Impact of Long-term cycling (>7500 cycles) on laminar Li₄Ti₅O₁₂ (LTO) Anode for its Application in Sodium-ion Batteries.

Sodium-ion batteries (SIBs) have emerged as a promising alternative to lithium-ion batteries (LIBs) for large-scale energy storage applications, primarily due to the abundance of sodium resources and their electrochemical performance similar to LIBs. In this study, LTO is synthesized using a surfactant-free solution process route and followed by its investigation under its long-term cycling behaviour to evaluate its suitability as an anode in SIBs. The synthesized LTO exhibited a cubic phase with an Fd3m space group [1], as Powder X-ray diffraction (PXRD) was revealed using Rigaku Ultima. The calculated band gap was approximately 3.87 eV. Cyclic voltammogram (CV) tests conducted under a lower scan rate of 0.1 mV/s showed two anodic peaks at 0.903 and 1.091 V and one cathodic peak at 0.693 V, indicating a three-phase Na⁺ storage mechanism in LTO [2]. The LTO electrode was cycled under a potential window of 3-0.2 V at a 0.1 C rate, delivering an initial discharge capacity of approximately 138.9 mAh/g at an intercalation potential of around 0.709 V. Under periodic rate capability (RC), the test cell delivered a 124.8 mAh/g capacity at a 0.2 C rate. The cell was cycled up to 10 C, and even after subsequent cycling, it could still deliver 137.5 mAh/g (0.1 C repeat), representing only a 1.079 % decrease in capacity. As part of the study, the LTO electrode underwent a galvanostatic charge-discharge (GCD) test for over 7500 cycles at a 5 C rate. During the first cycle, the cell delivered a capacity of 45.5 mAh/g, and at the end, it gave 40.65 mAh/g, with a capacity retention (CR) of 89.3 %. This suggests that the laminar morphology of the LTO anode, due to continuous cycling under high-stress conditions, leads to the formation of gaps between the sheets, which makes it easier for Na⁺ to interact with the material. The cycle count results are the highest reported cycle count compared to existing literature.

Moreover, ex-situ transmission electron microscopy (TEM) was conducted to understand sodium intercalation's phase boundary and any changes in the existing morphology. Additionally, time-of-flight secondary ion mass spectrometry (TOFSIMS) and X-ray photoelectron spectroscopy (XPS) were performed to study the cycled electrode's top surface at the charged and discharged state, providing valuable insights into the electrode's performance.