Method for repairing capacity of waste lithium ion battery

Abstract

The invention belongs to the field of batteries, and particularly relates to a method for repairing the capacity of a waste lithium ion battery. The charge-discharge cycle performance of the lithium ion battery is prolonged, and the use cost of the battery is reduced while the pressure of the waste lithium ion battery on the environment is reduced. The method comprises the following steps: deeply discharging the waste lithium ion battery; secondly, free electrolyte and gas in the inner cavity of the waste lithium ion battery are discharged, and impurities in the inner cavity of the waste lithium ion battery are brought out; then, injecting a first electrolyte into the inner cavity of the treated waste lithium ion battery, and standing for a set time; and testing the battery capacity, if the battery capacity reaches a set target value, finishing capacity restoration of the waste lithium ion battery, otherwise, continuing to execute the operation. The method is simple to operate and obvious in capacity recovery effect, and the cycle life of the lithium ion battery is greatly prolonged.

Description

Technical Field

[0001] The invention belongs to the field of batteries, and in particular relates to a method for repairing the capacity of waste lithium-ion batteries. Background Art

[0002] Lithium-ion battery is a secondary battery that mainly relies on the movement of lithium ions between the positive electrode and the negative electrode to work. + The Li is inserted and deintercalated back and forth between the two electrodes. + It is deintercalated from the positive electrode and intercalated into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; the opposite is true during discharge.

[0003] With the popularization of lithium-ion batteries, waste lithium-ion batteries will soon cause environmental problems. If waste lithium-ion batteries can be repaired, their capacity can be increased, and they can be put into use again, it can reduce environmental burden and save costs. Summary of the invention

[0004] The purpose of the present invention is to provide a method for restoring the capacity of waste lithium-ion batteries, so as to extend the charge and discharge cycle performance of lithium-ion batteries, reduce the pressure on the environment caused by waste lithium-ion batteries and reduce the cost of battery use.

[0005] The technical solution of the present invention is to provide a method for repairing the capacity of waste lithium-ion batteries, which is special in that it includes the following steps:

[0006] Step 1: Deeply over-discharge the waste lithium-ion battery;

[0007] Step 2, discharge the free electrolyte and gas in the inner cavity of the waste lithium ion battery, and take out the impurities in the inner cavity of the waste lithium ion battery; it should be noted that if the inner cavity of the waste lithium ion battery has free electrolyte after the treatment in step 1, the free electrolyte and gas in the inner cavity of the waste lithium ion battery are discharged, and the impurities in the inner cavity of the waste lithium ion battery are taken out; otherwise, the second electrolyte is injected into the inner cavity of the waste lithium ion battery treated in step 1, and after standing for a set time, the free electrolyte and gas in the inner cavity of the waste lithium ion battery are discharged, and the impurities in the inner cavity of the waste lithium ion battery are taken out;

[0008] Step 3, injecting the first electrolyte into the inner cavity of the waste lithium-ion battery treated in step 2, and leaving it to stand for a set time;

[0009] Step 4: Test the battery capacity. If the set target value is reached, the capacity repair of the used lithium-ion battery is completed. Otherwise, return to step 1.

[0010] Furthermore, in step 2, before discharging the free electrolyte and gas in the inner cavity of the waste lithium-ion battery, the step of vibrating the waste lithium-ion battery is also included.

[0011] Furthermore, the concentration of lithium ions in the second electrolyte is 1.2 mol / L.

[0012] Furthermore, in step 1, the waste lithium-ion battery is deeply over-discharged to a voltage equal to 0.01V using a constant resistance discharge method.

[0013] Furthermore, the first electrolyte is an electrolyte obtained by purifying the free electrolyte discharged in step 2 using a purification material.

[0014] Furthermore, the purification material is at least one of an activated molecular sieve, an activated carbon adsorbent, a silica gel adsorbent, an alumina adsorbent, a copper catalyst adsorbent, and a polyimide.

[0015] Furthermore, before step 1, the method also includes the step of determining whether there is free electrolyte in the inner cavity of the waste lithium-ion battery, and if so, discharging the free electrolyte and injecting a fourth electrolyte; the fourth electrolyte is a pure solvent electrolyte.

[0016] Furthermore, between step 3 and step 4, there is also a step of forming the lithium ion battery processed in step 3.

[0017] Furthermore, the first electrolyte includes a SEI film-forming additive.

[0018] Furthermore, after the lithium ion battery processed in step 3 is formed and before step 4 is performed, the following steps are also included:

[0019] After the free electrolyte in the inner cavity of the formed lithium-ion battery is discharged, the third electrolyte is injected into the inner cavity of the lithium-ion battery and left to stand for a set time.

[0020] The present invention also provides another method for restoring the capacity of waste lithium-ion batteries, which is special in that it comprises the following steps:

[0021] Step 1: Deeply over-discharge the waste lithium-ion battery;

[0022] Step 2, discharging the gas in the inner cavity of the waste lithium-ion battery;

[0023] Step 3, injecting a first electrolyte into the inner cavity of the waste lithium-ion battery treated in step 2, and leaving it to stand for a set time; the first electrolyte contains a SEI film repair additive;

[0024] Step 4, forming the lithium ion battery after the treatment in step 3;

[0025] Step 5: Test the battery capacity. If the set target value is reached, the capacity repair of the used lithium-ion battery is completed. Otherwise, return to step 1.

