| Summary: | Abstract Fast‐charging is highly demanded for applications requiring short charging time. However, fast‐charging triggers serious problems, leading to decline in charge acceptance and energy efficiency, accelerated capacity degradation, and safety risk. In this work, a three‐electrode coin cell with a Li metal reference electrode is designed to individually record the potential of two electrodes, and measure the impedance of each electrode by using a power‐optimized graphite‐LiNi0.80Co0.15Al0.05O2 electrode couple. It is shown that regardless of the state‐of‐charge the Li‐ion cell's impedance is contributed predominantly by the cathode, and that the cathode's impedance is dominated by the charge‐transfer resistance. In consistence with the impedance results, polarization of the Li‐ion cell is dominated by the cathode. It is surprised to find that no Li plating occurs on the graphite anode even if the charging rate is increased to 10 C (1 C = 1.30 mA cm−2). The results of this work indicate that low overall impedance with a high cathode‐to‐anode impedance ratio is the key to enabling safe fast‐charging, and that fast‐charging Li‐ion batteries without Li plating on the graphite anode is possible if the cathode and graphite anode are optimistically engineered.
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