Australian battery materials firm Altech Chemicals has released test results that show high purity (99.99%) 4N alumina prevents sodium leaching when used on a lithium-ion battery separator.
Test work by Germany’s Fraunhofer Institute for Ceramic Technologies and Systems (IKTS) showed high purity alumina (HPA) could prevent battery failure modes including thermal runaway, lithium plating on the anode and life cycle reduction.
The team recognised the contamination risk and heightened safety hazard while assessing how easily impurities (predominantly sodium) leach from lower quality alumina (sub-4N) and boehmite into the battery electrolyte solution.
The lithium-ion battery research specialist organisation said the industry had turned to cheaper low-grade alumina and boehmite as a coating material for battery separators as demand has increased.
Separator sheets are mostly coated with thin layers of alumina powder to maintain separator integrity under increasing operating temperatures of modern high-energy lithium-ion batteries
The Fraunhofer test work exposed various commercial grade alumina/boehmite powders to lithium battery electrolyte solution under controlled battery type conditions. This test showed severe sodium leaching and contamination of the organic electrolyte solution from lower grade powders.
The IKTS reported the sodium content in the electrolyte rose from an initial 0.5ppm up to 40 ppm for the test using low quality 3N alumina (99.9%). Similar leaching and electrolyte contamination were observed for the boehmite test (99.7% purity), where the sodium level in the electrolyte jumped 20-fold.
For the 4N alumina (99.99%), almost zero leaching of sodium was observed.
The report stated the lithium-ion battery industry incorrectly assumes that the sodium impurities contained within lower grade alumina and boehmite are “crystal bound”, and simply do not leach out of the alumina – this new test work proves this assumption to be incorrect
Altech managing director, Iggy Tan said: “The ramifications from these research findings for the portion of the lithium-ion battery industry that is transitioning – or is contemplating transitioning – to cheaper alumina substitutes for separator coatings, are set to be profound.
“It is hard to comprehend why lithium-ion battery manufacturers would transition to a lower quality alumina – when this material is introducing sodium into the battery electrolyte and as a result jeopardising battery safety and performance.
“The extra cost of a high purity alumina coating versus the lower grade material is minimal, likely less than $1 per kWh battery capacity or $100 for a typical EV. A small cost impact on the end product to ensure the highest level of battery safety and quality
“It is potentially catastrophic that many in the industry appear to be attempting to move to lower quality material as a battery separator coating. A minimum quality standard for all alumina used as coating material on battery separator sheets should be adopted by industry.”