Method for prolonging cycle life of lithium ion battery and preparation method of lithium ion battery

Abstract

The invention relates to the technical field of batteries, in particular to a method for prolonging the cycle life of a lithium ion battery and a preparation method of the lithium ion battery. The method for prolonging the cycle life of the lithium ion battery comprises the steps that S1, charging is conducted to 3.65-3.75 V under preset charging power, the preset charging power is smaller than or equal to 0.05 P, and P is the design power of a battery cell; s2, standing is carried out for 10 min to 60 min; s3, discharging to 2.0-2.5 V at a preset discharging power which is greater than or equal to 0.5 P; s4, standing is carried out; and S5, repeating the steps S1 to S4 for at least five times. According to the invention, the lithium iron phosphate battery cell is pretreated in a specific manner of charging at a low rate, discharging at a high rate and carrying out charging and discharging for multiple times, so that the lithium storage content of the negative electrode is increased, the lithium is continuously and slowly released in a subsequent working condition, and the cycle life of the battery cell is further prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a method for improving the cycle life of a lithium ion battery and a method for preparing the lithium ion battery. Background Art

[0002] Energy storage batteries have a wide range of applications, primarily including the following: 1. Transportation power supply: This is a key application area for energy storage batteries, providing power support for new energy vehicles. 2. Power energy storage: Energy storage batteries play a crucial role in power systems, storing excess power for emergencies. 3. Mobile communication power: Energy storage batteries provide stable power support for mobile communication devices, ensuring unimpeded communication. 4. New energy storage power supply: Energy storage batteries play a key role in the new energy sector, particularly in the storage and utilization of renewable energy sources such as wind and solar energy.

[0003] Energy storage battery applications are increasingly focused on cost-effectiveness. This means that when selecting and using energy storage batteries, factors such as cost, cycle life, safety, and overall lifecycle costs are of particular concern. Lithium iron phosphate batteries, with their significant advantages such as low production cost, high safety, and long cycle life, are widely used in various fields, such as electric vehicles, hybrid vehicles, energy storage systems, electric bicycles, and power tools. Lithium iron phosphate batteries are particularly preferred in applications where safety and cycle life are paramount.

[0004] The positive electrode material of a lithium iron phosphate battery is lithium iron phosphate (LiFePO4), while the negative electrode is typically made of graphite. The electrolyte is a mixture of an organic solvent and a lithium salt. In lithium-ion energy storage batteries, the performance focus currently on cycle life is paramount. This is also a key competitive metric among battery companies. To extend the life of lithium-ion batteries, the primary method currently used is to use a positive electrode lithium supplement. However, while effective, this approach increases the battery cell's bill of materials (BOM) cost. Summary of the Invention

[0005] In order to overcome the above-mentioned defects, the present invention proposes a method for improving the cycle life of a lithium-ion battery and a method for preparing a lithium-ion battery, which can significantly improve the cycle life of a lithium-ion battery without changing the battery cell system.

[0006] In a first aspect, the present invention provides a method for improving the cycle life of a lithium ion battery, comprising:

[0007] S1, charging to 3.65-3.75V at a preset charging power, wherein the preset charging power is less than or equal to 0.05P, where P is the design power of the battery cell;

[0008] S2, let it stand for 10-60 minutes;

[0009] S3, discharging to 2.0-2.5V at a preset discharge power, wherein the preset discharge power is greater than or equal to 0.5P;

[0010] S4, let it stand for 10-60 minutes;

[0011] S5, repeat steps S1-S4 at least 5 times.

[0012] In one technical solution of the above-mentioned method for improving the cycle life of a lithium-ion battery, in step S2, charging to 3.65-3.75V at a preset charging power includes:

[0013] At 0.01P-0.05P, the constant power supply is 3.65~3.75V.

[0014] In one technical solution of the above method for improving the cycle life of a lithium-ion battery, the constant power supply to 3.65-3.75V at 0.01P-0.05P includes:

[0015] At 0.05P, constant power supply is provided to 3.65V.

