Negative pole piece, preparation method of negative pole piece, secondary battery and electric device

Abstract

The invention relates to a negative pole piece, preparation of the negative pole piece, a secondary battery and an electric device. The negative pole piece comprises a negative current collector, an active substance layer and a passivation layer, and the active substance layer is arranged between the negative current collector and the passivation layer; wherein the active material layer comprises a negative electrode active material, the passivation layer comprises ion resin, and the ion resin comprises one or more of carboxymethyl cellulose and carboxymethyl cellulose metal salt.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a negative electrode plate and a preparation method thereof, a secondary battery and an electrical device. Background Art

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

[0003] With the widespread application and continuous development of lithium-ion batteries, the safety of lithium-ion batteries has received more and more attention. After multiple cycles of lithium-ion batteries, metallic lithium will be precipitated on the surface of the negative electrode, and metallic lithium dendrites will bring considerable safety risks.

[0004] Therefore, seeking 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] The present application is made in view of the above-mentioned problems, and one of its purposes is to provide a negative electrode sheet and a preparation method thereof, a secondary battery and an electrical device.

[0006] In order to achieve the above-mentioned object, the first aspect of the present application provides a negative electrode plate, comprising a negative electrode current collector, an active material layer and a passivation layer, wherein the active material layer is arranged between the negative electrode current collector and the passivation layer;

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

[0008] The negative electrode sheet provided by the present application has an active material layer and a passivation layer arranged on the current collector, and the passivation layer includes an ion resin, in which there are cations that can be exchanged with lithium ions, thereby effectively driving the rapid migration and uniform distribution of lithium ions, and the ion resin also contains a large number of hydrogen bonds, which can be cross-linked into a uniform and dense three-dimensional network structure, have a high deformation resistance, form protection for the active material layer, effectively reduce the interface reaction between the negative electrode and the electrolyte during the cycle, and can also alleviate the impact of the volume change of the negative electrode active material during the battery cycle. The passivation layer in the negative electrode sheet provided by the present application can be used as an artificial SEI to inhibit the generation and growth of lithium dendrites, thereby effectively improving the cycle performance of the battery.

[0009] In some embodiments, the 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 optionally 0.5 to 0.7; and / or,

[0010] The 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, optionally, M includes lithium; n2 is the degree of polymerization, x2 is 0.4 to 0.7, and can be optionally 0.5 to 0.7.

[0011] In some of the embodiments, the Young's modulus of the ionic resin is greater than or equal to 2.5 GPa, and can be optionally 18 GPa-27 GPa.

[0012] In some embodiments, the weight average molecular weight of the ionic resin is 50000Da-300000Da, and can be optionally 70000-250000Da.

[0013] In some embodiments, the thickness of the passivation layer is 1 to 8 μm, and can be 2 to 4 μm.

[0014] In some embodiments, the passivation layer is disposed around 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 graphite may be selected.

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

[0018] forming an active material layer on the negative electrode current collector, wherein the active material layer includes a negative electrode active material;

[0019] A passivation layer is formed on the active material layer, wherein the passivation layer includes an ionic resin, and the ionic resin includes one or more of carboxymethyl cellulose and a carboxymethyl cellulose metal salt.

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

[0021] In some embodiments, before forming the passivation layer on the active material layer, the method further includes:

[0022] A mask plate is arranged so as to shield the middle portion of the active material layer to be processed, and an area of ​​the mask plate is smaller than an 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 the present application provides a secondary battery, which includes the negative electrode plate described in the third aspect of the present application.

[0025] A fourth aspect of the present application provides an electrical device, which includes the secondary battery described in the fourth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure of a negative electrode plate according to one embodiment of the present application.

