Batteries are a very important factor when it comes to de-carbonizing electric power, which is in ever increasing demand for smart phones, laptops, cars and the power grid. The Li-ion technology is currently among the technologies most frequently employed for energy storage on batteries. It is used in electronic devices as well as electric cars. However, there are several drawbacks associated with the use of Li-ion batteries, the most problematic one being that they can catch fire owing to the presence of liquid organic electrolytes. Solid-state batteries offer a promising solution to this problem as they have a higher level of safety and also a longer lifespan.
Now (2020), scientists at the Joint Center for Energy Storage Research (JCESR) have made significant progress in understanding the mechanisms of solid-state batteries and making them potential successors to today’s lithium-ion (Li-ion) batteries. A major problem with solid-state batteries is that the diffusivity of Li-ions in the solid-state electrolyte cannot easily be enhanced, so it is typically slower than in the liquid organic electrolytes now used in Li-ion batteries. The scientists tried to overcome this problem by making use of the paddlewheel effect. This phenomenon can dramatically increase the rotational motion of normally static negative ions (anions) in the solid-state electrolyte framework which are responsible for the motion of the Li+ positive ions (cations). The study looked into this effect to show that anion dynamics in the framework of the solid were able to improve Li+ cation transport. The anion dynamics could be activated at room temperature by tuning the framework and were strongly coupled to cation diffusion by the paddlewheel effect.
Scientists have long sought to find a suitable replacement for common Li-ion batteries. In 2013, scientists designed and optimised a multifunctional all-solid-state battery that could use a bulk-type electrode. They found that for developing bulk-type electrodes all-solid-state batteries needed the material selection to be based not only on electrochemical criteria to ensure a high performance, but also on criteria linked to the sintering process, like the thermal properties and chemical compatibilities. To show the feasibility of thick, all-solid-state batteries, solid electrolytes were selected for designing electrodes.
In 2017, scientists invented new battery cells that had at least three times as much energy density as today’s lithium-ion batteries. Instead of liquid electrolytes, the researchers relied on glass electrolytes that made it possible to use an alkali-metal anode without the formation of dendrites. In experiments, the researchers’ cells demonstrated more than 1,200 cycles with low cell resistance. The engineers’ glass electrolytes allowed them to plate and strip alkali metals on both the cathode and the anode side without dendrites, which simplified battery cell fabrication.
In 2019, researchers created a battery based on sodium. Although the possible energy densities were clearly below those of lithium solid-state batteries, sodium had several other advantages: it was easily available and less expensive than lithium, making it particularly interesting for stationary applications, such as intermediate storage for renewable energies. In addition, the experiments showed that unlike lithium, sodium was less prone to the formation of metallic dendrites, which led to a short circuit that destroyed the battery.
In 2020, scientists designed a solid-state battery by utilizing, for the first time, a silver-carbon (Ag-C) composite layer as the anode. The team found that incorporating an Ag-C layer into a prototype pouch cell enabled the battery to obtain a larger capacity, a longer cycle life, and also enhanced its overall safety. Measuring just 5µm (micrometers) thick, the ultrathin Ag-C nanocomposite layer made it possible for the team to reduce anode thickness and increase energy density up to 900Wh/L. It also enabled them to make their prototype approximately 50 percent smaller by volume than a conventional lithium-ion battery.
There are several advantages to using solid-state batteries: they use solid electrolytes in place of the usual liquid organic electrolytes and thus have the potential for safer and longer-lasting batteries that can deliver higher energy density, which is needed by a wide variety of electrochemical energy storage applications, such as vehicles, robots, drones and more. As the most important component in solid-state batteries, the solid electrolyte determines its safety and cycle stability to a large extent.
Although the new solid electrolytes are still in the development stage, the advances are promising. A breakthrough would mean a dramatic increase in the safety of batteries and less frequent use of Li-ion batteries.