Positive plate, battery and electric equipment

Abstract

The invention discloses a positive plate, a battery and electric equipment, and belongs to the technical field of battery material preparation. Specifically, the two sides of the current collector are coated with the resistance layers, and the resistance layers are correspondingly coated on the edge position of the middle active material layer, so that the impedance of the edge position of the positive electrode can be increased, the lithium ion de-intercalation capability of the positive electrode in the corresponding area is reduced, and the lithium precipitation risk of the edge of the pole piece is reduced. More importantly, the thickness ratio of the resistive layer to the middle active material layer, the size ratio in the first direction and the specific structure of the coating are optimized, the optimal design and interval are provided, and when the design range of a corresponding formula is met, the overall performance of the battery cell cannot be deteriorated, and the problem of lithium precipitation at the edge of the battery cell can be solved.

Description

Technical Field

[0001] The present invention relates to a positive electrode sheet, a battery and an electrical device, belonging to the technical field of batteries. Background Art

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

[0003] In related technologies, 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 process requirements. However, lithium deposition often occurs at the edge of the negative electrode where the positive electrode is opposite to the negative electrode due to high-rate charge and discharge, which is called edge lithium deposition. This phenomenon seriously affects the cycle life and safety of high-rate charge and discharge lithium-ion batteries. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a positive electrode sheet and a lithium-ion battery that can improve the problem of lithium plating at the edge of the negative electrode sheet.

[0005] An object of the present invention is to provide a positive electrode sheet, comprising:

[0006] A positive electrode current collector comprising a coating portion and a tab sequentially connected along a first direction;

[0007] a coating layer disposed on at least one side of the coating portion along a thickness direction thereof; the coating layer comprising an intermediate active material layer and an edge layer, wherein both sides of the intermediate active material layer along the first direction are connected to the edge layers;

[0008] The edge layer includes an edge active material layer and a resistance layer stacked along the thickness direction of the coating portion, wherein the edge active material layer is arranged on a side of the resistance layer away from the coating portion;

[0009] Wherein, λ=[d2 / (d2-d1)]*(R1 / R2)^0.5, 1.24<λ<3, the impedance of the resistance layer is R1, and 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 resistance layer is d1.

[0010] Furthermore, in the coating layer, the two resistance layers have the same structure.

[0011] Furthermore, in the coating, a dimension of an edge layer disposed close to the positive electrode tab along the first direction is smaller than a dimension of an edge layer disposed away from the positive electrode tab along the first direction; and the two resistance layers have the same thickness.

[0012] Furthermore, in the coating, a ratio of a size of an edge layer disposed close to the positive electrode tab along the first direction to a size of an edge layer disposed away from the positive electrode tab along the first direction is 0.5 to 0.9.

[0013] Furthermore, the ratio of the thickness d1 of the resistance layer to the thickness d2 of the intermediate active material layer is 0.1 to 0.4; and the thickness d1 of the resistance layer is in the range of 3 μm to 30 μm.

[0014] Furthermore, a ratio of the impedance R1 of the resistance layer to the impedance R2 of the intermediate active material layer is 1.25 to 2.25.

[0015] Furthermore, the size of the resistance layer along the first direction ranges from 10 mm to 30 mm.

[0016] The present invention also provides a battery cell comprising the above positive electrode sheet.

[0017] Furthermore, it also includes a shell, which has a first wall arranged toward the positive electrode ear and a second wall arranged opposite to the first wall along a first direction; the distance from the end of the coated portion of the positive electrode sheet arranged close to the positive electrode ear to the first wall is a, the distance from the end of the coated portion of the positive electrode sheet arranged away from the positive electrode ear to the second wall is b, the distance from the end of the intermediate active material layer arranged close to the positive electrode ear to the first wall is c, and the distance from the end of the intermediate active material layer arranged away from the positive electrode ear to the second wall is d, wherein a>b, and c=d. The present invention also provides an electrical device comprising a battery cell.

[0018] Beneficial effects of the present invention:

[0019] In the present invention, a resistance layer is pre-coated at the edge of the positive electrode current collector. When the design range of the corresponding formula is met, the coating amount of the positive electrode active material at the edge is reduced, the total amount of lithium ions released is reduced, and the risk of lithium plating at the edge of the electrode is reduced, while not deteriorating the energy density of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1-3 Schematic diagram of the positive electrode structure in one embodiment of the present invention.

