A positive electrode sheet and use thereof

Abstract

The application provides a positive electrode sheet and application thereof. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material; the positive electrode active material comprises spinel lithium manganate and a ternary material; the X-ray diffraction pattern of the positive electrode sheet comprises a first characteristic peak with 2theta of 18.7+ / -0.5 degrees, a second characteristic peak with 2theta of 44.1+ / -0.2 degrees, a third characteristic peak with 2theta of 44.6+ / -0.2 degrees and a fourth characteristic peak with 2theta of 64.3+ / -0.5 degrees; the first characteristic peak has a peak intensity I1, the second characteristic peak has a peak intensity I2, the third characteristic peak has a peak intensity I3, and the fourth characteristic peak has a peak intensity I4; wherein I1 / (I2+I3) is greater than or equal to 2 and I2 / I4 is greater than or equal to 2. The application can ensure the stability of the positive electrode sheet and improve the cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a positive electrode sheet and its application. Background Technology

[0002] Spinel-type lithium manganese oxide (LiMn2O4) has promising applications as a positive electrode active material in lithium-ion batteries due to its low price, abundant reserves, environmental friendliness, and high energy density. However, during charge and discharge processes, Mn... 3+ The resulting Ginger-Taylor effect leads to lattice distortion and disproportionation reaction product Mn 2+ It is extremely easy to dissolve in the electrolyte, which causes a severe degradation in battery performance.

[0003] To simultaneously ensure battery energy density and cycle performance, lithium manganese oxide is often mixed with ternary materials as the cathode material. In existing technology, a hybrid scheme is provided: the average particle size ratio of lithium manganese oxide to ternary materials is 2–6, and the particle size range of both is 5–40 μm. This scheme utilizes the complementary volume changes of the two materials—lithium manganese oxide shrinking during charging and ternary materials expanding during charging—to improve battery capacity and cycle performance.

[0004] However, Li + The migration path in spinel-type lithium manganese oxide and layered ternary materials is related to the crystal structure and has anisotropy. Simple particle size control is insufficient to constrain the crystal phase characteristics of the material, resulting in poor stability of the cathode and affecting the cycle performance of the battery. Summary of the Invention

[0005] This invention provides a positive electrode sheet and its application. The invention reduces the Li content in the ternary material by controlling the peak intensities I1 (representing the characteristic peaks of the lithium manganese oxide (111) crystal plane and the ternary material (003) crystal plane), I2 (representing the characteristic peaks of the lithium manganese oxide (400) crystal plane), I3 (representing the characteristic peaks of the ternary material (104) crystal plane), and I4 (representing the characteristic peaks of the lithium manganese oxide (440) crystal plane) to satisfy the following relationship: I1 / (I2+I3)≥2 and I2 / I4≥2. + / Ni 2+ Mixing and dissolving manganese during cycling can suppress the stability of the positive electrode and thus improve the cycle performance of the battery.

[0006] In a first aspect, the present invention provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode active material; the positive electrode active material comprises spinel-type lithium manganese oxide and a ternary material; the X-ray crystal diffraction pattern of the positive electrode sheet comprises a first characteristic peak with a 2θ of 18.7 ± 0.5°, a second characteristic peak with a 2θ of 44.1 ± 0.2°, a third characteristic peak with a 2θ of 44.6 ± 0.2°, and a fourth characteristic peak with a 2θ of 64.3 ± 0.5°, wherein the peak intensity of the first characteristic peak is I1, the peak intensity of the second characteristic peak is I2, the peak intensity of the third characteristic peak is I3, and the peak intensity of the fourth characteristic peak is I4;

[0007] Among them, I1 / (I2+I3)≥2 and I2 / I4≥2.

[0008] According to one embodiment of the present invention, the stacking size D of the crystal planes of the lithium manganese oxide (440) is... (440) Compared with the average particle size D of lithium manganese oxide 50 The interval satisfies 0 <D (440) / D 50 <2%.

[0009] According to one embodiment of the present invention, 2≤I1 / (I2+I3)≤5.

[0010] According to one embodiment of the present invention, 2≤I2 / I4≤5.

[0011] According to one embodiment of the present invention, the spinel-type lithium manganese oxide and / or ternary material comprises one or more doping elements selected from Al, Ti, Sr, Zr, W, and Y.

