Naphthalene Monoimides with Peri-Annulated Disulfide Bridge-Synthesis and Electrochemical Redox Activity.

Nowadays, organosulfur compounds provide new options in the development of full organic ion batteries. However, many drawbacks (such as kinetics limitations during the reversible oxidation of disulfides with cleavage of S-S bond, as well as solubility in non-aqueous electrolytes) make their commercialization difficult. Herein, a new concept for the design of organosulfur compounds with regulated redox properties and limited solubility is proposed. As a proof-of-concept, we designed peri-disulfo-substituted 1,8-naphthalimide derivatives, in which the alkyl chain length and halogen substituents (Cl or Br) at positions 3 and 6 are varied. The compounds were synthesized by an originally developed procedure starting from tetrahalonaphthalic anhydride via nucleophilic substitution at both peri-positions in the respective imide. Using ionic liquid electrolyte, it was found that the new peri-dithiolo-1,8-naphthalimides can participate in n- and p-type redox reactions at about 2.0 V and above 4.0 V vs. Li/Li+, respectively. The redox potentials are sensitive mainly to whether Cl or Br substituents are available in the molecule architecture, while the alkyl chain length determines the kinetics of the redox reactions. Among all compounds, the chloro-substituted compound with the shorter alkyl chain displays the best kinetics for both low- and high-voltage redox reactions.

Lithium Manganese Sulfates as a New Class of Supercapattery Materials at Elevated Temperatures.

To make supercapattery devices feasible, there is an urgent need to find electrode materials that exhibit a hybrid mechanism of energy storage. Herein, we provide a first report on the capability of lithium manganese sulfates to be used as supercapattery materials at elevated temperatures. Two compositions are studied: monoclinic Li2Mn(SO4)2 and orthorhombic Li2Mn2(SO4)3, which are prepared by a freeze-drying method followed by heat treatment at 500 °C. The electrochemical performance of sulfate electrodes is evaluated in lithium-ion cells using two types of electrolytes: conventional carbonate-based electrolytes and ionic liquid IL ones. The electrochemical measurements are carried out in the temperature range of 20-60 °C. The stability of sulfate electrodes after cycling is monitored by in-situ Raman spectroscopy and ex-situ XRD and TEM analysis. It is found that sulfate salts store Li+ by a hybrid mechanism that depends on the kind of electrolyte used and the recording temperature. Li2Mn(SO4)2 outperforms Li2Mn2(SO4)3 and displays excellent electrochemical properties at elevated temperatures: at 60 °C, the energy density reaches 280 Wh/kg at a power density of 11,000 W/kg. During cell cycling, there is a transformation of the Li-rich salt, Li2Mn(SO4)2, into a defective Li-poor one, Li2Mn2(SO4)3, which appears to be responsible for the improved storage properties. The data reveals that Li2Mn(SO4)2 is a prospective candidate for supercapacitor electrode materials at elevated temperatures.

Dual-Ion Intercalation Chemistry Enabling Hybrid Metal-Ion Batteries.

To outline the role of dual-ion intercalation chemistry to reach sustainable energy storage, the present Review aimed to compare two types of batteries: widely accepted dual-ion batteries based on cationic and anionic co-intercalation versus newly emerged hybrid metal-ion batteries using the co-intercalation of cations only. Among different charge carrier cations, the focus was on the materials able to co-intercalate monovalent ions (such Li+ and Na+ , Li+ and K+ , Na+ and K+ , etc.) or couples of mono- and multivalent ions (Li+ and Mg2+ , Na+ and Mg2+ , Na+ and Zn2+ , H+ and Zn2+ , etc.). Furthermore, the Review was directed on co-intercalation materials composed of environmentally benign and low-cost transition metals (e. g., Mn, Fe, etc.). The effect of the electrolyte on the co-intercalation properties was also discussed. The summarized knowledge on dual-ion energy storage could stimulate further research so that the hybrid metal-ion batteries become feasible in near future.

