Li_1-xAl_xTi_2-x (PO₄)₃ (LATP) ceramics are claimed to be one of the most attractive for Solid State Electrolytes (SSEs) ceramics for the next generation of Li batteries.[1] This is due to its advantages, such as non-flammability, excellent electrochemical stability, no leakage risk, non-volatile materials, and low production costs. As the most important component of All Solid-State Lithium Battery (ASSLB), the high ionic conductivity, good interfacial compatibility and stability are the basic requirements, but some of them still remain a challenging. In addition, the search for suitable electrolytes with sufficiently high ionic conductivity does also includes the development of new eco-friendly processing techniques. 

As an alternative, solid electrolyte LATP ceramics have been successfully sintered by Cold Sintering Process (CSP) using transient liquid phase (TLP) and solid modifiers. This process allows samples to be sintered below 200 ºC, meaning that composites such as ceramics in polymer can be sintered.  And, of course, to reduce CO₂ emissions in line with the European Climate Law, which requires a reduction in net greenhouse gas emissions of at least 55% by 2030.[2]

Here, we have studied the CSP to sinter ceramic electrolytes at 150 ºC and ~700 MPa, to boost a competitive ionic conductivity. A screening upon the LAPT solid electrolyte, from morphology and particle size, the nature and content of TLP, including the effect of polymer addition, shows that SE show relative density in the range of 85 – 90 % of the theoretical value of LATP, and the total ionic conductivity achieved by CSP is competitive with those sintered by high temperature treatments. Electrochemical impedance spectroscopy (EIS) technique is employed during the sintering process as a control tool to monitor the densification.[3]

Moreover, EIS is also used during the cycling of the half-cells to identify limiting factors of the cold-sintered electrolyte kinetics and to predicts the overall electrochemical behaviour. The results suggest that ionic conductivity fading can occur in the prepared samples due to the low grain boundary ionic conductivity and secondary phases in the intergranular regions, and that additives used in the processing are critical to the final microstructure.  

The viability of a simple and innovative method of densifying ceramic powders at low temperatures by applying uniaxial pressure and using a transient acid solution is demonstrated.