Table 1

General requirements for lithium ion battery separators 1."

Fig 1

(a) COMSOL simulations for Li0|separator|Li4Ti5O12 cells showing how t+ and σ influence the voltage drop across the electrolyte in the separator (charging rate 10C; 98% SOC)14; (b) COMSOL simulations of electrolyte salt concentration as function of distance across the separator in a symmetric Li versus Li cell (to exclude effects of electrode structure), current densities relate to charging rates for a 3 mAh·cm?2 graphite electrode 13; (c) schematic diagram of lithium deposition on battery electrodes assembled with PP separator and GO-g-PAM modified PP separator 22; (d) schematic diagram of the manufacturing process of CPC separator; (e) schematic diagram of the influence of the pore distribution of the separator on the morphology of lithium electrodes 23. (a) Adapted with permission from Copyright 2016, American Chemical Society Publisher.(b) Adapted with permission from Copyright 2018, Springer Nature Publisher.(c) Adapted with permission from Copyright 2019, Springer Nature Publisher.(d, e) Adapted with permission from Copyright 2018, John Wiley and Sons Publisher."

Fig 2

Schematic diagram of uneven lithium deposition leading to the growth of lithium dendrites and penetrating the diaphragm in the battery 26. Adapted with permission from Copyright 2017, Springer Nature Publisher."

Fig 3

(a) Schematic diagram of the effect of current distribution on the utilization of the active electrode material 32; (b) schematic diagram of the morphological changes of Li-metal electrodes during cycling of PE separator and PE separator modified by polydopamine 33; (c) schematic diagram of the Li electrodeposition process in batteries assembled with PP and Si-PP separators 35. (a) Adapted with permission from Copyright 2019, Elsevier Publisher. (b) Adapted with permission from Copyright 2012, John Wiley and Sons Publisher. (c) Adapted with permission from Copyright 2020, Elsevier Publisher."

Fig 4

(a) Fabrication of a PBO nanoporous membrane, (b) stress-strain curve of PBO microporous membrane 37; (c) different situations of unmodified and PE/SiO2/PE separators after being pierced by dendrites, (d) schematic diagram showing the mechanism for the extended battery life using PE/SiO2/PE separator 46. (a, b) Adapted with permission from Copyright 2016, American Chemical Society Publisher. (c, d) Adapted with permission from Copyright 2016, John Wiley and Sons Publisher."

Fig 5

(a) Schematic diagram of the PEC-coated separators and unmodified separators in batteries, (b) the equivalent circuit of the cell containing a Janus separator and unmodified separator during internal shorting 47; schematic diagram showing the design and fabrication of smart battery (c) the voltage change detected before and after a short circuit in a battery with a traditional separator, (d) the voltage change detected before and after a short circuit in a battery with a polymer-metal-polymer separator 48. (a, b) Adapted with permission from Copyright 2020, John Wiley and Sons Publisher. (c, d) Adapted with permission from Copyright 2014, Springer Nature Publisher."

Fig 6

(a) The conceptual plan of the tri-layer membrane working in battery 60; (b) schematic diagram of the thermal induced shutdown process of PLA@PBS separator in Li-ion batteries 61; (c) safety mechanism of APP-CCS@ PFR in LIBs 62. (a) Adapted with permission from Copyright 2018, Elsevier Publisher. (b) Adapted with permission from Copyright 2017, Royal Society of Chemistry Publisher."

Fig 7

SEM images of polyolefin separators: (a) PP separator prepared by dry process; (b) PE separator prepared by wet process 3. AFM images of polyolefin separators: (c) Celgard 2325 and (d) Toray V20CFD 64. (e) Concentration profiles and (f) concentration density maps from diffusion simulations across the through-plane direction of PE and PP (the concentration difference is ~50 mmol?L-1 between top and bottom, top 1.25 mol?L-1 and bottom 1.20 mol?L-1); (g) schematic diagram of LIB setup with electrode particles touching the separator; (h) schematic diagram of separator's pores being partially blocked; (i) the concentration density distribution diagram of PE and PP with a few pores been blocked 16. (a, b) Adapted with permission from Copyright 2014, Royal Society of Chemistry Publisher. (c, d) Adapted with permission from Copyright 2014, Royal Society of Chemistry Publisher. (e–i) Adapted with permission from Copyright 2018, Royal Society of Chemistry Publisher."