[0021] Figure 4 Schematic diagram of the structure of the battery in the present invention.

[0022] Figure 5 The effect of the thickness of the resistance layer on the battery energy density.

[0023] Figure 6 The influence of the size of the resistance layer along the first direction on the battery energy density. DETAILED DESCRIPTION

[0024] 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 the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0025] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0026] It should be noted that the "ranges" disclosed in this application are defined in the form of lower limits and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. Ranges defined in this way can be inclusive or exclusive of the end values and can be combined arbitrarily, 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, and similarly, any upper limit can be combined with any other upper limit to form an unspecified range. In addition, although not explicitly stated, each point or single value between the endpoints of the range is included in the range. Thus, each point or single value can be combined as its own lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unspecified range.

[0027] For example, if ranges of 6-12 and 8-11 are listed for a particular parameter, it is understood that ranges of 6-11 and 8-12 are also contemplated. Furthermore, if minimum range values of 1 and 2 are listed, and if maximum range values of 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. Throughout this application, unless otherwise indicated, the numerical range "ab" is a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "1-5" indicates that all real numbers between "1-5" are listed herein, and "1-5" is merely a shorthand representation of these numerical combinations. Furthermore, when a parameter is stated as an integer greater than or equal to 3, this is equivalent to disclosing that the parameter is, for example, an integer of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. Throughout this application, "about" a numerical value indicates a range, meaning a range of ±9% of that value.

[0028] The battery module is formed by electrically connecting a certain number of battery cells together and placing them in a frame in order to protect the battery cells from external impact, heat, vibration, etc. The battery pack is the final state of the battery system installed in the electric vehicle. Most of the current battery packs are made by assembling various control and protection systems such as battery management systems (BMS) and thermal management components on one or more battery modules. With the development of technology, the battery module level can be omitted, that is, the battery pack is directly formed from battery cells. This improvement has improved the weight energy density and volume energy density of the battery system while significantly reducing the number of components. The batteries mentioned in this application include battery cells, battery modules or battery packs.

[0029] In this application, battery cells 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 do not limit this. Battery cells may be cylindrical, flat, rectangular, or other shapes, etc., and the embodiments of this application do not limit this. Battery cells are generally divided into three types based on the packaging method: cylindrical battery cells, prismatic battery cells, and soft-pack battery cells, and the embodiments of this application do not limit this.

[0030] A battery cell includes a housing, an electrode assembly, and an electrolyte. The electrode assembly and electrolyte are disposed within the housing. The electrode assembly consists of a positive electrode sheet, a negative electrode sheet, and a separator. A battery cell primarily operates by the movement of metal ions between the positive and negative electrode sheets. The positive electrode sheet 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 positive current collector uncoated with the positive active material layer protrudes from the positive current collector coated with the positive active material layer, and the positive current collector uncoated with the positive active material layer serves as the positive electrode tab. The negative electrode sheet 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 negative current collector uncoated with the negative active material layer protrudes from the negative current collector coated with the negative active material layer, and the negative current collector uncoated with the negative active material layer serves as the negative electrode tab.

[0031] In the prior art, disassembling the electrode assembly revealed that lithium deposition in the edge area of the negative electrode sheet of the lithium-ion battery is more serious than in the main area of the negative electrode sheet, and the greater the charging rate, the more obvious the edge lithium deposition phenomenon is.

[0032] The present invention aims to improve the problem of lithium deposition at the edge of the negative electrode without deteriorating the energy density of the battery. Figure 1 and Figure 3A positive electrode sheet is proposed, comprising a positive electrode current collector 1 and a coating 2. The positive electrode current collector 1 comprises a coating portion 12 and a positive electrode tab 11 connected in sequence along a first direction. The coating 2 is disposed on at least one side of the coating portion 12 along its thickness direction. In an embodiment of the present invention, a single coating 2 may be applied to one side of the coating portion 12 along its thickness direction, or a coating 2 may be applied to each side of the coating portion 12 along its thickness direction. A single coating 2 comprises an intermediate active material layer 21 and two edge layers 22. The intermediate active material layer 21 is connected to edge layers 22 on both sides along the first direction. The edge layers 22 comprise an edge active material layer 221 and a resistor 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 resistor layer 222 away from the coating portion 12.

