A low-cost method to quickly eliminate the polarization voltage of lithium-ion batteries

Abstract

The present invention relates to the technical field of batteries, and discloses a method for quickly eliminating the polarization voltage of a lithium-ion battery at a low cost, comprising the following steps: 1) charging or discharging the lithium-ion battery to a target voltage according to a set mode; 2) placing the lithium-ion battery that has reached the target voltage on hold for a certain period of time; 3) applying an external reverse micro current to the lithium-ion battery after being placed on hold for a short period of time to perform a short-term discharge or charging intervention; 4) placing the lithium-ion battery on hold for a period of time to perform a voltage test, and the measured voltage is the voltage of the lithium-ion battery after polarization elimination. The present invention can achieve a stable balance of the battery open circuit voltage in a relatively short period of time by applying a micro reverse current, which is conducive to screening out bad batteries with large self-discharge in a relatively short period of time, shortening the production cycle of batteries and their voltage matching, and improving the accuracy of static voltage matching. Existing detection equipment does not need to be modified or upgraded, and no additional costs are added.

Description

Technical Field

[0001] The invention patent relates to the technical field of batteries, and specifically, to a method for quickly eliminating the polarization voltage of lithium-ion batteries at low cost. Background Art

[0002] At present, batteries are increasingly used in mobile communications, electric vehicles, energy storage and other fields, covering almost all areas of our lives, production and scientific research. In large-scale battery applications, multiple single cells are usually required to be connected in series and parallel to form a battery pack. The consistency of the single cells directly affects the performance of the battery module, and even directly affects the safety and service life of the battery.

[0003] According to the principle of electrochemistry, a single cell will produce polarization after charging and discharging, causing its open circuit voltage to deviate from the equilibrium voltage of the battery. The greater the charge and discharge current, the more serious the polarization phenomenon, and the greater the deviation of the battery open circuit voltage from the equilibrium voltage, which seriously affects the consistency of the battery. Even after stopping charging and discharging, the polarization phenomenon of the battery will still exist for a certain period of time, and may even last for a long time, more than ten hours or even several days.

[0004] The use of lithium-ion batteries in groups must meet two conditions: (1) the defective batteries with large self-discharge are selected by the voltage difference before and after aging; (2) the voltage must be in a stable state when the batteries are grouped. In condition (1), the voltage before aging usually undergoes a charging process. After charging, the battery has a polarization voltage. If the polarization voltage is not eliminated, it will lead to a misjudgment of battery self-discharge. In condition (2), good batteries generally undergo a charging or discharging process before grouping, and also have a polarization voltage. If the polarization voltage is not eliminated, it will lead to a large voltage difference between single cells in the same group of batteries, affecting the overall performance of the battery group. Polarization is a normal chemical phenomenon after lithium-ion batteries are charged and discharged, and it is also a problem that cannot be avoided during the use of lithium-ion batteries. The traditional method of eliminating the polarization voltage of lithium-ion batteries after charging and discharging is to allow the battery to naturally eliminate polarization by placing it on hold for a long time to achieve voltage stability, or to accelerate the elimination of polarization voltage by storing the battery in a high temperature environment. This method may increase energy consumption costs, and the shortening of the shelf time to eliminate polarization voltage is limited, which seriously affects the battery output cycle and production efficiency.

[0005] The methods for eliminating battery polarization in the prior art are not only complicated and costly for battery manufacturers upstream of the application end, but many of the methods are also not universally applicable to existing general-purpose charging and discharging detection equipment. Summary of the invention

[0006] The purpose of the present invention is to provide a method for quickly eliminating the polarization voltage of a lithium-ion battery at a low cost, aiming to solve the problem of high cost of eliminating battery polarization in the prior art.

