Fig.1

The schematic diagram of the article's review structure"

Fig.2

(a) Schematic diagram of NASICON-type crystal structure, lithium ion occupancy, and ion transport pathways; (b) Schematic diagram of LATP crystal structure[33]; (c) Schematic diagram of LAGP crystal structure[34]"

Fig.3

(a) Difference Fourier maps in the xy plane at z=0 of ND diffraction data of LTP and LATP at different temperatures (displayed in blue for negative scattering length density and orange for positive scattering length density)[37]; (b), (c) Bond valence mismatch and negative nuclear density maps reconstructed by the maximum entropy method for LATP, revealing possible transport pathways[39]"

Fig.4

(a) The minimum migration energy path calculated by NEB-DFT[47]; (b) Migration energies of single-ion migration and cooperative migration in LATP calculated using DFT[44]; (c) Energy distribution diagram and schematic diagram of lithium-ion cooperative migration pathways in LATP-0.16 and LATP-0.50 (the inset is a schematic representation of the intermediate state along the migration path)[48]; (d) A heatmap predicted by DFT for the ease of NASICON synthesis, where the color of the block indicates the number of stable compounds containing a specific metal pair[49]"

Fig.5

(a) AIMD simulations of Li+ transport pathway in LGP and LAGP[46]; (b) Density plot of Li+ trajectory simulated by AIMD method at 500 K[48]; (c) The Van Hove correlation function of Li+ dynamics in AIMD simulations, demonstrating the cooperative effect of migration[44]"

Fig.6

(a) Photograph of the quenched glass-ceramic[57]; (b) Microstructure of microcracks on the surface of the ceramic sheet[57]; (c) Schematic diagram of the microcrack formation process[57]; (d) Ion conductivity distribution of the samples synthesized by the melt-quenching method and the sol-gel method as precursors[59]; (e) XRD patterns of samples sintered at 850 °C for 2 hours using a-LATP and c-LATP as precursors[60]; (f) Particle size distribution of the precursors obtained by the sol-gel method and the solid-phase synthesis method[61]"

Fig.7

(a) Process flowchart of the sol-gel synthesis method for LATP[71]; (b) XRD patterns of LATP synthesized under the same polymer concentration but different pH values[68]; (c) XRD patterns of LATP synthesized under the same pH value but different polymer concentrations[68]; (d) Comparison of the traditional calcination method and the improved carbon framework calcination method for sol-gel synthesis[69]; (e) Phase diagram of ionic conductivity distribution of sintered LATP under different sintering temperatures and holding times when the precursor is in the condition of excess phosphoric acid (LATPex)[70]"

Fig.8

(a) Schematic diagram of the coprecipitation method for the synthesis of LATP[77]; (b) FTIR spectra of LATP powders at different preheating temperatures[77]; (c) XRD patterns of LATP particles calcined at 500—1000 ℃ for 6 h[77]; (d) XRD patterns showing the effect of increased pH on the residual GeO2 in the coprecipitation method[76]"

Fig.9

(a) Flowchart of hydrothermal synthesis of LATP[81]; (b) Schematic diagram of the hydrothermal synthesis of rhombic intermediate products (Al-doped NH4TiOPO4 and Li3PO4)[82]; (c) Structure of LATP obtained through hydrothermal synthesis and lithium-ion dynamics information derived from nuclear magnetic resonance[40]"

Table 1

The advantages, disadvantages and application prospects of common synthesis methods"

Fig.10

(a) Flowchart of the process principle for synthesizing LATP via template method[88]; (b) Schematic diagram of the process for synthesizing LATP via direct ink writing method[89]; (c) Dark-field STEM images of LATP after deposition (AD) and annealing (A) synthesized via PLD method[90]; (d) Schematic diagram of the process principle for synthesizing LAGP via aerosol deposition method[92]"

Fig.11

(a) Relationship between room temperature DC conductivity and relative crystal content[55]; (b) XRD patterns of LATP sintered at different temperatures[69]; (c) XRD patterns of LAGP sintered at different temperatures[71]; (d) Electrolyte impedance plots of LATP sintered at 950 ℃ for different holding times[66]"

Fig.12

SEM images of sintering by (a) SPS (650 ℃, 8 min) and (b) traditional muffle furnace (850 ℃, 6 h)[108]; (c) Schematic diagram of FAST sintering technology equipment[101]; (d) Schematic diagram of UPS technology[102]; (e) Microwave-assisted sintering process and microstructure of sintered samples[105]; (f) Schematic diagram of the cold sintering process[58]"

Table 2

Common synthesis methods and performance parameters of synthesized samples"

Fig.13

(a) Schematic diagram of defect principles at grain boundaries of LASTP and LAYTP at low temperatures[112]; (b) Ionic conductivity plot of Li1.3Al0.3-x R x Ti1.7(PO4)3 with x=0.03 doping of Sc3+, Y3+, and Ga3+ at 423 K[113]; (c) Schematic diagram of the altered Li diffusion channels after the introduction of Mg in LAGP[117]; (d) Schematic diagram of the mechanism of Ta-doped LATP to slow down the reduction of Ti by Li[124]; (e) XPS characterization of the valence state ratio of Ti on the surface of LATP samples doped with different amounts of silicon after contact with Li[126]; (f) Schematic diagram of the principle of doping Nb at the P site in LATP and LAGP; (g) Comparison of bond lengths between PO4 and PO3S after sulfur doping in LATP (sulfur, phosphorus, and oxygen are represented by green, gray, and red, respectively) [134]; (h), (i) Schematic diagrams of changes in Raman spectral peaks of PO4 groups and partial bond lengths after Cl doping in LATP[136]; (j) XRD peaks of F-doped LATP, showing a shift to a smaller angle around 2θ=24.5° [138]; (k) Structural model of F-doped LATP and energy barrier diagrams for Li+ migration to the 36f position before and after doping[139]"

Fig.14

(a) Training data set diagram for Li-Zr-Cl neural network potential training (a total of 34,648 configurations), with the x-axis representing the distance-weighted Steinhart order parameter (OP) and the y-axis representing the density of each configuration[155]; (b) Schematic diagram of the solid-state electrolyte screening process, which screens 452 solid-state electrolyte candidates from 19,480 lithium-containing materials[156]; (c) Uncertainty prediction phase diagram based on Gaussian regression with UCB model in the search space, showing the ionic conductivity (S/cm) of LATP, where higher values correspond to brighter colors[17]; (d) Schematic diagram of the machine learning-assisted process for preparing high-performance solid-state electrolyte films[157]"

Fig.15

Schematic diagram of the current challenges and future application directions for the development of LATP and LAGP"