Cathode sheet, battery and electric device

Abstract

Provided in the present application are a cathode sheet, a battery and an electric device. The cathode sheet of the present application comprises a cathode current collector and a cathode active layer, wherein the cathode active layer comprises a nickel-cobalt-manganese ternary material and a lithium iron manganese phosphate material; an X-ray crystal diffraction pattern of the cathode sheet comprises a first characteristic peak having a 2θ angle of 18.67±0.5° and a second characteristic peak having a 2θ angle of 35.58±0.5°; the peak intensity of the first characteristic peak is I1, and the peak intensity of the second characteristic peak is I2; and 13≤I1 / I2≤30, and the mass percentage WMn 2+ of Mn2+ and the mass percentage WMn 4+ of Mn4+ in the cathode sheet satisfies: 22%≤WMn 2+ / WMn 4+≤62%. The cathode sheet of the present application is applied to a battery and has a high energy density, a good cycle performance and rate performance, and low material costs.

Description

Positive electrode plates, batteries, and electrical equipment

[0001] This application claims priority to Chinese Patent Application No. 202411751669.4, 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] In recent years, to meet consumers' demands for extended battery range, high-energy-density ternary (NCM) cathode materials have been widely used. However, compared to lithium iron phosphate cathode materials, ternary materials have higher costs, hindering the expansion of their application market. Cobalt is a rare metal with low abundance in the Earth's crust. Reducing the cobalt content in ternary materials can help lower battery manufacturing costs, but this also reduces the stability of the ternary material's crystal structure.

[0004] With the continuous in-depth research on cathode materials, lithium manganese iron phosphate (LFP) has gradually gained attention due to its combination of high energy density and low cost. Combining LFP with ternary materials, while meeting energy density requirements, helps reduce battery material costs, making it a highly promising cathode option for power batteries. However, LFP materials have a slow lithium-ion diffusion rate and are prone to Mn deposition. 2+ Dissolution is detrimental to battery cycle performance and rate capability. To improve the diffusion rate of lithium ions in lithium manganese iron phosphate, nanoscale particles are typically used. However, these small particles are difficult to effectively fill all pores during compaction, resulting in low electrode compaction density. When mixed with ternary materials, it is difficult to achieve high electrode compaction density, thus hindering the improvement of battery energy density.

[0005] Therefore, how to balance the high energy density, good cycle performance and rate performance, and low material cost of the hybrid cathode of lithium manganese iron phosphate and ternary materials 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. The application controls the relationship between the peak intensity I1 representing the characteristic peak of the (003) crystal plane in NCM and the peak intensity I2 representing the characteristic peak of the (311) or (131) crystal plane in LMFP to be 13 ≤ I1 / I2 ≤ 30, and controls the Mn content in the positive electrode to be within this range. 2+ mass percentage W Mn 2+ With Mn 4+mass percentage W Mn 4+ Satisfying 22% ≤ W Mn 2+ / W Mn 4+ With a density of ≤62%, the battery combines high energy density, good cycle performance and rate performance with low material cost.

[0007] The first aspect of this application provides a positive electrode sheet, including a positive electrode current collector and a positive electrode active layer, wherein the positive electrode active layer includes a nickel-cobalt-manganese ternary material and a lithium manganese iron phosphate material;

[0008] The X-ray crystal diffraction pattern of the positive electrode includes a first characteristic peak with a 2θ angle of 18.67±0.5° and a second characteristic peak with a 2θ angle of 35.58±0.5°. The peak intensity of the first characteristic peak is I1 and the peak intensity of the second characteristic peak is I2.

[0009] Where 13≤I1 / I2≤30, and the Mn in the positive electrode plate 2+ mass percentage W Mn 2+ With Mn 4+ mass percentage W Mn 4+ Satisfying 22% ≤ W Mn 2+ / W Mn 4+ ≤62%.

[0010] In one optional embodiment, the mass percentage of the lithium manganese iron phosphate material is 10% to 45% based on the total mass of the nickel-cobalt-manganese ternary material and the lithium manganese iron phosphate material.

[0011] In one optional embodiment, the molecular formula of the nickel-cobalt-manganese ternary material is Li. a Ni 1-x-y-z Co x Mn y A z O2, wherein A is selected from one or more of Al, B, Zr, Ti, W, Ta, and Ru, 0.8≤a≤1.3, 0≤x≤0.3, 0.1≤y≤0.5, and 0≤z≤0.02;

[0012] And / or, the molecular formula of the lithium manganese iron phosphate material is LiMn b Fe 1-b PO4, where 0.1≤b≤0.7.

[0013] In one optional embodiment, the surface of the lithium manganese iron phosphate material further includes a coating layer, the composition of which is selected from one or more of TiO2, ZrO2, Al2O3, and carbon materials.

[0014] In one alternative implementation, the nickel-cobalt-manganese ternary material is in the form of primary particles.

[0015] In one optional embodiment, the particle size of the primary particles is 1 to 10 μm.

