A composite lithium supplementing slurry for a lithium ion battery negative electrode and a lithium supplementing method thereof

Abstract

The present application relates to the technical field of lithium ion battery manufacturing, in particular to a composite lithium supplementing slurry for the negative electrode of a lithium ion battery and a lithium supplementing method thereof, and discloses a composite lithium supplementing slurry for the negative electrode of a lithium ion battery, which comprises stabilized lithium metal powder, a dispersing agent and a solvent, wherein the dispersing agent is a polyisobutylene-maleic anhydride copolymer; and the solvent is a non-polar solvent. The composite lithium supplementing slurry provided by the present application introduces a non-polar solvent as a dispersion medium on the basis of the preparation of a conventional lithium supplementing slurry, and adopts a polyisobutylene-maleic anhydride copolymer as a specific surfactant, utilizes the steric hindrance effect formed by the polyisobutylene-maleic anhydride copolymer in the non-polar solvent to uniformly disperse the stabilized lithium metal powder in the solvent, thereby solving the problems that lithium powder is easy to be deactivated and easy to be agglomerated in a polar solvent, achieving uniform coating of the lithium supplementing layer, and significantly improving the initial coulomb efficiency and cycle life of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery manufacturing technology, specifically to a composite lithium replenishment slurry for lithium-ion battery anodes and a lithium replenishment method thereof. Background Technology

[0002] Currently, during the first charge and discharge cycle of commercial lithium-ion batteries, a solid electrolyte interface (SEI) film forms on the surface of the negative electrode. This process irreversibly consumes a large amount of active lithium from the positive electrode, leading to a decrease in the battery's initial coulombic efficiency and a practically usable capacity far lower than the theoretical capacity. This is especially true when using high-capacity negative electrode materials such as silicon-based negative electrodes, where the significant volume expansion and continuous interfacial reactions exacerbate the consumption of active lithium, making it one of the key bottlenecks restricting the development of high-energy-density lithium-ion batteries.

[0003] To address this, the industry generally employs pre-lithiation technology, which involves adding extra active lithium to the electrodes before battery assembly to compensate for the lithium consumed in SEI film formation. Among existing negative electrode lithium replenishment technologies, using stabilized lithium metal powder (SLMP) is considered one of the most promising industrialization approaches. SLMP involves coating the surface of lithium metal powder with a dense protective layer, such as lithium carbonate or lithium phosphate, enabling it to remain temporarily stable under certain environmental conditions, thereby reducing the risk of spontaneous combustion of lithium metal powder during electrode preparation.

[0004] Although the stability of stabilized lithium metal powder technology has been improved in dry air, the following core problems still exist when it is applied to negative electrode lithium replenishment: Conventional polar solvent systems can erode the passivation protective layer on the surface of lithium powder, making lithium powder prone to deactivation and thermal runaway risk during slurry preparation; at the same time, lithium powder is prone to agglomeration and sedimentation in solvents due to its high surface energy, resulting in poor slurry stability, and existing dispersant systems such as NMP (N-methylpyrrolidone) and PVP (polyvinylpyrrolidone) cannot form effective steric hindrance on the lithium powder surface; this makes the thickness of the replenishment layer severely uneven during subsequent coating, with excessively high local lithium content easily causing lithium plating short circuits, and insufficient lithium replenishment due to excessively low lithium content, and the high shear dispersion process can also damage the lithium powder protective layer. As a result, existing lithium replenishment technology can never achieve both dispersion uniformity and lithium powder activity protection, and the requirements for the production environment are extremely harsh, making it difficult to achieve large-scale stable application on existing production lines. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings and deficiencies of the prior art and to provide a composite lithium replenishment slurry for lithium-ion battery anodes and a lithium replenishment method thereof.

[0006] The primary objective of this invention is to provide a composite lithium replenishment slurry for use as the negative electrode of a lithium-ion battery.

[0007] A second objective of this invention is to provide a method for preparing the aforementioned composite lithium replenishment slurry.

[0008] A third objective of the present invention is to provide a lithium replenishment method using the above-described composite lithium replenishment slurry.

[0009] A third objective of the present invention is to provide a lithium-ion battery obtained using the above-described lithium replenishment method.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] A composite lithium replenishing slurry for use as the negative electrode of a lithium-ion battery, the composite lithium replenishing slurry comprising stabilized lithium metal powder, a dispersant and a solvent, wherein the dispersant is a polyisobutylene-maleic anhydride copolymer; and the solvent is a non-polar solvent.

