Mechanism of Lithium Dendrites Formation and Suppression Strategies in Li Metal Batteries

This paper describes and summarizes the modifying progress established on Li metal anode in recent years. With the increasing demand for high-capacity batteries, Li-ion batteries, one of the most commercialized batteries, can no longer meet the demand. Thus, the high-energy-density lithium metal battery using lithium metal as anode is widely researched due to the lowest electrochemical potential (-3.04 V) of lithium and ultimate theoretical capacity (3860 mAh/g). However, the Li dendrites formation becomes the main obstacle for the commercialization as it will trigger thermal runaway and short circuit. In this paper, the growth process of Li dendrites was discussed, and various modifying solutions based on electrolytes, Li alloy and current collectors to suppress Li dendrites were summarized.

Reduction Mechanism of Solid Electrolyte Interphase Formation on Lithium Metal Anode: Fluorine-Rich Electrolyte

Metallic lithium is considered a promising anode that can significantly increase the energy density of rechargeable lithium-based batteries, but problems like uncontrollable growth of lithium dendrites and formation of dead lithium impede its application. Recently, a low-concentration single-salt two-solvent electrolyte, 1M LiTFSI/FDMA/FEC, has attracted attention because a high coulombic efficiency can be achieved even after many cycles owing to the formation of a robust solid electrolyte interface (SEI). However, the reaction mechanism and SEI structure remain unclear, posing significant challenges for further improvement. Here, a hybrid ab initio and reactive force field (HAIR) method revealed the underlying reaction mechanisms and detailed formation pathway. 1 ns HAIR simulation provides critical information on the initial reduction mechanism of solvent (FDMA and FEC) and salt (LiTFSI). FDMA and FEC quickly decompose to provide F- that builds LiF as the major component of the inner layer of inorganic SEI, which has been demonstrated to protect Li anode. Decomposition of FDMA also leads to a significant nitrogen-containing composition, producing Li-N-C, LixN, and other organic components that increase the conductivity of SEI to increase performance. XPS analysis confirms evolution of SEI morphology consistent with available experiments. These results provide atomic insight into SEI formation, which should be beneficial for the rational design of advanced electrolytes

The Growth Mechanism of Lithium Dendrites and its Coupling to Mechanical Stress

Operando high-resolution light microscopy with extended depth of field is used to observe large regions of an electrode during electrodeposition of lithium. The analysis of the morphology of the evolving deposit reveals that besides electrochemistry, mechanics and crystalline defects play a major role in the growth mechanism. Based on the findings, a growth mechanism is proposed that involves the diffusion of lithium atoms from the lithium surface into grain boundaries and the insertion into crystalline defects in the metal. Crystalline defects are a result of plastic deformation and hence mechanical stimulation augments the insertion of lithium.