[0026] Furthermore, in step 1, the waste lithium-ion battery is deeply over-discharged to a voltage equal to 0.01V by using a constant current or constant resistance discharge method.

[0027] The beneficial effects of the present invention are:

[0028] 1. The present invention over-discharges the battery with capacity decay to decompose the SEI film; then, discharges the free electrolyte and gas in the battery cavity after over-discharge to remove impurities in the battery cavity; finally, adds the first electrolyte into the battery cavity to complete the repair. The present invention is easy to operate, has obvious capacity recovery effect, and greatly prolongs the cycle life of lithium-ion batteries.

[0029] 2. The present invention adopts a vibration method to allow as many impurities as possible to be suspended in the free electrolyte and discharged, thereby avoiding the influence of impurities on battery performance.

[0030] 3. The present invention adopts a second electrolyte with a higher lithium ion concentration to remove impurities from the battery cavity, and at the same time can balance the lithium ion concentration in the final battery cavity electrolyte to about 1 mol / L, further improving battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Graph showing the discharge capacity retention rate of each sample in Example 1 and Example 2;

[0032] Figure 2 4 is a discharge capacity retention rate curve diagram of each sample in Example 4;

[0033] Figure 3 Graph showing the discharge capacity retention rate of each sample in Example 5;

[0034] Figure 4 Graph showing the discharge capacity retention rate of each sample in Example 6;

[0035] Figure 5 Graph showing the discharge capacity retention rate of each sample in Example 7;

[0036] Figure 6 This is a schematic diagram of the structure of a large-capacity lithium-ion battery in Example 8;

[0037] The reference numerals in the figure are: 1, single cell; 2, electrolyte shared chamber; 3, buffer tank; 4, first pipe section; 5, second pipe section; 6, third pipe section;

[0038] Figure 7 14 is a discharge capacity retention rate curve of each sample in Example 12. DETAILED DESCRIPTION

[0039] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0040] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0041] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "top, bottom" etc. is based on the orientation or positional relationship shown in the drawings, and 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 orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first, second, etc." are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0042] The capacity attenuation of lithium-ion batteries is largely due to the thickening of the SEI film and the increase in the internal resistance of the battery. Therefore, thinning the thickness of the SEI film and reducing the internal resistance of the battery can restore the battery capacity. The present invention over-discharges the battery with capacity attenuation to decompose the SEI film to thin the thickness of the SEI film; then, the free electrolyte and gas in the battery cavity after over-discharge are discharged to take out the impurities in the battery cavity, which include the original impurities in the battery cavity and the impurities generated after over-discharge. If there is less free electrolyte in the battery cavity after over-discharge, a second electrolyte can be injected into the battery cavity so that the solid impurities are suspended in the second electrolyte and discharged; finally, the first electrolyte is added to the battery cavity to complete the repair.

[0043] In order to discharge as many impurities as possible from the inner cavity of the battery after over-discharge, vibration can be adopted so that as many impurities as possible are suspended in the free electrolyte and discharged.

[0044] In actual operation, it is found that before over-discharge, some additives in the electrolyte will decompose during the over-discharge process, which greatly reduces the over-discharge repair effect. The present invention can discharge the original free electrolyte of the battery and replace it with a pure solvent electrolyte (electrolyte without additives). There will be no interference from additives during over-discharge, and a better repair effect can be obtained.

[0045] In the process of thinning the SEI film thickness by over-discharge, the SEI film may be damaged. In order to overcome this problem, the present invention considers that after the above-mentioned repair process, a small current formation can be performed to properly repair the damaged SEI film, thereby improving the battery capacity and the cycle life of the battery.

[0046] It should be noted that:

[0047] Because the repair process of the present invention involves multiple injection and discharge processes, it is more suitable for lithium-ion batteries with electrolyte injection and discharge ports, which can be lithium-ion single cells, and is also suitable for large-capacity batteries with shared chambers. The ports of the shared chamber can be used as injection and discharge ports.

[0048] Such a large capacity battery includes a battery pack body and at least one shared chamber;

[0049] The battery pack body includes a plurality of single cells connected in parallel; the single cell described here is a square shell battery, which includes an upper cover plate, a lower cover plate, a cylinder, a battery cell assembly and an electrolyte; the battery cell assembly described here can be called an electrode assembly, which is composed of a positive electrode, a diaphragm and a negative electrode arranged in sequence and assembled by a lamination or winding process. The battery cell assembly described here can also be a commercially available square shell battery; the upper cover plate, the cylinder and the lower cover plate form the outer shell of the square shell battery, and the battery cell assembly and the electrolyte are located in the outer shell of the single cell.

[0050] The shared chamber is fixed on the battery pack body, and the inner cavity of the shared chamber is connected with the inner cavity of each single battery.

[0051] When the shared chamber is fixed at the bottom of the battery pack body, it can be used as an electrolyte shared chamber. The electrolyte in the inner cavity of each single cell is connected through the electrolyte shared chamber, so that the electrolyte of all single cells is in the same system, reducing the difference between the electrolytes of each single cell, and improving the consistency between each single cell to a certain extent, thereby improving the cycle life of the large-capacity battery to a certain extent.

