Lithium Battery Research
Li Ion Battery Aging, Degradation, and Failure
Stephen J. Harris  sjharris(at)lbl.gov

 

Effects of Inhomogeneities on Lithium Battery Life: Degradation, Aging, and Failure

This site is devoted to lithium battery research aimed at understanding the mechanisms and problems that underlie the workings failure/degradation of Li-ion batteries. There is a focus here on knowledge derived from theoretical studies of batteries and battery materials; advanced diagnostic techniques, especially in situ or operando; and chemically detailed models of battery aging mechanisms. Many of these pages show lithium battery videos related to lithium battery life. At present, automotive Li batteries are greatly oversized and overengineered in orger to provide a longer life. Thus, more durable batteries can automatically have a higher energy density--both volumetric energy density and gravimetric energy density.

This approach--examining the impact of electrode heterogeneities on battery life and durability--is describled in the following video, showing Steve Harris giving the 2013 Kavli Lecture at the March APS meeting. An updated version of this work, presented at the 2014 Gordon Research Conference on Batteries is provided as a pdf here. The title of the talk is Li-ion Transport: Relationships to Heterogeneity and Failure.


 

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Li Transport
in Graphite Electrode

Plating

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LiCoO2 Particle 1

Molecular Dynamics

Tin Oxide Nanowires

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Dendrites and Fracture

 

Publications by Steve Harris

Steve Harris Resume

 

The goal of much of present day Lithium battery research is to develop higher energy density batteries. Consider 4 approaches:

(1) Positive electrodes with greater capacity. Such electrodes can be made, but their durability is poor.

(2) Higher voltage positive electrodes, up to 5 V. Such electrodes can be made, but we do not have electrolytes that are stable at such high voltages. Neither approach addresses volumetric energy density.

(3) Higher mass density (lower porosity) electrodes. This could lead to higher tortuosity. A reduction in porosity from 40% to 25% would again increase energy density by 25%.

(4) More durable electrodes. The connection between durability and energy density comes from the fact that in order to achieve long life, much of the energy in Li-ion batteries is never accessed. If we could access 80% of the battery's energy instead of, say, 65%, the energy density would increase by 25%. Importantly, both volumetric and gravimetric energy density would increase.

We believe that heterogeneity is the ultimate reason that many Li-ion batteries access only about 65% of their theoretical energy. That's because when the average state of charge (SOC) in an electrode is 65%, parts of the electrode are already at 100% state of charge, and at such high values for SOC, either plating or electrolyte oxidation occurs. See Figure 6 of"Particle Size Polydispersity in Li-ion Batteries."

Our work researching lithium battery problems is predicated on two hypotheses: First, that degradation and failure initiate at inhomogeneities (or heterogeneities) the the battery microstructure; and second, that these heterogeneities lead to an inhomogeneous transport of lithium ions. Inhomogeneities include any structures where there are rapidly varying spatial properties, such as the SEI lyer. The SEI film is an important site for generating lithium battery aging and failure. For this reason, we believe that a general study of degradation and failure can begin with identification and quantification of inhomogeneities (typically at the mesoscale) as well as measurements of Li transport and insertion into porous electrodes in the battery.  These measurements could then guide researchers towards other experiments and models that provide fundamental knowledge of durability (aging, degradation and failure) using advanced diagnostic techniques. We are especially interested in research that connects with models that take into account microstructural and nanoscale properties and inhomogeneities.

 

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Lithium Battery Research: LithiumBatteryResearch.com

 
   
 
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