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

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

[0029] Figure 4 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0030] Description of reference numerals:

[0031] 1. Secondary battery; 11. Shell; 12. Electrode assembly; 13. Cover plate; 2. Power-consuming device; 10. Negative electrode current collector; 20. Active material layer; 30. Passivation layer. DETAILED DESCRIPTION

[0032] Below, the negative electrode plate and its preparation method, secondary battery and electric device of the present application are described in detail with appropriate reference to the drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0033] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0035] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0036] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0037] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0038] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": 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 "ionic resin" refers to any resin that carries an electrical charge, including resins that carry negatively charged ions and resins that carry positively charged ions.

[0040] An important problem of lithium-ion batteries under long-term cycling and storage conditions is lithium dendrites. The lithium dendrites caused by the uneven deposition of lithium ions on the surface of the negative electrode will affect the interface stability between the graphite negative electrode and the electrolyte. As the number of cycles increases, the growth of lithium dendrites will continue to consume the electrolyte and cause irreversible deposition of active lithium, which will in turn produce more dead lithium and cause the battery's coulombic efficiency to decrease. At the same time, the continuous growth of lithium dendrites will bring considerable safety risks to the battery, which is mainly caused by lithium dendrites piercing the diaphragm. In the related art, inorganic salts are often used as negative electrode additives to construct artificial SEI films to improve the cycle performance of the battery. However, when inorganic salts are used as additives, the effect of improving the growth of lithium dendrites is not ideal.

[0041] Negative electrode

[0042] To solve the above technical problems, please refer to Figure 1 In one embodiment of the present application, a negative electrode sheet is provided, 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, and the active material layer 20 is disposed between the negative electrode current collector 10 and the passivation layer 30. Among them, the active material layer 20 includes a negative electrode active material, and the passivation layer 30 includes an ionic resin, and the ionic resin includes one or more of carboxymethyl cellulose and a metal salt of carboxymethyl cellulose. It should be noted that the negative electrode current collector 10 has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector 10.

[0043] The negative electrode sheet provided in the embodiment of the present application includes an active material layer 20 and a passivation layer 30, wherein the passivation layer 30 includes an ionic resin, wherein there are cations that can be exchanged with lithium ions, thereby effectively driving the rapid migration and uniform distribution of lithium ions, and the ionic resin also contains a large number of hydrogen bonds, which can be cross-linked into a uniform and dense three-dimensional network structure, and has a high deformation resistance, forming protection for the active material layer 20, effectively reducing the interface reaction between the negative electrode and the electrolyte during the cycle, and can also alleviate the impact of the volume change of the negative electrode active material during the battery cycle. The passivation layer 30 in the negative electrode sheet provided in the embodiment of the present application can be used as an artificial SEI to inhibit the generation and growth of lithium dendrites, thereby effectively improving the cycle performance of the battery.

[0044] Carboxymethyl cellulose and its salts are cellulose ethers in which a portion of the hydroxyl groups on the anhydroglucose ring in cellulose are substituted with carboxymethyl groups.

[0045] In some embodiments, the 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 optionally 0.5 to 0.7. x1 represents the "degree of substitution", which can be defined as the average number of hydroxyl groups in each glucose unit of cellulose replaced by carboxymethyl groups.

[0046] In the above “x1 is 0.4 to 0.7”, the value of x1 includes the minimum value and the maximum value of the range, and every value between the minimum value and the 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 a range consisting of any two values.

[0047] In some embodiments, the 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, and 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 replaced by carboxymethyl metal groups.

[0048] In the above “x2 is 0.4 to 0.7”, the values ​​of x2 include the minimum and maximum values ​​of the range, and 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 a range consisting of any two values.

[0049] It can be understood that n1 and n2 may be the same or different, and x1 and x2 may be the same or different.

