Positive electrode sheet, battery and electrical device

Abstract

Provided in the present application are a positive electrode sheet, a battery and an electrical device. The positive electrode sheet comprises a lithium manganese iron phosphate material. The crystal X-ray diffraction pattern of the positive electrode sheet contains a characteristic peak having a 2θ of 17.2±0.5° and corresponding to a (200) plane, and a characteristic peak having a 2θ of 29.7±0.5° and corresponding to a (020) plane. The average stacking size D(200) of the (200) plane, the average stacking size D(020) of the (020) plane, and the average particle size D(1) of the lithium manganese iron phosphate material satisfy the following relationship: D(200) / D(020)≥1.15 and 10％≤D(200) / Daverage≤30%. In the present application, by means of a limitation on the special crystal structure and particle size of the positive electrode sheet, the positive electrode sheet has a high lithium ion diffusion rate and cycling stability, such that batteries have both excellent cycling performance and rate performance.

Description

Positive electrode plates, batteries, and electrical equipment

[0001] This application claims priority to Chinese Patent Application No. 202411750625.X, filed on November 29, 2024, entitled "Positive Electrode Sheet, Battery and Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application belongs to the field of batteries and relates to a positive electrode, a battery, and an electrical device. Background Technology

[0003] Lithium iron phosphate (LiFePO4) has been widely used in lithium-ion battery cathode materials due to its high safety and cycle stability; however, its operating potential is relatively low, only 3.4V (vs. LiFePO4). + The energy density of lithium iron phosphate (LiFePO4) is much lower than that of ternary cathode materials, resulting in a lower energy density and a significant disadvantage in the field of power batteries. Lithium manganese iron phosphate (LFP), obtained by manganese doping of LFP, maintains high safety and good cycle stability while increasing the operating voltage to approximately 4.1V (vs. LiFePO4). + Li is a very promising new cathode material.

[0004] Compared to the layered structure of ternary lithium-ion batteries, lithium manganese iron phosphate (LFP) has an olivine-type structure, resulting in slower lithium-ion transport speeds and poorer rate performance. To address this issue, current technologies often reduce the particle size of LFP materials to shorten the lithium-ion transport distance. However, as the particle size decreases, the stability of the material's crystal structure also declines, particularly affecting the Mn content during charging and discharging. 2+ The dissolution phenomenon intensifies, leading to a decline in battery cycle performance.

[0005] Therefore, how to make lithium manganese iron phosphate materials have both fast lithium-ion transport rate and good structural stability when applied to batteries is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] This application provides a positive electrode, a battery, and an electrical device. By defining the special crystal structure and particle size of the positive electrode, this application enables the positive electrode to have a high lithium-ion diffusion rate and cycle stability, thereby enabling the battery to have both excellent cycle performance and rate performance.

[0007] The first aspect of this application provides a positive electrode, including lithium manganese iron phosphate material, wherein the X-ray crystal diffraction pattern of the positive electrode includes characteristic peaks of the (200) crystal plane with 2θ of 17.2 ± 0.5° and characteristic peaks of the (020) crystal plane with 2θ of 29.7 ± 0.5°.

[0008] The average packing size D(200) on the (200) crystal plane, the average packing size D(020) on the (020) crystal plane, and the average particle size D of the lithium manganese iron phosphate material 平均 The following relationship must be satisfied:

[0009] D(200) / D(020)≥1.15 and 10%≤D(200) / D 平均 ≤30%.

[0010] In one alternative implementation, D(200) / D(020)≤1.8.

[0011] In one optional embodiment, the average particle size D of the lithium manganese iron phosphate material is... 平均 The wavelength range is 300–1100 nm.

[0012] In one optional embodiment, the chemical composition of the lithium manganese iron phosphate material is LiMn. x Fe 1-x PO4, where 0.1 ≤ x ≤ 0.7.

[0013] In one optional embodiment, the lithium manganese iron phosphate material further includes a doping element, the doping element including Al. 3+ B 3+ Zr 4+ Ti 4+ W 6+ Ta 5+ Ru 5+ One or more of them.

