Positive plate and preparation method thereof, battery, battery pack and electric equipment

Abstract

The invention provides a positive plate and a preparation method thereof, a battery, a battery pack and electric equipment, the positive plate comprises a positive current collector and a positive active layer located on at least one side of the positive current collector, and the positive active layer comprises a positive active material and an ionic conductivity additive; one of the average particle diameter of the positive electrode active material and the average particle diameter of the ionic conductive additive is D1, the other is D2, and D1 / D2 is 1: 10-1: 100. When the positive plate provided by the invention is applied to the battery, the low-temperature performance of the battery can be improved.

Description

Technical Field

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

[0002] Batteries are common electrochemical devices with a wide range of applications. For example, with technological advancements and rising market demand, the application of lithium-ion batteries is expanding, from consumer electronics to electric vehicles and energy storage systems, with increasingly stringent requirements for battery performance. Furthermore, the diverse application scenarios of lithium-ion batteries, such as new energy vehicles in cold regions, aerospace, and Arctic exploration, all place stringent demands on the battery's low-temperature performance.

[0003] However, batteries generally have the problem of poor low-temperature performance. For example, for lithium-ion batteries, under low temperature conditions (usually below 0°C), the viscosity of the electrolyte of the lithium-ion battery increases, resulting in a slower lithium ion migration rate, a decrease in effective ion conductivity, and an increase in impedance, leading to severe polarization, which greatly reduces the battery's charge and discharge life.

[0004] Therefore, how to improve the low-temperature performance of batteries is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] The present invention provides a positive electrode sheet. The positive electrode sheet is applied to a battery and can improve the low-temperature performance of the battery.

[0006] The present invention provides a method for preparing a positive electrode sheet, which can prepare the above-mentioned positive electrode sheet, and the positive electrode sheet can improve the low-temperature performance of the battery. At the same time, the preparation method has simple process, low equipment requirements and low cost.

[0007] The present invention provides a battery that exhibits excellent low-temperature performance.

[0008] The present invention also provides a battery pack, which is composed of the above-mentioned battery and has excellent low-temperature performance.

[0009] The present invention also provides an electrical device comprising the battery or battery pack and having excellent low-temperature performance.

[0010] The present invention provides a positive electrode sheet, which includes a positive electrode current collector and a positive electrode active layer located on at least one side of the positive electrode current collector, wherein the positive electrode active layer includes a positive electrode active material and an ion conductive additive; an average particle size of the positive electrode active material and an average particle size of the ion conductive additive are D1 and D2, respectively, and the ratio of D1 to D2 is 1:10 to 1:100.

[0011] The positive electrode sheet as described above, wherein D1 / D2 is 1:20 to 1:50.

[0012] In the positive electrode sheet as described above, the average particle size of the positive electrode active material is D1, and the average particle size of the ion conductive additive is D2.

[0013] In the positive electrode sheet as described above, the average particle size of the ion conductive additive is D1, and the average particle size of the positive electrode active material is D2.

[0014] The positive electrode sheet as described above, wherein the intrinsic active ion migration energy barrier of the ion conductive additive in the temperature range of -80°C to 80°C is less than or equal to 0.4 eV; and / or the degree of change of the intrinsic active ion migration energy barrier of the ion conductive additive in the temperature range of -80°C to 80°C is less than 0.05 eV.

[0015] In the positive electrode sheet as described above, the mass percentage of the ion conductive additive in the positive electrode active layer is 0.5% to 5%.

[0016] The positive electrode sheet as described above, wherein the ion conductive additive includes NASICON type solid electrolyte, sulfide solid electrolyte, garnet-based ceramic solid electrolyte, perovskite type ceramic solid electrolyte, Li a MO b 、Li d One or more of E, the Li a MO b Where M is selected from metal elements, 2≤a≤8, 2≤b≤6; the Li d E in E represents an anionic group, and 1≤d≤3.

[0017] The positive electrode sheet as described above, wherein the NASICON type solid electrolyte includes lithium aluminum titanium phosphate and / or lithium aluminum germanium phosphate; and / or, the sulfide solid electrolyte includes Li6PS5X, X is selected from halogen; and / or, the garnet-based ceramic solid electrolyte includes lithium lanthanum zirconate; and / or, the perovskite type ceramic solid electrolyte includes lithium lanthanum titanate; and / or, the Li a MO b Including one or more of Li5FeO4, Li6CoO4, Li2NiO2, Li5AlO4, Li8ZrO6, Li8SnO6, Li5CoO4, Li4TiO4, Li4CrO4, Li3VO4, Li3CrO4, Li3NbO4, Li2MnO3, Li2SnO3, Li2CoO3, Li2RuO3; and / or, the Li dE includes one or more of Li2O, LiF, Li3N, Li2S, Li2CO3, LiCl, LiNO3, LiNO2, Li3PO4, and Li2SO4.

[0018] In the positive electrode sheet as described above, the positive electrode active material includes one or more of layered oxide materials, polyanion materials, and spinel structure materials.

[0019] The positive electrode sheet as described above, wherein the layered oxide material includes one or more of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide; and / or the polyanion material includes one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, and lithium cobalt phosphate; and / or the spinel structure material includes lithium manganese oxide and / or lithium nickel manganese oxide.

[0020] The positive electrode sheet as described above, wherein the positive electrode active layer further includes a conductive agent and a binder.

[0021] The present invention provides a method for preparing the positive electrode sheet as described above, which comprises the following steps: placing positive electrode slurry on at least one side surface of the positive electrode current collector to form the positive electrode active layer to prepare the positive electrode sheet.

