Cathode slurry, cathode sheet and preparation method thereof, and lithium ion battery

Abstract

The present application relates to a kind of positive slurry, positive pole piece and its preparation method, lithium ion battery.Positive slurry contains positive active material, binder, conductive agent, solvent and additive, the chemical formula of the additive is (NH4) x H y RO z , the mass fraction of additive is 0.005% to 2%.The above-mentioned positive slurry can improve the solid content of slurry by adding a specific content of additive, also can optimize the porosity of pole piece, and optimize the interface film of pole piece and electrolyte, reach in improving the processing property and stability of slurry while improving the cycle performance of high-voltage lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a positive electrode slurry, a positive electrode sheet and its preparation method, and a lithium-ion battery. Background Technology

[0002] In the lithium-ion battery cathode electrode fabrication process, a slurry is coated onto the current collector. Aqueous coating uses water as a solvent for the slurry, rather than slurries prepared with low-toxicity organic solvents such as NMP, thus offering advantages in environmental protection and energy saving. However, instability of the slurry often occurs during formulation, resulting in poor processability, poor electrode flexibility, and phenomena such as active material shedding and powdering, which in turn leads to the deterioration of battery performance.

[0003] Research has shown that, within a certain viscosity range, the solid content of the slurry affects its stability. Increased solid content leads to increased friction between the active material, binder, and conductive agent particles, resulting in more uniform slurry dispersion, improved stability, and enhanced electrode adhesion and peel strength. However, increased solid content also reduces solvent evaporation during drying, leading to decreased porosity among the active material, binder, and conductive agent particles. This can negatively impact lithium-ion insertion and extraction, negatively affecting battery performance. Summary of the Invention

[0004] Therefore, it is necessary to provide a positive electrode slurry, a positive electrode sheet and its preparation method, and a lithium-ion battery to solve the problem of unstable slurry causing active material to fall off and powder to shed.

[0005] A positive electrode slurry contains a positive electrode active material, a binder, a conductive agent, a solvent, and an additive, wherein the chemical formula of the additive is (NH4). x H y RO z Wherein, R is selected from: B, P, W, x>0, y≥0, z>0, and the values ​​of x, y, and z satisfy the charge balance of the chemical formula. The mass fraction of the additive in the positive electrode slurry is 0.005%-2%.

[0006] In one embodiment, the pH value of the positive electrode slurry is 7 to 11.

[0007] In one embodiment, the solid content of the positive electrode slurry is 60%-80%.

[0008] In one embodiment, the positive electrode active material has a mass fraction of 60% to 80% in the positive electrode slurry, the binder has a mass fraction of 1% to 5% in the positive electrode slurry, the conductive agent has a mass fraction of 1% to 6% in the positive electrode slurry, and the solvent has a mass fraction of 17% to 30% in the positive electrode slurry.

[0009] In one embodiment, the mass ratio of the additive to the positive electrode active material is (1-50):10000.

[0010] In one embodiment, the additive is selected from NH4B5O8, (NH4)2B4O7, NH4HB4O7, (NH4)3PO4, (NH4)2HPO4, (NH4)2WO4, and (NH4)6H2W. 12 O 40 One or more of them.

[0011] In one embodiment, the positive electrode active material is selected from one or more of doped or undoped lithium nickel manganese oxide, lithium cobalt phosphate, lithium manganese phosphate, and lithium nickel phosphate.

[0012] In one embodiment, the adhesive is selected from one or more of styrene-butadiene rubber, sodium carboxymethyl cellulose, acrylonitrile copolymer, polytetrafluoroethylene, polyacrylic acid, polyethylene oxide, polyvinylidene fluoride, polyvinyl alcohol, and polyacrylate.

[0013] In one embodiment, the solvent is water.

[0014] In one embodiment, the conductive agent is selected from one or more of acetylene black, carbon black, metal fibers, vapor-grown carbon fibers, carbon nanotubes, graphene and their mixed conductive slurries, and conductive graphite.

