Users of lithium-ion battery-powered products have noticed that battery capacity inevitably decreases over time. While the initial battery life was decent, after two years of frequent charge-discharge cycles, it's a completely different story. The good news is that scientists at the U.S. Department of Energy seem to have recently figured out one of the mechanisms causing battery "capacity reduction," and may be able to devise strategies to address this in the future. In a typical lithium-ion rechargeable battery, lithium ions can travel through the electrolyte between the anode and cathode, creating the current that powers the device. Capacity can be simply understood as the volume of lithium ions moving back and forth within the battery (during charging and discharging).
When manganese ions are stripped from the cathode of the battery, they react with the electrolyte near the anode and capture lithium ions.
This study by the U.S. Department of Energy found that the materials that make up the battery electrodes often break down, allowing certain metal ions (specifically manganese) to float freely and travel to the opposite electrode, where they then trap lithium ions.
Over time, more and more lithium ions cannot be used for normal operation (are locked up), and the battery capacity gradually decreases as a result, eventually leading to the inability to continue providing the ideal driving range.
Research paper co-author Daniel Abraham explained, "This is strictly related to the 'management' of manganese on the electrode and the number of 'trapped' lithium ions. However, now that we understand the underlying mechanism, we will find ways to overcome it in the future."