[0022] The method for preparing the positive electrode sheet as described above, wherein the preparation process of the positive electrode slurry includes: mixing the positive electrode active material and one of the ion conductive additives with an average particle size of D1 with a mixed liquid containing a conductive agent and a binder, and then adding the positive electrode active material and one of the ion conductive additives with an average particle size of D2 thereto to prepare the positive electrode slurry.

[0023] The present invention also provides a battery, comprising the positive electrode sheet as described above or a positive electrode sheet prepared according to the method for preparing the positive electrode sheet as described above.

[0024] The present invention also provides a battery pack, which includes the battery described above.

[0025] The present invention also provides an electrical device, which includes the battery or the battery pack as described above.

[0026] The present invention provides a positive electrode sheet, a battery, a battery pack, and an electrical device. The positive electrode sheet includes an ion conductive additive, which effectively forms a solid-solid contact with the positive electrode active material, thereby adding a solid-phase transmission channel for active ions, thereby shortening the migration distance of the active ions and reducing the actual tortuosity of the electrode sheet, thereby achieving efficient transmission of active ions, and this efficient transmission is not affected by the low temperature environment, so that the impedance of the battery at low temperatures is reduced. At the same time, the average particle size relationship between the positive electrode active material and the ion conductive additive is regulated within the range of 1:10 to 1:100. The surface roughness of the particles with larger particle size is large, which can provide a space for small particles to adhere. Therefore, the solid-solid contact area between the ion conductive additive and the positive electrode active material is significantly increased, thereby providing more solid-phase migration channels at the electrode sheet level, thereby achieving efficient transmission of active ions to a greater extent and reducing the DC impedance of the battery at low temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a diagram showing the working principle of an ion conductive additive according to one embodiment of the present invention;

[0028] Figure 2 This is a discharge voltage test diagram of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 at -20°C;

[0029] Figure 3 The discharge voltage test diagram of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 at -10°C is shown;

[0030] Figure 4 The discharge voltage test diagram of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 at 0°C;

[0031] Figure 5 This is a charging voltage test diagram of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 at -20°C;

[0032] Figure 6 This is a charging voltage test diagram of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 at -10°C;

[0033] Figure 7 This is a charging voltage test diagram of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 at 0°C. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below. The specific embodiments listed below are only for describing the principles and features of the present invention. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts are within the scope of protection of the present invention.

[0035] The present invention provides a positive electrode sheet, which includes a positive electrode current collector and a positive electrode active layer located on at least one side of the positive electrode current collector. The positive electrode active layer includes a positive electrode active material and an ion conductive additive. The average particle size of the positive electrode active material and the average particle size of the ion conductive additive are D1 and D2, respectively, and the ratio of D1 to D2 is 1:10 to 1:100.

[0036] The positive electrode sheet of the embodiment of the present invention includes a positive electrode current collector and a positive electrode active layer arranged on the surface of the positive electrode current collector, wherein the positive electrode current collector is generally aluminum foil.

[0037] The positive electrode active layer of the embodiment of the present invention includes a positive electrode active material and an ion conductivity additive. The ion conductivity additive refers to a substance used to improve the ion conductivity of the positive electrode active layer.

[0038] In the embodiment of the present invention, one of the average particle size of the positive electrode active material and the average particle size of the ion conductive additive is D1, and the other is D2, and D1 / D2 is 1:10 to 1:100, for example, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90 or 1:100, etc. The embodiment of the present invention does not limit the size relationship between the average particle size of the positive electrode active material and the ion conductive additive. The average particle size of the positive electrode active material can be larger than the average particle size of the ion conductive additive, or the average particle size of the positive electrode active material can be smaller than the average particle size of the ion conductive additive, as long as the ratio of the average particle size of the two is within the range of 1:10 to 1:100. The present invention also does not limit the particle shape of the positive electrode active material and the ion conductive additive, as long as the average particle size ratio is within the range of 1:10 to 1:100. It should be clarified that the average particle size of the present invention is d measured by a laser particle size analyzer. 50 Parameters indicated.

[0039] The battery's electrode is a porous electrode, and its tortuosity is closely related to its ion diffusion capacity. Tortuosity represents the degree of curvature of the porous electrode's transport pathway—that is, the ratio of the actual transport path of active ions in the coating to the coating thickness. The electrode's effective ionic conductivity is inversely proportional to its tortuosity: greater electrode tortuosity results in longer lithium-ion migration paths and lower effective ionic conductivity. Therefore, designing an electrode structure with low tortuosity is one effective means of improving electrode ion conductivity. Currently, the mainstream approach to reducing tortuosity is to optimize particle packing and control battery porosity. However, at low temperatures, the electrolyte viscosity increases and can even gel. This, on the one hand, dramatically reduces the liquid-phase transport capacity of active ions; on the other hand, the electrode pores cannot be wetted, and active ions cannot be transported within the pores without electrolyte. Therefore, simply optimizing the electrode pore structure and reducing tortuosity will only have limited impact on improving lithium-ion conductivity at low temperatures.

[0040] In the embodiment of the present invention, an ion conductive additive is added to the positive electrode sheet, such as Figure 1 As shown, the ion conductive additive forms effective solid-solid contact with the positive electrode active material, adding a solid-phase transport channel for active ions. This shortens the migration distance of active ions and reduces the actual tortuosity of the electrode sheet, thereby achieving efficient transport of active ions. This efficient transport is not affected by low-temperature environments, reducing the impedance of the battery at low temperatures. At the same time, when the average particle size relationship between the positive electrode active material and the ion conductive additive is regulated within the above range, the surface roughness of the larger particles is greater, providing a suitable surface for small particles to adhere. As a result, the solid-solid contact area between the ion conductive additive and the positive electrode active material is significantly increased, thereby providing more solid-phase migration channels at the electrode sheet level, thereby achieving more efficient transport of active ions and reducing the DC impedance of the battery at low temperatures.