[0015] A method for preparing the aforementioned positive electrode slurry includes the following steps:

[0016] A portion of the adhesive and the solvent are mixed to obtain a first gel-like adhesive liquid;

[0017] The additive is added to the first gel-like adhesive liquid and mixed to obtain the second gel-like adhesive liquid;

[0018] After mixing the positive electrode active material and the conductive agent, the second gel-like binder is added, and the mixture is then added to the remaining binder and mixed.

[0019] A method for preparing a positive electrode sheet includes the following steps:

[0020] The positive electrode slurry is coated onto the current collector, dried, and rolled.

[0021] A positive electrode sheet is prepared by the aforementioned preparation method.

[0022] A lithium-ion battery includes the aforementioned positive electrode, negative electrode, separator, and electrolyte.

[0023] Compared with traditional methods, the above-mentioned positive electrode slurry, positive electrode sheet and its preparation method, and lithium-ion battery have the following beneficial effects:

[0024] The above-mentioned positive electrode slurry is prepared by adding a specific amount of additive (NH4). x H y RO z Within a certain viscosity range, the additive can increase the solid content of the slurry and appropriately increase its pH value, thereby improving the stability of the positive electrode slurry and enhancing the adhesion and peel strength of the electrode sheet. The increased solid content reduces solvent usage, saving material and labor costs while improving coating efficiency. During the subsequent electrode baking process, some components of the additive can volatilize in gaseous form, thus not affecting the residual alkali on the electrode sheet. During volatilization, the positive electrode sheet can form uniform voids, improving its pore structure, increasing porosity, and optimizing the wettability between the positive electrode sheet and the electrolyte. The remaining additive components can optimize the interfacial film between the positive electrode sheet and the electrolyte, which is beneficial for the battery to operate at higher voltages, improving capacity retention during battery cycling, and extending battery life.

[0025] The aforementioned positive electrode sheet is formed by coating the aforementioned positive electrode slurry onto the current collector, drying, and rolling. The aforementioned lithium-ion battery has the aforementioned positive electrode sheet, and thus can obtain the corresponding beneficial effects. Attached Figure Description

[0026] Figure 1 The 3ITT curves of the positive electrode slurry in Example 10 and the comparative example are shown.

[0027] Figure 2 The image shows the viscoelastic curves of the positive electrode slurry in Example 10 and the comparative example. Detailed Implementation

[0028] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0030] The positive electrode slurry of one embodiment of the present invention contains a positive electrode active material, a binder, a conductive agent, a solvent, and additives.

[0031] The chemical formula of the additive is (NH4). x H y RO z Where R is selected from B, P, W, x > 0, y ≥ 0, z > 0, and the values ​​of x, y, and z satisfy the charge balance of the chemical formula. The mass fraction of the additive in the positive electrode slurry is 0.005%-2%.

[0032] In one example, the additive is selected from NH4B5O8, (NH4)2B4O7, NH4HB4O7, (NH4)3PO4, (NH4)2HPO4, (NH4)2WO4, and (NH4)6H2W. 12 O 40 One or more of the above additives. When the above additives are selected, some components of the additives can volatilize in the form of gas during the subsequent electrode baking process, which will not affect the residual alkali of the electrode. In addition, during the volatilization process, the electrode can form uniform pores, thereby improving the porosity of the electrode and optimizing the wettability of the electrode and the electrolyte.

[0033] Because the additive is weakly alkaline, its addition can raise the pH value of the cathode slurry. In one example, the addition of the additive raised the pH value of the cathode slurry by 0.5% to 5%.

[0034] In one example, the pH value of the positive electrode slurry is 7–11. Further, in another example, the pH value of the positive electrode slurry is 9.23–9.5. Optimizing the pH value of the positive electrode slurry is beneficial for improving its stability.

[0035] The addition of additives can increase the solid content of the cathode slurry. In one example, the solid content of the cathode slurry is 60% to 80%. In some specific examples, the solid content of the cathode slurry is 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, etc.

[0036] In one example, the mass fraction of the positive electrode active material in the positive electrode slurry is 60% to 80%.

[0037] Optionally, the positive electrode active material can be, but is not limited to, one or more of doped or undoped lithium nickel manganese oxide, lithium cobalt phosphate, lithium manganese phosphate, and lithium nickel phosphate. The above-mentioned positive electrode active materials have high operating voltages, with charging cut-off voltages above 4.8V, and also possess advantages such as high specific energy and low cost.

