Abstract
Separators in lithium-ion batteries (LIBs) play an important role for battery safety, so stable electrochemical performance and high mechanical strength of separators will always be of interest. On the basis of the fact that polydopamine (PDA) nanoparticles found in mussel have a strong adhesion ability, biomaterial surface nanoparticles modification methods are developed to increase electrochemical performance and enhance mechanical strength of polypropylene (PP) and polypropylene/polyethylene/polypropylene (PP/PE/PP) separators. The electrolyte uptake performance, ionic conductivities, discharging rate capabilities, yield stresses, and failure strains of PP and PP/PE/PP separators are all enhanced remarkably by PDA modification. Thermal shrinkage results show that thermal stabilities and the shrinkage percentage of PDA-modified separators are improved. The electrochemical testing results conclude that the discharging capacities of PP (increased by 3.77%~187.57%) and PP/PE/PP (increased by 2.31%~92.21%) separators increase remarkably from 0.1 C to 5.0 C. The ionic conductivities of PDA-modified PP and PP/PE/PP separators are 1.5 times and 6.1 times higher than that of unmodified PP and PP/PE/PP separators, which in turn increase the electrolyte uptake and ionic migration. In addition, mechanical properties of PP (yield stresses: 17.48%~100.11%; failure stresses: 13.45%~82.71%; failure strains: 4.08%~303.13%) and PP/PE/PP (yield stresses: 11.77%~296.00%; failure stresses: 12.50%~248.30%; failure strains: 16.53%~32.56%) separators are increased greatly.
Highlights
Lithium-ion batteries (LIBs) have been widely used in electrochemical energy conversion and storage for a wide range of applications, including electronic devices, electric vehicles and their energy systems, and so forth, due to their high energy density, long cycle life, zero memory effect, low self-discharge, and environmental friendliness [1,2,3,4,5,6,7]
Conventional polyolefin separators are intrinsically poorly compatible with electrolytes, due to their hydrophobic surface character and low surface energy, which result in low electrolyte uptake and poor lithium ion conductivity [11,12,13,14]
In order to investigate the effect of PDA nanoparticles modification on the morphologies of separators, the surface (Figure 3a,b,d,e) and cross-section (Figure 3c,f) microstructures of unmodified and PDA-modified separators were analyzed by extra-high resolution field emission scanning electron separator
Summary
Lithium-ion batteries (LIBs) have been widely used in electrochemical energy conversion and storage for a wide range of applications, including electronic devices, electric vehicles and their energy systems, and so forth, due to their high energy density, long cycle life, zero memory effect, low self-discharge, and environmental friendliness [1,2,3,4,5,6,7]. LIBs mainly consist of positive electrodes, negative electrodes, electrolytes, and macromolecular separators. Polymers 2020, 12, 648 placed between positive and negative electrodes to protect against an internal short circuit and provide favorable channels for lithium ions migration [8]. When separators suffer mechanical failure under external loading, the lithium dendrites may puncture the separators, leading to an internal short circuit or even the explosion of the batteries, due to direct contact between positive and negative electrodes [9,10]. LIBs, research concerning the stable electrochemical performance and high mechanical strength of separators remains an important research issue. Many external conditions affect the performance of materials, such as freezing, heat, physical design, and chemical corrosion [7,11,15,16,17]
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