Online repairing method of lithium iron phosphate battery

Abstract

The invention relates to an on-line repairing method of a lithium iron phosphate battery, which combines a battery management system for accurately acquiring the state information of a battery pack with a battery repairing technology, and puts forward to realize the balance between battery cells by repairing low-capacity battery cells. Different from the current active equalization and passive equalization limited by the short plate effect, the real-time repair equalization control method provided by the invention realizes equalization between the low-capacity battery cell and the high-capacity battery cell by supplementing the capacity of the low-capacity battery cell, so that the battery cruising ability is exerted to the greatest extent while the safe and reliable circulation of the battery is ensured, and the service life of the battery is prolonged. And the method is convenient and easy to implement and does not involve a complex circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to an online repair method for lithium iron phosphate batteries. Background Art

[0002] Compared with other rechargeable batteries, lithium-ion batteries have higher power density and energy density and are widely used in electric vehicles and smart grid energy storage systems. Since a single lithium-ion battery has a small capacity and low voltage, several batteries are usually connected in series and parallel to form a high-voltage, large-capacity battery pack.

[0003] Due to the inconsistency of materials and manufacturing processes, batteries from the same batch will also show differences in capacity, aging characteristics, and performance characteristics. Therefore, the state of charge and capacity of each single cell in the series battery pack will be unbalanced, and the degree of imbalance will increase with the increase in the number of charge and discharge cycles. During the charge and discharge process, the imbalance between single cells will cause some single cells to overcharge or over-discharge, resulting in a rapid decrease in battery capacity, shortened service life, and even direct damage to the battery, which may also cause an explosion. Therefore, it is extremely important for battery energy storage systems to propose an effective balancing method to reduce or eliminate the imbalance during battery use and maximize the performance of each single cell.

[0004] At present, the balancing methods proposed by scholars at home and abroad are mainly divided into two categories: active balancing and passive balancing. Active balancing is when the gap between cells is greater than a certain threshold, the power is balanced from high-capacity cells to low-capacity cells to achieve a consistent overall level and ensure that the current does not leak, but the control algorithm and circuit design are complex and costly. Passive balancing is to reduce the gap between high-capacity cells and low-capacity batteries by consuming the energy through resistors. This method is simple in principle and easy to implement. It is a commonly used method at present, but the balancing current is small and some energy is consumed on resistors. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention proposes an online repair method for lithium iron phosphate batteries, which combines the battery management system (BMS) that accurately collects battery pack status information with the battery repair technology, and proposes to achieve balance between cells by repairing low-capacity cells. Different from the currently proposed active balance and passive balance that are limited by the "short board effect", the real-time repair balance control method proposed in the present invention achieves balance between low-capacity cells and high-capacity cells by supplementing the capacity of low-capacity cells, while ensuring the safe and reliable cycle of the battery and maximizing the battery life. It is easy to implement and does not involve complex circuits.

[0006] The present invention is achieved through the following technical solutions:

[0007] The present invention relates to an online repair and balancing control method for lithium iron phosphate batteries. The method utilizes the BMS to quickly and accurately collect parameters such as voltage, current, and capacity of a battery pack, and implements charge and discharge control management according to the status information of the battery pack. The method performs pulse repair on low-capacity single cells, and compensates for the difference between cells by increasing the capacity of the low-capacity cells and reducing the internal resistance, thereby achieving balance between the cells and achieving the purpose of reducing the overall capacity attenuation rate of the battery pack and improving the cycle life.

[0008] The BMS integrates the functions of battery pack information collection, energy management, inter-module communication, charge and discharge control, and repair and balancing.

[0009] The lithium-ion battery includes one or more of an in-service lithium iron phosphate battery and a retired lithium iron phosphate battery.

[0010] The battery pack status information includes the voltage, SOC, capacity, internal resistance and coulombic efficiency of each cell.

[0011] The low-capacity single cell battery refers to: comparing the status information between each cell and comparing it with a preset threshold. If the threshold is exceeded, it is determined that the single cell battery with lower capacity needs to be repaired and balanced, wherein the preset threshold can be based on one or more of voltage consistency, SOC consistency, and capacity consistency.

[0012] The pulse repair refers to: converting part of the inactive lithium-containing compounds accumulated in SEI into active lithium ions through pulse repair to replenish lithium in the positive electrode, thereby reducing the internal resistance of the single cell and increasing the capacity, wherein the pulse repair includes one or more of positive and negative pulses, large current pulses, and small current pulses.

[0013] The cell balancing means that in the same lithium battery pack, the capacity and internal resistance of the single cells are controlled within a certain range, where the cell capacity difference is ≤1% and the internal resistance difference is ≤2 mΩ. Technical Effects

[0014] The present invention can perform real-time equalization management on the lithium-ion battery pack through the provided repair and equalization module. When a significant performance difference is found between individual single cells and other cells during the operation of the lithium-ion battery, the repair module can be activated to generate corresponding charge and discharge currents to repair the low-capacity cells and compensate for the differences between the cells, thereby achieving equalization control of the battery pack. This method can monitor and repair any cell inside the lithium-ion battery in real time without disassembling the battery for separate repair, making the lithium-ion battery maintenance and repair more efficient and effectively extending the service life of the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the overall process structure of the present invention;

[0016] Figure 2 It is the cycle curve of the battery pack before and after the repair and equalization of the present invention. DETAILED DESCRIPTION

[0017] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. The preferred embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0018] See attached Figure 1 The present invention adopts a lithium battery-specific BMS monitoring chip and repair integration technology, and adopts two control cores internally, namely the BMS monitoring chip and the microcontroller. The BMS monitoring chip is responsible for the detection and data analysis of all parameters of the batteries in the managed battery pack, including battery voltage, battery SOC, battery capacity, battery internal resistance and other parameter analysis and calculation, and outputs the repair control signal from the host computer to the microcontroller. The microcontroller is responsible for the detection of the repair control circuit and the output of the repair pulse.

