Electrode Engineering Using Carbonaceous Materials for Improving Electrochemical Performance of High-Voltage Lithium-Ion Batteries
Authors: Liu Yi-Hung , Tsai Tsung-Yu , Chen Wei-Cheng , Hsueh Chung-Hsuan , Kuo Yen-Shen 
Published: December 2024

Introduction

Lithium-ion batteries (LIBs) with high energy density, long cycle life, and affordability are crucial to meet the soaring demand for energy storage in electric vehicles and smart grid applications. The cathode material, a key constituent of LIBs, plays a pivotal role in determining energy density and cycle life. Therefore, improving cathode characteristics is typically a top priority to enhance battery performance. Among the array of cathode materials available, spinel LiNi0.5Mn1.5O4 (LNMO) stands out due to its high operating voltage (~4.7 V vs. Li/Li+), rapid ion transport, eco-friendliness, and cost-effectiveness, capturing researchers' attention. However, LNMO-based LIBs often encounter significant capacity deterioration in high-voltage environments. Factors such as Al foil (current collector) corrosion [1], active material deterioration [2], and electrolyte decomposition [3] are identified as leading causes of battery failure. This study aims to boost the electrochemical performance of high-voltage LIBs by employing advanced LNMO-based cathodes infused with various carbonaceous materials.

Experimental

Three approaches, utilizing three distinct carbonaceous materials, were employed to integrate with LNMO active materials for the fabrication of advanced LNMO-based electrodes.
In the first approach, carbon fibers (CFs) were utilized as current collectors, replacing the conventional Al foil. A slurry comprising LNMO-based active material, conductive agents, binders (optional), and solvents was thoroughly mixed and then cast onto CFs either through blade coating or vacuum filtration. After overnight drying, CF-based electrodes were obtained.
For the second approach, carbon blacks (CBs) were employed as conductive agents, which were subjected to various treatments including thermal, hydrothermal, and chemically oxidative reactions for modification. The modified CBs were then mixed with LNMO-based active material, binders, and solvents to form a slurry. The subsequent electrode fabrication process mirrored that of the first approach, utilizing blade coating.
In the third approach, polyvinylpyrrolidone (PVP) was introduced as an alternative to the commonly used PVDF binder. PVP was mixed with LNMO-based active material, CBs, and solvents to create a slurry. The resulting slurry was blade-coated onto CF substrate and subjected to a two-step thermal treatment, resulting in a partially carbonized PVP-based electrode.
The electrode materials underwent characterization using various techniques such as SEM, TEM, XRD, XPS, nitrogen adsorption, and Raman spectroscopy. Electrochemical tests were conducted using coin-type test cells (CR2032) to assess the tailored LNMO-based electrodes in terms of cycling stability, rate capability, and internal impedance. In these test cells, lithium metal foil served as the counter electrode, and 1.0 M LiPF6 in ethylene carbonate/diethylene carbonate (1:1 v/v) without additives functioned as the electrolyte.

Results and Discussion

Our findings indicate that the LNMO-based electrode utilizing CF as current collectors demonstrates significantly enhanced cycling stability and rate capability compared to its counterpart using Al foil. A typical electrode can maintain 98% capacity retention over 200 cycles under high-voltage operation (4.9 V vs. Li/Li+) and exhibits favorable rate performance with approximately 120 mAh g-1 at 5 C. This improvement is attributed to the 3D electrically conductive framework of CFs, which facilitates rapid electron/ion transport within the electrode. In terms of the conductive agent, hydrothermally treated CBs contribute to the enhanced high-voltage performance of LNMO-based cells due to their specific nitrogen-containing groups and structural defects. Furthermore, the partially carbonized PVP (PC-PVP) also positively impacts the cycling and rate performance of LNMO-based cells. The conformally coated PC-PVP layer functions not only as an electrically conductive binder but also as a protective barrier that mitigates electrolyte degradation at high voltages. Overall, these findings pave the way for a deeper understanding of the roles played by carbonaceous materials in high-voltage LIBs, offering a new avenue for future research and development in this field.

References

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[2] Y. K. Sun, K. J. Hong, J. Prakash and K. Amine, Electrochem. Commun., 4, 344-348 (2002).
[3] Y.H. Liu, W. C. Chen, C. H. Hsueh and C. L. Hsu, Mater. Today Chem., 25, 100934 (2022).