Positive pole piece and preparation method thereof, battery and power utilization device

Abstract

The invention relates to the technical field of batteries, in particular to a positive pole piece, a preparation method thereof, a battery and an electric device. The positive pole piece comprises a current collector and a positive coating and a protective layer which are stacked on the same side of the current collector, the protective layer comprises a first protective layer, the first protective layer is arranged on the current collector, the positive coating is arranged on the side, away from the current collector, of the first protective layer, and the first protective layer comprises a positive temperature coefficient semiconductor material. The positive electrode coating and the protective layer are laminated on the same side of the current collector, so that the stability of the positive electrode coating can be improved, the influence of short circuit risk factors on the positive electrode coating is reduced, and the risk of short circuit of the battery is reduced. For example, the risk of internal short circuit and explosion when the battery is abused by external extrusion, collision, puncture, high temperature or the like is reduced.

Description

Technical Field

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

[0002] Secondary batteries have been widely used in various consumer electronic products and electric vehicles due to their advantages such as high energy density, high output voltage, good safety, no pollution and no memory effect.

[0003] When a secondary battery is squeezed, collided or punctured, it is easy to catch fire or explode, thus causing serious harm. Therefore, the safety problem of secondary batteries (such as lithium-ion batteries) has greatly limited their application and popularity.

[0004] Therefore, it is necessary to improve secondary batteries and enhance their safety. Summary of the invention

[0005] The main purpose of the present invention is to provide a positive electrode plate, aiming to reduce the risk of short circuit in the battery.

[0006] To achieve the above-mentioned purpose, the present invention proposes a positive electrode plate, including a current collector and a positive electrode coating and a protective layer stacked on the same side of the current collector, the protective layer including a first protective layer, the first protective layer is arranged on the current collector, the positive electrode coating is arranged on the side of the first protective layer away from the current collector, and the first protective layer includes a positive temperature coefficient semiconductor material.

[0007] The first protective layer, a layered structure, is disposed between the positive electrode coating and the current collector to form a barrier on the positive electrode coating to reduce the impact of the risk environment outside the barrier on the stability of the positive electrode coating. For example, when the current collector generates more heat, the first protective layer can be blocked between the current collector and the positive electrode coating to reduce the impact of heat on the positive electrode coating. For example, in one embodiment, when the current collector generates more heat due to a short circuit, the first protective layer can react quickly, increase its own internal resistance, reduce the rate of heat generation of the pole piece, and thereby reduce the impact of heat on the positive electrode coating.

[0008] The positive electrode coating and the protective layer stacked on the same side of the current collector means that the positive electrode coating and the protective layer can be arranged on one side of the current collector at the same time, or on both sides of the current collector at the same time, and the arrangement positions of the positive electrode coating and the protective layer on the current collector are not limited. For example, the positive electrode coating can be arranged between the current collector and the protective layer, or the protective layer can be arranged between the current collector and the positive electrode coating.

[0009] Positive temperature coefficient semiconductor materials refer to materials whose resistance increases with increasing temperature. For example, the Curie temperature of barium titanate is 120°C. Before reaching the Curie temperature, the resistance of barium titanate changes very slowly with temperature. When the temperature exceeds the Curie temperature, the resistance of barium titanate itself increases sharply, and the resistivity is basically more than 1,000 times that of room temperature.

[0010] When the battery has an internal or external short circuit, the resistance of the first protective layer increases significantly, causing the internal resistance of the battery cell to increase exponentially, reducing the short-circuit current. For example, when a short circuit occurs inside the battery and a large amount of heat is generated, the internal resistance of the positive temperature coefficient semiconductor material in the first protective layer increases sharply, causing the internal resistance of the battery to increase, the current and voltage to decrease, and the oxidizability of the positive electrode active material to decrease, thereby avoiding a series of side reactions such as positive electrode oxidation of the electrolyte, reducing the large amount of heat generated by the side reactions, and thus reducing thermal runaway.

[0011] The protective layer comprises a first protective layer, the first protective layer is arranged on the current collector, and the positive electrode coating is arranged on a side of the first protective layer away from the current collector.

[0012] A first protective layer is provided between the positive electrode coating and the current collector to reduce the heat generation rate of the current collector during failure, thereby helping to protect the active materials in the positive electrode coating and improve the stability of the coating.

[0013] The present application laminates the positive electrode coating and the protective layer on the same side of the current collector, which can improve the stability of the positive electrode coating, reduce the influence of the positive electrode coating on the short circuit risk factors, and reduce the risk of short circuit in the battery. For example, it reduces the risk of internal short circuit and explosion when the battery is abused by external extrusion, collision, puncture or high temperature.

[0014] It is understandable that extrusion, collision, and puncture generally cause internal short circuits in the battery. During a short circuit, the battery will generate heat rapidly. The main function of the protective layer is to adjust the resistance at high temperature to control the short circuit current, control the battery temperature below the failure temperature, and reduce the risk of thermal runaway. The protective layer can also play a role in physical isolation and interface protection.

[0015] Optionally, the porosity of the first protective layer is less than the porosity of the positive electrode coating;

[0016] And / or, the thickness of the first protective layer ranges from 1 μm to 10 μm, preferably, from 4 μm to 10 μm.

[0017] The porosity of the first protective layer is smaller than that of the positive electrode coating, that is, the porosity of the positive electrode coating is increased, so that the positive electrode coating can be effectively infiltrated with the electrolyte, while the porosity of the first protective layer is smaller than that of the positive electrode coating. In comparison, the porosity of the first protective layer is small, and there is relatively less electrolyte in it, which makes the thermal conductivity of the first protective layer poor, reduces the conduction of heat, and reduces the risk of the heat generated by the current collector being conducted to the positive electrode coating through the pores of the first protective layer or the electrolyte in the pores.

[0018] The porosity of the first protective layer is less than the porosity of the positive electrode coating. For example, the porosity of the first protective layer is 1% to 10%, which means that the first protective layer has a certain density. The first protective layer has a small electronic resistivity, which reduces the contact impedance between the positive electrode coating and the current collector, thereby reducing the overall internal resistance of the battery and improving the power performance. In addition, the porosity of the first protective layer is small, and there is relatively little electrolyte in it, which makes the thermal conductivity of the first protective layer poor, reducing the conduction of heat. When the current collector generates a large amount of heat, the risk of heat being conducted to the positive electrode coating through the pores of the first protective layer or the electrolyte in the pores can be reduced.

[0019] The thickness of the first protective layer ranges from 1 μm to 10 μm, preferably from 4 μm to 10 μm. It is understandable that if the thickness of the first protective layer is too small, it cannot fully cover the current collector, and it is difficult to effectively protect the positive electrode coating. If the thickness of the first protective layer is too large, it will affect the performance of the battery cell, such as reduced capacity and increased internal resistance. Considering all factors, the thickness of the first protective layer is set in the above range.

[0020] Optionally, the first protective layer further includes at least one of a conductive agent, a solid electrolyte, a positive electrode active material, and a binder.

[0021] Solid electrolyte, a solid electrolyte is a solid ion conductor electrolyte.

[0022] The first protective layer includes a solid electrolyte, which has the characteristics of being non-flammable, high temperature resistant, non-volatile, and ion conductive. After adding the solid electrolyte to the first protective layer, the amount of liquid electrolyte used in the battery can be reduced, and therefore the flammability of the battery is greatly reduced.

[0023] The first protective layer includes a conductive agent to improve the resistivity of the first protective layer during normal use and reduce the impact on the resistance of the positive electrode plate. For example, when the first protective layer includes a positive temperature coefficient semiconductor material, considering that the positive temperature coefficient semiconductor material is a semiconductor material and the material resistance is too large, the first protective layer will increase the resistance of the plate itself. At this time, a conductive agent can be added to the first protective layer to improve the resistivity of the positive electrode plate. In addition, the thickness of the first protective layer can also be reduced, for example, the thickness of the first protective layer is 1 μm, thereby improving the resistivity of the positive electrode plate.

[0024] The first protective layer includes positive electrode active materials. By adding positive electrode active materials into the protective layer, the protective layer can protect the positive electrode coating without reducing the energy density of the battery. For example, the positive electrode active material includes lithium iron phosphate. The PO bonds in the lithium iron phosphate crystals are stable and difficult to decompose. Even at high temperatures or overcharge, the structure will not collapse and generate heat like lithium cobalt oxide, or form strong oxidizing substances. The decomposition temperature of lithium iron phosphate is about 600°C, so it has good stability.

[0025] The first protective layer includes a binder. By adding the binder, when the slurry of the first protective layer is coated on the surface of the current collector or the positive electrode coating, the protective layer can be effectively bonded to the surface of the current collector or the positive electrode coating.

[0026] Optionally, the mass percentage of the mass of the positive temperature coefficient semiconductor material to the mass of the first protective layer is in a range of greater than 0 and less than or equal to 80%;

[0027] The mass percentage of the mass of the conductive agent to the mass of the first protective layer is in the range of greater than or equal to 0 and less than or equal to 65%;

[0028] The mass percentage of the mass of the adhesive to the mass of the first protective layer is in the range of greater than or equal to 0 and less than or equal to 8%;

[0029] The mass percentage of the mass of the solid electrolyte to the mass of the first protective layer is in the range of greater than or equal to 0 and less than or equal to 5%;

[0030] The mass percentage of the mass of the positive electrode active material to the mass of the first protective layer is in the range of greater than or equal to 0 and less than or equal to 97%.

[0031] Those skilled in the art can mix and match the materials in the first protective layer as needed.

[0032] Optionally, the protective layer further includes a second protective layer, the positive electrode coating is disposed on the current collector, and the second protective layer is disposed on a side of the positive electrode coating away from the current collector.

[0033] The second protective layer is disposed on the surface of the positive electrode coating. When dendrites are generated at the negative electrode, the second protective layer can block the dendrites and reduce the direct contact of the dendrites with the positive electrode coating.

[0034] Optionally, the porosity of the second protective layer is greater than the porosity of the positive electrode coating;

[0035] And / or, the thickness of the second protective layer is in the range of 2 μm to 10 μm, preferably, 6 μm to 10 μm, preferably, 8 μm to 10 μm.

[0036] Providing a second protective layer on the surface of the positive electrode coating can reduce the contact between the surface of the positive electrode coating and the short-circuit point, thereby reducing the risk of short circuit in the battery. It can further reduce the direct contact between the surface of the positive electrode coating and the electrolyte, and reduce the probability of side reactions between the active materials in the positive electrode coating and the electrolyte. It can also be understood that the positive electrode plate is arranged relative to the negative electrode through the diaphragm, and the second protective layer on the surface of the positive electrode coating can also reduce the risk of direct contact between the positive and negative electrode plates and failure caused by local defects in the diaphragm. In this way, the second protective layer on the surface of the positive electrode coating also reduces the activity of the interface between the positive and negative electrode plates and improves the stability of the battery.

[0037] The protective layer includes a first protective layer and a second protective layer, and the positive electrode coating is arranged between the first protective layer and the second protective layer, so that the positive electrode coating is further protected by the two protective layers, thereby improving the stability of the positive electrode coating.

[0038] The porosity of the second protective layer is greater than the porosity of the positive electrode coating, which allows the second protective layer to effectively infiltrate the electrolyte, thereby helping the electrolyte to infiltrate the positive electrode coating, thereby helping to improve ion transmission.

[0039] The thickness of the second protective layer ranges from 2 μm to 10 μm, preferably from 6 μm to 10 μm, preferably from 8 μm to 10 μm. It is understandable that if the thickness of the second protective layer is too small, it cannot fully cover the positive electrode coating, and it is difficult to effectively protect the positive electrode coating. If the thickness of the second protective layer is too large, it will affect the performance of the battery cell, such as reduced capacity and increased internal resistance. Considering all factors, the thickness of the second protective layer is set in the above range.

[0040] Optionally, the second protective layer includes at least one of a positive temperature coefficient semiconductor material, a solid electrolyte, and a positive electrode active material.

[0041] It is understandable that a positive temperature coefficient semiconductor material may be added to the second protective layer.

[0042] It can be understood that when the above-mentioned positive electrode plate including a protective layer is used in a battery, and the protective layer includes a solid electrolyte, the amount of electrolyte used can be reduced. Since the electrolyte is flammable, reducing the amount of electrolyte used can reduce the flammability of the battery.

[0043] It can be understood that the components in the first protective layer and the second protective layer can be reasonably set as needed. For example, the first protective layer includes a positive temperature coefficient semiconductor material; or the first protective layer can include a positive temperature coefficient semiconductor material and a conductive agent; or the first protective layer can include a positive temperature coefficient semiconductor material and a solid electrolyte; or the first protective layer can include a solid electrolyte, a positive temperature coefficient semiconductor material and a conductive agent, etc., or positive electrode active materials can be added to the first protective layer and / or the second protective layer.

