A new generation of solid electrolytes
The first rechargeable lithium metal batteries have arrived, but industry research does not stop. Making these devices even more secure, durable and capable is essential in order to turn them into a competitive and widespread storage solution. The new solid-state electrolyte developed at the Hong Kong University of Science and Technology is also helping (HKUST). The innovation makes a real leap forward to metal lithium technology in the solid version but to understand its scope it is necessary to start from the beginning.
Rechargeable metal lithium batteries, advantages and disadvantages
Metallic lithium rechargeable batteries are secondary batteries with metallic lithium as the negative electrode. This paper material has excellent storage characteristics, starting with a high theoretical specific capacity of 3.860 mAh/g. In addition, the shallow redox potential and the reduced density (0,59 g/cm3) make it the ideal material. The disadvantages? The short life of cells is due to the low coulombic efficiency and the formation of dendrites. And since both these aspects depend on the electrolyte, it was clear from the outset that finding the best electrolytes could mean increasing the performance of these batteries.
Solid-state electrolytes In order to optimize the technology over time, we have moved from liquid to solid-state electrolytes such as polymers and inorganic ceramics. Polymers can make good interfacial contact with electrodes, ensuring the suppression of Li dendrites and good electrochemical stability, but they are limited by low ionic conductivity.
Organic ceramics can have high ion conductivity, although they suppress Li dendrites. However, they are characterized by poor interfacial contact with electrodes and mediocre chemical stability.
Porous crystalline polymers, the perfect solid-state electrolyte?
This is where the Hong Kong University of Science and Technology study comes into play. Scientists have focused their attention on a new generation of polymer electrolytes: porous crystalline polymers. These materials show great potential as solid electrolytic materials due to their high stability, the rapid and selective transport of lithium ions and the easy synthesis and scalability. In detail, the team developed a new strategy that combines a class of porous ionic covalent organic structures (iCOF) with a type of polymer called poly (ionic liquid) (PIL) for the manufacture of a high-performance solid electrolyte.
This new composite electrolyte has achieved exceptional ion conductivity and lithium ion transport capacity (>0.80) at room temperature. Using it in a metal lithium cell, the team found that the battery had an initial discharge capacity of 141.5 mAh/g at 1 °C at room temperature, with an impressive retention capacity at 87% over 800 cycles.The research paper, entitled “High-performance solid-state lithium-metal batteries made possible by organic covalent ion compounds”, was published in Advanced Energy Materials.