capacity in this cycle corresponds to 84 mah g fig4 b shows the third cycle differential capacity profiles differential capacity mah g v versus na ion cell voltage v for the hard carbon na 1 05 ni 0 40 mn 0 50 mg 0 025 ti 0 025 o 2 cell these symmetrical data demonstrate the excellent reversibility of the ion extraction insertion reactions in this na ion cell fig4 c shows the first four charge discharge cycles na ion cell voltage v versus cumulative cathode specific capacity mah g for the hard carbon na 1 05 ni 0 40 mn 0 50 mg 0 025 ti 0 025 o 2 cell these data demonstrate that the level of voltage hysteresis i e the voltage difference between the charge and discharge processes is extremely small indicating the excellent kinetics of the extraction insertion reactions fig4 d shows the cycle life performance cathode specific capacity mah g versus cycle number for the hard carbon na 1 05 ni 0 40 mn 0 50 mg 0 025 ti 0 025 o 2 cell the cell shows good reversibility referring to fig5 a 5 b 5 c and 5 d the data shown in fig5 a 5 b 5 c and 5 d are derived from the constant current cycling data for a na 1 05 ni 0 425 mn 0 525 o 2 active material in.