| dc.description.abstract | 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). | en_US |