[0014] In one optional embodiment, the positive electrode sheet includes a positive current collector and a positive active layer;

[0015] The positive electrode active layer comprises a positive electrode material, a conductive agent, and a binder in a mass ratio of (7-9):(0.5-2):(0.5-1);

[0016] The cathode material includes lithium manganese iron phosphate.

[0017] In one optional embodiment, the positive electrode material further includes one or more of ternary materials, lithium iron phosphate, lithium manganese oxide, and lithium cobalt oxide.

[0018] In one optional embodiment, the compaction density of the positive electrode sheet is >2.3 g / cm³. 3 .

[0019] A second aspect of this application provides a battery including the positive electrode provided in the first aspect of this application.

[0020] A third aspect of this application provides an electrical device, including the battery provided in the second aspect of this application.

[0021] The implementation of this application has at least the following beneficial effects:

[0022] This application controls the average packing size D(200) on the (200) crystal plane and the average packing size D(020) on the (020) crystal plane in the positive electrode to satisfy D(200) / D(020)≥1.15, ensuring that the diffusion channels of lithium ions in the lithium manganese iron phosphate crystal have a large end face and a relatively short path length, thereby improving the diffusion rate of lithium ions in the lithium manganese iron phosphate crystal and giving the positive electrode a good rate performance. It also simultaneously controls the average packing size D(200) on the (200) crystal plane and the average particle size D of the lithium manganese iron phosphate material. 平均 Satisfying 10% ≤ D(200) / D 平均 ≤30%, limiting Li + The ratio of the diffusion end face to the individual crystal particles ensures that the lithium manganese iron phosphate crystal structure maintains good stability during charge and discharge, thereby improving the cycle performance of the cathode. In summary, this application, by defining the specific crystal structure and particle size of the cathode, enables the cathode to possess high lithium-ion diffusion rate and cycle stability, thus giving the battery both excellent cycle performance and rate performance. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0024] Figure 1 is the XRD pattern of the positive electrode of Example 1. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] Compared to lithium iron phosphate, lithium manganese iron phosphate (LFP) maintains high safety and good cycle stability while significantly improving battery operating voltage, making it a very promising new cathode material. However, LFP has an olivine-type structure, where lithium ions are transported along the

[0010] crystal direction via 1D channels. This slow lithium-ion transport speed results in poor battery rate performance. While reducing particle size to shorten the lithium-ion transport distance can improve the material's structural stability, it also increases the Mn content. 2+ The dissolution phenomenon intensifies, leading to a decline in battery cycle performance.

[0027] In the crystal structure of lithium manganese iron phosphate, the (200) crystal plane is parallel to the

[0010] crystal direction. The larger the packing size of the (200) crystal plane, the greater the Li content in the

[0010] crystal direction. + The larger the diffusion end face, the more lithium-ion diffusion channels there are; the (020) crystal plane is perpendicular to the

[0010] crystal direction, and the larger the (020) crystal plane stack size, the more lithium-ion diffusion channels there are corresponding to the

[0010] crystal direction. + The longer the diffusion path, the better. Therefore, by controlling the stacking size of crystals in different crystal planes and the overall particle size of the material, the rate performance and cycle performance of lithium manganese iron phosphate cathodes can be improved.

[0028] Based on this, the first aspect of this application provides a positive electrode, including lithium manganese iron phosphate material, wherein the X-ray crystal diffraction pattern (XRD pattern) of the positive electrode includes characteristic peaks of the (200) crystal plane with 2θ of 17.2±0.5° and characteristic peaks of the (020) crystal plane with 2θ of 29.7±0.5°.

[0029] Among them, the average packing size D(200) on the (200) crystal plane, the average packing size D(020) on the (020) crystal plane, and the average particle size D of the lithium manganese iron phosphate material are... 平均 The following relationship must be satisfied:

[0030] D(200) / D(020)≥1.15 and 10%≤D(200) / D 平均 ≤30%.

[0031] This application controls D(200) / D(020) ≥ 1.15, ensuring that the diffusion channels of lithium ions in the lithium manganese iron phosphate crystal have a large end face and a relatively short path length, thereby improving the diffusion rate of lithium ions in the lithium manganese iron phosphate crystal and giving the positive electrode good rate performance. In addition, this application also controls 10% ≤ D(200) / D 平均 ≤30%, limiting Li + The ratio of the diffusion end face to the individual crystal particles enables the crystal structure to maintain good stability during charging and discharging, thereby improving the cycle performance of the lithium manganese iron phosphate cathode.