[0016] In one technical solution of the above method for improving the cycle life of a lithium-ion battery, in step S3, discharging to 2.0-2.5V at a preset discharge power includes:

[0017] At 0.5P-1P, constant power discharge to 2.0-2.5V.

[0018] In one technical solution of the above-mentioned method for improving the cycle life of a lithium-ion battery, the constant power discharge to 2.0-2.5V at 0.5P-1P includes:

[0019] At 1P, constant power discharge to 2.5V.

[0020] In one technical solution of the above-mentioned method for improving the cycle life of a lithium-ion battery, the step S5 of repeating steps S1-S4 at least five times includes:

[0021] S5, repeat steps S1-S4 for 5-45 times.

[0022] In one technical solution of the above method for improving the cycle life of a lithium-ion battery, before step S1, the method further includes:

[0023] Discharge to 2.0-2.5V.

[0024] In one technical solution of the above method for improving the cycle life of a lithium-ion battery, in step S2,

[0025] The standing time is 10 minutes.

[0026] In the step S4,

[0027] The standing time is 10 minutes.

[0028] In a second aspect, the present invention provides a method for preparing a lithium ion battery, comprising:

[0029] The battery cell after injection is formed;

[0030] The formed battery cell is treated by adopting the method for improving the cycle life of the lithium ion battery.

[0031] In one technical solution of the above-mentioned lithium-ion battery preparation method, the battery cell includes several cathode plates and several anode plates stacked at intervals, and a separator is provided between adjacent cathode plates and anode plates; wherein the electrode material of the anode plates is lithium ferrous phosphate.

[0032] The above one or more technical solutions of the present invention have at least one or more of the following beneficial effects:

[0033] In implementing the technical solution of the present invention, the battery cell undergoes a formation treatment after injection to ensure that the chemical reaction within the cell reaches a stable state. The cell is then further pretreated using the method for improving the cycle life of lithium-ion batteries proposed in the present invention. This method is equivalent to performing an activation process before the battery cycle begins, effectively improving the negative electrode's ability to store lithium ions, thereby enabling the battery to continuously and slowly release lithium ions during subsequent use, further extending the battery's service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The disclosure of the present invention will be more easily understood with reference to the accompanying drawings. Those skilled in the art will readily appreciate that these drawings are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Furthermore, similar numbers in the drawings represent similar components, wherein:

[0035] Figure 1 1 is a flow chart of main steps S2-S5 of a method for improving the cycle life of a lithium-ion battery according to an embodiment of the present invention;

[0036] Figure 2 1 is a flow chart of a method S1-S5 for improving the cycle life of a lithium-ion battery according to an embodiment of the present invention;

[0037] Figure 3 This is the state of the electrode after cycling according to Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0038] Some embodiments of the present invention are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0039] The present invention provides a method for improving the cycle life of lithium ion batteries. Figure 1 ,include:

[0040] S1, charging to 3.65-3.75V at a preset charging power, wherein the preset charging power is less than or equal to 0.05P, where P is the design power of the battery cell;

[0041] S2, let it stand for 10-60 minutes;

[0042] S3, discharging to 2.0-2.5V at a preset discharge power, wherein the preset discharge power is greater than or equal to 0.5P;

[0043] S4, let it stand for 10-60 minutes;

[0044] S5, repeating steps S1-S4 to a preset number of times, wherein the preset number of times is greater than or equal to 5 times.

[0045] The present invention performs a series of pretreatment steps on the lithium iron phosphate battery cell before performing the cycle test, which is the method of the present invention for improving the cycle life of lithium-ion batteries. These steps include charging the battery cell at a low rate and then discharging it at a high rate (i.e., within the capacity of the battery cell). By repeating this charge and discharge process multiple times, the content of lithium stored in the negative electrode can be effectively increased. In this way, in subsequent operating conditions, lithium ions can be continuously and slowly released, thereby significantly improving the cycle life of the battery cell. This pretreatment method not only improves the performance of the battery cell, but also extends its service life, making it exhibit better stability and reliability in practical applications.