[0052] When the shared chamber is fixed on the top of the battery pack body, it can be used as a gas connecting chamber. The gases in the inner cavities of each single battery are connected through the gas connecting chamber, so that the gas in the entire large-capacity battery cavity is balanced, which improves the cycle life of the large-capacity battery to a certain extent.

[0053] When the shared chamber is fixed to the side wall of the battery pack body, it can also serve as an electrolyte shared chamber and a gas connecting chamber at the same time. The gas and electrolyte in each single battery can enter the shared chamber at the same time. At this time, the gas is distributed in the upper half of the shared chamber, and the electrolyte is distributed in the lower half of the shared chamber; gas-liquid sharing can be achieved through a shared chamber.

[0054] The present invention is further described below in conjunction with specific embodiments.

[0055] Example 1

[0056] This embodiment uses waste lithium-ion single batteries as the repair object;

[0057] Take a plurality of waste 30Ah square shell lithium iron phosphate batteries produced by the same manufacturer and the same batch, test the initial capacity of the batteries, and screen 10 samples as samples 1 to 10 of this embodiment; after deep discharge of samples 1 to 10, inject the same lithium ion concentration and the same amount of second electrolyte into the inner cavity of each sample, let it stand for 24 to 72 hours, and then discharge the free electrolyte and gas in the inner cavity of the waste lithium ion battery; inject the first electrolyte into the inner cavity of each sample, let it stand for 24 to 72 hours, and then test the battery capacity. If the set target value is reached, the capacity repair of the waste lithium ion battery is completed; otherwise, repeat the above operation until the capacity is restored to the set target value.

[0058] It should be noted that:

[0059] 1. This embodiment selects waste lithium-ion single cells as samples. After over-discharge, there is almost no free electrolyte in the inner cavity. In order to make it easier to discharge impurities in the inner cavity of the battery after over-discharge, a second electrolyte is injected into the inner cavity of the battery after over-discharge. Impurities in the inner cavity of the battery are taken out by discharging the free second electrolyte, thereby avoiding the influence of impurities on the charge and discharge cycle performance of the battery. In some other embodiments, if there is free electrolyte in the inner cavity of the battery after over-discharge, and impurities can be well discharged by discharging the free electrolyte, the step of injecting the second electrolyte into the inner cavity of the battery after over-discharge can be omitted. In addition, in some other embodiments, the battery can be vibrated so that the impurities can be fully suspended in the free electrolyte and discharged.

[0060] 2. The concentration of lithium ions in the second electrolyte of this embodiment is 1.2 mol / L, and the injection volume is 20 ml.

[0061] 3. The purpose of selecting the second electrolyte with a lithium ion concentration greater than 1.0 mol / L is as follows:

[0062] a. After the battery has been used for a period of time, the lithium ion concentration in the electrolyte shows a downward trend. In this embodiment, by injecting a second electrolyte into the battery cavity, the concentration of lithium ions in the electrolyte in the battery cavity after overdischarge can be balanced, so that the concentration of the electrolyte in the free state or attached to the diaphragm or the positive and negative electrodes is close to 1.0 mol / L;

[0063] b. After standing for a certain period of time, the free electrolyte is discharged to remove impurities in the battery cavity, including the original impurities in the battery cavity and the impurities generated after over-discharge.

[0064] It should be noted here that the discharged electrolyte is a free electrolyte, and the concentration of the electrolyte attached to the diaphragm or the positive and negative electrodes is still close to 1.0 mol / L, ensuring that after the subsequent injection of the first electrolyte with a lithium ion concentration of 1.0 mol / L, the lithium ion concentration in the electrolyte in the battery cavity is still maintained at around 1.0 mol / L.

[0065] 4. The first electrolyte of this embodiment can be an electrolyte obtained by purifying the discharged free electrolyte using a purification material. The purification material can be at least one of an activated molecular sieve, an activated carbon adsorbent, a silica gel adsorbent, an alumina adsorbent, a copper catalyst adsorbent, and a polyimide. Water and other impurities in the electrolyte can be removed.

[0066] The components of the first electrolyte and the second electrolyte are: one or more of ethylene carbonate, propylene carbonate, vinylene carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl propargyl carbonate, 1,4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate or ethyl butyrate and lithium salt;

[0067] The lithium salt is one or more of LiPF6, LiClO4, LiBF4, LiBOB, LiODFB, LiTDI, LiTFSI and LiFSI.

[0068] The specific steps can be followed:

[0069] (1) Screening: multiple waste 30Ah square-shell lithium iron phosphate batteries produced by the same manufacturer and the same batch were tested for capacity on a charge and discharge tester, and 10 lithium-ion batteries with a capacity greater than 60% were screened out as samples 1 to 10 of this embodiment;

[0070] The specific method for testing capacity is: at 25℃±5℃, use a 5V-20A charge and discharge tester to charge at constant current (0.75C) to a voltage of 3.65V, then charge at constant voltage to a cutoff current of 1 / 20C, leave for 30 minutes, and then discharge at constant current to a cutoff voltage of 2.5V. This is one cycle. A total of 4 cycles are performed. The average value of the tested battery capacity is taken as the capacity base, calculated as 100% by mass.

[0071] (2) Overdischarge: Samples 1 to 10 were deeply overdischarged on a charge and discharge tester until the voltage was equal to 0.01 V. This embodiment adopts a constant resistance overdischarge method, and the resistance is determined according to the internal resistance of the battery cell. The smaller the internal resistance, the smaller the constant resistance value, and vice versa.

