An on-line floating charge method for lithium ion battery pack

Abstract

The present application relates to a kind of lithium ion battery pack online floating charge method, comprising the following contents: when lithium battery pack is charged to 100%SOC, the charging voltage of charging equipment is adjusted to floating voltage V floating;When lithium battery pack is in discharge state, and the SOC of lithium battery pack is less than 90%, the working state of charging equipment is adjusted to constant-current charging to SOC reaches 90%, and then long-term floating is charged with floating voltage V floatingThe present application is measured and calibrated floating voltage V floating by long-time standing voltage under multiple working conditions, avoids the problems such as battery overcharge, positive material phase transition, internal resistance rise caused by traditional fixed high-voltage floating, greatly reduces the damage of long-term floating to battery, effectively improves the cycle service life of lithium ion battery pack in online scene such as UPS, base station, standby power supply and the like.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically to an online float charging method for lithium-ion battery packs. Background Technology

[0002] Currently, lithium-ion batteries, as a green energy source, are being used more and more widely in fields such as new energy vehicles, mining energy, and home energy storage. Online charging and discharging refers to a continuous, interconnected working state of the lithium battery pack, charging equipment, and load. Under normal circumstances, the charging equipment and lithium battery pack jointly supply power to the load. When the charging equipment stops or the load power is much greater than the rated power of the charging equipment, the lithium battery pack can switch to supply power to the load with zero delay; when the load is disconnected or the load power is much less than the rated power of the charging equipment, the lithium battery pack stores energy through the charging equipment, preparing for subsequent discharge under operating conditions; the lithium battery pack itself is also in a state that can be switched at any time, such as charging, float charging, and discharging.

[0003] Unlike the commonly used charge / discharge states of lithium battery packs, online charge / discharge states can damage the lifespan of lithium battery packs due to prolonged float charging. In fields such as UPS power supplies and base station power supplies, because it is impossible to determine or accurately measure whether the energy during the charging phase is sufficient for the next discharge cycle, or to store as much energy as possible during charging to meet the time requirements of the next discharge cycle, or to compensate for capacity loss caused by self-discharge after the battery is fully charged, the float charging phase of lithium battery packs is generally performed for a long time using a constant voltage, low current mode after the lithium battery pack is fully charged. However, prolonged float charging can cause phase changes in the positive electrode material of the lithium battery and reduce its stability, increase the battery's internal resistance, change the battery's terminal structure, and reduce the permeability of the separator, thus affecting the battery's lifespan. Taking a lithium iron phosphate single cell as an example, the traditional float charging voltage is 3.4V~3.45V, slightly higher than the open circuit voltage of 3.333V~3.38V after full charge, but lower than the dynamic voltage of 3.65V when the single cell is charged to its cutoff point. Tests showed that after a single battery cell was fully charged and float-charged at 3.4V for an extended period of time, after one month of continuous and uninterrupted charging, the usable capacity of the battery had decreased to less than 80% of its original capacity. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned technical problems existing in the prior art and to provide an online float charging method for lithium-ion battery packs.

[0005] To address the shortcomings of the aforementioned technical problems, the present invention provides an online float charging method for lithium-ion battery packs, comprising the following: When the lithium battery pack is charged to 100% SOC, adjust the charging voltage of the charging equipment to the float charging voltage V. 浮 ; When the lithium battery pack is in a discharged state and its SOC is below 90%, adjust the charging equipment to constant current charging until the SOC reaches 90%, and then charge it with a float charging voltage V. 浮 Constant pressure long-term float charging.

[0006] As a further optimization of the online float charging method for lithium-ion battery packs of the present invention: the battery pack is a lithium iron phosphate battery pack.

[0007] As a further optimization of the online float charging method for lithium-ion battery packs of the present invention: the constant current charging current is 1C.

