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.

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.

Organic electrolytes react aggressively with lithium (Li) active materials, especially at 60 °C, exhibiting uncontrolled dendrite growth. Herein, β-poly­(vinylidene difluoride) (PVDF) polymer conformal coating on copper (Cu) is successfully prepared via electrospinning. The charge/discharge performance of the anode-free full cell configuration, either Cu@β-PVDF∥NMC or Cu@α-PVDF∥NMC, is very poor at room temperature. Interestingly, when the Cu@β-PVDF∥NMC cell treated with five charge/discharge cycles at 60 °C, termed thermal–electrochemical activation (TEA), achieves the capacity retention of 68.36 and 78.45% at the 20th cycle, it progresses in the following cycles at 25 and 60 °C, respectively. Even though it is treated with TEA, the Cu@α-PVDF∥NMC cell attains the capacity retention of only 35.36% at the 20th cycle at 60 °C. The adsorption of β-PVDF on the Li surface is more thermodynamically favorable than α-PVDF from the density functional theory calculation, whereas polar β-PVDF is seen as more effective in guiding the lithium cation flux. β-PVDF and the plated Li react to form a robust LiF-rich solid electrolyte interface . Unlike what is commonly perceived, TEA of β-PVDF can improve the interfacial chemistry and result in a compact deposition of lithium and stable cycling performance. The findings can apply to the conformal coating on Cu in anode-free batteries and other lithium metal batteries with liquid or solid electrolytes.

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Li1.5Al0.5Ge1.5(PO4)3 (LAGP), is among the promising solid electrolytes for next lithium battery generation. Nevertheless, its lower bulk and grain boundary ionic conductivity are among the major restrictions for its practical...