[0016] In one optional embodiment, the particle size of the lithium manganese iron phosphate material is 50–2000 nm.

[0017] In one optional embodiment, the compaction density of the positive electrode sheet is >2.6 g / cm³. 3 .

[0018] A second aspect of this application provides a battery including the positive electrode provided in the first aspect of this application.

[0019] A third aspect of this application provides an electrical device, including the battery provided in the second aspect of this application.

[0020] The implementation of this application has at least the following beneficial effects:

[0021] The cathode provided in this application controls the relationship between the peak intensity I1 of the characteristic peak representing the (003) crystal plane of the nickel-cobalt-manganese ternary material and the peak intensity I2 of the characteristic peak representing the (131) or (311) crystal plane of lithium manganese iron phosphate in the XRD pattern of the cathode: 13≤I1 / I2≤30. This ensures that the NCM particles in the cathode have high crystallinity and the LMFP crystal has low crystallinity, which is beneficial to maintaining the structural stability of the NCM crystal and effectively shortening the transport distance of lithium ions and electrons in the lithium manganese iron phosphate material, thus ensuring the cycle stability and rate performance of the battery. At the same time, controlling the Mn content in the cathode... 2+ mass percentage W Mn 2+ With Mn 4+ mass percentage W Mn 4+ Satisfying 22% ≤ W Mn 2+ / W Mn 4+ ≤62%, of which Mn 2+ Mainly from LMFP, Mn 4+ Mainly from NCM, controlling W Mn 2+ / W Mn 4+A concentration of ≥22% ensures a certain proportion of LMFP in the positive electrode, which helps reduce the overall material cost of the positive electrode or ensures a higher Mn content per unit LMFP. 2+ The proportion of Mn in LMFP is increased. 2+ The proportion of W is beneficial to improving the energy density of the battery; while W Mn 2+ / W Mn 4+ ≤62% limits the amount of Mn in the positive electrode. 2+ Excessive content can help inhibit Mn during circulation. 2+ Dissolution further ensures battery cycle performance. On the other hand, it can effectively limit LMFP content, reduce the adverse effects of low LMFP compaction density on energy density, and also affect Mn. 4+ The content limit can guarantee the content of NCM in the positive electrode or the Mn content per unit of NCM. 4+ Increase the content of Mn in unit NCM (cobalt-free or low-cobalt). 4+ The content can increase the positive electrode working voltage, which is beneficial to ensuring the energy density of the battery.

[0022] In summary, this application achieves this by controlling the content of 13 ≤ I1 / I2 ≤ 30 and 22% ≤ W in the positive electrode. Mn 2+ / W Mn 4+ With a density of ≤62%, the battery combines high energy density, good cycle performance and rate performance with low material cost. Attached Figure Description

[0023] Figure 1 is the XRD pattern of the positive electrode of Example 1. Detailed Implementation

[0024] 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.

[0025] Nickel-cobalt-manganese ternary materials possess high energy density, meeting consumers' demands for extended battery life. However, their cost is high. Reducing the cobalt content can lower raw material costs, but it also decreases crystal structure stability. Lithium iron manganese phosphate (LFP) combines high energy density with relatively low price. Using LFP in combination with ternary materials as a cathode material can reduce battery material costs. However, LFP has a slow lithium-ion diffusion rate and is prone to Mn oxidation. 2+Dissolution is detrimental to battery cycle performance and rate capability. Furthermore, lithium manganese iron phosphate particles are typically nano- or low-micron-sized, making it difficult for these small particles to effectively fill all pores during compaction, resulting in low electrode compaction density. When used in combination with ternary materials, it is difficult to achieve high electrode compaction density, thus hindering the full utilization of battery energy density.

[0026] To address the aforementioned issues arising from the blending of nickel-cobalt-manganese ternary materials and lithium manganese iron phosphate materials, this application restricts the crystal structures of both materials, combining highly crystalline nickel-cobalt-manganese ternary materials with low-crystalline lithium manganese iron phosphate materials to ensure the structural stability and rate performance of the electrode. Furthermore, the application explores the blending rules between nickel-cobalt-manganese ternary materials and lithium manganese iron phosphate materials to improve the aforementioned problems encountered during their blending.

[0027] Based on the above concept, the first aspect of this application provides a positive electrode sheet, including a positive current collector and a positive active layer, wherein the positive active layer includes a nickel-cobalt-manganese ternary material (NCM) and a lithium manganese iron phosphate material (LMFP);

[0028] The X-ray crystal diffraction pattern (XRD pattern) of the positive electrode includes a first characteristic peak with a 2θ angle of 18.67±0.5° and a second characteristic peak with a 2θ angle of 35.58±0.5°. The peak intensity of the first characteristic peak is I1 and the peak intensity of the second characteristic peak is I2.