[0033] It is understood that the first direction is the width of the coating portion 12, that is, the direction in which the positive electrode tab 11 extends outward from the coating portion 12. The positive electrode sheet is divided into a main region and two edge regions along the first direction. In the edge region, the resistor layer 222 is disposed on the coating portion 12, and the edge active material layer 221 is disposed on the side of the resistor layer 222 away from the coating portion 12. In the main region, the intermediate active material layer 21 is disposed on the coating portion 12. The surface of the edge active material layer 221 facing away from the coating portion 12 is flush with the surface of the intermediate active material layer 21 facing away from the coating portion 12.

[0034] In the present invention, a resistance layer 222 is added between the coating portion 12 and the edge active material layer 221. In this way, on the one hand, the impedance of the edge area of the positive electrode sheet can be increased, and the rate of lithium ion release from the edge area of the positive electrode sheet can be reduced. On the other hand, the coating amount of the positive electrode active material in the edge area of the positive electrode sheet can be reduced, and the total amount of lithium ions released from the edge area of the positive electrode sheet can be reduced, thereby ultimately reducing the risk of lithium plating in the edge area of the negative electrode sheet.

[0035] Among them, since the thickness of the resistance layer 222 is increased, the impedance of the edge area of the positive electrode sheet will inevitably increase, and the total amount of lithium ions released from the edge area of the positive electrode sheet will be reduced. Increasing the impedance of the resistance layer 222 will inevitably reduce the rate of lithium ion release from the edge area of the positive electrode sheet, but it will not necessarily reduce the total amount of lithium ions released from the edge area of the positive electrode sheet. Therefore, in order to reduce the risk of lithium plating in the edge area of the negative electrode sheet while ensuring that the energy density of the battery is not deteriorated, the impedance and thickness of the resistance layer and the intermediate active material layer can be optimized to give full play to the coordinated effect of the rate of lithium ion release and the total amount of lithium ion release.

[0036] Specifically, the optimization of the resistance layer 222 and the intermediate active material layer 21 needs to meet the following conditions:

[0037] [d2 / (d2-d1)]*(R1 / R2)^0.5, where d1 is the thickness of the resistor layer 222, d2 is the thickness of the intermediate active material layer 21, R1 is the impedance of the resistor layer 222, and R2 is the impedance of the intermediate active material layer 21. When 1.24<λ<3, the risk of lithium plating in the edge area of the negative electrode sheet can be reduced while ensuring that the energy density of the battery is not deteriorated. 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. The specific value of λ can be 1.4 or 1.5 or 1.6 or 1.7 or 1.8 or 1.9 or 2.0 or 2.1 or 2.2 or 2.3 or 2.4.

[0038] Furthermore, if the thickness of the resistive layer coating on any edge of the coating portion 12 is too great, the positive electrode active material will be less in the edge area of the positive electrode sheet, thereby deteriorating the energy density of the battery. If the thickness of the resistive layer coating on any edge of the coating portion 12 is too small, the total amount of lithium ions released from the edge area of the positive electrode sheet will still be high, which will still cause lithium deposition in the edge area of the negative electrode sheet.

[0039] Thus, in order to balance the impedance of the edge area of the positive electrode and the total amount of lithium ions released from the edge area of the positive electrode, see Figure 5 The thickness d1 of the resistance layer 222 at any side edge of the coating portion 12 is designed to be in the range of 3μm to 30μm, and the ratio of the thickness d1 of the resistance layer 222 to the thickness d2 of the intermediate active material layer 21 at any side edge of the coating portion 12 is 0.1 to 0.4. That is to say, while the thickness of the resistance layer 222 is in the range of 3μm to 30μm, the ratio to the thickness d2 of the intermediate active material layer 21 also needs to be in the range of 0.1 to 0.4, so as to ensure that the energy density of the battery is not deteriorated.

[0040] Preferably, the ratio of the thickness d1 of the resistance 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 resistance 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.

[0041] Preferably, the thickness d1 of the resistance layer 222 is in the range of 5 μm to 15 μm. Specifically, the thickness d1 of the resistance layer 222 may be 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, etc.

