UC San Diego

Lithium-ion battery (LIB) has been playing a vital part in the rapid adoption of electric vehicles and portable electronics. However, due to the limited energy density and poor safety properties of the current generation LIB, the development of longer-range electric vehicles has been largely hindered. There is an urgent need for the new material design for the next generation of LIB, especially on the anode side. Among all the candidates, lithium metal is considered as the holy grail for the next generation battery anodes because of its high theoretical capacity (3,860 mAh/g, or 2,061 mAh/cm3) and low electrochemical potential (–3.04 V versus the standard hydrogen electrode). Although extensive works have been done to prolong the cycle life of Li-metal batteries, including electrolyte engineering, interphase design, there are still a lot of studies need to be performed before the commercialization of the Lithium metal battery (LMB). Here, by utilizing a series of characterization tools, the mechanical behaviors, corrosion process and safety properties of the Lithium metal anode in liquid electrolytes have been quantitatively studied. In addition to that, a porous copper current collector is also designed and synthesized for Lithium metal anode with high cycling Coulombic efficiency (CE). To study how the mechanical properties of the Lithium metal anode would affect the performance of the LMB, a split cell with pressure load cell is designed to precisely control the external stack pressure on the LMB during cycling. By employing Cryogenic Focused Ion Beam/ Scanning Electron Microscopy (Cryo FIB/SEM) and Cryogenic Electron Microscopy (Cryo-EM), the effects of external uniaxial stack pressure on the Lithium metal plating/stripping are systematically explored. It is found that by applying a 350-kPa stack pressure on the cell, a nearly 100% dense Lithium can be plated in the electrochemical process. The reversibility of this ultra-dense Lithium is also demonstrated up to 30 cycles. Next, by using three dimensional (3D) reconstruction from Cryo FIB/SEM and Titration Gas Chromatography, the chemical corrosion process of the Lithium metal in liquid electrolyte is thoroughly understood. It is shown that by limiting the contact surface area between the Lithium metal and the electrolyte, the chemical corrosion of the Lithium metal can be largely mitigated. In addition to that, a stable Solid Electrolyte Interphase (SEI) is also crucial for the chemical stability of the Lithium metal anode. The optimized Lithium anode shows less than 0.8% active material loss after 10 days of corrosion in liquid electrolyte. Lastly the safety property of the LMB is quantitatively studied by using Differential Scanning Calorimetry (DSC). The key parameters in controlling the reactivity of the LMB is presented. It is shown that the morphology of the Lithium metal anode, the thermal stability of the cathode and the electrolyte salts and solvents all play a synergetic role in the overall safety of the LMB. By optimizing the all the parameters, a safe LMB is demonstrated which shows no thermal response up to 400˚C.