Effect of Crystallinity on Li Adsorption in. Polyethylene Oxide

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1 Supporting information for Effect of Crystallinity on Li Adsorption in Polyethylene Oxide Deya Das, Anand Chandrasekaran, Shruti Venkatram, and Rampi Ramprasad School of Materials Science and Engineering, Georgia Institute of Technology, 771 Ferst Drive NW, Atlanta, GA 30332, USA To whom correspondence should be addressed 1

2 Structural Details of Crystalline PEO In the case of soft materials such as polymers, where the inter chain interaction are governed by van der Waals (vdw) force, the choice of vdw functional while performing the calculations plays an important role. The crystalline structure was optimized using different vdw functionals and vdw-df2 functional was found to give structural parameters close to the experimental data 1 as listed in Table S1. Although, the values obtained in the absence of any vdw functional is the closest to experimentally obtained parameters, it fails to capture the actual physics in the system. Table 1: Comparison of structural parameters of crystalline PEO using different van der Waals functional with experimental data Method a (Å) b (Å) c (Å) α ( o ) β ( o ) γ ( o ) Exp PBE (no vdw) DFT-D DFT-D vdw-df Generation of Amorphous PEO Structure Three finite chains of PEO having hydrogenated both sides and containing 10 units of building block (-CH 2 -CH 2 -O) in each chain, were considered as the starting configuration. The flow chart of amorphous PEO generation is shown in Fig.S1 (a). Using classical molecular dynamics as implemented in LAMMPS simulation package, 2 we performed melt and quench method to generate the amorphous PEO and finally the structure was optimized using DFT as implemented in VASP. 3,4 The melting point of crystalline PEO is 338 K ( 5 Two different temperatures, well above the melting point, 500 and 600 K were chosen as initial temperature and three different cooling rates; 0.3, 1.67 and 2 K/s were investigated. The obtained struc- 2

3 tures were found to be similar and the structure obtained from the simulations with 600 K and 0.3 K/s cooling rate was considered. The density of the generated amorphous PEO is 1.08 gm/cm 3, close to experimental density of gm/cm 3. 6,7 The amorphousness of the structure was validated by comparing radial distribution function with crystalline case as shown in Fig. S1 (b). There is no long range order in amorphous PEO unlike crystalline case. Figure S1: (a) Flow chart of amorphous PEO generation and (b) radial distribution function of crystalline and amorphous PEO structure 3

4 Li-O Radial Distribution Function for All Li Positions in Crystalline and Amorphous PEO RDF Crystalline Li atom Li + ion RDF Amorphous Li atom Li + ion Distance from Li (Å) Figure S2: Li-O radial distribution function of all 27 and 20 positions in crystalline and amorphous PEO respectively. Li atom and Li + ion are denoted by solid and dashed red lines, respectively. In the same plot, the number of O atoms from Li atom (Li + ion) are plotted by solid (open) bars; blue and green colors denote crystalline and amorphous PEO, respectively. The black dashed lines are at 2.7 Å. 4

5 Density of States of Crystalline and Amorphous PEO upon Li/Li + Ion Adsorption Figure S3: Density of states before and after adsorption of neutral Li and Li + ion in crystalline and amorphous PEO. Fermi level is denoted by red dashed line. In the presence of neutral Li, defect states appeared near both valence band maximum (VBM) and conduction band minimum (CBM) are marked by red circles. On removal of this electron, i.e., in the case of the Li + case, the defect states close to CBM become empty as marked by red circles and the Fermi level shifts back to the same position as in Li-free crystalline/amorphous PEO. References (1) Takahashi, Y.; Tadokoro, H. Structural Studies of Polyethers, (-(CH2)m-O-)n. X. Crystal Structure of Poly(ethylene oxide). Macromolecules 1973, 6, (2) Plimpton, S. Fast Parallel Algorithms for Short-Range Molecular Dynamics. J. Comput. Phys 1995, 117,

6 (3) Kresse, G.; Hafner, J. Ab Initio Molecular Dynamics for Liquid Metals. Phys. Rev. B 1993, 47, (4) Kresse, G.; Joubert, D. From Ultrasoft Pseudopotentials to the Projector Augmented-wave Method. Phys. Rev. B 1999, 59, (5) Money, B. K.; Swenson, J. Dynamics of Poly(ethylene oxide) around Its Melting Temperature. Macromolecules 2013, 46, (6) Wunderlich, B. Crystal Structure, Morphology and Defects; Academic Press, New York, 1973; Vol. 1; pp (7) Lu, S.; Lei, Z.; Lixia, R.; S., H. B. Supporting information of Tailor-Made Onionlike Stereocomplex Crystals in Incompatible, Enantiomeric, Polylactide-Containing Block Copolymer Blends. Angew. Chem. Int. 2006, 45,