Positive electrode sheet, energy storage device, and electric device

Abstract

The disclosure provides a positive electrode sheet, an energy storage device and an electric equipment. The positive electrode sheet comprises a positive electrode active layer, the positive electrode active layer comprises a first transition metal sodium oxide and a second transition metal sodium oxide, both of which are in a granular form, the crystal structure of the first transition metal sodium oxide is in an O3 phase, and the crystal structure of the second transition metal sodium oxide is in a P2 phase; in the XRD pattern of the positive electrode sheet, the ratio of the diffraction peak intensity of the (002) crystal face to the diffraction peak intensity of the (003) crystal face is 1:(1.0-5.0), and the ultimate compaction density of the positive electrode active layer is 3.2 g / cm 3 -3.4 g / cm 3 .

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a positive electrode, an energy storage device, and an electrical appliance. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density and long cycle life, making them a widely researched and applied type of rechargeable battery. Lithium salts are an indispensable material in lithium-ion batteries. Currently, lithium salts face challenges such as limited raw material reserves and high costs, which restrict the production cost of lithium-ion batteries. Compared to lithium-ion batteries, sodium-ion batteries require sodium materials, which have advantages such as abundant reserves and wide distribution, offering considerable development prospects.

[0003] Currently, layered oxides, polyanionic compounds, and Prussian blue-based materials are common cathode active materials. Layered oxides with an O3 phase crystal structure have a high sodium ion content, providing a high specific capacity, and are therefore often used as cathode materials for sodium-ion batteries. However, O3 phase materials typically have poor cycle performance. Although optimizing the elemental composition, doping with metal elements, or coating the surface with P2 phase materials can improve cycle performance, the mixed materials still suffer from easy breakage during cycling, limiting further improvements in cycle performance. Summary of the Invention

[0004] In view of this, in order to improve the breakage problem of the mixed layered oxides during the cycling process and thus improve the cycle performance of the battery, it is necessary to provide a positive electrode sheet.

[0005] According to some embodiments of this disclosure, a positive electrode sheet is provided, the positive electrode sheet including a positive electrode active layer, the positive electrode active layer including a first transition metal sodium oxide and a second transition metal sodium oxide, both the first transition metal sodium oxide and the second transition metal sodium oxide are granular, the crystal structure of the first transition metal sodium oxide is O3 phase, and the crystal structure of the second transition metal sodium oxide is P2 phase.

[0006] In the XRD pattern of the positive electrode sheet, the ratio of the diffraction peak intensity of the (002) crystal plane to that of the (003) crystal plane is 1:(1.0~5.0), and the limiting compaction density of the positive electrode active layer is 3.2 g / cm³. 3 ~3.4g / cm 3 .

[0007] In some embodiments of this disclosure, the compressive strength of the mixture of the first transition metal oxide and the second transition metal sodium oxide in the positive electrode active layer is ≥200 MPa.

[0008] In some embodiments of this disclosure, the compressive strength of the second transition metal sodium oxide is greater than that of the first transition metal sodium oxide, wherein the compressive strength of the first transition metal sodium oxide is 50 MPa to 250 MPa and the compressive strength of the second transition metal sodium oxide is 150 MPa to 350 MPa.

[0009] In some embodiments of this disclosure, the particles of the first transition metal sodium oxide are primary particles, and the particles of the second transition metal sodium oxide are at least one of primary particles and secondary particles.

[0010] In some embodiments of this disclosure, the D of the first transition metal sodium oxide v 50 particles with a diameter of 6 μm to 14 μm, the D of the first transition metal sodium oxide v 10. The particle size is 3μm to 8μm, and the D of the first transition metal sodium oxide v The particle size of 90 is 14μm to 30μm.

[0011] In some embodiments of this disclosure, the D of the second transition metal sodium oxide v 50 particles with a diameter of 3μm to 8μm, the D of the second transition metal sodium oxide v 10. The particle size is 2μm to 5μm, and the D of the second transition metal sodium oxide v The particle size of 90 is 8μm to 18μm.

