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Deep Dive: (Almost) Everything You Need to Know About Electric Vehicle Batteries

Posted by admin on May. 3, 2021  /  Subscribe 0

By Rakshak Raveen, LCF Intern

The last few decades have seen a giant push to renewable and sustainable technology, with the automotive industry being a major driving force in that push. Starting with hybrids in the 90s, from companies like Toyota to the all-electric Tesla, the field has transformed to make electric vehicles (EVs) an integral part of our transportation system and the future of transportation. Battery technology has seen an impressive leap in innovation over this time period, and this is a driving force behind the changing attitudes towards EVs. The technology has improved greatly over time, but there is a current need for a breakthrough that experts suggest might help EVs claim dominance in the automotive market. The Department of Energy has invested heavily in this technology through Argonne National Laboratory's battery prototyping and modeling center. With that in mind, we want to share an analysis of where the technology is as of today and where it looks to go soon.  

Why is Battery Technology a key research area for EVs?

We have witnessed a significant leap in EV innovation and manufacturing in the last 30 years. The industry is at the cusp of taking root as a viable transportation option for the general population as well as some commercial applications, not just technology enthusiasts. For that to happen, however, the industry faces some monumental challenges in ensuring that EVs are just as accessible, usable, and easy to travel with as internal combustion engine (ICE) vehicles. One of the key metrics of measuring these factors is vehicle range. In the U.S. especially, which is driven by highways and automobiles, this metric is crucial. The technology has matured to give us good driving ranges with the optimization of the EV system and control design. However, if EVs can take the next step in improving vehicle range, the technology will be able to take a more solid stance in the automotive industry.

There have been different approaches to addressing this issue. The simplest method is to ensure that there are enough charging stations to enable easy cross-country travel. The return on investment (ROI) of electric vehicle supply equipment (EVSE) station hosting isn’t currently attractive in the short term, but the long-term outlook is becoming more positive as manufacturers and government entities are announcing their intentions to go electric and as the technology matures.  Another issue is that it currently takes longer to charge an EV than to fill up a tank with gasoline. This problem has spurred companies to pursue fast charging technology which has shown great promise in helping to bridge the time gap between EV and ICE vehicle fueling; innovations like fast chargers and under-road wireless charging for highways are currently being investigated as possible solutions. While these methods are all impressive feats of ingenuity and engineering, the problem could also be solved by creating a higher-capacity EV battery. Consequently, batteries have proven to be one of the key research areas for the field over the last 15 years.

For EVs to be acceptable alternatives to ICE vehicles, experts speculate that companies must bring the average cost down to under $30,000. This necessitates that batteries either have more storage without adding weight to the vehicle or be built with materials that are cheaper to source and produce. Both of these factors mean that the boundaries of batteries are being pushed constantly to achieve any gain possible.

Types of Batteries

1) Lead Acid – Originally invented in the 19th century, the lead-acid battery is one of the oldest battery technologies. Used in automobiles as an auxiliary battery, it is popular due to good power density, which is needed in ICE vehicles to power the starter and crank the engine. It generally uses lead sulfate plates as the cathode, lead as the anode, and sulfuric acid as the electrolyte.

2) Nickel Metal Hydride – This battery was conceptualized in Geneva in the 1960s with Daimler AG eventually claiming the patent as the battery was improved and stabilized. The battery uses nickel oxyhydroxide as a cathode, a metal hydride or nickel alloy as the anode, and potassium hydroxide as the electrolyte.

3) Sodium Nickel Chloride – Conceived during World War II, this battery technology was revamped in the 1980s. A molten salt, nickel tetrachloroaluminate, is generally used as an electrolyte with molten sodium as the anode and nickel as a cathode.

4) Lithium-Ion (Li-ion) – Developed originally in the 1970s, a functioning prototype was built by Sony in the 1990s. There are many viable chemistries for Li-ion batteries, and their primary commonality is that they all use lithium ions as their charge/energy carriers; this means that the cathode needs to be able to store and discharge those ions when the battery is charged and discharged. Because of their ability to store and discharge lithium ions, metal oxides are usually chosen as the cathode, and there are many metal oxides to choose from each with its own unique benefits and drawbacks. Graphite is chosen as the anode in most cases. The electrolytes chosen need to be a mixture of a non-aqueous carbonate along with some lithium anion salts. There are numerous types of Li-ion batteries which usually are differentiated by the cathode used; these are separated by numerous factors including sourcing of elements, performance characteristics, safety, and economics.

5) Ultracapacitors (UC) – Ultracapacitors are technically not batteries, but they can store and release charges. As the name suggests, it is based on a regular capacitor, but the design is more efficient, allowing it to store more energy. The main difference is that ultracapacitors use a liquid electrolyte with a porous separator instead of a solid dielectric. Using this method increases the surface area of the electrodes, essentially increasing the amount of power the ultracapacitor can produce. Ultracapacitors can be as much as 100 times more power-dense than their regular counterparts.

Comparison:

These batteries can only be discussed together using multiple criteria to compare their efficacy.

