Novel Solvent-free Mg-ion Conducting Solid State Polymer Electrolyte
- Chemtronergy, LLC
- University of Akron
Demands for energy storage devices (i.e. batteries) have been increased significantly in recent years, particularly for mobile devices (i.e. cellphones, laptops, etc.), electric vehicles, and renewable energy harvesting systems requiring high quality and sustainable power storage systems. To better serve a wide range of applications, these devices should possess high energy densities, wide operation temperatures, high safety and operation durability, and be economically affordable. Lithium-ion based batteries (LIB) have demonstrated practical energy densities of 100~300 Wh/kg. However, the batteries face some increasing challenges, ranging from high costs due to availability of lithium sources to safety concerns. Redox flow batteries have shown much promise for grid energy storage applications, but their low energy density makes them less attractive for long duration energy storage. Consequently, other metal ion batteries are gradually gaining increasing interests as potential candidates for energy storage devices. A magnesium-based rechargeable battery technology is a viable ‘environmentally friendly, non-toxic’ alternative to the state-of-the-art Li-ion based battery technologies from the standpoint of high volumetric capacity, low costs and safety. While substantial efforts have been dedicated to the development of the magnesium-based battery technology in the past two decades, the battery technologies face challenges of a limited ionic conductivity and electrochemical oxidative stability of the electrolytes, thus resulting in low power/energy density. To overcome the aforementioned challenges, under this SBIR Phase I project, Chemtronergy teaming with the University of Akron has developed a unique Mg-ion conducting solvent-free solid-state polymer electrolyte (SPE) composite membrane with enhanced conductivity and stability for advanced energy storage applications. Significant progresses were made in Phase I to construct and evaluate both the binary and ternary systems consisting of UV-curable Poly(ethylene glycol) diacrylate (PEGDA), Mg(TFSI)2 salt, and without /or with a plasticizer, respectively. Studies of the PEGDA molecular weight effects on the SPE ionic conductivity showed that corresponding ionic conductivity increased with the PEGDA molecular weight. Due to the availability and costs of the polymer, the PEGDA with a molecular weight of 700 (PEGDA-700) was chosen for the construction of SPE for this project. Significant development efforts were also made evaluate the effects of the Mg salt, and the types of plasticizers (succinonitrile – SCN, and Ethylene carbonate – EC) on the SPE membranes properties, including the crystal melting temperature, glass transition temperature, and conductivity at various temperatures. Optimum compositions were discovered for maximum conductivity. The SPE properties were further enhanced through an addition of nano-ceramic powders. The study of the ceramic filler effect on the composite SPE at temperatures ranging from 25ºC to 90ºC demonstrated superior conductivities as high as 9.1x10-4 and 1.24x10-3 S/cm at 30ºC and 40ºC, respectively, which were nearly 1.6 times higher than that of baseline SPE membrane without nano ceramic addition. The tensile strength studies on the corresponding composite SPE membranes showed that the SPE mechanical strength was not compromised with the ceramic addition. Small-scale membrane fabrication process was developed for manufacturing composite SPE membranes consisting of the ternary PEGDA/SCN/Mg(TFSI)2 and nano ceramic powders for scaling up applications. UV photopolymerization was also incorporated properly into the tape-casting/curing process, resulting in the fabrication of small scale flexible and sizable SPE membranes successfully. The electrochemical performances of the PEGDA/SCN/Mg(TFSI)2 and PEGDA/EC/Mg(TFSI)2 membranes were conducted through the linear sweep voltammetry (LSV) and cyclic voltammetry (CV) experiments on both half-cell and symmetric-cell configurations. LSV experiments showed that the SPE membrane was stable up to 2.4 V versus Mg/Mg+2; however, the current responses in CV measurement showed very low current density in the tens of µA/cm2 range, indicating that the potential energy barrier must be very high for Mg ions stripping to occur from the Mg metal electrode. This poses a great challenge for the intended solid-state Mg ion battery applications, requiring an alternative solution to mitigate the high potential energy barrier.
- Research Organization:
- CHEMTRONERGY, LLC
- Sponsoring Organization:
- USDOE Office of Science (SC), Engineering & Technology. Office of Small Business Innovation Research (SBIR) and Small Business Technology Transfer (STTR) Programs
- DOE Contract Number:
- SC0020479
- OSTI ID:
- 1860457
- Type / Phase:
- SBIR (Phase I)
- Report Number(s):
- DOE-CTG-20479
- Country of Publication:
- United States
- Language:
- English
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