Self-discharge screening method for lithium iron phosphate cells

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a self-discharge screening method of lithium iron phosphate cells. The method comprises the followingsteps: discharging a capacity-graded cell to a cut-off voltage; storing for a certain time T1, and testing the open-circuit voltage OCV1 of the battery cell; storing for a certain time T2, and testing the open-circuit voltage OCV2 of the cell; continuously discharging the cell to the cut-off voltage, and testing the discharge capacity C residue of the cell; calculating the voltage drop deltaOCV =OCV1-OCV2 of the cell within the time T2; and if the cell simultaneously satisfies Avg (deltaOCV)-3.8 stdev (deltaOCV) < = deltaOCV < Avg (deltaOCV) + 3.8 stdev (deltaOCV) and 0.05 * nominal capacity< = C residue (0.1 * nominal capacity), determining that the cell is qualified. The qualified cells screened by the method are stored for 60 days, 2mV is taken as a voltage range, and the misjudgmentrate is less than 0.05%.

Description

technical field [0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a self-discharge screening method for lithium iron phosphate batteries. Background technique [0002] Lithium-ion batteries are more and more widely used in mobile phones, power tools and other products. Due to the low voltage and capacity of lithium-ion batteries, multiple lithium-ion batteries must be connected in series to meet the requirements of these tools. This requires that the consistency of these single cells connected in series is very high. [0003] In the lithium battery production process, there are currently two commonly used self-discharge screening methods for lithium iron phosphate batteries: conventional full-charge storage and 0% SOC storage. The conventional full-charge storage method is to charge the formed cell with constant current and constant voltage to full charge, test the open-circuit voltage once, test the open-circuit vol...

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Problems solved by technology

[0004] However, after a certain period of storage, there are still a certain proportion of defective products in the good products obtained by the above two self-discharge screening methods. This proportion is recorded as the misjudgment rate, and the misjudgment rate is usually 0.5% to 3%.

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