With the rapid growth of the electric vehicle industry, battery technology has received significant attention and research interest. To date, lithium-ion batteries (LIBs) remain the dominant choice for most applications due to their high energy/power density, efficiency, long cycle life, and relatively low production costs. However, lithium-ion technology also faces inherent limitations, with long charging times being one of the primary barriers to the widespread adoption of electric vehicles (EVs) compared to internal combustion engine (ICE) vehicles. Consequently, accelerating the charging process is considered a key factor in overcoming range limitations and improving user acceptance.
Currently, the most common charging technology relies on conductive charging via charging cables. For fast charging, direct current (DC) is used, and the charging equipment is integrated into charging stations. The Combined Charging System (CCS) has become the standard for charging infrastructure in Europe, enabling vehicles to communicate and set charging parameters dynamically.

Limitations of Conventional Charging and the Need for Pulse Charging
Traditional charging follows the constant current-constant voltage (CC-CV) approach, in which the battery is charged at a constant current until a predefined voltage threshold is reached, after which the process switches to a constant voltage phase. While this method efficiently utilizes the battery’s full capacity, it results in prolonged charging times due to the extended CV phase. To shorten the required charging time, fast charging approaches have been explored, typically aiming to charge the battery within 30 minutes or less using high current. However, two major factors limit fast charging: 1. Lithium plating on the anode (caused by high current), 2. Electrolyte oxidation at the cathode (caused by high voltage). Both phenomena lead to an irreversible loss of active lithium, resulting in capacity fade and reduced battery lifespan.
The fast-charging capability of a battery is highly dependent on its chemistry, architecture, and design, making the optimization of charging methods a complex and multidimensional problem. The most common fast-charging strategy is simply increasing the constant current, but this approach often accelerates battery degradation. An alternative and promising strategy is pulse charging, where pulsed current is applied instead of a continuous charge. Positive pulses can reduce polarization overpotential, regenerate lithium plating, and potentially mitigate battery degradation. However, pulse charging remains largely confined to laboratory-scale studies and has not yet been widely adopted in practical applications.

Research Focus and Literature Review
This study aims to investigate the impact of pulse charging on lithium-ion batteries, focusing on two main aspects: 1. A comprehensive literature review to summarize existing research findings and identify key factors influencing the effectiveness of pulse charging. 2. Implementation of these insights into battery models for validation and further development in simulation studies. This work primarily presents the first step, focusing on the theoretical study of pulse charging and its effects.
One particularly interesting aspect of pulse charging research is the divergence in reported findings. Some studies highlight its benefits, such as extended cycle life and reduced charging time, while others claim that its impact is negligible or even detrimental. For example, as shown in [1], pulse charging does not provide significant advantages over continuous charging when the average charging current and depth of discharge remain the same. In some cases, it even results in lower charge utilization and efficiency.
To better understand the effects of pulse charging, the literature review considers multiple key parameters, including Pulse frequency, Duty cycle, time, RMS current, current amplitude, negative pulse current.
The impact of pulse charging is analyzed on two levels: 1. Electrochemical processes within the battery, such as charge transfer, electrolyte diffusion, and lithium plating. 2. Macroscopic battery performance, including capacity retention, internal resistance, and cycle life.
For example, in the case of pulse frequency, existing studies suggest that high-frequency pulses are generally more beneficial for battery longevity than low-frequency pulses. Since different electrochemical processes (e.g., charge transfer and electrolyte diffusion) have distinct time constants, a specific pulse frequency can help remove charge accumulation in the double-layer capacitance (DL), reduce overpotential, and improve ionic conductivity. Additionally, pulse charging can reduce concentration polarization, facilitating ion diffusion and improving overall battery efficiency.
To further understand the frequency-dependent behavior of lithium-ion batteries, Nyquist plots derived from Electrochemical Impedance Spectroscopy (EIS) were analyzed. The impedance of the full cell is dominated by different internal resistances across various frequency ranges [2]:
– Low-frequency range (10 mHz to 0.5 Hz)  Dominated by solid-phase and electrolyte-phase impedance.
– Mid-frequency range (0.5 Hz to 200 Hz)  Dominated by the double-layer capacitance.
– Intermediate-to-high frequency range (2 Hz to 1 kHz)  Dominated by the solid electrolyte interphase (SEI).
– Overall, the impedance in the intermediate-to-high frequency range is controlled by a combination of DL and SEI effects.
These findings indicate that in the mid-to-high frequency range, the double-layer capacitance plays a crucial role. The DL acts as a temporary charge storage, absorbing most of the high-frequency load without directly affecting lithium-ion diffusion or causing structural damage to the electrode materials. Conversely, in the low-frequency range, the impedance is dominated by solid-phase diffusion and electrolyte resistance. Lithium ions require longer transport times, leading to higher concentration polarization, which accelerates battery degradation [3]. This conclusion aligns well with previous literature findings [4].
Furthermore, there exists an optimal frequency (often referred to as f_Zmin) that is most beneficial for battery lifetime. This is the frequency at which the impedance (Z) is minimized, also corresponding to the point where the imaginary part of the impedance equals zero. The real part of the impedance also reaches a local minimum at or near this frequency [3].

