Negative electrode sheet, method for manufacturing the same, secondary battery, and power using device

Abstract

The application relates to a negative electrode sheet, a preparation method thereof, a secondary battery and a power utilization device. The negative electrode sheet comprises a negative electrode current collector, an active material layer and a passivation layer, the active material layer is arranged between the negative electrode current collector and the passivation layer; wherein the active material layer comprises a negative electrode active material, the passivation layer comprises an ionic resin, and the ionic resin comprises one or more of carboxymethyl cellulose and a carboxymethyl cellulose metal salt.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, specifically to a negative electrode sheet and its preparation method, a secondary battery, and an electrical device. Background Technology

[0002] Lithium-ion batteries are widely used in various large-scale power devices, energy storage systems, and consumer products due to their advantages such as high operating voltage, high energy density, no memory effect, and environmental friendliness. They are especially widely used in the field of new energy vehicles such as pure electric vehicles and hybrid electric vehicles.

[0003] With the widespread application and continuous development of lithium-ion batteries, their safety is receiving increasing attention. After multiple cycles, metallic lithium will precipitate on the surface of the negative electrode, and lithium dendrites pose a significant safety risk.

[0004] Therefore, the search for lithium-ion batteries with excellent cycle performance is one of the key areas of focus for those skilled in the art. Summary of the Invention

[0005] This application is made in view of the above-mentioned issues, and one of its objectives is to provide a negative electrode sheet and a method for preparing the same, a secondary battery, and an electrical device.

[0006] To achieve the above objectives, the first aspect of this application provides a negative electrode sheet, including a negative electrode current collector, an active material layer, and a passivation layer, wherein the active material layer is disposed between the negative electrode current collector and the passivation layer.

[0007] The active material layer includes a negative electrode active material, and the passivation layer includes an ion exchange resin, wherein the ion exchange resin includes one or more of carboxymethyl cellulose and carboxymethyl cellulose metal salt.

[0008] The negative electrode sheet provided in this application has an active material layer and a passivation layer disposed on the current collector. The passivation layer includes an ion exchange resin containing cations that can exchange with lithium ions, thereby effectively driving the rapid migration and uniform distribution of lithium ions. Furthermore, the ion exchange resin contains a large number of hydrogen bonds, enabling it to cross-link into a uniform and dense three-dimensional network structure with high resistance to deformation, thus protecting the active material layer and effectively reducing interfacial reactions between the negative electrode and the electrolyte during cycling. It can also mitigate the impact of volume changes in the negative electrode active material during battery cycling. The passivation layer in the negative electrode sheet provided in this application can act as an artificial SEI, inhibiting the generation and growth of lithium dendrites, thereby effectively improving the battery's cycle performance.

[0009] In some embodiments, the general molecular formula of the carboxymethyl cellulose is [C6H7O2(OH)]. 3-x1 (OCH2COOH)x1 ] n1 n1 is the degree of polymerization, x1 is 0.4 to 0.7, and can be selected as 0.5 to 0.7; and / or,

[0010] The general molecular formula of the carboxymethyl cellulose metal salt is [C6H7O2(OH)]. 3-x2 (OCH2COOM) x2 ] n2 M includes one or more of lithium, sodium, potassium, rubidium and cesium, and optionally, M includes lithium; n2 is the degree of polymerization, and x2 is 0.4 to 0.7, optionally 0.5 to 0.7.

[0011] In some embodiments, the Young's modulus of the ion exchange resin is greater than or equal to 2.5 GPa, and may be selected as 18 GPa-27 GPa.

[0012] In some embodiments, the weight-average molecular weight of the ion exchange resin is 50,000 Da-300,000 Da, and optionally 70,000-250,000 Da.

[0013] In some embodiments, the thickness of the passivation layer is 1–8 μm, optionally 2 μm–4 μm.

[0014] In some embodiments, the passivation layer is disposed circumferentially on the active material layer to form a hollow, closed structure.

[0015] Optionally, the area of ​​the hollow region accounts for 10% to 30% of the area of ​​the active material layer.

[0016] In some embodiments, the negative electrode active material includes at least one of graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, and may be selected as graphite.