[0038] In one example, the solvent has a mass fraction of 17% to 30% in the positive electrode slurry.

[0039] In one example, the solvent is water, which can be, but is not limited to, deionized water, ultrapure water, high-purity water, distilled water, etc.

[0040] In one example, the binder has a mass fraction of 1% to 5% in the positive electrode slurry.

[0041] In one example, the adhesive is a water-based adhesive, such as, but not limited to, one or more of styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), acrylonitrile copolymers (LA132, LA133), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and polyacrylate.

[0042] In one example, the conductive agent has a mass fraction of 1% to 6% in the positive electrode slurry.

[0043] In one example, the conductive agent is selected from one or more of the following: acetylene black, carbon black and other particulate conductive agents; metal fibers, vapor-grown carbon fibers, carbon nanotubes and other fibrous conductive agents; graphene and its mixed conductive slurry; and conductive graphite.

[0044] In one example, NH4HB4O7 was selected as the additive, and its mass fraction in the positive electrode slurry was 0.1‰ to 0.12‰. Experiments showed that this example exhibited excellent battery cycle capacity retention at both room temperature and high temperature.

[0045] In one example, the additives used were a mixture of (NH4)2B4O7 and (NH4)2WO4 in a mass ratio of (1–2):1, with the additive mass fraction in the positive electrode slurry being 0.9‰–0.92‰. Experiments showed that the positive electrode sheet prepared using the positive electrode slurry of this example exhibited excellent peel strength, effectively preventing electrode powder shedding.

[0046] The above-mentioned positive electrode slurry is prepared by adding a specific amount of additive (NH4). x H y RO zWithin a certain viscosity range, the additive can increase the solid content of the slurry and appropriately increase its pH value, thereby improving the stability of the positive electrode slurry and enhancing the adhesion and peel strength of the electrode sheet. The increased solid content reduces solvent usage, saving material and labor costs while improving coating efficiency. During the subsequent electrode baking process, some components of the additive can volatilize in gaseous form, thus not affecting the residual alkali on the electrode sheet. During volatilization, the positive electrode sheet can form uniform voids, improving its pore structure, increasing porosity, and optimizing the wettability between the positive electrode sheet and the electrolyte. The remaining additive components can optimize the interfacial film between the positive electrode sheet and the electrolyte, which is beneficial for the battery to operate at higher voltages, improving capacity retention during battery cycling, and extending battery life.

[0047] The present invention also provides a method for preparing the positive electrode slurry of any of the above examples, comprising the following steps:

[0048] A portion of the adhesive and the solvent are mixed to obtain a first gel-like adhesive liquid;

[0049] The additive is added to the first gel-like adhesive liquid and mixed to obtain the second gel-like adhesive liquid;

[0050] After mixing the positive electrode active material and the conductive agent, the second gel-like binder is added, and the mixture is then added to the remaining binder and mixed.

[0051] This invention also provides a method for preparing a positive electrode sheet, comprising the following steps:

[0052] The positive electrode slurry of any of the above examples is coated onto the current collector, dried, and rolled.

[0053] In one example, the current collector comprises a conductive film. The conductive film is, for example, aluminum foil.

[0054] Furthermore, in one example, the current collector also includes a coating layer disposed on at least one side of the conductive film. The coating layer prevents corrosion of the conductive film by an increase in the pH value of the positive electrode slurry.

[0055] The coating material can include, for example, carbon materials, inorganic oxides, and solid electrolytes. Examples of carbon materials include carbon black and graphite catheters. Examples of inorganic oxides include WO2, Al2O3, and SiO2.

[0056] In one example, the coating thickness is 0.1–5 μm.

[0057] The present invention also provides a positive electrode sheet prepared by the above-described method for preparing a positive electrode sheet.

[0058] The present invention will be further described in detail below through specific embodiments. These embodiments will enable those skilled in the art to have a more comprehensive understanding of the present invention, but will not limit the present invention in any way.

