A process method for lithium supplementation of lithium iron phosphate cathode and its application

Abstract

The present invention relates to a process method for lithium supplementation of lithium iron phosphate cathode and its application. The process method comprises the following steps: (1) mixing lithium iron phosphate and a lithium supplement agent, and performing a first stirring to obtain a main powder material; (2) mixing a first conductive agent, a binder, a dispersant, a solvent and the obtained main powder material, and performing a second stirring to obtain the mixed material; (3) mixing a second conductive agent and the obtained mixed material, and performing a third stirring to obtain a cathode slurry, thus completing the process method for lithium supplementation of lithium iron phosphate cathode. In the first step of the present invention, lithium supplementation of the cathode and lithium iron phosphate material are mixed into a main powder material, so that the lithium supplement agent is fully and uniformly distributed in the system of the main powder material, and then the main powder material is mixed with the remaining materials to form a cathode slurry, thereby ensuring the stability of the discharged material, solving the problem of too rapid increase in viscosity during the preparation of the slurry, and improving the performance of the battery cell.

Description

Technical Field

[0001] The invention belongs to the field of positive electrodes of lithium-ion batteries, and relates to a process method for lithium supplementation of lithium iron phosphate positive electrodes and its application. Background Art

[0002] Lithium-ion batteries are widely used in fields such as digital electronic products, power tools, electric vehicles, energy storage, etc. Currently, consumers have put forward higher requirements for their high energy density and high power density. Compared with the currently commercially applied graphite anode material, silicon has a higher capacity. Using it as the anode material can significantly improve the energy density of lithium-ion batteries. However, due to problems such as its low initial Coulomb efficiency and 300% volume expansion, silicon-based materials severely restrict their commercial application. Through prelithiation, the irreversible lithium consumed in the formation of SEI during the first charge of the full cell of silicon materials can be compensated, thereby improving the energy density of the battery.

[0003] Currently, the common lithium supplementation technologies are mainly divided into two categories: positive electrode lithium supplementation and negative electrode lithium supplementation. In terms of negative electrode lithium supplementation, for example, CN105977450A discloses a method for plating lithium on a negative electrode sheet of a lithium-ion battery. The negative electrode sheet is plated with lithium by a vacuum coating method (under the protection of an inert gas), and a lithium plating layer is formed on the surface of the negative electrode sheet. However, due to the high activity of metallic lithium powder or lithium foil, it is difficult to control the safety and the lithium supplementation effect is not good. Therefore, it is very necessary to develop a lithium supplementation method that is both safe, simple and has a good lithium supplementation effect.

[0004] Compared with negative electrode lithium supplementation, positive electrode lithium supplementation has higher safety, stronger operability and higher equipment compatibility. The method of using a positive electrode lithium supplementation additive by mixing a positive electrode active material with a high lithium content and a very low reversible capacity with a traditional positive electrode active material in a certain proportion and using it as a new positive electrode active material for battery assembly has gradually become a research hotspot.

[0005] CN116207264A discloses a positive electrode lithium supplementation slurry, a preparation method and an application, a lithium-ion battery. The positive electrode lithium supplementation slurry includes a lithium supplementation material, a dispersant, a conductive additive and a solvent. Among them, the lithium supplementation material is lithium oxide, and the mass percentage content of the lithium supplementation material is 1-90 wt% of the lithium supplementation slurry. The lithium supplementation slurry provided by the invention has a simple preparation process. After adding a dispersant, it is not easy to agglomerate to form secondary large particles, and the particle size can be greatly reduced. The positive electrode lithium supplementation additive in the slurry can be effectively decomposed to compensate for the lithium ions lost due to the formation of the SEI film during charge and discharge, so as to ensure that more lithium ions can be embedded in the positive electrode material again, improve the capacity utilization of the positive electrode material, and ultimately improve the energy density of the lithium-ion battery.