[0072] (3) Injection: In the glove box, open the battery injection port and inject 20 ml of the second electrolyte using a syringe. After injection, seal the battery and let it stand for 24-72 hours.

[0073] In this embodiment, the components of the second electrolyte are: 30% ethylene carbonate, 15% propylene carbonate, 1% vinylene carbonate, 20% dimethyl carbonate, 20% ethyl methyl carbonate, 14% diethyl carbonate, and 1.2 mol / L lithium hexafluorophosphate.

[0074] (4) Impurity removal: discharge the free electrolyte and gas in the inner cavity of each sample, and remove the impurities in the inner cavity of the waste lithium-ion battery.

[0075] (5) Liquid injection: Inject the first electrolyte into the inner cavity of each sample and let it stand for 24-72 hours.

[0076] The components of the first electrolyte in this embodiment are: 30% ethylene carbonate, 15% propylene carbonate, 1% vinylene carbonate, 20% dimethyl carbonate, 20% ethyl methyl carbonate, 14% diethyl carbonate, and 1.0 mol / L lithium hexafluorophosphate;

[0077] (6) Charge and discharge test:

[0078] (6.1) Directly test the capacity of the repaired battery at 0.5-1C on a charge and discharge tester;

[0079] (6.2) At 25℃±5℃, use a 5V-20A charge and discharge tester to charge at constant current (0.75C) to a voltage of 3.65V, then charge at constant voltage to a current of 1 / 20C, leave for 30 minutes, and then discharge at constant current to a cut-off voltage of 2.5V. This is one cycle. Test the capacity of the battery after the 100th and 200th cycle discharge. Combined with the initial cycle capacity of the battery, calculate the capacity retention rate at the 100th and 200th charge and discharge cycles.

[0080] For specific test data, see Table 1 and Figure 1 shown.

[0081] Table 1

[0082]

[0083] From Table 1 and Figure 1 It can be seen that after completing one repair, the capacity of the lithium-ion single battery in this embodiment is greater than the initial capacity, and it is considered to be restored to the set target value.

[0084] After 100 and 200 charge and discharge cycles, the capacity and capacity retention rate are still higher than the initial capacity and initial capacity retention rate.

[0085] When the repaired lithium-ion battery has been charged and discharged for a period of time, its capacity decays again and it can be repaired multiple times using the method of this embodiment.

[0086] Example 2

[0087] This embodiment serves as a comparative example of Embodiment 1, and uses waste lithium-ion single cells as the repair object; different from Embodiment 1, this embodiment does not perform step (2) in Embodiment 1, and only uses steps (3), (4) and (5) to repair the waste lithium-ion single cells.

[0088] The specific steps can be followed:

[0089] (1) Screening: The capacities of a plurality of waste 30Ah square-shell lithium iron phosphate batteries produced by the same manufacturer and the same batch are tested on a charge and discharge tester, and two lithium-ion batteries with capacities greater than 60% are screened out as samples 11 and 12 of this embodiment; the specific method for testing the capacity is the same as that of embodiment 1 and is not repeated here.

[0090] (2) Injection: In the glove box, open the battery injection port and inject 20 ml of the second electrolyte using a syringe. After injection, seal the battery and let it stand for 24-72 hours.

[0091] (3) Impurity removal: Expel the gas and free electrolyte from the inner cavity of each sample, and remove the impurities in the inner cavity of the waste lithium-ion battery.

[0092] (4) injecting the first electrolyte into the inner cavity of each sample and letting it stand for 24-72 hours;

[0093] The first electrolyte and the second electrolyte are the same as those in Example 1.

[0094] (5) The charge and discharge test was performed using the method of step (6) in Example 1.

[0095] For specific test data, see Table 2 and Figure 1 shown.

[0096] Table 2

[0097]

[0098] From Table 2 and Figure 1 It can be seen that the capacity can also be increased by replacing the liquid, but the increase is less than that in Example 1.

[0099] Example 3

[0100] Different from Example 1, this embodiment executes the repair process in Example 1 twice in a loop. The specific execution process is:

[0101] Two new 24Ah square-shell lithium iron phosphate batteries were taken and charged and discharged for 200 times as samples 13 and 14 of this embodiment;

[0102] After deep discharge of sample 13 and sample 14, the second electrolyte with the same lithium ion concentration and the same amount was injected into the inner cavity of each sample. After standing for 24 to 72 hours, the free electrolyte and gas in the inner cavity of the waste lithium ion battery were discharged to remove the impurities in the inner cavity of the waste lithium ion battery; the first electrolyte was injected into the inner cavity of each sample, and after standing for 24 to 72 hours, the battery capacity was tested. After that, the above operation was repeated once after 200 charge and discharge cycles. The specific test data is shown in Table 3.

[0103] Table 3

[0104]

[0105] It can be seen from Table 3 that when the capacity of the repaired lithium-ion battery decays to the point where it needs to be repaired again after a period of charge and discharge cycles, the method of the present invention can be used to repair it multiple times.

[0106] Example 4

[0107] This embodiment uses waste lithium-ion single batteries as the repair object;

[0108] Different from Example 1, in this example, for multiple samples, a second electrolyte with different lithium ion concentrations is injected in step (3).

