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OVERVIEW

OVERVIEW. Rampi Ramprasad, Steve Boggs, Greg Sotzing (U. Connecticut) Curt Breneman (RPI) Mike Chung (Pennsylvania State U.) Sanat Kumar (Columbia U.) Bob Weiss (U. Akron). ENERGY STORAGE TECHNOLOGIES. Capacitors are the only option for rapid discharge (e.g., pulsed power) applications.

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OVERVIEW

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  1. OVERVIEW • Rampi Ramprasad, Steve Boggs, Greg Sotzing (U. Connecticut) • Curt Breneman (RPI) • Mike Chung (Pennsylvania State U.) • Sanat Kumar (Columbia U.) • Bob Weiss (U. Akron)

  2. ENERGY STORAGE TECHNOLOGIES • Capacitors are the only option for rapid discharge (e.g., pulsed power) applications

  3. AN EXAMPLE: PULSED POWER • Rapid release of electrical energy from an energy storage capacitor allows power to be amplified many-fold at modest average power consumption

  4. MATERIAL REQUIREMENTS • High dielectric constant & Low loss • High breakdown strength (intrinsic & extrinsic) • Large band gap, minimal defect states & high crystallinity • Easy processability • Good mechanical, thermal & thermodynamic stability

  5. THE CURRENT “STANDARD” • Biaxially-oriented polypropylene (BOPP) • Breakdown field of 700 V/micron (for 10 micron thick films) • Low dielectric constant of 2.2 • Polyvinyledene fluoride (PVDF) • High breakdown field and high dielectric constant (12) • But displays ferroelectric loss (due to coercivity)

  6. OUR STRATEGY • Design new classes of polymers by systematic and rational chemical modification of polymer backbones and functionalization, starting with polypropylene/polyethylene • Development of new synthesis strategies, and new methods to rapidly compute the dielectric constant, breakdown strength and morphology • Identify the fundamental materials factors that control dielectric response, breakdown and crystallinity • And to develop a framework to solve the “inverse” problem

  7. THE SYNERGY

  8. QUANTUM MECHANICAL COMPUTATIONS[DENSITY FUNCTIONAL THEORY (DFT)1] • Chun-Sheng Liu, Ghanshyam Pilania, Chenchen Wang • Rampi Ramprasad • University of Connecticut 1As implemented in the VASP and FHI-aims software packages

  9. CRITERIA FOR INITIAL SCREENING • High dielectric constant • Large band gap • Other imminent considerations: breakdown strength, defect states, crystallinity & stability

  10. OUR GOALS • Given a polymer, compute the dielectric constant1 and band gap2 rapidly and accurately from first principles • Screen a large number of known and unknown polymers CH2, GeF2, CH(OH), etc. 1Baroni et al, RMP 73, 515 (2001) 2Krukau et al, JCP 125, 224106 (2006)

  11. VAN DER WAALS INTERACTIONS • Polymer interchain interactions are controlled by vdW forces • Conventional DFT fails to capture vdW interactions • Lattice parameters, volumes and densities predicted incorrectly • Errors carry over to dielectric constants a b c

  12. VDW INTERACTIONS IN DFT • We consider 10 polymers for which reliable crystallographic information is available • Conventional DFT functionals (LDA, PBE) • vdW-augmented functionals (PBE-D2, PBE-TS)1,2 • Assessment of functionals based on geometry predictions Description? 1Tkatchenko & Scheffler, PRL 102, 073005 (2009) 2Grimme, J. Comp. Chem. 27, 1787 (2006)

  13. PREDICTIONS OF GEOMETRY a b c

  14. LDA PBE PBE-D2 PBE-TS THE ASSESSMENT Root-mean-square error

  15. INITIAL POLYMER SUB-FAMILY XY2 X = C, Si, Ge Y = H, F, Cl • We assume orthorhombic crystal structure, and include vdW interactions • -XY2- homopolymers (9 systems) • -[(CH2)2-(XY2)2]- heteropolymers (12 systems)

  16. DIELECTRIC CONSTANT ... along c-axis ... average • Small electronic (open symbols) but large ionic (filled symbols) -GeF2- -(CH2)2-(GeF2)2- Dielectric constant Dielectric constant -CH2- Band Gap (eV) [HSE Hybrid Functional] Band Gap (eV) [HSE Hybrid Functional]

  17. ORIGIN OF LARGE IONIC DIELECTRIC CONSTANT Ge-F Stretching F-Ge-F Wagging

  18. AN ALTERNATE FAST METHODESTIMATION OF CRYSTAL DIELECTRIC CONSTANT FROM SINGLE-CHAIN COMPUTATIONS • Amenable to “high-throughput” computations Volume defined through charge density cutoff Effective medium mixing rules

  19. VALIDATION OF SINGLE-CHAIN APPROACH ... along c-axis ... average • We are now ready to extensively explore the chemical space! Chain Approach Chain Approach Crystal Approach Crystal Approach

  20. HIGH-THROUGHPUT SCREENING“UNRESTRICTED SEARCH” - FIRST ROUND XY2 X = C, Si, Ge Y = H, F, Cl • Automated “high-throughput” search via chain approach • Repeat unit consists of 4 -XY2- building blocks • A total of 6561 possibilities (94), but reduced to 165

  21. THE RESULT Red: Electronic Blue: Total -GeF2-GeF2-GeF2-SiF2- • An insight: dielectric constant and band gap can be independently controlled Promising Candidates -GeF2- -GeF2-GeF2-GeF2-CH2- -(CH2)2-(GeF2)2- Dielectric constant -CH2- Band Gap (eV)

  22. HIGH-THROUGHPUT SCREENINGSECOND ROUND -CH2-, -CH(OH)-, -CH(CN)-, -CH(COOH)-, -CH(NH2), -CH(SCN)-, -CO-, -NH-, etc. • Automated “high-throughput” search via chain approach • Chosen building blocks will allow for exploiting the dipole orientational contributions

  23. A PREVIEW Blue: First Round Gray: “Second” Round • Note: dielectric constant and band gap can be independently controlled -GeF2-GeF2-GeF2-CH2- -(CH2)2-(GeF2)2- Dielectric constant a-[-CH2-CH(OH)-] -CH2- Band Gap (eV)

  24. Open Issues Morphology? (Kumar) Breakdown strength? (Boggs) Chemical defects? (Ramprasad) “Inverse” design? (Breneman) SUMMARY

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