Antioxidative Carbon Dot-Reinforced Polymer Electrolytes Enabling 4.8 V High-Voltage Solid-State Lithium Metal Batteries

Employing high-capacity cathodes such as lithium-rich layered oxides (LRLO) under high-voltage conditions represents an efficient strategy to boost battery capacity. However, this approach gives rise to critical challenges, including reactive oxygen species (ROS)-related side reactions, inadequate interfacial stability of the electrolyte, and compromised electrochemical stability. Herein, a multifunctional solid-state polymer electrolyte (denoted as SPE/BCCDs) is developed, featuring a robust cross-linked framework constructed via a synergistic approach integrating bacterial cellulose (BC) and antioxidative carbon dots (CDs). Through abundant intermolecular hydrogen-bonding interactions, the CDs are monodispersed within the BC polymer matrix to construct a continuous ion transport pathway while retaining exceptional radical-scavenging capabilities and a lithiophilic nature. As expected, the stabilization of the solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) layers leads to a marked enhancement in the stability of the LRLO cathode. Therefore, the obtained SPE/BCCDs possesses an ultrawide electrochemical window (4.97 V), an ultrahigh ionic conductivity (1.18 mS cm⁻¹), and a high Li⁺ transference number (0.42) at 25 °C. Consequently, the assembled Li||LRLO batteries maintain an exceptional capacity retention of 86.9% over 500 cycles even under a high charging voltage of 4.8 V. This proposed SPE/BCCDs clarifies the synergistic mechanism between ROS quenching and the ion transport matrix, offering novel insights into the design of high-voltage-tolerant polymer electrolytes.