Abstract
Li-ion batteries are widely used as energy storage devices due to their excellent electrochemical performance. The cubic Li7La3Zr2O12 (c-LLZO) compound is regarded as a promising candidate as a solid-state electrolyte for lithium-ion batteries due to its high bulk Li-ion conductivity, excellent thermal performance, and chemical stability. The standard manufacturing procedure involves the high-temperature and lengthy annealing of powders. However, the formation of the tetragonal modification of LLZO and other undesired side phases results in the deterioration of electrochemical properties. The mechanical milling of precursor powders can enhance the powders’ reactivity and can result in an easier formation of c-LLZO. The aim of this work was to study the influence of selected milling and annealing parameters on c-LLZO compound formation. The starting powders of La(OH)3, Li2CO3, and ZrO2 were subjected to milling in various ball mills, under different milling conditions. The powders were then annealed at various temperatures for different lengths of times. These studies showed that the phase transformation processes of the powders were not very sensitive to the milling parameters. On the other hand, the final phase composition and microstructure strongly depended on heat treatment conditions. Low temperature annealing (750 °C) for 3 h produced 90% of c-LLZO in the powder structure.
Highlights
From an energy storage technology point of view, rechargeable Li-ion batteries are the most advanced energy storage devices
The Li7La3Zr2O12 (LLZO) compound is regarded to be a promising candidate as the solid-state electrolyte for lithium-ion batteries due to its high bulk Li-ion conductivity, excellent thermal performance, and chemical stability [5]
Various processing routes can be applied for solid-state electrolytes: sol-gel synthesis techniques have been attempted with varying degrees of effectiveness [7]; laser annealing is another important fabrication technique [8]; spark plasma sintering has been used, with a porous microstructure being reported [9], along with calcination and cold compaction of the powders [10]; hot press sintering has been developed [11]
Summary
From an energy storage technology point of view, rechargeable Li-ion batteries are the most advanced energy storage devices. Li-ion batteries possess the highest energy densities (the capability to store energy per unit weight or volume) among all rechargeable batteries, which is important regarding its applications in large electrical power storage systems such as electrical vehicles [1,2,3] These batteries typically have relatively low self-discharge rates compared to Ni-metal hydride or Ni-Cd batteries. Several works have been devoted to the determination of the influence of milling parameters on the phase composition and structure of the final product [18,19,20,21,22,23,24,25]. This work was focused on the development of the chosen technological parameters related to milling and annealing and their influence on the phase composition of the final ceramic, while the electrochemical properties of the synthesized powders were not studied. The aim of this work was to study the influence of selected milling and annealing parameters on the possibility of c-LLZO compound formation
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