[0012] According to one embodiment of the present invention, the average particle size D of the spinel-type lithium manganese oxide is... 50 The size ranges from 2 to 10 μm.

[0013] According to one embodiment of the present invention, the ternary material is a secondary particle, and the average particle size of the primary single crystal particles constituting the secondary particle is 0.2 to 2 μm.

[0014] According to one embodiment of the present invention, the average particle size of the primary single crystal particles constituting the secondary particles is 1.5 to 2 μm.

[0015] In a second aspect, the present invention provides a battery comprising the above-described positive electrode.

[0016] A third aspect of the present invention provides an electrical device comprising the battery described above.

[0017] The implementation of this invention has at least the following beneficial effects:

[0018] The positive electrode provided by this invention controls the peak intensities I1 (representing the characteristic peaks of the lithium manganese oxide (111) crystal plane and the ternary material (003) crystal plane), I2 (representing the characteristic peaks of the lithium manganese oxide (400) crystal plane), and I3 (representing the characteristic peaks of the ternary material (104) crystal plane) to satisfy the relationship: I1 / (I2+I3)≥2, ensuring that Li in the ternary material... + / Ni 2+ The lower degree of mixing and the higher crystallinity of spinel-type lithium manganese oxide on the (111) crystal plane, which is less soluble in manganese, are beneficial to improving the crystal structure stability of ternary materials and lithium manganese oxide. At the same time, the peak intensity I2 of the characteristic peak of the lithium manganese oxide (400) crystal plane and the peak intensity I4 of the characteristic peak of the lithium manganese oxide (440) crystal plane in the cathode sheet are limited to satisfy the relationship: I2 / I4≥2. This ensures that the crystallinity of lithium manganese oxide on the (440) crystal plane, which is highly soluble in manganese, is low, further ensuring the crystal structure stability of lithium manganese oxide, inhibiting manganese dissolution during cycling, and improving the cycle stability of the cathode. Attached Figure Description

[0019] Figure 1 This is the X-ray crystal diffraction pattern of Embodiment 1 of the present invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode active material, wherein the positive electrode active material comprises spinel-type lithium manganese oxide and ternary materials; the X-ray crystal diffraction pattern of the positive electrode sheet includes a first characteristic peak with 2θ of 18.7±0.5°, a second characteristic peak with 2θ of 44.1±0.2°, a third characteristic peak with 2θ of 44.6±0.2°, and a fourth characteristic peak with 2θ of 64.3±0.5°, wherein the peak intensity of the first characteristic peak is I1, the peak intensity of the second characteristic peak is I2, the peak intensity of the third characteristic peak is I3, and the peak intensity of the fourth characteristic peak is I4; wherein, I1 / (I2+I3)≥2 and I2 / I4≥2.

[0022] Due to Li +The migration path in spinel-type lithium manganese oxide and ternary materials is related to the crystal structure and exhibits anisotropy. Simply controlling the material particle size at the physical level to improve the cycle performance of the battery cannot be effectively improved. This invention controls the peak intensity I1 (i.e., the first characteristic peak intensity), the peak intensity I2 (i.e., the second characteristic peak intensity), and the peak intensity I3 (i.e., the third characteristic peak intensity) of the characteristic peaks representing the (111) crystal plane of lithium manganese oxide and the (003) crystal plane of ternary materials, the characteristic peaks of the (400) crystal plane of lithium manganese oxide, and the characteristic peaks of the (104) crystal plane of ternary materials, respectively, to satisfy the relationship: I1 / (I2+I3)≥2, thus ensuring that Li in the ternary material... + / Ni 2+ The lower degree of mixing and the higher crystallinity of spinel-type lithium manganese oxide on the (111) crystal plane, which is not easily soluble in manganese, are beneficial to improving the crystal structure stability of ternary materials and lithium manganese oxide. At the same time, the peak intensity I2 of the characteristic peak of the lithium manganese oxide (400) crystal plane and the peak intensity I4 of the characteristic peak of the lithium manganese oxide (440) crystal plane (i.e., the peak intensity of the fourth characteristic peak) are limited to satisfying the relationship: I2 / I4≥2. This ensures that the crystallinity of lithium manganese oxide on the (440) crystal plane, which is extremely soluble in manganese, is low, further ensuring the crystal structure stability of lithium manganese oxide, inhibiting manganese dissolution during cycling, and improving the cycle stability of the cathode.

