Highly transparent sustainable biogel electrolyte based on cellulose acetate for application in electrochemical devices

In this study, an easy and low-cost production method for a cellulose acetate-based gel polymer containing lithium perchlorate and propylene carbonate is described, as well as the investigation of its properties for potential use as an electrolyte in electrochemical devices. Cellulose acetate, a biopolymer derived from natural matrix, is colourless and transparent, as confirmed by the UV-Vis spectroscopy, with 85 % transparency in visible spectrum. The gels were prepared and tested at different concentrations and proportions to optimise their properties. Thermogravimetry, XRD, and FTIR analyses revealed crucial characteristics, including a substantial 90 % mass loss between 150 and 250 °C, a semi-crystalline nature with complete salt dissociation within the polymer matrix, and a decrease in intensity at 1780 cm-1 with increasing Li+ ion concentration, suggesting an improvement in ionic conduction capacity. In terms of electrochemical performance, the gel containing 10 % by mass of cellulose acetate and 1.4 M of LiClO4 emerged as the most promising. It exhibited a conductivity of 2.3 × 10-4 S.cm-1 at 25 °C and 3.0 × 10-4 S.cm-1 at 80 °C. Additionally, it demonstrated an ideal shape of cyclic voltammetry curves and stability after 400 cycles, establishing its suitability as an electrolyte in electrochemical devices.

Polymer Competitive Solvation Reduced Propylene Carbonate Cointercalation in a Graphitic Anode

Polymer electrolytes have been studied as an alternative to organic liquid electrolytes but suffer from low ionic conductivity. Propylene carbonate (PC) proves to be an interesting solvent but is incompatible with graphitic anodes due to its cointercalation effect. In this work, adding poly(ethylene oxide) (PEO) into a PC-based electrolyte can alter the solvation structure as well as transform the solution into a polymer electrolyte with high ionic conductivity. By spectroscopic techniques and calculations, we demonstrate that PEO can compete with PC in solvating the Li⁺ ions, reducing the Li⁺-PC bond strength, and making it easier for PC to be desolvated. Due to the unique solvation structure, PC-cointercalation-induced graphite exfoliation is inhibited, and the reduction stability of the electrolyte is improved. This work will extend the applications of the PC-based electrolytes, deepen the understandings of the solvation structure, and spur designs of advanced electrolytes.

Investigations of Thermal Stability and Solid Electrolyte Interphase on Na2Ti3O7/C as a Non-carbonaceous Anode Material for Sodium Storage Using Non-flammable Ether-based Electrolyte

In order to become commercially viable, sodium-ion batteries need to deliver long cycle life with good capacity and energy density while still ensuring safety. Electrolyte plays a key role forming solid electrolyte interphase (SEI) layers at low potential, which affects the thermal stability and cycle life of the anode materials under consideration. In this study, an ether-based non-flammable electrolyte, 1 M NaBF₄ in tetraglyme, is tested for sodium storage using a non-carbonaceous anode material Na₂Ti₃O₇/C, and the results are compared with those obtained with the popularly used carbonate-based electrolyte, 1 M NaClO₄ in ethylene carbonate (EC) and propylene carbonate (PC) (v/v = 1:1). The Na₂Ti₃O₇/C versus Na cells using 1 M NaBF₄ in tetraglyme show a much higher first cycle Coulombic efficiency (73%) than those using 1 M NaClO₄ in EC/PC (33%). Thermal stability studies using differential scanning calorimetry (DSC) conclusively show that Na₂Ti₃O₇/C electrodes cycled with 1 M NaBF₄ in tetraglyme are more thermally stable than the one cycled with 1 M NaClO₄ in EC/PC. Further investigations on the formation of SEI layers were performed using attenuated total reflection-Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, and DSC studies. These studies unambiguously demonstrate that the SEI formed on Na₂Ti₃O₇/C using 1 M NaBF₄ in tetraglyme is not only less resistive but also more stable than the SEI formed using 1 M NaClO₄ in EC/PC.