[0042] For example, the ratio of the thickness d1 of the resistance layer 222 to the thickness d2 of the intermediate active material layer 21 is 0.2, and the thickness d1 of the resistance 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.

[0043] Furthermore, when the size of the resistance layer 222 at any side edge of the coating portion 12 along the first direction is too large, the content of the positive electrode active material lost is greater, thereby deteriorating the energy density of the battery. When the size of the resistance layer 222 at any side edge of the coating portion 12 along the first direction is too small, the improvement of the lithium deposition phenomenon at the edge of the negative electrode sheet is not obvious enough, so that the benefit of setting the resistance layer 222 is reduced, and the improvement of the cycle performance of the lithium-ion battery is also weakened. Therefore, see Figure 6 The size of the resistor layer 222 along the first direction at any edge of the resistor layer 222 needs to be controlled within a range of 10 mm to 30 mm. This achieves an optimal balance between the improvement of lithium deposition at the edges of the negative electrode sheet and the loss of energy density in the lithium-ion battery. This significantly improves lithium deposition at the edges of the negative electrode sheet while minimizing the degradation of the battery's energy density. Specifically, the size of the resistor layer 222 along the first direction can be 10 mm, 13 mm, 16 mm, 21 mm, 24 mm, 27 mm, 30 mm, etc.

[0044] Furthermore, on the basis that the thickness and the dimension along the first direction of the resistance layer 222 have been controlled within an appropriate range, in order to avoid the impedance of the edge area of the positive electrode sheet being too large, which would cause excessive heat loss in the battery itself and affect the operating voltage and discharge time of the battery, and to avoid the impedance of the edge area of the positive electrode sheet being too small, which would fail to effectively reduce the risk of lithium deposition in the edge area of the negative electrode sheet. Thus, the ratio of the impedance R1 of the resistance layer 222 and 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 resistance layer 222 and the impedance R2 of the intermediate active material layer 21 is 1.5, 1.75, 2, etc.

[0045] In some embodiments, in order to reduce the manufacturing cost of the slurry and coating equipment, and to improve the coating efficiency, the solid content and solid components of the resistor layer 222 in the two edge layers 22 are designed to be consistent. Specifically, the solid content of the resistor layer 222 is 30% to 40%. Taking the mass percentage of the solid components in the resistor layer 222 as 100%, the resistor 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 if it exceeds this range, the risk of edge lithium deposition can at least be avoided.

[0046] Among them, the polymer material has at least the function of providing coating adhesion, and is one or more of polyvinylidene fluoride and its copolymers, polyacrylates, polymethacrylates, polystyrene and polyacrylonitrile. Polyvinylidene fluoride (PVDF) is preferred, which is consistent with the conventional positive electrode active material coating adhesive. The conductive material has at least the function of providing 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; preferably conductive carbon black, acetylene black, graphene, and carbon nanotubes. The inorganic material can serve as the coating skeleton and reduce the conductivity of the coating, and can be selected from at least one of magnesium oxide, aluminum oxide, titanium dioxide, zirconium oxide, silicon dioxide, silicon carbide, boron carbide, calcium carbonate, aluminum silicate, calcium silicate, and potassium titanate. Preferably aluminum oxide, silicon dioxide, and silicon carbide.

[0047] In the resistor layer formula after curing and drying,

[0048] The mass ratio of the polymer material is 10% to 30%, for example, 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, preferably 15% to 25%;

[0049] The mass ratio of the conductive material is 40% to 80%, for example, 41%, 42%, 43%, 44%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 76%, 77%, 78%, 79%, etc., including but not limited to the above ratios, preferably 50% to 70%;

[0050] The mass proportion of inorganic materials is 10% to 30%, for example, 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 proportions, preferably 15% to 25%.

[0051] In some embodiments, in order to facilitate coating control, the two resistance layers 222 in the coating layer 2 are designed to have the same structure, that is, the resistance layers 222 located on both sides of the coating portion 2 are symmetrically arranged. Figure 1 As shown, in the coating 2, the two resistance layers 222 have the same size along the first direction, the same thickness, and the contact surface between each resistance layer 222 and the corresponding edge active material layer 221 is parallel to the first direction.