Fig 8

(a) Contact angle of Celgard and ATP-PVA/Celgard separators; dynamic wetting process of (b) Celgard and (c) ATP-PVA/Celgard by the liquid electrolyte (LE) drops (6 mL) released from 5 mm height; (d) schematic illustration of the device for studying the climbing behavior of LE in separators; climbing behaviors of (e) ATP-PVA/Celgard and (f) Celgard 77. Adapted with permission from Copyright 2020, Elsevier Publisher."

Fig 9

(a) The schematic diagram of stretching the separator along four different directions; the tensile behavior and failure modes of three separators stretched along four directions: (b) PP-D-U; (c) PP-D-B; (d) PE-W-B 79; (e) average elastic modulus vs. load for different separators 80; (f) the compression stress-strain curves and SEM images of the surface and cross-section at different stress: (f) PP-D-U, (g) PP-D-B, (h) PE-W-B 79. (a–d) Adapted with permission from Copyright 2021, Springer Nature Publisher. (e) Adapted with permission from Copyright 2013, Elsevier Publisher. (f–h) Adapted with permission from Copyright 2021, Springer Nature Publisher."

Fig 10

(a) Photograph images of the PE and GFP separators obtained after thermal storage at different temperatures for 30 min; (b) TGA curves of PE and GFP separators; (c) DSC curves of PE and GFP separators 85; (d) infrared thermography of the PP and modified separators at a heating rate of 5 ℃·s-1 87; (e) thermal distributions of pure PVDF-HFP, PVDF-HFP/LLZO (4.29% (w)) and Celgard 2500 separators, respectively 89. (a–c) Adapted with permission from Copyright 2021, Elsevier Publisher. (d) Adapted with permission from Copyright 2019, Royal Society of Chemistry Publisher. (e) Adapted with permission from Copyright 2019, Elsevier Publisher."

Fig 11

LSV curves of Li/stainless steel battery assembled with different separators 91. Adapted with permission from Copyright 2021, Elsevier Publisher."

Fig 12

(a) EIS spectra of LIBs with SFEG and Celgard 2400 separators 93; (b) impedance measurements recorded at 25 ℃ in a stainless steel |separator| stainless steel configuration for unmodified and polyelectrolyte modified PE separators, (c) Arrhenius plot of the electrolyte conductivity vs temperature 14. (a) Adapted with permission from Copyright 2021, John Wiley and Sons Publisher. (b, c) Adapted with permission from Copyright 2016, American Chemical Society Publisher."

Fig 13

Schematic of a simplified AC impedance spectrum 94. Adapted with permission from Copyright 2010, Springer Nature Publisher."

Fig 14

Comparison of the electrochemical performance of aramid coating separators: (a) ionic conductivity; lithium transfer numbers of (b) pristine PE, (c) Al2O3/PE, and (d) ANF-SiO2/PE 98. Adapted with permission from Copyright 2021, Elsevier Publisher."

Fig 15

SEM images of Celgard 2250 separator after 200 cycles, the Li foil shows many dendrites from the top view (a) and the cross-sectional view (b), SEM images of the separator modified with SiO2 after 200 cycles, the top view (c) and the cross-sectional view (d), it can be seen that the lithium foil is very flat 38; top-view SEM images of deposited Li on Cu foil in Li/Cu cells assembled with different separators at 1, 10, and 20 mAh·cm?2 plating capacities and 1 mA?cm?2 current density, (e) PE, (f) SiO@PAA-PE 100; in situ observation of the Li dendrite growth process: (g) schematic diagram of the in situ cell, and (h) photograph of transparent Li/Li symmetrical cells for in situ investigation, (i) optical images (top view) of the discharged Li metal wrapped by blank separator, (j) optical images (top view) of the discharged Li metal wrapped by NS protected 38. (a–d) Adapted with permission from Copyright 2020, John Wiley and Sons Publisher. (e, f) Adapted with permission from Copyright 2021, John Wiley and Sons Publisher. (g–j) Adapted with permission from Copyright 2020, John Wiley and Sons Publisher."

Fig 16

(a) EIS spectra of the cells assembled with PP and C@PP separators 101; EIS spectra of the cells with different separators and electrolytes, which were obtained (b) before cycling and (c) after 100 cycles at 55 ℃ and 0.5C 102. (a) Adapted with permission from Copyright 2021, Elsevier Publisher. (b, c) Adapted with permission from Copyright 2020, Elsevier Publisher."

Table 2

Summary of test methods for battery separators."