A positive electrode sheet, a battery, and an electric device

Abstract

The application discloses a positive plate, a battery and an electric device, and belongs to the technical field of battery material preparation. Specifically, the application coats an electric resistance layer on both sides of a current collector, and the electric resistance layer is coated at the edge position of the middle active material layer, so that the impedance of the edge position of the positive plate is increased, the lithium ion extraction ability of the corresponding area of the positive plate is reduced, and the lithium precipitation risk of the edge of the plate is reduced. More importantly, the thickness ratio of the electric resistance layer to the middle active material layer, the size ratio along the first direction, and the specific structure of the coating are optimized, and an optimal design and interval are proposed. When the design range meets the corresponding formula, the overall performance of the battery cell can be improved without deteriorating the overall performance of the battery cell, and the lithium precipitation problem of the edge of the battery cell can be improved.

Description

Technical Field

[0001] This invention relates to a positive electrode, a battery, and an electrical device, belonging to the field of battery technology. Background Technology

[0002] With increasing environmental pollution, the new energy industry is attracting more and more attention. Within this industry, battery technology is a crucial factor in its development. The development of battery technology requires consideration of various design factors, such as energy density and cycle life.

[0003] Due to the inherent structure of lithium-ion batteries, the negative electrode needs to be designed to be larger than the positive electrode to meet the manufacturing requirements. At the edge of the positive electrode opposite the negative electrode, lithium deposition often occurs at the edge of the corresponding negative electrode due to high-rate charging and discharging, which is called edge lithium deposition. This seriously affects the cycle life and safety of high-rate charging and discharging lithium-ion batteries. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a positive electrode and a lithium-ion battery that can improve the edge lithium plating problem of the negative electrode.

[0005] One object of the present invention is to provide a positive electrode plate, the positive electrode plate comprising: The positive current collector includes a coating portion and an electrode tab connected sequentially along a first direction; A coating is disposed on at least one side of the coated portion along its thickness direction; the coating includes an intermediate active material layer and an edge layer, wherein the edge layer is connected to both sides of the intermediate active material layer along the first direction; The edge layer includes an edge active material layer and a resistive layer stacked along the thickness direction of the coating portion, wherein the edge active material layer is disposed on the side of the resistive layer away from the coating portion; Where λ = [d2 / (d2-d1)] (R1 / R2)^0.5, 1.24<λ<3, the impedance of the resistive layer is R1, the impedance of the intermediate active material layer is R2; the thickness of the intermediate active material layer is d2, and the thickness of the resistive layer is d1.

[0006] Furthermore, in the coating, the two resistive layers have the same structure.

[0007] Furthermore, in the coating, the dimension of the edge layer disposed near the positive electrode tab along the first direction is smaller than the dimension of the edge layer disposed away from the positive electrode tab along the first direction; the thickness of the two resistive layers is the same.

[0008] Furthermore, in the coating, the ratio of the dimension of the edge layer disposed near the positive electrode tab along the first direction to the dimension of the edge layer disposed away from the positive electrode tab along the first direction is 0.5 to 0.9.

[0009] Furthermore, the ratio of the thickness d1 of the resistive layer to the thickness d2 of the intermediate active material layer is 0.1 to 0.4; the thickness d1 of the resistive layer ranges from 3 μm to 30 μm.

[0010] Furthermore, the ratio of the impedance R1 of the resistive layer to the impedance R2 of the intermediate active material layer is 1.25 to 2.25.

[0011] Furthermore, the size of the resistive layer along the first direction ranges from 10mm to 30mm.

[0012] The present invention also provides a battery cell comprising the above-mentioned positive electrode sheet.

[0013] Furthermore, it also includes a housing, which has a first wall disposed toward the positive electrode tab and a second wall disposed opposite to the first wall along a first direction; the distance from the end of the coated portion of the positive electrode sheet near the positive electrode tab to the first wall is a, the distance from the end of the coated portion of the positive electrode sheet away from the positive electrode tab to the second wall is b, the distance from the end of the intermediate active material layer near the positive electrode tab to the first wall is c, and the distance from the end of the intermediate active material layer away from the positive electrode tab to the second wall is d, where a > b and c = d. The present invention also provides an electrical device comprising a single battery cell.

