Recently a group of scientists tried to develop a water-based battery electrolyte. This solution is believed to be able to produce a smartphone battery that is more secure than lithium-ion.
The scientists realized it using a high concentrated salt that would help produce a protective layer of electrodes. That way, the electrode shield will help the electrode hold more energy.
Currently the safe battery in question is still in the early development stage, because the main problem of this battery is its electrolyte is not last long. Mentioned, the amount of charging battery (charging process) that can be done on this battery is only about 70 cycles.
So, if a device uses a battery with a water-based electrolyte that is safer than lithium-ion will only last for about 2 months. Meanwhile, lithium-ion batteries can last for hundreds of charging cycles.