Repairing method for old lithium ion battery

Abstract

The invention discloses a method for repairing an old lithium ion battery. The method mainly comprises the following steps: performing an over-discharge step on the old lithium ion battery; and heating the old lithium ion battery. According to the method, the SEI layer on the surface of the battery negative plate is promoted to be decomposed to a certain extent through the over-discharge operation, the thickness of the SEI layer is reduced, composition and structure reforming of the SEI layer in the subsequent steps is facilitated, dead lithium in the battery negative electrode is activated, and lithium participates in the subsequent charge-discharge cycle; by heating the old lithium ion battery, lattice structures of positive and negative electrode materials of the battery are changed, so that the original structure is recovered, and the capacity of the battery can be maintained.

Description

Technical Field

[0001] This invention belongs to the field of batteries, specifically a method for repairing old lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries are rechargeable batteries that primarily function by the movement of lithium ions between the positive and negative electrodes. During charging and discharging, Li... + During charging, Li intercalates and deintercalates back and forth between the two electrodes, and during charging... + The lithium is extracted from the positive electrode and inserted into the negative electrode through the electrolyte, putting the negative electrode in a lithium-rich state; the opposite occurs during discharge.

[0003] With the widespread use of lithium-ion batteries, the disposal of these batteries is poised to pose environmental problems. If these batteries could be repaired to increase their capacity and reused, it would reduce the environmental burden and save costs. Summary of the Invention

[0004] The purpose of this invention is to provide a method for repairing old lithium-ion batteries, so as to extend the charge-discharge cycle performance of lithium-ion batteries, reduce the environmental impact of old lithium-ion batteries, and reduce the cost of battery use.

[0005] This method mainly includes the following steps:

[0006] Perform an over-discharge procedure on old lithium-ion batteries;

[0007] Perform a heating step on the old lithium-ion battery.

[0008] This invention uses an over-discharge operation to cause the SEI layer on the surface of the battery negative electrode to decompose to a certain extent, reducing the thickness of the SEI layer. This facilitates the restructuring of the SEI layer composition and structure in subsequent steps, while also activating the "dead lithium" in the battery negative electrode, allowing lithium to participate in subsequent charge-discharge cycles.

[0009] By heating old lithium-ion batteries, the lattice structure of the positive and negative electrode materials changes, thereby restoring their original structure and maintaining the battery capacity.

[0010] Furthermore, since gas is generated during the discharge process, in order to avoid the battery swelling due to excessive gas production, which would affect the battery performance, or even cause the battery casing to tear and leak, the above method also includes a venting step.

[0011] This exhaust step can be performed at the following times:

[0012] 1. Exhaust gas is performed synchronously during over-discharge;

[0013] 2. Perform the over-discharge step, then the exhaust step, and finally the heating step;

[0014] 3. After performing the over-discharge and heating steps, the final step is to perform the exhaust step.

[0015] Furthermore, the above method also includes a fluid replenishment step.

[0016] This fluid resuscitation procedure can be performed at the following times:

[0017] 1. Perform the liquid replenishment step after completing the over-discharge step;

[0018] 2. Perform the liquid replenishment step after completing the over-discharge and heating steps;

[0019] This electrolyte replenishment step can solve the problem of poor conductivity caused by insufficient electrolyte content in the old battery to be repaired. In addition, the replenishment step also performs a venting step, which can prevent the battery from swelling due to excessive gas production, which would affect the battery performance, or even cause the battery casing to tear and leak.

[0020] Furthermore, the electrolyte formulation injected in the above replenishment step is: solvent, lithium salt, fluoroether, and 1,3-phenylenevinyl nitrile; the solvent is a mixed solution of ethylene carbonate and ethyl methyl carbonate, and the lithium salt is lithium difluorosulfonylimide.

[0021] Furthermore, the above method also includes a clamping step for the screened used lithium-ion batteries.

[0022] Furthermore, the aforementioned discharge cutoff voltage ranges from 0.01V to 2.4V.

[0023] Furthermore, the discharge cutoff voltage is 0.01V.

[0024] Furthermore, the heating temperature range mentioned above is 40 to 60°C.

[0025] Furthermore, the heating temperature mentioned above is 50°C.