[0012] In some embodiments of this disclosure, the chemical formula of the first transition metal sodium oxide is Na. x1 Ni 1-y1-z1- w1 Fe y1 Mn z1 M w1 O2, where 0.8≤x1≤1, 0≤y1+z1+w1≤1; the chemical formula of the second transition metal sodium oxide is Na. x2 Ni 1-y2-z2-w2 Fe y2 Mn z2 M w2 O2, where 0.67≤x2≤0.8, 0≤y2+z2+w2≤1; in the first transition metal sodium oxide and the second transition metal sodium oxide, M is independently selected from one or more of Li, Mg, Y, Ca, Al, Ti, Zr, V, Cr, Cu, Nb, Sn, Sb, Bi and Zn.

[0013] In some embodiments of this disclosure, the mass ratio of the first transition metal sodium oxide to the second transition metal sodium oxide in the positive electrode is (1-8):1.

[0014] In some embodiments of this disclosure, the specific capacity of the positive electrode at a charge / discharge rate of 0.1C is above 140mAh / g.

[0015] In some embodiments of this disclosure, the positive electrode retains more than 90% of its capacity after 100 cycles at a charge-discharge rate of 1.0C.

[0016] Furthermore, this disclosure also provides an energy storage device, which includes an electrode assembly and an electrolyte, wherein at least a portion of the electrode assembly is immersed in the electrolyte, and the electrode assembly includes a negative electrode and a positive electrode according to any of the above embodiments.

[0017] Furthermore, this disclosure also provides an electrical device including functional components and an energy storage device as described in any of the above embodiments, the energy storage device being used to supply power to the functional components.

[0018] The positive electrode sheet provided in this disclosure includes a first transition metal sodium oxide and a second transition metal sodium oxide. The first transition metal sodium oxide has an O3 phase crystal structure, and the second transition metal sodium oxide has a P2 phase crystal structure. This disclosure, through experiments, shows that mixing the first and second transition metal sodium oxides according to suitable particle properties and proportions can achieve a limiting compaction density of 3.2 g / cm³ for the positive electrode active layer when the ratio of the diffraction peak intensity of the (002) crystal plane to the diffraction peak intensity of the (003) crystal plane is 1:(1.0~5.0). 3 ~3.4g / cm 3 This can effectively improve the problem of particle breakage in the positive electrode active layer, thereby improving the cycle stability of the positive electrode sheet. Attached Figure Description

[0019] Figure 1 The above are XRD diffraction diagrams of the positive electrode active materials in Examples 1 to 4. Detailed Implementation

[0020] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items, and "more" as used herein includes two or more items.

[0022] In this invention, unless otherwise stated, the sum of the parts of each component in the composition may be 100 parts by weight. Unless otherwise specified, the percentages (including weight percentages) in this invention are based on the total weight of the composition. Furthermore, "wt%" in this document represents mass percentage, and "at%" represents atomic percentage.

[0023] In this document, unless otherwise stated, the reaction steps may be performed in the order described herein or not. For example, other steps may be included between reaction steps, and the order of reaction steps may be appropriately interchanged. This is something that those skilled in the art can determine based on conventional knowledge and experience. Preferably, the reaction methods described herein are performed sequentially.

[0024] This disclosure provides a positive electrode sheet comprising a positive electrode active material, which includes a first transition metal sodium oxide and a second transition metal sodium oxide. Both the first and second transition metal sodium oxides are granular. The first transition metal sodium oxide has an O3 phase crystal structure, and the second transition metal sodium oxide has a P2 phase crystal structure. In the XRD pattern of the positive electrode sheet, the ratio of the diffraction peak intensity of the (002) crystal plane to that of the (003) crystal plane is 1:(1.0~5.0), and the limiting compaction density of the positive electrode active layer is 3.2 g / cm³. 3 ~3.4g / cm 3 .

[0025] Based on the difference in sodium ion occupancy, layered oxides can generally be divided into O3 phase and P2 phase. It can be understood that this positive electrode contains a first transition metal sodium oxide in the O3 phase and a second transition metal sodium oxide in the P2 phase. The main peak in the XRD pattern of the first transition metal sodium oxide in the O3 phase corresponds to its (003) crystal plane, and the main peak in the XRD pattern of the second transition metal sodium oxide in the P2 phase corresponds to its (002) crystal plane. Therefore, the overall XRD pattern of this positive electrode has diffraction peaks corresponding to both the (003) and (002) crystal planes. The relative intensity between the diffraction peaks of the (003) and (002) crystal planes is directly related to the ratio of the two sodium-nickel-iron-manganese oxides.