[0041] In the present invention, unless otherwise specified, the active ions are ions that are intercalated and deintercalated in the positive and negative electrodes to realize battery charging and discharging. For example, for lithium-ion batteries, the active ions are lithium ions, and for sodium-ion batteries, the active ions are sodium ions.

[0042] For example, if Figure 1 As shown, the positive electrode active layer is located on the surface of the positive electrode current collector ( Figure 1 The lower side of the positive electrode active layer is the current collector side, and the upper side is the electrode surface (also the surface of the positive electrode active layer facing away from the positive electrode current collector). Taking the positive electrode delithiation of lithium-ion batteries as an example, compared with the ordinary positive electrode sheet without the introduction of ion conductive additives, the positive electrode sheet of the embodiment of the present invention ( Figure 1By introducing an ion conductive additive into the positive electrode active layer of a positive electrode sheet containing an ion conductive additive, and synergistically regulating the particle sizes of the positive electrode active material and the ion conductive additive so as to satisfy the D1 / D2 ratio of 1:10 to 1:100, the solid-solid contact between the ion conductive additive and the positive electrode active material can be increased, the lithium ion migration path can be shortened, the battery impedance can be reduced, and the low-temperature performance of the battery can be improved.

[0043] Specifically, the embodiment of the present invention performs scanning electron microscopy (SEM) on the cross section of the positive electrode sheet to obtain the particle size of each particle, and statistically averages these particle sizes to obtain the average particle size of the positive electrode active material and the average particle size of the ion conductive additive.

[0044] In one specific embodiment, D1 / D2 is 1:20 to 1:50, for example, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, or 1:50. When D1 / D2 is within the above range, the solid-solid contact area between the ion conductive additive and the positive electrode active material is further increased, thereby further improving the transfer rate of active ions and lowering the DC impedance of the battery at low temperatures.

[0045] In one specific embodiment, the average particle size of the positive electrode active material is D1, and the average particle size of the ion conductive additive is D2. That is, the average particle size of the positive electrode active material is smaller than the average particle size of the ion conductive additive. The positive electrode active material can adhere to the surface of the ion conductive additive, increasing the contact area between the positive electrode active material and the ion conductive additive, shortening the migration distance of active ions, and reducing the actual tortuosity of the electrode sheet, thereby increasing the transmission rate of active ions and reducing the DC resistance of the battery.

[0046] In one specific embodiment, the average particle size of the ion conductive additive is D1, and the average particle size of the positive electrode active material is D2, i.e., the average particle size of the positive electrode active material is larger than the average particle size of the ion conductive additive. The ion conductive additive can adhere to the surface of the positive electrode active material, increasing the contact area between the positive electrode active material and the ion conductive additive, thereby increasing the number of solid-phase migration channels at the electrode layer, thereby achieving efficient transport of active ions and reducing battery resistance.

[0047] In a specific embodiment, the intrinsic active ion migration energy barrier of the ion conductive additive in the temperature range of -80°C to 80°C is less than or equal to 0.4eV, for example, 0.1eV, 0.15eV, 0.2eV, 0.25eV, 0.3eV, 0.35eV or 0.4eV, etc. The intrinsic active ion migration energy barrier of the embodiment of the present invention refers to the energy obstacle that needs to be overcome for ions to migrate in the material. When the intrinsic active ion migration energy barrier of the ion conductive additive in the temperature range of -80°C to 80°C is within the above range, the ion conductive additive is structurally stable within the operating temperature range of the battery (such as a lithium ion battery) and has a three-dimensional active ion (such as lithium ion) transmission channel, which is conducive to ensuring the efficient transmission of active ions at room temperature / low temperature, thereby improving the room temperature / low temperature performance of the battery.

[0048] In one specific embodiment, the degree of change in the intrinsic active ion migration energy barrier of the ion conductive additive in the temperature range of -80°C to 80°C is less than 0.05 eV. The higher the ambient temperature, the lower the intrinsic active ion migration energy barrier of the ion conductive additive. That is, the degree of change in the embodiment of the present invention refers to the difference between the intrinsic active ion migration energy barrier at -80°C ± 2°C and the intrinsic active ion migration energy barrier at 80°C ± 2°C. When the degree of change of the ion conductive additive is within the above range, the structure of the ion conductive additive in the temperature range of -80°C to 80°C is more stable, which ensures the transmission of active ions (such as lithium ions) at room temperature / low temperature to a greater extent, thereby further improving the high temperature / low temperature performance of the battery.

[0049] Specifically, the embodiment of the present invention uses the climbing elastic band (CINEB) method to calculate the intrinsic active ion migration energy barrier of the ion conductive additive for the positive electrode sheet through VASP software.

[0050] In a specific embodiment, the mass percentage of the ion conductive additive in the positive electrode active layer is 0.5% to 5%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%. When the mass percentage of the ion conductive additive is within the above range, the solid-solid contact area between the ion conductive additive and the positive electrode active material can be significantly increased, the migration distance of active ions (such as lithium ions) can be shortened, and the actual tortuosity of the electrode sheet can be reduced, thereby achieving efficient transmission of active ions. At the same time, it can avoid the reduction in battery capacity due to a decrease in the amount of positive electrode active material added, thereby ensuring the low-temperature performance of the battery.

[0051] In a specific embodiment, the ion conductive additive includes NASICON solid electrolyte, sulfide solid electrolyte, garnet-based ceramic solid electrolyte, perovskite ceramic solid electrolyte, Li a MO b 、Lid One or more of E, Li a MO b M is selected from metal elements, 2≤a≤8, 2≤b≤6; Li d E in E represents an anionic group, and 1≤d≤3.

