Role of impurity phases present in orthorhombic-Li2MnSiO4 towards the Li-reactivity and storage as LIB cathode

Abstract The present study includes the synthesis of pure/impure orthorhombic phase of Li2MnSiO4 (LMS) and investigates the role of impurities towards Li-reactivity, thereby the Li-storage. The pure phase formation is confirmed by Rietveld refinement, followed by other characterizations like TGA, XPS, HR-TEM, and FTIR. EPR and XPS confirm the presence of a single (Mn+2) and the mixed oxidation state of Mn (Mn+2/Mn+3/Mn+4) in the synthesized samples. Results show that two different impurities, i.e., MnO2 and Li2SiO3, play different roles in affecting the Li-storage properties of pure LMS. The total conductivity of the LM-LMS sample (having the impurities of Li2SiO3 and MnO2) increases to 2.920 × 10-6 (±0.001), which is approximately ten times that of pure LMS (P-LMS). Furthermore, lithium-ion diffusivity is also affected by the presence of these impurities. The highest diffusion coefficient of 1.192 × 10-13 cm2 S-1 is also observed for the impure LM-LMS sample. The higher conductivity and diffusion of Li-ion in LM-LMS led to the highest Li-reactivity and delivers an initial discharge capacity of 187(±5) mAhg−1, which is almost 43% higher than that of L-LMS (LMS with Li2SiO3 impurity only), i.e.,106(±5) and 58% of P-LMS (78 ± 5) when cycled at the 10 mAg−1.