[0017] A second aspect of this application provides a method for preparing a negative electrode sheet, comprising the following steps:

[0018] An active material layer is formed on the negative electrode current collector, the active material layer comprising a negative electrode active material;

[0019] A passivation layer is formed on the active material layer, the passivation layer comprising an ion exchange resin, the ion exchange resin comprising one or more of carboxymethyl cellulose and carboxymethyl cellulose metal salts.

[0020] In some embodiments, the passivation layer is formed using physical vapor deposition, which may be an evaporation method or a sputtering method, and may further be a vacuum evaporation method.

[0021] In some embodiments, the process further includes the following prior to forming a passivation layer on the active material layer:

[0022] A mask is provided to block the middle part of the active material layer to be treated, and the area of ​​the mask is smaller than the area of ​​the active material layer.

[0023] Optionally, the area of ​​the mask plate is 10% to 30% of the area of ​​the active material layer.

[0024] A third aspect of this application provides a secondary battery comprising the negative electrode sheet described in the third aspect of this application.

[0025] The fourth aspect of this application provides an electrical device that includes the secondary battery described in the fourth aspect of this application. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the negative electrode sheet according to one embodiment of this application.

[0027] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0028] Figure 3 yes Figure 2 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0029] Figure 4 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0030] Explanation of reference numerals in the attached figures:

[0031] 1. Secondary battery; 11. Casing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device; 10. Negative current collector; 20. Active material layer; 30. Passivation layer. Detailed Implementation

[0032] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode sheet, its preparation method, secondary battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0033] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0035] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0036] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0037] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0038] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0039] The term "ion exchange resin" refers to any resin that carries a charge, including resins that carry negatively charged ions and resins that carry positively charged ions.

[0040] A significant problem with lithium-ion batteries under long-term cycling and storage conditions is lithium dendrite formation. Uneven deposition of lithium ions on the negative electrode surface leads to lithium dendrite formation, which affects the interfacial stability between the graphite negative electrode and the electrolyte. With increasing cycle count, the growth of lithium dendrites continuously depletes the electrolyte and causes irreversible deposition of active lithium, resulting in a significant amount of dead lithium and a decrease in battery coulombic efficiency. Simultaneously, the continuous growth of lithium dendrites poses a considerable safety risk to the battery, primarily due to dendrites piercing the separator. Related technologies often employ inorganic salts as negative electrode additives to construct an artificial SEI film to improve battery cycle performance; however, the effect of inorganic salts as additives in reducing lithium dendrite growth is not ideal.

[0041] Negative electrode sheet

[0042] To resolve the above technical issues, please refer to Figure 1 This application provides a negative electrode sheet, including a negative electrode current collector 10 and a negative electrode film layer disposed on at least one surface of the negative electrode current collector 10. The negative electrode film layer includes an active material layer 20 and a passivation layer 30, with the active material layer 20 disposed between the negative electrode current collector 10 and the passivation layer 30. The active material layer 20 includes a negative electrode active material, and the passivation layer 30 includes an ion exchange resin, wherein the ion exchange resin includes one or more of carboxymethyl cellulose and carboxymethyl cellulose metal salts. It should be noted that the negative electrode current collector 10 has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the opposite surfaces of the negative electrode current collector 10.

[0043] The negative electrode sheet provided in this application includes an active material layer 20 and a passivation layer 30. The passivation layer 30 includes an ion exchange resin containing cations that can exchange with lithium ions, thereby effectively driving the rapid migration and uniform distribution of lithium ions. Furthermore, the ion exchange resin contains a large number of hydrogen bonds, enabling it to crosslink into a uniform and dense three-dimensional network structure with high resistance to deformation. This forms a protective layer for the active material layer 20, effectively reducing the interfacial reaction between the negative electrode and the electrolyte during cycling, and mitigating the impact of volume changes in the negative electrode active material during battery cycling. The passivation layer 30 in the negative electrode sheet provided in this application can act as an artificial SEI, suppressing the generation and growth of lithium dendrites, thereby effectively improving the battery's cycle performance.

[0044] Carboxymethyl cellulose and its salts are cellulose ethers in which some of the hydroxyl groups on the dehydrated glucose ring of cellulose are replaced by carboxymethyl groups.