[0046] In one embodiment, in step S1, charging to 3.65-3.75V at a preset charging power includes:

[0047] At 0.01P-0.05P, the constant power supply is 3.65~3.75V.

[0048] Typically, the design power of a battery cell is calculated based on its design capacity. In one embodiment, the lithium iron phosphate cell is 280Ah and has a rated voltage of 3.2V. The calculation process of P is 280A*3.2V=896W, and 0.05P is 0.05*896=44.8W.

[0049] In one embodiment, the constant power supply to 3.65-3.75V at 0.01P-0.05P includes:

[0050] At 0.05P, constant power supply is provided to 3.65V.

[0051] In one embodiment, in step S3, discharging to 2.0-2.5V at a preset discharge power includes:

[0052] At 0.5P-1P, constant power discharge to 2.0-2.5V.

[0053] In one embodiment, the constant power discharge to 2.0-2.5V at 0.5P-1P includes:

[0054] At 1P, constant power discharge to 2.5V.

[0055] In one embodiment, the preset number of times is 5-45 times, that is, steps S1-S4 are repeated 5-45 times.

[0056] In the present invention, a specific charging and discharging method is employed during the cyclic process from steps S1 to S4. Specifically, charging is performed under a relatively high constant power condition, followed by discharging under a relatively low constant power condition. Combining these two operations and performing them cyclically effectively preconditions the lithium iron phosphate battery cells before cycling. This method aims to fully activate and rejuvenate the battery cells, thereby improving their performance.

[0057] However, the number of cycles must be controlled within a reasonable range. If the number of cycles is too small, the activation effect of the battery cell will be insignificant and the expected activation effect cannot be achieved. Conversely, if the number of cycles is too large, not only will the activation effect not be further improved, but the cycle life of the battery cell will be degraded, and it may even cause irreversible damage to the battery cell.

[0058] In one embodiment, referring to Figure 2 Before step S1, the method further includes:

[0059] Discharge to 2.0-2.5V.

[0060] First discharge the battery cell, and then proceed to the subsequent charge and discharge cycle steps.

[0061] When discharging, you can choose constant current discharge at medium or low rates, such as constant current discharge at 0.5 C. Discharging the battery cell first can make the battery system reach a relatively stable state.

[0062] In one embodiment, in step S3, the standing time is 10 minutes.

[0063] In one embodiment, in step S5, the standing time is 10 minutes.

[0064] Lithium-ion batteries experience electrochemical polarization and concentration polarization during charge and discharge, causing the electrode potential to deviate from the equilibrium potential. Resting the battery can eliminate this polarization effect, restore the equilibrium potential, and optimize discharge performance. Setting a reasonable rest period between charge and discharge allows the battery's internal chemical reactions to reach equilibrium, helping to improve overall battery performance.

[0065] The core of this invention lies in the fact that it does not require any changes or adjustments to the existing battery cell system. Instead, it uses a specific activation method to effectively regulate the behavior of the negative electrode material during the lithium ion storage process. This innovative method not only significantly reduces the polarization phenomenon of the initial battery cell during the charge and discharge process, but also significantly improves the performance of the lithium iron phosphate battery cell during the early cycle process. Specifically, by regulating this activation process, the capacity decay rate of the battery cell during the use phase is greatly slowed, thereby extending the overall service life of the battery cell and improving its reliability and stability in practical applications.

[0066] The present invention also provides a method for preparing a lithium ion battery, comprising:

[0067] The battery cell after injection is formed;

[0068] The formed battery cell is treated by adopting the method for improving the cycle life of the lithium ion battery.

