Ambient-atmosphere processed flexible all-solid-state lithium-ion battery using flexible and robust hybrid solid electrolyte membrane

Hybrid solid electrolytes (HSEs) are contemplated as promising solutions for better safety and improved energy density of flexible Li-ion batteries (LIBs) due to their high thermal stability and electrochemical properties. In the present study, HSE membranes (HSEMs) were developed using Li_6.4La₃Zr_1.4Ta_0.6O₁₂(LLZTO) as an inorganic filler with Poly(vinylidene fluoride-co-hexafluoropropylene) PVDF-HFP as a polymer matrix in assistance of lithium salt (LiTFSI) to attain ultra-thin, robust, flexible and high-performance membrane. The optimized ultrathin and robust HSEM (∼20 µm) illustrate high ionic conductivity of 3.48 mScm⁻¹ (after surface activation with little amount of liquid electrolyte) at room temperature with high flexibility, high thermal stability (upto 340 °C), good electrochemical stability (∼4.8 V vs. Li) and mechanical strength. Multi-walled carbon nanotubes (MWCNTs) based self-subsistent composite electrodes (Lithium iron phosphate (LFP)/Lithium titanate (LTO) as anode) were prepared using a surface-engineered tape-casting method. Here, we report a groundbreaking strategy for fabricating flexible all-solid-state lithium-ion batteries (FASSLIB) using MWCNTs-based composite electrodes and highly conductive HSEM. This design exemplifies the potential of the FASSLIB concept by achieving exceptional electrochemical performance. The selection of these components prioritized low toxicity, manufacturability, and electrochemical compatibility to enable ambient assembly and achieve a desirable combination of flexibility, safety, efficient interfacial contacts, and superior chemo-mechanical stability during operation. Notably, the individual (LFP and LTO self-subsistent composite) electrodes demonstrate exceptional performance in half-cell configurations employing HSEM as a solid electrolyte cum separator. The LFP and LTO half-cells exhibited a remarkable discharge capacity of 135 ( ± 5) mAhg⁻¹ at 0.1 C rate, demonstrating exceptional stability. Capitalizing on the demonstrably excellent electrochemical performance of HSEMs, an innovative, mass-productive, and unique approach was employed to fabricate FASSLIBs under ambient conditions, exhibiting remarkable discharge capacity, ∼ 115 ( ± 5) mAhg⁻¹ at 1 C rate with 99 % Coulombic efficiency even after 100 charge-discharge cycles. This excellent electrochemical performance of FASSLIB is ascribed to high ionic conductivity, large lithium transference number, and reversible electrode/electrolyte interface. Remarkably, these FASSLIBs exhibit outstanding stability in air and humid environments, signifying their potential for real-world applications. The fabrication process is both straightforward and adaptable, allowing for large-scale production. This applies to creating the components and assembling the battery under normal atmospheric conditions. This work marks a significant advance toward safe, flexible, and efficient energy storage for modern technological applications.