Revolutionary Electrolyte Promises Safer Lithium-Ion Batteries

Abstract

Herein, we present a gel polymer electrolyte (GPE) improving nonflammability of lithium-ion batteries (LIBs) by blocking radical-initiated chain reactions which cause thermal runaway and finally fire issues. The polymer that makes up the nonflammable GPE was (1) soluble in carbonate electrolytes, (2) cross-linkable in the presence of a popularly used lithium salt such as LiPF6, (3) gelated only with 2 wt % in electrolytes, and (4) radical-scavenging by its functional side chains. Electrolytes having the polymer were thermally gelated within battery cells after the cells were assembled by a conventional way. LIB cells with the GPE were durable against external thermal and mechanical shocks without sacrificing cell performances. The high transference number of lithium ions and liquid-equivalent ionic conductivity of the GPE at only 2% solid content having a stable solid-electrolyte interphase layer formed even improved cell performances at normal operation conditions.

A collaborative research team, led by Professor Hyun-Kon Song in the School of Energy and Chemical Engineering at UNIST, Dr. Seo-Hyun Jung from Research Center for Advanced Specialty Chemicals at Korea Research Institute of Chemical Technology (KRICT), and Dr. Tae-Hee Kim from the Ulsan Advanced Energy Technology R&D Center at Korea Institute of Energy Research (KIER), has achieved a groundbreaking milestone in battery technology. Their remarkable achievement in developing a non-combustible gel polymer electrolyte (GPE) is set to revolutionize the safety of lithium-ion batteries (LIBs) by mitigating the risks of thermal runaway and fire incidents.

Historically, the potential flammability of LIBs has been a concern, particularly in electric vehicles, where fire hazards pose a threat to underground parking lots. In response to this critical issue, the research team has successfully developed a non-combustible polymer semi-solid electrolyte that effectively curbs the occurrence of battery fires.

Conventionally, non-combustible electrolytes have relied on the addition of flame retardant additives or solvents with extremely high boiling points. However, such approaches often resulted in a significant decrease in ion conductivity, compromising the overall performance of the electrolyte.

In their breakthrough research, the team introduced a trace amount of polymer into the electrolyte, creating a semi-solid electrolyte. This novel approach dramatically increased the lithium ion conductivity by 33% compared to existing liquid electrolytes. Moreover, the pouch-type batteries incorporating this non-combustible semi-solid electrolyte exhibited a remarkable 110% improvement in life characteristics, effectively preventing unnecessary electrolyte reactions during the formation and operation of the solid-electrolyte interphase (SEI) layer.

The key advantage of this innovative electrolyte lies in its exceptional performance and non-combustibility. By suppressing radical chain reactions with fuel compounds during the combustion process, the polymer semi-solid electrolyte effectively inhibits the occurrence of battery fires. The research team demonstrated the excellence of the developed polymer by quantitatively analyzing its ability to stabilize and suppress radicals.

Jihong Jeong, a researcher at UNIST's Department of Energy and Chemical Engineering, emphasized, "The interaction between the polymerized material inside the battery and volatile solvents allows us to effectively suppress radical chain reactions. Through electrochemical quantification, this breakthrough will greatly contribute to understanding the mechanism of non-combustible electrolytes."

Jihong Jeong, a researcher in the School of Energy and Chemical Engineering, emphasized, "The interaction between the polymerized material inside the battery and volatile solvents allows us to effectively suppress radical chain reactions. Through electrochemical quantification, this breakthrough will greatly contribute to understanding the mechanism of non-combustible electrolytes."

Co-first author Mideum Kim, a master's degree student in Energy and Chemical Engineering at UNIST and the Korea Institute of Chemical Research, further confirmed the exceptional safety of the battery itself through various experiments. The team's comprehensive approach included applying the non-combustible semi-solid electrolyte to pouch-type batteries, ensuring the evaluation of electrolyte non-combustibility extended to practical battery applications.

Professor Song stated, "The research team's multidisciplinary composition, involving electrochemistry from UNIST, polymer synthesis from the Korea Institute of Chemistry's Fine Chemical Research Center, and battery safety testing by the Ulsan Next Generation Battery Research and Development Center at the Korea Energy Technology Institute, has been instrumental in achieving this breakthrough. The use of non-combustible semi-solid electrolytes, which can be directly incorporated into existing battery assembly processes, will accelerate the future commercialization of safer batteries."

The research study has applied for five patents in Korea and two overseas, further highlighting the significance of this achievement. Additionally, it has been selected as a supplementary cover for ACS Energy Letters, with publication online on October 13, 2023. This study has been made possible through the support of the National Research Foundation of Korea (NRF), the Ministry of Science and ICT (MSIT), the Korea Evaluation Institute of Industrial Technology (KEIT), the Korea Research Institute of Chemical Technology, and Samsung SDI Co., Ltd.

Journal Reference

Jihong Jeong, Mideum Kim, Hyeju Shin, et al., "Fire-Inhibiting Nonflammable Gel Polymer Electrolyte for Lithium-Ion Batteries," ACS Energy Lett., (2023).