[0006] CN114583296A discloses a lithium-ion battery and a method for compensating lithium in the positive electrode thereof, belonging to the field of lithium-ion batteries. The method for compensating lithium in the positive electrode of a lithium-ion battery includes: using a lithium compensation composition in the lithium-ion battery and adding an additive to the electrolyte of the lithium-ion battery. Among them, the lithium compensation composition includes a lithium compensation material and a reducing agent. The lithium compensation material includes one or more of lithium orthosilicate and lithium metasilicate; the reducing agent includes one or more of elemental sulfur, elemental phosphorus, elemental boron, molybdenum sulfide, tungsten sulfide, titanium sulfide, lithium sulfide, magnesium sulfide, calcium sulfide, lanthanum sulfide, tantalum sulfide, and iron sulfide; among them, the additive includes one or more of lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, 1,3-propane sultone, and fluorinated ether. This lithium compensation method can effectively improve the energy density and cycle life of lithium-ion batteries.

[0007] Currently, the process of compensating lithium in the positive electrode often forms a mixed colloid by mixing the lithium compensation material for the positive electrode with the positive electrode powder, and then proceeds with subsequent coating. Usually, due to the uncertainty of the addition sequence, the viscosity of the subsequent slurry rises too fast after discharging, resulting in difficulties in subsequent coating improvement. How to improve the process of compensating lithium in the positive electrode and enhance the performance of the battery is a technical problem that urgently needs to be solved. Summary of the Invention

[0008] To solve the above technical problems, the present invention provides a process method and its application for compensating lithium in a lithium iron phosphate positive electrode. In the first step of the present invention, the lithium compensation for the positive electrode and the lithium iron phosphate material are mixed into a main body powder, so that the lithium compensator is fully uniform in the system of the main body powder, and then the main body powder is mixed with the remaining materials to form a positive electrode slurry, thereby ensuring the stability of the discharge, solving the problem of too rapid increase in viscosity during the preparation of the slurry, and improving the performance of the battery cell.

[0009] To achieve this purpose, the present invention adopts the following technical solutions:

[0010] In the first aspect, the present invention provides a process method for compensating lithium in a lithium iron phosphate positive electrode. The process method includes the following steps:

[0011] (1) Mix lithium iron phosphate and a lithium compensator, and perform a first stirring to obtain a main body powder;

[0012] (2) Mix a first conductive agent, a binder, a dispersant, a solvent, and the obtained main body powder, and perform a second stirring to obtain the mixture;

[0013] (3) Mix a second conductive agent and the obtained mixture, and perform a third stirring to obtain a positive electrode slurry, thus completing the process method for compensating lithium in the lithium iron phosphate positive electrode.

[0014] In the first step of the present invention, a cathode lithium supplement and a lithium iron phosphate material are mixed into a main powder material, so that the lithium supplement is fully uniform in the system of the main powder material, and then the main powder material is mixed with the remaining materials to form a cathode slurry, thereby ensuring the stability of the discharge, solving the problem of too rapid increase in viscosity during the slurry preparation process, and improving the performance of the battery cell.

[0015] Preferably, the lithium supplement in step (1) includes Li 5 FeO 4 .

[0016] Preferably, the mass of the lithium iron phosphate in step (1) is 95-96% of the mass of the cathode slurry, and the mass fraction can be 95%, 95.1%, 95.2%, 95.3%, 95.4%, 95.5%, 95.6%, 95.7%, 95.8%, 95.9% or 96%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0017] Preferably, the mass of the lithium supplement in step (1) is 1-3% of the mass of the cathode slurry, and the mass fraction can be 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8% or 3%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0018] Preferably, the revolution speed of the first stirring in step (1) is 15-25 r / min, and the speed can be 15 r / min, 16 r / min, 17 r / min, 18 r / min, 19 r / min, 20 r / min, 21 r / min, 22 r / min, 23 r / min, 24 r / min or 25 r / min, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0019] Preferably, the dispersion speed of the first stirring in step (1) is 180-220 r / min, and the dispersion speed can be 180 r / min, 185 r / min, 190 r / min, 195 r / min, 200 r / min, 205 r / min, 210 r / min, 215 r / min or 220 r / min, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0020] Preferably, the time of the first stirring in step (1) is 10 to 30 min. The time can be 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, 22 min, 24 min, 26 min, 28 min, or 30 min, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0021] Preferably, the mass of the first conductive agent in step (2) is 0.1 to 0.6% of the mass of the positive electrode paste. The mass fraction can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or 0.6%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0022] Preferably, the first conductive agent in step (2) includes conductive carbon black.