[0008] As a further optimization of the online float charging method for lithium-ion battery packs of the present invention: the V 浮 Obtained by the following method: The lithium-ion battery pack was charged at 1C to 90% SOC, and the voltage V1 was collected after 30 seconds of rest and the voltage V2 was collected after 5430 seconds of rest. The lithium-ion battery pack was charged to 90% SOC at 6.6kW, and the voltage V3 was collected after 30 seconds of rest and the voltage V4 was collected after 5430 seconds of rest. Choose the lowest voltage V among V1, V2, V3, and V4. min and the highest voltage V max ; Calculate V 浮 V 浮 = (V min +V max ) / 2.

[0009] As a further optimization of the online float charging method for lithium-ion battery packs of the present invention: when collecting V1, V2, V3, and V4, the ambient temperature of the lithium battery pack is controlled at 25±2℃.

[0010] As a further optimization of the online float charging method for lithium-ion battery packs of the present invention: through V 浮 When charging a lithium-ion battery pack, if the highest single-cell voltage at the end of the final charge exceeds 3.5V, the total float charge voltage should be readjusted.

[0011] As a further optimization of the online float charging method for lithium-ion battery packs of the present invention, the specific method for readjusting the total float charging voltage is as follows: the total float charging voltage is gradually reduced in steps of 0.01-0.03V, and the highest single-cell voltage at the end of the charging process is detected again after each reduction, until the highest single-cell voltage is no higher than 3.5V, and this voltage value is taken as the new float charging voltage V. 浮 .

[0012] As a further optimization of the online float charging method for lithium-ion battery packs of the present invention: the charging device is a programmable DC power supply or a charger.

[0013] The present invention has the following beneficial effects: 1. This invention calibrates the float charge voltage V through multi-condition, long-term static voltage measurement. 浮 This avoids problems such as battery overcharging, positive electrode material phase change, and increased internal resistance caused by traditional fixed high-voltage float charging, significantly reducing the damage to batteries caused by long-term float charging and effectively improving the cycle life of lithium-ion battery packs in online scenarios such as UPS, base stations, and backup power supplies.

[0014] 2. This invention uses SOC as the core threshold for automatic switching: when fully charged, it enters constant voltage float charging; when discharged to below 90% SOC, it automatically starts 1C high-current fast charging; after quickly recovering to 90% SOC, it returns to float charging. This ensures sufficient reserve capacity and avoids prolonged high-stress charging, achieving seamless switching between charging, float charging, and discharging. Attached Figure Description

[0015] Figure 1 This is the circuit diagram of a battery pack float charge test platform. Detailed Implementation

[0016] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0017] Using a 20Ah, 36-cell lithium iron phosphate battery pack as the test object, and under the conditions of an ambient temperature of 25±2℃ and a programmable DC power supply as the charging equipment, the online float charging method of this lithium-ion battery pack is described in detail (circuit diagram of the test platform is shown in Figure 1). Figure 1 (As shown).

[0018] Calibration process of float charge voltage Vfloat: Voltage was collected after 1C charging to 90% SOC.

[0019] The battery pack was charged to 90% SOC using a constant current of 1C (20A), then charging was stopped and the battery was left to stand. The data collected are as follows: After 30 seconds of rest, the battery pack terminal voltage V1 was measured to be 121.66V.

[0020] After 5430 seconds of rest, the battery pack terminal voltage V2 was measured to be 120.27V.

[0021] 2.6.6kW constant power charging to 90% SOC voltage acquisition.

[0022] The battery pack was charged to 90% SOC at a constant power of 6.6kW, then charging was stopped and the battery was left to stand. The data collected are as follows: After 30 seconds of rest, the battery pack terminal voltage V3 was measured to be 121.99V.

[0023] After 5430 seconds of rest, the battery pack terminal voltage V4 was measured to be 120.35V.

[0024] Calculate the initial float charge voltage.

[0025] Take the extreme values ​​of the four sets of voltages V1, V2, V3, and V4: Minimum voltage V min =120.27V, highest voltage V max =121.99V.

[0026] Calculate using the formula: V 浮 =(V min +V max ) / 2=(120.27+121.99)÷2=121.13V, simplified to 121V.

[0027] At 90% SOC, using 121V for float charging with a float charging current not exceeding 0.1A, the highest single-cell voltage of the battery pack after 2 hours of float charging is 3.36V, which is lower than 3.5V and requires no adjustment.