[0044] Optionally, the mass percentage of the positive temperature coefficient semiconductor material in the second protective layer to the mass of the second protective layer is in a range of greater than or equal to 0 and less than or equal to 80%;

[0045] The mass percentage of the mass of the solid electrolyte in the second protective layer to the mass of the second protective layer is in the range of greater than or equal to 0 and less than or equal to 5%;

[0046] The mass percentage of the mass of the positive electrode active material in the second protective layer to the mass of the second protective layer is in the range of greater than or equal to 0 and less than or equal to 97%;

[0047] The second protective layer includes a conductive agent, and the mass percentage of the conductive agent in the second protective layer to the mass of the second protective layer is in a range of greater than or equal to 0 and less than or equal to 65%;

[0048] The second protective layer includes an adhesive, and the mass percentage of the mass of the adhesive in the second protective layer to the mass of the second protective layer is in a range of greater than or equal to 0 and less than or equal to 8%.

[0049] The protective layer obtained according to the above formula can improve the resistivity of the battery when it is working normally, and can also effectively protect the positive electrode coating when a short circuit occurs in the battery.

[0050] Optionally, the first protective layer includes a positive temperature coefficient semiconductor material and a conductive agent, and the mass ratio of the positive temperature coefficient semiconductor material to the conductive agent is in the range of (50% to 80%): (20% to 50%), preferably, (50% to 65%): (35% to 50%); the second protective layer includes a positive electrode active material, a conductive agent, a binder, and a solid electrolyte, and the mass ratio of the positive electrode active material, the conductive agent, the binder, and the solid electrolyte is in the range of (74% to 95%): (2% to 8%): (2% to 8%): (1% to 10%), preferably, (85% to 94%): (2% to 5%): (2% to 5%): (2% to 5%).

[0051] Alternatively, the first protective layer includes a positive temperature coefficient semiconductor material and a conductive agent, and the mass ratio of the positive temperature coefficient semiconductor material to the conductive agent is in the range of (50% to 80%): (20% to 50%), preferably, (50% to 65%): (35% to 50%); the second protective layer includes a positive electrode active material, a conductive agent, a binder, and a positive temperature coefficient material, and the mass ratio of the positive electrode active material, the conductive agent, the binder, and the positive temperature coefficient material is in the range of (70% to 97%): (1% to 5%): (1% to 5%): (1% to 20%), preferably, (85% to 92%): (1.5% to 2.5%): (1.5% to 2.5%): (5% to 10%).

[0052] It can be understood that, in one embodiment, the first protective layer includes a positive temperature coefficient semiconductor material and a conductive agent, and the mass ratio of the positive temperature coefficient semiconductor material to the conductive agent ranges from (50% to 80%): (20% to 50%), preferably, (50% to 65%): (35% to 50%); the second protective layer includes a positive electrode active material, a conductive agent, a binder, and a solid electrolyte, and the mass ratio of the positive electrode active material, the conductive agent, the binder, and the solid electrolyte ranges from (74% to 95%): (2% to 8%): (2% to 8%): (1% to 10%), preferably, (85% to 94%): (2% to 5%): (2% to 5%): (2% to 5%).

[0053] In particular, the positive electrode active material of the second protective layer includes lithium iron phosphate and / or lithium iron manganese phosphate. Lithium iron phosphate and / or lithium iron manganese phosphate have good stability. Adding them to the second protective layer and arranging them on the surface of the positive electrode coating can reduce the interfacial stability of the positive electrode active material in the positive electrode coating. In particular, when the positive electrode active material in the positive electrode coating includes a ternary material, the interfacial reaction activity of the ternary material itself can be effectively reduced to improve its stability.

[0054] It can be understood that in another embodiment, the first protective layer includes a positive temperature coefficient semiconductor material and a conductive agent, and the mass ratio of the positive temperature coefficient semiconductor material to the conductive agent is in the range of (50% to 80%): (20% to 50%), preferably, (50% to 65%): (35% to 50%); the active material in the second protective layer and the active material in the positive electrode coating include a ternary material, and the second protective layer includes a ternary material, a conductive agent, a binder, and a positive temperature coefficient material, and the mass ratio of the ternary material, the conductive agent, the binder, and the positive temperature coefficient material is in the range of (70% to 97%): (1% to 5%): (1% to 5%): (1% to 20%), preferably, (85% to 92%): (1.5% to 2.5%): (1.5% to 2.5%): (5% to 10%).

[0055] In particular, the positive electrode active material in the second protective layer and the positive electrode active material in the positive electrode coating both include ternary materials. On this basis, positive temperature coefficient materials are added to the formula. When an internal or external short circuit occurs in the battery, the resistance of the protective layer increases significantly, causing the internal resistance of the battery cell to increase exponentially, reducing the short circuit current and thereby improving the stability of the ternary material.

[0056] Optionally, the mass percentage range of the mass of the positive temperature coefficient semiconductor material in the first protective layer to the mass of the first protective layer is greater than 0 and less than or equal to 80%;

[0057] The mass percentage of the mass of the conductive agent in the first protective layer to the mass of the first protective layer is in the range of greater than or equal to 0 and less than or equal to 65%;

[0058] The mass percentage of the mass of the binder in the first protective layer to the mass of the first protective layer is in the range of greater than or equal to 0 and less than or equal to 8%;

[0059] The mass percentage of the mass of the solid electrolyte in the first protective layer to the mass of the first protective layer is in the range of greater than or equal to 0 and less than or equal to 5%;

[0060] The mass percentage of the mass of the positive electrode active material in the first protective layer to the mass of the first protective layer is in the range of greater than or equal to 0 and less than or equal to 97%;

[0061] The thickness of the first protective layer ranges from 1 μm to 10 μm, and the thickness of the second protective layer ranges from 2 μm to 10 μm.

[0062] When the protective layer includes both the first protective layer and the second protective layer, and the formula is within the above range, the thickness range of the first protective layer is 1μm to 10μm, and the thickness range of the second protective layer is 2μm to 10μm, the test performance of the battery can be effectively improved. For example, in some of the above schemes, the battery passes the hot box test, external short circuit test, and puncture test, indicating that the above scheme has a better protective effect on the battery.

[0063] Optionally, the thickness of the positive electrode coating ranges from 45 μm to 300 μm, preferably, from 60 μm to 90 μm;

[0064] And / or, the protective layer comprises a positive temperature coefficient semiconductor material, the positive temperature coefficient material comprises at least one of a ceramic-based positive temperature coefficient material or a polymer-based positive temperature coefficient material, preferably, the ceramic-based positive temperature coefficient material comprises at least one of niobium titanate, tantalum titanate, strontium titanate, barium titanate, and lead titanate, the polymer-based positive temperature coefficient material comprises at least one of polyethylene, epoxy resin, ethylene-ethyl acrylate copolymer, polybutylene, cellulose acetate, polyamide, and a conductive agent;

[0065] And / or, the protective layer includes a solid electrolyte, the solid electrolyte includes at least one of an oxide, a sulfide, an oxysulfide and an oxynitride, preferably, the oxide includes at least one of P2O5, B2O3, SiO2, Li2O, the sulfide includes at least one of Li2S and SiS2, the oxysulfide includes at least one of LiS-SiS2 doped with Li3PO4, LiAlO2, Li2SiO3, the oxynitride includes at least one of LiPON, LiSiPON, LiSON;

[0066] And / or, the protective layer includes a conductive agent, and the conductive agent includes at least one of Ketjen black, graphite, graphene, and carbon nanotubes;

[0067] And / or, the protective layer includes a positive electrode active material, and the positive electrode active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, and a ternary material;

[0068] And / or, the protective layer includes a binder, and the binder includes at least one of polyvinylidene fluoride, polyacrylonitrile, polytetrafluoroethylene, polyvinyl alcohol, and polyurethane.

[0069] The thickness of the positive electrode coating ranges from 45 μm to 300 μm, preferably from 60 μm to 90 μm. It is understandable that if the thickness of the positive electrode coating is too large, the resistance of the electrode itself will be large, affecting the internal resistance and power performance of the battery cell. Considering comprehensively, the thickness of the positive electrode coating is set in the above range.

[0070] It can be understood that the protective layer includes a positive temperature coefficient semiconductor material, and the positive temperature coefficient material includes but is not limited to at least one of a ceramic-based positive temperature coefficient material or a polymer-based positive temperature coefficient material. Preferably, the ceramic-based positive temperature coefficient material includes but is not limited to at least one of niobium titanate, tantalum titanate, strontium titanate, barium titanate, and lead titanate. The polymer-based positive temperature coefficient material includes but is not limited to at least one of polyethylene, epoxy resin, ethylene-ethyl acrylate copolymer, polybutene, cellulose acetate, and polyamide, as well as a conductive agent. It can be understood that the polymer-based positive temperature coefficient material is generally a non-conductive material. In order to achieve conductivity, a certain conductive agent is compounded in the polymer-based positive temperature coefficient material. At high temperature, the polymer-based positive temperature coefficient material expands and destroys the conductive path of the conductive particle parts, thereby achieving the purpose of increasing the resistance.

[0071] It can be understood that the protective layer includes a solid electrolyte, which includes but is not limited to at least one of oxides, sulfides, sulfur oxides and nitrogen oxides. Preferably, the oxides include but are not limited to at least one of P2O5, B2O3, SiO2, and Li2O, the sulfides include but are not limited to at least one of Li2S and SiS2, the sulfur oxides include but are not limited to at least one of LiS-SiS2 doped with Li3PO4, LiAlO2, and Li2SiO3, and the nitrogen oxides include but are not limited to at least one of LiPON, LiSiPON, and LiSON.

[0072] It is understandable that the protective layer includes a conductive agent, which includes but is not limited to at least one of Ketjen black, graphite, graphene, and carbon nanotubes.

[0073] It is understood that the protective layer includes a positive electrode active material, and the positive electrode active material includes but is not limited to at least one of lithium iron phosphate, lithium iron manganese phosphate, and a ternary material;

[0074] It is understandable that the protective layer includes a binder, and the binder includes but is not limited to at least one of polyvinylidene fluoride, polyacrylonitrile, polytetrafluoroethylene, polyvinyl alcohol, and polyurethane.

[0075] Optionally, the protective layer comprises a positive temperature coefficient semiconductor material, and Dv50 of the positive temperature coefficient semiconductor material is 0.2 μm≤Dv50<1 μm;

[0076] And / or, the protective layer comprises a solid electrolyte, the Dv50 of the solid electrolyte is 0.5 μm ≤ Dv50 ≤ 3 μm, and the specific surface area of ​​the solid electrolyte is 2 m 2 / g to 6m 2 / g;

[0077] And / or, the protective layer comprises a positive electrode active material, the Dv50 of the positive electrode active material is 0.2 μm≤Dv50<1.4 μm, and the specific surface area of ​​the positive electrode active material is 8 m 2 / g to 12m 2 / g.

[0078] The Dv50 of the positive temperature coefficient semiconductor material is 0.2μm≤Dv50<1μm. It is understandable that the positive temperature coefficient semiconductor material needs to be evenly dispersed in the protective layer. If the particle size is too large, it is not conducive to the uniform dispersion of the positive temperature coefficient semiconductor material. When the temperature rises, the local resistance change of the protective layer is inconsistent, which is not conducive to the stability of the positive electrode coating. When the particle size is too small, the dispersion processing performance is relatively poor. Therefore, after comprehensive consideration, the Dv50 of the positive temperature coefficient semiconductor material is set in the above range.

[0079] The Dv50 of the solid electrolyte is 0.5μm≤Dv50≤3μm, and the specific surface area of ​​the solid electrolyte is 2m 2 / g to 6m 2 / g, preferably, 3m 2 / g to 5m 2 It can be understood that the Dv50 and specific surface area of ​​the solid electrolyte are set within the above ranges, so that it can be effectively dispersed in the protective layer, formed into a suitable thickness, and evenly arranged on the positive electrode coating.

[0080] The protective layer includes a positive electrode active material, the Dv50 of the positive electrode active material is 0.2 μm ≤ Dv50 < 1.4 μm, and the specific surface area of ​​the positive electrode active material is 8 m 2 / g to 12m 2 / g. It is understandable that by selecting the Dv50 and specific surface area of ​​the positive electrode active material to be set within the above range, the protective layer is easier to evenly cover the surface of the positive electrode coating, and the protective effect is better. In addition, it can also effectively improve the conduction rate of lithium ions and reduce the transmission impedance of the pole piece, which has a certain effect on improving the power performance of the battery cell.

[0081] Optionally, the positive electrode coating includes a ternary material, a conductive agent, and a binder, and the mass ratio of the ternary material, the conductive agent, and the binder ranges from (90% to 98%): (1% to 5%): (1% to 5%).

