Formation process for improving charging and discharging energy efficiency of 314Ah lithium iron phosphate cell

Abstract

The invention discloses a formation process for improving the charging and discharging energy efficiency of a 314Ah lithium iron phosphate battery cell, and relates to the technical field of lithium ion battery manufacturing, in particular to the formation process for improving the charging and discharging energy efficiency of the 314Ah lithium iron phosphate battery cell. Comprising the following steps of battery cell pretreatment, first constant-current charging, first constant-voltage charging, first shelving, first constant-current discharging, second constant-current charging, second constant-voltage charging, second shelving, second constant-current discharging and battery cell post-treatment. The 314Ah lithium iron phosphate battery cell treated by the formation process disclosed by the invention can store and release electric energy more efficiently, the energy utilization efficiency is remarkably improved, the operation cost is reduced, and the economic benefit and market competitiveness of an energy storage system are enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery manufacturing, and in particular to a formation process for improving the charging and discharging energy efficiency of a 314Ah lithium iron phosphate battery cell. Background Art

[0002] With the vigorous promotion of clean energy and the sharp increase in energy storage demand around the world, lithium iron phosphate batteries have played an important role in large-scale energy storage systems due to their high safety, long cycle life and relatively stable electrochemical performance. However, the current formation process of 314Ah lithium iron phosphate batteries for energy storage mostly adopts traditional standard processes, which have many limitations.

[0003] In the traditional formation process, the charging process often does not fully consider the polarization effect and temperature influence of the battery cell, resulting in uneven distribution of charging current, overcharging in some areas, and insufficient lithium ion embedding in some areas, which not only reduces the charging efficiency, but also affects the overall performance and life of the battery. At the same time, the voltage and current control during the formation process is not precise enough to form an ideal solid electrolyte interface film (SEI film) inside the battery cell, resulting in poor stability and uniformity of the SEI film, which is prone to rupture and repair in subsequent charge and discharge cycles, causing irreversible capacity loss, thereby reducing the charge and discharge energy efficiency. In addition, the shelf time and condition settings in the traditional formation process lack pertinence, cannot fully optimize the chemical reaction balance inside the battery cell, and are not conducive to the full activation of the electrode material, limiting the further improvement of the battery cell performance.

[0004] Based on this, a formation process is now provided to improve the charging and discharging energy efficiency of 314Ah lithium iron phosphate batteries, which can eliminate the drawbacks of existing devices. Summary of the invention

[0005] The purpose of the present invention is to provide a formation process for improving the charge and discharge energy efficiency of 314Ah lithium iron phosphate batteries, so as to solve the shortcomings of the current products in the background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A formation process for improving the charging and discharging energy efficiency of a 314Ah lithium iron phosphate battery cell comprises the following steps:

[0008] Step 1: Perform cell pretreatment, place the 314Ah lithium iron phosphate system cells after injection in an environment of 25±3℃, let it stand for 24±2h, and then conduct a comprehensive appearance inspection on the cells after storage to remove cells with potential quality problems;

[0009] Step 2: Perform the first constant current charging, use a current of 0.12C-0.2C to charge the battery cell at a constant current, set the charging cut-off voltage to 3.5V-3.6V, and use a high-precision temperature sensor and voltage monitoring device to monitor the temperature and voltage changes of the battery cell in real time during the charging process. When the battery cell temperature rises to 37℃-39℃, suspend charging, and quickly reduce the battery cell temperature to about 28℃ through cooling methods such as air cooling or liquid cooling, and then resume charging;

[0010] Step 3: Perform the first constant voltage charge. When the first constant current charge reaches the set cut-off voltage, switch to constant voltage charging mode and keep the voltage constant at 3.5V-3.6V. When the charging current drops to 0.06C-0.1C, continue to maintain the constant voltage charging state for 25-40 minutes.

[0011] Step 4: Perform the first standby, and standby the battery cells that have completed the first constant voltage charging for 1-2 hours;

[0012] Step 5: Perform the first constant current discharge, use a current of 0.3C-0.5C to discharge the battery cell at a constant current, and set the discharge cut-off voltage to 2.2V-2.5V;

[0013] Step 6: Perform secondary constant current charging, charge the battery cell with a current of 0.24C-0.36C, increase the charging cut-off voltage to 3.65V-3.75V, and adjust the charging current in real time according to the temperature and voltage response of the battery cell during the charging process;

[0014] Step 7: Perform secondary constant voltage charging. When the secondary constant current charging reaches the set cut-off voltage, switch to constant voltage charging mode and keep the voltage at 3.65V-3.75V until the charging current drops to 0.04C-0.06C.

