Background
We are working to understand and substantially improve lithium ion battery performance, lifetime, and safety.
To accomplish that, we are developing a new methodology for performing firstprinciples quantum molecular dynamics (QMD) simulations
at an unprecedented scale, harnessing the nation’s largest
supercomputers, to understand key aspects of the chemistry and dynamics
in lithiumion (Liion) batteries, particularly at interfaces. By virtue
of its power and generality, the new methodology and code so developed
will enable corresponding breakthroughs in understanding the gamut
of materials systems from liquids to solids, from metals to insulators, from molecules to nanostructures to bulk.
Liion batteries have
revolutionized personal electronics and have the potential to do the
same for transportation and electrical distribution. In transportation
in particular, a significant advance in battery performance and lifetime
will allow the transition from current gasoline and dieselbased
vehicles to plugin hybrids and allelectrics with comparable or better
power, range, and cost. This, in turn, would greatly reduce the nation’s
dependence on fossil fuels and carbon emissions associated with them.
An advance in safety will have significant implications for aviation as
well, as the recent grounding of Boeing 787s worldwide due to Liion
battery fires has made all too clear.
However, progress in improving the performance, lifetime, and safety
of Liion batteries has been hindered by an incomplete understanding of
the basic chemistry and dynamics.
Using supercomputers at Lawrence Livermore National Laboratory (LLNL)
and Lawrence Berkeley National Laboratory (LBNL), the team will combine
current stateoftheart quantum mechanical methods and new methodology
being developed to reach the length and time scales required to capture
the essential dynamics of these complex, multiphase Liion systems. In
so doing, we aim to achieve a breakthrough in the understanding of these
ubiquitous electrochemical systems, and thereby pave the way for
fundamental advances in these technologies.

Key limitations of current Liion technologies center on the formation and evolution of the solidelectrolyte interphase (SEI) layer
between anode and electrolyte, a product of electrolyte decomposition.
Particularly, longterm reliability is affected as the flow of Li+ into
and out of the anode is impeded during the charging cycle, and also the
electrical characteristics of the battery degrade as the SEI layer
forms.
However,
the SEI layer is critical for performance, since it helps prevent
further decomposition of the electrolyte at the anode interface. In
practice, a thin, stable SEI layer with high Li+ ion conductivity and
low electrical conductivity is required. Any dynamic buildup or
modification of the SEI film during operation must be avoided. A sudden
change/malfunction of the SEI layer could pose a significant safety
concern.
To date,
there has not been a comprehensive theoretical understanding of the
details of SEI layer formation and evolution, which has hindered
progress in the design of optimal electrolyte/anode systems.

To understand these processes, we are undertaking QMD simulations of an
extensive series of systems, beginning with bulk pureelectrolyte
systems, proceeding to mixed electrolytes with various salts, and
finally to complete liquidonanode simulations. The initial
simulations, requiring configurations of up to 1,000 atoms, are being
carried out using the massively parallel Qbox planewave code developed
at LLNL. Larger simulations, requiring 10,000 atoms or more, will be
carried out using the new Discontinuous Galerkin (DG)
methodology being developed as a cornerstone of the present work. It is
only with the advent of computational resources on the scale now
available and breakthrough new quantum mechanical and numerical methods
which can effectively harness them, that this research is now possible.
Project
The primary goals of this project are:
 To develop and implement a new discontinuous approach to quantum mechanical materials calculations to make possible complex, realistic simulations of unprecedented size.
 To apply the new methodology to reach for the first time the length and time scales necessary to accurately model solidelectrolyte interfaces in lithiumion batteries, thus paving the way for breakthroughs in understanding, device performance, and safety.
 To make the resulting codes available to the larger research community for application to the gamut of physical systems amenable to such largescale quantum mechanical calculations.
To accomplish the above goals, we are applying and further developing the massively parallel Qbox planewave quantum molecular dynamics (QMD) code for liquid and small solidliquid interface calculations within its reach (< ~2000 atoms), while developing new Discontinuous Galerkin (DG) and Pole Expansion and Selected Inversion (PEXSI) methods to reach systems of 10,000 atoms or more to model full liquidonanode configurations. Of particular interest in this regard is the solidelectrolyte interphase (SEI) layer, a key factor in battery performance, lifetime, and safety.
The new DG methodology achieves planewave accuracy in both total energy and forces with a basis size on the order of minimal Gaussians. The basis is strictly local, orthonormal, and systematically improvable, thus enabling high accuracy and efficient largescale parallel implementation. These remarkable properties are made possible by releasing the constraint of continuity through the DG formulation of the KohnSham equations. This permits construction of a highly efficient representation of KohnSham wavefunctions in the computational domain as a straightforward union of KohnSham solutions in any chosen set of subdomains. In practice, a large computational unit cell is partitioned into subdomains ("elements") containing just a few atoms each. The KohnSham equations can then be solved in each of the small subdomains in parallel to form the desired highly efficient basis for the full domain.
The new PEXSI methodology is a Fermi operator based approach which removes the O(N^3) scaling bottleneck inherent in conventional wavefunction based KohnSham approaches, where N is the number of atoms, by eliminating the need to compute wavefunctions altogether; computing instead needed densities, energies, and forces directly from the KohnSham Hamiltonian without diagonalization, while retaining strict systematic improvability and applicability to metals and insulators alike. In combination with atomicorbital bases, our initial implementation has accomplished KohnSham calculations on systems of over 45,000 atoms.
By combining the new DG and PEXSI approaches, we seek to reach for the first time the length and time scales necessary to accurately model complex solidelectrolyte Liion systems.
Having reached a sufficient level of robustness and efficiency, we have now released a parallel implementation of PEXSI (see Software page). Current work centers on the development and application of the combined DGPEXSI methodology and code which, when complete, will be released also.

