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Operando Degradation Diagnostics and Fast Charging Analytics in Lithium-Ion Batteries
Fast charging is crucial to the proliferation of electric vehicles. Fast charging is limited by lithium plating, which is the deposition of lithium metal on the anode surface instead of intercalation of lithium into the anode. Lithium plating causes capacity fade, increases cell resistance, and presents safety issues. A fast charging strategy was implemented using a battery management system (BMS) that avoided lithium plating by predicting the anode impedance. Commercial pouch cells modified with a reference electrode were cycled with and without the BMS. Cells cycled with the BMS avoided lithium plating but experienced significant degradation at the cathode. Cells cycled without the BMS underwent extensive lithium plating at the anode. Capacity loss was differentiated into irreversible and irretrievable capacity to understand electrode-based degradation mechanisms. Post-mortem analysis on harvested electrodes showed that the BMS cycled cells exhibited minimal anode degradation and had a two-times higher capacity loss on the cathode. The cells cycled without the BMS had extensive anode degradation caused by lithium plating and a seven-times higher capacity loss on the anode.
Understanding and preventing the aging mechanisms of lithium-ion batteries is necessary to prolong battery life. Traditional full cell measurements are limited because they cannot differentiate between degradation processes that occur separately on anode and cathode. A reference electrode was inserted into commercial cylindrical lithium-ion cells to deconvolute the anode and cathode performance from the overall cell performance. Two configurations of the reference electrode placement inside the cell were tested to find a location that was stable and had minimal interference on the full cell performance. The reference electrode inside the mandrel of the cylindrical cell had stable potential measurements for 80 cycles and at different C-rates and had minimal impact on the full cell performance.