Energy density in lithium-ion batteries refers to the amount of energy stored per unit mass, typically measured in watt-hours per kilogram (Wh/kg). It plays a significant role in the battery’s performance, but it also affects the lifespan of lithium-ion batteries in several ways.
Relationship Between Energy Density and Lifespan
- Higher energy density generally means more energy is packed into the battery’s cells, which can lead to increased stress on the battery materials during charge and discharge cycles. This stress can accelerate degradation of the battery’s internal components, thereby reducing its overall cycle life and lifespan. For example, batteries with very high energy density (~250 Wh/kg) provide maximum specific energy but tend to have shorter cycle lives compared to those operated within a lower usable energy range.
- To prolong battery life, manufacturers and users often limit the usable energy range (depth of discharge or DoD) even if the battery has a high energy density. For instance, electric vehicle (EV) batteries typically operate between 85% charge and 25% discharge, effectively using about 60% of their energy capacity. This strategy reduces stress on the battery and extends lifespan, but it means the full high energy density capability is not fully utilized.
- Cycle life inversely correlates with energy density stress factors. Lithium-ion batteries with very high energy densities (around 250 Wh/kg) may last for fewer cycles (often 500 to 1,500 full charge-discharge cycles), while operating within moderated energy ranges (about 150 Wh/kg effective energy) can extend their life to thousands of partial cycles, as seen in lithium iron phosphate (LiFePO4) batteries known for their longevity but typically lower energy density.
- Temperature, charge/discharge rates, and depth of discharge, all impacted by the battery’s energy density and management, influence capacity degradation and internal resistance increase, which ultimately shorten lifespan. Frequent deep discharges or fast charging with high energy density batteries accelerate internal resistance rise and capacity loss.
Summary Table
| Aspect | Effect of High Energy Density | Effect of Lower/Managed Energy Density |
|---|---|---|
| Energy stored (Wh/kg) | Higher (up to ~250 Wh/kg) | Moderate (around 150 Wh/kg effective) |
| Cycle life (full cycles) | Shorter (~500-1,500 cycles) | Longer (up to 3,000-5,000 partial cycles) |
| Depth of discharge (DoD) | Often full or deep discharges reducing lifespan | Limited DoD (e.g., 85%-25%) prolongs lifespan |
| Internal resistance increase | Faster increase, causing performance drop | Slower increase, maintaining performance longer |
| Typical lifespan (years) | 8-10 years (can be shorter if stressed) | Up to 15 years with careful management |
In conclusion, while higher energy density lithium-ion batteries provide greater capacity and longer run times per charge, this comes at the cost of increased stress and faster degradation, resulting in shorter lifespans if not properly managed. Battery systems that moderate energy usage and avoid deep discharge cycles can maximize the lifespan by balancing energy density with durability.
Original article by NenPower, If reposted, please credit the source: https://nenpower.com/blog/how-does-energy-density-affect-the-lifespan-of-lithium-ion-batteries-2/