[0109] In this embodiment, a plurality of waste 30Ah square shell lithium iron phosphate batteries produced by the same manufacturer and the same batch are taken to test the initial capacity of the batteries, and 10 samples are selected as samples 15 to 24 of this embodiment; after deep discharge of samples 15 to 24, a second electrolyte of different concentrations is injected into the inner cavity of each sample, and after standing for a set time, the free electrolyte and gas in the inner cavity of the waste lithium ion battery are discharged to remove impurities in the inner cavity of the waste lithium ion battery; the first electrolyte is injected into the inner cavity of each sample, and after standing for 24 to 72 hours, the battery capacity is tested. If the set target value is reached, the capacity repair of the waste lithium ion battery is completed, otherwise, the above operation is repeated until the capacity is restored to the set target value.

[0110] The specific steps are the same as those in Example 1 and will not be repeated here.

[0111] For specific test data, see Table 4 and Figure 2 shown.

[0112] Table 4

[0113]

[0114] From Table 4 and Figure 2It can be seen that when the concentration of lithium ions in the second electrolyte is 1.2 mol / L, the repair effect is best.

[0115] Example 5

[0116] This embodiment uses waste lithium-ion single batteries as the repair object;

[0117] Different from Example 1, this embodiment adopts different over-discharge voltages in step (2) for multiple samples.

[0118] In this embodiment, a plurality of new 24Ah square-shell lithium iron phosphate batteries were taken and charged and discharged for 200 times, and used as samples 25 to 36 of this embodiment;

[0119] The capacity of samples 25 to 34 was tested after deep discharge (every two samples were over-discharged to the same voltage), and the capacity after 200 charge and discharge cycles was tested after over-discharge;

[0120] Samples 35 and 36 were deeply discharged to 0.01V, and the second electrolyte with the same lithium ion concentration was injected into the inner cavity of each sample. After standing for a set time, the free electrolyte and gas in the inner cavity of the waste lithium-ion battery were discharged, and the impurities in the inner cavity of the waste lithium-ion battery were taken out; the first electrolyte was injected into the inner cavity of each sample, and after standing for 24 to 72 hours, the battery capacity was tested, and the capacity of 200 charge and discharge cycles after over-discharge was tested.

[0121] The specific steps are the same as those in Example 1 and will not be repeated here.

[0122] For specific test data, see Table 5 and Figure 3 shown.

[0123] Table 5

[0124]

[0125] From Table 5 and Figure 3 It can be seen that the lower the over-discharge termination voltage, the more obvious the repair effect. And the best repair effect is achieved by replacing the electrolyte in the battery cavity after over-discharge.

[0126] Example 6

[0127] Different from the first embodiment, the present embodiment further includes a step of forming the lithium-ion battery after the liquid is replaced, based on the first embodiment.

[0128] In this embodiment, a plurality of new 24Ah square shell lithium iron phosphate batteries are taken, and after 200 charge and discharge cycles, they are used as samples 37 to 46 of this embodiment; after deep discharge of samples 37 to 46, the second electrolyte with the same lithium ion concentration and the same amount is injected into the inner cavity of each sample, and after standing for 24 to 72 hours, the free electrolyte and gas in the inner cavity of the waste lithium ion battery are discharged; the first electrolyte (SEI film-forming additive is added to the first electrolyte) is injected into the inner cavity of each sample, and after standing for 24 to 72 hours, the formation is carried out, and the battery capacity is tested. If the set target value is reached, the capacity repair of the waste lithium ion battery is completed, otherwise, the above operation is repeated until the capacity is restored to the set target value.

[0129] Before the formation, the process from step (1) to step (5) in Example 1 can be adopted, and after step (5), each sample is formed:

[0130] The specific parameters are as follows:

[0131] On a 5V, 20A charge and discharge tester, charge with a constant current of 0.1C until the voltage reaches 3.5V. After leaving it for 1-24 hours, discharge it with 0.1C to 2.5V. This is a formation cycle. After formation, perform charge and discharge tests on each sample:

[0132] a. Test the capacity of the repaired battery directly at 0.5-1C on the charge and discharge tester;

[0133] b. At 25℃±5℃, use a 5V-20A charge and discharge tester to charge at constant current (0.75C) to a voltage of 3.65V, then charge at constant voltage to a current of 1 / 20C, leave for 30 minutes, and then discharge at constant current to a cut-off voltage of 2.5V. This is one cycle. Test the capacity of the battery after the 200th and 400th cycle discharge. Combined with the initial cycle capacity of the battery, calculate the capacity retention rate of the 200th and 400th charge and discharge cycles.

[0134] For specific test data, see Table 6 and Figure 4 shown.

[0135] Table 6

[0136]

[0137]

[0138] From Table 6 and Figure 4 It can be seen that after completing one repair, the capacity of the lithium-ion single battery in this embodiment is greater than the capacity before the repair, and it is considered to be restored to the set target value.

[0139] After repair, it still has a good capacity retention rate after 200 charge and discharge cycles.

[0140] Example 7

[0141] Different from Example 6, this embodiment further includes a step of replacing the liquid of the formed lithium-ion battery based on Example 6.

