Lithium Dendrite Growth Suppression in Anode-Free Lithium Battery Using Bifunctional Electrospun Gel Polymer Electrolyte Membrane
Authors: Nikodimos Yosef , Su Wei-Nien , Hwang Bing-Joe 
Published: September 2023

Anode free Li metal battery (AFLMB) are being intensively investigating in recent years as a means to achieve higher capacity when compared with standard Li metal batteries. However, the severe electrolyte decomposition during plating/stripping cycles, that causes fast Li dendrite growth and quick capacity fading, is challenging for its commercialization. Herein, poly (vinylidene fluoride-hexafluoropropylene) polymer containing Li1.6Al0.4Mg0.1Ge1.5(PO4)3 ceramic filler (90:10 w% ratio, PVDF-HFP-10) gel polymer electrolyte (GPE) is employed for the first time in AFLMB to suppress the Li dendrite growth and homogeneous Li deposition is achieved during Li metal plating/stripping. The PVDF-HFP-10 based membrane is manufactured using electrospinning technique, which is well known and effective technique to increase the amount of crystalline β-phase of PVDF-HFP, on Cu collector foil. Particularly, a pure crystalline β-phase of PVDF-HFP has been observed in the adhesion layer sticked with Cu collector as confirmed from the analysis of Fourier Transform Infrared Spectroscopy (FTIR) and Raman spectroscopy measurements. The adhesion layer is further investigated using X-ray absorption spectroscopy (XAS), grazing angle X-ray diffraction (GAXRD) and X-ray photoelectron spectroscopy (XPS) techniques. The GAXRD analysis reveals Cu collector undergoes slight reconstruction of its (100) facets surface to (200) facets in the presence of the adhesion layer. Moreover, depth XPS analysis confirmed that the alignment of F atoms in the adhesion layer is toward the Cu collector which can play an important role for homogeneous Li deposition. Based on these findings, a novel approach is developed to prepare GPE, without peeling off the electrospun PVDF-HFP membrane from Cu collector to take advantage of the adhesion layer. The electrospun PVDF-HFP membrane GPE unpeeled off from its Cu collector (Cu@PVDF-HFP-10) prepared using novel method provides bifunctional applications, as electrolyte and as an artificial solid-electrolyte interphase (ASEI). The strong electrostatic interaction between the fiber sheet and its collector foil forms an adhesion layer (⁓0.5μm) which acts as ASEI prevents electrolyte decomposition. The Cu@PVDF-HFP-10|Li anode free cell enables uniform and highly compacted Li platting, excellent electrochemical performance, and high coulombic efficiency (CE) even at a high current density up to 5 mA cm−
2 (CE, 97.14%) after 200 cycles using 2 mAh cm−
2 capacity loading. Conversely, nonuniform and thick Li deposition is observed in the GPE prepared by conventional method (PVDF-HFP-10), due to poor contact between the membrane and the electrode, achieved only 90.08% CE after 100 cycles at 5 mA cm−
2. Post-cycling analyses using titration-gas chromatography (TGC) and XPS techniques indicated that the new strategy is conducive to prevent dead Li metal formation as well as to create a carbonate-free, robust, and stable SEI convenient to develop sustainable AFLMB system. Cycling performance of the Cu@PVDF-HFP-10 GPE utilized in the Cu|NMC AFLMB configuration delivered much better electrochemical performance than the PVDF-HFP-10 GPE (prepared by traditional method) and organic liquid electrolytes.