|Schematic representation of the super-valent battery during charge/discharge process. Wang et al. Click to enlarge.
A team from the University of Science and Technology Beijing is proposing a new super-valent battery based on aluminium ion intercalation and deintercalation. In an open access paper published in the Nature Publishing Group’s Scientific Reports, the researchers report that the cell can provide a discharge capacity at a current density of 50 mA g−1 of 165 mAh g-1 in the initial cycle and retain 116 mAh g-1 after 100 cycles.
The new cell uses vanadium oxide (VO2) nanorods synthesized through a low temperature hydrothermal method as the cathode material and high-purity aluminum foil as the anode. The battery exhibits excellent reversibility and relatively long cycle life compared to earlier Al-ion efforts, the team said. Even with very high current densities of 100 mA g-1 and 200 mA g-1, the corresponding capacities could still retain 106 and 70 mAh g-1, respectively.
Nowadays, due to their outstanding energy and power density, Li-ion batteries have become a mainstay for EES [electrical energy storage]. However, the concerns regarding the high cost and the limited lithium reserves in the earth’s crust have driven the researchers to search more sustainable alternative energy storage solutions. Sodium-ion and magnesium-ion batteries, as new energy storage systems in portable devices, have attracted much attention of the investigators. Most recently, aluminium-ion battery with multivalent metal ions transmitting internally has been studied preliminarily.
Owing to its low cost, easy operation and high security, the aluminium-ion battery has exhibited excellent prospects. However, the capacity and the cycle life are not satisfying at present. Some multivalent metal elements, such as aluminium and titanium, are abundant metallic elements in the earth’s crust with low price. Most important of all, comparing to Li-ion and Na-ion batteries with only one charge transferred in one redox couple, batteries with multivalent metal ions running between anodes and cathodes can transfer more charges in one redox couple, indicating a promising energy storage device for large capacity. Herein, we define this kind of battery as super-valent battery.—Wang et al.
Similar to the mechanism of Li-ion batteries, Al ions shuttle back and forth between the electrolyte and electrodes in the super-valent battery. When one Al ion moves from anode to cathode, the researchers explain, three charges will transfer in the external circuits as compensation. This capability can lead to large capacities in the super-valent batteries, the researchers suggested.
As an example, they mentioned that if two Al ions could insert into V4O8, the theoretical capacity could reach as high as 485 mAhg-1.
Their results represent a new strategy for the development of inexpensive and stable energy storage, the researchers said. Although the energy density of the current new system is “a bit low” compared to some new battery systems such as aqueous rechargeable lithium batteries, the low-cost and potential capacity gains inherent in this super-valent approach will encourage research in this area to continue, they suggested.
Due to the variable valence and relative stability at different valence state of transition metal, the transition metal oxides and transition metal salts should be given priority attention to develop new kind of cathode materials. In order to let Al3+ ions shuttle back and forth in the electrode materials in this super-valent battery, materials with large channel or layered structure should also be the our first priority.
… More researches need to be done in the future to further analyze the storage mechanism of metal ions and commercialize the super-valent batteries, including the exploration of cathode materials with higher cell voltages and specific capacities, electrolyte optimization and seeking other multivalent metal ions for super-valent batteries.—Wang et al.
Wei Wang, Bo Jiang, Weiyi Xiong, He Sun, Zheshuai Lin, Liwen Hu, Jiguo Tu, Jungang Hou, Hongmin Zhu & Shuqiang Jiao (2013) “A new cathode material for super-valent battery based on aluminium ion intercalation and deintercalation,” Scientific Reports 3, Article number: 3383 doi: 10.1038/srep03383