Because of its ultrahigh specific capacity, lithium metal holds great promise for revolutionizing current rechargeable battery technologies. Nevertheless, the unavoidable formation of dendritic Li, as well as the resulting safety hazards and poor cycling stability, have significantly hindered its practical applications. A mainstream strategy to solve this problem is introducing porous media, such as solid electrolytes, modified separators, or artificial protection layers, to block Li dendrite penetration. However, the scientific foundation of this strategy has not yet been elucidated. Herein, using experiments and simulation we analyze the role of the porous media in suppressing dendritic Li growth and probe the underlying fundamental mechanisms. It is found that the tortuous pores of the porous media, which drastically reduce the local flux of Li moving toward the anode and effectively extend the physical path of dendrite growth, are the key to achieving the nondendritic Li growth. On the basis of the theoretical exploration, we synthesize a novel porous silicon nitride submicron-wire membrane and incorporate it in both half-cell and full-cell configurations. The operation time of the battery cells is significantly extended without a short circuit. The findings lay the foundation to use a porous medium for achieving nondendritic Li growth in Li metal-based batteries.

Limited understanding of the lithium (Li) nucleation and growth mechanism has hampered the implementation of Li-metal batteries. Herein, we unravel the evolution of the morphology and inner structure of Li deposits using focused ion beam scanning electron microscopy (FIB/SEM). Ball-shaped Li deposits are found to be widespread and stack up at a low current density. When the current density exceeds the diffusion-limiting current, bush-shaped deposition appears that consists of Li-balls, Li-whiskers, and bulky Li. Cryogenic transmission electron microscopy (cryo-TEM) further reveals that Li-balls are primarily amorphous, whereas the Li-whiskers are highly crystalline. Additionally, the solid electrolyte interface (SEI) layers of the Li-balls and whiskers show a difference in structure and composition, which is correlated to the underlying deposition mechanism. The revealed Li nucleation and growth mechanism and the correlation with the nanostructure and chemistry of the SEI provide insights toward the practical use of rechargeable Li-metal batteries.

Dendrite formation on the electrode surface of high energy density lithium (Li) batteries causes safety problems and limits their applications. Suppressing dendrite growth could significantly improve Li battery performance. Dendrite growth and morphology is a function of the cation concentration gradient in the electrolyte near the anode interface. Most research into dendrites in batteries focuses on dendrite formation in isotropic electrolytes (i.e., electrolytes with an isotropic diffusion coefficient). In this work, an anisotropic diffusion reaction model is developed to study the anisotropic mass transport effect on dendrite growth in Li batteries. The model uses a Lagrangian particle-based method to model dendrite growth in an anisotropic electrolyte solution. The model is verified by comparing the numerical simulation results with analytical solutions, and its accuracy is shown to be better than previous particle-based anisotropic diffusion models. Several parametric studies of dendrite growth in an anisotropic electrolyte are performed and the results demonstrate the effects of anisotropic transport on dendrite growth and morphology, and show the possible advantages of anisotropic electrolytes for dendrite suppression.

SUMMARYDendrite formation on the anode surface of high energy density lithium batteries is closely related to the safety and capacity of batteries; therefore, the suppression of dendrite growth could significantly improve battery performance and lifetime. Many reports demonstrate the close relation between local mass transport and dendrite growth, and most of the research focuses on improving the transport properties of isotropic electrolytes (electrolytes with a uniform diffusion coefficient). Recent research reveals strong dendrite suppression effects with anisotropic electrolytes which have a directional diffusivity; however applying anisotropic electrolytes to existing battery systems is challenging. In this paper we propose several hybrid structured electrolyte designs which can generate local non-uniform mass transport properties and induce dendrite suppression effects while still using conventional isotropic electrolytes. A numerical study is done to consider three hybrid electrolyte designs and shows that using a columnized solid structure with a typical isotropic liquid electrolyte can significantly suppress dendrite growth without sacrificing battery performance. The effects of the columnized hybrid electrolyte compare well with experimental data and suggest that through careful design of a columnar structure the benefits of an anisotropic electrolyte can be achieved without the need for developing new anisotropic liquid electrolytes.