[0029] Where 13≤I1 / I2≤30, and the Mn in the positive electrode plate 2+ mass percentage W Mn 2+ With Mn 4+ mass percentage W Mn 4+ Satisfying 22% ≤ W Mn 2+ / W Mn 4+ ≤62%.

[0030] The first characteristic peak represents the (003) crystal plane of the nickel-cobalt-manganese ternary material, and the second characteristic peak represents the (131) crystal plane of lithium manganese phosphate crystal or the (311) crystal plane of lithium iron phosphate crystal. The peak intensity I1 of the first characteristic peak reflects the crystallinity of the NCM crystal on the (003) crystal plane, and the peak intensity I2 of the second characteristic peak reflects the crystallinity of the LMFP crystal on the (311) or (131) crystal plane. The greater the characteristic peak intensity, the higher the crystallinity of that crystal plane. By limiting the peak intensity I1 / I2 of the NCM characteristic peak and the LMFP characteristic peak in the XRD pattern of the cathode to ≥13, it is possible to ensure that the NCM particles in the cathode have a high degree of crystallinity, which is beneficial to maintaining the structural stability of the NCM crystal. Under this peak intensity ratio, the crystallinity of the LMFP crystal in the cathode is low, which can effectively shorten the lithium-ion diffusion and electron transport distance, and ensure the cycle stability and rate performance of the battery. Besides crystallinity, the ratio of I1 to I2 can also reflect the relative content of NCM and LMFP to a certain extent. Controlling 13≤I1 / I2≤30 helps to ensure that NCM and LMFP in the cathode have a suitable ratio, taking into account both the energy density and material cost of the battery.

[0031] Furthermore, manganese in NCM is predominantly in the +4 oxidation state, while in LMFP it is predominantly in the +2 oxidation state. Experimental studies have shown that controlling the Mn content in the cathode plate... 2+ mass percentage W Mn 2+ With Mn 4+ mass percentage W Mn 4+ Satisfying 22% ≤ W Mn 2+ / W Mn 4+ ≤62%, of which W Mn 2+ / W Mn 4+ A concentration of ≥22% ensures a certain mixing ratio of LMFP, which helps reduce the overall material cost of the mixed cathode, or ensures a higher Mn content per unit LMFP. 2+ The proportion of Mn in LMFP is increased. 2+ The proportion of W is beneficial to improving the energy density of the battery; while W Mn 2+ / W Mn 4+ ≤62% limits the amount of Mn in the positive electrode. 2+ Excessive content can help inhibit Mn during circulation. 2+ Dissolution further ensures battery cycle performance. On the other hand, it can effectively limit LFMP content, reduce the adverse effects of low LMFP compaction density on energy density, and also affect Mn. 4+The content limit can guarantee the content of NCM in the positive electrode or the Mn content per unit of NCM. 4+ Increase the content of Mn in unit NCM (cobalt-free or low-cobalt). 4+ The content can increase the positive electrode working voltage, which is beneficial to ensuring the energy density of the battery.

[0032] In summary, this application controls the relationship between the peak intensity I1 representing the characteristic peak of the (003) crystal plane in NCM and the peak intensity I2 representing the characteristic peak of the (311) or (131) crystal plane in LMFP to be 13≤I1 / I2≤30, and controls the Mn content in the cathode to be within the range of 13≤I1 / I2≤30. 2+ mass percentage W Mn 2+ With Mn 4+ mass percentage W Mn 4+ Satisfying 22% ≤ W Mn 2+ / W Mn 4+ With a density of ≤62%, the battery combines high energy density, good cycle performance and rate performance with low material cost.

[0033] Under the condition that Mn meets the above requirements 2+ The content of Mn 4+ Based on the limited content, experimental research has found that when the mass ratio of lithium iron phosphate material is 10% to 45% based on the total mass of nickel-cobalt-manganese ternary materials and lithium manganese iron phosphate materials, the material cost of the battery can be further reduced, and the battery can have both high energy density, good cycle performance and rate performance.

[0034] For example, the mass percentage of lithium manganese iron phosphate material can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or any two of the above values.

[0035] In one specific embodiment, the molecular formula of the nickel-cobalt-manganese ternary material is Li. a Ni 1-x-y-z Co x Mn y A z O2, wherein A is selected from one or more of Al, B, Zr, Ti, W, Ta, and Ru, with 0.8≤a≤1.3, 0≤x≤0.3, 0.1≤y≤0.5, and 0≤z≤0.02. Within the above composition range, NCM is in a cobalt-free or low-cobalt state, which is beneficial to further reduce the material cost of the electrode. In addition, by doping with elements such as Al, B, Zr, Ti, W, Ta, and Ru, the structural stability of the material can be further enhanced, reducing unfavorable phase transitions in the material lattice during charging and discharging.