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

[0051] x1 and x2 can be measured by instruments and methods known in the art, such as by ashing method. The specific method can be referred to as follows: weigh 0.2000g (accurate to 0.1mg) of the sample to be tested, place it in a 30mL porcelain crucible, place it in a muffle furnace after ashing, burn it at 700℃ for 1h, and take it out after cooling; transfer all the residues in the porcelain crucible to a 150mL conical flask with distilled water, add 3 to 4 drops of methyl orange indicator solution to the conical flask, and titrate with sulfuric acid standard solution. When the solution is red, continue to add 10mL of sulfuric acid standard solution, record the total volume of sulfuric acid standard solution used, then heat to boiling, and titrate with sodium hydroxide standard solution after 10min until the color of the solution changes from red to yellow, and record the volume of sodium hydroxide standard solution used. The formula for substitution degree is as follows:

[0052]

[0053]

[0054] Where DS is the degree of substitution; M H2SO4 is the molar concentration of sulfuric acid standard solution, mol / L; M NaOH is the molar concentration of sodium hydroxide standard solution, mol / L; V H2SO4 V is the total volume of the sulfuric acid standard solution used for titration, 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 resin is greater than or equal to 2.5 GPa, and can be selected as 18 GPa-27 GPa. When the Young's modulus of the ion resin is within this range, the passivation layer 30 can have a higher deformation resistance, further improving the cycle performance of the battery. The larger the Young's modulus, the stronger the barrier to lithium dendrites during the cycle, which can improve the cycle, but it should not be too large.

[0056] The values ​​of the above-mentioned Young's modulus include the minimum and maximum values ​​of the above-mentioned range, and every value between such 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 ionic resin has a well-known meaning in the art and can be measured using well-known instruments and methods in the art, such as the AFM force-displacement curve measurement method, specifically using an NSG-10 single crystal silicon probe, with a tip curvature radius of about 10nm and an elastic coefficient (Kc) range of 3.1 to 37.6N / m. Before the measurement, the specific Kc value of the probe is determined by the thermal modulation method. TM The two-dimensional morphology of the sample was measured in the 3D mode, and the force-displacement curve (referred to as force curve) of the sample was recorded (rate of 2 μm / s). All tests were completed at 25°C and 40% relative humidity. The data of the effective force curve was analyzed and fitted using NanoScope Analysis software, and the compressive Young's modulus of the sample was calculated based on the elastic mechanics contact model.

[0058] In some embodiments, the weight average molecular weight of the ionic resin is 50000-300000Da, and can be 70000-250000Da. The weight average molecular weight within the above range has better film-forming properties. Too large or too small a weight average molecular weight is not conducive to film formation.

[0059] The above-mentioned value of "50000Da-300000Da" includes the minimum and maximum values ​​of the range, and each value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiment and the following point values: 60000Da, 70000Da, 80000Da, 90000Da, 100000Da, 110000Da, 120000Da, 130000Da, 14000Da, 15000Da, 16000Da, 170000Da, 180000Da, 190000Da, 200000Da, 210000Da, 220000Da, 230000Da, 240000Da, 250000Da, 260000Da, 270000Da, 280000Da, 290000Da, 300000Da, 310000Da, 320000Da, 330000Da, 340000Da, 350000Da, 360000Da, 370000Da, 380000Da, 390000Da, 400000Da, 410000Da, 420000Da, 430000Da, 440000Da, 450000Da, 460000Da, 470000Da, 480000Da, 490000Da, 51 ... 0 Da, 150000 Da, 160000 Da, 170000 Da, 180000 Da, 190000 Da, 200000 Da, 210000 Da, 220000 Da, 230000 Da, 240000 Da, 250000 Da, 260000 Da, 270000 Da, 280000 Da, 290000 Da; or a range consisting of any two values.

[0060] The weight average molecular weight of the ionic resin has a well-known meaning in the art and can be measured using instruments and methods known in the art, for example, the viscosity of its aqueous solution can be measured 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 ionic resin can be estimated using the viscosity by the following formula:

[0061] η[Pa S]=8.91×10 -4 +1.30×10 -5 C 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 the viscosity, c is the concentration of CMC, M w is the molecular weight as described by Kulicke in Polymer, Vol. 37, No. 13, pp. 2723-2731, 1996.

