Lithium ion battery capacity grading method

Abstract

The invention relates to a capacity grading method for a lithium ion battery, the lithium ion battery is a lithium iron phosphate battery, and the method comprises the following steps: (1) fully charging the formed lithium ion battery to 3.65 V with low current, constant current and constant voltage; (2) discharging the lithium ion battery to 2.5 V at low current and constant current; (3) fully charging the lithium ion battery to 3.65 V at low power and constant power; (4) discharging the lithium ion battery to 2.5 V at low power and constant power; and (5) charging the lithium ion battery to 5-8% SOC at low power and constant power. According to the capacity grading method of the lithium ion battery, related performance of the battery cell in a constant power state can be reflected during capacity grading, a better SEI film can be formed, and the cycle life of the battery cell is further prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a lithium battery capacity division method. Background Art

[0002] Lithium-ion batteries have the advantages of high voltage, high specific energy, and long charge and discharge life. Therefore, they are widely used in products in many fields such as electronic products, portable small appliances, and energy storage systems.

[0003] In actual use, battery packs composed of several single lithium-ion batteries have been widely used due to different requirements of battery capacity for products. However, under the same process conditions, the capacity of single lithium-ion batteries produced in batches is different. If these single lithium-ion batteries with different capacities are directly combined into a battery pack in series and parallel, during the process of charging and discharging the battery pack, some single lithium-ion batteries will often be overcharged, while other single lithium-ion batteries will not be fully charged, thus affecting the service life of the battery pack. Therefore, it is very important to carry out capacity separation of processed single lithium-ion batteries.

[0004] The capacity division process will also affect the maintenance of the SEI film of the negative electrode sheet, as well as its stability and durability, and thus affect the cycle performance of the lithium battery. In addition, incorrect capacity division technology will directly lead to lithium deposition in the negative electrode of the lithium battery, forming "lithium dendrites", which will seriously threaten the safety performance of the lithium battery and cause internal short circuit or even explosion of the lithium battery.

[0005] At present, the capacity division process in the industry generally adopts constant current and constant voltage charging and constant current discharging charging and discharging process, but it will also affect the stability of the SEI film, reduce the cycle life of the lithium battery, and the charging efficiency needs to be improved. Summary of the invention

[0006] The purpose of the present invention is to provide a lithium ion battery capacity division method, which can not only reflect the relevant performance of the battery cell under the constant power state during capacity division, but also form a better SEI film, further improve the cycle life of the battery cell, and in addition, the charging efficiency is high, reducing the charging time and loss.

[0007] The technical solution adopted by the present invention to solve the above problem is: a lithium ion battery capacity division method, wherein the lithium ion battery is a lithium iron phosphate battery, comprising the following steps: (1) Fully charge the lithium-ion battery after formation treatment to 3.65V with a small constant current and constant voltage; (2) The lithium-ion battery is discharged at a low constant current to 2.5V; (3) The lithium-ion battery is fully charged to 3.65V at a low constant power; (4) The lithium-ion battery is discharged at a low constant power to 2.5V; (5) Lithium-ion batteries are charged at low constant power to 5-8% SOC.

[0008] Preferably, the small current is 0.3-0.5 C. In step (1), the formation stage is not fully charged, and the first full charge using a small current is conducive to effectively activating the chemical reaction of the battery cell; step (2) is the first discharge, and the small current discharge is conducive to fully utilizing the capacity of the battery cell.

[0009] More preferably, the small current is 0.3C.

[0010] Preferably, the low power is 0.5-1P. In both step (3) and step (4), low power is used, that is, low power charging and discharging is used in the constant power stage. As the voltage decreases in the constant power discharge stage, the current gradually increases, and the polarization gradually increases. Low power can reduce polarization, making the chemical system of the entire battery cell more stable and reliable.

[0011] More preferably, the low power is 0.5P.

[0012] In addition, constant power charging is adopted in step (5). At the initial stage of constant power charging, the voltage gradually increases and the current value is relatively large at the beginning of charging. Therefore, the internal polarization of the battery cell is relatively large, the chemical system of the battery cell is relatively unstable, and the voltage variation range is large, which is more conducive to the screening of self-discharge. The constant power charging amount is controlled at 5-8% SOC and cannot exceed 10%, because the screening of self-discharge is more obvious when the voltage is in a period of rapid increase.

[0013] Preferably, the time interval between each step is 30-60 minutes, which is conducive to the full infiltration and absorption of the electrolyte and the cooling of the battery cell after charging and discharging.

[0014] Preferably, the ambient temperature for volume separation is 30-35°C, which is conducive to the stability of the SEI film and allows the positive and negative electrodes to rebound fully, truly reflecting the thickness of the internal winding core.

[0015] Compared with the prior art, the advantages of the present invention are: The lithium-ion battery capacity division method of the present invention can not only reflect the relevant performance of the battery cell under the constant power state (for example: the constant power capacity and internal resistance of the battery cell) during capacity division, but also form a better SEI film, further improving the cycle life of the battery cell. In addition, the charging efficiency is high, reducing the charging time and loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The graph is a cycle life curve of the lithium-ion battery after capacity division in Examples 1-3 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below with reference to the accompanying drawings. Example 1

[0018] The lithium-ion battery model is 48173170-120Ah (rated capacity 120Ah, rated power 384W), and the quantity is 20 pieces. The positive electrode material is Defang Nano DY-1 lithium iron phosphate, the negative electrode material is Shanshan FSN-1 artificial graphite, the diaphragm is Cangzhou Mingzhu 12+4 coated diaphragm, and the electrolyte is Xinzhoubang HJ-1 electrolyte. The positive electrode slurry viscosity is 9000mPa.s, the negative electrode slurry viscosity is 6500mPa.s, and the positive electrode compaction is 2.4g / cm 3 , negative electrode compaction 1.55g / cm 3 After injection, let it stand at 45℃ for 36 hours to soak.

