Operando Investigations of Deposition Mechanisms in Li-metal batteries
Examensarbete för masterexamen
Lithium-ion batteries today are widely used in laptops, smartphones, electric vehicles, and other devices. However, due to the increasing demand for high energy density storage systems, one should look beyond this current state-of-the-art technology. One concept is to use Li-metal as anode material instead of graphite. Its use is promising because of its ultra-high theoretical specific capacity, 3860 mAh/g vs 372 mAh/g for graphite, and low potential of -3.04 V vs Standard Hydrogen Electrode (SHE). However, several drawbacks limit the commercialization of Li-metal batteries, such as a low coulombic efficiency (CE) and dendrite growth, which causes safety issues. To suppress dendrite growth and have high CE, uniform Li-metal deposition at charging is crucial. One of the approaches to obtain high CE is by optimizing the electrolyte composition. In literature, it has been shown that the use of LiNO3 as an additive within the electrolyte improves the CE and leads to stable cycling; however, the detailed mechanism and link to the deposition process is still unclear. To investigate the impact of the LiNO3 additive within the electrolyte in Li-metal batteries, Li-Cu cells were assembled and galvanostatically cycled. It was observed that with an increase of LiNO3 concentration, coulombic efficiency and cycling stability were increased. Operando X-ray Tomographic Microscopy was performed to link the electrochemical results to the morphology of deposited Li-metal. The results show a clear difference in the morphology of deposited Li between the systems with and without LiNO3 added to the electrolyte. The Li-deposition morphology with added LiNO3 is uniform and dense whereas without LiNO3 it is sparse and clearly dendritic.