[0063] The carboxymethyl cellulose or carboxymethyl cellulose metal salt of the present application can be prepared or obtained by commercial purchase or methods known in the art. In some embodiments, other carboxymethyl cellulose metal salts other than sodium carboxymethyl cellulose can be prepared by the following method:

[0064] Treating sodium carboxymethyl cellulose with acid to obtain carboxymethyl cellulose; and

[0065] The MOH solution was added to the obtained carboxymethyl cellulose and heated.

[0066] It should be noted that the MOH solution is in excess relative to the amount of carboxymethyl groups in the 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 to 8 μm. It is understandable that 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, 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-forming effect and interface 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, and if the thickness of the passivation layer 30 is too large, it will reduce the Li + interface transport properties.

[0068] In some embodiments, the thickness of the active material layer 20 is greater than 40 μm, and may be 40 μm to 79 μm. It is understandable that 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, 75 μm.

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

[0070] The thickness of the passivation layer 30, the thickness of the active material layer 20 and the thickness of the negative electrode film layer can be measured by using a micrometer, for example, a micrometer of model Mitutoyo293-100 with an accuracy of 0.1 μm can be used for measurement. It should be noted that the thickness of the passivation layer 30, the thickness of the active material layer 20 and the thickness of the negative electrode film layer in the present application refers to the thickness of the passivation layer 30, the active material layer 20 and the negative electrode film layer in the negative electrode sheet after cold pressing and used for assembling the battery.

[0071] The negative electrode active material described in the present application is not particularly limited, and may specifically 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, the present application is not limited to these materials, and other traditional 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 weight ratio of the negative electrode active material in the active material layer 20 is 70-100 weight % based on the total weight of the active material layer.

[0073] In some embodiments, the active material layer 20 may further 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 weight ratio of the binder in the active material layer is 0-30% by weight, based on the total weight of the active material layer.

[0074] In some embodiments, the active material layer 20 may further 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 weight ratio of the conductive agent in the active material layer is 0-20% by weight, based on the total weight of the active material layer.

[0075] In some embodiments, the active material layer 20 may further include other additives, such as a thickener (such as sodium carboxymethyl cellulose (CMC-Na)), etc. The weight ratio of the other additives in the active material layer is 0-15% by weight, based on the total weight of the active material layer.

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

[0077] During the battery cycle, the polarization distribution of the negative electrode is uneven due to uneven temperature and expansion force. 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. The uneven polarization can easily lead to lithium deposition. The passivation layer 30 is arranged circumferentially around the active material layer 20 to form a hollow closed structure, which can effectively solve the lithium deposition problem.

[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 are not limited to 15%, 20%, 22%, 24%, 26%, 28%, 30%. Further optionally, the area of ​​the hollow region accounts for 10% to 20% of the area of ​​the active material layer 20. The second aspect of the embodiment of the present application provides a method for preparing a negative electrode sheet, comprising:

[0079] S10, forming an active material layer 20 on the negative electrode current collector 10, wherein the active material layer 20 includes a negative electrode active material;

[0080] S30 , forming a passivation layer 30 on the active material layer 20 , wherein the passivation layer 30 includes an ionic resin, and the ionic resin includes one or more of carboxymethyl cellulose and carboxymethyl cellulose metal salt.

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

[0082] Physical vapor deposition includes at least one of evaporation and sputtering. Evaporation includes but is not limited to at least one of vacuum evaporation, thermal evaporation, and electron beam evaporation (EBEM). Sputtering includes but is 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 0.05-0.2μ / min, and further optionally 0.07-0.15μ / min. The deposition rate will affect the film-forming effect of the passivation layer. A lower deposition rate will cause the deposited film to be loose and easy to form large particles, affecting the compactness of the passivation layer. However, too high a deposition rate will increase the internal stress of the film, resulting in increased defects in the film layer, and in severe cases, the film layer will rupture.