[0019] The use process of the present invention is as follows: first, the battery packs are connected to the system respectively, and during the normal cycle charge and discharge process, the status information of each single cell is collected in real time. When the performance difference of each single cell reaches the set threshold, the measured data will be transmitted to the microcontroller in real time. The microcontroller analyzes and organizes the transmitted data, and then outputs the corresponding pulse current according to the status of the low-capacity battery cell, and actively balances and repairs the low-capacity battery cell until the capacity, internal resistance and other values ​​of the low-capacity battery cell reach within the threshold range, and the battery pack continues to be recycled.

[0020] In this scheme, different samples were selected to verify the effect of the present invention, as follows:

[0021] Table 1 Repair effect of low-capacity cells in the same battery pack Example Cell Type Capacity retention rate (%) Initial internal resistance (mΩ) Capacity increase (%) Internal resistance(mΩ) Capacity after repair (%) Monomer 1 LFP 76.57 17.25 3.50 15.06 80.07 Monomer 2 LFP 74.19 18.94 5.31 15.49 79.50 Monomer 3 LFP 79.47 15.24 1.79 15.13 81.26 Monomer 4 LFP 77.40 16.99 2.64 14.98 80.04 Monomer 5 LFP 76.33 18.43 3.28 16.24 79.61 Monomer 6 LFP 78.56 15.69 1.86 15.34 80.42 Monomer 7 LFP 76.89 17.09 2.87 16.18 79.76 Monomer 8 LFP 77.13 16.74 2.46 15.94 79.59 Monomer 9 LFP 78.27 15.36 1.62 14.86 79.89 Comparison monomer LFP 80.58 14.65 / / /

[0022] Compared with the prior art, this method uses active repair and balancing technology to increase the capacity of low-capacity cells and reduce internal resistance to compensate for the difference between them and other cells. The present invention has a significant repair effect on single cells in different states, with the capacity increase being between 1-5% and the internal resistance reduction being between 1-2 mΩ. The capacity of the cells after active repair and balancing is increased to a capacity and internal resistance similar to those of the comparison cells, reaching the threshold range, achieving balanced operation of each cell, and contributing to the improvement of the cycle stability of the battery pack. Compared with battery packs that do not use active repair and balancing technology, battery packs that use this repair and balancing technology (starting repair at the 30th cycle) have a capacity retention rate that is increased by about 5% under the same 130-cycle cycle (see Appendix). Figure 2 ).

[0023] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principle and purpose of the present invention. The protection scope of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. Each implementation scheme within its scope shall be subject to the constraints of the present invention.

Claims

1. An online repair method for a lithium iron phosphate battery, characterized in that: BMS is used to quickly and accurately collect parameters such as voltage, current, and capacity of the battery pack, and to implement charge and discharge control management based on the battery pack status information. It performs pulse repair on low-capacity single cells, and compensates for the differences between cells by increasing the capacity of low-capacity cells and reducing internal resistance, thereby achieving balance between cells and achieving the purpose of reducing the overall capacity attenuation rate of the battery pack and increasing the cycle life.

2. The online repair method of lithium iron phosphate battery according to claim 1, characterized in that: The battery management system integrates the functions of battery pack information collection, energy management, inter-module communication, charge and discharge control, and repair and balancing.

3. The online repair method of lithium iron phosphate battery according to claim 1, characterized in that: The lithium-ion battery includes one or more of an in-service lithium iron phosphate battery and a retired lithium iron phosphate battery.

4. The online repair method of lithium iron phosphate battery according to claim 1, characterized in that: The battery pack status information includes the voltage, SOC, capacity, internal resistance and coulombic efficiency of each cell.

5. The online repair method of lithium iron phosphate battery according to claim 1, characterized in that: The low-capacity single cell battery is determined by comparing the status information between each cell. If it exceeds a preset threshold, it is determined that the single cell battery with lower capacity needs to be repaired and balanced. The preset threshold can be based on one or more of voltage consistency, SOC consistency, and capacity consistency.

6. The online repair method of lithium iron phosphate battery according to claim 1, characterized in that: The pulse repair is to convert the inactive lithium-containing compounds accumulated in SEI into active lithium ions through pulse current to replenish lithium in the positive electrode, thereby reducing the internal resistance of the single cell and increasing the capacity, wherein the pulse repair includes one or more of positive and negative pulses, large current pulses, and small current pulses.

7. The online repair method of lithium iron phosphate battery according to claim 1, characterized in that: The cell balancing means that in the same lithium battery pack, the capacity and internal resistance of the single cells are controlled within a certain range, where the cell capacity difference is ≤1% and the internal resistance difference is ≤2 mΩ.

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