Sulfide solid electrolytes (S-SEs) based all-solid-state batteries (ASSBs) have received particular attention due to their outstanding ionic conductivity and higher energy density over conventional lithium-ion batteries. Nevertheless, chemical instability toward...
Li7La3Zr2O12 (LLZO) garnet is
one kind of solid electrolyte drawing extensive attention due to its
good ionic conductivity, safety, and stability toward lithium metal
anodes. However, the stability problem during synthesis and storage
results in high interfacial resistance and prevents it from practical
applications. We synthesized air-stable dual-doped Li6.05La3Ga0.3Zr1.95Nb0.05O12 ((Ga, Nb)-LLZO) cubic-phase garnets with ionic conductivity
of 9.28 × 10–3 S cm–1. The
impurity-phase species formation on the garnet pellets after air exposure
was investigated. LiOH and Li2CO3 can be observed
on the garnet pellets by Raman spectroscopy, X-ray diffraction (XRD),
and X-ray photoelectron spectroscopy (XPS) once the garnets are exposed
to humid air or come in contact with water. The (Ga, Nb)-LLZO garnet
is found to form less LiOH and Li2CO3, which
can be further reduced or removed after drying treatment. To confirm
the stability of the garnet, an electrochemical test of the Li//Li
symmetric cell was also performed in comparison with previously reported
garnets (Li7La2.75Ca0.25Zr1.75Nb0.25O12, (Ca, Nb)-LLZO). The dual-doped (Ga,
Nb)-LLZO showed less polarized and stable plating/stripping behavior
than (Ca, Nb)-LLZO. Through Rietveld refinement of XRD patterns of
prepared materials, dopant Ga was found to preferably occupy the Li
site and Nb takes the Zr site, while dopant Ca mainly substituted
La in the reference sample. The inherited properties of the dopants
in (Ga, Nb)-LLZO and their structural synergy explain the greatly
improved air stability and reduced interfacial resistance. This may
open a new direction to realize garnet-based solid electrolytes with
lower interfacial resistance and superior air stability.
Zinc metal is considered a promising anode material for aqueous zinc ion batteries. However, it suffers from dendrite growth, corrosion, and low coulombic efficiency (CE) during plating/stripping. Herein, a concentrated hybrid (4 m Zn(CF 3 SO 3 ) 2 + 2 m LiClO 4 ) aqueous electrolyte (CHAE) to overcome the challenges facing the Zn anode is reported. The developed electrolyte achieves dendrite-free Zn plating/stripping and obtains an excellent CE of ≈100%, surpassing the previously reported values. The combination of synchrotron-based in operando transmission X-ray microscopy, X-ray diffraction, and ex situ X-ray photoelectron spectroscopy analyses indicate that the denser, anion-derived passivation layer formed using the CHAE facilitates homogeneous current distribution and better prevents freshly deposited Zn from directly contacting the electrolyte than the looser, solvent-derived layers formed from a dilute hybrid aqueous electrolyte (DHAE). The beneficial effects of the CHAE on the compact, dense, and stable salt-anion-derived passivation layer can be attributed to its unique solvation structure, which suppresses the water-related side reactions and widens the electrochemical potential window. In the hybrid Zn||LiFePO 4 configuration, the CHAE-based cell delivered a stable performance of CE >99% and capacity retention >90% after 285 cycles. In contrast, the DHAE-based cell exhibits capacity retention of <65% after 170 cycles.
It is essential to decouple the interfacial reactions taking place at the anode and cathode in rechargeable batteries. However, due to the reactive nature of Li, it is challenging to use Li‐metal batteries (LMBs) protocol to decouple the interfacial reactions. The by‐products from the anode or cathode become mixed in Li/NMC111 cells, which make decoupling interfacial reactions difficult. Here, reactions at electrodes are successfully decoupled and demystified using a protocol combining anode‐free LMB (AFLMB) with online electrochemical mass spectroscopy. LiPF6 in ethylene carbonate (EC)/diethyl carbonate (DEC) and EC/ethyl methyl carbonate (1:1 v/v%) electrolytes are used to compare interfacial reactions in Li/NMC111 and Cu/NMC111 cells. In Cu/NMC111, the evolution of CO2, CO, and C2H4 gases at the initial stage of first charging is due to interfacial reactions at Cu surface due to solid–electrolyte‐interphase formation. However, the evolution of CO2 and CO gases at high voltage in the entire cycles is associated with chemical and/or electrochemical electrolyte oxidation at the cathode. This work paves a new concept to decouple interfacial reactions at electrodes for developing electrochemically stable electrolytes to improve the performance with the long‐cycling life of AFLMBs and LMBs.
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