[0032] The average stacking size D(200) refers to the average thickness of the lithium manganese iron phosphate material grains perpendicular to the (200) crystal plane in the positive electrode, and the average stacking size D(020) refers to the average thickness of the lithium manganese iron phosphate material grains perpendicular to the (020) crystal plane in the positive electrode. Both of these can be calculated using the Debye-Scherrer formula.

[0033] Specifically, D(200) is calculated using Equation 1: D(200)=Kγ / (FWHM) 200 ×cosθ 200 Formula 1;

[0034] In Equation 1, the unit of D(200) 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... FWHM 200 θ is the full width at half maximum (FWHM) of the characteristic peak of the (200) crystal plane, in radians; 200 It is half the 2θ value of the (200) crystal plane, in degrees;

[0035] D(020) is calculated using Equation 2: D(020)=Kγ / (FWHM) 020 ×cosθ 020 Formula 2;

[0036] In Equation 2, the unit of D(020) 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... FWHM 020 θ is the full width at half maximum (FWHM) of the characteristic peak of the (020) crystal plane, in radians; 020 It is half the 2θ value of the (020) crystal plane, in °.

[0037] In detail, λ is the wavelength of the cathode rays used in X-ray diffraction, determined by the cathode material (i.e., the target material) of the X-ray tube and the operating conditions of the X-ray tube. In X-ray crystal diffraction, a copper target Kα is typically used to emit cathode rays with a wavelength of [wavelength missing]. The equivalent in nm is 0.154056 nm. Similarly, if D(200) and D(020) are expressed in nm, they need to be multiplied by 0.1 based on Equations 1 and 2.

[0038] Half-width at half-height, also known as half-peak width, refers to the width of the characteristic peak at half its height. During the calculation, the unit needs to be converted to radians (rad).

[0039] FWHM in Formula 1200 and θ 200 And FWHM in Equation 2 020 and θ 020 All of these can be obtained from the XRD pattern of the positive electrode.

[0040] Average particle size D 平均 This refers to the average of the maximum diameters of multiple lithium manganese iron phosphate particles present in the positive electrode. The maximum diameter of multiple lithium manganese iron phosphate particles can be obtained by scanning electron microscopy (SEM).

[0041] In a preferred embodiment, D(200) / D(020) ≤ 1.8. When D(200) / D(020) is in the range of 1.15 to 1.8, the lithium manganese iron phosphate material can have both good lithium-ion diffusion rate and better structural stability.

[0042] In one specific embodiment, the average particle size D of the lithium manganese iron phosphate material is... 平均 The range is 300–1100 nm. By controlling the average packing size D(200) on the (200) crystal plane and the average packing size D(020) on the (020) crystal plane, lithium manganese iron phosphate material can enable the cathode to have both good structural stability and lithium ion diffusion rate within the above wide particle size range.

[0043] For example, the average particle size D of lithium manganese iron phosphate material 平均 It can be 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm, or any two of the above values.

[0044] The structural stability and performance of lithium manganese iron phosphate materials are also affected by the manganese and iron content. Due to the high Mn content... 3+ / Mn 2+ The redox potential is higher than that of Fe. 3+ / Fe 2+ Therefore, under the same battery voltage, materials with higher manganese content can provide higher energy density, while the redox reaction of ferrous ions is more stable, which helps to maintain the structural stability of the material during multiple charge and discharge cycles.

[0045] In one specific embodiment, the chemical composition of the lithium manganese iron phosphate material is LiMn. x Fe 1-x PO4, where 0.1 ≤ x ≤ 0.7.

[0046] Controlling x within the above range is beneficial for lithium manganese iron phosphate materials to have both high energy density and structural stability.

[0047] For example, x can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or any range of two of the above values.

[0048] Furthermore, the electrical performance of lithium manganese iron phosphate can be improved through elemental doping. Doping elements can include Al. 3+ B 3+ Zr 4+ Ti 4+ W 6+ Ta 5+ Ru 5+ One or more of the above elements can be used for doping to improve conductivity and crystal structure stability.

