Structural And Electrical Properties Of The Glasses And Glass-ceramics In Li₂O-Ta₂O₅-Nb₂O₅-ZrO₂-SiO₂ System

Solid electrolytes with characteristics such as non-leakage and non-flammability are the key to solve the safety and reliability problems of rechargeable lithium batteries.the crystal structure framework of LiTaSiO₅titanite compound with suitably sized lithium diffusion channels and well-connected Li⁺permeation network is a promising solid electrolyte for applications,but its room temperature conductivity is only on the order of10^-7 S/m.It has been shown that the introduction of additional lithium ions at high-energy positions by replacing Ta⁵⁺with Zr⁴⁺can achieve ion co-migration and thus greatly improve the conductivity of LiTaSiO₅.In this paper,the structure and ionic conductivity of Li₂O-Ta₂O₅-Zr O₂-Si O₂ and Li₂O-Ta₂O₅-Nb₂O₅-Zr O₂-Si O₂ system glasses,glass-ceramics and Zr⁴⁺and Nb⁵⁺co-doped LiTaSiO₅ sphene compounds are investigated,aiming to obtain new solid electrolyte materials with excellent overall performance and ionic conductivity.The main research results are as follows:1.With the increase of Nb₂O₅ addition,its presence in the glass matrix gradually transitions from[Nb O₆]octahedral to[Nb O₆]octahedral/[Nb O₄]tetrahedral coexistence form,the lightly deformed[Nb O₆]octahedral enters the network interruption point position of the glass[Si O₄]tetrahedral composition,destroys the network structure of the glass and plays the role of network modifier;the[Nb O₄]tetrahedra participate in the composition of the network structure of the glass,playing the role of the glass network formers.With the increase of Nb₂O₅ doping,the ionic conductivity of the glass samples first increases and then decreases.When the content of Nb₂O₅ is 5.88 mol%,26.47Li₂O-14.71Ta₂O₅-5.88Zr O₂-47.06Si O₂-5.88Nb₂O₅ glass sample has the best room temperature ionic conductivity(1.437×10^-7 S/cm)and the smallest activation energy（0.528 e V）,and its ionic conductivity is higher than that of the glass sample without Nb₂O₅glass sample by 1 order of magnitude.2.The main crystalline phase of Li₂O-Ta₂O₅-Zr O₂-Si O₂-Nb₂O₅ glass-ceramic samples was Li Ta O₃ when the Nb₂O₅ doping amount was 0～5.88 mol%,and Li Ta3O8 when the Nb2O5 doping amount was 11.77 mol%.The introduction of Nb2O5（0 5.88 mol%）improved the degree of connectivity between the grains in the glass-ceramics,and the optimal doping amount of Nb2O5 was 5.88 mol%,when the grains were more tightly interconnected and more uniformly distributed with less porosity,26.47Li2O-14.71Ta2O5-5.88 Zr O2-47.06 Si O2-5.88Nb2O5 glass-ceramic sample has the best room temperature ionic conductivity（1.438 × 10-6 S/cm）,which is 2 orders of magnitude higher than that of the non-Nb2O5-doped glass-ceramic sample（8.047 × 10-8 S/cm）;compared with the glass sample of the same design component（1.437 × 10-7 S/cm）,its conductivity was improved by 1 order of magnitude,which has potential for application as a solid electrolyte.3.The co-doping of Zr4+ and Nb5+ caused different degrees of lattice strain in the bulk structure of LiTaSiO5 and regulated the ion migration energy barrier.The introduction of the appropriate amount of Nb5+ reduced the energy gradient of particle diffusion,which was beneficial to the grain growth during sintering,reducing the number of grain boundaries and forming a densified ceramic structure.The ionic conductivity of the ceramic samples increases and then decreases with the increase of Nb5+ doping.When the doping amount of Nb5+ is 0.1875 mol,the Li1.125Ta0.6875Nb0.1875Zr0.125 Si O5 ceramic sample has a uniform morphology,the best fusion and connection between grains,a density of 4.48 g/cm3,the best room temperature ionic conductivity（3.521 × 10-5 S/cm）and the smallest activation energy（0.225 e V）;its ionic conductivity increases to 2.28 × 10-4 S/cm at 150 ℃.The ionic conductivity of Li1.125Ta0.6875 Nb0.1875 Zr0.125 Si O5 is improved by one order of magnitude at room temperature compared to that of Li1.125Ta0.875Zr0.125 Si O5 without Nb5+ doping;when applied to all-solid-state battery,it can withstand a voltage of at least 6 V.4.26.47Li2O-14.71Ta2O5-5.88 Zr O2-47.06 Si O2-5.88Nb2O5 glass ceramics and Li1.125Ta0.6875Nb0.1875Zr0.125 Si O5 ceramics have good ionic conductivity and good chemical stability in air and moisture,and can be used as all-solid-state lithium-ion battery The solid electrolyte candidate material for all-solid-state lithium-ion batteries.