Original Contributions to the Electrochemistry and Materials Science of Sodium-Ion Battery Electrodes Fabricated from Nigerian Natural Graphite and Biowaste Carbon Sources

Sodium-ion batteries represent a promising next-generation energy storage technology suitable for stationary applications in Nigeria's expanding renewable energy sector, and developing electrode materials from locally available natural graphite and agricultural biowaste carbon sources could establish a domestic battery materials value chain. This dissertation makes original contributions to the electrochemistry and materials science of hard carbon and modified natural graphite negative electrode materials for sodium-ion batteries, derived from Nigerian natural graphite deposits from Kogi State and pyrolysis of palm kernel shells and sugarcane bagasse from South East and South West Nigeria. Natural graphite was characterised by X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopy, and subjected to chemical and thermal treatments to create expanded graphite and reduced graphene oxide variants. Hard carbon was synthesised from biomass precursors at carbonisation temperatures of 700 to 1200 degrees Celsius and characterised by the same suite of structural methods. Sodium-ion electrochemical performance was evaluated in half-cell and full-cell configurations using galvanostatic charge-discharge, cyclic voltammetry, and electrochemical impedance spectroscopy. Sodium storage mechanisms were elucidated by operando synchrotron X-ray diffraction and pair distribution function analysis. Results show that hard carbon derived from palm kernel shells carbonised at 1000 degrees Celsius delivers reversible capacity of 312 milliampere hours per gram and 89 percent capacity retention over 500 cycles. Operando analysis reveals a two-stage sodium storage mechanism combining plateau adsorption in nanopores and sloping region intercalation. Full cell demonstrations with Prussian blue analogue cathodes confirm practical performance. The dissertation establishes original electrode chemistry knowledge for a Nigerian sodium-ion battery materials research programme. Keywords: sodium-ion batteries, hard carbon, natural graphite, electrochemistry, energy storage