No abstract

Sodium (Na) metal is considered a promising anode material for high-energy Na batteries due to its high theoretical capacity and abundant resources. However, uncontrollable dendrite growth during the repeated Na plating/stripping process leads to the issues of low Coulombic efficiency and short circuits, impeding the practical applications of Na metal anodes. Herein, we propose a silver-modified carbon nanofiber (CNF@Ag) host with asymmetric sodiophilic features to effectively improve the deposition behavior of Na metal. Both density functional theory (DFT) calculations and experiment results demonstrate that Na metal can preferentially nucleate on the sodiophilic surface with Ag nanoparticles and uniformly deposit on the whole CNF@Ag host with a “bottom-up growth” mode, thus preventing unsafe dendrite growth at the anode/separator interface. The optimized CNF@Ag framework exhibits an excellent average Coulombic efficiency of 99.9% for 500 cycles during Na plating/stripping at 1 mA cm–2 for 1 mAh cm–2. Moreover, the CNF@Ag-Na symmetric cell displays stable cycling for 500 h with a low voltage hysteresis at 2 mA cm–2. The CNF@Ag-Na//Na3V2(PO4)3 full cell also presents a high reversible specific capacity of 102.7 mAh g–1 for over 200 cycles at 1 C. Therefore, asymmetric sodiophilic engineering presents a facile and efficient approach for developing high-performance Na batteries with high safety and stable cycling performance.

Nonuniform ion flux triggers uneven lithium (Li) deposition and continuous dendrite growth, severely restricting the lifetime of Li-metal batteries (LMBs). Herein, an electronegative poly(pentafluorophenyl acrylate) (PPFPA) polymer brush-grafted Celgard separator signed as PPFPA-g-Celgard is designed to precisely construct one-dimensionally directed Li + flux at the nanoscale so as to realize faster ion transport and ultra-stable Li deposition. The grafting of PPFPA polymer chains is enabled by the simple bio-inspired engineering of surface-initiated atom transfer radical polymerization chemistry. Both theoretical and experimental analyses demonstrate an obvious increase by almost two times in Li + affinity and ion transfer kinetics for PPFPA-g-Celgard over the Celgard separator. Reversible and stable Li plating/stripping can be realized by rapidly switching from 0.5 to 6 mA cm -2 . Besides, the Li | PPFPAg-Celgard | LiFePO 4 full cell exhibits universal and long-term cyclability with a capacity retention of 83% over 700 cycles in ether electrolyte and 92.9% for over 300 cycles in carbonate electrolyte as well. This study represents a new direction for the general design of advanced separators with typical surface topochemistry and self-limited ion transport channels in the application of high-performance LMBs.

Lithium–sulfur (Li–S) batteries have attracted numerous attention owing to their overwhelming theoretical capacity. However, the dissolution and shuttle effect of lithium polysulfides (LiPSs) have seriously limited the development of Li–S batteries. Herein, we rationally designed a dual-engineered nanofibrous composite separator with a Janus structure to both physically and chemically block LiPS shuttling in Li–S batteries. The separator, consisting of a cross-linked poly­(vinyl alcohol)/poly­(acrylic acid) (CPP) composite nanofiber matrix and the electrosprayed poly­(vinyl alcohol) (PVA)/zeolitic imidazolate framework-8 (ZIF-8) layer on the cathode side, is fabricated through a facile electrospinning–electrospray coupling approach and signed as CPP@PVA/ZIF-8. The intrinsic narrow size and opened Lewis acid sites of ZIF-8 both confine free transport of LiPS anions. Meanwhile, the cross-linked CPP layer with abundant electronegative groups (−COOH) can shield the LiPS shuttle while ensuring the integrity of the flexible separator. Benefiting from the unique Janus structure, the CPP@PVA/ZIF-8 separator demonstrates a high initial capacity of 1125 mAh g–1 at a good coulombic efficiency of 98% over 300 cycles at 0.1 C. This work not only establishes a combined strategy to immobilize LiPSs but also provides novel interfacial engineering modification ideas for the development of high-performance separators in Li–S batteries.

No abstract