image: Figure 1. Design strategy. (a) The corresponding Arrhenius behavior and apparent activation energy derived from RSEI in Nyquist plots at various temperatures of Li||Li symmetric cells with different electrolytes. All Li||Li cells were cycled for 10 rounds at 1 mA cm−2 and 1 mAh cm−2 to establish a stable SEI. (b) Comparison of EaSEI values. (c) The corresponding Arrhenius behavior and apparent activation energy derived from RCEI in Nyquist plots at various temperatures of NCM||NCM symmetric cells with different electrolytes. Schematics of the interphases formed in PFE (d) and PAFE (e). (f) Flammability tests of BE and PAFE electrolytes. Protection mechanisms of the SEI and CEI formed in BE (g) and PAFE (h).
Credit: ©Science China Press
Lithium metal batteries (LMBs) are promising candidates for next-generation energy storage due to their exceptionally high theoretical capacity and low electrochemical potential. However, their instability under high voltage, especially above 4.4 V, has hindered commercialization. A key challenge lies in the formation of unstable and uneven interfaces that cause dendrite growth, capacity fading, and safety risks.
Now, a research team led by Prof. Danni Lei and Prof. Chengxin Wang at Sun Yat-sen University has developed a ternary composite electrolyte additive system PAFE that addresses these critical issues. The work, published in National Science Review, demonstrates how this new electrolyte enables stable cycling of lithium metal batteries at a high cut-off voltage of 4.7 V.
The PAFE electrolyte incorporates aluminum ethoxide (Al(EtO)3), fluoroethylene carbonate (FEC), and pentafluorocyclotriphosphazene (PFPN) into a carbonate-based electrolyte. Al(EtO)₃ acts as a crosslinking agent, forming a three-dimensional polymer network that ensures uniform deposition of inorganic components such as LiF, Li3N, Li3P, and Al2O3 in both the solid-electrolyte interphase (SEI) and cathode-electrolyte interphase (CEI).
This uniform interphase significantly reduces the activation energy required for lithium-ion transport, thereby ensuring smooth ion flow and reducing internal stress. Experimental results show that PAFE reduces the interfacial Li-ion migration energy barrier to 48 kJ/mol and suppresses dendrite growth. The PFPN additive also enhanced flame retardancy, improving the safety profile of the electrolyte.
When tested in full cells using commercial-grade Ni-rich NCM811 cathodes and lithium metal anodes, PAFE-supported cells retained 80% of their capacity after 140 cycles at an ultrahigh voltage of 4.7 V. Furthermore, 1 Ah pouch cells demonstrated excellent long-term cycling performance with no visible swelling, even under high-voltage operation.
This research demonstrates that by precisely regulating the additive reactions in the electrolyte, the desired interfacial structure can be "designed" during the initial stage of battery operation. This not only improves the performance of lithium metal batteries under high voltage but also provides a reference interfacial strategy for constructing future systems with higher voltage and energy density.
From a practical application perspective, the additives in the PAFE electrolyte are readily available, the synthesis method is simple, and it is compatible with existing battery manufacturing processes, offering good prospects for engineering scale-up.
By precisely and effectively adjusting the “additive” — the small but crucial component — we can significantly enhance the stability of the large lithium metal battery system. This is the highlight of the PAFE system: optimizing microscopic structures to drive a leap in macroscopic performance, laying a solid foundation for the development of high energy density energy storage devices.
This achievement has been published in National Science Review. Original article link: https://doi.org/10.1093/nsr/nwaf182