[0052] Of course, in some other embodiments, taking into account the actual situation that the positive electrode sheet does not exist independently, but needs to be placed in the shell together with the negative electrode sheet and the isolation membrane to form an electrode assembly. That is to say, the inventors found that the problem of lithium deposition in the edge area of the negative electrode sheet is not only due to the design of the structure of the electrode assembly itself, but also related to the constraint of the battery shell on the electrode assembly.

[0053] Specifically, see Figure 4 The lithium-ion battery also includes a shell 3 and an electrode assembly, the electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, wherein the positive electrode ear 11 of the positive electrode sheet and the negative electrode ear of the negative electrode sheet are located on the same layer of the electrode assembly; the electrode assembly is arranged in the shell 3; the shell 3 has a first wall 31 arranged toward the positive electrode ear 11 of the positive electrode sheet and a second wall 32 arranged opposite to the first wall 31 along a first direction; a lower plastic part for insulation is arranged between the first wall 31 and the electrode assembly, and a bottom support sheet for lifting the electrode assembly to avoid interference with the arc angle at the bottom of the shell is arranged between the second wall 32 and the electrode assembly; a positive electrode column and a negative electrode column are arranged on the first wall 31, the positive electrode column and the positive electrode ear are electrically connected, and the negative electrode column and the negative electrode ear are electrically connected; wherein, the distance from the end of the coating part of the positive electrode sheet close to the positive electrode ear 11 to the first wall 31 is a, and the distance from the end of the coating part of the positive electrode sheet away from the positive electrode ear 11 to the second wall 32 is b, and the distance a is greater than the distance b.

[0054] As far as the inventors are aware, during the charging and discharging process of lithium-ion batteries, the electrodes expand due to the cyclic intercalation and deintercalation of lithium ions in the positive and negative electrodes. Since the electrode assembly is housed within a casing, the casing constrains this expansion. Consequently, electrolyte absorbed by the positive and negative electrodes, as well as the separator, is squeezed out. This hinders lithium ion transport during the cycle, leading to lithium deposition in the electrode assembly, severely impacting the battery's cycle performance and lifespan.

[0055] As described above and known to the inventors, the inventors have discovered that due to the structural strength distribution of the shell itself, that is, along the first direction, the strength at the two end edges of the shell is much greater than the strength in the middle of the shell. In other words, the distribution of the binding force of the shell on the electrode assembly is that the binding force on the electrode assembly in the middle of the shell is small, while the binding force on the electrode assembly at the two end edges is large, that is, the closer to the two end edges of the shell, the greater the binding force of the shell on the electrode assembly.

[0056] Therefore, in order to adapt to the distribution of the binding force of the shell on the electrode assembly, that is, to adapt to the different widths of lithium deposition in the edge areas on both sides of the negative electrode, under the premise of meeting the thickness of the above-mentioned resistance layer 222 and the size design along the first direction, see Figure 2As shown, in the coating 2, the size of the edge layer 22 arranged near the positive electrode ear 11 along the first direction is smaller than the size of the edge layer 22 arranged away from the positive electrode ear 11 along the first direction; the thickness of the two resistance layers 222 is the same, so that the lithium plating phenomenon at the edge of the negative electrode sheet is improved while minimizing the impact on the energy density of the battery.

[0057] Furthermore, in the coating 2, the ratio of the size of the edge layer 22 disposed near the positive electrode tab 11 along the first direction to the size 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 size of the edge layer 22 disposed near the positive electrode tab 11 along the first direction to the size 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.

[0058] Of course, for the best design, the distance from the end of the intermediate active material layer 21 close to the positive electrode ear 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 ear 11 to the second wall is d, c = d (see Figure 4 shown).

[0059] In some embodiments, the intermediate active material layer 21 and the edge active material layer 221 each contain the following components by mass: 75-95% of the positive electrode active material, 1-15% of the conductive agent, and 1-15% of the binder.

[0060] The positive electrode active material may be one or more of lithium cobalt oxide, lithium iron phosphate, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, and lithium titanate. For example, the positive electrode active material may be obtained by mixing lithium cobalt oxide and lithium iron phosphate in a certain mass percentage, or by mixing nickel cobalt manganese ternary material and lithium titanate in a certain mass percentage. Alternatively, lithium cobalt oxide, lithium iron phosphate, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, or lithium titanate may be used alone as the positive electrode active material, and the present invention does not impose any specific limitation thereto.