[0014] The beneficial effects of this invention are: In this invention, a resistive layer is pre-coated at the edge of the positive electrode current collector. While conforming to the design range of the corresponding formula, the coating amount of positive electrode active material at the edge is reduced, the total amount of lithium ions is reduced, the risk of lithium plating at the electrode edge is reduced, and the energy density of the battery is not degraded. Attached Figure Description

[0015] Figure 1-3 This is a schematic diagram of the positive electrode structure in one embodiment of the present invention.

[0016] Figure 4 This is a schematic diagram of the battery structure in this invention.

[0017] Figure 5 This illustrates the effect of the resistive layer thickness on the battery energy density.

[0018] Figure 6 The effect of the size of the resistive layer along the first direction on the battery energy density. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0020] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0021] It is important to note that 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 the specific range. Ranges defined in this way can include endpoints or exclude endpoints, and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. Any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value, or with other lower or upper limits, to form an unspecified range.

[0022] For example, if ranges of 6-12 and 8-11 are listed for specific parameters, it is understood that ranges of 6-11 and 8-12 are also expected. Furthermore, if the minimum range values ​​are listed as 1 and 2, and the maximum range values ​​are listed as 3, 4, and 5, 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 “1-5” means that all real numbers between “1-5” have been listed herein; “1-5” is simply a shortened representation of these numerical combinations. Additionally, when a parameter is stated as an integer ≥3, it is equivalent to disclosing that the parameter is, for example, an integer 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. In this application, “about” a numerical value represents a range, indicating a range of ±9% of that value.

[0023] A battery module is formed by electrically connecting a certain number of battery cells together and placing them in a frame to protect them from external impacts, heat, vibration, etc. A battery pack is the final state of the battery system installed in an electric vehicle. Currently, most battery packs are made by assembling a battery management system (BMS), thermal management components, and other control and protection systems onto one or more battery modules. With technological advancements, the battery module layer can be omitted, meaning that the battery pack can be formed directly from battery cells. This improvement increases the gravimetric and volumetric energy density of the battery system while significantly reducing the number of components. The battery mentioned in this application includes battery cells, battery modules, or battery packs.

[0024] In this application, the battery cell may include lithium-ion secondary batteries, lithium-ion primary batteries, lithium-sulfur batteries, sodium-lithium-ion batteries, sodium-ion batteries, or magnesium-ion batteries, etc., and the embodiments of this application are not limited to these. The battery cell may be cylindrical, flat, cuboid, or other shapes, etc., and the embodiments of this application are not limited to these. Battery cells are generally divided into three types according to their packaging method: cylindrical battery cells, cuboid / square battery cells, and pouch battery cells, and the embodiments of this application are not limited to these.

[0025] A battery cell includes a casing, electrode assembly, and electrolyte. The electrode assembly and electrolyte are housed within the casing. The electrode assembly consists of a positive electrode, a negative electrode, and a separator. The battery cell primarily functions by the movement of metal ions between the positive and negative electrode plates. The positive electrode includes a positive current collector and a positive active material layer. The positive active material layer is coated on the surface of the positive current collector. The uncoated positive current collector protrudes beyond the coated positive current collector and serves as the positive electrode tab. The negative electrode includes a negative current collector and a negative active material layer. The negative active material layer is coated on the surface of the negative current collector. The uncoated negative current collector protrudes beyond the coated negative current collector and serves as the negative electrode tab.

[0026] In existing technologies, disassembly of electrode components reveals that lithium plating is more severe in the edge region of the negative electrode sheet than in the body region of the negative electrode sheet, and the higher the charging rate, the more pronounced the edge lithium plating phenomenon becomes.

[0027] This invention aims to improve the lithium plating problem at the edge of the negative electrode without degrading the battery's energy density. (See also...) Figure 1 and Figure 3A positive electrode sheet is proposed, comprising a positive current collector 1 and a coating 2. The positive current collector 1 includes a coating portion 12 and a positive electrode tab 11 connected sequentially along a first direction. The coating 2 is disposed on at least one side of the coating portion 12 along its thickness direction. In embodiments of the present invention, a coating 2 can be applied to one side of the coating portion 12 along its thickness direction, or a coating 2 can be applied to each side along its thickness direction. A single coating 2 includes an intermediate active material layer 21 and two edge layers 22. The intermediate active material layer 21 is connected to the edge layers 22 on both sides along the first direction. The edge layer 22 includes an edge active material layer 221 and a resistive layer 222 stacked along the thickness direction of the coating portion 12. The edge active material layer 221 is disposed on the side of the resistive layer 222 away from the coating portion 12.