[0082] It is understandable that the positive electrode active materials in the positive electrode coating of the present application include but are not limited to ternary materials. Considering that the ternary materials have poor thermal stability in some cases (such as ternary high-nickel positive electrode materials), when the battery is subjected to external extrusion, collision, puncture or high temperature abuse, an internal short circuit occurs and it is easy to catch fire and explode. For this reason, the ternary materials need more protection from the protective layer. The positive electrode coating includes a ternary material, a conductive agent, and a binder. The mass ratio of the ternary material, the conductive agent, and the binder is in the range of (90% to 98%): (1% to 5%): (1% to 5%).

[0083] Optionally, the Dv50 of the ternary material is 4 μm ≤ Dv50 ≤ 12 μm, and the specific surface area of ​​the ternary material is 0.5 m 2 / g to 1.5m 2 / g;

[0084] And / or, the ternary material includes at least one of 6-series ternary material, 7-series ternary material, 8-series ternary material, 9-series ternary material, and cobalt-free high-nickel ternary material;

[0085] And / or, the ternary material comprises a single crystal material, the Dv50 of the single crystal material is 2 μm≤Dv50≤7 μm, and the specific surface area is 0.8 m 2 / g to 1.4m2 / g;

[0086] And / or, the ternary material comprises a polycrystalline material, the Dv50 of the polycrystalline material is 7 μm ≤ Dv50 ≤ 15 μm, and the specific surface area is 0.5 m 2 / g to 0.8m 2 / g.

[0087] It can be understood that the Dv50 and specific surface area of ​​the ternary material are set within the above range, which can meet the performance and production cost requirements of the ternary material.

[0088] Optionally, the present application also provides a method for preparing the positive electrode sheet as described above, comprising:

[0089] preparing protective layer materials and positive electrode coating materials;

[0090] The protective layer material and the positive electrode coating material are arranged on a current collector to form a positive electrode plate, wherein the positive electrode plate comprises the current collector and a positive electrode coating and a protective layer stacked on the same side of the current collector, wherein the protective layer comprises a first protective layer, wherein the first protective layer is arranged on the current collector, the positive electrode coating is arranged on a side of the first protective layer away from the current collector, and the first protective layer comprises a positive temperature coefficient semiconductor material.

[0091] Optionally, the step of providing the protective layer material in the current collector includes:

[0092] preparing a first protective layer material, wherein the first protective layer material comprises a positive temperature coefficient semiconductor material;

[0093] The first protective layer material is deposited onto the current collector by using a vapor deposition technique to provide a first protective layer on the current collector.

[0094] Vapor deposition technology is a new technology that uses physical and chemical processes in the gas phase to change the surface composition of the workpiece and form a metal or compound coating with special properties (such as a super-hard wear-resistant layer or special optical and electrical properties) on the surface. According to the nature of the process, vapor deposition can be divided into two categories: chemical vapor deposition (CVD) and physical vapor deposition (PVD).

[0095] Chemical vapor deposition is a technology that mainly uses one or several gas phase compounds or single substances containing thin film elements to undergo chemical reactions on the surface of the substrate to form a thin film.

[0096] Physical vapor deposition. The main methods of physical vapor deposition are: vacuum evaporation, sputtering coating, arc plasma coating, ion plating and molecular beam epitaxy.

[0097] In the present application, the first protective layer material can be deposited onto the current collector by vapor deposition to set the first protective layer on the current collector. The deposition method of the present application can be selected as needed.

[0098] For example, vacuum evaporation method and vacuum ion plating technology can be used. The density and uniformity of the coating are relatively good and the porosity is low. They are more suitable for growing thin films in the lithium battery industry.

[0099] Optionally, the step of depositing the first protective layer material onto the current collector by using a vapor deposition technique includes sputtering the positive temperature coefficient semiconductor material and the conductive agent onto the current collector simultaneously.

[0100] In order to make the conductive agent uniformly dispersed in the first protective layer, the positive temperature coefficient semiconductor material and the conductive agent are sputtered onto the current collector at the same time to improve the conductive uniformity of the first protective layer.

[0101] Optionally, after the step of placing the protective layer material and the positive electrode coating material on the current collector to form a positive electrode sheet, the method further includes:

[0102] preparing a second protective layer material, wherein the second protective layer material includes a positive temperature coefficient semiconductor material;

[0103] The second protective layer material is deposited onto the surface of the positive electrode plate by using a vapor deposition technique to provide a second protective layer on the positive electrode plate.

[0104] That is, vapor deposition may also be used in the process of preparing the second protective layer. It is understandable that in order to facilitate the passage of ions through the second protective layer, the thickness of the second protective layer formed in this way is preferably within 2 μm, for example, 1 μm to 2 μm.

[0105] The present application also provides a battery, the battery comprising the positive electrode sheet as described above;

[0106] Alternatively, the battery includes a positive electrode sheet prepared by the method for preparing a positive electrode sheet.

[0107] The present application also provides an electrical device, which includes the battery as described above.

[0108] The positive electrode plate of the present application includes a current collector and a positive electrode coating and a protective layer stacked on the same side of the current collector, the protective layer includes a first protective layer, the first protective layer is arranged on the current collector, the positive electrode coating is arranged on the side of the first protective layer away from the current collector, and the first protective layer includes a positive temperature coefficient semiconductor material. The positive temperature coefficient semiconductor material makes the resistance of the first protective layer increase significantly when the current collector generates a large amount of heat, so that the internal resistance of the battery cell increases exponentially and reduces the risk of short circuit. That is, stacking the positive electrode coating and the protective layer on the same side of the current collector can improve the stability of the positive electrode coating, reduce the influence of short circuit risk factors on the positive electrode coating, and reduce the risk of short circuit in the battery. For example, reduce the risk of internal short circuit and explosion when the battery is abused by external extrusion, collision, puncture or high temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0109] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0110] Figure 1 This is a schematic structural diagram of a positive electrode sheet according to an embodiment of the present application;

[0111] Figure 2 This is a schematic structural diagram of a positive electrode sheet according to another embodiment of the present application;

[0112] Figure 3 This is a schematic structural diagram of a positive electrode sheet according to another embodiment of the present application;

[0113] Figure 4 This is a schematic structural diagram of a positive electrode sheet according to another embodiment of the present application;

[0114] Figure 5 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0115] Figure 6 yes Figure 5 An exploded view of a battery cell according to an embodiment of the present application is shown;

[0116] Figure 7 is a schematic diagram of a battery module according to an embodiment of the present application;

[0117] Figure 8 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0118] Fig. 9 yes Figure 8 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0119] Fig.10 It is a schematic diagram of an electrical device using a battery cell according to an embodiment of the present application as a power source.

[0120] Description of Figure Numbers:

[0121] Label name Label name 1 Battery Pack 5 Battery Cell 2 Upper box 51 case 3 Lower box 52 Electrode assembly 4 Battery Module 53 Cover 100 Positive electrode 10 current collector 20 Protective layer 21 First protective layer 22 Second protective layer 30 Cathode coating

[0122] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0123] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0124] Below, the positive electrode plate and its preparation method, battery and electrical device of the present application are specifically disclosed in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0125] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0126] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0127] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0128] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0129] Secondary batteries have been widely used in various consumer electronic products and electric vehicles due to their advantages such as high energy density, high output voltage, no pollution and no memory effect.

[0130] Secondary batteries can easily catch fire or explode when subjected to abnormal conditions such as squeezing, collision or puncture, causing serious harm.

[0131] Therefore, it is necessary to improve secondary batteries to reduce the risk of causing serious harm.

[0132] A positive electrode plate proposed in the present application includes a current collector and a positive electrode coating and a protective layer stacked on the same side of the current collector, the protective layer includes a first protective layer, the first protective layer is arranged on the current collector, the positive electrode coating is arranged on the side of the first protective layer away from the current collector, and the first protective layer includes a positive temperature coefficient semiconductor material.

[0133] The current collector refers to the structure or part that collects current. In lithium-ion batteries, it mainly refers to metal foil, such as copper foil and aluminum foil. The current collector is used as a substrate to attach the positive or negative active material, and plays the role of collecting the current generated by the active material and outputting a large current to the outside. Generally, aluminum foil is used as the positive current collector, and copper foil is used as the negative current collector.

[0134] The first protective layer, a layered structure, is disposed between the positive electrode coating and the current collector to form a barrier on the positive electrode coating to reduce the impact of the risk environment outside the barrier on the stability of the positive electrode coating. For example, when the current collector generates more heat, the first protective layer can be blocked between the current collector and the positive electrode coating to reduce the impact of heat on the positive electrode coating. For example, in one embodiment, when the current collector generates more heat due to a short circuit, the first protective layer can react quickly, increase its own internal resistance, reduce the rate of heat generation of the pole piece, and thereby reduce the impact of heat on the positive electrode coating.

[0135] The positive electrode coating and the protective layer stacked on the same side of the current collector means that the positive electrode coating and the protective layer can be arranged on one side of the current collector at the same time, or on both sides of the current collector at the same time, and the arrangement positions of the positive electrode coating and the protective layer on the current collector are not limited. For example, the positive electrode coating can be arranged between the current collector and the protective layer, or the protective layer can be arranged between the current collector and the positive electrode coating.

[0136] Positive temperature coefficient semiconductor materials refer to materials whose resistance increases with increasing temperature. For example, the Curie temperature of barium titanate is 120°C. Before reaching the Curie temperature, the resistance of barium titanate changes very slowly with temperature. When the temperature exceeds the Curie temperature, the resistance of barium titanate itself increases sharply, and the resistivity is basically more than 1,000 times that of room temperature.

[0137] When the battery has an internal or external short circuit, the resistance of the first protective layer increases significantly, causing the internal resistance of the battery cell to increase exponentially, reducing the short-circuit current. For example, when a short circuit occurs inside the battery and a large amount of heat is generated, the internal resistance of the positive temperature coefficient semiconductor material in the first protective layer increases sharply, causing the internal resistance of the battery to increase, the current and voltage to decrease, and the oxidizability of the positive electrode active material to decrease, thereby avoiding a series of side reactions such as positive electrode oxidation of the electrolyte, reducing the large amount of heat generated by the side reactions, and thus reducing thermal runaway.

[0138] The protective layer comprises a first protective layer, the first protective layer is arranged on the current collector, and the positive electrode coating is arranged on a side of the first protective layer away from the current collector.

[0139] like Figure 1 As shown, the protective layer includes a first protective layer 21 , the first protective layer 21 is disposed on the current collector 10 , and the positive electrode coating 30 is disposed on a side of the first protective layer 21 away from the current collector 10 .

[0140] A first protective layer is provided between the positive electrode coating and the current collector to reduce the heat generation rate of the current collector during the failure process, thereby helping to protect the active materials in the positive electrode coating and improve the stability of the coating.

[0141] The present application laminates the positive electrode coating and the protective layer on the same side of the current collector, which can improve the stability of the positive electrode coating, reduce the influence of the positive electrode coating on the short circuit risk factors, and reduce the risk of short circuit in the battery. For example, it reduces the risk of internal short circuit and explosion when the battery is abused by external extrusion, collision, puncture or high temperature.

[0142] It is understandable that extrusion, collision, and puncture generally cause internal short circuits in the battery. During a short circuit, the battery will generate heat rapidly. The main function of the protective layer is to adjust the resistance at high temperature to control the short circuit current, control the battery temperature below the failure temperature, and reduce the risk of thermal runaway. The protective layer can also play a role in physical isolation and interface protection.

[0143] In one embodiment, the porosity of the first protective layer is less than the porosity of the positive electrode coating; and / or the thickness of the first protective layer is in the range of 1 μm to 10 μm, preferably, 4 μm to 10 μm.

[0144] The porosity calculation formula is P = [V / V0] * 100%. V0 is the volume of the material in its natural state, and V is the volume of all voids in the material. Punch the pole piece into small discs with a diameter of ≤16mm, and record the thickness of the small discs; then use a porosity tester to test and obtain the porosity of the pole piece.

[0145] The porosity of the first protective layer is less than the porosity of the positive electrode coating. For example, the porosity of the first protective layer is 1% to 10%, which means that the first protective layer has a certain density. The first protective layer has a small electronic resistivity, which reduces the contact impedance between the positive electrode coating and the current collector, thereby reducing the overall internal resistance of the battery and improving the power performance. In addition, the first protective layer has a small porosity and contains relatively little electrolyte, which makes the thermal conductivity of the first protective layer poor, reducing the conduction of heat. When the current collector generates a large amount of heat, the risk of heat being conducted to the positive electrode coating through the pores of the first protective layer or the electrolyte in the pores can be reduced.

