Lithium supplementing slurry, lithium supplementing pole piece and battery

Abstract

The invention belongs to the technical field of batteries, and particularly relates to lithium supplementing slurry, a lithium supplementing pole piece and a battery. The lithium supplementing slurry comprises a lithium supplementing additive, a conductive agent, a binder and a dispersant, the dispersant is selected from one or more of PVP, hexadecyl trimethyl ammonium bromide, ethanol and NMP, and the particle size of the lithium supplementing additive is 0.01-15 [mu] m. According to the method for prime coating of the lithium supplementing slurry, pretreatment procedures such as slurry mixing are involved, and conventional optimization methods such as particle size control of a lithium supplementing additive and adjustment of the proportion and introduction mode of a conductive agent can be considered; in addition, the stability and the coating uniformity of the prime coat slurry can be realized by introducing the dispersing agent and controlling the gravure prime coat process parameters.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and particularly relates to a lithium supplementing slurry, a lithium supplementing electrode sheet and a battery. Background Art

[0002] Since the 21st century, lithium-ion batteries have been widely used in various fields of society. Under the background of "dual carbon" of "carbon peak and carbon neutrality", the energy structure transformation in the fields of power, consumption, energy storage, etc. has further put forward higher requirements and challenges for the energy density and cycle life of lithium-ion batteries. A key problem restricting the improvement of energy density is that during the first charge and discharge process of lithium-ion batteries, irreversible decomposition of solvents and lithium salts in the electrolyte will occur on the surface of the negative electrode, forming a corresponding solid electrolyte interface (SEI) film, permanently consuming the active lithium inside the battery, resulting in a low initial Coulomb efficiency (ICE) of the lithium-ion battery, and showing a decrease in capacity and energy density. To address this problem, the industry has proposed a lithium supplementing strategy: by pre-placing an additional lithium source in the battery to make up for the loss of active lithium during the first charge and discharge process, the corresponding capacity and energy can be effectively improved.

[0003] In the existing lithium supplementing strategies, the positive electrode lithium supplementing additive is generally added during the mixing process of the positive electrode slurry. Due to its advantages such as simple operation, air stability and safety, it has a more promising commercial application prospect. Existing lithium supplementing additives can be roughly divided into binary lithium compounds (such as Li2O, Li2O2, Li2S, Li3N, LiF, etc.), doped and modified binary lithium compounds (such as Li2O / Co, Li2S / Ni, etc.), ternary lithium compounds (Li5FeO4, Li2NiO2, etc.), organic lithium salts (CH3COOLi, Li2C2O4, etc.). However, their conductivity is poor, resulting in too high decomposition overpotential. Therefore, modification in terms of its decomposition kinetics is more beneficial to its actual large-scale application.

[0004] In the existing positive electrode lithium supplementing schemes, since most positive electrode lithium supplementing additives (such as Li2O, Li5FeO4, Li2C2O4, etc.) have problems such as poor conductivity, insufficient decomposition kinetics and affecting the manufacturing process, after addition, it is necessary to comprehensively consider the lithium supplementing effect in the actual battery and the impact on the subsequent cycle performance. The main solutions can be divided into the material level and the electrode structure level. At the material level, it can be achieved by (a) reducing the particle size of the lithium supplementing additive; (b) optimizing the conductive agent system and proportion; (c) introducing a decomposition catalyst, etc. At the electrode structure level, the lithium supplementing agent can be placed at the bottom of the current collector, the top of the current collector, the separator layer, the electrolyte, etc.

[0005] The following possible problems exist in the optimization process at the material level: (a) After the particle size of the lithium supplement additive is reduced, the nano-scale electron tunneling effect can be utilized to optimize the electronic conductivity and reduce the decomposition overpotential. However, in practical applications, the use of high-energy ball milling and other methods in the preparation of nano-scale particles will increase the preparation cost, and due to their large specific surface area, adding them during the cathode slurry mixing process will also cause certain process problems (such as changes in slurry viscosity and stability, etc.). (b) Optimizing the conductive agent system and its proportion can optimize the conductivity and reduce the decomposition overpotential by adjusting the conductive agent system such as SP, CNT, graphene, etc. (such as high specific surface area SP, CNT skeleton, graphene point-plane contact, etc.) and the addition amount. However, during the actual lithium supplement process, the increase in the conductive agent will occupy the proportion of the lithium supplement agent, and a certain balance is required between the two. On the premise of ensuring conductivity, it is necessary to improve the proportion of the lithium supplement agent as much as possible to ensure the lithium supplement efficiency. (c) Introducing a decomposition catalyst can lower the energy barrier of the lithium supplement agent decomposition reaction and improve the reaction kinetics. However, the situation is similar to (b), and it is necessary to balance the catalytic performance and the lithium supplement efficiency, and the impact of the addition of the catalyst on the subsequent battery cycle performance needs to be considered.

