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The influence of voltage consistency on the serial use of lithium-ion batteries

by:dcfpower     2021-03-16
u003cpu003eu003cpu003eSummary: Test the cycle life of power 18650 single battery under different charging voltage and the over-discharge cycle life of different discharge current. Quantitatively results in the difference in battery SOC in the battery pack, and simulates the inconsistency of the battery pack voltage caused by the self-discharge of a single battery in series use, so that the single battery is over-discharged during the cycle, resulting in the attenuation of the battery pack's cycle life. A three-electrode system was used to measure the potential relationship between the positive and negative electrodes of the real battery during charging and discharging, and the method to improve the battery's overdischarge resistance was analyzed. u003c/pu003eu003cpu003eKeywords: ; Consistency; Overcharge; Over-discharge; Series u003cpu003e The consistency of lithium battery pack is the user's requirement for the battery. In the field of multiple series and parallel, the inconsistency of the battery affects the performance of the battery, and even brings some safety hazards. There are many factors that cause battery inconsistency in multi-series parallel use. There are many reasons for the battery itself, such as inconsistent capacity, inconsistent self-discharge rate, inconsistent internal resistance, and inconsistent life. There are also external reasons, such as different battery heat dissipation environments and different internal resistances between batteries. , And even the detection circuit causes uneven discharge of each way. This article mainly discusses the impact of inconsistent voltage on the parallel use of multiple strings. Inconsistent battery voltage is a problem often encountered in actual use, and voltage is also the most important monitoring parameter of the battery management system. In practical applications, the main causes of battery voltage inconsistency are uneven capacity and battery self-discharge, and battery voltage inconsistency mainly affects the series use of batteries. u003c/pu003eu003c/pu003eu003c/pu003eu003cpu003e The battery used in this test is a cylindrical power 18650 battery. u003c/pu003eu003cpu003eThe overcharge cycle life test of the single battery adopts 2 C constant current charging, respectively at different voltages to a constant voltage until the current is less than 0.05 C, and then discharges to 2.5 V at a constant current of 10 C. The over-discharge cycle life test of the single battery adopts 2 C constant current charging, 4.2 V constant voltage until the current is less than 0.05 C, and then 1 C, 10 C constant current discharge to 1.0, 2.5 V. The cycle life test of the 5S1P combination adopts 2 C constant current to 21.0 V, 21.0 V constant voltage to 0.05 C, and 10 C discharge to 12.5 V. During the test, single-cell battery overcharge and overdischarge protection is not performed. u003c/pu003eu003cpu003eu003cpu003e For the three-electrode test of the battery, the reference electrode uses a nickel wire with a diameter of 1mm. The nickel wire is wrapped around the metal lithium sheet and ground on the glass surface to make the fresh lithium metal tight Wrapped on a nickel wire as a metal lithium reference electrode. After discharging the 18650 battery, remove its battery cover with pliers. Then insert the reference electrode into the center hole of the electrode assembly, and inject electrolyte into the center hole, put on the pre-drilled PP plastic cover, seal it with Parafilm tape, and finally put it in a dry room with a humidity less than 1% Perform a three-electrode system measurement. u003c/pu003eu003c/pu003e Test content: 1.1 The cycle life of a single battery with different charging voltage 1.2 The cycle life of a single battery over-discharge 1.3 The impact of the same voltage on the cycle life of a battery pack 1.4 Real battery three-electrode system charge and dischargeu003cp u003eThis article measured the cycle performance of 18650 lithium-ion batteries discharged to different voltages under different charging voltages and different discharge currents, and artificially caused initial SOC differences. Simulated battery self-discharge resulted in inconsistent series battery pack voltages, and no single cell overcharged Under the protection of the battery, the cycle life of the battery is caused by the over-discharge of a single battery, which causes the battery pack to fail. The test of the three-electrode system of the real battery shows the relationship of the change of the negative electrode potential at the end of discharge, and theoretically analyzes the methods and means to improve the battery's overdischarge resistance. u003cpu003eDownload information [File size: 1.04 MB Download times: Times] Click to download the file: The impact of voltage consistency on the use of lithium-ion batteries in series_Mo Zhibo.pdfu003c/pu003eu003cpu003eu003c/pu003eu003c/pu003e pu003eu003c/pu003e
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