Polymer‐based electrolytes have attracted ever‐increasing attention for all‐solid‐state lithium (Li) metal batteries due to their ionic conductivity, flexibility, and easy assembling into batteries, and are expected to overcome safety issues by replacing flammable liquid electrolytes. However, it is still a critical challenge to effectively block Li dendrite growth and improve the long‐term cycling stability of all‐solid‐state batteries with polymer electrolytes. Here, the interface between novel poly(vinylidene difluoride) (PVDF)‐based solid electrolytes and the Li anode is explored via systematical experiments in combination with first‐principles calculations, and it is found that an in situ formed nanoscale interface layer with a stable and uniform mosaic structure can suppress Li dendrite growth. Unlike the typical short‐circuiting that often occurs in most studied poly(ethylene oxide) systems, this interface layer in the PVDF‐based system causes an open‐circuiting feature at high current density and thus avoids the risk of over‐current. The effective self‐suppression of the Li dendrite observed in the PVDF–LiN(SO2F)2 (LiFSI) system enables over 2000 h cycling of repeated Li plating–stripping at 0.1 mA cm−2 and excellent cycling performance in an all‐solid‐state LiCoO2||Li cell with almost no capacity fade after 200 cycles at 0.15 mA cm−2 at 25 °C. These findings will promote the development of safe all‐solid‐state Li metal batteries.

Solid polymer electrolytes have emerged as promising alternatives to current liquid electrolytes due to their advantages in battery safety and stability. Among various polymer electrolytes, poly(vinylidene fluoride) (PVDF)‐based electrolytes with high ionic conductivity, large mechanical strength, and excellent electrochemical and thermal stability have a great potential for practical applications. However, fundamental issues, such as how the Li ions transport in the PVDF‐based electrolytes and how the residual solvent affects the cell performance, are unclear. Here, we demonstrate that the solvation effect due to a small amount of residual N,N‐dimethylformamide (DMF) bound into the electrolytes plays a critical role in ionic transport, interface stability, and cell performance. With the residual DMF existing in the electrolytes in a bound state not as free solvent, the ionic conduction could be realized by the Li‐ion transport among the interaction sites between the bound DMF and PVDF chains. Regulating the solvation effect in the electrolytes can make the PVDF‐based solid‐state Li metal batteries a significantly improved cycling performance at 25 °C (e. g., over 1000 cycles with a capacity retention of more than 94 %). These findings would promote the development of next‐generation Li metal batteries with high energy density and safety.

