| 摘要: | 在儲能領域當中，電極材料提供離子傳輸與儲存，對於提升電化學效能至關重要。而在鋰離子電池(LIBs)技術中，由於矽和鋰金屬都具有高理論電容(>3000 mAh g-1)，因此使他們成為下一代陽極LIBs的候選。然而，Si陽極卻具有一些關鍵的問題，例如在鋰化/脫鋰過程中體積的急遽變化、不穩定的固態電解質界面(SEI)和低的導電性等限制。由於石墨烯具有的高比表面積、高電導率和良好的機械性能等多種性能，因此使用石墨烯作為電極材料進行多功能性的表面改質，是一個理想的策略。
在本文中，提出了兩種使用電化學剝離石墨烯(ECG)修飾矽表面作為陽極材料的策略。首先，通過噴霧乾燥法將ECG包覆的Si奈米顆粒(Si NPs)呈現出獨特的核殼結構，且具有微米級的球形和空隙空間、可預留體積膨脹空間並提升矽的導電性。結果顯示，少層的ECG包裹的矽球(Si@FL-GB) 陽極顯示出2882.3 mAh g-1的高初始放電電容值、在0.2 A g-1時的初始庫倫效率(ICE)為86.9%以及在高電流密度(3 A g-1)下達到1360.9 mAh g-1的高性能。 其次，我們通過引入氨氣(NH3)作為氮的前驅物將Si@ECGB的表面層，將其改質成Si3N4和氮摻雜的石墨烯，以做後續研究。此方法可用於增加電導率、離子遷移率並保護鋰離子電池陽極，在本文中表明，由於有效的鋰化/脫鋰，可以使Si@N-ECGB在300次循環中維持優異的電化學性能(在5 A g-1時為1171.9 mAh g-1)和穩定性(在3 A g-1高達998.1 mAhg-1)，並且在全電池中(Si@ECGB?NMC 811 (Ni:Mn:Co=8:1:1))，該電池具有很高的初始電容量(170 mAh g-1)和實現在100個循環後約84%的維持率。這項工作為實現LiB的高電容量和穩定性提供了潛在的策略。
此外，對於阻礙鋰金屬電池 lithium metal batteries (LMBs)應用的關鍵問題，包括枝晶生長和重複循環過程中的低庫倫效率，因此我們利用水熱法對ECG表面進行氟化改質，然後藉由電泳沉積(EPD)，在沒有任何黏著劑的情況下塗佈到銅箔中(對電極)，這些提議被用於LMBs中的人造固態電解質界面(ASEI)，透過FECG增強的ASEI表現出平滑的Li鍍層以及無枝晶鋰剝落的現象。在結果中表明，使用1 wt% LiNO3混合進1 M LiFSi 之電解液所組裝的半電池展示了高穩定性，在1mAh cm-2 的100個循環中達到了99%的平均庫倫效應 average coulombic efficiency (ACE)。並且極化曲線也顯示了長達250小時的優異性能，同等也說明了新穎的石墨烯氟化方式所構成的ASEI可以成功地在無陽極鋰離子電池anode free lithium batteries（AFLBs）中被使用。
;The surface area of electrode materials in energy storage is critical to enhancing the electrochemical performance through a facile path of ion transportation in the active materials. Furthermore, the improvement by surface modification of electrode materials is proposed by using graphene because of its extraordinarily high surface area, high electric conductivity, and good mechanical properties.
In lithium-ion batteries (LIBs) technology, both Si and lithium metal are candidates for next-generation of anode LIBs due to the high theoretical capacity (> 3000 mAh g-1 ). However, Si anode has critical issues, including the impressive volume change through the lithiation/ delithiation process, unstable solid electrolyte interphase (SEI), and loss off electrical contact. Herein, two strategies were promoted to modify the Si surface as anode materials using electrochemically exfoliated graphene (ECG). First, ECG encapsulated Si nanoparticle (Si NPs) with a spray dry method that exhibited an unique structure with a micro-size ball-like and a void space, which preserves the volume expansion and increases silicon′s electrical conductivity. As a result, the Si@few-layer ECG ball (Si@FL-GB) anode demonstrates a high initial discharge capacity up to 2882.3 mAh g-1 with 86.9% of the initial coulombic efficiency (ICE) at 0.2 A g-1, and high performance at 1360.9 mAh g-1 at high current density (3 A g-1). Second, the surface of Si@ECGB is modified by introducing NH3 gas (Nitrogen resources) that changed a surface layer to Si3N4 and N-doped graphene. This method helps increase the ionic mobility, electrical conductivity and maintain stability in anode LIBs. The electrochemical performance shows that Si@N-ECGB exhibits excellent performance up to 171.9 mAh g-1 (5 A g-1) and high stability of 998.1 mAh g-1 (3 A g-1) until 300 cycles, due to the efficient lithiation/delithiation that maintains the strength of the Si@N-ECGB. In the practical application, Si@N-ECGB||NMC 811 (Ni:Mn:Co=8:1:1) is assembled into full-cell batteries that achieved 170 mAh g-1 initial capacity with high capacity retention up to ~ 84% after 100 cycles. Therefore, these provide a potential strategy for contributing to achieve the high stability anode LIBs.
Also, lithium metal batteries (LMBs) have a critical problem hindering the application, including dendrite growth and low coulombic efficiency during repeated cycles. We modified the surface of ECG by fluorination process with the solvothermal method, then coated into Cu (counter electrode) without any binder by electrophoretic deposition (EPD). These proposed artificial solid electrolyte interphase (ASEI) in LMBs. The ASEI reinforced with F-ECG exhibit smooth Li plating/stripping with no sign dendrites. As a result, F-ECG half-cell in 1 M LiFSi with 1 wt% LiNO3 electrolyte possesses high stability for 100 cycles with average coulombic efficiency (ACE) up to 99 % in 1 mA cm-2 for 1 mAh cm-2. The polarization profile also showed remarkable performance for up to 250 hours. Finally, graphene′s novel fluorination successfully designed ASEI by forming LiF for anode free lithium batteries (AFLBs). |
