Electrode Materials Based on Carbon and Metal-Organic Framework Structures with Built-In Chemically Active and Functional Elements (Review)

Currently, the maximum specific energy capacity of 260 W h/kg has been achieved in lithium chemical power sources (CCSs), while in capacitors, it is 5–10 W h/kg. Traditional thick-film technology for the production of CCS and capacitor structures has not provided the necessary dynamics of growth in the specific energy capacity of CCS and supercapacity capacitor structures for more than 10 years. There is also a tendency to reduce significantly the specific energy capacity in order to improve the level of safety and long-term operation [1–9]. At the same time, there are reports of higher results in specific energy capacity. However, this is usually associated with a simultaneous decrease in the number of cycles or operational safety. A promising direction for achieving a specific energy capacity of current sources of more than 300 W h/kg is the creation of electrode materials in the form of a carbon matrix with a high specific surface area, into which a chemically active material is embedded. Carbon materials (graphite, amorphous carbon, metal-organic framework structures (MOFs)) currently occupy a dominant position as electrode materials [10–14]. In the paper, we present an overview of various types of carbon matrices with a high specific surface area and the technology of filling them with chemically active and auxiliary materials. The primary attention is paid to promising matrices based on metal-organic frameworks and commercially available rolled carbon materials such as Busofit. Their structural features are considered, and a classification is presented. The main methods and approaches to the synthesis of both the MOFs themselves and composite materials based on them are considered. As one of the options for changing the properties of MOFs and composite materials based on them, an approach based on doping MOFs with a ZIF-67 structure with another metal is presented. In particular, a scientific team of authors has implemented the synthesis of cobalt MOFs, in which Co is partially replaced by manganese at the synthesis stage. Besides, a simple synthesis technique by coprecipitation in an aqueous solution, but modified by ultrasonic exposure, which reduces the duration of synthesis, is used. Electrochemical studies show that the specific electrochemical capacity of electrodes from pyrolyzed MOFs with partial substitution of cobalt with manganese is significantly higher than that of materials without manganese. At an increase in the manganese content in MOFs, both the specific capacity and the energy density increase. Doping MOFs with Mn allows for a significant improvement (from 100 to 298 F g–1 at a current density of 0.25 A g–1) in the electrochemical characteristics of electrode materials for hybrid supercapacitors based on them. The results obtained by the authors indicate that the substitution of cobalt with manganese is an effective way to improve the electrochemical characteristics of MOFs.