# Constructing Enhanced Composite Solid-State Electrolytes with Sb/Nb Co-Doped LLZO and PVDF-HFP
## 3 Results and Discussion  
The XRD patterns of LLZSNO with different contents of Nb are shown in Figure 2a. The diffraction peaks of the samples all match well with the cubic phase LLZO (PDF#80-0457) [31], indicating that LLZO with Sb/Nb co-doping was successfully synthesized. Interestingly, the diffraction peaks of the samples also show a tendency to shift toward higher angles. According to Bragg's law [32], this is related to the decrease in the interplanar distance. The variation of the lattice parameter after co-doping could be obtained through Rietveldrefinement, as shown in Figure 2b. It was found that the lattice parameter decreased with Sb/Nb co-doping; this is likely due to the crystal lattice deformation of garnet LLZO. There are three locations in the cubic LLZO that can accommodate Li: tetrahedral void 24 d, regular octahedral void 48 g, and partial octahedral void 96 h. Due to the mutual repulsion of Li\({}^{+}\), it generally occupies void 96 h. Considering that the 96 h is very close and only half of it can be occupied by Li\({}^{+}\), per formula unit Li\({}_{7}\)La\({}_{3}\)Zr\({}_{2}\)O\({}_{12}\) can provide a total of 9 Li\({}^{+}\) vacancies by the 24 d and 96 h. Li\({}^{+}\) in cubic LLZO is randomly disordered at 24 d and 96 h [33]. More significantly, due to the substitution of partial Zr\({}^{4+}\) by high-valence Nb\({}^{5+}\) and Sb\({}^{5+}\) cations, Li\({}^{+}\) vacancies were generated, resulting in an increase in conductivity. As shown in Figure 2c, the Raman spectra of garnet further show the effect of co-doping on the LLZO. The peaks near 205, 240, 350, 393, 484, and 650 cm\({}^{-1}\) are the characteristic peaks of cubic LLZO [34], which is consistent with the XRD results. This part of the characteristic peak shifts to the right as a whole, and the blue shift means an enhancement of the bonding energy in the region. The results show that LLZO with co-doping has a larger relative displacement than that with only Sb-doping, which indicates that the Nb substitution has a positive effect on the structure of LLZO. This is attributed to the partial structure change of LLZO, which leads to an increase in Li vacancy and more disorder characteristic of Li\({}^{+}\) in the lattice. The spectral bandwidth intensity increases at about 531 cm\({}^{-1}\) after co-doping, indicating a higher degree of distortion of ZrO\({}_{6}\)[35]. Moreover, it can be observed that the peak of the Nb-O bond appears at 750 cm\({}^{-1}\) after co-doping, while the intensity of the Zr-O bond decreases simultaneously, which suggests that the Nb occupies the Zr-site. The valence of Sb in the synthesized LLZSNO was determined by XPS, as shown in Figure 2d. The results show that, compared to the standard electron-binding energy, the peak of 531.1 eV proved that the valence state of the Sb in the LLZSNO should be Sb\({}^{5+}\), which achieves the expected goal of the experiment. Figure 2: (**a**) XRD patterns of LLZSNO powder; (**b**) Rietveld Refined of XRD; (**c**) Raman of LLZSO and LLZSNO; and (**d**) XPS energy spectrum of LLZSNO in Sb 3d orbit. As displayed in Figure 3, all samples of Li\({}_{6.7-\text{x}}\)La\({}_{3}\)Zr\({}_{1.7-\text{x}}\)Sb\({}_{0.3}\)Nb\({}_{\text{x}}\)O\({}_{12}\) (x = 0.05, 0.10, 0.15, and 0.20) show the Nyquist plots consisting of semicircular arcs and straight lines inclined at approximately 45\({}^{\circ}\). The equivalent circuit consists of CPE1, CPE2, and R1, which represent grain-boundary capacitance, electrolyte resistance, and grain-boundary resistance, respectively [36]. It can be seen that the impedances of Li\({}_{6.7-\text{x}}\)La\({}_{3}\)Zr\({}_{1.7-\text{x}}\)Sb\({}_{0.3}\)Nb\({}_{\text{x}}\)O\({}_{12}\) are about 1750 \(\Omega\), 720 \(\Omega\), 930 \(\Omega\), and 1080 \(\Omega\) (for x = 0.05, 0.10, 0.15, and 0.20), in which LLZSNO prepared when x = 0.05 has the smallest impedance. [PERSON] [37] elucidated Li diffusion in LLZO using density-based trajectories calculated by molecular dynamics simulations.