[0059] Example 1

[0060] This embodiment provides a method for preparing a positive electrode sheet, including the following steps:

[0061] (1) Take 3g of CMC and 125g of deionized water and stir to mix to obtain gel-like adhesive liquid A.

[0062] (2) Take 0.06g of additive NH4B5O8 and add it to the above gel-like adhesive liquid A. Continue to stir evenly to obtain gel-like adhesive liquid B.

[0063] (3) Take 276g of lithium nickel manganese oxide and 15g of conductive carbon black and mix them evenly. Then add the above-mentioned colloidal binder B, stir and mix evenly, then add 24g of binder SBR with a solid content of 25%, and continue to stir and mix evenly to obtain the positive electrode slurry.

[0064] (4) The above positive electrode slurry is uniformly coated on aluminum foil containing a 2μm carbon coating layer, and after drying and rolling, a positive electrode sheet is obtained.

[0065] Example 2

[0066] This embodiment provides a method for preparing a positive electrode sheet, including the following steps:

[0067] (1) Take 3g of CMC and 125g of deionized water and stir to mix to obtain gel-like adhesive liquid A.

[0068] (2) Take 0.05g of additive NH4B5O8 and add it to the above gel-like adhesive liquid A. Continue to stir evenly to obtain gel-like adhesive liquid B.

[0069] (3) Take 276g of lithium nickel manganese oxide and 15g of conductive carbon black and mix them evenly. Then add the above-mentioned colloidal binder B and stir to mix evenly. Then add 24g of binder SBR with a solid content of 25% and continue to stir to mix evenly to obtain the positive electrode slurry.

[0070] (4) The above positive electrode slurry is uniformly coated on aluminum foil containing a 1μm carbon coating layer, and after drying and rolling, a positive electrode sheet is obtained.

[0071] Example 3

[0072] This embodiment provides a method for preparing a positive electrode sheet, including the following steps:

[0073] (1) Take 3g of CMC and 125g of deionized water and stir to mix to obtain gel-like adhesive liquid A.

[0074] (2) Take 0.2g of additive (NH4)2B4O7 and add it to the above gel-like adhesive liquid A. Continue to stir evenly to obtain gel-like adhesive liquid B.

[0075] (3) Take 276g of lithium nickel manganese oxide and 15g of conductive carbon black and mix them evenly. Then add the above-mentioned colloidal binder B, stir and mix evenly, then add 24g of binder SBR with a solid content of 25%, and continue to stir and mix evenly to obtain the positive electrode slurry.

[0076] (4) The above positive electrode slurry is uniformly coated on aluminum foil containing a 2μm carbon coating layer, and after drying and rolling, a positive electrode sheet is obtained.

[0077] Example 4

[0078] This embodiment provides a method for preparing a positive electrode sheet, including the following steps:

[0079] (1) Take 3g of CMC and 125g of deionized water and stir to mix to obtain gel-like adhesive liquid A.

[0080] (2) Take 0.03g of additive (NH4)2B4O7 and add it to the above gel-like adhesive liquid A. Continue to stir evenly to obtain gel-like adhesive liquid B.

[0081] (3) Take 276g of high voltage lithium nickel manganese oxide material and 15g of conductive carbon black and mix them evenly. Then add the above-mentioned gel-like binder B, stir and mix evenly, and then add 24g of binder SBR with a solid content of 25%. Continue to stir and mix evenly to obtain the positive electrode slurry.

[0082] (4) The obtained slurry is uniformly coated on aluminum foil containing a 2μm WO2 coating, and after drying and rolling, a positive electrode sheet is obtained.

[0083] Example 5

[0084] This embodiment provides a method for preparing a positive electrode sheet, including the following steps:

[0085] (1) After stirring and mixing 3g CMC with 125g deionized water, a gel-like adhesive liquid A is obtained.

[0086] (2) Add 0.04g (NH4)3PO4 of slurry additive to the above-mentioned gel-like adhesive liquid A and continue to stir evenly to obtain gel-like adhesive liquid B.

[0087] (3) Take 276g of lithium nickel manganese oxide and 15g of conductive carbon black and mix them evenly. Then add the above-mentioned colloidal binder B, stir and mix evenly, then add 24g of binder SBR with a solid content of 25%, and continue to stir and mix evenly to obtain the positive electrode slurry.