[0045] In some embodiments, the general molecular formula of the carboxymethyl cellulose is [C6H7O2(OH)]. 3-x1 (OCH2COOH) x1 ] n1 n1 is the degree of polymerization, and x1 is 0.4 to 0.7, which can be selected as 0.5 to 0.7. x1 represents the "degree of substitution", which can be defined as the average number of hydroxyl groups replaced by carboxymethyl groups in each glucose unit of cellulose.

[0046] In the above "x1 is 0.4 to 0.7", the value of x1 includes the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 0.42, 0.44, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56, 0.58, 0.6, 0.62, 0.64, 0.66, 0.68; or any range consisting of any two values.

[0047] In some embodiments, the general molecular formula of the carboxymethyl cellulose metal salt is [C6H7O2(OH)]. 3-x2 (OCH2COOM) x2 ] n2 M includes one or more of lithium, sodium, potassium, rubidium, and cesium, and optionally, M includes lithium; n2 is the degree of polymerization, and x2 is 0.4 to 0.7, optionally 0.5 to 0.7. x2 represents the "degree of substitution", which can be defined as the average number of hydroxyl groups in each glucose unit of cellulose that are replaced by carboxymethyl metal groups.

[0048] In the above "x2 is 0.4 to 0.7", the value of x2 includes the minimum and maximum value of this range, as well as every value between the minimum and maximum value. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 0.42, 0.44, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56, 0.58, 0.6, 0.62, 0.64, 0.66, 0.68; or any range consisting of any two values.

[0049] Understandably, n1 and n2 can be the same or different, and x1 and x2 can be the same or different.

[0050] The values ​​of x1 and x2 affect the film quality of the passivation layer 30. The higher the values ​​of x1 and x2, the fewer hydrogen bonds between molecules in the ion exchange resin and the lower the viscosity, which is not conducive to cross-linking between molecules. As a result, the passivation layer 30 formed has poor density and poor coverage of the active material layer 20.

[0051] x1 and x2 can be determined using instruments and methods known in the art, such as the ashing method. Specifically, the following method can be used: Weigh 0.2000 g (accurate to 0.1 mg) of the sample to be tested and place it in a 30 mL porcelain crucible. After ashing, place it in a muffle furnace and ignite at 700 °C for 1 hour. After cooling, remove it. Transfer all the residue in the porcelain crucible to a 150 mL Erlenmeyer flask using distilled water. Add 3–4 drops of methyl orange indicator to the Erlenmeyer flask and titrate with a standard sulfuric acid solution. When the solution turns red, continue adding 10 mL of standard sulfuric acid solution, recording the total volume of standard sulfuric acid solution used. Then heat to boiling and titrate with a standard sodium hydroxide solution for 10 minutes until the solution color changes from red to yellow. Record the volume of standard sodium hydroxide solution used. The formula for the degree of substitution is as follows:

[0052]

[0053]

[0054] In the formula, DS represents the degree of substitution; M H2SO4 M represents the molar concentration of the sulfuric acid standard solution, in mol / L. NaOH V represents the molar concentration of the sodium hydroxide standard solution, in mol / L. H2SO4 V represents the total volume of the standard desulfurized acid solution used in the titration, in mL; NaOH is the total volume of sodium hydroxide standard solution used, mL; m is the mass of the sample to be tested, g.

[0055] In some embodiments, the Young's modulus of the ion exchange resin is greater than or equal to 2.5 GPa, and can be selected as 18 GPa-27 GPa. Within this range, the Young's modulus of the ion exchange resin enables the passivation layer 30 to have higher resistance to deformation, further improving the cycle performance of the battery. A higher Young's modulus results in stronger resistance to lithium dendrite formation during cycling, thus improving cycle performance, but it should not be too high.

[0056] The values ​​of the Young's modulus mentioned above include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 10 GPa, 11 GPa, 12 GPa, 13 GPa, 14 GPa, 15 GPa, 16 GPa, 17 GPa, 18 GPa, 19 GPa, 20 GPa, 21 GPa, 22 GPa, 23 GPa, 24 GPa, 25 GPa, and 26 GPa.

