Lithium ion battery sectional type rapid charging method capable of reducing polarization

Abstract

The invention relates to a lithium ion battery sectional type quick charging method for reducing polarization, which comprises the following steps of: firstly, carrying out stepped constant-current and constant-voltage charging on a battery cell: dividing into N constant-current and constant-voltage charging stages, and carrying out constant-current and constant-voltage charging in each constant-current and constant-voltage charging stage to a corresponding limited voltage or limited capacity; and performing constant-voltage charging on the battery cell until the final current is reached. In the charging process of the lithium ion battery, multi-stage capacity cut-off and multi-stage voltage termination are combined, the charging process is divided into multi-stage constant-current and constant-voltage charging, constant-current and constant-voltage charging in each stage reaches the limited voltage or the limited capacity, and the constant-current and constant-voltage charging is stopped until the voltage reaches the upper limit voltage of the battery. According to the sectional type rapid charging method, the polarization lithium concentration difference between the interior and the exterior of the graphite particles can be effectively eliminated, diffusion of lithium into the graphite particles can be improved, damage to the graphite structure can be avoided, the rapid charging time of the battery can be optimized, and the cycle performance of the battery can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery charging, and particularly to a segmented fast charging method for lithium-ion batteries to reduce polarization. Background Art

[0002] As a widely used commercial battery, lithium-ion batteries have been deployed on an unprecedented scale in related fields such as electric vehicles, energy storage systems, and 3C devices, and have broad application prospects in the future. People have put forward higher requirements for future lithium-ion batteries. While pursuing long battery life and high safety performance, they have also begun to pay attention to the fast charging performance of lithium batteries. Therefore, when designing the battery core, it is necessary to take into account the fast charging performance of the battery.

[0003] For lithium-ion batteries, during the charging process, the negative electrode potential is basically close to the metal lithium potential, which is extremely likely to cause the precipitation of lithium dendrites. In addition, during high-rate charging, a series of problems such as lithium plating, mechanical effects, and heat release will lead to the attenuation of battery capacity and power. Therefore, when designing the battery core, it is necessary to consider the electrochemical characteristics inside the lithium-ion battery. Especially for lithium-ion batteries with a graphite negative electrode system, the destruction of the graphite negative electrode crystal structure and the loss of battery capacity caused by lithium precipitation under high-rate charging should be avoided, resulting in a reduction in battery life. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a segmented fast charging method for lithium-ion batteries to reduce polarization, which not only optimizes the fast charging time of the battery but also improves the battery cycle performance.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: The present invention first provides a segmented fast charging method for lithium-ion batteries to reduce polarization, which includes the following steps: First, the battery core is charged with stepped constant current and constant voltage: divided into N constant current and constant voltage charging stages, and each constant current and constant voltage charging stage is charged with constant current and constant voltage to the corresponding limited voltage or limited capacity; Then, the battery core is charged with constant voltage until the final current.

[0006] During the charging process of the lithium-ion battery, the present invention combines multi-stage capacity cut-off and multi-stage voltage termination, divides the charging process into multi-stage constant current and constant voltage charging. Each stage of constant current and constant voltage charging is carried out until the limited voltage or limited capacity is reached. After the voltage reaches the upper limit voltage of the battery, the charging rate is reduced and the constant current and constant voltage mode is used to charge to the final current. This can effectively eliminate the polarization lithium concentration difference inside and outside the graphite particles, is beneficial to improving the diffusion of lithium into the graphite particles, and can also avoid the damage of the graphite structure. It not only optimizes the fast charging time of the battery but also improves the battery cycle performance. The traditional constant current and constant voltage charging only relies on voltage control, while the segmented charging of the present invention combines the limitation of voltage or capacity, calibrates the capacity and voltage simultaneously, and dynamically corrects the SOC error. In addition, for the battery system, the method of the present invention can also combine the single-cell voltage equalization strategy to optimize the charging efficiency of inconsistent batteries.

