Summary
- Lithium-ion batteries are commonly used in electric vehicles, with sodium-based batteries also being developed
- Batteries use intercalation to physically stuff charged compounds between material gaps
- Separators keep the anode and cathode separate, allowing charged compounds to move between them
- Battery lifetime is measured in cycles with capacity degradation over time
- Cells should be charged to lower voltages to reduce wear-out and stored at mid charge when not in use
Article
Modern electric vehicle batteries have evolved from lithium-ion batteries, originally used in portable electronics, to sodium-based batteries. These batteries all utilize intercalation, where charged compounds are physically inserted into the structure of other substances. This process allows for chemical transformations to occur in the electrolyte and facilitates the flow of current between the anode and cathode. The use of a separator keeps the anode and cathode apart, preventing direct contact. The construction of lithium cells involves depositing cathode metal oxides on a thin foil conductor and graphite on the anode. Cells are governed by the Arrhenius equation, with temperature and voltage playing crucial roles in accelerating cell aging.
Accelerated lifetime testing is employed to determine battery performance, with temperature and voltage as key variables in cell degradation. Factors such as side reactions, degradation of electrolytes, and internal resistance increase contribute to capacity degradation and reduced battery efficiency over time. Understanding these processes is essential for optimizing cell life and performance. Cells degrade gradually, losing capacity and increasing internal resistance until they are no longer functional. Thermal management is crucial to prevent unwanted reactions within the cell that could lead to thermal runaway or irreversibly damage the cell.
Battery lifetime is measured in cycles, with a typical target of 80% capacity retention per charge/discharge cycle. Electric vehicles rely on the battery’s capacity to determine the vehicle miles traveled per cycle, allowing for direct comparative analysis. Power vs. Energy trade-offs in lithium-ion batteries showcase the balance between energy density and power, with lower-cost batteries typically designed for longer duration and lower power output. Batteries are rated for hour durations to reflect the length of time a storage system can generate at full output before needing recharging.
Matching battery design to intended use is crucial for optimizing performance and cost-effectiveness. Higher power-to-energy ratio batteries have quicker charge and discharge rates, making them more suitable for applications requiring fast energy delivery. Economically, faster storage deployment can help amortize the storage cost more quickly. Understanding the relationship between power, energy, and battery duration can help optimize battery design for specific applications. Overall, understanding the fundamental workings of lithium batteries, including the effects of temperature and voltage on performance, is essential for maximizing their efficiency and longevity in various applications.
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