Optimization of the Lithium Battery: Past, Present, and Future
Written by PengCheng Zhu '26
Edited by Jacqueline Cho '24
“Expanded lithium-ion polymer battery from an Apple iPhone 3GS.” An Apple iPhone 3GS's Lithium-ion polymer battery, which has expanded due to a short circuit failure. The battery is shown in situ on top of the rear phone case; pictured behind is an intact iPhone 3GS for size comparison. Matthew Taylor, Wikimedia Commons. 15 September 2013.
We usually don’t consciously realize it, but lithium ion batteries are everywhere around us. They power our phones and laptop computers—and increasingly our cars, too. They’re light, relatively fast charging, and durable. But if you have ever had an older phone, you know of the absolute inconvenience a degraded lithium ion battery presents when your phone is already down to 20% power after a mere two hours. More ominously, lithium ion batteries sometimes make news headlines, not as an energy-storage device, but as a flash bomb—remember when a Tesla car spontaneously combusted ? Or when the same thing happened to Samsung phones ?
To understand why lithium ion batteries occasionally burst into flames, we first have to understand how the battery works. In essence, batteries provide energy through the movement of electrons from a more positive to more negative energy potential. In lithium batteries, the electrons in neutral lithium metal have high energy potential, so when lithium gives up its electron to become a positive ion, the electrons flow towards a lower energy potential, which creates free energy that is used by the electronic device. The rest of the battery are structural materials like graphite to stabilize lithium in both its metal or ionic form. Therefore, when lithium ion batteries combust, it is usually a failure of the battery design to keep the lithium in either form stable .
Despite the occasional failure of lithium ion batteries, their designs have come a long way since their invention.
The first breakthrough was harnessing lithium as an energy source. Early experimenters designed solid-state batteries, but the lithium did not cluster back neatly when the battery was recharged, instead forming narrow and messy dendrites that quickly rendered the battery useless. The trick was to dissolve the lithium in a liquid and add graphite to structure the lithium as it deposits, which reduced dendrite formation significantly. After researchers locked down this basic design, lithium ion batteries became a game of optimization: use a little less electrolyte here, a little less copper plating there. Soon the battery went from packing under 100 watt-hours of energy per kilogram in the 1990s to hitting 200 watt-hours per kilogram by 2010. These improvements have directly translated into better products for consumers: the first Tesla Model S offered a range of 210 miles, but the improvements in lithium-ion batteries means the newest Tesla Models now can go up to 390 miles without recharging. Despite these advances, these batteries degrade over time and are still somewhat bulky. How then will researchers improve the lithium ion battery?
Some groups are trying to improve the energy density of lithium ion batteries. While graphite is important for keeping the lithium stable, it is not an active component. Therefore, more graphite in a battery means lower energy density. Completely replacing graphite with silicon would in theory increase the energy density of lithium ion batteries by 10 times. However, the structure of the silicon swells when lithium deposits on it by a significant amount—approximately by 300%. This swelling would cause serious problems in ultra-thin electronic devices where every cubic centimeter of space is precious. Instead, companies are doping the battery with more silicon in gradual increments to increase the energy density of the battery. While energy density could also be increased with solid-state batteries, further research must be done to prevent the associated problem of dendrite formations. Many approaches are being drawn up to eliminate dendrites,  but certainly much more research is needed before solid-state lithium batteries end up in our phones, laptops, and cars .
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