[0036] In one specific embodiment, the molecular formula of lithium manganese iron phosphate material is LiMn. b Fe 1-b PO4, where 0.1 ≤ b ≤ 0.7. The structural stability and performance of lithium manganese iron phosphate materials are also affected by the manganese and iron content. Due to Mn 3+ / Mn 2+ The redox potential is higher than that of Fe. 3+ / Fe 2+ Therefore, at the same battery voltage, materials with higher manganese content can provide higher energy density, while the redox reaction of ferrous ions is relatively stable, which helps maintain the structural stability of the material during multiple charge-discharge cycles. Controlling b within the above range is beneficial for ensuring suitable iron and manganese content in lithium manganese iron phosphate materials, thus enabling the cathode to possess both high energy density and structural stability.

[0037] To improve the rate performance of lithium manganese iron phosphate (LMFP) materials, a coating layer can be applied to the surface of the LMFP material. The coating layer can be composed of one or more of TiO2, ZrO2, Al2O3, and carbon materials. By applying these coating layers, side reactions between the electrolyte and LMFP can be reduced, helping to maintain interfacial stability and lower interfacial impedance. Furthermore, carbon materials have good electrical conductivity, which can improve the electronic conductivity of LMFP, thereby increasing the battery's charge and discharge speed and improving its rate performance. Meanwhile, metal oxide coating layers such as TiO2, ZrO2, and Al2O3 have higher density, further reducing side reactions between the electrolyte and LMFP, resulting in superior interfacial stability for the LMFP material.

[0038] Common ternary materials include single-crystal and polycrystalline particles. During charging and discharging, polycrystalline ternary particles experience uneven grain shrinkage, leading to microcracks within the particles. This causes electrolyte penetration and exacerbates side reactions between the cathode and the electrolyte. In contrast, single-crystal particles can significantly suppress the formation of these microcracks, exhibiting higher crystal structure stability. Furthermore, compared to polycrystalline particles, the XRD pattern of single-crystal particles shows higher crystallinity on the (003) crystal plane. Therefore, the nickel-cobalt-manganese ternary material of this application is preferably a primary particle.

[0039] Furthermore, the particle size of the aforementioned primary particles is 1–10 μm. Micron-sized primary particles have higher crystallinity and can achieve higher compaction density.

[0040] For example, the particle size of a primary particle can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or any two of the above values.

[0041] In this application, the particle size can be obtained by observation using a scanning electron microscope.

[0042] In one specific embodiment, the lithium manganese iron phosphate material has a particle size of 50–2000 nm. This nanoscale lithium manganese iron phosphate material can shorten the lithium-ion transport path and improve the rate performance of the battery.

[0043] For example, the particle size of lithium manganese iron phosphate material can be 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, 1500nm, 1600nm, 1700nm, 1800nm, 1900nm, 2000nm, or any two of the above values.

[0044] This application enables the cathode sheet to achieve a compaction density of 2.6 g / cm³ by specifying the crystal structure of the nickel-cobalt-manganese ternary material and the lithium manganese iron phosphate material in the cathode sheet, as well as the mixing ratio of the two. 3 This leads to the attainment of high energy density.

[0045] The positive electrode sheet of this application can have its positive active layer directly disposed on one or both surfaces of the positive current collector, or a transition layer to improve the performance of the electrode sheet can be added between the positive current collector and the positive active layer to form a positive electrode sheet.

[0046] The positive electrode current collector can be made of conventionally used materials, such as aluminum foil or carbon-coated aluminum foil.

[0047] The positive electrode active layer typically includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material includes lithium manganese iron phosphate and nickel-cobalt-manganese ternary materials. This application does not specifically limit the types of conductive agents and binders; they can be selected from those conventionally used in the battery industry. Specifically, conductive agents include, but are not limited to, one or more of carbon black, carbon nanotubes, conductive graphite, and graphene; binders include, but are not limited to, one or more of CMC, SBR, PAA, SA, and PTFE.

[0048] In one specific embodiment, the positive electrode active layer comprises a positive electrode active material, a conductive agent, and a binder in a mass ratio of (7-9):(0.5-2):(0.5-1).

[0049] Specifically, the positive electrode of this application can be obtained by the following method:

[0050] 1) After mixing the nickel-cobalt-manganese ternary material precursor with a lithium source, the mixture is subjected to a first pre-sintering treatment, a first sintering treatment, a second sintering treatment, and an annealing treatment in sequence to obtain the nickel-cobalt-manganese ternary material.

[0051] The first pre-sintering treatment is carried out at a temperature of 300–550℃ for 1–4 hours; the first sintering treatment is carried out at a temperature of 600–850℃ for 1–4 hours; the second sintering treatment is carried out at a temperature of 900–1100℃ for 0.5–3 hours; and the annealing treatment is carried out at a temperature of 600–850℃ for 1–4 hours.

[0052] 2) After mixing lithium source, iron source, manganese source and phosphorus source, the mixture is subjected to a second pre-sintering treatment and a third sintering treatment in sequence to obtain lithium manganese iron phosphate material;

[0053] The second pre-sintering treatment is carried out at a temperature of 300–450℃ for 1–4 hours; the third sintering treatment is carried out at a temperature of 650–800℃ for 2–12 hours.

