Laser-Patterned Electrodes Boost Fast-Charging Performance

Researchers at the National Renewable Energy Laboratory (NREL) have developed a novel laser-based process to alter electrode microstructures for improved battery performance. Compatible with industry-standard roll-to-roll manufacturing, the method uses laser pulses to optimize patterns in electrode pore networks. These tweaks can boost lithium-ion battery performance and charging capacity for electric vehicles. 

The precision process, developed through NREL’s multi-year BatMan project, was demonstrated with roll-to-roll equipment typically used in battery manufacturing lines to bond active material mixtures onto foil surfaces. Roller-based techniques like laser processing are more efficient and cost-effective than conventional material manufacturing methods. 

 

A roll-to-roll line processes double-sided electrode material. Image used courtesy of NREL (by Donal Finegan)

 

The demonstration processed 2,296 feet of double-sided electrode material for lithium-ion batteries. With private-sector partners supplying imaging and laser technologies, the BatMan team significantly improved manufacturing efficiency and technical performance. Its roll-to-roll equipment could process up to 32.8 feet of 160-millimeter-wide electrodes per minute. In prototype trials, the laser-ablated electrodes offered twice as much battery capacity and a longer cycle life for fast charging at 4C. 

Since NREL has demonstrated the scaled-up process enabled 100% more capacity after 800 charging cycles, the researchers plan to refine the technology further for performance, safety, and quality. 

 

NREL’s roll-to-roll laser processing demonstration for electrode materials. Image used courtesy of NREL

 

Why Electrode Microstructures Matter

Electrode thickness, material choice, and structural design all play a role in determining capacity, voltage, and charging capabilities. These features often come with trade-offs. For example, doubling electrode thickness from 50 μm to 100 μm increases energy density by 16% but could reduce cycle life by damaging the lithium plating, according to NREL. 

 

NREL microstructure modeling. Image used courtesy of NREL (by Dennis Schroeder)

 

Despite offering technical benefits, thicker lithium-ion battery electrodes introduce production challenges. Electrodes with a large surface area require wetting, where a liquid electrolyte is injected into the cell. Slurry-processing thicker electrodes could cause poor wetting and low rate capabilities. Wetting can be costly and complex since it’s difficult to spread liquid electrolytes evenly on solid surfaces. Insufficient wettability performance—the rate of pore saturation and the spatial location of unwetted volumes—reduces energy density and efficiency. 

This is where adjusting the pattern of electrode microstructures comes in handy. Microstructure porosity is a crucial factor in wettability, among other considerations like the electrode and electrolyte contact angle, electrolyte viscosity and density, and the pore network’s tortuosity. 

Pore networks are patterns of microscopic holes in the electrode. Optimizing electrolyte saturation through the pore network in wetting can speed up ionic diffusion, where ions move faster during charging and discharging without damaging the cell. 

 

A structured graphite electrode prepared using NREL’s laser system. Scanning electron microscopy images show three perspectives for the holes and grooved lines. Image used courtesy of the study authors (Figure 1-a, b, and c)

 

NREL used advanced ionic diffusion models and genetic algorithms to specify the ideal pore arrangement—a hexagonal pattern with pores half as deep as the electrode coating thickness. The models indicated that cylindrical channels in this pattern were 6.25 times more efficient for fast charging than grooved lines with structures limited to a 5% electrode volume loss. By keeping the volume loss minimal at 1-2%, wetting could be conducted five to 20 times faster than in the unstructured electrode. 

 

Ideal channel dimensions. Image used courtesy of the study authors (Figure 1-d)

 

Laser-Ablated Electrodes

California-based Liminal Insights supplied NREL with its EchoStat acoustic imaging platform, which employs ultrasound imaging and machine learning to analyze each cell’s condition while in production. The team found the electrodes could wet faster and more uniformly with laser ablation compared to baseline cells. 

NREL used a high-precision femtosecond laser ablation system from Amplitude Laser Group to configure the electrode pore networks. This technique emits light pulses in femtoseconds, equal to 10−15 of a second. Amplitude’s laser system included high-speed scanning optics controlled by galvanometers, which are sensitive instruments that measure low electrical currents. NREL and Amplitude customized the laser control power, frequency, position, and pulses for high precision. 

Scanning electron microscopy and X-ray nano-computed tomography were used to visualize the electrode structure’s morphological features. They found that improving the uniformity of structures minimized lithium plating during fast charging.

 

Laboratory workflow for the BatMan project. Image used courtesy of NREL (by Alfred Hicks)

 

The team assembled small battery cells to analyze the performance of the optimized electrode architectures in partnership with Clarios, a battery manufacturing company that provided commercial 27 Ah batteries for additional analysis. In addition to unlocking 100% more capacity after 800 charge cycles, BatMan’s processing method reduced wetting time and improved lithium-ion propagation. 

There was also minimal added manufacturing cost, at under $1.50 per kWh (about 1.7%) for a 50 MWh factory.