Polymer Composite Electrolytes and Their Interfacial Engineering for Lithium Batteries

Although solid-state materials are growing attention for their application in energy storage devices, poor electrochemical properties including low ionic conductivity, high interfacial resistance, limited transference number and low cycle life are among major challenges to commercialize such electrochemical systems. Owing to compelling physicochemical and structural properties, in recent years two-dimensional (2D) materials have emerged as promising candidates to address the challenges in lithium-based batteries (LIBs). A comprehensive overview of the role and potentials of 2D materials to overcome the slow kinetics and limited electrochemical properties of the Li batteries is discussed. Part of this research was focused in utilizing phosphorene 2D material as an electrolyte additive and understanding the Li+ ion conduction mechanism in this composite electrolyte. Here, we report a novel quasi-solid Li+ ion conductive nanocomposite polymer electrolyte containing black phosphorous (BP) nanosheets. The developed electrolyte was successfully cycled against Li metal (over 550 h cycling) at 1 mA.cm-2 at room temperature. The cycling overpotential dropped by 75% in comparison to BP-free polymer composite electrolyte indicating lower interfacial resistance at the electrode/electrolyte interfaces. This study revealed that the coordination number of Li+ ions around TFSI- pairs and ethylene oxide (EO) chains decreases at the Li metal/electrolyte interface, which facilitates the Li+ transport through the polymer host. In addition, interfacial engineered electrode/electrolyte design was introduced to address slow Li+ ion transport an undesired degradation reaction at the electrode/self-standing polymer electrolyte interfaces. This work represents an in-situ UV crosslinked integrated network of electrolyte and active electrode materials with controlled interfacial resistance and voltage polarizations. This method was shown to provide a uniform morphology of composite polymer electrolyte with a low thickness of 20-40 um. The interfacial engineered self-standing polymer batteries decreased the interfacial resistance as high as seven folds compared to conventional self-standing polymer batteries. This modification has led to promising cycling results and provided 70 % capacity retention over 100 cycles at high current densities of 170 mA.g-1. This work offers novel methods to tune the bulk and interfacial ionic conductivity of polymer electrolytes that may lead to a new generation of lithium polymer batteries with high ionic conduction kinetics and stable long-life cycling

Elevated-Temperature 3D Printing of Hybrid Solid-State Electrolyte for Li-Ion Batteries

While 3D printing of rechargeable batteries has received immense interest in advancing the next generation of 3D energy storage devices, challenges with the 3D printing of electrolytes still remain. Additional processing steps such as solvent evaporation were required for earlier studies of electrolyte fabrication, which hindered the simultaneous production of electrode and electrolyte in an all-3D-printed battery. Here, a novel method is demonstrated to fabricate hybrid solid-state electrolytes using an elevated-temperature direct ink writing technique without any additional processing steps. The hybrid solid-state electrolyte consists of solid poly(vinylidene fluoride-hexafluoropropylene) matrices and a Li+-conducting ionic-liquid electrolyte. The ink is modified by adding nanosized ceramic fillers to achieve the desired rheological properties. The ionic conductivity of the inks is 0.78 × 10 −3 S cm−1. Interestingly, a continuous, thin, and dense layer is discovered to form between the porous electrolyte layer and the electrode, which effectively reduces the interfacial resistance of the solid-state battery. Compared to the traditional methods of solid-state battery assembly, the directly printed electrolyte helps to achieve higher capacities and a better rate performance. The direct fabrication of electrolyte from printable inks at an elevated temperature will shed new light on the design of all-3D-printed batteries for next-generation electronic devices