[0142] In this embodiment, a plurality of new 24Ah square shell lithium iron phosphate batteries are taken, and after 200 charge and discharge cycles, they are used as samples 47 to 51 of this embodiment; after deep discharge of samples 47 to 51, the second electrolyte with the same lithium ion concentration and the same amount is injected into the inner cavity of each sample, and after standing for 24 to 72 hours, the free electrolyte and gas in the inner cavity of the waste lithium ion battery are discharged; the first electrolyte (SEI film forming additive is added to the first electrolyte) is injected into the inner cavity of each sample, and after standing for 24 to 72 hours, it is formed, and after the free electrolyte in the inner cavity of the lithium ion battery after formation is discharged, the third electrolyte (wherein the third electrolyte is a conventional electrolyte) is injected into the inner cavity of the lithium ion battery, and it is left to stand for a set time. Test the battery capacity, if the set target value is reached, the capacity repair of the waste lithium ion battery is completed, otherwise, repeat the above operation until the capacity is restored to the set target value.

[0143] For specific test data, see Table 7 and Figure 5 shown.

[0144] Table 7

[0145]

[0146] From Table 7 and Figure 5 It can be seen that after completing one repair, the capacity of the lithium-ion single battery in this embodiment is greater than the capacity before the repair, and it is considered to be restored to the set target value.

[0147] After repair, it still has a good capacity retention rate after 200 charge and discharge cycles.

[0148] Example 8

[0149] Different from the above-mentioned embodiment, this embodiment uses waste large-capacity lithium-ion batteries as the repair object.

[0150] The structure of the waste large-capacity lithium-ion battery in this embodiment is as follows: Figure 6 As shown, it includes a plurality of parallel-connected waste lithium-ion single cells and an electrolyte sharing chamber, and the electrolyte areas in the inner cavities of each waste lithium-ion single cell are connected through the electrolyte sharing chamber.

[0151] Repair is achieved by connecting a repair device to the electrolyte shared chamber port, the repair device includes a buffer tank, the top and bottom of the buffer tank are provided with through holes and are connected to a first pipe segment and a second pipe segment that penetrate the through holes, a valve K1 is provided on the first pipe segment, a valve K3 is provided on the second pipe segment, and a third pipe segment is connected to the second pipe segment between K3 and the bottom through hole, and a valve K2 is provided on the third pipe segment.

[0152] In some other embodiments, a vacuum pump may be directly connected to the electrolyte shared chamber port to extract (drain) liquid, and a liquid injection device may be directly connected to the electrolyte shared chamber port to inject liquid.

[0153] It should be noted that, since the inner cavity of the large-capacity battery (including the inner cavity of each single cell and the inner cavity of the electrolyte sharing chamber) contains a large amount of free electrolyte, in order to prevent the additives contained therein from decomposing during the over-discharge process and affecting the repair effect, the difference between this embodiment and Embodiment 1 is that before over-discharge, the free electrolyte in the inner cavity of the large-capacity battery is extracted and a pure solvent electrolyte is injected for the subsequent repair process.

[0154] In addition, after over-discharging, the large-capacity battery has a large amount of free electrolyte in its inner cavity, and direct discharge of the free electrolyte can remove the impurities in the inner cavity. Therefore, the present embodiment is different from the first embodiment in that the second electrolyte does not need to be injected into the inner cavity of the large-capacity battery.

[0155] The specific steps can be followed:

[0156] (1) Screening: A plurality of waste 2700Ah large-capacity lithium-ion batteries were tested for their capacities on a charge-discharge tester, and 5 large-capacity lithium-ion batteries with capacities greater than 60% were screened out as samples 52 to 56 of this embodiment;

[0157] The specific method for testing capacity is: at 25℃±5℃, use a 5V-1500A charge and discharge tester to charge at constant current (0.5C) to a voltage of 3.65V, then charge at constant voltage to a cutoff current of 1 / 20C, leave for 30 minutes, and then discharge at constant current to a cutoff voltage of 2.5V. This is one cycle. A total of 4 cycles are performed. The average value of the tested battery capacity is taken as the capacity base, calculated as 100% by mass.

[0158] (2) Liquid replacement: In the glove box, connect one end of the electrolyte sharing chamber to the third pipe section of the repair device; open valves K1 and K2, close valve K3, connect valve K1 to the vacuum pump, and draw the free electrolyte in the inner cavity of the large-capacity battery into the buffer tank; close valves K1 and K2, open valve K3, and discharge the electrolyte in the buffer tank; close valve K3, open valve K1, inject pure solvent electrolyte into the buffer tank, and close valve K1. At this time, the pressure in the inner cavity of the large-capacity battery is lower than the pressure in the buffer tank. Therefore, open valve K2, and the electrolyte in the buffer tank will automatically flow into the inner cavity of the large-capacity battery; close valves K1, K2 and K3; wherein the pure solvent electrolyte is selected from one or more of EC, PC, DMC, DEC, EMC, EP, and PP.

[0159] (3) Overdischarge: Samples 52 to 56 were deeply overdischarged on a charge and discharge tester until the voltage was equal to 0.01 V. This embodiment adopts a constant resistance overdischarge method, and the resistance is determined according to the internal resistance of the battery cell. The smaller the internal resistance, the smaller the constant resistance value, and vice versa.

[0160] (4) Draining: Open valves K2 and K3, connect a vacuum pump to valve K3, and draw out the free electrolyte from the inner cavity of the electrolyte sharing chamber and the inner cavity of each single cell; then close valves K2 and K3.