[0012] Preferably, the surface of the stabilized lithium metal powder is coated with a protective layer, the material of which is selected from one or more of lithium carbonate, lithium phosphate, and lithium fluoride.

[0013] Preferably, the nonpolar solvent is selected from one or more of n-hexane, cyclohexane, n-heptane, isooctane, petroleum ether, toluene, and xylene.

[0014] Preferably, the content of the stabilized lithium metal powder is 70-90% of the composite lithium replenishment slurry.

[0015] Preferably, the content of the dispersant is 0.5-5% of the composite lithium supplement slurry.

[0016] Preferably, the number-average molecular weight Mn of the polyisobutylene-maleic anhydride copolymer is 5000~20000 Daltons.

[0017] Preferably, the solid content of the composite lithium replenishing slurry is 15-25%.

[0018] The preparation method of the above-mentioned composite lithium replenishment slurry specifically includes the following steps:

[0019] (1) The polyisobutylene-maleic anhydride copolymer is dissolved in a non-polar solvent to form an oil phase dispersion;

[0020] (2) Under stirring conditions, stabilized lithium metal powder is added to the oil phase dispersion for preliminary dispersion to obtain lithium powder suspension;

[0021] (3) The lithium powder suspension was kneaded and dispersed with high solid content to obtain a uniform intermediate slurry;

[0022] (4) The uniform intermediate slurry is gradient diluted to obtain a composite lithium supplement slurry.

[0023] The lithium replenishment method using the above-mentioned composite lithium replenishment slurry specifically includes the following steps:

[0024] (1) Obtain a negative electrode sheet, wherein the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector;

[0025] (2) The composite lithium replenishment slurry is applied to the surface of the negative electrode active material layer by coating to form a wet film;

[0026] (3) The wet film is subjected to gradient drying to obtain a lithium replenishment layer;

[0027] (4) The lithium replenishment layer is disposed on the surface of the negative electrode active material layer away from the negative electrode current collector to obtain the lithium replenishment negative electrode sheet.

[0028] A lithium-ion battery, the lithium-ion battery comprising the above-mentioned lithium-added negative electrode sheet.

[0029] The present invention has the following advantages and effects compared with the prior art:

[0030] (1) This invention uses a novel dispersion system composed of a non-polar solvent and a polyisobutylene-maleic anhydride copolymer to replace the traditional polar solvent system, fundamentally solving the technical problem that stabilized lithium metal powder is prone to agglomeration and sedimentation and surface protective layer failure during slurry preparation. The spatial steric layer formed by the copolymer on the lithium powder surface realizes the long-term stable dispersion of lithium powder in non-polar medium. At the same time, the inertness of the non-polar solvent on the lithium powder surface protective layer effectively avoids the loss of lithium powder activity and greatly reduces the safety risks in slurry preparation and coating processes.

[0031] (2) The present invention combines high solid content kneading dispersion and gradient coating drying process to achieve high precision uniform coating of lithium replenishment layer on the surface of negative electrode sheet, avoid defects such as local lithium plating or insufficient lithium replenishment, thereby significantly improving the first coulombic efficiency and cycle life of battery.

[0032] (3) The present invention is highly compatible with existing lithium-ion battery production lines and has a wide process window, providing a practical solution for the industrial application of negative electrode lithium replenishment technology. Detailed Implementation

[0033] The present invention will be further described below with reference to embodiments, but this is not intended to limit the present invention in any way. Any modifications or substitutions made based on the teachings of the present invention shall fall within the protection scope of the present invention.

[0034] The raw materials involved in the following embodiments are as follows:

[0035] Stabilized lithium metal powder is a known substance and can be prepared according to existing technology. Specifically, refer to the method described in patent CN201810566499.0. The average particle size D50 of the stabilized lithium metal powder is 8 micrometers, the surface coating layer is lithium phosphate with a coating layer thickness of about 15 nanometers, and the nominal active lithium content is 97.5%. Before use, it should be vacuum dried at 50°C for 6 hours and stored in an argon glove box.