[0023] Preferably, the solvent in step (2) includes N-methylpyrrolidone.

[0024] Preferably, the binder in step (2) includes polyvinylidene fluoride.

[0025] Preferably, the mass of the binder in step (2) is 0.2 to 0.8% of the mass of the positive electrode paste. The mass fraction can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, or 0.8%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0026] Preferably, the dispersant in step (2) includes polyvinylpyrrolidone.

[0027] Preferably, the mass of the dispersant in step (2) is 0.1 to 0.5% of the mass of the positive electrode paste. The mass fraction can be 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0028] Preferably, the revolution speed of the second stirring in step (2) is 10 to 20 r / min. The revolution speed can be 10 r / min, 11 r / min, 12 r / min, 13 r / min, 14 r / min, 15 r / min, 16 r / min, 17 r / min, 18 r / min, 19 r / min, or 20 r / min, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0029] Preferably, the dispersion speed of the second stirring in step (2) is 180 - 220 r / min. The dispersion speed can be 180 r / min, 190 r / min, 200 r / min, 210 r / min, 220 r / min, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0030] Preferably, the time of the second stirring in step (2) is 5 - 15 min. The time can be 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0031] Preferably, the second conductive agent in step (3) includes carbon nanotubes.

[0032] Preferably, the mass of the second conductive agent in step (3) is 0.2 - 0.7% of the mass of the positive electrode paste. The mass fraction can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0033] Preferably, the revolution speed of the third stirring in step (3) is 15 - 25 r / min. The revolution speed can be 15 r / min, 16 r / min, 17 r / min, 18 r / min, 19 r / min, 20 r / min, 21 r / min, 22 r / min, 23 r / min, 24 r / min, 25 r / min, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0034] Preferably, the time of the third stirring in step (3) is 100 - 140 min. The time can be 100 min, 105 min, 110 min, 115 min, 120 min, 125 min, 130 min, 135 min, 140 min, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0035] Preferably, the viscosity of the mixture in step (2) is 12000 - 14000 MPa·s. For example, it can be 12000 MPa·s, 12500 MPa·s, 13000 MPa·s, 13500 MPa·s, or 14000 MPa·s, but is not limited to the listed values. Other unlisted values within the range are equally applicable.

[0036] Preferably, the solid content of the mixture in step (2) is 71-72%, and the solid content can be 71%, 71.1%, 71.2%, 71.3%, 71.4%, 71.5%, 71.6%, 71.7%, 71.8%, 71.9% or 72%, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0037] Preferably, the viscosity of the positive electrode slurry in step (3) is 11000-13000 MPa·s. For example, it can be 11000 MPa·s, 11500 MPa·s, 12000 MPa·s, 12500 MPa·s or 13000 MPa·s, but not limited to the listed values. Other unlisted values within the range are equally applicable.

[0038] Maintaining the stability of the slurry viscosity can ensure the consistency of the thickness during the coating process. If the viscosity is too high, it will cause uneven surface tension of the coated electrode sheet, resulting in uneven thickness, and it is more likely to form particle blockage of the coating die head, causing scratches on the electrode sheet and affecting the later performance of the battery cell. If the viscosity of the slurry is too low, normal coating cannot be achieved, and it is difficult to form a uniform and stable coating.

[0039] Preferably, the solid content of the positive electrode slurry in step (3) is 65-66%, and the solid content can be 65%, 65.1%, 65.2%, 65.3%, 65.4%, 65.5%, 65.6%, 65.7%, 65.8%, 65.9% or 66%, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0040] As a preferred technical solution of the process method for lithium supplementation of the lithium iron phosphate positive electrode described in the first aspect of the present invention, the process method includes:

[0041] (1) Mix lithium iron phosphate and a lithium supplementing agent, and perform the first stirring to obtain a main body powder material;

[0042] (2) Mix a first conductive agent, a binder, a dispersant, a solvent and the obtained main body powder material, and perform the second stirring to obtain a mixture with a viscosity of 12000-14000 MPa·s;

[0043] (3) Mix a second conductive agent and the obtained mixture, and perform the third stirring to obtain a positive electrode slurry with a viscosity of 11000-13000 MPa·s, thus completing the process method for lithium supplementation of the lithium iron phosphate positive electrode.

