Materials Design by Quantum-Chemical and Other

arXiv:1312.0699v2 [cond-mat.mtrl-sci] 15 Jan 2014 est swl spoomsiemtraswt o workfun low with L materials for photoemissive materials as well designer as of density examples new and Recent terials. O:10.1039/b000000x DOI: aeil einb unu-hmcladohrTheoreti- K other and a Storage Materials Energy Quantum-Chemical toemissive to Applications by Means: cal/Computational Design Materials INTRODUCTION 1 oe na ra spsil ag fptnilmodification potential of range possible as broad as an cover produ energy clean storage, etc. fie tion, energy emerging as such ma important applications, for control of race potentially the can in that competition terials increased the to attributed c be that practice”) to reduction (“actual witho testing an practice”) perimental ma is to theoretical There reduction on (“conceptual based design granted. terials solely are patents patents and of million annually, number a US increasing of the quarter in a a filed half about than are More applications produce patent year. Apple conversion. each million and and applications Bosch, patent storage IBM, of energy thousands as of such fields companies, the Major de in and efforts screening con appliances sign materials electrical computational e of For systematic supplier well. ducts major as a industry private Bosch, the Sim ample, in seen efforts. be design can electrolyte initiatives and Center materials DOE Joint of electrode program as the in Hub”) within (“Battery underway Research example Storage also Energy for of well, are and as efforts NSF programs as design other such materials agencies, Major various DOE. 1 through approximately dollars with million materials designer e and test design perimentally explore, Materials computationally the to rati funds Initiative government in Genome US funds The substantial gov- design. invest materials by industry nal funded the by projects or Major ernments r of materials. of development designed terms the in tionally in harvested work increasingly hard are of rea methodologies decades such within now of is fruits goal the this and processors, comput- faster parallel ever with using combined ers size, system the to compared rxmto n(er iersaigcmuainleffort ap computational of scaling levels linear various (near) at in proximation equation Schrödinger of the grails algorith solve efficient holy of the that advent the of With one physics. and been chemistry has design materials Rational Introduction 1 computation theoretical other and quantum-chemical how of h rsn ae icse oercn eeomnsi the in developments recent some discusses paper present The rl N aroly ´ 2–4 aet aeawy enfruae ota they that so formulated been always have Patents . emeth ´ ∗ a nalso an tex- ut 1 ilar lds ms 00 ch o- x- x- as a- c- tosadipoe rgtesaedsusda illustrati as discussed are brightness improved and ctions lmascnb sdfrrtoa aeil design. materials rational for used be can means al s ------o n iartp atre ihhg aaiyadenerg and capacity high with batteries type Li-air and i-ion edo ainldsg o nrysoaeadphotoemissiv and storage energy for design rational of field 1 ons nemlclrinteractions underlying intermolecular meta pounds, transition the in gaps and band effects, correlation such codes electron phenomena, certain these for limitations While sever have methods approach. wit DFT functionals correlation the and el exchange various core and model trons to pseudoptentials effective wavefunctions, Espresso h xlrto fmtras uhcdsicueSIESTA include codes in Such used also materials. are of ones based exploration grid the adaptive or wavelet as codes well based Gauss as representation solids. 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PQS , 9 ehdta undotpriual rcia for practical particularly out turned that method 12 FreeON , 14 . 