Anode-Free Sodium Metal Pouch Cell Using Cu3P Nanowires In Situ Grown on Current Collector.

Anode-free sodium metal battery (AFSMB) promises high energy density but suffers from the difficulty of maintaining high cycling stability. Nonuniform sodium (Na) deposition on the current collector is largely responsible for capacity decay in the cycling process of AFSMB. Here, a unique copper phosphide (Cu3P) nanowire is constructed on copper (Cu3P@Cu) as a sodium deposition substrate by an in situ growth method. Superior electrochemical performance of Cu3P@Cu anode is delivered in asymmetric cells with an average Coulombic efficiency of 99.8% for over 800 cycles at 1 mA cm-2 with 1 mA h cm-2. The symmetric cell of Cu3P@Cu displayed a cycling lifespan of over 2000 h at 2 mA cm-2 with 1 mA h cm-2. Cryo-transmission electron microscope characterization and first principles calculation revealed that the low Na+ absorption energy and low Na+ diffusion energy barrier on Na3P promoted uniform Na nucleation and deposition, thus enhancing the Na surface stability. Moreover, anode-free Na3V2(PO4)3//Cu3P@Cu full pouch cell delivered a considerable cycling capacity of ≈15 mA h in 170 cycles, demonstrating its practical feasibility.

Prediction of Novel Trigonal Chloride Superionic Conductors as Promising Solid Electrolytes for All-Solid-State Lithium Batteries.

Recently emerging lithium ternary chlorides have attracted increasing attention for solid-state electrolytes (SSEs) due to their favorable combination between ionic conductivity and electrochemical stability. However, a noticeable discrepancy in Li-ion conductivity persists between chloride SSEs and organic liquid electrolytes, underscoring the need for designing novel chloride SSEs with enhanced Li-ion conductivity. Herein, an intriguing trigonal structure (i.e., Li3SmCl6 with space group P3112) is identified using the global structure searching method in conjunction with first-principles calculations, and its potential for SSEs is systematically evaluated. Importantly, the structure of Li3SmCl6 exhibits a high ionic conductivity of 15.46 mS cm-1 at room temperature due to the 3D lithium percolation framework distinct from previous proposals, associated with the unique in-plane cation ordering and stacking sequences. Furthermore, it is unveiled that Li3SmCl6 possesses a wide electrochemical window of 0.73-4.30 V vs Li+/Li and excellent chemical interface stability with high-voltage cathodes. Several other Li3MCl6 (M = Er, and In) materials with isomorphic structures to Li3SmCl6 are also found to be potential chloride SSEs, suggesting the broader applicability of this structure. This work reveals a new class of ternary chloride SSEs and sheds light on strategy for structure searching in the design of high-performance SSEs.

First-Principles Study on Polymer Electrolyte Interface Engineering for Lithium Metal Anodes.

Modifying the interface between the lithium metal anode (LMA) and the electrolyte is crucial for achieving high-performance lithium metal batteries (LMBs). Recent research indicates that altering Li-metal interfaces with polymer coatings is an effective approach to extend LMBs' cycling lifespan. However, the physical properties of these polymer-Li interfaces have not yet been fully investigated. Therefore, the structural stability, electronic conductivity, and ionic conductivity of polymer-Li interfaces were examined based on first-principles calculations in this study. Several representative polymer compounds utilized in LMBs were assessed, including polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyethylene oxide (PEO). Our research revealed that lithium fluoride is formed upon fluoropolymer degradation, explaining previously observed experimental results. Polymers containing nitrile groups exhibit strong adhesion to lithium metal, facilitating the formation of the stable interface layer. Regarding electronic conductivity, the fluoropolymers preserve a good insulating property, which diminished marginally in the presence of lithium, but that of PAN and PEO significantly reduces. Additionally, lithium diffusion on PTFE and PEO demonstrates low diffusion barriers and high coefficients, enabling easy transportation. Overall, our investigation reveals that the interfaces formed between various polymers and LMA have distinct characteristics, providing new fundamental insights for designing composites with tailored interface properties.