Magnesium batteries represent a promising alternative to lithium-ion systems due to the abundance of magnesium, its high theoretical volumetric capacity, and inherent safety advantages. However, the development of practical magnesium batteries faces significant challenges at electrode-electrolyte interfaces, which critically influence performance metrics such as cycle life, Coulombic efficiency, and rate capability. Understanding and controlling these interfacial phenomena is essential for advancing magnesium battery technology.

A primary challenge in magnesium batteries is the formation and stability of the solid-electrolyte interphase (SEI) on the magnesium anode. Unlike lithium systems, where a stable SEI can form and enable reversible cycling, magnesium often exhibits poor SEI characteristics. The native SEI on magnesium tends to be ionically insulating, impeding magnesium ion transport and leading to high overpotentials during plating and stripping. This results in low Coulombic efficiency and dendritic growth, which can cause short circuits. Research indicates that the composition of the SEI in magnesium batteries is highly dependent on the electrolyte chemistry. For example, conventional electrolytes containing chloride ions tend to form a more conductive SEI compared to chloride-free systems. The SEI in magnesium systems often comprises magnesium oxides, hydroxides, and carbonates, which are electronically insulating but may allow limited ionic conduction under specific conditions.

Cathode-electrolyte interactions present another critical interface challenge. Many candidate cathode materials for magnesium batteries, such as transition metal oxides and sulfides, suffer from sluggish magnesium ion diffusion and incompatibility with conventional electrolytes. The interfacial resistance at the cathode can dominate overall cell impedance, particularly in systems using organic electrolytes. Chevrel phase materials (Mo6S8) have shown relatively good compatibility with magnesium electrolytes due to their open structure that facilitates magnesium ion insertion. However, their low operating voltage and limited capacity restrict practical energy density. Higher voltage cathodes, such as vanadium oxides or manganese-based compounds, often exhibit poor interfacial stability, leading to electrolyte decomposition and rapid capacity fade. Surface reactions between the cathode and electrolyte can form passivation layers that block active sites and increase polarization.

Strategies to stabilize interfaces in magnesium batteries focus on tailored surface modifications and electrolyte engineering. For anode protection, artificial SEI layers created through surface coatings or electrolyte additives have demonstrated improved performance. Thin layers of magnesium boride or magnesium fluoride deposited on the anode surface can enhance interfacial kinetics while suppressing side reactions. Inorganic-organic hybrid coatings combining polymers with ceramic materials have also shown promise in facilitating uniform magnesium deposition. Electrolyte additives that preferentially adsorb on the anode surface, such as ionic liquids or boron-based compounds, can modify the SEI composition to improve ionic conductivity.

For cathode interfaces, surface coatings play a vital role in mitigating degradation. Atomic layer deposition of aluminum oxide or titanium oxide on cathode particles has been shown to reduce interfacial resistance and prevent electrolyte decomposition. These coatings act as physical barriers while allowing magnesium ion transport. Composite cathode designs incorporating conductive polymers or carbon matrices can improve electronic conductivity and maintain structural integrity during cycling. Electrolyte formulation is equally critical; weakly coordinating anions like magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2) in ether-based solvents have demonstrated better compatibility with high-voltage cathodes compared to traditional Grignard-based electrolytes.

The electrolyte itself must be carefully designed to address multiple interfacial challenges simultaneously. A suitable magnesium electrolyte should exhibit high oxidative stability for cathode compatibility, good reductive stability for anode protection, and high ionic conductivity. Recent advances in non-nucleophilic electrolytes based on boron clusters or aluminum complexes have expanded the electrochemical window while maintaining reasonable magnesium deposition efficiency. Multivalent ion transport across interfaces remains inherently slower than in lithium systems due to higher charge density, emphasizing the need for optimized solvation structures that minimize desolvation penalties at interfaces.

Operando characterization techniques have provided valuable insights into interfacial processes in magnesium batteries. X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy reveal the dynamic evolution of interface composition and resistance during cycling. Scanning probe microscopy has visualized morphological changes at magnesium electrodes, highlighting the importance of uniform current distribution for preventing dendrites. These tools enable rational design of interface stabilization strategies by correlating electrochemical performance with structural and chemical changes at interfaces.

Long-term interface stability remains a key hurdle for magnesium batteries, particularly for applications requiring extended cycle life. The dissolution of cathode materials into the electrolyte and the continuous consumption of electrolyte components through side reactions can progressively degrade performance. Accelerated aging tests under varying temperature and voltage conditions help identify failure mechanisms and validate mitigation approaches. Interface engineering must also account for manufacturing scalability, as complex surface treatments or sensitive electrolyte formulations may pose challenges for large-scale production.

Comparative studies between magnesium and lithium interfaces reveal fundamental differences that require distinct solutions. While lithium battery technology benefits from decades of interface optimization, magnesium systems demand new approaches tailored to their unique chemistry. The bivalency of magnesium ions introduces stronger electrostatic interactions with host materials and electrolytes, necessitating careful balance between stability and kinetics at interfaces. Future research directions include developing in situ interface characterization methods, exploring new classes of interface-stabilizing additives, and designing hierarchical electrode architectures that minimize interfacial strain during cycling.

Practical implementation of magnesium batteries will depend on achieving robust interfaces across all cell components while maintaining cost competitiveness. Advances in interface science must be coupled with improvements in electrolyte formulation, electrode materials, and cell engineering to realize the full potential of this technology. The interplay between these factors determines whether magnesium batteries can transition from promising prototypes to commercial energy storage solutions. Continued research efforts focused on understanding and controlling interfacial phenomena will be critical for overcoming existing limitations and unlocking the performance required for diverse applications ranging from portable electronics to grid-scale storage.

The development of magnesium batteries illustrates the central role of interfaces in electrochemical energy storage systems. While challenges remain, systematic investigation of SEI formation, cathode-electrolyte interactions, and stabilization strategies provides a pathway toward practical devices. As understanding of these interfacial processes deepens, the performance gap between magnesium and established battery technologies will narrow, potentially enabling a new generation of safe, high-energy-density storage systems based on abundant materials.