13 onm e.Sm fthese of Some few. a name to , 8 xie tt properties, state excited , 5 . dPho- nd 6 eexamples ve rQuantum or 15 ecodes re y/power . tentials com- l epo- re ma- e evel tron ges, eful han hin ec- ian 10 as n- e , , 2.1 Li-ion batteries 2 RESULTS AND DISCUSSION developments in the field of materials design for Li-ion and develop materials with both high power and energy densities, Li-air batteries first, then describes approaches about the de- the present author has recently proposed 20 the use of function- velopment of improved photoemissive materials. alized hexagonal boron nitride (h-BN) monolayers as intercalation materials. In this case the intercalation would happen into the surface of a 2D material directly from the electrolyte, 2 Results and Discussion avoiding the slow diffusion inside the crystallites. The charging process would be similarly fast, allowing for large current 2.1 Li-ion batteries densities. Here, two materials based on BN are briefly dis- Most Li-ion batteries operate through the intercalation and cussed. The first one is a 3D material, Li3BN2, the second deintercalation of Li-ions in the positive electrode (cathode of one is a 2D one, BNCN, a cyano (-CN) group functionalized the discharge process) electroactive materials. There is a great h-BN. effort to optimize the properties of the electroactive crystals. The optimization parameters include the gravimetric and vol- 2.1.1 Li3BN2It has been known for decades that the re- umetric energy densities of the electroactive materials, their action of molten Li3N with h-BN can produce various phases 21 capacities (concentration of Li that can intercalate), the power of the Li3BN2 crystalline material . α-Li3BN2 has a layered densities (how fast the charging and discharging may occur), structure as shown in Fig. 1, with two Li ions being mobile the voltage associated with the corresponding electrochemi- per formula unit, while the third Li is part of a 1D rod-like cal reaction, the electrolytes that have to sustain the voltages polymer, with repeating -Li-N-B-N- sequence. The polymeric and currents that occur and the economy of the materials in- chains and the mobile Li ions are placed in separate layers in volved, to name a few optimization parameters. Most design the α-Li3BN2 phase (space group P42/mnm). The cell reac- 20 efforts focus on layered crystalline cathode materials, such as tion proposed is 2Li + LiBN2 → Li3BN2 on discharge. The 16,17 n− spinels or polyanionic compounds . In order to computa- formal charge of the BN2 linear anion changes from n=-1 tionally predict the voltage associated with an electrochemi- to n=-3 on discharge. Since no heavy transition metal atoms cal cell reaction, one has to calculate the Gibbs free energy are involved, one may use the PBEsol functional 22,23 to ob- change associated with the reaction, express it in terms of eV- tain realistic optimum crystal structures and reaction energies. s and divide by the number of electrons transferred during the The Quantum Espresso 7 software has been used, with ultra- reaction per molecule of product. The reaction energy is al- soft pseudopotentials and 50 rydberg wavefunction cutoff, us- most always approximated as the difference of the electronic ing a 6x6x6 k-space grid. The residual forces were smaller energies of the products and reactants which is usually a good than 1.d-4 Ry/bohr at the optimum structures. Experimental approximationwhen no gas molecules are involved that would lattice parameters a=b and c have been reproduced with an ac- cause large entropy changes 17–19. However, the accurate cal- curacy of smaller than 1% and 2.5% errors, respectively. Note culation of reaction energies and other properties of solids is that the c-direction is perpendicular to the layers mentioned. often problematic, especially in case of transition metal com- In the Li-deintercalated structure, the lattice parameters a=b pounds. It turns out, that DFT(GGA)+U methods are capa- and c become 1.2 and 3.3 % shorter, which indicates a cell ble to provide reaction energies and voltages that compare volume shrinking of 5.6 %, or 2.8% per two-electron transfer. well with experiments for this class of materials 17–19. Perhaps Note that such a relatively small cell volume change counts the best intercalation material designed for cathode applica- as acceptable for Li-ion battery electrode applications 17. The tions so far, is Li3Cr(BO3)(PO4) a polyanionic material with cell reaction energy is calculated to be ∆E = -7.23 eV, indicat- 17 + sidorenkite (Na3MnPO4CO3) structure . This material has ing a cell voltage of U=3.61 V (assuming an Li/Li anode). not been synthesized yet. Lithium intercalation in the deinter- The gravimetric and volumetric energy densities are 3247 calated Cr(BO3)(PO4) structure occurs at calculated voltages Wh/kg and 5919 Wh/L, respectively. These values are sig- + 17 of 4.2-5.1 V, relative to Li/Li , resulting in theoretical energy nificantly larger than those obtained for Li3Cr(BO3)(PO4) . densities