The high luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN will provide unprecedented instantaneous luminosity of around \(5.0-7.5\times 10^{34}\,\textrm{cm}^{-2}\,\textrm{s}^{-1}\) . The CMS detector is therefore undergoing an extensive Phase-2 upgrade program to prepare for these demanding conditions. In the barrel region of the CMS Electromagnetic Calorimeter (ECAL), the lead tungstate crystals will continue to perform well. The APDs will also continue to be operational, with some increase in noise, which will be mitigated by reducing the temperature at which ECAL is operated. However, the entire readout and trigger electronics will need to be replaced to cope with the harsh conditions and increased trigger latency requirements at the HL-LHC. The upgraded detector will have a 25 times higher readout granularity at hardware trigger level, and a sampling rate increase by a factor of 4. In terms of physics performance, it will match the outstanding energy resolution of the current ECAL detector, while significantly enhancing the time resolution for electrons and photons above 50 GeV.