Novel method for activating zero-voltage lithium iron phosphate cell

Abstract

The invention discloses a novel method for activating a zero-voltage lithium iron phosphate cell, and relates to the technical field of lithium ion batteries, and the method comprises the following steps: S1, pretreating the zero-voltage lithium iron phosphate cell; s2, pre-charging the pre-processed zero-voltage battery cell by adopting pulse micro-current; s3, carrying out constant current-constant voltage segmented charging on the lithium iron phosphate battery core after the pulse type micro-current pre-charging is finished; s4, after the constant current-constant voltage segmented charging is finished, carrying out activating treatment on the lithium iron phosphate cell; s5, secondary charging is conducted on the activated lithium iron phosphate battery cell, and performance testing is conducted on the charged lithium iron phosphate battery cell. Pulse micro-current is adopted for pre-charging, on the premise that the internal structure of the battery is not damaged, a battery electrode material can be slowly activated, the damaged structure can be repaired, and the performance of the lithium iron phosphate battery cell can be effectively improved. Compared with a traditional constant-current charging method, impact of large current on the battery is effectively avoided, and the safety of the activation process is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a novel method for activating a zero-voltage lithium iron phosphate battery cell. Background Art

[0002] During the production, transportation, use, and storage of lithium iron phosphate batteries, the cell voltage may drop to zero. This can occur for a variety of reasons, including internal short circuits, overdischarge, and self-discharge from long-term storage. Failure to effectively activate zero-voltage lithium iron phosphate cells not only wastes resources but also compromises the overall performance and safety of the battery system. The incorporation of a large number of zero-voltage cells into a battery module can lead to voltage imbalance, reducing the battery pack's energy density and cycle life, and potentially even causing safety incidents.

[0003] Currently, the main activation methods for zero-voltage lithium iron phosphate batteries include constant current charging, constant voltage charging, and a combination of the two. However, these methods have many shortcomings. When activating zero-voltage batteries, the constant current charging method can easily damage the internal structure of the battery due to the excessive initial current, resulting in increased internal resistance, accelerated capacity decay, and even safety issues such as thermal runaway. Although the constant voltage charging method is relatively mild, the activation time is too long, the efficiency is low, and it is difficult to fully restore the performance of some deeply discharged zero-voltage batteries. In addition, most existing activation methods do not fully consider the chemical reactions and state changes within the battery, lack precise control over the activation process, and cannot perform personalized activation operations based on the actual conditions of the battery.

[0004] Several patents and research efforts are currently underway to improve the activation of zero-voltage (ZV) cells. For example, some patents propose adding specific additives during the charging process, but these additives can introduce new impurities, potentially impacting the battery's long-term stability. Other studies have attempted to improve activation efficiency by optimizing the charging curve, but these efforts have been less than ideal. Therefore, a novel method for activating ZV lithium iron phosphate (LiFePO4) cells has been proposed. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems in the prior art and to propose a novel method for activating zero-voltage lithium iron phosphate batteries.

[0006] A novel method for activating a zero-voltage lithium iron phosphate battery cell comprises the following steps:

[0007] S1. Pre-treating the zero-voltage lithium iron phosphate battery cell;

[0008] S2, pre-charging the pre-treated zero-voltage battery cell with a pulsed micro-current;

[0009] S3, performing constant current-constant voltage segmented charging on the lithium iron phosphate battery cell after the pulsed micro-current pre-charging is completed;

[0010] S4. Recharge the lithium iron phosphate battery cell and perform a performance test on the lithium iron phosphate battery cell after charging.

[0011] Preferably, in step S1, pre-processing the zero-voltage lithium iron phosphate battery cells includes: using high-precision battery testing equipment to measure the open circuit voltage, internal resistance and temperature of the lithium iron phosphate battery cells, and using non-destructive testing technology to check whether there are obvious short circuits, open circuits or other physical damages inside the lithium iron phosphate battery cells, eliminating the lithium iron phosphate battery cells detected to have severe physical damage, and placing the qualified zero-voltage lithium iron phosphate battery cells in a constant temperature environment to ensure that the chemical reaction inside the battery proceeds stably.

[0012] Preferably, in step S2, pre-charging the pre-treated zero-voltage battery cell with a pulsed micro-current includes: during the pre-charging process, monitoring the voltage change of the battery cell in real time, and stopping the pulsed micro-current pre-charging when the battery cell voltage rises to 0.5V-1V;

[0013] The parameters of the pulsed microcurrent are set as follows: the initial pulse current amplitude is controlled between 0.01C-0.05C, where C is the rated current of the lithium iron phosphate battery cell, the pulse width is 10-30ms, and the pulse interval is 100-300ms.