[0044] In the second aspect, the present invention provides a positive electrode slurry, which is obtained by using the process method described in the first aspect.

[0045] In a third aspect, the present invention provides a positive electrode sheet, which contains the positive electrode sheet as described in the second aspect.

[0046] In a fourth aspect, the present invention provides a battery, which contains the positive electrode sheet as described in the third aspect.

[0047] Compared with the prior art, the present invention has at least the following beneficial effects:

[0048] In the first step of the present invention, the positive electrode lithium supplement and the lithium iron phosphate material are mixed into the main powder material, so that the lithium supplement agent is fully uniform in the system of the main powder material, and then the main powder material is mixed with the remaining materials to form a positive electrode slurry, thereby ensuring the stability of the discharge, solving the problem of too rapid increase in viscosity during the slurry preparation process, and improving the performance of the battery cell. Among them, the areal density of the electrode can reach more than 192 g / ㎡, and the thickness can be as low as less than 169.3 mm. Specific Embodiments

[0049] To facilitate the understanding of the present invention, the following examples are listed. Those skilled in the art should understand that the examples are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0050] According to one aspect of the present invention, a process method for supplementing lithium to a lithium iron phosphate positive electrode is provided, and the process method includes the following steps:

[0051] (1) Mix lithium iron phosphate and a lithium supplement agent, and perform a first stirring to obtain a main powder material;

[0052] (2) Mix a first conductive agent, a binder, a dispersant, a solvent and the obtained main powder material, and perform a second stirring to obtain the mixture;

[0053] (3) Mix a second conductive agent and the obtained mixture, and perform a third stirring to obtain a positive electrode slurry, thus completing the process method for supplementing lithium to the lithium iron phosphate positive electrode.

[0054] In some embodiments, the lithium supplement agent in step (1) includes Li 5 FeO 4 .

[0055] In some embodiments, the mass of the lithium iron phosphate in step (1) is 95-96% of the mass of the positive electrode slurry.

[0056] In some embodiments, the mass of the lithium supplement agent in step (1) is 1-3% of the mass of the positive electrode slurry.

[0057] In some embodiments, the revolution speed of the first stirring in step (1) is 15-25 r / min.

[0058] In some embodiments, the dispersion speed of the first stirring in step (1) is 180 - 220 r / min.

[0059] In some embodiments, the time of the first stirring in step (1) is 10 - 30 min.

[0060] In some embodiments, the mass of the first conductive agent in step (2) is 0.1 - 0.6% of the mass of the positive electrode paste.

[0061] In some embodiments, the first conductive agent in step (2) includes conductive carbon black.

[0062] In some embodiments, the solvent in step (2) includes N-methylpyrrolidone.

[0063] In some embodiments, the binder in step (2) includes polyvinylidene fluoride.

[0064] In some embodiments, the mass of the binder in step (2) is 0.2 - 0.8% of the mass of the positive electrode paste.

[0065] In some embodiments, the dispersant in step (2) includes polyvinylpyrrolidone.

[0066] In some embodiments, the mass of the dispersant in step (2) is 0.1 - 0.5% of the mass of the positive electrode paste.

[0067] In some embodiments, the revolution speed of the second stirring in step (2) is 10 - 20 r / min.

[0068] In some embodiments, the dispersion speed of the second stirring in step (2) is 180 - 220 r / min.

[0069] In some embodiments, the time of the second stirring in step (2) is 5 - 15 min.

[0070] In some embodiments, the second conductive agent in step (3) includes carbon nanotubes.

[0071] In some embodiments, the mass of the second conductive agent in step (3) is 0.2 - 0.7% of the mass of the positive electrode paste.

[0072] In some embodiments, the revolution speed of the third stirring in step (3) is 15 - 25 r / min.

[0073] In some embodiments, the time of the third stirring in step (3) is 100 - 140 min.

[0074] In some embodiments, the viscosity of the mixture in step (2) is 12000 - 14000 MPa·s.

