Polymeric Aromatic Amines As Promising Cathode Materials for Dual-Ion Batteries
Authors: Obrezkov Filipp A. , Ramezankhani Vahid , Troshin Pavel A. , Stevenson Keith J. 
Published: May 2020

The rapidly growing demand for portable electronics and electric vehicles together with the increasing role of renewable energy sources dictate new requirements for the performance characteristics and environmental friendliness of electrochemical energy storage devices for mobile and stationary applications. Despite the lithium-ion batteries have occupied a dominant position on the market of high-capacity and high-power energy storage devices for decades, their capabilities seem limited to meet the current market trends. The reason for this is a potential depletion of lithium reserves, which will lead to higher prices for lithium-containing electrode materials. The difficulties with recycling also make a significant contribution to the overall set of problems associated with massive utilization of Li+ intercalation compounds.
In the view of the aforementioned reasons, there is a growing interest in the development of post-lithium energy storage devices, including Na+-, K+-ion, dual-ion, redox-flow and other battery technologies. In this regard, dual-ion systems deserve special attention due to a favorable combination of their performance characteristics such as high charge/discharge current rates, moderate specific capacities of electrode materials, high operation voltages and environmental friendliness.
Dual-carbon batteries are the most extensively studied due to the availability and low cost of electrode materials. However, their serious drawbacks such as high cutoff voltage (above 5 V)[1,2] leading to the rapid electrolyte degradation, and the low specific capacity on the cathode side (<110 mAh/g)[2] encourage researchers for the development of alternative cathode materials.
Polymeric aromatic amines represent very promising replacement for carbon-based cathode materials in dual-ion batteries because of their optimal discharge potentials (3—4 V), the ability to operate at high charge/discharge current rates (up to 300 C)[3], impressive specific capacities in lithium cells (up to 185 mAh/g)[4] and compatibility with potassium and sodium systems and even aqueous electrolytes.
Herein, we report a comprehensive study of a large group of novel polymeric materials based on aromatic amines with high theoretical specific capacities (>160 mAh/g). In particular, we designed polymeric cathodes, which can operate efficiently at high current rates (100C) while demonstrating still high specific capacities (84 mAh/g).[5] Since dual-ion batteries involve the usage of large amounts of electrolyte salt, the development of cheaper and more concentrated electrolyte formulations is of crucial importance. In that context, the application of concentrated solution of KPF6 in diglyme[6] as an electrolyte allowed us to assemble potassium batteries with the cathode energy densities of up to 593 Wh/kg.[7] To the best of our knowledge, this is the highest value yet reported for cathodes used in potassium batteries.
Considering the outstanding power densities demonstrated for polyamine-based cathodes, their further molecular design and optimization coupled with the development of improved electrolytes are expected to deliver cheap and eco-friendly ultrafast batteries, which are of special interest in the view of multiple applications including grid-scale energy storage and especially “electric push” devices emerging at the interface between the metal-ion batteries and supercapacitors.[8]

This study was financially supported by the Russian Foundation for Basic Research, project 19-33-90233.

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