Cold isostatic sintering to enhance the ionic conductivity of LiFePO4

Abstract We report on novel cold sintering technique (e.g. Cold Isostatic Sintering (CIS)) to enable fabrication of dense LiFePO4 (LFP) cathodes. This approach might be ideal to assembly a solid state Li-Ion batteries as the room processing temperature can effectively prevent undesired thermal degradation between the layers (e.g. electrolyte and anode). Different processing setups and solvents are investigated (H2O, 0.1 M LiOH, ethanol, dimethyl sulfoxide (DMSO)). Our analysis rationalizes the complex mechano-chemical interaction between liquid and particle (i.e. congruent vs incongruent dissolution) during the transient liquid phase sintering. Materials prepared using cold isostatic under 400 MPa with 10 vol.% of DMSO can reach ionic and electronic conductivities as high as 1.9 × 10-3 S/cm and 1.2 × 10-4 S/cm. They outperform benchmark values for samples produced using uniaxial cold sintering process. It is anticipated that the even pressure distribution generated using an isostatic sintering technique offers an industrially scalable and reliable processing route to assemble an operational solid battery with remarkably improved performance. In comparison with traditional firing, the absence of heating enables fabrication of LFP cathodes at a fraction of embodied energy.