[0023] For spinel-type lithium manganese oxide, the surface energy of the (111), (400), and (440) crystal planes increases progressively, meaning the (111) plane is the most stable and least prone to manganese dissolution, while the (440) plane is the most prone to manganese dissolution. For ternary materials, the ratio of the peak intensities corresponding to the (003) and (104) crystal planes, I(003) / I(104), can reflect the relative strengths of Li. + / Ni 2+ The degree of mixing; the larger this ratio, the better for Li. + / Ni 2+ The lower the degree of mixing, the better it is for improving the stability of the crystal structure and avoiding a large amount of Ni. 2+ Occupy Li + The lattice sites of Li +Migration path blockage. In the XRD pattern of the hybrid cathode, the characteristic peaks of both the spinel-type lithium manganese oxide (111) crystal plane and the ternary material (003) crystal plane are located at 18.7±0.5°. The peak intensity I1 of this characteristic peak can simultaneously reflect the crystallinity of the lithium manganese oxide (111) crystal plane and the ternary material (003) crystal plane. The characteristic peak located at 44.1±0.2° in the XRD pattern corresponds to the spinel-type lithium manganese oxide (400) crystal plane, and the peak located at 44.6±0.2° is... The characteristic peaks correspond to the (104) crystal plane of the ternary material, and the peak intensities are represented by I2 and I3, respectively. By controlling the XRD characteristic peak intensity of the positive electrode to I1 / (I2+I3)≥2, it is possible to ensure that the (111) crystal plane of lithium manganese oxide, which is not easily soluble in manganese, has a higher crystallinity than the (400) crystal plane, and that the ratio of the characteristic peak intensities of the (003) crystal plane to the (104) crystal plane of the ternary material is relatively high, thereby improving the crystal structure stability of lithium manganese oxide and reducing the Li in the ternary material. + / Ni 2+ The degree of mixing. At the same time, the fourth characteristic peak located at 64.3±0.5° in the XRD pattern corresponds to the (440) crystal plane of lithium manganese oxide, which limits the relationship between the peak intensity I2 of the characteristic peak of the (400) crystal plane of lithium manganese oxide and the peak intensity I4 of the characteristic peak of the (440) crystal plane of lithium manganese oxide in the cathode sheet: I2 / I4≥2, which ensures that the crystallinity of lithium manganese oxide in the (440) crystal plane of easily soluble manganese is low, further ensuring the crystal structure stability of lithium manganese oxide, inhibiting cycle dissolution of manganese, and improving the cycle stability of the cathode.

[0024] In a preferred embodiment, the stacking size D of the (440) crystal plane of lithium manganese oxide (440) Compared with the average particle size D of lithium manganese oxide 50 The interval satisfies 0 <D (440) / D 50 <2%. Because the spinel-type lithium manganese oxide (440) crystal face has the highest surface energy, it is most prone to manganese dissolution, leading to crystal structure collapse. By controlling 0... <D (440) / D 50 <2%, ensuring that the stacking size of the lithium manganese oxide (440) crystal plane is much smaller than the average particle size of lithium manganese oxide, thereby improving the crystal structure stability of lithium manganese oxide and inhibiting cyclic manganese dissolution.

[0025] According to further research by the inventors, it was found that the electrochemical performance of the positive electrode is better when 2≤I1 / (I2+I3)≤5 ​​and / or 2≤I2 / I4≤5.

[0026] In a preferred embodiment, the spinel-type lithium manganese oxide and / or ternary material comprises one or more doping elements selected from Al, Ti, Sr, Zr, W, and Y. Adding certain doping elements during the preparation of the active material is beneficial for improving the crystal structure stability or conductivity of the material.

[0027] In a preferred embodiment, the mass ratio of spinel-type lithium manganese oxide to ternary material is 1:9 to 9:1, preferably 3:7 to 7:3. Exemplary examples include mass ratios of 1:9, 2:7, 3:7, 1:3, 2:8, 4:5, 7:3, 9:1, 9:3, 9:5, 9:7, or any combination of two of these values. Controlling the mass ratio of spinel-type lithium manganese oxide to ternary material within these ranges facilitates the production of high-energy-density, low-cost hybrid cathode sheets.

