materializeCSS collapsible active change icon.

You don't need the use javascript for this

delete javascript and use only css

html

<ul class="collapsible" data-collapsible="accordion">
  <li>
      <div class="collapsible-header">
       <i class="material-icons">expand_less</i>First</div>
   </li>
   <li>
      <div class="collapsible-header">
       <i class="material-icons">expand_less</i>Second</div>
   </li>
</ul>

css

  .collapsible li.active i {
  -ms-transform: rotate(180deg); /* IE 9 */
  -webkit-transform: rotate(180deg); /* Chrome, Safari, Opera */
  transform: rotate(180deg);
}

As an addition to Hakan's answer, You can use the collapsible-header class to avoid changing other icons within the collapsible class (accordion content). The CSS code that worked for me is:

CSS

.collapsible-header.active i {
-ms-transform: rotate(180deg); /* IE 9 */
-webkit-transform: rotate(180deg); /* Chrome, Safari, Opera */
transform: rotate(180deg);
}