Abstract
Coating conducting polymers onto active cathode materials has been proven to mitigate issues at high current densities stemming from the limited conducting abilities of the metal-oxides. In the present study, a carbon coating was applied onto nickel-rich NMC622 via polymerisation of furfuryl alcohol, followed by calcination, for the first time. The formation of a uniform amorphous carbon layer was observed with scanning- and transmission-electron microscopy (SEM and TEM) and X-ray photoelectron spectroscopy (XPS). The stability of the coated active material was confirmed and the electrochemical behaviour as well as the cycling stability was evaluated. The impact of the heat treatment on the electrochemical performance was studied systematically and was shown to improve cycling and high current performance alike. In-depth investigations of polymer coated samples show that the improved performance can be correlated with the calcination temperatures. In particular, a heat treatment at 400 °C leads to enhanced reversibility and capacity retention even after 400 cycles. At 10C, the discharge capacity for carbon coated NMC increases by nearly 50% compared to uncoated samples. This study clearly shows for the first time the synergetic effects of a furfuryl polymer coating and subsequent calcination leading to improved electrochemical performance of nickel-rich NMC622.
Highlights
Ni-rich NMC, LiNixMnyCozO2 has attracted great attention in the battery community due to a combination of high reversible capacity (180–250 mAh g−1) and high operating voltage (~3.8 V vs. Li+/Li) that stems from twodimensional lithium-ion diffusion and good lithium-ion conductivity [1]
An amorphous carbon coating was successfully applied onto NMC622 materials by acid catalyst polymerisation of furfuryl alcohol followed by a calcination step for the first time
X-ray photoelectron spectroscopy (XPS) analysis showed the temperature dependency of the carbon coating, which was confirmed by the transmission electron microscopy (TEM) analysis of the coated NMC samples
Summary
The delay in structural degradation stems from an effective protective layer that prevents the material from HF-based surface side reactions and lowers the charge transfer resistance of Li+ and transition metals dissolution Their inherently low electronic conductivity results in a poor electrochemical performance at high current rates, which challenges their ability in high power applications [24,25,26,27]. To solve this problem, a carbon coating on the surface of metal-oxide particles is one of the strategies demonstrated in the literature. Achieving homogeneous coatings on micrometre-sized commercial NMC cathode materials remains challenging In this regard, amorphous carbon-based materials from polymerisation offer homogeneous coverage and high electronic conductivity. A final calcination step creates a uniform amorphous carbon layer
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