LiFePO4 battery pack consistency

What is the SOC of a LiFePo 4 battery?

As a matter of fact, most HEVs sustain their LiFePO 4 battery SOC in the range of 40–70% because the bus voltage will be relatively stable as a result of its flat OCV and resistance over the SOC range of 40–70% [8].

What is the capacity of LiFePo 4 cells?

Capacities of 16 commercial power-type LiFePO 4 cells are measured and the results are shown in Fig. 2 a. The maximum capacity is 7.83 Ah, the minimum capacity is 7.35 Ah, and the difference is 0.48 Ah (6%). Cells with the number of 3, 4, 5, 6, 9, 11, 13 and 14 are chosen to compose the small battery pack with the average capacity of 7.6 Ah.

What causes the capacity degradation of LiFePo 4 batteries?

In the Ref. [27], [28], [35], capacity fading mechanisms of LiFePO 4 batteries are deeply investigated and it is proved that the loss of lithium inventory is the major cause of capacity degradation. Based on these references, we believe there is no exception for the battery modules in this paper.

Is there cell SoC inconsistency for LiFePo 4 cells in HEVs?

Due to the demanding conditions in HEV and flat OCV of the LiFePO 4 cells, little literature has reported the inconsistency of the LiFePO 4 cells in HEV. This paper first explores characteristics of LiFePO 4 cells in HEVs and reveals that identification of cell SOC inconsistency for LiFePO 4 battery packs in HEVs is extremely difficult.

What is power-type graphite/LiFePo 4 battery?

Power-type Graphite/LiFePO 4 battery is becoming one of most promising batteries as the auxiliary power source for HEV owning to its favorable performances in power density, energy density, lifespan and safety [7], [8]. Tens to hundreds of cells are connected in series and parallel to provide sufficient power for HEVs [9], [10], [11].

What is mean-plus-difference model for battery pack?

We propose a Mean-plus-Difference Model (M+D Model) for battery pack. Mean model represents the whole pack and difference model investigates inconsistency. OCV differences are estimated using cell difference model for LiFePO 4 pack. SOC strategy is proposed to identify SOC inconsistency by lowering pack SOC in HEV.