Extending Lifespan of Lithium Metal Electrodes Via Surface Structure Regulation Strategies
Authors: Peng Zhe , Zhang Zhenggang , Wang Muqin , Ren Feihong , Wang Deyu 
Published: February 2020

Li metal is an ideal anode material for high-energy secondary batteries owing to its ultrahigh capacity (3860 mAh g-
1) and the lowest reduction potential (-3.04 V vs. S.H.E.). To achieve practical application of Li metal electrodes, two fundamental challenges need to be resolved: (1) accommodating the large change in electrode volume during cycling that creates significant mechanical instability and cracks in electrodes and their interfaces; (2) preventing the side reactions of Li metal towards the electrolyte that produce a solid electrolyte interphase (SEI) layer, which cannot withstand mechanical deformation and continuously break and repair during cycling, resulting in low Coulombic efficiency and short cycling life.

To address the harmful problematic of instable interfaces of Li metal anodes, we have developed a series of protective structures to provide efficacious volume confinement of Li metal surfaces, with aim of stabilizing the SEI layers for high Coulombic efficiency and long lifespan of the Li metal anodes (Figure 1). In the first protective model, we have fabricated a porous Al2O3 layer as an inorganic “host” to accommodate the deposited Li, and in parallel, a reinforced SEI was in-situ formed across this porous layer by using an electrolyte additive (Figure 1a). Based on its synergetic effect, such a composite structure has enabled a Coulombic efficiency of Li plating/stripping as high as 97.5-98% in carbonate-based electrolyte [1]. In the second protective model, we have synthesized a 3D porous Cu current collector with in-situ formed Li2O as reinforcing agent (Figure 1b). On one hand, the 3D Cu structure could efficiently reduce the local current density with aim of hindering the growth of Li dendrite; on the other hand, the Li2O reinforcing agent could stabilize the structure by extending the cycling life of Li anodes for more than 150 cycles [2]. In the third protective model, we have realized the formation of 3D SEI layer across a carbonaceous porous structure (Figure 1c). Thanks to the rigid carbonaceous structure with related 3D SEI layer coating, the Li plating/stripping efficiency was higher than 98% for more than 300 cycles [3].

Recently, our group has developed a plasma modified Porous 3D Carbon paper was fabricated and explored to store Li metal and stabilize Li plating/stripping processes. Using a mesoplasma technic, a high-quality sponge carbon layer was deposited on the top of the 3D carbon paper. Based on this Sponge Carbon layer coated 3D Carbon Paper (SCCP) as a host, Li ions are intercalated in the graphitic carbon paper skeletons then followed by Li metal plating, leading to the entire Li metal deposition underneath the sponge carbon layer, meanwhile the sponge Carbon layer acts as a physical barrier to mechanically block dendrite growth towards the electrolyte. In corrosive carbonate electrolyte, the Coulombic efficiency of Li metal plating/stripping processes could achieve 98-99% at high capacity of 3-4 mAh cm-2. Dendrite-free surface was also observed on the protected Li foil in a Li-LiFePO4 coin cell after 1000 cycles (6 months cycling). These results demonstrate the ability of the SCCP structure to protect Li metal in high-energy density batteries for long-term operation.

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Figure 1