[0026] The beneficial effects of this invention are:

[0027] 1. This invention repairs batteries by over-discharging and then reheating them. Over-discharging old batteries reduces the thickness of the SEI film and activates dead lithium in the battery. Heating the battery changes the crystal structure of the positive and negative electrode materials, thereby restoring their original structure. This not only increases the battery capacity but also improves the capacity retention rate, thus completing the battery repair and improving the battery's cycle performance.

[0028] 2. The present invention also adds a liquid replenishment step to replenish the electrolyte consumed in the old battery. After replenishment, it can be ensured that the capacity decay of the repaired battery is slow, thereby further improving the cycle performance of the subsequent battery.

[0029] 3. In the over-discharge step of the present invention, a restraining force is applied to the battery, which can prevent the old battery from over-discharging and bulging during the heating process, thereby improving the battery repair effect. Attached Figure Description

[0030] Figure 1 This is a graph showing the capacity improvement rate in Example 1;

[0031] Figure 2 This is a graph showing the capacity improvement rate in Example 2;

[0032] Figure 3 The conductivity test curves of the mixed solution of ethylene carbonate, ethyl methyl carbonate, and lithium difluorosulfonyl imide in Example 3 are shown.

[0033] Figure 4 This is a graph showing the capacity improvement rate in Example 3. Detailed Implementation

[0034] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0035] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0036] The main reasons for the decline in lithium-ion battery capacity are as follows:

[0037] 1. Thickening of the SE I film in lithium-ion batteries can lead to a series of negative effects.

[0038] First, a thicker SE I film leads to an increase in battery impedance. Impedance is an indicator of the internal resistance of a battery. Increased impedance means that the internal resistance of the battery is increased, which affects the movement speed of lithium ions and thus reduces the performance and efficiency of the battery.

[0039] Secondly, the thickening of the SEI film also leads to irreversible lithium loss. During battery aging, the SEI film thickens due to the deposition of electrolyte reaction products. This process is accompanied by the consumption of lithium ions, resulting in irreversible lithium loss. Lithium is a crucial element in batteries, and its loss directly reduces battery capacity.

[0040] Furthermore, the thickening of the SE I film not only affects the negative electrode of the battery, but also blocks the active particles of the positive electrode, increasing impedance and leading to a reduction in available active material and capacity. This means that the energy and power that the battery can provide will gradually decrease during storage and use.

[0041] SEI film thickening is an important phenomenon in the aging process of lithium-ion batteries. It directly affects the performance and lifespan of the battery by increasing impedance, causing lithium loss, and reducing usable capacity.

[0042] 2. Electrolyte decomposition and consumption

[0043] The decomposition and consumption of electrolyte will reduce its conductivity, thereby leading to a decrease in the battery's cycle performance.

[0044] In order to restore the capacity and capacity retention of old batteries, the basic operation of the technical means adopted in this invention is to perform an over-discharge step on the old lithium-ion battery and a heating step on the old lithium-ion battery.

[0045] This invention causes the SEI layer on the surface of the battery negative electrode to decompose to a certain extent by discharging, thereby reducing the thickness of the SEI layer. This facilitates the restructuring of the SEI layer composition and structure in subsequent steps. At the same time, it activates the "dead lithium" in the battery negative electrode, allowing lithium to participate in subsequent charge and discharge cycles (increasing the capacity of old batteries).

[0046] Heating old lithium-ion batteries alters the crystal structure of the positive and negative electrode materials, restoring their original structure and thus maintaining their capacity (improving the capacity retention rate of old batteries).

[0047] Example 1

[0048] In this embodiment, 12 square lithium-ion batteries with a nominal capacity decay of 90% from the same batch of the same manufacturer and 20Ah were selected as old lithium-ion batteries to be repaired.

[0049] Among them, two square-shell lithium-ion batteries, namely Sample 1 and Sample 2, were subjected to over-discharge treatment at an over-discharge cutoff voltage of 2.0V, and then normal charge and discharge tests were performed.

[0050] Among them, two square-shell lithium-ion batteries, as Sample 3 and Sample 4, were subjected to over-discharge treatment at an over-discharge cutoff voltage of 1.0V, and then normal charge and discharge tests were performed.

[0051] Among them, two square-shell lithium-ion batteries, as samples 5 and 6, were subjected to over-discharge treatment at an over-discharge cutoff voltage of 0.01V, and then normal charge and discharge tests were performed.

