Elixir 1.5 is powered by the latest Erlang/OTP 20. One the nice things this brings is iex history persistence.
Enabling shell history
As always, the Elixir hexdocs are a great place to learn more: https://hexdocs.pm/iex/IEx.html#module-shell-history
Older version
For Erlang/OTP 19 and below
Try using https://github.com/ferd/erlang-history
https://elixir-lang.org/blog/2017/07/25/elixir-v1-5-0-released/