Abstract
Organic cathode materials for lithium batteries are becoming increasingly popular because they have high theoretical redox voltage, high gravimetric capacity, low cost, easy processing and sustainability. However, their development is limited by their solubility in the electrolyte, which leads to rapid deterioration of the battery upon cycling. We developed a Janus membrane, which consists of two layers – a commercial polypropylene separator (Celgard) and a 300–600 nm layer of exfoliated graphite that was applied by a simple and environmentally friendly process. The submicron graphite layer is only permeable to Li+ and it drastically improves the battery performance, as measured by capacity retention and high coulombic efficiency, even at 2C rates. Post-mortem analysis of the battery indicates that the new membrane protects the anode against corrosion, and cathode dissolution is reduced. This graphite-based membrane is expected to greatly expedite the deployment of batteries with organic cathodes.
Highlights
Among organic cathode materials, conjugated carbonyl compounds have been intensively scrutinized because of a combination of desirable properties, such as low cost, good theoretical capacity, reversible oxidative behavior, high discharge potential and commercial availability[13,14,15,16]
Scanning electron microscopy (SEM) of a G-separator shows that the graphite interlayer (Fig. 1b) is smooth, uniform in thickness, devoid of cracks or aggregates and it completely covers the porous morphology of the Celgard (Fig. 1c).The thickness of the graphite layer is dependant of the smearing time
The dense layers of graphite have an average thicknesses of 360 ± 50 nm (Fig. 1d) and 640 ± 70 nm (Fig. 1e), which correspond to an additional mass of 2% and 4% for the membrane (0.25 and 0.5%, respectively, relative to the battery mass)
Summary
Among organic cathode materials, conjugated carbonyl compounds have been intensively scrutinized because of a combination of desirable properties, such as low cost, good theoretical capacity, reversible oxidative behavior, high discharge potential and commercial availability[13,14,15,16]. In order to solve this problem, chemical modifications such as polymerisation[22,23], functionalization[24,25] and immobilization on carbon materials[26,27] have improved cycling stability and coulombic efficiency These modified cathode materials, which are often prepared by complex processes, contain considerable amounts of inactive mass that cause a decreases of the energy density. Separator, coined as G-separator, acts as a selective layer for the transport of Li+ between electrodes, and protects the lithium anode from corrosion by inhibiting the diffusion of dissolved PTCDA This graphite interlayer, which adds less than 0.5% to the weight of the battery material, significantly improves cycling stability with a coulombic efficiency near 100% after 100 cycles. We envision that the G-separator can be implemented on a large scale, leading to the deployment of lighter, more sustainable batteries
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