[0075] In some embodiments, the solid content of the mixture in step (2) is 71-72%.

[0076] In some embodiments, the viscosity of the positive electrode slurry in step (3) is 11000-13000 MPa·s.

[0077] In some embodiments, the solid content of the positive electrode slurry in step (3) is 65-66%.

[0078] In some embodiments, based on the mass fraction of the positive electrode slurry being 100%, 95-96% lithium iron phosphate, 1-3% lithium supplement agent, 0.1-0.6% first conductive agent, 0.2-0.8% binder, 0.1-0.5% dispersant, 0.2-0.7% second conductive agent, and solvent are taken, and after mixing, a mixture with a solid content of 71-72% is prepared;

[0079] The process method for lithium supplementation of the lithium iron phosphate positive electrode includes:

[0080] (1) Mix lithium iron phosphate and a lithium supplement agent, and perform a first stirring to obtain a main body powder material;

[0081] (2) Mix the first conductive agent, binder, dispersant, solvent, and the obtained main body powder material, and perform a second stirring to obtain the mixture with a viscosity of 12000-14000 MPa·s;

[0082] (3) Mix the second conductive agent and the obtained mixture, and perform a third stirring to obtain a positive electrode slurry with a viscosity of 11000-13000 MPa·s, completing the process method for lithium supplementation of the lithium iron phosphate positive electrode.

[0083] According to another aspect of the present invention, a positive electrode slurry is provided, and the positive electrode slurry is obtained by using the above process method.

[0084] According to another aspect of the present invention, a positive electrode sheet is provided, and the positive electrode sheet contains the above positive electrode slurry.

[0085] According to another aspect of the present invention, a battery is provided, and the battery contains the above positive electrode sheet.

[0086] Example 1

[0087] This example provides a process method for lithium supplementation of a lithium iron phosphate positive electrode. Based on the mass fraction of the positive electrode slurry being 100%, 95.2% lithium iron phosphate, 2% Li 5 FeO 4 , 0.4% conductive carbon black, 0.5% polyvinylidene fluoride, 0.2% polyvinylpyrrolidone, 0.5% carbon nanotubes, and 1.2% N-methylpyrrolidone are taken;

[0088] The process method includes:

[0089] (1) Mix lithium iron phosphate and Li 5 FeO 4 , and conduct the first stirring to obtain the main powder material;

[0090] (2) Mix conductive carbon black, polyvinylidene fluoride, polyvinylpyrrolidone, N-methylpyrrolidone and the obtained main powder material, and conduct the second stirring to obtain the mixture with a viscosity of 13000 MPa·s;

[0091] (3) Mix carbon nanotubes and the obtained mixture, and conduct the third stirring to obtain the positive electrode slurry with a viscosity of 12000 MPa·s, thus completing the process method for lithium supplementation of the lithium iron phosphate positive electrode.

[0092] Example 2

[0093] This example provides a process method for lithium supplementation of the lithium iron phosphate positive electrode. Based on the mass fraction of the positive electrode slurry being 100%, take 95% lithium iron phosphate, 3% Li 5 FeO 4 , 0.1% conductive carbon black, 0.8% polyvinylidene fluoride, 0.1% polyvinylpyrrolidone, 0.7% carbon nanotubes and 0.3% N-methylpyrrolidone;

[0094] The process method includes:

[0095] (1) Mix lithium iron phosphate and Li 5 FeO 4 , and conduct the first stirring to obtain the main powder material;

[0096] (2) Mix conductive carbon black, polyvinylidene fluoride, polyvinylpyrrolidone, N-methylpyrrolidone and the obtained main powder material, and conduct the second stirring to obtain the mixture with a viscosity of 12000 MPa·s;

[0097] (3) Mix carbon nanotubes and the obtained mixture, and conduct the third stirring to obtain the positive electrode slurry with a viscosity of 11000 MPa·s, thus completing the process method for lithium supplementation of the lithium iron phosphate positive electrode.