[0028] In a preferred embodiment, the average particle size D of spinel-type lithium manganese oxide is... 50 The particle size ranges from 2 to 10 μm. For example, spinel-type lithium manganese oxide has particle sizes of 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any combination of two of these values. Since the particle size of lithium manganese oxide is directly related to its crystallinity, generally speaking, larger particle sizes indicate higher crystallinity and improved crystal structure stability. However, when the particle size exceeds a certain value, it can affect the crystallinity of Li. + The diffusion rate is low, which is detrimental to capacity utilization and rate performance improvement. Therefore, spinel-type lithium manganese oxide with a particle size within the above range results in a more stable cathode structure and better electrochemical performance.

[0029] In a preferred embodiment, the ternary material is a secondary particle, and the average particle size of the primary single-crystal particles constituting the secondary particle is 0.2–2 μm. For example, the average particle size of the primary single-crystal particles is 0.2 μm, 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, or any combination of two of the above values. The secondary ternary material has a lower cost compared to the single-crystal ternary material, and the particle size of the primary particles within the above range is beneficial for shortening the lithium-ion diffusion distance and improving the rate performance of the battery.

[0030] In a preferred embodiment, the ternary material is a secondary particle, and the average particle size of the primary single-crystal particles constituting the secondary particle is 1.5–2 μm. For example, the average particle size of the primary single-crystal particles is 1.5 μm, 1.8 μm, 2 μm, or any combination of two of these values. Ternary secondary particles have a lower cost than single-crystal ternary materials, and the particle size of the primary particles within the aforementioned range is beneficial for shortening the lithium-ion diffusion distance and improving the rate performance of the battery.

[0031] In a preferred embodiment, the porosity of the positive electrode sheet is 20-45%. For example, the porosity of the positive electrode sheet is 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 35%, 45%, or any combination of two of these values. Controlling the microstructure of the positive electrode active material while maintaining a porosity within the aforementioned range is more beneficial for improving the cycle performance of the battery.

[0032] In a preferred embodiment, the compaction density of the positive electrode sheet is 2.4–3.8 g / cm³. 3 For example, the compaction density of the positive electrode is 2.4 g / cm³. 3 2.6g / cm 3 2.8g / cm 3 3g / cm 3 3.3g / cm 3 3.4g / cm 3 3.6g / cm 3 3.8g / cm 3 Alternatively, it could be a range consisting of any two of the above values. While controlling the microstructure of the positive electrode active material's crystals, a compaction density within the aforementioned range is beneficial for improving the battery's energy density.

[0033] The positive current collector of the present invention can be selected from the positive current collectors conventionally used in the art, such as aluminum foil, composite aluminum foil, and carbon-coated aluminum foil.

[0034] The positive electrode sheet of the present invention further includes a conductive agent and a binder, wherein the conductive agent includes, but is not limited to, one or more of carbon black, carbon nanotubes, conductive graphite, and graphene; the binder includes, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and hydrogenated nitrile butadiene rubber (HNBR).

[0035] In one specific implementation, the positive electrode sheet can be prepared using the following method:

[0036] 1) Preparation of secondary ternary material particles: Nickel, cobalt, and manganese sources are mixed in stoichiometric ratio (molar ratio) to prepare a 2 mol / L mixed salt solution. A 4 mol / L sodium hydroxide solution is used as a precipitant and ammonia as a complexing agent. The solution is introduced into a nitrogen-filled reactor. The pH of the system is controlled at 11, the stirring rate is 600 r / min, the reaction temperature is 58℃, and the reaction is carried out for 24 h. After washing and drying, a ternary precursor is obtained. The above precursor is mixed evenly with a lithium source (lithium excess coefficient 1.05) and pre-calcined at 300-500℃ for 3-6 h. Then, it is sintered at a sintering temperature (T1) of 600-900℃ for 5-12 h. The mixture is then pulverized by an air jet mill. The feeding pressure P1 of the air jet mill and the sintering temperature T1 satisfy the relationship: P1 = T1 / 500-1. The desired secondary ternary material particles can then be obtained.

[0037] 2) Preparation of spinel-type lithium manganese oxide: The lithium source and manganese source are mixed according to the stoichiometric ratio and ball-milled for 2 hours to make them uniform. The mixture is then sintered at 700-950℃ (sintering temperature T2) for 2-8 hours. After pulverization by an air jet mill, the feeding pressure P2 of the air jet mill and the sintering temperature T2 satisfy the following relationship: P2=T2*0.0024-1.48. The desired spinel-type lithium manganese oxide can then be obtained.

