Development of a Li-Ion Capacitor Pouch Cell Prototype by Means of a Low-Cost, Air-Stable, Solution Processable Fabrication Method

Due to the dual advantage of capacitive and faradaic charge storage mechanisms, Li-ion capacitors (LICs) are regarded as a promising energy storage technology for many high-power applications. However, high cost and intricacy of indispensable pre-lithiation step in LIC fabrication are the major stumbling block against its widespread commercial interest. In this regard, operando pre-lithiation through incorporating lithium containing sacrificial salt in the positive electrode holds high potential to solve this issue. Herein, we present an industrially compatible fabrication method based on a solution processable positive electrode consisting of an activated carbon mixed with a low-cost, air-stable dilithium squarate as sacrificial salt. Through careful optimization of electrode design, laboratory scale cells are upscaled to pouch cell prototypes. Fabricated LIC pouch cells deliver high specific energy (i.e. max. 58 Wh kg −1 AM ) and power (i.e. max. 8190 W kg −1 AM ) with respect to active electrode mass. Moreover, cycle life and floating tests performed at room temperature show capacitance retention of 83% after 80000 charge-discharge cycles and 100% retention after 1000 floating hours at 3.8 V. However, the accelerated aging tests at 70 °C induce fast device failure. Post-mortem analyses reveal different ageing mechanisms for cycled and floated LIC pouch cells.