## 4 Conclusions  
Thin PVDF-HFP membranes with a highly porous and multilayered structure were designed and fabricated via a combination of evaporation-induced phase separation and selective solvent etching. The thicknesses of two-, three-, and four-layer PVDF-HFP membranes are approximately 13.5, 15.2 and 23.9 \(\upmu\)m, respectively. The thicknesses of the membranes are considerably thinner than that of the commercial Celgard separator (27 \(\upmu\)m) and the values reported in most works. The developed multilayered membrane demonstrated high porosity and superior electrolyte wettability, leading to a large electrolyte uptake of 228.5%. Moreover, due to the unique layered structure, the PVDF-HFP membranes possessed high mechanical strength along the transversal direction, which is close to that of a commercial Celgard separator. The thermal stability of the developed membranes was found to be better as compared to the Celgard separator. Considering the electrochemical properties, the LIB cell adopting the three-layer membrane exhibited the highest capacity, the best rate capability, and compatible cycling stability, making it a preferable thin separator for high-power (fast charging) LIBs with superior cycle performance and high safety.  
In future work, enhanced performance and improved safety of layered PVDF-HFP separators can be acquired through precise control of the thickness of each PVDF-HFP and PS layer. The obtained results can be used in the strategy in the engineering of separators for application in high-power LIBs. The feasibility of these materials to other potential applications such as actuators and supercapacitors can be considered.  
The following are available online at [[https://www.mdpi.com/2077-0375/11/1/41/s1](https://www.mdpi.com/2077-0375/11/1/41/s1)]([https://www.mdpi.com/2077-0375/11/1/41/s1](https://www.mdpi.com/2077-0375/11/1/41/s1)), Figure S1: Photograph of the E-flex dip coater used in this study, Figure S2: Photograph of the temperature and humidity controller, Figure S3: Surface morphology of the backside of the film (facing the substrate) using bare copper and PSS-coated copper substrates, Figure S4: Surface morphology of the porous PVDF-HFP film after coating with a PS solution with different concentrations. The spin-coating was done at a rotational speed of 1000 rpm for 40 s, Figure S5: Surface morphology of the porous PVDF-HFP film after coating with a 5 wt.% PS solution at different rotational speeds, Figure S6: Cross-sectional morphology of the two-layer structured porous PVDF-HFP membrane prepared with a thicker PS coating layer, Scheme S1: Effect of the PS layer thickness on the adhesion between PVDF-HFP layers.  
Conceptualization, V.-T.B. and H.-S.C.; Data curation, V.-T.B., V.-T.N. and J.H.K.; Formal analysis, V.-T.N., N.-A.N., L.L.L. and J.H.K.; Funding acquisition, H.-S.C.; Investigation, N.-A.N. and H.-S.C.; Methodology, V.-T.B.; Project administration, H.-S.C.; Supervision, H.-S.C.; Writing--original draft, V.-T.N. and H.-S.C.; Writing--review & editing, N.-A.N., R.U., L.L.L., H.-S.K. and H.-S.C. All authors have read and agreed to the published version of the manuscript.  
This research was supported by grants from the National Research Foundation (NRF) (NRF-2020R1A4A2002590, NRF-2019H1D3A2A01062040, NRF-2017R1A2B4007875, NRF-2020R1I1A1A01072495) funded by the Ministry of Science and ICT, Republic of Korea.  
Not applicable.  
The authors declare no conflict of interest.