[0038] 3) Mix the above-mentioned ternary material secondary particles with spinel-type lithium manganese oxide at a mass ratio of 1:9 to 9:1. Then mix the mixed active material with conductive agent and binder at a mass ratio of (7 to 9):(0.5 to 2):(0.5 to 1). Add an appropriate amount of solvent and stir evenly to dissolve the binder to obtain a positive electrode slurry. Coat the slurry onto the surface of the positive electrode current collector. After drying, roll-cut the slurry at 0.5 to 0.7 MPa to obtain the desired positive electrode sheet.

[0039] In the above preparation process, steps 1) and 2) are not in any particular order.

[0040] In step 1), the nickel source is a soluble nickel source, which may be selected from, but is not limited to, nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate; the cobalt source is a soluble cobalt source, which may be selected from, but is not limited to, cobalt sulfate, cobalt nitrate, and cobalt chloride; and the manganese source is a soluble manganese source, which may be selected from, but is not limited to, manganese sulfate, manganese nitrate, and manganese chloride. The lithium source may be one or more of lithium carbonate, lithium hydroxide, lithium acetate, and lithium nitrate.

[0041] In step 2), the lithium source can be one or more of lithium carbonate, lithium hydroxide, lithium acetate, and lithium nitrate. The manganese source can be selected from, but is not limited to, manganese sulfate, manganese nitrate, manganese chloride, manganese carbonate, and manganese oxide.

[0042] When ternary materials and / or lithium manganese oxide contain doped elements, the doping element source can be added before the sintering process, mixed evenly, and then subjected to subsequent sintering to obtain element-doped ternary materials and / or lithium manganese oxide materials.

[0043] The present invention does not impose any particular limitation on the coating method of the positive electrode paste, such as doctor blade coating, roller coating, spray coating, dip coating, screen printing, etc.

[0044] After coating, the slurry is dried to remove the solvent. The drying process can be carried out in an oven at a temperature of 80–150°C for 1–5 hours.

[0045] After drying, the formed positive electrode coating needs to be rolled to improve the compaction density and mechanical strength of the positive electrode sheet.

[0046] A second aspect of the present invention provides a battery comprising the positive electrode provided in the first aspect. In addition to the aforementioned positive electrode, the battery of the present invention also includes a negative electrode, a separator, and an electrolyte.

[0047] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be selected from negative electrode current collectors conventionally used in the art, such as copper foil, composite copper foil, and carbon-coated copper foil. The negative electrode active material layer can also refer to conventional compositions in the art; for example, the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder. The negative electrode active material can be selected from negative electrode active materials conventionally used in the art, including but not limited to one or more of natural graphite, artificial graphite, silicon-carbon materials, silicon-oxygen materials, hard carbon, and metallic lithium. The conductive agent includes, but is not limited to, one or more of carbon black, carbon nanotubes, conductive graphite, and graphene. The binder includes, but is not limited to, one or more of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), and polytetrafluoroethylene (PTFE). The separator can be selected from one of the following: polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene bilayer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene trilayer composite membrane (PP / PE / PP), cellulose nonwoven separator, and separator with ceramic coating. The ceramic filler in the ceramic coating can be selected from one or more of alumina, silica, boehmite, and aluminum hydroxide. The lithium salt in the electrolyte includes, but is not limited to, one or more of LiPF6, LiFSI, LiBOB, LiDFP, LiBF4, LiNO3, LiAsF6, and LiTFSI. The electrolyte solvent includes, but is not limited to, one or more of ethyl methyl carbonate (EMC), ethylene carbonate (EC), diethyl carbonate (DEC), diethyl adipate (DEC), propylene carbonate (PC), ethyl acetate (EA), and dimethyl glycol ether (DME).

[0048] In this embodiment of the invention, the negative electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the negative electrode coating, such as the negative electrode active material, conductive agent, and binder, can be dispersed in a preset solvent, such as water, to prepare a negative electrode slurry. The slurry is then coated on the surface of the negative electrode current collector and, after drying, rolling and other processes, the negative electrode sheet is obtained.

