The conventional lithium-ion batteries (LIBs) have long relied on graphite anodes and transition metal oxide cathodes since their initial commercialization. However, the persistent demand for higher energy density has highlighted the intrinsic limitations of these electrode materials. Graphite, as a dependable anode material, faces capacity constraints, necessitating the exploration of alternatives to meet escalating energy storage needs. Simultaneously, transition metal oxide cathodes, while effective, encounter challenges related to energy density and overall performance. To address these limitations, ongoing research endeavors focus on innovating new electrode materials capable of surpassing existing constraints and pushing the boundaries of energy density. This pursuit is crucial to meet the evolving requirements of applications such as electric vehicles and portable electronic devices, propelling the exploration of advanced electrode materials beyond conventional graphite anodes and transition metal oxide cathodes. The lithium (Li) metal anode is considered as a critical constituent in advanced electrochemical energy storage systems. Despite its inherent attributes of high theoretical capacity and low electrode potential, the practical application of Li metal anode confronts formidable impediments, prominently stemming from challenges associated with irreversible reaction with electrolyte and dendritic growth of Li. To overcome these challenges, a careful electrolyte design is necessary to create stable solid electrolyte interphase (SEI) and to control morphology of Li deposition. In this study, different types of additives are adopted based on following strategies; 1) utilizing AgNO3 as an electrolyte additive in carbonated-based electrolyte using polyacrylonitrile nanofiber support to enhance Li deposition morphology and SEI stability, 2) enhancing electrochemical performance of Li metal anode through different metal nitrate additives and understanding sustainable release mechanism of the additives.
1. Li dendrite formation increases irreversible Li reaction with electrolyte and decreases Coulombic efficiency of the cell. Unstable SEI layer by reduction of carbonate-based electrolyte deteriorates the problem and limit cycle life of Li metal anodes. In order to address these issues, we adopted AgNO3-containing polyacrylonitrile (PAN) interlayer to prevent dendrite formation and enhance SEI stability. The strategy to support AgNO3 on PAN overcome the solubility limitation of AgNO3 in carbonate-based electrolytes. Slowly released Ag+ reduce on Li surface acting as a nucleation seed and induce uniform Li deposition. At the same time, NO3- react with Li to form Li3N-rich SEI. Li metal anode with AgNO3/PAN shows excellent Li plating morphology and electrochemical performance; Full cell using lithium cobalt oxide (LCO) cathode with an AgNO3/PAN interlayer shows an excellent capacity retention of 85.8% with a high Coulombic efficiency (CE) of 99.6% after 100 charge-discharge cycles (@0.54 C).
2. Lithium nitrate is a widely used additive in LMBs, recently, researchers have shifted their focus to other nitrates. Many agree that NO3- involve in Li+ solvation structure and participate in N-rich SEI formation. However, the effect of cations remains to be explored, especially in carbonate-based electrolyte with very limited solubility. Here, we compare the electrochemical performance of different metal nitrate additives (LiNO3, AgNO3, RbNO3) and their role in SEI formation. The experimental results indicate that the cell with AgNO3 has thin Li deposition layer and anion derived SEI. The cell with RbNO3 has limited capacity due to saturation of Rb ions. Among the metal nitrate additives, LiNO3 additive has the longest cycle life. By optimizing the ratio of different metal nitrate additives, the cycle stability of Li metal anode has been improved.
상용화 초기부터 지금까지 리튬 이온 배터리는 흑연 음극과 금속 산화물 양극재에 의존하고 있다. 그러나 고에너지 밀도에 대한 수요가 증가하자 기존 전극 물질에 대한 한계가 부각되었다. 빠르게 성장하는 전기차 시장과 전기차에서 요구하는 에너지 밀도를 충족시키기 위해 기존의 전극 물질보다 높은 에너지 밀도를 가지고 있는 물질에 대한 관심과 연구가 증가하고 있다. 이 문제를 해결하기 위해 리튬 배터리의 음극재로서 리튬 금속이 대체 물질로서 제안되었다. 리튬 금속 음극은 높은 이론 용량과 높은 에너지 밀도를 제공하지만 전해액과 리튬의 비가역적 부반응과 리튬의 덴드라이트 성장으로 인한 문제등으로 인해 상용화에 어려움이 있다. 위의 문제를 극복하기 위해 본 연구에서는 다양한 질산금속염을 리튬 금속 전지에 첨가제로 적용하는 방법을 진행하였다.
1) 질산 은을 폴리아크릴로나이트릴 나노 섬유에 담지하여 카보네이트 전해액에 첨가제로써 사용하였다. 금속 은과 질산염을 통해 균일한 리튬 전착을 유도하고 리튬 이온 전도도가 높은 질산 리튬이 포함된 고체 전해질 계면층을 형성함으로써 리튬 금속 음극의 안정성과 수명을 향상시켰다.
2) 질산 리튬, 질산 은, 질산 루비듐을 위와 같은 방식으로 카보네이트 전해액에 적용하였다. 질산염과 함께 다양한 양이온이 함께 존재할 때 리튬의 형상과 전기화학적 성능을 비교하여 메커니즘을 분석하였다. 루비듐 이온이 포화 상태로 인한 질산염 공급 제한, 은 금속과 리튬의 비가역적 합금반응을 통한 용량저하 및 SEI 차이, 등으로 인해 최적화 비율을 사용하여 지속적인 첨가제 공급을 통해 리튬 금속의 사이클 수명을 향상시켰다.
