技术挑战的阻碍。用锚定材料修饰隔膜被视为克服这些问题并实现长期循环稳定性和高倍率性能的有效方法。本文基于结合能和扩散势垒的讨论，研究了八种磷的同素异形体α-P、β-P、γ-P、δ-P、ε-P、ζ-P、θ-P和η-P作为锂硫电池隔膜的锚定材料。结果表明，磷多晶型物的晶体结构对于其作为锂硫电池锚定材料的适用性至关重要。结合能结果表明，除ε-P外，所有其他磷同素异形体都能在Li2Sn物种的结合强度和完整性之间取得平衡。其中，由P4正方形组成的ε-P是一种强锚定材料，可能导致Li2S簇的分解。此外，对于锂原子和硫化锂，最便捷的扩散路径都沿着磷单层中的凹槽，包括救生艇形状（α-P、γ-P、δ-P和ε-P）、波浪形状（β-P、ζ-P）和背对背形状（θ-P、η-P）的凹槽。除ε-P外，所有其他磷同素异形体都可用于修饰锂硫电池的隔膜。但其中，由P6六边形组成的α-P、β-P、γ-P和δ-P可以作为锂原子和硫化锂扩散的更合适基底，具有较低的势垒。因此，由P6六边形组成的α-P、β-P、γ-P和δ-P是磷同素异形体中作为锂硫电池隔膜修饰材料的良好选择。此外，还讨论了α-P、β-P、γ-P和δ-P之间的结构相关性，以及从α-P到β-P、从β-P到γ-P和从γ-P到δ-P可能的转变途径。
