Method for grouping lithium secondary battery packs

A method for grouping lithium secondary battery packs, comprising the steps of:

• Step (1):
• charging and discharging batteries for 1-3 cycles, recording a last discharge capacity C0 of each of the batteries, setting a capacity lower limit, and determining the batteries with the C0 thereof not less than the capacity lower limit to be eligible batteries, wherein the capacity lower limit is a minimum eligible capacity defined by industry technology and normally equal to or higher than a rated capacity C5;
• Step (2):
• discharging continuously the batteries with 0.01-0.5 C5 to a discharge cut-off voltage Vd of 2.0-3.0V so as to discharge the batteries to a power empty state;
• Step (3):
• storing the batteries processed in Step (2) for time t1 in an environment with a temperature ranging between 20-50° C., and measuring and recording a battery voltage V1 of each of the batteries after being stored;
• storing continuously the batteries for time t2 in the environment with the temperature ranging between 20-50° C., and measuring a battery voltage V2 of each of the batteries after being stored, calculating a voltage difference ΔV=V2-V1, and setting a range of ΔV to be from −20mV to 10mV, wherein t1 ranges from 1 to 48 hours and t2 ranges from 24-240 hours;
• Step (4):
• grouping the eligible batteries in Step (3) into a plurality of battery packs each including a specified number of series batteries according to a certain capacity grouping standard, and welding each of the battery packs to form a battery assembly, wherein a capacity difference of the batteries in one of the battery packs is not greater than 5% of the rated capacity C5.

A method for grouping lithium secondary battery packs, comprising the steps of:

• Step (1):
• charging and discharging batteries for 2-3 cycles, recording a second last discharge capacity C0 of each of the batteries, setting a capacity lower limit, and determining the batteries with the C0 thereof not less than the capacity lower limit to be eligible batteries, wherein the capacity lower limit is a minimum eligible capacity defined by industry technology and normally equal to or higher than a rated capacity C5, and wherein a last discharge capacity is controlled to be 90-99.9% of the rated capacity C5 so that a remaining capacity of the batteries is 0.1-10% of the rated capacity C5 to make the batteries in a low-charged state;
• Step (2):
• storing the batteries processed in Step (1) for time t1 in an environment with a temperature ranging between 20-50° C., and measuring and recording a battery voltage V1 of each of the batteries after being stored;
• storing continuously the batteries for time t2 in the environment with the temperature ranging between 20-50° C., and measuring a battery voltage V2 of each of the batteries after being stored, calculating a voltage difference AV=V2-V1, and setting a range of AV to be from −20mV to 10mV, wherein t1 ranges from 1 to 48 hours and t2 ranges from 24-240 hours;
• Step (3):
• grouping the eligible batteries in Step (2) into a plurality of battery packs each including a specified number of series batteries according to a certain capacity grouping standard, and welding each of the battery packs to form a battery assembly, wherein a capacity difference of the batteries in one of the battery packs is not greater than 5% of the rated capacity C5.