> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ionworks.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Mechanical Degradation

> How particle expansion, cracking, and silicon swelling cause mechanical degradation and accelerate capacity fade.

**Mechanical degradation** refers to the structural damage that occurs in batteries due to repeated expansion and contraction during cycling. While [SEI growth](/guide/batteries-101/sei) and [lithium plating](/guide/batteries-101/lithium-plating) are electrochemical processes, mechanical degradation causes physical damage—cracking particles, breaking electrical connections, and deforming cell structures—that leads to capacity loss and resistance increase.

## Volume Changes During Cycling

During each charge and discharge cycle, lithium ions move in and out of the active material particles in each electrode. This insertion and extraction cause the particles to **expand and contract**, introducing mechanical stresses and deformations.

### Material-Dependent Expansion

The extent of this expansion varies depending on the material:

| Material | Volume Change    | Notes                                    |
| -------- | ---------------- | ---------------------------------------- |
| Graphite | Moderate (\~10%) | Standard anode material                  |
| Silicon  | Extreme (\~400%) | High capacity but significant challenges |

<Note>
  Silicon is well known for its extreme expansion—swelling up to four times its
  original volume during lithiation. While silicon offers much higher capacity
  than conventional graphite anodes, this significant volume change presents a
  major challenge, leading to mechanical instability and faster degradation.
</Note>

Understanding the mechanics of batteries is not only important to extend battery life but also to enable new chemistries.

## Types of Mechanical Degradation

The following are some specific examples of how mechanical effects degrade batteries:

<Steps>
  <Step title="Particle Cracking">
    Repeated expansion and contraction creates stress within active material
    particles, leading to surface cracks that expose fresh material to the
    electrolyte, promoting additional SEI formation and increasing resistance.
  </Step>

  <Step title="Binder Cracking">
    Stress can also crack the binder that holds particles together, reducing
    electrical conductivity and causing loss of active material as sections of
    the electrode become electrically isolated.
  </Step>

  <Step title="Jellyroll Collapse">
    In cylindrical cells, the wound electrode assembly (jellyroll) can deform or
    collapse due to internal pressure changes and electrode swelling, leading to
    uneven current distribution and localized degradation.
  </Step>

  <Step title="Electrolyte Pumping">
    Repeated volume changes during cycling can pump electrolyte in and out of
    electrode pores, leading to electrolyte redistribution, dry spots, and
    accelerated local degradation.
  </Step>
</Steps>

## Related Topics

* [Degradation Overview](/guide/batteries-101/degradation)—how mechanical effects contribute to LAM
* [SEI Growth](/guide/batteries-101/sei)—accelerated by particle cracking exposing fresh surfaces
* [Lithium Plating](/guide/batteries-101/lithium-plating)—another major degradation mechanism
* [Electrode Essentials](/guide/batteries-101/electrode-essentials)—electrode materials and their properties
* [State of Health](/guide/batteries-101/state-of-health)—tracking capacity fade from active material loss