[0069] The present invention further provides a method for manufacturing a lithium-ion battery, comprising the following steps: first, subjecting the injected battery cell to a conventional formation treatment to ensure that the chemical reaction within the cell reaches a stable state; then, further pre-treating the cell after the formation treatment using the method for improving the cycle life of lithium-ion batteries proposed in the present invention. This method is equivalent to performing an activation process before the battery cycle begins, effectively improving the negative electrode's ability to store lithium ions, thereby enabling the battery to continuously and slowly release lithium ions during subsequent use, further extending the battery's service life.

[0070] In one embodiment, the battery cell includes a plurality of cathode plates and a plurality of anode plates stacked at intervals, with a separator provided between adjacent cathode plates and anode plates; wherein the electrode material of the anode plates is lithium ferrous phosphate.

[0071] Next, the cycle performance test of the lithium ion battery prepared by the present invention was carried out.

[0072] Lithium iron phosphate, conductive agent SP, and binder PVDF are mixed in a specific ratio. Through a series of preparation steps, including stirring, coating, cold pressing, and slitting, the positive electrode sheet for winding is produced. This process ensures uniform mixing of the components, providing a good foundation for battery performance.

[0073] Next, artificial graphite, conductive agent SP, and binder (CMC / SBR) are mixed in a specific ratio. Through stirring, coating, cold pressing, and slitting, the negative electrode sheet for winding is produced. These steps ensure that the negative electrode sheet has excellent conductivity and mechanical strength, thereby ensuring stability and reliability during battery cycling.

[0074] After the positive and negative electrodes are wound into a core using a winding process, the core is coated with an insulating film to ensure safety and stability during subsequent processes. The coated core is then placed into a square aluminum casing. After baking, liquid injection, formation, and capacity testing, the lithium-ion battery cell is finally manufactured. These processes are designed to ensure the performance and safety of the cell in actual use.

[0075] Finally, the prepared cells were subjected to cycle tests to evaluate the battery's cycling performance. The test results showed that the lithium-ion battery prepared by the present invention exhibited excellent stability and a long service life during the cycling process, verifying its reliability and superiority in practical applications.

[0076] Example 1

[0077] 1. Adjust the temperature of the constant temperature box to 25℃±2℃, and then let it stand for 2 hours; perform the following charge and discharge cycle steps under this temperature condition;

[0078] 2. Discharge at 0.5C until the voltage reaches 2.5V;

[0079] 3. Let the battery sit for 10 minutes;

[0080] 4. Then charge at a constant power of 0.05P until the voltage reaches 3.65V;

[0081] 5. Let the battery sit for another 10 minutes;

[0082] 6. Then discharge at a constant power of 1P until the voltage drops to 2.5V;

[0083] 7. After discharging, let the battery rest for another 10 minutes;

[0084] 8. Repeat steps 4 to 7 for a total of 5 cycles;

[0085] 9. After completing the cycle, let the battery rest for 2 hours;

[0086] 10. Charge at a constant power of 0.5P until the voltage reaches 3.65V;

[0087] 11. After charging is complete, let the battery sit for 10 minutes;

[0088] 12. Then discharge at a constant power of 0.5P until the voltage drops to 2.5V;

[0089] 13. After discharging, let the battery rest for another 10 minutes;

[0090] 14. Finally, repeat the process steps 10 to 13.

[0091] Example 2

[0092] 1. Adjust the temperature of the constant temperature box to 25℃±2℃, and then let it stand for 2 hours; perform the following charge and discharge cycle steps under this temperature condition;

[0093] 2. Discharge at 0.5C until the voltage reaches 2.3V;

[0094] 3. Let the battery sit for 10 minutes;

[0095] 4. Then charge at a constant power of 0.05P until the voltage reaches 3.65V;

[0096] 5. Let the battery sit for another 10 minutes;

[0097] 6. Then discharge at a constant power of 1P until the voltage drops to 2.0V;

[0098] 7. After discharging, let the battery rest for another 10 minutes;

[0099] 8. Repeat steps 4 to 7 for a total of 15 cycles;

[0100] 9. After completing the cycle, let the battery rest for 2 hours;

[0101] 10. Charge at a constant power of 0.5P until the voltage reaches 3.65V;

[0102] 11. After charging is complete, let the battery sit for 10 minutes;

[0103] 12. Then discharge at a constant power of 0.5P until the voltage drops to 2.5V;

[0104] 13. After discharging, let the battery rest for another 10 minutes;

[0105] 14. Finally, repeat the process steps 10 to 13.

