The low current is considered one of the sticking points in the development of solid-state batteries. This causes the batteries to take a relatively long time to charge. It usually takes about 10 to 12 hours until a solid-state battery is full again. The new cell type designed by scientists at Research Centre Jülich (Germany), on the other hand, takes less than an hour to recharge.
“With the concepts described so far, only very low charging and discharging currents were possible, which can be traced back to problems at the internal solid-state interfaces. This is where our concept comes in, which is based on an inexpensive combination of materials and which we have already patented,” explains Dr. Hermann Tempel, head of a research group at the Jülich Institute for Energy and Climate Research.
In conventional lithium-ion batteries, a liquid electrolyte is used, which usually contacts the electrodes very well. With their structured surface, the electrodes absorb the liquid like a sponge, creating a large contact surface. In principle, two solids cannot be connected to each other so completely. The contact resistance between the electrodes and the electrolyte is correspondingly higher. The result: Low charging and discharging currents.
“In order to nevertheless enable the greatest possible flow of current across the shift boundaries, we have constructed all components from very similar materials. Anode, cathode and electrolyte are all made of different phosphate compounds, which allow charging rates of over 3C (at a capacity of about 50 mAh/g). This is ten times higher than the values usually found in specialist literature,” says Tempel.
The solid electrolyte, to which the phosphate electrodes are applied on both sides by screen printing, serves as the carrier material. The materials used are inexpensive and relatively easy to process. Unlike conventional lithium-ion batteries, the new solid-state battery is also largely free of toxic or hazardous substances.
“In initial tests, the new battery cell proved quite stable over 500 charging and discharging cycles and still had 84 percent of its original capacity,” reports Dr. Shicheng Yu. “However, there is still room for improvement here. In theory, a loss of less than one percent should even be feasible,” says Shicheng Yu, who developed and tested the battery as part of a funding programme of the China Scholarship Council (CSC) at the Jülich Institute for Energy and Climate Research.
The energy density is currently around 120 milliampere-hours per gram (mAh/g), already very high, even if it is still slightly lower than that of today’s lithium-ion batteries. In addition to the development for electric mobility, there are other possible fields of application for solid state batteries. In the opinion of Institute Director Rüdiger A. Eichel, such batteries could prove to be advantageous in applications that require long operating times and safe operation, such as in medical technology or integrated components in the Smart Home area.