[0015] Step 8: Perform a secondary standby, and standby the battery after the secondary constant voltage charging for 1-2 hours;

[0016] Step nine: Perform a secondary constant current discharge, using a current of 0.25C-0.35C to discharge the battery cell at a constant current, and the discharge cut-off voltage is 2.2V-2.5V;

[0017] Step 10: Post-process the battery cells, add liquid to the battery cells to the reserved amount, weld the sealing pins, divide the capacity, and finally perform initial charge and discharge energy experiments and cycle performance experiments. Based on the performance test results, use data analysis and modeling technology to further fine-tune and adjust the parameters in the formation process.

[0018] On the basis of the above technical solution, the present invention also provides the following optional technical solution:

[0019] In an optional solution: in the step 1, during the pretreatment of the battery cell, the temperature of the static environment is 25° C. and the static time is 24 hours.

[0020] In an optional solution: in step one, during the first constant current charging, the charging current is 0.16C and the charging cut-off voltage is 3.55V.

[0021] In an optional solution: in step 1, during the first constant voltage charging, when the charging current drops to 0.08C, the constant voltage charging is continued for 30 minutes.

[0022] In an optional solution: in the step 1, the first holding time is 1.5 hours.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention effectively reduces polarization and side reactions of the battery cell during the charging and discharging process by precisely controlling key parameters such as charging current, voltage and shelf time in the formation process, thereby reducing ohmic loss and irreversible capacity loss. The charging and discharging energy efficiency of the 314Ah lithium iron phosphate battery cell treated by the formation process of the present invention can be improved by 1.1% compared with the traditional formation process, which means that in a large-scale energy storage system, electric energy can be stored and released more efficiently, significantly improving energy utilization efficiency, reducing operating costs, and enhancing the economic benefits and market competitiveness of the energy storage system.

[0025] 2. The optimized formation process adopted in the present invention helps to form a more uniform, dense and stable SEI film, while improving the structure and performance of the electrode material, reducing the capacity decay and performance degradation of the battery during long-term cycling. After testing, the battery cell using the formation process of the present invention can maintain good stability during long-term use, reduce the frequency of battery replacement and maintenance costs, improve the reliability and service life of the energy storage system, and bring long-term economic benefits and use value to users.

[0026] 3. The present invention monitors and precisely controls parameters such as temperature, current, and voltage in real time, and arranges a reasonable shelf time, which ensures the stability and uniformity of the electrochemical reaction inside the battery cell and reduces the fluctuations in battery cell performance and individual differences caused by improper formation processes. This enables the battery to maintain relatively stable performance under different working environments and charging and discharging conditions, provides a strong guarantee for the stable operation of the energy storage system, reduces the risk of system failures caused by unstable battery performance, and improves the safety and reliability of the energy storage system.

[0027] 4. The formation process of the present invention has high flexibility, and the parameters of each step can be appropriately adjusted and optimized according to the actual production situation of the battery cell, the characteristics of the raw materials, and the specific application requirements. For example, in actual production, if there are differences in raw material batches or fluctuations in the performance of production equipment, the performance consistency of the battery cell can be ensured by fine-tuning the formation process parameters. This flexibility enables the present invention to adapt to different production conditions and market demands, provides enterprises with more room for process optimization, and helps enterprises to improve production efficiency, reduce production costs, and enhance market competitiveness while ensuring product quality. It also provides strong support for the continued development and innovation of lithium iron phosphate battery technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a comparison chart of energy efficiency of initialization charge and discharge of Example 1 of the present invention and Comparative Example 1.

[0029] Figure 2 This is a test flow chart of the initialization charge and discharge process of Example 1 and Comparative Example 1 of the present invention.

[0030] Figure 3 This is a test flow chart of the 25°C cycle test process for Example 1 and Comparative Example 1 of the present invention.

[0031] Figure 4 This is a test flow chart of the 45°C cycle test process for Example 1 and Comparative Example 1 of the present invention.

[0032] Figure 5 This is a graph of the capacity retention at 25°C of Example 1 of the present invention and Comparative Example 1.

[0033] Figure 6 It is a data diagram of 25°C cyclic charge and discharge energy efficiency of Example 1 of the present invention and Comparative Example 1.