[0006] The following problems may exist in the optimization process at the electrode structure level: (a) The lithium supplement agent in the top layer of the current collector and the separator layer may reduce the decomposition kinetics due to electron contact problems. (b) The bottom coating of the current collector can enable the lithium supplement agent to have good contact with the foil and the cathode material, but the preparation of the bottom coating involves process problems such as process manufacturing.

[0007] In the method of bottom coating the current collector, the coating uniformity is jointly determined by factors such as slurry viscosity and coating speed, and the slurry viscosity is determined by the basic physical properties of the solid and liquid phases. After simply mixing the lithium supplement agent with the conductive agent, binder, and solvent, the coating effect may be poor, and it is impossible to balance the slurry stability and coating uniformity. Moreover, the unevenly coated bottom coating not only cannot optimize the decomposition kinetics of the lithium supplement agent, but may even deteriorate the decomposition kinetics. Summary of the Invention

[0008] The object of the present invention is to provide a lithium supplement slurry, a lithium supplement electrode sheet, and a battery.

[0009] In the first aspect of the present invention, a lithium supplement slurry is provided. The lithium supplement slurry includes a lithium supplement additive, a conductive agent, a binder, and a dispersant. The dispersant is selected from one or more of polyvinylpyrrolidone, cetyltrimethylammonium bromide, ethanol, and N-methylpyrrolidone, and the particle size of the lithium supplement additive is 0.01 - 15 μm.

[0010] In one or more embodiments, the lithium supplement additive is selected from one or more of lithium oxalate, lithium hydroxide, and Li2CO3.

[0011] In one or more embodiments, the conductive agent is selected from one or more of conductive carbon black, carbon nanotubes, and graphene.

[0012] In one or more embodiments, the binder is selected from one or more of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid.

[0013] In one or more embodiments, based on the total mass of the lithium supplement slurry, the content of the lithium supplement additive is 50-95%.

[0014] In one or more embodiments, based on the total mass of the lithium supplement slurry, the content of the conductive agent is 3-25%.

[0015] In one or more embodiments, based on the total mass of the lithium supplement slurry, the content of the binder is 1.5-15%.

[0016] In one or more embodiments, based on the total mass of the lithium supplement slurry, the content of the dispersant is 0.5-10%.

[0017] In one or more embodiments, the particle size of the lithium supplement additive is 0.01-1 μm.

[0018] In a second aspect of the present invention, there is provided a lithium supplement slurry mixture, which includes the lithium supplement slurry described in the first aspect of the present invention and water.

[0019] In one or more embodiments, the lithium supplement slurry mixture has one or more of the following characteristics:

[0020] The method for preparing the lithium supplement slurry mixture includes: mixing the lithium supplement slurry and water evenly;

[0021] The viscosity of the lithium supplement slurry mixture is 300-5000 mPa·s;

[0022] The solid content of the lithium supplement slurry mixture is 10-30 wt%.

[0023] In a third aspect of the present invention, there is provided a method for preparing a lithium supplement slurry, the method including the steps of providing a lithium supplement additive with a particle size of 0.01-15 μm, and then mixing the lithium supplement additive, a conductive agent, a binder, and a dispersant, where the dispersant is selected from one or more of polyvinylpyrrolidone, cetyltrimethylammonium bromide, ethanol, and N-methylpyrrolidone.

[0024] In a fourth aspect of the present invention, there is provided a foil including a lithium supplement undercoat layer, the lithium supplement undercoat layer is provided on one or both sides of the foil, and the lithium supplement undercoat layer includes a lithium supplement additive, a conductive agent, a binder, and optionally a dispersant, and the particle size of the lithium supplement additive is 0.01-15 μm.

[0025] In one or more embodiments, the foil including the lithium replenishing undercoat has one or more of the following features:

[0026] The thickness of the lithium-replenishing bottom coating on one side is 10-20 μm;

[0027] The surface density of the lithium-replenishing bottom coating on one side is 0.3-2.5 mg / cm 2 ;

[0028] The foil material is aluminum foil;

[0029] The foil material including the lithium supplementing bottom coating has a thickness of 10-45 μm.

[0030] The fifth aspect of the present invention provides a method for preparing the foil comprising the lithium-replenishing undercoat layer as described in the fourth aspect of the present invention, the method comprising the steps of coating the lithium-replenishing slurry mixture as described in the second aspect of the present invention on one or both sides of the foil and drying.