[0146] The thickness of the first protective layer ranges from 1 μm to 10 μm, preferably from 4 μm to 10 μm. It is understandable that if the thickness of the first protective layer is too small, it cannot fully cover the current collector, and it is difficult to effectively protect the positive electrode coating. If the thickness of the first protective layer is too large, it will affect the performance of the battery cell, such as reduced capacity and increased internal resistance. Considering all factors, the thickness of the first protective layer is set in the above range.

[0147] In the above 1% to 10%, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., as well as the range values ​​between any two of the above point values.

[0148] In the above-mentioned 1μm to 10μm, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc., and the range values ​​between any two of the above-mentioned point values.

[0149] In the above-mentioned 4μm to 10μm, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc., and the range values ​​between any two of the above-mentioned point values.

[0150] In one embodiment, the first protective layer further includes at least one of a conductive agent, a solid electrolyte, a positive electrode active material, and a binder.

[0151] Solid electrolyte, a solid electrolyte is a solid ion conductor electrolyte.

[0152] The first protective layer includes a solid electrolyte, which has the characteristics of being non-flammable, high temperature resistant, non-volatile, and ion conductive. After adding the solid electrolyte to the first protective layer, the amount of liquid electrolyte used in the battery can be reduced, and therefore the flammability of the battery is greatly reduced.

[0153] The first protective layer includes a conductive agent to improve the resistivity of the first protective layer during normal use and reduce the impact on the resistance of the positive electrode plate. For example, when the first protective layer includes a positive temperature coefficient semiconductor material, considering that the positive temperature coefficient semiconductor material is a semiconductor material and the material resistance is too large, the first protective layer will increase the resistance of the plate itself. At this time, a conductive agent can be added to the first protective layer to improve the resistivity of the positive electrode plate. In addition, the thickness of the first protective layer can also be reduced, for example, the thickness of the first protective layer is 1 μm, thereby improving the resistivity of the positive electrode plate.

[0154] The first protective layer includes positive electrode active materials. By adding positive electrode active materials into the protective layer, the protective layer can protect the positive electrode coating without reducing the energy density of the battery. For example, the positive electrode active material includes lithium iron phosphate. The PO bonds in the lithium iron phosphate crystals are stable and difficult to decompose. Even at high temperatures or overcharge, the structure will not collapse and generate heat like lithium cobalt oxide, or form strong oxidizing substances. The decomposition temperature of lithium iron phosphate is about 600°C, so it has good stability.

[0155] The first protective layer includes a binder. By adding the binder, when the slurry of the first protective layer is coated on the surface of the current collector or the positive electrode coating, the protective layer can be effectively bonded to the surface of the current collector or the positive electrode coating.

[0156] In one embodiment, the mass percentage range of the mass of the positive temperature coefficient semiconductor material to the mass of the first protective layer is greater than 0 and less than or equal to 80%; the mass percentage range of the mass of the conductive agent to the mass of the first protective layer is greater than or equal to 0 and less than or equal to 65%; the mass percentage range of the mass of the binder to the mass of the first protective layer is greater than or equal to 0 and less than or equal to 8%; the mass percentage range of the mass of the solid electrolyte to the mass of the first protective layer is greater than or equal to 0 and less than or equal to 5%; the mass percentage range of the mass of the positive electrode active material to the mass of the first protective layer is greater than or equal to 0 and less than or equal to 97%.

[0157] In the above-mentioned greater than 0, less than or equal to 80%, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, etc., and the range values ​​between any two of the above-mentioned point values.

[0158] In the above-mentioned greater than or equal to 0 and less than or equal to 65%, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 0, 1%, 2%, 3%, 4%, 5%, 8%, 10%, 20%, 30%, 40%, 50%, 60%, 65%, etc., and the range values ​​between any two of the above-mentioned point values.

[0159] In the above-mentioned greater than or equal to 0 and less than or equal to 8%, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 0, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, etc., and the range values ​​between any two of the above-mentioned point values.

[0160] In the above-mentioned greater than or equal to 0 and less than or equal to 5%, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 0, 1%, 2%, 3%, 4%, 5%, etc., and the range values ​​between any two of the above-mentioned point values.

[0161] In the above-mentioned greater than or equal to 0, less than or equal to 97%, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 0, 1%, 2%, 3%, 4%, 5%, 8%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 97%, etc., and the range value between any two of the above-mentioned point values.

[0162] For example, in one embodiment, the first protective layer includes a positive temperature coefficient semiconductor material and a conductive agent, and the mass ratio of the positive temperature coefficient semiconductor material to the conductive agent is in the range of (50% to 80%): (20% to 50%); or, the first protective layer includes a positive electrode active material, a conductive agent, a binder, and a positive temperature coefficient semiconductor material; the mass ratio of the positive electrode active material, the conductive agent, the binder, and the positive temperature coefficient semiconductor material is in the range of (70% to 97%): (1% to 5%): (1% to 5%): (1% to 20%); or, the first protective layer includes a positive electrode active material, a conductive agent, a binder, a solid electrolyte, and a positive temperature coefficient semiconductor material, and the mass ratio of the positive electrode active material, the conductive agent, the binder, the solid electrolyte, and the positive temperature coefficient semiconductor material is in the range of (74% to 94%): (2% to 8%): (2% to 8%): (1% to 5%): (1% to 5%).

[0163] In one embodiment, the protective layer further includes a second protective layer, the positive electrode coating is disposed on the current collector, and the second protective layer is disposed on a side of the positive electrode coating away from the current collector.

[0164] The second protective layer is disposed on the surface of the positive electrode coating. When dendrites are generated at the negative electrode, the second protective layer can block the dendrites and reduce the direct contact of the dendrites with the positive electrode coating.

[0165] In one embodiment, the porosity of the second protective layer is greater than the porosity of the positive electrode coating; and / or the thickness of the second protective layer ranges from 2 μm to 10 μm, preferably, from 6 μm to 10 μm, preferably, from 8 μm to 10 μm.

[0166] like Figure 2 As shown, the protective layer includes a second protective layer 22 , the positive electrode coating 30 is disposed on the current collector 10 , and the second protective layer 22 is disposed on a side of the positive electrode coating 30 away from the current collector 10 .

[0167] Providing a second protective layer on the surface of the positive electrode coating can reduce the contact between the surface of the positive electrode coating and the short-circuit point, thereby reducing the risk of short circuit in the battery. It can further reduce the direct contact between the surface of the positive electrode coating and the electrolyte, and reduce the probability of side reactions between the active materials in the positive electrode coating and the electrolyte. It can also be understood that the positive electrode plate is arranged relative to the negative electrode through the diaphragm, and the second protective layer on the surface of the positive electrode coating can also reduce the risk of direct contact between the positive and negative electrode plates and failure caused by local defects in the diaphragm. In this way, the second protective layer on the surface of the positive electrode coating also reduces the activity of the interface between the positive and negative electrode plates and improves the stability of the battery.

[0168] like Figure 3 As shown, the protective layer 20 includes a first protective layer 21 and a second protective layer 22, and the positive electrode coating 30 is disposed between the first protective layer 21 and the second protective layer 22, so that the positive electrode coating is further protected by the two protective layers, thereby improving the stability of the positive electrode coating. Figure 4 As shown, the first protective layer 21 and the second protective layer 22 may be disposed on both sides of the current collector 10 , and the positive electrode coating 30 is disposed between the first protective layer 21 and the second protective layer 22 .

[0169] The porosity of the second protective layer is greater than the porosity of the positive electrode coating, which allows the second protective layer to effectively infiltrate the electrolyte, thereby helping the electrolyte to infiltrate the positive electrode coating, thereby helping to improve ion transmission.

[0170] The thickness of the second protective layer ranges from 2 μm to 10 μm, preferably from 6 μm to 10 μm, preferably from 8 μm to 10 μm. It is understandable that if the thickness of the second protective layer is too small, it cannot fully cover the positive electrode coating, and it is difficult to effectively protect the positive electrode coating. If the thickness of the second protective layer is too large, it will affect the performance of the battery cell, such as reduced capacity and increased internal resistance. Considering all factors, the thickness of the second protective layer is set in the above range.

[0171] In the above-mentioned 2μm to 10μm, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc., and the range values ​​between any two of the above-mentioned point values.

[0172] In the above-mentioned 6μm to 10μm, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 6μm, 7μm, 8μm, 9μm, 10μm, etc., as well as the range values ​​between any two of the above-mentioned point values.

[0173] In one embodiment, the second protective layer includes at least one of a positive temperature coefficient semiconductor material, a solid electrolyte, and a positive electrode active material.

[0174] It is understandable that a positive temperature coefficient semiconductor material may be added to the second protective layer.

[0175] It can be understood that when the above-mentioned positive electrode plate including a protective layer is applied in a battery, and the protective layer includes a solid electrolyte, the amount of electrolyte used can be reduced. Since the electrolyte is flammable, reducing the amount of electrolyte used can reduce the flammability of the battery. It can also be understood that the solid electrolyte is arranged in the second protective layer, which is more effective than being arranged in the first protective layer.

[0176] In one embodiment, the mass percentage range of the mass of the positive temperature coefficient semiconductor material in the second protective layer to the mass of the second protective layer is greater than or equal to 0 and less than or equal to 80%; the mass percentage range of the mass of the solid electrolyte in the second protective layer to the mass of the second protective layer is greater than or equal to 0 and less than or equal to 5%; the mass percentage range of the mass of the positive electrode active material in the second protective layer to the mass of the second protective layer is greater than or equal to 0 and less than or equal to 97%; the second protective layer includes a conductive agent, and the mass percentage range of the mass of the conductive agent in the second protective layer to the mass of the second protective layer is greater than or equal to 0 and less than or equal to 65%; the second protective layer includes a binder, and the mass percentage range of the mass of the binder in the second protective layer to the mass of the second protective layer is greater than or equal to 0 and less than or equal to 8%.

[0177] In the above-mentioned greater than or equal to 0 and less than or equal to 80%, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 0, 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, etc., and the range values ​​between any two of the above-mentioned point values.

[0178] In the above-mentioned greater than or equal to 0 and less than or equal to 65%, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 0, 1%, 2%, 3%, 4%, 5%, 8%, 10%, 20%, 30%, 40%, 50%, 60%, 65%, etc., and the range values ​​between any two of the above-mentioned point values.

[0179] In the above-mentioned greater than or equal to 0 and less than or equal to 8%, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 0, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, etc., and the range values ​​between any two of the above-mentioned point values.

[0180] In the above-mentioned greater than or equal to 0 and less than or equal to 5%, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 0, 1%, 2%, 3%, 4%, 5%, etc., and the range values ​​between any two of the above-mentioned point values.

[0181] In the above-mentioned greater than or equal to 0, less than or equal to 97%, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 0, 1%, 2%, 3%, 4%, 5%, 8%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 97%, etc., and the range value between any two of the above-mentioned point values.

[0182] The protective layer obtained according to the above formula can improve the resistivity of the battery during normal operation, and can also effectively protect the positive electrode coating when the battery is short-circuited. For example, in one embodiment, the second protective layer includes a positive temperature coefficient semiconductor material and a conductive agent, and the mass ratio of the positive temperature coefficient semiconductor material to the conductive agent is in the range of (50% to 80%): (20% to 50%); or, the second protective layer includes a positive electrode active material, a conductive agent, a binder, and a positive temperature coefficient semiconductor material; the mass ratio of the positive electrode active material, the conductive agent, the binder, and the positive temperature coefficient semiconductor material is in the range of (70% to 97%): (1% to 5%): (1% to 5%): (1% to 20%); or, the second protective layer includes a positive electrode active material, a conductive agent , binder, solid electrolyte, positive temperature coefficient semiconductor material, the mass ratio range of positive electrode active material, conductive agent, binder, solid electrolyte, positive temperature coefficient semiconductor material is (74% to 94%): (2% to 8%): (2% to 8%): (1% to 5%): (1% to 5%); or, the second protective layer includes positive electrode active material, conductive agent, binder, solid electrolyte; the mass ratio range of positive electrode active material, conductive agent, binder, solid electrolyte is (74% to 95%): (2% to 8%): (2% to 8%): (1% to 10%).

[0183] In one embodiment, the first protective layer includes a positive temperature coefficient semiconductor material and a conductive agent, and the mass ratio of the positive temperature coefficient semiconductor material to the conductive agent is in the range of (50% to 80%): (20% to 50%), preferably, (50% to 65%): (35% to 50%); the second protective layer includes a positive electrode active material, a conductive agent, a binder, and a solid electrolyte, and the mass ratio of the positive electrode active material, the conductive agent, the binder, and the solid electrolyte is in the range of (74% to 95%): (2% to 8%): (2% to 8%): (1% to 10%), preferably, (85% to 94%): (2% to 5%): (2% to 5%): (2% to 5%); or, the first A protective layer includes a positive temperature coefficient semiconductor material and a conductive agent, and the mass ratio of the positive temperature coefficient semiconductor material to the conductive agent is in the range of (50% to 80%): (20% to 50%), preferably, (50% to 65%): (35% to 50%); the second protective layer includes a positive electrode active material, a conductive agent, a binder, and a positive temperature coefficient material, and the mass ratio of the positive electrode active material, the conductive agent, the binder, and the positive temperature coefficient material is in the range of (70% to 97%): (1% to 5%): (1% to 5%): (1% to 20%), preferably, (85% to 92%): (1.5% to 2.5%): (1.5% to 2.5%): (5% to 10%).

