Vertically Aligned Polymer Separators Enable Fast Charging in Lithium Metal Batteries

A joint research team led by Professors Dong Ki Yoon and Hye Ryung Byon from the Department of Chemistry at the Korea Advanced Institute of Science and Technology has developed a next-generation battery separator technology that directs lithium-ion transport pathways by regulating the molecular alignment of liquid-crystalline polymers. Published in the peer-reviewed journal ACS Nano, the study demonstrates that vertically aligning these polymer molecules establishes direct routes that move lithium ions rapidly and uniformly toward electrodes, addressing long-standing transport bottlenecks in high-energy energy storage systems.

Lithium metal batteries offer significantly higher energy storage capacities than conventional batteries, yet their practical performance during rapid charging has remained constrained by internal structural degradation. During the charging process, lithium can accumulate into sharp, branch-like formations known as dendrites. These dendritic structures represent a primary mechanism behind reduced operational life and can physically compromise the internal separator material, creating severe stability risks that include potential battery fires and explosions.

For everyday users of electric vehicles and smartphones, current energy storage configurations frequently cause inconvenience through prolonged charging intervals and steadily deteriorating operating lifespans. Although high-energy-density batteries are essential to lengthen device usage times and expand electric vehicle driving ranges, rapid charging protocols have historically been limited because internal chemical deposits degrade electrochemical performance while increasing the risk of thermal failure.

To overcome these challenges, the investigators utilized liquid crystal materials, which uniquely exhibit both the ordered spatial characteristics of solid matter and the fluid mobility of liquids. Because the orientation of liquid crystal molecules can be systematically controlled through surface treatments and adjacent processing methods, the research team exploited this molecular adaptability to form regularly organized structural pathways designed specifically for lithium-ion migration.

Using this liquid-crystal alignment control method, the researchers fabricated a porous liquid-crystalline polymer separator containing nanoscale pores and incorporated polyethylene glycol chains to actively facilitate lithium-ion movement. The researchers specifically controlled the alignment direction of the liquid-crystal molecules into either vertical or horizontal orientations, allowing them to systematically compare how molecular geometry influences lithium-ion transport behavior.

The comparative assessments revealed that the liquid-crystalline polymer separator with vertically aligned molecules created an unobstructed pathway directly toward the battery electrodes. In comparison to horizontally aligned configurations, the vertical arrangement reduced the tortuosity of the ion transport pathways by approximately 2.5-fold, enabling lithium ions to travel at accelerated speeds with enhanced uniformity while effectively suppressing dendrite formation and elevating operational stability.

When incorporated into an operational lithium metal battery, the separator demonstrated durable fast-charging capabilities under rigorous operating demands. Tested at a 4C charging rate—a benchmark where a battery theoretically completes a full charge in roughly 15 minutes, compared to 30 minutes at 2C and one hour at 1C—the battery retained 94 percent of its initial capacity across 100 charge-discharge cycles. Co-corresponding authors Professor Dong Ki Yoon and Professor Hye Ryung Byon, alongside co-first authors Geunjung Lee and Dr. Rak Hyeon Choi at KAIST, noted that controlling polymer alignment offers an effective design strategy for realizing safe, rapid-charging batteries with high energy densities.

Elaborating on the broader implications of the findings, Professor Dong Ki Yoon noted that controlling the molecular alignment of liquid-crystalline polymers provides an effective approach for engineering precise lithium-ion transport pathways. Yoon emphasized that tailoring these molecular routes directly improves overall battery performance while reinforcing internal stability during operation. The researchers anticipate that this alignment strategy will serve as a foundational technology for next-generation, high-energy-density battery systems, particularly for electric vehicles that require extended driving ranges without sacrificing rapid recharging capabilities.

Subject of Research: Molecular alignment of liquid-crystalline polymer separators for fast-charging lithium metal batteries

Article Title: KAIST opens a 'highway' for lithium ions with liquid-crystalline polymers, developing next-generation fast-charging battery technology

Article References: KAIST opens a 'highway' for lithium ions with liquid-crystalline polymers, developing next-generation fast-charging battery technology. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

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Keywords: KAIST, liquid-crystalline polymers, lithium metal batteries, battery separators, molecular alignment, fast charging, lithium dendrites, polyethylene glycol, ion transport pathways, pathway tortuosity, 4C charging rate, capacity retention, Department of Chemistry, Dong Ki Yoon, Hye Ryung Byon, ACS Nano, nanoscale pores