Dissolution and ionization of sodium superoxide in sodium–oxygen batteries

Abstract

With the demand for high-energy-storage devices, the rechargeable metal–oxygen battery has attracted attention recently. Sodium–oxygen batteries have been regarded as the most promising candidates because of their lower-charge overpotential compared with that of lithium–oxygen system. However, conflicting observations with different discharge products have inhibited the understanding of precise reactions in the battery. Here we demonstrate that the competition between the electrochemical and chemical reactions in sodium–oxygen batteries leads to the dissolution and ionization of sodium superoxide, liberating superoxide anion and triggering the formation of sodium peroxide dihydrate (Na2O2·2H2O). On the formation of Na2O2·2H2O, the charge overpotential of sodium–oxygen cells significantly increases. This verification addresses the origin of conflicting discharge products and overpotentials observed in sodium–oxygen systems. Our proposed model provides guidelines to help direct the reactions in sodium–oxygen batteries to achieve high efficiency and rechargeability.

How to Control the Discharge Product in Sodium–Oxygen Batteries: Proposing New Pathways for Sodium Peroxide Formation

“…These results are consistentw ith those recently shown by Landa-Medrano et al, [33,34] who demonstrated gas evolution in Na/O 2 batteries when the discharged cell was left under rest conditions due to the partial dissolution of NaO 2 .H owever, uncertainties emergea gain with the product resultingf romt his degradation process. [14,23,[32][33][34] In addition, previous kinetic and theoretical investigations also support the occurrence of the reaction shown in Equation (2). [13,35] Indeed, Amine and co-workers recently provided experimental evidences upporting this reaction pathway in lithium-based systems.…”

“…[1][2][3][4][5][6][7] Among these, Na/O 2 batteries have attracted intensive researchi nterest in the pastf ive years due to their excellent kinetics. [8] Several fundamental studies of their cell chemistry have been published recently: [9][10][11][12][13][14] In general, either sodiums uperoxide (NaO 2 )o rs odium peroxide (Na 2 O 2 )a re reported as major discharge products.A na nalogy for discharge product formation might be found in past and recent research intoL i/O 2 batteries: Secondary Li/O 2 batteries were first demonstrated by Abrahama nd Jiang in the mid-1990s. [15] It is reported that lithium peroxide (Li 2 O 2 )i st he primary discharge product, whereas LiO 2 is considered to be thermodynamically unstable.H owever, recently,t he superoxide,L iO 2 ,h as also been reported as an anosized, substrate-supported discharge product when using suitable graphene-based cathodes.…”

Alkali‐Oxygen Batteries Based on Reversible Superoxide Chemistry

“…charge product to be NaO 2 with ag radualt ransitiont o Na 2 O 2 ·2H 2 O. [36] This change wasm onitored using X-ray diffraction and Raman spectroscopy (Figure 7). This transition was monitored over time and complete conversion to Na 2 O 2 ·2H 2 O was observedw ithin 12 hours.T he authors also note that this process appeared to be independento ft he rest or chargep ro-tocols.…”

High-efficiency and high-power rechargeable lithium–sulfur dioxide batteries exploiting conventional carbonate-based electrolytes

“…The discharge mechanisms and nature of discharge products such as their morphology and stability can be significantly altered by the properties of the electrolyte, such as donor numbers or dielectric constants202122232425. The critical dependency on the electrolyte in the metal-gas system compared with conventional lithium/sodium ion batteries is most likely due to the generation of gas radicals, which are an important intermediate for the discharge reaction.…”