[0031] According to a sixth aspect of the present invention, a pole piece is provided, comprising a foil comprising a lithium-replenishing primer layer as described in the fourth aspect of the present invention and an electrode slurry layer arranged on a side of the lithium-replenishing primer layer away from the foil; preferably, the content of the lithium-replenishing additive is 0.5-10wt% based on the total mass of the pole piece.

[0032] A seventh aspect of the present invention provides a battery, comprising the pole piece described in the sixth aspect of the present invention.

[0033] The present invention has the following beneficial effects:

[0034] (1) In the lithium-replenishing electrode of the present invention, the method of foil primer coating (coating the lithium-replenishing slurry on the bottom layer of the foil) can optimize the electronic contact between the lithium-replenishing additive and the foil, improve its decomposition kinetics, effectively reduce the decomposition overpotential, and achieve a lower decomposition voltage and a higher actual decomposition capacity of the lithium-replenishing additive.

[0035] (2) In the pretreatment of the primer slurry, the particle size of the lithium replenishing additive can be controlled through sand grinding pretreatment, and the proportion of the conductive agent can be optimized to ensure the lithium replenishing efficiency of the lithium replenishing additive.

[0036] (3) By introducing dispersants and controlling the gravure coating process parameters, a uniform primer layer can be achieved while ensuring the stability of the slurry, thus avoiding problems such as non-uniform primer layer leading to dynamic deterioration.

[0037] (4) For the bottom-coated foil prepared by this method, there is also conductive carbon (such as SP) in the bottom coating layer, which can replace the commercial carbon-coated aluminum foil and be directly used as the positive electrode coating foil, saving the preparation cost. The bottom-coated foil prepared by the method of the present invention can take into account the advantages of lithium supplementation for the positive electrode and carbon-coated aluminum foil. It can not only use the lithium supplementation additive in the bottom coating to achieve lithium supplementation for the positive electrode and improve the battery capacity, but also utilize the remaining bottom coating carbon layer after lithium supplementation to optimize the electronic contact between the positive electrode and the foil.

[0038] (5) The present invention uses the gravure bottom coating method to bottom coat the bottom coating slurry including the lithium supplementation additive onto the surface of the foil, which can be used for subsequent positive electrode slurry coating.

[0039] (6) In the method of bottom coating the lithium supplementation slurry of the present invention, pretreatment processes such as slurry mixing are involved, which can take into account conventional optimization methods such as controlling the particle size of the lithium supplementation additive, adjusting the proportion of the conductive agent and the introduction method, etc. In addition, by introducing a dispersant and controlling the gravure bottom coating process parameters, the stability and coating uniformity of the bottom coating slurry can be achieved.

[0040] (7) By adding a dispersant in the method of the present invention, the solid content and viscosity of the lithium supplementation slurry can be within the scope of the present invention. If only water is added to adjust the viscosity, it is impossible to control the solid content and viscosity of the slurry to meet the requirements of the present invention. Description of the Drawings

[0041] Figure 1 is a schematic structural diagram of the lithium-supplemented electrode in one or more embodiments of the present invention, wherein 1 - foil; 2 - lithium supplementation slurry layer; 3 - positive electrode slurry layer.

[0042] Figure 2 is a judgment diagram of the bottom coating appearance uniformity after the bottom coating slurry of the example and the comparative example of the present invention is bottom coated onto the foil.

[0043] Figure 3 is the appearance diagram of the bottom coating slurry prepared in Comparative Example 3 after standing for 24 hours. Detailed Embodiments

[0044] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art for the present invention. In case of conflict, the definition in this specification shall prevail.

[0045] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0046] In this text, terms such as "comprising", "including", "containing" and similar terms cover the meanings of "consisting essentially of" and "consisting of". For example, when this text discloses that "A comprises B and C", "A consists essentially of B and C" and "A consists of B and C" should be considered to have been disclosed in this text.

[0047] In this text, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of a numerical range or percentage range should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0048] In this text, unless otherwise specified, the percentage refers to the mass percentage and the ratio refers to the mass ratio.

[0049] In this text, when describing embodiments or examples, it should be understood that it is not used to limit the present invention to these embodiments or examples. On the contrary, all alternatives, modifications and equivalents of the methods and materials described in the present invention can be covered within the scope defined by the claims.

[0050] In this text, for the sake of concise description, all possible combinations of all technical features in each embodiment or example are not described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered to be within the scope described in this specification.

[0051] The present invention provides a lithium supplement slurry, the lithium supplement slurry includes a lithium supplement additive, a conductive agent, a binder and a dispersant, the dispersant is selected from one or more of PVP, cetyltrimethylammonium bromide, ethanol and NMP, and the particle size of the lithium supplement additive is 0.010 - 15 μm.

