Batterieforscher 💥 So altern AKKUS kaum noch! Aus Obduktion lernen! Prof. Waldmann | Geladen Podcast

The introduction highlights that battery cells often age much faster than manufacturers claim. Researchers at ZSW open thousands of cells to understand the reasons for this aging, identifying mechanisms like lithium plating and recently, sodium plating in sodium-ion cells, especially at low temperatures.

Professor Thomas Waldmann explains that battery capacity decreases over time due to chemical reactions, such as lithium ions being trapped and becoming unavailable for charging/discharging. Key mechanisms include lithium metal deposition (lithium plating/dendrite growth) on the anode and the continuous growth of a film on the anode. These irreversible processes consume lithium ions, leading to capacity loss.

Batteries experience calendar aging even when not in use, influenced by storage conditions like temperature and state of charge. While aging cannot be completely stopped, it can be significantly slowed down. A battery generally reaches its 'end of life' when its capacity drops to 70-80%, though it can often be repurposed for 'second life' applications, such as stationary storage units, as demonstrated by E-Netz Südhessen with used EV batteries.

High temperatures accelerate unwanted chemical reactions in batteries, leading to issues like increased film growth on the anode or gas formation, which can damage the cell. While brief exposure to high temperatures might not be problematic, prolonged exposure can cause irreversible damage. Once a battery's capacity is lost due to high temperatures, it cannot be recovered.

Fast charging generally causes faster battery aging, though modern battery management systems (BMS) in EVs mitigate this by regulating charging speed and temperature. Pre-heating in winter reduces the negative impact of cold. For home storage systems, low temperatures can trigger lithium metal deposition on the anode, causing aging. Placing batteries near a warm house wall can be beneficial, but adhering to manufacturer guidelines on ambient temperature is crucial. Storage in a cool cellar (15-20°C) is ideal for battery longevity. For safety, LFP batteries can be stored in basements.

Storing batteries fully charged (100%) significantly accelerates aging. A medium state of charge is optimal, while full discharge can lead to harmful deep discharge. Lower temperatures during storage are better, but extreme cold (like a freezer) should be avoided. If a battery has been stored cold, it should be brought to room temperature for a few hours before recharging. For devices with programmable BMS, charging only to 90% and using slower charging rates (e.g., 5-10 hours instead of 0.5-1 hour) can considerably extend battery life.

Cell design, including anode, cathode, electrolyte, and separator, significantly influences aging. Anode aging, often composed of graphite or silicon-graphite, is common. The quality of the solid electrolyte interphase (SEI) film, formed during initial cycles, is critical. Researchers found that in some silicon-graphite anodes, silicon degrades, reducing capacity. In cylindrical cells, winding deformation can occur, especially near current collector welds. Tesla's tabless design helps prevent these deformations.

Cylindrical, pouch, and prismatic cell formats don't inherently age faster or slower; aging depends more on electrode materials and cell chemistry. Different applications dictate unique aging profiles: smartphones, used daily, experience significant cyclic aging; garden tools, used weekly, age slower; EVs primarily experience calendar aging while parked, with cyclic aging during charging or dynamic driving; and electric trucks, used continuously, see more cyclic aging. Recent studies suggest dynamic driving in EVs might paradoxically reduce aging, a topic requiring further research.

ZSW's team performs 'post-mortem' analysis, opening battery cells to understand why they've aged or failed. By comparing aged cells to new ones, they identify aging mechanisms through chemical and analytical methods. They can determine the cause of cell failure, including accident cases, by examining components like anodes, cathodes, separators, and electrolytes. Techniques like scanning electron microscopy reveal structural changes and element migration, such as manganese from the cathode depositing on the anode, a common aging mechanism.

In commercial lithium-ion cells, the primary aging mechanisms are lithium plating (at low temperatures) and SEI growth (at high temperatures). Lithium metal reacts with the electrolyte, losing cyclizable lithium, while SEI growth on graphite particles causes capacity loss. For newer sodium-ion cells, researchers have observed similar sodium plating, particularly at low temperatures. Early commercial sodium-ion cells tested showed significantly shorter lifespans than advertised (80 cycles versus several thousand), highlighting ongoing development needs, despite the innovative nature of Chinese manufacturers in bringing these technologies to market.