Even if lithium-ion batteries are more known on the market and considered the most reliable, cheap and safe to use, lithium-sulfur batteries are catching up fast. There were several problems reported to the lithium-sulfur batteries but they will be solved in the close future as the capacity of the lithium-sulfur batteries is several times the one of the lithium-ion. That is the most important point that must make the lithium-sulfur batteries a dream come true. They will revolutionize the automotive industry, we won’t be dependent on oil companies, and we will pollute less.
Lithium-sulfur batteries are made from 2 electrodes, one of lithium and one of sulfur, paired with carbon. The charging and the discharging of the battery involves the movement of lithium ions between the two electrodes(identical process as the lithium-ion batteries). But the capacity of lithium-sulfur batteries is higher than that of lithium-ion batteries because of one important fact: the way the ions are assimilated at the electrodes. The difference is made at the sulfur electrode, as each sulfur atom is able to host two lithium ions. In comparison, lithium-ion batteries store for each atom host only 0.5 to 0.7 lithium.
If in theory things look simple always practical wakes us up to reality. In fact only the atoms of sulfur near the surface of the material accept lithium ions and this is mostly because sulfur is an insulating material making it difficult for electrons and ions to move in and out. But things do not stop here. Major problems have be seen regarding functionality and reliability. As sulfur binds to lithium ions, it forms eventually dilithium sulfide and as well some intermediate products like polysulfides. After few dozens of cycles the polysulfides dissolve in the battery’s liquid electrolyte and will settle in other areas of the battery, where they can block charging and discharging making the battery useless. When it comes to safety, the risk is increased: the lithium electrode can grow branchlike structures while in use and could cause a short circuit. If the battery heats up, the metal can melt and if it comes into contact with water, it can start a fire. The battery’s electrolyte can also catch fire.
Chemical giant BASF from Ludwigshafen, Germany, teamed up with Sion Power, Tucson, Arizona, to develop a lithium-sulfur battery cell prototype.
“Compared to existing technologies used in electric vehicles, the plan is to increase driving distance at least 5 to 10 times” for a given-size battery, says Thomas Weber, CEO of a subsidiary of BASF called BASF Future Business.
Well 5-10 times represents a huge increase in capacity which other experts cannot approve. 3 times is more reasonable but BASF is confident in their statement. Beside this the alliance with Sion Power will help the product be much faster developed and could come much more easier to the market. Weber says that the safety issues have already been solved and the goal of BASF is to further improve the materials in order to get the theoretical capacity these batteries have. And BASF has a plan to make this reality.
Sion Power has addressed the issue related to the limited numbers of recharge cycles and they have produced already a battery that can store twice as much energy than a conventional lithium-ion battery. Sion Power is confident that their batteries can last the lifetime of a car but it seems they did not measure the reliability in time yet. Their plan is to reach 1000 recharge cycles with a battery pack that provides a 300 mile range.
Let’s just hope all of these will be solved fast, so the lithium-sulfur battery will go on the market and in the automotive industry soon.