Magnesium metal batteries (MMBs), featuring magnesium as the anode, emerge as a promising yet challenging alternative to conventional lithium-ion batteries in the rechargeable battery sector. Despite their potential for lower costs and greater sustainability due to magnesium’s abundance, and a higher volumetric energy density which is critical for applications in electric vehicles and portable electronics, these advantages are not easily realized. Magnesium’s lower reactivity, compared to lithium, potentially offers safer battery solutions, mitigating risks like thermal runaway and fires associated with lithium-ion batteries. Additionally, the double positive charge of magnesium ions might lead to enhanced battery life and reduced degradation compared to lithium ions. However, the development of magnesium batteries is significantly hindered by substantial technical challenges. Key among these is the difficulty in creating effective anodes that can efficiently integrate magnesium ions. Issues such as inconsistent Mg deposition and the controversial formation of Mg dendrites adversely affect Coulombic efficiency and safety, posing major obstacles to the advancement of MMBs. Moreover, the use of Mg foil as an anode is not feasible for high-energy-density and flexible batteries. Therefore, while MMBs hold the promise of a more sustainable and safer energy storage future, they face complex technical barriers that must be addressed to unlock their full potential.
In a new study published in Advanced Materials led by Professor Wei Ai and Professor Wei Huang and conducted by Jingxuan Bi, Yuhang Liu, Zhuzhu Du, Ke Wang, Wanqing Guan, and Haiwei Wu from the Frontiers Science Center for Flexible Electronics and Xi’an Institute of Flexible Electronics at the Northwestern Polytechnical University, the researchers developed flexible MMBs by employing a unique triple-gradient scaffold. This scaffold was crafted from a combination of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) and softwood cellulose fibers (SWCF). The distinct gradient design in this scaffold aimed to address critical challenges commonly associated with MMBs, particularly the issues of uneven Mg deposition and dendrite growth.
The authors designed a flexible, paper-like scaffold with a triple-gradient structure. This structure included gradients in three key aspects, firstly, conductivity to ensure efficient electron transport. Secondly, magnesiophilicity this to regulate the affinity towards magnesium ions to promote uniform deposition. Thirdly, pore Size which will control the ion flow and accommodating volume changes during battery operation.
The scaffold was made by carefully adjusting the ratios of MWCNTs-COOH to SWCF. This adjustment was crucial in achieving the desired gradient properties. The processing method employed was akin to traditional papermaking, suggesting the potential for scalability in industrial applications. The authors conducted detailed structural and chemical analyses of the scaffold to confirm the gradient properties and ensure its suitability for use in MMBs.
One of the most significant findings was the uniform deposition of Mg on the scaffold. The triple-gradient design effectively guided a bottom-up Mg deposition process, which is critical for enhancing battery performance and lifespan. The fabricated MMBs displayed a high volumetric energy density of 244 Wh L-1. This is also a significant achievement, as it surpasses the energy density of many current magnesium and even some lithium-ion batteries. The batteries demonstrated stable performance over 1200 hrs at 3 mA cm-2/3 mAh cm-2 in symmetrical cells. This stability is essential for practical applications of MMBs. The successful application of the triple-gradient scaffold in a full-cell configuration with a PM-Mo6S8 cathode underscored its adaptability. The use of materials and processes compatible with industrial standards also points towards the scalability of this technology.
In conclusions, the authors’ work represents an important advancement in the field of flexible energy storage. They addressed key challenges in magnesium battery technology, and paves the way for the development of next-generation flexible, high-energy-density batteries. Such batteries could have a wide range of applications, especially in the realm of portable and wearable electronics. The scalability and adaptability of the approach also suggest potential applications in larger-scale energy storage systems, contributing to the advancement of renewable energy technologies. The successful integration of the triple-gradient scaffold into a full-cell configuration, with a PM-Mo6S8 cathode, also demonstrates the versatility and adaptability of the design across various metal-battery systems. This could lead to broader applications beyond magnesium-based batteries, potentially benefiting lithium, sodium, and zinc-based energy storage systems.
Bi, J., Liu, Y., Du, Z., Wang, K., Guan, W., Wu, H., Ai, W., Huang, W., Bottom-Up Magnesium Deposition Induced by Paper-Based Triple-Gradient Scaffolds Toward Flexible Magnesium Metal Batteries. Adv. Mater. 2023, 2309339. https://doi.org/10.1002/adma.202309339