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New high-performance Na-ion battery with SO2-based catholyte; potential for other non-Li-metal-based battery systems

Researchers in South Korea have demonstrated new type of room-temperature and high-energy density sodium rechargeable battery using a sulfur dioxide (SO2)-based inorganic molten complex catholyte that serves as both a Na+-conducting medium and cathode material (i.e. catholyte).

As reported in an open access paper in Nature’s Scientific Reports, the new battery showed a discharge capacity of 153 mAh g−1 based on the mass of catholyte and carbon electrode with an operating voltage of 3 V; good rate capability; and excellent cycle performance over 300 cycles. In particular, the researchers suggested, the non-flammability and intrinsic self-regeneration mechanism of the new inorganic liquid electrolyte can accelerate the commercialization of Na rechargeable batteries.

(a) The first and second galvanostatic voltage profiles of a Na–SO2 cell at 0.1C (=150 mA g−1 and 0.34 mA cm−2). The cutoff voltage for charge is 4.05 V. (b) Discharge rate capability of a Na–SO2 cell. The charging rate is fixed at 0.2C. (c) Cycle performance of a Na–SO2 cell at a rate of 0.5C discharge and 0.2C charge for 100 cycles. Jeong et al. Click to enlarge.

Here we report a Na–SO2 rechargeable battery system using NaAlCl4⋅2SO2 electrolyte. We found that the optimized carbon cathode enables a reversible reaction of the catholyte with high capacity, good rate capability, a long life-span over 300 cycles, and an estimated theoretical energy density of 407 Wh kg−1 (based on the discharged product including carbon cathode). This value is comparable with those of other high-energy Na rechargeable batteries. Moreover, non-flammability, low vapor pressure, and unique self-regeneration mechanism of the inorganic electrolyte presented here would be noteworthy merits of Na–SO2 system over other Na rechargeable battery systems.

—Jeong et al.

For their study, the researchers constructed a 2032 coin-type Na–SO2 cell using a Na-metal anode and a porous carbon cathode with NaAlCl4⋅2SO2 as a catholyte.

The cell delivers a discharge capacity of ~1800 mAh g−1 based on the carbon cathode at a rate of 0.1C (=150 mA g−1 or 0.34 mA cm−2). This corresponds to an areal capacity of 4.1 mAh cm−2—comparable to typical values of commercial Li-ion batteries (3–5 mAh cm−2) and much higher than those of reported Li–O2 and Na–O2 batteries.

The Na–SO2 cell also showed a high capacity of 897 mAh g−1 is observed even at a significantly high current density of 5C (7500 mA g−1 or 17 mA cm−2).

Given that the rate capability is one of the most challenging issues in NAS, ZEBRA, and Na–O2 batteries, the excellent power capability could give the Na–SO2 battery a critical edge over other Na rechargeable batteries previously reported.

—Jeong et al.

However, they authors noted in their paper, a low round-trip energy efficiency (~80%) needs to be further ameliorated. The Na–SO2 cell showed relatively good capacity retention during cycling, with 75% of the initial capacity after 100 cycles, even under full depth-of-discharge condition, accompanied by high columbic efficiencies during cycling (average of ~99%).

They demonstrated that the cell chemistry is based on the highly reversible redox reaction of SO2 with tetrachloroaluminate and the use of the NaAlCl4⋅2SO2 inorganic electrolyte enables the highly reliable Na–SO2 system in terms of long cycle life as well as safety.

Considering the many favorable features and promises discussed in this report, the Na–SO2 battery can be a viable system for next cost-effective energy storage system. Further, the SO2-based inorganic electrolyte can be widely applied to battery systems adopting other metallic anodes like Ca, K, Al, and Mg, which paves the way for the development of various non-lithium metal-based battery systems.

—Jeong et al.


  • Goojin Jeong, Hansu Kim, Hyo Sug Lee, Young-Kyu Han, Jong Hwan Park, Jae Hwan Jeon, Juhye Song, Keonjoon Lee, Taeeun Yim, Ki Jae Kim, Hyukjae Lee, Young-Jun Kim & Hun-Joon Sohn (2015) “A room-temperature sodium rechargeable battery using an SO2-based nonflammable inorganic liquid catholyte” Scientific Reports 5, Article number: 12827 doi: 10.1038/srep12827



Given that PbSO4 batteries have 20% losses or so in cycling, I'm not terribly concerned with that.  What I'd like to see is something with better cycle life, low self-discharge and good working temperature range.  That plus cheap equals potential for mass usage.

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