[0098] Example 3

[0099] This example provides a process method for lithium supplementation of the lithium iron phosphate positive electrode. Based on the mass fraction of the positive electrode slurry being 100%, take 96% lithium iron phosphate, 2% Li 5 FeO 4 , 0.6% conductive carbon black, 0.2% polyvinylidene fluoride, 0.5% polyvinylpyrrolidone, 0.2% carbon nanotubes and 0.5% N-methylpyrrolidone;

[0100] The process method includes:

[0101] (1) Mix lithium iron phosphate and Li 5 FeO 4 , conduct the first stirring to obtain the main powder material;

[0102] (2) Mix conductive carbon black, polyvinylidene fluoride, polyvinylpyrrolidone, N-methylpyrrolidone and the obtained main powder material, conduct the second stirring to obtain the mixture with a viscosity of 14000 MPa·s;

[0103] (3) Mix carbon nanotubes and the obtained mixture, conduct the third stirring to obtain the positive electrode slurry with a viscosity of 13000 MPa·s, and complete the process method for lithium supplementation of the lithium iron phosphate positive electrode.

[0104] Example 4

[0105] This example provides a process method for lithium supplementation of the lithium iron phosphate positive electrode. The difference from Example 1 is that the viscosity of the mixture in step (2) is 11000 MPa·s.

[0106] Example 5

[0107] This example provides a process method for lithium supplementation of the lithium iron phosphate positive electrode. The difference from Example 1 is that the viscosity of the mixture in step (2) is 15000 MPa·s.

[0108] Example 6

[0109] This example provides a process method for lithium supplementation of the lithium iron phosphate positive electrode. The difference from Example 1 is that the viscosity of the positive electrode slurry in step (3) is 10000 MPa·s.

[0110] Example 7

[0111] This example provides a process method for lithium supplementation of the lithium iron phosphate positive electrode. The difference from Example 1 is that the viscosity of the positive electrode slurry in step (3) is 14000 MPa·s.

[0112] Comparative Example 1

[0113] This comparative example provides a process method for lithium supplementation of the lithium iron phosphate positive electrode. The difference from Example 1 is that: the lithium supplementing agent is not mixed in step (1), but mixed in step (2).

[0114] Comparative Example 2

[0115] This comparative example provides a process method for lithium supplementation of the lithium iron phosphate positive electrode. The difference from Example 1 is that: the lithium supplementing agent is not mixed in step (1), but mixed in step (3).

[0116] The obtained positive electrode slurry is assembled into a lithium iron phosphate lithium-ion battery according to the processes of baking, rolling, die-cutting, winding, and hot pressing, and tested. The testing methods include weighing the electrode sheet and measuring the thickness with a laser of the equipment. The test results are shown in Table 1.

[0117] Table 1

[0118] Test number Positive electrode areal density (g / ㎡) Thickness of the positive electrode after cold pressing (mm) Example 1 192 169.3 Example 2 193 169.5 Example 3 192 169.8 Example 4 191 169.0 Example 5 193 169.6 Example 6 191 169.4 Example 7 191 169.9 Comparative example 1 193 172 Comparative example 2 194 173

[0119] In the first step of the present invention, the positive electrode lithium supplement and the lithium iron phosphate material are mixed into the main powder, so that the lithium supplement agent is fully uniform in the system of the main powder, and then the main powder is mixed with the remaining materials to form the positive electrode slurry, thereby ensuring the stability of the discharge, solving the problem of too rapid increase in viscosity during the slurry preparation process, and improving the performance of the battery cell.

[0120] Comparing Example 1 with Examples 4-5, it can be seen that when the viscosity of the mixture is too low, the areal density of the electrode sheet after cold pressing decreases, and when the viscosity of the mixture is too high, the thickness of the electrode sheet after cold pressing increases.

[0121] Comparing Example 1 with Examples 6-7, it can be seen that when the viscosity of the positive electrode slurry is too high or too low, the thickness of the electrode sheet after cold pressing increases, and the areal density of the battery electrode sheet decreases.

[0122] Comparing Example 1 with Comparative Example 1, it can be seen that when the lithium supplement agent is not mixed in step (1) but in step (2), it results in too large areal density of the electrode sheet, too thick cold pressing thickness, and uneven dispersion.

[0123] Comparing Example 1 with Comparative Example 2, it can be seen that when the lithium supplement agent is not mixed in step (1) but in step (2), it results in too large areal density of the electrode sheet, too thick cold pressing thickness, and uneven dispersion.

