Bivalence Mn 5 O 8 with Hydroxylated Interphase for High-Voltage Aqueous Sodium-Ion Storage

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1 NY-BEST Annual Energy Storage Technology Conference 2017 Bivalence Mn 5 O 8 with Hydroxylated Interphase for High-Voltage Aqueous Sodium-Ion Storage Speaker: Xiaoqiang Shan Advisor: Prof. Xiaowei Teng 2017/10/ University of New Hampshire. All rights reserved.

2 Electrochemical Energy Storage Ragone Plot Advantages: High power Long cycle life Low cost Environment-friendly Kotz, R. et al., Electrochimica Acta, 45, , (2000)

3 Aqueous Na-ion Storage Motivation Kim, H. et al, Chem. Rev., 114, (2014) Limitation: low energy density (E = 1 Τ2 CV 2 ) with a narrow thermodynamically potential window ~ 1.23 V Goal: Improve potential window with kinetically inhibited hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) Categories Li Na Cation radii 0.7 Å 1.0 Å Molecular weight ~ 7 g/mol ~ 23 g/mol E 0 (vs. Li/Li + ) 0 V V Cost - carbonates $5000/ton $150/ton * Capacity (mah/g) metal 3829 mah/g 1165 mah/g

4 Mn 5 O 8 Material Synthesis Approach 270 C in air (i) Oxidation of Mn 3 O 4 with suitable size (oxygen and nitrogen mixture, 250 C to 550 C) (i) Decomposition of -MnOOH (air) (ii) Decomposition of -MnOOH (low oxygen pressure, 400 C) Oswald, H. R. et al, Nature, 207, 72 (1965) Brunner, P., Diss. Univ. Bern, (1962) Feitknecht, W., Pure and App. Chem., 9, 423 (1964) Property of our Mn 5 O 8 : Bivalent manganese oxide (Mn 2+ 2Mn 4+ 3O 8 ) Layered structure with twodimensional [Mn 4+ 3O 8 ] octahedral sheets and Mn 2+ cationic layer Abundant defects within inter/intra-layer

5 Mn 5 O 8 Nanoparticles Pair distribution analysis of X-ray and neutron total scattering confirms Mn 5 O 8 nanoparticles with trace amount Mn 3 O 4 High purity Mn 5 O 8 obtained by annealing Mn 3 O 4 nanoparticles with longer time and slightly higher temperature (300 C, 12 hours) Highly crystalline monoclinic structure with an average particle size ~ 19 nm Shan, X. et al, Nat. Commun, 7, (2016) Shan, X. et al, Front. Energy, (2017)

6 Wide Potential Window in Half-Cell A wide potential window (2.5 V) in aqueous half-cell ( ~ 0.6 V overpotential towards HER and/or OER) i = i 1 + i 2 = k 1 v + k 2 v 1/2 (i 1 : surface-controlled capacitive current; i 2 : diffusion-limited redox current) Much larger capacitive contribution of Mn 5 O 8 nanoparticle for the high-rate capability compared with Mn 5 O 8 and Mn 3 O 4 bulk as well as Mn 3 O 4 nanoparticle (18 nm)

7 Hydroxylated Interphase verified by soft-xas Hydroxylated species (water features at 535 ev/575 ev) on surface of cycled Mn 5 O 8, an ice-like well-ordered hydroxylated interphase A decreased intensity ratio of Mn 2+ to Mn 4+ for the oxidized Mn 5 O 8 (0.8 V) compared to the reduced one (-1.7 V) indicating the oxidation of Mn 2+ to Mn 4+

8 DFT Calculations High activation energy of water dissociation on hydroxylated Mn 5 O 8 (the only endothermic reaction step at 1.23 V), limiting step of HER and/or OER The limiting potentials (all reaction steps are exothermic) of water splitting for hydroxylated Mn 5 O 8, Mn 5 O 8 and Mn 3 O 4 determined to be 1.86 V, 1.64 V and 1.68 V

9 Electrochemical Full-Cell Measurements Pseudocapacitor type electrode Energy density (23 Wh kg -1 ) at 20 A g -1 with nearly 100 % coulombic efficiency and 85 % energy efficiency Energy and power densities up to 40 Wh kg -1 and W kg -1 (gravimetric)

10 Conclusions Bivalent Mn 5 O 8 layered materials with an ice-like well-ordered hydroxylated interphase exhibits a high resistance to gas evolution reactions, achieving a stable potential window of 3.0 V, and therefore a high Na-ion storage capacity in the aqueous electrolyte. The high capacity hydroxylated Mn 5 O 8 material with better safety and low cost offers an alternative energy storage approach to non-aqueous Li-ion batteries.

11 Acknowledgements Chemical Engineering Department of University of New Hampshire Advisor: Prof. Xiaowei Teng Daniel S. Charles (PDF analysis) Prof. Guofeng Wang & Yinkai Lei (DFT calculations, University of Pittsburgh), Dr. Wanli Yang & Ruimin Qiao (soft X-ray experiment, Lawrence Berkeley National Laboratory), Dr. Mikhail Feygenson (neutron experiment, Oak Ridge National Laboratory), Dr. Dong Su (TEM, Brookhaven National Laboratory) Funding: Department of Energy