How are Different Metal Oxalates Influencing Li-Ion-Batteries?

Recycling of the large return volumes of lithium-ion batteries with environmental and economic impact is mandatory. But recycling releases impurities: Not only during crushing but also during leaching, impurities can be introduced and found in the recycled material. These can have a significant impact on performance (lifetime, capacity, …). For this reason, their influence is studied. The electrochemical knowledge gained can be fed into the recycling process so that critical impurities will be eliminated. This closes the recycling cycle.

In this work, the influence of different metal oxalates (formed in part during leaching with oxalic acid) on the calendar aging of lithium-ion batteries and their chemical behavior in the electrolyte is investigated. To study their chemical behaviour, Karl Fischer and HF titration is used. For calendar aging, 3-electrode PAT cells are used, in each of which the electrolyte is mixed with one of the metal oxalates nickel, cobalt, manganese, aluminum and copper in the highest possible concentration. Then they are all formed and stored at elevated temperature and SoC for 28 days. The internal resistance is determined daily to quantify the aging.

It was found that the metal oxalates do not react significantly with the electrolyte without applying a voltage. But if oxygen enters the solution, it probably reacts with the electrolyte to form water, which reacted with the conducting salt to form HF. This explains the stagnation of the water content and the slope of the HF content over time. The results of the calendar aging trend show that with copper or nickel additions the internal resistance increases less rapidly over time. It is postulated that with these additives the conductivity increase. It has been shown that certain additives influence the calendar aging of lithium-ion batteries. Expected impurities from the processes must now be fed into so that their influences can be recorded and recycling can be optimized. In the long term, this increases the useful life of materials.