Researchers from the University of Western Ontario (UWO), University of Toronto and Glabat Solid-State Battery Inc. have clarified the phase evolution of a prenucleator (MoS₂) in all-solid-state lithium batteries (ASSLBs) for promoting fast Li nucleation and selective Li deposition. A paper on their work is published in the journal Advanced Energy Materials.

Schematic illustration of MoS₂ evolution and Li deposition process. Yang et al.

Solid polymer electrolytes (SPEs) have demonstrated their potential application in ASSLBs due to their promising properties such as high flexibility, easy fabrication, low cost/density, and high electrochemical/chemical stability. However, undesirable Li dendrite growth under high current densities because of the nonuniform Li nucleation and growth has significantly hindered the development of high‐rate ASSLBs.

Here, the phase evolution of a Li prenucleator (MoS₂) is shown in working ASSLBs that renders a highly active nucleator (Mo), where Mo promotes fast Li nucleation and Li dendrite suppression. During plating, Li shows strong affinity with Mo, which guides Li fast nucleating and selectively depositing on Mo surface with a large specific surface, thus reducing the local current density. Moreover, a fast diffusion of Li atom on Mo (110) surface promotes uniform Li deposition and limits the Li dendrite growth. Benefitting from the reduced local current density as well as the improved Li dendrite suppression, Li–Li symmetric cells within MoS₂ prenucleator demonstrate excellent electrochemical performance, achieving cycle lifetimes as high as 1000 h for 1 mA cm^-2/1 mAh cm^-2 and 780 h for 0.5 mA cm^-2/2 mAh cm^-2.

Its practical application is further proved by the Li-LiFePO₄ (LFP) full cell testing. The Li-LFP ASSLBs demonstrated high capacity retention of 78% after 3000 cycles at a high current density of 1 mA cm^-2.

—Yang et al.

To realize the practical application of ASSLBs, a reasonable operating current density is required. Nevertheless, the undesirable Li dendrite growth under high current densities remains challenging that hindered the improvement of operating current density. Typically, the current densities used in Li-Li symmetric cells and full cells are less than 0.5 mA cm^-2, which can’t meet the requirements of ASSLBs in practical application.

Prof. Xueliang (Andy) Sun’s team from UWO and Prof. Chandra Veer Singh from University of Toronto proposed a prenucleator (MoS₂) to suppress Li dendrite under high operating current densities via controlling the Li nucleation and deposition process. Additionally, the phase evolution of the prenucleator in working ASSLBs was clarified.

The results show that the reduction product (Mo) is the true nucleator, which plays an important role in facilitating Li fast nucleator and selective deposition, thus suppressing Li dendrite growth.

The Li anode with MoS₂ prenucleator show reduced overpotential and improved Li stability, enabling the assembled ASSLBs with excellent cycling stability under high current density.

Resources

• Xiaofei Yang, Chandra Veer Singh, Xueliang Sun, et al. (2020) “Phase Evolution of a Prenucleator for Fast Li Nucleation in All-Solid-State Lithium Batteries” Advanced Energy Materials doi: 10.1002/aenm.202001191