of 1705 Wh/kg and 4814 Wh/L with capacities of Especially the gravimetric energy density is almost twice as 17 354 mAh/g . For comparison, LiCoO2 cathode materials in large for Li3BN2 as for Li3Cr(BO3)(PO4). Li3BN2 appears current Li-ion batteries have a theoretical energy density of to be greatly superior to Li3Cr(BO3)(PO4) also in terms of 568 Wh/kg (2868 Wh/L) and charge capacity of 273 mAh/g gravimetric and volumetric capacity densities with the respec- − (1379 mhA/cm 3) 4. tive values of 899 mAh/g and 1638 mAh/cm3. It is surpris- While the energy density of Li3Cr(BO3)(PO4) and related ing that Li3BN2 has not been tested as cathode electroac- materials is very attractive, their power density (the rate of tive material yet. The reason is probably that only the alpha charging and discharging) remains low, as the process of inter- phase can be expected to preserve its layered structure after calation/deintercalation is relatively slow, rendering the charg- the deintercalation of mobile Li-ions. The monoclinic phase ing of Li-ion batteries typically an overnight long process. To has been considered recently for application as part of a con-

2 2 RESULTS AND DISCUSSION 2.2 Li-air batteries

values 363 mAh/g and 1236 mAh/cm3. These values indicate great potential for example for use in portable electronics devices. BNCN and analogous functionalized h-BN compunds can serve as universal intercalation electrode materials capable to intercalate alkali, alkaline earth, Al and other cations (un- less conversion reactions happen) thus allowing for batteries based on the transfer of cations other than Li+. Note that in principle similar functionalization of graphene can also be envisioned, however the patterned and polarized h-BN surface is a much better candidate for electrophile and nucleophile attack by functionalization agents, such as molten salts. In case of graphene, all atoms are equivalent for functionalization, while for h-BN only half of the atoms can be subject of, say, nucleophile attack, leaving the other half un- functionalized providing space for intercalation of cations and free N atoms in the BN surface to contribute to the complex- ation and binding of the intercalating ions as well as to the storage of the extra negative charge per formula unit due to discharge. Therefore, h-BN appears to be a better candidate

Fig. 1 Perspective view of the layered structure of α-Li3BN2 in a to build 2D intercalation structures than graphene. Doped 3x3x3 supercell. Color code: Li - violet, B - magenta, N - blue. graphene structures may have similar properties to h-BN for covalent functionalization. Functional groups should be selected based on whether they make h-BN a strong electron 24 version based anode material . The high melting point of acceptor after the functionalization, when positive electrode α o 21 -Li3BN2, about 900 C is also indicative of the stability materials are designed. For negative electrode materials, the of the polymeric chains with -Li-N-B-N- repeating units, as functional group should be selected such that the resulting the Li ions that are not incorporated in the chains are known layer will be a good electron donor. These considerations are to be very mobile as excellent Li-ion conductivity values in- analogous to the design of charge transfer salts 25. 21 dicate . Therefore, the present calculations also predict the While transition metal compounds currently dominate Li- existence of stable phases with the stoichiometry of LixBN2 ion battery electroactive materials, there is a lot of potential in with 1 < x < 3. Furthermore, potentially also the beta and the conjugated π-electron systems and their functionalized deriva- α monoclinic phase would be transformed to -Li3BN2 after re- tives to be utilized as electroactive materials. Concepts of peated charge/discharge cycles, as the alpha phase appears as these systems, such as the principles of charge transfer com- the energetically most favorable packing of the polymeric -Li- pounds, have practically been completely ignored in energy N-B-N- rods. storage development so far. As a direct continuation of the 2.1.2 BNCNNaThe reaction of molten sodium cyanide present work, a great variety of functionalization of h-BN will with h-BN is expected to lead to the cyano-functionalization be explored to ﬁnd the best novel anode and cathode mate- of B sites on both sides of the h-BN monolayers