[0026] In traditional techniques, when the ratio of the diffraction peak intensity of the (002) crystal plane to that of the (003) crystal plane of the positive electrode is 1:(1.0~5.0), the O3 phase material is significantly more abundant, making it difficult to achieve a minimum compaction density of 3.2 g / cm³ after mixing. 3 Furthermore, the cycle performance of this positive electrode is significantly poor.

[0027] This disclosure, during its research, discovered that when O3 phase material and P2 phase material are mixed in a certain ratio and a high ultimate compaction density is achieved, the particle shape in the positive electrode active layer can be kept more stable and less prone to breakage, thereby maintaining cycle stability for a longer period of time. The positive electrode sheet provided in this disclosure includes a first transition metal sodium oxide and a second transition metal sodium oxide. The first transition metal sodium oxide has an O3 phase crystal structure, and the second transition metal sodium oxide has a P2 phase crystal structure. This disclosure, through experiments, found that mixing the first and second transition metal sodium oxides according to suitable particle properties and ratios can achieve an ultimate compaction density of 3.2 g / cm³ for the positive electrode active layer when the ratio of the diffraction peak intensity of the (002) crystal plane to the diffraction peak intensity of the (003) crystal plane is 1:(1.0~5.0). 3 ~3.4g / cm 3 This can effectively improve the breakage problem of the first transition metal sodium oxide in the O3 phase, thereby improving the cycle stability of the positive electrode. In addition, thanks to the increase in the limiting compaction density, the volumetric energy density of the positive electrode can also be improved.

[0028] It is understandable that in the preparation process of the positive electrode sheet, after coating the slurry and drying, the electrode sheet needs to undergo cold pressing to form a compacted positive electrode active layer. Generally speaking, the higher the compaction density, the more active material can be accommodated in the same volume, and the higher the energy density of the battery. The compaction density of the positive electrode active layer can be calculated by dividing the areal density of the positive electrode active layer by its thickness. The compaction density of the positive electrode active layer is directly related to the material used in the positive electrode active layer and usually has a limiting compaction density. When the positive electrode active layer is compressed to a density exceeding the limiting compaction density, it will cause severe particle breakage in the material, resulting in a significant decrease in the specific capacity and cycle performance of the electrode sheet. Therefore, it is usually necessary to control the compaction density of the positive electrode active layer to be near its limiting compaction density.

[0029] The ultimate compaction density can be tested according to test methods known to those skilled in the art. For example, in this application, the ultimate compaction density is tested as follows: by gradually increasing the rolling pressure, the crease of the electrode sheet is made opaque when folded once, but transparent when folded twice. The compaction density at this point is the ultimate compaction density.

[0030] In some examples of this embodiment, the compaction density of the positive electrode active layer may be 3.2 g / cm³. 3 3.23 g / cm 3 3.25g / cm 3 3.28g / cm 3 3.3g / cm 3 3.33 g / cm 3 3.35g / cm 3 3.38g / cm 3 3.4g / cm 3 Alternatively, the compaction density of the positive electrode active layer can be within the range of any two of the above compaction densities.

[0031] In some examples of this embodiment, the positive electrode may further include a current collector, with the positive active layer disposed on the current collector. Furthermore, the material of the current collector may be selected from metallic materials. For example, the material of the current collector may be selected from one or more of copper, aluminum, iron, and silver.

[0032] In some examples of this embodiment, the first transition metal sodium oxide contains sodium and a transition metal element, and its chemical formula may be: Na x1 Ni 1-y1-z1-w1 Fe y1 Mn z1 M w1 O2, where 0.8 ≤ x1 ≤ 1, 0 ≤ y1 + z1 + w1 ≤ 1, and M can be selected from one or more of Li, Mg, Y, Ca, Al, Ti, Zr, V, Cr, Cu, Nb, Sn, Sb, Bi, and Zn. It is understood that y1, z1, and w1 can all be 0; when y1, z1, or w1 is 0, it indicates that the first transition metal sodium oxide does not contain the corresponding metal element. In some examples of this embodiment, y1, z1, and w1 are all greater than 0 and their sum is less than 1, meaning that the first transition metal sodium oxide simultaneously includes Ni, Fe, Mn, and M. For example, the chemical formula of the first transition metal sodium oxide can be Na. 0.94 Ni 0.29 Fe 0.32 Mn 0.36 Zn 0.03 O2.