[0161] (5) Liquid injection: Inject the first electrolyte into the buffer tank and fill it with inert protective gas, then close valve K1 and open valve K2 to allow the first electrolyte in the buffer tank to be injected into the electrolyte sharing chamber and the inner cavity of each single battery, and then close valve K2.

[0162] The first electrolysis includes one or more of EC, PC, DMC, DEC, EMC, EP, PP, and at least one of the following substances with a content of no more than 2%:

[0163] Soluble lithium salts such as propylene sulfate, trimethyl borate, benzyl imide, 1-(trifluoroacetyl)imidazole, lithium dodecanesulfonate, 2,4-dimethylpyrrole-3,5-diethyl terephthalate, PA6, PA12, PMMA, PVC, cyclohexaneboronic acid pinacol ester, 3-cyclobutene sulfone, VC, 1,3-propane sultone, and lithium hexafluorophosphate.

[0164] (6) Charge and discharge test: The capacity of the repaired large-capacity lithium-ion battery is directly tested at 0.5C on the charge and discharge tester.

[0165] The specific test data are shown in Table 8.

[0166] Table 8

[0167]

[0168]

[0169] It can be seen from Table 8 that after completing one repair, the capacity of the large-capacity lithium-ion battery of this embodiment is greater than the initial capacity, and it is considered to be restored to the set target value.

[0170] Example 9

[0171] This example is used as a comparative example, and two waste large-capacity lithium-ion batteries are repaired. Unlike Example 8, this example does not perform the above steps (2) and (3), and only uses steps (4) and (5) for repair. Specific test data are shown in Table 9.

[0172] Table 9

[0173]

[0174] It can be seen from Table 9 that for large-capacity lithium-ion batteries, only using steps (4) and (5) for repair does not produce a significant repair effect.

[0175] Example 10

[0176] Different from Example 8, this example further includes a step of forming the large-capacity lithium-ion battery after the treatment in step (5) based on Example 8.

[0177] Take a plurality of waste 2700Ah large-capacity lithium-ion batteries, test the initial capacity of the batteries, and screen a plurality of samples of the present embodiment; after deep discharging the plurality of samples, discharge the free electrolyte and gas in the inner cavity of the waste lithium-ion batteries; inject the first electrolyte (SEI film-forming additive is added to the first electrolyte) into the inner cavity of each sample, let it stand for 24 to 72 hours, perform formation, and test the battery capacity. If the set target value is reached, the capacity repair of the waste lithium-ion battery is completed; otherwise, repeat the above operation until the capacity is restored to the set target value.

[0178] The specific parameters are as follows:

[0179] On a 5V, 1500A charge and discharge tester, the battery was charged at a constant current of 0.1C until the voltage reached 3.5V. After 1-24 hours of storage, the battery was discharged at 0.1C to 2.5V. This was a formation cycle. After the formation was completed, the charge and discharge tests were performed on each sample. After one repair, the capacity of the large-capacity lithium-ion battery in this embodiment was greater than the capacity before the repair, and it was considered to have recovered to the set target value. After the repair, the battery still had a good capacity retention rate after 200 charge and discharge cycles.

[0180] Embodiment 11

[0181] Different from Example 10, this embodiment further includes a step of replacing the liquid of the large-capacity lithium-ion battery after formation based on Example 10.

[0182] Take a plurality of waste 2700Ah large-capacity lithium-ion batteries, test the initial capacity of the batteries, and select a plurality of samples as the samples of this embodiment; after deep discharge of each sample, discharge the free electrolyte and gas in the inner cavity of the waste lithium-ion battery; inject the first electrolyte (add SEI film-forming additive to the first electrolyte) into the inner cavity of each sample, let it stand for 24 to 72 hours, perform formation, discharge the free electrolyte in the inner cavity of the lithium-ion battery after formation, and inject the third electrolyte (wherein the third electrolyte is a conventional electrolyte) into the inner cavity of the lithium-ion battery, and let it stand for a set time. Test the battery capacity, if the set target value is reached, the capacity repair of the waste lithium-ion battery is completed, otherwise, repeat the above operation until the capacity is restored to the set target value.

[0183] The test shows that after one repair, the capacity of the lithium-ion single battery of this embodiment is greater than the capacity before the repair, and it is considered to have recovered to the set target value. After the repair, after 200 charge and discharge cycles, it still has a good capacity retention rate.

[0184] Example 12

[0185] Different from the above-mentioned embodiment, this embodiment repairs the waste lithium-ion single battery by replenishing liquid and forming after over-discharging.

[0186] The specific steps can be followed:

[0187] (1) Screening: A plurality of waste 30Ah square-shell lithium iron phosphate batteries produced by the same manufacturer and the same batch were tested for their initial capacity on a charge and discharge tester, and four lithium-ion batteries with a capacity greater than 80% were screened out, two of which were used as samples 59 to 60 of this embodiment; and the other two were used as comparative samples 1 and 2;

[0188] The specific method for testing capacity is: at 25℃±5℃, use a 5V-20A charge and discharge tester to charge at constant current (0.75C) to a voltage of 3.65V, then charge at constant voltage to a cutoff current of 1 / 20C, leave for 30 minutes, and then discharge at constant current to a cutoff voltage of 2.5V. This is one cycle. A total of 4 cycles are performed. The average value of the tested battery capacity is taken as the capacity base, calculated as 100% by mass.