[0034] Figure 7 This is a graph of the capacity retention at 45°C of Example 1 of the present invention and Comparative Example 1.

[0035] Figure 8 It is a graph showing the energy efficiency of 45°C cyclic charge and discharge of Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0037] In one embodiment, Figure 1-Figure 8 As shown, a formation process for improving the charging and discharging energy efficiency of a 314Ah lithium iron phosphate battery cell includes the following steps:

[0038] Step 1: Cell pretreatment

[0039] After the injection, place the 314Ah lithium iron phosphate system battery cell in an environment of 25±3℃ and let it stand for 24±2h to allow the electrolyte to penetrate more deeply into the pores and internal structure of the electrode material, ensuring that lithium ions can be smoothly transferred between the electrolyte and the electrode material during the formation process, while keeping the electrode material in a stable initial state.

[0040] Carry out a comprehensive appearance inspection on the shelved battery cells, including whether the outer shell is damaged or deformed, whether the top cover is firmly welded, etc., and eliminate any battery cells with potential quality problems to ensure that the battery cells entering the formation process have good initial quality.

[0041] Step 2: First constant current charging

[0042] The battery cell is charged with a constant current of 0.12C-0.2C, and the charging cut-off voltage is set to 3.5V-3.6V. During the charging process, a high-precision temperature sensor and voltage monitoring device are used to monitor the temperature and voltage changes of the battery cell in real time.

[0043] When the cell temperature rises to 37°C-39°C, suspend charging, and quickly reduce the cell temperature to around 28°C through air cooling or liquid cooling, and then resume charging to prevent high temperature from causing intensified side reactions inside the cell, ensuring the safety and stability of the charging process, while improving the lithium ion embedding efficiency and reducing irreversible capacity loss.

[0044] Step 3: First constant voltage charging

[0045] When the first constant current charge reaches the set cut-off voltage, it will immediately switch to constant voltage charging mode to keep the voltage constant at 3.5V-3.6V. At this time, the charging current will gradually decrease.

[0046] When the charging current drops to 0.06C-0.1C, continue to maintain the constant voltage charging state for 25-40 minutes, so that the lithium ions inside the battery cell can be more evenly and fully embedded in the electrode material, promoting the stable formation of the SEI film, and by extending the constant voltage charging time, it helps to repair the local lithium ion concentration unevenness that may occur during the first constant current charging process, and improve the overall performance and consistency of the battery cell.

[0047] Step 4: First Shelve

[0048] The battery cell that has completed the first constant voltage charge should be placed aside for 1-2 hours to allow the electrochemical reaction inside the battery cell to reach a relative equilibrium state, further stabilize and optimize the SEI film, and make the lithium ion distribution in the electrode material more uniform, laying a good foundation for the subsequent charging and discharging process.

[0049] Step 5: First constant current discharge

[0050] The battery cell is discharged at a constant current of 0.3C-0.5C, and the discharge cut-off voltage is set to 2.2V-2.5V. During the discharge process, the temperature and voltage changes of the battery cell are continuously monitored to ensure that the discharge process is safe, stable and controllable.

[0051] The purpose of this discharge is to activate the electrode material of the battery cell, promote the release of lithium ions, optimize the crystal structure of the electrode material to a certain extent, and further adjust the performance of the SEI film to improve its stability and ion conductivity in subsequent charge and discharge cycles.

[0052] Step 6: Secondary constant current charging

[0053] The battery cell is charged with a constant current of 0.24C-0.36C for the second time, and the charging cut-off voltage is increased to 3.65V-3.75V. According to the temperature and voltage response of the battery cell during the charging process, the charging current is adjusted in real time to avoid overcharging or undercharging, ensuring that the battery cell is in the best charging state.

[0054] For example, when the temperature of the battery cell rises too quickly or the voltage is close to the cut-off voltage, the charging current is appropriately reduced to maintain a stable charging process. At the same time, the lithium ion embedding dynamics inside the battery cell are optimized so that the lithium ions can be more evenly distributed in the electrode material, further improving the energy density and charge and discharge performance of the battery cell.

[0055] Step 7: Secondary constant voltage charging

[0056] When the secondary constant current charging reaches the set cut-off voltage, it switches to constant voltage charging mode, keeping the voltage unchanged at 3.65V-3.75V until the charging current drops to 0.04C-0.06C.