[0124] The present invention uses the above examples to illustrate the detailed process equipment and process flow of the present invention, but the present invention is not limited to the above detailed process equipment and process flow, that is, it does not mean that the present invention must rely on the above detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A process for lithium supplementation of lithium iron phosphate cathode, characterized in that, the process method includes the following steps: (1) Mix lithium iron phosphate and lithium supplement agent, and conduct the first stirring to obtain the main powder material; (2) Mix the first conductive agent, binder, dispersant, solvent and the obtained main powder material, and conduct the second stirring to obtain the mixture; (3) Mix the second conductive agent and the obtained mixture, and conduct the third stirring to obtain the cathode slurry, thus completing the process for lithium supplementation of lithium iron phosphate cathode; The lithium supplement agent described in step (1) is Li 5 FeO 4 ; The mass of the lithium iron phosphate in step (1) is 95 - 96% of the mass of the cathode slurry; The mass of the lithium supplement agent in step (1) is 1 - 3% of the mass of the cathode slurry; The viscosity of the cathode slurry in step (3) is 11000 - 13000 MPa·s.

2. The process for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, The revolution speed of the first stirring in step (1) is 15 - 25 r / min.

3. The process for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, The dispersion speed of the first stirring in step (1) is 180 - 220 r / min.

4. The process for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, The time of the first stirring in step (1) is 10 - 30 min.

5. The process for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, The mass of the first conductive agent in step (2) is 0.1 - 0.6% of the mass of the cathode slurry.

6. The process for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, The first conductive agent in step (2) includes conductive carbon black.

7. The process for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, The solvent in step (2) includes N-methylpyrrolidone.

8. The process for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, The binder in step (2) includes polyvinylidene fluoride.

9. The process for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, The mass of the binder in step (2) is 0.2 - 0.8% of the mass of the cathode slurry.

10. The process for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, The dispersant in step (2) includes polyvinylpyrrolidone.

11. The process for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, The mass of the dispersant in step (2) is 0.1 - 0.5% of the mass of the cathode slurry.

12. The process for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, The revolution speed of the second stirring in step (2) is 10 - 20 r / min.

13. The process for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, The dispersion speed of the second stirring in step (2) is 180 - 220 r / min.

14. The process for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, The time of the second stirring in step (2) is 5 - 15 min.

15. The process method for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, the second conductive agent in step (3) includes carbon nanotubes.

16. The process method for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, the mass of the second conductive agent in step (3) is 0.2 - 0.7% of the mass of the cathode slurry.

17. The process method for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, the revolution speed of the third stirring in step (3) is 15 - 25 r / min.

18. The process method for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, the time of the third stirring in step (3) is 100 - 140 min.

19. The process method for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, the viscosity of the mixture in step (2) is 12000 - 14000 MPa·s.

20. The process method for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, the solid content of the mixture in step (2) is 71 - 72%.

21. The process method for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, the solid content of the cathode slurry in step (3) is 65 - 66%.

22. The process method for lithium supplementation of lithium iron phosphate cathode according to claim 1, characterized in that, the process method includes: (1)Mix lithium iron phosphate and Li 5 FeO 4 , conduct the first stirring to obtain the main powder material; (2) Mix the first conductive agent, binder, dispersant, solvent and the obtained main body powder, and conduct the second stirring to obtain a mixture with a viscosity of 12000 - 14000 MPa·s; (3) Mix the second conductive agent and the obtained mixture, and conduct the third stirring to obtain a cathode slurry with a viscosity of 11000 - 13000 MPa·s, completing the process method for lithium supplementation of the lithium iron phosphate cathode; the mass of the lithium iron phosphate in step (1) is 95 - 96% of the mass of the cathode slurry; the mass of the lithium supplementing agent in step (1) is 1 - 3% of the mass of the cathode slurry.

23. A cathode slurry, characterized in that, the cathode slurry is obtained by using the process method according to any one of claims 1 - 22.

24. A cathode plate, characterized in that, the cathode plate contains the cathode plate as described in claim 23.

25. A battery, characterized in that, the battery contains the cathode plate as described in claim 24.