[0007] As a further improvement of the above solution of the present invention, during each stage of constant current and constant voltage charging, the voltage and the charged capacity of the battery cell are detected in real time, and it is judged whether to jump to the next stage of constant current and constant voltage charging according to the following conditions: When the voltage of the battery cell reaches the limited voltage corresponding to this stage of constant current and constant voltage charging and the charged capacity of the battery cell does not reach the limited capacity corresponding to this stage of constant current and constant voltage charging, the constant current charging is stopped and the constant voltage charging is switched. When the current of the battery cell drops to the final current or the charged capacity of the battery cell reaches the limited capacity corresponding to this stage of constant current and constant voltage charging, it jumps to the next stage of constant current and constant voltage charging; Or, when the charged capacity of the battery cell reaches the limited capacity corresponding to this stage of constant current and constant voltage charging and the voltage of the battery cell does not reach the limited voltage corresponding to this stage of constant current and constant voltage charging, it directly jumps to the next stage of constant current and constant voltage charging.

[0008] As a further improvement of the above solution of the present invention, the constant current and constant voltage charging process is divided into 20 stages of constant current and constant voltage charging. Among them, the 3rd - 16th stages of constant current and constant voltage are the fast charging stages, and the rest of the constant current and constant voltage stages are non-fast charging stages. The battery cell power in the fast charging stage is 5 - 85%, preferably 8 - 80%.

[0009] As a further improvement of the above solution of the present invention, the fast charging stage includes four stages, where: the 3rd constant current and constant voltage stage is the first fast charging stage, the 4th - 7th constant current and constant voltage stages are the second fast charging stage, the 8th - 14th constant current and constant voltage stages are the third fast charging stage, and the 15th - 16th constant current and constant voltage stages are the fourth fast charging stage. The charging rates of the first fast charging stage, the second fast charging stage, the third fast charging stage, and the fourth fast charging stage decrease in sequence, and the charging rate of each stage is constant. And between any two adjacent stages, the rest time of the battery cell is 0. The fast charging stage is further divided into four major stepped chargings. The current decreases as the SOC increases, and each time entering the next stepped charging, the current decreases. According to the segmented fast charging method, the polarization lithium concentration difference inside and outside the graphite particles can be effectively eliminated, which is beneficial to improving the diffusion of lithium into the graphite particles, and can also avoid the damage of the graphite structure. Further dividing the fast charging stage into stages is to illustrate that the current in each step is constant and the current decreases as the SOC increases, eliminating battery polarization, and in each step, the dual conditions of multi-stage voltage and capacity are specified in detail.

[0010] As a further improvement of the above solution of the present invention, the specified voltage and specified capacity corresponding to each constant current and constant voltage charging stage are obtained by calibrating the capacity of the battery cell.

[0011] As a further improvement of the above solution of the present invention, the capacity calibration includes the following steps: S1. Constant current and constant voltage charge the battery cell at a predetermined rate until it is fully charged. S2. After leaving the battery cell fully charged in step S1 to rest for a predetermined time, discharge it at a constant current at a predetermined rate until it is emptied, and obtain the initial discharge capacity of the battery cell, denoted as Cs0. S3. After leaving the battery emptied in step S2 to rest for a predetermined time, perform N constant current and constant voltage charging stages, and detect the voltage and the charged capacity of the battery cell in real time. Each constant current and constant voltage charging stage is cut off according to X%Cs0(i) of the electricity until the battery reaches the Nth constant current and constant voltage charging stage; then charge it at a constant voltage until it is fully charged; obtain the specified voltage and the specified capacity X%Cs0(i) corresponding to each constant current and constant voltage charging stage, 1 ≤ i ≤ N, and i is an integer. According to the adapted fast charging performance of the battery cell, it is preferred to ensure that the battery cell is charged within a certain SOC range within a specified time.

[0012] As a further improvement of the above solution of the present invention, in the 1st charging stage, the value of X% ranges from 4.9% to 7.9%, preferably 7.9%; in the 2nd charging stage, the value of X% ranges from 5% to 8%, preferably 8%; in the 3rd charging stage, the value of X% is 15%; in the 4th - 19th charging stages, the value of X% is 5%. According to the adapted fast charging performance of the battery cell, it is preferred to ensure that the battery cell is charged within a certain SOC range within a specified time.