[0052] The NASICON solid electrolyte of the embodiment of the present invention refers to a sodium superion conductor solid electrolyte.

[0053] In the embodiment of the present invention, M is selected from metal elements, for example, one or more of iron (Fe), nickel (Ni), cobalt (Co), aluminum (Al), zirconium (Zr), tin (Sn), manganese (Mn), titanium (Ti), vanadium (V), niobium (Nb), ruthenium (Ru), chromium (Cr), etc.

[0054] In the embodiment of the present invention, E represents an anionic group, which can be selected from O 2- 、F - 、N 3- 、S 2- 、CO3 2- 、NO3 - 、Cl - PO4 3- 、NO2 - 、SO4 2- One or more of the following.

[0055] When the above-mentioned compounds are used as ion conductive additives, the above-mentioned compounds can better achieve solid-solid contact with the positive electrode active material, increase the solid-solid contact area, and thus reduce the actual tortuosity of the electrode to a greater extent. At the same time, the active ions can be efficiently transported in the above-mentioned compounds, so that the transmission rate of the active ions in the electrode is higher. At the same time, the intrinsic active ion migration energy barrier of the above-mentioned compounds is low, thereby enabling the battery to achieve better low-temperature performance.

[0056] In a specific embodiment, the NASICON solid electrolyte includes lithium aluminum titanium phosphate (Li 1+x Al x Ti 2-x (PO4)3, LATP, 0≤x≤2) and / or lithium aluminum germanium phosphate (Li 1+x Al x Ge 2-x (PO4)3, LAGP, 0≤x≤2).

[0057] In a specific embodiment, the sulfide solid electrolyte includes Li6PS5X, where X is selected from halogens, such as Li6PS5Cl, Li6PS5Br, Li6PS5I, etc.

[0058] In a specific embodiment, the garnet-based ceramic solid electrolyte includes lithium lanthanum zirconate (Li7La3Zr2O 12 , LLZO).

[0059] In a specific embodiment, the perovskite ceramic solid electrolyte includes lithium lanthanum titanate (Li 3x La 2 / 3-x TiO3, LLTO). Wherein, 0<x≤0.12.

[0060] In one embodiment, Li a MO b Including one or more of lithium-rich lithium ferrite (Li5FeO4), Li6CoO4, Li2NiO2, Li5AlO4, Li8ZrO6, Li8SnO6, Li5CoO4, Li4TiO4, Li4CrO4, Li3VO4, Li3CrO4, Li3NbO4, Li2MnO3, Li2SnO3, Li2CoO3, and Li2RuO3.

[0061] In one embodiment, Li d E includes one or more of lithium oxide (Li2O), lithium fluoride (LiF), lithium nitride (Li3N), lithium sulfide (Li2S), lithium carbonate (Li2CO3), lithium chloride (LiCl), lithium nitrate (LiNO3), lithium nitrite (LiNO2), lithium phosphate (Li3PO4), and lithium sulfate (Li2SO4).

[0062] In the example of the embodiment of the present invention, the conductive additive is selected from the above-mentioned compound, which can further increase the contact area between the ion conductive additive and the positive electrode active material, and the ion conductive additive has high ion conductivity. At the same time, the intrinsic active ion migration energy barrier of the above-mentioned compound is low, thereby improving the low-temperature performance of the battery.

[0063] In a specific embodiment, the positive electrode active material includes one or more of layered oxide materials, polyanion materials, and spinel structure materials.

[0064] Illustratively, the layered oxide materials of the embodiments of the present invention include lithium cobaltate, lithium nickel cobalt manganeseate, lithium nickel cobalt aluminumate, lithium nickelate, lithium manganeseate, lithium titanate, lanthanum cobaltate, lanthanum nickelate, calcium titanate, barium titanate, and the like.

[0065] Illustratively, the polyanion materials of the embodiments of the present invention include lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium polyacrylate, lithium polyphosphate, lithium polystyrene sulfonate, and the like.

[0066] Illustratively, the spinel structure materials of the embodiments of the present invention include lithium manganese oxide, lithium nickel manganese oxide, spinel iron lithium oxide, spinel cobalt lithium oxide, spinel aluminum lithium oxide, spinel magnesium lithium oxide, and the like.

[0067] The positive electrode active material of the embodiment of the present invention uses the above-mentioned compound, which can improve the energy performance of the battery and can better match the ion conductive additive, further increase the contact area between the ion conductive additive and the positive electrode active material, and reduce the tortuosity of the electrode, thereby improving the low-temperature performance of the battery.

[0068] In a specific embodiment, the layered oxide material includes lithium cobalt oxide (LiCoO2, LCO), lithium nickel cobalt manganese oxide (LiNi x Co y Mn 1-x-y O2, NCM ternary materials, 0<x<1, 0<y<1, 1-xy>0), lithium nickel cobalt aluminum oxide (LiNi x Co y Al 1-x-y O2, NCA ternary material, one or more of 0<x<1, 0<y<1, 1-xy>0).

[0069] In a specific embodiment, the polyanion material includes lithium iron phosphate (LiFePO4, LFP), lithium manganese iron phosphate (LiFe x Mn 1-x PO4, LMFP, 0<x<1), lithium manganese phosphate (LiMnPO4, LFP), lithium vanadium phosphate (Li3V2(PO4)3, LVP), lithium cobalt phosphate (LiCoPO4, LCP) or one or more thereof.

[0070] In a specific embodiment, the spinel structure material includes lithium manganese oxide (LiMn2O4, LMO) and / or lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4, LNMO).

