Study of the Li+ intercalation/de-intercalation behavior of SrLi2Ti6O14 by in-situ techniques

The lithium ion intercalation/de-intercalation behavior of SrLi2Ti6O14 is studied using in-situ X-ray diffraction (in-situ XRD) and in-situ electrochemical impedance spectroscopy (in-situ EIS) techniques. Significant volume expansion and contraction is observed during Li+ intercalation and de-intercalation, respectively. At voltages of 2.5-0.5 V, the entire Li+ intercalation process can be divided into two stages. In stage I, corresponding to the 2.5-1.3 V range, ∼60.2% lithium intercalation capacity is obtained with only ∼40.3% relative lattice volume expansion. In contrast, only an ∼39.8% lithium intercalation capacity is obtained with 59.7% lattice volume expansion in stage II, which occurs in a voltage range of 1.3-0.5 V. The results from in-situ EIS reveal that a relatively small charge transfer resistance Rct can be obtained for charging/discharging at voltages of 2.5-1.3 V. Moreover, Rct increases with increasing lattice volume expansion when lithium is inserted into the SrLi2Ti6O14 lattice at voltages lower than 1.3 V. Cyclic testing in different voltage ranges shows that, compared with ranges of 2.5-0.8 V and 1.42-0.8 V, the best cyclic performance is achieved at voltages of 2.5-1.3 V. This may be attributed to reduced changes in the lattice volume and decreased lithium intercalation resistance.