Development of full-cell lithium-ion batteries with innovative NFA-SiO2/C electrode components

In this doctoral study, advanced electrode materials for next-generation lithium-ion batteries were systematically designed, synthesized, and evaluated with the dual goals of achieving high energy density and long cycle life. On the cathode side, three different compositions of LiNi0.8FexAlyO2 (NFA) layered oxides were developed as high-Ni cathode materials, while on the anode side, amorphous SiO2 and its carbon-coated derivative (SiO2/C) were synthesized. A comprehensive set of characterization methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and various electrochemical testing protocols, were employed to reveal the structural, morphological, chemical, and electrochemical features of the materials. Both half-cell and full-cell configurations were investigated, and the outcomes provided new insights into the design of cost-effective and sustainable electrode systems for high-performance lithium-ion batteries. The NFA cathodes were synthesized using a sol-gel route, which allowed for precise control over particle morphology and elemental distribution. XRD analyses confirmed that all three cathodes crystallized into a well-defined layered structure belonging to the rhombohedral R-3m space group, with no detectable secondary phases. Fe and Al co-doping led to measurable changes in lattice parameters; specifically, Fe substitution enlarged the interlayer spacing, which can facilitate faster Li-ion diffusion kinetics and reduce cation mixing. SEM micrographs showed that all cathode particles had spherical morphologies with relatively uniform size distributions, although increasing Fe content introduced localized surface irregularities. TEM imaging further confirmed the preservation of the layered stacking sequences, while also demonstrating that Fe–Al incorporation stabilized the crystalline order at the nanoscale. XPS results indicated the coexistence of Ni+2 and Ni+3 oxidation states, with Fe and Al doping contributing to surface charge compensation and improved electronic stability. Raman spectra displayed the expected vibration modes for layered oxides, with NFA 1 showing sharper peaks and narrower linewidths compared to NFA 2 and NFA 3, suggesting a higher degree of structural ordering. Similarly, FTIR spectra confirmed the stability of characteristic metal–oxygen stretching vibrations, with subtle shifts attributable to Fe incorporation. Collectively, these analyses revealed that while all three NFA compositions preserved the essential layered framework, NFA1 exhibited the most stable and ordered crystal structure, correlating directly with its superior electrochemical performance. The anode materials were synthesized via the Stöber process to produce amorphous SiO2 spheres. XRD patterns confirmed the amorphous nature of pristine SiO2, while SEM and TEM imaging revealed highly uniform spherical morphologies with smooth surfaces. A subsequent carbon-coating step produced SiO2/C core–shell structures, xxiv verified by TEM images showing a continuous carbon layer enveloping the silica spheres. XPS spectra confirmed the presence of sp2-hybridized carbon species alongside Si-O-Si bonds, demonstrating successful carbon encapsulation. Raman spectroscopy identified distinct D and G bands characteristic of graphitic domains, indicating that the carbon layer possessed partial graphitization, which enhances electronic conductivity. FTIR results confirmed the preservation of Si-O-Si linkages and the addition of surface carbon-related functional groups. From a structural standpoint, the carbon coating endowed SiO2 with significantly improved electrical conductivity and mechanical robustness, mitigating the well-known challenges of silicon-based anodes such as large volume expansion and unstable solid-electrolyte interphase (SEI) formation. Electrochemical evaluation validated these observations, as the SiO2-C anode exhibited higher coulombic efficiency, reduced irreversible capacity losses, and better long-term cycle stability compared to bare SiO2. Among the three NFA cathodes tested in half-cell configurations against lithium metal, NFA 1 clearly outperformed NFA 2 and NFA 3. After 100 cycles, NFA 1 maintained a capacity of 148.34 mAh/g with 83,22% capacity retention, significantly higher than the other two compositions. The increasing Fe content in NFA 2 and NFA 3 led to noticeable degradation in both capacity and retention, suggesting that while Fe substitution can stabilize the layered framework and act as a cost-effective replacement for cobalt, excessive Fe content compromises structural integrity and cycle life. The balance between Fe and Al was found to be critical: moderate Fe doping (as in NFA1) improved Li-ion transport and structural stability, whereas higher levels disrupted long-term cycling. These findings highlight the dual advantage of Fe substitution-environmental and economic sustainability combined with electrochemical stability-while emphasizing the necessity of compositional optimization. Electrochemical testing of the anode materials reinforced the structural findings. Bare SiO2 showed poor cycling stability and significant irreversible capacity losses, consistent with previous literature. In contrast, SiO2/C delivered markedly improved performance, attributed to the carbon shell's ability to enhance conductivity, accommodate volume changes, and form a more stable SEI. This demonstrates that carbon encapsulation is an effective strategy to unlock the potential of silica-based anodes, which have historically suffered from structural and electrochemical limitations. In full-cell performance, an original cell design was achieved by combining the NFA1 cathode with the SiO2/C anode. This full cell initially reached a capacity of 153.75 mAh/g, and by the 100th cycle, it retained 134.50 mAh/g, corresponding to a capacity retention of 87.47%. Additionally, for comparison, a full cell was constructed using a commercial NCA cathode and SiO2/C anode. This cell initially reached a capacity of 158.41 mAh/g and retained 129.68 mAh/g at the end of 100 cycles, corresponding to 77.84% capacity retention. Considering these results, it was determined that the addition of iron significantly enhances capacity performance in nickel-rich LiNiO2-derived cathodes by improving structural stability and redox behavior. Furthermore, the discharge capacities of the NFA1-SiO2/C and NCA-SiO2/C full cells were compared to increasing current rates ranging from C/10 to 2C. Both cells delivered high discharge capacities at low current; however, while the capacity of the NCA cell dropped significantly with increasing current rate, the iron-doped NFA cell maintained higher capacity retention. Electrochemical impedance spectroscopy (EIS) tests were conducted on the NFA 1-SiO2/C full cell before cycling and after 100 cycles. The Rct value was determined to be 93.50 ohms before cycling and increased to 122.50 ohms xxv after cycling. All the data obtained indicate that the NFA1-SiO2/C full cell represents a unique combination rarely seen in the literature, and offers a promising alternative, particularly for electric vehicles and high-capacity energy storage systems. This thesis provides several key contributions to the field of lithium-ion battery research. First, it experimentally demonstrates that Fe substitution for Co in high-Ni cathodes is a viable strategy to reduce costs and improve sustainability, provided that the Fe content is optimized. Second, it shows that carbon encapsulation of SiO2 is an effective route to stabilize anodes based on abundant, low-cost materials, overcoming limitations associated with high volume changes and poor conductivity. Most importantly, it validates a novel full-cell system, NFA 1-SiO2/C, which combines these two optimized electrodes into a single high-performance battery. The results establish a foundation for future research on Fe-doped Ni-rich cathodes and silica-based composite anodes, and they highlight the practical feasibility of such materials in real-world energy storage systems.