[0084] In some embodiments, before forming the passivation layer 30 on the active material layer 20, the method further includes step S20:

[0085] S20 , setting a mask plate so that the mask plate covers the middle portion of the active material layer 20 to be processed, and the area of ​​the mask plate is smaller than the area of ​​the active material layer 20 .

[0086] It should be noted that the middle portion is intended to form a hollow area and is not limited to the middle portion in a strict sense, as long as the periphery of the active material layer 20 can be exposed.

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

[0088] Secondary battery

[0089] A third aspect of the embodiments of the present 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] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0091] [Positive electrode]

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

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

[0094] In some embodiments, the positive electrode 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 material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material on a polymer material substrate. Among them, the metal material includes at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. The polymer material 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 include a positive electrode active material for a battery known in the art.

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

[0097] The weight ratio of the positive electrode active material in the positive electrode film layer is 80-100 weight percent, based on the total weight of the positive electrode film layer.

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

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

[0100] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry, wherein the positive electrode slurry has a solid content of 40-80wt%, and the viscosity at room temperature is adjusted to 5000-25000mPa·s, the positive electrode slurry is coated on the surface of the positive electrode collector, and after drying, the positive electrode sheet is formed by cold pressing with a cold rolling mill; the compaction density of the positive electrode sheet is 2-2.7g / cm 3 , optional 2.2-2.4g / cm 3 The thickness of the positive electrode film is 51-191 μm.

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

[0102] [Negative electrode]

[0103] The negative electrode plate adopts the negative electrode plate provided in the first aspect of the present application.

[0104] [Electrolytes]

[0105] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

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

[0107] In some embodiments, the electrolyte salt of the lithium ion secondary battery can 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 difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

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

[0109] In some embodiments, the solvent can be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene 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), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

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

[0111] [Isolation film]

[0112] In some embodiments, the secondary battery further includes a separator.

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

[0114] In some embodiments, the isolation film has a thickness of 5-30 μm, and optionally 7-18 μm.

[0115] In some embodiments, the air permeability of the isolation membrane may be 100s / 100mL-300s / 100mL; alternatively, the air permeability of the isolation membrane may be 150s / 100mL-250s / 100mL, tested according to national standard GB / T 36363-2018.

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

[0117] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0118] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0119] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0120] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 2 The secondary battery 1 is a square structure as an example.

[0121] In some embodiments, reference Figure 3 , the outer packaging may include a shell 11 and a cover plate 13. Among them, the shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 22 contained in the secondary battery 1 can be one or more, and those skilled in the art can select according to specific actual needs.

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

[0123] In the battery module, the plurality of secondary batteries 1 may be arranged in sequence along the length direction of the battery module. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 1 may be fixed by fasteners.

[0124] Optionally, the battery module may further include a housing having a receiving space, and the plurality of secondary batteries 1 are received in the receiving space.

[0125] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may 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 a plurality of battery modules disposed in the battery box. The battery box includes an upper box body and a lower box body, and the upper box body can be covered on the lower box body to form a closed space for accommodating the battery modules. The plurality of battery modules can be arranged in the battery box in any manner.

[0127] Electrical devices

[0128] The fourth aspect of the embodiments of the present application provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as 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., but are not limited thereto.

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

[0130] Figure 4 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0131] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0132] Example

[0133] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0134] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0135] 1. Preparation of Carboxymethyl Cellulose Metal Salt

[0136] Sodium carboxymethyl cellulose was dispersed in an ethanol / water mixture (volume ratio 95:5), then a 20 wt % HCl solution was added, acid-treated at 35° C. for 2 hours, filtered, 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] The carboxymethyl cellulose was dispersed in an ethanol / water mixture (volume ratio 90:10), then added to an aqueous solution of LiOH (7wt%) and reacted at 50°C for 2 hours. It was then washed three times with an ethanol / water mixture (volume ratio 85:15) and dried at 105°C for 12 hours to obtain lithium carboxymethyl cellulose.