[0028] Online float charging control execution process.

[0029] 1. After the fully charged battery pack is fully charged to 100% SOC, the charging equipment immediately adjusts the output voltage to 121V and enters the constant voltage long-term float charging state.

[0030] 2. Discharge triggers fast charging to replenish the battery pack online under load. When the monitored SOC drops to 89% (below 90%), the charging equipment automatically switches to 1C (20A) constant current charging to quickly recharge to 90% SOC.

[0031] 3. Once the recharge cycle is complete and the float charging capacity is restored to 90% SOC, the charging device will switch back to 121V constant voltage float charging and remain in online standby mode.

[0032] 4. The cyclic operation system continuously executes closed-loop logic: 100% SOC → constant voltage float charging → discharge to <90% SOC → 1C fast charging back to 90% SOC → constant voltage float charging. The entire charging, float charging, and discharging process can be switched without delay, always maintaining sufficient reserve capacity and low-stress battery operation.

[0033] After implementing this method, the 36-cell battery pack maintained stable cell voltage within the range of 3.45V to 3.49V under long-term online float charging, without overcharging, polarization accumulation, or excessive cell voltage difference. After 180 days of continuous online float charging, the battery pack capacity retention rate was ≥95%, far superior to traditional fixed float charging voltage schemes. This effectively avoids problems such as rapid capacity decay and increased internal resistance, significantly extending battery life in online standby scenarios.

[0034] Those skilled in the art can make conventional adjustments to parameters such as charging current, correction step size, and control threshold within the scope of the claims, based on the battery pack capacity, number of series, material, and application scenario. Such modifications do not depart from the essence of the present invention.

Claims

1. A method for online float charging of a lithium-ion battery pack, characterized in that, Includes the following: When the lithium battery pack is charged to 100% SOC, adjust the charging voltage of the charging equipment to the float charging voltage V. 浮 ; When the lithium battery pack is in a discharged state and its SOC is below 90%, adjust the charging equipment to constant current charging until the SOC reaches 90%, and then charge it with a float charging voltage V. 浮 Constant pressure long-term float charging.

2. The online float charging method for a lithium-ion battery pack as described in claim 1, characterized in that, The battery pack is a lithium iron phosphate battery pack.

3. The online float charging method for a lithium-ion battery pack as described in claim 2, characterized in that, The constant current charging current is 1C.

4. The online float charging method for a lithium-ion battery pack as described in claim 2, characterized in that, The V 浮 Obtained by the following method: The lithium-ion battery pack was charged at 1C to 90% SOC, and the voltage V1 was collected after 30 seconds of rest and the voltage V2 was collected after 5430 seconds of rest. The lithium-ion battery pack was charged to 90% SOC at 6.6kW, and the voltage V3 was collected after 30 seconds of rest and the voltage V4 was collected after 5430 seconds of rest. Choose the lowest voltage V among V1, V2, V3, and V4. min and the highest voltage V max ; Calculate V 浮 V 浮 = (V min +V max ) / 2.

5. The online float charging method for a lithium-ion battery pack as described in claim 4, characterized in that, When collecting data for V1, V2, V3, and V4, the ambient temperature of the lithium battery pack was controlled at 25±2℃.

6. The online float charging method for a lithium-ion battery pack as described in claim 4, characterized in that, Through V 浮 When charging a lithium-ion battery pack, if the highest single-cell voltage at the end of the final charge exceeds 3.5V, the total float charge voltage should be readjusted.

7. The online float charging method for a lithium-ion battery pack as described in claim 6, characterized in that, The specific method for readjusting the total float charging voltage is as follows: gradually reduce the total float charging voltage in steps of 0.01-0.03V, and re-detect the highest single-cell voltage at the end of charging after each reduction, until the highest single-cell voltage does not exceed 3.5V, and use this voltage value as the new float charging voltage V. 浮 .

8. The online float charging method for a lithium-ion battery pack as described in claim 1, characterized in that, The charging device is a programmable DC power supply or a charger.

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