Binder-Free 3D LiFePO4/Porous Aluminum Network Electrodes for High Areal Capacity and Long-Term Stable Lithium-Ion Batteries

Significance 

Lithium-ion batteries (LIBs) are currently one of the leading energy storage technologies due to their high energy density, long cycle life, and relatively low self-discharge rates. However, the increasing demands in electric vehicles, portable electronics, and grid storage require further advancements in battery performance, especially in terms of energy density, cost-effectiveness, and manufacturing scalability. The electrode design can influence the battery’s overall capacity, rate capability, and longevity and traditional electrode configurations typically include active materials, conductive additives, and binders which are essential for mechanical stability and current distribution, however, they add considerable weight and volume and by this reduce the overall energy density. Moreover, conventional fabrication methods, such as slurry casting, face limitations when there is an attempt to increase electrode thickness and active material loading, which will result in poor electrochemical performance due to inefficient electron and ion transport pathways. To address these challenges, several electrode designs were proposed that can accommodate higher mass loadings of active materials with minimal inactive components and the development of three-dimensional (3D) electrode architectures has shown promise in this regard. 3D electrodes are characterized by their porous and conductive structures, improved ion and electron transport, enhanced mechanical stability, and greater active material utilization. Despite these advantages, the implementation of 3D electrode designs in practical applications has been hindered by several challenges. These include the complexity and cost of manufacturing processes, difficulties in scaling up production, and the need to maintain structural integrity and performance over repeated charge-discharge cycles. Addressing these issues requires novel approaches that are not only effective but also economically viable and scalable.

To this end, new study published in Journal of Materials Chemistry A and led by Professor Xiaowei Zhang, Zhiyong Zhao, Peng Wang from the Beijing Normal University in collaboration with Hongyi Gao and Professor Ge Wang from the University of Science and Technology Beijing and Ioanna Maria Pateli and Professor John Irvine from the University of St Andrews, developed a new in situ powder infiltration method to integrate LiFePO4 (LFP) nanoparticles into highly porous aluminum networks (pAlN) to create binder-free, three-dimensional positive electrodes. This innovative approach aims to leverage the benefits of 3D electrode architectures while addressing the aforementioned challenges of cost and scalability.

The researchers began by preparing the porous aluminum network (pAlN) substrate using a sintering and dissolution process. Aluminum wool and powder, combined with NaCl nanoparticles, served as the pore-forming template. They added magnesium powder to enhance sintering properties and energy absorption capacity. The powder mixture underwent hot pressing and sintering, then the NaCl template was dissolved to form the initial pAlN substrate. An acid treatment further removed impurities and reduced the resistance value of the pAlN skeleton from 3.12 kΩ to 2.5 Ω. They revealed an interconnected porous network structure with an estimated porosity of 80%. The inclusion of aluminum wool improved the long-range electronic conductivity and mechanical strength of the aluminum foam, establishing a robust framework for subsequent experiments.

The authors fabricated the 3D LFP/pAlN electrode using the pAlN substrate which was dipped into an LFP precursor solution containing LiNO3, Fe(NO3)3·9H2O, NH4H2PO4, and CTAB, along with pre-added LFP nanoparticles. This mixture was then calcined, forming post-synthesized LFP nanoparticles that acted as binders, connecting pre-added LFP nanoparticles to the conductive pAlN substrate. Citric acid and CTAB were used as co-fuels and reducing agents, while sucrose and multi-walled carbon nanotubes (MWCNTs) were added to enhance conductivity. They confirmed the dense distribution of active LFP nanoparticles on the pAlN substrate and the formation of orthorhombic olivine-type LiFePO4 crystals, with no detectable impurity phases. The presence of small, in situ-formed LFP nanoparticles (<100 nm) effectively bridged the aluminum nanosheets of the pAlN substrate and larger pre-added LFP nanoparticles (~200 nm).