[0057] The Young's modulus of the ion exchange resin has a meaning known in the art and can be measured using instruments and methods known in the art, such as the AFM force-displacement curve method. Specifically, an NSG-10 type single-crystal silicon probe is selected, with a tip curvature radius of approximately 10 nm and an elastic modulus (Kc) ranging from 3.1 to 37.6 N / m. The specific Kc value of the probe is determined using a thermal modulation method before measurement. PeakForce Tapping in an ICON type AFM... TM The two-dimensional morphology of the samples was determined under the specified conditions, and the force-displacement curves (referred to as force curves) were recorded (at a rate of 2 μm / s). All tests were performed at 25℃ and 40% relative humidity. The data from the fitted effective force curves were analyzed using NanoScope Analysis software, and the compressive Young's modulus of the samples was calculated based on the elasticity contact model.

[0058] In some embodiments, the weight-average molecular weight of the ion exchange resin is 50,000-300,000 Da, optionally 70,000-250,000 Da. A weight-average molecular weight within this range provides better film-forming properties. A weight-average molecular weight that is too high or too low is detrimental to film formation.

[0059] The values ​​in the range "50000Da-300000Da" include the minimum and maximum values ​​within this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 60000Da, 70000Da, 80000Da, 90000Da, 100000Da, 110000Da, 120000Da, 130000Da, 14000... 0Da, 150000Da, 160000Da, 170000Da, 180000Da, 190000Da, 200000Da, 210000Da, 220000Da, 230000Da, 240000Da, 250000Da, 260000Da, 270000Da, 280000Da, 290000Da; or a range consisting of any two values.

[0060] The weight-average molecular weight of the ion exchange resin has a meaning known in the art and can be determined using instruments and methods known in the art. For example, the viscosity of its aqueous solution can be determined according to ASTM D 1439-03, and the molecular weight can be estimated from the viscosity of the standard resin aqueous solution. According to one method, the molecular weight of the ion exchange resin can be estimated using the viscosity by the following formula:

[0061] η[Pa S]=8.91×10 -4 +1.30×10 -5 cM w 0.9 +5.33×10 -8 c 2 M w 1.8 +4.60×10 -

[0062] 15 c 4.34 M w 3.91 Where η is viscosity, c is CMC concentration, and M w It refers to molecular weight, as described by Kulicke in Polymer, Vol. 37, No. 13, pp. 2723-2731, 1996.

[0063] The carboxymethyl cellulose or carboxymethyl cellulose metal salts of this application can be prepared or obtained by commercially available methods or methods known in the art. In some embodiments, other carboxymethyl cellulose metal salts besides sodium carboxymethyl cellulose can be prepared by the following methods:

[0064] Carboxymethyl cellulose is obtained by acid treatment of sodium metal; and

[0065] Add MOH solution to the obtained carboxymethyl cellulose and heat it.

[0066] It should be noted that the MOH solution is in excess relative to the amount of carboxymethyl groups in carboxymethyl cellulose to ensure that all carboxyl hydrogens in the carboxymethyl groups are replaced by M. M can be one or more of lithium, sodium, potassium, rubidium, and cesium.

[0067] In some embodiments, the thickness of the passivation layer 30 is 1–8 μm. Understandably, the thickness of the passivation layer may include, but is not limited to: 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, and 7.5 μm. Further, it can be selected as 2 μm to 4 μm. When the thickness of the passivation layer is within the above range, the film formation effect and interfacial dynamics performance are better. If the thickness of the passivation layer 30 is too small, the coating effect on the active material layer 20 is poor; if the thickness of the passivation layer 30 is too large, it will reduce the Li... + Interface transport performance.

[0068] In some embodiments, the thickness of the active material layer 20 is greater than 40 μm, and can be selected from 40 μm to 79 μm. Understandably, the thickness of the active material layer 20 may include, but is not limited to: 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, and 75 μm.

[0069] The thickness of the negative electrode film is 40 μm to 80 μm.

[0070] The thicknesses of the passivation layer 30, the active material layer 20, and the negative electrode film can be measured using a micrometer, such as a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm. It should be noted that the thicknesses of the passivation layer 30, the active material layer 20, and the negative electrode film in this application refer to the thicknesses of the passivation layer 30, the active material layer 20, and the negative electrode film in the negative electrode sheet used for assembling the battery after cold pressing and compaction.

[0071] The negative electrode active material described in this application is not particularly limited, and may include, but is not limited to, at least one of graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The graphite may include at least one of natural graphite and artificial graphite. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0072] The negative electrode active material accounts for 70-100% of the weight of the active material layer 20, based on the total weight of the active material layer.

