Abstract
Bulk-type all-solid-state batteries (ASSBs) consisting of composite electrodes of homogeneously mixed fine particles of both active materials and solid electrolytes (SEs) exhibit a high safety, high energy density, and long cycle life. SE nanoparticles are required for the construction of ion-conducting pathways as a response to the particle size reduction of active materials; however, simple and low-cost milling processes for producing nanoparticles cause a collapse in the crystal structure and eventually amorphization, decreasing the conductivity. This study develops a heat treatment process in water vapor for the low-temperature crystallization of ultrafine SE amorphous particles and the size control of crystalline nanoparticles. An ultrafine (approximately 5 nm) amorphous powder of Li1.3Al0.3Ti1.7(PO4)3 (LATP), as a typical oxide-type SE, is produced via wet planetary ball milling in ethanol. The water vapor induces a rearrangement of the crystal framework in LATP and accelerates crystallization at a lower temperature than that in air. Further, since particle growth is also promoted by water vapor, depending on the heating temperature and time, this heat treatment process can be also applied to the size control of crystalline LATP nanoparticles. A combination of the wet planetary ball milling and heat treatment in water vapor will accelerate the practical application of bulk-type ASSBs.
Highlights
All-solid-state batteries (ASSBs) have attracted signi cant attention as next-generation batteries because they can solve the safety issue that results from the organic liquid electrolytes used in current Li-ion batteries.[1,2,3] Traditional electrolytes possess safety risks due to the ammability of organic solvents and HF formation that attacks the active materials of the electrodes.[4,5] Solid electrolytes (SEs), on the other hand, offer high stabilities against temperature, air, and moisture; replacing liquid electrolytes with SEs contributes to the high safety and cycle life of Li-ion batteries
Water vapor accelerates the particle growth rate by heating at 400 C. These results indicate a particle size reduction and the potential for future selection of cathode materials for fabricating composite electrodes of ASSBs, and further, demonstrate a low-temperature heating process that can suppress compositional shi s and side reactions
The single-nanometer size of a-LATP calculated from the Sw value was con rmed by the transmission electron microscopy (TEM) observations, exhibiting a primary particle size below 10 nm and agglomerates of several tens of nanometers (Fig. 1b)
Summary
All-solid-state batteries (ASSBs) have attracted signi cant attention as next-generation batteries because they can solve the safety issue that results from the organic liquid electrolytes used in current Li-ion batteries.[1,2,3] Traditional electrolytes possess safety risks due to the ammability of organic solvents and HF formation that attacks the active materials of the electrodes.[4,5] Solid electrolytes (SEs), on the other hand, offer high stabilities against temperature, air, and moisture; replacing liquid electrolytes with SEs contributes to the high safety and cycle life of Li-ion batteries. In the water vapor atmosphere, the crystallization is accelerated due to multiple factors, such as promoted hydrolysis of organic compounds[28,29] and surface diffusion of hydroxyl groups.[30,31] In particular, the increasing adsorption–desorption cycles of water vapor on metal ions under heating induce a reformation of metal–oxygen bonds by the dehydration condensation in amorphous solids.
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