[0052] In this text, controlling the particle size of the lithium supplement additive in the lithium supplement slurry within the range defined in this text can make the prepared lithium supplement slurry mixture more stable. When using this lithium supplement slurry mixture to prepare a foil including a lithium supplement bottom coating, it can be observed that the appearance uniformity on the side of the lithium supplement bottom coating of the foil including the lithium supplement bottom coating is better, without vertical stripes or wavy patterns. In this text, the method for judging the stability of the lithium supplement slurry mixture is to observe the difference in the solid content of the upper and lower layers after standing the lithium supplement slurry mixture. For example, it can be left standing for 18 - 36 h (such as 24 h). If the difference in the solid content between the upper and lower layers after standing is ≤ 2 wt%, it can be judged that the stability is good. Based on the total height of the slurry, the sampling position for the upper layer is preferably at 3 / 4 of the distance from the bottom, and the sampling position for the lower layer is preferably at 1 / 4 of the distance from the bottom. The battery prepared using the lithium supplement additive of the present invention has a higher first charge capacity and a higher 1000 - cycle capacity retention rate. If the particle size of the lithium supplement additive is too small, it will affect the manufacturing process, making the prepared lithium supplement slurry and lithium supplement slurry mixture prone to agglomeration and affecting the stability of the lithium supplement slurry mixture. In this text, under the same other conditions, changing the particle size of the lithium supplement additive within the range defined in this text does not affect the discharged solid content and discharged viscosity of the lithium supplement slurry mixture.

[0053] In some embodiments, the lithium supplement additive is selected from one or more of lithium oxalate, lithium hydroxide, and Li₂CO₃; preferably one or two of lithium oxalate and Li₂CO₃.

[0054] In some embodiments, the conductive agent is selected from one or more of SP, CNT, and graphene; preferably SP.

[0055] In some embodiments, the binder is selected from one or more of CMC, SBR, and PAA.

[0056] In some embodiments, based on the total mass of the lithium supplement slurry, the content of the lithium supplement additive is 50 - 95%, such as 50%, 60%, 70%, 80%, 89%, 95%, preferably 70 - 89%, 70 - 80%, 80 - 89%.

[0057] In some embodiments, based on the total mass of the lithium supplement slurry, the content of the conductive agent is 3 - 25%, such as 5%, 10%, 15%, 20%, preferably 5 - 20%.

[0058] In some embodiments, based on the total mass of the lithium supplement slurry, the content of the binder is 1.5-15%, such as 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, preferably 4-5%. In some embodiments, the binder is PAA. In other embodiments, the binder is CMC and SBR. The dosages of CMC and SBR can be selected according to the conventional usage methods in the field of electrode preparation, such as 1:(0.1-10), such as 1:1.

[0059] In some embodiments, based on the total mass of the lithium supplement slurry, the content of the dispersant is 0.5-10%, such as 1%, 3%, 5%, 6%, 8%, 10%, preferably 1-10%.

[0060] In some embodiments, the particle size of the lithium supplement additive is 0.01-1 μm, such as 0.02 μm, 0.05 μm, 0.1 μm, 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, preferably 0.5-1 μm.

[0061] The present invention provides a lithium supplement slurry mixture comprising the lithium supplement slurry of the present invention. The lithium supplement slurry mixture further comprises water. In some embodiments, the lithium supplement slurry mixture comprises the lithium supplement slurry of the present invention and water. In some embodiments, the viscosity of the lithium supplement slurry mixture is 300-5000 mPa·s, such as 500 mPa·s, 800 mPa·s, 1000 mPa·s, 1200 mPa·s, 1500 mPa·s, 2000 mPa·s, 3000 mPa·s, preferably 800-1200 mPa·s. In some embodiments, the solid content of the lithium supplement slurry mixture is 10-30 wt%, such as 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 25 wt%, preferably 10-18 wt%.

[0062] The present invention provides a method for preparing a lithium supplement slurry, the method comprising providing a lithium supplement additive with a particle size of 0.01-15 μm, and then mixing the lithium supplement additive, a conductive agent, a binder and a dispersant, wherein the dispersant is selected from one or more of PVP, CTAB, ethanol and NMP. Preferably, the lithium supplement additive, the conductive agent, the binder and the dispersant are as described in any embodiment herein. Herein, the method for controlling the particle size of the lithium supplement additive can be selected from methods such as manual grinding, ball milling, sand milling and stirring and mixing slurries.

