A quantitative figure of merit for battery SEI films and their use as functional solid- state electrolytes

• 成果类型: Article
• 署名作者: Liu, Bo; Zhao, Dingyi; Lyle, Katelyn; Yuan, Xintong; Chen, Po - Hung; Zhang, Xinyue; Kim, Jin Koo; Wang, Tian - Yu; Wu, Haoyang; Wang, Chongzhen; Yu, Jiayi; Liang, Keyue; Kim, Jung Tae; Liang, Kaiyan; Li, Yuzhang
• 署名单位: University of California System; University of California Los Angeles; University of California System; University of California Los Angeles
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-13788
• DOI: 10.1073/pnas.2425556122
• 发表日期: 2025-07-29
• 关键词: transference number; polymer electrolyte; lithium; conductivity; interphase; performance; interfaces; BEHAVIOR; DESIGN

摘要

As a key passivation film that governs battery operation, the solid electrolyte interphase (SEI) has long been credited for enabling high-performance batteries or blamed for their eventual death. However, qualitative descriptions of the SEI often found in the literature (e.g., conductive, passivating) highlight our incomplete understanding of this layer, where even the most basic properties foundational to SEI function remain difficult to measure. Here, we quantify SEI conductivities and SEI transference numbers using a separator-free Cu|SEI|Li architecture that treats the SEI as a functional solid-state electrolyte (SSE). We find that while any SEI property alone (e.g., electronic conductivity) is weakly correlated (R2 < 0.67) with battery performance (e.g., Coulombic efficiency), a strong correlation (R2 > 0.99) can be achieved by defining the SEI cT number as a product between the SEI transference number (T) and the ratio of SEI conductivities (c). Analogous to the thermoelectric figure of merit (i.e., zT), SEI cT quantitatively benchmarks the holistic impact of SEI properties on battery performance and underscores the pitfalls of citing such properties in isolation. Perhaps most strikingly, we demonstrate that Li metal deposition and stripping at room temperature is possible in our separator-free Cu|SEI|Li cell, confirming that the SEI can function precisely as an SSE. Together, these results enrich our understanding of the SEI, not just as a passivation layer but as a functional structure that can potentially have important implications for solid-state batteries.