As the world shifts from fossil fuels to renewable energy sources like solar and wind power, the need for reliable energy storage systems (ESSs) has grown.
While lithium-ion batteries are commonly used, they have safety risks due to their flammable electrolytes.
A safer alternative is the flowless zinc-bromine battery (FLZBB), which uses non-flammable electrolytes and offers a simpler, more cost-effective battery platform.
An FLZBB contains a positive electrode, a negative electrode, an electrolyte, and a separator.
Unlike conventional zinc-bromine batteries, the electrolyte in an FLZBB is held in a gel-like container rather than being pumped. Graphite felt (GF) is often used as an electrode material due to its stability in acidic electrolytes.
However, in FLZBBs, bromine and polybromide ions formed during charging can escape from the GF-positive electrode and reach the negative electrode, causing self-discharge.
This issue significantly reduces the battery’s performance and lifespan. Many studies have attempted to address this problem, but self-discharge remains a significant challenge.
To solve this issue, a team of researchers led by Professor Chanho Pak and graduate student Youngin Cho from the Gwangju Institute of Science and Technology in Korea developed a new electrode: the nitrogen-doped mesoporous carbon-coated graphite felt (NMC/GF).
Their study was published in the Chemical Engineering Journal.
The researchers created the NMC/GF electrodes using a cost-effective evaporation-induced self-assembly method. In this process, the GF felt is coated with precursor materials mixed in a solvent, then dried and cured.
When used in an FLZBB, these new electrodes effectively prevented the crossover of active materials and reduced self-discharge. The success of this approach is due to the mesopores in the GF fibers of the NMC/GF electrodes.
“The NMC coating on the GF electrodes introduced mesopores with strategically embedded nitrogen sites, which captured the bromine and bromine complexes in the positive electrode, suppressing bromine crossover and self-discharge,” explained Prof. Pak.
The NMC coating also made the originally hydrophobic GF electrodes ultrahydrophilic, improving their contact with the electrolyte and enhancing electrochemical performance. Additionally, it incorporated abundant oxygen and nitrogen species, which sped up bromine reactions and boosted performance further.
The FLZBB with NMC/GF electrodes showed excellent Coulombic and energy efficiencies of 96% and 76%, respectively, at a current density of 20 mA cm-2. It also achieved a high-rate areal capacity of 2 mAh cm-2 and exhibited unprecedented durability, with stable charge/discharge cycling over 10,000 cycles. Moreover, the thick GF electrode can potentially lower the overall cost of the battery.
“The development of the FLZBB positive electrode, which maintains long-term operation over 10,000 cycles with high efficiencies, will accelerate the development of stable ESSs and eco-friendly energy conversion,” said Prof. Pak. “The NMC/GF positive electrode can also be used in other aqueous batteries.”
This technology can lead to practical applications of FLZBBs, resulting in safer ESSs and more stable renewable energy systems, making a significant impact on future energy storage solutions.
Source: KSR.