[0013] As a further improvement to the above solution of the present invention, the capacity of the battery cell is recalibrated every set number of cyclic charge-discharge periods, and the obtained discharge capacity of the battery cell is denoted as Cs x , where x is the number of capacity calibrations, and the cyclic charge-discharge period is 50 - 150 cycles; preferably 100 cycles.

[0014] As a further improvement to the above solution of the present invention, in the fast charging stage, the charging current in the first fast charging stage is 2.1Cs x - 3Cs x , the charging current in the second fast charging stage is 1.8Cs x - 2.7Cs x , the charging current in the third fast charging stage is Cs x - 1.6Cs x , and the charging current in the fourth fast charging stage is 0.6Cs x - Cs x .

[0015] As a further improvement to the above solution of the present invention, the charging current in the non-fast charging stage is 0.33Cs x - 0.5Cs x .

[0016] Compared with the prior art, the present invention has the following beneficial effects: During the charging process of the lithium-ion battery of the present invention, multi-stage capacity cut-off and multi-stage voltage termination are combined, and the charging process is divided into multi-stage constant current and constant voltage charging. Each stage of constant current and constant voltage charging is carried out until the limited voltage or limited capacity is reached. After the voltage reaches the upper limit voltage of the battery, the charging rate is reduced and the constant voltage method is used to charge to the final current. By combining capacity and voltage calibration simultaneously and dynamically correcting the SOC error, it can effectively eliminate the polarization lithium concentration difference inside and outside the graphite particles, which is beneficial to improving the diffusion of lithium into the graphite particles, and can also avoid the damage of the graphite structure. It not only optimizes the fast charging time of the battery but also improves the battery cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the stepwise constant current and constant voltage charging process in a method for segmented fast charging of a polarization-reduced lithium-ion battery provided by an embodiment of the present invention; Figure 2 It is a schematic diagram of the stepwise constant current and constant voltage charging process in the comparative example; Figure 3 It is a test result diagram of the discharge capacity retention rate obtained by cyclic charge and discharge of the embodiment and the comparative example DETAILED DESCRIPTION OF THE EMBODIMENTS For the convenience of understanding the present invention, the present invention will be described more comprehensively below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0019] Embodiment Refer to Figure 1 , this embodiment provides a segmented fast charging method for a lithium-ion battery to reduce polarization, which includes the following steps: First, the battery cell is charged with constant current and constant voltage in a stepped manner: divided into N constant current and constant voltage charging stages, and each constant current and constant voltage charging stage is charged with constant current and constant voltage to the corresponding limited voltage or limited capacity; then the battery cell is charged with constant voltage until the final current.

[0020] In this embodiment, during each constant current and constant voltage charging stage, the voltage and the charged capacity of the battery cell are detected in real time, and it is judged whether to jump to the next constant current and constant voltage charging stage according to the following conditions: When the voltage of the battery cell reaches the limited voltage corresponding to this constant current and constant voltage charging stage and the charged capacity of the battery cell does not reach the limited capacity corresponding to this constant current and constant voltage charging stage, the constant current charging is stopped and the constant voltage charging is switched. When the current of the battery cell drops to the final current or the charged capacity of the battery cell reaches the limited capacity corresponding to this constant current and constant voltage charging stage, it jumps to the next constant current and constant voltage charging stage; Or, when the charged capacity of the battery cell reaches the limited capacity corresponding to this constant current and constant voltage charging stage and the voltage of the battery cell does not reach the limited voltage corresponding to this constant current and constant voltage charging stage, it directly jumps to the next constant current and constant voltage charging stage.