[0019] A lithium-ion battery capacity division method comprises the following steps: (1) Fully charge the lithium-ion battery after formation treatment to 3.65V at 0.3C constant current and constant voltage; (2) The lithium-ion battery is discharged at a constant current of 0.3C to 2.5V; (3) The lithium-ion battery is fully charged to 3.65V at a constant power of 0.5P; (4) The lithium-ion battery is discharged to 2.5V at a constant power of 0.5P; (5) The lithium-ion battery is charged to 3.295V at a constant power of 0.5P. Example 2

[0020] The lithium-ion battery model is 48173170-120Ah (rated capacity 120Ah, rated power 384W), and the quantity is 20 pieces. The positive electrode material is Defang Nano DY-1 lithium iron phosphate, the negative electrode material is Shanshan FSN-1 artificial graphite, the diaphragm is Cangzhou Mingzhu 12+4 coated diaphragm, and the electrolyte is Xinzhoubang HJ-1 electrolyte. The positive electrode slurry viscosity is 9110mPa.s, the negative electrode slurry viscosity is 6620 mPa.s, and the positive electrode compaction is 2.4g / cm 3 , negative electrode compaction 1.55g / cm 3 After injection, let it stand at 45℃ for 36 hours to soak.

[0021] A lithium-ion battery capacity division method comprises the following steps: (1) Fully charge the lithium-ion battery after formation treatment to 3.65V at 0.4C constant current and constant voltage; (2) The lithium-ion battery is discharged at a constant current of 0.4C to 2.5V; (3) The lithium-ion battery is fully charged to 3.65V at a constant power of 0.6P; (4) The lithium-ion battery is discharged to 2.5V at a constant power of 0.6P; (5) The lithium-ion battery is charged to 3.295V at a constant power of 0.5P. Example 3

[0022] The lithium-ion battery model is 48173170-120Ah (rated capacity 120Ah, rated power 384W), and the quantity is 20 pieces. The positive electrode material is Defang Nano DY-1 lithium iron phosphate, the negative electrode material is Shanshan FSN-1 artificial graphite, the diaphragm is Cangzhou Mingzhu 12+4 coated diaphragm, and the electrolyte is Xinzhoubang HJ-1 electrolyte. The positive electrode slurry viscosity is 8993mPa.s, the negative electrode slurry viscosity is 6496mPa.s, and the positive electrode compaction is 2.4g / cm 3 , negative electrode compaction 1.55g / cm 3 After injection, let it stand at 45℃ for 36 hours to soak.

[0023] A lithium-ion battery capacity division method comprises the following steps: (1) Fully charge the lithium-ion battery after formation treatment to 3.65V at 0.5C constant current and constant voltage; (2) The lithium-ion battery is discharged at a constant current of 0.5C to 2.5V; (3) The lithium-ion battery is fully charged to 3.65V at a constant power of 0.8P; (4) The lithium-ion battery is discharged to 2.5V at a constant power of 0.8P; (5) The lithium-ion battery is charged to 3.295V at a constant power of 0.5P.

[0024] Comparative Example 1 The difference from Example 1 is that the volume separation method is different. The volume separation method is carried out according to the conventional volume separation process: (1) Fully charge the lithium-ion battery after formation treatment to 3.65V at 0.5C constant current and constant voltage; (2) The lithium-ion battery is discharged at a constant current of 0.5C to 2.5V; (3) The lithium-ion battery is charged to 3.65V at 1C constant current and constant voltage; (4) The lithium-ion battery is discharged at a constant current of 1C to 2.5V; (5) Lithium-ion batteries are charged at a constant current of 0.5C for 9 minutes.

[0025] The lithium-ion batteries prepared by dividing the capacity of Examples 1 to 3 and Comparative Example 1 were subjected to cycle life testing, specifically: charging and discharging at constant power 1CP, 100% DOD, 25° C., and a voltage range of 2.5V-3.65V.

[0026] Cycle life test results are as follows Figure 1 As shown, from Figure 1 It can be seen that the cycle life of the embodiment is better than that of the comparative example 1 (conventional fractionation process).

[0027] In addition to the above embodiments, the present invention also includes other implementation modes. Any technical solutions formed by equivalent transformation or equivalent replacement should fall within the protection scope of the claims of the present invention.

Claims

1. A method for dividing the capacity of a lithium-ion battery, wherein the lithium-ion battery is a lithium iron phosphate battery, characterized in that: The following steps are involved: (1) Fully charge the lithium-ion battery after formation treatment to 3.65V with a small constant current and constant voltage; (2) The lithium-ion battery is discharged at a low constant current to 2.5V; (3) The lithium-ion battery is fully charged to 3.65V at a low constant power; (4) The lithium-ion battery is discharged at a low constant power to 2.5V; (5) Lithium-ion batteries are charged at low constant power to 5-8% SOC.

2. The lithium-ion battery capacity division method according to claim 1, characterized in that: The small current is 0.3-0.5C.

3. The lithium-ion battery capacity division method according to claim 2, characterized in that: The small current is 0.3C.

4. The lithium-ion battery capacity division method according to claim 1, characterized in that: The low power is 0.5-1P.

5. The lithium-ion battery capacity division method according to claim 4, characterized in that: The low power is 0.5P.

6. The lithium-ion battery capacity division method according to claim 1, characterized in that: The time interval between each step was 30-60 min.

7. The lithium-ion battery capacity division method according to claim 1, characterized in that: The ambient temperature for dispensing is 30-35℃.

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