[0033] In some examples of this embodiment, the second transition metal sodium oxide contains sodium and a transition metal element, and its chemical formula may be: Na x2 Ni 1-y2-z2-w2 Fe y2 Mn z2 M w2O2, where 0.67≤x2≤0.8, 0≤y2+z2+w2≤1, and M can be selected from one or more of Li, Mg, Y, Ca, Al, Ti, Zr, V, Cr, Cu, Nb, Sn, Sb, Bi, and Zn. It is understood that y2, z2, and w2 can all be 0; when y2, z2, or w2 is 0, it indicates that the first transition metal sodium oxide does not contain the corresponding metal element. In some examples of this embodiment, y2 and z2 are both greater than 0 and their sum is less than 1, meaning that the first transition metal sodium oxide simultaneously includes Ni, Fe, and Mn. For example, the chemical formula of the second transition metal sodium oxide can be Na. 0.77 Ni 0.23 Fe 0.56 Mn 0.51 O2.

[0034] In some examples of this embodiment, the compressive strength of the mixture of the first transition metal sodium oxide and the second transition metal sodium oxide in the positive electrode active layer can be between 200 MPa and 500 MPa. For example, the compressive strength of the mixture can be 200 MPa, 250 MPa, 300 MPa, 350 MPa, 400 MPa, 450 MPa, or 500 MPa, or it can be within the range of any two of the above compressive strengths. By controlling the compressive strength of the mixture of the first and second transition metal sodium oxides to be above 200 MPa, it is beneficial to achieve a higher ultimate compaction density for the electrode.

[0035] In some examples of this embodiment, the compressive strength of the first transition metal sodium oxide is greater than that of the second transition metal sodium oxide. By controlling the compressive strength of the first transition metal sodium oxide to be higher than that of the second transition metal sodium oxide, the problem of particle breakage in the positive electrode active layer during cycling can be further improved.

[0036] Furthermore, in some examples of this embodiment, the compressive strength of the first transition metal sodium oxide can be between 150 MPa and 350 MPa. For example, the compressive strength of the first transition metal sodium oxide can be 150 MPa, 200 MPa, 220 MPa, 250 MPa, 280 MPa, 300 MPa, or 350 MPa, or the compressive strength of the first transition metal sodium oxide can be within the range of any two of the above compressive strengths.

[0037] Furthermore, in some examples of this embodiment, the compressive strength of the second transition metal sodium oxide can be between 50 MPa and 250 MPa. For example, the compressive strength of the second transition metal sodium oxide can be 50 MPa, 100 MPa, 120 MPa, 150 MPa, 180 MPa, 200 MPa, or 250 MPa, or the compressive strength of the second transition metal sodium oxide can be within the range of any two of the above compressive strengths.

[0038] In some examples of this embodiment, the difference between the compressive strength of the first transition metal sodium oxide and the compressive strength of the second transition metal sodium oxide can be 50 MPa or more. Further, the difference between the compressive strength of the first transition metal sodium oxide and the compressive strength of the second transition metal sodium oxide can be 100 MPa or more.

[0039] In some examples of this embodiment, the D of the first transition metal sodium oxide v 50 particles with a diameter of 6μm to 14μm, D of the first transition metal sodium oxide v 10. Particle size of first transition metal sodium oxide D v The particle size of 90 particles ranges from 14 μm to 30 μm. The particle size of the first transition metal sodium oxide can be obtained by statistically analyzing the particle sizes of multiple first transition metal sodium oxide particles.

[0040] In some examples of this embodiment, the D of the second transition metal sodium oxide v 50 particles with a diameter of 3μm to 8μm, D of the second transition metal sodium oxide v 10. Particle size of second transition metal sodium oxide is 2μm~5μm. v The particle size of 90 is 8μm to 18μm.

