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Sodium (Na) is a cheaper alternative to lithium (Li), hence, the interest for creating materials for sodium-ion batteries grew drastically over the recent years, including materials for anode – a negatively charged electrode, which is opposite to cathode – a positively charged electrode. During charging the battery, sodium ions are moving from cathode to anode through the electrolytic fluid (current-carrying conductor), and when the battery is discharging – from anode to cathode.
The scientists attempted to create such material from molybdenum di-sulphide, which is used as motor lubricant, and graphene – two-dimensional crystal consisting of a single layer of carbons assembled in a hexagonal latitude. The task was to set certain characteristics (capacity, stability, running time) in the synthesised material by way of precise substitution to allow efficient reaction between the sodium ions and the new materials.
“We can remove atoms of sulphur or molybdenum from the material, and we will have the so-called “vacancies”. We are filling these vacancies with atoms of other chemical elements, e.g., nitrogen, nickel, selenium and cobalt. Any such action will result in changing the reaction rate and the electrical conductivity of the received material affecting its functional properties”, the Russian Scientific Foundation is citing Anastasia Fedorenko, the Candidate of Physical and Mathematical Sciences.
The capacity of amorphous carbon materials used as anode in sodium-ion batteries normally does not exceed 300 mA-h/g, and such materials lose about 20% of their capacity after 1,000 cycles of battery operation. The experiments showed that the energy capacity of the new material constitutes 320 mA-h/g, and its properties persist during 1,200 cycles of the battery charge/discharge. Hence, the new material most likely will find commercial application.