[0049] In one specific implementation, amorphous carbon can also be coated on the surface of the lithium manganese iron phosphate material to improve its conductivity and thus enhance the rate performance of the battery.

[0050] The positive electrode sheet of this application can adopt conventional settings in the art, such as including a positive current collector and a positive active layer. The positive active layer can be directly disposed on one side or both surfaces of the positive current collector, or a transition layer to improve the electrode performance can be added between the positive current collector and the positive active layer to form a positive electrode sheet.

[0051] The positive electrode current collector can be made of conventionally used materials, such as aluminum foil or carbon-coated aluminum foil.

[0052] The positive electrode active layer typically includes a positive electrode material, a conductive agent, and a binder. In this application, the positive electrode material includes lithium manganese iron phosphate material, and may further include one or more of ternary materials, lithium iron phosphate materials, and lithium manganese oxide materials.

[0053] In one specific embodiment, the positive electrode active layer comprises a positive electrode material, a conductive agent, and a binder in a mass ratio of (7–9):(0.5–2):(0.5–1). Within this mass ratio range, it is beneficial for the battery to possess both high capacity, electronic conductivity, and electrode adhesion stability.

[0054] This application does not impose any particular limitation on the types of conductive agents and binders, which can be selected from those commonly used in the battery field. Specifically, conductive agents include, but are not limited to, one or more of the following: carbon black, carbon nanotubes, conductive graphite, and graphene; binders include, but are not limited to, one or more of the following: polyvinylidene fluoride (PVDF), acrylic-modified PVDF, polyacrylate polymers, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber.

[0055] Positive electrode sheets that meet the above-mentioned specific crystal structure and particle size requirements of lithium manganese iron phosphate materials can be obtained by simultaneously controlling the sintering temperature, sintering time, crushing pressure and the rolling pressure during the positive electrode sheet preparation process.

[0056] Specifically, the positive electrode in this application can be obtained by the following method:

[0057] 1) After the lithium source, iron source, manganese source and phosphorus source are mixed evenly according to the stoichiometric ratio, water is added to form a slurry, and then the precursor powder is formed by spray drying.

[0058] 2) The above precursor powder is sintered at 550-900℃ for 3-10 hours in an inert gas atmosphere to obtain sintered material; the sintered material is then processed by an air jet mill to obtain lithium manganese iron phosphate particles, wherein the feeding pressure of the air jet mill is 0.2-0.8 MPa.

[0059] In this step, the sintering temperature T (°C) and the feeding pressure P (MPa) of the air jet mill are controlled to satisfy the following relationship: P = (3 × T - 1300) / 1750;

[0060] 3) The lithium manganese iron phosphate particles obtained in step 2) are used as positive electrode active materials and mixed evenly with conductive agent and binder. Solvent is added to form positive electrode slurry. The positive electrode slurry is coated on the surface of current collector, dried, and then rolled at 0.5-0.7 MPa to obtain positive electrode sheet.

[0061] In the above preparation method, the iron source can be selected from one or more of ferrous sulfate, ferrous oxalate, ferrous nitrate, ferrous hydroxide, and ferric phosphate.

[0062] The manganese source can be selected from one or more of manganese sulfate, manganese nitrate, manganese carbonate, manganese phosphate, manganese oxalate, manganese oxide, and manganese tetroxide.

[0063] The lithium source can be one or more of lithium carbonate, lithium hydroxide, lithium acetate, and lithium nitrate. To compensate for lithium loss, the lithium excess coefficient can be set to 1.01–1.13.

[0064] The phosphorus source can be one or more of phosphoric acid, lithium dihydrogen phosphate, and iron phosphate.

[0065] It should be noted that in step 1), carbon sources such as glucose, β-cyclodextrin, sucrose, and starch can also be added and mixed with raw materials such as lithium, iron, manganese, and phosphorus sources. These carbon sources can act as reducing agents to promote the formation of lithium manganese iron phosphate, or as coating sources to form a conductive carbon layer on the surface of the lithium manganese iron phosphate particles to improve the material's conductivity.

[0066] Similarly, when the positive electrode sheet contains other positive electrode materials besides lithium manganese iron phosphate particles, the lithium manganese iron phosphate particles can be mixed with other positive electrode materials in step 3 to participate in the positive electrode sheet fabrication process as positive electrode active materials.

