The cost of rechargeable lithium-ion batteries used in cell phones, laptops and cars has fallen dramatically over the past 30 years and has been a major driver of the rapid growth of these technologies. But attempts to quantify cost declines have yielded vague and conflicting results, hampering attempts to predict the technology's future or design useful policy and research priorities.

Now, MIT researchers have conducted an exhaustive analysis of the falling prices of these batteries, the dominant rechargeable technology in the world today. The new study looks back at more than 30 years of history, including analyzing the original underlying data sets and documents as much as possible to derive the technology's trajectory.
The researchers found that the cost of these batteries has dropped by 97 percent since they were first commercially available in 1991. The rate of improvement is much faster than many analysts have claimed, and comparable to that of solar photovoltaic panels, which some once considered a special case. The new findings are reported today in the journal Energy and Environmental Science in a paper by MIT postdoc Micah Ziegler and associate professor Jessika Trancik.

Trancik said that while it was clear that the cost of some clean energy technologies, such as solar and wind, had come down significantly, when they started looking at the falling prices of lithium-ion batteries, they saw that there was very big differences. Similar divergences appear in tracing other important aspects of battery development, such as increasing energy density (energy stored within a given volume) and specific energy (energy stored within a given mass).

These trends are so influential in getting us where we are now, and in thinking about what might happen in the future. Trancik, an associate professor at MIT's Institute for Data, Systems, and Society, said. While it is known that falling battery costs have been a boost to the recent increase in electric vehicle sales, it is not clear how large the decline will be. "Through this detailed analysis, we were able to confirm that lithium-ion battery technology has improved in terms of cost at a rate comparable to that of solar technology, especially photovoltaic modules, which are often touted as the cornerstone of clean energy innovation," she said. A gold standard.

It may seem odd that there is so much uncertainty and disagreement about how much lithium-ion battery costs have fallen, and what factors are causing it, but in reality, much of the information exists in the form of data that companies hold closely, the researchers said. Hard to get. Most lithium-ion batteries aren't sold directly to consumers -- you can't run to your typical corner drugstore to buy replacement batteries for your iPhone, your PC, or your electric car. Instead, manufacturers buy lithium-ion batteries and use them in electronics and cars. Large companies like Apple or Tesla buy batteries in the millions, or make their own, at prices negotiated or internally accounted for but never publicly disclosed.

In addition to helping drive the ongoing electrification of transportation, further declines in the cost of lithium-ion batteries could increase the use of batteries in stationary applications to compensate for the intermittent supply of clean energy sources such as solar and wind. Both applications could play an important role in helping curb the world's emissions of climate-changing greenhouse gases. I can't overstate the importance of these trends in clean energy innovation in getting us to where we are now, where we're starting to look like we can see rapid electrification of vehicles, we're seeing rapid growth in renewable energy technologies, and of course, coping with There's still a lot to do with climate change, but this is truly a game-changer. Trancik said.

Ziegler noted that the new findings do more than trace the history of battery development, but help guide the future. Combing through all the published literature on lithium-ion battery cost reductions, he found that measures of historical improvement were very different. And in various papers, researchers are using these trends to suggest how to further reduce the cost of lithium-ion technology, or when cost targets can be met. But because the underlying data are so different, the researchers' recommendations can vary widely. Some studies show that for some applications, the cost of lithium-ion batteries won't drop as quickly, while others are much more optimistic. This discrepancy in data ultimately has practical implications for research priorities and the setting of government incentives.

The researchers mined the original sources of the published data, and in some cases found that some of the original data had been used by multiple studies that were later cited as separate sources, or that the original data source had been lost en route. While most studies focus only on cost, Ziegler said, it is clear that such a one-dimensional analysis may underestimate the rate of improvement in lithium-ion technology; in addition to cost, weight and volume are also key factors in automotive and portable electronics. So, the team added a second track to the study, which also analyzed improvements in these parameters.

Lithium-ion batteries were not adopted because they had cheaper battery technology available. Lithium-ion technology has been adopted because it allows you to put portable electronics in your hand, because it allows you to make power tools that last longer and have more power, and it allows us to make power tools that can provide A car with enough mileage.

This broader analysis helps define what's possible in the future, he added. Lithium-ion technology may improve in some applications faster than predicted by just looking at one performance metric. By looking at multiple metrics, you can basically get a clearer picture of the rate of improvement, suggesting that they may improve faster for applications that relax mass and volume constraints.

Trancik added that the new research could play an important role in energy-related policymaking. Published data trends for the few clean technologies whose costs have dropped significantly over time such as wind, solar, and now lithium-ion batteries tend to be cited repeatedly, not only in academic papers but also in policy documents and industry reports, Many important climate policy conclusions are based on these trends. For this reason, it's important to get them right. There really is a need to be careful with the data and up our game across the board when dealing with technical data and tracking these trends.

The cost of batteries determines the price parity of electric vehicles versus combustion-engine vehicles, said Venkat Viswanathan, an associate professor of mechanical engineering at Carnegie Mellon University who was not involved in the work. As such, predicting battery cost declines may be one of the most critical challenges in ensuring an accurate understanding of EV adoption.

Viswanathan added that discovering costs could come down faster than previously thought would enable wider adoption, increase volume, and lead to further cost reductions. .........The datasets curated, analyzed and published in this paper will have a lasting impact on society.