Revitalizing carbon anodes for high-performance potassium-ion batteries through liquid phase oxidation

Researchers have introduced a significant advancement in the development of potassium-ion batteries (PIBs), addressing critical limitations in their practical application. PIBs hold considerable promise as a sustainable alternative to lithium-ion batteries, primarily due to the abundant and cost-effective nature of potassium. However, their widespread adoption has been hindered by challenges related to slow storage kinetics and unsatisfactory cycle life. This new investigation demonstrates that a targeted liquid phase oxidation strategy can substantially improve the performance of soft carbon anodes, opening new pathways for next-generation energy storage solutions.

Unlocking Carbon's Potential for Potassium Storage

The research focuses on pitch-derived needle coke (NC), a readily available soft carbon material recognized for its unique layered configuration and high electrical conductivity. Despite these advantages, the relatively large size of potassium ions and the compact interlayer spacing within pristine carbon structures impede efficient ion diffusion and overall electrochemical characteristics. Previous attempts to introduce porosity or defects have shown some success, but a delicate balance is required to maximize performance without compromising the material's structural integrity or electronic transport properties. This study pioneers the use of liquid phase oxidation with hydrogen peroxide (H₂O₂) to precisely modify the carbon structure.

The team's approach centered on incorporating oxygenated functional groups onto the surface of needle coke via a single-step liquid phase oxidation process using varying concentrations of H₂O₂. Following this treatment, the oxidized needle coke samples (ONC-x) underwent comprehensive material characterization using techniques such as X-ray Diffraction (XRD), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), and High-Resolution Transmission Electron Microscopy (HR-TEM). Electrochemical tests, including cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), galvanostatic intermittent titration technique (GITT), and electrochemical impedance spectroscopy (EIS), meticulously evaluated the battery performance of the modified anodes.

Engineering Carbon's Architecture for Superior Performance

A critical finding emerged from the optimization of the oxidation level: the ONC-5 sample, treated with 5 mol L−1 H₂O₂, exhibited the most favorable structural changes. This optimal modification led to an expansion of the carbon interlayer spacing and the creation of abundant oxygenated functional groups and resultant defects. These structural enhancements served a dual purpose: they acted as additional active sites for potassium storage and provided sufficient pathways for K+ migration across adjacent carbon layers. The expanded spacing specifically facilitated the rapid intercalation and deintercalation of potassium ions, a key factor in improving battery performance.

These architectural modifications translated directly into significantly improved electrochemical performance. The ONC-5 anode delivered a remarkable reversible capacity of 322.7 mAh g−1, a substantial increase compared to the pristine needle coke's 237.9 mAh g−1. Furthermore, it demonstrated superior rate capability, maintaining 98.9 mAh g−1 at a high current density of 2 A g−1, nearly double that of the untreated anode. Critically, the ONC-5 anode also displayed excellent cycling stability, retaining a capacity of 106.4 mAh g−1 after 500 cycles at 1 A g−1, far surpassing other samples. The diffusion coefficient of K+ was highest for the ONC-5 anode, confirming its enhanced kinetic properties.

Charting a Course for Next-Generation Energy Storage

While the study presents a compelling route to higher-performance PIBs, it also identifies an important limitation: excessive oxidation can compromise the structural integrity of the needle coke, diminishing its electrical conductivity and leading to inferior potassium storage performance. This highlights the importance of precise control over the oxidation process. The successful demonstration of this modification strategy provides valuable insights for the industrialization and technological advancement of PIBs, offering a feasible approach to enhance the potassium storage performance of soft carbon anodes for more sustainable and efficient energy storage solutions.

Dr. Chang Liu from Liaoning University, a corresponding author, stated, "Our findings represent a substantial step forward in overcoming the inherent limitations of soft carbon anodes for potassium-ion batteries. By carefully tuning the oxidation process, we have created an anode material that not only boasts impressive energy storage capacity but also exceptional stability. This work truly underscores the potential for chemical modification to unlock superior performance in next-generation battery technologies, paving the way for more environmentally friendly and cost-effective energy solutions."

Corresponding Author: Chang Liu

Original Source: https://doi.org/10.1007/s44246-024-00106-3

Contributions: All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Junjun Yao and Chang Liu. The first draft of the manuscript was written by Junjun Yao and Chang Liu. Yaming Zhu contributed to the resources and methodology of the study. Ying sun contributed to the validation and methodology of the study and Daming Feng contributed the methodology of the study. Yali Yao and Quanxing Mao conducted to the investigation of the study. Tianyi Ma contributed to the reviewing and editing of the article. And all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.