[0067] In step 3), this application does not specifically limit the solvent used to form the positive electrode slurry; it can be a positive electrode slurry solvent commonly used in the art, such as N-methylpyrrolidone (NMP). This application also does not specifically limit the coating method of the positive electrode slurry; for example, it can be blade coating, roller coating, spray coating, dip coating, screen printing, etc.

[0068] 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.

[0069] The method for preparing the positive electrode sheet provided in this application controls the sintering temperature of lithium manganese iron phosphate to 550–900℃, the sintering time to 3–10 h, and the feeding pressure during the air jet milling process to 0.2–0.8 MPa. Furthermore, by limiting the relationship between the sintering temperature T and the feeding pressure P of the air jet mill to: P = (3 × T - 1300) / 1750, lithium manganese iron phosphate material with suitable particle size and crystal structure can be obtained. In addition, the mechanical pressure applied to the positive electrode coating during the positive electrode sheet rolling process also affects the crystal orientation and particle structure of the lithium manganese iron phosphate material. This application achieves this by using a positive electrode rolling process pressure of 0.5–0.7 MPa, ultimately obtaining a material that satisfies D(200) / D(020) > 1.15 and 10% <D(200) / D 平均 Positive electrode with less than 30% characteristics.

[0070] A second aspect of this application provides a battery that includes the positive electrode provided in the first aspect of this application. Because it includes the aforementioned positive electrode, this battery possesses both good rate performance and cycle performance.

[0071] It is conceivable that, in addition to the aforementioned positive electrode, the battery of this application also includes a negative electrode, an electrolyte, and a separator.

[0072] This application does not strictly limit the negative electrode active material in the negative electrode sheet, which may be selected from at least one of graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrode), tin-based negative electrode materials (mainly including tin and tin alloy).

[0073] The negative electrode usually also includes conductive agents and binders, the types of which can be referred to the types of conductive agents and binders in the positive electrode mentioned above, and will not be elaborated here.

[0074] This application does not strictly limit the choice of electrolyte, which can refer to conventional compositions in the art, typically including a solvent and a lithium salt. The solvent can be ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc. The lithium salt can be one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0075] This application does not strictly limit the choice of diaphragm material, such as polypropylene diaphragm (PP), polyethylene diaphragm (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun diaphragm (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven fabric diaphragm, and diaphragm with ceramic coating.

[0076] The battery of this application can be prepared by the following method:

[0077] The positive electrode, separator, and negative electrode are wound or stacked to obtain a bare cell, which is then packaged into a pre-stamped aluminum-plastic film bag. After the packaged battery is dried at 85°C, the electrolyte is injected into the dried battery. The battery undergoes resting, formation, and secondary sealing to complete the battery manufacturing process.

[0078] A third aspect of this application provides an electrical device, including the battery provided in the second aspect of this application.

[0079] This application does not limit the specific type of electrical equipment, and may include any device that requires battery power, such as electric vehicles, mobile phones, smart home devices, robots, drones, e-cigarettes, and speakers.

[0080] The following provides a more detailed description of the positive electrode sheet and its applications through specific embodiments.

[0081] Example 1

[0082] This embodiment provides a positive electrode sheet, the preparation method of which includes the following steps:

[0083] 1) Lithium carbonate, iron phosphate, manganese tetroxide, and lithium dihydrogen phosphate are mixed in a stoichiometric ratio (Mn:Fe molar ratio = 6:4), and glucose is added to the mixture, wherein the excess coefficient of lithium is 1.03 and the excess coefficient of glucose is 1.2; the above materials are mixed and ground evenly by sand milling, and then water is added to form a slurry. After removing iron, the slurry is dried by spray dryer to obtain mixed precursor powder.

[0084] 2) The above-mentioned dried powder was sintered at 750°C for 4 hours in an inert gas atmosphere; after air jet milling, iron removal, and sieving and classification, lithium manganese iron phosphate particles were obtained, wherein the feeding pressure of the air jet mill was 0.5 MPa.