[0036] Polyisobutylene-maleic anhydride copolymer is a known substance and can be prepared using existing technology. Specifically, the method developed by Daqing Chemical Research Center can be referred to: Polyisobutylene (CAS No.: 9003-27-4) with a number average molecular weight of 12000 and maleic anhydride (CAS No.: 108-31-6) are added to a reactor at a mass ratio of 10:1 and reacted at 180℃ for 120 minutes under nitrogen protection to obtain maleic anhydride-grafted polyisobutylene copolymer. The number average molecular weight Mn of the polyisobutylene-maleic anhydride copolymer is approximately 12000, the maleic anhydride content is approximately 18%, and the CAS No. of the polyisobutylene-maleic anhydride copolymer is 26426-80-2.

[0037] n-Heptane is a commercially available analytical grade product, dried before use. For further purification, please refer to existing technical methods, specifically the method described in patent CN201510902614.3. Before use, it should be dried using 4A molecular sieves to remove moisture, with the moisture content controlled below 50 ppm. The CAS number for n-heptane is 142-82-5.

[0038] The negative electrode is a commercially available artificial graphite negative electrode, with single-sided coating, an areal density of 95 g / m², a compaction density of 1.55 g / cm³, and a width of 150 mm.

[0039] The testing methods involved in this invention are as follows:

[0040] Viscosity testing method: Using a rotational viscometer (such as the DVS+ type), place approximately 500 ml of slurry in the sample container, ensuring the rotor is immersed to an appropriate depth below the liquid surface, for example, about 1-3 cm. Under a constant temperature environment of 25±2℃, set the rotor speed to 12 rpm, and read the stable viscosity value after rotating for 30 seconds. Each sample is tested in parallel 3 times, and the average value is taken as the final viscosity.

[0041] Test method for solid content: Take about 0.8-1.2g of slurry and coat it evenly on the surface of copper foil. Dry it at 140℃ until the mass no longer changes. Record the mass before and after drying and convert it into the percentage of solid content of the slurry.

[0042] Test method for slurry stability: The storage stability of the slurry is evaluated through a static settling experiment. The prepared composite lithium-supplementing slurry is placed in a sealed container and allowed to stand for 24 hours under an argon atmosphere. The appearance of the slurry is observed for stratification, precipitation, or clear liquid separation. Subsequently, samples are taken from the top of the liquid surface and the bottom of the container, and their solid content is tested. The absolute difference (ΔS) between the solid content of the upper and lower layers is calculated. When ΔS ≤ 2wt%, the slurry is considered to have good stability; when ΔS > 2wt%, it is considered to have poor stability.

[0043] Method for judging coating uniformity: After the lithium slurry is coated and dried, observe the appearance of the coating under natural light. If there are no obvious vertical lines, wavy lines, shrinkage cavities, pinholes or other defects, the coating appearance uniformity is judged to be good; if there are obvious vertical lines, wavy lines or other coating defects, the coating appearance uniformity is judged to be poor.

[0044] Battery testing methods: After cell assembly, the cells are first left to stand at 45℃ for 10 hours to ensure full electrolyte wetting. The initial charge-discharge test is conducted on a battery test cabinet: charging at a constant current of 0.5C to 3.65V, then switching to a constant current of 0.01C to the cutoff voltage of 4.3V; after standing for 5 minutes, discharging at a constant current of 0.5C to 2.5V, and recording the initial discharge capacity. Cycling performance testing is conducted at 25℃, with 1000 charge-discharge cycles at 0.5C. The ratio of the capacity after 1000 cycles to the initial cycle capacity is recorded as the capacity retention rate.

[0045] Example 1

[0046] This embodiment discloses a composite lithium replenishment slurry for lithium-ion battery anodes and a lithium replenishment method thereof, specifically including the following steps:

[0047] Step 1: Preparation of oil phase dispersion

[0048] In a glove box filled with high-purity argon, place 500 mL of dry n-heptane into a 1 L glass reaction flask. Weigh 3.0 g of polyisobutylene-maleic anhydride copolymer and slowly add it to the n-heptane. Place the reaction flask on a magnetic stirrer and stir at 400 rpm for 45 minutes at room temperature until the copolymer is completely dissolved, yielding a clear and transparent oil-phase dispersion.

