First-Principles Computational Methodology for Designing Advanced Lithium Batteries,

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Principal Investigators
Kwai S. Chan
Wuwei Liang

Inclusive Dates:  10/01/08 – Current

Background - Energy storage and battery materials represent a major growth market for fundamental research, applied research and technology development. The U.S. Department of Energy has established an extensive technology program to advance the development of lithium-based batteries to enable a larger market penetration of hybrid electrical vehicles, plug-in hybrid electrical vehicles, and electric vehicles. This fundamental research project addresses the need to increase the power, efficiency, durability and the calendar life of current Li batteries by developing the methodology for identifying new cathode and anode materials.

Approach - The objectives of this program are to: (1) develop a multi-scale computational methodology for designing Li batteries, (2) apply this methodology to screening novel cathode and anode materials, (3) apply this methodology to designing the optimum electrode geometry and morphology, and (4) verify the computational methodology and the optimum design by critical experiments. First-principles molecular dynamics methods have been used to model the lithium insertion process in Si and compute the corresponding intercalation potential, volume change, and the theoretical fracture stress and strain of lithium silicides, LixSi. A micromechanical modeling approach is also being developed for computing the local stresses and strains associated with lithium intercalation of Si anodes of three different morphologies, including nanospheres, nanowires, and nanoplatelets. The various length-scale models will be integrated into a continuum framework for predicting electrode failure caused by insertion-induced stresses.

Accomplishments - First-principles molecular dynamics computations have been performed to simulate the insertion of Li into Si during lithiation and the deinsertion of Li from LixSi during delithiation. The energy of formation and the unit-cell volume for relevant crystalline and amorphous LixSi phases have been obtained. These results have been used to develop an understanding of the lithiation and delithiation processes by computing the open circuit voltage and the volume changes as a function of the Li mole fraction, x, in the LixSi. These results, which are compared against literature data in Figure 1, will be used in conjunction with the volume change data to obtain the transformation stresses associated with lithiation and delithiation in the design of advanced Si-based Li-ion batteries.

Figure 1. Computed open circuit voltage as a function of mode fraction, x, of Li in LixSi compared against literature data.

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