[0085] 3) The above-mentioned lithium manganese iron phosphate particles, conductive agent carbon black, and binder PVDF are mixed evenly in a mass ratio of 9:0.5:0.5. NMP is added and stirred evenly to prepare positive electrode slurry. The positive electrode slurry is coated on the surface of aluminum foil, dried and rolled to obtain positive electrode sheet. The rolling pressure is 0.6MPa.

[0086] Example 2

[0087] This embodiment provides a positive electrode sheet, which is basically the same as the preparation steps in Embodiment 1. The difference is that the sintering temperature in step 2) is 900℃, the sintering time is 2h, the feeding pressure of the air jet mill is 0.8MPa, and the rolling pressure of the positive electrode sheet in step 3) is 0.7MPa.

[0088] Example 3

[0089] This embodiment provides a positive electrode sheet, which is basically the same as the preparation steps in Embodiment 1. The difference is that the sintering temperature in step 2) is 550℃, the sintering time is 7h, the feeding pressure of the air jet mill is 0.2MPa, and the rolling pressure of the positive electrode sheet in step 3) is 0.5MPa.

[0090] Example 4

[0091] This embodiment provides a positive electrode sheet, which is basically the same as the steps in Embodiment 1, except that in step 1), the molar ratio of Mn element in manganese tetroxide to Fe element in iron phosphate is 5:5, and TiO2 (accounting for 0.5wt% of the total content of raw materials) is added as a dopant source during the raw material mixing process; in step 2), the sintering temperature is 550℃, the sintering time is 5h, and the feeding pressure of the air jet mill is 0.2MPa; in step 3), the rolling pressure of the positive electrode sheet is 0.5MPa.

[0092] Example 5

[0093] This embodiment provides a positive electrode sheet, which is basically the same as the steps in Embodiment 1, except that in step 1), the molar ratio of Mn element in manganese tetroxide to Fe element in iron phosphate is 3:7; in step 2), the sintering temperature is 800℃, the sintering time is 3h, and the feeding pressure of the air jet mill is 0.6MPa; and in step 3), the rolling pressure of the positive electrode sheet is 0.5MPa.

[0094] Example 6

[0095] This embodiment provides a positive electrode sheet, which is basically the same as the steps in Embodiment 1, except that in step 1), the molar ratio of Mn element in manganese tetroxide to Fe element in iron phosphate is 1:9; in step 2), the sintering temperature is 850℃, the sintering time is 3h, and the feeding pressure of the air jet mill is 0.7MPa; and in step 3), the rolling pressure of the positive electrode sheet is 0.6MPa.

[0096] Example 7

[0097] This embodiment provides a positive electrode sheet, which is basically the same as the steps in Embodiment 1, except that in step 1), the molar ratio of Mn element in manganese tetroxide to Fe element in iron phosphate is 6:4; in step 2), the sintering temperature is 800℃, the sintering time is 5h, and the feeding pressure of the air jet mill is 0.6MPa.

[0098] Step 3) is replaced with: Lithium manganese iron phosphate particles and single-crystal ternary material LiNi with an average particle size of 2.5 μm. 0.55 Co 0.05 Mn 0.4 O2 is mixed at a mass ratio of 3:7 to obtain the positive electrode active material. The positive electrode material is mixed with conductive agent carbon black and binder PVDF at a mass ratio of 9:0.5:0.5. NMP is added and stirred evenly to obtain positive electrode slurry. The positive electrode slurry is coated on the surface of aluminum foil, dried and rolled to obtain the positive electrode sheet. The rolling pressure is 0.5MPa.

[0099] Comparative Example 1

[0100] This comparative example provides a positive electrode sheet, which is basically the same as the steps in Example 1, except that the sintering temperature in step 2) is 1100℃, the sintering time is 2h, the feeding pressure of the air jet mill is 0.9MPa, and the rolling pressure of the positive electrode sheet in step 3) is 0.7MPa.

[0101] Comparative Example 2

[0102] This comparative example provides a positive electrode sheet, which is basically the same as the steps in Example 1, except that the sintering temperature in step 2) is 900℃, the sintering time is 10h, the feeding pressure of the air jet mill is 0.1MPa, and the rolling pressure of the positive electrode sheet in step 3) is 0.7MPa.

