Comparative Performances of Birnessite and Cryptomelane MnO₂ as Electrode Material in Neutral Aqueous Lithium Salt for Supercapacitor Application

Abstract

International audienceNa-doped Birnessite-type manganese oxide (δ-MnO2) has been synthesized using the chemical method and characterized through X-ray diffraction and SEM, showing the lamellar structure and high crystal structure. A comparative study of the electrochemical performances of this material with those of the commercial Cryptomelane-type MnO2 has then been undertaken in ten neutral aqueous electrolytes for supercapacitor applications. Aqueous electrolytes, containing a lithium salt, LiX (where X = SO42-, NO3-, CH3CO2-, CH3SO3-, ClO4-, C7H15CO2-, TFSI-, Beti-, BOB-, or Lact-), have been first prepared under neutral pH conditions to reach the salt concentration, providing the maximum in conductivity. Their transport properties are then investigated through conductivities, viscosities, and self-diffusion coefficient measurements. Second, the thermal behaviors of these electrolytic aqueous solutions are then evaluated by using a differential scanning calorimeter from (213.15 to 473.15) K in order to access their liquid range temperatures. Cyclic voltammograms (CV) in three electrode configurations are thereafter investigated using Na Birnessite and Cryptomelane as working electrode material from (−0.05 to 1.5) V versus Ag/AgCl at various sweep rates from (2 to 100) mV*s-1. According to anion nature/structure and manganese oxide material type, different CV responses are observed, presenting a pure capacitive profile for Beti- or C6H13CO2- and an additional pseudocapacitive signal for the smallest anions, such as ClO4- and NO3-. The capacitances, energies, and efficiencies are finally calculated. These results indicate clearly that electrolytes based on a mineral lithium salt under neutral pH condition and high salt concentration (up to 5 mol*L-1) have better electrochemical performances than organic ones, up to 1.4 V with good material stability and capacity retention. The relationship between transport properties, electrostatic and steric hindrance considerations of hydrated ions, and their electrochemical performances is discussed in order to understand further the lithium intercalation-deintercalation processes in the lamellar or tunnel structure of investigated MnO2

Charge Storage in Cation Incorporated α-MnO2

“…The interstitial and substitutional mechanisms we identify as leading to charge storage are supported by the large observed capacity of cryptomelane (KMn 8 O 16 ) 39,40 and the enhanced capacity of α-MnO 2 when pre-intercalated with large amounts of Na + . 36 In the limit of non-interacting defects and thin-film α-MnO 2 , the interstitial cation mechanism shown in Figure 4a will result in 1.5 electrons transferred per Mn-center (See SI Section H), with a small additional contribution from the substitutional cation mechanism, also shown in Figure 4a.…”

A review of electrolyte materials and compositions for electrochemical supercapacitors

“…Regarding the anions, Boisset et al 127 carried out in-depth research on the effect of anions on the ES performance in neutral aqueous electrolytes containing different lithium salts, in which Birnessite-type and Cryptomelane-type MnO 2 electrode materials were used. As shown in Fig.…”

Microwave-assisted rapid synthesis of birnessite-type MnO2 nanoparticles for high performance supercapacitor applications

“…Among these forms, d-MnO 2 (also known as birnessite-type MnO 2 ) has gained special attention as an electrode material for supercapacitors because of its thin sheetlike lamellar structure stabilized by alkali ions (Na + or K + ) and crystallized water, which is similar to that of hydrated ruthenium oxide [12]. Such structure can be beneficial to facilitate the cations' intercalation/deintercalation process [13,14] Several methods have been developed to prepare various birnessite-type MnO 2 nanostructures, including hydrothermal synthesis [15][16][17], microemulsion route [18], polyol-reflux [19], oxidation reaction procedure [13,14,20], and electrodeposition [21]. Compared with these synthetic methods, microwave-assisted route is a very fast, simple, and effective method for synthesis of MnO 2 materials [22,23].…”