Synthesis and Characterization of Transition Metal Doped Lithium Composites for Application in Lithium Ion Based Batteries

The research aims to enhance the physicochemical and electrochemical properties of cathode materials for application in lithium-ion batteries, specifically Li₂TMSiO₄ (TM=Transitions metals) silicates. These materials have high theoretical capacity, but most often suffer from poor conductivity. To improve their performance, methods like particle size reduction, coating, and ion doping were being employed. Among different transition metals-based silicates, Li₂MnSiO₄ is of particular interest, but often faces issues with cycling performance due to low conductivity and stability. Further, the structural characterization of the different lithium composites had shown that Li₂CoSiO₄ exhibited high crystallinity with an orthorhombic crystal structure. Therefore, trivalent ions doping and anionic doping were carried out to enhance conductivity and electrochemical properties of Li₂MnSiO₄ and Li₂CoSiO₄silicates. The resulting silicates i.e. LiMnAlSiO₄ and LiMnCoAlSiO₄ displayed patterns similar to Li₂MnSiO₄, indicating a mixture of polymorphs. The addition of dopants did not only alter the structure but significantly improves the properties of the silicates. In terms of electrical characterization, cyclic voltammetry measurements showed different potential values for the composites, where Li₂CoSiO₄ displayed cathodic and anodic potentials with slight variations and a decrease in cathodic current after 10 cycles. LiMnAlSiO₄ showed stable potentials but a 28% drop in current, while LiMnCoAlSiO₄ had minimal changes in potentials and currents. Moreover, the electrochemical impedance spectroscopy demonstrated that LiMnAlSiO₄ and LiMnCoAlSiO₄ had undergone least charge transfer resistance compared to Li₂CoSiO₄, indicating improved Li⁺ ion diffusion. Based on these results, LiMnCoAlSiO₄ showed better stability, resistance and conductivity compared to LiMnAlSiO₄ and Li₂CoSiO₄. Further investigations will be carried out to explore the thermal stability of the composites beyond 400°C and to evaluate the potential of LiMnCoAlSiO₄ as an electrode material. Overall, the study demonstrated the ortho-rhombic structures of transition metal-doped Li₃SiO₄ composites and highlighted the superior performance of the quaternary composite LiMnCoAlSiO₄ in terms of electrical conductivity, capacitance, and structural stability.