This paper present an energy-efficient block-concatenated BCH (BC-BCH) decoder which can achieve superior decoding performance for NAND flash storage systems. To enhance the error-correcting capability, an additional decoding step with single parity-check (SPC) block is newly employed. A novel memory based syndrome updating method effectively improves the energy efficiency as well as the decoding latency. Using the proposed methods, a prototype chip is implemented to decode a (36443, 32768) BC-BCH code in 65nm CMOS process. The proposed decoder provides a decoding throughput of 6.37Gb/s and an efficiency of 2.4pJ/bit, being superior to the state-of-the-art hard-decision decoders for storages.