Spacing in <li> tags with display table-cell

I’ve four li tags and they all contains images in it. Now, I want to show images vertically center and for this I’ve used display: table-cell for all li and on image I’ve used vertical-align middle. But margin isn’t working when I am trying to put spacing between li’s.

Here is the JSFiddle

HTML

<div class="achievements">
<h2>Our <span>Achievements</span></h2>
<ul>
  <li>
      <img src="images/award-1.png">
  </li>
  <li>
      <img src="images/award-2.png">
  </li>
  <li>
      <img src="images/award-3.png">
  </li>
  <li>
      <img src="images/award-4.png">
  </li>
</ul>

</div>

CSS

.achievements ul {
  margin: 0;
  padding: 0;
  list-style: none;
}
.achievements ul li {
  min-width: 304px;
  min-height: 208px;
  vertical-align: middle;
  display: table-cell;
  box-sizing: border-box;
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  box-shadow: 0px 0px 3px #aaa;
  color: #000;
  margin-right: 14px;
  padding-bottom: 32px;
  max-width: 303px;
  background: #fff;
  font-family:'gafata';
  padding-top: 32px;
  line-height: 23px;
  text-align:center;
}
.achievements ul li img {
  vertical-align: middle;
}

solution

Use border-spacing to add spacing between the cells.

In order for this to have an effect on the table, the border-collapse value should be separate (the default value) as opposed to collapse.

Updated Example

.achievements ul {
  margin: 0;
  padding: 0;
  list-style: none;
  display:table;
  border-spacing: 10px;
  border-collapse: separate;
}

If you want to center the table, simply add margin:0 auto. (example)