[0103] Comparative Example 3

[0104] This comparative example provides a positive electrode sheet, which is basically the same as the steps in Example 1, except that the sintering temperature in step 2) is 500°C, the sintering time is 3h, the feeding pressure of the air jet mill is 0.3MPa, and the rolling pressure of the positive electrode sheet in step 3) is 0.5MPa.

[0105] Comparative Example 4

[0106] This comparative example provides a positive electrode sheet, which is basically the same as the steps in Example 7, except that the sintering temperature in step 2) is 800°C, the sintering time is 5h, the feeding pressure of the air jet mill is 0.3MPa, and the rolling pressure of the positive electrode sheet in step 3) is 0.5MPa.

[0107] Application examples

[0108] The positive electrode sheets of the above embodiments and comparative examples are applied to lithium-ion batteries. The specific preparation method of the lithium-ion battery is as follows:

[0109] A mixture of graphite, carbon black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) binder is mixed evenly in a mass ratio of 9:0.5:0.5. An appropriate amount of water is added as a solvent to obtain a negative electrode slurry. This slurry is then coated onto the surface of a copper foil, dried, and rolled to obtain a negative electrode sheet.

[0110] A bare cell is obtained by stacking the positive electrode, separator, and negative electrode using a polypropylene separator. The bare cell is then packaged in a pre-stamped aluminum-plastic film bag. After drying the packaged battery at 85°C, a 1 mol / L LiPF6-EC / DEC (v / v = 1:1) electrolyte is injected into the dried battery. The battery undergoes resting, formation, and secondary sealing before testing.

[0111] Test case

[0112] 1. The following performance tests were conducted on the positive electrode sheets of the above embodiments and comparative examples. The test results are shown in Table 1:

[0113] A. XRD Test

[0114] Test method: The prepared positive electrode was tested using an XRD diffractometer with a Cu target (40kV, 40mA) and a scan rate of 10° / min. The XRD pattern of the positive electrode was obtained, and the full width at half maximum (FWHM) of the characteristic peak of the (200) crystal plane with 2θ of 17.2±0.5° was then analyzed from the XRD pattern. 200 And the full width at half maximum (FWHM) of the characteristic peak of the (020) crystal plane with 2θ of 29.7 ± 0.5°. 020 And combined with Equation 1: D(200)=Kγ / (FWHM 200 ×cosθ 200 And Equation 2: D(020)=Kγ / (FWHM) 020 ×cosθ 020 D(200) and D(020) are calculated.

[0115] Figure 1 shows the XRD pattern of the positive electrode of Example 1. As shown in Figure 1, the positive electrode of this example includes the characteristic peak of the (200) crystal plane with a 2θ of 17.2 and the characteristic peak of the (020) crystal plane with a 2θ of 29.7. The full width at half maximum (FWHM) of the characteristic peak of the (200) crystal plane is 0.0022 and the FWHM of the (020) crystal plane is 0.0035. According to Equation 1, D(200) is 63.0 nm and D(020) is 40.8 nm.

[0116] B. Average particle size test

[0117] Test method: The microstructure of the positive electrode sheet was photographed using a scanning electron microscope (SEM). The magnification was set to allow clear observation of the lithium manganese iron phosphate particles. The longest diameter of the lithium manganese iron phosphate particles present in the positive electrode sheet was measured, and the average value was calculated as the average particle size D. 平均 .

[0118] 2. The lithium-ion batteries made from the positive electrode sheets of the above embodiments and comparative examples were tested for the following performance. The test results are shown in Table 2:

[0119] A. Ratio Performance

[0120] Test method: The above-mentioned lithium-ion batteries were subjected to constant current charge-discharge tests at current densities of 1C and 2C within a voltage range of 2–4.3V. The reversible specific capacity C1 and C2 at 1C and 2C were recorded respectively. The capacity retention rate R of the battery at 2C relative to 1C was used as the metric. 倍率 =C2 / C1×100%, reflecting the effect of different LMFPs on Li + The effect of diffusion rate.

[0121] B. Cyclic performance

[0122] Test method: The above-mentioned lithium-ion battery was subjected to constant current charge-discharge test at a current density of 1C within a voltage window of 2-4.3V, and its reversible specific capacity C after 300 cycles was recorded. 300 Capacity retention R relative to the initial capacity C0 循环 =C 300 / C0×100% reflects the crystal structure stability of different LMFP cathodes during the charge and discharge process.