[0028] It is understood that the first direction is the width direction of the coating portion 12, that is, the direction in which the positive electrode tab 11 extends outward relative to the coating portion 12. The positive electrode sheet is divided into a main body region and two edge regions along the first direction; in the edge regions, the resistive layer 222 is disposed in the coating portion 12, and the edge active material layer 221 is disposed on the side of the resistive layer 222 away from the coating portion 12; in the main body region, the intermediate active material layer 21 is disposed in the coating portion 12; the surface of the edge active material layer 221 facing away from the coating portion 12 and the surface of the intermediate active material layer 21 facing away from the coating portion 12 are flush.

[0029] In this invention, a resistive layer 222 is added between the coating portion 12 and the edge active material layer 221. This increases the impedance of the edge region of the positive electrode, reducing the rate of lithium ion extraction from the edge region of the positive electrode. It also reduces the amount of positive active material coating on the edge region of the positive electrode, reducing the total amount of lithium ions extracted from the edge region of the positive electrode, thereby ultimately reducing the risk of lithium plating on the edge region of the negative electrode.

[0030] Increasing the thickness of the resistive layer 222 will inevitably increase the impedance of the edge region of the positive electrode and reduce the total amount of lithium ions removed from the edge region of the positive electrode. Increasing the impedance of the resistive layer 222 will inevitably reduce the rate of lithium ion removal from the edge region of the positive electrode, but it will not necessarily reduce the total amount of lithium ions removed from the edge region of the positive electrode. Therefore, in order to reduce the risk of lithium plating in the edge region of the negative electrode while ensuring that the energy density of the battery is not deteriorated, the impedance and thickness of the resistive layer and the intermediate active material layer can be optimized to give full play to the synergistic effect of the rate and the total amount of lithium ions removed.

[0031] Specifically, the optimization of the resistive layer 222 and the intermediate active material layer 21 needs to satisfy λ = [d2 / (d2-d1)]. (R1 / R2)^0.5, where d1 is the thickness of the resistive layer 222, d2 is the thickness of the intermediate active material layer 21, R1 is the impedance of the resistive layer 222, and R2 is the impedance of the intermediate active material layer 21. When 1.24 < λ < 3, the risk of lithium plating at the edge of the negative electrode can be reduced while ensuring that the energy density of the battery is not degraded. Preferably, λ can be in the range of 1.4 to 2.4; of course, λ can also be in the range of 1.4 to 2.3, or in the range of 1.5 to 2.4, or in the range of 1.5 to 2.3. Specifically, the value of λ can be 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, or 2.4.

[0032] Furthermore, if the resistive layer coating thickness on any side edge of the coating portion 12 is too large, it will result in less positive electrode active material in the edge region of the positive electrode, thereby deteriorating the energy density of the battery. If the resistive layer coating thickness on any side edge of the coating portion 12 is too small, the total amount of lithium ions released from the edge region of the positive electrode will still be large, which will still lead to lithium plating in the edge region of the negative electrode.

[0033] Thus, in order to balance the impedance of the edge region of the positive electrode and the total amount of lithium ions extracted from the edge region of the positive electrode, see [reference needed]. Figure 5 The thickness d1 of the resistive layer 222 on any side edge of the coating portion 12 is designed to be in the range of 3μm to 30μm. Also, at any side edge of the coating portion 12, the ratio of the thickness d1 of the resistive layer 222 to the thickness d2 of the intermediate active material layer 21 is 0.1 to 0.4. In other words, while the thickness of the resistive layer 222 is in the range of 3μm to 30μm, the ratio of the thickness d1 of the resistive layer 222 to the thickness d2 of the intermediate active material layer 21 must be in the range of 0.1 to 0.4 in order to ensure that the energy density of the battery is not degraded.

