If I simply use class apa
instead of article
I can compile the code and bib entry without error message.
Try the following MWE (package filecontents
is only used to get a compiling MWE with TeX code and bib file):
\RequirePackage{filecontents}
\begin{filecontents}{\jobname.bib}
@article{velikonja2015asymmetric,
title={On asymmetric shape of electric double layer capacitance curve},
author={Velikonja, Alja{\v{z}} and Kralj-Igli{\v{c}}, Veronika and
Igli{\v{c}}, Ale{\v{s}}},
journal={Int. J. Electrochem. Sci},
volume={10},
pages={1--7},
year={2015}
}
\end{filecontents}
\documentclass{apa} % article
\title{Demo Bibtex}
\author{John Smith}
\begin{document}
\maketitle
Some claim \cite{velikonja2015asymmetric}.
\bibliographystyle{apacite}
\bibliography{\jobname}
\end{document}
and the resulting pdf:

EDIT:
With class report
and biblatex
with biber
:
\RequirePackage{filecontents}
\begin{filecontents}{\jobname.bib}
@article{velikonja2015asymmetric,
title={On asymmetric shape of electric double layer capacitance curve},
author={Velikonja, Alja{\v{z}} and Kralj-Igli{\v{c}}, Veronika and
Igli{\v{c}}, Ale{\v{s}}},
journal={Int. J. Electrochem. Sci},
volume={10},
pages={1--7},
year={2015},
}
\end{filecontents}
\documentclass{report} % article
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[english]{babel}
\usepackage{csquotes}
\usepackage[%
backend=biber,
style = authoryear,
]{biblatex}
\addbibresource{\jobname.bib}
\title{Demo Bibtex}
\author{John Smith}
\begin{document}
\maketitle
Some claim \cite{velikonja2015asymmetric}.
\printbibliography
\end{document}
and the result:
