First-Principles Computational Methodology for Designing Advanced Lithium Batteries, 18-R9890

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Principal Investigators
Kwai S. Chan
Wuwei Liang

Inclusive Dates:  10/01/08 – 09/30/10

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 Li-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: (1) to develop a multi-scale computational methodology for designing Li batteries, (2) to apply this methodology to screening novel cathode and anode materials, (3) to apply this methodology to designing the optimum electrode geometry and morphology, and (4) to verify the computational methodology and the optimum design by critical experiments. First-principles molecular dynamics methods have been utilized to model the lithium insertion process in Si and Type I silicon clathrates (Si46), including computations of the intercalation potential, volume change, and the theoretical fracture stress and strain of the lithiated compounds, LixSi and LixSi46. A micromechanical modeling approach has also been developed for computing the local stresses and strains associated with lithium intercalation of Si and Si46 anodes of three different morphologies, including nanospheres, nanowires and nanoplatelets. The various length-scale models have been integrated into a continuum framework for predicting electrode failure caused by insertion-induced stresses.

Accomplishments - First-principles molecular dynamics computations via the Car-Parrinello molecular dynamic method have been performed to simulate the insertion of Li into silicon clathrate, Si46, to form LixSi46 during lithiation. First-principles computational results show that the Li insertion process in silicon clathrate appears to be different from amorphous silicon or crystalline silicon, and involves the storage of Li atoms in the open and accessible spaces within the cage structure of the clathrate, as shown in Figure 1. As a result, silicon clathrates can be lithiated with higher energy densities, less lithiation strain and better resistance to pulverization than existing silicon anodes. These attributes make Type I silicon clathrates (Si46) a promising anode material for Li-ion batteries.

Insertion of Li atoms into the fullerene-like structures in a unit cell of Si46 forms Li48Si46. Si atoms are purple and Li atoms are blue.

Figure 1. Insertion of Li atoms into the fullerene-like structure in a unit cell of Si46 forms Li48Si46. Si atoms are purple and Li atoms are blue.

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