[0061] The conductive agent may be one or more of conductive carbon black, conductive graphite, acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fibers.

[0062] The binder can be any binder well known to those skilled in the art, without particular limitation, such as one or more of chitosan, xanthan gum, gellan gum, gum arabic, polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium carboxymethyl cellulose, polymethacryloyl, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, polyacrylamide, styrene-butadiene rubber, sodium alginate, polyethylene glycol, guar gum, guar gum polymer, and guar gum copolymer. In the embodiment of the present invention, PVDF is selected.

[0063] In some embodiments, the thickness of the positive electrode current collector is selected in the range of 4 μm to 20 μm, preferably 8 μm to 16 μm, such as 10 μm, 12 μm, 13 μm, 16 μm, etc. The positive electrode current collector is made of aluminum foil.

[0064] In summary, the present application also provides a battery, which includes a positive electrode sheet and a negative electrode sheet; the positive electrode sheet is the positive electrode sheet described above.

[0065] Since the battery of the present application includes the positive electrode sheet described above, the beneficial effects of the positive electrode sheet on the battery can be found above and will not be repeated here.

[0066] In some embodiments, the lithium-ion battery further comprises a negative electrode sheet, and the slurry of the negative electrode active material layer of the negative electrode sheet comprises the following components in parts by weight: 90-99 wt % of negative electrode active material, 0.01-3 wt % of thickener, 0.01-3 wt % of binder, and 0.01-3 wt % of conductive agent.

[0067] The type of negative electrode active material in the negative electrode active material layer is not limited and can be selected according to needs. 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 composite.

[0068] 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); the thickener in the negative electrode active material layer includes but is not limited to carboxymethyl cellulose or an inorganic salt thereof.

[0069] In some embodiments, the lithium-ion battery further includes an isolation membrane. The type of the isolation membrane can be any isolation membrane well known to those skilled in the art without any particular limitation, such as one or more of polyethylene, polypropylene, polyacrylonitrile, polyacrylonitrile fiber, polyamic acid, polyimide, polyamide, polydopamine, polyarylethersulfone, polyvinylidene fluoride, polyethylene oxide, polyethylene terephthalate, polyester, non-woven fabric membrane, and cellulose paper-based isolation membrane.

[0070] In some embodiments, the lithium-ion battery further includes an electrolyte, which can be any electrolyte well known to those skilled in the art without particular limitation. The solvent is at least one of ethyl methyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, and diethylene glycol dimethanol ether; and the electrolyte salt is at least one of sodium perchlorate, sodium bis(oxalato)borate, and sodium hexafluorophosphate.

[0071] The technical solutions described in the embodiments of the present application are applicable to various battery-powered electrical devices, such as mobile phones, portable devices, laptop computers, electric vehicles, electric toys, electric tools, electric vehicles, ships and spacecraft, etc. For example, spacecraft include airplanes, rockets, space shuttles and spacecraft, etc.

[0072] Example 1

[0073] 1. Preparation of positive electrode sheet:

[0074] A. Polymer material, conductive material, and inorganic material are added to a certain mass of N-methylpyrrolidone (NMP) in a certain mass ratio and mixed evenly. After being evenly dispersed, a slurry for the resistor layer is obtained. The solid content is 35%. Based on the mass percentage of the solid components in the resistor layer 222 being 100%, the resistor layer 222 contains 25wt% silicon dioxide, 50wt% conductive carbon black, and 25wt% polyvinylidene fluoride. The slurry is then coated on aluminum foil (10μm thick) to obtain an aluminum foil with a resistor layer.

