try this patterns
1. using plain html tag
<div class="swiper-slide fit slide-1" data-pages-bg-image="assets/images/banner_1.jpg">
2. using content_tag
if your ruby version greater than 2.3
<%= content_tag(:div, "blah blah", 'data-pages-bg-image' => "asets/images/banner_1.jpg", class: "swiper-slide fit slide-1") %>
or not (1.9 etc)
<%= content_tag(:div, 'blah blah', "data-pages-bg-image" => "assets/images/banner_1.jpg" :class => "swiper-slide fit slide-1") %>
example)
<section id="tabs">
<ul>
<li><%= content_tag(:a, "text", :href=> "#", :data => { :flights => "6" } ) %></li>
<li><%= content_tag(:a, "text", :href=> "#", :data => { :flights => "5" } ) %></li>
<li><%= content_tag(:a, "text", :href=> "#", :data => { :flights => "5" } ) %></li>
</ul>
</section>