[0034] Preferably, the ratio of the thickness d1 of the resistive layer 222 to the thickness d2 of the intermediate active material layer 21 is 0.15 to 0.3. Specifically, the ratio of the thickness d1 of the resistive layer 222 to the thickness d2 of the intermediate active material layer 21 can be 0.18, 0.2, 0.23, 0.25, 0.28, etc.

[0035] Preferably, the thickness d1 of the resistive layer 222 is in the range of 5μm to 15μm. Specifically, the thickness d1 of the resistive layer 222 can be 6μm, 8μm, 10μm, 12μm, 14μm, etc.

[0036] For example, if the ratio of the thickness d1 of the resistive layer 222 to the thickness d2 of the intermediate active material layer 21 is 0.2, and the thickness d1 of the resistive layer is 12 μm, then the thickness d2 of the intermediate active material layer 21 is 60 μm, and the thickness of the edge active material layer is 48 μm.

[0037] Furthermore, when the dimension of the resistive layer 222 along the first direction at any edge of the coating portion 12 is too large, the amount of positive electrode active material lost is greater, thereby deteriorating the energy density of the battery. Conversely, when the dimension of the resistive layer 222 along the first direction at any edge of the coating portion 12 is too small, the improvement on lithium plating at the edge of the negative electrode is not significant enough, reducing the benefit of setting the resistive layer 222 and weakening the improvement on the cycle performance of the lithium-ion battery. Therefore, see... Figure 6 It is necessary to control the dimension of the resistive layer 222 along the first direction on any side edge of the resistive layer 222 to be within the range of 10mm to 30mm, so as to achieve an optimal balance between the improvement effect of lithium plating at the edge of the negative electrode and the energy density loss of the lithium-ion battery, thereby significantly improving the lithium plating phenomenon at the edge of the negative electrode while minimizing the degradation of the battery's energy density. Specifically, the dimension of the resistive layer 222 along the first direction can be 10mm, 13mm, 16mm, 21mm, 24mm, 27mm, 30mm, etc.

[0038] Furthermore, given that the thickness and dimensions of the resistive layer 222 along the first direction are controlled within a suitable range, to avoid excessive heat loss in the battery due to excessive impedance in the edge region of the positive electrode, which would affect the battery's operating voltage and discharge time, and to avoid insufficient impedance in the edge region of the positive electrode, which would fail to effectively reduce the risk of lithium plating in the edge region of the negative electrode, the ratio of the impedance R1 of the resistive layer 222 to the impedance R2 of the intermediate active material layer 21 is designed to be 1.25 to 2.25. Specifically, the ratio of the impedance R1 of the resistive layer 222 to the impedance R2 of the intermediate active material layer 21 is 1.5, 1.75, 2, etc.

[0039] In some embodiments, to reduce the manufacturing cost of the slurry and coating equipment, and to improve coating efficiency, the solid content and solid composition of the resistive layer 222 in both edge layers 22 are designed to be consistent. Specifically, the solid content of the resistive layer 222 is 30%~40%. Based on the mass percentage of the solid component in the resistive layer 222 being 100%, the resistive layer 222 contains 10wt%-30wt% polymer material, 40wt%-80wt% conductive material, and 10wt%-30wt% inorganic material. Of course, those skilled in the art will understand that this is only a preferred range; as long as the above definition of λ is met, even exceeding this range can at least mitigate the risk of edge lithium plating.

[0040] The polymeric material provides at least the adhesive strength of the coating and is one or more selected from polyvinylidene fluoride (PVDF) and its copolymers, polyacrylates, polymethyl methacrylates, polystyrene, and polyacrylonitrile. PVDF is preferred, and it should be consistent with conventional positive electrode active material coating adhesives. The conductive material provides at least the conductivity and can be selected from at least one of conductive carbon-based materials, including conductive carbon black, acetylene black, graphite, graphene, carbon nanotubes, and carbon nanofibers; conductive carbon black, acetylene black, graphene, and carbon nanotubes are preferred. The inorganic material can serve as the coating framework and reduce the conductivity of the coating, and can be selected from at least one of magnesium oxide, alumina, titanium dioxide, zirconium oxide, silicon dioxide, silicon carbide, boron carbide, calcium carbonate, aluminum silicate, calcium silicate, and potassium titanate. Alumina, silicon dioxide, and silicon carbide are preferred.

