Tech Insights

Enhancing Lithium-Ion Battery Life With Pulsed Charging

May 03, 2024 by Jake Hertz

Research demonstrates charging with high-frequency current pulses minimizes aging effects in lithium-ion batteries.

The need for batteries has surged dramatically, but maintenance issues, such as capacity and degradation over time, still require careful battery management to maintain optimal performance. Balancing the demand for reliable power with the complexities of the battery life cycle remains a major challenge in harnessing the full potential of these indispensable energy sources.

Researchers in Berlin have discovered that pulsed current charging can extend the life cycle in commercial NMC532/graphite batteries by 100%. The findings could address problems in the aging process in lithium-ion batteries.

 

Could pulsed charging be the secret to longer battery life?

Could pulsed charging be the secret to longer battery life? Image used courtesy of Adobe Stock

 

Lithium-Ion Battery Aging

The major components of a lithium-ion battery are the electrode (anode and cathode), electrolyte, and separator. During initial charge-discharge cycles, lithium ions from the positive electrode penetrate the separator, enter the electrolyte, and deposit on the negative electrode internally. Through the outer circuit, electrons from the positive electrode enter the negative electrode, initiating an oxidation-reduction reaction involving the electrons, solvent, and lithium ions. 

After this reaction, a thin film of lithium salts called the solid electrolyte interphase (SEI) layer is formed on electrodes, which can only be penetrated by lithium ions. The SEI layer is essential to lithium-ion (Li-on) batteries’ cycling stability, performance, and long-term stability of charge capacity retention. Unstable batteries will eventually consume lithium ions, reducing charge capacity and raising internal charge transfer resistance.

 

Formation of SEI in Li-ion batteries

Formation of SEI in Li-ion batteries. Image courtesy of Tateyama et al.

 

Naturally, understanding the aging process in Li-ons is essential for extending their life cycle. A common aging mechanism is the continuous growth of the SEI on the anode, which leads to lithium depletion and reduced capacity. The SEI layer also hinders lithium-ion movement, increasing interface impedance and causing higher discharge over-potential, further diminishing capacity. Additionally, high-quality Li-ons using NMC532 (LiNi0.5Mn0.3Co0.2O2) and graphite electrodes can suffer structural cracking and electrode exfoliation, contributing to capacity loss. 

 

Enhancing Battery Durability With Pulsed Current

In collaboration with the Technical University of Berlin and Aalborg University, researchers from the Helmholtz Association of German Research Centers have found a new way to extend the Li-on battery’s cycle life using a high-frequency pulsed charging protocol.

Experiments demonstrated that pulsed charging (PC) minimized aging effects by evenly distributing lithium ions and reducing mechanical stress on the graphite anode. This maintained structural stability and prevented electrode cracks. Tests comparing constant current (CC) and PC charging methods revealed that CC charging led to thicker SEI layers at the anode, decreasing capacity and causing more cracks in the NMC532 and graphite electrodes. PC charging, on the other hand, resulted in thinner SEI layers and fewer structural changes in electrode materials. 

Typically, Li-ion diffusion in the electrolyte is slower than electron transport, causing polarization. PC charging balances electron and ion transport, reducing SEI thickening and the risk of Li plating. Additionally, it allows electrode materials to relax structurally between pulses, easing mechanical stress and reducing structural degradation.

 

PC charging for enhancing stability in NMC/graphite Li-ions

PC charging for enhancing stability in NMC/graphite Li-ions. Image courtesy of Guo et al.

 

Researchers found high-frequency pulsed charging protocols, particularly those using square-wave current, significantly improved the battery's service life by doubling the cycle life while maintaining 80% capacity retention. Specifically, the study showed a frequency of 2,000 Hz is advantageous, hinting that higher frequencies may bring more benefits. 

 

Changing the Future of Batteries

The research findings offer significant potential for extending battery life and improving efficiency. As research advances, PC charging may become a standard for boosting Li-ion performance and longevity, and further research should explore how different factors influence the charging protocol.