국립 부경대학교

부경대, ‘흑연 5배’ 고성능 실리콘/탄소 복합 음극재 개발
- 공업화학과 채수종 교수 연구성과 … <어드밴스드 머티리얼스>에 실려

△ 고성능 다공성 실리콘/탄소 복합 음극재 합성과정 

차세대 이차전지의 기존 음극재인 흑연보다 용량이 5배나 높은 실리콘/탄소 복합 음극재가 개발돼 주목받고 있다.

국립부경대학교는 채수종 교수(공업화학과) 연구팀이 최근 고성능 다공성 실리콘/탄소 복합 음극재를 개발했다고 밝혔다.

채 교수 연구팀은 4 나노미터(nm) 미만의 실리콘 일차 입자가 마이크로미터(μm) 크기의 입자를 형성해 972 m2/g의 큰 비표면적(단위부피 당 표면적)을 갖는 다공성 실리콘을 개발했다.

다공성 실리콘은 리튬을 저장할 때 발생하는 부피 팽창으로 인한 열화를 효과적으로 제어할 수 있는 구조적 장점이 있지만, 실리콘의 크기가 수 나노미터 이하로 작아지면 소결 현상(입자들이 열적 활성화 과정을 거쳐 하나의 덩어리로 되는 과정)으로 인해 실리콘 일차 입자의 크기가 쉽게 커지거나 내부 공극(입자 사이의 틈)을 잃어버리는 문제가 있었다.


△  피치 유무에 따른 다공성 실리콘의 변화

연구팀은 원유에서 추출한 피치(원유나 콜타르 등을 증류시킨 뒤 남는 검은 찌꺼기)를 다공성 실리콘 내부로 균일하게 침투시키는 방식으로 이 문제를 해결했다.

연구팀이 실시간투과전자현미경으로 분석한 결과 다공성 실리콘 내부에 존재하는 피치가 탄화하며 고온에서 실리콘의 소결 현상을 억제했다. 또 이렇게 탄화된 피치는 전지 구동 중 실리콘의 극심한 부피 변화와 열화를 방지하는 것으로 나타났다.

이렇게 개발된 다공성 실리콘/탄소 복합 음극재는 흑연 음극재 대비 약 5배의 용량을 내는 것으로 확인됐다. 특히 완전지(full cell) 평가에서는 450회 충？방전 후에도 초기 용량의 80 %를 유지해 소결 현상을 해결하지 못한 다공성 실리콘/탄소 복합재와 비교하면 15배 이상 향상된 수명을 보였다.

채 교수는 미국 퍼시픽노스웨스트국립연구소(PNNL)의 제이슨 장(Jason Zhang) 박사 연구팀과 공동으로 연구를 진행했고, 이번 연구성과는 재료과학 분야 세계적 학술지 <어드밴스드 머티리얼스(Advanced Materials)> 최신호 온라인에 게재됐다.

채 교수는 “석유계 피치를 활용한 저렴하고 쉬운 공정으로 기존 다공성 실리콘 음극재의 문제점을 해결할 수 있는 핵심적인 기술을 개발했다. 이번에 개발한 음극재는 우수한 특성으로 전기차 주행거리 향상을 위한 차세대 실리콘 음극재로 활용 가능할 것으로 기대한다.”라고 밝혔다. <부경투데이>

PKNU developed high-capacity silicon (Si)/carbon nanocomposite anode materials that are '5 times stronger than graphite'

- The outcome of research by Prof. Chae Su-Jong at Industrial Chemistry Dept. ... published on <Advanced Materials>

A silicon/carbon composite anode material with a capacity that is five times higher than that of graphite, which is the existing anode material for next-generation secondary batteries, has been developed and is attracting academia's attention.

Pukyong National University announced that a research team led by Professor Chae Su-Jong (Dept. of Industrial Chemistry) has recently developed a high-capacity porous silicon/carbon composite anode material.

Professor Chae's research team developed porous silicon with a large specific surface area (surface area per unit volume) of 972 m2/g by forming micrometer (μm)-sized particles of silicon primary particles smaller than 4 nanometers (nm).

Porous silicon has a structural advantage in that it can effectively control depletion due to the volume expansion that occurs when lithium is stored. However, when the size of silicon is reduced to a few nanometers or less, there was a problem in that the size of the silicon primary particles easily increases due to the sintering phenomenon (A process in which particles undergo depleting activation and become one united body) or there was a problem of lost in the internal pore (gaps between the particles).

△ Changes in porous silicon with and without pitch

Professor Chae's research team went through this problem by making pitch extracted from crude oil (black grounds left after distilling crude oil or coal tar) uniformly soak into the porous silicon.

As a result of analysis by the research team with a real-time transmission electron microscope, the pitch existing inside the porous silicon was carbonized and suppressed the sintering of silicon at high temperatures. In addition, this carbonized pitch was found to prevent extreme volume change and depletion of silicon during battery operation.

It was confirmed that the developed porous silicon/carbon composite anode material has about five times the capacity of graphite anode material. Especially, in the evaluation of the full cell, it maintained 80% of its initial capacity even after 450 charging and discharging, showing 10 times of the lifespan compared to the porous silicon/carbon composite, which did not overcome the sintering phenomenon.

Professor Chae conducted research jointly with Dr. Jason Zhang's research team at Pacific Northwest National Laboratory (PNNL) in the US, and the results of this research have been published online in the latest issue of <Advanced Materials>, an international journal in the field of materials science.

Professor Chae said, "We have developed a core technology that can solve the problems of the existing porous silicon anode material with an inexpensive and easy process using petroleum-based pitch. I expect that the anode material developed this time can be used as a next-generation silicon anode material to improve the mileage of electric vehicles due to its excellent characteristics." <Pukyong Today>