which then rials of this class of compounds. Band structures, conduc- intercalate Na+ ions, as depicted in Fig. 2. This structure tivities, charge distributions and structural changes upon in- is expected to lead to fast charging and discharging due to tercalation/deintercalation will be analyzed to understand the the sterically unhindered access of Na+ ions to the interca- mechanism of charge storage in these materials. The experi- lation sites. Using the above methodology and a ≈ 30 A˚ vac- mental testing of some of these materials is already underway uum layer to separate layers of BNCNNa, the electrochemical through collaborative work at Illinois Institute of Technology properties of BNCNNa have been computed. Both interca- and elsewhere. lated and deintercalated structures are stable and preserve the covalent cyano functionalized B centers. With Li atoms in- 2.2 Li-air batteries stead of Na, the covalent functionalization would break up and LiCN and h-BN would form. The voltage of the Na + Li-air batteries are considered as the ultimate large energy BNCN → BNCNNa electrochemical cell is calculated to be density batteries that would enable long range all electric ve- U = 2.87 V, associated with a cell reaction energy of 2.87 eV hicles. They produce electrical energy through the reaction + (assuming an Na/Na anode). The gravimetric and volumetric of metallic Li with O2 taken from the air, whereby the dis- energy densities are 1042 Wh/kg and 3547 Wh/L, the capacity charge product must be Li2O2 in order the battery be recharge-

3 REFERENCES

number of MgO monolayers, we were the first to propose using this variation to optimize the brightness (angular distribution) of emitted electrons through overlayer deposition. Recent experimental results 29 have confirmed our predictions and point out the drastic change in the angular distribution of emitted electrons due to MgO overlayers on Ag(001). Ultra- thin oxide monolayers over metal surfaces change the electro- static boundary conditions on the surface and thus they may significantly decrease or increase the workfunctions and the shape and occupation of surface bands which leads to drastic changes in the properties of the emitted electrons 26. In the Fig. 2 Perspective view of the cyano functionalized h-BN second example, we have pointed out that the workfunction monolayer with intercalated Na ions in a 3x3x1 supercell. Color of the seasoned, high quantum efficiency Cs Te photoemis- code: Na - violet, B - magenta, N - blue, C - gray. 2 sive material can be lowered from ≈ 3 eV to about 2.4 eV by acetylation resulting in Cs2TeC2 while its quantum efficiency is preserved 27. Analogous compounds Cs PdC and able. The fact that Li2O2 is an aggressive oxidant and may 2 2 explosively oxidize the carbon electrode in which it forms and Cs2PtC2 exist and we have managed to synthesize Li2TeC2 (x-ray diffraction confirms theoretically predicted structure) 30 deposits makes Li-O2/peroxide batteries unsafe. A thorough analysis 15 by the present author about the thermochemistry as the first member of ternary acetylides with Te. This design was motivated by the goal of turning Cs Te into an eas- and kinetics of Li-oxalate, Li2C2O4, with the availability of 2 ier to excite π-electron system. Our current research direc- catalysts for selective and energy-efficient CO2/oxalate con- tions in the photocathode field focus on the theoretical screen- versions indicates that instead of O2, CO2 should be taken from air (or from a tank) to construct a high energy and power ing of various inorganic and organic overlayers on metals and density battery that can be safely used and is of environmen- semiconductors to lower workfunctions, optimize brightness, tally benign and economic materials. The details of the de- quantum yield and life time of such photocathodes in the of- sign based on existing experimental data can be found in Ref. ten harsh temperature, imperfect vacuum and electromagnetic field environments they are used. 15. A key component of the energy-efficiency of CO2/oxalate cathodes is the catalyst that reduces the overpotential of CO2 reduction to nearly zero. While such catalysts are known, for 3 Conclusions example copper complexes or oxygen molecule in selected 15 ionic liquid electrolytes , the applicability of these catalysts The present paper discusses several examples of materials de- may vary in the various implementations, therefore there is a sign using quantum chemical and other theoretical / computa- need for the development of additional robust catalysts to op- tional methods to develop improved Li-ion and Li-air batteries timize the performance of metal-CO2/oxalate batteries. and improved photoemissive materials. The experimental testing of some of these designs is underway. 