[0063] The present invention also provides a method for preparing a lithium supplement slurry mixture, which includes uniformly mixing the lithium supplement slurry and water. In some embodiments, the method includes the step of mixing and adjusting the viscosity of the lithium supplement slurry of the present invention with water. Preferably, the method further includes the step of grinding the mixture of the lithium supplement slurry and water after mixing and adjusting the viscosity of the lithium supplement slurry of the present invention with water.

[0064] The present invention provides a foil including a lithium supplement bottom coating, the lithium supplement bottom coating is provided on one or both sides of the foil, the lithium supplement bottom coating includes a lithium supplement additive, a conductive agent, a binder, and an optional dispersant, and the particle size of the lithium supplement additive is 0.01-15 μm. In some embodiments, the dispersant is cetyltrimethylammonium bromide. In some embodiments, the lithium supplement additive, the conductive agent, and the binder are as described in any embodiment herein.

[0065] In some embodiments, the foil is a current collector for preparing a pole piece. Herein, the foil is a current collector for preparing a positive pole piece, preferably an aluminum foil.

[0066] In some embodiments, the thickness of the foil including the lithium supplement bottom coating is 10-45 μm, such as 15 μm, 19 μm, 21 μm, 25 μm, 27 μm, 31 μm, 35 μm, 39 μm, 41 μm, 43 μm, 45 μm, and preferably 39-45 μm.

[0067] In some embodiments, the thickness of the lithium supplement bottom coating on one side is 10-20 μm, such as 12 μm, 13 μm, 15 μm, 16 μm, 18 μm, 20 μm, and preferably 13-16 μm.

[0068] In some embodiments, the surface density of the lithium supplement bottom coating on one side is 0.3-2.5 mg / cm 2 , such as 0.3 mg / cm 2 , 0.5 mg / cm 2 , 0.6 mg / cm 2 , 0.7 mg / cm 2 , 0.8 mg / cm 2 , 1.0 mg / cm 2 , 1.3 mg / cm 2 , 1.5 mg / cm 2 , 2.0 mg / cm 2 , and preferably 0.5-0.7 mg / cm 2 .

[0069] The present invention provides a method for preparing a foil material including a lithium-replenishing bottom coating of the present invention, the method comprising the steps of coating the lithium-replenishing slurry mixture of the present invention on one or both sides of the foil material and drying. Preferably, the coating method is extrusion coating, transfer coating, gravure coating, electrospinning coating or spray drying, preferably gravure coating. In some embodiments, in the gravure coating method, the coating speed is 5-25m / min. In some embodiments, in the gravure coating method, the drying temperature is 60-100°C. In some embodiments, a gravure micro-coating and drying all-in-one machine is used, and after coating, it enters a matching oven cavity to achieve heating and drying.

[0070] The present invention also provides a pole piece, the pole piece comprising a foil material comprising a lithium-supplementing bottom coating layer of the present invention and an electrode slurry layer disposed on a side of the lithium-supplementing bottom coating layer away from the foil material. In some embodiments, the content of the lithium-supplementing additive is 0.5-10wt%, such as 1wt%, 2wt%, 3wt%, 5wt%, 8wt%, preferably 2-5wt%, 1-2wt%, based on the total mass of the pole piece.

[0071] In some embodiments, the electrode sheet is a positive electrode sheet, and the electrode slurry layer is a positive electrode slurry layer.

[0072] The present invention also provides a method for preparing a pole piece, the method comprising the steps of coating electrode slurry on both sides of the foil material including the lithium supplementing bottom coating layer and drying the coating.

[0073] Herein, the electrode slurry may be a conventional slurry in the battery field, and may include a lithium source (eg, lithium iron phosphate), a conductive agent (eg, SP), a binder (PVDF), a solvent (NMP), and the like.

[0074] The present invention also provides a battery, comprising the pole piece of the present invention.

[0075] Preferably, the initial charging capacity of the battery is ≥2.1Ah, for example, 2.1Ah, 2.15Ah, 2.2Ah, 2.25Ah, 2.3Ah, 2.35Ah, 2.4Ah, 2.45Ah, 2.5Ah, 2.6Ah, preferably 2.2-2.5Ah, 2.24-2.43Ah.

[0076] Preferably, the capacity retention rate of the battery after 1000 cycles is ≥92%, for example, 92%, 92.1%, 92.2%, 92.3%, 92.4%, 92.5%, 92.6%, 92.7%, 92.8%, 92.9%, 93%, preferably 92-93%, 92.1-92.8%.

