How the Charging Rate of Lithium Ion Batteries Affect Their Lifetime and Safety.

lithium ion batteries charging
Image courtesy of ABB.

What would we do without lithium Ion Batteries? I mean everything from our cell phones, tablets, laptops and other devices relies on the very latest in battery storage technology. As consumers we want it all right? We want cheap batteries, that never have to be recharge and weigh next to nothing.

A big order to fill.

In fact lithium ion batteries are getting better rapidly. There is a considerable amount of research funding and resources being focuses at meeting our needs for today and for tomorrow. I mean how will I power my augmented reality glasses and my personal home robot.

Moverio BT-300 Smart Glasses (AR/Developer Edition) Uses Lithium Ion Batteries

Not to mention electric vehicles like the new Tesla Roadster.

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The new Tesla all electric Roadster called the fastest production car ever, owes it all to the lithium ion battery

State-of-the-art lithium ion batteries are powering a revolution in clean transport and high-end consumer electronics, but there is still plenty of scope for improving charging time. Currently, reducing charging time by increasing the charging current compromises battery lifetime and safety.

A new technique developed by researchers at Technische Universität München, Forschungszentrum Jülich, and RWTH Aachen University, published in Elsevier’s Materials Today, provides a unique insight into how the charging rate of lithium ion batteries can be a factor limiting their lifetime and safety.

“The rate at which lithium ions can be reversibly intercalated into the graphite anode, just before lithium plating sets in, limits the charging current,” explains Johannes Wandt, PhD, of Technische Universität München (TUM).

Lithium ion batteries consist of a positively charged transition metal oxide cathode and a negatively charged graphite anode in a liquid electrolyte. During charging, lithium ions move from the cathode (deintercalate) to the anode (intercalate). However if the charging rate is too high, lithium ions deposit as a metallic layer on the surface of the anode rather than inserting themselves into the graphite.

This undesired lithium plating side reaction causes rapid cell degradation and poses a safety hazard.

Dr. Wandt and Dr. Hubert A. Gasteiger, Chair of Technical Electrochemistry at TUM, along with colleagues from Forschungzentrum Jülich and RWTH Aachen University, set out to develop a new tool to detect the actual amount of lithium plating on a graphite anode in real-time. The result is a technique the researchers call operando electron paramagnetic resonance (EPR).

What is electrochemistry

Electrochemistry is the study of chemical processes that cause electrons to move. This movement of electrons is called electricity, which can be generated by movements of electrons from one element to another in a reaction known as an oxidation-reduction (“redox”) reaction

“The easiest way to observe lithium metal plating is by opening a cell at the end of its lifetime and checking visually by eye or microscope,” said Dr. Wandt.

There are also nondestructive electrochemical techniques that give information on whether lithium plating has occurred during battery charging.

Neither approach, however, provides much if any information about the onset of lithium metal plating or the amount of lithium metal present during charging. EPR, by contrast, detects the magnetic moment associated with unpaired conduction electrons in metallic lithium with very high sensitivity and time resolution on the order of a few minutes or even seconds.

“In its present form, this technique is mainly limited to laboratory-scale cells, but there are a number of possible applications,” explains Dr. Josef Granwehr of Forschungzentrum Jülich and RWTH Aachen University.

So far, the development of advanced fast charging procedures has been based mainly on simulations but an analytical technique to experimentally validate these results has been missing. The technique will also be very interesting for testing battery materials and their influence on lithium metal plating. In particular, electrolyte additives that could suppress or reduce lithium metal plating.

Dr. Wandt highlights that fast charging for electric vehicles could be a key application to benefit from further analysis of the work.

Until now, there has been no analytical technique available that can directly determine the maximum charging rate, which is a function of the state of charge, temperature, electrode geometry, and other factors, before lithium metal plating starts.

The new technique could provide a much-needed experimental validation of frequently used computational models, as well as a means of investigating the effect of new battery materials and additives on lithium metal plating.

The researchers are now working with other collaborators to benchmark their experimental results against numerical simulations of the plating process in simple model systems.

Dr. Rüdiger-A. Eichel of Forschungzentrum Jülich and RWTH Aachen University, explained further:

Our goal is to develop a toolset that facilitates a practical understanding of lithium metal plating for different battery designs and cycling protocols.

The role of lithium ion batteries for energy storage is critical and increasing. There are several other battery chemistry that are being developed that may eventually prove to be more effective both cost wise and charging time.

Super capacitors are also looking very promising especially for applications where you need a fast charge and/or a fast release of maximum energy. This could said for all device I suppose, but for vehicles this is perfect. It may be that we will see super-capacitors over take the lithium ion battery in the next few years or maybe it will another possible way to store electric current.

The home and commercial renewable energy market is now demanding a cost effective energy storage system to complement wind and solar electric generation. Once this is achieved the dream of moving to 100 percent renewable energy will be within reach.

About Gordon Smith
Gordon's expertise in the area of industrial energy efficiency and alternative energy. He is an experienced electrical engineer with a Masters degree in Alternative Energy technology. He is the co-founder of several renewable energy media sites including Solar Thermal Magazine.

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