2.3 Photoemissive materials Another example of materials design discussed here concerns 4 Acknowledgements photoemissive materials. Improved photocathodes are needed for future electron and light sources, such as x-ray free elec- Discussions with Drs. L. Shaw (IIT), K. C. Harkay and G. tron lasers, energy recovery linacs and dynamic and ultrafast Srajer (Argonne) are gratefully acknowledged. The Li-air bat- transmission electron microscopes. The improvements must tery and the photocathode research has been supported by the concern the brightness, the quantum yield, the workfunction U.S. DOE Office of Science, under contract No. DE-AC02- and the chemical inertness and lifetime of the photocathodes. 06CH11357 and NSF (No. PHY-0969989). Some of our recent works provide examples of related designs 26–28. In the first example, we have shown 26 using band References structure calculations that the angular distribution of emitted 1 Linear-Scaling Techniques in Computational Chemistry and Physics, electrons can drastically change when depositing an ultrathin ed. R. Zalesny, M. G. Papadopoulos, P. G. Mezey and J. Leszczynski, (2-4 monolayers) MgO layer on the Ag(001) crystal surface. Springer, Berlin, Heidelberg, New York, 1st edn, 2011, vol. 13. While a lot of electronic structure studies have been carried out on the MgO:Ag(001) system to explain the experimen- a Address: Physics Department, Illinois Institute of Technology, Chicago, Illi- tally observed variation of its catalytic activity with varying nois 60616, USA, [email protected]

4 REFERENCES REFERENCES

2 P. Albertus et al., High Specific Energy Li/O2-CO2 Battery; assignee: Bosch LLC; US Patent Application 12/907,205, 2010. 3 S. C. Jones et al., Polymer Materials As Binder for a CFx Cathode; assignee: Contour Energy Systems Inc.; US Patent Application 13/010,431, 2011. 4 K. Nemeth, M. van Veenendaal and G. Srajer, Electrochemical energy storage device based on carbon dioxide as electroactive species, assignee: US. Dept. of Energy, Patent (granted), US8389178, 2013. 5 J. M. Pearce, Nature, 2012, 491, 519–521. 6 J. Hafner, J Comput Chem 29: 20442078, 2008, 2008, 29, 20442078. 7 P. Gianozzi et.al, J. Phys.: Condens. Matter, 2009, 21, 395502. 8 J. Paier et al., J. Chem. Phys., 2006, 124, 154709. 9 V. I. Anisimov et al., Phys. Rev. B, 1991, 44, 943. 10 Soler, Jos M. et al., J. Phys. Cond. Mat., 2002, 14, 2745. 11 M. J. Frisch et al., GAUSSIAN09, 2013, Gaussian, Inc., Wallingford CT, http://www.gaussian.com. 12 J. Baker et al., WIREs Comput. Mol. Sci., 2012, 2, 63. 13 N. Bock, M. Challacombe, C. K. Gan, G. Henkelman, K. Nemeth, A. M. N. Niklasson, A. Odell, E. Schwegler, C. J. Tymczak and V. Weber, FREEON, 2013, Los Alamos National Laboratory (LA-CC 01-2; LA-CC- 04-086), Copyright University of California., http://www.freeon.org/. 14 S. Suhai, Phys. Rev. B, 1983, 27, 3506. 15 K. Németh and G. Srajer, RSC Advances, 2014, 4, 1879. 16 B. C. Melot and J.-M. Tarascon, Acc. Chem. Res., 2013, 46, 1226–1238. 17 G. Hautier et al., J. Mater. Chem., 2011, 21, 1714717153. 18 F. Zhou et al., Electrochem. Comm., 2004, 6, 1144–1148. 19 A. Jain et al., Phys. Rev. B, 2011, 84, 045115. 20 K. Nemeth, Functionalized Boron Nitride Materials as Electroactive Species in Electrochemical Energy Storage Devices, patent pending, assignee: Nemeth’s Materials Design LLC, 2013. 21 H. Yamane et al., J. Solid State Chem., 1987, 71, 1–11. 22 J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett., 1996, 77, 3865. 23 J. P. Perdew et al., Phys. Rev. Lett., 2008, 100, 136406. 24 T. H. Mason et al., J. Phys. Chem. C, 2011, 115, 16681–16688. 25 J. Huang et al., Phys. Chem. Chem. Phys., 2008, 10, 2625. 26 K. Németh, K.C. Harkay et.al, Phys. Rev. Lett., 2010, 104, 046801. 27 J. Z. Terdik and K. Németh et al., Phys. Rev. B, 2012, 86, 035142. 28 A. Ruth and K. Németh et al., J. Appl. Phys., 2013, 113, 183703. 29 T. C. Droubay et al., Phys. Rev. Lett., submitted, 2013. 30 K. Németh, A. K. Unni and J. Kaduk et al., The synthesis of ternary acetylides with Te, to be published.