arXiv subjects

Karoly Nemeth

Publications and source records attributed to Karoly Nemeth.

9 recordsLinked to original sources

arXiv2023

High energy and high power primary Li-CF$_x$ batteries enabled by the combined effects of the binder and the electrolyte

Several effective methods have been developed recently to demonstrate simultaneous high energy and high power density in Li - carbon fluoride (CF$_x$) batteries. These methods can achieve as high as 1000 Wh/kg energy density at 60-70 kW/kg power density (40-50 C rate) in coin cells and 750 Wh/kg energy density at 12.5 kW/kg power density (20 C rate) in pouch cells. This performance is made possible by ingenious nano-architecture design, controlled porosity, boron doping and electrolyte additives. In the present study, we show that a similarly great performance, 931 Wh/kg energy density at 59 kW/kg power density, can be achieved by using a polyacrylonitrile binder and a LiBF4 electrolyte in Li - graphite fluoride coin cells. We also demonstrate that the observed effect is the result of the right combination of the binder and the electrolyte. We propose that the mechanistic origin of the observed phenomena is an electro-catalytic effect by the polyacrylonitrile binder. While our proposed method has a competitive performance, it also offers a simple implementation and a scalable production of high energy and high power primary Li-CF$_x$ cells.

cond-mat.mtrl-sci↗

arXiv2020

Radical Anion Functionalization of Two-Dimensional Materials as a Means of Engineering Simultaneously High Electronic and Ionic Conductivity Solids

A radical anion based functionalization of the basal plane of two-dimensional (2D) materials is proposed in the present study. Simple charge neutral radical functionalizations typically detach from the basal planes upon reduction. For example, epoxy oxygens irreversibly detach from graphene when reduced by an alkali metal. The radical anion functionalization of 2D materials results in a stable reduced state that can reversibly be oxidized and has high ionic conductivity due to the great mobility of the cations between the negatively charged functional groups on the surface. Depending on the oxidation state of these systems, a high concentration of hole states can also be realized allowing for good electronic conductivity. These properties can further allow for improved energy storage devices via transition metal free cathode active species, solid electrolytes, electroconductive additives, separators, coatings for metal anodes and heat conductors through a single material. One possible realization of the above principles is the 2D salt An(BN)2OBX3, where A is an alkali atom (Li, Na, etc; 0=<n=<2) or alkaline earth (Mg, etc; 0=<n=<1) and X is a halide (typically F or Cl). This material can be derived from the basal plane functionalization of hexagonal boron nitride, h-BN, with .OBX3^- radical anions in the presence of the A cations. One potential source of .OBX3^- radical anions is their recombined form, the [X3B-O-O-BX3]2- anion, which can be found in the Lewis adduct of an AnO2 ionic peroxide with BX3: An[X3B-O-O-BX3]. The individual radical anions can be obtained by thermally splitting the O-O bond in the recombined anion. Transition metal free all-solid-state batteries with Li, Na and Mg anodes, thermal stability and high energy and power densities may be realizable using An(BN)2OBX3.

cond-mat.mtrl-sci↗

arXiv2018

Simultaneous Oxygen and Boron Trifluoride Functionalization of Hexagonal Boron Nitride: A Designer Cathode Material for Energy Storage

Covalent functionalization is a way to tune the electrochemical properties of hexagonal boron nitride (h-BN) monolayers. The wide band gap insulator h-BN may become metallic conductor upon functionalization with strong oxidants, such as fluorosulfonyl radicals ($\cdot$OSO$_2$F), as known since 1978 [N. Bartlett et al., J. Chem. Soc. Chem. Comm. {\bf 5}, 200 (1978)], with electrical conductivity of 1.5 S/cm [C. Shen et al., J. Solid State Chem. {\bf 147}, 74 (1999)] that greatly surpasses commercial cathode material Li$_{x}$CoO$_{2}$ while retaining excellent ionic conductivity. Functionalized boron nitrides (FBN-s) have great potential for cathode applications in energy storage devices, for example in solid state batteries. While fluorosulfonyl functionalization is unlikely to result in rechargeable cathodes, similarly to graphene fluoride (CF$_x$), some other FBN-s discussed here may do. In the present work, fluorene, oxygen and combined oxygen and boron trifluoride functionalizations are studied, on the basis of band structure calculations. Due to the open surfaces of FBN-s, fast ionic diffusion with Li, Na and Mg ions is possible, enabling batteries with voltages of 2.1-5.6 V, theoretical energy densities of 800-1200 Wh/kg and fast charge and discharge.

cond-mat.mtrl-sci↗

arXiv2015

The Synthesis of Ternary Acetylides with Tellurium: Li2TeC2 and Na2TeC2

The synthesis of ternary acetylides Li2TeC2 and Na2TeC2 is presented as the first example of ternary acetylides with metalloid elements instead of transition metals. The synthesis was carried out by the direct reaction of the corresponding bialkali acetylides with tellurium powder in liquid ammonia. Alternatively, the synthesis of Na2TeC2 was also carried out by the direct reaction of tellurium powder and two equivalents of NaC2H in liquid ammonia leading to Na2TeC2 and acetylene gas through an equilibrium containing the assumed NaTeC2H molecules besides the reactants and the products. The resulting crystalline materials were characterized by x-ray diffraction. Implications of these new syntheses on the synthesis of other ternary acetylides with metalloid elements and transition metals are also discussed.

