A method for manufacturing lithium ion cells includes the steps of: 1) coating a collector roll along an unreeling direction thereof to form one or more strip coated areas, two side edges of the coated area each being provided with an uncoated area to form tabs thereon; 2) compacting the coated collector roll and obtaining a compacted collector roll; 3) cutting the compacted collector roll into anode plates/cathode plates having different sizes each having a tab and rounded corners; 4) recombining an anode plate/a cathode plate with a separator; cutting the separator after recombination to form rounded corners at a position corresponding to the rounded corners of the anode plate/cathode plate and further obtain a mono-cell or a half-cell having different sizes; 5) stacking the mono-cells and half-cells into a step preliminary cell; and 6) hot pressing the stacked preliminary cell to form a whole lithium ion cell via bonding of the anode plates/cathode plates with the separator.