Tailored cathode electrolyte interphase via ethylene carbonate-free electrolytes enabling stable and wide-temperature operation of high-voltage LiCoO2

Abstract

Raising the charge cut-off voltage of LiCoO₂ (LCO) cathodes provides a straightforward approach to increasing the energy density of lithium-ion batteries (LIBs). However, when the charge cut-off voltage exceeds 4.55 ​V (vs. Li/Li⁺), the cathode-electrolyte interphase (CEI) becomes unstable, failing to protect the LCO cathode from severe interfacial side reactions and structural instability. These issues accelerate battery degradation and severely hinder the practical application of high-energy-density LIBs. Moreover, ethylene carbonate (EC)-based electrolytes exhibit more pronounced parasitic reactions than EC-free electrolytes under high voltage, further exacerbating performance limitations. Therefore, optimizing the components and structure of the CEI with EC-free electrolytes remains a challenge. In this work, we aim to construct a robust and chemically stable F-/B-containing CEI on the surface of LCO cathodes using an EC-free electrolyte design. By replacing EC with more anti-oxidative propylene carbonate (PC) and fluoroethylene carbonate (FEC) solvents, the oxidative stability of the electrolyte is significantly improved. This promotes the formation of LiF within the CEI, thereby enhancing its mechanical strength. Meanwhile, the introduction of the sacrificial film-forming additive lithium bis(oxalato)borate (LiBOB) facilitates the generation of oxalates (Li₂C₂O₄) and B-containing crosslinked polymers (LiB_xO_y) within the CEI. These components exhibit high electrochemical stability and flexibility, compensating for the limitations of the LiF-rich CEI and further enhancing the overall structural stability of the CEI. This combination results in a rigid-flexible coupling architecture composed of inorganic-rich components (LiF and Li₂C₂O₄) embedded in B-containing crosslinked polymers (LiB_xO_y), ensuring both mechanical integrity and chemical stability of the CEI. Consequently, this tailored CEI effectively mitigates interfacial layer cracking and regeneration, reducing irreversible structural degradation and interfacial side reactions in high-voltage LCO cathodes. Based on these improvements, the EC-free PC-based electrolyte enables superior performance of LCO cathodes at 4.6 ​V, achieving 82% capacity retention at 0.5C over 200 cycles. Furthermore, graphite||LCO full cells demonstrate enhanced cycling stability at 4.5 ​V and enable operation across a wide temperature range (−40 to 80 ​°C), highlighting the effectiveness of the rigid-flexible coupling CEI derived from the tailored electrolyte. By moving away from conventional EC-based electrolyte formulas, this work provides new insights into designing high-performance, wide-temperature, and sustainable PC-based electrolytes.