Newly developed battery hits 850 cycles, retains 99.95% capacity

 China scientists’ breakthrough organic flow battery, remains at 99.95% capacity after 850 Cycles

Chinese researchers achieved a breakthrough in their development of organic flow batteries, creating novel ORAMs which helped them achieve significant numbers in aqueous flow batteries. In the recent findings by researchers from the Dalian Institute of Chemical Physics, they were able to retain as much as 99.95% capacity even after running 850 cycles with their new cell. This latest development is novel naphthalene derivative-based electrolytes which are air-stable, overcoming the challenges and effects of not using inert gases. With new organic molecules, the organic flow battery performed well for 600 cycles without a drop in capacity. This new breakthrough in battery technology is promising. Researchers at the Dalian Institute of Chemical Physics have developed novel naphthalene-based organic redox-active molecules (ORAMs) for aqueous organic flow batteries. The newly developed ORAMs demonstrate that they can achieve stable cycling in normal ait-atmosphere conditions, a press release said. A redox flow battery is a type of electrochemical cell in which electric current is generated by components dissolved in liquids stored on opposite sites of a membrane. Advantages of redox flow batteries include their ability to scale power and low cost of ownership. However, low cycle energy and the use of rare metals like vanadium have limited their use. 

According to the Dalian Institute of Chemical Physics' press release, organic redox-active molecules (ORAMs) now bring promising developments for aqueous organic flow batteries (AOFBs), centring on air-stable naphthalene-based organic materials. The researchers focused on chemical and in-situ electrochemical methods to synthesize active naphthalene derivatives to purify the ORAMs and make them cost-effective and scalable. In their tests, its naphthalene flow batteries using 1.5 mol/L electrolytes produce a stable performance that reached up to 850 cycles or around 40 days while retaining 99.95% capacity. Notably, its battery performed up to 600 cycles or as much as 22 cycles and remained at full capacity while being exposed to air. Research is on going to develop organic redox flow batteries, in which organic materials are used, which are widely available and easier to produce. Depending on the solvent used for the electrolyte, organic redox batteries can be classified into two major categories: aqueous and non-aqueous. An aqueous organic flow battery (AOFB) uses water as an electrolyte, whereas a non-aqueous organic flow battery (NAOFB) uses an organic solvent. 

Breakthroughs and Developments

Batteries are best known for being the top power source for devices or electronics which are not connected to a direct plug, but it is notorious for their planet-exhaustive development, particularly as they require rare Earth metals. Many companies have since looked for alternative components that would make it cost-effective and less harmful through mining, centring on lithium-free power cells. The current main source of alternative energy sources target on lithium-ion batteries, and it is known for its typical use of fossil fuels, which are ironically, harmful to the environment. Murdoch University researchers have since found a suitable electrode alternative that is abundant in bio-waste products, as chicken eggshells were found to be capable of powering batteries. While there are many already looking into new power cell developments, organic flow batteries are among those which are promising in today's day and age, meant for large-capacity applications. China's Dalian Institute of Chemical Physics has discovered a breakthrough for AOFBs with the new ORAMs, centring on air-stable energy storage for future applications.

Challenges

Various types of AOFBs are in the works, classified based on the pH of the electrolyte, neutral and acid, and offer cost and scale benefits. However, the organic redox-active molecules (ORAMs) used in the batteries are prone to deactivation due to side reactions if not used with an inert gas. This can increase the cost of battery maintenance since the capacity loss is irreversible and severely degrades the battery’s lifespan as well. A team led by Zhang Changkun and Li Xianfeng, both professors at the Dalian Institute of Chemical Physics, developed novel naphthalene-based derivatives with active hydroxyls and dimethylamine scaffolds which provide stability in air and can, therefore, be used in AOFBs. 

What was Achieved? 

The researchers used a combination of chemical and in situ electrochemical methods to synthesize the active naphthalene derivatives. This approach not only made it easier to purify the ORAMs but is also scalable and cost-effective. The electrochemical step added another advantage since the researchers could now introduce hydrophilic alkylamine scaffolds into the naphthalene derivatives. This serves as protection from unintended side reactions while also improving the solubility of the molecules in the water-based electrolyte. In their tests, the researchers found that the naphthalene flow battery, when used with a 1.5 mol/L electrolyte, has stable cycling performance for up to 850 cycles (approximately 40 days). The capacity of the battery was recorded at 50 Ah per liter. The researchers introduced a continuous air flow in the catholyte to test whether the AOFB could work with air exposure. They found that the battery performed well for 600 cycles (approximately 22 days) without a drop in performance or capacity. The researchers designed pilot-scale battery packs with their new synthesis and operation procedures. They tested them for stability and performance in the lab. With a capacity of 330 Ah, the pilot battery packs demonstrated cycling stability for 270 cycles (27 days) and capacity retention of 99.95% per cycle. In addition to the performance improvements, the researchers also worked on the scalability of naphthalene derivatives production and achieved outputs of 11 pounds (five kg) per pot, the press release added. 

Application in the Future

ORAMs were infamous for their renowned instability as well as high costs, but the researchers were able to synthesize active naphthalene derivatives which helped reduce the cost of molecular synthesis. In their study, the team's as-prepared naphthalene derivatives were able to deliver a "multisubstituted framework with hydrophilic alkylamine scaffolds" that help protect against possible reactions. This outcome was said to improve its solubility in aqueous electrolytes, opening up the future for its AOFB applications. According to Professor Li Xianfeng, Dalian Institute of Chemical Physics of the Chinese Academy of Sciences (CAS), “This study is expected to open a new field in the design of air-stable molecular for sustainable and air-stable electrochemical energy storage”.