Effect of negative/positive capacity ratio on the rate and cycling performances of LiFePO4/graphite lithium-ion batteries. (October 2018)

• Record Type: Journal Article
• Authors: Abe, Yusuke; Kumagai, Seiji
• Is Part Of: Journal of energy storage. Volume 19(2018)
• Page Start: 96
• Page End: 102
• Publication Date: 2018-10
• Subjects: Lithium ion battery -- N/P ratio -- Cell design -- Capacity balancing -- Lithium iron phosphate -- Graphite; Energy storage -- Periodicals; Energy storage -- Research -- Periodicals; 621.3126
• DOI: 10.1016/j.est.2018.07.012
• Languages: English
• ISSNs: 2352-152X

Abstract

Highlights: Influence of capacity balancing of negative/positive electrode on the performances of LiFePO4 /graphite lithium-ion batteries. Rate and cycling performance of LiFePO4 /graphite cells at N/P ratios of 0.87–1.20. Lower N/P ratio realized superior rate capability from the initial service, but caused larger capacity fading after cycling. Higher N/P ratio initially restricted cell specific capacity, however, possessing the better rate capability after cycling. Abstract: The influence of the capacity ratio of the negative to positive electrode (N/P ratio) on the rate and cycling performances of LiFePO4 /graphite lithium-ion batteries was investigated using 2032 coin-type full and three-electrode cells. LiFePO4 /graphite coin cells were assembled with N/P ratios of 0.87, 1.03 and 1.20, which were adjusted by varying the mass of the graphite negative electrode. Three-electrode cells were also assembled with similar N/P ratios to understand the potential variations of the positive and negative electrodes. The cycling performances of the coin cells were evaluated by repeating the charge-discharge cycle 5000 times (1 C-rate for the 1st–1000th cycle and 2 C-rate for the 1001st–5000th cycle) at cell voltages of 2.5–4.2 V, during which their rate performances were intermittently evaluated (0.1–10 C-rate). Prior to the charge-discharge cycling test, the highest cell specific capacity was obtained from the lowest N/P ratio of 0.87. The coin cell with the highest N/P ratio of 1.20 exhibited the highest capacity retention of 86.5% at 1 or 2 C-rate in the 5000 cycle test. The results obtained using the three-electrode cells showed that the higher N/P ratio elevated the working potential ranges of the positive and negative electrodes. The lower N/P ratio led to deeper Li-ion intercalation for the negative electrode, lowering the potential of both the positive and negative electrodes. The lower N/P ratio was beneficial for achieving full performances from the initial service, but caused larger capacity fading due to the aging by cycling. The higher N/P ratio rather restricted the performances at the initial service, which was useful to prevent the cycling-derived capacity fading. The lowering of rate performance owing to the charge-discharge cycling, particularly at the high current densities of 5 and 10 C-rates, was enhanced by the decrease in the N/P ratio.