Electrochemical Performance Of Graphite Anodes Research Articles

Enhanced Electrochemical Performance of Graphite Anodes for Lithium-Ion Batteries by Dry Coating with Hydrophobic Fumed Silica

Coating of electrode materials for lithium-ion batteries is usually performed in order to improve performance, safety and the processability of the raw material. Here, we apply a dry coating method of graphite with hydrophobic fumed silica particles. This method excludes the use of any harmful solvents and the nano-scale particles cover and stick to the graphite substrate by only adhesive forces. Furthermore, this dry coating method is easily mass-scalable and a high throughput can be obtained in a short processing time. The nanoparticle coating reduces the van-der-Waals forces between the graphite particles and leads in this way to better flowability of the graphite powder which is important for further processing and the production of electrode tapes. Furthermore, these core-shell particles were processed to composite negative graphite electrodes in combination with the water soluble binder sodium carboxy-methylcellulose. Electrodes obtained with the coated material displayed a smooth surface, a high mechanical stability and outperformed the unmodified ones in the electrochemical investigations.

Surface Active Sites: An Important Factor Affecting the Sensitivity of Carbon Anode Material toward Humidity

We report that various kinds of active sites on graphite surface including active hydrophilic sites markedly affect the electrochemical performance of graphite anodes for lithium-ion batteries under different humidity conditions. After depositing metals such as Ag and Cu by immersion and heat-treating, these active sites on the graphite surface were removed or covered and its electrochemical performance under the high humidity conditions was markedly improved. This suggests that lithium-ion batteries can be assembled under less strict conditions and provides a valuable direction toward lowering the manufacturing cost for lithium-ion batteries.

Effect of nickel coating on electrochemical performance of graphite anodes for lithium ion batteries

Among the different materials often studied and proposed as negative electrodes for lithium-ion batteries, graphite anodes are the most used in commercial batteries. For this study, synthetic graphite was tested. During the first discharge 0.2 Li ions were consumed for the formation of the SEI film and the capacity reaches about 387 mAh/g. But at the end of the first charge only 72% of the initial charge was recovered (the reversible capacity is about 279 mAh/g). In order to improve this performance we have deposited metallic nickel on graphite with the intention to obtain a homogeneous thin layer able to modify the nature of the SEI film, to allow the diffusion of lithium ions through the protective layer, and also to increase the performance of graphite electrodes. The results show a decrease of the irreversible capacity loss (16% instead of 28% for pure graphite electrodes) as well as better cycleability for a nickel-deposited graphite electrode with only 11% weight ratio of nickel. On the other hand, an increase of the nickel content decreases this performance.

Dimethyl carbonate (DMC) electrolytes – the effect of solvent purity on Li–ion intercalation into graphite anodes

Graphite electrodes cycled in single solvent electrolytes based on dimethyl carbonate (DMC) exhibit surprising and unfamiliar behavior. The electrochemical performance of graphite anodes cycled vs. Li metal in DMC electrolytes, containing 1 M LiPF 6 is strongly dependent on the solvent purity. The behavior of the graphite anodes in electrolytes containing “pure” DMC is dependent mainly on the identity of the contamination present in the native solvent. It was found that methanol is causing deterioration in the electrochemical performance of the cycled graphite electrode, while carbon dioxide and mainly carbonochloridic acid methyl ester are enhancing the performance. It was established that it is essential to investigate and understand the processes and materials used during the production of battery grade solvents, in order to clarify the roll of traces of chemical compounds responsible for the variation and modification in the electrochemical behavior of the cycled electrodes.