[0138] The aqueous solution of LiOH can be replaced by KOH, RbOH, CsOH, Ca(OH)2 as needed, so as to obtain potassium carboxymethyl cellulose, rubidium carboxymethyl cellulose, cesium carboxymethyl cellulose and calcium carboxymethyl cellulose for subsequent preparation of negative electrode sheets. It is particularly noted that when replaced by aqueous solutions of other alkalis, the amount of the alkali in the aqueous solution is excessive relative to the carboxylic acid group in the carboxymethyl cellulose.

[0139] 2. Preparation of secondary batteries

[0140] Example 1

[0141] 1. Preparation of positive electrode

[0142] The positive electrode active material lithium iron phosphate (gram capacity of 139 mAh / g), the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 94:4:2, added to the solvent N-methylpyrrolidone (NMP), and stirred and mixed thoroughly to obtain the positive electrode slurry; then the positive electrode slurry is evenly coated on the positive electrode collector aluminum foil, and then dried, cold pressed, and cut to obtain the positive electrode sheet.

[0143] 2. Preparation of negative electrode sheet

[0144] According to the weight ratio of 95:1.5:3.1:0.4, the negative electrode active material artificial graphite (gram capacity of 340mAh / g), the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) were mixed, and the solvent deionized water was added, and the mixture was stirred and mixed to obtain the active material layer slurry. The active material layer slurry was coated on the negative electrode current collector copper foil and dried to form the active material layer, wherein the coating weight of the negative electrode slurry was 0.132g / 1540.25mm 2 The coating thickness was 80 μm (based on weight excluding solvent).

[0145] The copper foil with the active material layer was placed in a vacuum coating machine, and dried carboxymethyl cellulose was placed in an evaporation boat. The chamber was evacuated to 5×10-5 Torr, and gradually raised the temperature to 110°C so that the film deposition rate was 0.15 μ / min, and carboxymethyl cellulose with a thickness of 5 μm was deposited on the active material layer to form a passivation layer.

[0146] 3. Preparation of Electrolyte

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

[0148] 4. Preparation of isolation membrane

[0149] PE porous film is used as the isolation membrane.

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

[0151] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare cell, the tabs are welded to the bare cell, and the bare cell is placed in an aluminum shell, and baked at 80°C to remove water, and then the electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery then goes through the processes of static, hot and cold pressing, formation, shaping, and testing in sequence to obtain a lithium-ion secondary battery.

[0152] Embodiments 2 to 18

[0153] The preparation method is basically the same as that in Example 1, except that the negative electrode plate material and its parameters are substituted for 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 of Example 1, except that the passivation layer is omitted in the negative electrode plate.

[0156] Comparative Example 2

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

[0158] 3. Performance Test

[0159] 1. Cycle performance test

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

[0161] At 25℃, place the test battery in a high temperature box for testing. Charge it to 3.65V at a constant current rate of 1C, let it stand for 5 minutes, then charge it at a constant voltage of 3.65V to a current of 0.05C, and let it stand for 30 minutes. After charging, discharge it to 2.5V at a constant current of 1C, which is a charge and discharge cycle. Perform cyclic charge and discharge tests on the battery according to this method until the discharge capacity decays to 80%, and record the number of cycles.

[0162] (2) High temperature (45°C) cycle test

[0163] At 45℃, place the test battery in a high temperature box for testing. Charge it to 3.65V at a constant current rate of 1C, let it stand for 5 minutes, then charge it at a constant voltage of 3.65V to a current of 0.05C, and let it stand for 30 minutes. After charging, discharge it to 2.5V at a constant current of 1C, which is one charge and discharge cycle. Perform cyclic charge and discharge tests on the battery according to this method until the discharge capacity decays to 80%, and record the number of cycles.

