Safer battery enclosures may be one solution to the issues plaguing lithium-ion batteries.
The recently released data from Samsung regarding the fires associated with the Galaxy Note 7, indicate that the battery design appears to be the primary case of the fires. This is another instance in a string of lithium-ion (Li+) battery issues over the past decade.
The problem is that no matter how well you design a Li+ cell and battery pack, there will always be some small statistical chance that a cell will fail and trigger a fire. The chance increases exponentially if there is physical damage to the battery, as in the case of the Tesla electric car fires.
The issue arises from the very chemistry of the battery. The most common chemistry is lithium-cobalt-oxide, which contains a flammable electrode and reactive substance under pressure. When a cell is damaged or the cell overheats, there is potential for fire. Once one cell catches fire, the fire can spread to other cells causing a chain reaction called thermal runaway propagation (TRP).
Despite the dangers of Li+, the use of these batteries continues to spread unabated into other applications ranging from hover boards to cars to home energy storage and even airplanes. The reason for vendors choose Li+ is that is has a high energy density and life cycle charge durability, as well as low self-discharge rate and little if any memory effects.
In many cases, such as the Tesla solutions for cars and home storage, the battery cells are incased in liquid. So, if any cell is damaged and catches fire, the liquid prevents TRP by preventing the spread to other cells. While Tesla cites very low statistics on the potential cell failures (one in 50 million), third party data is not available.
NASA also experimented with a machined aluminum battery carriers for replacing its current battery technology with Li+ used in everything from spacesuits to space craft. The individual aluminum holes physically separate the battery cells. However, the aluminum solution is heavy and does meet NASA’s goals of a 200Wh/kg.
NASA’s LLB2 machined-aluminum battery pack. (Image: NASA)
NASA is now working with KULR Technology to develop a more compact and equally effective battery pack solution based on carbon fiber carriers. This new carrier uses 0.2mm to 0.5mm carbon fibers arranged through a proprietary process onto a flexible substrate with a velvet-like material. This material is then wrapped around a polycarbonate mold for the battery cells and infused with water.
Once molds are assembled and sealed, the solution forms a vaporizing heat sink. When a cell fails, the combination of the water and carbon fiber distribute and neutralize the short burst of heat from the moment the cell catches fire and prevents TPR to adjoining cells.
As with any battery pack experiencing a damaged cell, it would need to be replaced, but the potential damage to other cells and the rest of the system are mitigated. The net result is a safe and lightweight dense battery pack solution for space applications.
KULR Technology’s LiB-TRS battery enclosure. (Image KULR)
The same system being developed for space applications could be adapted to uses such as personal transportation devices and renewable energy storage. This is not a complete solution to the Li+ battery flammability issue, but it is a unique solution for creating a safer battery pack.
It is doubtful that the industry is going to move away from Li+ batteries anytime soon. So, safer battery enclosures may be one solution to the issues plaguing these batteries.
--Jim McGregor is founder and principal analyst of Tirias Research.