探討 H-Nb2O5 鋰擴散機制

Abstract

氧化鈮材料具有高充放電速率的表現，被視為一類新型鋰離子電池材料。本篇研究主要計算以下數據: 鋰離子的吸附能(Eads)、活化能(Ea)、擴散係數(D)。透過這些數據探討鋰離子在氧化鈮中的充電機制。從吸附能的結果發現大多 pocket site (7/13)吸附能都低於 -3.4 eV ，比例上比 vertical window (3/9)或 horizontal window (2/7)來的多。另外我們發現鋰離子在 pocket to pocket遷移時的 Ea 最大(0.59 eV)，讓我們知道充電時，鋰離子會偏好先吸附在 pocket site ，此外鋰離子在 horizontal window 遷移時的 Ea 最小(0.16 eV)。我們透過 Ab initio Molecular Dynamic (AIMD)的方法計算鋰的擴散行為，結果顯示鋰主要在 horizontal window 內移動，其擴散係數在 600K 時達到了 4.63 × 10−6 m2 s−1。最後實驗上拉曼光譜與頻率計算的結果，也輔助了我們上述提出的充電機制。Niobium oxide-based materials are regarded as a new type of Li-ion battery anodes due to their high charge/discharge rates. In the present study, we computationally examine adsorption energy (Eads), activation barrier (Ea), and diffusion coefficient (D) to systematically resolve the mechanisms in the charge processes at the molecular level. In the Eads calculations, we found that most of pocket sites (7/13) have higher Eads (> -3.4 eV) than vertical window (3/9) and horizontal window (2/7) sites. Additionally, pocket-pocket diffusion has the highest Ea (0.59 eV). Those energetic results indicate that Li initially adsorbs and prefers to stay in the pocket sites during the charge process. On the other hand, Li has the lowest Ea (0.16 eV) in the horizontal window diffusion. Our Ab initio Molecular Dynamic (AIMD) results also found that diffuse along the b axis has the greatest diffusion coefficient (4.63 × 10−6 m2 s−1at 600K). Those results suggested the horizontal window diffusion along b axis is the preferential pathway for Li transport in the charge processes. Finally, our vibrational computations along with the operando Raman spectra confirmed those proposed mechanisms.