[0014] Preferably, in step S3, performing constant current-constant voltage segmented charging on the lithium iron phosphate battery cell after the pulsed micro-current pre-charging is completed includes:

[0015] Constant current charging stage

[0016] Perform constant current charging on the lithium iron phosphate battery cell, adjust the charging current to 0.1C-0.3C, and continuously monitor the voltage and temperature of the lithium iron phosphate battery cell during constant current charging. When the voltage of the lithium iron phosphate battery cell reaches 3.0V-3.2V, stop constant current charging;

[0017] Constant voltage charging stage

[0018] Switch the charging mode to constant voltage charging and set the charging voltage to 3.2V-3.6V. During the constant voltage charging process, the charging current will gradually decrease as the voltage of the lithium iron phosphate battery cell increases. When the charging current decreases to 0.02C-0.05C, stop constant voltage charging.

[0019] Preferably, in step S4, the secondary charging of the lithium iron phosphate battery cell includes: adopting a constant current-constant voltage charging method, with a constant current charging current of 0.2C-0.5C, charging to 3.6V-3.65V, and stopping charging when the charging current decreases to 0.02C-0.05C;

[0020] The performance test of the lithium iron phosphate battery cell after charging is completed. The performance test includes measuring the capacity, internal resistance, and charge and discharge efficiency parameters of the battery cell.

[0021] Compared with the existing technology, the advantages of the present invention are:

[0022] 1. The present invention adopts pulsed microcurrent for pre-charging, which can slowly activate the battery electrode material and repair the damaged structure without damaging the internal structure of the battery. Compared with the traditional constant current charging method, it effectively avoids the impact of large current on the battery and improves the safety of the activation process.

[0023] 2. The present invention divides the charging process into two stages: constant current and constant voltage, and accurately controls the charging current and voltage according to the voltage changes of the battery cell, so that the chemical reaction inside the battery can proceed in an orderly manner, thereby improving the activation efficiency and the degree of recovery of battery performance, so that the activated battery cell can be better restored to normal use.

[0024] 3. During the entire activation process, the present invention monitors the voltage, temperature, internal resistance and other parameters of the battery cell in real time, and adjusts the charging parameters in time according to the monitoring results, thereby achieving precise control of the activation process and improving the success rate and reliability of activation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Flow chart of the method of the present invention.

[0026] Figure 2 2 is a comparison chart of the DC internal resistance of the embodiment and the comparative example in the present invention.

[0027] Figure 3 The figure is a comparison chart of the discharge capacity retention rate of the embodiment of the present invention and the comparative example at different discharge rates.

[0028] Figure 4 The figure is a comparison chart of the discharge capacity retention rate of the embodiment of the present invention and the comparative example under high and low temperature conditions.

[0029] Figure 5 The figure is a comparison of the discharge capacity retention rates of the embodiments of the present invention and the comparative examples at different cycle times at 25°C and 1C. DETAILED DESCRIPTION

[0030] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0031] Reference Figure 1 As shown, a novel method for activating a zero-voltage lithium iron phosphate battery cell comprises the following steps:

[0032] S1, pre-treating the zero-voltage lithium iron phosphate battery cell;

[0033] S2, pre-charging the pre-treated zero-voltage battery cell with a pulse micro-current;

[0034] S3, constant current-constant voltage segmented charging the lithium iron phosphate battery cell after the pulse micro-current pre-charging is completed;

[0035] S4, secondary charging the lithium iron phosphate battery cell, and testing the performance of the lithium iron phosphate battery cell after the charging is completed.

[0036] In the step S1, the pre-treating the zero-voltage lithium iron phosphate battery cell includes: measuring the open-circuit voltage, internal resistance and temperature of the lithium iron phosphate battery cell using a high-precision battery detection device, and checking whether there is obvious short circuit, open circuit or other physical damage inside the lithium iron phosphate battery cell through non-destructive testing technology (such as ultrasonic testing, X-ray testing, etc.), and removing the lithium iron phosphate battery cell with serious physical damage detected to avoid causing safety accidents in the subsequent activation process, and placing the qualified zero-voltage lithium iron phosphate battery cell in a constant temperature environment (for example, 25℃±2℃) to ensure that the chemical reaction inside the battery is stable.

