Lithium-ion batteries have gained widespread use in consumer electronics due to their high energy density and low weight. However, for electric vehicle applications, further improvements in capacity and safety are highly challenging but necessary for lowering the cost and extending the driving distance. Materials with high lithium storage capacity, such as silicon and tin based alloys, have recently been extensively studied for their potential applications as Lithium battery anodes. But the large-volume change associated with lithiation and delithiation severely hinders the practical employments. [1][2][3][4][5][6][7] Despite the intensive efforts, [6][7][8][9][10][11][12] an effective low-cost solution to the volume-change problem remains elusive.Here, we developed a new conductive polymer through a combination of material synthesis,x-ray spectroscopy, density functional theory, and battery cell testing. Contrasting other polymer binders, the tailored electronic structure of the new polymer enables lithium doping under the battery environment. The polymer thus maintains both electric conductivity and

The dilemma of employing high-capacity battery materials and maintaining the electronic and mechanical integrity of electrodes demands novel designs of binder systems. Here, we developed a binder polymer with multi-functionality to maintain high electronic conductivity, mechanical adhesion, ductility, and electrolyte uptake. These critical properties are achieved by designing polymers with proper functional groups. Through synthesis, spectroscopy and simulation, electronic conductivity is optimized by tailoring the key electronic state, which is not disturbed by further modifications of side chains. This fundamental allows separated optimization of the mechanical and swelling properties without detrimental effect on electronic property. Remaining electrically conductive, the enhanced polarity of the polymer greatly improves the adhesion, ductility, and more importantly, the electrolyte uptake to the levels of those available only in non-conductive binders before. We also demonstrate directly the performance of the developed conductive binder by achieving full-capacity cycling of silicon particles without using any conductive additive.3

Electronic structure of disordered semiconducting conjugated polymers was studied. Atomic structure was found from a classical molecular dynamics simulation and the charge patching method was used to calculate the electronic structure with the accuracy similar to the one of density functional theory in local density approximation. The total density of states, the local density of states at different points in the system and the wavefunctions of several states around the gap were calculated in the case of poly(3-hexylthiophene) (P3HT) and polythiophene (PT) systems to gain insight into the origin of disorder in the system, the degree of carrier localization and the role of chain interactions. The results indicated that disorder in the electronic structure of alkyl substituted polythiophenes comes from disorder in the conformation of individual chains, while in the case of polythiophene there is an additional contribution due to disorder in the electronic coupling between the chains. Each of the first several wavefunctions in the conduction and valence band of P3HT is localized over several rings of a single chain.It was shown that the localization can be caused in principle both by ring torsions and chain bending, however the effect of ring torsions is much stronger. PT wavefunctions are more complicated due to larger interchain electronic coupling and are not necessarily localized on a single chain.

We developed an ab-initio multiscale method for simulation of carrier transport in large disordered systems, based on direct calculation of electronic states and electron-phonon coupling constants. It enabled us to obtain the never seen before rich microscopic details of carrier motion in conjugated polymers, which led us to question several assumptions of phenomenological models, widely used in such systems. The macroscopic mobility of disordered poly(3-hexylthiophene) (P3HT) polymer, extracted from our simulation, is in agreement with experimental results from the literature. 2Nenad Vukmirović et al.Charge carrier motion in disordered conjugated polymers: a multiscale ab-initio study Semiconducting conjugated polymers have been used in many electronic applications from field-effect transistors, 1,2 light-emitting diodes 3,4 to solar cells 5,6 due to relative ease to synthesize and mold them into different shapes. However, one of the major bottlenecks in conjugated polymer applications is the low carrier mobility. 7 There is therefore a great interest to understand

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We present a new approach to carry out non-adiabatic molecular dynamics to study the carrier mobility in an organic monolayer. This approach allows the calculation of a 4802 atom system for 825 fs in about three hours using 51,744 computer cores while maintaining a plane wave pseudopotential density functional theory level accuracy for the Hamiltonian. Our simulation on a pentathiophene butyric acid monolayer reveals a previously unknown new mechanism for the carrier transport in such systems: the hole wave functions are localized by thermo fluctuation induced disorder, while its transport is via charge transfer during state energy crossing. The simulation also shows that the system is not in thermo dynamic equilibrium in terms of adiabatic state populations according to Boltzmann distribution. Our simulation is achieved by introducing a linear time dependence approximation of the Hamiltonian within a fs time interval, and by using the charge patching method to yield the Hamiltonian, and overlapping fragment method to diagonalize the Hamiltonian matrix.

We performed direct calculations of carrier hopping rates in strongly disordered conjugated polymers based on the atomic structure of the system, the corresponding electronic states and their coupling to all phonon modes. We found that the dependence of hopping rates on distance and the dependence of the mobility on temperature are significantly different than the ones stemming from the simple Miller-Abrahams model, regardless of the choice of the parameters in the model. A model that satisfactorily describes the hopping rates in the system and avoids the explicit calculation of electron-phonon coupling constants was then proposed and verified. Our results indicate that, in addition to electronic density of states, the phonon density of states and the spatial overlap of the wavefunctions are the quantities necessary to properly describe carrier hopping in disordered conjugated polymers.The carrier mobility of conjugated polymer materials is the most important physical property 1-6 for their application in organic electronic devices. Realistic polymer materials contain both crystalline (ordered) and amorphous (disordered) regions.7 Charge carrier transport is often limited by the presence of amorphous regions. In these regions the electronic states are localized due to presence of disorder and carrier transport takes place by phononassisted carrier hopping 8 between localized states. Such transport is traditionally modeled by assuming a certain density of electronic states in energy and space and a certain form of hopping probabilities between them.6,9-12 Different models are distinguished by the electronic density of states (DOS) assumed in the model, which is usually the tail of the Gaussian 9,10,12 or the exponential 11 distribution. The transition rates are typically assumed to decay exponentially with the distance between localized states, 9-12 in the Miller-Abrahams (MA) form.13 Free parameters that appear in the models are fitted to the experimental mobility measurements.From the applications of such models, it is widely understood that the mobility of the material strongly depends on the electronic DOS which is therefore believed to be the most important material property when charge transport is concerned.14 On the other hand, much less effort has been put into understanding how different forms of the transition rates affect the transport and in particular whether the MA expression is suitable at all. To address these questions, in this letter we perform direct ab-initio calculations of the transition rates between electronic states starting from atomic structure of the system, followed by explicit calculation of electronic state wavefunctions and their coupling to phonons. We find strong deviations of the transition rate dependence on distance from the MA form and analyze the consequences of this on electronic transport.Electronic structure calculations were performed using the plane wave pseudopotential approach and the charge patching method for organic systems introduced in Ref. 15 which gives the ac...

We present large-scale calculations of electronic structure of strongly disordered conjugated polymers. The calculations have been performed using the density functional theory based charge patching method for the construction of single-particle Hamiltonian and the overlapping fragments method for the efficient diagonalization of that Hamiltonian. We find that the hole states are localized due to the fluctuations of the electrostatic potential and not by the breaks in the conjugation of the polymer chain. The tail of the density of hole states exhibits an exponentially decaying behavior. The main features of the electronic structure of the system can be described by an one-dimensional nearest neighbor tight-binding model with a correlated Gaussian distribution of on-site energies and constant off-site coupling elements.