▲Professor Jeong-Goo Kang, KAIST Department of Materials Science and Engineering, PhD candidate Ki-hwan Kim (Photo source: KAIST)


Synthesis of Porous Carbon Hollow Structures with Large Surface Area through Polymer Resin Orientation Change

A KAIST research team synthesized porous carbon hollow structures with large surface area through changes in polymer resin orientation, and based on this, developed anode and cathode materials to implement high-performance hybrid lithium ion batteries.

Professor Jeong-Goo Kang's research team at KAIST's Department of Materials Science and Engineering announced on the 21st that they have developed a high-energy, high-power hybrid lithium ion battery capable of rapid charging with excellent performance.

Currently, lithium ion batteries are representative commercialized energy storage devices that have become essential components across the entire electronics industry, from smart electronic devices to electric vehicles, earning them the designation of "the second semiconductor."

However, fundamental limitations remain. Due to characteristics such as slow electrochemical reaction rates, limited electrode materials, low output density, long charging times, and large volumes resulting from anode and cathode asymmetry, development of high-performance electrode materials and next-generation energy storage devices is necessary.

To address these issues, hybrid batteries, which are currently being actively researched, combine battery-type anodes with capacitor-type cathodes, and because they possess both the advantages of high storage capacity and fast charge/discharge speeds, they are receiving attention as next-generation energy storage devices that can replace existing lithium ion batteries.

To implement hybrid batteries with high-energy and high-power density, improvements in electrical conductivity and ion diffusion rates of battery-type anodes, increases in energy storage capacity of capacitor-type cathodes, and optimization of both electrodes according to their different ion storage mechanisms are required.

Accordingly, Professor Kang's research team presented a new synthesis method capable of synthesizing porous carbon structures with large surface area through changes in polymer resin orientation, and based on this, developed anode and cathode materials to successfully implement high-energy and high-power hybrid lithium ion energy storage devices.

The research team added melamine to the resorcinol-formaldehyde (Resorcinol-Formaldehyde) resin synthesis process to change the resin orientation from linear to twisted form. When the twisted-form resin undergoes carbonization, more micropores were formed, and a carbon structure with a surface area 12 times larger than that generated from resin with a conventional linear structure was produced.

▲Schematic diagram of the synthesis process of cathode and anode materials based on porous carbon hollow structures formed through polymer resin orientation change (Image source: KAIST)

The carbon structure generated through this process was used as a cathode material for capacitors, and the research team confirmed that not only are many ions adsorbed on the surface due to the large surface area, but ions can also diffuse rapidly through hollow structures and mesopores, exhibiting high capacity and rate characteristics.

Furthermore, the research team synthesized carbon hollow structures with molecularly-sized germanium particles inserted through a synthesis method of inserting germanium (Ge) precursors with high energy storage capacity into the twisted-form resin structure, which was then used as a battery-type anode material.

The molecularly-sized germanium particles inserted into the porous carbon structure not only suppress performance degradation caused by large volume expansion during charge/discharge cycles, but also enable lithium ions to diffuse rapidly into the interior, and the research team confirmed that these materials exhibit high cycle life and rate characteristics.

The research team configured the developed anode and cathode as a full cell to implement high-performance hybrid lithium ion batteries. This hybrid lithium ion battery was confirmed to possess both energy density comparable to existing commercialized lithium ion batteries and power density characteristics of capacitors, and as a next-generation energy storage device capable of rapid charging from seconds to minutes, it is expected to be applicable to electric vehicles, drones, smart electronic devices, and more.

Professor Kang stated, "The hybrid lithium ion battery, which has high energy density (285 Wh/kg) on an electrode basis and enables rapid charging through high power density (22,600 W/kg), will become a new breakthrough to overcome the limitations of current energy storage systems," adding, "it will be applicable and can expand the range of utilization for all electronic devices, including electric vehicles."

▲Schematic diagram of hybrid lithium ion battery and device characteristic implementation photo (Image source: KAIST)

This research result, with PhD candidate Ki-hwan Kim from KAIST's Department of Materials Science and Engineering as the first author, was published in the international journal "ACS Nano" on April 4th. (Paper title: Coiled Conformation Hollow Carbon Nanosphere Cathode and Anode for High-Energy Density and Ultrafast Chargeable Hybrid Energy Storage)