Formation and capacity grading method of lithium ion battery

The invention provides a formation and capacity grading method of a lithium ion battery. The formation and capacity grading method comprises the following steps of 1) charging the lithium ion battery for 2-3 hours with a current in small flow; 2) allowing the charged lithium ion battery to stand and age at a certain temperature; 3) charging the lithium ion battery to rated voltage with a current in middle flow, forwarding to charge with constant voltage, and ending charging after a cutoff current is reached; 4) allowing the lithium ion battery after charging is completed to stand for 5-30 minutes; and 5) discharging the lithium ion battery with different discharge rates to a cutoff voltage, dividing discharge capacity by charge capacity to obtain initial charge efficiency of each lithium ion battery under the discharge rate so that the average initial charge efficiency of the lithium ion battery under the discharge rate is obtained, the capacity of the lithium ion batteries in mass production under different