[0057] During the constant voltage charging stage, by precisely controlling the rate of decrease of the charging current, the lithium ions inside the battery cell can be deeply embedded in the crystal lattice of the electrode material, further improving the quality of the SEI film and the structural stability of the electrode, reducing the polarization phenomenon of the battery during subsequent use, thereby improving the charging and discharging energy efficiency and cycle life of the battery cell.

[0058] Step 8: Secondary Shelving

[0059] The battery cell is left alone for 1-2 hours after the second constant voltage charging to allow the electrochemical reaction inside the battery cell to reach a more stable state, further optimizing the performance of the battery. At the same time, the performance of the battery cell is brought to a relatively stable level so that it can be put into actual energy storage applications.

[0060] Step 9: Secondary constant current discharge

[0061] The battery cell is discharged at a constant current of 0.25C-0.35C, and the discharge cut-off voltage is still 2.2V-2.5V. Through this discharge, the performance of the battery cell after secondary formation is fully tested and optimized, and the battery cell reaches a stable initial state, preparing for its long-term stable operation in the energy storage system.

[0062] Step 10: Post-processing of battery cells

[0063] The formed cells are refilled to the reserved capacity, the sealing pins are welded, the capacity is divided, and finally the initial charge and discharge energy test and cycle performance test are carried out. According to the performance test results, data analysis and modeling technology are used to further optimize and adjust the parameters in the formation process, such as charging current, voltage, shelf time, etc., to continuously improve the charge and discharge energy efficiency and overall performance of the cells, so that they can always maintain the best performance in energy storage applications and adapt to different working conditions and application scenarios.

[0064] The above embodiment discloses a formation process for improving the charging and discharging energy efficiency of a 314Ah lithium iron phosphate battery cell. A comparative experiment was conducted using the above process, and the process results are as follows:

[0065] Embodiment 1:

[0066] Cell pretreatment: Place 10 314Ah cells in an environment with a temperature of 25°C for 24 hours, then perform an appearance inspection and remove unqualified cells.

[0067] First constant current charging: Use 0.16C current to charge the battery cell at constant current, and set the charging cut-off voltage to 3.55V. During the charging process, when the battery cell temperature rises to 38℃, the charging is suspended, and the air cooling system is used to reduce the battery cell temperature to below 28℃ before continuing the charging.

[0068] First constant voltage charging: When the first constant current charging reaches 3.55V, switch to constant voltage charging, keep the voltage unchanged, and when the charging current drops to 0.08C, continue constant voltage charging for 30 minutes.

[0069] First standby: The battery cell that has completed the first constant voltage charging should be set aside for 1.5 hours.

[0070] First constant current discharge: Use 0.4C current to discharge the battery cell at a constant current, and set the discharge cut-off voltage to 2.3V.

[0071] Secondary constant current charging: The battery cell is charged with a secondary constant current at a current of 0.3C, and the charging cut-off voltage is set to 3.7V. According to the temperature and voltage changes of the battery cell, the charging current is adjusted in time to ensure that the battery cell is in the best charging state.

[0072] Secondary constant voltage charging: When the secondary constant current charging reaches 3.7V, switch to constant voltage charging mode and keep the voltage unchanged until the charging current drops to 0.05C.

[0073] Secondary shelf life: The battery cells after the secondary constant voltage charging shall be shelf life for 1.5 hours.

[0074] Secondary constant current discharge: Use 0.3C current to discharge the battery cell at a constant current, and the discharge cut-off voltage is set to 2.3V.

[0075] Post-processing of battery cells: refill the battery cells to the required capacity, weld the sealing pins, divide the capacity, and finally conduct the initial charge and discharge energy test and cycle performance test. Figure 2 , 25℃ cycle test process see Figure 3 , 45℃ cycle test process see Figure 4 .

[0076] Comparative Example 1:

[0077] After briefly placing the battery cell in a normal temperature and humidity environment, it is directly charged to 3.65V at a constant current of 0.2C, and then charged at a constant voltage until the current drops to 0.05C.

[0078] After standing for 1 hour, the battery was discharged at a constant current of 0.2C to 2.5V.

[0079] After repeating the above charging and discharging steps once, the formation process is completed.

[0080] like Figure 1 As shown, the charge and discharge energy efficiency of the 314Ah lithium iron phosphate battery cell treated by the formation process of the present invention can be improved by 1.1% compared with the traditional formation process, which means that in a large-scale energy storage system, electric energy can be stored and released more efficiently, which significantly improves energy utilization efficiency, reduces operating costs, and enhances the economic benefits and market competitiveness of the energy storage system.