[0041] In the formula of the resistive layer after curing and drying, The mass percentage of polymeric materials is 10% to 30%, such as 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, etc., including but not limited to the above percentages, with 15% to 25% being preferred; The conductive material has a mass ratio of 40% to 80%, such as 41%, 42%, 43%, 44%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 76%, 77%, 78%, 79%, etc., including but not limited to the above ratios, with 50% to 70% being preferred; The mass ratio of inorganic materials is 10% to 30%, such as 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, etc., including but not limited to the above ratios, with 15% to 25% being preferred.

[0042] In some embodiments, for ease of coating control, the two resistive layers 222 in the coating 2 are designed to have identical structures; that is, the resistive layers 222 located at the two edges of the coating portion 2 are symmetrically arranged. For example, see... Figure 1 As shown, in coating 2, the two resistive layers 222 have the same dimensions along the first direction, the two resistive layers 222 have the same thickness, and the contact surface of each resistive layer 222 and the corresponding edge active material layer 221 is arranged parallel to the first direction.

[0043] Of course, in some other embodiments, considering the actual situation that the positive electrode does not exist independently, but needs to be housed in the housing together with the negative electrode and the separator to form an electrode assembly, the inventors found that the problem of lithium plating at the edge of the negative electrode is not only due to the design of the electrode assembly structure itself, but also related to the constraint of the battery housing on the electrode assembly.

[0044] Specifically, see Figure 4 The lithium-ion battery also includes a housing 3 and an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The positive tab 11 of the positive electrode and the negative tab of the negative electrode are located on the same layer of the electrode assembly. The electrode assembly is disposed inside the housing 3. The housing 3 has a first wall 31 facing the positive tab 11 of the positive electrode and a second wall 32 opposite to the first wall 31 along a first direction. A lower plastic part for insulation is disposed between the first wall 31 and the electrode assembly. A bottom support piece for lifting the electrode assembly to avoid interference with the arc corner of the bottom of the housing is disposed between the second wall 32 and the electrode assembly. A positive electrode post and a negative electrode post are disposed on the first wall 31. The positive electrode post and the positive tab are electrically connected, and the negative electrode post and the negative tab are electrically connected. The distance from the end of the coating portion of the positive electrode near the positive tab 11 to the first wall 31 is a, and the distance from the end of the coating portion of the positive electrode away from the positive tab 11 to the second wall 32 is b. The distance a is greater than the distance b.

[0045] As the inventors know, during the charging and discharging process of lithium-ion batteries, lithium ions undergo cyclic insertion and extraction reactions on the positive and negative electrodes, causing the electrodes to expand. Since the electrode assembly is housed within a casing, this casing restricts the expansion of the electrode assembly. Consequently, the electrolyte absorbed by the positive and negative electrodes and the separator is squeezed out, hindering lithium ion transport during cycling and leading to lithium plating on the electrode assembly. This severely affects the battery's cycle performance and lifespan.

[0046] As described above and as known to the inventors, the inventors have discovered that due to the distribution of structural strength of the shell itself, that is, along the first direction, the strength at both ends of the shell is much greater than the strength at the middle of the shell. In other words, the distribution of the binding force of the shell on the electrode assembly is such that the binding force on the electrode assembly is small at the middle of the shell and large at both ends of the shell. That is, the closer to the two ends of the shell, the greater the binding force of the shell on the electrode assembly.

[0047] Therefore, in order to adapt to the distribution of the binding force of the casing on the electrode assembly, that is, to accommodate the different lithium plating widths on both sides of the negative electrode, while satisfying the thickness of the resistive layer 222 and the dimensional design along the first direction, see [reference needed]. Figure 2As shown, in coating 2, the dimension of the edge layer 22 disposed near the positive electrode tab 11 along the first direction is smaller than the dimension of the edge layer 22 disposed away from the positive electrode tab 11 along the first direction; the two resistive layers 222 have the same thickness, thus improving the lithium plating phenomenon at the edge of the negative electrode while minimizing the impact on the energy density of the battery.