[0041] By controlling the particle size range of the first and second transition metal sodium oxides, the first transition metal sodium oxide is less prone to breakage during the compaction process after mixing, thereby further improving the cycle performance of the positive electrode. Furthermore, the compressive strength of transition metal sodium oxides is related to the particle size and morphology of the material. Therefore, controlling the particle size of the first and second transition metal sodium oxides is also beneficial for ensuring that they possess suitable compressive strength.

[0042] In some examples of this embodiment, the particles of the first transition metal sodium oxide are primary particles. Here, primary particles refer to the first transition metal sodium oxide particles being single crystals. Single crystals have higher internal bonding strength. By controlling the particles of the first transition metal sodium oxide to be primary particles, it is less likely for them to pulverize during compaction, thereby ensuring that the compaction density of the positive electrode active layer can be effectively improved.

[0043] In some examples of this embodiment, the particles of the second transition metal sodium oxide can be at least one of primary particles and secondary particles. Secondary particles refer to particles of the second transition metal sodium oxide formed by the aggregation of multiple grains. Compared to the bonding strength within grains, the bonding strength between adjacent grains is lower, but the compressive strength of the P2 phase second transition metal sodium oxide is generally high; therefore, secondary particles can also be used to reduce material costs.

[0044] In some examples of this embodiment, the compaction density of the first transition metal sodium oxide is ≥3.0 g / cm³. 3 The compacted density of the second transition metal sodium oxide is ≥3.4 g / cm³. 3 .

[0045] In some examples of this embodiment, the mass ratio of the first transition metal sodium oxide and the second transition metal sodium oxide in the positive electrode active layer can be controlled to be (1-8):1. Further, the mass ratio of the first transition metal sodium oxide and the second transition metal sodium oxide can be controlled to be (1-5):1. For example, the mass ratio of the first transition metal sodium oxide and the second transition metal sodium oxide can be controlled to be 1:1, 6:4, 7:3, or 4:1, or the mass ratio of the first transition metal sodium oxide and the second transition metal sodium oxide can also be within the range of any two of the above ratios.

[0046] In some examples of this embodiment, the positive electrode may also include at least one of a binder and a conductive agent.

[0047] In some examples of this embodiment, the total mass percentage of the first transition metal sodium oxide and the second transition metal sodium oxide in the positive electrode active layer is more than 90%. Further, the total mass percentage of the first transition metal sodium oxide and the second transition metal sodium oxide can be between 90% and 98%. For example, the total mass percentage of the first transition metal sodium oxide and the second transition metal sodium oxide can be 90%, 92%, 94%, 95%, 96%, 97%, or 98%. Of course, the total mass percentage of the first transition metal sodium oxide and the second transition metal sodium oxide can also be within any of the above two percentages.

[0048] In some examples of this embodiment, the proportion of binder in the positive electrode active layer can be 1% to 6%. For example, the proportion of binder can be 1%, 2%, 3%, 4%, 5%, or 6%, and of course, the proportion of binder can also be within any of the above two percentages.

[0049] In some examples of this embodiment, the proportion of the conductive agent in the positive electrode active layer can be 1% to 6%. For example, the proportion of the conductive agent can be 1%, 2%, 3%, 4%, 5%, or 6%, and of course, the proportion of the conductive agent can also be within any of the above two percentages.

[0050] Furthermore, in some examples, the adhesive may be selected from one or more of polyvinylidene fluoride, perfluoroethylene, polyacrylic acid, and sodium alginate. For example, the adhesive may be polyvinylidene fluoride.

[0051] In some examples, the conductive agent may be selected from one or more of conductive carbon black, acetylene black, Ketjen black, graphene, and carbon nanotubes. For example, the conductive agent may be conductive carbon black.

[0052] In some examples of this embodiment, the positive electrode retains more than 90% of its capacity after 100 cycles at a charge-discharge rate of 1.0C.

[0053] In some examples of this embodiment, the specific capacity of the positive electrode at a discharge rate of 0.1C is above 140 mAh / g.