[0049] Step 2: Dispersion of Stabilized Lithium Metal Powder

[0050] Maintain an argon atmosphere in the glove box. Place the oil-phase dispersion prepared in step one under stirring, with the stirring speed set to 400 rpm. Weigh 100 g of dried, stabilized lithium metal powder and slowly add it to the dispersion in 10 portions using a stainless steel spatula, with approximately 1 minute intervals between each addition. After all the lithium powder has been added, increase the stirring speed to 1000 rpm and continue stirring for 3 hours to obtain a preliminarily dispersed lithium powder suspension.

[0051] Step 3: High solids content kneading and dispersion

[0052] Transfer the lithium powder suspension obtained in step two to a 2-liter planetary vacuum mixer. Start the mixer, setting the revolution speed to 30 rpm and the rotation speed to 1500 rpm. Turn on the vacuum pump and evacuate the mixer to -0.098 MPa. Observe the torque change of the mixer during vacuum mixing. When the torque increases from the initial 15 Nm to 40 Nm, turn off the vacuum pump, add 50 mL of n-heptane to the mixer, reducing the torque to approximately 20 Nm, and continue mixing. Repeat this solvent addition operation three times. The entire kneading process lasts for 2 hours.

[0053] Step 4: Gradient dilution

[0054] Keep the mixer running, but reduce the speed to 600 rpm (autorotation) and 15 rpm (revolution). Prepare the diluent: Take 500 ml of n-heptane and add 3.0 g of polyisobutylene-maleic anhydride copolymer, stirring until dissolved. Add the diluent to the mixer in 5 portions, 100 ml each time, stirring for 45 minutes after each addition. The final slurry has a calculated solids content of approximately 18.5%.

[0055] Step 5: Filtration and Degassing

[0056] The diluted slurry was filtered through a 300-mesh stainless steel wire mesh under nitrogen protection. The filtered slurry was transferred to a 1-liter vacuum degassing reactor, stirred at 150 rpm, and vacuumed to -0.095 MPa for 45 minutes for degassing. After degassing, the slurry was allowed to stand and age for 3 hours under nitrogen protection to obtain the composite lithium-added slurry. A small amount of the slurry was coated onto a glass plate, and the coating surface was observed to be smooth and free of particles. The fineness of the slurry was tested with a scraper fineness meter, and the result was 15 micrometers, which matched the original particle size of the lithium powder, indicating that there were no large agglomerates.

[0057] Step Six: Pre-treatment of Negative Electrode Sheets

[0058] Take a roll of artificial graphite negative electrode sheet and place it in a vacuum drying oven to dry at 100℃ for 18 hours. Immediately after drying, transfer the electrode sheet to a nitrogen-protected transition chamber connected to the coating machine, with the dew point of the transition chamber controlled at -45℃.

[0059] Step 7: Coating

[0060] A slot extrusion coating machine was used for coating. The coating parameters were set as follows: coating gap 200 micrometers, coating speed 5 meters / minute, slurry feed flow rate 120 ml / minute, die angle 2 degrees, and vacuum-assisted pressure -50 Pa. The composite lithium-added slurry prepared in step 5 was pumped to the coating machine tank via a diaphragm pump, and the tank was kept under positive nitrogen pressure. The coating machine was started, and the lithium-added slurry was uniformly coated on the surface of the active material layer of the negative electrode sheet, with the wet film thickness controlled at 120 micrometers.

[0061] Step 8: Gradient Drying

[0062] The coated wet electrode sheets enter a 20-meter-long drying oven. The oven is divided into four temperature zones, set at 45℃, 55℃, 65℃, and 75℃ respectively along the electrode's direction of travel. High-purity nitrogen gas is continuously introduced into the oven at a flow rate of 1 m / s. The total time for the electrode sheets to pass through the oven is approximately 4 minutes.

[0063] Step Nine: Detention Processing

[0064] The dried electrode sheets are passed through an 8-meter-long constant temperature and humidity chamber at a speed of 0.8 meters per minute. The temperature in the chamber is controlled at 35°C and the relative humidity at 15%. The electrode sheets remain in the chamber for 10 minutes.

[0065] Step 10: Collect the roll

[0066] After the deposition treatment, the electrode sheets enter the winding device, with the winding tension set at 80 Newtons. The winding is carried out under nitrogen protection. After winding, the roll is placed into an aluminum foil composite film bag and vacuum-sealed.