The team evaluated the electrochemical performance of the 3D LFP/pAlN electrode using the galvanostatic charge/discharge and electrochemical impedance spectroscopy which demonstrated that the 3D electrode, prepared with a 0.5 M post-LFP precursor solution, exhibited the highest performance, with an LFP mass loading of 65 mg cm−2. This electrode displayed a typical charge-discharge plateau around 3.4 V with a specific capacity of 101 mA h g−1. They measured the areal capacity at 6.56 mA h cm−2 at an areal current density of 0.55 mA cm−2, and this outperformed conventional 2D slurry-casting electrodes and other recently reported 3D electrodes. Moreover, they found a single depressed semicircle in the Nyquist plot, which means lower charge-transfer resistance and confirmed the fast electron and ion transport within the 3D electrode. The cycling performance showed a capacity retention of 94.1% after 100 cycles at an areal current density of 2.32 mA cm−2 and demonstrated excellent long-term electrochemical stability with a high coulombic efficiency of 97.9%. The researchers also investigated the impact of different organic fuels on the microstructure and electrochemical performance of the 3D LFP/pAlN electrode. They compared the use of citric acid-CTAB mixed fuel with urea-CTAB and glycine-CTAB fuels and found that the citric acid-CTAB combination provided superior specific capacity and physicochemical properties. In their studies, the amount of CTAB was optimized to enhance the infiltration of the precursor solution and increase the active LFP material loading.

In conclusion, Professor Xiaowei Zhang and colleagues successfully developed a novel in situ powder infiltration method to integrate LFP nanoparticles into pAlN creating a binder-free, 3D positive electrode with significantly enhanced performance characteristics. Additionally, the resulting 3D LFP/pAlN electrode demonstrated a higher areal capacity over traditional 2D slurry-casting electrodes and other recently reported 3D electrode structures which translates to longer battery life and more energy storage in a compact form, essential for applications in electric vehicles, portable electronics, and grid storage. Moreover, the new approach can be readily adapted for large-scale industrial production, making high-performance LIBs more accessible and affordable. Moreover, the authors’ incorporation of aluminum wool and powder into the pAlN substrate enhances the mechanical strength and electrical conductivity of the aluminum foam and can provide a robust framework that is better to withstand the physical stresses associated with repeated charge-discharge cycles and ultimately lead to longer-lasting batteries with higher durability. Furthermore, the reported maintenance (94.1%) for the 3D LFP/pAlN electrode of its capacity after 100 cycles at a high areal current density, with an impressive high coulombic efficiency of 97.9% demonstrates excellent and exceptional stability which is essential in the development of reliable batteries that can endure extended use without significant degradation.

Binder-Free 3D LiFePO4/Porous Aluminum Network Electrodes for High Areal Capacity and Long-Term Stable Lithium-Ion Batteries - Advances in Engineering

About the author

Xiaowei Zhang received her Ph.D. degree in Materials Science and Engineering from the University of Science and Technology Beijing in 2015. She then worked as a postdoc fellow in the Department of Physics at Peking University from 2015 to 2018. She is now an associate professor at Beijing Normal University. Her research interest mainly focuses on organic-inorganic hybrid materials and their applications in energy storage, catalysis, and optoelectronics.

About the author

Ge Wang received her Ph.D. in Chemistry from the Michigan Technological University in 2002. Currently, she is a professor and Ph.D. supervisor in the School of Material Science and Engineering at the University of Science and Technology Beijing. In 2012, she became a special chair professor endowed by the Chang Jiang Scholars Program of the Ministry of Education. Her research interests focus on creating complex materials structures with nanoscale precision using chemical approaches, and studying the functionalities including catalytic, energy storage, and energy saving properties, etc.

About the author

John T.S. Irvine is a professor at the School of Chemistry, University of St Andrews. He has established a significant international research grouping investigating fundamental electrochemistry, solid-state chemistry, and materials science addressing critical energy problems. His research has ranged from detailed fundamentals to strategic and applied science and has had a major impact across academia, industry, and government.

Reference

Zhiyong Zhao, Xiaowei Zhang, Peng Wang, Ioanna Maria Pateli, Hongyi Gao, Ge Wang and John Irvine. New approaches to three-dimensional positive electrodes enabling scalable high areal capacity. J. Mater. Chem. A, 2024, 12, 1736-1745

Go to J. Mater. Chem. A

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