Abstract
Conductive carbon nanocoatings (conductive carbon layers—CCL) were formed onα-Al2O3model support using three different polymer precursors and deposition methods. This was done in an effort to improve electrical conductivity of the material through creating the appropriate morphology of the carbon layers. The best electrical properties were obtained with use of a precursor that consisted of poly-N-vinylformamide modified with pyromellitic acid (PMA). We demonstrate that these properties originate from a specific morphology of this layer that showed nanopores (3-4 nm) capable of assuring easy pathways for ion transport in real electrode materials. The proposed, water mediated, method of carbon coating of powdered supports combines coating from solution and solid phase and is easy to scale up process. The optimal polymer carbon precursor composition was used to prepare conductive carbon nanocoatings on LiFePO4cathode material. Charge-discharge tests clearly show that C/LiFePO4composites obtained using poly-N-vinylformamide modified with pyromellitic acid exhibit higher rechargeable capacity and longer working time in a battery cell than standard carbon/lithium iron phosphate composites.
Highlights
There are many reports on the improvement of electrochemical performance of electrode materials for lithiumion batteries using carbon coatings [1,2,3,4,5,6,7,8,9]
To avoid these destructive effects, the carbon conductive layers should stick well to the electrode material and be able to reduce an interface area of the electrode/electrolyte composite. This reduction is needed to retard the growth of the solid electrolyte interface (SEI) that is responsible for the magnitude of the ion transport across the interface
The modification of PNVF by pyromellitic acid improves the polymer carbonization and the carbon layer formation. This may result from the fact that the planar structure of the PMA molecules serves as a nucleus of the graphite domains, which compete with the formation of the disordered structures
Summary
There are many reports on the improvement of electrochemical performance of electrode materials for lithiumion batteries using carbon coatings [1,2,3,4,5,6,7,8,9]. Characteristic of carbon coatings deposited on electrodes is that they can react with the electrolyte thereby giving rise to the formation of passive insulating layers To avoid these destructive effects, the carbon conductive layers should stick well to the electrode material and be able to reduce an interface area of the electrode/electrolyte composite. In view of the above, the formation of nanochannels (the appropriate porous structure) in the conductive carbon layers (CCL) can provide suitable pathways for the transport of ions (e.g., Li+) from the electrolyte to the cathode and vice versa. Such a composite material should assure a sufficient electrical conductivity
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