[0067] Step 11: Roll forming

[0068] The wound lithium-added electrode sheet was rolled at room temperature with a linear pressure of 200 N / mm. After rolling, the thickness of the lithium-added layer was about 8 micrometers, the areal density was about 1.2 g / m², and the lithium-added amount was about 0.12 mg / cm².

[0069] Battery assembly: The above-mentioned lithium-ion negative electrode sheet and lithium iron phosphate positive electrode sheet are processed into battery cells through processes such as electrode rolling, die cutting, slitting, assembly, baking, electrolyte injection (1M LiPF6 in DEC:EC:EMC=1:1:1Vol%), formation, and aging.

[0070] Example 2

[0071] Repeat the steps of Example 1, except that:

[0072] The amount of polyisobutylene-maleic anhydride copolymer added in step one was changed to 1.0 g, which is 1% of the lithium powder mass. During the high-solids kneading process in step three, a slower torque increase was observed, rising from an initial 14 N·m to a maximum of only 28 N·m, and the number of times solvent was replenished was reduced to 2. After filtration and degassing in step five, slight precipitation appeared in the slurry after standing for 1 hour. Observation of the coated lithium-added layer under an electron microscope revealed a small number of lithium powder agglomerates with a size of approximately 50 micrometers. These agglomerates formed local protrusions after subsequent rolling.

[0073] Unless otherwise specified, the remaining steps are the same as in Example 1, and the battery is assembled and tested.

[0074] Example 3

[0075] Repeat the steps of Example 1, except that:

[0076] The amount of polyisobutylene-maleic anhydride copolymer added in step one was changed to 7.0 grams, which is 7% of the lithium powder mass. When preparing the oil-phase dispersion, the copolymer dissolution rate was observed to be slightly slower than in Example 1. The stirring time was extended to 50 minutes for complete dissolution, resulting in a clear and transparent solution with no undissolved particles. During the high-solids kneading process in step three, the initial torque was 16 N·m, slightly higher than the 15 N·m in Example 1. As kneading progressed, the torque gradually increased to 45 N·m, at which point solvent was added, and the torque dropped back to 22 N·m. This addition operation was repeated three times. The torque change was stable throughout the process, with no sudden torque increase or equipment overload. After filtration and degassing in step five, the slurry viscosity was 1280 mPa·s (shear rate 10 s⁻¹), and the thixotropic index was 6.5. The slurry exhibited good fluidity during coating, with neat coating edges and no serrated defects. After drying, the lithium-added layer surface was smooth and clean. Electron microscopy revealed uniform lithium powder distribution with no visible agglomerates.

[0077] Unless otherwise specified, the remaining steps are the same as in Example 1, and the battery is assembled and tested.

[0078] Example 4

[0079] Repeat the steps of Example 1, except that:

[0080] In the high-solids-content kneading step three, the rotation speed was reduced to 800 rpm and the revolution speed to 15 rpm. The torque changed gradually throughout the kneading process, increasing from an initial 15 N·m to a maximum of only 23 N·m. The kneading time was extended to 3 hours. After filtration and degassing in step five, the slurry fineness test result was 25 micrometers, slightly larger than the original lithium powder particle size. After coating, the lithium-added layer was observed under an electron microscope, revealing a small number of agglomerates with a size of approximately 30 to 40 micrometers.

[0081] Unless otherwise specified, the remaining steps are the same as in Example 1, and the battery is assembled and tested.

[0082] Example 5

[0083] Repeat the steps of Example 1, except that:

[0084] In step one, n-heptane was replaced with an equal volume of isooctane, while the amount of polyisobutylene-maleic anhydride copolymer added remained at 3.0 g. During the high-solids-content kneading process in step three, the torque variation was essentially the same as in Example 1, with the highest torque reaching 38 N·m. After filtration and degassing in step five, the slurry had a solids content of 18.2% and a viscosity of 950 mPa·s. The coated lithium-added layer had a smooth appearance, and electron microscopy revealed uniform lithium powder distribution with no visible agglomerates.

[0085] Unless otherwise specified, the remaining steps are the same as in Example 1, and the battery is assembled and tested.

[0086] Example 6

[0087] Repeat the steps of Example 1, except that:

[0088] In step eight, drying, the four temperature zones of the oven were uniformly set to 80℃, using a constant temperature drying method instead of gradient temperature drying. After drying, fine cracks appeared on the surface of the electrode. Electron microscopy revealed numerous micron-sized pinholes and cracks on the surface of the lithium replenishment layer.

