# Voltage hysteresis mode
Voltage hysteresis in batteries refers to a phenomenon where the battery’s voltage response to a given charge or discharge level differs based on its history, i.e., whether it is being charged or discharged. This hysteresis creates a "lag" in the voltage, meaning that the voltage does not immediately or accurately reflect the State of Charge (SoC), complicating SoC estimation, particularly in batteries like lithium-ion and nickel-based chemistries.
[State of charge](https://viadean.notion.site/State-of-charge-12b1ae7b9a328070a6adce8f0d456e1d)

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[First-order phase transition for lithium iron phosphate](https://viadean.notion.site/First-order-phase-transition-for-lithium-iron-phosphate-12b1ae7b9a328001ba5ef9f9c0f41e8a)

[Charge direction dependent reaction pathways for silicon](https://viadean.notion.site/Charge-direction-dependent-reaction-pathways-for-silicon-12b1ae7b9a328080ab25e080ccabe45d)

[Graphite anode color](https://viadean.notion.site/Graphite-anode-color-12b1ae7b9a328091b2dedbe83904eaca)

[The path dependency of cell expansion](https://viadean.notion.site/The-path-dependency-of-cell-expansion-12b1ae7b9a3280ed928acf9d59421d7a)

[Rate and power capability](https://viadean.notion.site/Rate-and-power-capability-12b1ae7b9a32801094e1f1e959da250b)

[State estimation approaches](https://viadean.notion.site/State-estimation-approaches-12b1ae7b9a32800eaa90fe7434f84509)

[The Preisach model](https://viadean.notion.site/The-Preisach-model-12b1ae7b9a32808ca479d858ff9378c4)

### Key Concepts in Voltage Hysteresis Mode

1. **Hysteresis Loop**:
- When a battery is charged and discharged, the voltage often follows a different path during each process, forming what’s known as a "hysteresis loop." For example, a battery at a certain SoC may exhibit a higher voltage during charging than during discharging.
- This loop effect means that even with a constant SoC, the measured voltage can vary depending on whether the battery was recently charged or discharged.
2. **Challenges for SoC Estimation**:
- Since many SoC estimation methods rely heavily on voltage measurements (such as Open Circuit Voltage or OCV), voltage hysteresis can introduce errors. Voltage-based SoC algorithms may misinterpret the state due to these differences, causing inaccuracies, particularly in situations requiring high precision, like electric vehicles and energy storage systems.
- Hysteresis makes it difficult for algorithms to rely solely on instantaneous voltage measurements; as a result, more complex methods, like **model-based SoC estimation** (Kalman filtering, neural networks), are often required to account for hysteresis effects.
3. **Mitigation and Adaptation**:
- **Relaxation Time**: One way to deal with voltage hysteresis is to allow the battery to "relax" after charging or discharging, giving its voltage time to stabilize closer to the true open-circuit voltage.
- **Temperature Control**: Temperature fluctuations can exacerbate hysteresis effects, so maintaining a consistent battery temperature can help reduce the impact.
- **Advanced Algorithms**: Some Battery Management Systems (BMS) use adaptive algorithms that model the battery’s hysteresis behavior, adjusting SoC estimates based on the battery's charge-discharge history.

### :point_right:More on [viadean.notion.site](https://viadean.notion.site/Voltage-hysteresis-mode-12a1ae7b9a3280c884dee0a2d5b0773d)