An international team of researchers has developed a new strategy for dendrite-free lithium-metal batteries based on the use of interlayer and intralayer atomic channels in graphite formed by pre-tunnelling the graphite layers. The obtained atomic channels enable the free and fast diffusion of lithium with enhanced kinetics. atomic channels.

An open-access paper on the work is published in the RSC journal Energy & Environmental Science.

Despite the enticing properties of lithium used as an anode material in energy storage systems—such as the extremely high theoretical capacity of 3860 mA h g^-1—practical application is still hindered by the safety issues resulting from lithium dendrite growth.

The inhomogeneous and uncontrollable aggregation of Li at electrode/electrolyte interface would always lead to notorious dendrite growth and limit their further application due to the unsatisfying electrochemical performance and severe safety issues. Since the surface diffusion of Li in anode is much faster than bulk diffusion, tuning diffusion/deposition of Li on anode surface has been regarded as a mainstream method to induce its uniform deposition.

Previous works focus on constructing three-dimensional open-structure carbon skeletons and/or introducing guidable seeds, such as Au, Ag metal nanoparticles and Co, Ni single atoms. Prior to its surface deposition, Li⁺ would have to overcome a large energy barrier to intercalate into graphite layers, leading to a layer expansion of ~0.2 Å,14,15 and it would be restrained in a typical C₆LiC₆ state in bulk, sacrificing its diffusibility. Consequently, graphite bulk has rarely been considered for carrying dense and rapid Li flux, and the potential for diffusion of multilayer Li through graphite layers has not been fully utilized. By using density functional theory (DFT) calculations and in-situ transmission electron microscopy (TEM), pioneering work reported by Kuhne et al. has demonstrated the feasibility of multilayer compact Li existing between two graphene layers, which far exceeds the typical C₆LiC₆ structure. However, the intercalation and diffusion property of the reported bi-layer graphite sheets is inequivalent to the bulk carbon they exfoliated from. Additionally, their non-scalable material preparation makes them far from practical application in high-performance LMBs. Inspired by this work, a new Li diffusion pathway through bulk carbon can be constructed by pre-tunnelling graphite layers. The obtained atomic channels can allow the free and fast diffusion of superdense Li with much enhanced kinetics and safety.

In this contribution, by adopting a molecular tunnelling strategy, we construct a bulk diffusion Li conductor (BDLC) with abundant atomic channels for superdense Li transportation. Via pre-tunnelling graphite layers (layer spacing large as ~7 Å), introducing voids and lithium-philic sites simultaneously, the interlayer and intralayer channels for Li diffusion are thus built. Different from the conventional surface diffusion/deposition mechanism, the atomic channel can effectively alleviate the dendrite issues caused by nonuniform surface deposition, and achieve rapid bulk diffusion.

—Zhou et al.

Comparative illustration of graphite layers and atomic channels. Schematic illustration of (a) typical Li⁺ intercalation in graphite layers and (b) superdense Li diffusion in atomic channels. Zhou et al.

Pairing the new anode material with high-loading LiFePO₄ (LFP) cathodes achieves a high areal capacity of 3.9 mA h cm^-2, and 100% capacity retention over 370 cycles.

The bulk diffusion strategy would provide a new perspective that is different from conventional surface diffusion, and would expand the knowledge about superdense Li diffusion and redefine research of Li dendrite inhibition as well.

—Zhou et al.

Resources

• Shiyuan Zhou, Weixin Chen, Jie Shi, Gen Li, Fei Pei, Sangui Liu, Weibin Ye, Liang-Ping Xiao, Mingsheng Wang, Dan Wang, Yu Qiao, Ling Huang, Gui-Liang Xu, Hong-Gang Liao, Jian-Feng Chen, Khalil Amine and Shi-Gang Sun (2021) “Efficient Diffusion of Superdense Lithium via Atomic Channel for Dendrite-Free Lithium-Metal Batteries” Energy Environ. Sci. doi: 10.1039/D1EE02205A