Direct Ink Printing of PVdF Composite Polymer Electrolytes with Aligned BN Nanosheets for Lithium-Metal Batteries

The use of polymer electrolytes is of great interest for lithium-metal batteries (LMBs) due to their stability with lithium metal. However, the low thermal conductivity of polymer electrolytes poses a significant barrier to minimizing the formation of local hot spots during electrochemical reactions in lithium batteries that may lead to dendritic plating of Li or thermal runaway events. Electrolyte nanocomposites with proper distribution of thermally conductive nanomaterials offer an opportunity to address this shortcoming. Utilizing a custom-designed direct ink writing (DIW) process, we show that highly aligned boron nitride (BN) nanosheets can be embedded in poly(vinylidene fluoride-hexafluoropropylene) (PVdF) polymer composite electrolytes (CPE-BN), enabling novel architectural designs for safe Li-metal batteries. It is observed that the CPE-BN electrolytes possess a 400% increase in their in-plane thermal conductivity, which enables faster heat distribution in the CPE-BN electrolyte compared to the polymer electrolytes without BN nanosheets. The CPE-BN containing symmetric lithium cell exhibits stable Li plating/stripping for over 2000 cycles without short-circuiting due to the suppression of dendritic lithium. The lithium-ion half-cells made with the CPE-BN show stable cycling performance at 1C charge-discharge rate for 250 cycles with 90% capacity retention. This reported DIW-printed PVdF composite polymer electrolyte could be used as a model for developing new architectures for other electrolytes or electrodes, thus enabling new chemistry and improved performances in energy-storage devices.