All-solid-state battery (ASSB) is considered a promising candidate for next generation battery due to the non-flammable, high energy density, and no leakage. However, the solid state of electrolyte results in low ion conductivity, poor connectivity, and strong interfacial resistance between electrode and electrolyte. Amorphous oxide solid electrolyte is introduced to improve these problems. The amorphous structure ensures the easy transition of Li ions because of the sufficient structure defects. The sable electrochemical property of oxide avoids harmful gas generation during cycling. High Li content in compounds promise high ion conductivity due to more ion carriers. Moreover, decreasing solid electrolyte particles to nanoscale also benefits ion conductivity owing to the larger connect area between electrode and electrolyte. Thus, amorphous oxide nanoparticles are regarded as the promising candidate for solid electrolytes. Amorphous Li3BO3, Li4GeO4, and Li5AlO4 nanoparticles are selected as target material because of the high Li content, simultaneously, the B, Ge, and Al can act as good glass former. Induction thermal plasma characterized by electroless discharge, high temperature (> 10E4 K), and rapid quenching rate (10E3-10E6 K/s) is appropriate for synthesis of amorphous nanoparticles with high purity. In this dissertation, amorphous Li3BO3, Li4GeO4, and Li5AlO4 nanoparticles are synthesized by induction thermal plasma, the formation mechanism and formation ability of amorphous nanoparticles with high Li content during plasma process are also investigated.

In chapter 1, the method of induction thermal plasma and ASSB are generally reviewed. Meanwhile, the objective of this dissertation is put forward.

In chapter 2, synthesis of amorphous Li3BO3 nanoparticles by induction thermal plasma is conducted systematically with the investigation of the formation mechanism. Agglomerates in products are observed due to the lower temperature of nanoparticle growth region. Lithium borate nanoparticles are synthesized after Li2O nucleation, Li2O and LiBO2 co-condensation, and coagulation. The Li3BO3 is mainly synthesized at the early stage of condensation after a series of borate unit transformation. The by-product Li2CO3 is formed during collection by uncondensed Li2O reacting with H2O, and CO2 in atmosphere. Enhanced quenching rate leads to higher amorphous Li3BO3 degree because of the impediment of particle order growth. While, the enhanced quenching rate also results in insufficient borate unit transformation, which increases the percentage of by-products.

In chapter 3, amorphous Li4GeO4 nanoparticles are successfully synthesized by induction thermal plasma. Formation mechanism is investigated based on thermodynamic analysis, and the nucleation phase is identified as Li2O. The Li4GeO4 and Li2GeO3 nanoparticles are mainly synthesized at early and following stages of co-condensation respectively because of the discrepancy in Li2O and GeO saturation ratio. The enlarged intratetrahedron O-Ge-O angle distribution is achieved in high Ge molar content and quenching rate, which increases disorder in short range. The high quenching rate also allows the broader intertetrahedron Ge-O-Ge angle distribution to be preserved, acquiring the more chaotic state in intermediate range order. Enhanced amorphous Li4GeO4 degree and fraction of high temperature phase γ-Li4GeO4 are obtained in high Ge content and quenching rate conditions. However, the excessive quenching rate and Ge content result in more by-product Li2GeO3 synthesis.

In chapter 4, thermal plasma synthesis and formation mechanism of amorphous Li5AlO4 nanoparticles are studied. The synthesis and nucleation of Al2O3 occur simultaneously. The Li5AlO4 is mainly synthesized after aluminate unit transformation from [AlO6] octahedron to [AlO4] tetrahedron with Li and LiO vapor condensation. The increased Li/Al molar ratio and quenching rate contribute to amorphous Li5AlO4 nanoparticles formation due to more LiO participating in reactions and the promoted aluminate unit transformation. However, the enhanced quenching rate also causes more early solidification of nanoparticles. The transformation time is shortened, and more [AlO6] octahedrons are preserved in products.

In chapter 5, the formation ability of amorphous nanoparticles with high Li content synthesized by induction thermal plasma is investigated by comparing experiment results of Li-B-O, Li-Ge-O and Li-Al-O systems. The formation ability is discussed from amorphous structure and chemical composition, respectively. The system with a network built by strong bonds prefers to achieve amorphous structure after plasma process because the topological disorder network is more easily preserved. The shorter time lag of co-condensation benefits the synthesis of products with uniform chemical composition. Meanwhile, the sample structure unit transformation also contributes to reducing the by-product synthesis.

In chapter 6, the summarized conclusion and future works are presented. In summary, the results from this study provide an insightful understanding of amorphous nanoparticles with high Li content synthesized induction thermal plasma, which contributes to the development of ASSB with high performance.