Endowing CuTCNQ with a new role: a high-capacity cathode for K-ion batteries

Abstract

Herein, copper-tetracyanoquinodimethane (CuTCNQ) with phase-I kinetics character has been proposed as an effective cathode for potassium-ion batteries. In a voltage range of 2-4.1 V (vs. K+/K), both cuprous cations (Cu+) and organic anions (TCNQ-) are electrochemically active, and they render a three-electron redox mechanism, thereby enabling CuTCNQ to yield a high specific discharge capacity of 244 mA h g-1. Even after 50 cycles, the discharge capacity of 170 mA h g-1 is retained at 50 mA g-1. In addition, when the current density is elevated to 1000 mA g-1, the discharge capacity is still maintained at 125 mA h g-1. These test data are among the best results reported for high-potential cathodes of potassium-ion batteries.

Sulfonylamide‐Based Ionic Liquids for High‐Voltage Potassium‐Ion Batteries with Honeycomb Layered Cathode Oxides

“…It is evident that few high‐voltage cathodes exist (exhibiting average working voltages of close to or beyond 4 V); Prussian organic moieties and polyanionic compounds such as KVOPO 4 , KVP 2 O 7 , KVPO 4 F, amongst others dominating as high‐voltage cathode candidates. Potassium‐based oxides tend to show low average voltage; however, this prevailing notion was recently obliterated by the design of tellurium‐doped K 2/3 Ni 2/3 Te 1/3 O 2 (or equivalently as K 2 Ni 2 TeO 6 , for simplicity) and K 2/3 Ni 1/3 Co 1/3 Te 1/3 O 2 (K 2 NiCoTeO 6 ) as high‐voltage layered cathode materials (Figure a) . Despite the alluring prospects of using these high‐voltage cathode materials to develop a high‐voltage battery system, instability of organic electrolytes at high‐voltage operation coupled with the high reactivity of potassium metal anode continues to cast doubt on the safety of electrolytes based on organic solvents …”

“…To assess the phase stability of KTFSA-based ionic liquids, differential scanning calorimetry (DSC) measurements were conducted (as shown in Figures S1a and S1c). An endothermic peak manifesting the melting point (T m ) could be clearly seen in Pyr 13 TFSA. T m shifts to lower temperatures with the addition of KTFSA, and another peak emerges, suggesting that the interaction between the K + and TFSAfrom Pyr 13 TFSA alters the crystal structure of the ionic liquid to a metastable state.…”

“…Generally, the ionic conductivity of ionic liquids can be correlated to their viscosity, as dictated by the Walden rule. [24] Arrhenius plots of the ionic conductivity of KTFSA/Pyr 13…”

“…Described herein are the physicochemical and electrochemical properties of ionic liquids based on KTFSA salt in Pyr 13 TFSA, to address the fundamental aspects about the functionalities of related ionic liquids that we identify. It is revealed that the redox potential for potassium dissolution / deposition using KTFSA ionic liquids is lower than for their lithium and sodium counterparts, resulting in a wider electrochemical window (around 6.0 V).…”

Advancements and Challenges in Potassium Ion Batteries: A Comprehensive Review

“…The designing of high‐voltage KIBs are considered to be a challenge due to the limited availability of high‐voltage cathodes and high‐voltage stable electrolytes. In recent years, some cathode materials (K 2/3 Ni 2/3 Te 1/3 O 2 , K 2/3 Ni 1/3 Co 1/3 Te 1/3 O 2 ) have been explored in this aspect . Hence the main challenge is to develop electrolyte which can withstand at high voltages.…”