Characterization of an Electroactive Polymer for OverchargeProtection in Secondary Lithium Batteries

This report describes Characterization of an Electroactive Polymer for OverchargeProtection in Secondary Lithium Batteries

Design Principles for the Use of Electroactive Polymers for Overcharge Protection of Lithium-Ion Batteries

Abstract A continuum-scale model is presented to explain how electroactive polymers such as polythiophene can be used to provide overcharge protection for lithium-ion batteries. The model shows how the cell is transformed upon overcharge from a battery to a resistor with a resistivity that varies with position across the separator. Upon discharge or open circuit, self discharge transforms the resistor back into a battery, and normal cycling can be resumed. A simplified model yields a design equation that shows how the potential at which the cell shorts depends on the current density, separator thickness, and the variation of the electronic conductivity and the oxidation potential of the polymer with degree of oxidation. The shorting voltage is independent of the choice of positive electrode and scales with the potential of the charged negative electrode

In Situ Observation and Mathematical Modeling of Lithium Distribution within Graphite

© The Author(s) 2017. Published by ECS. All rights reserved. Lithium forms ordered stages when it reacts with graphite. These stages have distinct colors; therefore, optical microscopy gives direct information about the lithium concentration in the graphite. Here we present in situ optical images during charging and discharging of a graphite electrode. Stages are observed to coexist with each other even after extended rest. There is considerable spatial nonuniformity on the microscale. To predict this concentration distribution, we employ a model which combines porous-electrode theory and Cahn-Hilliard phase-field theory to describe the flux of lithium within the graphite. The model closely matches the experimental voltage and concentration distribution. The spatial nonuniformity can be approximated with a relatively simple model of distributed resistances. Finally, we discuss the implications of using the phase-field model instead of a solid-solution model for prediction of lithium plating. The two models give similar predictions of cell voltage and risk of lithium plating under many operating conditions, with the main difference being the relaxation of concentration gradients within particles during rest. The distributed-resistance model shows a higher risk of lithium plating because well-connected particles are overworked as their more-resistive neighbors require a higher driving force for passage of current

The Role of Interlayer Chemistry in Li‐Metal Growth through a Garnet‐Type Solid Electrolyte

Securing the chemical and physical stabilities of electrode/solid-electrolyte interfaces is crucial for the use of solid electrolytes in all-solid-state batteries. Directly probing these interfaces during electrochemical reactions would significantly enrich the mechanistic understanding and inspire potential solutions for their regulation. Herein, the electrochemistry of the lithium/Li7La3Zr2O12-electrolyte interface is elucidated by probing lithium deposition through the electrolyte in an anode-free solid-state battery in real time. Lithium plating is strongly affected by the geometry of the garnet-type Li7La3Zr2O12 (LLZO) surface, where nonuniform/filamentary growth is triggered particularly at morphological defects. More importantly, lithium-growth behavior significantly changes when the LLZO surface is modified with an artificial interlayer to produce regulated lithium depositions. It is shown that lithium-growth kinetics critically depend on the nature of the interlayer species, leading to distinct lithium-deposition morphologies. Subsequently, the dynamic role of the interlayer in battery operation is discussed as a buffer and seed layer for lithium redistribution and precipitation, respectively, in tailoring lithium deposition. These findings broaden the understanding of the electrochemical lithium-plating process at the solid-electrolyte/lithium interface, highlight the importance of exploring various interlayers as a new avenue for regulating the lithium-metal anode, and also offer insight into the nature of lithium growth in anode-free solid-state batteries.

The Role of Interlayer Chemistry in Li-Metal Growth through a Garnet-Type Solid Electrolyte

Securing the chemical and physical stabilities of electrode/solid-electrolyte interfaces is crucial for the use of solid electrolytes in all-solid-state batteries. Directly probing these interfaces during electrochemical reactions would significantly enrich the mechanistic understanding and inspire potential solutions for their regulation. Herein, the electrochemistry of the lithium/Li7La3Zr2O12-electrolyte interface is elucidated by probing lithium deposition through the electrolyte in an anode-free solid-state battery in real time. Lithium plating is strongly affected by the geometry of the garnet-type Li7La3Zr2O12 (LLZO) surface, where nonuniform/filamentary growth is triggered particularly at morphological defects. More importantly, lithium-growth behavior significantly changes when the LLZO surface is modified with an artificial interlayer to produce regulated lithium depositions. It is shown that lithium-growth kinetics critically depend on the nature of the interlayer species, leading to distinct lithium-deposition morphologies. Subsequently, the dynamic role of the interlayer in battery operation is discussed as a buffer and seed layer for lithium redistribution and precipitation, respectively, in tailoring lithium deposition. These findings broaden the understanding of the electrochemical lithium-plating process at the solid-electrolyte/lithium interface, highlight the importance of exploring various interlayers as a new avenue for regulating the lithium-metal anode, and also offer insight into the nature of lithium growth in anode-free solid-state batteries.