[0184] It can be understood that, in one embodiment, the first protective layer includes a positive temperature coefficient semiconductor material and a conductive agent, and the mass ratio of the positive temperature coefficient semiconductor material to the conductive agent ranges from (50% to 80%): (20% to 50%), preferably, (50% to 65%): (35% to 50%); the second protective layer includes a positive electrode active material, a conductive agent, a binder, and a solid electrolyte, and the mass ratio of the positive electrode active material, the conductive agent, the binder, and the solid electrolyte ranges from (74% to 95%): (2% to 8%): (2% to 8%): (1% to 10%), preferably, (85% to 94%): (2% to 5%): (2% to 5%): (2% to 5%).

[0185] In particular, the positive electrode active material of the second protective layer includes lithium iron phosphate and / or lithium iron manganese phosphate; lithium iron phosphate and / or lithium iron manganese phosphate have good stability. Adding them to the second protective layer and arranging them on the surface of the positive electrode coating can reduce the interfacial stability of the positive electrode active material in the positive electrode coating. In particular, when the positive electrode active material in the positive electrode coating includes a ternary material, the interfacial reaction activity of the ternary material itself can be effectively reduced to improve its stability.

[0186] It can be understood that in another embodiment, the first protective layer includes a positive temperature coefficient semiconductor material and a conductive agent, and the mass ratio of the positive temperature coefficient semiconductor material to the conductive agent is in the range of (50% to 80%): (20% to 50%), preferably, (50% to 65%): (35% to 50%); the active material in the second protective layer and the active material in the positive electrode coating include a ternary material, and the second protective layer includes a ternary material, a conductive agent, a binder, and a positive temperature coefficient material, and the mass ratio of the ternary material, the conductive agent, the binder, and the positive temperature coefficient material is in the range of (70% to 97%): (1% to 5%): (1% to 5%): (1% to 20%), preferably, (85% to 92%): (1.5% to 2.5%): (1.5% to 2.5%): (5% to 10%).

[0187] In particular, the positive electrode active material in the second protective layer and the positive electrode active material in the positive electrode coating both include ternary materials. On this basis, positive temperature coefficient materials are added to the formula. When an internal or external short circuit occurs in the battery, the resistance of the protective layer increases significantly, causing the internal resistance of the battery cell to increase exponentially, reducing the short circuit current and thereby improving the stability of the ternary material.

[0188] In one embodiment, the mass percentage range of the mass of the positive temperature coefficient semiconductor material in the first protective layer to the mass of the first protective layer is greater than 0 and less than or equal to 80%; the mass percentage range of the mass of the conductive agent in the first protective layer to the mass of the first protective layer is greater than or equal to 0 and less than or equal to 65%; the mass percentage range of the mass of the binder in the first protective layer to the mass of the first protective layer is greater than or equal to 0 and less than or equal to 8%; the mass percentage range of the mass of the solid electrolyte in the first protective layer to the mass of the first protective layer is greater than or equal to 0 and less than or equal to 5%; the mass percentage range of the mass of the positive electrode active material in the first protective layer to the mass of the first protective layer is greater than or equal to 0 and less than or equal to 97%; the thickness range of the first protective layer is 1μm to 10μm, and the thickness range of the second protective layer is 2μm to 10μm.

[0189] For example, in one embodiment, the first protective layer includes a positive temperature coefficient semiconductor material and a conductive agent, the mass ratio of the positive temperature coefficient semiconductor material to the conductive agent is in the range of (50% to 80%): (20% to 50%), and the thickness of the first protective layer is in the range of 4μm to 10μm; the second protective layer includes a positive electrode active material, a conductive agent, a binder, and a solid electrolyte; the mass ratio of the positive electrode active material, the conductive agent, the binder, and the solid electrolyte is in the range of (74% to 95%): (2% to 8%): (2% to 8%): (1% to 10%), and the thickness of the second protective layer is in the range of 2μm to 10μm; or, the first protective layer includes a positive temperature coefficient semiconductor material and a conductive agent, the positive temperature coefficient semiconductor material The mass ratio of the positive electrode material to the conductive agent is in the range of (50% to 80%): (20% to 50%), and the thickness of the first protective layer is in the range of 4μm to 10μm; the second protective layer includes a positive temperature coefficient semiconductor material and a conductive agent, and the mass ratio of the positive temperature coefficient semiconductor material to the conductive agent is in the range of (50% to 80%): (20% to 50%), and the thickness of the second protective layer is in the range of 8μm to 10μm; or, the first protective layer includes a positive electrode active material, a conductive agent, a binder, a solid electrolyte, and a positive temperature coefficient semiconductor material, and the mass ratio of the positive electrode active material, the conductive agent, the binder, the solid electrolyte, and the positive temperature coefficient semiconductor material is in the range of (74% to 94%): (2% to 8%): (2 % to 8%): (1% to 5%): (1% to 5%), the thickness range of the first protective layer is 4μm to 10μm; the second protective layer includes a positive electrode active material, a conductive agent, a binder, and a solid electrolyte; the mass ratio of the positive electrode active material, the conductive agent, the binder, and the solid electrolyte is in the range of (74% to 95%): (2% to 8%): (2% to 8%): (1% to 10%), the thickness range of the second protective layer is 8μm to 10μm; or, the first protective layer includes a positive electrode active material, a conductive agent, a binder, and a positive temperature coefficient semiconductor material; the mass ratio of the positive electrode active material, the conductive agent, the binder, and the positive temperature coefficient semiconductor material is in the range of (70% to 97%): (1% to 5%) ): (1% to 5%): (1% to 20%), the thickness range of the first protective layer is 4μm to 10μm; the second protective layer includes a positive electrode active material, a conductive agent, a binder, and a solid electrolyte; the mass ratio of the positive electrode active material, the conductive agent, the binder, and the solid electrolyte is in the range of (74% to 95%): (2% to 8%): (2% to 8%): (1% to 10%), and the thickness range of the second protective layer is 8μm to 10μm; or, the first protective layer includes a positive temperature coefficient semiconductor material and a conductive agent, the mass ratio of the positive temperature coefficient semiconductor material to the conductive agent is in the range of (50% to 80%): (20% to 50%), and the thickness range of the first protective layer is 4μm to 10μm;The second protective layer includes a positive electrode active material, a conductive agent, a binder, a solid electrolyte, and a positive temperature coefficient semiconductor material. The mass ratio of the positive electrode active material, the conductive agent, the binder, the solid electrolyte, and the positive temperature coefficient semiconductor material is in the range of (74% to 94%): (2% to 8%): (2% to 8%): (1% to 5%): (1% to 5%), and the thickness of the second protective layer is in the range of 8μm to 10μm. ;

[0190] By setting the first protective layer and the second protective layer within the above-mentioned formula and thickness range, the test performance of the battery can be effectively improved. For example, in some schemes, the battery passes the hot box test, external short circuit test, and puncture test, indicating that the above scheme has a better protective effect on the battery.

[0191] In one embodiment, the thickness of the positive electrode coating ranges from 45 μm to 300 μm, preferably, from 60 μm to 90 μm; and / or, the protective layer comprises a positive temperature coefficient semiconductor material, the positive temperature coefficient material comprises at least one of a ceramic-based positive temperature coefficient material or a polymer-based positive temperature coefficient material, preferably, the ceramic-based positive temperature coefficient material comprises at least one of niobium titanate, tantalum titanate, strontium titanate, barium titanate, and lead titanate, the polymer-based positive temperature coefficient material comprises at least one of polyethylene, epoxy resin, ethylene-ethyl acrylate copolymer, polybutylene, cellulose acetate, polyamide, and a conductive agent; and / or, the protective layer comprises a solid electrolyte, the solid electrolyte comprises at least one of an oxide, a sulfide, a sulfur oxide, and a nitrogen oxide, preferably, the oxide comprises P 2O5, B2O3, SiO2, Li2O, the sulfide includes at least one of Li2S and SiS2, the sulfur oxide includes at least one of LiS-SiS2 doped with Li3PO4, LiAlO2, Li2SiO3, the nitrogen oxide includes at least one of LiPON, LiSiPON, LiSON; and / or the protective layer includes a conductive agent, the conductive agent includes at least one of Ketjen black, graphite, graphene, and carbon nanotubes; and / or the protective layer includes a positive electrode active material, the positive electrode active material includes at least one of lithium iron phosphate, lithium iron manganese phosphate, and a ternary material; and / or the protective layer includes a binder, the binder includes at least one of polyvinylidene fluoride, polyacrylonitrile, polytetrafluoroethylene, polyvinyl alcohol, and polyurethane.

[0192] The thickness of the positive electrode coating ranges from 45 μm to 300 μm, preferably from 60 μm to 90 μm. It is understandable that if the thickness of the positive electrode coating is too large, the resistance of the electrode itself is large, which affects the internal resistance and power performance of the battery cell. Considering comprehensively, the thickness of the positive electrode coating is set in the above range.

[0193] In the above-mentioned 45μm to 300μm, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiment and 45μm, 47μm, 49μm, 50μm, 55μm, 60μm, 70μm, 80μm, 90μm, 100μm, 120μm, 140μm, 160μm, 180μm, 200μm, 210μm, 230μm, 250μm, 280μm, 300μm, etc., and the range value between any two of the above-mentioned point values.

[0194] In the above-mentioned 60μm to 90μm, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 60μm, 64μm, 68μm, 70μm, 75μm, 77μm, 80μm, 84μm, 88μm, 90μm, etc., and the range values ​​between any two of the above-mentioned point values.

[0195] It can be understood that the protective layer includes a positive temperature coefficient semiconductor material, and the positive temperature coefficient material includes but is not limited to at least one of a ceramic-based positive temperature coefficient material or a polymer-based positive temperature coefficient material. Preferably, the ceramic-based positive temperature coefficient material includes but is not limited to at least one of niobium titanate, tantalum titanate, strontium titanate, barium titanate, and lead titanate. The polymer-based positive temperature coefficient material includes but is not limited to at least one of polyethylene, epoxy resin, ethylene-ethyl acrylate copolymer, polybutene, cellulose acetate, and polyamide, as well as a conductive agent. It can be understood that the polymer-based positive temperature coefficient material is generally a non-conductive material. In order to achieve conductivity, a certain conductive agent is compounded in the polymer-based positive temperature coefficient material. At high temperature, the polymer-based positive temperature coefficient material expands and destroys the conductive path of the conductive particle parts, thereby achieving the purpose of increasing the resistance.

[0196] It can be understood that the protective layer includes a solid electrolyte, which includes but is not limited to at least one of oxides, sulfides, sulfur oxides and nitrogen oxides. Preferably, the oxides include but are not limited to at least one of P2O5, B2O3, SiO2, and Li2O, the sulfides include but are not limited to at least one of Li2S and SiS2, the sulfur oxides include but are not limited to at least one of LiS-SiS2 doped with Li3PO4, LiAlO2, and Li2SiO3, and the nitrogen oxides include but are not limited to at least one of LiPON, LiSiPON, and LiSON.

[0197] It is understandable that the protective layer includes a conductive agent, which includes but is not limited to at least one of Ketjen black, graphite, graphene, and carbon nanotubes.

[0198] It is understood that the protective layer includes a positive electrode active material, and the positive electrode active material includes but is not limited to at least one of lithium iron phosphate, lithium iron manganese phosphate, and a ternary material;

[0199] It is understandable that the protective layer includes a binder, and the binder includes but is not limited to at least one of polyvinylidene fluoride, polyacrylonitrile, polytetrafluoroethylene, polyvinyl alcohol, and polyurethane.

[0200] In one embodiment, the protective layer includes a positive temperature coefficient semiconductor material, and the Dv50 of the positive temperature coefficient semiconductor material is 0.2 μm ≤ Dv50 < 1 μm; and / or, the protective layer includes a solid electrolyte, and the Dv50 of the solid electrolyte is 0.5 μm ≤ Dv50 ≤ 3 μm, and the specific surface area of ​​the solid electrolyte is 2m 2 / g to 6m 2 / g; and / or, the protective layer includes a positive electrode active material, the Dv50 of the positive electrode active material is 0.2μm≤Dv50<1.4μm, and the specific surface area of ​​the positive electrode active material is 8m 2 / g to 12m 2 / g.