[0077] The present invention also provides an application selected from the following group:

[0078] (1) Application of controlling the particle size of the lithium supplement additive and / or using the gravure coating method in improving the uniformity on the side of the lithium supplement bottom coating of the foil including the lithium supplement bottom coating;

[0079] (2) Application of controlling the particle size of the lithium supplement additive and / or using the gravure coating method in improving the stability of the lithium supplement slurry mixture;

[0080] (3) Application of using the lithium supplement slurry, the lithium supplement slurry mixture and / or the electrode sheet of the present invention in preparing a battery with a high first charge capacity and / or a high 1000-cycle capacity retention rate.

[0081] In some embodiments, the lithium supplement additive, the gravure coating method, the foil including the lithium supplement bottom coating, the lithium supplement bottom coating, the lithium supplement slurry, the lithium supplement slurry mixture, and the battery are as described in any one of the embodiments herein.

[0082] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions noted in the following embodiments are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise specified, percentages and parts are calculated by weight.

[0083] Cetyltrimethylammonium bromide (CTAB); Polyvinylpyrrolidone (PVP); N-Methylpyrrolidone (NMP); Super P conductive carbon black (SP); Carbon nanotubes (CNT); Polyvinylidene fluoride (PVDF); Sodium carboxymethyl cellulose (CMC); Styrene-butadiene rubber (SBR); Polyacrylic acid (PAA).

[0084] Test method for viscosity: Place 450 - 500 ml of the sample to be tested in a DVS + rotational viscometer. Keep the rotor at the center position of the liquid surface and immerse it about 1 - 3 cm below the liquid surface of the sample to be tested. Record the corresponding viscosity data under the test conditions of 25 ± 2 °C, 12 rpm, and 30 s.

[0085] Test method for solid content: Take about 0.8 - 1.2 g of the slurry and evenly coat it on the surface of the copper foil. Dry it at 140 °C until the mass no longer changes. Record the mass before and after drying and convert it to the percentage of the solid content of the slurry.

[0086] Gravure coating method: Use a curing and hardening film coating compounding machine to achieve precision micro gravure coating production. The coating speed is 5 - 25 m / min, and the oven temperature is 60 - 100 °C.

[0087] Example 1

[0088] Preparation of lithium - supplement slurry: Add each active material according to the mass ratio, stir and mix evenly, grind with a sand mill at a rotation speed of 500 rpm for 4 h. Among them, the particle size of lithium oxalate is 1 μm, accounting for 85 wt%, SP accounts for 5 wt%, PAA accounts for 5 wt%, PVP accounts for 5 wt%. Add water to adjust the viscosity, and continue to grind with the sand mill for 2 h. The solid content of the discharged lithium - supplement slurry mixture is 15 wt%, and the discharged viscosity is 1000 mPa·s for standby.

[0089] Foil bottom - coating: Coat the lithium - supplement slurry on both sides of the aluminum foil by gravure coating, and dry to obtain the lithium - supplement bottom - coated foil. The thickness of the single - side bottom - coating is about 15 μm, and the surface density of the bottom - coating on both sides is 0.6 mg / cm 2 . The total thickness of the lithium - supplement bottom - coated foil is 43 μm.

[0090] Preparation and coating of the positive - electrode slurry: Lithium iron phosphate, SP, and PVDF are uniformly dispersed in the NMP solvent according to the mass ratio of 90%:5%:5% to form the positive - electrode slurry. Coat it on both sides of the lithium - supplement bottom - coated foil. The coating thickness and coating density on both sides are the same. After drying, a lithium - supplement positive - electrode plate is obtained, and the mass of the lithium - supplement agent (lithium oxalate) accounts for 2% of the total mass of the positive electrode.

[0091] Battery assembly: Perform processes such as pole - piece rolling, die - cutting, slitting, assembly, baking, liquid injection (1M LiPF6 in DEC:EC:EMC = 1:1:1 Vol%), formation, and aging on the above - mentioned lithium - supplement positive - electrode plate and the conventional graphite negative - electrode plate to make a battery cell.

[0092] Example 2

[0093] Repeat the steps of Example 1, with the differences being:

[0094] Preparation of lithium - supplement slurry: Add each active material according to the mass ratio, stir and mix evenly, grind with a sand mill at a rotation speed of 500 rpm for 4 h. Among them, the particle size of Li2CO3 is about 1 μm, accounting for 70 wt%; SP accounts for 20 wt%, CMC accounts for 2 wt%, SBR accounts for 2 wt%, CTAB accounts for 6 wt%. Add water to adjust the viscosity, and continue to grind with the sand mill for 2 h. The solid content of the discharged lithium - supplement slurry mixture is 12 wt%, and the discharged viscosity is 800 mPa·s for standby.