[0123] For ease of comparison, the chemical composition of the prepared lithium manganese iron phosphate material is also given in Table 1. The Ti doping amount in Table 1 refers to the doping amount of Ti element in the lithium manganese iron phosphate material, and the ternary material ratio refers to the mass ratio of ternary material in the cathode material of the cathode sheet.

[0124] Table 1

[0125] Table 2

[0126] Combining Tables 1 and 2, the following conclusions can be drawn:

[0127] Comparing Examples 1-7 with Comparative Examples 1-4, it can be seen that D(200) / D(020)≥1.15 in Examples 1-7, and 10%≤D(200) / D50≤30%. The average rate performance and cycle capacity retention of the batteries in Examples 1-7 are not less than 90%.

[0128] The ratio of D(200) / D(020) in Comparative Example 1 is 1.01, indicating that the lithium-ion transport path in the

[0010] crystal direction is relatively long, which is not conducive to the rapid transport of lithium ions, resulting in the R corresponding to this cathode being... 倍率 Only 89.27%; similarly for Comparative Example 4, D(200) / D(020) is too small, affecting the diffusion rate of lithium ions in lithium manganese iron phosphate particles, thus reducing its R 倍率 A significant decrease compared to Example 7;

[0129] In Comparative Example 2, D(200) / D(020) = 1.10, D(200) / D 平均 =7.2%, indicating that

[0010] Li crystallographic orientation + If the size of the diffusion end face is too small relative to the crystal grain, it is also detrimental to Li. + Transmission is difficult, and the material's structural stability is poor, leading to its R... 倍率 Only 83.51%, R 循环 Only 79.1%;

[0130] In Comparative Example 3, D(200) / D 平均 =37.2%, indicating that

[0010] Li crystallographically + If the diffusion end face is too large relative to the particle size, Mn is prone to occur during cycling. 2+ Dissolution also leads to a rapid decline in cycling performance, with its R... 循环 Only 86.3%.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 therein. Such 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 this application.

Claims

1. A positive electrode plate, wherein, The positive electrode includes lithium manganese iron phosphate material, and the X-ray crystal diffraction pattern of the positive electrode includes characteristic peaks of the (200) crystal plane with 2θ of 17.2±0.5° and characteristic peaks of the (020) crystal plane with 2θ of 29.7±0.5°. The average packing size D(200) on the (200) crystal plane, the average packing size D(020) on the (020) crystal plane, and the average particle size D of the lithium manganese iron phosphate material 平均 The following relationship must be satisfied: D(200) / D(020)≥1.15 and 10%≤D(200) / D 平均 ≤30%.

2. The positive electrode according to claim 1, wherein, D(200) / D(020)≤1.

8.

3. The positive electrode according to claim 1 or 2, wherein, The average particle size D of the lithium manganese iron phosphate material 平均 The wavelength range is 300–1100 nm.

4. The positive electrode according to any one of claims 1-3, wherein, The chemical composition of the lithium manganese iron phosphate material is LiMn. x Fe 1-x PO4, where 0.1 ≤ x ≤ 0.

7.

5. The positive electrode according to claim 4, wherein, The lithium manganese iron phosphate material also includes doping elements, including Al. 3+ B 3+ Zr 4+ Ti 4+ W 6+ Ta 5+ Ru 5+ One or more of them.

6. The positive electrode according to any one of claims 1-5, wherein, The positive electrode sheet includes a positive current collector and a positive active layer; The positive electrode active layer comprises a positive electrode material, a conductive agent, and a binder in a mass ratio of (7-9):(0.5-2):(0.5-1); The cathode material includes lithium manganese iron phosphate.

7. The positive electrode according to any one of claims 1-6, wherein, The cathode material also includes one or more of ternary materials, lithium iron phosphate, lithium manganese oxide, and lithium cobalt oxide.

8. The positive electrode according to claim 7, wherein, The compaction density of the positive electrode sheet is >2.3 g / cm³. 3 .

9. A battery, wherein, Includes the positive electrode sheet as described in any one of claims 1-8.

10. An electrical appliance, wherein, Includes the battery as described in claim 9.

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