[0049] In one specific embodiment, the battery of the present invention can be prepared by the following method: a bare cell is obtained by winding or stacking a positive electrode sheet, a separator, and a negative electrode sheet, and then the bare cell is packaged into a pre-stamped aluminum-plastic film bag. After the packaged battery is dried at 85°C, electrolyte is injected into the dried battery. After the battery is left to stand, formed, and resealed, the battery of the present invention is obtained.

[0050] A third aspect of the present invention provides an electrical device including the battery as described above. The present invention does not particularly limit the type of electrical device; it can be any electrical device including the battery, including but not limited to mobile phones, portable devices, laptops, electric bicycles, electric vehicles, electric toys, energy storage devices, etc.

[0051] The following will provide a detailed description of the positive electrode sheet provided by the present invention and its applications through specific embodiments.

[0052] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, materials and instruments in the art, and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0053] Example 1

[0054] 1) Preparation of secondary ternary material particles: Nickel sulfate, cobalt sulfate, and manganese sulfate were mixed in a stoichiometric ratio (Ni:Co:Mn molar ratio = 1:1:1) to prepare a 2 mol / L mixed salt solution. A 4 mol / L sodium hydroxide solution was used as a precipitant and ammonia water as a complexing agent. The solution was introduced into a reaction vessel purged with nitrogen. The pH of the system was controlled at 11, the stirring rate was 600 r / min, the reaction temperature was 58℃, and the reaction was carried out for 24 h. After washing and drying, a ternary precursor was obtained. The above precursor was mixed with lithium hydroxide (lithium excess coefficient 1.05) and pre-calcined at 350℃ for 3 h, and then sintered at a sintering temperature T1 of 750℃ for 8 h (sintering time). The secondary ternary material particles were obtained by crushing under a pressure of 0.5 MPa.

[0055] 2) Preparation of spinel-type lithium manganese oxide (LiMn2O4): Lithium carbonate and manganese trioxide were mixed in stoichiometric ratio and ball-milled for 2 hours to make the mixture uniform. The mixture was sintered at a sintering temperature T2 of 750℃ for 5 hours and then crushed under a pressure of 0.32 MPa to obtain spinel-type lithium manganese oxide.

[0056] 3) Mix the above-mentioned ternary material secondary particles with spinel-type lithium manganese oxide at a mass ratio of 7:3, then mix the mixed active material with conductive agent carbon black and binder PVDF at a mass ratio of 8:1:1, add an appropriate amount of N-methylpyrrolidone (NMP) solvent, stir evenly to dissolve the binder, and obtain a positive electrode slurry. Coat the slurry onto the surface of aluminum foil, dry, roll press and cut to obtain different positive electrode sheets. The rolling pressure is 0.5 MPa.

[0057] 4) The above positive electrode was characterized by XRD. The peak intensities I1, I2, I3 and I4 corresponding to the characteristic peaks at 18.7±0.5°, 44.1±0.2°, 44.6±0.2° and 64.3±0.5° in the XRD pattern are recorded and listed in Table 1.

[0058] Example 2

[0059] The process is basically the same as in Example 1, except that the sintering temperature T1 in the ternary material preparation process is changed to 800℃, the sintering time is 8h, and the crushing pressure is 0.6MPa; the sintering temperature T2 in the lithium manganese oxide preparation process is changed to 850℃, the corresponding sintering time is 8h, and the crushing pressure is 0.56MPa.

[0060] Example 3

[0061] The process is basically the same as in Example 1, except that the sintering temperature T1 in the ternary material preparation process is changed to 850°C, the sintering time is 8h, and the crushing pressure is 0.7MPa; the sintering temperature T2 in the lithium manganese oxide preparation process is changed to 800°C, the corresponding sintering time is 5h, and the crushing pressure is 0.44MPa.

[0062] Example 4

[0063] The process is basically the same as in Example 1, except that the sintering temperature T1 in the ternary material preparation process is changed to 750°C, the sintering time is 8h, and the crushing pressure is 0.5MPa; and the sintering temperature T2 in the lithium manganese oxide preparation process is changed to 950°C, the corresponding sintering time is 8h, and the crushing pressure is 0.8MPa.

