In a conventional battery design—most commonly lithium-ion—two solid metal electrodes are used with a liquid lithium salt acting as an electrolyte. Ionic particles move from one electrode (the cathode) to the other (the anode) as the battery charges, and in reverse as it discharges. The liquid lithium salt electrolyte is the medium that allows that movement. If you’ve ever seen a battery corrode or get punctured, the “battery acid” that oozes (or sometimes explodes) out is the liquid electrolyte.

In a solid-state battery, both the positive and negative electrodes and the electrolyte between them are solid pieces of metal, alloy, or some other synthetic material.

Solid-state batteries promise a few distinct advantages over their liquid-filled cousins: better battery life, faster charging times, and a safer experience.

Solid-state batteries compress the anode, cathode, and electrolyte into three flat layers instead of suspending the electrodes in a liquid electrolyte. That means you can make them smaller—or at least, flatter—while holding as much energy as a larger liquid-based battery. So, if you replaced the lithium-ion or lithium-polymer battery in your phone or laptop with a solid-state battery the same size, it would get a much longer charge. Alternatively, you can make a device that holds the same charge much smaller or thinner.

Solid-state batteries are also safer, since there’s no toxic, flammable liquid to spill, and they don’t output as much heat as conventional rechargeable batteries. When applied to batteries that power current electronics or even electric cars, they might recharge much faster, too—ions could move much more quickly from the cathode to the anode.

According to the latest research, a solid-state battery could outperform conventional rechargeable batteries by 500% or more in terms of capacity, and charge up in a tenth of the time.
Several reasons contribute to the movement away from cobalt content in lithium-ion batteries. Prices of the mineral have multiplied over recent years. Cobalt, which is typically combined with nickel and manganese in electric-car batteries, is relatively scarce. Given the ambitious expansion plans of lithium-ion producers, the world will face cobalt shortages by the early 2020s, according to Bloomberg New Energy Finance. This is keeping prices of lithium-ion batteries high and preventing major automakers from lining up long-term supply deals on favorable terms. 
Most of the world’s cobalt is mined in the Democratic Republic of the Congo (DRC), which is known for corruption and human rights violations, including its cobalt “artisanal miners,” who are often children. In 2016, Amnesty International released a report tracing the sale of cobalt, used in lithium-ion batteries, from mines where children as young as 7 and adults work in perilous conditions. 
Mark Dummett, business and human rights researcher for the report, said, “The glamourous shop displays and marketing of state of the art technologies are a stark contrast to the children carrying bags of rocks, and miners in narrow man-made tunnels risking permanent lung damage.” Children told Amnesty International they worked for up to 12 hours a day in the mines, carrying heavy loads to earn between $1-2 a day. In 2014 approximately 40,000 children worked in mines across southern DRC, many of them mining cobalt, according to UNICEF. A recent cobalt tax increase by the DRC is also bringing new urgency to electric vehicle manufacturers. Tech companies have started to heed the call to discontinue trading relationships with suppliers of DRC cobalt, as the wallet speaks loudly alongside their consciences.
The battery energy density is the proportion of energy that can be included in a particular unit (mass or capacity). The energy density of a battery is generally expressed in two ways : The gravimetric energy density of a battery is a measure of how much energy a battery contains in comparison to its weight, and is typically expressed in Watt-hours/kilogram (W-hr/kg). The volumetric energy density of a battery is a measure of how much energy a battery contains in comparison to its volume, and is typically expressed in Watt-hours/liter (W-hr/l).
Lithium ion (Li-Ion) has the better energy density from the three most popular chemical compositions currently, so therefore Lithium batteries are still dominated by the application of all portable electronic devices. Although Lithium batteries has advantage on the battery energy; Ni-Battery (Ni-Cd and Ni-MH) has a better linear discharge characteristics, so they are well suited for use with Linear Regulator.