[0054] The method for preparing the positive electrode sheet disclosed herein may include the following steps: mixing granular first transition metal sodium oxide and granular second transition metal sodium oxide to form a slurry; coating the slurry onto a current collector; drying and compacting the slurry to form a positive electrode active layer on the current collector. The ratio of the first and second transition metal sodium oxides can be controlled so that the ratio of the diffraction peak intensity of the (002) crystal plane to the diffraction peak intensity of the (003) crystal plane of the positive electrode active layer is 1:(1.0~5.0). Furthermore, considering the material types and morphologies of the first and second transition metal sodium oxides, the ultimate compaction density of the positive electrode active layer reaches 3.2 g / cm³. 3 ~3.4g / cm 3 .

[0055] Furthermore, this disclosure also provides an energy storage device. The energy storage device includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode and the negative electrode are disposed opposite to each other, and the electrolyte is disposed between the positive electrode and the negative electrode. The positive electrode includes a positive electrode plate as described in the above embodiments.

[0056] In some examples of this embodiment, the energy storage device may be a sodium-ion battery. In this energy storage device, the negative electrode may include one or more of the negative electrode materials of a sodium-ion battery, such as graphite, hard carbon, and silicon-carbon materials.

[0057] In some examples of this embodiment, the energy storage device may also include a diaphragm, which may be disposed between the positive and negative electrodes.

[0058] Furthermore, this disclosure also provides an electrical device that includes functional components and an energy storage device as described in the above embodiments, the energy storage device being used to supply power to the functional components. For example, the electrical device may be an energy storage power station, an electric vehicle, or a portable electronic device.

[0059] To facilitate understanding and implementation of the present invention, the following more detailed and easily implemented embodiments and comparative examples are provided for reference. The various embodiments and advantages of the present invention will become apparent from the description and performance results of the following specific embodiments and comparative examples. Unless otherwise specified, the raw materials used in the following experimental examples and comparative examples are all commercially available.

[0060] Example 1

[0061] Na using O3 phase 0.94 Ni 0.29 Fe 0.32 Mn 0.36 Zn 0.03 O2 is a first transition metal sodium oxide, and the particles of this first transition metal sodium oxide are primary particles, whose D v 50 particles have a diameter of 12 μm, D v 10 particles with a diameter of 7 μm, D v The particle size of 90 is 18μm, the compressive strength is 310MPa, and the powder compaction density is 3.1g / cm³. 3 .

[0062] Na using P2 phase 0.77 Ni 0.23 Fe 0.56 Mn 0.51 O2 is a second transition metal sodium oxide, and the particles of this second transition metal sodium oxide are primary particles with a D v 50 particles have a diameter of 7 μm, D v 10 particles with a diameter of 3 μm, D v The particle size of 90 is 11μm, the compressive strength is 190MPa, and the powder compaction density is 3.5g / cm³. 3 .

[0063] The first transition metal sodium oxide and the second transition metal sodium oxide are mixed at a mass ratio of 7:3 to form the positive electrode active material. The positive electrode active material is mixed with binder (polyvinylidene fluoride) and conductive agent (Super P) at a mass ratio of 96:2:2 and dispersed in N-methylpyrrolidone to form a positive electrode slurry. The positive electrode slurry is coated onto the current collector and then dried to form a positive electrode sheet.

[0064] A coin cell is assembled from a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode is a sodium metal sheet, the separator is a glass fiber separator, and the electrolyte is a carbonate electrolyte, which includes a sodium salt, a solvent, and an additive. The sodium salt is sodium hexafluoroborate, the solvent is a mixture of ethylene carbonate and dimethyl carbonate, and the additive is fluoroethylene carbonate.

[0065] Example 2

[0066] The raw materials and specific preparation process used in Example 2 are basically the same as those in Example 1, the only difference being that the mass ratio of the first transition metal sodium oxide and the second transition metal sodium oxide is 8:2.

[0067] Example 3

[0068] The raw materials and specific preparation process used in Example 3 are basically the same as those in Example 1, the only difference being that the mass ratio of the first transition metal sodium oxide and the second transition metal sodium oxide is 6:4.

