What are the storage methods of lithium-ion battery?

The study assesses the cylindrical 9Ah LiFePO4 graphite battery, studies the variation of battery capacity, voltage and a-c resistance, etc. under condition of 55/45/23 ℃ and - 10 ℃ during and after storage period. And it is emphatically tested that under 45/23 ℃, the parameter changes of battery d-c resistance, power capacity, constant current inflow ratio and coulomb/ability effectiveness before and after storage period. And it is also analyzed how these parameters affect the performance of the vehicle battery pack, coming up with a storage method of the LiFePO4 graphite battery.

Lifepo4 test with cylindrical type 32131 aluminum shell lithium iron phosphate graphite battery as the research object, the rated capacity of 9 ah, positive and negative active material of lifepo4 lithium iron phosphate, artificial graphite respectively.45/55 ℃ storage use DHP200 type electric heating constant temperature incubator; Using low temperature refrigerator at low temperature; Electrical test equipment for CT - 3008 - w - 5 v100a - TF test tankan internal resistance test equipment for HIOKI3554 battery internal resistance tester, AC1kHz.

Battery storage experiment No.1

(1) select 60 or more monomer battery, at room temperature, 4500 ma (0.5 C) current charge and discharge cycle within the range of 3.65 ~ 2 v 3 weeks, before the test cell capacity value, * SOC state at 100%, 50% and 100% respectively (each SOC20 battery only) end, the capacity to achieve stability, shelved after 15 h, after measuring the voltage and ac impedance data under test;

(2) select 4 only 100%, 50%, 0% respectively put battery SOC state only a total of 12 people 55 ℃ in the oven for 28 days. Select 4 only 100%, 50%, 0% respectively battery SOC state only a total of 12 in 45 ℃ oven for 28 days. Select 4 only 100%, 50%, 0% respectively battery SOC state only a total of 12 in 23 ℃ air conditioning room for 28 days. Select 4 only 100%, 50%, 0% respectively put battery SOC state only a total of 12 people - 10 ℃ refrigerator for 28 days. Put aside in the process, every 7 days for these battery internal resistance and voltage test;

(3) after the shelve, battery test cabinet, at room temperature, 4500 ma (0.5 C) current put charging cycles within the range of 3.65 ~ 2 v 3 weeks, after storage battery capacity.

Data and discussion: experiment No.1- the variation of battery voltage, internal resistance, capacity in storage period of 28 days

In figure 1 shows the battery storage experiment voltage (open circuit voltage) changes during the 28 days, from figure 1 shows the stored procedure under different temperature, different state of SOC in the open circuit voltage change is not obvious, the consistency of * is under 50% SOC state, is 0% SOC state change *.This with lifepo4 battery lithium iron phosphate graphite system in the condition of different SOC has a lot to do with the polarization of, generally, the series in the empty battery that is 0% when the SOC polarization *, SOC polarization * 50% smaller. From figure 1 0% SOC voltage change of the relationship is also visible at different temperatures, temperature is advantageous to the battery quickly reach a steady state after the polarization. Using this principle, the whole car model equipping the battery group, by heating, fast the polarization state of the battery.

Ac impedance changes in the process of experimental battery storage 28 days as shown in figure 2, from figure 2 shows, ac impedance test value decreases with the increase of temperature, this is due to the higher the temperature, battery inside the components of conductive ability is stronger. But after storage, then return to a normal temperature test, all battery internal resistance were similar, but different SOC, storage battery after a-c internal resistance under the different temperature was more obvious.45/55 ℃ high temperature, 100% of SOC conditions after storage battery internal resistance increases significantly bigger, this is because after high temperature and high SOC storage batteries lifepo4 / lithium iron phosphate graphite system in SEI thickening on the surface of the graphite anode, electrolyte LiPF6 trace decomposition, the SEI components formed large impedance of inorganic salt such as LiF, etc.

In chart 1, it shows the parameter changes of battery capacity after 28 days storage. From the data, it is shown that compared to the high SOC, it is more beneficial to capacity in low SOC. In addition to some capacity loss in the low temperature of 0% SOC, - 10 ℃, in other 0% SOC, the battery capacity has a certain degree of increase. The emergence of this phenomenon may be because after storage, the anode material particle cracks and forms a new interface, to have activity of lithium-ion de-intercalation. In fact, this phenomenon also appears in some battery having circulation directly without storage. In the initial few weeks cycle process, capacity is also increasing.

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