Fast charging of lithium-ion batteries could lead to considerable growth and increased adoption of electric vehicles in the marketplace. Many researchers and developers are committed to accomplishing this without causing considerable harm or degradation to the batteries. One such insightful study by Drees R, Lienesch F, Kurrat M, has contributed valuable understanding on this subject. A brief summary of their findings is given below:
The study utilizes the Electrode Equivalent Circuit Model (EECM) to devise an optimized fast-charging strategy, aiming to enhance battery performance & durability.
Key Takeaways:
1. The Challenge of Conventional Charging Methods:
- The conventional Constant Current-Constant Voltage (CCCV) charging often leads to lithium-plating, causing severe degradation of battery lifespan & safety.
2. Leveraging the EECM:
- The study advanced & utilized the EECM to compute an optimized fast-charging strategy that controls the negative electrode's potentials to inhibit lithium-plating.
- A multi-step fitting parameterization method was developed to improve simulation fidelity & enhance modeling accuracy.
3. Optimized Fast-Charging Strategy:
- The optimized fast-charging strategy allows a maximum current of 3C and a minimum voltage of 10 mV for the negative electrode.
- This strategy was applied to Nickel Manganese Cobalt Oxide (NMC622) / Graphite (G) cells & achieved a State of Charge (SOC) from 0 to 80% in 29 minutes.
4. Comparative Results:
- In contrast to the optimized approach, conventional 3C CCCV caused a 20% capacity fade after 100 cycles due to lithium-plating, as detected by optical microscopy.
- However, the optimized 3C fast-charging strategy led to a mere 2% capacity fade per 100 cycles in the initial 300 cycles, with no visible lithium-plating.
5. Change of Resistance during Cycling:
- Resistance change was analyzed using current-interrupt tests.
- While the negative electrode's resistance did not change significantly for either charging strategy, the resistance of the positive electrode increased significantly, leading to increased charging time for the conventional 3C CCCV.
- This outcome emphasizes that positive electrode degradation is the primary factor limiting charging speed during cycling.
6. Implications and Future Directions:
- The optimized 3C fast-charging strategy, devised using EECM, led to better capacity retention & shorter mean charging times as the battery ages compared to conventional CCCV fast-charging.
- The study suggests the potential for more high-performance, long-lasting lithium-ion batteries, paving the way for advancements in the automotive & consumer electronics industries.
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