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.
The synthesis of diamino-aryl-1,4,5,8-naphtalenetetra-carboxylic diimide molecule (NTCDA-(aryl-NH2)2) was reported. This molecule was characterized by elemental analysis, SEM, IR and TGA. A organic Li-ion electrode with NTCDA-(aryl-NH2)2 as active material was tested and a reversible behavior was observed with a multiple electrons process delivering about 100 mAh.g-1 at an average potential of 2.45 V vs. Li/Li+. In parallel, the diazotization study of this molecule was investigated with a three-electrode assembly. Then, the electrochemical reduction of freshly formed NTCDA-(aryl-N2 +)2 ions was followed by cyclic voltammetry experiments. An irreversible cathodic wave at around 0.0 V vs. Ag/AgNO3 that is associated to the reduction of the in-situ generated NTCDA-(aryl-N2 +)2 ions was observed. The blocking effect of the grafted layer deposited on the glassy carbon surface was verified with ferrocene as a redox probe. Finally, the immobilization of this molecule on Ketjen black carbon powder by spontaneous reduction of freshly formed NTCDA-(aryl-N2 +)2 ions was realized in a one-pot reaction. The redox-active carbon with a loading of grafted groups estimated between 26.4 and 36.7 wt. %, depending of the method of modification, cycled at high rate for thousands of cycles.
Energy storage technology is a critical research area for the success of portable electronic devices and electrical transportation. Such applications need affordable, durable, safe and environmentally friendly battery materials with high energy density. Organic cathode materials are currently promising candidates because they fulfill most of these requirements for an active battery material1. However, they usually suffer from a major limitation, namely their solubility in organic electrolytes2. Even a very low solubility translates into a decreased capacity upon cycling due to the loss of active material. 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. For example, 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) is an inexpensive red pigment that is widely investigated as an active material for energy devices. However, Li-PTCDA batteries suffer from poor and irreversible cycling stability due to the dissolution in the electrolyte. Even more problematic, the dissolved PTCDA migrates through the porous separator and deposits on the anode surface causing irreversible damage3. In order to solve this problem, chemical modifications such as polymerisation, functionalization and immobilization on carbon materials have improved cycling stability. However, 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. We developed a Janus membrane, which consists of two layers – a commercial polypropylene separator (CelgardTM) 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 lithium batteries using organic moities as active materials. References [1] Armand, M. & Tarascon, J. M. Building better batteries. Nature 451, 652–657 (2008). [2] Zhao, Q., Zhu, Z. & Chen, J. Molecular Engineering with Organic Carbonyl Electrode Materials for Advanced Stationary and Redox Flow Rechargeable Batteries. Adv. Mater. 29, 1–25 (2017). [3] Wang, J., Wang, X., Li, H., Yang, X. & Zhang, Y. Intrinsic factors attenuate the performance of anhydride organic cathode materials of lithium battery. J. Electroanal. Chem. 773, 22–26 (2016).
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