Current understanding and applications of the cold sintering process

In traditional ceramic processing techniques, high sintering temperature is necessary to achieve fully dense microstructures. But it can cause various problems including warpage, overfiring, element evaporation, and polymorphic transformation. To overcome these drawbacks, a novel processing technique called “cold sintering process (CSP)” has been explored by Randall et al. CSP enables densification of ceramics at ultra-low temperature (≤ 300 °C) with the assistance of transient aqueous solution and applied pressure. In CSP, the processing conditions including aqueous solution, pressure, temperature, and sintering duration play critical roles in the densification and properties of ceramics, which will be reviewed. The review will also include the applications of CSP in solid-state rechargeable batteries. Finally, the perspectives about CSP is proposed

Synthesis of SnO2 nanoparticles with varying particle sizes and morphologies by hydrothermal method

Using ammonia solution and tin chloride as the precursors: tin oxide nanoparticles with different particle sizes and morphologies were synthesised by varying the concentration, heating temperature and ripening time via hydrothermal method. The particles synthesised were characterised by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The TEM micrographs show that rod-like nanoparticles were synthesised when the SnCl 4 solution concentration was less than 1.0 mol/L, which was changed to oval shape when the concentration increased above 2.0 mol/L. Polygonal shaped nanoparticles were observed at 220 °C for 48 hours. It was also found that changing temperature had little effect on the morphology but great influence on the size of the particles, which increased from 10 nm to 120 nm from 160 °C to 220 °C and 12 nm to 55 nm from 6 h to 48 h at 200 °C, respectively. XRD patterns indicated that all of nanoparticles synthesised were tin oxide

Microstructure and ionic conductivities of NASICON-type Li₁.₃A1₀.₃Ti₁.₇(PO₄)₃ solid electrolytes produced by cold sintering assisted process

Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a promising solid electrolyte for lithium-ion batteries. However, it is challenging to densify LATP ceramics at reduced sintering temperature while preserving their electrical properties. Herein, LATP ceramics were pre-densified via cold sintering process (CSP) at 250 °C for 1 h and exhibited room temperature ionic conductivity of 2.01 × 10−6 S/cm. Subsequent post-annealing at as low as 900 °C for 1 h resulted in two orders of magnitude improvement in both grain boundary conductivity and total conductivity, compared to those of as-CSPed LATP. The optimal total conductivity (4.29 × 10−4 S/cm) obtained from post-annealed material is among the best reported values so far. It is also 5 times greater than the conductivity (8.51 × 10−5 S/cm) of the conventionally sintered LATP. We propose that post-annealing effectively eliminates amorphous insulating phases generated during CSP and promotes crack-free microstructure with moderate grain growth, which collectively contributes to dramatically enhanced conductivity. This work unambiguously demonstrates that CSP-assisted process can avoid the detrimental effects of high temperature associated with conventional sintering on microstructure and conductivity, and thus is a cost-effective processing route for fabrication of solid-state electrolytes for battery applications

Supplementary information files for Microstructure and ionic conductivities of NASICON-type Li₁.₃A1₀.₃Ti₁.₇(PO₄)₃ solid electrolytes produced by cold sintering assisted process

Supplementary files for article Microstructure and ionic conductivities of NASICON-type Li₁.₃A1₀.₃Ti₁.₇(PO₄)₃ solid electrolytes produced by cold sintering assisted process Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a promising solid electrolyte for lithium-ion batteries. However, it is challenging to densify LATP ceramics at reduced sintering temperature while preserving their electrical properties. Herein, LATP ceramics were pre-densified via cold sintering process (CSP) at 250 °C for 1 h and exhibited room temperature ionic conductivity of 2.01 × 10−6 S/cm. Subsequent post-annealing at as low as 900 °C for 1 h resulted in two orders of magnitude improvement in both grain boundary conductivity and total conductivity, compared to those of as-CSPed LATP. The optimal total conductivity (4.29 × 10−4 S/cm) obtained from post-annealed material is among the best reported values so far. It is also 5 times greater than the conductivity (8.51 × 10−5 S/cm) of the conventionally sintered LATP. We propose that post-annealing effectively eliminates amorphous insulating phases generated during CSP and promotes crack-free microstructure with moderate grain growth, which collectively contributes to dramatically enhanced conductivity. This work unambiguously demonstrates that CSP-assisted process can avoid the detrimental effects of high temperature associated with conventional sintering on microstructure and conductivity, and thus is a cost-effective processing route for fabrication of solid-state electrolytes for battery applications.  </p