Ultra-thick LATP-LFP ceramic cathodes by HPLT for high performance All Solid-State Li-Metal Batteries
ARIAS-SERRANO B. 1, RODRÍGUEZ DE LOS SANTOS I. 1, ROMERO GARCÍA I. 1, LEVENFELD LAREDO B. 1, VÁREZ ÁLVAREZ A. 1
1 Universidad Carlos III de Madrid, UC3M, Madrid, Spain
Composite cathodes combining solid-state electrolytes (SSEs) and cathode active materials (CAMs) in All-Solid-State-Batteries (ASSBs) benefit from an extended interaction of the SSEs and the CAMs in a mixed ion- and electron-conductive SSE-CAM structure. Ideally, SSE and CAM should form an interconnected 3D-network with a low interfacial impedance improving charge transfer and transport and therefore minimizing loss in the battery [1,2]. Among SSEs, phosphate-based NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP) combines competitive ionic conductivity, good chemical stability, and promising thermal stability with phosphate-based CAMs such as LiFePO4 (LFP), LiCoPO4 or LiMn0.5Fe0.5PO4 at 700-800 °C in inert atmosphere [3-5].
A main drawback of thick electrodes is their limited ionic diffusion so thus lowering their rate cyclability compared to conventional electrodes. Although previous research revealed that for additive-free single-phase electrodes an appropriate porosity is necessary to have sufficient electrochemical activity , a relatively compact structure in dual-phase all-ceramic cathodes is beneficial for shortening the diffusion pathways for both ions and electrons . The present work was focused on the preparation for the first time of ultra-thick dual-phase LATP-LFP ceramic cathodes for ASSBs via a combined approach based on a facile high-pressure low-temperature (HPLT) technique followed by direct co-firing. Variable-loading (40-55 vol.% of solids) of commercially available LATP and carbon coated LFP powders (40:60 wt.%) were pre-mixed with a multicomponent binder comprised of PP, PW and SA (50:46:4 wt.%) in a Haake Rheomex at 180 °C and pressed at 50 MPa and 190 °C for 50 min in a hot plate press. A one-step debinding and sintering strategy, consisting of 1h-dwells at 190, 400 and 600 °C followed by a 2h-dwell at 650-850 °C in flowing Ar/H2 atmosphere, was applied to the pressed LATP-LFP disk-shaped samples of 800-1000 µm of nominal thickness and 16 mm of diameter. XRD studies confirmed that no secondary phases can be detected in samples sintered up to 700 °C, whereas a significant fraction of impurities such as Li2FeTi(PO4)3 and AlPO4 can be found in samples sintered at higher temperatures. Combined SEM/EDS investigations showed a homogeneous distribution of LATP and LFP phases in a relatively compact structure (porosity <20 vol.%) with no evidence of diffusion across the LATP-LFP interphase. The electrochemical performance of ceramic LATP-LFP disks was evaluated at 30 °C by electrochemical impedance spectroscopy using gold electrodes and chronopotentiometry in two-electrode coin cells (CR2032) with commercial separators/liquid electrolytes and Li-metal at C/50-C/2 in a potential range from 4.0 to 2.8 V. The processed composites with a high mass loading (120 mg/cm2) were stable and demonstrated competitive ionic and electronic conductivities, a high areal capacity (>20 mAh/cm2), promising cycling capabilities (167 mAh/g at C/10), and a high coulombic efficiency (99 %).
 Grey, C. P. et al. (2020). Nature communications, 11(1), 6279
 Chen, C. et al. (2021). Advanced Energy Materials, 11(13), 2003939
 Xu, Q. et al. (2022). Small, 18(21), 2200266
 Manthiram, A. (2020). Nature communications, 11(1), 1550
 Gellert, M. et al. (2018). Ionics, 24, 1001-1006
 Sotomayor, M. E. et al. (2018). Journal of Materials Chemistry A, 6(14), 5952-5961