[0007] The present invention is implemented as follows: a method for quickly eliminating the polarization voltage of a lithium-ion battery at a low cost, comprising the following steps:

[0008] 1) charging or discharging the lithium-ion battery to a target voltage according to a set mode;

[0009] 2) placing the lithium-ion battery that has reached the target voltage on hold for a certain period of time;

[0010] 3) applying an external reverse micro current to the lithium-ion battery after being shelved to perform short-time discharge or charge intervention, including: performing discharge intervention on the lithium-ion battery charged in step 1), or performing charge intervention on the lithium-ion battery discharged in step 1);

[0011] 4) After the lithium-ion battery is left alone for a period of time, a voltage test is performed, and the measured voltage is the voltage of the lithium-ion battery after polarization is eliminated.

[0012] Furthermore, in step 1), the setting mode includes but is not limited to constant current, constant voltage or constant current constant voltage mode, and the target voltage is the voltage corresponding to charging or discharging the lithium-ion battery to a certain state of charge according to the setting mode.

[0013] Furthermore, in step 2), the holding time is 0 to 100 hours.

[0014] Furthermore, in step 3), the direction of the tiny current is opposite to the direction of the discharge or charge current in step 1), the magnitude of the tiny current is 0 to 0.5C, and the tiny current action time is 0 to 100 hours.

[0015] Furthermore, in step 3), the amount of charge of the lithium-ion battery that is changed due to the tiny current does not exceed 1% of the total charge of the lithium-ion battery.

[0016] Furthermore, in the process of step 3) discharge intervention or charging intervention, it is divided into the 1st intervention stage, the 2nd intervention stage, ..., the Nth intervention stage in sequence from the beginning of intervention, and the tiny current in the 1st intervention stage ≥ the tiny current in the 2nd intervention stage ≥ ... ≥ the tiny current in the Nth intervention stage.

[0017] Furthermore, the intervention time of the first intervention stage ≤ the intervention time of the second intervention stage ≤ … ≤ the intervention time of the Nth intervention stage.

[0018] Furthermore, in the process of step 3) discharge intervention or charge intervention, it is divided into the first intervention stage, the first pause stage, the second intervention stage, the second pause stage, ..., the Nth intervention stage in sequence from the beginning of intervention. After the small current acts for a certain period of time in each intervention stage, it pauses for a period of time, and then enters the next intervention stage until the discharge intervention or charge intervention is completed.

[0019] Furthermore, the discharge intervention or charge intervention process of step 3) is determined based on the polarization curve of the lithium-ion battery.

[0020] Furthermore, in step 4), the holding time is 0 to 100 hours.

[0021] Compared with the prior art, the present invention provides a low-cost method for quickly eliminating the polarization voltage of a lithium-ion battery, which has the following benefits: by applying a small reverse current, the battery can reach a stable open-circuit voltage balance in a relatively short time, which is beneficial for screening out defective batteries with large self-discharge in a relatively short time, shortening the production cycle of batteries and their voltage matching, and improving the accuracy of static voltage matching. Existing detection equipment does not need to be modified or upgraded, and no additional cost is added. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention provides a method for rapidly eliminating the polarization voltage of a lithium-ion battery at a low cost. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution 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. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0024] The implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0025] The same or similar numbers in the drawings of this embodiment correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right" and the like indicate directions or positional relationships based on the directions or positional relationships shown in the drawings, it is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limitations on this patent. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0026] Reference Figure 1 The figure shows a preferred embodiment of the present invention.

[0027] A method for quickly eliminating the polarization voltage of a lithium-ion battery at a low cost comprises the following steps:

[0028] 1) Charge or discharge the lithium-ion battery to the target voltage according to the set mode;

[0029] 2) The lithium-ion battery that has reached the target voltage is left alone for a certain period of time;

[0030] 3) applying an external reverse micro current to the shelved lithium-ion battery for short-term discharge or charge intervention, including: discharging the lithium-ion battery charged in step 1), or charging the lithium-ion battery discharged in step 1);

[0031] 4) After the lithium-ion battery is left aside for a period of time, a voltage test is performed. The measured voltage is the voltage of the lithium-ion battery after polarization is eliminated.

