Pulse Current Charging for Lithium-Ion Batteries and Beyond

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The charging strategies for batteries have attracted widespread attention from international research institutions and industries. Advanced charging protocols such as pulse current (PC) charging are considered beneficial for extending the lifetime of lithium-ion batteries (LIBs). A typical PC charging protocol consists of a constant current (CC) charging phase followed by a relaxation period. Previous studies have shown that PC charging can significantly enhance battery stability 1,2 . However, the specific mechanisms through which PC charging improves battery performance are not yet fully understood, which to some extent limits the optimization of charging protocols. In this study 3 , we used commercial 18650-type LIBs (HTCNR18650, nominal capacity: 2200 mAh, voltage: 3.6 V), with Li(Ni₀.₅Co₀.₂Mn₀.₃)O₂ (NMC532) as the cathode material and graphite as the anode. The batteries were tested under three different charging conditions: constant current (CC) charging, Pulse-100 charging, and Pulse-2000 charging. The pulse frequencies for PC charging were set at 100 Hz and 2000 Hz, respectively, with a duty cycle of 50% in both cases. The average current was kept the same across all three charging modes (1C, i.e., 2.2A), with the voltage range set between 2.5–4.2 V. After every 100 cycles, we paused the aging test and conducted a reference performance test (RPT) to assess the battery's health status. The experimental results indicate that PC charging significantly improves the cycling stability of commercial NMC532/graphite LIBs, as shown in Figure 1. Electrochemical diagnostics reveal that PC charging effectively reduces the rate of impedance rise and minimizes the degradation of electrode materials. Through in-situ and ex-situ Raman spectroscopy and X-ray absorption spectroscopy analysis, we investigated the chemical and structural evolution of electrode materials during PC and CC charging. Specifically, under PC charging conditions, lithium-ion intercalation in graphite is more uniform, Ni in NMC532 reaches a higher oxidation state, and Ni–O bond length variation is smaller. Moreover, PC charging effectively suppresses electrolyte decomposition and mitigates the continuous thickening of the solid electrolyte interphase (SEI) layer on the graphite anode. This study demonstrates that PC charging strategies can significantly enhance the cycling stability of commercial NMC532/graphite batteries, extending their cycle life from 500 cycles to over 1000 cycles. These findings not only provide new insights into optimizing existing LIB charging protocols but also promote the development and application of future battery technologies. Acknowledgement This study's subsequent research and related conference travel were funded by the Danish Independent Foundation (Grant Number: 5249-00027B). Reference (1) Huang, X.; Liu, W.; Meng, J.; Li, Y.; Jin, S.; Teodorescu, R.; Stroe, D. I. Lifetime Extension of Lithium-Ion Batteries With Low-Frequency Pulsed Current Charging. IEEE J Emerg Sel Top Power Electron 2023 , 11 (1), 57–66. https://doi.org/10.1109/JESTPE.2021.3130424. (2) Huang, X.; Li, Y.; Acharya, A. B.; Sui, X.; Meng, J.; Teodorescu, R.; Stroe, D. I. A Review of Pulsed Current Technique for Lithium-Ion Batteries. Energies (Basel) 2020 , 13 (10), 1–18. https://doi.org/10.3390/en13102458. (3) Guo, J.; Xu, Y.; Exner, M.; Huang, X.; Li, Y.; Liu, Y.; Wang, H.; Kowal, J.; Zhang, Q.; Kristensen, P. K.; Wang, D.; Pedersen, K.; Gurevich, L.; Stroe, D. I.; Adelhelm, P. Unravelling the Mechanism of Pulse Current Charging for Enhancing the Stability of Commercial LiNi0.5Mn0.3Co0.2O2/Graphite Lithium-Ion Batteries. Adv Energy Mater 2024 , 2400190 , 1–14. https://doi.org/10.1002/aenm.202400190. Figure 1

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