Porsche has filed a new patent with the European Patent Office that describes a method for calculating a lithium-ion battery’s remaining capacity. It takes into account the reversible capacity losses caused by the anode overhang (AOH) effect, which can skew the results of simple capacity measurements. The intended result is improved battery management and longevity.
What Is The Anode Overhang Effect?
The AOH effect is the intentional design of a lithium-ion battery in which a cell’s anode extends beyond the area covered by the cathode, causing an overhang. It’s designed into lithium-ion batteries to avoid cathode overhang, which can cause accelerated aging, increased dendrite growth, and more serious safety concerns, such as spontaneous combustion.
The anode and cathode are thin layers placed on top of each other with a separating layer in between. In mass cell production, it’s difficult to perfectly align these layers. Should the cathode overhang the anode, the aforementioned problems can occur, so battery makers design the AOH effect into the battery to avoid it.
Problems Caused By The AOH Effect
While the AOH effect creates a safer battery, it causes temporary capacity loss, which mimics premature aging, even though the battery remains in good health. These capacity losses are reversible, but current measuring methods don’t compensate for the AOH effect, leading to inaccurate calculation of the remaining capacity.
Porsche’s Solution
Porsche’s patent integrates the charge or discharge current to get an accurate base capacity, and then subtracts the capacity lost to the AOH effect from this value. However, it also takes into account:
- How long the battery has been charged or discharged
- Its temperature
- How much charge there is in the battery
Porsche says that its patent is unique in that its algorithm can correct for reversible capacity losses and integrate factors such as the charging and discharging history, as well as the battery’s age. In this way, the algorithm can more accurately calculate the battery’s rated capacity, despite the skewing AOH effect. This will lead to:
- Better battery management
- An accurate calculation of the remaining capacity
- A longer battery lifespan
- A more precise way to assess battery health