[0021] In this embodiment, the constant current and constant voltage charging process is divided into 20 constant current and constant voltage charging stages (i.e., N = 20). Among them, the 3rd to 16th constant current and constant voltage stages are fast charging stages, and the remaining constant current and constant voltage stages are non-fast charging stages. In the fast charging stage, the battery cell power is 5% - 85%, preferably 8% - 80%. Among them, the fast charging stage includes four stages, where: the 3rd constant current and constant voltage stage is the first fast charging stage, the 4th to 7th constant current and constant voltage stages are the second fast charging stage, the 8th to 14th constant current and constant voltage stages are the third fast charging stage, and the 15th to 16th constant current and constant voltage stages are the fourth fast charging stage. The charging rates of the first fast charging stage, the second fast charging stage, the third fast charging stage, and the fourth fast charging stage decrease in sequence, and the charging rate of each stage is constant. And between any two adjacent stages, the rest time of the battery cell is 0.

[0022] The limited voltage and limited capacity corresponding to each constant current and constant voltage charging stage are obtained by calibrating the capacity of the battery cell. The capacity calibration includes the following steps: S1. Constant current and constant voltage charge the battery cell to full charge at a predetermined rate. S2. After resting the battery cell charged to full charge in step S1 for a predetermined time, discharge it at a constant current to empty at a predetermined rate (the same rate as in step S1) to obtain the initial discharge capacity of the battery cell, denoted as Cs0. S3. After resting the battery discharged in step S2 for a predetermined time, perform N constant current and constant voltage charging stages, and detect the voltage and the charged capacity of the battery cell in real time. Each constant current and constant voltage charging stage is cut off according to X%Cs0(i) power until the battery reaches the Nth constant current and constant voltage charging stage; then charge it at a constant voltage to full charge; obtain the limited voltage and limited capacity X%Cs0(i) corresponding to each constant current and constant voltage charging stage, 1 ≤ i ≤ N, and i is an integer. Specifically, in the 1st charging stage, the value of X% is 4.9% - 7.9%; in the 2nd charging stage, the value of X% is 5% - 8%; in the 3rd charging stage, the value of X% is 15%; in the 4th to 19th charging stages, the value of X% is 5%.

[0023] Re-calibrate the capacity of the battery cell every set number of cyclic charge and discharge cycles, and re-obtain the discharge capacity of the battery cell, denoted as Cs x , x is the number of capacity calibrations, and the cyclic charge and discharge cycle is 50 - 150 cycles. In this embodiment, the cyclic charge and discharge cycle is 100 cycles. In the fast charging stage, the charging current in the first fast charging stage is 2.1Cs x ~3Cs x , the charging current in the second fast charging stage is 1.8Cs x ~2.7Cs x , the charging current in the third fast charging stage is Cs x ~1.6Cs x, the charging current in the fourth fast charging stage is 0.6Cs x ~Cs x . The charging current in the non-fast charging stage is 0.33Cs x ~0.5Cs x .

[0024] Next, at room temperature, 5 batteries (all 5 batteries are produced in the same batch) are selected according to the method of this embodiment for 500 charge and discharge cycle tests. First, the capacities of the 5 batteries are calibrated. After obtaining the limiting voltages of the 5 batteries, the average value is taken. Here, only the specific data of one battery is listed. The initial discharge capacity Cs0 of the battery cell obtained by the initial capacity calibration is 116.5 Ah. After each 100 cycles, the capacity is recalibrated to obtain a new limiting capacity. The limiting capacities and limiting voltages in the initial stages are as shown in Table 1 below: Table 1

[0025] After repeating this 499 times, the average discharge capacity retention rate of the 5 batteries is as Figure 3 shown by curve 1 in

[0026] Comparative example At room temperature, the battery is charged according to the ordinary step charging method. The charging process is as Figure 2 shown, and specifically includes the following steps: First, the battery cell is charged with constant current in steps: divided into 6 charging stages, and each constant current charging stage is charged with constant current to the corresponding limiting capacity; then the battery cell is charged with constant voltage until the final current.

[0027] In this comparative example, the multi-stage constant current charging includes 6 stages, where the fast charging stage is the 2nd to 5th stages, and the non-fast charging stage is the 1st and 6th stages.