[0037] In the step S2, the pre-charging the pre-treated zero-voltage battery cell with a pulse micro-current includes: monitoring the voltage change of the battery cell in real time during the pre-charging process, and stopping the pulse micro-current pre-charging when the battery cell voltage rises to 0.5V-1V; the function of the pulse micro-current pre-charging is to slowly activate the electrode material inside the battery and repair the possible damaged electrode structure, while avoiding further damage to the battery caused by excessive current;

[0038] The parameters of the pulse micro-current are set as follows: the initial pulse current amplitude is controlled between 0.01C-0.05C, where C is the rated current of the lithium iron phosphate battery cell, the pulse width is 10-30ms, and the pulse interval is 100-300ms.

[0039] In the step S3, the constant current-constant voltage segmented charging the lithium iron phosphate battery cell after the pulse micro-current pre-charging is completed includes:

[0040] Constant current charging stage

[0041] Constant current charging the lithium iron phosphate battery cell, and adjusting the charging current to 0.1C-0.3C, and continuously monitoring the voltage and temperature of the lithium iron phosphate battery cell during the constant current charging process, and stopping the constant current charging when the voltage of the lithium iron phosphate battery cell reaches 3.0V-3.2V; the purpose of the constant current charging is to quickly raise the voltage of the battery cell and accelerate the chemical reaction inside the battery, but the charging current should not be too large to avoid damaging the battery;

[0042] Constant voltage charging stage

[0043] Switch the charging mode to constant voltage charging and set the charging voltage to 3.2V-3.6V. During the constant voltage charging process, the charging current will gradually decrease as the voltage of the lithium iron phosphate battery cell increases. When the charging current decreases to 0.02C-0.05C, stop the constant voltage charging. The purpose of constant voltage charging is to make the electrode material inside the battery cell fully react and further improve the capacity and performance of the battery.

[0044] In the step S4, the secondary charging of the activated battery cell includes: using a constant current-constant voltage charging method, with a constant current charging current of 0.2C-0.5C, charging to 3.6V-3.65V, and stopping charging when the charging current decreases to 0.02C-0.05C;

[0045] The performance test of the lithium iron phosphate battery cell after charging is completed. The performance test includes measuring the capacity, internal resistance, and charge and discharge efficiency parameters of the battery cell. For the lithium iron phosphate battery cell whose performance reaches or is close to the normal battery cell standard, it is determined that the activation is successful and can be put into use; for the lithium iron phosphate battery cell whose performance still does not meet the standard, it can be reactivated or otherwise processed according to the specific situation.

[0046] Example

[0047] S1. Cell pretreatment

[0048] Fifty zero-voltage lithium iron phosphate cells were selected, and their open-circuit voltage, internal resistance, and temperature were measured using high-precision battery testing equipment. Ultrasonic and X-ray tests were used to check whether there was any physical damage inside the cells. Four cells with obvious short circuit or open circuit problems were removed, and the remaining 46 cells were placed in a constant temperature environment of 25°C for 2 hours to stabilize the cell temperature.

[0049] S2, pulse micro-current pre-charging

[0050] 46 pre-conditioned cells were connected to a pulse charging device, with an initial pulse current amplitude of 0.02C, a pulse width of 20ms, and a pulse interval of 200ms. During the pre-charging process, the cell voltages were monitored in real time. After approximately three hours of pre-charging, the voltages of 42 cells rose to around 0.8V, and the pulsed micro-current pre-charging was stopped.

[0051] S3, constant current-constant voltage segmented charging

[0052] Constant current charging stage

[0053] The charging current of the 42 battery cells was adjusted to 0.2C, and constant current charging was performed. The voltage and temperature of the battery cells were continuously monitored. When the battery cell voltage reached 3.1V, constant current charging was stopped. This stage took about 2 hours.

[0054] Constant voltage charging stage

[0055] Switch the charging mode to constant voltage charging and set the charging voltage to 3.4V. As charging progresses, the charging current gradually decreases. When the charging current decreases to 0.03C, stop constant voltage charging. This stage takes about 3 hours.

[0056] S4. Secondary charging and performance testing

[0057] 42 lithium iron phosphate cells were recharged with a constant current of 0.3C and charged to 3.62V. They were then charged with a constant voltage, and charging was stopped when the charging current decreased to 0.03C. After charging, the cells were performance tested. The results showed that the capacity of 41 cells had recovered to more than 90% of the rated capacity, and the internal resistance was close to the level of normal cells. It was determined that these 41 cells were successfully activated, with an activation success rate of 82%.