[0032] Compared with the existing methods, the low-cost method for quickly eliminating the polarization voltage of lithium-ion batteries provided in this embodiment has the following benefits: by applying a small reverse current, the battery can reach a stable open-circuit voltage balance in a shorter time, which is beneficial for screening out defective batteries with large self-discharge in a shorter time, shortening the production cycle of batteries and their voltage matching, and improving the accuracy of static voltage matching. Existing detection equipment does not need to be modified or upgraded, and no additional cost is added.

[0033] In step 1), the lithium-ion battery is charged or discharged to a target voltage according to a set mode, wherein the set mode includes but is not limited to a constant current, a constant voltage or a constant current constant voltage mode, and the target voltage is a voltage corresponding to a certain state of charge when the lithium-ion battery is charged or discharged according to the set mode.

[0034] Usually, the rated voltage of lithium-ion batteries is 3.7V due to material changes, while the rated voltage of lithium-ion batteries with lithium iron phosphate positive electrodes is 3.2V. The final charge voltage of a fully charged lithium-ion battery is generally 4.2V, and that of a lithium iron phosphate positive electrode is 3.65V. The final discharge voltage of a lithium-ion battery is 2.75V to 3.0V (the battery manufacturer gives the operating voltage range or the final discharge voltage, and the parameters are slightly different, generally 3.0V, and that of a lithium iron phosphate positive electrode is 2.5V). Continuing to discharge below 2.5V (2.0V for a lithium iron phosphate positive electrode) is called over-discharge, which can damage the battery.

[0035] For example, some lithium-ion batteries are marked with 3.7V or 4.2V, but the manufacturers mark them differently. 3.7V refers to the balanced voltage (typical voltage) of the battery during discharge, while 4.2V refers to the voltage when it is fully charged. Common rechargeable 18650 lithium batteries are marked with 3.6 or 3.7V, and 4.2V when fully charged. This has little to do with the power (capacity). The mainstream capacity of 18650 batteries ranges from 1800mAh to 2600mAh (the capacity of 18650 power batteries is mostly between 2200 and 2600mAh), and the mainstream capacity is even marked with 3500 or 4000mAh or above.

[0036] The charging process of lithium-ion batteries is generally divided into two stages. First, constant current charging, and then constant voltage charging when it is close to the termination voltage. For example, a lithium-ion battery with a capacity of 800mAh has a termination charging voltage of 4.2V. During the charging process, the lithium-ion battery is first charged with a constant current of 800mA (charging current is 1C). At the beginning, the battery voltage is boosted with a large slope. When the battery voltage is close to 4.2V, it is changed to 4.2V constant voltage charging. The current gradually decreases, and the voltage does not change much. When the charging current drops to 0.1C (about 80mA), it is considered to be close to full and the charging can be terminated (some chargers start the timer after reaching 1 / 10C and end the charging after a certain period of time). If the lithium-ion battery is overcharged, over-discharged or overcurrent during the charging or discharging process, it will cause damage to the battery or reduce its service life. When charging lithium-ion batteries, the corresponding charger is usually used to avoid battery damage or safety hazards caused by mismatch between the battery and the charger.

[0037] In step 2), the lithium-ion battery that has reached the target voltage is left for a certain period of time, which is 0 to 100 hours, and can be 5 minutes, 10 minutes, 30 minutes, 60 minutes, 2 hours, 3 hours, 5 hours, 10 hours, 20 hours, 30 hours, 50 hours, 100 hours, etc. Usually, only a short period of time, such as 5 minutes, is required before step 3) can be performed for discharge or charging intervention.

[0038] In step 3), the direction of the tiny current is opposite to the direction of the discharge or charging current in step 1), the magnitude of the tiny current is 0 to 0.5C, the action time of the tiny current is 0 to 100 hours, and the amount of charge state of the lithium-ion battery caused by the tiny current does not exceed 1% of the total charge of the lithium-ion battery.

[0039] The small current is 0~0.5C, which refers to the charging rate (C-rate) of the rechargeable battery. C is the first letter of Capacity, which is used to indicate the ratio of the current size when the battery is charged and discharged. For example: for a 1200mAh battery, 1C means 1200mA, and 0.2C means 240mA; when the rated capacity of the rechargeable battery is 1100mAh, it means that the discharge time at 1100mA (1C) can last for 1 hour, and the discharge time at 200mA (0.2C) can last for 5 hours. The charging can also be calculated in this way.