Besides frequency, the root mean square (RMS) current is another critical factor affecting battery performance. Although constant current (CC) charging and pulse charging may share the same average current, they differ in their RMS values. The RMS current represents the effective current stress applied to the battery over time. Since pulse currents involve high peak values, their RMS current is typically higher than that of continuous CC charging. Particularly, when both positive and negative pulse currents are used, the RMS value increases significantly. This leads to greater electrical stress on the battery, resulting in faster degradation and higher energy losses. However, in low-temperature environments, where lithium plating is a major concern, higher RMS current-induced heat generation could be advantageous. This trade-off needs further verification through simulation and experimental studies.
Frequency and RMS current are the two most influential parameters among all pulse charging factors, fundamentally determining whether pulse charging has a more positive or negative impact on lithium-ion batteries compared to the conventional CC-CV method. In general, the main reasons for the ineffectiveness of pulse charging can be attributed to high RMS current and/or deviation from f_Zmin [3]. In addition to these key parameters, the study also examined other aspects of pulse charging, such as charging time, charging efficiency, anode potential evolution, and battery temperature development. The conclusions drawn from this investigation were further illustrated through graphical representations, providing a comprehensive understanding of the effects of pulse charging on battery performance.
These findings provide a strong theoretical foundation for future simulations and optimization of fast-charging techniques. The next steps involve incorporating these insights into battery simulation models, followed by experimental validation. The
This study provides a strong theoretical foundation for future simulation efforts and the optimization of fast-charging strategies. The next step will focus on incorporating the insights and hypotheses derived from the theoretical analysis into simulation models, followed by experimental validation and refinement of the related theories. Ultimately, the developed models will be integrated into the digital twin of lithium-ion batteries, enabling the optimization of fast-charging strategies for batteries based on different materials and actual battery states. This approach aims to achieve more efficient battery management and extend the cycle life of lithium-ion batteries.

References
[1] Keil P, Jossen A. Charging protocols for lithium-ion batteries and their impact on cycle life—An experimental study with different 18650 high-power cells. Journal of Energy Storage 2016;6:125–41.
[2] Zhang Q, Wang D, Yang B, Cui X, Li X. Electrochemical model of lithium-ion battery for wide frequency range applications. Electrochimica Acta 2020;343:136094.
[3] Vermeer W, Stecca M, Mouli GRC, Bauer P. A Critical Review on The Effects of Pulse Charging of Li-ion Batteries:217–24.
[4] Huang X, Li Y, Acharya AB, Sui X, Meng J, Teodorescu R et al. A Review of Pulsed Current Technique for Lithium-ion Batteries. Energies 2020;13(10):2458.