Thermodynamics of the double sulfates Na2M2+(SO4)2·nH2O (M = Mg, Mn, Co, Ni, Cu, Zn, n = 2 or 4) of the blödite-kröhnkite family.

The double sulfates with the general formula Na2M2+(SO4)2·nH2O (M = Mg, Mn, Co, Ni, Cu, Zn, n = 2 or 4) are being considered as materials for electrodes in sodium-based batteries or as precursors for such materials. These sulfates belong structurally to the blödite (n = 4) and kröhnkite (n = 2) family and the M cations considered in this work were Mg, Mn, Co, Ni, Cu, Zn. Using a combination of calorimetric methods, we have measured enthalpies of formation and entropies of these phases, calculated their Gibbs free energies (Δf G°) of formation and evaluated their stability with respect to Na2SO4, simple sulfates MSO4·xH2O, and liquid water, if appropriate. The Δf G° values (all data in kJ mol-1) are: Na2Ni(SO4)2·4H2O: -3032.4 ± 1.9, Na2Mg(SO4)2·4H2O: -3432.3 ± 1.7, Na2Co(SO4)2·4H2O: -3034.4 ± 1.9, Na2Zn(SO4)2·4H2O: -3132.6 ± 1.9, Na2Mn(SO4)2·2H2O: -2727.3 ± 1.8. The data allow the stability of these phases to be assessed with respect to Na2SO4, MSO4·mH2O and H2O(l). Na2Ni(SO4)2·4H2O is stable with respect to Na2SO4, NiSO4 and H2O(l) by a significant amount of ≈50 kJ mol-1 whereas Na2Mn(SO4)2·2H2O is stable with respect to Na2SO4, MnSO4 and H2O(l) only by ≈25 kJ mol-1. The values for the other blödite-kröhnkite phases lie in between. When considering the stability with respect to higher hydrates, the stability margin decreases; for example, Na2Ni(SO4)2·4H2O is still stable with respect to Na2SO4, NiSO4·4H2O and H2O(l), but only by ≈20 kJ mol-1. Among the phases studied and chemical reactions considered, the Na-Ni phase is the most stable one, and the Na-Mn, Na-Co, and Na-Cu phases show lower stability.

Selective sodium intercalation into sodium nickel-manganese sulfate for dual Na-Li-ion batteries.

Double sodium transition metal sulfates combine in themselves unique intercalation properties with eco-compatible compositions - a specific feature that makes them attractive electrode materials for lithium and sodium ion batteries. Herein, we examine the intercalation properties of novel double sodium nickel-manganese sulfate, Na2Ni1/2Mn1/2(SO4)2, having a large monoclinic unit cell, through electrochemical and ex situ diffraction and spectroscopic methods. The sulfate salt Na2Ni1/2Mn1/2(SO4)2 is prepared by thermal dehydration of the corresponding hydrate salt Na2Ni1/2Mn1/2(SO4)2·4H2O having a blödite structure. The intercalation reactions on Na2Ni1-xMnx(SO4)2 are studied in two model cells: half-ion cell versus Li metal anode and full-ion cell versus Li4Ti5O12 anode by using lithium (LiPF6 dissolved in EC/DMC) and sodium electrolytes (NaPF6 dissolved in EC:DEC). Based on ex situ XRD and TEM analysis, it is found that sodium intercalation into Na2Ni1/2Mn1/2(SO4)2 takes place via phase separation into the Ni-rich monoclinic phase and Mn-rich alluaudite phase. The redox reactions involving participation of manganese and titanium ions are monitored by ex situ EPR spectroscopy. It has been demonstrated that manganese ions from the sulfate salt are participating in the electrochemical reaction, while the nickel ions remain intact. As a result, a reversible capacity of about 65 mA h g-1 is reached. The selective intercalation properties determine sodium nickel-manganese sulfate as a new electrode material for hybrid lithium-sodium ion batteries that is thought to combine the advantages of individual lithium and sodium batteries.