  We have been developing a high-pressure xenon gas time projection chamber
(TPC) to search for neutrinoless double beta ($0\nu\beta\beta$) decay of
$^{136}$Xe. The unique feature of this TPC is in the detection part of
ionization electrons, called ELCC. ELCC is composed of multiple units, and one
unit covers 48.5 $\mathrm{cm}^2$. A 180 L size prototype detector with 12
units, 672 channels, of ELCC was constructed and operated with 7.6 bar natural
xenon gas to evaluate the performance of the detector at around the Q value of
$^{136}$Xe $0\nu\beta\beta$. The obtained FWHM energy resolution is (0.73 $\pm$
0.11) % at 1836 keV. This corresponds to (0.60 $\pm$ 0.03) % to (0.70 $\pm$
0.21) % of energy resolution at the Q value of $^{136}Xe$ $0\nu\beta\beta$.
This result shows the scalability of the AXEL detector with ELCC while
maintaining high energy resolution. Factors determining the energy resolution
were quantitatively evaluated and the result indicates further improvement is
feasible. Reconstructed track images show distinctive structures at the
endpoint of electron tracks, which will be an important feature to distinguish
$0\nu\beta\beta$ signals from gamma-ray backgrounds.
