On September 15, 2021, it was reported that materials scientists at Nanyang Technological University (NTUSingapore) in Singapore have found a way to prevent internal short circuits, which are a major cause of fires in lithium (Li)-ion batteries.
Professor Jason Xu (right) holds a short-circuited battery in his right hand, along with a lithium-ion battery using NTU's short-circuit protection layer technology. Dr. Linghui Yu (back left) holds the short-circuit protection layer on the battery separator. (NTU Singapore)
Billions of lithium-ion batteries are produced annually for use in massive battery packs in mobile phones, laptops, personal mobile devices, electric vehicles, and airplanes.
Global battery demand will grow, and by 2030 electric vehicles alone will require 2,700 GWh of lithium-ion batteries annually, equivalent to approximately 225 billion mobile phone batteries.
Even with an estimated failure rate of less than one in a million, Singapore still saw 26 fires involving e-bikes and 42 fires involving personal mobile devices in 2020.
In most lithium-ion battery fires, the cause is the buildup of lithium deposits called dendrites (tiny, thread-like tendrils) that are charging as they pass through the separator between the positive (cathode) and negative (anode) electrodes of the battery, causing a short circuit and leading to an uncontrolled chemical fire.
To prevent such short circuits from occurring, Professor Xu Zhichuan and his research team from the School of Materials Science and Engineering invented an additional "anti-short circuit layer" on the diaphragm to prevent any dendrites from reaching the cathode.
“We know that for lithium-ion batteries to function properly, lithium ions must be able to move between the positive and negative electrodes during charge and discharge cycles,” explained Professor Xu, Director of the Energy Storage and Renewable Energy Industry Cluster at the Energy Institute (ERI@N) of Nanyang Technological University. “However, the transfer of lithium ions also means that dendrite formation is unavoidable for current commercial lithium-ion batteries.”
Instead of preventing dendrite formation, we decided to utilize their inherent properties by coating the diaphragm with an additional conductive material, allowing the dendrites to connect to it. Once a dendrite establishes a connection, it will be unable to continue its connection and grow further, thus preventing it from reaching the other side.
Working principle of the "anti-short circuit layer"
A lithium-ion battery can be likened to two bookshelves in a library, facing each other (cathode and anode) and separated by channels (separators). During charging, lithium ions move from the cathode to the anode, and during discharging, the reverse occurs.
Nanjing University's "anti-short shelf" is similar to placing a librarian's desk between two bookshelves in the middle of an aisle—so that when the pile of old books reaches the librarian's desk (dendritic), they stop there, while the librarian continues to interact with them.
Professor Xu's team tested more than 50 different lithium-ion battery components in the laboratory, and no short circuits were detected during the charging phase, even when the batteries were used outside their lifespan.
Short-circuit protection layers are commonly used materials in battery manufacturing and can be easily integrated into current separator manufacturing processes, facilitating adoption and scaling by companies. The team estimates that the cost increase from adopting this technology will be approximately 5% higher than the current production cost of lithium-ion batteries.
The NTU short-circuit protection layer (held by tweezers in the upper right corner) prevents short circuits in lithium-ion batteries. (Source: NTU Singapore)
Kelvin Lim, CEO of Durapower Group, commented independently on the technology's potential, saying, "This technological breakthrough is significant for our business, which currently relies heavily on lithium-ion batteries for electric vehicles and stationary energy storage applications. At the same time, this new invention will help improve the safety of lithium-ion batteries and extend their lifespan, meaning longer driving range for electric vehicles and longer operating time for battery storage solutions."
In his independent statement, Dr. Avishek Kumar, CEO and co-founder of energy storage technology company V-FlowTech, said, "This invention solves the most critical thermal runaway problem in lithium-ion energy storage solutions and will prove to be one of the biggest drivers of the large-scale adoption of lithium-ion energy storage technology."
