Nitrogen-Doped Mesoporous Carbon Cathode for Bromine Crossover Control

The patent applies porous carbon materials with specific pore sizes (micro-pores <2 nm and meso-pores 2-50 nm) to the positive electrode. These pores capture and immobilize bromine and bromine complexes through adsorption, preventing their crossover to the negative electrode. The porous structure provides high surface area for bromine accommodation while maintaining ion transport pathways, thus extending battery lifespan without significantly complicating the electrode structure.

The patent uses composite materials combining carbon precursors (such as polyacrylonitrile, polyacrylic acid, or carboxymethyl cellulose) with nitrogen source materials to create nitrogen-doped porous carbon coatings on the graphite felt. This composite approach enhances the electrode's ability to interact with bromine species through nitrogen-containing functional groups, improving reliability while maintaining manufacturing feasibility through a single coating process.

The patent employs preliminary action by preparing a slurry mixture containing all necessary components (carbon precursor, nitrogen source, pore-forming agents, and binders) before applying it to the graphite felt. This pre-mixed slurry is then coated onto the electrode surface and subjected to a single pyrolysis treatment that simultaneously creates the porous structure, dopes nitrogen into the carbon matrix, and forms the protective coating. This approach simplifies manufacturing compared to sequential processing steps.

The patent utilizes parameter changes by controlling the pyrolysis temperature (typically 600-900°C) and atmosphere to transform the organic slurry into a porous nitrogen-doped carbon structure. By optimizing these thermal processing parameters, the single-step pyrolysis process achieves multiple objectives: carbonization, pore formation, nitrogen doping, and coating consolidation, thereby maintaining ease of manufacture while achieving improved battery lifespan.

The patent merges multiple functions into a single coating layer: the porous structure formation, nitrogen doping, and bromine capture capability are all achieved simultaneously through one pyrolysis process. The slurry contains carbon precursors that form the porous matrix, nitrogen sources that provide doping elements, and pore-forming agents that create the desired pore architecture. This merging approach enhances bromine capture while avoiding the need for separate coating, doping, and pore-formation steps.

The patent applies self-service by designing a slurry system where the components automatically organize into the desired porous structure during pyrolysis. The pore-forming agents (such as surfactants or polymers) self-assemble into templates that create uniform pores upon removal, while the nitrogen source material incorporates into the carbon matrix through thermal decomposition. This self-organizing behavior reduces the need for complex external control mechanisms during the coating process.