[0106] Example 3

[0107] 1. Adjust the temperature of the constant temperature box to 25℃±2℃, and then let it stand for 2 hours; perform the following charge and discharge cycle steps under this temperature condition;

[0108] 2. Discharge at 0.5C until the voltage reaches 2.0V;

[0109] 3. Let the battery sit for 10 minutes;

[0110] 4. Then charge at a constant power of 0.05P until the voltage reaches 3.65V;

[0111] 5. Let the battery sit for another 10 minutes;

[0112] 6. Then discharge at a constant power of 1P until the voltage drops to 2.2V;

[0113] 7. After discharging, let the battery rest for another 10 minutes;

[0114] 8. Repeat steps 4 to 7 for a total of 30 cycles;

[0115] 9. After completing the cycle, let the battery rest for 2 hours;

[0116] 10. Charge at a constant power of 0.5P until the voltage reaches 3.65V;

[0117] 11. After charging is complete, let the battery sit for 10 minutes;

[0118] 12. Then discharge at a constant power of 0.5P until the voltage drops to 2.5V;

[0119] 13. After discharging, let the battery rest for another 10 minutes;

[0120] 14. Finally, repeat the process steps 10 to 13.

[0121] Example 4

[0122] 1. Adjust the temperature of the constant temperature box to 25℃±2℃, and then let it stand for 2 hours; perform the following charge and discharge cycle steps under this temperature condition;

[0123] 2. Discharge at 0.5C until the voltage reaches 2.5V;

[0124] 3. Let the battery sit for 10 minutes;

[0125] 4. Then charge at a constant power of 0.05P until the voltage reaches 3.65V;

[0126] 5. Let the battery sit for another 10 minutes;

[0127] 6. Then discharge at a constant power of 1P until the voltage drops to 2.5V;

[0128] 7. After discharging, let the battery rest for another 10 minutes;

[0129] 8. Repeat steps 4 to 7 for a total of 45 cycles;

[0130] 9. After completing the cycle, let the battery rest for 2 hours;

[0131] 10. Charge at a constant power of 0.5P until the voltage reaches 3.65V;

[0132] 11. After charging is complete, let the battery sit for 10 minutes;

[0133] 12. Then discharge at a constant power of 0.5P until the voltage drops to 2.5V;

[0134] 13. After discharging, let the battery rest for another 10 minutes;

[0135] 14. Finally, repeat the process steps 10 to 13.

[0136] Comparative Example 1

[0137] 1. Adjust the temperature of the constant temperature box to 25℃±2℃, and then let it stand for 2 hours; perform the following charge and discharge cycle steps under this temperature condition;

[0138] 2. Charge at a constant power of 0.5P to 3.65V;

[0139] 3. Let the battery sit for 10 minutes;

[0140] 4. Discharge to 2.5V at a constant power of 0.5P;

[0141] 5. Let the battery sit for another 10 minutes;

[0142] 6. Finally, repeat steps 2 to 5.