[0040] The action time of the small current is 0 to 100 hours, which can be 5 minutes, 10 minutes, 30 minutes, 60 minutes, 2 hours, 3 hours, 5 hours, 10 hours, 20 hours, 30 hours, 50 hours, 100 hours, etc.

[0041] During the process of discharge intervention or charge intervention, the amount of charge state change of the lithium-ion battery caused by the tiny current does not exceed 1% of the total charge of the lithium-ion battery. Discharge intervention or charge intervention has little effect on the total charge of the lithium-ion battery, but can eliminate the polarization voltage of the lithium-ion battery in a relatively short time.

[0042] In the process of discharge intervention or charge intervention in step 3), the intervention is divided into the first intervention stage, the second intervention stage, ..., and the Nth intervention stage in sequence from the beginning of the intervention. In each intervention stage, a small current of a certain magnitude acts (discharges or charges) for a certain time, wherein the small current in the first intervention stage ≥ the small current in the second intervention stage ≥ ... ≥ the small current in the Nth intervention stage. As the intervention stage proceeds, the small current of the intervention becomes smaller and smaller, so that the entire intervention process transitions smoothly.

[0043] Usually, the intervention time of the first intervention stage can be set to be ≤ the intervention time of the second intervention stage ≤ … ≤ the intervention time of the Nth intervention stage. This makes the intervention process smoother and achieves a better effect of eliminating polarization.

[0044] Alternatively, in step 3) during the discharge intervention or charge intervention, it can be divided into the first intervention stage, the first pause stage, the second intervention stage, the second pause stage, ..., the Nth intervention stage in sequence from the beginning of the intervention, and after the small current acts for a certain period of time in each intervention stage, it pauses for a period of time, and then enters the next intervention stage until the discharge intervention or charge intervention is completed. In each pause stage, pausing the discharge intervention or charge intervention of the lithium-ion battery is equivalent to putting the lithium-ion battery on hold for a period of time between every two intervention stages. The duration of the intervention stage and the pause stage can be controlled by a timer or a timer. This is also conducive to quickly eliminating the polarization voltage of the lithium-ion battery.

[0045] In the process of discharge intervention or charge intervention in step 3), there are several intervention stages, and the magnitude of the small current in each intervention stage and the duration of the action are determined based on the polarization curve of the lithium-ion battery. Usually, the polarization curves of lithium-ion batteries of the same type are not much different and can be determined by conventional test detection.

[0046] In step 4), the lithium-ion battery is left for a period of time before a voltage test is performed. The measured voltage is the voltage of the lithium-ion battery after polarization is eliminated. The leaving time is 0 to 100 hours (hours), which can be 5 minutes, 10 minutes, 30 minutes, 60 minutes, 2 hours, 3 hours, 5 hours, 10 hours, 20 hours, 30 hours, 50 hours, 100 hours, etc. Usually, the voltage test can be performed after leaving for 1 to 3 hours.

[0047] Specific embodiment 1: A method for quickly eliminating the polarization voltage of a 18650 lithium-ion battery of a nickel-cobalt-manganese-oxide ternary positive electrode material system by constant current and constant voltage charging to 4.2V, comprising the following steps:

[0048] 1) Charge the battery to 4.2V in constant current and constant voltage charging mode, with a cut-off current of 0.05C;

[0049] 2) After charging the battery according to step 1, let it stand for 5 minutes;

[0050] 3) After the rest period, the battery was discharged at a constant current according to the following process flow: in the first stage, the battery was discharged at a small current of 0.1C for 1 minute; in the second stage, the battery was discharged at a small current of 0.05C for 1 minute; in the third stage, the battery was discharged at a small current of 0.02C for 2 minutes; in the fourth stage, the battery was discharged at a small current of 0.01C for 2 minutes. The whole process resulted in a battery capacity change of -0.35%;

[0051] 4) After step 3, let the battery stand for 1 hour and then test the voltage. This voltage is the voltage after the battery is depolarized.

