Towards Understanding and Designing of Advanced Li-ion Batteries from First-principles

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Lithium ion batteries (LIBs) have been the most prominent electrochemical energy storage technology over the past decades and enabled the wireless evolution of portable electronic devices. Yet the expanded use of renewable but intermittent energy sources coupled with increasing demand for electric transportation vehicles put forward requirements to electrochemical energy storage techniques for higher capacity, lower cost, and fast rate capacity. State-of-the-art LIB electrodes are typically lithium transition metal oxides and phosphates, which store (release) the electrical energy via the Li extraction and re-accommodation, accompanied by redox reactions of TM cations. The specific capacity of the electrode is therefore limited by the safe amount of Li can be removed from the system without causing structure collapse and the number of electrons per TM cation that can participate in the redox reaction. To boost the capacity and energy density, conversion reaction electrode materials which can overcome the inherent structural limitation and anionic redox active electrodes with oxygen ions complementarily providing the charge-compensating electrons were introduced to the rechargeable battery chemistry. Here we use the density functional theory (DFT) based first-principles calculations to understand the electrochemical charge and discharge of the conversion reaction electrodes via exploring the equilibrium and non-equilibrium thermodynamics with a mechanistic method as designed. We provide detailed information for the origin of large voltage hysteresis and volume expansion which have been hindering the practical application of conversion reaction materials and offer tips on alleviating them through reasonably operation range restrictions. Our findings are reproducible among several well-known transition metal (TM) oxide/sulfide conversion-type electrodes (e.g. Co3O4, NiO, CuS). For the anionic redox active electrodes, we demonstrate how the coordination structure and bonding environment enable the reversible oxygen redox in the 3d metal oxides. The specific redox active Li6-O local Li-excess configuration as identified for the iron oxide electrode enriches the anionic redox battery chemistry with a low-cost high energy density battery designed. For the manganese oxide anionic redox active electrodes, we predict novel materials with improved properties compared to the original system through high-throughput DFT screening. On the other hand, using kinetics calculations we discover a novel 2-dimensional material with superior electric and ionic conductivity compared to traditional 2-dimensional nano sheet like graphene which can be used to boost the rate capacity of state-of-the-art LIBs. We accurately reveal the mechanism of the kinetics-dominated electrochemical sodiation and lithiation reactions of selenium. We clarify the relationship between the stability and ionic conductivity of the complex borohydride based lithium ion conductors and giving guidance on their further investigations. Our findings will shed light on the development of the next generation, high energy density, and fast rate advanced lithium ion batteries.

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  • 02/18/2019
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