[0088] (4) The above positive electrode slurry is uniformly coated on an aluminum foil containing a 1μm WO2 coating, and then dried and rolled to obtain a positive electrode sheet.

[0089] Example 6

[0090] This embodiment provides a method for preparing a positive electrode sheet, including the following steps:

[0091] (1) Take 3g of CMC and 125g of deionized water and stir to mix to obtain gel-like adhesive liquid A.

[0092] (2) Take 0.16g of additive (NH4)2HPO4 and add it to the above gel-like adhesive liquid A. Continue to stir evenly to obtain gel-like adhesive liquid B.

[0093] (3) Take 276g of lithium nickel manganese oxide and 15g of conductive carbon black and mix them evenly. Then add the above-mentioned colloidal binder B and stir to mix evenly. Then add 24g of binder SBR with a solid content of 25% and continue to stir to mix evenly to obtain the positive electrode slurry.

[0094] (4) The above positive electrode slurry is uniformly coated on aluminum foil containing a 1μm carbon coating layer, and after drying and rolling, a positive electrode sheet is obtained.

[0095] Example 7

[0096] This embodiment provides a method for preparing a positive electrode sheet, including the following steps:

[0097] (1) Take 3g of CMC and 125g of deionized water and stir to mix to obtain gel-like adhesive liquid A.

[0098] (2) Take 0.02g of additive (NH4)2WO4 and add it to the above gel-like adhesive liquid A. Continue to stir evenly to obtain gel-like adhesive liquid B.

[0099] (3) Take 276g of lithium nickel manganese oxide and 15g of conductive carbon black and mix them evenly. Then add the above-mentioned colloidal binder B, stir and mix evenly, then add 24g of binder SBR with a solid content of 25%, and continue to stir and mix evenly to obtain the positive electrode slurry.

[0100] (4) The above positive electrode slurry is uniformly coated on an aluminum foil containing a 2μm SiO2 coating layer, and then dried and rolled to obtain a positive electrode sheet.

[0101] Example 8

[0102] This embodiment provides a method for preparing a positive electrode sheet, including the following steps:

[0103] (1) Take 3g of CMC and 125g of deionized water and stir to mix to obtain gel-like adhesive liquid A.

[0104] (2) Take 0.02g of additive (NH4)6H2W 12 O 40 Add the above gel-like adhesive liquid A and continue stirring until homogeneous to obtain gel-like adhesive liquid B.

[0105] (3) Take 276g of lithium nickel manganese oxide and 15g of conductive carbon black and mix them evenly. Then add the above-mentioned colloidal binder B, stir and mix evenly, then add 24g of binder SBR with a solid content of 25%, and continue to stir and mix evenly to obtain the positive electrode slurry.

[0106] (4) The above positive electrode slurry is uniformly coated on an aluminum foil containing a 1.5μm SiO2 coating layer, and then dried and rolled to obtain a positive electrode sheet.

[0107] Example 9

[0108] This embodiment provides a method for preparing a positive electrode sheet, including the following steps:

[0109] (1) Take 3g of CMC and 125g of deionized water and stir to mix to obtain gel-like adhesive liquid A.

[0110] (2 Take 0.05g of additive NH4B5O8 and 0.05g of additive (NH4)2HPO4 and add them to the above gel-like adhesive liquid A. Continue to stir evenly to obtain gel-like adhesive liquid B.

[0111] (3) Take 276g of lithium nickel manganese oxide and 15g of conductive carbon black and mix them evenly. Then add the above-mentioned colloidal binder B, stir and mix evenly, then add 24g of binder SBR with a solid content of 25%, and continue to stir and mix evenly to obtain the positive electrode slurry.

[0112] (4) The above positive electrode slurry is uniformly coated on an aluminum foil containing a 1μm SiO2 coating, and then dried and rolled to obtain a positive electrode sheet.

[0113] Example 10

[0114] This embodiment provides a method for preparing a positive electrode sheet, including the following steps:

[0115] (1) Take 3g of CMC and 125g of deionized water and stir to mix to obtain gel-like adhesive liquid A.

