Co-precipitation synthesis of pseudocapacitive λ-MnO₂ for 2D MXene (Ti₃C₂T_x) based asymmetric flexible supercapacitor

The rapid growth of wearable/portable electronics imposes a development of flexible, lightweight and highly efficient energy storage devices. In this work, we have synthesized λ-MnO₂ nanoplates through one step co-precipitation method and used for flexible asymmetric supercapacitor (SC). The structural, morphological and electrochemical properties of synthesized λ-MnO₂ were systematically investigated. The optical and electronic properties of λ-MnO₂ were studied using UV–vis spectroscopy and density functional theory (DFT) calculations. The pseudocapacitive λ-MnO₂ nanoplates-like electrode showed a maximum specific capacitance of 288.5 F g⁻¹ at the scan rate of 5 mV s⁻¹. To check the practicability, symmetric (λ-MnO₂//λ-MnO₂) as well as asymmetric (λ-MnO₂//AC and λ-MnO₂//Ti₃C₂T_x MXene) SCs were fabricated and their performances were compared. The asymmetric λ-MnO₂//Ti₃C₂T_x MXene SC demonstrated a maximum energy density of 15.5 Wh kg⁻¹ at the power density 1100 W kg⁻¹ along with 86.3 % of capacitive retention after 5000 cycles. Besides, to confirm the suitability of these electrodes for flexible energy storage, a flexible λ-MnO₂//Ti₃C₂T_x asymmetric SC was fabricated using PVA: Na₂SO₄ gel polymer electrolyte that operated in the potential window of 2 V and supplies high areal energy density of 39.9 μWh cm⁻² at a power density of 8586 μW cm⁻². Therefore, the λ-MnO₂ prepared with a simple and scalable co-precipitation method may play a promising role in flexible energy storage.