high interfacial impedance between SSEs and electrodes, and relatively high fabrication cost, which impede their applications. SSEs with high ionic conductivity, wide electrochemical window and low interfacial impedance are critical in developing ASSBs with high specific energy and power density. [2,3] Currently, among various SSEs, sulfide SSEs have a Li-ion conduction capability comparable to that of organic liquid electrolytes (≈10 -2 S cm -1 at room temperature). [4][5][6][7][8][9][10] Various sulfide materials with a high Li-ion conductivity of 10 -3 -10 -2 S cm -1 at room temperature, such as Li 10 GeP 2 S 12 (LGPS), [5] Li 10 SnP 2 S 12 , [6] and Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , [7] have been investigated. Among them, a family of sulfide SSEs, lithium argyrodites Li 6 PS 5 X (X = Cl, Br), [8] are attracting more attention due to high Li-ion conductivity (e.g., Li 5.3 PS 4.3 ClBr 0.7 : 2.4 × 10 -2 S cm -1 ; [9] Li 6 PS 5 Cl (denoted as LPSCl): 3.15 × 10 -3 S cm -1 [10] ) and relatively good electrochemical compatibility. The ASSB cells using argyrodites have demonstrated good cycling and rate performance. For example, recently, a sandwiched SSE separator of LPSCl-LGPS-LPSCl has been designed to prevent the growth of Li dendrites and thus enable superior cycling performance of ASSB cells; [11] and LPSCl SSE has also been matched with the silicon anode, capable of operating with high current densities and achieving a long cycle. [12] One drawback of pressed sulfide SSE separator layers is that micro-cracks easily appear and expands during Li plating/stripping in sulfide electrolytes due to the rigidness of sulfide powders, leading to short circuit in ASSB cells. [13] Thus a thicker sulfide SSE layer (e.g., ≈0.5-1.2 mm) via pressing sulfide powder was usually used in laboratory-type cells to guarantee the long-term cycling performance of the ASSBs, [13a,b,14] but this way reduces the cell-level energy density and is detrimental to scalable fabrication. Thus, it is desired to prepare sulfide SSE membranes with a small thickness and compact structure for advanced ASSBs.To obtain a thin, free-standing sulfide SSE membrane, a soft polymeric component is often used. Recently, much progress in sulfide-polymer composite solid electrolytes (CSEs) has been made. [15][16][17][18] Among them, Luo et al. prepared a 65 µm-thick bendable sulfide SSE using LPSCl and poly(ethylene oxide) (PEO), [16] and their ASSB cell of LiNi 0.7 Co 0.2 Mn 0.1 O 2 (LiNi x Co y Mn 1-x-y O 2 , denoted as NCM)||CSE||lithium-indium All-solid-state batteries (ASSBs) using sulfide electrolytes have attracted everincreasing interest due to high ionic conductivity of the sulfides. Nevertheless, a thin, strong solid-state sulfide electrolyte membrane maintaining high ionic conductivity is highly desired for ASSBs. Here, a thin, flexible composite solid electrolyte membrane composed of argyrodite sulfide Li 6 PS 5 Cl and a polar poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) framework is prepared via an electrospinning-infil...

No abstract

Ionic conducting polymer electrolytes for solid-state lithium-ion batteries have attracted ever-increasing attention because of their decent ionic conductivity, flexibility, no liquid leakage, and good processability. Poly­(vinylidene fluoride) (PVDF)-based polymer electrolytes have recently stood out among the polymer electrolytes due to their high room temperature ionic conductivity. However, the interface between PVDF-based polymer electrolytes and lithium metal decays over time until the batteries break down. Here, we introduce a small amount of poly­(acrylic acid) (PAA) into a PVDF-based polymer electrolyte and synthesize an organic–organic composite electrolyte that alleviates the interfacial reaction with lithium metal, which shows great superiority over other modification methods such as coating. The cycle life of lithium symmetric cells is prolonged from 130 to 850 h at 0.44 mA cm–2 due to the effective suppression of interfacial reaction. The much more stable interface also enables excellent cycle performance in a solid-state LiCoO2||Li cell at 30 °C with a capacity decay of 0.03% per cycle for 1000 cycles, which is much lower than that of a cell without blending PAA (0.13% per cycle for only 450 cycles). The results would shed light on the applications of PVDF-based polymer electrolytes in solid-state lithium metal batteries.

Solid polymer electrolytes with large ionic conductivity, high ionic transference number, and good interfacial compatibility with electrodes are highly desired for solid‐state batteries. However, unwanted polarizations and side reactions occurring in traditional dual‐ion polymer conductors hinder their practical applications. Here, single‐ion polymer conductors (SIPCs) with exceptional selectivity for Li‐ion conduction (Li‐ion transference number up to 0.93), high room‐temperature ionic conductivity of about 10−4 S cm−1, and a wide electrochemical stability window (>4.5 V, vs Li/Li+) are prepared by precisely regulating the ion–dipole interactions between Li+ and carbonyl/cyano groups. The resulting SIPCs show an excellent electrochemical stability with Li metal during long‐term cycling at room temperature and 60 °C. LiFePO4‐based solid‐state cells containing the SIPCs exhibit good rate and cycling performance in a wide temperature range from −20 to 90 °C. By the same way of ion–dipole interaction regulation, sodium‐ and potassium‐based SIPCs with both high ionic conductivity and high cationic transference numbers are also prepared. The findings in this work provide guidance for the development of high‐performance SIPCs and other metal‐ion systems beyond Li+.

No abstract

No abstract