[0052] Specific embodiment 2: A method for rapidly eliminating the polarization voltage of a 18650 lithium-ion battery of a nickel-cobalt-lithium-manganese oxide ternary positive electrode material system by constant current discharge to 3.65V, comprising the following steps:

[0053] 1) Discharge the battery to 3.65V in constant current discharge mode;

[0054] 2) After the battery is discharged according to step 1, let it stand for 5 minutes;

[0055] 3) After the rest period, the battery was charged with constant current according to the following process: in the first stage, it was charged with a small current of 0.02C for 1 minute; in the second stage, it was charged with a small current of 0.01C for 2 minutes. The whole process resulted in a battery capacity change of +0.07%;

[0056] 4) After step 3, let the battery stand for 1 hour and then test the voltage. This voltage is the voltage after the battery is depolarized.

[0057] In the above embodiments, by applying a small reverse current, the battery can reach a balanced and stable open circuit voltage in a relatively short time, which is beneficial for screening out bad batteries with large self-discharge in a relatively short time, shortening the production cycle of batteries and their voltage matching, and improving the accuracy of static voltage matching. Existing detection equipment does not need to be modified or upgraded, and no additional cost is added.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for rapidly eliminating the polarization voltage of a lithium-ion battery at low cost, characterized in that: The following steps are involved: 1) charging or discharging the lithium-ion battery to a target voltage according to a set mode; 2) placing the lithium-ion battery that has reached the target voltage on hold for a certain period of time; 3) applying an external reverse micro current to the lithium-ion battery after being shelved to perform short-time discharge or charge intervention, including: performing discharge intervention on the lithium-ion battery charged in step 1), or performing charge intervention on the lithium-ion battery discharged in step 1); 4) After the lithium-ion battery is left for 1 to 3 hours, a voltage test is performed, and the measured voltage is the voltage of the lithium-ion battery after polarization is eliminated; In step 1), the setting mode includes constant current, constant voltage or constant current constant voltage mode, and the target voltage is the voltage corresponding to charging or discharging the lithium-ion battery to a certain state of charge according to the setting mode; In step 2), the holding time is 0 to 5 minutes; In step 3), the direction of the tiny current is opposite to the direction of the discharge or charge current in step 1), the magnitude of the tiny current is 0-0.1C, and the action time of the tiny current is 0-10 minutes; In step 3), the amount of charge that causes the state of charge of the lithium-ion battery to change due to the tiny current does not exceed 1% of the total charge of the lithium-ion battery.

2. A method for rapidly eliminating polarization voltage of a lithium-ion battery at low cost as claimed in claim 1, characterized in that: In step 3) the process of discharge intervention or charge intervention, it is divided into the 1st intervention stage, the 2nd intervention stage, ..., the Nth intervention stage in sequence from the beginning of intervention, and the tiny current in the 1st intervention stage ≥ the tiny current in the 2nd intervention stage ≥ ... ≥ the tiny current in the Nth intervention stage.

3. A method for rapidly eliminating the polarization voltage of a lithium-ion battery at low cost as claimed in claim 2, characterized in that: The intervention time of the first intervention stage ≤ the intervention time of the second intervention stage ≤…≤ the intervention time of the Nth intervention stage.

4. A method for rapidly eliminating polarization voltage of a lithium-ion battery at low cost as claimed in claim 1, characterized in that: In the process of step 3) discharge intervention or charge intervention, the process is divided into the first intervention stage, the first pause stage, the second intervention stage, the second pause stage, ..., the Nth intervention stage in sequence from the beginning of intervention. After the small current acts for a certain period of time in each intervention stage, it pauses for a period of time, and then enters the next intervention stage until the discharge intervention or charge intervention is completed.

5. A method for rapidly eliminating the polarization voltage of a lithium-ion battery at low cost as claimed in any one of claims 2 to 4, characterized in that: The process of the discharge intervention or charge intervention in step 3) is determined based on the polarization curve of the lithium-ion battery.

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