[0075] B. 95 wt% of lithium iron phosphate, 3 wt% of a conductive agent, and 2 wt% of a binder are fully stirred and mixed in a certain amount of N-methylpyrrolidone to form a positive electrode active material slurry with a solid content of 73%; the positive electrode active material layer slurry is then coated on the above-mentioned aluminum foil using a coating machine, and then dried, rolled, slit, and die-cut to obtain a positive electrode sheet; wherein the positive electrode sheet needs to meet the following requirements: the positive electrode sheet includes a positive electrode collector, the positive electrode collector includes a positive electrode ear 11 and a coating portion 12, and a resistance layer is provided on either side edge of the coating portion 12, wherein the coating portion along the first direction The size is 280 mm, the size of the resistance layer at any side edge along the first direction is 10 mm, and the thickness d1 of the resistance layer at any side edge of the coating portion is 9 μm; an intermediate active material layer 21 is provided on the side of the two resistance layers away from the coating portion 12, and an intermediate active material layer 21 is provided on the coating portion 12 and between the two resistance layers; wherein the thickness d2 of the intermediate active material layer 21 is 60 μm; the ratio of the impedance R1 of the resistance layer at any side edge of the coating portion to the impedance R2 of the intermediate active material layer 21 is 1.375; that is, λ = 1.38.

[0076] 2. Preparation method of negative electrode sheet: 95wt% artificial graphite, 2wt% conductive agent, 2.6wt% SBR, and 0.4wt% CMC binder are fully stirred and mixed in deionized water according to a certain weight ratio to form a negative electrode active material slurry with a solid content of 56%.

[0077] 3. Preparation method of the test battery: The negative electrode sheet obtained in the above step, the positive electrode sheet obtained in the above step and the separator (the separator is a polyethylene film with a thickness of 9 μm) are wound to form a core, placed in a soft package, baked to remove moisture, and then injected with electrolyte [lithium salt LiPF6 is dissolved in a solvent to prepare a 1 mol / L electrolyte, organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): vinylene carbonate (VC) = 30:40:28:2, mass ratio)], and the test battery is obtained after hot pressing process.

[0078] Example 2

[0079] The difference between Example 2 and Example 1 is that the thickness d1 of the resistance layer is 18 μm, and the ratio of the impedance R1 of the resistance layer to the impedance R2 of the intermediate active material layer is 1.75, that is, λ=1.89.

[0080] Example 3

[0081] The difference between Example 3 and Example 1 is that the thickness d1 of the resistance layer is 24 μm, and the ratio of the impedance R1 of the resistance layer to the impedance R2 of the intermediate active material layer is 2, that is, λ=2.36.

[0082] Comparative Example 1

[0083] The differences between Comparative Example 1 and Example 1 are: the thickness d1 of the resistance layer is 0 μm, the dimension of the resistance layer along the first direction is 0 μm, and the ratio of the impedance R1 of the resistance layer to the impedance R2 of the intermediate active material layer is 0; that is, λ=0.

[0084] Comparative Example 2

[0085] The difference between Reference Document 2 and Example 1 is that the thickness d1 of the resistance layer is 6 μm, and the ratio of the impedance R1 of the resistance layer to the impedance R2 of the intermediate active material layer is 1.25; that is, λ=1.24.

[0086] Comparative Example 3

[0087] The difference between Reference Document 3 and Example 1 is that the thickness d1 of the resistance layer is 30 μm, and the ratio of the impedance R1 of the resistance layer to the impedance R2 of the intermediate active material layer is 2.25; that is, λ=3.

[0088] The test batteries of Examples 1 to 3 and Comparative Examples 1 to 3 prepared above were subjected to the following performance tests, respectively. The test process is as follows:

[0089] (1) Energy density test:

[0090] Battery Energy Density: The battery under test is allowed to stand at 25°C for 30 minutes. It is then charged at a constant current rate of 0.33C until the voltage reaches the rated voltage. Then, it is charged at a constant voltage until the charge / discharge rate reaches 0.05C. The battery is then allowed to stand at room temperature for 30 minutes, and then discharged at a rate of 0.33C to 2.5V. The resulting capacity is the actual battery energy (C) in Wh. This capacity is then divided by the weight of the battery (W) in kg. The battery's energy density (VED) is calculated as C / W in Wh / kg.

[0091] (2) Testing lithium deposition

[0092] At a constant temperature of 25°C, the battery was charged at a constant current of 1C to 4.25V, then charged at a constant voltage of 4.25V until the current dropped to 0.05C, and then discharged at a constant current of 1C to 2.8V. This cycle was repeated until the 500th cycle. After 500 cycles at 25°C, the battery was fully charged. After charging, the battery cells were disassembled and the lithium deposition state at the interface of the negative electrode edge was observed.

