Decarbonising manufacturing of solid electrolytes for lithium-ion battery applications

Producing LATP ceramics at reduced sintering temperature while preserving their good electrical performance.

All-solid-state batteries (ASSBs) are promising solutions for energy storage and electric vehicle applications. Solid-state electrolytes are critical components to enable ASSBs.

Compared to the liquid electrolytes found in conventional lithium batteries, solid-state electrolytes, in particular, inorganic oxide electrolyte, could endow ASSBs significantly higher energy densities and greater safety. However, manufacturing of solid-state electrolytes is quite challenging. 

Li1.3Al0.3Ti1.7(PO4)3 (LATP) is one of the most famous oxide electrolytes because of its high electrical conductivity (10-4 - 10-3 S/cm at room temperature) and remarkable stability against exposure to air/moisture.

However, the manufacturing of LATP ceramics is conventionally conducted at high temperature (1000 - 1200 °C) and prolonged dwell time (2 - 12 h). Such a harsh processing condition not only causes the decomposition of LATP, but also deteriorates electrical conductivity of LATP ceramics.

In addition, conventional manufacturing methods leads to high energy consumption and high carbon emission. Therefore, it is important to find an alternative manufacturing route which enables the production of LATP ceramics at a reduced sintering temperature while preserving their good electrical performance.

Research aims

Cold sintering process (CSP) is a novel ceramic processing technique, by which ceramic powders can be consolidated at ultra-low temperature (< 300 °C) within a short time (15 - 60 min). In this work, LATP ceramics will be produced by CSP-assisted process. The effect of processing variables (mainly processing temperature) on the evolution of microstructure and electrical conductivity will be investigated.

Methodology

LATP ceramics were produced by CSP and subsequent heat treatment (at temperatures much lower than those used for the conventional sintering). For comparison, LATP ceramics were also fabricated by conventional sintering.

Findings

We first produced LATP ceramics by CSP at 250 °C for 1 h. The as-CSPed materials were then heated at as low as 900 °C for short time (1 h) to achieve dense microstructure and high electrical conductivity up to 4.29 × 10-4 S/cm. The obtained conductivity in this work is comparable to the best reported values so far.

For comparison, the best total conductivity from LATP ceramics produced by conventional method at 1000 °C for 1 h is only 8.51 × 10-5 S/cm, which is five times lower than the corresponding value from above CSPed LATP.

Direct comparison of our results with those obtained from other processing routes, such as hot press sintering, spark plasma sintering, microwave sintering, clearly demonstrate the advantages of the CSP-assisted process over all other techniques for fabrication of solid-state electrolytes, such as reduced temperature and processing time, controllable microstructure, and low energy consumption. 

Impact

As a low energy consumption and decarbonising processing route, CSP-assisted process enables the manufacture of functional ceramics with excellent performance – something other processing routes cannot currently deliver.

References

Experts involved