Structural Properties and Bandgap Energy of Ga-doped Garnet-type Li7La3Zr2O12 (LLZO) Solid Electrolyte Depending on Sintering Atmosphere

Year 2025, Volume: 29 Issue: 2, 160 - 170, 30.04.2025

Sevda Saran

https://doi.org/10.16984/saufenbilder.1590407

Abstract

Developing solid-state batteries for higher energy densities and safety has been a popular research subject in recent years. Since their first report, Li7La3Zr2O12 (LLZO) solid electrolytes have attracted extended attention due to their high ionic conductivity, chemical stability, and wide electrochemical window. Although LLZO fulfills all the requirements for high energy density and a longer lifespan, its intrinsic electronic conductivity accelerates the Li dendrite growth short-circuiting the battery. In this study, we have applied air and oxygen sintering atmospheres to prepare two types of Ga-doped LLZO pellets, to identify the effect of sintering atmospheres on the physical properties such as crystal phase, ionic conductivity, roughness, and electronic band gap energy (Eg). Both the crystal structures were found to be in cubic phase with a relatively small amount of secondary phase impurities. On the other hand, the oxygen-sintered sample showed better properties with high ionic conductivity of 1.04x10-4 Scm-1, lower surface root-mean-square roughness of 0.1833 µm, and a relative density of 90.5%. Furthermore, the electronic indirect band gap energy of the oxygen-sintered sample was larger, Eg=5.77 eV, which is desired for lower electrical conductivity. It is important to note that the precise determination of Eg values of powders would be erroneous through Ultraviolet-Visible (UV-Vis) absorption spectroscopy due to the scattering effects of solids. So, to the best of our knowledge, for the first time, this study reports Eg values of oxygen and air-sintered LLZO determined by the Kubelka-Munk model on Ultraviolet-Visible-Near Infra-Red (UV-Vis-NIR) diffuse reflectance spectroscopy.

Keywords

Garnet-type LLZO solid electrolyte, Sintering atmosphere, DRS, Band gap energy

Project Number

21406002

Ga-katkılı garnet-benzeri Li7La3Zr2O12 (LLZO) katı elektrolitinin sinterleme atmosferine bağlı olarak optik, yapısal ve iletkenlik özellikleri

Abstract

Daha yüksek enerji yoğunluklu ve güvenlikli katıhal pilleri geliştirmek son yıllarda popüler bir araştırma konusu olmuştur. İlk raporlarından bu yana, Li7La3Zr2O12 (LLZO) katı elektrolitleri yüksek iyonik iletkenlikleri, kimyasal kararlılıkları ve geniş elektrokimyasal pencereleri nedeniyle oldukça ilgi görmektedir. LLZO, pillerde yüksek enerji yoğunluğu ve daha uzun bir kullanım ömrü için tüm gereklilikleri karşılasa da sahip olduğu elektronik iletkenliği, Li dendrit büyümesini hızlandırarak pilin kısa devre yapmasına neden olur. Bu çalışmada, ısıl işlem atmosferlerinin kristal faz, iyonik iletkenlik, pürüzlülük ve elektronik bant aralığı enerjisi (Eg) gibi fiziksel özellikler üzerindeki etkisini belirlemek için iki tür Ga-katkılı LLZO peleti hava ve oksijen atmosferlerinde sinterlenmiştir. Her iki kristal yapının da safsızlık olmaksızın kübik fazda oluştuğu belirlenmiştir. Öte yandan, oksijen altında sinterlenmiş numune daha yüksek bir iyonik iletkenlik, 1.04x10-4 Scm-1, daha düşük bir yüzey pürüzlülüğü, 0.1833 µm ve %90.5’ lik bir bağıl yoğunluk ile daha iyi özellikler göstermiştir. Ayrıca, oksijen altında sinterlenmiş numunenin elektronik bant aralığı enerjisi daha yüksek olarak belirlenmiştir, Eg = 5.77 eV. Elektromanyetik dalgaların saçılma etkilerinden dolayı toz numunelerin Eg değerlerinin Morötesi-Görünür (UV-Vis) soğurma spektroskopisi ile hassas bir şekilde belirlenmesinin hatalı olacağını belirtmek önemlidir. Bu nedenle, bildiğimiz kadarıyla, bu çalışmada ilk kez, LLZO’ nun Morötesi-Görünür-Yakın Kızılötesi (UV-Vis-NIR) dağınık yansıma spektroskopisi ile Eg değerleri Kubelka-Munk modeli kullanılarak belirlenmiştir.

Keywords

Garnet- benzeri LLZO kati elektrolit, Tavlama sıcaklığı, DRS, Bant aralığı enerjisi

Project Number

21406002

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