[0143] Comparative Example 2

[0144] 1. Adjust the temperature of the constant temperature box to 25℃±2℃, and then let it stand for 2 hours; perform the following charge and discharge cycle steps under this temperature condition;

[0145] 2. Discharge at 0.5C until the voltage reaches 2.5V;

[0146] 3. Let the battery sit for 10 minutes;

[0147] 4. Then charge at a constant power of 0.05P until the voltage reaches 3.65V;

[0148] 5. Let the battery sit for another 10 minutes;

[0149] 6. Then discharge at a constant power of 1P until the voltage drops to 2.5V;

[0150] 7. After discharging, let the battery rest for another 10 minutes;

[0151] 8. Repeat steps 4 to 7 for a total of 60 cycles;

[0152] 9. After completing the cycle, let the battery rest for 2 hours;

[0153] 10. Charge at a constant power of 0.5P until the voltage reaches 3.65V;

[0154] 11. After charging is complete, let the battery sit for 10 minutes;

[0155] 12. Then discharge at a constant power of 0.5P until the voltage drops to 2.5V;

[0156] 13. After discharging, let the battery rest for another 10 minutes;

[0157] 14. Finally, repeat the process steps 10 to 13.

[0158] To ensure the accuracy and reliability of the experimental data and minimize possible accidental errors during the testing process, the cycling performance tests were conducted on Examples 1 to 4 and Comparative Examples 1 and 2 according to the procedures of the above Examples and Comparative Examples. Specifically, the process steps 10 to 13 were repeated, and the cycle capacity retention data at 50, 250, and 500 cycles were recorded.

[0159] To further ensure the representativeness and accuracy of the experimental data, three batteries were selected for each test example for cycle performance testing. This was done to increase the sample size and improve the reliability and statistical significance of the data. The cell numbers of these three batteries were labeled 1, 2, and 3, respectively, to facilitate clear identification and differentiation of each battery's performance in subsequent data analysis and comparison.

[0160] The test results of Examples 1 to 4 and Comparative Examples 1 to 2 are shown in Table 1.

[0161] Table 1 Cyclic test results of Examples 1-4 and Comparative Examples 1-2

[0162]

[0163]

[0164] From the data shown in Table 1, it can be seen that before the lithium iron phosphate battery cell is subjected to a cycle test, the capacity retention rate of the battery is significantly improved under the same number of cycles through the pretreatment method of the present invention. Specifically, when the cycle test reaches the 50th week, it can be seen that the cycle capacity retention rate of the battery of Example 1 reaches more than 99%, while Example 2 exceeds 99.3%, and the performance of Example 3 is even more outstanding, reaching more than 99.5%, and Example 4 also exceeds 99.4%. In comparison, the cycle capacity retention rate of the battery in the control group is only 98.7% (Comparative Example 1) and 98.3% (Comparative Example 2) under the best conditions, which is obviously a significant gap compared with the examples.

[0165] As the number of cycles increases, this difference becomes more significant when the number of cycles reaches 500 weeks. At this time, the battery cycle capacity retention rate of Example 1 is still maintained at more than 95.3%, while Example 2 exceeds 96.4%. The performance of Example 3 is even more remarkable, reaching more than 97.5%, and Example 4 also performs well, exceeding 97.4%. In the best case, the cycle capacity retention rate of the battery in the control group is only 95.1% (Comparative Example 1) and 88.5% (Comparative Example 2), which is further widened compared with the examples. This result fully proves that the method of improving the cycle life of lithium-ion batteries by pre-treating lithium iron phosphate batteries before the cycle test of the present invention can significantly improve the cycle performance and capacity retention rate of the battery.

[0166] SOH (State of Health) is an important indicator to measure the performance status of the battery. It represents the ratio of the actual capacity of the battery during use to the nominal capacity when it was new from the factory, that is, the ratio of the current fully charged energy of the battery to the fully charged energy of the fresh battery. The SOH value range is usually from 100% (indicating that the battery is in a brand new state) to 0% (indicating that the battery is completely scrapped). When the SOH of the battery is below a certain threshold, such as 60% or 70%, it usually means that the performance of the battery has begun to decline significantly. This decline may have a negative impact on the endurance and driving experience of electrical equipment such as electric vehicles.