[0073] In some embodiments, the active material layer 20 may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The binder constitutes 0-30% by weight of the active material layer, based on the total weight of the active material layer.

[0074] In some embodiments, the active material layer 20 may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, carbon black (e.g., acetylene black or Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent constitutes 0-20% by weight of the active material layer, based on the total weight of the active material layer.

[0075] In some embodiments, the active material layer 20 may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). The other additives constitute 0-15% by weight of the active material layer, based on the total weight of the active material layer.

[0076] In some embodiments, the passivation layer 30 is disposed circumferentially on the active material layer 20 to form a hollow, closed structure.

[0077] During battery cycling, uneven temperature and expansion force lead to uneven polarization distribution of the negative electrode sheet. The temperature in the middle is high (affected by heat dissipation), the expansion force is small, and the polarization is small; the temperature at the head and bottom is low, the expansion force is large, and the polarization is large. Uneven polarization easily leads to lithium plating. However, by setting the passivation layer 30 in the circumferential direction of the active material layer 20 to form a hollow closed structure, the lithium plating problem can be effectively solved.

[0078] In some optional embodiments, the area of ​​the hollow region accounts for 10% to 30% of the area of ​​the active material layer 20, and may also include, but is not limited to, 15%, 20%, 22%, 24%, 26%, 28%, and 30%. More optionally, the area of ​​the hollow region accounts for 10% to 20% of the area of ​​the active material layer 20. A second aspect of this application provides a method for preparing a negative electrode sheet, comprising:

[0079] S10. An active material layer 20 is formed on the negative electrode current collector 10, the active material layer 20 including a negative electrode active material;

[0080] S30. A passivation layer 30 is formed on the active material layer 20. The passivation layer 30 includes an ion exchange resin, which includes one or more of carboxymethyl cellulose and carboxymethyl cellulose metal salts.

[0081] In some embodiments, the passivation layer 30 is formed using physical vapor deposition.

[0082] Physical vapor deposition (PVD) methods include at least one of selective evaporation and sputtering. Evaporation methods include, but are not limited to, at least one of vacuum evaporation, thermal evaporation deposition, and electron beam evaporation (EBEM). Sputtering methods include, but are not limited to, magnetron sputtering.

[0083] In some embodiments, the passivation layer 30 is formed by vacuum evaporation. Optionally, the deposition rate of the vacuum evaporation method is 0.05–0.2 μ / min, and more preferably 0.07–0.15 μ / min. The deposition rate affects the passivation layer formation effect. A lower deposition rate will result in a loose film that is prone to forming large particles, affecting the compactness of the passivation layer. However, an excessively high deposition rate will increase the internal stress of the film, leading to increased defects within the film layer, and in severe cases, causing the film layer to crack.

[0084] In some embodiments, step S20 is further included before the passivation layer 30 is formed on the active material layer 20:

[0085] S20. Set up a mask to block the middle part of the active material layer 20 to be treated. The area of ​​the mask is smaller than the area of ​​the active material layer 20.

[0086] It should be noted that the above-mentioned central part is intended to form a hollow area and is not limited to the exact center in a strict sense. As long as the periphery of the active material layer 20 can be exposed, it is acceptable.

[0087] In some alternative embodiments, the area of ​​the mask is 10% to 30% of the area of ​​the active material layer 20.

[0088] Secondary batteries

[0089] A third aspect of the embodiments of this application provides a secondary battery, including any device in which an electrochemical reaction occurs to convert chemical energy into electrical energy, such as a lithium-ion secondary battery or a sodium-ion secondary battery.

[0090] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0091] [Positive electrode plate]

[0092] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0093] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0094] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material on the polymer substrate. The metal material includes at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. The polymer substrate includes at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0095] In some embodiments, the positive electrode active material may comprise a positive electrode active material known in the art for use in batteries.

[0096] As an example, the positive electrode active material of a lithium-ion secondary battery may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials of batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0097] The positive electrode active material accounts for 80-100% of the weight of the positive electrode film, based on the total weight of the positive electrode film.

[0098] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. The binder constitutes 0-20% by weight of the positive electrode film layer, based on the total weight of the positive electrode film layer.