[0064] Example 5

[0065] The process is basically the same as in Example 1, except that the sintering temperature T1 in the ternary material preparation process is changed to 750℃, the sintering time is 8h, and the crushing pressure is 0.5MPa; the sintering temperature T2 in the lithium manganese oxide preparation process is changed to 770℃, the corresponding sintering time is 5h, and the crushing pressure is 0.37MPa.

[0066] Example 6

[0067] The process is basically the same as in Example 1, except that the sintering temperature T1 in the ternary material preparation process is changed to 750℃, the sintering time is 8h, and the crushing pressure is 0.5MPa; the sintering temperature T2 in the lithium manganese oxide preparation process is changed to 860℃, the corresponding sintering time is 8h, and the crushing pressure is 0.58MPa.

[0068] Example 7

[0069] The process is basically the same as in Example 1, except that the sintering temperature T1 in the ternary material preparation process is changed to 700℃, the sintering time is changed to 8h, and the crushing pressure is changed to 0.4MPa; the sintering temperature T2 in the lithium manganese oxide preparation process is changed to 930℃, the corresponding sintering time is changed to 2h, and the crushing pressure is changed to 0.75MPa.

[0070] Example 8

[0071] The process is basically the same as in Example 1, except that the sintering temperature T1 in the ternary material preparation process is changed to 750℃, the sintering time is 8h, and the crushing pressure is 0.5MPa; the sintering temperature T2 in the lithium manganese oxide preparation process is changed to 930℃, the corresponding sintering time is 2h, and the crushing pressure is 0.75MPa.

[0072] Example 9

[0073] The process is basically the same as in Example 1, except that the sintering temperature T1 in the ternary material preparation process is changed to 700℃, the sintering time is 8h, and the crushing pressure is 0.4MPa; the sintering temperature T2 in the lithium manganese oxide preparation process is changed to 910℃, the corresponding sintering time is 2h, and the crushing pressure is 0.70MPa.

[0074] Comparative Example 1

[0075] The process is basically the same as in Example 1, except that the sintering temperature T1 in the ternary material preparation process is changed to 600℃, the sintering time is 5h, and the crushing pressure is 0.3MPa; the sintering temperature T2 in the lithium manganese oxide preparation process is changed to 900℃, the corresponding sintering time is 2h, and the crushing pressure is 0.68MPa.

[0076] Comparative Example 2

[0077] The process is basically the same as in Example 1, except that the sintering temperature T1 in the ternary material preparation process is changed to 700℃, the sintering time is 8h, and the crushing pressure is 0.5MPa; the sintering temperature T2 in the lithium manganese oxide preparation process is changed to 720℃, the corresponding sintering time is 2h, and the crushing pressure is 0.50MPa.

[0078] Comparative Example 3

[0079] The process is basically the same as in Example 1, except that the sintering temperature T1 in the ternary material preparation process is changed to 650℃, the sintering time is 5h, and the crushing pressure is 0.3MPa; the sintering temperature T2 in the lithium manganese oxide preparation process is changed to 700℃, the corresponding sintering time is 2h, and the crushing pressure is 0.50MPa.

[0080] Test case

[0081] I. The following performance tests were performed on the positive electrode sheets of the above embodiments and comparative examples:

[0082] 1. XRD test

[0083] Test method: The prepared positive electrode was placed on a sample holder, and the X-ray source was set to a copper target (40kV, 40mA) with a wavelength of [wavelength missing]. The scanning range of the goniometer was adjusted from 2θ = 10° to 80°, and the scanning speed was approximately 10° / min, for testing.

[0084] 2. Scanning electron microscopy test

[0085] Test method: Place the positive electrode sheet into the sample chamber of a scanning electron microscope (SEM) and maintain the vacuum level to the set requirement. Adjust the SEM focus and aperture until the material particles are clearly visible. Measure the maximum diameter of multiple lithium manganese oxide particles and calculate the average value to obtain D. 50 (Units are μm). The average particle size D of the primary single-crystal particles in the secondary particles of the ternary material. 三元一次 The testing method is similar.

[0086] 3. Calculate D (440)

[0087] D (440) =Kγ / ( FWHM 440 ×cosθ 440 Formula 1;

[0088] In Equation 1, D (440) The unit is K is the Scherrer constant, with a value of 0.89; γ is the wavelength of the cathode ray used in X-ray diffraction, in units of... Values FWHM 440θ is the full width at half maximum (FWHM) of the characteristic peak of the (440) crystal plane, in radians; 440 It is half the 2θ value of the (440) crystal plane, in degrees (°). 440 The value is 1 / 2*(64.3±0.5°).