[0089] Unless otherwise specified, the remaining steps are the same as in Example 1, and the battery is assembled and tested.

[0090] Comparative Example 1

[0091] This comparative example uses a prior art lithium replenishment method and is compared with the present invention.

[0092] Step 1: Following standard methods, stabilized lithium metal powder and polyvinylidene fluoride are mixed at a mass ratio of 100:5. N-methylpyrrolidone is added to adjust the solid content to 18%. The mixture is stirred and dispersed for 3 hours under argon protection to obtain the lithium supplementation slurry. No dispersant is added to the slurry.

[0093] Step 2: Apply the above slurry to the same graphite negative electrode surface using a coating machine, with coating parameters consistent with those in Example 1.

[0094] Step 3: Vacuum dry at 80℃ for 12 hours to obtain the lithium-filled electrode sheet.

[0095] During the preparation process, a small amount of exothermic reaction was observed during slurry stirring, with the slurry temperature rising by approximately 3°C. During the drying process after coating, trace amounts of combustible gas were detected at the oven outlet. Electron microscopy revealed uneven distribution of lithium powder on the lithium-filled electrode, with a large number of agglomerates larger than 100 micrometers.

[0096] Battery assembly and battery testing were performed using the method described in Example 1.

[0097] Comparative Example 2

[0098] This comparative example attempts to use a polar solvent system but adds the surfactant of this invention to investigate whether it can improve the dispersion effect.

[0099] Repeat the steps of Comparative Example 1, with the difference that:

[0100] In step one, 3 grams of polyisobutylene-maleic anhydride copolymer (same as in Example 1) were added during slurry preparation. The results showed that the polyisobutylene-maleic anhydride copolymer had poor solubility in N-methylpyrrolidone, resulting in a turbid solution. After stirring for 3 hours, undissolved copolymer flocculent matter remained in the solution. After slurry coating, numerous white spots appeared on the surface of the lithium-added layer, which, upon analysis, were identified as undissolved copolymer precipitation.

[0101] Battery assembly and battery testing were performed using the method described in Example 1.

[0102] Comparative Example 3

[0103] This comparative example uses a nonpolar solvent but does not add a surfactant to examine the necessity of the surfactant.

[0104] Repeat the steps of Example 1, except that:

[0105] In step one, no polyisobutylene-maleic anhydride copolymer was added; only pure n-heptane was used as the dispersion medium. In step two, when lithium powder was added, it was observed that the lithium powder rapidly settled to the bottom after addition, and stirring could not effectively suspend it. After stirring for 2 hours, the lithium powder was completely deposited at the bottom of the container, with clear n-heptane on top. A uniform slurry could not be obtained; during coating, the lithium powder settled in the tank, clogging the pipeline and preventing normal coating operations.

[0106] Due to the unavailability of qualified lithium-filled electrode sheets, this comparative example does not undergo battery assembly testing.

[0107] Comparative Example 4

[0108] This comparative example attempts to prepare lithium replenishment slurry using an aqueous system to investigate the effect of different solvent systems on the stability of lithium powder.

[0109] Step 1: Take 500 ml of deionized water, add 3.0 g of sodium carboxymethyl cellulose, stir to dissolve, and use as a dispersion medium.

[0110] Step 2: While stirring, slowly add 100 grams of stabilized lithium metal powder.

[0111] Immediately after the addition of lithium powder, a violent reaction was observed, producing a large number of bubbles. The slurry temperature rose sharply to approximately 60°C, and some of the lithium powder floated on the surface and burned, producing white smoke. Due to the excessively vigorous reaction, slurry preparation could not continue.

[0112] This comparative example demonstrates that aqueous systems are completely unsuitable for dispersing stabilized lithium metal powders.

[0113] Comparative Example 5

[0114] This comparative example provides a conventional negative electrode sheet without lithium replenishment as a comparison.

[0115] The same artificial graphite negative electrode sheet as in Example 1 was used directly, without any lithium replenishment treatment.

[0116] Battery assembly and battery testing were performed using the method described in Example 1.

[0117] Test case

[0118] The lithium-added slurry and lithium-added electrode prepared in the above embodiments and comparative examples were subjected to performance tests, including slurry stability testing, coating appearance uniformity assessment, and battery electrochemical performance testing. The test results are summarized in Tables 1 and 2.

