A composite electrolyte with homogeneous heat and ion transfer for high-safety solid-state lithium batteries

Abstract

Realizing homogeneous heat and ion transfer in solid-state electrolytes is critical but remains challenging. Herein, we revealed that localized temperature hotspots in polyvinylidene fluoride electrolyte trigger side reactions and Li dendrite growth. We rationally designed a composite electrolyte by coupling modified boron nitride nanosheets (M-BNNS), enabling higher in-plane (0.735 W m⁻¹ K⁻¹) and out-of-plane (0.173 W m⁻¹ K⁻¹) thermal conductivities for temperature homogenization. Moreover, the grafted functional hydroxyl (–OH) and N–H groups on M-BNNS can regulate Li⁺ flux through hydrogen-bonding-induced ligand adsorption, delivering a high ionic conductivity (6.43 × 10⁻⁴ S cm⁻¹), while tailoring the Li⁺ coordination to generate inorganic-rich interphases. Consequently, a record critical current density of 4.2 mA cm⁻² was achieved. The Li‖LiNi_0.8Co_0.1Mn_0.1O₂ cells exhibit robust cyclability under high-rate (1000 cycles at 5C), high-loading cathodes (15 mg cm⁻²), and high-temperature (550 cycles at 60 °C) conditions. The four-layer pouch cells maintain thermal stability under abusive overcharging (10 V) conditions. This work provides a promising strategy for designing intrinsically safe electrolytes for solid-state batteries.