[0081] After testing, the battery cell using the formation process of the present invention has a capacity retention rate of 96.72% and 90.98% at 25°C and 45°C respectively after charge and discharge cycles (25°C / 1200 times, 45°C / 1000 times), while the capacity retention rate of the battery cell processed by the traditional process is 92.78% and 87.18% at the same number of cycles (see attached Figure 5 and attached Figure 6 ), and the energy efficiency of Example 1 during the cycle is significantly higher than that of Comparative Example 1 (see Appendix Figure 7 and attached Figure 8), which enables the 314Ah lithium iron phosphate battery cells for energy storage to maintain good stability during long-term use, reduces the frequency of battery replacement and maintenance costs, improves the reliability and service life of the energy storage system, and brings long-term economic benefits and use value to users.

[0082] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A formation process for improving the charging and discharging energy efficiency of 314Ah lithium iron phosphate batteries, characterized in that: The following steps are involved: Step 1: Perform cell pretreatment, place the 314Ah lithium iron phosphate system cells after injection in an environment of 25±3℃, let it stand for 24±2h, and then conduct a comprehensive appearance inspection on the cells after storage to remove cells with potential quality problems; Step 2: Perform the first constant current charging, use a current of 0.12C-0.2C to charge the battery cell at a constant current, set the charging cut-off voltage to 3.5V-3.6V, and use a high-precision temperature sensor and voltage monitoring device to monitor the temperature and voltage changes of the battery cell in real time during the charging process. When the battery cell temperature rises to 37℃-39℃, suspend charging, and quickly reduce the battery cell temperature to about 28℃ through cooling methods such as air cooling or liquid cooling, and then resume charging; Step 3: Perform the first constant voltage charge. When the first constant current charge reaches the set cut-off voltage, switch to constant voltage charging mode and keep the voltage constant at 3.5V-3.6V. When the charging current drops to 0.06C-0.1C, continue to maintain the constant voltage charging state for 25-40 minutes. Step 4: Perform the first standby, and standby the battery cells that have completed the first constant voltage charging for 1-2 hours; Step 5: Perform the first constant current discharge, use a current of 0.3C-0.5C to discharge the battery cell at a constant current, and set the discharge cut-off voltage to 2.2V-2.5V; Step 6: Perform secondary constant current charging, charge the battery cell with a current of 0.24C-0.36C, increase the charging cut-off voltage to 3.65V-3.75V, and adjust the charging current in real time according to the temperature and voltage response of the battery cell during the charging process; Step 7: Perform secondary constant voltage charging. When the secondary constant current charging reaches the set cut-off voltage, switch to constant voltage charging mode and keep the voltage at 3.65V-3.75V until the charging current drops to 0.04C-0.06C. Step 8: Perform a secondary standby, and standby the battery after the secondary constant voltage charging for 1-2 hours; Step nine: Perform a secondary constant current discharge, using a current of 0.25C-0.35C to discharge the battery cell at a constant current, and the discharge cut-off voltage is 2.2V-2.5V; Step 10: Post-process the battery cells, add liquid to the battery cells to the reserved amount, weld the sealing pins, divide the capacity, and finally perform initial charge and discharge energy experiments and cycle performance experiments. Based on the performance test results, use data analysis and modeling technology to further fine-tune and adjust the parameters in the formation process.

2. A formation process for improving the charge and discharge energy efficiency of 314Ah lithium iron phosphate battery cells according to claim 1, characterized in that: In the step 1, during the pretreatment of the battery cell, the temperature of the static environment is 25° C. and the static time is 24 hours.

3. A formation process for improving the charge and discharge energy efficiency of 314Ah lithium iron phosphate battery cells according to claim 1, characterized in that: In the first step, during the first constant current charging, the charging current is 0.16C and the charging cut-off voltage is 3.55V.

4. A formation process for improving the charge and discharge energy efficiency of 314Ah lithium iron phosphate battery cells according to claim 1, characterized in that: In the step 1, during the first constant voltage charging, when the charging current drops to 0.08C, the constant voltage charging is continued for 30 minutes.

5. A formation process for improving the charge and discharge energy efficiency of 314Ah lithium iron phosphate battery cells according to claim 1, characterized in that: In the step 1, the first holding time is 1.5 hours.

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