A low-cost pre-metallation strategy based on inorganic sacrificial salts that decompose on the first charge.

In this work we report the use of the aprotic ionic liquid (AIL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr₁₄TFSI) and the protic ionic liquid (PIL) 1-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr_H4TFSI) in view of the realization of potassium ion batteries. Physicochemical characterization of electrolytes reveals features comparable to those obtained for lithium and sodium ion technologies. Electrochemical performance is evaluated in combination with olive pits derived hard carbon electrodes with and without a film-forming additive at room temperature and at 60°C. Similar to our previous study, the use of Pyr_H4TFSI is not applicable due to the lack of electrochemical stability below 2 V vs. K⁺/K, while reversible K⁺ insertion/deinsertion is demonstrated for Pyr₁₄TFSI. Electrochemical impedance spectroscopy and post-mortem analysis reveal an unstable formation of the solid electrolyte interphase within the HC electrode.

Herein we report a series of lithium ion capacitors (LICs) with extraordinary energy-to-power ratios based on olive pit recycled carbons and supported on graphene as a conducting matrix. LICs typically present limited energy densities at high power densities due to the sluggish kinetics of the battery-type electrode. To circumvent this limitation, the hard carbon (HC) was embedded in a reduced graphene oxide (rGO) matrix. The addition of rGO into the negative electrode not only forms a 3D interpenetrating carbon network but also wraps HC particles, facilitating ion diffusion and enhancing the electronic conductivity notably at high power densities. Electrochemical impedance spectroscopy (EIS) analysis reveals that charge-transfer resistance at electrode-electrolyte interphase and the charge-transport resistance within the electrode are considerably lower in the presence of rGO. In addition, charge-transport resistance remains constant upon cycling even at increasing current densities. Capacity gain at high current densities, owing to the reduction of the electrode resistance, triggers the overall LIC performance, allowing for the assembly of an ultrafast LIC delivering up to 200 Wh kg⁻¹_AM at low power rates and 100 Wh kg⁻¹_AM at a power of 10 kW kg⁻¹_AM.

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.