[0095] Foil bottom - coating: Coat the lithium - supplement slurry on both sides of the aluminum foil by gravure coating, and dry to obtain the lithium - supplement bottom - coated foil. The thickness of the single - side bottom - coating is about 13 μm, and the surface density of the bottom - coating on both sides is 0.5 mg / cm 2 . The total thickness of the lithium - supplement bottom - coated foil is 39 μm.

[0096] The mass of the lithium - supplement agent (Li2CO3) accounts for 2% of the total mass of the positive electrode.

[0097] Unless otherwise specified, the remaining steps are the same as those in Example 1.

[0098] Example 3

[0099] Repeat the steps of Example 1, with the differences being: in the lithium supplement slurry, the proportion of lithium oxalate is 89 wt%, the proportion of SP is 5 wt%, the proportion of PAA is 5 wt%, the proportion of ethanol is 1 wt%, add water to adjust the viscosity, and continue to grind with a sand mill for 2 h. The solid content of the discharged lithium supplement slurry mixture is 18 wt%, and the discharged viscosity is 1200 mPa·s.

[0100] Foil bottom coating: The thickness of the single-sided bottom coating is 16 μm, and the surface density of the double-sided bottom coating is 0.7 mg / cm 2 . The total thickness of the lithium supplement bottom-coated foil is 45 μm.

[0101] The mass of the lithium supplement agent (lithium oxalate) accounts for 2% of the total mass of the positive electrode.

[0102] Example 4

[0103] Repeat the steps of Example 1, with the differences being: in the lithium supplement slurry, the proportion of lithium oxalate is 80 wt%, the proportion of SP is 5 wt%, the proportion of PAA is 5 wt%, the proportion of NMP is 10 wt%, add water to adjust the viscosity, and continue to grind with a sand mill for 2 h. The solid content of the discharged lithium supplement slurry mixture is 10 wt%, and the discharged viscosity is 1000 mPa·s.

[0104] Foil bottom coating: The thickness of the single-sided bottom coating is 15 μm, and the surface density of the double-sided bottom coating is 0.6 mg / cm 2 . The total thickness of the lithium supplement bottom-coated foil is 43 μm.

[0105] The mass of the lithium supplement agent (lithium oxalate) accounts for 2% of the total mass of the positive electrode.

[0106] Comparative Example 1 (without lithium supplement slurry bottom-coated foil)

[0107] Preparation and coating of the positive electrode slurry: Lithium iron phosphate, SP, and PVDF are uniformly dispersed in the NMP solvent according to a mass ratio of 90%:5%:5% to form a positive electrode slurry, which is coated on the double-sided surface of the aluminum foil. The coating thickness and coating density on both sides are the same. After drying, a positive electrode sheet is obtained. The thickness of the aluminum foil and the areal loading of the positive electrode surface are the same as those in Example 1.

[0108] The method of Example 1 is used for battery assembly and battery testing.

[0109] Comparative Example 2 (without dispersant)

[0110] Repeat the steps of Example 1, with the differences being:

[0111] The proportion of lithium oxalate is 90 wt%, the proportion of SP is 5 wt%, the proportion of PAA is 5 wt%. Add water to adjust the viscosity, and grind for 2 h with a sand mill. The solid content of the discharged lithium supplement slurry mixture is 8 wt%, and the discharged viscosity is 1000 mPa·s.

[0112] Foil bottom coating: The bottom coating thickness on one side is 15 μm, and the bottom coating areal density on both sides is 0.6 mg / cm 2 . The total thickness of the lithium supplement bottom-coated foil is 43 μm.

[0113] The mass of the lithium supplement agent (lithium oxalate) accounts for 2% of the total mass of the positive electrode.

[0114] Comparative Example 3

[0115] Repeat the steps of Comparative Example 2, with the difference that: add water to adjust the viscosity, and grind for 2 h with a sand mill. The solid content of the discharged lithium supplement slurry mixture is 12 wt%, and the discharged viscosity is 5500 mPa·s.

[0116] Foil bottom coating: The bottom coating thickness on one side is 15 μm, and the bottom coating areal density on both sides is 0.6 mg / cm 2 . The total thickness of the lithium supplement bottom-coated foil is 43 μm.

[0117] The mass of the lithium supplement agent (lithium oxalate) accounts for 2% of the total mass of the positive electrode.

[0118] Comparative Example 4

[0119] Repeat the steps of Example 1, with the difference that: the particle size of lithium oxalate is 50 μm.

[0120] Test Example

[0121] Battery test procedure:

[0122] 1. First charge and discharge: Stand at 45 °C for 10 h, charge at a constant current of 0.5C to 3.65 V, charge at a constant current of 0.01C to 4.3 V, discharge at a constant current of 0.5C to 2.5 V, and record the first discharge capacity of the battery.