[0116] (2) Take 0.15g of additive (NH4)2B4O7 and 0.1g of additive (NH4)2WO4 and add them to the above gel-like adhesive liquid A. Continue to stir evenly to obtain gel-like adhesive liquid B.

[0117] (3) Take 276g of lithium nickel manganese oxide and 15g of conductive carbon black and mix them evenly. Then add the above-mentioned colloidal binder B, stir and mix evenly, then add 24g of binder SBR with a solid content of 25%, and continue to stir and mix evenly to obtain the positive electrode slurry.

[0118] (4) The above positive electrode slurry is uniformly coated on an aluminum foil containing a 1μm Al2O3 coating, and after drying and rolling, a positive electrode sheet is obtained.

[0119] Comparative Example

[0120] The preparation method of the positive electrode sheet in this comparative example includes the following steps:

[0121] (1) Take 3g of CMC and 125g of deionized water and stir to mix to obtain gel-like adhesive liquid A.

[0122] (2) Take 276g of lithium nickel manganese oxide and 15g of conductive carbon black and mix them evenly. Then add the above-mentioned colloidal binder B, stir and mix evenly, then add 24g of binder SBR with a solid content of 25%, and continue to stir and mix evenly to obtain the positive electrode slurry.

[0123] (3) The obtained slurry is uniformly coated on aluminum foil, and after drying and rolling, a positive electrode sheet is obtained.

[0124] The solid content and pH value of the positive electrode slurry in Examples 1-10 and the comparative examples are shown in Table 1.

[0125] The positive electrode sheets prepared in Examples 1-10 and the comparative examples were assembled with lithium metal sheets, separators, and electrolytes to form lithium-ion half-cells. A Blue Battery testing cabinet was used to test them at 3.5-4.9V (vs Li / Li). + The battery was subjected to cycle performance testing within the voltage range of ), and the results are shown in Table 1.

[0126] Table 1. Performance test results of lithium-ion batteries

[0127]

[0128] As shown in Table 1, compared to the comparative examples, the addition of the above additives in Examples 1-10 increased both the solid content and pH of the cathode slurry, indicating that adding an appropriate amount of additives can increase the solid content of the slurry and reduce coating costs. Furthermore, the pH value of the cathode slurry increased after adding the above additives, and the higher the amount of additive added, the higher the pH value of the cathode slurry. Among them, the cathode slurry in Example 10 had the highest pH value, at 9.46.

[0129] As shown in Table 1, compared to the comparative examples, the addition of the above-mentioned additives significantly improved the cycling performance of the positive electrode slurry batteries in Examples 1-10. The comparative example batteries, after 100 cycles at room temperature, showed a capacity decay to 97.51% of their initial capacity, and after 100 cycles at high temperature, a capacity decay to 94.34% of their initial capacity. The batteries assembled with the positive electrode plates after the addition of additives showed improved first-cycle discharge capacity and capacity retention rate after 100 cycles at both room temperature and high temperature. This is attributed to the fact that after the positive electrode plates are baked, the remaining components of the additives optimize the interface film between the positive electrode plate and the electrolyte, which is beneficial for the battery to operate at higher voltages. The addition of additives improves the capacity retention rate during battery cycling and enhances the battery's cycling performance. In particular, Example 4 showed better battery cycle capacity retention rate than the other examples, regardless of whether it was at room temperature or high temperature.

[0130] Figure 1 The figures show the 3ITT curves of the positive electrode slurry in Example 10 and the comparative example. The first segment simulates the static state of the sample, the second segment simulates the state under high shear, and the third segment simulates the recovery process of the slurry after shearing. In Example 10, the viscosity values ​​in the first and third segments of the curves are essentially unchanged with the shear rate, indicating that the entire slurry system is relatively stable. This demonstrates that adding additives can effectively improve the stability of the slurry.