[0054] 3) According to 22% ≤ W Mn 2+ / W Mn 4+ The mass ratio of nickel-cobalt-manganese ternary material to lithium manganese iron phosphate is determined by a proportion of ≤62%. The nickel-cobalt-manganese ternary material and lithium manganese iron phosphate are mixed according to the determined mass ratio to obtain a mixed active material. The mixed active material is mixed with a conductive agent and a binder to form a slurry, which is then coated onto the positive electrode current collector. After drying and rolling, the positive electrode sheet is obtained.

[0055] The above preparation method allows for adjustments to the composition, pre-sintering temperature, sintering temperature, sintering time, and annealing time of nickel-cobalt-manganese ternary materials and lithium manganese iron phosphate materials during their preparation. These adjustments can affect the crystallinity and W of both materials. Mn 2+ and W Mn 4+ By regulating the I1 / I2 and W in the positive electrode, the desired effect can be achieved. Mn 2+ / W Mn 4+ Through regulation, 13 ≤ I1 / I2 ≤ 30 and 22% ≤ W were prepared. Mn 2+ / W Mn 4+ ≤62% of the positive electrode material.

[0056] Further, in step 1), the precursor of the nickel-cobalt-manganese ternary material can be in the form of nickel-cobalt-manganese oxides or hydroxides. When the ternary material contains doping elements, the precursor is in the form of nickel-cobalt-manganese oxides or hydroxides of the doping elements. The lithium source can be one or more of lithium carbonate, lithium hydroxide, lithium acetate, and lithium nitrate.

[0057] To compensate for the lithium loss caused by the volatilization of lithium in the form of lithium oxide during the subsequent high-temperature process, the lithium excess coefficient can be set to 1.01 to 1.3.

[0058] Further, in step 2), 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 1.01 to 1.1. The iron source can be selected from, but is not limited to, one or more of ferrous sulfate, ferrous oxalate, ferrous nitrate, ferrous hydroxide, and ferric phosphate. The manganese source can be selected from, but is not limited to, one or more of manganese sulfate, manganese nitrate, manganese carbonate, manganese phosphate, manganese oxalate, manganese oxide, and manganese tetroxide. The phosphorus source can be one or more of phosphoric acid, lithium dihydrogen phosphate, and ferric phosphate.

[0059] When the surface of the lithium manganese iron phosphate material is also coated, the coating source can be added and fully mixed with the pre-sintering material before the second pre-sintering treatment, and then the third sintering treatment can be carried out to complete the coating process.

[0060] This application does not impose any particular limitation on the preparation steps of the slurry in step 1), which can adopt the conventional slurry preparation steps for positive electrode sheets. For example, a mixture of nickel-cobalt-manganese ternary materials and lithium manganese iron phosphate materials can be dispersed with a conductive agent and a binder in a solvent (such as N-methylpyrrolidone) and stirred evenly to form a slurry.

[0061] This application does not impose any particular limitation on the coating method of the slurry on the positive electrode current collector, such as doctor blade coating, roller coating, spray coating, dip coating, screen printing, etc.

[0062] After coating, the slurry is dried to remove the solvent; the drying process can be completed in an oven.

[0063] Rolling can further improve the compaction density and mechanical strength of the positive electrode sheet. The rolling pressure can be controlled within the range of 0.5 to 3 MPa. For example, the rolling pressure can be 0.5 MPa, 1.0 MPa, 1.5 MPa, 2.0 MPa, 2.5 MPa, 3.0 MPa, or any two of the above values.

[0064] 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 excellent rate performance, energy density, and cycle performance.

[0065] 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.

[0066] This application does not strictly limit the negative electrode active material in the negative electrode sheet, which may be selected from one or more of graphite, hard carbon, soft carbon, silicon, silicon suboxide, and lithium metal.

[0067] 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.

[0068] This application does not strictly limit the choice of electrolyte, which can refer to the conventional composition in the art, and usually includes solvent and lithium salt. The solvent can be one or more of EMC, EC, DMC, DEC, PC, DME, and EA; the lithium salt can be one or more of LiPF6, LiFSI, LiBOB, LiDFP, LiBF4, LiNO3, LiAsF6, and LiTFSI.

[0069] This application does not strictly limit the choice of membrane material, such as polypropylene membrane (PP), polyethylene membrane (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun membrane (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven membrane, and membrane with ceramic coating. The ceramic filler in the ceramic coating can be selected from one or more of alumina, silica, boehmite, and aluminum hydroxide.

[0070] The battery of this application can be prepared by the following method:

[0071] 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.

[0072] A third aspect of this application provides an electrical device, including the battery provided in the second aspect of this application.

[0073] 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.

[0074] The following provides a more detailed description of the positive electrode sheet and its applications through specific embodiments.

[0075] In the following examples and comparative examples, the particle size of the nickel-cobalt-manganese ternary material and the lithium manganese iron phosphate material was obtained by scanning electron microscopy (SEM).

