Tool Steel Metallurgy Fundamentals for High Volume Battery Component Manufacturing Dies
Powder metallurgy tool steels with cryogenic phase stabilization eliminate edge chipping and cut amortized tooling costs by over eighty percent in battery dies.
Separator Micro-Puncture
Meaning
A localized failure of the insulating barrier between battery electrodes occurs when a sharp object or dendrite penetrates the material. Preventing separator micro-puncture is a primary goal in the design of high-safety cells to avoid internal short circuits. This event can lead to a rapid temperature rise and potential thermal runaway if the energy is not dissipated.
Penetration Resistance
The mechanical strength of the polymer determines its ability to withstand the growth of lithium dendrites. A material with high resistance to separator micro-puncture allows for higher charging speeds without compromising safety. Testing this property involves measuring the force required for a needle to pass through the film.
High puncture strength is often balanced against the need for high porosity.
Failure Sequence
When a breach occurs, the direct contact between the anode and cathode creates a small area of high current density. The heat from this separator micro-puncture can melt the surrounding plastic, expanding the hole and increasing the severity of the short. Modern separators include ceramic coatings to stop the spread of these defects.
Safety Testing
Manufacturers conduct nail penetration tests to simulate a worst-case scenario for a battery pack. If the separator micro-puncture does not result in fire, the design is considered resilient. This evaluation is part of the certification process for cells used in electric vehicles.