[0058] Comparative Example

[0059] Fifty zero-voltage lithium iron phosphate cells of the same specifications and quantity as in the example were activated using a conventional constant-current charging method. The charging current was set to 0.1C, and the cells were directly charged to 3.65V. During the charging process, 12 cells exhibited abnormal heating and voltage fluctuations, resulting in charging being stopped. Performance testing of the remaining 38 cells revealed that only 29 cells recovered to over 80% of their rated capacity. Internal resistance was also generally high, resulting in an activation success rate of only 58%.

[0060] By comparing the examples and the comparative examples, it can be seen that the novel activation method of the present invention is significantly superior to the traditional constant current charging activation method in terms of activation success rate and battery performance recovery degree. At the same time, the battery cells of the examples and the comparative examples were selected for HPPC, rate discharge, high and low temperature discharge and 25°C cycle tests. The electrical performance of the examples is significantly better than that of the comparative examples (see Figures 2-5 ), therefore, the method of the present invention can activate the zero-voltage lithium iron phosphate battery cell more safely and efficiently, so that the performance of the battery cell can be better restored, which has significant technical advantages.

[0061] It is understood from common technical knowledge that the present invention may be implemented by other embodiments that do not depart from its spirit or essential features. Therefore, the embodiments disclosed above are, in all respects, merely illustrative and not exclusive. All modifications within the scope of the present invention or equivalent to the scope of the present invention are intended to be encompassed by the present invention.

Claims

1. A novel method for activating zero-voltage lithium iron phosphate batteries, characterized by: The following steps are involved: S1. Pre-treating the zero-voltage lithium iron phosphate battery cell; S2, pre-charging the pre-treated zero-voltage battery cell with a pulsed micro-current; S3, performing constant current-constant voltage segmented charging on the lithium iron phosphate battery cell after the pulsed micro-current pre-charging is completed; S4. Recharge the lithium iron phosphate battery cell and perform a performance test on the lithium iron phosphate battery cell after charging.

2. A novel method for activating a zero-voltage lithium iron phosphate battery cell according to claim 1, characterized in that: In step S1, pre-processing the zero-voltage lithium iron phosphate battery cell includes: using high-precision battery testing equipment to measure the open circuit voltage, internal resistance and temperature of the lithium iron phosphate battery cell, and using non-destructive testing technology to check whether there is an obvious short circuit, open circuit or other physical damage inside the lithium iron phosphate battery cell, eliminating the lithium iron phosphate battery cells detected to have serious physical damage, and placing the qualified zero-voltage lithium iron phosphate battery cells in a constant temperature environment to ensure that the chemical reaction inside the battery proceeds stably.

3. The novel method for activating a zero-voltage lithium iron phosphate battery cell according to claim 1, characterized in that: In the step S2, pre-charging the pre-treated zero-voltage battery cell with a pulsed microcurrent includes: during the pre-charging process, monitoring the voltage change of the battery cell in real time, and stopping the pulsed microcurrent pre-charging when the battery cell voltage rises to 0.5V-1V; The parameters of the pulsed microcurrent are set as follows: the initial pulse current amplitude is controlled between 0.01C-0.05C, where C is the rated current of the lithium iron phosphate battery cell, the pulse width is 10-30ms, and the pulse interval is 100-300ms.

4. The novel method for activating a zero-voltage lithium iron phosphate battery cell according to claim 1, characterized in that: In step S3, performing constant current-constant voltage segmented charging on the lithium iron phosphate battery cell after the pulsed micro-current pre-charging is completed includes: Constant current charging stage Perform constant current charging on the lithium iron phosphate battery cell, adjust the charging current to 0.1C-0.3C, and continuously monitor the voltage and temperature of the lithium iron phosphate battery cell during constant current charging. When the voltage of the lithium iron phosphate battery cell reaches 3.0V-3.2V, stop constant current charging; Constant voltage charging stage Switch the charging mode to constant voltage charging and set the charging voltage to 3.2V-3.6V. During the constant voltage charging process, the charging current will gradually decrease as the voltage of the lithium iron phosphate battery cell increases. When the charging current decreases to 0.02C-0.05C, stop constant voltage charging.

5. The novel method for activating a zero-voltage lithium iron phosphate battery cell according to claim 1, characterized in that: In the step S4, the secondary charging of the lithium iron phosphate battery cell includes: using a constant current-constant voltage charging method, with a constant current charging current of 0.2C-0.5C, charging to 3.6V-3.65V, and stopping charging when the charging current decreases to 0.02C-0.05C; The performance test of the lithium iron phosphate battery cell after charging is completed. The performance test includes measuring the capacity, internal resistance, and charge and discharge efficiency parameters of the battery cell.

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