[0189] (2) Overdischarge: Samples 59 to 60 were deeply overdischarged on a charge and discharge tester to a voltage of 0.1-0.01 V (the preferred cutoff voltage in this embodiment is 0.1 V). This embodiment adopts a constant resistance overdischarge method. At this voltage, the SEI film is electrochemically decomposed and gas is generated.

[0190] (3) Liquid injection: In the glove box, open the battery liquid injection port, exhaust the air, and inject 20 ml of the first electrolyte using a syringe. After the liquid injection is completed, seal the battery and let it stand for 8 hours.

[0191] (4) Formation: At room temperature, the battery treated in step (3) is formed using a low current formation method.

[0192] (5) Charge and discharge test:

[0193] (5.1) Directly test the capacity of the repaired battery on a charge and discharge tester;

[0194] (5.2) At 25℃±5℃, use a 5V-20A charge and discharge tester to charge at constant current (0.75C) to a voltage of 3.65V, then charge at constant voltage to a current of 1 / 20C, leave for 30 minutes, and then discharge at constant current to a cut-off voltage of 2.5V. This is one cycle. Test the capacity of the battery after the 80th cycle discharge. Combined with the battery's initial cycle capacity, calculate the capacity retention rate at the 80th charge and discharge cycle.

[0195] For specific test data, see Figure 7 shown.

[0196] from Figure 7 It can be seen that after completing one repair and 80 charge and discharge cycles, the capacity of samples 59 and 60 is higher than that of comparison samples 1 and 2, proving that this embodiment has a better repair effect.

[0197] The repair method of this embodiment can also be used to repair large-capacity lithium-ion batteries.

Claims

1. A method for restoring the capacity of waste lithium-ion batteries, characterized in that: The following steps are involved: Step 1: Deeply over-discharge the waste lithium-ion battery; Step 2, discharging the free electrolyte and gas in the inner cavity of the waste lithium-ion battery, and taking out the impurities in the inner cavity of the waste lithium-ion battery; Step 3, injecting the first electrolyte into the inner cavity of the waste lithium-ion battery treated in step 2, and leaving it to stand for a set time; Step 4: Test the battery capacity. If the set target value is reached, the capacity repair of the used lithium-ion battery is completed. Otherwise, return to step 1.

2. The method for restoring the capacity of waste lithium-ion batteries according to claim 1, characterized in that: In step 2, before discharging the free electrolyte and gas in the inner cavity of the waste lithium-ion battery, the step of vibrating the waste lithium-ion battery is also included.

3. The method for restoring the capacity of waste lithium-ion batteries according to claim 2, characterized in that: The concentration of lithium ions in the second electrolyte is 1.2 mol / L.

4. The method for restoring the capacity of waste lithium-ion batteries according to claim 1, characterized in that: In step 1, the waste lithium-ion battery is deeply over-discharged to a voltage of 0.01V using a constant resistance discharge method.

5. The method for restoring the capacity of waste lithium-ion batteries according to claim 1, characterized in that: The first electrolyte is the electrolyte obtained by purifying the free electrolyte discharged in step 2 using a purification material.

6. The method for restoring the capacity of waste lithium-ion batteries according to claim 5, characterized in that: The purification material is at least one of an activated molecular sieve, an activated carbon adsorbent, a silica gel adsorbent, an alumina adsorbent, a copper catalyst adsorbent, and polyimide.

7. The method for restoring the capacity of waste lithium-ion batteries according to any one of claims 1 to 6, characterized in that: Before step 1, the method also includes the step of determining whether there is free electrolyte in the inner cavity of the waste lithium-ion battery, and if so, discharging the free electrolyte and injecting a fourth electrolyte; the fourth electrolyte is a pure solvent electrolyte.

8. The method for restoring the capacity of waste lithium-ion batteries according to any one of claims 1 to 6, characterized in that: The method further includes, between step 3 and step 4, a step of forming the lithium ion battery after the treatment in step 3.

9. The method for restoring the capacity of waste lithium-ion batteries according to claim 8, characterized in that: The first electrolyte includes a SEI film-forming additive.

10. The method for restoring the capacity of waste lithium-ion batteries according to claim 8, characterized in that: After the lithium ion battery processed in step 3 is formed, before step 4 is performed, the following steps are also included: After the free electrolyte in the inner cavity of the formed lithium-ion battery is discharged, the third electrolyte is injected into the inner cavity of the lithium-ion battery and left to stand for a set time.

11. A method for restoring the capacity of waste lithium-ion batteries, characterized in that: The following steps are involved: Step 1: Deeply over-discharge the waste lithium-ion battery; Step 2, discharging the gas in the inner cavity of the waste lithium-ion battery; Step 3, injecting a first electrolyte into the inner cavity of the waste lithium-ion battery treated in step 2, and leaving it to stand for a set time; the first electrolyte contains a SEI film repair additive; Step 4, forming the lithium ion battery after the treatment in step 3; Step 5: Test the battery capacity. If the set target value is reached, the capacity repair of the used lithium-ion battery is completed. Otherwise, return to step 1.

12. The method for restoring the capacity of waste lithium-ion batteries according to claim 11, characterized in that: In step 1, the waste lithium-ion battery is deeply over-discharged to a voltage of 0.01V by using a constant current or constant resistance discharge method.

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