Charge Separation Nanoclay in Gel Polymer Electrolytes: Empowering Sustainable Anion Storage

The dual-ion battery (DIB) represents a significant advancement in sustainable energy storage. It employs intercalation-type graphite as a cathode, enabling anion penetration into interlayers during high-potential charges, resulting in an elevated operational voltage exceeding 5V. DIBs distinguish themselves from conventional lithium-ion batteries by moving away from transition metal oxide cathodes, like Lithium cobalt oxide (LCO), offering a more eco-friendly and cost-effective alternative. However, DIBs face challenges due to high operating voltages causing electrolyte decomposition, which leads to a passivation layer on the electrodes, increased resistance, and potential performance degradation.<br/><br/>To tackle the issue of electrolyte decomposition, researchers are exploring high-concentration electrolytes (HCE) enriched with lithium salts. These electrolytes predominantly contain contact ion pairs (CIP) and aggregates (AGG), enhancing electrochemical stability. Notable efforts have been made using a 4.0 M LiFSI in TMS, but increased salt concentrations lead to higher viscosity, reducing ionic conductivity.<br/><br/>Another approach is incorporating gel polymer electrolyte (GPE), known for its high voltage stability, moderate ionic conductivity, and safety attributes. However, as ionic conductivity increases, mechanical integrity decreases. To address this, functional groups are added to the polymer matrix, reducing anion-solvent interactions and promoting a stable anode interface. Nevertheless, a trade-off remains between physical rigidity and ionic conductivity.<br/><br/>Additives are essential to enhance GPE mechanical stability and modify ion solvation. These additives include carbon-based conductive fillers, ceramics, polymers, and nanoparticles, improving ion conduction and cell performance. Facilitating anion mobility and integration is crucial for optimizing dual-ion battery performance, necessitating additives that dynamically interact with anions, promote a stable surface interface, and align with sustainability standards.<br/><br/>This study explores GPEs infused with surface-charged nano clay as an innovative additive for DIBs. Nanoclay, due to its abundant availability and non-toxic nature, enhances GPE's mechanical resilience and influences cation and anion solvation structures. The investigation involves a comparative analysis of three nano clay variants with distinct characteristics. Zeta potential, nuclear magnetic resonance (NMR), molecular dynamics (MD) simulations, and density functional theory (DFT) calculations confirm the findings.<br/><br/>Halloysite (HS), with its tubular morphology, stands out as a superior candidate. It fosters a slender, homogeneous cathode electrolyte interface (CEI) with reduced anion-solvent interactions and fewer salt decomposition products. The tubular structure of HS improves anion transport pathways, optimizing DIB operation. Consequently, a DIB full-cell incorporating HS-GPE exhibits impressive rate capability, exceeding 60 mAh/g at 50 C-rate, and remarkable stability, sustaining over 5000 cycles at 20 C-rate.