[0164] (3) High temperature (60°C) cycle test

[0165] At 60℃, place the test battery in a high temperature box for testing. Charge it to 3.65V at a constant current rate of 1C, let it stand for 5 minutes, then charge it at a constant voltage of 3.65V to a current of 0.05C, and let it stand for 30 minutes. After charging, discharge it to 2.5V at a constant current of 1C, which is a charge and discharge cycle. Perform cyclic charge and discharge tests on the battery according to this method until the discharge capacity decays to 80%, and record the number of cycles.

[0166] 2. Lithium dendrites

[0167] After each secondary battery prepared above was cycled 200 times according to the charge and discharge method described in "1. Cycle Performance Test", the secondary battery was disassembled in an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), and the surface morphology of the negative electrode was visually observed to determine whether lithium dendrites were generated. If there were no white spots on the negative electrode, it was determined that there were no lithium dendrites; if there were sporadic white spots on the negative electrode, it was determined that the lithium dendrites were slight; if there were dense white spots on the negative electrode, it was determined that the lithium dendrites were severe.

[0168] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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 above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims, and the specification and drawings may be used to interpret the contents of the claims.

[0170] Table 1

[0171]

Claims

1. A negative electrode plate, characterized in that: It comprises a negative electrode current collector, an active material layer and a passivation layer, wherein the active material layer is arranged between the negative electrode current collector and the passivation layer; The active material layer includes a negative electrode active material, the passivation layer includes an ion resin, and the ion resin includes one or more of carboxymethyl cellulose and carboxymethyl cellulose metal salt.

2. The negative electrode sheet according to claim 1, characterized in that: The 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 optionally 0.5 to 0.7; and / or, The 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, optionally, M includes lithium; n2 is the degree of polymerization; x2 is 0.4 to 0.7, optionally 0.5 to 0.

7.

3. The negative electrode sheet according to claim 1 or 2, characterized in that: The Young's modulus of the ion resin is greater than or equal to 2.5 Gpa, and can be selected to be 18 Gpa-27 Gpa.

4. The negative electrode sheet according to claim 1 or 2, characterized in that: The weight average molecular weight of the ionic resin is 50000Da-300000Da, and can be optionally 70000-250000Da.

5. The negative electrode sheet according to any one of claims 1 to 4, characterized in that: The thickness of the passivation layer is 1 to 8 μm, and can be optionally 2 to 4 μm.

6. The negative electrode sheet according to any one of claims 1 to 4, characterized in that: The passivation layer is arranged around the active material layer to form a hollow closed structure; optionally, the area of ​​the hollow region accounts for 10% to 30% of the area of ​​the active material layer.

7. The negative electrode sheet according to any one of claims 1 to 4, characterized in that: 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 graphite may be selected.

8. A method for preparing a negative electrode sheet according to any one of claims 1 to 7, characterized in that: The following steps are involved: forming an active material layer on the negative electrode current collector, wherein the active material layer includes a negative electrode active material; A passivation layer is formed on the active material layer, wherein the passivation layer includes an ionic resin, and the ionic resin includes one or more of carboxymethyl cellulose and a carboxymethyl cellulose metal salt.

9. The preparation method according to claim 8, characterized in that: The passivation layer is formed by a physical vapor deposition method, which may be an evaporation method or a sputtering method, and may further be a vacuum evaporation method.

10. The preparation method according to claim 9, characterized in that: Before forming a passivation layer on the active material layer, the method further includes: Setting a mask plate so that the mask plate covers the middle part of the active material layer to be processed, and the area of ​​the mask plate is smaller than the area of ​​the active material layer; Optionally, the area of ​​the mask plate is 10% to 30% of the area of ​​the active material layer.

11. A secondary battery comprising the negative electrode sheet according to any one of claims 1 to 7.

12. An electric device comprising the secondary battery according to claim 11.

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