The increasing prevalence of electric vehicles has introduced significant challenges in the field of lithium-ion batteries (LIBs), particularly under the demanding operating conditions present in vehicles. One critical issue is the formation of lithium plating on graphite anodes at low temperatures, which, combined with other degradation mechanisms, compromises battery performance and longevity.
This study investigates the use of Electrochemical Impedance Spectroscopy (EIS) as a diagnostic tool for evaluating the state of health (SoH) and identifying safety risks in lithium-ion batteries. By integrating advanced analytical techniques, including Differential Capacity Analysis (dQ/dV) and Distribution of Relaxation Times (DRT), the research aims to enhance the interpretation of impedance data. These methods provide insights into critical battery behaviors, such as lithium plating and other degradation mechanisms, enabling the detection of safety-critical conditions and contributing to the development of safer and more reliable lithium-ion battery systems.
To validate the detection methods, an initial antemortem characterization was conducted to evaluate the cell’s state before initiating the aging process. The cell was aged at -10°C to induce a specific degradation mechanism, lithium plating. Aging was carried out until the cell reached 80% of its state of health (SoH), with diagnostic checkups performed every 100 cycles, as well as an initial and final evaluation, to monitor the cell’s progression. Two diagnostic techniques were employed: dQ/dV analysis, based on capacity cycles, and DRT analysis, derived from EIS data obtained during the checkups. Finally, a postmortem analysis was performed to validate the diagnostic methods and confirm the presence of lithium plating.
Using electrochemical diagnostic techniques, the evolution of various degradation phenomena during aging has been identified. Through dQ/dV analysis, significant changes were observed, particularly in peaks I and IV, corresponding to lithium intercalation in the graphite anode (associated with lithium plating) and phase transitions in the cathode, respectively. DRT analysis further revealed shifts in peaks related to charge transfer and diffusive resistance. Post-mortem analysis confirmed the presence of metallic lithium on the anode and particle cracking in the NMC cathode particles, validating the findings from the diagnostic techniques.
This poster provides valuable insights into degradation mechanisms in NMC-based lithium-ion cells by combining post-mortem validation with non-destructive electrochemical diagnostics performed during cycling. The methodology enables the precise detection of key phenomena, such as lithium plating, paving the way for improved strategies to monitor and prevent battery failures in real-world scenarios.