An Introduction to Lithium Ion Batteries

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TL;DR

The growing dominance of electric vehicles has been powered by continuing improvements in lithium ion batteries over the last few decades. Lithium ion battery prices have dropped steeply, but battery energy densities have only increased linearly for the last few decades. Dropping prices have powered the usage of lithium ion cells in electric vehicles and grid scale storage, but have also started to create environmental burdens and geopolitical risks.

A Very Brief History of the Lithium Ion Battery

Early lithium batteries were produced at Exxon by researchers in the early 70s, but these devices were expensive and impractical. The discovery of reversible intercalation of lithium ions in graphite (see diagram below) in the mid 1970s suggested a new technological path forward. (Intercalation is the reversible insertion or removal of a compound into a layered material like graphite)

Graphite intercalation compounds have ions (represented above in purple), inserted between layers of graphite sheets. Reversible graphite intercalation allows for the repeated insertion and removal of ions between graphite sheets. Reversible lithium ion intercalation is the foundational technology underpinning the lithium ion battery (source).

The first lithium ion cells were produced in 1979 by researchers at multiple institutions. The first commercial lithium ion battery was produced by Sony in 1991 after several additional years of research and development (source). Commercialization funded continuing research into improving lithium ion batteries. Prices have dropped steeply in the decades since initial commercialization but energy densities have only risen linearly in the years since as the diagram below shows.

Development of lithium batteries between 1970-2015, showing the cost (blue, left axis) and energy density (red, right axis) of Li-ion batteries following their commercialization by Sony in 1991.The energy densities of Li-or LiAl-metal anode batteries against four cathodes, commercialized in the years indicated and withdrawn from the market for reasons of safety or market appeal, are shown in gray and refer to the right axis. Caption and image adapted from (source).

As of 2016, 28 gigawatt hours (GWh) of lithium ion batteries were manufactured worldwide, with 16.4 GWh manufactured in China. As we learned in our subscriber issue from Tuesday, PRC (People’s Republic of China) battery manufacturers have continued to innovate rapidly and maintain a leading position in the global market.

Lithium Ion Cell Science

At a high level, a lithium ion battery has three regions, an anode, a cathode, and a separator. During discharge, negative current flows from the anode, and positively charged lithium ions intercalate from the anode through the separator to the cathode. During charging, negative current flows from the cathode to the anode, pushed by a power source, and lithium ions flow from the cathode to the anode. The diagrams below illustrate the components of a lithium ion battery and the discharging and charging processes.

Lithium ion batteries have a negative anode separated from a positive cathode by a porous separator. Anodes are usually formed using graphite, and cathodes from lithium metal oxides. The electrolytes are conductors (liquid or solid) that facilitate movement of charge. Ions move from the anode to the cathode during discharging and back through during recharging as the next two diagrams show. (source).

A diagrammatic representation of how a lithium ion battery is discharged. Negative current flows from the anode through the load and positively charged lithium ions move through the porous separator to compensate (source).

Diagrammatic representation of lithium ion recharging. A power source drives electrons to the anode and pulls electrons from the cathode. Lithium ions migrate back to the anode from the cathode (source).

Anodes are usually graphite as we mentioned above. Cathodes are usually lithium metal oxides such as lithium cobalt oxide, lithium iron phosphate, and lithium manganese oxide.

Market Dynamics

The lithium ion cell market has been growing sharply over the last several years, driven in large part by electrical vehicle usage (see first plot below). Electric vehicles have become increasingly attractive for everyday consumers, as the range of electric vehicles continues to increase (see second plot below). Note though that these sharp increases in electric vehicle range are largely not due to increases in lithium ion energy density, but rather due to innovative packaging techniques that allow vehicle manufacturers to package more lithium ion cells within the car volume.

The market for lithium ion cells has been growing rapidly over the last decade. Growth is driven increasingly by electric vehicle usage and the large PRC market (source).

Electric vehicle ranges have risen rapidly in the last few years, driven by innovative methods of packing more cells in the vehicle body and some increases in lithium ion cell density (source).

Discussion

As global manufactured volumes of lithium ion increase dramatically, coming up with strategies for lithium ion waste management and recycling will become increasingly important. Lithium-ion batteries use cobalt, which is primarily mined in the Democratic Republic of the Congo (source). The PRC has been investing heavily in mining, and as has happened with rare metals, American companies could find themselves at the mercy of PRC leverage. More robust recycling pipelines, and ethically mined minerals would reduce the environmental and human burden of large scale lithium ion cell manufacturing.

Highlights for the Week

• https://www.wsj.com/articles/americas-naval-strategy-is-at-sea-11619543738: the US needs a naval strategy that can keep up with the PRC. As we learned in our issue on CSSC, the Chinese naval industrial complex is vast and increasingly more capable than that of the US. A strong naval strategy can help the US navigate the shifting waters of Indo-Pacific

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Deep Into the Forest is a newsletter by Deep Forest Sciences, Inc. We’re a deep tech R&D company specializing in the use of AI for deep tech development. We do technical consulting and joint development partnerships with deep tech firms. Get in touch with us at partnerships@deepforestsci.com! We’re always welcome to new ideas!

Credits

Author: Bharath Ramsundar, Ph.D.
Editor: Sandya Subramanian