“…For the Ni 2p XPS spectra (Figure 3f), pristine Ni(HCO 3 ) 2 hollow spheres showed a single Ni 2p 3/2 peak at 856.4 eV, while the first charged sample had three Ni 2p 3/2 peaks at 850.4, 856.4, and 858.6 eV, which can be attributed to Ni, Ni 2+ , and Ni 3+ , respectively. 29 For the 10th charged sample, there were only two Ni 2p 3/2 peaks at 850.4 eV (Ni) and 858.8 eV (Ni 3+ ). Overall, the contributions from the further oxidation of Ni 2+ into Ni 3+ and the reversible reactions between HCO 3 − and Li x C 2 (x = 0, 1, or 2) should be invoked to calculate the new theoretical capacity of Ni(HCO 3 ) 2 , yielding 1928 mAh g −1 (n = 13 at x = 2).…”