11:00 AM - ES04.06.07
Mechanisms of Critical Current Densities in Solid Electrolytes for Preventing the Lithium Metal Penetration
Peng Bai1,Jinzhao Guo1
Washington University in St. Louis1
Li-ion batteries are currently the most energy-dense battery technology. If the intercalation anode (e.g. graphite) can be completely removed and Li ions stored in the intercalation cathode can be reduced into a thin film of Li metal anode during recharge, the energy density of the state-of-the-art Li-ion battery will be nearly doubled. However, the formation of Li metal anode in liquid electrolytes has been plagued by the dendrite penetration and low cycling efficiency for decades [1,2]. While solid electrolytes in principle could solve both problems, recent studies revealed that Li metal dendrites can easily penetrate the garnet Li7La3Zr2O12 (LLZO) solid electrolyte at current densities lower than 1 mA cm-2 [3-12]. This relatively low critical current density (CCD) prohibits the battery using solid electrolyte from fast charging, therefore will significantly limit the application, especially for electric vehicles. Accurately understanding the mechanisms of CCD has become an urgent need for designing high-rate, dendrite-proof solid electrolytes.
In this study, we first analyzed 16 sets of reported experimental data, and discovered for the first time a linear relationship between the CCD, Jc, and the ratio of the total conductivity σtotal and the thickness of the solid electrolyte pellet L, i.e. Jc ∝ σtotal/L. This linear relationship resembles the proved limiting current in liquid electrolytes, i.e. Jlim ∝ Dapp/L , suggesting that the solid electrolyte may also have a limiting current, even though prevailing understandings prefer that the near unity transference number ensures an infinitely high limiting current. Inspired by the electrochemical methods used in studying lithium electrodeposition in liquid electrolytes, further investigations of the transport properties of LLZO solid electrolytes led to the discovery of the limiting current in the I-V curve, which is consistent with the CCD discovered from the standard constant current cycling. Quantitative explanations and a simple mathematical model were provided to better understand the mechanisms of the CCD.
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