[0201] Dv50 is the particle size corresponding to when the cumulative particle size distribution percentage of a sample reaches 50%. Its physical meaning is that particles with a particle size larger than it account for 50%, and particles with a particle size smaller than it also account for 50%. Dv50 is also called the median diameter or median particle size. Dv50 is often used to indicate the average particle size of powders.

[0202] Among the sample particles, 50% of the total volume of the particles have a particle size larger than this value, and another 50% of the total volume of the particles have a particle size smaller than this value; Dv50 can represent the median particle size of the sample.

[0203] Dv50 can be tested by methods known in the art. For example, GB / T19077-2016 can be referred to, and a Malvern laser particle size analyzer can be used for characterization testing, such as a Malvern Mastersizer-3000 or other instrument.

[0204] The Dv50 of the positive temperature coefficient semiconductor material is 0.2μm≤Dv50<1μm. It is understandable that the positive temperature coefficient semiconductor material needs to be evenly dispersed in the protective layer. If the particle size is too large, it is not conducive to the uniform dispersion of the addition. When the temperature rises, the local resistance change of the protective layer is inconsistent, which is not conducive to the stability of the protective positive electrode coating. When the particle size is too small, the dispersion processing performance is relatively poor. Therefore, considering comprehensively, the Dv50 of the positive temperature coefficient semiconductor material is set in the above range.

[0205] The Dv50 of the solid electrolyte is 0.5μm≤Dv50≤3μm, and the specific surface area of ​​the solid electrolyte is 2m 2 / g to 6m2 It can be understood that the Dv50 and specific surface area of ​​the solid electrolyte are set within the above ranges, so that it can be effectively dispersed in the protective layer, formed into a suitable thickness, and evenly arranged on the positive electrode coating.

[0206] The protective layer includes a positive electrode active material, the Dv50 of the positive electrode active material is 0.2 μm ≤ Dv50 < 1.4 μm, and the specific surface area of ​​the positive electrode active material is 8 m 2 / g to 12m 2 / g. It is understandable that by selecting the Dv50 and specific surface area of ​​the positive electrode active material to be set within the above range, the protective layer is easier to evenly cover the surface of the positive electrode coating, and the protective effect is better. In addition, it can also effectively improve the conduction rate of lithium ions and reduce the transmission impedance of the pole piece, which has a certain effect on improving the power performance of the battery cell.

[0207] In the above 0.2μm≤Dv50<1μm, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 0.99μm, etc., and the range values ​​between any two of the above point values.

[0208] In the above 0.5μm≤Dv50≤3μm, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm, 1.5μm, 2μm, 2.5μm, 3μm, etc., and the range values ​​between any two of the above point values.

[0209] Above 2m 2 / g to 6m 2 / g, the value includes the minimum and maximum values ​​of the range, and each value between the minimum and maximum values, and specific examples include but are not limited to the point value in the embodiment and 2m 2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g, etc., as well as the range value between any two of the above point values.

[0210] In the above 0.2μm≤Dv50<1.4μm, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm, 1.2μm, 1.3μm, 1.39μm, etc., and the range value between any two of the above point values.

[0211] Above 8m 2 / g to 12m 2 / g, the value includes the minimum and maximum values ​​of the range, and each value between the minimum and maximum values, and specific examples include but are not limited to the point values ​​in the embodiment and 8m 2 / g, 9m 2 / g, 10m 2 / g, 11m 2 / g, 12m 2 / g, etc., as well as the range value between any two of the above point values.

[0212] In one embodiment, the positive electrode coating includes a ternary material, a conductive agent, and a binder, and the mass ratio of the ternary material, the conductive agent, and the binder ranges from (90% to 98%): (1% to 5%): (1% to 5%).

[0213] Ternary materials, ternary positive electrode materials are layered nickel cobalt manganese (aluminum) lithium oxide composite materials. Nickel, cobalt, and manganese are transition metal elements. The solid solution formed can be mixed in any proportion. The increase in the proportion of nickel elements can improve the battery specific energy, the increase in the proportion of manganese elements can ensure structural stability, and the increase in the proportion of cobalt elements can stabilize the layered structure of the material, which is beneficial to the cycle performance and rate performance of the battery. In addition, it can also be understood that ternary materials can also include materials that do not contain cobalt, for example, ternary materials obtained by using other metal elements instead of cobalt, such as ternary materials obtained by using Mo, Nb, etc. instead of cobalt.

[0214] It is understandable that the positive electrode active materials in the positive electrode coating of the present application include but are not limited to ternary materials. Considering that the ternary materials have poor thermal stability in some cases (such as ternary high-nickel positive electrode materials), when the battery is subjected to external extrusion, collision, puncture or high temperature abuse, an internal short circuit occurs and it is easy to catch fire and explode. For this reason, the ternary materials need more protection from the protective layer. The positive electrode coating includes a ternary material, a conductive agent, and a binder. The mass ratio of the ternary material, the conductive agent, and the binder is in the range of (90% to 98%): (1% to 5%): (1% to 5%).

[0215] In the above (90% to 98%): (1% to 5%): (1% to 5%), the values ​​include the minimum and maximum values ​​of the range, and every value between such minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 90%:5%:5%, 95%:2.5%:2.5%, 98%:1%:1%, etc., as well as the range values ​​between any two of the above point values.

[0216] In one embodiment, the Dv50 of the ternary material is 4 μm ≤ Dv50 ≤ 12 μm, and the specific surface area of ​​the ternary material is 0.5 m 2 / g to 1.5m 2 / g; and / or, the ternary material includes at least one of 6-series ternary materials, 7-series ternary materials, 8-series ternary materials, 9-series ternary materials, and cobalt-free high-nickel ternary materials; and / or, the ternary material includes a single crystal material, the Dv50 of the single crystal material is 2μm≤Dv50≤7μm, and the specific surface area is 0.8m 2 / g to 1.4m 2 / g; and / or, the ternary material includes a polycrystalline material, the Dv50 of the polycrystalline material is 7μm≤Dv50≤15μm, and the specific surface area is 0.5m 2 / g to 0.8m 2 / g.

[0217] It can be understood that the Dv50 and specific surface area of ​​the ternary material are set within the above range, which can meet the performance and production cost requirements of the ternary material.

[0218] 6 series ternary materials refer to ternary materials with a molar ratio of nickel metal greater than or equal to 60% and less than 70%. 7 series ternary materials refer to ternary materials with a molar ratio of nickel metal greater than or equal to 70% and less than 80%. 8 series ternary materials refer to ternary materials with a molar ratio of nickel metal greater than or equal to 80% and less than 90%. 9 series ternary materials refer to ternary materials with a molar ratio of nickel metal greater than or equal to 90%, such as Ni90, Ni92, Ni95, etc. As the nickel content gradually increases, the battery energy density also increases. The higher the nickel, the greater the energy density of the battery cell, but cobalt is forced to decrease. The medium nickel ternary material has a relatively high nickel content, low nickel, and a high cobalt content, so its stability is guaranteed enough. In addition, single crystal materials generate less heat and have high stability, and their stability performance is much higher than that of high nickel materials. Single crystal medium nickel ternary currently achieves a good balance in multiple dimensions such as economy, stability, energy density, and cycle life.

[0219] Cobalt-free ternary materials refer to ternary materials that do not contain cobalt, for example, ternary materials in which the cobalt element can be replaced by other elements.

[0220] Cobalt-free high-nickel ternary materials, in the absence of cobalt, the molar ratio of nickel metal is greater than or equal to 90%. Common cobalt-free materials are lithium nickel oxide and lithium nickel manganese oxide.

[0221] Single crystal ternary materials and polycrystalline ternary materials are named according to the morphology of the materials themselves. From the morphology point of view, single crystal is a single dispersed particle, while the corresponding polycrystalline ternary material is a secondary particle of primary particle agglomeration.

[0222] Compared with polycrystalline materials, single crystal materials are more suitable for high voltage. At the same time, there are no grain boundaries inside single crystal materials, which can improve the cycle stability of ternary materials and extend the cycle life of batteries. Under the same ratio of nickel, cobalt and manganese, the gram capacity of single crystal ternary materials is slightly lower than that of polycrystalline ternary materials, but because of its higher voltage, the overall energy density of the material is already similar to that of the current high-nickel ternary materials. The disadvantage of single crystal ternary materials is that the rate performance is poor, the production process is more complicated, and the material price is relatively high.

[0223] In the above 4μm≤Dv50≤12μm, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, etc., and the range values ​​between any two of the above point values.

[0224] Above 0.5m 2 / g to 1.5m 2 / g, the value includes the minimum value and the maximum value of the range, and each value between the minimum value and the maximum value, and specific examples include but are not limited to the point value in the embodiment and 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, etc., as well as the range value between any two of the above point values.

[0225] In one embodiment, the present application also provides a method for preparing a positive electrode plate as above, comprising: preparing a protective layer material and a positive electrode coating material; setting the protective layer material and the positive electrode coating material on a current collector to form a positive electrode plate, the positive electrode plate comprising a current collector and a positive electrode coating and a protective layer stacked on the same side of the current collector, the protective layer comprising a first protective layer, the first protective layer being arranged on the current collector, the positive electrode coating being arranged on a side of the first protective layer away from the current collector, and the first protective layer comprising a positive temperature coefficient semiconductor material.

[0226] In one embodiment, the step of setting the protective layer material on the current collector includes: preparing a first protective layer material, the first protective layer material including a positive temperature coefficient semiconductor material; depositing the first protective layer material onto the current collector using a vapor deposition technique to set a first protective layer on the current collector.

[0227] Vapor deposition technology is a new technology that uses physical and chemical processes in the gas phase to change the surface composition of the workpiece and form a metal or compound coating with special properties (such as a super-hard wear-resistant layer or special optical and electrical properties) on the surface. According to the nature of the process, vapor deposition can be divided into two categories: chemical vapor deposition (CVD) and physical vapor deposition (PVD).

[0228] Chemical vapor deposition is a technology that mainly uses one or several gas phase compounds or single substances containing thin film elements to undergo chemical reactions on the surface of the substrate to form a thin film.

[0229] Physical vapor deposition. The main methods of physical vapor deposition are: vacuum evaporation, sputtering coating, arc plasma coating, ion plating and molecular beam epitaxy.

[0230] In the present application, the first protective layer material can be deposited onto the current collector by vapor deposition to set the first protective layer on the current collector. The deposition method of the present application can be selected as needed.

[0231] For example, vacuum evaporation method and vacuum ion plating technology can be used, and the density and uniformity of the coating are relatively good; they are more excellent for growing thin films in the lithium battery industry.

[0232] Compared with the coating method, the vapor deposition method has a stronger bonding force between the protective layer and the current collector, the porosity of the protective layer is smaller and denser, and the thickness of the protective layer can be more easily adjusted and controlled according to design requirements.

[0233] For example, in one embodiment, pure strontium titanate target and C target are used as target materials, and the co-sputtering method of pure strontium titanate target and C target is used for deposition, so that the mass ratio of strontium titanate and C in the protective layer is 1:1; the sputtering thickness is 1μm to 5μm. Before deposition, the steps of cleaning the vacuum sputtering chamber and cleaning the plating hanger are included. The vacuum sputtering chamber is evacuated, generally to above 6.6Pa, and then the heated diffusion pump is turned on. After sufficient preheating, the high valve is opened and the diffusion pump is used to evacuate to ≤10 -2 Pa low vacuum, for example, can be 10 -4 Pa to 10 -5 Pa. Then turn on the baking function to heat the plated parts to the required temperature (depending on the specific situation, it can also be turned off or set at different temperatures for sputtering). Then perform ion bombardment, the vacuum degree is generally between 10Pa and 10 -1 Pa, ion bombardment voltage 200V to 1kV negative high voltage, bombardment time 5min to 30min. Then carry out evaporation deposition, adjust evaporation current 50A to 200A according to requirements, deposition time 5min to 30min, until the deposition is completed. Cool the plated part to a certain temperature in the vacuum chamber, for example, below 25°C.

[0234] In one embodiment, the step of depositing the first protective layer material onto the current collector by using a vapor deposition technique includes sputtering a positive temperature coefficient semiconductor material and a conductive agent onto the current collector simultaneously.

[0235] In order to make the conductive agent uniformly dispersed in the first protective layer, the positive temperature coefficient semiconductor material and the conductive agent are sputtered onto the current collector at the same time to improve the conductive uniformity of the first protective layer.

[0236] In one embodiment, the step of setting the protective layer material on the current collector includes: preparing a first protective layer material, preparing the first protective layer material into a first protective layer material slurry; and coating the first protective layer material slurry to the current collector to set a first protective layer on the current collector.

