Testing has begun on battery additive firm BioSolar’s second batch of commercial-grade prototype 21700 lithium-ion cells that use silicon anodes.
The US firm announced on 14 January that its technology partner Top Battery had begun production and testing of the new cells that incorporate “additional cell design work”.
BioSolar is preparing two different types of commercial grade 21700 prototype cells: the first based on the use of silicon alloy anode material comprised of silicon micro-particles (Si-MP), and the second based on the use of pure silicon anode material comprised of Si nano-particles (Si-NP). The primary difference between the two is that the dimensions of Si-MP particles are much larger than those of Si-NP.
The Korean firm Top Battery is preparing the commercial grade prototype lithium-ion battery cells incorporating silicon anode materials imbedded with BioSolar’s additive technology. The companies signed a joint development agreement in June 2017.
The initial testing at Top Battery is scheduled to be completed in March, with BioSolar anticipating further testing at an unknown date being performed by a manufacturing and development partner (whose names cannot be disclosed) using their own in-house qualification testing and analysis.
Once the tests are completed, the prototype batteries will be sent to potential manufacturing and development partners for in-house qualification testing and analysis.
Dr. David Lee, CEO of BioSolar, told BEST: “The main objective of the second batch design was to narrow the cell-to-cell capacity variation after cell formation. The second batch cell design is very close to that of the first, but adjustments have been made to optimize the capacity and power capability within the validation range through cell engineering.”
He added: “In mid-2019, we completed the testing and analysis needed to obtain key performance metrics related to power and energy capabilities for the first batch of commercial grade prototype lithium-ion batteries. We were pleased to find the power and energy capabilities of the first batch of 21700 cells were closer to meeting end-goal metrics than previously expected for this initial product, but there were sizable cell-to-cell performance variation.
“Therefore, the next step was to narrow the cell-to-cell capacity variation after cell formation which requires additional 21700 cell design work. Narrower cell capacity distribution will allow consistent cell quality during manufacturing.”
The 21700 lithium-ion cells are designed for power tools, but BioSolar intends to use knowledge gained from its R&D to develop batteries for electric vehicles.
Lee said the objectives for the majority of consumer and commercial energy storage applications in high-growth markets depended on the advancement of battery technologies. This clear trend led the company to transition its focus and technology to meet the needs of the electric vehicle category.
Silicon is attracting attention from researchers because of its natural abundance, non-toxicity, and theoretical storage capacity of nearly 4200 mAh/g, around 10 times more than conventional graphite anodes.
However, silicon anodes suffer from large volume expansion and contraction during cycling, which pulverises the material over time and leads to battery failure.