Sacrificial pre-metallation strategy could compensate for the irrevers-ible consumption of metal ions and reduce the potential of anode, thereby elevating the cycle performance as well as open-circuit voltage for full metal ion capacitors (MICs). However, suffered from mas-sive-dosage abuse, exorbitant decomposition potential, and side effects of decomposition residue, the wide applicationof sacrificial approach was restricted. Herein, assisted with density functional theory calculations, strongly coupled interface (M–O–C, M = Li/Na/K) and electron donating group have been put forward to regulate the band gap and highest occupied molecular orbital level of metal oxalate -(M2C2O4), reducing polarization phenomenon and Gibbs free energy required for decomposition, which eventually decrease the practical decomposition potential from 4.50 to 3.95 V. Remarkably, full sodium ion capacitors constituted of commercial materials (activated carbon//hard carbon) could deliver a prominent energy density of 118.2 Wh -kg?1 as well as excellent cycle stability under an ultra-low dosage pre-sodiation reagent of 15–30 wt％ (far less than currently 100 wt％). Noteworthily, decomposition mechanism of sacrificial compound and the relative influence on the system of MICs after pre-metallation were initially revealed by in situ differential electrochemical mass spectrometry, offering in-depth insights for comprehending the function of cathode additives. In addition, this breakthrough has been successfully utilized in high performance lithium/potassium ion capacitors with -Li2C2O4/K2C2O4 as pre-metallation reagent, which will convincingly promote the commercialization of MICs.