[0071] The positive electrode active material of the embodiment of the present invention uses the above-mentioned compound, which can further improve the energy performance of the battery. In addition, the contact area between the ion conductive additive and the positive electrode active material is larger, and the transmission rate of lithium ions in the battery is higher, thereby enabling the battery to exhibit higher low-temperature performance.

[0072] In a specific embodiment, the positive electrode active layer further includes a conductive agent and a binder.

[0073] The conductive agent of the embodiment of the present invention includes but is not limited to carbon-based materials, such as carbon black, acetylene black, Super-P, carbon nanotubes, graphene, etc.

[0074] The binder of the embodiment of the present invention includes, but is not limited to, polyvinylidene fluoride (PVDF), polyvinyl pyrrolidone (PVP), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), and the like.

[0075] The addition of a conductive agent and a binder to the positive electrode active layer of the embodiment of the present invention can make the contact between the ion conductive additive and the positive electrode active material closer, ensure the rapid transmission of active ions in the electrode sheet, and at the same time avoid the pulverization of the positive electrode active layer, which leads to a decrease in the safety performance of the battery, thereby improving the low-temperature performance and safety performance of the battery.

[0076] The present invention provides a method for preparing the above-mentioned positive electrode sheet, comprising the following steps: placing positive electrode slurry on at least one side surface of a positive electrode current collector to form a positive electrode active layer, thereby preparing a positive electrode sheet.

[0077] Specifically, the positive electrode slurry includes a positive electrode active material and an ion conductive additive. During implementation, the positive electrode active material and the ion conductive additive are first mixed with a solvent to obtain a positive electrode slurry after uniform mixing. The positive electrode slurry is then applied to at least one surface of a positive electrode current collector and dried to form a positive electrode active layer. The positive electrode sheets are then rolled and slit.

[0078] The embodiment of the present invention does not limit the specific choice of solvent, for example, N-methylpyrrolidone (NMP) can be selected.

[0079] The embodiment of the present invention does not limit the specific parameters of the mixing, as long as the positive electrode active material and the ion conductive additive can be uniformly mixed with the solvent.

[0080] The embodiment of the present invention does not limit the specific selection of the positive electrode current collector, for example, aluminum foil can be selected.

[0081] The embodiment of the present invention does not limit the specific coating parameters, as long as the positive electrode slurry can be evenly coated on the surface of the positive electrode current collector.

[0082] The embodiment of the present invention does not limit the specific parameters of drying, as long as the positive electrode slurry can be dried.

[0083] The embodiment of the present invention can prepare a positive electrode sheet including an ion conductive additive through the above-mentioned positive electrode sheet preparation method, and the positive electrode sheet can improve the low-temperature performance of the battery. At the same time, the preparation method is simple to operate, has low equipment requirements and is low cost.

[0084] In a specific embodiment, the preparation process of the positive electrode slurry includes: mixing the positive electrode active material and the ion conductive additive with an average particle size of D1 with a mixed solution containing a conductive agent and a binder, and then adding the positive electrode active material and the ion conductive additive with an average particle size of D2 thereto to prepare the positive electrode slurry. In detail, in the above-mentioned preparation process of the positive electrode slurry, the substance with a smaller average particle size (i.e., the positive electrode active material and the ion conductive additive with an average particle size of D1) is first mixed with the mixed solution of the conductive agent and the binder, and then the substance with a larger average particle size (i.e., the positive electrode active material and the ion conductive additive with an average particle size of D2) is added to prepare the positive electrode slurry.

[0085] Specifically, a mixed solution containing a conductive agent and a binder is first prepared, and then the positive electrode active material and the ion conductive additive with a smaller average particle size are mixed with the mixed solution. After the mixture is evenly mixed, the positive electrode active material and the ion conductive additive with a larger average particle size are added and mixed. After the mixture is evenly mixed, a positive electrode slurry is obtained.

[0086] In a specific embodiment, the preparation process of the positive electrode slurry includes: adding a binder to N-methylpyrrolidone (NMP) to dissolve it, stirring it evenly to obtain a binder emulsion, then adding a conductive agent, and at the same time assisting NMP spraying to mix the conductive agent evenly to obtain a conductive emulsion, and then adding the positive electrode active material and the ion conductive additive with a smaller average particle size, stirring and dispersing it evenly, and finally adding the positive electrode active material and the ion conductive additive with a larger average particle size and stirring them evenly to obtain a positive electrode slurry.

[0087] The embodiments of the present invention can improve the dispersibility of the positive electrode active material and the ion conductive additive in the positive electrode slurry by distributing and dispersing the positive electrode active material and the ion conductive additive with different particle sizes, avoid agglomeration of the positive electrode active material and the ion conductive additive, and at the same time disperse small particles first and then disperse large particles, so that the small particles can be more evenly adsorbed to the surface of the large particles, so that the solid-solid contact area between the positive electrode active material and the ion conductive additive is larger, further realizing efficient transmission of active ions, and making the low-temperature performance of the battery better.

[0088] The present invention further provides a battery comprising the above-mentioned positive electrode sheet or a positive electrode sheet prepared according to the above-mentioned method for preparing the positive electrode sheet. The battery exhibits excellent low-temperature performance.

[0089] In a specific embodiment, the battery also includes a negative electrode sheet, which includes a negative electrode collector and a negative electrode active layer arranged on the surface of the negative electrode collector, and the negative electrode active layer includes a negative electrode active material, a conductive agent and a binder, wherein the negative electrode collector is generally copper foil, and the negative electrode active material is selected from one or more of graphite, hard carbon, soft carbon, mesophase carbon microbeads, silicon-based negative electrode materials and lithium-containing metal composite oxide materials.

