Donald Sadoway, a materials scientist at the Massachusetts Institute of Technology, is considered one of the smartest and most creative battery scientists in the world. So admired is Sadoway that, when former Microsoft CEO Bill Gates wanted to learn about batteries, he took Sadoway’s course. Afterwards, he approached Sadoway and the two discussed the topic of how to rethink battery design from a blank page of paper. That discussion led to the founding of Ambri, a startup company that is based on Sadoway’s ideas for how to build a better battery. And at the heart of Ambri is Sadoway’s concept of a high-temperature liquid metal battery whose cathode and anode literally float one on top of each other.
Ambri’s first attempt at a prototype involved the metals antimony and magnesium. The concept worked, but the high melting point of magnesium (650 degrees Celsius) and the relatively high cost of that material made the prototype battery too expensive to compete against lower-cost batteries like lithium ion and lead-acid. So Sadoway and his research team kept working. In a paper just published in the journal Nature, the team released the results of their second prototype, which uses an old standby material of the battery industry: lead.
The battery consists of three basic inputs: lithium salts, lead, and antimony. The lithium serves as the anode, or negative electrode, which holds the energy in storage while the battery is being charged. Alloyed together, the lead and the antimony form the cathode, or positive electrode, which releases electrons during the discharge of the battery. Once the battery is heated so that the alloy mixture and the metallic lithium melt into liquids (which requires a temperature of 253 degrees Celsius), the battery can start cycling through charges and discharges. The lower temperature means that there are fewer parasitic losses during cycling, which makes the battery more efficient (the paper claims a 73% round trip efficiency, which is similar to the efficiency of many flow battery technologies).
More interestingly, Sadoway’s team calculates that the cost of input materials for the battery would be a mere $68 per kWh, which compares favorably to almost every other battery chemistry. Finally, the Nature paper shows that accelerated testing of the battery predicts that, after 10 years of daily 100% cycling, the battery will still have a usable capacity above 85% of the capacity the battery had when it went through its first charge/discharge cycle. In that regard, it compares to accelerated testing of other high quality batteries.
Will Ambri’s new battery take over the market share of the other incumbent battery technologies? It’s not likely. Because the battery needs to be kept at a high temperature, it won’t function well in situations that require maximum flexibility and uncertainty. However, it will be an excellent choice for any application that requires a long-duration and highly consistent charge/discharge cycle. Although that’s a niche of the overall stationary energy storage industry, it could eventually be a large one. Decades from now, when people talk about lead batteries, they might just be referring to Ambri’s molten battery, not their car starter batteries.
Tags: Advanced Batteries, Grid-Tied Energy Storage, Science & Technology, Smart Energy Program
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