Batteries face the challenges of long life cycle, high power density, low cost and reliability to meet the requirements of large-scale energy storage devices, e.g. smart grid. The room-temperature rechargeable magnesium battery is a type of electrochemical energy storage system based on magnesium anode. Mg metal is a promising material with earth-abundant supply and low cost (the cost of magnesium is less than 5 percent of that of the lithium). Mg anode offers large volumetric energy density (3833 mAh/cm3) and contributes to dendrite-free plating during the electrochemical cycling. Meanwhile, the standard reduction potential of Mg-ion is only 0.6 V higher than that of the Li-ion. This means that the magnesium-based batteries can output similar energy density as the lithium ion batteries as long as they are matched with the suitable cathodes. Moreover, the stable deposition and stripping of the magnesium ions are conducive to the alleviation of the anode volume change as well as the electrolyte consumption, which thereby improve the cycle stability and the power density of the magnesium-based batteries. Therefore, the magnesium-based batteries are capable of meeting the requirements of next generation energy storage systems without seriously compromising the energy density.

However, the sluggish Mg2+ transport in host lattices and the low capacity of inorganic framework cathodes still limit the wide application of the magnesium batteries. Li-Mg dual-salt electrolyte can activate the reaction dynamics of cathodes through predominant Li+ insertion (instead of Mg2+), but while maintaining the advantages of magnesium anode in this hybrid Li-Mg system. The strategy of Li-salt mediation expands the pool of the cathode material candidates for magnesium batteries. Recently, Prof. Li Chilin from Shanghai Institute of Ceramics, Chinese Academy of Sciences, developed Mg-organic battery based on renewable rhodizonate salt (such as Na2C6O6) as cathode of multi-electron transfer activated by Mg-Li dual-salt electrolyte (See Figure attached). The relevant results were published in ACS Nano, a journal from American Chemical Society (DOI: 10.1021/acsnano.7b09177).

The nanostructured organic system is expected to reach a high reversible capacity of 350-400 mAh/g (three electron transfer) due to the existence of high-density carbonyl groups (C=O) as redox sites. Organic cathode wired by reduced graphene oxide enables a high-rate performance of 200 and 175 mAh/g at 2.5 (5 C) and 5 A/g (10 C), respectively, which also benefits from no dendrite formation at the magnesium anode even under the high current density and after the long-term cycling. Such sound performance is promoted by a high intrinsic diffusion coefficient (10-12-10-11 cm2/s), large pesudocapacitance contribution (>60%) of Li-ion in Na2C6O6, and suppressed exfoliation of C6O6 layers by a firmer non-Li pinning (via Na-O-C or Mg-O-C). This Mg-organic system can achieve a long-term cycling for at least 600 cycles, and has a high energy density up to 525 Wh/kg and power density over 4490 W/kg for active cathode materials, exceeding the level of high-voltage insertion cathodes with typical inorganic structures.

Li’s group has devoted to the strategic studies on improving the dynamics of the magnesium-based batteries for a long time and has achieved some important results. They have developed a Mg/fluorinated graphene battery with exposed redox sites activated by a prior anionic insertion (Adv. Funct. Mater. 2015, 25, 6519-6526), high capacity dual-salt Mg-based batteries based on polysulfide conversion cathode (Adv. Funct. Mater. 2015, 25, 7300-7308), and solution to Mg-S batteries with high rate and long cycle life (Adv Mater. 2018, 30, 1704166).

This work was supported by the National Key R & D Program of China, National Natural Science Foundation of China, “Hundred Talents” Program of Chinese Academy of Sciences, and “Thousand Talents” Program of Shanghai.

High-Capacity Mg？Organic Batteries Based on Nanostructured Rhodizonate Salts Activated by Mg？Li Dual-Salt Electrolyte [Image by Li Chilin]

Source: Shanghai Institute of Ceramics, CAS

For more information, please contact

Prof. Li Chilin

Shanghai Institute of Ceramics

Email: chilinli@mail.sic.ac.cn