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In order to study the structural EPZ-6438 of Na2Li2Ti6O14, in-situ XRD is detected between 1.0 and 3.0 V as displayed in Fig. 11. For the first XRD pattern, six characteristic peaks at 26.74, 28.96, 32.29, 33.71, 43.94 and 45.17° are close to the (4 0 2), (1 1 3), (5 1 1), (2 0 4), (0 2 2) and (0 2 4) planes of Na2Li2Ti6O14 (JCPDS card No.52-0690) and the peaks at 38.70 and 41.36° are attributed to beryllium oxide based on the JCPDS card No.78-1557. With the gradual inserting of lithium ions in the structure, all feature peaks of Na2Li2Ti6O14 shift towards to lower angles. After a discharge process to 1.0 V, all six feature peaks move to 26.37, 28.65, 31.95, 33.10, 43.15 and 44.90°. Furthermore, it can be noticed that there is a new peak appearing at 44.06° referring to beryllium oxide, which is covered by the diffraction peak of Na2Li2Ti6O14 in the initial XRD pattern. The evolution of diffraction peaks is contributed to 1.97 Li per formula storage in the structure of Na2Li2Ti6O14 (Fig. S2a). Then the changed Bragg positions return to the pristine angles after it is recharged to 3.0 V, indicating the high electrochemical reversibility of Na2Li2Ti6O14 structure during lithiation/delithiation process. The transformation of feature peaks in the initial cycle can be clearly seen in the patterns of relative intensity versus 2θ as shown in Fig. 12a. Besides, a close-up shot of three typical XRD patterns (the initial pattern, discharge to 1.0 V and recharge to 3.0 V) for three different angle ranges is presented Fig. 12b–d. These results further confirm the reversible changes of feature peaks during the initial cycle between 1.0 and 3.0 V.