[0048] Furthermore, in coating 2, the ratio of the dimension of the edge layer 22 disposed near the positive electrode tab 11 along the first direction to the dimension of the edge layer 22 disposed away from the positive electrode tab 11 along the first direction is 0.5 to 0.9. Specifically, the ratio of the dimension of the edge layer 22 disposed near the positive electrode tab 11 along the first direction to the dimension of the edge layer 22 disposed away from the positive electrode tab 11 along the first direction can be 0.5, 0.6, 0.7, 0.8, 0.9, etc.

[0049] Of course, for optimal design, the distance from the end of the intermediate active material layer 21 closest to the positive electrode tab 11 to the first wall is c, and the distance from the end of the intermediate active material layer 21 furthest from the positive electrode tab 11 to the second wall is d, where c = d (see...). Figure 4 (As shown).

[0050] In some embodiments, both the intermediate active material layer 21 and the edge active material layer 221 contain the following components by mass percentage: 75-95% positive electrode active material, 1-15% conductive agent and 1-15% binder.

[0051] The positive electrode active material can be one or more of lithium cobalt oxide, lithium iron phosphate, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, and lithium titanate. For example, the positive electrode active material can be obtained by mixing lithium cobalt oxide and lithium iron phosphate in a certain mass percentage, or by mixing nickel-cobalt-manganese ternary materials and lithium titanate in a certain mass percentage, or by using lithium cobalt oxide, lithium iron phosphate, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, or lithium titanate alone as the positive electrode active material. This invention does not impose specific limitations.

[0052] The conductive agent can be one or more of the following: conductive carbon black, conductive graphite, acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fiber.

[0053] The adhesive can be any adhesive well known to those skilled in the art, without any special limitations, such as chitosan, xanthan gum, gellan gum, gum arabic, polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium carboxymethyl cellulose, polymethacrylamide, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, polyacrylamide, styrene-butadiene rubber, sodium alginate, polyethylene glycol, guar gum, guar gum polymers and guar gum copolymers. In the embodiments of this invention, PVDF is selected.

[0054] In some embodiments, the thickness of the positive electrode current collector is selected in the range of 4μm to 20μm, preferably 8μm to 16μm, such as conventionally selected 10μm, 12μm, 13μm, 16μm, etc. The positive electrode current collector is made of aluminum foil.

[0055] In summary, this application also provides a battery, which includes a positive electrode and a negative electrode; the positive electrode is the positive electrode described above.

[0056] Since the battery of this application includes the positive electrode plate described above, the beneficial effects of the positive electrode plate on the battery are described above and will not be repeated here.

[0057] In some embodiments, the lithium-ion battery further includes a negative electrode sheet, wherein the slurry of the negative electrode active material layer of the negative electrode sheet contains the following components in parts by weight: 90-99 wt% negative electrode active material, 0.01-3 wt% thickener, 0.01-3 wt% binder, and 0.01-3 wt% conductive agent.

[0058] The type of negative electrode active material in the negative electrode active material layer is not limited and can be selected according to requirements. As an example, the negative electrode active material includes at least one of natural graphite, artificial graphite, hard carbon, soft carbon, silicon, and silicon-carbon composites.

[0059] The conductive agent in the negative electrode active material layer includes, but is not limited to, at least one of acetylene black, Ketjen black, CNT, SWCNT, Super p, VGCF, and graphene; the binder in the negative electrode active material layer includes, but is not limited to, styrene-butadiene rubber (SBR); and the thickener in the negative electrode active material layer includes, but is not limited to, carboxymethyl cellulose or its inorganic salt.

[0060] In some embodiments, the lithium-ion battery further includes a separator membrane. The separator membrane can be any type of separator membrane known to those skilled in the art and is not particularly limited, such as one or more of polyethylene, polypropylene, polyacrylonitrile, polyacrylonitrile fiber, polyamic acid, polyimide, polyamide, polydopamine, polyarylethersulfone, polyvinylidene fluoride, polyethylene oxide, polyethylene terephthalate, polyester, nonwoven fabric membrane, and cellulose paper-based separator membrane.

[0061] In some embodiments, the lithium-ion battery further includes an electrolyte, which can be any electrolyte well known to those skilled in the art and is not particularly limited. The solvent is at least one of methyl ethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, and diethylene glycol diethanol ether; the electrolyte salt is at least one of sodium perchlorate, sodium bis(oxalate)borate, and sodium hexafluorophosphate.

