Researchers Uncover Findings for Advancing Development of More Stable All-Solid-State Batteries

Scientists from the Korea Institute of University of Science and Technology’s (KIST) Center for Energy Materials Research, headed by Dr. Sang-baek Park, recently announced a new innovative development. The research involves the development of a breakthrough material design strategy that could solve the issue of high interfacial resistance between the solid electrolyte (SE) and the cathode of all-solid-state batteries (ASSBs). The scientists from KIST worked in collaboration with the research team of Professor Hyun-jung Shin of Sungkyunkwan University.

 

Image used courtesy of KIST 

 

All-Solid-State-Batteries

ASSBs typically use a SE rather than a liquid electrolyte (LE). In lithium-ion batteries (LIBs) with LEs, there is a risk of combustion due to the inherent high volatility and flammability. This is one of the reasons why the solid nature of the electrolyte in ASSBs is appreciated among researchers and makes the technology a potential substitute for present LE-based LIBs. ASSBs with SEs have been shown to tolerate a wider temperature range  (−30 to 100°C) than LE-based LIBs while providing reliable performance. At low temperatures, the ionic conductivity of LEs has been shown to drop, as well as the performance. Additionally, the reactive nature of LEs at high temperatures has been shown to accelerate the 

decomposition and deterioration of other battery components. This can cause swelling of batteries and contribute to their malfunction. 

In addition to a wider temperature range tolerance, ASSBs can be manipulated to increase energy density. By adopting lithium metal as an anode, the SE contact with this other solid contact can prevent the formation of dendrites. These tree-like projections can lead to a short in the circuit, battery failure, and can also lead to fires or other safety hazards.

For consumers looking at a future geared toward electric vehicles (EVs) and electronic consumer wearables, LIBs that have reportedly led to explosions or combustion is such products, making a strong case for using ASSBs instead. Despite this, some challenges pose an obstacle to their commercialization.

 

The Research

The SE’s of ASSBs suffer from low ionic conductivity, unstable cycling stability, and exhibit high interfacial resistance at solid-solid interfaces. All of these factors impede performance. To tackle these issues, the KIST-Sungkyunkwan University joint research team worked together to identify the crystal structure of the material that directly affects the solid interface. The team used epitaxial film technology to grow a thin film along the direction in which the crystals of the substrate were formed. Epitaxial films are usually arranged in a highly organized atomic arrangement following their substrates. These are used as seed crystals. The result of using this film technology was the formation of cathode films under varying conditions that had different exposed crystal planes.

The research team analyzed the effect of the exposed crystal plane on the interface between the SE and the cathode material. The result indicated that the closely-packed structure of the exposed crystal plane suppressed the leakage of a transition metal of the cathode material into the electrolyte. This was shown to improve the stability and output of the ASSB.

 

Dr. Sang-baek Park of KIST’s Center for Energy Materials Research. Image used courtesy of KIST 

 

In a news release, Dr. Park provided his comments: "This means that improving the cathode material itself by increasing the density of the crystal plane and adjusting the direction of the interface between the crystals can ensure high performance and stability.” Park added: "We plan to accelerate the development of all-solid-state battery materials by overcoming the instability of the solid electrolyte and solid cathode interface and imparting improved ion-charge exchange characteristics through this study, which has investigated the mechanism of all-solid-state battery degradation."