[0052] Among them, two square-shell lithium-ion batteries, as control sample 1 and control sample 2, were only subjected to normal charge and discharge tests;

[0053] Specific experimental data for this embodiment are shown in Table 1, Table 2, and Table 3. Figure 1 As shown.

[0054] Table 1 shows the capacity values ​​of 8 batteries after 400 cycles.

[0055]

[0056]

[0057] Table 2 shows the capacity gain rate of 8 batteries after 400 cycles.

[0058] Cycle number Comparison Sample 1 Comparison Sample 2 Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 0 100.00％ 100.00％ 100.00％ 100.00％ 100.00％ 100.00％ 100.00％ 100.00％ 10 100.00％ 100.03％ 100.23％ 100.31％ 101.31％ 100.91％ 102.76％ 103.26％ 100 99.50％ 99.38％ 99.54％ 99.59％ 100.47％ 100.51％ 100.87％ 101.70％ 200 98.80％ 98.57％ 98.67％ 98.72％ 99.27％ 99.37％ 99.76％ 100.13％ 300 98.10％ 97.76％ 98.01％ 97.99％ 98.71％ 98.74％ 98.93％ 99.35％ 400 97.56％ 97.16％ 97.48％ 97.48％ 97.84％ 97.84％ 98.51％ 98.86％

[0059] The above tests show that the discharge cutoff voltage is inversely proportional to the extent of capacity recovery of the old battery. To improve the repair effect of the old battery, 0.01V was selected as the discharge cutoff voltage.

[0060] Example 2

[0061] In this embodiment, 12 square lithium-ion batteries with a nominal capacity decay of 90% from the same batch of the same manufacturer and 20Ah were selected as old lithium-ion batteries to be repaired. The old lithium-ion batteries were repaired by over-discharging and then heating.

[0062] At room temperature, the discharge cutoff voltage was set to 0.01V, and the lithium ions of 12 old batteries to be repaired were discharged in a constant resistance discharge manner, and then left to stand for 5 hours.

[0063] The 12 over-discharged used batteries to be repaired were divided into 6 groups. Five of these groups were placed in an oven with two batteries each. The five groups of used batteries to be repaired were heated at 40℃, 45℃, 50℃, 55℃, and 60℃, respectively. After the heating treatment, they were allowed to stand at room temperature and were designated as Sample 1 to Sample 10. Among them, Sample 1 and Sample 2 were heated at 40℃, Sample 3 and Sample 4 at 45℃, Sample 5 and Sample 6 at 50℃, Sample 7 and Sample 8 at 55℃, and Sample 9 and Sample 10 at 60℃.

[0064] In addition, two old batteries to be repaired that underwent only the over-discharge step were used as control sample 1 and control sample 2 (control sample 1 and control sample 2 did not undergo the heating step);

[0065] The capacity of the repaired battery was directly tested at 1C (20A) on a charge-discharge tester. At 25℃±5℃, the battery was charged at constant current (1C) to a voltage of 3.65V using a 5V-20A charge-discharge tester, then charged at constant voltage to a current of 1 / 20C (1A), rested for 10 minutes, and then discharged at constant current to a cutoff voltage of 2.5V. This constituted one cycle. Data from 300 cycles of the repaired battery were tested.

[0066] Specific experimental data for this embodiment are shown in Tables 3 and 4. Figure 2 As shown.

[0067] Table 3 shows the capacity values ​​of 12 batteries after 300 cycles.

[0068]

[0069] Table 4 shows the capacity gain rate of 12 batteries after 300 cycles.

[0070]

[0071] From Tables 3 and 4 above, and Figure 2 It can be seen that the lithium-ion battery exhibits the greatest capacity increase after over-discharge at an over-discharge cutoff voltage of 0.1V and then heating at 50℃ (i.e., the sample heated to 50℃ showed an increase of more than 4%), and also has a better capacity retention rate after 300 charge-discharge cycles following over-discharge and heating repair.

[0072] Example 3

[0073] Since gas is generated inside the battery during the over-discharge step, in order to avoid excessive gas pressure inside the battery causing problems with the battery's charging and discharging performance later, this embodiment differs from Embodiment 2 in that an venting step is added during the repair process. This venting step can be performed simultaneously with the over-discharge, after the over-discharge, or after the heating step.

