Precise Control of Li⁺ Directed Transport via Electronegative Polymer Brushes on Polyolefin Separators for Dendrite‐Free Lithium Deposition

Abstract

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.

Enhancing Li ion conduction through polyethylene glycol brushes towards long-life solid-state lithium metal batteries

“…2b). 48 Subsequently, we measured the ionic conductivities of PE CPE and PE-PEG CPE in a temperature range from 30 to 80 °C. The corresponding Nyquist plots at 30 °C are shown in Fig.…”

Molecular/Ionic Designs in the Electrolyte and Interphases for Lithium Metal Anode

“…[61] Functional groups containing O and N atoms, such as carbonyl (À C=O) groups, imino (À NHÀ ) groups, and carboxy (À COOH) bonds are typical lithophilic functional groups. [55][56][57][58][62][63][64][65] Because O atom (3.44) is more electronegative than Li atom (0.98), the interaction between O and Li atoms is very similar to the "Li bond" explained by Lewis acid-base theory. [61] For example, O atoms with an extra pair of electrons in the carboxyl functional group are expected to become electron-rich donors, acting as Lewis bases and strongly absorbing Lewis acidic Li + through acid-base interaction.…”

“…Zheng et al developed electronegative poly(pentafluorophenyl acrylate) (PPFPA) polymer brush-grafted Celgard separator (PPFPA-g-Celgard) to create highly ordered ion transport nanochannels using polydopamine (PDA)-assisted surface-initiated ATRP (SI-ATRP) method (Figure 3d). [64] The most electronegative sites between F and O atoms on the surface of the polar PPFPA polymer chain enhance the electrolyte wettability and Li + affinity of Celgard separators. It is preferable to achieve rapid and uniform Li + transport and a low ion concentration gradient, which prevents the growth of Li dendrites.…”

Functional Separators for Long-Life and Safe Li Metal Batteries: A Minireview

“…Various strategies have been proposed to address the above challenges in LMBs, including constructing functional artificial SEI [ 11 , 12 , 13 , 14 ], electrolyte engineering [ 15 , 16 , 17 ], separator modification [ 18 , 19 , 20 , 21 , 22 , 23 ], solid-state electrolyte design [ 24 , 25 ], and the construction of 3D composite Li metal anodes [ 26 , 27 , 28 , 29 ]. Among these strategies, separator modification plays an important role, because it would result in little change in the volume/mass of the battery, and thus would have little effect on the energy density of the Li metal battery.…”