[0093] No lithium deposition: the interface is golden.

[0094] Point-like lithium deposition: The length and width of the lithium deposition area are both less than 1mm, and the number of points on a single surface is less than 5;

[0095] Linear lithium deposition: The width of the lithium deposition area is less than 3mm and the length is greater than 10mm;

[0096] Surface lithium deposition: width of lithium deposition area>3mm;

[0097] Here are the results:

[0098] Table 1

[0099]

[0100] As can be seen from Table 1:

[0101] It can be seen from the above data that the lower the λ value, the more serious the edge lithium deposition, and the larger the λ value, the more serious the deterioration of the energy density. When 1.24<λ<3 (Examples 1-3), not only the total amount of lithium ions released from the edge area of the positive electrode sheet is reduced, but also the lithium ion release rate of the edge area of the positive electrode sheet is slowed down, thereby preventing lithium deposition in the edge area of the negative electrode sheet; and at this time, the energy density of Examples 1-3 is almost the same as that of Comparative Example 1, and it can be considered that there is almost no loss in the energy density of the battery.

[0102] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A positive electrode sheet, characterized in that: include: A positive electrode current collector (1) comprising a coating portion (12) and a positive electrode tab (11) connected in sequence along a first direction; a coating layer (2) disposed on at least one side of the coating portion (12) along the thickness direction thereof; the coating layer (2) comprises an intermediate active material layer (21) and an edge layer (22), and the edge layer (22) is connected to both sides of the intermediate active material layer (21) along the first direction; The edge layer (22) comprises an edge active material layer (221) and a resistance layer (222) stacked along the thickness direction of the coating portion (12), wherein the edge active material layer (221) is arranged on a side of the resistance layer (222) away from the coating portion (12); Wherein, λ=[d2 / (d2-d1)]*(R1 / R2)^0.5, 1.24<λ<3, the impedance of the resistance layer (222) is R1, and the impedance of the intermediate active material layer (21) is R2; the thickness of the intermediate active material layer (21) is d2, and the thickness of the resistance layer (222) is d1.

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

3. The positive electrode sheet according to claim 1, characterized in that In the coating (2), the size of the edge layer (22) disposed close to the positive electrode tab (11) along the first direction is smaller than the size of the edge layer (22) disposed away from the positive electrode tab (11) along the first direction; and the two resistance layers (222) have the same thickness.

4. The positive electrode sheet according to claim 3, characterized in that In the coating (2), a ratio of a size of an edge layer (22) disposed close to the positive electrode tab (11) along the first direction to a size of an edge layer (22) disposed away from the positive electrode tab (11) along the first direction is 0.5 to 0.

9.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The ratio of the thickness d1 of the resistance layer (222) to the thickness d2 of the intermediate active material layer (21) is 0.1 to 0.4; the thickness d1 of the resistance layer (222) ranges from 3 μm to 30 μm.

6. The positive electrode sheet according to claim 5, characterized in that: The ratio of the impedance R1 of the resistance layer (222) to the impedance R2 of the intermediate active material layer (21) is 1.25 to 2.

25.

7. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The size of the resistance layer (222) along the first direction ranges from 10 mm to 30 mm.

8. A battery, characterized in that: The positive electrode sheet comprises the positive electrode sheet according to any one of claims 1 to 7.

9. The battery according to claim 8, characterized in that The invention also includes a shell, wherein the shell has a first wall arranged toward the positive electrode ear (11) and a second wall arranged opposite to the first wall along a first direction; the distance from the end of the coating portion (12) of the positive electrode sheet arranged close to the positive electrode ear (11) to the first wall is a, the distance from the end of the coating portion (12) of the positive electrode sheet arranged away from the positive electrode ear (11) to the second wall is b, the distance from the end of the intermediate active material layer (21) arranged close to the positive electrode ear (11) to the first wall is c, and the distance from the end of the intermediate active material layer (21) arranged away from the positive electrode ear (11) to the second wall is d, wherein a>b, and c=d.

10. An electrical device, characterized in that: A battery comprising the battery according to claim 8 or 9.

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