Abstract:

Inhibiting the growth of lithium dendrites is one of the key problems to be solved in lithium metal batteries (LMBs). Coating graphene on the electrode surface can effectively prevent lithium dendrites growth. However, the effect of graphene layer spacings on lithium dendrites growth is not clear. In this paper, the first principal calculation was employed to explore it from adsorption and diffusion of lithium atoms on the graphene. The calculation results show that the layer spacings section of 0.45—0.55 nm can obviously inhibit the lithium dendrites growth, which exhibits the lower binding energy and diffusion energy barrier of lithium atoms. When the layer spacings are smaller than 0.45 nm, the diffusion of lithium atoms is difficult. For the larger layer spacings (> 0.55 nm), lithium atoms prefer to adsorb and aggregate between the graphene layers, leading to the lithium dendrites growth. Besides, the doping effect of graphene with layer spacing of 0.45 nm on the lithium dendrites growth was investigated. Under the optimal interlayer spacing, the B-doped and N-doped graphene can promote the diffusion of lithium atoms between the graphene layers and avoid the uneven deposition of lithium, thereby suppressing the formation of lithium dendrites.

Key words: graphene, layer spacings, lithium dendrites, adsorption, first principle

摘要：

抑制锂枝晶生长是锂金属电池中亟需解决的关键问题之一。电极表面涂覆石墨烯可以有效抑制锂枝晶生长。然而，目前对石墨烯层间距影响锂枝晶生长的机制尚不明晰。采用第一性原理计算方法从吸附和扩散两个角度考察了石墨烯层间距对锂枝晶生长的影响。结果表明，石墨烯的层间距为0.45 ~ 0.55 nm时，电极表面对锂原子的吸附较弱，锂原子扩散性能最好，有利于抑制锂枝晶的生长。若小于该层间距，锂原子在层间的扩散较难。反之，锂原子则会在石墨烯层上吸附聚集，导致锂枝晶的快速生长。此外，在最佳层间距下，B掺杂和N掺杂改性的石墨烯，能促进锂原子在石墨烯层间的扩散，避免锂的不均匀沉积，从而抑制锂枝晶的形成。

关键词: 石墨烯, 层间距, 锂枝晶, 吸附, 第一性原理