[0123] 2. Subsequent cycle performance: Charge and discharge at 0.5C for 1000 cycles at 25 °C, and record the capacity retention rate corresponding to the capacity after 1000 cycles compared to the capacity after 1 cycle.

[0124] After the battery test procedure, the battery capacity and cycle performance are summarized in Table 1 as follows:

[0125] Table 1

[0126]

[0127]

[0128] Compare the first charge capacities of the batteries after lithium supplementation in each example and comparative example. With the same cathode loading, the first charge capacities of Examples 1-4 are higher, indicating that the lithium supplementation effect of the electrode sheets in the examples is better.

[0129] The uniformity of the undercoat appearance is determined by the appearance after coating. Non-uniform appearances may show vertical stripes or wavy patterns, as Figure 2 shown.

[0130] The stability of the slurry is determined by the appearance and the solid content of the upper and lower layers after standing for 24 hours. Unstable slurries settle and there are obvious differences in the solid content of the upper and lower layers (solid content difference > 2 wt%), as Figure 3 shown. Based on the total height of the slurry, the sampling position of the upper layer is at 3 / 4 of the distance from the bottom, and the sampling position of the lower layer is at 1 / 4 of the distance from the bottom.

Claims

1. A lithium supplement slurry, characterized in that, The lithium supplement slurry includes a lithium supplement additive, a conductive agent, a binder, and a dispersant. The dispersant is selected from one or more of polyvinylpyrrolidone, cetyltrimethylammonium bromide, ethanol, and N-methylpyrrolidone. The particle size of the lithium supplement additive is 0.01 - 15 μm.

2. The lithium supplement slurry according to claim 1, characterized in that, The lithium supplement slurry has one or more of the following characteristics: The lithium supplement additive is selected from one or more of lithium oxalate, lithium hydroxide, and Li2CO3; The conductive agent is selected from one or more of conductive carbon black, carbon nanotubes, and graphene; The binder is selected from one or more of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid; Based on the total mass of the lithium supplement slurry, the content of the lithium supplement additive is 50 - 95%; Based on the total mass of the lithium supplement slurry, the content of the conductive agent is 3 - 25%; Based on the total mass of the lithium supplement slurry, the content of the binder is 1.5 - 15%; Based on the total mass of the lithium supplement slurry, the content of the dispersant is 0.5 - 10%; The particle size of the lithium supplement additive is 0.01 - 1 μm.

3. A lithium supplement slurry mixture, characterized in that, The lithium supplement slurry mixture includes the lithium supplement slurry according to claim 1 or 2 and water.

4. The lithium supplement slurry mixture according to claim 3, characterized in that The lithium supplement slurry mixture has one or more of the following characteristics: The preparation method of the lithium supplement slurry mixture includes: mixing the lithium supplement slurry and water evenly; The viscosity of the lithium supplement slurry mixture is 300 - 5000 mPa·s; The solid content of the lithium supplement slurry mixture is 10 - 30 wt%.

5. A method for preparing a lithium supplement slurry, characterized in that, The method includes the steps of providing a lithium supplement additive with a particle size of 0.01 - 15 μm, and then mixing the lithium supplement additive, the conductive agent, the binder, and the dispersant. The dispersant is selected from one or more of polyvinylpyrrolidone, cetyltrimethylammonium bromide, ethanol, and N-methylpyrrolidone.

6. A foil including a lithium supplement bottom coating, characterized in that, The lithium supplement undercoat is provided on one or both sides of the foil. The lithium supplement undercoat includes a lithium supplement additive, a conductive agent, a binder, and an optional dispersant. The particle size of the lithium supplement additive is 0.01 - 15 μm.

7. The foil material including a lithium supplement bottom coating according to claim 6, wherein, The foil including the lithium supplement undercoat has one or more of the following characteristics: The thickness of the single-sided lithium supplement undercoat is 10 - 20 μm; The areal density of the single-sided lithium supplementing bottom coating is 0.3 - 2.5 mg / cm 2 ; The foil is an aluminum foil; The thickness of the foil including the lithium supplement undercoat is 10 - 45 μm.

8. A method for preparing the foil including a lithium supplement bottom coating according to claim 6 or 7, characterized in that, The method includes the steps of coating the lithium supplement slurry mixture according to claim 3 or 4 on one or both sides of the foil and drying.

9. A pole piece, the pole piece includes the foil including the lithium supplement undercoat according to claim 6 or 7 and an electrode slurry layer provided on the side of the lithium supplement undercoat facing away from the foil; preferably, based on the total mass of the pole piece, the content of the lithium supplement additive is 0.5 - 10 wt%.

10. A battery, characterized in that, The battery includes the pole piece according to claim 9.

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