Charge Storage Behavior of Carbon Nanoparticles toward Alkali Metal Ions at Fast-Charging Rates

Rechargeable batteries with high-rate capability are needed for vehicle electrification. It is important to understand charge storage behavior in battery electrode materials. We have investigated the charge storage capacity and mechanism of alkali metal ions Li+, Na+, and K+ in graphite and hard carbon (HC) nanoparticles of 50 nm in particle size. The charge storage capacity of the carbon nanoparticles follows the order: Li+ > K+ > Na+ in the potential window between 3.00 and 0.01 V vs the individual metal/metal ion couple. Above the plateau regions (above 0 V vs Na/Na+, 0.25 V vs K/K+, and 0.35 V vs Li/ Li+), the storage of the alkali metal ions proceeds via a capacitive mechanism due to charge adsorption on the surface and defective sites, leading to a similar specific storage capacity. In the potential range between 3.0 and 0.01 V vs Li/Li+ and at 1 A/g, graphite and HC nanoparticles deliver Li+ storage capacities of 690 and 564 mAh/g, respectively. The significantly higher Li+ storage capacity of the graphite nanoparticles than the theoretical capacity of commercial graphite (372 mAh/g) is due to the extra Li+ storage via the capacitive mechanism. However, at an extremely high current density (e.g., 100 A/g), the high (e.g., A/g), HC nanoparticles store more Li+ (324 mAh/g) than the graphite nanoparticles (262 mAh/g). This study sheds light on alkali metal ion storage behavior in carbon nanoparticles and suggests that electrodes fabricated with carbon nanoparticles hold great promise for developing fast-charging rechargeable batteries.

Automated summary

The study on the Li+ storage capacity of graphite and hard carbon (HC) nanoparticles at different current densities suggests that HC nanoparticles exhibit higher storage capacity at extremely high current density levels.