[0099] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, carbon black (e.g., acetylene black or Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent constitutes 0-20% by weight of the positive electrode film, based on the total weight of the positive electrode film.

[0100] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, wherein the solid content of the positive electrode slurry is 40-80 wt%, the viscosity at room temperature is adjusted to 5000-25000 mPa·s, the positive electrode slurry is coated on the surface of the positive current collector, dried, and then cold-pressed using a cold rolling mill to form the positive electrode sheet; the compacted density of the positive electrode sheet is 2-2.7 g / cm³. 3 The concentration can be selected as 2.2-2.4 g / cm³. 3 The thickness of the positive electrode film is 51-191 μm.

[0101] The thickness T of the positive electrode film can be measured using a micrometer, such as a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm. It should be noted that the thickness of the positive electrode film mentioned in this application refers to the thickness of the positive electrode film in the positive electrode sheet used for assembling the battery after cold pressing and compaction.

[0102] [Negative electrode plate]

[0103] The negative electrode sheet is the negative electrode sheet provided in the first aspect of this application.

[0104] [Electrolytes]

[0105] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0106] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0107] In some embodiments, the electrolyte salt of the lithium-ion secondary battery may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0108] The concentration of the electrolyte salt is typically 0.5-5 mol / L.

[0109] In some embodiments, the solvent may be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0110] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0111] [Isolation membrane]

[0112] In some implementations, the secondary battery also includes a separator.

[0113] In some embodiments, the separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each base film can be the same or different, without particular limitation.

[0114] In some embodiments, the thickness of the separator is 5-30 μm, optionally 7-18 μm.

[0115] In some embodiments, the air permeability of the separator can be 100s / 100mL-300s / 100mL; optionally, the air permeability of the separator can be 150s / 100mL-250s / 100mL, as tested according to the national standard GB / T 36363-2018.

[0116] The thickness of the isolation can be measured using a micrometer, for example, a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm.

[0117] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0118] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0119] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0120] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured secondary battery 1.

[0121] In some implementations, refer to Figure 3 The outer packaging may include a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The shell 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The secondary battery 1 may contain one or more electrode assemblies 22, which can be selected by those skilled in the art according to specific practical needs.

[0122] In some embodiments, the secondary battery 1 can be assembled into a battery module, and the number of secondary batteries 1 contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0123] In the battery module, multiple secondary batteries 1 can be arranged sequentially along the length of the battery module. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 1 can be secured with fasteners.

[0124] Optionally, the battery module may also include a housing with a receiving space in which a plurality of secondary batteries 1 are received.

[0125] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0126] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0127] Electrical appliances

[0128] A fourth aspect of this application provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0129] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0130] Figure 4 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0131] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0132] Example

[0133] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0134] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0135] I. Preparation of Carboxymethyl Cellulose Metal Salts

[0136] Sodium carboxymethyl cellulose was dispersed in an ethanol / water mixture (volume ratio 95:5), then 20 wt% HCl solution was added, and the mixture was acid-treated at 35°C for 2 hours. After filtration, the mixture was washed three times with an ethanol / water mixture (volume ratio 85:15) and dried at 105°C for 12 hours to obtain carboxymethyl cellulose.

[0137] Carboxymethyl cellulose was dispersed in an ethanol / water mixture (90:10, v / v), and then added to an aqueous solution of LiOH (7 wt%). The mixture was reacted at 50 °C for 2 hours. The mixture was then washed three times with an ethanol / water mixture (85:15, v / v) and dried at 105 °C for 12 hours to obtain lithium carboxymethyl cellulose.

[0138] The aqueous solution of LiOH can be arbitrarily replaced with KOH, RbOH, CsOH, or Ca(OH)2 as needed to obtain potassium carboxymethyl cellulose, rubidium carboxymethyl cellulose, cesium carboxymethyl cellulose, and calcium carboxymethyl cellulose for subsequent preparation of negative electrode sheets. It should be noted that when replacing with an aqueous solution of other bases, the amount of base used in the aqueous solution is in excess relative to the carboxylic acid groups in the carboxymethyl cellulose.

