The Ubiquitous Lithium-Ion Battery

Used in smartphones, laptops, and just about every portable electronic device, lithium-ion batteries lay at the heart of modern consumer technology. Unfortunately, lithium-ion batteries are often reduced to a mAh rating on device specifications, and beyond that number, little else about the battery is disclosed. Considering how prominent lithium-ion batteries are, this article elucidates their chemistry, where lithium comes from, and the environmental impacts of lithium extraction and battery disposal in order to shed some light on an inconspicuous piece of ubiquitous hardware.

To begin, lithium lies in the first column of the periodic table, a group called the Alkali Metals. The group or family includes lithium (Li) and sodium (Na) along with others. Table salt, or NaCl, is a mineral composed of sodium and chlorine ions (Na⁺ and Cl^- respectively). Everyone knows table salt is safe to be around. It can’t fuel a fire, much less spontaneously ignite; however, you might have heard that sodium metal will.

The difference between sodium in table salt and sodium metal is their electron configuration. Sodium metal is highly reactive when exposed to water because it wants to eject its loosely held outermost valence electron. Once sodium loses an electron, the size of the atom becomes smaller because its nucleus of three positive protons can pull the remaining two negative electrons closer. In the ionic state, there is little to no chance of the remaining electrons being stolen unless purposefully done in a lab, so a sodium ion is inherently stable. Essentially, sodium, and therefore lithium because it is in the same family, are highly reactive as metals so they’re conversely stable as ions. Thus, lithium is a good candidate for rechargeable batteries because it is a stable, small, and light charged particle.

 A battery has four principal components: the negative anode, the positive cathode, the electrolyte, and a membrane. The anode of a Li-ion battery is often graphite, a type of elemental or pure carbon also used for pencil lead. The cathode is a lithium-containing compound like lithium cobalt oxide or lithium iron phosphate (LiCoO₂ and LiFePO₄). The electrolyte is a lithium-based salt suspended in an organic solvent, and the membrane allows lithium ions to pass through and prevents a short circuit by separating the anode and cathode.

When charged, electrons are stored in a lithium-graphite complex that allows Li⁺ to keep its positive charge – remember, lithium metal is highly reactive. During discharge, electrons travel through the device circuitry towards the cathode. Electronics use moving electrons to do work such as making light or powering a processor. Meanwhile, small Li⁺ ions move through the electrolyte and membrane towards the cathode to balance the reaction. During recharge, electrons are sent to the anode causing Li⁺ ions to repeat their earlier journey in reverse. Li⁺ is the positive charge carrier that balances the reaction but doesn't do any measurable work.

Lithium-ion batteries are popular because they store a lot of electrons in a small and light package. Their chemistry favors high energy density, which means that they supply current at a steady rate. Furthermore, LIBs do not require any maintenance, and they are not prone to memory effects. For example, I can recharge my phone at 20%, 40%, or 57.2%, without significantly harming the battery or reducing capacity (2).

Now that we know a little bit more about how a rechargeable battery works, I will talk about where lithium comes from. Most lithium reserves are in the form of salts, but some large lithium ore deposits exist in Australia, China, and Russia (3). Currently, extracting lithium from salt deposits is more profitable than mining ore (3). Lithium salt refineries separate lithium from other compounds by evaporation. As water evaporates, salt compounds fall out of solution or precipitate.

To understand separation-by-precipitation, imagine leaving a glass of salt water in the window. If the salt water solution in highly concentrated, as the water evaporates, you will see salt crystals forming at the bottom of the glass before the water completely evaporates. Precipitation occurs when the solution becomes saturated, or when there is more salt than water available to dissolve it. Depending on the salt, precipitation occurs at different levels of water. So the trick at lithium refineries is getting a lithium compound, often lithium carbonate (Li₂CO₃), to precipitate independently of other salts.

South American salt flats contain vast lithium reserves. Chile followed by Argentina lead the world in lithium production, but over 40% of the global lithium supply remains untapped in Bolivia’s Salar de Uyuni (4). The Salar, though, has high concentrations of magnesium, an element that makes separation difficult due to chemical similarities to lithium (5). Furthermore, The Salar lies 3,000 feet above sea level where evaporation is slower (8). If and when Bolivia decides to tap into its lithium reserves these problems will have to be addressed. The more pressing question, though, is how to harvest and allocate lithium reserves for maximum output.

One report estimates it would take 35% of the world’s lithium carbonate reserves to replace 900 million gas-powered cars with electric vehicles running on 10 kWh batteries (3). A Nissan Leaf, one of the first electric vehicles available from a large manufacturer, has a 24 kWh battery, which suggests that their 10 kWh estimate for battery capacity was highly conservative. Based on current successful recycling programs for lead-acid car batteries, Li-ion car batteries will likely have high recycling rates if they can achieve similar industry standards. Consumer electronics, on the other hand, are only recycled 20-40% of the time (2).

Once in the landfill, metals from the cathode and internal circuitry, like cobalt, copper, nickel, and lead can leach out in concentrations that exceed regulatory limits (6). These metals threaten environmental quality and human health (6). Tests such as the Wet Extraction Test (WET) or Total Threshold Limit Concentration (TTLC) are used to determine if a metal is likely to escape the confines of a landfill (6).

Recycling has the double benefit of keeping hazardous metals out of landfills while simultaneously reducing demand for raw materials. LIBs present significant recycling challenges when compared to simpler car batteries that are 70% lead by weight and produce high-quality materials that can be reused in new batteries (2). Car battery recycling is economically viable given a small number of internal elements and set battery chemistry and form specifications. Currently, Li-ion batteries are far from standard. First, one must consider the cathode material that contains valuable metals like cobalt (7). Cobalt based cathodes are commercially viable to recycle but iron based ones are not. Second, recent studies suggest that recycling the actual lithium isn’t economical or energy efficient (7). Third, each device requires its own unique form factor, so disassembling the batteries presents its own challenge.

For LIB recycling to catch on, several changes must occur. First, there must be enough LIBs in circulation to sustain demand (3). Second, lithium battery chemistry must be standardized so companies can count on their recycling process to remain relevant (7). Third, standard battery dimensions, like those in the car battery industry, would ease the recycling process. Finally, recycled materials must meet manufacturers’ quality standards. Some companies are reluctant to purchase recycled material because virgin materials improve battery lifetime and performance (7).

Recycling poses significant challenges and benefits. A well-developed recycling process could substantially reduce raw material demand and landfill impact of the growing EV market. Since consumer electronics are becoming ever more popular, and car companies plan on using lithium-ion batteries as well, research devoted to recycling LIBs could have exceptional benefits for reducing landfill contamination and preserving unique environments like the South American salt flats. Given that portable electronics' use will certainly continue and likely proliferate, it is of the utmost importance that all ecological ramifications of those devices are brought to the attention of the public. That attention starts with a deeper understanding of what a lithium-ion battery is.

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