A technology has been developed to use nitrogen-doped single-walled carbon nanotubes to improve the performance of secondary battery cathode materials, raising expectations that it will be possible to overcome the limitations of silicon in the future.

The Korea Electrotechnology Research Institute (KERI) announced on the 23rd that Dr. Han Joong-tak and student researcher Lee Do-geun of the Nano Convergence Research Center developed a manufacturing technology for a 'silicon-nitrogen doped carbon composite anode material' that secures high capacity and high stability of lithium-ion battery anode materials.

Silicon has an energy density about 10 times higher than graphite, the existing negative electrode material for lithium-ion batteries, but has the disadvantage of expanding 3 to 4 times in volume during continuous charging and discharging.

In addition, there is a problem that silicon particles break easily, reducing the performance of the battery, so they cannot be used alone as a negative electrode material, and a technology is being developed to add some silicon to graphite to complement each other's strengths and weaknesses.

Currently, many researchers are working to increase the amount of silicon added by solving the problem of silicon using carbon nanomaterials, a new material of the future.

Among them, KERI's plan is to overcome the limitations of silicon by using 'nitrogen-doped single-walled carbon nanotubes' and 'graphene'. It has been overcome.

Carbon nanotubes are divided into multi-walled and single-walled, and single-walled ones are thin and transparent, so their physical properties and electrical conductivity are much better.

Nitrogen has a high affinity for lithium ions and is an electrochemically stable element. When applying them to silicon composite anode materials, theoretically, they are a very good match, but carbon nanotubes tend to clump together, so a technology to disperse them was absolutely necessary for commercialization.

In particular, single-walled carbon nanotubes are much more difficult to disperse than multi-walled ones because their diameter is only 1 to 2 nanometers (nm).

Based on the nano-fusion technology that it has accumulated for over 10 years, KERI has developed a groundbreaking technology for the first time in the world to disperse single-walled carbon nanotubes in a way similar to kneading flour.

And through this technology, they succeeded in effectively inserting lithium-ion-loving nitrogen between carbon atoms (doping).

When the 'nitrogen-doped single-walled carbon nanotube' developed in this way is applied to the negative electrode material of a lithium-ion battery, it has the effect of increasing the speed at which lithium ions move to silicon, thereby increasing the charging speed and improving the stability of the charge/discharge cycle.

In addition, Dr. Han Joong-tak's team secured stability by suppressing the volume expansion of silicon by wrapping the outside of the cathode material with a mesh-structured graphene that has excellent electrical conductivity and mechanical strength.

The research team also confirmed the effectiveness of the results through 100 cycles of lithium-ion battery charging and discharging. As a result, while lithium-ion batteries with existing silicon composite anode materials had only about 30% of their battery performance remaining, batteries with KERI's 'silicon-nitrogen-doped carbon composite anode materials' maintained over 82% of their performance.

KERI’s Dr. Han-Joong Tak said, “Our carbon nanomaterial composite cathode material makes up for the shortcomings of silicon and has the advantage of maintaining high capacity stably for a long time,” adding, “It is at a level where we do not need to add conductive materials such as carbon black, which were previously added to improve the conductivity and performance of battery electrodes.”

The research team believes that this technology can also be used for the cathode of 'all-solid-state batteries' where the lithium diffusion speed is important. The excellence of the research results was recently recognized and published in a paper in 'Advanced Functional Materials', an internationally renowned academic journal in the field of materials engineering. The 'JCR Impact Factor', which evaluates the influence of academic journals, is 19, which puts it in the top 3.7% of the field.

KERI has completed the evaluation of a lithium-ion battery full cell using the developed composite cathode material and has completed the patent application. Based on this, it is expected that the related technology will receive much attention from companies that need high-capacity lithium-ion batteries, and it plans to find companies in demand and promote technology transfer.

Meanwhile, KERI is a government-funded research institute under the National Research Council of Science and Technology of the Ministry of Science and ICT.