[0090] The conductive agent and the binder in the negative electrode active layer of the embodiment of the present invention can be selected from conventional materials in the art.

[0091] The battery of the embodiment of the present invention also includes a diaphragm, which is a diaphragm known in the art that can be used in batteries and is stable to the electrolyte used. It can include one or more of polyolefins, aromatic polyamides, polytetrafluoroethylene, and polyethersulfone, and can be specifically configured as needed.

[0092] The present invention also provides a battery pack including the above-mentioned battery. The battery pack has the same advantages as the above-mentioned positive electrode sheet, which will not be described in detail.

[0093] Generally, a battery pack includes multiple batteries as described above, which are connected as single cells to form a battery pack. These batteries can be electrically connected using conventional methods in the art, such as series connection, parallel connection, or a combination of these connection methods, without particular limitation.

[0094] The embodiment of the present invention further provides an electrical device including the above-mentioned battery or battery pack. The electrical device has the same advantages as the above-mentioned positive electrode sheet, which will not be described in detail.

[0095] The electrical equipment in the embodiments of the present invention can be conventional electrical equipment in this field, such as power equipment (such as electric vehicles, electric cars), electronic equipment (such as mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (such as watches, bracelets, VR glasses, etc.), energy storage power stations, etc., without special restrictions.

[0096] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the embodiments described are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0097] The present invention is further described below by way of specific examples and comparative examples. Unless otherwise specified, the reagents, materials, and instruments used below are all conventional reagents, materials, and instruments, all of which are commercially available, and the reagents and materials involved can also be synthesized by conventional synthesis methods.

[0098] Example 1

[0099] The average particle size of lithium iron phosphate (LiFePO4, LFP) is D1 (d 50 =120nm), the average particle size of lithium aluminum titanium phosphate (LATP) positive electrode ion conductive additive is D2 (d 50 =2.5μm), and D1:D2 is 1:20.8. The cathode slurry formulation: The mass ratios of LFP main material, LATP ion conductivity additive, conductive carbon black, and PVDF binder are 94.6:1.7:1.5:2.2, and the solids content of the cathode slurry is 61.5%. The intrinsic active ion migration energy barrier of LATP (lithium ion diffusion energy barrier) was calculated using the climbing elastic band (CINEB) method and VASP software. The intrinsic active ion migration energy barrier of LATP (lithium ion diffusion energy barrier) is 0.18 eV (see Table 1).

[0100] The method for preparing the battery of this embodiment includes the following steps:

[0101] 1. Mix PVDF and NMP to prepare a slurry with a solid content of 7%. Stir at a low speed of 15 Hz for 1 hour to ensure that there are no bubbles or powder flocculation on the surface of the slurry.

[0102] 2. Add conductive carbon black to the glue solution, spray NMP to assist dispersion, stir at a low speed of 15 Hz for 1 hour, and stir and disperse the conductive carbon black evenly.

[0103] 3. Add the LFP main material to the conductive adhesive prepared in step 2 in two portions, adding 50% each time, and stir at 15 Hz until evenly dispersed. Then, evacuate the mixture and stir at 40 Hz for 2 hours, maintaining the slurry temperature below 40°C. Test the slurry viscosity; at low shear rate, it should be between 1000 and 1200 mPa·s.

[0104] 4. Add the LATP positive ion conductivity additive to the slurry from step 3 all at once and stir at 15 Hz until evenly dispersed. Then, evacuate the mixture and stir at 40 Hz for 2 hours, maintaining the slurry temperature below 40°C. Test the slurry viscosity, which should increase by 5% to 10%.

[0105] 5. Coating process: The coating is applied to the surface of the aluminum foil by a roller at a speed of 10m / min, and then placed in a 120℃ oven for drying.

[0106] 6. Roll the electrode from step 5 to a compaction density of 2.5 g / cm 3The obtained electrode thickness is 140±3μm.

[0107] 7. Design the negative electrode capacity / positive electrode capacity ratio (N / P) to be 1.1 and make the natural graphite negative electrode sheet.

[0108] 8. Cut the electrode into 6cm*7cm size and use the lamination process to make 3 positive and 4 negative soft-pack batteries.

[0109] Example 2

[0110] The preparation method of the battery of this embodiment is substantially the same as that of embodiment 1, except that the positive electrode ion conductive additive is a mixture of LATP and Li2O, with a mixture ratio (mass ratio) of 1:1, wherein the particle size of LATP is d 50 =2.5μm, Li2O particle size d 50 =6μm.

[0111] Example 3

[0112] The preparation method of the battery of this embodiment is similar to that of embodiment 1, except that the LATP particle size d 50 =1.2μm.

[0113] Example 4

[0114] The preparation method of the battery of this embodiment is similar to that of embodiment 1, except that the LATP particle size d 50 =4.8μm.

[0115] Example 5

[0116] The preparation method of the battery of this embodiment is similar to that of embodiment 1, except that the LATP particle size d 50 =6μm.

[0117] Example 6

[0118] The preparation method of the battery in this embodiment is similar to that in embodiment 1, except that the LATP particle size d 50 =9.6μm.

[0119] Example 7

[0120] The preparation method of the battery in this embodiment is similar to that in embodiment 1, except that the LATP particle size d 50 =12μm.

[0121] Example 8

[0122] The preparation method of the battery in this embodiment is similar to that in embodiment 1, except that the particle size d of LFP is 50 =2.5μm, LATP particle size d 50 =120nm.

[0123] Example 9

[0124] The preparation method of the battery in this embodiment is similar to that in embodiment 1, except that the particle size d of LFP is 50 =6μm, LATP particle size d 50 =120nm.