[0167] In the embodiment of the present invention, by increasing the number of low-rate charging and high-rate discharging, the effect can be significantly improved. Specifically, when the SOH retention rate of the battery reaches 79%, the number of cycles will increase significantly. However, it should be noted that it is not simply a matter of repeating the above-mentioned charge and discharge process as many times as possible. When the number of activations of the battery reaches a certain level, the effect of further improvement will gradually deteriorate. If the number of activations is continuously increased, it may even cause lithium deposition on the electrode. For example, in the case of Comparative Example 2, the surface of the electrode after the cycle is as follows: Figure 3 This situation will worsen the battery's cycle performance and have a negative impact on the battery's health. Therefore, in practical applications, it is necessary to reasonably control the number and frequency of charge and discharge to ensure the best performance and longest service life of the battery.

[0168] This invention proposes a method for pre-treating lithium iron phosphate batteries before cycling to improve their cycle life. Specifically, the method involves charging the battery at a low rate and then discharging it at a high rate (i.e., within the battery's capacity). By repeating this charge and discharge process multiple times, the lithium content stored in the negative electrode can be effectively increased. This allows lithium ions to be released continuously and slowly during subsequent operation, significantly improving the battery's cycling performance.

[0169] The advantages of this method are mainly reflected in the following aspects:

[0170] ① No changes are required to the battery cell system, maintaining the original structure and material properties of the battery cell.

[0171] ② There is no need to significantly change the existing lithium iron phosphate battery manufacturing process, thus avoiding additional process adjustments and cost investment.

[0172] ③After being treated by this method, the lithium iron phosphate battery cells showed obvious performance improvement in the early cycle tests, and the cycle stability was significantly improved.

[0173] The present invention provides a simple and efficient pretreatment method, which can significantly improve the cycle life of lithium iron phosphate batteries without adding additional costs and complicated processes, and has high practical value and application prospects.

[0174] It should be pointed out that although the various steps in the above embodiments are described in a specific order, those skilled in the art will understand that in order to achieve the effects of the present invention, different steps do not have to be performed in such an order. They can be performed simultaneously (in parallel) or in other orders. These changes are within the scope of protection of the present invention.

[0175] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A method for improving the cycle life of a lithium ion battery, characterized in that: include: S1, charging to 3.65-3.75V at a preset charging power, wherein the preset charging power is less than or equal to 0.05P, where P is the design power of the battery cell; S2, let stand for 10-60 minutes; S3, discharging to 2.0-2.5V at a preset discharge power, wherein the preset discharge power is greater than or equal to 0.5P; S4, let stand for 10-60 minutes; S5, repeat steps S1-S4 at least 5 times.

2. The method according to claim 1, characterized in that In step S1, charging to 3.65-3.75V at a preset charging power includes: At 0.01P-0.05P, the constant power supply is 3.65~3.75V.

3. The method according to claim 2, characterized in that The constant power supply to 3.65-3.75V at 0.01P-0.05P includes: At 0.05P, constant power supply to 3.65V.

4. The method according to claim 1, characterized in that: In step S3, discharging to 2.0-2.5V at a preset discharge power includes: At 0.5P-1P, constant power discharge to 2.0-2.5V.

5. The method according to claim 4, characterized in that The constant power discharge to 2.0-2.5V at 0.5P-1P includes: At 1P, constant power discharge to 2.5V.

6. The method according to claim 1, characterized in that The step S5, repeating steps S1-S4 at least 5 times, comprises: S5, repeat steps S1-S4 for 5-45 times.

7. The method according to claim 1, characterized in that Before step S1, the method further includes: Discharge to 2.0-2.5V.

8. The method according to claim 1, characterized in that In the step S2, The standing time is 10 minutes; In step S4, the standing time is 10 minutes.

9. A method for preparing a lithium ion battery, characterized in that: include: The battery cell after liquid injection is formed; The formed battery cell is treated by the method for improving the cycle life of the lithium ion battery.

10. The method according to claim 9, characterized in that The battery cell comprises a plurality of cathode plates and a plurality of anode plates which are stacked at intervals, and a separator is arranged between adjacent cathode plates and anode plates; wherein the electrode material of the anode plates is lithium iron phosphate.

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