Lower energy requirements for batteries using enhanced conductive additive

Lithium-ion batteries (LiBs) is the predominant commercial form of rechargeable battery widely used in personal electronics, electric vehicles and grid storage systems. The performance LIBs rely on the effectiveness of the cathode which can influence their capacity, lifespan, and charging rate. Nickel manganese cobalt oxide (NMC) cathodes are commonly used due to their high energy density and stability, however, optimizing the performance of these cathodes is still a challenge and one method to enhance cathode performance is to improve the electron and ion transport pathways within the cathode material. Carbon black (CB) is commonly added to cathodes as a conductive additive to facilitate electron transport, although its role in ionic transport within the cathode matrix is less clear. To this end, new study published in Journal of Materials Chemistry A and conducted by PhD candidate Donghyuck Park, Dr Peter Sherrell, Fangxi Xie and led by Professor Amanda Ellis from The University of Melbourne in the Department of Chemical Engineering, the researchers developed a novel method to modify CB  surface using mild oxidation treatments by using hydrogen peroxide (H₂O₂) and nitric acid (HNO₃) which resulted in introducing specific oxygen-containing functional groups onto the CB surface without significantly compromising its structural properties. They found using Raman spectroscopy that the H₂O₂-treated CBs maintained a consistent D/G intensity ratio which indicates minimal defect generation. In contrast, the 70% HNO₃ treatment significantly increased defect density as shown by a higher D/G ratio. The authors performed X-ray photoelectron spectroscopy analysis and demonstrated an increase in oxygen content on the CB surface with specific functional groups (hydroxyl, carbonyl, and carboxyl) that changes based on treatment conditions. For instance, the H₂O₂ treatment resulted in an increase in the hydroxyl and carbonyl groups whereas HNO₃ treatment introduced carboxyl groups. They also evaluated the impact of the modified CBs on the electrochemical performance of NMC622 cathodes and found using cyclic voltammetry tests at a scan rate of 0.1 mV s⁻¹ that cathodes with carbonyl-modified CB (CB=O) showed the highest peak currents, which means faster lithium-ion intercalation and deintercalation reactions. Moreover, they assessed the rate performance of the cathodes at various C-rates. At 0.75C, both the CB=O cathode and CB with hydroxyl groups (CB-OH) delivered a substantial improvement in performance compared to the pristine CB cathode. In contrast, the cathode with carboxyl groups (CB-COOH) showed much poorer performance. The authors also performed electrochemical impedance spectroscopy measurements and showed the CB=O cathode to display lower impedance across all frequency ranges, which indicates reduced resistance at the cathode-electrolyte interface and more efficient charge transfer processes. Furthermore, the researchers proposed a mechanism for the observed enhancement in rate performance. According to the authors, the presence of carbonyl groups on the CB surface improved the wettability of the electrolyte and facilitated better contact and interaction between the electrolyte and the cathode active material. This increased the electrochemically active surface area and enhanced the efficiency of lithium-ion transport. The carbonyl groups likely reduced the energy barrier for lithium-ion movement at the electrode-electrolyte interface which results in lower overpotentials and faster charge/discharge reactions. Their proposed mechanism was supported by the observed overpotential measurements where the CB=O cathode demonstrated the lowest overpotential during both charging and discharging processes and indicated that less energy was required to achieve high-rate performance.  Additionally, the team tested their innovative modified CBs with other common cathode materials such as NMC811, lithium manganese oxide, and nickel cobalt aluminum oxide and showed improved rate performance across all these different cathode materials. Their findings highlight the versatility of the proposed surface modification approach and its potential for widespread application in various lithium-ion battery technologies.

In conclusion, Professor Amanda Ellis and colleagues provided valuable knowledge on how surface functional groups on CB can influence electrochemical processes within the cathode which can guide future research and development in optimizing conductive additives for LiBs. There are practical implications of the authors’ findings, first, the use of mild chemical treatments is a cost-effective method for improving battery performance which can be easily integrated into existing manufacturing processes without significant additional costs. Moreover, the new method is simple and effective which makes it feasible for large-scale production and battery manufacturers to adopt these modifications and produce improved and high-performance batteries. Furthermore, the reported improved rate performance expands the potential applications of LIBs to be used in high-power tools, fast-charging consumer electronics, and high-capacity energy storage systems for renewable energy integration. Finally, with the enhanced battery performance we expect broader adoption of electric vehicles and renewable energy systems which will ultimately contribute to reduced environmental impact and the transition to a more sustainable energy future.