[0076] Examples 1-11 and Comparative Examples 1-16

[0077] Examples 1-11 and Comparative Examples 1-16 each provide a positive electrode sheet, the preparation method of which includes the following steps:

[0078] 1) Preparation of nickel-cobalt-manganese single-crystal ternary material: Nickel-cobalt-manganese hydroxide precursor is mixed with lithium hydroxide, the excess coefficient of lithium source is 1.05, and the mixture is subjected to first pre-sintering treatment, first sintering treatment, second sintering treatment and annealing treatment in sequence to obtain nickel-cobalt-manganese ternary material with a particle size range of 1 to 3 μm.

[0079] The first pre-sintering treatment was carried out at a temperature of 350℃ for 2 hours; the first sintering treatment was carried out at a temperature of 750℃ for 3.5 hours; the second sintering treatment was carried out at a temperature of 1000℃ for 2 hours; and the annealing treatment was carried out at a temperature of 750℃ for 2 hours.

[0080] 2) Preparation of lithium manganese iron phosphate material: manganese tetroxide, iron phosphate, phosphoric acid and lithium carbonate are mixed with an excess coefficient of lithium source of 1.02. After a second pre-sintering treatment, excess glucose (excess coefficient of about 1.2) is added as a reducing agent and coating agent. After a third sintering treatment, carbon-coated lithium manganese iron phosphate material with a particle size range of 100-1000 nm is obtained.

[0081] The second pre-sintering treatment was carried out at a temperature of 350℃ for 2 hours; the third sintering treatment was carried out at a temperature of 750℃ for 4 hours.

[0082] 4) The nickel-cobalt-manganese ternary material obtained in the above process is mixed with carbon-coated manganese iron lithium phosphate material to obtain a mixed active material; the mixed active material is mixed with conductive agent carbon black and binder PVDF in a mass ratio of 9:0.5:0.5 to make a slurry, which is coated on aluminum foil, dried and rolled to obtain a positive electrode sheet with a rolling pressure of 0.5MPa.

[0083] The composition of lithium manganese iron phosphate and nickel cobalt manganese ternary materials, as well as the mass percentage of lithium manganese iron phosphate material in the mixed active materials, differed in the positive electrode sheets of Examples 1-11 and Comparative Examples 1-16 during the preparation process, as detailed in Table 1.

[0084] Taking Example 1 as an example, the NCM composition is LiNi 0.55 Co 0.05 Mn 0.4 O2 can be achieved by controlling the molar ratio of nickel, cobalt, and manganese in the nickel-cobalt-manganese ternary precursor to 0.55:0.05:0.4, with the LMFP composition being LiMn. 0.6 Fe 0.4 PO4 can be achieved by controlling the molar ratio of Mn in the manganese source to Fe in the iron source to be 0.6:0.4.

[0085] Example 12

[0086] This embodiment provides a positive electrode sheet, the preparation steps of which are basically the same as those in Example 1. The difference is that the preparation process of the nickel-cobalt-manganese single crystal ternary material is as follows: the nickel-cobalt-manganese hydroxide precursor is mixed with lithium hydroxide, and then 0.5 wt% TiO2 is added. After passing through the first pre-sintering treatment, the first sintering treatment, the second sintering treatment, and the annealing treatment in sequence, titanium-doped nickel-cobalt-manganese single crystal ternary material is obtained. The particle size range is 1 to 3 μm. The time and temperature of the first pre-sintering treatment, the first sintering treatment, the second sintering treatment, and the annealing treatment are the same as those in Example 1.

[0087] Comparative Example 17

[0088] This comparative example provides a positive electrode sheet, the preparation method of which includes the following steps:

[0089] 1) Preparation of nickel-cobalt-manganese polycrystalline ternary material: A 2 mol / L mixed salt solution of nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate with a Ni:Co:Mn molar ratio of 0.55:0.05:0.4 was prepared. 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 at 600 r / min, the reaction temperature at 58℃, and the reaction time was 24 h. After washing and drying, a ternary precursor was obtained. The precursor was mixed with lithium hydroxide (lithium excess coefficient 1.05) and pre-calcined at 500℃ for 4 h, and then sintered at 750℃ for 6 h to obtain the nickel-cobalt-manganese polycrystalline ternary material. The secondary particle size range of this material is 2-10 μm, and the primary particle size range of the secondary particles is 1.5-2 μm.

[0090] 2) The preparation method of carbon-coated lithium manganese iron phosphate is the same as in Example 1;

[0091] 3) The nickel-cobalt-manganese ternary material is mixed with carbon-coated lithium manganese iron phosphate to obtain a mixed active material. The mass ratio of carbon-coated lithium manganese iron phosphate in the mixed active material is 19.97%. The mixed active material is mixed with conductive agent carbon black and binder PVDF in a mass ratio of 9:0.5:0.5 to form a slurry. The slurry is coated on aluminum foil, dried and rolled to obtain a positive electrode sheet. The rolling pressure is 0.5 MPa.