cond-mat.mtrl-sci↗

arXiv2014

Ultrahigh Energy Density Li-ion Batteries Based on Cathodes of 1D Metals with -Li-N-B-N- Repeating Units in alpha-LixBN2 (1<x<3)

Ultrahigh energy density batteries based on alpha-Li_xBN2 (1 Li3BN2 electrochemical cell reaction leads to a voltage of 3.62 V (vs Li/Li$^{+}$), theoretical energy densities of 3251 Wh/kg and 5927 Wh/L, with capacities of 899 mAh/g and 1638 mAh/cm3, while the cell volume of alpha-Li3BN2 changes only 2.8% per two-electron transfer. These values are far superior to the best existing or theoretically designed intercalation or conversion-based positive electrode materials. For comparison, the theoretical energy density of a Li-O2/peroxide battery is 3450 Wh/kg (including the weight of O2), that of a Li-S battery is 2600 Wh/kg, that of Li3Cr(BO3)(PO4) (one of the best designerintercalation materials) is 1700 Wh/kg, while already commercialized LiCoO2 allows for 568 Wh/kg. alpha-Li3BN2 is also known as a good Li-ion conductor with experimentally observed 3 mS/cm ionic conductivity and 78 kJ/mol (~ 0.8 eV) activation energy of conduction. The attractive features of alpha-LixBN2 (1<x<3) are based on a crystal lattice of 1D conjugated polymers with -Li-N-B-N- repeating units. When some of the Li is deintercalated from alpha-Li3BN2 the crystal becomes a metallic electron conductor, based on the underlying 1D conjugated pi-electron system. Thus alpha-LixBN2 (1<x<3) represents a new type of 1D conjugated polymers with great potential for energy storage and other applications.

cond-mat.mtrl-sci↗

arXiv2014

Materials Design by Quantum-Chemical and other Theoretical/Computational Means: Applications to Energy Storage and Photoemissive Materials

The present paper discusses some recent developments in the field of rational design for energy storage and photoemissive materials. Recent and new examples of designer materials for Li-ion and Li-air type batteries with high capacity and energy/power density as well as photoemissive materials with low workfunctions and improved brightness are discussed as illustrative examples of how quantum-chemical and other theoretical computational means can be used for rational materials design.

cond-mat.mtrl-sci↗

arXiv2013

CO2/oxalate Cathodes as Safe and Efficient Alternatives in High Energy Density Metal-Air Type Rechargeable Batteries

We present theoretical analysis on why and how rechargeable metal-air type batteries can be made significantly safer and more practical by utilizing CO2/oxalate conversions instead of O2/peroxide or O2/hydroxide ones, in the positive electrode. Metal-air batteries, such as the Li-air one, may have very large energy densities, comparable to that of gasoline, theoretically allowing for long range all-electric vehicles. There are, however, still significant challenges, especially related to the safety of their underlying chemistries, the robustness of their recharging and the need of supplying high purity O2 from air to the battery. We point out that the CO2/oxalate reversible electrochemical conversion is a viable alternative of the O2-based ones, allowing for similarly high energy density and almost identical voltage, while being much safer through the elimination of aggressive oxidant peroxides and the use of thermally stable, non-oxidative and environmentally benign oxalates instead.

cond-mat.mtrl-sci↗

arXiv2013

Searching for low-workfunction phases in the Cs-Te system: the case of Cs2Te5

We have computationally explored workfunction values of Cs2Te5, an existing crystalline phase of the Cs-Te system and a small bandgap semiconductor, in order to search for reduced workfunction alternatives of Cs2Te that preserve the exceptionally high quantum efficiency of the Cs2Te seasoned photoemissive material. We have found that the Cs2Te5(010) surface exhibits a workfunction value of ~ 1.9 eV when it is covered by Cs atoms. Cs2Te5 is analogous to our recently proposed low-workfunction materials, Cs2TeC2 and other ternary acetylides [J. Z. Terdik, et al., Phys. Rev. B 86, 035142 (2012)], in as much as it also contains quasi one-dimensional substructures embedded in a Cs-matrix, forming the foundation for anomalous workfunction anisotropy, and low workfunction values. The one-dimensional substructures in Cs2Te5 are polytelluride ions in a tetragonal rod packing. Cs2Te5 has the advantage of simpler composition and availability as compared to Cs2TeC2, however its low workfunction surface is less energetically favored to the other surfaces than in Cs2TeC2.

cond-mat.mtrl-sci↗

arXiv2005

Geometry Optimization of Crystals by the Quasi-Independent Curvilinear Coordinate Approximation

The quasi-independent curvilinear coordinate approximation (QUICCA) method [K. Németh and M. Challacombe, J. Chem. Phys. {\bf 121}, 2877, (2004)] is extended to the optimization of crystal structures. We demonstrate that QUICCA is valid under periodic boundary conditions, enabling simultaneous relaxation of the lattice and atomic coordinates, as illustrated by tight optimization of polyethylene, hexagonal boron-nitride, a (10,0) carbon-nanotube, hexagonal ice, quartz and sulfur at the $Γ$-point RPBE/STO-3G level of theory.

physics.chem-ph↗