Electrophoretic Deposition of Polyethylene Oxide-Based Gel-Polymer Electrolyte for 3D Lithium-Ion Batteries

Abstract

Despite the advances made in lithium-ion batteries (LIBs) over the last few decades, improved energy and power density is still required for portable devices, transit, and stationary applications [1-3]. Along with developing new materials, optimizing the shape of the battery electrodes is critical for improving the battery performance since the structure of these electrodes has a large impact on ion movement and reaction kinetics. The appeal of 3D structured batteries comes from certain operating features that are not available with conventional 2D geometries. One important feature is the ability to increase areal capacity (mAh cm−2) within a given footprint area of the electrode .Up to today, various methods were employed to coat the foam-type 3D electrodes with polymer or solid-state electrolytes: spin coating, layer-by-layer, and drop coating. Nonetheless, only a number of full-cell operation cases were disclosed, which led to the conclusion that, despite many attempts, drawbacks still exist in solving the homogeneous coating problem of polymer electrolytes.In this work, we report on the simple and facile coating process of polymer electrolyte on the intricate 3D structured NiO@Ni foam anode with the electrophoretic technique. To the best of our knowledge, it was not yet reported in the literature. The conformally coated polymer layer is proven to be very thin and homogeneous without any defects. The NiO@Ni foam/PEO configuration without the use of a commercial separator displayed stable cyclability up to 100 cycles with capacity retention of 88% and coulombic efficiency of 99%. The results are very promising for solving the problem of integrating polymer electrolytes onto any 3D structured anodes.In summary, a facile and simple electrophoretic technique was employed to conformally coat PEO gel-polymer electrolyte onto foam-type NiO/Ni anode for LIBs for the first time. Two electrodes of NiO/Ni foam as a working electrode and Pt metal as a counter electrode were used for the EPD process. Where the PEO solution acted as an electrolyte and, in the end, formed on the NiO/Ni foam surface. Through investigating various layers of PEO, it was concluded that the method allowed obtaining homogeneous thin films of around 2.66 μm for optimal 10 layers, which were free of cracks and defects. The electrochemical performance of the gel-polymer electrolyte PEO with commercially available liquid electrolyte 1M LiPF6 electrolyte solution in EC/EMC/DC was comparable to the traditional separator when used without it in a half-cell with lithium. The cycling stability results displayed an outstanding performance for the PEO electrolyte, delivering a capacity of 406 mAh g-1 at a 0.1 C rate after the 100th cycle. The stability of the formed PEO on the surface of the anode was demonstrated by FTIR analysis after 100 cycles. The stated simple approach allowed a cell operation at room temperature without a commercial separator, which is an excellent result for further developing high-energy-density full 3D batteries.