[0062] The technical solutions described in the embodiments of this application are applicable to various battery-powered devices, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, electric vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0063] Example 1 1. Preparation of positive electrode: A. Polymer materials, conductive materials, and inorganic materials are added to a certain mass of N-methylpyrrolidone (NMP) in a certain mass ratio and mixed evenly until they are evenly dispersed to obtain a slurry for the resistive layer. The solid content is 35%, and based on the mass percentage of the solid components in the resistive layer 222 being 100%, the resistive layer 222 contains 25wt% silicon dioxide, 50wt% conductive carbon black, and 25wt% polyvinylidene fluoride. The slurry is then coated onto aluminum foil (10μm thick) to obtain an aluminum foil with a resistive layer.

[0064] B. A positive electrode active material slurry is prepared by thoroughly mixing 95 wt% lithium iron phosphate, 3 wt% conductive agent, and 2 wt% binder in a certain amount of N-methylpyrrolidone, with a solid content of 73%. The positive electrode active material slurry is then coated onto the aluminum foil using a coating machine. Following drying, rolling, slitting, and die-cutting, a positive electrode sheet is obtained. The positive electrode sheet must meet the following requirements: It includes a positive electrode current collector, which comprises a positive electrode tab 11 and a coating portion 12. A resistive layer is disposed on any edge of the coating portion 12. The coating portion is positioned along a first direction... The size is 280mm, and the dimension of the resistive layer on any side edge along the first direction is 10mm. The thickness d1 of the resistive layer on any side edge of the coating part is 9μm. An intermediate active material layer 21 is provided on the side of each resistive layer away from the coating part 12. An intermediate active material layer 21 is provided on the coating part 12 and located between the two resistive layers. The thickness d2 of the intermediate active material layer 21 is 60μm. The ratio of the impedance R1 of the resistive layer on any side edge of the coating part to the impedance R2 of the intermediate active material layer 21 is 1.375, that is, λ=1.38.

[0065] 2. Preparation method of negative electrode sheet: 95wt% artificial graphite, 2wt% conductive agent, 2.6wt% SBR, 0.4wt% CMC binder are mixed evenly in deionized water according to a certain weight ratio to prepare negative electrode active material slurry with a solid content of 56%.

[0066] 3. Test battery preparation method: The negative electrode sheet, the positive electrode sheet, and the separator (polyethylene film with a thickness of 9μm) obtained in the above steps are wound into a core, placed in a soft pack, baked to remove moisture, and then injected with electrolyte [LiPF6 lithium salt is dissolved in a solvent to prepare a 1mol / L electrolyte, organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): ethylene carbonate (VC) = 30:40:28:2, mass ratio)], and the test battery is obtained after hot pressing formation process.

[0067] Example 2 The difference between Example 2 and Example 1 is that the thickness d1 of the resistive layer is 18 μm, and the ratio of the impedance R1 of the resistive layer to the impedance R2 of the intermediate active material layer is 1.75; that is, λ=1.89.

[0068] Example 3 The difference between Example 3 and Example 1 is that the thickness d1 of the resistive layer is 24 μm, and the ratio of the impedance R1 of the resistive layer to the impedance R2 of the intermediate active material layer is 2; that is, λ=2.36.

[0069] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the thickness d1 of the resistive layer is 0 μm, the dimension of the resistive layer along the first direction is 0 μm, and the ratio of the impedance R1 of the resistive layer to the impedance R2 of the intermediate active material layer is 0; that is, λ=0.

[0070] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the thickness d1 of the resistive layer is 6 μm, and the ratio of the impedance R1 of the resistive layer to the impedance R2 of the intermediate active material layer is 1.25; that is, λ=1.24.

[0071] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the thickness d1 of the resistive layer is 30 μm, and the ratio of the impedance R1 of the resistive layer to the impedance R2 of the intermediate active material layer is 2.25; that is, λ=3.