[0125] Example 10

[0126] The preparation method of the battery in this embodiment is similar to that in embodiment 1, except that the particle size d of LFP is 50 =9.6μm, LATP particle size d 50 =120nm.

[0127] Example 11

[0128] The preparation method of the battery of this embodiment is substantially the same as that of embodiment 1, except that the ion conductive additive is LLZO.

[0129] Example 12

[0130] The preparation method of the battery of this embodiment is substantially the same as that of embodiment 1, except that the ion conductive additive is Li6PS5Cl.

[0131] Example 13

[0132] The preparation method of the battery of this embodiment is substantially the same as that of embodiment 1, except that the ion conductive additive is Li2O.

[0133] Example 14

[0134] The preparation method of the battery of this embodiment is substantially the same as that of embodiment 1, except that the ion conductive additive is Li2CO3.

[0135] Example 15

[0136] The preparation method of the battery of this embodiment is substantially the same as that of embodiment 1, except that the ion conductive additive is LLTO.

[0137] Example 16

[0138] The preparation method of the battery of this embodiment is substantially the same as that of embodiment 1, except that the ion conductive additive is Li5FeO4.

[0139] Example 17

[0140] The preparation method of the battery of this embodiment is substantially the same as that of embodiment 1, except that the ion conductive additive is Li3PO4.

[0141] Example 18

[0142] The preparation method of the battery of this embodiment is substantially the same as that of embodiment 1, except that the positive electrode active material is lithium cobalt oxide.

[0143] Example 19

[0144] The preparation method of the battery of this embodiment is substantially the same as that of embodiment 1, except that the positive electrode active material is lithium nickel cobalt manganese oxide.

[0145] Example 20

[0146] The preparation method of the battery of this embodiment is substantially the same as that of Example 1, except that the mass ratio of the LFP main material, the LATP ion conductive additive, the conductive carbon black, and the PVDF binder is 95.8:0.5:1.5:2.2.

[0147] Example 21

[0148] The preparation method of the battery of this embodiment is substantially the same as that of Example 1, except that the mass ratio of the LFP main material, the LATP ion conductive additive, the conductive carbon black, and the PVDF binder is 91.3:5:1.5:2.2.

[0149] Example 22

[0150] The preparation method of the battery of this embodiment is substantially the same as that of embodiment 1, except that the mass ratio of the LFP main material, the LATP ion conductive additive, the conductive carbon black, and the PVDF binder is 90.8:5.5:1.5:2.2.

[0151] Comparative Example 1

[0152] The preparation method of the battery of this comparative example is roughly the same as that of Example 1, except that the average particle size d of the positive electrode ion conductive additive LATP is 50 =250nm.

[0153] Comparative Example 2

[0154] The preparation method of the battery of this comparative example is roughly the same as that of Example 1, except that the positive electrode sheet of the battery does not include lithium aluminum titanium phosphate (LATP) positive electrode ion conductivity additive, and the formula of the positive electrode slurry: the mass ratio of LFP main material, conductive carbon black, and PVDF binder is 96.3:1.5:2.2.

[0155] Comparative Example 3

[0156] The preparation method of the battery of this comparative example is roughly the same as that of Example 1, except that the average particle size d of the positive electrode ion conductive additive LATP is 50 =12.6μm.

[0157] Comparative Example 4

[0158] The preparation method of the battery in this comparative example is roughly the same as that in Example 1, except that the average particle size d of LFP is 50 =250nm, LATP average particle size d 50 =120nm.

[0159] Table 1

[0160]

[0161] Table 2

[0162]

[0163] Test example

[0164] The batteries of the embodiment and the comparative example were subjected to discharge DC impedance tests at 0° C., −10° C., and −20° C., respectively, including the following steps:

[0165] 1. Adjust the ambient temperature, set the battery to 80% SOC, let it rest for 30 minutes, and then test the open circuit voltage (OCV).

[0166] 2. Discharge the battery with a 3C current for 30 seconds, and record the voltage data (U0 / U0) at 0s / 0.5s / 15s / 30s respectively. 0.5 / U 15 / U 30 ), with 2.0V as the discharge cut-off voltage;

[0167] 3. Discharge DC impedance (DCIR1) uses the formula DCIR1=(U0-U t ) / I and record the discharge DC impedance at different times, see Table 3.

[0168] The batteries of the embodiment and the comparative example were subjected to charging DC impedance tests at 0° C., −10° C., and −20° C., respectively, including the following steps:

[0169] 1. Adjust the ambient temperature, set the battery to 25% SOC, let it rest for 30 minutes, and then test the open circuit voltage (OCV).

[0170] 2. Charge the battery with 0.5C current for 30s, and record the voltage data at 0s / 0.5s / 15s / 30s respectively (U0 ’ / U 0.5 ’ / U 15 ’ / U 30 ’ ), with 3.8V as the charging cut-off voltage;

[0171] 3. The charging DC impedance (DCIR2) adopts the formula DCIR2=(U0-U t ) / I and record the charging DC impedance at different times, see Table 4.

[0172] The discharge voltage test diagrams of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 at -20°C, -10°C and 0°C are shown as follows: Figure 2 、 3 ,4,by Figure 2 、 Figure 3 、 Figure 4 It can be seen that among Example 1, Example 2, Comparative Example 1 and Comparative Example 2, the discharge voltage of Example 1 and Example 2 is higher, indicating that the discharge DC resistance is lower and the battery has stronger low-temperature power performance.

[0173] The charging voltage test diagrams of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 at -20°C, -10°C and 0°C are shown as follows: Figure 5 、 6 ,7, by Figure 5 、 Figure 6 、 Figure 7 It can be seen that among Example 1, Example 2, Comparative Example 1 and Comparative Example 2, the charging voltage of Example 1 and Example 2 is lower, indicating that the charging DC resistance is lower and the battery has better low-temperature fast charging performance.