1) Performance Criteria

*Power - Transfer of energy over time

Ah- The amount of electric charge stored

Batteries have a wide spread of values based on their specific chemistries and other conditions. In terms of specific energy and energy density, Li-ion has the highest potential of all though it lags a bit in the power categories. There is a tradeoff depending on the type of vehicle being designed. Since long-range vehicles need more energy storage, they use Li-ion while smaller, lower-range vehicles and hybrids may use alternative chemistries such as NiMH and NaNiCl. This trend is seen in European car markets where smaller cars are traditionally more popular; because of this, these vehicles often don’t use Li-ion batteries and instead go for cheaper alternatives. Li-ion is, however, the undisputed king when it comes to a standard-sized or larger vehicle. As opposed to lead-acid, Li-ion presents a harder choice due to the number of differing, viable chemistries on offer.

Ultracapacitors tend to have extremely high-power densities but miserable energy densities. Ultracapacitors are hence not considered as a singular source of energy but are instead used in tandem with other battery chemistries which are then regulated by appropriate battery management to ensure good energy and power flexibility.

2) Recycling:  

Batteries typically use a variety of elements, and most chemistries have a good mix of expensive or hard-to-source elements; as previously discussed, this makes sourcing a major concern. Another aspect to consider is the proper recycling of batteries. Recycling old, used batteries is a very effective way to alleviate the necessity of mining for these source elements, and this has the added effect of cutting the cost of production once there are enough batteries in circulation. Consequently, there is the added ethical responsibility of ensuring that any battery chemistry that might be toxic to the environment is disposed of safely. Batteries tend to use heavy metals like lead, mercury, cadmium, and nickel which can contaminate soil, air, and water. Thus, long-term sustainability dictates that the issue of recycling be considered carefully.

Lead-acid is a technology that has been used for long enough in the automotive industry that there is almost a complete chain for recycling set up in the United States. Most states have laws in effect that incentivize the recycling of these batteries. Since there are only two types of lead-acid batteries in circulation, the U.S. can recycle up to 98% of lead-acid batteries. The battery is crushed into tiny pieces and the plastic and lead are extracted, purified, and sent back through the supply chain.

Sodium nickel chloride batteries have an advantage over Li-ion in that most of their ingredients are common; some companies have found ways to integrate their recycling into stainless steel smelting forges (which need nickel for the alloy). Additionally, they’ve found suitable uses for the ceramic and salt byproducts which are sold as substitutes for limestone in construction. These are known as pyrometallurgical recycling processes. Since NaNiCl batteries are not primarily used in EVs, they tend to be hard to collect and transport. Europe has made some progress in this respect by mandating the collection of spent batteries in most such uses.

Nickel metal hydride (NiMH) batteries, like sodium nickel chloride, are also extensively easier to recycle as they have remained almost the same for several years, enabling their recycling processes to be similar. Numerous companies recycle NiMH batteries that are already able to handle the number of batteries thrown away every year. Generally, they are harvested by mechanical separation after ensuring the batteries are inert and viable to be recycled.

A detriment to the EV industry is that the battery recycling chains are not set up for most new chemistries. These chemistries are scarcely used in the quantities desired to set up chains to a functioning level, and if they are, they are not nearly as pervasive as the lead-acid recycling network. Li-ion is a battery chemistry that suffers significantly from this. Due to the vast number of different specific chemistries employed and researched over the last fifteen years, it has been hard to set up a singular system to recycle batteries. Although Li-ion is used in consumer electronics (using single chemistry) and stable recycling chains are present for them, the chemistries of EV Li-ion batteries are too different to be recycled in the same way. However, with EV battery chemistries converging to include just a handful of different types for EVs (NMC, NCA, and LMO), recyclers are now finding it easier to set up chains to handle them. Generally, companies use a mixture of hydrometallurgical processes and mechanical separation to recycle batteries. Though this remains true for nearly all Li-ion batteries, there can still be variations in battery chemistry which make it a more tedious task to set up the exact chemical reactions to extract the maximum necessary elements in the most efficient way. Another restriction facing EV battery recyclers is the fact that most of these batteries are in use for at least 8 to 10 years if not more, which makes EV battery recycling a long-term project.

Apart from secondary recycling companies, manufacturers like Tesla and Rivian are thinking ahead about how to reuse their batteries as secondary grid storage after their lifetime as EV batteries which can provide many more years of viable usage before the batteries need to be retired (and hopefully recycled). For more information about battery second life uses, check out LCF's "Life After Usefulness" blog.

As the EV industry expands, there will be a stabilization in the type of EV battery used, and when that is achieved, recycling can be integrated much more easily and efficiently as it has in the case of lead-acid.

Conclusion

As evidenced over the last two years, Li-ion has become the de-facto chemistry of choice for almost all EV battery manufacturers. While there are many reasons for this, the drop in cost and the potential for that price to drop further is one of the most important factors. Experts have indicated that if the cost of batteries drops below $100/KWh, EVs can become affordable alternatives for the everyday driver (an average under $30,000). This, along with growing infrastructure for charging, has the potential to achieve that target, bringing about a revolutionary change in the auto industry.

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