We applied ultrahigh hydraulic pressure to fabricate highly compacted LiFePO4 (LFP) cathode and graphite anode flakes. Scanning electron microscopic characterization confirmed the significant compaction of electrodes without destruction. The highest density of LFP cathode and graphite anode was found to be 3.2 and 2.0 g/cm(3) with 250 MPa loading, respectively. The high-density electrodes were demonstrated to possess better cyclic performance and rate capability. Electro-chemical tests showed that the specific capacity of compacted LFP and graphite at a 2C rate were 140 and 349 mAh/g, respectively. After using these highly compacted electrodes to assemble a LFP/graphite square battery, we obtained a volumetric energy density up to 733 Wh/L.