[0092] Test case

[0093] A. The following performance tests were performed on the positive electrode sheets prepared in the above embodiments and comparative examples:

[0094] 1. XRD test

[0095] Test method: XRD diffractometer was used with Cu target (40kV, 40mA) and scan rate of 10° / min to obtain the XRD pattern of the positive electrode. The first characteristic peak 2θ1 at 18.67±0.5° and the second characteristic peak 2θ2 at 35.58±0.5° in the XRD pattern were recorded, and the peak intensities I1 and I2 of the two characteristic peaks were obtained. The value of I1 / I2 was calculated and recorded in Table 1.

[0096] Figure 1 is the XRD pattern of the positive electrode of Example 1. As shown in Figure 1, the positive electrode of Example 1 includes a first characteristic peak with a 2θ angle of 18.67° and a peak intensity of 6796, and also includes a second characteristic peak with a 2θ angle of 35.58° and a peak intensity of 432.

[0097] 2. Mn 2+ With Mn 4+ Content testing

[0098] Test method: The LMFP (LiMn) in the cathode was analyzed by photoelectron spectroscopy (EDS). b Fe 1-b PO4) and NCM (Li a Ni 1-x-y-z Co x Mn y A z The molar percentage of each element in O2 can be used to calculate the Mn content in the cathode based on the mixing ratio of LMFP and NCM. 2+ With Mn 4+ Content, specifically, W Mn 2+ / W Mn 4+ =W LMFP / M LMFP ×b / [(1-W LMFP ) / M NCM ×y], where M LMFP With M NCM The values ​​represent the relative molecular masses of lithium manganese iron phosphate and the ternary material, respectively. The calculation results are listed in Table 1.

[0099] 3. Compacted density test

[0100] Test method: Take the rolled electrode sheet, cut off a section using a circular or square cutter, measure the thickness and weigh it. Wash away the positive electrode material with an acetone-alcohol mixture and dry it. Weigh the remaining aluminum foil and measure its thickness. Divide the difference in weight by the area to calculate the areal density. Divide the areal density by the thickness difference to obtain the compacted density. The test results are listed in Table 2.

[0101] B. Assemble the positive electrode sheets of the above embodiments and comparative examples with lithium metal negative electrodes to form coin cells, and test the following performance of the cells:

[0102] 1. Cyclic performance test

[0103] Test method: Constant current charge-discharge cycle test was performed with a current density of 1C within a voltage window of 2.5 to 4.5V. The discharge capacity C1 of the first cycle and the discharge capacity C2 after 200 cycles were recorded. The capacity retention rate R was recorded. 循环 = (C2 / C1) × 100%.

[0104] 2. Ratio Performance Test

[0105] Test method: The above-mentioned coin cell half-cells were subjected to constant current charge-discharge tests at current densities of 1C and 2C within a voltage range of 2.5–4.5V. 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% reflects the rate performance of the battery.

[0106] 3. Mass energy density

[0107] Test method: Charge and discharge tests were performed on the above coin cells at a current density of 1 / 3C to obtain capacity-voltage curves. The energy of the battery was obtained by integrating the discharge curves and then divided by the mass of the mixed active material in the corresponding positive electrode of the battery to obtain the mass energy density.

[0108] 4. Material Costs

[0109] Calculation method: Calculations are made based on the price and energy density of the corresponding cathode materials available on the market. For example, LiNi 0.55 Co 0.05 Mn 0.4 The energy cost of O2 is ¥260 / kWh, and LiNi 0.8 Co 0.1 Mn 0.1 The energy cost of O2 is ¥280 / kWh, and LiMn 0.6 Fe 0.4 The energy cost of PO4 is ¥160 / kWh, and that of LiMn... 0.1 Fe 0.9 The energy cost of PO4 is ¥200 / kWh, and that of LiMn... 0.3 Fe 0.7 The energy cost of PO4 is ¥180 / kWh. The material cost of the cathode is calculated based on the ratio of ternary materials to lithium manganese iron phosphate materials in the mixed cathode: Material cost = Energy cost of LMFP × W LMFP +NCM energy cost+(1-W) LMFP).

[0110] The test results for the button cells are listed in Table 2.

[0111] Table 1

[0112] Table 2

[0113] Combining Tables 1 and 2, the following conclusions can be drawn:

[0114] 1) When the positive electrode simultaneously satisfies 13 ≤ I1 / I2 ≤ 30 and 22% ≤ W Mn 2+ / W Mn 4+ When the content is ≤62%, the corresponding positive electrode exhibits a high compaction density (>2.6 g / cm³). 3 High energy density (>600Wh / kg), excellent cycle performance and rate performance (R 循环 >90% and R 倍率 >90%), and has a low material cost (<270￥ / kWh).

