Modification And Properties Of Li₂ZrO₃-based Li-ion Conductors And Related All-solid-state Batteries

All-solid-state lithium batteries use a non-flammable solid electrolyte instead of a flammable organic electrolyte,which has the advantages of high energy density,wide operating temperature and high safety performance.The development and research of all-solid-state lithium batteries are becoming a hot topic in the field of new energy.Li₂ZrO₃ is a Li-ion conductive compound with high thermodynamic stability to Li metal.But the room temperature conductivity of Li₂ZrO₃ is low,there is little research on its modification and application in solid-state batteries.Taking Li₂ZrO₃ as the object,this thesis intends to improve the ionic conductivity of Li₂ZrO₃ by optimizing the preparation process and ion-doping,explore the conductive mechanism of this material,and carry out related research on the application in solid-state batteries.The following research works were carried out in this thesis:（1）Li-ion conduction channel of monoclinic Li₂ZrO₃ was calculated and simulated by soft BV software.The results showed that there were three-dimensional Li-ion conduction paths in Li₂ZrO₃ crystal,and Li-ions migrated through the oxygen octahedral vacancy-oxygen tetrahedral vacancy-oxygen octahedral vacancy.Al³⁺doped Li₂ZrO₃ ceramics were prepared by a Sol-Gel-like method,and Zr sites were replaced by Al³⁺-ions to introduce oxygen vacancies in the Li₂ZrO₃lattice.The results showed that the Al³⁺doped Li₂ZrO₃ ceramics had a monoclinic crystal structure,and the Li-ion conductivity of Li₂ZrO₃ at room temperature increased from 8.02×10^-5 S cm^-1 to 3.06×10^-4 S cm^-1 with 0.04 mol Al³⁺doping.Compared with undoped Li₂ZrO₃ ceramics,the activation energy of Al³⁺doped ceramics decreased from 0.12 to 0.06 e V.（2）Li₂ZrO₃ and halogen doped Li₂ZrO₃ powders were prepared by a Sol-Gel-like method.The effects of sintering in air and anoxic conditions on the phase of Li₂ZrO₃ ceramics were studied.It was found that Li₂ZrO₃ceramics sintered by the anoxic condition in the crucible had a tetragonal phase with higher symmetry than monoclinic and contained more oxygen vacancies than those sintered in air.The ionic conductivity of anoxic sintered Li₂ZrO₃ reached 2.8×10^-4 S cm^-1 at room temperature.Halogen-doped specimens sintered in air also yielded Li₂ZrO₃ tetragonal phase,while halogen-doped ceramics sintered in an anoxic environment had ionic conductivities as high as 5×10^-4 S cm^-1.（3）Tetragonal Li₂ZrO₃ powders and PEO polymer were combined to prepare rigid and flexible composite solid electrolyte films by solution pouring method.When 20 wt%Li₂ZrO₃ powders were added to PEO,the crystallinity of the composite electrolyte film decreased from 22.7%to14.3%,and the ionic conductivity at room temperature was 6.76×10^-6 S cm^-1.The electrochemical stability window of the composite electrolyte increased from 3.3 V to 4.2 V,and the polarization voltage of the lithium symmetric battery decreased from 0.1 V to 0.05 V.The specific discharge capacity of Li/electrolyte/NCM811 all-solid-state battery assembled with Li₂ZrO₃/PEO composite electrolyte increased from 0 to 119 m Ah g^-1 at room temperature.