[0139] II. Preparation of Secondary Batteries

[0140] Example 1

[0141] 1. Preparation of positive electrode sheet

[0142] Lithium iron phosphate (specific capacity of 139 mAh / g), acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 94:4:2 and added to N-methylpyrrolidone (NMP) solvent. After thorough mixing, a positive electrode slurry was obtained. The positive electrode slurry was then uniformly coated onto the positive electrode current collector aluminum foil, followed by drying, cold pressing, and slitting to obtain the positive electrode sheet.

[0143] 2. Preparation of negative electrode sheet

[0144] The active material, artificial graphite (specific capacity 340 mAh / g), conductive agent, styrene-butadiene rubber (SBR) binder, and thickener, sodium carboxymethyl cellulose (CMC), were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as solvent, and the mixture was thoroughly stirred to obtain an active material layer slurry. This slurry was then coated onto the copper foil of the negative electrode current collector and dried to form the active material layer. The coating weight of the negative electrode slurry was 0.132 g / 1540.25 mm. 2 The coating thickness is 80 μm (by weight excluding solvent).

[0145] A copper foil with an active material layer is placed in a vacuum coating machine, and dried carboxymethyl cellulose is placed in an evaporation boat. The chamber is then evacuated to a vacuum level of 5 × 10⁻⁶.-5 Torr gradually increases the temperature to 110℃ to achieve a film deposition rate of 0.15 μ / min, depositing a 5 μm thick carboxymethyl cellulose layer on the active material layer to form a passivation layer.

[0146] 3. Preparation of electrolyte

[0147] Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3:7 to obtain an organic solvent; LiPF6 was dissolved in the above organic solvent, and then fluoroethylene carbonate (FEC) was added and mixed evenly to obtain an electrolyte; wherein the concentration of LiPF6 was 1 mol / L, and the mass percentage of fluoroethylene carbonate (FEC) was 2% based on the total mass of the electrolyte.

[0148] 4. Preparation of the separating membrane

[0149] PE porous film is used as the separator.

[0150] 5. Preparation of lithium-ion secondary batteries

[0151] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. They are then wound to obtain a bare cell. Tabs are welded onto the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. Electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and testing to obtain a lithium-ion rechargeable battery.

[0152] Examples 2-18

[0153] The preparation method is basically the same as that in Example 1, except that the negative electrode material and its parameters are replaced with the corresponding parameters in Example 1, as shown in Table 1.

[0154] Comparative Example 1

[0155] The preparation method is basically the same as that in Example 1, except that the passivation layer is omitted in the negative electrode sheet.

[0156] Comparative Example 2

[0157] The preparation method is basically the same as that in Example 1, except that sodium hydroxymethyl cellulose is used instead of carboxymethyl cellulose.

[0158] III. Performance Testing

[0159] 1. Cyclic performance test

[0160] (1) Cyclic test at room temperature (25℃)

[0161] At 25℃, the test battery was placed in a high-temperature chamber. It was sequentially charged at a constant current rate of 1C to 3.65V, allowed to rest for 5 minutes, and then charged at a constant voltage of 3.65V to a current of 0.05C, allowed to rest for 30 minutes. After charging, it was discharged at a constant current rate of 1C to 2.5V; this constitutes one charge-discharge cycle. This method was used to perform cyclic charge-discharge tests on the battery until the discharge capacity decreased to 80%, and the number of cycles was recorded.

[0162] (2) High temperature (45℃) cycle test

[0163] The test battery was placed in a high-temperature chamber at 45℃. It was charged sequentially at a constant current rate of 1C to 3.65V, allowed to rest for 5 minutes, and then charged at a constant voltage of 3.65V to a current of 0.05C, allowed to rest for 30 minutes. After charging, it was discharged at a constant current rate of 1C to 2.5V, completing one charge-discharge cycle. This method was used to perform cyclic charge-discharge tests on the battery until the discharge capacity decreased to 80%, and the number of cycles was recorded.

[0164] (3) High temperature (60℃) cycle test

[0165] The test battery was placed in a high-temperature chamber at 60℃. It was charged sequentially at a constant current rate of 1C to 3.65V, allowed to rest for 5 minutes, and then charged at a constant voltage of 3.65V to a current of 0.05C, allowed to rest for 30 minutes. After charging, it was discharged at a constant current rate of 1C to 2.5V, completing one charge-discharge cycle. This method was used to perform cyclic charge-discharge tests on the battery until the discharge capacity decreased to 80%, and the number of cycles was recorded.