[0072] The test batteries of Examples 1 to 3 and Comparative Examples 1 to 3 prepared above were subjected to the following performance tests, and the test procedures were as follows: (1) Energy density test: Battery energy density: The battery under test was left to stand at 25°C for 30 minutes, then charged at a constant current rate of 0.33C until the voltage reached the rated voltage. Subsequently, it was charged at a constant voltage until the charge / discharge rate reached 0.05C, at which point charging was stopped. The battery was then left at room temperature for 30 minutes, and then discharged at a rate of 0.33C to 2.5V. The resulting capacity is taken as the actual battery energy C, in Wh. This is then divided by the cell weight W, in kg, to obtain the battery energy density VED = C / W, in Wh / kg.

[0073] (2) Testing lithium plating Under a constant temperature environment of 25℃, the battery was charged to 4.25V with a constant current of 1C, then charged to 0.05C with a constant voltage of 4.25V, and then discharged to 2.8V with a constant current of 1C. This charge-discharge cycle was repeated until the 500th cycle. After the battery was fully charged at 25℃ for 500 cycles, the individual battery cells were disassembled, and the lithium plating state at the interface of the negative electrode edge was observed.

[0074] No lithium plating: golden yellow at the interface.

[0075] Point-like lithium deposition: The length and width of the lithium deposition area are both <1mm, and the number on a single side is <5; Linear lithium plating: The width of the lithium plating region is <3mm, and the length is >10mm; Planar lithium plating: The width of the lithium plating region is >3 mm; The results are as follows: Table 1

[0076] As can be seen from Table 1: The data above shows that the lower the λ value, the more severe the edge lithium plating; the higher the λ value, the more severe the deterioration of energy density. When 1.24 < λ < 3 (Examples 1-3), not only does the total amount of lithium ions released from the edge region of the positive electrode decrease, but the rate of lithium ion release from the edge region of the positive electrode also slows down, thus preventing lithium plating from occurring in the edge region of the negative electrode. Moreover, the energy density of Examples 1-3 is almost the same as that of Comparative Example 1, so it can be considered that there is almost no loss in the energy density of the battery.

[0077] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A positive electrode plate, characterized in that, include: The positive current collector (1) includes a coating portion (12) and a positive electrode tab (11) connected sequentially along a first direction. A coating (2) is disposed on at least one side of the coated portion (12) along its thickness direction; the coating (2) includes an intermediate active material layer (21) and an edge layer (22), wherein the intermediate active material layer (21) is connected to the edge layer (22) on both sides along the first direction. The edge layer (22) includes an edge active material layer (221) and a resistive layer (222) stacked along the thickness direction of the coating portion (12), wherein the edge active material layer (221) is disposed on the side of the resistive layer (222) away from the coating portion (12); In the coating (2), the ratio of the dimension of the edge layer (22) disposed near the positive electrode tab (11) along the first direction to the dimension of the edge layer (22) disposed away from the positive electrode tab (11) along the first direction is 0.5 to 0.9; The ratio of the thickness d1 of the resistive layer (222) to the thickness d2 of the intermediate active material layer (21) is 0.1 to 0.4; the thickness d1 of the resistive layer (222) ranges from 3 μm to 30 μm. The ratio of the impedance R1 of the resistive layer (222) to the impedance R2 of the intermediate active material layer (21) is 1.25~2.25; The size of the resistive layer (222) along the first direction ranges from 10mm to 30mm.

2. The positive electrode sheet according to claim 1, characterized in that, In the coating (2), the two resistive layers (222) have the same structure.

3. The positive electrode sheet according to claim 1, characterized in that, The two resistive layers (222) have the same thickness.

4. A battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 1-3.

5. The battery according to claim 4, characterized in that, It also includes a housing, which has a first wall disposed toward the positive electrode tab (11) and a second wall disposed opposite to the first wall along a first direction; the distance from the end of the coating portion (12) of the positive electrode sheet near the positive electrode tab (11) to the first wall is a, the distance from the end of the coating portion (12) of the positive electrode sheet away from the positive electrode tab (11) to the second wall is b, the distance from the end of the intermediate active material layer (21) near the positive electrode tab (11) to the first wall is c, and the distance from the end of the intermediate active material layer (21) away from the positive electrode tab (11) to the second wall is d, wherein a > b and c = d.

6. An electrical appliance, characterized in that, Includes the battery as described in claim 4 or 5.

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