[0074] Example 4

[0075] The difference between this embodiment and Embodiment 3 is that a fluid replenishment step is added during the repair process; specifically, the specific execution process of the repair process in this embodiment is as follows:

[0076] Over-discharge

[0077] At room temperature, set the discharge cutoff voltage to 0.01V and discharge the old battery to be repaired using the constant resistance discharge method, then let it stand for 5 hours.

[0078] heating

[0079] The old battery to be repaired is placed in an oven and heated at 50°C for 12 hours, and then left to stand until it reaches room temperature.

[0080] fluid replacement

[0081] Open the vent of the battery to be repaired in the glove box, then add liquid to the battery, let it stand for 30 minutes, and then seal the vent.

[0082] Charge and discharge test

[0083] The capacity of the repaired battery was directly tested at 1C (20A) on a charge-discharge tester. At 25℃±5℃, the battery was charged at constant current (1C) to a voltage of 3.65V using a 5V-20A charge-discharge tester, then charged at constant voltage to a current of 1 / 20C (1A), rested for 10 minutes, and then discharged at constant current to a cutoff voltage of 2.5V. This constituted one cycle. Data from 300 cycles of the repaired battery were tested.

[0084] In this embodiment, 14 square lithium-ion batteries of 20Ah each with a nominal capacity decayed to 90% were selected from the same batch of batteries from the same manufacturer.

[0085] Two batteries were grouped together and labeled as Sample 1 and Sample 2. The repair method for the two samples was to simply place them in an oven and perform heat repair at 50°C.

[0086] Two batteries are grouped together and labeled as Sample 3 and Sample 4. The repair method for the two samples is: over-discharge is performed only according to the discharge cutoff voltage of 0.01V.

[0087] Two batteries are grouped together and labeled as Sample 5 and Sample 6. The repair method for the two samples is as follows: after over-discharging at a discharge cutoff voltage of 0.01V, they are placed in an oven and heated at 50℃.

[0088] Two batteries are grouped together and labeled as Sample 7 and Sample 8. The repair method for the two samples is as follows: after over-discharging at a discharge cutoff voltage of 0.01V, they are placed in an oven and heated at 50℃, and finally injected with conventional electrolyte.

[0089] Two batteries are grouped together and labeled as Sample 9 and Sample 10. The repair method for the two samples is as follows: after over-discharging at a discharge cutoff voltage of 0.01V, conventional electrolyte is injected and finally placed in an oven and heated at 50℃.

[0090] Two batteries are grouped together and labeled as Sample 11 and Sample 12. The repair method for the two samples is as follows: after over-discharging at a discharge cutoff voltage of 0.01V, they are placed in an oven and heated at 50℃, and finally injected with self-made electrolyte.

[0091] Two batteries are grouped together and labeled as Sample 13 and Sample 14. The repair method for the two samples is as follows: after over-discharging at a discharge cutoff voltage of 0.01V, the self-made electrolyte is injected and finally placed in an oven and heated at 50℃.

[0092] The self-made electrolyte formulation injected during the above experiment included a solvent and a lithium salt; the solvent was a mixed solution of ethylene carbonate and ethyl methyl carbonate; the reason for choosing ethylene carbonate and ethyl methyl carbonate as the electrolyte solvent is as follows:

[0093] After dissolving, ethylene carbonate has a relatively low viscosity. For lithium-ion battery electrolytes, lower viscosity means lower ion migration resistance, which translates to better battery performance. Furthermore, ethylene carbonate has the advantage of good compatibility with graphite-based anode materials, allowing for high-concentration use.

[0094] Ethyl methyl carbonate has high electrical conductivity and excellent low-temperature performance. Combining ethylene carbonate and ethyl methyl carbonate in a certain ratio can effectively reduce the viscosity of the electrolyte while maximizing the electrical conductivity, and also achieves good low-temperature performance.

[0095] In this embodiment, lithium bisfluorosulfonylimide is selected as the lithium salt; the reason for choosing lithium bisfluorosulfonylimide as the electrolyte lithium salt is as follows:

[0096] Compared to traditional lithium salts, lithium bis(fluorosulfonyl)imide exhibits superior overall performance:

[0097] First, lithium bisfluorosulfonylimide has a larger anionic radius, making it easier to dissociate into lithium ions and improve the conductivity of the electrolyte. Second, its decomposition temperature is above 200℃, giving it better thermal stability and improving the high-temperature resistance of the electrolyte. Third, it can improve discharge charge performance in low-temperature environments and maintain capacitance retention in high-temperature environments, thus improving the high and low temperature performance of lithium batteries. Therefore, using lithium bisfluorosulfonylimide in electrolytes can significantly improve the cycle life, rate capability, and safety of batteries.