[0069] Example 4

[0070] The raw materials and specific preparation process used in Example 4 are basically the same as those in Example 1, the only difference being that the mass ratio of the first transition metal sodium oxide and the second transition metal sodium oxide is 5:5.

[0071] Example 5

[0072] The preparation process of Example 5 is basically the same as that of Example 1. The only difference is that the compressive strength of the first transition metal sodium oxide material used in Example 5 is different. The particles of the first transition metal sodium oxide are primary particles with a compressive strength of 260 MPa.

[0073] Example 6

[0074] The preparation process of Example 6 is basically the same as that of Example 1. The only difference is that the compressive strength of the first transition metal sodium oxide material used in Example 6 is different. The particles of the first transition metal sodium oxide are primary particles with a compressive strength of 210 MPa.

[0075] Example 7

[0076] Example 7 is prepared in a basically the same way as Example 1, except that the compressive strength of the first transition metal sodium oxide material used in Example 7 is slightly different. The first transition metal sodium oxide particles are primary particles with a compressive strength of 140 MPa. Comparative Example 1

[0077] The raw materials and specific preparation process used in Comparative Example 1 are basically the same as those in Example 1, except that the mass ratio of the first transition metal sodium oxide and the second transition metal sodium oxide is 1:4.

[0078] Comparative Example 2

[0079] The raw materials and specific preparation process used in Comparative Example 2 are basically the same as those in Example 1, except that the mass ratio of the first transition metal sodium oxide and the second transition metal sodium oxide is 20:1.

[0080] Comparative Example 3

[0081] The preparation process of Comparative Example 3 is basically the same as that of Example 1. The only difference is that the compressive strength of the first transition metal sodium oxide material used in Comparative Example 5 is slightly different. The particles of the first transition metal sodium oxide are primary particles with a compressive strength of 100 MPa.

[0082] Comparative Example 4

[0083] The preparation process of Comparative Example 4 is basically the same as that of Example 1. The only difference is that the compressive strength of the first transition metal sodium oxide material used in Comparative Example 5 is slightly different. The particles of the first transition metal sodium oxide are primary particles with a compressive strength of 60 MPa.

[0084] Experiment 1: XRD tests were performed on the positive electrode active layers prepared as in Examples 1 to 7 and Comparative Examples 1 to 3. The peak intensity ratio between the (002) and (003) crystal planes was calculated. The results are shown in Table 1. The XRD patterns of Examples 1 to 4 are shown in Table 1. Figure 1 .

[0085] Experiment 2: The compressive strength of the positive electrode active material mixed as in Examples 1 to 6 and Comparative Examples 1 to 5 was tested, and the ultimate compaction density of the prepared positive electrode active layer was also tested. The results are shown in Table 1.

[0086] Experiment 3: Charge-discharge tests were conducted on the coin cells prepared as described in Examples 1 to 7 and Comparative Examples 1 to 4. The initial discharge specific capacity at a discharge rate of 0.1C within a voltage range of 2.0-4.1V and the capacity retention rate after 100 cycles at a charge-discharge rate of 1.0C / 1.0C were calculated. The results are shown in Table 1.

[0087] Table 1

[0088]

[0089] Reference Figure 1 As shown, the relative peak intensity of the (003) crystal plane in Examples 2, 1, 3 and 4 decreases sequentially, corresponding to the sequential increase in the mass ratio of the first transition metal sodium oxide.

[0090] Referring to Table 1, it can be seen that in Examples 1 to 6, the ratio of the diffraction peak intensity of the (002) crystal plane to that of the (003) crystal plane was controlled to be 1:(1.0 to 5.0), and the ultimate compaction density of the positive electrode active layer was controlled to reach 3.2 g / cm³. 3 The above allows the battery electrode to maintain a specific capacity of 140 mAh / g and a capacity retention rate of over 90%. In Example 7, the first transition metal sodium oxide has a low compressive strength, resulting in a lower compressive strength of the mixed cathode material, leading to a decrease in the ultimate compaction density, but still maintaining a high capacity retention rate. In contrast, although Comparative Example 1 uses a larger amount of P2 phase transition metal sodium oxide, it not only has a lower discharge specific capacity but also poorer cycle performance than the other examples. This is mainly because the cathode active layer in Comparative Example 1 is still relatively easy to break during cycling, limiting further improvement in cycle performance. Comparative Example 2 has a higher proportion of O3 phase transition metal sodium oxide, which also leads to significantly poorer cycle performance. The ultimate compaction density of the cathode active layer in Comparative Examples 3-4 is low, and their cycle performance is also significantly worse, mainly because the cathode active layer still suffers from severe breakage during cycling.

