Unfortunately, not in R2018b. (Thank you for providing that information.)
From the documentation:
‘Starting in R2019b, you can specify table variable names that are not valid MATLAB® identifiers. Such variable names can include spaces, non-ASCII characters, and can have any character as the leading character. When you access such a variable name, enclose it quotation marks.’
So if you upgrade to R2019b or later, this will work:
T1 = array2table(rand(4));
T1.Properties.VariableNames = {...
'a_output_efficiency %'...
'b_output_efficiency %'...
'c_efficiency %'...
'd_efficiency %'};
I verified that it does (in R2020a).
.
