Maximizing interface stability in all-solid-state lithium batteries through entropy stabilization and fast kinetics

Abstract

The positive electrode|electrolyte interface plays an important role in all-solid-state Li batteries (ASSLBs) based on garnet-type solid-state electrolytes (SSEs) like Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO). However, the trade-off between solid-solid contact and chemical stability leads to a poor positive electrode|electrolyte interface and cycle performance. In this study, we achieve thermodynamic compatibility and adequate physical contact between high-entropy cationic disordered rock salt positive electrodes (HE-DRXs) and LLZTO through ultrafast high-temperature sintering (UHS). This approach constructs a highly stable positive electrode|electrolyte interface, reducing the interface resistance to 31.6 Ω·cm² at 25 °C, making a 700 times reduction compared to the LiCoO₂ | LLZTO interface. Moreover, the conformal and tight HE-DRX | LLZTO solid-state interface avoids the transition metal migration issue observed with HE-DRX in liquid electrolytes. At 150 °C, HE-DRXs in ASSLBs (Li|LLZTO | HE-DRXs) exhibit an average specific capacity of 239.7 ± 2 mAh/g at 25 mA/g, with a capacity retention of 95% after 100 cycles relative to the initial cycle-a stark contrast to the 76% retention after 20 cycles at 25 °C in conventional liquid batteries. Our strategy, which considers the principles of thermodynamics and kinetics, may open avenues for tackling the positive electrode|electrolyte interface issue in ASSLBs based on garnet-type SSEs.

Fig. 1. Schematic of the construction of the highly stable HE-DRX | LLZTO interface.

Schematic of the construction of the highly stable HE-DRX | LLZTO interface using the UHS process: the high reaction temperature of the UHS technology enables the rapid synthesis of the HE-DRX positive electrode on the LLZTO surface, while the short sintering time and the stability of the HE-DRXs ensure a conformal positive electrode interface without any side reactions.

Fig. 2. Synthesis and characterization of HE-DRXs.

a Rapid synthesis of TM6 with UHS at 1100 °C in 3 s. b XRD pattern of TM6 synthesized by UHS. c TEM-EDS mapping of the TM6 particle. d XPS spectra of Mn 2p. SEM images of TM2 (e), TM4 (f) and TM6 (g) sintered at 1150 °C for 10 s. h Comparison of synthesis temperature and sintering temperature of TM2, TM4, and TM6.

Fig. 3. Chemical stability of TM6 and LLZTO.

a In situ XRD patterns of LLZTO and TM6. b DSC of TM2 and LLZTO, TM4 and LLZTO, and TM6 and LLZTO. EDS mapping (c) and Line profiles (d) of the TM6 | LLZTO interface. e TEM images of TM6 | LLZTO interface. f XRD patterns of LLZTO and TM6 heated by UHS. g Comparison of chemical stability between different positive electrodes and LLZTO. h Each individual component of TM6 vs LLZTO pseudobinary phase diagram. The most likely reaction products are shown in Supplementary Table 2.

Fig. 4. Characterization of the TM6 | LLZTO interface.

a Schematic of the in situ synthesis of HE-DRXs on dense LLZTO. SEM images (b–d) and SEM/EDS mapping (e) of TM6 | LLZTO interface. f XRD of the in situ synthesized TM6. g Zoomed in EIS of TM6 symmetric cells. h EIS of LiCoO₂ symmetric cells.

Fig. 5. Electrochemical performance of TM6-ASSLBs.

a Charge/Discharge profiles of the all-solid-state battery at different rates from 25 mA/g to 100 mA/g. XRD patterns (b) and SEM/ EDS images of the HE-DRX-ASSLBs c before and d after cycling. e Cycling performance and f Coulombic efficiency of the HE-DRX-ASSLBs at 25 mA/g. All electrochemical measurements were performed at 150 °C without organic electrolyte and external pressure.