[0091] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0092] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A positive electrode plate, characterized in that, The positive electrode includes a positive active layer, which includes a first transition metal sodium oxide and a second transition metal sodium oxide. Both the first transition metal sodium oxide and the second transition metal sodium oxide are granular. The crystal structure of the first transition metal sodium oxide is O3 phase, and the crystal structure of the second transition metal sodium oxide is P2 phase. In the XRD pattern of the positive electrode sheet, the ratio of the diffraction peak intensity of the (002) crystal plane to that of the (003) crystal plane is 1:(1.0~5.0), and the limiting compaction density of the positive electrode active layer is 3.2 g / cm³. 3 ~3.4g / cm 3 ; In the positive electrode active layer, the compressive strength of the mixture of the first transition metal sodium oxide and the second transition metal sodium oxide is ≥200MPa.

2. The positive electrode sheet according to claim 1, characterized in that, The compressive strength of the first transition metal sodium oxide is greater than that of the second transition metal sodium oxide. The compressive strength of the first transition metal sodium oxide is 150 MPa to 350 MPa, and the compressive strength of the second transition metal sodium oxide is 50 MPa to 250 MPa.

3. The positive electrode sheet according to any one of claims 1 to 2, characterized in that, The particles of the first transition metal sodium oxide are primary particles, and the particles of the second transition metal sodium oxide are at least one of primary particles and secondary particles.

4. The positive electrode sheet according to claim 3, characterized in that, D of the first transition metal sodium oxide v 50 particles with a diameter of 6μm~14μm, the D of the first transition metal sodium oxide v 10 Particle sizes of 3μm~8μm, the D of the first transition metal sodium oxide v The particle size of 90 is 14μm~30μm.

5. The positive electrode sheet according to claim 3, characterized in that, D of the second transition metal sodium oxide v 50 particles with a diameter of 3μm~8μm, the D of the second transition metal sodium oxide v 10. The particle size is 2μm~5μm, and the D of the second transition metal sodium oxide v The particle size of 90 is 8μm~18μm.

6. The positive electrode sheet according to any one of claims 1-2 and 4-5, characterized in that, The chemical formula of the first transition metal sodium oxide is Na. x1 Ni 1-y1-z1-w1 Fe y1 Mn z1 M w1 O2, where 0.8≤x1≤1, 0≤y1+z1+w1≤1; the chemical formula of the second transition metal sodium oxide is Na. x2 Ni 1-y2-z2-w2 Fe y2 Mn z2 M w2 O2, where 0.67≤x2≤0.8, 0≤y2+z2+w2≤1; in the first transition metal sodium oxide and the second transition metal sodium oxide, M is independently selected from one or more of Li, Mg, Y, Ca, Al, Ti, Zr, V, Cr, Cu, Nb, Sn, Sb, Bi and Zn.

7. The positive electrode sheet according to any one of claims 1-2 and 4-5, characterized in that, In the positive electrode, the mass ratio of the first transition metal sodium oxide to the second transition metal sodium oxide is (1~8):

1.

8. The positive electrode sheet according to any one of claims 1-2 and 4-5, characterized in that, The specific capacity of the positive electrode at a discharge rate of 0.1C is above 140 mAh / g; and / or, The positive electrode retains more than 90% of its capacity after 100 cycles at a charge-discharge rate of 1.0C.

9. An energy storage device, characterized in that, include: The device includes an electrode assembly and an electrolyte, with at least a portion of the electrode assembly immersed in the electrolyte. The electrode assembly includes a negative electrode and a positive electrode according to any one of claims 1 to 8.

10. An electrical appliance, characterized in that, It includes functional components and an energy storage device as described in claim 9, wherein the energy storage device is used to supply power to the functional components.

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