[0166] 2. Lithium dendrites

[0167] Each of the prepared secondary batteries was cycled 200 times according to the charge-discharge method described in "1. Cycle Performance Test". The secondary batteries were then disassembled in an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm). The surface morphology of the negative electrode was visually observed to determine whether lithium dendrites had formed. No white spots on the negative electrode indicated no lithium dendrites; scattered white spots indicated slight lithium dendrite formation; and dense white spots indicated severe lithium dendrite formation.

[0168] 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.

[0169] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

[0170] Table 1

[0171]

Claims

1. A negative electrode sheet, characterized by, The negative electrode tab includes a negative electrode current collector, an active material layer, and a passivation layer, the active material layer being disposed between the negative electrode current collector and the passivation layer; The active material layer includes a negative electrode active material, and the passivation layer includes an ionic resin, the ionic resin including one or more of carboxymethyl cellulose and a carboxymethyl cellulose metal salt, the passivation layer being disposed in a circumferential direction of the active material layer to form a hollow closed structure, a hollow region exposing the active material layer.

2. The negative electrode sheet according to claim 1, characterized by, The carboxymethyl cellulose has a general molecular formula of [C6H7O2(OH) 3-x1 (OCH2COOH) x1 ] n1 n1 is a degree of polymerization; x1 is 0.4-0.7; and / or, The carboxymethyl cellulose metal salt has a general molecular formula of [C6H7O2(OH) 3-x2 (OCH2COOM) x2 ] n2 M includes one or more of lithium, sodium, potassium, rubidium, and cesium; n2 is a degree of polymerization; and x2 is 0.4-0.

7.

3. The negative electrode sheet according to claim 2, characterized by x1 is 0.5-0.7; and / or x2 is 0.5-0.

7.

4. The negative electrode sheet according to claim 2, characterized by M includes lithium.

5. The negative electrode sheet according to any one of claims 1 to 4, wherein The ionic resin has a Young's modulus of greater than or equal to 2.5 GPa.

6. The negative electrode sheet according to claim 5, characterized by The ionic resin has a Young's modulus of 18 GPa-27 GPa.

7. The negative electrode sheet according to any one of claims 1 to 4, wherein The ionic resin has a weight average molecular weight of 50,000 Da-300,000 Da.

8. The negative electrode sheet according to claim 7, characterized by The ionic resin has a weight average molecular weight of 70,000 Da-250,000 Da.

9. The negative electrode sheet according to any one of claims 1 to 8, wherein The passivation layer has a thickness of 1-8 μm.

10. The negative electrode sheet according to claim 9, wherein The passivation layer has a thickness of 2 μm-4 μm.

11. The negative electrode sheet according to any one of claims 1 to 8, wherein The hollow region has an area of 10%-30% of an area of the active material layer.

12. The negative electrode sheet according to any one of claims 1 to 8, wherein The negative electrode active material includes at least one of graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, and lithium titanate.

13. The negative electrode sheet according to claim 12, wherein The negative electrode active material is graphite.

14. A method of producing the negative electrode sheet according to any one of claims 1 to 13, characterized by, The method includes the following steps: forming an active material layer on a negative electrode current collector, the active material layer including a negative electrode active material; forming a passivation layer on the active material layer, the passivation layer including an ionic resin, the ionic resin including one or more of carboxymethyl cellulose and a carboxymethyl cellulose metal salt; The method further includes the following step before forming the passivation layer on the active material layer: disposing a mask plate so that the mask plate shields a middle portion of the active material layer to be processed, the mask plate having an area smaller than an area of the active material layer.

15. The method of claim 14, wherein, The passivation layer is formed by a physical vapor deposition method.

16. The method of claim 15, wherein, The passivation layer is formed by an evaporation method or a sputtering method.

17. The method of claim 15, wherein, The passivation layer is formed by a vacuum evaporation method.

18. The method of claim 15, wherein, The mask plate has an area of 10%-30% of an area of the active material layer.

19. A secondary battery including the negative electrode tab of any one of claims 1-12.

20. An electrical device including the secondary battery of claim 19.

Images