[0089] II. The following performance tests were performed on the batteries of the above embodiments and comparative examples:

[0090] Cyclic performance test

[0091] Test Method: Using lithium metal as the negative electrode, a 1 mol / L LiPF6-EC / DEC electrolyte (v / v = 1:1), and a PE separator, coin cells were assembled from the above positive electrode sheets. Constant current charge-discharge tests were performed on the coin cells at a current density of 1C within a voltage window of 2.5–4.5V. The capacity retention rate R of the reversible specific capacity C300 relative to the initial capacity C0 after 300 cycles was recorded. 循环 =C300 / C0*100%, and the test results are shown in Table 1.

[0092] Table 1

[0093]

[0094]

[0095] As shown in Table 1, when I1 / (I2+I3)≥2 and I2 / I4≥2, the coin cell assembled with the corresponding positive electrode exhibits good cycle stability (>90%). In Comparative Example 1, I2 / I4≥2 but I1 / (I2+I3)<2. The lithium manganese oxide in the positive electrode has a lower crystallinity on the (440) crystal plane of easily soluble manganese, which is beneficial to suppress manganese dissolution during cycling. However, I1 / (I2+I3)<2 indicates that the I(003) / I(104) ratio of the ternary material is relatively small, i.e., Li + / Ni 2+ The mixing phenomenon is quite serious, affecting the stability of its crystal structure and correspondingly reducing the cycle performance of the battery. In Comparative Example 2, I1 / (I2+I3)≥2 but I2 / I4<2, indicating that the crystallinity of lithium manganese oxide crystals in the cathode is relatively low on the (400) crystal plane where manganese is not easily dissolved, resulting in a serious manganese dissolution phenomenon during cycling, leading to the degradation of the battery's cycle performance. In Comparative Example 3, I1 / (I2+I3)<2 and I2 / I4<2, corresponding to the unstable crystal structure of lithium manganese oxide in the cathode and the ternary material Li + / Ni 2+ The mixing phenomenon is quite serious, which leads to a rapid decline in battery cycle capacity.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions 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 plate, characterized in that, It includes a positive electrode current collector and a positive electrode active material, wherein the positive electrode active material includes spinel-type lithium manganese oxide and ternary materials; The X-ray crystal diffraction pattern of the positive electrode includes a first characteristic peak with a 2θ of 18.7 ± 0.5°, a second characteristic peak with a 2θ of 44.1 ± 0.2°, a third characteristic peak with a 2θ of 44.6 ± 0.2°, and a fourth characteristic peak with a 2θ of 64.3 ± 0.5°. The peak intensities of the first characteristic peak are I1, the second characteristic peak is I2, the third characteristic peak is I3, and the fourth characteristic peak is I4. Among them, I1 / (I2+I3)≥2 and I2 / I4≥2.

2. The positive electrode sheet according to claim 1, characterized in that, The stacking size D of the (440) crystal plane of the lithium manganese oxide (440) The average particle size D of the lithium manganese oxide 50 The interval satisfies 0 <D (440) / D 50 <2%.

3. The positive electrode sheet according to claim 1, characterized in that, 2≤I1 / (I2+I3)≤5.

4. The positive electrode sheet according to claim 1, characterized in that, 2≤I2 / I4≤5.

5. The positive electrode sheet according to any one of claims 1-4, characterized in that, The spinel-type lithium manganese oxide and / or ternary materials contain one or more doping elements selected from Al, Ti, Sr, Zr, W, and Y.

6. The positive electrode sheet according to any one of claims 1-5, characterized in that, The average particle size D of the spinel-type lithium manganese oxide 50 The size ranges from 2 to 10 μm.

7. The positive electrode sheet according to any one of claims 1-6, wherein the ternary material is a secondary particle, and the average particle size of the primary single crystal particles constituting the secondary particle is 0.2-2 μm.

8. The positive electrode sheet according to claim 7, wherein the average particle size of the primary single crystal particles constituting the secondary particles is 1.5 to 2 μm.

9. A battery, characterized in that, The battery includes the positive electrode sheet as described in any one of claims 1-8.

10. An electrical appliance, characterized in that, The electronic device includes the battery as described in claim 9.

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