Tetravalent metal phosphates (M(HPO₄)₂, M = Zr, Sn, and Ti) have robust layered structures with interlayer d spacings over 7.5 Å, but show poor electrical conductivity. On the other hand, single-atomic-layered reduced graphene oxide (rGO) sheets exhibit a high electrical conductivity. In this work, the combination of rGO and M(HPO₄)₂ is explored for their potential as anode materials for lithium ion batteries (LIBs). Specifically, rGO/M(HPO₄)₂ composites are prepared, and their electrochemical performances are investigated systematically. In comparison with bare M(HPO₄)₂, the rGO/M(HPO₄)₂ composites exhibit larger specific capacity, higher rate capability, better cyclic stability, lower voltage for lithium ion insertion and extraction, and improved first Coulombic efficiency. We propose that the superior electrochemical performances of the composites are primarily contributed to the large interlayer space of M(HPO₄)₂ and the rGO sheets cladded on the surfaces of the layered M(HPO₄)₂. The attached rGO sheets bridge the layers together forming a network that is beneficial for the electron and ion diffusion within the composites, thus enhancing the discharge/charge rate capability of the composites. In addition, the attached rGO sheets provide extra anchoring sites for Li⁺; the specific capacity of the composites as anode materials is thus enhanced.

中文翻译：

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层状M（HPO ₄）₂（M = Zr，Sn和Ti）与氧化石墨烯还原的复合材料作为锂离子电池的负极材料

四价金属磷酸盐（M（HPO ₄）₂，M = Zr，Sn和Ti）具有坚固的层状结构，层间d间距超过7.5Å，但导电性较差。另一方面，单原子层还原的氧化石墨烯（rGO）片材表现出高电导率。在这项工作中，rGO和M（HPO ₄）_2的组合被用作锂离子电池（LIBs）的负极材料。具体而言，制备了rGO / M（HPO ₄）₂复合材料，并对其电化学性能进行了系统的研究。与裸M（HPO ₄）_2相比，rGO / M（HPO ₄）_2种复合材料具有更大的比容量，更高的倍率性能，更好的循环稳定性，更低的锂离子插入和提取电压以及更高的首次库仑效率。我们认为，复合材料的优异电化学性能主要是由于M（HPO ₄）_2的层间空间大以及rGO薄板包覆在层状M（HPO ₄）₂的表面上。附着的rGO板将这些层桥接在一起，形成一个网络，该网络有利于复合材料内的电子和离子扩散，从而增强了复合材料的放电/充电速率能力。此外，所附的rGO床单为Li ⁺提供了更多的锚固位置; 因此提高了复合材料作为阳极材料的比容量。