[0119] Table 1. Test results of slurry properties

[0120] Group Dispersant dosage (%) Solvent type Kneading process Slurry stability (24hΔS) Slurry viscosity (mPa·s) Slurry fineness (μm) Coating appearance uniformity Example 1 3 n-Heptane High solids content kneading 0.8% 1050 15 good Example 2 1 n-Heptane High solids content kneading 3.5% 820 25 Difference Example 3 7 n-Heptane High solids content kneading 1.1% 2350 16 better Example 4 3 n-Heptane low-speed kneading 2.8% 980 25 good Example 5 3 Isooctane High solids content kneading 0.7% 950 15 good Example 6 3 n-Heptane High solids content kneading 0.9% 1080 15 Difference Comparative Example 1 0 NMP Regular stirring Unable to test (settlement) 850 ＞100 Difference Comparative Example 2 3 NMP Regular stirring Unable to test (flocculation). 1200 ＞50 Difference Comparative Example 3 0 n-Heptane Regular stirring Unable to test (settlement) - - - Comparative Example 4 - water - 4.2% - - -

[0121] As can be seen from Table 1:

[0122] 1. Comparing Examples 1-3, it is evident that the amount of dispersant has a significant impact on slurry stability. In Example 1, the slurry stability was best when the dispersant content was 3%, resulting in a good coating appearance. In Example 2, the dispersant content was too low (1%), leading to poorer slurry stability and agglomeration. In Example 3, the dispersant content was too high (7%), resulting in a slight increase in slurry viscosity, good coating performance, and a smooth coating surface. However, slight serrated marks appeared at the edges compared to Example 1, but overall, the coating requirements were still met.

[0123] 2. Comparing Example 1 and Comparative Examples 1-4, it is evident that the specific polyisobutylene-maleic anhydride copolymer and non-polar solvent combination of the present invention are irreplaceable. Comparative Example 1 used the polar solvent NMP without a dispersant, resulting in severe lithium powder agglomeration; Comparative Example 2 added the dispersant of the present invention to the polar solvent NMP, but poor dissolution of the dispersant led to flocculation; Comparative Example 3 used a non-polar solvent without a dispersant, resulting in complete sedimentation of the lithium powder; Comparative Example 4 used an aqueous system, but the lithium powder reacted violently and could not be prepared.

[0124] 3. Comparing Example 6 and Example 1, it can be seen that other non-polar solvents (isooctane) used in this invention can also achieve good dispersion effects, indicating that the technical solution of this invention has universality.

[0125] 4. Comparing Examples 1 and 4, it can be seen that the high-solids-content kneading process is crucial to the slurry dispersion effect. In Example 4, low-speed kneading was used, resulting in insufficient shear force, excessively fine slurry (25μm), and poor coating appearance.

[0126] 5. Comparing Examples 1 and 6, it can be seen that the drying process has a significant impact on the appearance of the coating. In Example 6, constant temperature drying was used, resulting in cracks and pinholes in the coating, leading to a poor appearance.

[0127] Table 2. Battery electrochemical performance test results

[0128] Group Initial charge capacity (Ah) Initial discharge capacity (Ah) First Coulomb efficiency (%) 1000-cycle capacity retention (%) Example 1 2.31 2.24 96.8 92.3 Example 2 2.18 2.11 94.3 89.5 Example 3 2.32 2.25 96.9 91.2 Example 4 2.22 2.15 95.6 89.5 Example 5 2.30 2.23 96.7 92.1 Example 6 2.20 2.13 94.8 86.2 Comparative Example 1 1.95 1.88 86.5 85.5 Comparative Example 2 1.90 1.83 1.83 84.2 Comparative Example 3 - - - - Comparative Example 4 - - - - Comparative Example 5 1.88 1.81 89.2 84.7

[0129] As can be seen from Table 2:

[0130] 1. Comparing Example 1 and Comparative Example 5, it can be seen that the lithium replenishment technology of the present invention significantly improves battery performance. The initial charge capacity of Example 1 is increased by 22.9% compared with Comparative Example 5 without lithium replenishment, the initial coulombic efficiency is increased from 89.2% to 96.8%, and the cycle performance is also increased from 84.7% to 92.3%.