[0174] Table 3

[0175]

[0176]

[0177] Table 4

[0178]

[0179] As can be seen from the table, compared to Comparative Examples 1-4, Examples 1-22 of the present invention effectively improved the low-temperature performance of the battery by adding an ion conductive additive to the positive electrode sheet and controlling the ratio of the average particle size of the positive electrode active material to the average particle size of the ion conductive additive to the average particle size of the smaller average particle size to the larger average particle size within a range of 1:10 to 1:100. Furthermore, Examples 1, 2, 4, 5, 8, 9, 11-16, 18, 19, 20, and 21, compared to Examples 3, 6, 7, and 10, further limited D1 / D2 to 1:20 to 1:50, further improving the low-temperature performance of the battery. Compared to Examples 17 and 22, Examples 1, 2, 4, 5, 8, 9, 11-16, 18, 19, 20, and 21 further limited the mass percentage of the ion conductive additive in the positive electrode active layer and the type of the ion conductive additive, thereby achieving even better low-temperature performance.

[0180] The above describes in detail the preferred embodiments of the present invention and their experimental verification. It should be understood that numerous modifications and variations based on the concepts of the present invention can be made by those skilled in the art without inventive effort. Therefore, any technical solution that can be derived by those skilled in the art based on the concepts of the present invention through logical analysis, reasoning, or limited experimentation based on the existing technology should be within the scope of protection defined by the claims.

[0181] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode sheet, characterized in that: The invention comprises a positive electrode current collector and a positive electrode active layer located on at least one side of the positive electrode current collector, wherein the positive electrode active layer comprises a positive electrode active material and an ion conductive additive; an average particle size of the positive electrode active material and an average particle size of the ion conductive additive are D1 and D2, respectively, and the ratio of D1 to D2 is 1:10 to 1:

100.

2. The positive electrode sheet according to claim 1, characterized in that D1 / D2 is 1:20~1:

50.

3. The positive electrode sheet according to claim 1, characterized in that The average particle size of the positive electrode active material is D1, and the average particle size of the ion conductive additive is D2.

4. The positive electrode sheet according to claim 1, characterized in that The average particle size of the ion conductive additive is D1, and the average particle size of the positive electrode active material is D2.

5. The positive electrode sheet according to claim 1, characterized in that: The intrinsic active ion migration energy barrier of the ion conductive additive in the temperature range of -80°C to 80°C is less than or equal to 0.4 eV; And / or, the degree of change of the intrinsic active ion migration energy barrier of the ion conductive additive in the temperature range of -80°C to 80°C is less than 0.05 eV.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The mass percentage of the ion conductive additive in the positive electrode active layer is 0.5% to 5%.

7. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The ion conductive additives include NASICON solid electrolytes, sulfide solid electrolytes, garnet-based ceramic solid electrolytes, perovskite ceramic solid electrolytes, Li a MO b 、Li d One or more of E, the Li a MO b Where M is selected from metal elements, 2≤a≤8, 2≤b≤6; the Li d E in E represents an anionic group, and 1≤d≤3.

8. The positive electrode sheet according to claim 7, characterized in that: The NASICON solid electrolyte includes lithium aluminum titanium phosphate and / or lithium aluminum germanium phosphate; and / or, the sulfide solid electrolyte comprises Li6PS5X, where X is selected from halogens; and / or, the garnet-based ceramic solid electrolyte comprises lithium lanthanum zirconate; And / or, the perovskite ceramic solid electrolyte includes lithium lanthanum titanate; and / or, the Li a MO b Including one or more of Li5FeO4, Li6CoO4, Li2NiO2, Li5AlO4, Li8ZrO6, Li8SnO6, Li5CoO4, Li4TiO4, Li4CrO4, Li3VO4, Li3CrO4, Li3NbO4, Li2MnO3, Li2SnO3, Li2CoO3, and Li2RuO3; and / or, the Li d E includes one or more of Li2O, LiF, Li3N, Li2S, Li2CO3, LiCl, LiNO3, LiNO2, Li3PO4, and Li2SO4.

9. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The positive electrode active material includes one or more of layered oxide materials, polyanion materials, and spinel structure materials.

10. The positive electrode sheet according to claim 9, characterized in that: The layered oxide material includes one or more of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide; And / or, the polyanion material includes one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, and lithium cobalt phosphate; And / or, the spinel structure material includes lithium manganese oxide and / or lithium nickel manganese oxide.

11. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The positive electrode active layer further includes a conductive agent and a binder.

12. A method for preparing a positive electrode sheet according to any one of claims 1 to 11, characterized in that: The method comprises the following steps: placing a positive electrode slurry on at least one side surface of the positive electrode current collector to form the positive electrode active layer to obtain the positive electrode sheet.

13. The method for preparing a positive electrode sheet according to claim 12, wherein: The preparation process of the positive electrode slurry includes: mixing the positive electrode active material and one of the ion conductive additives with an average particle size of D1 with a mixed solution containing a conductive agent and a binder, and then adding the positive electrode active material and one of the ion conductive additives with an average particle size of D2 to obtain the positive electrode slurry.

14. A battery, characterized in that: A positive electrode sheet comprising the positive electrode sheet according to any one of claims 1 to 11 or a positive electrode sheet prepared according to the method for preparing the positive electrode sheet according to claim 12 or 13.

15. A battery pack, characterized in that: Including the battery according to claim 14.

16. An electrical device, characterized in that: Comprising the battery according to claim 14 or the battery pack according to claim 15.

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