Failure mechanism and voltage regulation strategy of low N/P ratio lithium iron phosphate battery

Abstract

Generally, the ratio of negative to positive electrode capacity (N/P) of a lithium-ion battery is a vital parameter for stabilizing and adjusting battery performance. Low N/P ratio plays a positive effect in design and use of high energy density batteries. This work further reveals the failure mechanism of commercial lithium iron phosphate battery (LFP) with a low N/P ratio of 1.08. Postmortem analysis indicated that the failure of the battery resulted from the deposition of metallic lithium onto the negative electrode (NE), which makes the SEI film continuously form and damage to result the progressive consumption of electrolytes. The incremental capacity analysis method is applied to visually show the whole process of battery failure. According to the three-electrode test results, we adjusted the cut-off voltage of the full battery from 3.65 V to 3.5 V, which enhance the cut-off potential of NE from −0.1 V to −0.045 V to avoid the lithium metal deposition. Besides, the life and capacity retention of battery increases from 600 cycles (70.24%) to more than 2300 cycles (82.3%) without reducing the initial capacity at 1 C. This work reveals the relationship between cut-off voltage and N/P ratio, and provides guidance for battery design and use.