Speaker
Description
Sodium-ion batteries (SIBs) offer an efficient energy storage solution for large-scale applications. Na4Fe3(PO4)2P2O7 (NFPP) is recognized as a promising candidate for electrode material in SIBs: it is able to intercalate reversibly up to 3 moles of Na ions. The main disadvantage of NFPP is its very low electronic conductivity, which hinders the Na+ mobility. To increase NFPP conductivity, a conventional strategy involves its coating with various carbonaceous materials in an amount of about 10-15 wt. %. However, the presence of a large amount of electrochemically inactive carbonaceous additives in the electrode composition is a major contributor to the lower overall energy density of the battery cells, which is one of the most important characteristics for practical application.
To overcome the reduced energy density, the purpose of the present contribution is to decorate NFPP with carbon additives with a minimal amount of 1 wt. %: carbon black (CB) and reduced graphene oxide (rGO). The composites NFPP/CB and NFPP/rGO have been prepared by a dry-coating method. The galvanostatic/potentiostatic tests have been performed at 20 and 40 C in Na half-cells. Electrochemical performance has been evaluated in terms of capacity and cycling stability, while the origin of the kinetic response is studied by electrochemical impedance spectroscopy (EIS). The contributions of the Faradaic and capacitive reactions in NFPP/CB and NFPP/rGO have been compared. The effect of the carbon additive on the Na-ion diffusion has been studied by three electrochemical methods: EIS, cyclic voltammetry (CV) and galvanostatic intermittent titration technique (GITT). The difference in the electrochemical behaviour of NFPP/CB and NFPP/rGO has been discussed based on the data for the electrolyte resistance (Re), electrolyte/electrode interfacial resistance (RSEI), and charge-transfer resistance (Rct). The results show a clear distinction in the role of the two types of carbon additives.
Keywords: Sodium-ion Batteries, Electrochemical Techniques, Sodium Diffusion Kinetics
Acknowledgement:
We acknowledge the project “Master” (KП-06-ДO02/3 dated 18.05.2023) and the infrastructure support of the contract “National Center of Excellence Mechatronics and Clean Technologies” (BG16RFPR002-1.014-0006) under “Research, Innovation and Digitization for Smart Transformation” program 2021-2027.