[0028] In this comparative example, during each constant current and constant voltage charging stage, the charged capacity of the battery cell is detected in real time. When the charged capacity of the battery cell during constant current charging reaches the limiting capacity, it jumps to the next constant current and constant voltage charging stage.

[0029] In this comparative example, the limiting capacity corresponding to each constant current charging stage is obtained by calibrating the capacity of the battery cell. The capacity calibration includes the following steps: S1. Charge the battery cell with constant current and constant voltage to full charge at a predetermined rate (the same as in the embodiment); S2. After leaving the battery cell charged to full charge in step S1 for a predetermined period of time, discharge it with constant current at a predetermined rate (the same as in the embodiment) until it is emptied, and obtain the initial discharge capacity of the battery cell, denoted as Cs0; S3. After leaving the battery discharged in step S2 for a predetermined duration, perform 6 charging stages, and detect the voltage and the charged capacity of the battery cell in real time. Each constant current charging stage is cut off according to X%Cs0(i) of the battery capacity until the battery reaches the 6th charging stage; then perform constant voltage charging until full charge; obtain the limited capacity X%Cs0(i) corresponding to each constant current charging stage, where 1 ≤ i ≤ 6 and i is an integer. Specifically, in the first constant current charging stage, charging stops when 8%Cs is charged; in the second constant current charging stage, charging stops when 7%Cs is charged; in the third constant current charging stage, charging stops when 20%Cs is charged; in the fourth constant current charging stage, charging stops when 35%Cs is charged; in the fifth constant current charging stage, charging stops when 10%Cs is charged; Re-calibrate the capacity of the battery cell every set number of charge-discharge cycles, and re-obtain the discharge capacity of the battery cell, denoted as Cs x , where x is the number of capacity calibrations, and the charge-discharge cycle is 100 cycles. In the fast charging stage, the charging current in the second constant current charging stage is 2.5Cs x , the charging current in the third constant current charging stage is 2.3Cs x , the charging current in the fourth constant current charging stage is 1.3Cs x , the charging current in the fifth constant current charging stage is 0.8Cs x , and the charging currents in the first constant current charging stage and the sixth constant current and constant voltage charging stage are 0.33Cs x .

[0030] Next, at room temperature, select 5 batteries (the same batch as the batteries in the examples) according to the comparative example method and perform 500 charge-discharge cycle tests. First, calibrate the capacity of the 5 batteries, obtain the average value of the limited voltages of the 5 batteries, and only list the specific data of one of the batteries here. The initial discharge capacity Cs0 of the battery cell obtained from the initial capacity calibration is 116.2 Ah. After each subsequent 100-week cycle, perform capacity re-calibration to obtain a new limited capacity. The limited capacities and limited voltages at each stage for the first time are shown in Table 2 below: Table 2

[0031] After repeating this 499 times, the average discharge capacity retention rate of the 5 batteries is as Figure 3 shown by curve 2 in

[0032] From Figure 3 the results of the battery room temperature cycle test, it can be seen that compared with the ordinary stepped charging method, the segmented fast charging method for reducing the polarization of lithium-ion batteries in the present invention can significantly improve the cycle life of lithium-ion batteries with a graphite negative electrode system.

[0033] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0034] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A segmented fast charging method for lithium-ion batteries with reduced polarization, characterized in that: It includes the following steps: First, the battery cell is charged with step-by-step constant current and constant voltage: divided into N constant current and constant voltage charging stages, each constant current and constant voltage charging stage is charged with constant current and constant voltage to the corresponding limited voltage or limited capacity; Then charge the battery cell at a constant voltage until the final current.