[0115] 2) Compared to Examples 1 and 2, Comparative Examples 1 and 2 used LiNi 0.8 Co 0.1 Mn 0.1 O2, to satisfy 22% ≤ W Mn 2+ / W Mn 4+ ≤62%, W in the system LMFP If the value is too low, the corresponding I1 / I2 > 30 does not meet the requirements, leading to an increase in material cost per unit energy (≥270 RMB / kWh). Although Example 4 also used LiNi... 0.8 Co 0.1 Mn 0.1 O2, but its I1 / I2 ratio is similar to W Mn 2+ / W Mn 4+ All requirements are met, and the material cost per unit energy is only ¥263 / kWh.

[0116] 3) In Comparative Examples 3, 4, 5, 6, and 7, the molar percentage of manganese in the LMFP used was relatively small, in order to satisfy 22% ≤ W Mn 2+ / W Mn 4+ ≤62%, W in the system LMFPIf the value is too high, the corresponding I1 / I2 ≤ 13 does not meet the requirement, resulting in a decrease in the compaction density of the electrode (< 2.6 g / cm³). 3 Furthermore, the mass energy density and rate performance are both affected.

[0117] 4) In comparative examples 8, 10, and 13, I1 / I2 meets the requirements, while W... Mn 2+ / W Mn 4+ ≥62% does not meet the requirements, W in the system Mn 2+ Too high a concentration of Mn during battery cycling 2+ The dissolution phenomenon is quite severe, leading to a decrease in cycle performance (R). 循环 <90%).

[0118] 5) In Comparative Example 12, I1 / I2 meets the requirements, while W Mn 2+ / W Mn 4+ ≤22%, W LMFP The lower cost leads to higher material costs (¥270 / kWh).

[0119] 6) In comparative examples 11, 15, and 16, I1 / I2 ≤ 13 and W Mn 2+ / W Mn 4+ ≥62% corresponds to low cathode compaction density and deterioration in rate and cycle performance; in Comparative Example 14, I1 / I2≤13 and W Mn 2+ / W Mn 4+ ≤20% corresponds to low cathode compaction density, low energy density, and poor rate performance; comparative examples 8 and 13 show that although its W LMFP It is between 10% and 45%, but corresponds to W Mn 2+ / W Mn 4+ If the W value is too high, the cycle stability of the battery will decrease, indicating that W... Mn 2+ / W Mn 4+ It can also affect battery performance.

[0120] 7) Compared with Example 1, Comparative Example 17 prepared a polycrystalline ternary material with a smaller particle size, lower I1, and a smaller I1 / I2. Because the polycrystalline ternary material is prone to microcracks during charging and discharging, electrolyte penetration and side reactions between the electrolyte and the positive electrode are aggravated, resulting in faster degradation of cycle performance.

[0121] 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 sheet, comprising a positive current collector and a positive active layer, wherein, The positive electrode active layer comprises nickel-cobalt-manganese ternary materials and lithium iron phosphate materials; The X-ray crystal diffraction pattern of the positive electrode includes a first characteristic peak with a 2θ angle of 18.67±0.5° and a second characteristic peak with a 2θ angle of 35.58±0.5°. The peak intensity of the first characteristic peak is I1 and the peak intensity of the second characteristic peak is I2. Where 13≤I1 / I2≤30, and the Mn in the positive electrode plate 2+ mass percentage W Mn 2+ With Mn 4+ mass percentage W Mn 4+ Satisfying 22% ≤ W Mn 2+ / W Mn 4+ ≤62%.

2. The positive electrode according to claim 1, wherein, Based on the total mass of the nickel-cobalt-manganese ternary material and the lithium manganese iron phosphate material, the mass ratio of the lithium manganese iron phosphate material is 10% to 45%.

3. The positive electrode according to claim 1 or 2, wherein, The molecular formula of the nickel-cobalt-manganese ternary material is Li. a Ni 1-x-y-z Co x Mn y A z O2, wherein A is selected from one or more of Al, B, Zr, Ti, W, Ta, and Ru, 0.8≤a≤1.3, 0≤x≤0.3, 0.1≤y≤0.5, and 0≤z≤0.02; And / or, the molecular formula of the lithium manganese iron phosphate material is LiMn b Fe 1-b PO4, where 0.1≤b≤0.

7.

4. The positive electrode according to any one of claims 1-3, wherein, The surface of the lithium manganese iron phosphate material also includes a coating layer, the composition of which is selected from one or more of TiO2, ZrO2, Al2O3, and carbon materials.

5. The positive electrode according to any one of claims 1-4, wherein, The nickel-cobalt-manganese ternary material is a primary particle.

6. The positive electrode according to claim 5, wherein, The particle size of the primary particles is 1–10 μm.

7. The positive electrode according to any one of claims 1-6, wherein, The particle size of the lithium manganese iron phosphate material is 50–2000 nm.

8. The positive electrode according to any one of claims 1-7, wherein, The compaction density of the positive electrode sheet is >2.6 g / cm³. 3 .

9. A battery, wherein, The battery 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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