by All-solid-state batteries, also known as dream batteries, are the next generation of batteries that many battery manufacturers are eagerly trying to bring to the market. These batteries differ from lithium-ion batteries as they utilize a solid electrolyte instead of a liquid one, thereby reducing the risk of explosion. They are in high demand across various sectors, including automobiles and energy storage systems (ESS). However, all-solid-state batteries face challenges in maintaining the high pressure required for stable operation, which directly affects battery performance, energy density, and capacity. To address this, Dr. Hun-Gi Jung and his team at the Energy Storage Research Center at the Korea Institute of Science and Technology (KIST) have identified the degradation factors that cause rapid capacity degradation and shortened lifespan in all-solid-state batteries operating at similar pressures to lithium-ion batteries. The findings of this research have been published in the journal Advanced Energy Materials.
Unlike previous studies, the research team discovered that degradation can occur both inside and outside the cathode of all-solid-state batteries, highlighting the reliability of these batteries in low-pressure environments. During repeated charging and discharging, the cathode and anode of all-solid-state batteries undergo volume changes, resulting in interfacial degradation such as side reactions and contact loss between active materials and solid electrolytes. This, in turn, increases interfacial resistance and compromises cell performance.
To address this issue, external devices are currently used to maintain high pressure. However, this approach reduces energy density as the weight and volume of the battery increase. Therefore, researchers are now focusing on the development of internal modifications within the all-solid-state cells to ensure optimal performance even in low-pressure environments.
The research team conducted a study by repeatedly operating a coin-type all-solid-state battery with a sulfide-based solid electrolyte in a low-pressure environment of 0.3 MPa, which is similar to a coin-type lithium-ion battery. After 50 charge-discharge cycles, the team observed that the NCM cathode layer had doubled in volume, and analysis of cross-sectional images confirmed the development of severe cracks between the cathode active material and the solid electrolyte. This analysis revealed that, in addition to interfacial contact loss, the cracking of the cathode material and irreversible cathode phase transformation were the primary causes of degradation during low-pressure operation.
Furthermore, the research team replaced the lithium in the cathode with an isotope (6Li) to distinguish it from the lithium present in the solid electrolyte. By using time-of-flight secondary ion mass spectrometry (TOF-SIMS), they were able to identify, for the first time, the mechanism through which lithium consumption in the cathode contributes to the overall reduction in cell capacity. The repeated charge-discharge cycles caused sulfur, a decomposed product of the solid electrolyte, to enter the cracks in the cathode material and form lithium sulfide, a non-conductive byproduct. This depletion of active lithium ions triggered cathode phase transformation, leading to a reduction in the capacity of all-solid-state batteries.
By identifying the root cause of degradation in all-solid-state batteries operating in low-pressure environments, these analytical methods provide valuable insights for addressing the cycling characteristics that are poorer than those of conventional lithium-ion batteries. Overcoming this challenge is crucial to securing the commercial viability of all-solid-state batteries by eliminating the need for external auxiliary devices, which have been a major contributing factor to rising production costs.
Dr. Hun-Gi Jung of KIST emphasized the importance of developing new cathode and anode materials that can operate in a pressure-free or low-pressure environment, instead of the current pressurized environment, for the successful commercialization of all-solid-state batteries. The implementation of low-pressure all-solid-state batteries in medium to large-scale applications, such as electric vehicles, has the potential to leverage existing lithium-ion battery manufacturing facilities.
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1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it