2. The method for rapid charging of lithium-ion batteries with reduced polarization according to claim 1, characterized in that: In each constant current and constant voltage charging stage, the voltage and charging capacity of the battery cell are detected in real time, and whether to jump to the next constant current and constant voltage charging stage is determined according to the following conditions: When the cell voltage reaches the limited voltage corresponding to the constant current and constant voltage charging stage and the cell charging capacity does not reach the limited capacity corresponding to the constant current and constant voltage charging stage, the constant current charging is stopped and switched to constant voltage charging. When the cell current drops to the final current or the cell charging capacity reaches the limited capacity corresponding to the constant current and constant voltage charging stage, it jumps to the next constant current and constant voltage charging stage. Alternatively, when the charged capacity of the battery cell reaches the limited capacity corresponding to the constant current and constant voltage charging stage and the battery cell voltage does not reach the limited voltage corresponding to the constant current and constant voltage charging stage, it directly jumps to the next constant current and constant voltage charging stage.

3. The lithium-ion battery segmented fast charging method for reducing polarization according to claim 1, characterized in that: The constant current constant voltage charging process is divided into 20 constant current constant voltage charging stages, among which the 3rd to 16th constant current constant voltage stages are fast charging stages, and the remaining constant current constant voltage stages are non-fast charging stages. The battery cell power in the fast charging stage is 5-85%.

4. The lithium-ion battery segmented fast charging method for reducing polarization according to claim 3, characterized in that: The fast charging stage includes four stages, wherein the 3rd constant current and constant voltage stage is the first fast charging stage, the 4th to 7th constant current and constant voltage stages are the second fast charging stage, the 8th to 14th constant current and constant voltage stages are the third fast charging stage, and the 15th to 16th constant current and constant voltage stages are the fourth fast charging stage. The charging rates of the first fast charging stage, the second fast charging stage, the third fast charging stage, and the fourth fast charging stage decrease successively, and the charging rates of each stage are constant, and the battery cell rest time between any two adjacent stages is 0.

5. The lithium-ion battery segmented fast charging method for reducing polarization according to claim 1, characterized in that: The limited voltage and limited capacity corresponding to each constant-current and constant-voltage charging stage are obtained by calibrating the capacity of the battery cell.

6. The lithium-ion battery segmented fast charging method for reducing polarization according to claim 5, characterized in that: The capacity calibration comprises the following steps: S1. Charge the battery cell at a predetermined rate with constant current and constant voltage until it is fully charged; S2. After the fully charged cell in step S1 is set aside for a predetermined period of time, it is discharged at a predetermined rate at a constant current until it is empty, and the initial discharge capacity of the cell is obtained, which is recorded as Cs0; S3. After the battery discharged in step S2 is left for a predetermined period of time, N constant current and constant voltage charging stages are performed, and the voltage and charging capacity of the battery cell are detected in real time. Each constant current and constant voltage charging stage is terminated according to the X%Cs0(i) power until the battery reaches the Nth constant current and constant voltage charging stage; then constant voltage charging is adopted to fully charge the battery; and the limiting voltage and limiting capacity X%Cs0(i) corresponding to each constant current and constant voltage charging stage are obtained, 1≤i≤N, and i is an integer.

7. The lithium-ion battery segmented fast charging method for reducing polarization according to claim 6, characterized in that: In the first charging stage, X% is 4.9% to 7.9%; in the second charging stage, X% is 5% to 8%; in the third charging stage, X% is 15%; in the fourth to nineteenth charging stages, X% is 5%.

8. The lithium-ion battery segmented fast charging method for reducing polarization according to claim 6, characterized in that: The capacity of the battery cell is recalibrated every set cycle of charge and discharge, and the discharge capacity of the battery cell is recorded as Cs. x , x is the number of capacity calibration times, and the cycle charge and discharge period is 50-150 cycles.

9. The lithium-ion battery segmented fast charging method for reducing polarization according to claim 8, characterized in that: In the fast charging stage, the charging current of the first fast charging stage is 2.1Cs x ~3Cs x , the charging current of the second fast charging stage is 1.8Cs x ~2.7Cs x , the charging current in the third fast charging stage is Cs x ~1.6Cs x , the charging current of the fourth fast charging stage is 0.6Cs x ~Cs x .

10. The lithium-ion battery segmented fast charging method for reducing polarization according to claim 8, characterized in that: The charging current in the non-fast charging stage is 0.33Cs x ~0.5Cs x .

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