Due
to the great advantages of low cost, high capacity, and excellent
safety, the Zn metal is a promising candidate material for rechargeable
aqueous battery systems. However, its practical applications have
been restricted by the uncontrollable dendrite growth and electrode
side reactions (such as corrosion, passivation, and hydrogen evolution
reactions) during the plating process. Herein, we reveal that the
dendrite growth would expose the electrode to more highly active tips,
exacerbating the passivation of the electrode and the decomposition
of the electrolyte by in situ optical microscopies. We propose a low-cost,
nontoxic, low-concentration (less than 1 g/L), and effective electrolyte
additive, saccharin sodium, which can guide an even Zn deposition
without obvious electrode side reactions in the charge/discharge process.
The saccharin anion acts as a “traffic assistant” of
Zn2+ and demonstrates its great potential for practical
application. The assembled Zn symmetrical battery shows an excellent
cycling performance at a high current density and capacity (an extremely
long cycle life over 3800 h is obtained at 5 mA/cm2 and
8 mA h/cm2, and 20 mA/cm2 and 5 mA h/cm2 show a lifetime over 800 h), and the full cell (coupled to
an AC electrode) presents a stable cycle life with a capacity retention
of 86.4% even after 8000 cycles at 5 mA/cm2. The saccharin
sodium proposed in this work is promising to solve the anode problems
in advanced Zn batteries.