[0237] It is understandable that, in addition to providing the first protective layer on the current collector by using the vapor deposition technology, the first protective layer can also be prepared by coating the slurry onto the current collector by coating.

[0238] Optionally, the step of setting the protective layer material in the current collector includes: preparing a positive electrode coating material, preparing the positive electrode coating material into a positive electrode coating material slurry; applying the positive electrode coating material slurry to the current collector, drying, and forming a positive electrode coating on the current collector; preparing a second protective layer material, preparing the second protective layer material into a second protective layer material slurry; and applying the second protective layer material slurry to the surface of the positive electrode coating to set a second protective layer on the surface of the positive electrode coating.

[0239] In the step of preparing the positive electrode coating, the positive electrode coating material slurry can be applied to the current collector and dried to form a positive electrode coating on the current collector; in addition, a second protective layer material can be prepared, the second protective layer material can be prepared into a second protective layer material slurry, and the second protective layer material slurry can be applied to the surface of the positive electrode coating to set a second protective layer on the surface of the positive electrode coating.

[0240] In one embodiment, after the step of setting the protective layer material and the positive electrode coating material on the current collector to form the positive electrode plate, it also includes: preparing a second protective layer material, the second protective layer material includes a positive temperature coefficient semiconductor material; depositing the second protective layer material on the surface of the positive electrode plate by using a vapor deposition technology to set a second protective layer on the positive electrode plate.

[0241] That is, vapor deposition may also be used in the process of preparing the second protective layer. It is understandable that in order to facilitate the passage of ions through the second protective layer, the thickness of the second protective layer formed in this way is preferably within 2 μm, for example, 1 μm to 2 μm.

[0242] The present application also provides a battery, the battery comprising the positive electrode plate as described above; or, the battery comprising the positive electrode plate prepared by the method for preparing the positive electrode plate as described above.

[0243] In addition, the battery (secondary battery, battery module, battery pack) and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0244] In one embodiment of the present application, a secondary battery is provided.

[0245] Typically, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charge and discharge process, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through. The separator is the separator improved above in this application.

[0246] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector.

[0247] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0248] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0249] In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material may adopt a positive electrode active material for lithium-ion batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0250] The battery will be accompanied by Li deintercalation and consumption during the charge and discharge process, and the molar content of Li is different when the battery is discharged to different states. In the list of positive electrode materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode material is used in the battery system, and the molar content of Li will change after charge and discharge cycles.

[0251] In the list of positive electrode materials in this application, the molar content of O is only a theoretical value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0252] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0253] In some embodiments, the positive electrode film layer may further include a conductive agent, for example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0254] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0255] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0256] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0257] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0258] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0259] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0260] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0261] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0262] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0263] The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs.

[0264] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0265] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0266] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0267] In some embodiments, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0268] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0269] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 5 The battery cell 5 is a square structure as an example.

[0270] In some embodiments, reference Figure 6 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the diaphragm can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0271] In some embodiments, a battery cell pool may be assembled into a battery module. The number of battery cells contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0272] Figure 7 4 is an example of a battery module. Figure 7In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0273] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0274] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0275] Figure 8 and Fig. 9 1 is a battery pack 1 as an example. Figure 8 and Fig. 9 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0276] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0277] As an electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0278] Fig.10 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the power consumption device's requirements for high power and high energy density of battery cells, a battery pack or a battery module can be used.

[0279] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is usually required to be light and thin, and a battery cell may be used as a power source.

[0280] Example

[0281] Example 1

[0282] Preparation of positive electrode

[0283] Deposition of the first protective layer on the current collector

[0284] The current collector is made of aluminum and has a thickness of 12μm.

[0285] Target preparation: SrTiO3 target (purity 99.9%) and C target (SrTiO3 and C), two targets are co-sputtered, pre-plating cleaning: including cleaning and pre-treatment of the plated parts and cleaning of the vacuum chamber and plated fixtures. Vacuum, first evacuate to above 6.6Pa, then turn on the heated diffusion pump, after preheating is sufficient, open the high valve, and use the diffusion pump to ≤10 -2 Pa half bottom vacuum. Turn on the baking function and bake the plated parts to 130℃. Ion bombardment, vacuum degree at 10 -1 Pa, ion bombardment voltage 500V negative high voltage, off-bombardment time is 15min. Evaporation deposition, adjust the evaporation current to 100A according to the requirements, and the deposition time is 30min. Cooling, the plated parts are cooled to below 50℃ in the vacuum chamber. After taking out the furnace and taking out the parts, close the vacuum chamber, turn off the main power supply, and clean the site. The mass ratio of the first protective layer finally formed on the surface of the current collector is SrTiO3:C=1:1; the sputtering thickness is 2μm.

[0286] Preparation of cathode coating

[0287] Preparation of positive electrode coating slurry: The positive electrode material (lithium nickel cobalt manganese oxide LiNi 0.8 Co 0.1 Mn 0.1 O2, Dv50 is 12μm, specific surface area is 0.6m 2 / g), conductive agent (graphene), binder (polyvinylidene fluoride) are dissolved in solvent (N-methylpyrrolidone (NMP)) in a mass ratio of 95%:3%:2%. The positive electrode slurry is coated on the above-mentioned current collector (coated on the side of the first protective layer away from the current collector), and dried at 85-100°C and then cold pressed, and then trimmed and cut into pieces, and dried at 85°C under vacuum conditions for 4 hours to make positive electrode sheets. The thickness of the positive electrode coating is 80μm. The preparation method of the positive electrode coating in each embodiment and comparative example is the same as that in Example 1.

[0288] Preparation of the second protective layer

[0289] Preparation of the second protective layer slurry: lithium iron phosphate (Dv50 is 0.5 μm, specific surface area is 10 m 2 / g), conductive agent (graphene), binder (polyvinylidene fluoride), solid electrolyte P2O5 (Dv50 is 1μm, specific surface area is 4m 2 / g) additives are dissolved in a solvent (N-methylpyrrolidone (NMP)) at a mass ratio of 94%: 2%: 2%: 2% to obtain a protective layer slurry. The protective layer slurry is coated on the above-mentioned current collector (coated on the side of the positive electrode coating away from the current collector), dried at 85-100°C, cold pressed, and then trimmed and cut into pieces, and dried at 95°C under vacuum conditions for 4 hours to make a positive electrode sheet. The thickness of the second protective layer is 6μm.

[0290] Preparation of negative electrode

[0291] The first active material of the negative electrode, graphite, the conductive agent Super P, the binder styrene butadiene rubber (SBR) and the thickener CMC-Na were dispersed in deionized water at a mass ratio of 96:1:1.5:1.5 and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry was coated on the negative electrode current collector copper foil and dried at 85°C, then cold pressed, trimmed, cut into pieces, and dried at 95°C under vacuum conditions for 12 hours to make a negative electrode sheet.

[0292] Diaphragm

[0293] A 12 μm polyethylene film was selected as the isolation film.

[0294] Preparation of electrolyte

[0295] The electrolyte is 1 mol / L lithium hexafluorophosphate (LiPF6), the solvent system is EC / DEC / EMC, the volume ratio is 2:3:5, and the additive mass accounts for 1wt% FEC and 1wt% VC.

[0296] Preparation of batteries

[0297] The positive electrode sheet, separator, and negative electrode sheet prepared in the above steps are stacked in order, so that the separator is located between the positive and negative electrode sheets to isolate the positive and negative electrodes, and the bare battery cell is wound, and the tabs are welded, and the bare battery cell is placed in an outer package. The electrolyte prepared above is injected into the dried battery cell, and after packaging and standing, it is slowly formed, and then shaped to prepare a lithium-ion battery.

[0298] Example 2

[0299] On the basis of Example 1, the formulas of the positive electrode coating, the first protective layer and the second protective layer are kept unchanged, and the thicknesses of the first protective layer and the second protective layer are adjusted.

[0300] Example 3

[0301] On the basis of Example 1, the positive electrode coating and the first protective layer are kept unchanged, and the second protective layer is prepared in the same manner as the first protective layer in Example 1.

[0302] Example 4

[0303] On the basis of Example 3, the formulas of the positive electrode coating, the first protective layer and the second protective layer are kept unchanged, and the thicknesses of the first protective layer and the second protective layer are adjusted.

[0304] Example 5

[0305] On the basis of Example 1, the positive electrode coating and the second protective layer are kept unchanged, and the formula of the first protective layer is adjusted.

[0306] The first protective layer formula is: lithium iron phosphate (Dv50 is 0.5μm, specific surface area is 10m 2 / g), conductive agent (graphene), binder (polyvinylidene fluoride), solid electrolyte P2O5 (Dv50 is 1μm, specific surface area is 4m 2 / g) and positive temperature coefficient material strontium titanate (Dv50 is 0.5μm) in a mass ratio of 90%:3%:3%:2%:2%.

[0307] Example 6

[0308] On the basis of Example 5, the formulas of the positive electrode coating, the first protective layer and the second protective layer are kept unchanged, and the thicknesses of the first protective layer and the second protective layer are adjusted.

[0309] Example 7

[0310] On the basis of Example 1, the positive electrode coating and the second protective layer are kept unchanged, and the formula of the first protective layer is adjusted.

[0311] The first protective layer formula is: lithium iron phosphate (Dv50 is 0.5μm, specific surface area is 10m 2 / g), conductive agent (graphene), binder (polyvinylidene fluoride), and positive temperature coefficient material strontium titanate (Dv50 is 0.5μm) in a mass ratio of 90%:2%:2%:6%.

[0312] Example 8

[0313] On the basis of Example 7, the formulas of the positive electrode coating, the first protective layer and the second protective layer are kept unchanged, and the thicknesses of the first protective layer and the second protective layer are adjusted.

[0314] Example 9 and Example 10

[0315] On the basis of Example 1, the thickness range of the first protective layer is adjusted (1 μm, 10 μm).

[0316] Example 11 and Example 12

[0317] On the basis of Examples 9 and 10, the formulas of the positive electrode coating, the first protective layer and the second coating are kept unchanged, and the thickness of the second protective layer is adjusted.

[0318] Example 13 and Example 14

[0319] On the basis of Example 5, the types of the active material of the first protective layer, the solid electrolyte material, and the positive temperature coefficient material are adjusted.

[0320] Example 15 and Example 16

[0321] On the basis of Examples 13 and 14, the formulas of the positive electrode coating, the first protective layer and the second protective layer are kept unchanged, and the thicknesses of the first protective layer and the second protective layer are adjusted.

[0322] Embodiment 17

[0323] Based on Example 1, no second protective layer is provided.

[0324] Embodiment 18

[0325] Based on Example 17, the thickness of the first protective layer is adjusted.

[0326] Embodiment 19

[0327] Based on Example 1, the active material in the second protective layer was adjusted.

[0328] Embodiment 20

[0329] On the basis of Example 19, the thickness of the first protective layer and the second protective layer are adjusted.

[0330] Embodiment 21

[0331] Based on Example 1, the formula of the second protective layer was adjusted.

[0332] The second protective layer formula is: lithium iron phosphate (Dv50 is 0.5μm, specific surface area is 10m 2 / g), conductive agent (graphene), binder (polyvinylidene fluoride), solid electrolyte P2O5 (Dv50 is 1μm, specific surface area is 4m 2 / g) and positive temperature coefficient material strontium titanate (Dv50 is 0.5μm) in a mass ratio of 90%:3%:3%:2%:2%.

[0333] Embodiment 22

[0334] Based on Example 1, the formula of the second protective layer was adjusted.

[0335] The second protective layer formula is: lithium iron phosphate (Dv50 is 0.5μm, specific surface area is 10m 2 / g), conductive agent (graphene), binder (polyvinylidene fluoride), and positive temperature coefficient material strontium titanate (Dv50 is 0.5μm) in a mass ratio of 90%:2%:2%:6%.

[0336] Embodiment 23

[0337] Based on Example 21, the thicknesses of the first protective layer and the second protective layer are adjusted.

[0338] Embodiment 24

[0339] Based on Example 22, the thickness of the first protective layer and the second protective layer are adjusted.

[0340] Example 25 and Example 26

[0341] On the basis of Example 1, the thickness range of the second protective layer is adjusted (2 μm, 10 μm).

[0342] Example 27 and Example 28

[0343] Based on Examples 25 and 26, the thickness of the first protective layer is adjusted.

[0344] Comparative Example 1

[0345] On the basis of Example 1, only the positive electrode coating is provided on the current collector, and the first protective layer and the second protective layer are not provided.

[0346] Comparative Example 2

[0347] Based on Example 1, the first protective layer is not provided.