[0131] Figure 2 This is a viscoelastic curve of the positive electrode slurry in Example 10 and the comparative example. From... Figure 2 As can be seen, the slurry in the comparative example is viscous, with a loss modulus larger than the storage modulus, and the loss modulus is not constant, indicating an unstable internal structure. The slurry in Example 10 has better viscoelasticity, and it is evident that the storage modulus and loss modulus are in a stable period during the early stage of energy storage strain, indicating better stability of the slurry.

[0132] Peel strength tests were conducted on the positive electrode sheets prepared in Examples 1-10 and the comparative examples, and the results are shown in Table 2. As can be seen from Table 2, the peel strength of the positive electrode sheets in Examples 1-10 was significantly higher than that in the comparative examples. After adding the additive, the peel strength of the positive electrode sheets increased from 1.6 to 2.3-2.8, an increase of 43.75%-75%. Among them, Example 10, with an additive content of 0.91‰, exhibited the highest electrode peel strength. This demonstrates that the introduction of an appropriate amount of slurry additive can optimize the electrode peel strength.

[0133] Table 2. Peel force test results of positive electrode sheet

[0134]

[0135] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0136] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A positive electrode slurry, characterized by, The positive electrode active material, a binder, a conductive agent, a solvent, and an additive having a chemical formula of (NH4) x H y RO z wherein R is selected from P, W, x>0, y≥0, z>0, the values of x, y, and z satisfy the charge balance of the chemical formula, the mass fraction of the additive in the positive electrode slurry is 0.005% to 2%, and the solvent is water.

2. The positive electrode slurry of claim 1, wherein The pH value of the positive electrode slurry is 7-11.

3. The positive electrode slurry of claim 1, wherein the lithium transition metal phosphate is LiFePO4. The solid content of the positive electrode slurry is 60%-80%.

4. The positive electrode slurry of claim 1, wherein the lithium transition metal phosphate is LiFePO4. The mass fraction of the positive electrode active material in the positive electrode slurry is 60%-80%, the mass fraction of the binder in the positive electrode slurry is 1%-5%, the mass fraction of the conductive agent in the positive electrode slurry is 1%-6%, and the mass fraction of the solvent in the positive electrode slurry is 17%-30%.

5. The positive electrode slurry of claim 1, wherein the lithium transition metal phosphate is LiFePO4. The mass ratio of the additive to the positive electrode active material is (1-50):10000.

6. The positive electrode slurry of claim 1, wherein the lithium transition metal phosphate is LiFePO4. The additive is selected from one or more of (NH4)3PO4, (NH4)2HPO4, (NH4)2WO4, and (NH4)6H2W 12 O 40 O 7. The positive electrode slurry of claim 1, wherein the lithium transition metal phosphate is LiFePO4. The positive electrode active material is selected from one or more of doped or non-doped lithium nickel manganese phosphate, lithium cobalt phosphate, lithium manganese phosphate, and lithium nickel phosphate.

8. The positive electrode slurry of claim 1, wherein The binder is selected from one or more of styrene butadiene rubber, sodium carboxymethyl cellulose, acrylonitrile multivariate copolymer, polytetrafluoroethylene, polyacrylic acid, polyethylene oxide, polyvinylidene fluoride, polyvinyl alcohol, and polyacrylate.

9. The positive electrode slurry of claim 1, wherein The conductive agent is selected from one or more of carbon black, metal fiber, vapor phase growth carbon fiber, carbon nanotube, graphene and its mixed conductive slurry, and conductive graphite.

10. A method for producing the positive electrode slurry according to any one of claims 1 to 9, characterized by, The method comprises the following steps: Part of the binder and the solvent are mixed to obtain a first gel-like bonding liquid; The additive is added to the first gel-like bonding liquid and mixed to obtain a second gel-like bonding liquid; The positive electrode active material and the conductive agent are mixed, and then added to the second gel-like bonding liquid, and the remaining binder is added after mixing.

11. A method of making a positive electrode sheet, characterized by, The method comprises the following steps: The positive electrode slurry according to any one of claims 1-9 is coated on a current collector, dried, and rolled.

12. A positive electrode sheet characterized by comprising: The positive electrode is prepared by the preparation method of claim 11.

13. A lithium-ion battery, characterized by, The positive electrode, the negative electrode, the separator, and the electrolyte are prepared according to claim 12.

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