[0098] To determine the optimal ratio of different proportions of ethylene carbonate and ethyl methyl carbonate as solvents, and different contents of lithium bis(fluorosulfonyl)imide, the following tests were conducted in this example:

[0099] Ethylene carbonate and ethyl methyl carbonate were mixed at mass ratios of 3:7, 4:6, and 5:5. Different masses of lithium bis(fluorosulfonyl)imide were then added to the mixture, and the conductivity was tested. Simultaneously, the conductivity of the electrolyte in a commercially available battery was tested, yielding the following results: Figure 3The graph shows that the optimal ratio of ethylene carbonate to ethyl methyl carbonate is 4:6, and the conductivity of the solvent is best when the lithium bis(fluorosulfonyl)imide concentration is 1.2 mol / L, which is much better than that of commercially available electrolytes. Figure 3 In this context, 280 refers to the standard electrolyte used in commercially available 280Ah square lithium-ion batteries.

[0100] Specific experimental data for this embodiment are shown in Tables 5 and 6. Figure 4 As shown.

[0101] Table 5 shows the capacity values ​​of 14 batteries after 250 cycles.

[0102] Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Sample 7 Sample 8 Sample 9 Sample 10 Sample 11 Sample 12 Sample 13 Sample 14 0 17.93 17.95 18.10 18.10 17.88 17.93 18.00 18.00 17.85 17.86 17.82 17.84 17.90 17.90 10 17.96 17.96 18.34 18.27 18.27 18.20 18.53 18.47 18.33 18.39 18.39 18.41 18.41 18.46 100 17.84 17.86 18.19 18.20 17.98 17.99 18.26 18.19 18.03 18.08 18.07 18.11 18.13 18.17 200 17.69 17.74 17.97 17.99 17.80 17.82 18.08 18.01 17.87 17.91 17.91 17.95 18.01 18.04 250 17.59 17.65 17.84 17.86 17.65 17.66 17.95 17.86 17.74 17.78 17.79 17.83 17.91 17.93

[0103] Table 6 shows the capacity improvement rate of 12 batteries after 250 cycles.

[0104]

[0105]

[0106] From Tables 5 and 6 above and Figure 4 It can be seen that,

[0107] Firstly, the capacity improvement and capacity retention rates of samples 5 to 12 were higher than those of samples 3 and 4. In other words, the repair effect of the combination of over-discharge, heating and liquid replenishment was better than that of over-discharge combined with heating. Furthermore, the capacity improvement and capacity retention rates of samples 3 and 4 were higher than those of samples 3 and 4. In other words, the repair effect of the combination of over-discharge and heating was better than that of over-discharge alone or heating alone.

[0108] Secondly, among samples 9 to 12, the capacity improvement and capacity retention of samples 11 and 12 are higher than those of samples 9 and 10, indicating that the self-made electrolyte has a significantly better repair effect on the battery than conventional electrolyte.

Claims

1. A method of repairing old lithium-ion batteries, characterized by, The method comprises the following steps: The method further comprises a discharging step.

2. The method of claim 1, wherein: The method further comprises a liquid supplementing step.

3. The method of claim 1, wherein: The method further comprises a discharging step.

4. The method of claim 2, wherein: The electrolyte injected in the liquid supplementing step comprises a solvent and a lithium salt.

5. The method of claim 1 to 4, wherein: The solvent is a mixture of ethylene carbonate and ethyl methyl carbonate at a ratio of 4:6, and the lithium salt is lithium bisfluorosulfonylimide at 1.2 mol.

6. The method of claim 1, wherein: The method further comprises a clamping step for the selected lithium battery to be repaired.

7. The method of claim 6, wherein: The discharging cut-off voltage range is 0.01V to 2.4V.

8. The method of claim 1, wherein: The discharging cut-off voltage is 0.01V.

9. The method of claim 8, wherein: The heating temperature range is 40 to 60℃. The heating temperature is 50℃.

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