Understanding the mechanism of Li nucleation and growth is essential for providing long cycle life and safe lithium ion batteries or lithium metal batteries. However, no quantitative report on Li metal deposition is available, to the best of our knowledge. We propose a model for quantitatively understanding the Li nucleation and growth mechanism associated with the solid−electrolyte interphase (SEI) formation, which we name the Li-SEI model. The current transients at various overpotentials initiate the nucleation and growth of Li metal on bare Cu foil. The Li-SEI model considering a three-dimensional diffusion-controlled instantaneous process (J 3D-DC ) with the simultaneous reduction of electrolyte decomposition (J SEI ) due to the SEI fracture is employed for investigating the Li nucleation and growth mechanism. The individual contributions of experimental and theoretical transient states, i.e., the fundamental kinetic values of diffusion coefficient (D), rate of nucleation (N 0 ), and rate constant of electrolyte decomposition (k SEI ), can be determined from the Li-SEI model. Interestingly, J SEI increases with time, indicating that the current contributing from the electrolyte decomposition increases with time due to the SEI fracture upon Li deposition. Meanwhile, the k SEI increases with overpotential, indicating the SEI fracture is more serious at higher overpotential or higher growth rate. The k SEI is smaller in the electrolyte with fluoroethylene carbonate (FEC) additive, indicating that FEC additive can significantly suppress the SEI fracture during Li metal deposition. This proposed model opens a new way to quantitatively understand the Li nucleation and growth mechanism and electrolyte decomposition on various substrates or in different electrolytes.

Anode-free lithium metal batteries are the most promising candidate to outperform lithium metal batteries due to higher energy density and reduced safety hazards with the absence of metallic lithium anode during initial cell fabrication. In general, researchers report capacity retention, reversible capacity, or rate capability of the cells to study the electrochemical performance of anode-free lithium metal batteries. However, evaluating the behavior of batteries from limited aspects may easily overlook other information hidden deep inside the meretricious results or even lead to misguided data interpretation. In this work, we present an integrated protocol combining different types of cell configuration to determine various sources of irreversible coulombic efficiency in anode-free lithium metal cells. The decrypted information from the protocol provides an insightful understanding of the behaviors of LMBs and AFLMBs, which promotes their development for practical applications.

Currently, concentrated electrolyte solutions are attracting special attention because of their unique characteristics such as unusually improved oxidative stability on both the cathode and anode sides, the absence of free solvent, the presence of more anion content, and the improved availability of Li + ions. Most of the concentrated electrolytes reported are lithium bis(fluorosulfonyl)imide (LiFSI) salt with ether-based solvents because of the high solubility of salts in ether-based solvents. However, their poor anti-oxidation capability hindered their application especially with high potential cathode materials (>4.0 V). In addition, the salt is very costly, so it is not feasible from the cost analysis point of view. Therefore, here we report a locally concentrated electrolyte, 2 M LiPF 6 , in ethylene carbonate/diethyl carbonate (1:1 v/v ratio) diluted with fluoroethylene carbonate (FEC), which is stable within a wide potential range (2.5−4.5 V). It shows significant improvement in cycling stability of lithium with an average Coulombic efficiency (ACE) of ∼98% and small voltage hysteresis (∼30 mV) with a current density of 0.2 mA/cm 2 for over 1066 h in Li||Cu cells. Furthermore, we ascertained the compatibility of the electrolyte for anode-free Li−metal batteries (AFLMBs) using Cu||LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC, ∼2 mA h/ cm 2 ) with a current density of 0.2 mA/cm 2 . It shows stable cyclic performance with ACE of 97.8 and 40% retention capacity at the 50th cycle, which is the best result reported for carbonate-based solvents with AFLMBs. However, the commercial carbonate-based electrolyte has <90% ACE and even cannot proceed more than 15 cycles with retention capacity >40%. The enhanced cycle life and well retained in capacity of the locally concentrated electrolyte is mainly because of the synergetic effect of FEC as the diluent to increase the ionic conductivity and form stable anion-derived solid electrolyte interphase. The locally concentrated electrolyte also shows high robustness to the effect of upper limit cutoff voltage.

Herein, we report hierarchical 3D NiMn-layered double hydroxide (NiMn-LDHs) shells grown on conductive silver nanowire (Ag NWs) cores as efficient, low-cost, and durable oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) bifunctional electrocatalysts for metal–air batteries. The hierarchical 3D architectured Ag NW@NiMn-LDH catalysts exhibit superb OER/ORR activities in alkaline conditions. The outstanding bifunctional activities of Ag NW@NiMn-LDHs are essentially attributed to increasing both site activity and site populations. The synergistic contributions from the hierarchical 3D open-pore structure of the LDH shells, improved electrical conductivity, and small thickness of the LDHs shells are associated with more accessible site populations. Moreover, the charge transfer between Ag cores and metals of LDH shells and the formation of defective and distorted sites (less coordinated Ni and Mn sites) strongly enhance the site activity. Thus, Ag NW@NiMn-LDH hybrids exhibit a 0.75 V overvoltage difference between ORR and OER with excellent durability for 30 h, demonstrating the distinguished bifunctional electrocatalyst reported to date. Interestingly, the homemade rechargeable Zn–air battery using the hybrid Ag NW@NiMn-LDHs (1:2) catalyst as the air electrode exhibits a charge–discharge voltage gap of ∼0.77 V at 10 mA cm–2 and shows excellent cycling stability. Thus, the concept of the hierarchical 3D architecture of Ag NW@NiMn-LDHs considerably advances the practice of LDHs toward metal–air batteries and oxygen electrocatalysts.

Graphene-like sulfur-containing graphitic carbon nitride (S-GCN) nanosheets were successfully prepared and thoroughly characterized. A simple synthetic method by a thermal condensation approach was reported for the preparation of S-GCN with trithiocyanuric acid (TCA) as precursor. The electrochemical performances of the 4-nitrophenol (4-NP) sensors were assessed by cyclic voltammetry (CV), amperometry, and differential pulse voltammetry (DPV). Ultrathin S-GCN nanosheets have been employed to enhance electrocatalytic activity, showing remarkable electrochemical behavior toward 4-NP. We thus obtained a wide linear response range from 0.05 to 90 μM, a relatively low detection limit (0.0016 μM), and excellent sensitivity in 0.1 M acetate buffer (ABS, pH 5.5), surpassing the existing modified electrodes in the literature. Moreover, the fabricated S-GCN electrode is selective in the presence of many potentially interfering species. As a result, the S-GCN contains (C with N and S) heteroatoms that probably induced the higher electrocatalytic activity and electrical conductivity behavior toward 4-NP. Besides, the structural defect to generate more active sites on the surface of S-GCN that could boost the fast electron transfer is provoked during the reduction of 4-NP. As a consequence, it is probably sensitive enough for quantitative detection of 4-NP in real samples. S-GCN was also applied to the hydrogenation of 4-NP by NaBH4 under ambient conditions. Thus, implementation of S-GCN nanosheets offers the advantages of simplicity, reliability, durability, and low cost.