[0131] 2. Comparing Example 1 and Comparative Examples 1-2, it can be seen that the lithium replenishment effect brought about by the specific technical solution of the present invention is significantly better than that of the existing polar solvent system. The initial charge capacity of Comparative Examples 1 and 2 is much lower than that of Example 1, and the cycle performance is also poor.

[0132] 3. Comparing Examples 1-3, it is evident that the amount of dispersant has a significant impact on battery performance. In Example 1, the dispersant content was moderate (3%), resulting in the best performance across all aspects. In Example 2, insufficient dispersant (1%) led to uneven lithium powder dispersion, resulting in a decreased lithium replenishment effect, and both the initial charge capacity and cycle performance were lower than in Example 1. In Example 3, the dispersant content was slightly higher (7%), resulting in a slightly improved initial charge capacity compared to Example 1, but slightly lower cycle performance.

[0133] 4. Comparing Examples 1 and 4, it can be seen that the kneading process has a significant impact on battery performance. In Example 4, the kneading shear force was insufficient, resulting in incomplete dispersion of lithium powder, and the initial charge capacity and cycle performance were both lower than those of Example 1.

[0134] 5. Comparing Examples 1 and 6, it is evident that the drying process significantly impacts the integrity of the lithium replenishment layer structure. The isothermal drying in Example 6 resulted in coating defects, leading to lower initial coulombic efficiency and cycle performance compared to Example 1.

[0135] 6. Comparing Example 6 and Example 1, it can be seen that excellent battery performance can be obtained by using different non-polar solvents (isooctane), indicating that the technical solution of the present invention has good universality.

[0136] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A composite lithium replenishing slurry for the negative electrode of a lithium-ion battery, characterized in that, The composite lithium replenishment slurry comprises stabilized lithium metal powder, a dispersant, and a solvent, wherein the dispersant is a polyisobutylene-maleic anhydride copolymer; and the solvent is a non-polar solvent.

2. The composite lithium supplementation slurry according to claim 1, characterized in that, The surface of the stabilized lithium metal powder is coated with a protective layer, the material of which is selected from one or more of lithium carbonate, lithium phosphate, and lithium fluoride.

3. The composite lithium replenishing slurry according to claim 1, characterized in that, The nonpolar solvent is selected from one or more of n-hexane, cyclohexane, n-heptane, isooctane, petroleum ether, toluene, and xylene.

4. The composite lithium replenishing slurry according to any one of claims 1 or 2, characterized in that, The content of the stabilized lithium metal powder is 70-90% of the composite lithium replenishment slurry.

5. The composite lithium replenishing slurry according to claim 1, characterized in that, The content of the polyisobutylene-maleic anhydride copolymer is 0.5-5% of the composite lithium supplement slurry.

6. The composite lithium replenishing slurry according to any one of claims 1 or 5, characterized in that, The number-average molecular weight (Mn) of the polyisobutylene-maleic anhydride copolymer is 5000~20000 Daltons.

7. The composite lithium supplementation slurry according to any one of claims 1 to 6, characterized in that, The solid content of the composite lithium replenishing slurry is 15-25%.

8. A method for preparing the composite lithium-supplementing slurry according to any one of claims 1 to 7, characterized in that, Specifically, the following steps are included: (1) The polyisobutylene-maleic anhydride copolymer is dissolved in the nonpolar solvent to form an oil phase dispersion; (2) Under stirring conditions, the stabilized lithium metal powder is added to the oil phase dispersion for preliminary dispersion to obtain a lithium powder suspension; (3) The lithium powder suspension is kneaded and dispersed with high solid content to obtain a uniform intermediate slurry; (4) The uniform intermediate slurry is gradient diluted to obtain the composite lithium supplementation slurry.

9. A method for lithium replenishment using the composite lithium replenishment slurry according to any one of claims 1 to 7, characterized in that, Specifically, the steps include the following: (1) Obtain a negative electrode sheet, wherein the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector; (2) The composite lithium replenishing slurry according to any one of claims 1 to 7 or the composite lithium replenishing slurry prepared by the preparation method according to claim 8 is applied to the surface of the negative electrode active material layer by coating to form a wet film; (3) The wet film is subjected to gradient drying to obtain a lithium replenishment layer; (4) The lithium replenishment layer is disposed on the surface of the negative electrode active material layer away from the negative electrode current collector to obtain a lithium replenishment negative electrode sheet.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the lithium-replenishing negative electrode sheet as described in claim 9.