[0348] Battery performance test steps

[0349] Hot box test

[0350] First, charge the battery to full charge using 0.33C constant current and constant voltage, then place it in an environmental chamber, heat it from room temperature to the set temperature (national standard 130℃±2℃) at a rate of 5℃ / min, and maintain this temperature for 30 minutes before stopping heating and observing for 1 hour. The battery is required not to catch fire or explode.

[0351] External short circuit test

[0352] First, charge the battery to full charge using 0.33C constant current and constant voltage, and then use a short-circuit tester to force the positive and negative poles of the battery to be externally short-circuited for 10 minutes. The external short-circuit resistance is required to be controlled ≤5mΩ, and the battery is required not to catch fire or explode.

[0353] Acupuncture test

[0354] First, charge the battery to full charge using 0.33C constant current and constant voltage. Then use a φ5mm~φ8mm high-temperature resistant steel needle (the cone angle of the needle tip is 45°~60°, and the surface of the needle is smooth, free of rust, oxide layer and oil) to penetrate the battery plate at a speed of (25±5)mm / s from a direction perpendicular to the battery plate. The penetration position should be close to the geometric center of the pierced surface. The steel needle stays in the battery and is observed for 1 hour. The battery is required not to catch fire or explode.

[0355] Table 1 List of Examples

[0356]

[0357]

[0358]

[0359] Table 2 Example List

[0360]

[0361]

[0362] Table 3 Performance parameter list

[0363]

[0364]

[0365]

[0366] It can be seen from the above table that, by comparing the embodiments with the comparative examples, providing a protective layer in the positive electrode coating can improve the pass rate of the battery in the hot box test, the needle penetration test, and the external short circuit test. Moreover, when two protective layers are provided at the same time, the battery test phenomenon performs better than when only one protective layer is provided.

[0367] As shown in Example 1 and Example 2, when the formulas of the first protective layer and the second protective layer remain unchanged, the thickness of the first protective layer and the second protective layer are adjusted, and the performance of the battery is improved. For example, the thickness of the first protective layer and the second protective layer in Example 1 is less than that in Example 2. At this time, the battery in Example 1 fails the puncture test, while the battery in Example 2 passes the puncture test.

[0368] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention's specification and drawings, or directly / indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A positive electrode sheet, characterized in that: It includes a current collector and a positive electrode coating and a protective layer stacked on the same side of the current collector, the protective layer includes a first protective layer, the first protective layer is arranged on the current collector, the positive electrode coating is arranged on the side of the first protective layer away from the current collector, and the first protective layer includes a positive temperature coefficient semiconductor material.

2. The positive electrode sheet according to claim 1, characterized in that: The porosity of the first protective layer is less than the porosity of the positive electrode coating; And / or, the thickness of the first protective layer ranges from 1 μm to 10 μm, preferably, from 4 μm to 10 μm.

3. The positive electrode sheet according to claim 1 or 2, characterized in that: The first protective layer further includes at least one of a conductive agent, a solid electrolyte, a positive electrode active material, and a binder.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The mass percentage of the mass of the positive temperature coefficient semiconductor material to the mass of the first protective layer is in the range of greater than 0 and less than or equal to 80%; The mass percentage of the mass of the conductive agent to the mass of the first protective layer is in the range of greater than or equal to 0 and less than or equal to 65%; The mass percentage of the mass of the adhesive to the mass of the first protective layer is in the range of greater than or equal to 0 and less than or equal to 8%; The mass percentage of the mass of the solid electrolyte to the mass of the first protective layer is in the range of greater than or equal to 0 and less than or equal to 5%; The mass percentage of the mass of the positive electrode active material to the mass of the first protective layer is in the range of greater than or equal to 0 and less than or equal to 97%.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The protective layer further includes a second protective layer, and the second protective layer is arranged on a side of the positive electrode coating layer away from the current collector.

6. The positive electrode sheet according to claim 5, characterized in that: The porosity of the second protective layer is greater than the porosity of the positive electrode coating; And / or, the thickness of the second protective layer is in the range of 2 μm to 10 μm, preferably, 6 μm to 10 μm, preferably, 8 μm to 10 μm.

7. The positive electrode sheet according to claim 5 or 6, characterized in that: The second protective layer includes at least one of a positive temperature coefficient semiconductor material, a solid electrolyte, and a positive electrode active material.

8. The positive electrode sheet according to any one of claims 5 to 7, characterized in that: The mass percentage of the mass of the positive temperature coefficient semiconductor material in the second protective layer to the mass of the second protective layer is in the range of greater than or equal to 0 and less than or equal to 80%; The mass percentage of the mass of the solid electrolyte in the second protective layer to the mass of the second protective layer is in the range of greater than or equal to 0 and less than or equal to 5%; The mass percentage of the mass of the positive electrode active material in the second protective layer to the mass of the second protective layer is in the range of greater than or equal to 0 and less than or equal to 97%; The second protective layer includes a conductive agent, and the mass percentage of the conductive agent in the second protective layer to the mass of the second protective layer is in a range of greater than or equal to 0 and less than or equal to 65%; The second protective layer includes an adhesive, and the mass percentage of the mass of the adhesive in the second protective layer to the mass of the second protective layer is in a range of greater than or equal to 0 and less than or equal to 8%.

9. The positive electrode sheet according to any one of claims 5 to 8, characterized in that: The first protective layer comprises a positive temperature coefficient semiconductor material and a conductive agent, and the mass ratio of the positive temperature coefficient semiconductor material to the conductive agent is in the range of (50% to 80%): (20% to 50%), preferably, (50% to 65%): (35% to 50%); the second protective layer comprises a positive electrode active material, a conductive agent, a binder, and a solid electrolyte, and the mass ratio of the positive electrode active material, the conductive agent, the binder, and the solid electrolyte is in the range of (74% to 95%): (2% to 8%): (2% to 8%): (1% to 10%), preferably, (85% to 94%): (2% to 5%): (2% to 5%): (2% to 5%); Alternatively, the first protective layer includes a positive temperature coefficient semiconductor material and a conductive agent, and the mass ratio of the positive temperature coefficient semiconductor material to the conductive agent is in the range of (50% to 80%): (20% to 50%), preferably, (50% to 65%): (35% to 50%); the second protective layer includes a positive electrode active material, a conductive agent, a binder, and a positive temperature coefficient material, and the mass ratio of the positive electrode active material, the conductive agent, the binder, and the positive temperature coefficient material is in the range of (70% to 97%): (1% to 5%): (1% to 5%): (1% to 20%), preferably, (85% to 92%): (1.5% to 2.5%): (1.5% to 2.5%): (5% to 10%).

10. The positive electrode sheet according to claim 8, characterized in that: The mass percentage of the mass of the positive temperature coefficient semiconductor material in the first protective layer to the mass of the first protective layer is in the range of greater than 0 and less than or equal to 80%; The mass percentage of the mass of the conductive agent in the first protective layer to the mass of the first protective layer is in the range of greater than or equal to 0 and less than or equal to 65%; The mass percentage of the mass of the binder in the first protective layer to the mass of the first protective layer is in the range of greater than or equal to 0 and less than or equal to 8%; The mass percentage of the mass of the solid electrolyte in the first protective layer to the mass of the first protective layer is in the range of greater than or equal to 0 and less than or equal to 5%; The mass percentage of the mass of the positive electrode active material in the first protective layer to the mass of the first protective layer is in the range of greater than or equal to 0 and less than or equal to 97%; The thickness of the first protective layer ranges from 1 μm to 10 μm, and the thickness of the second protective layer ranges from 2 μm to 10 μm.

11. The positive electrode sheet according to any one of claims 1 to 10, characterized in that: The thickness of the positive electrode coating ranges from 45 μm to 300 μm, preferably from 60 μm to 90 μm; And / or, the protective layer comprises a positive temperature coefficient semiconductor material, the positive temperature coefficient material comprises at least one of a ceramic-based positive temperature coefficient material or a polymer-based positive temperature coefficient material, preferably, the ceramic-based positive temperature coefficient material comprises at least one of niobium titanate, tantalum titanate, strontium titanate, barium titanate, and lead titanate, the polymer-based positive temperature coefficient material comprises at least one of polyethylene, epoxy resin, ethylene-ethyl acrylate copolymer, polybutylene, cellulose acetate, polyamide, and a conductive agent; And / or, the protective layer includes a solid electrolyte, the solid electrolyte includes at least one of an oxide, a sulfide, an oxysulfide and an oxynitride, preferably, the oxide includes at least one of P2O5, B2O3, SiO2, Li2O, the sulfide includes at least one of Li2S and SiS2, the oxysulfide includes at least one of LiS-SiS2 doped with Li3PO4, LiAlO2, Li2SiO3, the oxynitride includes at least one of LiPON, LiSiPON, LiSON; And / or, the protective layer includes a conductive agent, and the conductive agent includes at least one of Ketjen black, graphite, graphene, and carbon nanotubes; And / or, the protective layer includes a positive electrode active material, and the positive electrode active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, and a ternary material; And / or, the protective layer includes a binder, and the binder includes at least one of polyvinylidene fluoride, polyacrylonitrile, polytetrafluoroethylene, polyvinyl alcohol, and polyurethane.

12. The positive electrode sheet according to any one of claims 1 to 11, characterized in that: The protective layer comprises a positive temperature coefficient semiconductor material, and the Dv50 of the positive temperature coefficient semiconductor material is 0.2 μm≤Dv50<1 μm; And / or, the protective layer comprises a solid electrolyte, the Dv50 of the solid electrolyte is 0.5 μm ≤ Dv50 ≤ 3 μm, and the specific surface area of ​​the solid electrolyte is 2 m 2 / g to 6m 2 / g; And / or, the protective layer comprises a positive electrode active material, the Dv50 of the positive electrode active material is 0.2 μm≤Dv50<1.4 μm, and the specific surface area of ​​the positive electrode active material is 8 m 2 / g to 12m 2 / g.

13. The positive electrode sheet according to any one of claims 1 to 12, characterized in that: The positive electrode coating includes a ternary material, a conductive agent, and a binder. The mass ratio of the ternary material, the conductive agent, and the binder ranges from (90% to 98%): (1% to 5%): (1% to 5%).

14. The positive electrode sheet according to claim 13, characterized in that: The Dv50 of the ternary material is 4 μm≤Dv50≤12 μm, and the specific surface area of ​​the ternary material is 0.5 m 2 / g to 1.5m 2 / g; And / or, the ternary material includes at least one of 6-series ternary material, 7-series ternary material, 8-series ternary material, 9-series ternary material, and cobalt-free high-nickel ternary material; And / or, the ternary material comprises a single crystal material, the Dv50 of the single crystal material is 2 μm≤Dv50≤7 μm, and the specific surface area is 0.8 m 2 / g to 1.4m 2 / g; And / or, the ternary material comprises a polycrystalline material, the Dv50 of the polycrystalline material is 7 μm ≤ Dv50 ≤ 15 μm, and the specific surface area is 0.5 m 2 / g to 0.8m 2 / g.

15. A method for preparing a positive electrode sheet according to any one of claims 1 to 14, characterized in that: include: preparing protective layer materials and positive electrode coating materials; The protective layer material and the positive electrode coating material are arranged on a current collector to form a positive electrode plate, wherein the positive electrode plate comprises the current collector and a positive electrode coating and a protective layer stacked on the same side of the current collector, wherein the protective layer comprises a first protective layer, wherein the first protective layer is arranged on the current collector, the positive electrode coating is arranged on a side of the first protective layer away from the current collector, and the first protective layer comprises a positive temperature coefficient semiconductor material.

16. The method for preparing a positive electrode sheet according to claim 15, characterized in that: The step of placing the protective layer material in the current collector comprises: preparing a first protective layer material, wherein the first protective layer material comprises a positive temperature coefficient semiconductor material; The first protective layer material is deposited onto the current collector by using a vapor deposition technique to provide a first protective layer on the current collector.

17. The method for preparing a positive electrode sheet according to claim 16, characterized in that: The step of depositing the first protective layer material onto the current collector by using a vapor deposition technique includes sputtering the positive temperature coefficient semiconductor material and the conductive agent onto the current collector simultaneously.

18. The method for preparing a positive electrode sheet according to any one of claims 15 to 17, characterized in that: After the step of placing the protective layer material and the positive electrode coating material on the current collector to form a positive electrode sheet, the method further includes: preparing a second protective layer material, wherein the second protective layer material includes a positive temperature coefficient semiconductor material; The second protective layer material is deposited onto the surface of the positive electrode plate by using a vapor deposition technique to provide a second protective layer on the positive electrode plate.

19. A battery, characterized in that: The battery comprises a positive electrode sheet as claimed in any one of claims 1 to 14; Alternatively, the battery comprises a positive electrode sheet prepared by the method for preparing a positive electrode sheet according to any one of claims 15 to 18.

20. An electrical device, characterized in that: The electrical device comprises the battery as claimed in claim 19.

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