Li ion capacitor (LIC) has emerged as an exciting approach to synergistically combine low potential Li ion battery electrode with high potential supercapacitor electrode. Although wide cell potential window can be achieved through such coupling, current LICs continue to operate at a deliberately constricted cell potential window (2–3V) due to electrolyte degradation concerns caused by the presence of graphitic structure. Herein, highly stable 4V LIC with high energy and power density was rationally designed with 3D amorphous carbon positive electrode which demonstrated exceptional tolerance to high voltage as compared to graphitic carbon. The as-assembled 4V LIC, coupled with high capacity MnFe2O4/carbon negative electrode, exhibited remarkable capacity retention of 86.5% after cycling for 6000 cycles at 2Ag−1, with ca. 100% coulombic efficiency (indicating minimal electrolyte decomposition), while achieving high energy density of 157Whkg−1 at power density of 200Wkg−1. This work demonstrates the advantages of employing amorphous carbon as compared to more graphitic carbon as positive electrode and thus, serves as a guideline for designing stable 4V LIC with amorphous carbon.